Jupiter appears in pastel colors in this photo because the observation was taken in near-infrared light. Credit: NASA, ESA, and E. Karkoschka (University of Arizona).

Infrared astronomy deals with the detection and analysis of infrared radiation (wavelengths longer than red light). Except at wavelengths close to visible light, infrared radiation is heavily absorbed by the atmosphere, and the atmosphere produces significant infrared emission. Consequently, infrared observatories have to be located in high, dry places or in space. The infrared spectrum is useful for studying objects that are too cold to radiate visible light, such as planets and circumstellar disks. Longer infrared wavelengths can also penetrate clouds of dust that block visible light, allowing observation of young stars in molecular clouds and the cores of galaxies.[1] Some molecules radiate strongly in the infrared. This can be used to study chemistry in space; more specifically it can detect water in comets.[2]

## Astronomy

This is a three-color far-infrared image of M51, the Whirlpool Galaxy. Credit: ESA and the PACS Consortium.{{free media}}

Far-infrared astronomy deals with objects visible in far-infrared radiation (extending from 30 µm towards submillimeter wavelengths around 450 µm).

"Red, green and blue correspond to the 160-micron, 100-micron and 70-micron wavelength bands of the Herschels Photoconductor Array Camera and Spectrometer, PACS instruments [in the far-infrared image on the right]."[3]

"Glowing light from clouds of dust and gas around and between the stars is visible clearly. These clouds are a reservoir of raw material for ongoing star formation in this galaxy. Blue indicates regions of warm dust that is heated by young stars, while the colder dust shows up in red."[3]

## Infra-reds

The wavelength of infrared light ranges from 0.75 to 300 micrometers. Infrared falls in between visible radiation, which ranges from 380 to 750 nanometers, and submillimeter waves. Infrared rays can be emitted, fluoresced, or reflected by an astronomical object.

Def. electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation, having a wavelength between 700 nm and 1 mm is called infrared.

Def. [e]lectromagnetic radiation having a wavelength approximately between 1 micrometre and 1 millimetre; perceived as heat is called infrared radiation.

Def. the spectroscopic study of the interaction of matter with infrared radiation; used as an analytical tool to identify (mostly organic) compounds is called infrared spectroscpy.

"Infrared and optical astronomy are often practiced using the same telescopes, as the same mirrors or lenses are usually effective over a wavelength range that includes both visible and infrared light. ... Infrared light is absorbed at many wavelengths by water vapor in the Earth's atmosphere, so most infrared telescopes are at high elevations in dry places, above as much of the atmosphere as possible. There are also infrared observatories in space, including the Spitzer Space Telescope and the Herschel Space Observatory. ... Infrared radiation with wavelengths just longer than visible light, known as near-infrared, behaves in a very similar way to visible light, and can be detected using similar solid state devices. For this reason, the near infrared region of the spectrum is commonly incorporated as part of the "optical" spectrum, along with the near ultraviolet. Many optical telescopes, such as those at Keck Observatory, operate effectively in the near infrared as well as at visible wavelengths.

## Colors

Astronomers typically divide the infrared spectrum as follows:[4]

Designation Abbreviation Wavelength
Near Infrared NIR (0.7–1) to 5 µm
Mid Infrared MIR 5 to (25–40) µm
Far Infrared FIR (25–40) to (200–350) µm.

These are the approximate ranges for photon energies of the infrared bands:

 Division Name Wavelength Photon Energy Near-infrared 0.75-1.4 µm 0.9-1.7 eV Short-wavelength infrared 1.4-3 µm 0.4-0.9 eV Mid-wavelength infrared 3-8 µm 150-400 meV Long-wavelength infrared 8–15 µm 80-150 meV Far infrared 15 - 1,000 µm 1.2-80 meV

## Theoretical infrared radiation astronomy

Def. the astronomical observation and study of objects, cooler than most stars, using the infrared part of the electromagnetic spectrum is called infrared astronomy.

## Bands

This is Saturn imaged with the Stockholm Infrared Camera (SIRCA) in the H2O band. Credit: M. Gålfalk, G. Olofsson and H.-G. Florén, Nordic Optical Telescope.

At the right is Saturn imaged by the Stockholm Infrared Camera (SIRCA) in the H2O infrared band to show the presence of water vapor. The image is cut off near the top due to the presence of Saturn's rings.

## Clouds

The Trifid Nebula is a giant star-forming cloud of gas and dust located 5,400 light-years away in the constellation Sagittarius. Credit: NASA/JPL-Caltech/J. Rho (SSC/Caltech).

"The glowing Trifid Nebula [in the image at right] is revealed in an infrared view from NASA's Spitzer Space Telescope. The Trifid Nebula is a giant star-forming cloud of gas and dust located 5,400 light-years away in the constellation Sagittarius."[5]

"The false-color Spitzer image reveals a different side of the Trifid Nebula. Where dark lanes of dust are visible trisecting the nebula in a visible-light picture, bright regions of star-forming activity are seen in the Spitzer picture. All together, Spitzer uncovered 30 massive embryonic stars and 120 smaller newborn stars throughout the Trifid Nebula, in both its dark lanes and luminous clouds. These stars are visible in the Spitzer image, mainly as yellow or red spots. Embryonic stars are developing stars about to burst into existence."[5]

"Ten of the 30 massive embryos discovered by Spitzer were found in four dark cores, or stellar "incubators," where stars are born. Astronomers using data from the Institute of Radioastronomy millimeter telescope in Spain had previously identified these cores but thought they were not quite ripe for stars. Spitzer's highly sensitive infrared eyes were able to penetrate all four cores to reveal rapidly growing embryos."[5]

"Astronomers can actually count the individual embryos tucked inside the cores by looking closely at this Spitzer image taken by its infrared array camera (IRAC). This instrument has the highest spatial resolution of Spitzer's imaging cameras. The embryos are thought to have been triggered by a massive "type O" star, which can be seen as a white spot at the center of the nebula. Type O stars are the most massive stars, ending their brief lives in explosive supernovas. The small newborn stars probably arose at the same time as the O star, and from the same original cloud of gas and dust."[5]

"This Spitzer mosaic image uses data from IRAC showing light of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8.0 microns (red)."[5]

## Submillimeters

Combined observations from NASA's Spitzer Space Telescope and the newly completed Atacama Large Millimeter/submillimeter Array (ALMA) in Chile have revealed the throes of stellar birth, as never before, in the well-studied object known as HH 46/47. Credit: NASA/JPL-Caltech/ALMA.

"Combined observations [in the image at right] from NASA's Spitzer Space Telescope and the newly completed Atacama Large Millimeter/submillimeter Array (ALMA) in Chile have revealed the throes of stellar birth, as never before, in the well-studied object known as HH 46/47."[6]

"Herbig-Haro (HH) objects form when jets shot out by newborn stars collide with surrounding material, producing small, bright, nebulous regions. To our eyes, the dynamics within many HH objects are obscured by enveloping gas and dust. But the infrared and submillimeter light seen by Spitzer and ALMA, respectively, pierces the dark cosmic cloud around HH 46/47 to let us in on the action. (Infrared light has longer wavelengths than what we see with our eyes, and submillimeter light has even longer wavelengths.)"[6]

"In this image, the shorter-wavelength light appears blue and longer-wavelength light, red. Blue shows gas energized by the outflowing jets. The green colors trace a combination of hydrogen gas molecules and dust that follows the boundary of the gas cloud cocooning the young star. The reddish-colored areas, created by excited carbon monoxide gas, reveal that the gas in the two lobes blown out by the star's jets is expanding faster than previously thought. This faster expansion has an influence on the overall amount of turbulence in the gaseous cloud that originally spawned the star. In turn, the extra turbulence could have an impact on whether and how other stars might form in this gaseous, dusty, and thus fertile, ground for star-making."[6]

"The Spitzer observations show twin supersonic jets emanating from the central star that blast away surrounding gas and set it alight into two bubbly lobes. HH 46/47 happens to sit on the edge of its enveloping cloud in such a way that the jets pass through two differing cosmic environments. The rightward jet, heading into the cloud, is plowing through a "wall" of material, while the leftward jet's path out of the cloud is relatively unobstructed, passing through less material. This orientation serves scientists well by offering a handy compare-and-contrast setup for how the outflows from a developing star interact with their surroundings."[7]

"Young stars like our sun need to remove some of the gas collapsing in on them to become stable, and HH 46/47 is an excellent laboratory for studying this outflow process, [...] Thanks to Spitzer, the HH 46/47 outflow is considered one of the best examples of a jet being present with an expanding bubble-like structure."[8]

## Gaseous objects

This image from NASA's Spitzer Space Telescope shows a dying star (center) surrounded by a cloud of glowing gas and dust. Credit: NASA/JPL-Caltech/J. Hora (Harvard-Smithsonian CfA).

"This image [at right] from NASA's Spitzer Space Telescope shows a dying star (center) surrounded by a cloud of glowing gas and dust. Spitzer has pierced through the dust to highlight a never-before-seen feature -- a giant ring of material (red) slightly offset from the cloud's core which consists of material that was expelled from the aging star."[9]

"The star and its cloud halo constitute a "planetary nebula" called NGC 246. When a star like our own Sun begins to run out of fuel, its core shrinks and heats up, boiling off the star's outer layers. Leftover material shoots outward, expanding in shells around the star. This ejected material is then bombarded with ultraviolet light from the central star's fiery surface, producing huge, glowing clouds -- planetary nebulas -- that look like giant jellyfish in space."[9]

"In this image, the expelled gases appear green, and the ring of expelled material appears red. Astronomers believe the ring is likely made of hydrogen molecules that were ejected from the star in the form of atoms, then cooled to make hydrogen pairs. The new data will help explain how planetary nebulas take shape, and how they nourish future generations of stars."[9]

"This image composite was taken on Dec. 6, 2003, by Spitzer's infrared array camera, and is composed of images obtained at four wavelengths: 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red)."[9]

## Rocky objects

The image shows the Orion nebula surrounded by a ring of dust. Credit: NASA/JPL-Caltech/T. Megeath (University of Toledo).

"This infrared image [at right] from NASA's Spitzer Space Telescope shows the Orion nebula, our closest massive star-making factory, 1,450 light-years from Earth. The nebula is close enough to appear to the naked eye as a fuzzy star in the sword of the popular hunter constellation."[10]

"The nebula itself is located on the lower half of the image, surrounded by a ring of dust. It formed in a cold cloud of gas and dust and contains about 1,000 young stars. These stars illuminate the cloud, creating the beautiful nebulosity, or swirls of material, seen here in infrared."[10]

"This image shows infrared light captured by Spitzer's infrared array camera. Light with wavelengths of 8 and 5.8 microns (red and orange) comes mainly from dust that has been heated by starlight. Light of 4.5 microns (green) shows hot gas and dust; and light of 3.6 microns (blue) is from starlight."[10]

## Hydrogens

This is the spectral series of hydrogen, on a logarithmic scale. Credit: OrangeDog.

The emission spectrum of atomic hydrogen is divided into a number of spectral series, with wavelengths given by the Rydberg formula. These observed spectral lines are due to electrons moving between energy levels in the atom. The spectral series are important in astronomy for detecting the presence of hydrogen and calculating red shifts.

Paschen series (n′ = 3) Brackett series (n′ = 4) Pfund series (n′ = 5)
n Designation λ (nm) n Designation λ (nm) n Designation λ (nm)
4 α 1870 5 α 4050 6 α 7460
5 β 1280 6 β 2620 7 β 4650
6 γ 1090 7 γ 2160 8 γ 3740
7 δ 1005 8 δ 1940 9 δ 3300
8 ε 954 9 ε 1820 10 ε 3040
${\displaystyle \infty }$ 820 ${\displaystyle \infty }$ 1460 ${\displaystyle \infty }$ 2280

## Heliums

"Spectra of the helium 2.06 µm and hydrogen 2.17 µm lines ... confirm the existence of an extended region of high-velocity redshifted line emission centered near [Sgr A*/IRS 16]."[11]

There are additional infrared lines of emission from helium: 1012.0 , 2112, 2166, 2188, and 2346 nm.[12]

## Lithiums

Lithium has an infrared line at 812.6 nm.[13]

## Borons

There are B I lines at 1624.0371 and 1624.4670 nm.[14]

## Carbons

Carbon has infrared emission lines: "C III at 0.971 µm and C IV at 2.075 µm"[12].

## Oxygens

Molecular oxygen "airglow emissions [have been] measured by using vertical-viewing photometers [on-board a sounding rocket for the] O2(1Δg) bands at 1.27 μm; and OH (X2π) Meinel bands near 1.7 μm."[15].

"[T]the O2 (0,0) atmosphere band at 7620 A [has been] measured in a steady IBC II(plus) aurora simultaneously with N2 emissions and the auroral electron flux."[16]

## Fluorines

"The most accessible lines suited for F measurements, the vibration-rotation transition of the HF molecule, are located in the K band, requiring the use of high-resolution, IR spectrographs mounted on 8 m class telescope to target halo stars ... not available until recently."[17]

## Irons

Iron has at least three emission lines occurring in the solar corona at 789.194 nm from Fe XI and at 1074.680 nm and 1079.795 nm from Fe XIII.[18]

## Nickels

Nickel has an emission line at 802.421 nm occurring in the solar corona from Ni XV.[18]

## Rubidiums

"Rubidium abundances [may be] determined from the Rb I 7800 Å line via synthetic spectra for a sample of M, MS, and S [red] giants."[19]

## Compounds

Wisps of green are organic molecules called Polycyclic Aromatic Hydrocarbons (PAHs) that have been illuminated by the nearby star formation. Credit: NASA/JPL-Caltech/L. Cieza (Univ. of Texas at Austin)).

"Baby stars are forming near the eastern rim of the cosmic cloud Perseus, in this infrared image from NASA's Spitzer Space Telescope."[20]

"The baby stars are approximately three million years old and are shown as reddish-pink dots to the right of the image. The pinkish color indicates that these infant stars are still shrouded by the cosmic dust and gas that collapsed to form them. These stars are part of the IC348 star cluster, which consists of over 300 known member stars."[20]

"The Perseus Nebula can be seen as the large green cloud at the center of the image. Wisps of green are organic molecules called Polycyclic Aromatic Hydrocarbons (PAHs) that have been illuminated by the nearby star formation. Meanwhile, wisps of orange-red are dust particles warmed by the newly forming stars. The Perseus Nebula is located about 1,043 light-years away in the Perseus constellation."[20]

"The image is a three channel false color composite, where emission at 4.5 microns is blue, emission at 8.0 microns is green, and 24-micron emission is red."[20]

## Carbon dioxide

"[T]he P16 line [occurs] in the 3 CO2 absorption band near 8708 Å".[21]

## Atmospheres

The diagam is a plot of atmospheric transmittance in part of the infrared region. Credit: U.S. Navy.

The principal limitation on infrared sensitivity from ground-based telescopes is the Earth's atmosphere. Water vapor absorbs a significant amount of infrared radiation, and the atmosphere itself emits at infrared wavelengths. For this reason, most infrared telescopes are built in very dry places at high altitude, so that they are above most of the water vapor in the atmosphere. Suitable locations on Earth include Mauna Kea Observatory at 4205 meters above sea level, the ALMA site at 5000 m in Chile and regions of high altitude ice-desert such as Dome C in Antarctic. Even at high altitudes, the transparency of the Earth's atmosphere is limited except in infrared windows, or wavelengths where the Earth's atmosphere is transparent.[22] The main infrared windows are listed below:

Wavelength range
(micrometres)
Astronomical bands Telescopes
0.65 to 1.0 R and I bands All major optical telescopes
1.1 to 1.4 J band Most major optical telescopes and most dedicated infrared telescopes
1.5 to 1.8 H band Most major optical telescopes and most dedicated infrared telescopes
2.0 to 2.4 K band Most major optical telescopes and most dedicated infrared telescopes
3.0 to 4.0 L band Most dedicated infrared telescopes and some optical telescopes
4.6 to 5.0 M band Most dedicated infrared telescopes and some optical telescopes
7.5 to 14.5 N band Most dedicated infrared telescopes and some optical telescopes
17 to 25 Q band Some dedicated infrared telescopes and some optical telescopes
28 to 40 Z band Some dedicated infrared telescopes and some optical telescopes
330 to 370 Some dedicated infrared telescopes and some optical telescopes
450 submillimeter Submillimeter telescopes

## Venus

This is a false-color near-infrared image of lower-level clouds on the night side of Venus, obtained by the Near Infrared Mapping Spectrometer aboard the Galileo spacecraft as it approached the planet's night side on February 10, 1990. Credit: NASA/JPL.

"The Herzberg II system of O2 has been a known feature of Venus' nightglow since the Venera 9 and 10 orbiters detected its c(0)-X(v″) progression more than 3 decades ago."[23]

"Spectroscopic observations of the differential Doppler shift in a CO2 absorption line on Venus show that the upper atmospheric wind near the equator appears to have both a retrograde motion of about -85 ± 10 m s-1 ... and ... a periodically varying component, with an amplitude of about 40 ± 14 m s-1 and a period of 4.3 ± 0.2 days."[21]

At right is a false-color near-infrared image of the lower-level clouds on the night side of Venus, obtained by the Near Infrared Mapping Spectrometer aboard the Galileo spacecraft as it approached the planet's night side on February 10, 1990.

"Bright slivers of sunlit high clouds are visible above and below the dark, glowing hemisphere. The spacecraft is about 100,000 kilometers (60,000 miles) above the planet. An infrared wavelength of 2.3 microns (about three times the longest wavelength visible to the human eye) was used. The map shows the turbulent, cloudy middle atmosphere some 50-55 kilometers (30- 33 miles) above the surface, 10-16 kilometers or 6-10 miles below the visible cloudtops. The red color represents the radiant heat from the lower atmosphere (about 400 degrees Fahrenheit) shining through the sulfuric acid clouds, which appear as much as 10 times darker than the bright gaps between clouds. This cloud layer is at about -30 degrees Fahrenheit, at a pressure about 1/2 Earth's surface atmospheric pressure. Near the equator, the clouds appear fluffy and blocky; farther north, they are stretched out into East-West filaments by winds estimated at more than 150 mph, while the poles are capped by thick clouds at this altitude."[24]

## Earth

The two images allow comparison of an optical astronomy image of Earth with an infrared astronomy image. Credit: NASA.
This is the first full-disk thermal infrared (IR) image taken by GOES 14, showing radiation with a wavelength of 10.7 micrometers emanating from Earth. Credit: GOES science team.
This Galileo spacecraft image was taken through the infrared (9680 nm) filter, which enhances the visibility of the land masses. Credit: Galileo orbiter, NASA/JPL.

The images at top right are from the optical astronomy and infrared telescopes aboard the MESSENGER spacecraft.

The optical astronomy image delineates gaseous, liquid, and rocky portions of the Earth's atmosphere, oceans, and land masses. The infrared astronomy image detects primarily the rocky objects or land masses of Earth.

The second image at right is the "first full-disk thermal infrared (IR) image, [taken by GOES 14,] showing radiation with a wavelength of 10.7 micrometers emanating from Earth."[25]

"Infrared images are useful because they provide information about temperatures. A wavelength of 10.7 micrometers is 15 times longer than the longest wavelength of light (red) that people can see, but scientists can turn the data into a picture by having a computer display cold temperatures as bright white and hot temperatures as black. The hottest (blackest) features in the scene are land surfaces; the coldest (whitest) features in the scene are clouds."[25]

"In the heat of the midday sun, the exposed rock in sparsely vegetated mountain ranges and high-altitude deserts in western North and South America are dark. In North America, the temperatures cool (fade to lighter grey) along a gradient from west to east, as the semi-deserts of the West and South-west transition to the grasslands and crop-lands of the Great Plains, which transition to forests in the East."[25]

"A band of scattered storms across the equatorial Pacific shows the location of the Inter-tropical Convergence Zone, which is a belt of showers and thunderstorms that persists near the equator year round. Need help precisely locating the equator? Look for the dark (hot) spots in the Pacific Ocean west of South America: those are the Galapagos Islands, and the equator passes through the northern tip of the largest island."[25]

"Perhaps the most significant features related to U.S. weather appear in the upper right quadrant of the disk: the remnants of Tropical Storm Claudette drenching the eastern Gulf Coast, Tropical Depression Ana unwinding over Puerto Rico and the Dominican Republic, and Hurricane Bill approaching from the central Atlantic."[25]

At left is an image from the Galileo spacecraft. The "Galileo raw image of Earth [is] taken from 2.7 million km 3 days after the first flyby. Africa and the Middle East can be seen at the top and Antarctica at the bottom. Weather systems are visible in the clouds over the Atlantic and Indian oceans. The image was taken through the infrared (9680 nm) filter, which enhances the visibility of the land masses."[26]

## Moon

This image of Earth's moon is a three-colour composite of reflected near-infrared radiation from the Sun. Credit: ISRO/NASA/JPL-Caltech/Brown Univ./USGS.
The mid-infrared image of the Moon was taken during a 1996 lunar eclipse by the SPIRIT-III instrument aboard the orbiting Midcourse Space Experiment satellite. Credit: DCATT Team, MSX Project, BMDO (Ballistic Missile Defense Organization of the US DoD).

Four radiometers aboard Luna 13 recorded infrared radiation from the Moon's surface indicating a noon temperature of 117 ±3 °C.

"NASA's Moon Mineralogy Mapper, an instrument on the Indian Space Research Organization's Chandrayaan-1 mission, took [the image at right] of Earth's moon. It is a three-colour composite of reflected near-infrared radiation from the sun, and illustrates the extent to which different materials are mapped across the side of the moon that faces Earth. Small amounts of water were detected on the surface of the moon at various locations. This image illustrates their distribution at high latitudes toward the poles. Blue shows the signature of water, green shows the brightness of the surface as measured by reflected infra-red radiation from the sun and red shows a mineral called pyroxene."[27]

"The mid-infrared image of the Moon [at left] was taken during a 1996 lunar eclipse by the SPIRIT-III instrument aboard the orbiting Midcourse Space Experiment satellite. At these wavelengths, MSX was able to characterize the thermal (heat) distribution of the lunar surface during the eclipse. The brightest regions are the warmest, and the darkest areas are the coolest. The well-known crater Tycho is the bright object to the south of center. Numerous other craters are also seen as bright spots, indicating that their temperature is higher than in the surrounding dark mare. The Moon is geologically inactive for the most part, and any temperature differences are a result primarily of variations in solar heating (rather than volcanoes, for example). The Moon lacks an atmosphere to moderate temperatures, which can vary from 130 degrees Celsius (265 degrees Fahrenheit) in the sun to -110 degrees Celcius (-170 degrees Fahrenheit) in the shade."[28]

## Mars

Methane is found in the Martian atmosphere by carefully observing the planet throughout several Mars years with NASA's Infrared Telescope Facility and the W.M. Keck telescope, both at Mauna Kea, Hawaii. Credit: NASA.

At right is an image generated by detecting methane in the Martian atmosphere by carefully observing the planet throughout several Mars years with NASA's Infrared Telescope Facility and the W.M. Keck telescope, both at Mauna Kea, Hawaii. The methane "plumes were seen over areas that show evidence of ancient ground ice or flowing water. Plumes appeared over the Martian northern hemisphere regions such as east of Arabia Terra, the Nili Fossae region, and the south-east quadrant of Syrtis Major, an ancient volcano about 745 miles across."[29]

## Asteroids

"On October 7, 2009, the presence of water ice was confirmed on the surface of [24 Themis] using NASA’s Infrared Telescope Facility. The surface of the asteroid appears completely covered in ice. As this ice layer is sublimated, it may be getting replenished by a reservoir of ice under the surface. Organic compounds were also detected on the surface.[30][31][32][33]

Trace amounts of water would be continuously produced by high-energy solar protons impinging oxide minerals present at the surface of the asteroid. The hydroxyl surface groups (S–OH) formed by the collision of protons (H+) with oxygen atoms present at oxide surface (S=O) can further be converted in water molecules (H2O) adsorbed onto the oxide minerals surface. The chemical rearrangement supposed at the oxide surface could be schematically written as follows:

2 S-OH → S=O + S + H2O

or,

2 S-OH → S–O–S + H2O

where S represents the oxide surface.[34]

## Jupiter

An infrared image of GRS (top) shows its warm center, taken by the ground based Very Large Telescope. An image made by the Hubble Space Telescope (bottom) is shown for comparison. Credit: NASA/JPL/ESO and NASA/ESA/GSFC.
This is an infrared image of Jupiter taken by the ESO's Very Large Telescope. Credit: ESO/F. Marchis, M. Wong, E. Marchetti, P. Amico, S. Tordo.
Infrared observations taken at the Keck II telescope in Hawaii reveal a bright spot where the impact occurred. The spot looks black at visible wavelengths. Credit: Paul Kalas/Michael Fitzgerald/Franck Marchis/LLNL/UCLA/UC Berkeley/SETI Institute
These images show the distribution of acetylene around the north and south poles of Jupiter. Credit: NASA/JPL/GSFC.

"Spectra from the Voyager I IRIS experiment confirm the existence of enhanced infrared emission near Jupiter's north magnetic pole in March 1979."[35] "Some species previously detected on Jupiter, including CH3D, C2H2, and C2H6, have been observed again near the pole. Newly discovered species, not previously observed on Jupiter, include C2H4, C3H4, and C6H6. All of these species except CH3D appear to have enhanced abundances at the north polar region with respect to midlatitudes."[35]

The image at lower right is "of Jupiter taken in infrared light on the night of [August 17, 2008,] with the Multi-Conjugate Adaptive Optics Demonstrator (MAD) prototype instrument mounted on ESO's Very Large Telescope. This false color photo is the combination of a series of images taken over a time span of about 20 minutes, through three different filters (2, 2.14, and 2.16 microns). The image sharpening obtained is about 90 milli-arcseconds across the whole planetary disc, a real record on similar images taken from the ground. This corresponds to seeing details about 186 miles wide on the surface of the giant planet. The great red spot is not visible in this image as it was on the other side of the planet during the observations. The observations were done at infrared wavelengths where absorption due to hydrogen and methane is strong. This explains why the colors are different from how we usually see Jupiter in visible-light. This absorption means that light can be reflected back only from high-altitude hazes, and not from deeper clouds. These hazes lie in the very stable upper part of Jupiter's troposphere, where pressures are between 0.15 and 0.3 bar. Mixing is weak within this stable region, so tiny haze particles can survive for days to years, depending on their size and fall speed. Additionally, near the planet's poles, a higher stratospheric haze (light blue regions) is generated by interactions with particles trapped in Jupiter's intense magnetic field."[36]

The image at the top of this page shows Jupiter in the near infrared. "Five spots -- one colored white, one blue, and three black are scattered across the upper half of the planet. Closer inspection by NASA's Hubble Space Telescope reveals that these spots are actually a rare alignment of three of Jupiter's largest moons -- Io, Ganymede, and Callisto -- across the planet's face. In this image, the telltale signatures of this alignment are the shadows [the three black circles] cast by the moons. Io's shadow is located just above center and to the left; Ganymede's on the planet's left edge; and Callisto's near the right edge. Only two of the moons, however, are visible in this image. Io is the white circle in the center of the image, and Ganymede is the blue circle at upper right. Callisto is out of the image and to the right. ... Jupiter appears in pastel colors in this photo because the observation was taken in near-infrared light. Astronomers combined images taken in three near-infrared wavelengths to make this color image. The photo shows sunlight reflected from Jupiter's clouds. In the near infrared, methane gas in Jupiter's atmosphere limits the penetration of sunlight, which causes clouds to appear in different colors depending on their altitude. Studying clouds in near-infrared light is very useful for scientists studying the layers of clouds that make up Jupiter's atmosphere. Yellow colors indicate high clouds; red colors lower clouds; and blue colors even lower clouds in Jupiter's atmosphere. The green color near the poles comes from a thin haze very high in the atmosphere. Ganymede's blue color comes from the absorption of water ice on its surface at longer wavelengths. Io's white color is from light reflected off bright sulfur compounds on the satellite's surface. ... In viewing this rare alignment, astronomers also tested a new imaging technique. To increase the sharpness of the near-infrared camera images, astronomers speeded up Hubble's tracking system so that Jupiter traveled through the telescope's field of view much faster than normal. This technique allowed scientists to take rapid-fire snapshots of the planet and its moons. They then combined the images into one single picture to show more details of the planet and its moons."[37]

On July 19, 2009, a new black spot about the size of Earth was discovered in Jupiter's southern hemisphere by an amateur astronomer. Thermal infrared analysis showed it was warm and spectroscopic methods detected ammonia. JPL scientists confirmed that another impact event on Jupiter had occurred, probably a small undiscovered comet or other icy body.[38][39][40]

"These images [at right] show the distribution of the organic molecule acetylene at the north and south poles of Jupiter, based on data obtained by NASA's Cassini spacecraft in early January 2001. It is the highest-resolution map of acetylene to date on Jupiter. The enhanced emission results both from the warmer temperatures in the auroral hot spots, and probably also from an enhanced abundance in these regions. The detection helps scientists understand the chemical interactions between sunlight and molecules in Jupiter's stratosphere."[41]

## Europa

Frozen sulfuric acid on Jupiter's moon Europa is depicted in this image produced from data gathered by NASA's Galileo spacecraft. Credit: NASA/JPL.

"Frozen sulfuric acid on Jupiter's moon Europa is depicted in this image produced from data gathered by NASA's Galileo spacecraft. The brightest areas, where the yellow is most intense, represent regions of high frozen sulfuric acid concentration. Sulfuric acid is found in battery acid and in Earth's acid rain."[42]

"This image is based on data gathered by Galileo's near infrared mapping spectrometer."[42]

"Europa's leading hemisphere is toward the bottom right, and there are enhanced concentrations of sulfuric acid in the trailing side of Europa (the upper left side of the image). This is the face of Europa that is struck by sulfur ions coming from Jupiter's innermost moon, Io. The long, narrow features that crisscross Europa also show sulfuric acid that may be from sulfurous material extruded in cracks."[42]

## Comets

This is an infrared image of the periodic comet Schwassmann-Wachmann I (P/SW-1) in a nearly circular orbit just outside that of Jupiter. Credit: NASA/JPL-Caltech/D. Cruikshank (NASA Ames) & J. Stansberry (University of Arizona.
These images are of comet Holmes. The contrast has been enhanced for the right image to show anatomy. Credit: NASA/JPL-Caltech/W. Reach (SSC-Caltech).

"NASA's new Spitzer Space Telescope has captured [the image right] of an unusual comet that experiences frequent outbursts, which produce abrupt changes in brightness. Periodic comet Schwassmann-Wachmann I (P/SW-1) has a nearly circular orbit just outside that of Jupiter, with an orbital period of 14.9 years. It is thought that the outbursts arise from the build-up of internal gas pressure as the heat of the Sun slowly evaporates frozen carbon dioxide and carbon monoxide beneath the blackened crust of the comet nucleus. When the internal pressure exceeds the strength of the overlying crust, a rupture occurs, and a burst of gas and dust fragments is ejected into space at speeds of 450 miles per hour (200 meters per second)."[43]

"This 24-micron image of P/SW-1 was obtained with Spitzer's multiband imaging photometer. The image shows thermal infrared emission from the dusty coma and tail of the comet. The nucleus of the comet is about 18 miles (30 kilometers) in diameter and is too small to be resolved by Spitzer. The micron-sized dust grains in the coma and tail stream out away from the Sun. The dust and gas comprising the comet's nucleus is part of the same primordial materials from which the Sun and planets were formed billions of years ago. The complex carbon-rich molecules they contain may have provided some of the raw materials from which life originated on Earth."[43]

"Schwassmann-Wachmann 1 is thought to be a member of a relatively new class of objects called "Centaurs," of which 45 objects are known. These are small icy bodies with orbits between those of Jupiter and Neptune. Astronomers believe that Centaurs are recent escapees from the Kuiper Belt, a zone of small bodies orbiting in a cloud at the distant reaches of the solar system."[43]

"Two asteroids, 1996 GM36 (left) and 5238 Naozane (right) were serendipitously captured in the comet image. Because they are closer to us than the comet and have faster orbital velocities, they appear to move relative to the comet and background stars, thereby producing a slight elongated appearance. The Spitzer data have allowed astronomers to use thermal measurements, which reduce the uncertainties of visible-light albedo (reflectivity) measurements, to determine their size. With radii of 1.4 and 3.0 kilometers, these are the smallest main-belt asteroids yet measured by infrared means."[43]

In the second image pair, "NASA's Spitzer Space Telescope captured the picture on the left of comet Holmes in March 2008, five months after the comet suddenly erupted and brightened a millionfold overnight. The contrast of the picture has been enhanced on the right to show the anatomy of the comet."[44]

"Every six years, comet 17P/Holmes speeds away from Jupiter and heads inward toward the sun, traveling the same route typically without incident. However, twice in the last 116 years, in November 1892 and October 2007, comet Holmes mysteriously exploded as it approached the asteroid belt. Astronomers still do not know the cause of these eruptions."[44]

"Spitzer's infrared picture at left reveals fine dust particles that make up the outer shell, or coma, of the comet. The nucleus of the comet is within the bright whitish spot in the center, while the yellow area shows solid particles that were blown from the comet in the explosion. The comet is headed away from the sun, which lies beyond the right-hand side of the picture."[44]

"The contrast-enhanced picture on the right shows the comet's outer shell, and strange filaments, or streamers, of dust. The streamers and shell are a yet another mystery surrounding comet Holmes. Scientists had initially suspected that the streamers were small dust particles ejected from fragments of the nucleus, or from hyperactive jets on the nucleus, during the October 2007 explosion. If so, both the streamers and the shell should have shifted their orientation as the comet followed its orbit around the sun. Radiation pressure from the sun should have swept the material back and away from it. But pictures of comet Holmes taken by Spitzer over time show the streamers and shell in the same configuration, and not pointing away from the sun. The observations have left astronomers stumped."[44]

"The horizontal line seen in the contrast-enhanced picture is a trail of debris that travels along with the comet in its orbit."[44]

"The Spitzer picture was taken with the spacecraft's multiband imaging photometer at an infrared wavelength of 24 microns."[44]

## Saturn

This is a mosaic of 35 individual exposures taken with infrared radiation. Credit: NASA.
This is a false-color composite taken in the infrared of Saturn's south polar region. Credit: NASA/JPL/University of Arizona/University of Leicester.
This is an infrared image of Saturn's north pole. Credit: Cassini VIMS Team, University of Arizona, JPL, ESA and NASA.
This false-color mosaic shows Saturn's north polar region in infrared from the unlit side. Credit: NASA/JPL/University of Arizona.
This image of Saturn is in the infrared. Credit: NASA/E. Karkoschka (University of Arizona).
These infrared false-colour images from NASA's Cassini spacecraft chronicle a day in the life of a huge storm that developed from a small spot that appeared 12 weeks earlier in Saturn's northern mid-latitudes. Credit: NASA/JPL-Caltech/SSI.

At right is an infrared astronomy image of Saturn. "This is the sharpest image of Saturn's temperature emissions taken from the ground; it is a mosaic of 35 individual exposures made at the W.M. Keck I Observatory, Mauna Kea, Hawaii on Feb. 4, 2004. The images to create this mosaic were taken with infrared radiation. The black square at 4 o'clock represents missing data."[45]

"In the most precise reading of Saturn's temperatures ever taken from Earth, a new set of infrared images suggests a warm "polar vortex" at Saturn's south pole - the first warm polar cap ever to be discovered in the solar system. The vortex is punctuated by a compact spot that is the warmest place on the planet."[46]

"The puzzle isn't that Saturn's south pole is warm; after all, it has been exposed to 15 years of continuous sunlight, having just reached its summer Solstice late in 2002. But both the distinct boundary of a warm polar vortex some 30 degrees latitude from the southern pole and a very hot "tip" right at the pole were completely unexpected. If the increased southern temperatures are the result of the seasonal variations of sunlight, then temperatures should increase gradually with increasing latitude. But they don't – the tropospheric temperature increases toward the pole abruptly near 70 degrees latitude from 88 to 89 Kelvin (- 301 to -299 degrees Fahrenheit) and then to 91 Kelvin (-296 degrees Fahrenheit) right at the pole. Near 70 degrees latitude, the stratospheric temperature increases even more abruptly from 146 to 150 Kelvin (-197 to -189 degrees Fahrenheit) and then again to 151 Kelvin (-188 degrees Fahrenheit) right at the pole."[46]

The second image at right is "constructed from data collected in the near-infrared wavelengths of light, the auroral emission is shown in green. The data represents emissions from hydrogen ions in of light between 3 and 4 microns in wavelength. In general, scientists designated blue to indicate sunlight reflected at a wavelength of 2 microns, green to indicate sunlight reflected at 3 microns and red to indicate thermal emission at 5 microns. Saturn's rings reflect sunlight at 2 microns, but not at 3 and 5 microns, so they appear deep blue. Saturn's high altitude haze reflects sunlight at both 2 and 3 microns, but not at 5 microns, and so it appears green to blue-green. The heat emission from the interior of Saturn is only seen at 5 microns wavelength in the spectrometer data, and thus appears red. The dark spots and banded features in the image are clouds and small storms that outline the deeper weather systems and circulation patterns of the planet. They are illuminated from underneath by Saturn's thermal emission, and thus appear in silhouette. The composite image was made from 65 individual observations by Cassini's visual and infrared mapping spectrometer on 1 November 2008. The observations were each six minutes long."[47]

The third image at right shows Saturn's northern polar region with "the aurora and underlying atmosphere, seen at two different wavelengths of infrared light as captured by NASA's Cassini spacecraft. Energetic particles, crashing into the upper atmosphere cause the aurora, shown in blue, to glow brightly at 4 microns (six times the wavelength visible to the human eye). The image shows both a bright ring, as seen from Earth, as well as an example of bright auroral emission within the polar cap that had been undetected until the advent of Cassini. This aurora, which defies past predictions of what was expected, has been observed to grow even brighter than is shown here. Silhouetted by the glow (cast here to the color red) of the hot interior of Saturn (clearly seen at a wavelength of 5 microns, or seven times the wavelength visible to the human eye) are the clouds and haze that underlie this auroral region."[48]

Also on the right is a fourth image of Saturn's north polar region in infrared. "This striking false-color mosaic was created from 25 images taken by Cassini's visual and infrared mapping spectrometer over a period of 13 hours, and captures Saturn in nighttime and daytime conditions. The visual and infrared mapping spectrometer acquires data simultaneously at 352 different wavelengths, or spectral channels. Data at wavelengths of 2.3, 3.0 and 5.1 microns were combined in the blue, green and red channels of a standard color image, respectively, to make this false-color mosaic."[49]

"This image was acquired on 24 February 2007, while the spacecraft was 1.58 million km (1 million miles) from the planet and 34.6 degrees above the ring plane. The solar phase angle was 69.5 degrees. In this view, Cassini was looking down on the northern, unlit side of the rings, which are rendered visible by sunlight filtering through from the sunlit, southern face."[49]

"On the night side (right side of image), with no sunlight, Saturn's own thermal radiation lights things up. This light at 5.1 microns wavelength (some seven times the longest wavelength visible to the human eye) is generated deep within Saturn, and works its way upward, eventually escaping into space. Thick clouds deep in the atmosphere block that light. An amazing array of dark streaks, spots and globe-encircling bands is visible instead. Saturn's strong thermal glow at 5.1 microns even allows these deep clouds to be seen on portions of the dayside (left side), especially where overlying hazes are thin and the glint of the sun off of them is minimal. These deep clouds are likely made of ammonium hydrosulfide and cannot be seen in reflected light on the dayside, since the glint of the sun on overlying hazes and ammonia clouds blocks the view of this level."[49]

"A pronounced difference in the brightness between the northern and southern hemispheres is apparent. The northern hemisphere is about twice as bright as the southern hemisphere. This is because high-level, fine particles are about half as prevalent in the northern hemisphere as in the south. These particles block Saturn's glow more strongly, making Saturn look brighter in the north."[49]

"At 2.3 microns (shown in blue), the icy ring particles are highly reflecting, while methane gas in Saturn's atmosphere strongly absorbs sunlight and renders the planet very dark. At 3.0 microns (shown in green), the situation is reversed: water ice in the rings is strongly absorbing, while the planet's sunlit hemisphere is bright. Thus the rings appear blue in this representation, while the sunlit side of Saturn is greenish-yellow in color. Within the rings, the most opaque parts appear dark, while the more translucent regions are brighter. In particular, the opaque, normally-bright B ring appears here as a broad, dark band separating the brighter A (outer) and C (inner) rings."[49]

"At 5.1 microns (shown in red), reflected sunlight is weak and thus light from the planet is dominated by thermal (i.e., heat) radiation that wells up from the planet's deep atmosphere. This thermal emission dominates Saturn's dark side as well as the north polar region (where the hexagon is again visible) and the shadow cast by the A and B rings. Variable amounts of clouds in the planet's upper atmosphere block the thermal radiation, leading to a speckled and banded appearance, which is ever-shifting due to the planet's strong winds."[49]

The fifth infrared image of Saturn is a detailed false color image. "[T]aken in January 1998 by the Hubble Space Telescope [it] shows the ringed planet in reflected infrared light. Different colors [indicate] varying heights and compositions of cloud layers generally thought to consist of ammonia ice crystals. The eye-catching rings cast a shadow on Saturn's upper hemisphere, while the bright stripe seen within the left portion of the shadow is infrared sunlight streaming through the large gap in the rings known as the Cassini Division."[50]

"Two of Saturn's many moons have also put in an appearance (in the full resolution version), Tethys just beyond the planet's disk at the upper right, and Dione at the lower left."[50]

The panoramic images at right "from NASA's Cassini spacecraft chronicle a day in the life of a huge storm that developed from a small spot that appeared 12 weeks earlier in Saturn's northern mid-latitudes."[51]

"This storm is the largest and most intense observed on Saturn by NASA's Voyager or Cassini spacecraft. The storm is still active. As seen in these and other Cassini images, the storm encircles the planet - whose circumference at these latitudes is 300,000 kilometres. From north to south, it covers a distance of about 15,000 kilometres, which is one-third of the way around the Earth. It encompasses an area of 4 billion square kilometres, or eight times the surface area of Earth. This storm is about 500 times the area of the biggest of the southern hemisphere storms ... observed by Cassini."[51]

"The highest clouds in the image are probably around 100 millibars pressure, 100 kilometres above the regular undisturbed clouds. These false colors show clouds at different altitudes. Clouds that appear blue here are the highest and are semitransparent, or optically thin. Those that are yellow and white are optically thick clouds at high altitudes. Those shown green are intermediate clouds. Red and brown colors are clouds at low altitude unobscured by high clouds, and the deep blue color is a thin haze with no clouds below. The base of the clouds, where lightning is generated, is probably in the water cloud layer of Saturn's atmosphere. The storm clouds are likely made out of water ice covered by crystallized ammonia."[51]

"Taken about 11 hours -- or one Saturn day -- apart, the two mosaics in the lower half of this image product consist of 84 images each. The mosaic in the middle was taken earlier than the mosaic at the bottom. Both mosaics were captured on Feb. 26, 2011, and each of the two batches of images was taken over about 4.5 hours."[51]

"Two enlargements from the earlier, middle mosaic are shown at the top of this product. The white lines below the middle mosaic identify those parts of the mosaic that were enlarged for these close-up views. The enlargement on the top left shows the head of the storm, and that on the top right shows the turbulent middle of the storm. Cassini observations have shown the head of the storm drifting west at a rate of about 2.8 degrees of longitude each Earth day (28 meters per second, or 63 miles per hour). The central latitude of the storm is the site of a westward jet, which means that the clouds to the north and south are drifting westward more slowly or even drifting eastward. In contrast, clouds at Saturn's equator drift eastward at speeds up to 450 meters per second (1,000 miles per hour). "[51]

"Both of the long mosaics cover an area ranging from about 30 degrees north latitude to 51 degrees north latitude. The views stretch from about 138 degrees west longitude on the left to 347 degrees west longitude on the right, passing through 360/0 degrees west longitude near the far right of the mosaics."[51]

"The images were taken with the Cassini spacecraft narrow-angle camera using a combination of spectral filters sensitive to wavelengths of near-infrared light. The images filtered at 889 nanometers are projected as blue. The images filtered at 727 nanometers are projected as green, and images filtered at 750 nanometers are projected as red."[51]

"The views were acquired at a distance of approximately 2.4 million kilometres from Saturn and at a sun-Saturn-spacecraft angle (phase angle) of 62 degrees. Both the top and bottom images are simple cylindrical map projections, defined such that a square pixel subtends equal intervals of latitude and longitude. At higher latitudes, the pixel size in the north-south direction remains the same, but the pixel size in the east-west direction becomes smaller. The pixel size is set at the equator, where the distances along the sides are equal. The images of the long mosaics have a pixel size of 53 kilometres at the equator, and the two close-up views have a pixel size of 9 kilometres per pixel at the equator."[51]

## Uranus

This Hubble Space Telescope image shows Uranus in the near-infrared. Credit: NASA, ESA, L. Sromovsky (University of Wisconsin, Madison), H. Hammel (Space Science Institute), and K. Rages (SETI).
This is an infrared composite of Uranus obtained with Keck Observatory adaptive optics. Credit: Lawrence Sromovsky, University of Wisconsin-Madison/ W. M. Keck Observatory.

At right is an infrared image of Uranus "showing Ariel in transit across Uranus, taken on July 26, 2006. Due to the planet's extreme axial tilt--carried through in the tilt of its satellites's orbits--transits are only possible near the equinoxes. Taken in the near-infrared, atmospheric banding and the planet's oblateness are readily apparent."[52]

The second pair of images on the left are an "infrared composite ... of the two hemispheres of Uranus obtained with Keck adaptive optics. The component colors of blue, green, and red were obtained from images made at near infrared wavelengths of 1.26, 1.62, and 2.1 microns respectively. The images were obtained on July 11 and 12, 2004. The representative balance of these infrared images which were selected to display the vertical structure of atmospheric features gives a reddish tint to the rings, an artifact of the process. The North pole is at 4 o'clock."[53]

## Neptune

This is an infrared image of Neptune using adaptive optics (AO). Credit: NASA/JPL-Caltech/Cornell.
These are infrared images of Neptune. Credit: VLT/ESO/NASA/JPL/Paris Observatory.
In these Hubble images of Neptune the clouds are tinted pink because they are reflecting near-infrared light. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

At right is an infrared image of Neptune using adaptive optics (AO) on the Mount Palomar 200-inch Hale Telescope.

"Neptune has never looked so clear in infrared light. Surprisingly, Neptune radiates about twice as much energy as it receives from the sun. A fascinating feature of the above photograph is that it was taken far from distant Neptune, through the Earth's normally blurry atmosphere. The great clarity of this recently released image was made possible by "rubber mirror" adaptive optics technology. Here, mirrors in the Palomar High Angular Resolution Observer (PHARO) instrument connected to the 200-inch Hale Telescope flex to remove the effects of turbulence in the Earth's atmosphere."[54]

At right are three images of Neptune using infrared astronomy. "Thermal images of planet Neptune taken with VISIR on ESO's Very Large Telescope, obtained on 1 and 2 September 2006. These thermal images show a 'hot' south pole on Neptune. These warmer temperatures provide an avenue for methane to escape out of the deep atmosphere. Scientists say Neptune's south pole is 'hotter' than anywhere else on the planet by about 10°C. The average temperature on Neptune is about minus 200 degrees Celsius. The upper left image samples temperatures near the top of Neptune's troposphere (near 100 mbar pressure). The hottest temperatures are located at the lower part of the image at Neptune's south pole (see the graphic at the upper right). The lower two images, taken 6.3 hours apart, sample temperatures at higher altitudes in Neptune's stratosphere. They do show generally warmer temperatures near, but not at, the south pole. In addition they show a warm area which can be seen in the lower left image and rotated completely around the planet in the lower right image."[55]

The set of four images at right are taken with the Hubble Space Telescope on June 25-26, 2011, just before Neptune arrived at the same location in space where it was discovered nearly 165 (Earth) years before (i.e. 1 Neptunian year on July 11, 2011).

"The snapshots were taken at roughly four-hour intervals [of a 16 h rotation period], offering a full view of the planet. The images reveal high-altitude clouds in the northern and southern hemispheres. The clouds are composed of methane ice crystals."[56]

"The snapshots show that Neptune has more clouds than a few years ago, when most of the clouds were in the southern hemisphere. These Hubble views reveal that the cloud activity is shifting to the northern hemisphere. It is early summer in the southern hemisphere and winter in the northern hemisphere."[56]

"The clouds are tinted pink because they are reflecting near-infrared light."[56]

## TW Hydrae

"TW Hydrae, a star 176 light-years from Earth in the constellation Hydra ... which has about the same mass as the sun, is surrounded by a dense ring of gas and dust. ... Its circumstellar disk is estimated to between 3 million and 10 million years old, and most protoplanetary disks are thought to last only 2 million to 3 million years. ... [Using the] ESA's Herschel Space Telescope, which is sensitive to the required infrared wavelengths [to measure the amount of deuterium] ... The ratio of deuterium to hydrogen appears constant in Earth's region of space, which means ... measuring hydrogen deuteride [yields] how much regular molecular hydrogen is present. ... TW Hydrae's disk is at least 16,650 times the mass of the Earth. Considering the planets in the solar system may have arisen from a disk only as little as 3,300 times the mass of the Earth, the matter in TW Hydrae's disk would be ample to form a planetary system. "This ... seems to point towards different systems finding disparate pathways to making planets. ... Signs of hydrogen deuteride remain difficult to detect around distant stars".[57].

## IRC +10420

"IRC +10420 ... is a peculiar F8I+ hypergiant with a large far-infrared excess attributed to circumstellar dust"[58]. The Brα, Pfγ, and Brγ lines are in emission, "with Hα showing a double peaked profile".[58] A Teff range of 6000 K to 6500 K fit the spectral photometry.[58] A Teff range of ~6060 K to ~6300 K is a cyan star. "Based on the model fit, the contribution of the photosphere at the observed wavelengths is: ... Brγ (60%), Pfγ (8%), and Brα (6%), the rest of the continuum emission is due to thermally radiating dust."[58]

## Cygnus X-3

"[S]pectral features [have been identified] in the near infrared I and K bands. These are ... characteristic of Wolf-Rayet stars: strong, broad emission lines of He I and He II, but no strong hydrogen lines. These observations strongly suggest the presence of a dense wind in the Cyg X-3 system, and may indicate that the companion is a fairly massive helium star"[12].

## Star-forming regions

Newborn stars peek out from beneath their natal blanket of dust in this dynamic image of the Rho Ophiuchi dark cloud from NASA's Spitzer Space Telescope. Credit: NASA/JPL-Caltech/Harvard-Smithsonian CfA).

"Newborn stars peek out from beneath their natal blanket of dust in this dynamic image of the Rho Ophiuchi dark cloud [in the image at right] from NASA's Spitzer Space Telescope. Called "Rho Oph" by astronomers, it's one of the closest star-forming regions to our own solar system. Located near the constellations Scorpius and Ophiuchus, the nebula is about 407 light years away from Earth."[59]

"Rho Oph is a complex made up of a large main cloud of molecular hydrogen, a key molecule allowing new stars to form from cold cosmic gas, with two long streamers trailing off in different directions. Recent studies using the latest X-ray and infrared observations reveal more than 300 young stellar objects within the large central cloud. Their median age is only 300,000 years, very young compared to some of the universe's oldest stars, which are more than 12 billion years old."[59]

"This false-color image of Rho Oph's main cloud, Lynds 1688, was created with data from Spitzer's infrared array camera, which has the highest spatial resolution of Spitzer's three imaging instruments. Blue represents 3.6 micron light, green is 4.5 micron light, orange is 5.8, and red is 8.0. The multiple wavelengths reveal different aspects of the dust surrounding and between the embedded stars, yielding information about the stars and their birthplace."[59]

"The colors in this image reflect the relative temperatures and evolutionary states of the various stars. The youngest stars are surrounded by dusty disks of gas from which they, and their potential planetary systems, are forming. These young disk systems show up as yellow-green tinted stars in this image. Some of these young stellar objects are surrounded by their own compact nebulae. More evolved stars, which have shed their natal material, are blue-white."[59]

## Orion

Comparison of the constellation Orion is viewed in visible and infrared light. Credit: Howard McCallon, Infrared: NASA/IRAS.{{free media}}

"Seen here [on the right] is a comparison of the constellation Orion viewed in visible and infrared light. In the infrared image from NASA’s IRAS mission we can see clouds of dust and gas invisible to the human eye. The bright spots are the locations where stars are being born."[60]

## Technology

These are before-and-after images that demonstrate the added source resolution of relatively new technology: ultra-precise starlight control. Credit: Lee Rannals.

The two images at right are "of HD 157728, a nearby star 1.5 times larger than the Sun. The star is centered in both images, and its light has been mostly removed by the adaptive optics system and coronagraph. The remaining starlight leaves a speckled background against which fainter objects cannot be seen. On the left, the image was made without the ultra-precise starlight control that Project 1640 is capable of. On the right, the wavefront sensor was active, and a darker square hole formed in the residual starlight, allowing objects up to 10 million times fainter than the star to be seen. Images were taken on June 14, 2012 with Project 1640 on the Palomar Observatory’s 200-inch Hale telescope."[61]

“We are blinded by this starlight, [...] Once we can actually see these exoplanets, we can determine the colors they emit, the chemical compositions of their atmospheres, and even the physical characteristics of their surfaces.”[62]

“Imaging planets directly is supremely challenging, [...] Imagine trying to see a firefly whirling around a searchlight more than a thousand miles away.”[63]

"The project is based on four instruments that take infrared photos of light generated by stars and the warm planets that orbit them. The instruments are now operating, and produce some of the highest-contrast images ever created."[61]

"The project is helping to create images that reveal celestial objects 1 million to 10 million times fainter than the star at the center of the image."[61]

“High-contrast imaging requires each subsystem perform flawlessly and in complete unison to differentiate planet light from starlight, [...] Even a small starlight leak in the system can inundate our photodetectors and pull the shroud back down over these planets.”[64]

“The more we learn about them, the more we realize how vastly different planetary systems can be from our own, [...] All indications point to a tremendous diversity of planetary systems, far beyond what was imagined just 10 years ago. We are on the verge of an incredibly rich new field.”[65]

“In order to understand the origin of Earth, we need to understand the origin of planets in general, [...] How do they form, how do they evolve? How does our solar system with both gas giant and rocky small planets compare to others? These are questions that are very important to humanity.”[66]

## Detectors

The infrared band may be divided up “based on the response of various detectors:[67]

• Near infrared: from 0.7 to 1.0  µm (from the approximate end of the response of the human eye to that of silicon).
• Short-wave infrared: 1.0 to 3  µm (from the cut off of silicon to that of the MWIR atmospheric window. InGaAs covers to about 1.8  µm; the less sensitive lead salts cover this region.
• Mid-wave infrared: 3 to 5  µm (defined by the atmospheric window and covered by indium antimonide [InSb] and HgCdTe and partially by lead selenide [PbSe]).
• Long-wave infrared: 8 to 12, or 7 to 14  µm: the atmospheric window (Covered by HgCdTe and microbolometers).
• Very-long wave infrared (VLWIR): 12 to about 30  µm, covered by doped silicon.

These divisions are justified by the different human response to this radiation: near infrared is the region closest in wavelength to the radiation detectable by the human eye, mid and far infrared are progressively further from the visible spectrum. Other definitions follow different physical mechanisms (emission peaks, vs. bands, water absorption) and the newest follow technical reasons (The common silicon detectors are sensitive to about 1,050 nm, while InGaAs' sensitivity starts around 950 nm and ends between 1,700 and 2,600 nm, depending on the specific configuration). Unfortunately, international standards for these specifications are not currently available.

The boundary between visible and infrared light is not precisely defined. The human eye is markedly less sensitive to light above 700 nm wavelength, so longer wavelengths make insignificant contributions to scenes illuminated by common light sources. But particularly intense light (e.g., from IR lasers, or from bright daylight with the visible light removed by colored gels) can be detected up to approximately 780 nm, and will be perceived as red light, although sources of up to 1050 nm can be seen as a dull red glow in intense sources.[68] The onset of infrared is defined (according to different standards) at various values typically between 700 nm and 800 nm.

## Commonly used subdivisions

A commonly used sub-division scheme is:[69]

 Division Name Abbreviation Wavelength Characteristics Near-infrared NIR, IR-A DIN 0.75-1.4 µm Defined by the water absorption, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO2 glass (silica) medium. Image intensifiers are sensitive to this area of the spectrum. Examples include night vision devices such as night vision goggles. Short-wavelength infrared SWIR, IR-B DIN 1.4-3 µm Water absorption increases significantly at 1,450 nm. The 1,530 to 1,560 nm range is the dominant spectral region for long-distance telecommunications. Mid-wavelength infrared MWIR, IR-C DIN. Also called intermediate infrared (IIR) 3-8 µm In guided missile technology the 3-5 µm portion of this band is the atmospheric window in which the homing heads of passive IR 'heat seeking' missiles are designed to work, homing on to the Infrared signature of the target aircraft, typically the jet engine exhaust plume Long-wavelength infrared LWIR, IR-C DIN 8–15 µm This is the "thermal imaging" region, in which sensors can obtain a completely passive picture of the outside world based on thermal emissions only and requiring no external light or thermal source such as the sun, moon or infrared illuminator. Forward-looking infrared (FLIR) systems use this area of the spectrum. This region is also called the "thermal infrared." Far infrared FIR 15 - 1,000 µm (see also far-infrared laser).

NIR and SWIR is sometimes called "reflected infrared" while MWIR and LWIR is sometimes referred to as "thermal infrared." Due to the nature of the blackbody radiation curves, typical 'hot' objects, such as exhaust pipes, often appear brighter in the MW compared to the same object viewed in the LW.

## Herschel Space Observatory

This shows the Herschel Space Observatory outside the Large Space Simulator at ESA's European Space Research and Technology Centre (ESTEC). Credit: Apoc2400.

The European Space Agency's Herschel Space Observatory has aboard the Photodetector Array Camera and Spectrometer (PACS). "The camera operates in three bands centred on 70, 100, and 160 μm, respectively, and the spectrometer covers the wavelength range between 51 and 220 μm."[70]

## Spitzer Space Telescope

The image shows the Spitzer Space Telescope prior to launch. Credit: NASA/JPL/Caltech.

"The Spitzer Space Telescope [imaged at the right] is a space-borne, cryogenically-cooled infrared observatory capable of studying objects ranging from our Solar System to the distant reaches of the Universe. Spitzer is the final element in NASA's Great Observatories Program, and an important scientific and technical cornerstone of the Astronomical Search for Origins Program."[71]

The telescope specifications are 85 cm diameter (33.5 Inches), f/12 lightweight Beryllium, cooled to less 5.5 K.[71] Its wavelength range is 3 - 180 µm.[71]

## Hypotheses

1. Infrared results can provide new interpretations of previous phenomena.

## References

1. Staff (11 September 2003). Why infrared astronomy is a hot topic. ESA. Retrieved 11 August 2008.
2. Infrared Spectroscopy – An Overview. NASA/IPAC. Retrieved 11 August 2008.
3. ESA and the PACS Consortium (26 June 2009). Herschels Daring Test: A Glimpse of Things to Come. NASA. Retrieved 2017-07-21.
4. IPAC Staff. Near, Mid and Far-Infrared. NASA ipac. Retrieved 2007-04-04.
5. J. Rho (January 12, 2005). Spitzer/IRAC View of the Trifid Nebula. Pasadena, California USA: NASA/JPL/Caltech. Retrieved 2014-03-06.
6. Alberto Noriega-Crespo (November 11, 2013). Bubbly Newborn Star. Pasadena, California USA: NASA/JPL/Caltech. Retrieved 2014-03-06.
7. Hector Arce (November 11, 2013). Spitzer and ALMA Reveal a Star's Bubbly Birth. Pasadena, California USA: NASA/JPL/Caltech. Retrieved 2014-03-06.
8. Alberto Noriega-Crespo (November 11, 2013). Spitzer and ALMA Reveal a Star's Bubbly Birth. Pasadena, California USA: NASA/JPL/Caltech. Retrieved 2014-03-06.
9. J. Hora (August 8, 2004). Ring of Stellar Death. Pasadena, California USA: NASA/JPL/Caltech. Retrieved 2014-03-06.
10. Tom Megeath, Rob Gutermuth, Joe Hora, Lori Allen, Kevin Flaherty, John Stauffer, Lee Hartmann, James Muzerolle, Phil Myers, Nick Siegler, Erick Young, and Giovanni Fazio (August 14, 2006). Orion's Inner Beauty. Pasadena, California USA: NASA/JPL/California Institute of Technology. Retrieved 2014-03-06.CS1 maint: multiple names: authors list (link)
11. T. R. Geballe, K. Krisciunas, J. A. Bailey, and R. Wade (April 1, 1991). "Mapping of infrared helium and hydrogen line profiles in the central few arcseconds of the Galaxy". The Astrophysical Journal 370 (4): L73-6. doi:10.1086/185980. Retrieved 2012-08-03.
12. M. H. van Kerkwijk, P. A. Charles, T. R. Geballe, D. L. King, G. K. Miley, L. A. Molnar, E. P. J. van den Heuvel, M. van der Kils & J. van Paradlja (February 20, 1992). "Infrared helium emission lines from Cygnus X-3 suggesting a Wolf-Rayet star companion". Nature 355: 703-5. Retrieved 2012-08-03.
13. L. A. Yakovina, Ya. V. Pavlenko (October 2001). "On the lithium abundance determination in the atmospheres of super-Li-RICH CARBON stars using the resonance and subordinate Li I lines. I". Kinematika i Fizika Nebesnykh Tel 17 (5): 446-58. Retrieved 2012-08-03.
14. Katia Cunha and Verne V. Smith (February 20, 1999). "A Determination of the Solar Photospheric Boron Abundance". The Astrophysical Journal 512 (2). doi:10.1086/306796. Retrieved 2012-08-03.
15. R. J. Thomas and R. A. Young (January 1981). "Measurement of atomic oxygen and related airglows in the lower thermosphere". Journal of Geophysical Research: Oceans 86 (08): 7389-93. doi:10.1029/JC086iC08p07389. Retrieved 2013-01-16.
16. Paul D. Feldman (January 1978). "Auroral excitation of optical emissions of atomic and molecular oxygen". Journal of Geophysical Research 83 (A6): 2511-6. doi:10.1029/JA083iA06p02511. Retrieved 2013-01-16.
17. Sara Lucatello, Thomas Masseron, Jennifer A. Johnson, Marco Pignatari, Falk Herwig (March 1, 2011). "Fluorine and Sodium in C-rich Low-Metallicity Stars". The Astrophysical Journal 729 (1): 13. doi:10.1088/0004-637X/729/1/40. Retrieved 2013-01-16.
18. P. Swings (July 1943). "Edlén's Identification of the Coronal Lines with Forbidden Lines of Fe X, XI, XIII, XIV, XV; Ni XII, XIII, XV, XVI; Ca XII, XIII, XV; a X, XIV". The Astrophysical Journal 98 (07): 116-28. doi:10.1086/144550. Retrieved 2013-01-18.
19. David L. Lambert, Verne V. Smith, Maurizio Busso, Roberto Gallino, and Oscar Straniero (September 1, 1995). "The Chemical Composition of Red Giants. IV. The Neutron Density at the s-Process Site". The Astrophysical Journal 450 (09): 302-17. doi:10.1086/176141. Retrieved 2013-08-01.
20. Lucas Cieza, Luisa Rebull, and Jes Jorgensen (October 25, 2006). Perseus' Stellar Neighbors. Pasadena, California USA: NASA/JPL/California Institute of Technology. Retrieved 2014-03-06.CS1 maint: multiple names: authors list (link)
21. W. A. Traub and N. P. Carleton (January 1, 1979). "Retrograde winds on Venus - Possible periodic variations". The Astrophysical Journal 227 (1): 329-33. doi:10.1086/156734. Retrieved 2013-01-20.
22. IR Atmospheric Windwows. Retrieved 2009-04-09.
23. A. García Muñoz, F. P. Mills, T. G. Slanger, G. Piccioni, P. Drossart (December 2009). "Visible and near-infrared nightglow of molecular oxygen in the atmosphere of Venus". Journal of Geophysical Research: Planets 114 (E12). doi:10.1029/2009JE003447. Retrieved 2013-01-16.
24. Sue Lavoie (January 29, 1996). PIA00124: Infrared Image of Low Clouds on Venus. Pasadena, California, USA: NASA/JPL. Retrieved 2013-01-20.
25. Warren Wiscombe (August 19, 2009). First IR Image from Newest Weather Satellite Captures Hurricane Bill. NASA/NOAA. Retrieved 2012-11-26.
26. NASAGalileo (March 14, 2003). Earth - Galileo Raw image of Earth showing Antarctica and Africa. Greenbelt, Maryland USA: NASA Goddard Space Flight Center. Retrieved 2013-04-01.
27. Yvette Smith (September 25, 2009). Water Detected at High Latitudes on the Moon. NASA. Retrieved 2012-11-26.
28. DCATT Team (1996). MSX Showcase A Gallery of Infrared Images. Pasadena, California USA: California Institute of Technology. Retrieved 2013-08-02.
29. Phil Davis (June 24, 2011). Methane on Mars. National Aeronautics and Space Administration. Retrieved 2012-07-20.
30. Ron Cowen (8 October 2009). Ice confirmed on an asteroid. Science News. Retrieved 9 October 2009.
31. Nancy Atkinson (8 October 2009). More water out there, ice found on an asteroid, In: International Space Fellowship. Retrieved 11 October 2009.
32. Campins, Humberto; Hargrove, K; Pinilla-Alonso, N; Howell, ES; Kelley, MS; Licandro, J; Mothé-Diniz, T; Fernández, Y et al. (2010). "Water ice and organics on the surface of the asteroid 24 Themis". Nature 464 (7293): 1320–1. doi:10.1039/nature09029. PMID 20428164.
33. Rivkin, Andrew S.; Emery, Joshua P. (2010). "Detection of ice and organics on an asteroidal surface". Nature 464 (7293): 1322–3. doi:10.1038/nature09028. PMID 20428165.
34. More Water Out There, Ice Found on an Asteroid | International Space Fellowship
35. Sang J. Kim, John Caldwell, A.R. Rivolo, R. Wagener, Glenn S. Orton (November 1985). "Infrared polar brightening on Jupiter. III - Spectrometry from the Voyager 1 IRIS experiment". Icarus 64 (2): 233-48. doi:10.1016/0019-1035(85)90088-0. Retrieved 2012-07-09.
36. ESO/F. Marchis, M. Wong, E. Marchetti, P. Amico, S. Tordo (October 2, 2008). Sharpening up Jupiter. ESO Santiago, Chile: ESO. Retrieved 2012-07-11.CS1 maint: multiple names: authors list (link)
37. Phil Davis (May 3, 2011). Triple Eclipse. National Aeronautics and Space Administration. Retrieved 2012-07-20.
38. Mystery impact leaves Earth-sized mark on Jupiter. CNN. July 21, 2009.
39. Overbye, Dennis (July 22, 2009). All Eyepieces on Jupiter After a Big Impact. New York Times.
40. Amateur astronomer spots Earth-size scar on Jupiter, Guardian, July 21, 2009
41. Sue Lavoie (December 31, 2010). Acetylene at Jupiter's North and South Poles. Ministry of Space Exploration. Retrieved 2013-02-06.
42. Sue Lavoie (September 30, 1999). PIA02500: Sulfuric Acid on Europa. Washington DC USA: NASA's Office of Space Science. Retrieved 2013-06-24.
43. Dale Cruikshank (December 18, 2003). Comet Schwassmann-Wachmann 1. Pasadena, California, USA: NASA, JPL, California Institute of Technology. Retrieved 2012-11-26.
44. W. Reach (October 10, 2008). Anatomy of a Busted Comet. Pasadena, California, USA: NASA, JPL, California Institute of Technology. Retrieved 2012-11-26.
45. "File:Saturn polar vortex.jpg". Wikimedia Commons (San Francisco, California: Wikimedia Foundation, Inc). October 3, 2009. Retrieved 2012-07-21.
46. Carolina Martinez and Laura K. Kraft (February 3, 2005). Saturn's Bull's-Eye Marks Its Hot Spot. NASA. Retrieved 2012-07-21.
47. Samantha Harvey (March 29, 2011). Glowing Southern Lights. NASA. Retrieved 2012-07-21.
48. Sue Lavoie (November 12, 2008). PIA11396: Saturn's Polar Aurora. Tucson, Arizona: JPL/NASA/University of Arizona. Retrieved 2012-07-21.
49. Samantha Harvey (September 20, 2011). Neon Saturn. NASA. Retrieved 2012-07-21.
50. Yvette Smith (March 23, 2008). The Colors of Saturn. NASA. Retrieved 2012-07-21.
51. Andy Ingersoll, Ulyana Dyudina, Shawn Ewald, Carolyn Porco, Daiana DiNino, Joe Mason (July 6, 2011). A Day in the Life. Cassini Imaging Central Laboratory for Operations. Retrieved 2012-11-26.CS1 maint: multiple names: authors list (link)
52. Erimus (February 28, 2011). "File:Arieluranus.jpg". San Francisco, California: Wikimedia Foundation, Inc. Retrieved 2012-07-21.
53. Samantha Harvey (August 19, 2004). Uranus from Earth. NASA and Keck Observatory. Retrieved 2012-07-21.
54. Phil Davis (June 16, 2011). Neptune in Infrared. National Aeronautics and Space Administration. Retrieved 2012-07-20.
55. VLT/ESO/NASA/JPL/Paris Observatory (September 18, 2007). Neptune's 'Hot' South Pole (VISIR/VLT). Santiago, Chile: European Southern Observatory. Retrieved 2012-07-11.
56. Donna Weaver, Ray Villard, Keith Noll (July 12, 2011). Neptune Completes Its First Circuit Around The Sun Since Its Discovery. Baltimore, Maryland, USA: NASA/Space Telescope Science Institute. Retrieved 2012-11-26.CS1 maint: multiple names: authors list (link)
57. Charles Q. Choi (January 30, 2013). Star Not Too Old to Have Planets After All. Yahoo! News. Retrieved 2013-01-31.
58. René D. Oudmaijer, T.R. Geballe, L.B.F.M. Walters, and K.C. Sahu (1994). "Discovery of near-infrared hydrogen line emission in the peculiar F8 hypergiant IRC +10420". Astronomy and Astrophysics 281 (1): L33-6. Retrieved 2012-08-02.
59. G.G. Fazio, P.C. Myers, L. Allen, S.T. Megeath, E.T. Young, J. Muzerolle, N.J. Evans II, G.A. Blake, P.M. Harvey, D.W. Koerner, L.G. Mundy, D.L. Padgett, A.I. Sargent, K.R. Stapelfeldt, and E.F. van Dishoeck (February 11, 2008). Young Stars in Their Baby Blanket of Dust. Pasadena, California USA: NASA/JPL/Caltech. Retrieved 2014-03-06.CS1 maint: multiple names: authors list (link)
60. Howard McCallon (1990). Orion Visible and Infrared. Pasadena, California USA: NASA/JPL. Retrieved 2017-07-21.
61. Lee Rannals (July 6, 2012). Sifting Through Starlight To Find New Planets. Red Orbit .com. Retrieved 2014-03-06.
62. Ben R. Oppenheimer (July 6, 2012). Sifting Through Starlight To Find New Planets. Red Orbit .com. Retrieved 2014-03-06.
63. Charles Beichman (July 6, 2012). Sifting Through Starlight To Find New Planets. Red Orbit .com. Retrieved 2014-03-06.
64. Richard Dekany (July 6, 2012). Sifting Through Starlight To Find New Planets. Red Orbit .com. Retrieved 2014-03-06.
65. Gautam Vasisht (July 6, 2012). Sifting Through Starlight To Find New Planets. Red Orbit .com. Retrieved 2014-03-06.
66. Lynne Hillenbrand (July 6, 2012). Sifting Through Starlight To Find New Planets. Red Orbit .com. Retrieved 2014-03-06.
67. Miller, Principles of Infrared Technology (Van Nostrand Reinhold, 1992), and Miller and Friedman, Photonic Rules of Thumb, 2004. ISBN 9780442012106
68. D.R. Griffin, R Hubbard, G Wald (1947). "The Sensitivity of the Human Eye to Infra-Red Radiation". J. Opt. Soc. Am. 37 (7): 546–553. doi:10.1364/JOSA.37.000546.
69. James Byrnes (2009). Unexploded Ordnance Detection and Mitigation. Springer. pp. 21–22. ISBN 9781402092527.
70. Edwin A. Bergin, Thomas Henning, Ewine van Dishoeck, Göran Pilbratt (January 30, 2013). Herschel sizes up massive protoplanetary disc. European Space Agency. Retrieved 2013-02-01.CS1 maint: multiple names: authors list (link)
71. About Spitzer. Fast Facts. Retrieved 2014-03-06.