Radiation astronomy/Planets

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This is a multicolor image from the Pan-STARRS1 telescope of the free-floating planet PSO J318.5-22, in the constellation of Capricornus. Credit: N. Metcalfe & Pan-STARRS 1 Science Consortium.

"PSO J318.5-22 is a confirmed,[1][2] extrasolar object and candidate planet that does not appear to be orbiting a star. It is approximately 80 light-years away, and belongs to the Beta Pictoris moving group of stars.[3] The object was discovered in 2013 in images taken by the Pan-STARRS PS1 wide-field telescope. The object's age is inferred to be 12 million-years, the same age as the Beta Pictoris group.[4]

“We have never before seen an object free-floating in space that looks like this. It has all the characteristics of young planets found around other stars, but it is drifting out there all alone".[5]

“Planets found by direct imaging are incredibly hard to study, since they are right next to their much brighter host stars. PSO J318.5-22 is not orbiting a star so it will be much easier for us to study. It is going to provide a wonderful view into the inner workings of gas-giant planets like Jupiter shortly after their birth”.[6]

Backgrounds[edit]

The near-infrared image shows the GJ 758 solar system. Credit: Max Planck Institute for Astronomy.
This astrometric analysis consists of motions of point-sources near GJ 758 across five epochs (E1–E5), measured relative to GJ 758’s position. Credit: M. Janson et al., National Astronomical Observatory of Japan.

When the overwhelming radiation from the star GJ 758 is reduced and the star itself eclipsed by a disk, secondary radiation sources appear in the background. These are labeled B and C?.

Subsequent observations with the Subaru Telescope revealed C? to be a background star rather than an object in orbit around GJ 758.

"The source tentatively referred to as “GJ 758 C” [follows] the background star track".[7]

"GJ 758 B exhibits common proper motion with its parent star as well as systematic orbital motion towards the northwest, whereas all other point-sources follow the expected trajectory for background stars (solid arrows). The object referred to as “GJ 758 C” [...] is unambiguously identified as a background star (motion highlighted by dashed blue arrows). The grey plus signs are 1σ error bars. The circle marked as “PSF” shows the size of the resolution element in H-band on [High Contrast Instrument for the Subaru Next Generation Adaptive Optics] HiCIAO."[7]

Visuals[edit]

This annotated image shows key features of the Fomalhaut system, including the newly discovered planet Fomalhaut b, and the dust ring. Credit: Credit: NASA, ESA, and Z. Levay (STScI).

The "annotated image [at right] shows key features of the Fomalhaut system, including the newly discovered planet Fomalhaut b, and the dust ring. Also included are a distance scale and an insert, showing how the planet has moved around its parent star over the course of 21 months. The Fomalhaut system is located approximately 25 light-years from the Earth."[8]

The extrasolar planet is in orbit around Fomalhaut and is estimated "to be no more than three times Jupiter's mass ... In 2004, the coronagraph in the High Resolution Camera on Hubble's Advanced Camera for Surveys produced the first-ever resolved visible-light image of a large dust belt surrounding Fomalhaut. It clearly showed that this structure is in fact a ring of protoplanetary debris approximately 21.5 billion miles across with a sharp inner edge. This large debris disk is similar to the Kuiper Belt, which encircles the solar system and contains a range of icy bodies from dust grains to objects the size of dwarf planets, such as Pluto."[9]

"Observations taken 21 months apart by Hubble's Advanced Camera for Surveys' coronagraph show that the object is moving along a path around the star and therefore is gravitationally bound to it. The planet is 10.7 billion miles from the star, or about 10 times the distance of the planet Saturn from the sun."[9]

"A follow-up image in 2006 showed that one of the objects is moving through space with Fomalhaut but changed position relative to the ring since the 2004 exposure. The amount of displacement between the two exposures corresponds to an 872-year-long orbit as calculated from Kepler's laws of planetary motion."[9]

"The planet mysteriously dimmed by half a stellar magnitude between the 2004 and 2006 observations."[9]

Blues[edit]

This image captured by the SOFI instrument on ESO’s New Technology Telescope at the La Silla Observatory shows the free-floating planet CFBDSIR J214947.2-040308.9 in infrared light. Credit: ESO/P. Delorme.

"This image [at the right] captured by the SOFI instrument on ESO’s New Technology Telescope at the La Silla Observatory shows the free-floating planet CFBDSIR J214947.2-040308.9 in infrared light. This object, which appears as a faint blue dot at the centre of the picture and is marked with a cross, is the closest such object to the Solar System. It does not orbit a star and hence does not shine by reflected light; the faint glow it emits can only be detected in infrared light. The object appears blueish in this near-infrared view because much of the light at longer infrared wavelengths is absorbed by methane and other molecules in the planet's atmosphere. In visible light the object is so cool that it would only shine dimly with a deep red colour when seen close-up."[10]

CFBDSIR J214947.2-040308.9 "seems to be part of a nearby stream of young stars known as the AB Doradus Moving Group."[10]

"This is the first isolated planetary mass object ever identified in a moving group, and the association with this group makes it the most interesting free-floating planet candidate identified so far."[10]

“Looking for planets around their stars is akin to studying a firefly sitting one centimetre away from a distant, powerful car headlight. This nearby free-floating object offered the opportunity to study the firefly in detail without the dazzling lights of the car messing everything up.”[10]

"Free-floating objects like CFBDSIR2149 are thought to form either as normal planets that have been booted out of their home systems, or as lone objects like the smallest stars or brown dwarfs. In either case these objects are intriguing — either as planets without stars, or as the tiniest possible objects in a range spanning from the most massive stars to the smallest brown dwarfs."[10]

"The association with the AB Doradus Moving Group would pin down the mass of the planet to approximately 4–7 times the mass of Jupiter, with an effective temperature of approximately 430 degrees Celsius. The planet’s age would be the same as the moving group itself — 50 to 120 million years."[10]

TW Hydrae[edit]

These images, taken a year apart by NASA's Hubble Space Telescope, reveal a shadow moving counterclockwise around a gas-and-dust disk encircling the young star TW Hydrae. Credit: NASA, ESA and J. Debes (STScl).

"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".[11]

"These images [on the right], taken a year apart by NASA's Hubble Space Telescope, reveal a shadow moving counterclockwise around a gas-and-dust disk encircling the young star TW Hydrae. The two images at the top show an uneven brightness across the disk. Through enhanced image processing (images at the bottom), the darkening becomes even more apparent."[12]

The "shadow [was noticed] after analyzing 18 years' worth of observations of TW Hydrae, which is about 8 million years old and lies 192 light-years from Earth, in the constellation Hydra. The images, taken by NASA's Hubble Space Telescope, showed that the shadow rotates around the 41-billion-mile-wide (66 billion kilometers) disk once every 16 years."[13]

"This is the very first disk where we have so many images over such a long period of time, therefore allowing us to see this interesting effect. That gives us hope that this shadow phenomenon may be fairly common in young stellar systems."[12]

"An unseen exoplanet is the best explanation for the shadow."[12]

The "alien world itself isn't casting the shadow; rather, the planet's gravity has twisted and tilted the inner portion of the dust-and-gas disk, blocking starlight headed toward the outer reaches."[13]

The "planet lies about 100 million miles (160 million km) from TW Hydrae — about the distance from Earth to the sun. That's way too close to the star for Hubble or any other telescope now in operation to photograph it directly. (Planets that orbit so tightly are drowned out by their parent stars' overwhelming glare.)"[13]

"The putative planet must be about five times more massive than Jupiter to sculpt the inner disk in this manner."[12]

"What is surprising is that we can learn something about an unseen part of the disk by studying the disk's outer region and by measuring the motion, location and behavior of a shadow. This study shows us that even these large disks, whose inner regions are unobservable, are still dynamic, or changing in detectable ways which we didn't imagine."[12]

CHXR 73 b[edit]

CHXR 73 b is a star which lies at the border between planet and brown dwarf. Credit: NASA/ESA/K. Luhman (Penn State University, USA).

"Astronomers using the NASA/ESA Hubble Space Telescope have photographed one of the smallest objects ever seen around a normal star beyond our Sun. Weighing in at 12 times the mass of Jupiter, the object is small enough to be a planet. The conundrum is that it's also large enough to be a brown dwarf, a failed star."[14]

"New, more sensitive telescopes are finding smaller and smaller objects of planetary-mass size. These discoveries have prompted astronomers to ask the question, are planetary-mass companions always planets?"[14]

"The object is so far away from its star that it is unlikely to have formed in a circumstellar disk."[14]

"The study of substellar objects in orbit around a star allows us to determine the age, and over time also the mass of the companion. Such studies help us to improve out understanding of the formation and inner structure of brown dwarfs and planets."[15]

Kepler-1520 b[edit]

The planetary system of KIC 12557548 consists of one extrasolar planet, named Kepler-1520 b which appears to possess a tail of dust and gas formed in a similar fashion to that of a comet[16] but, as opposed to the tail of a comet, it contains molecules of pyroxene and aluminium(III) oxide. Based on the rate at which the particles in the tail are emitted, the mass of the planet has been constrained to less than 0.02 Earth masses — a higher-mass planet would have too much gravity to sustain the observed rate of mass loss.[17] [18]

Kepler-1520 is at J2000 19h 23m 51.8899s[19] +51° 30′ 16.98″[19] in the constellation Cygnus, with an apparent magnitude in the visible of 16.7,[18] spectral class K4V[20] details

  1. mass = 0.76 ± 0.03[21]
  2. radius = 0.71 ± 0.026[21]
  3. luminosity = 0.14[18]
  4. surface gravity (log g) = 4.610 +0.018 or −0.031 cgs[21]
  5. temperature = 4677 +82 or -71[21]
  6. metallicity/Fe = 0.04 ± 0.15[21]
  7. rotation = 22.91±0.24 days[22]
  8. age in gyr = 4.47[21]

The star is particularly important, as measurements taken by the Kepler spacecraft indicate that the variations in the star's light curve cover a range from about 0.2% to 1.3% of the star's light being blocked.[18] This indicates that there may be a rapidly disintegrating planet, a prediction not yet conclusively confirmed, in orbit around the star, losing mass at a rate of 1 Earth mass every billion years.[18] The planet itself is about 0.1 Earth masses,[23] or just twice the mass of Mercury, and is expected to disintegrate in about 100[23]-200 million years.[18] The planet orbits its star in just 15.7 hours,[18] at a distance only two stellar diameters away from the star's surface,[16] and has an estimated effective temperature of about 2255 K.[23] The orbital period of the planet is one of the shortest ever detected in the history of the extrasolar planet search.[24] In 2016, the planet was confirmed as part of a data release by the Kepler spacecraft.

K2-33 b[edit]

The planet is best known for its remarkably young age, which is estimated to be about 9.3 million years.[25]

Given this age, the planetary system most likely formed back near the end of the Miocene epoch of the Earth's history. Observations made on the planet confirmed that it was in fact a fully formed exoplanet, not just a protoplanet that was still in the stages of developing. The mass and radius of the exoplanet further help constrain this statement.[25][26]

  1. semimajor = 0.0409 +0.0021 or −0.0023 AU[27]
  2. eccentricity = 0.0[25]
  3. orbital period = 5.424865 +0.000035 −0.000031[2] d[25]
  4. inclination = 89.1 +0.6 or −1.1[25]
  5. mass = 3.6 MJ.[26]
  6. mean radius = 5.04 +0.34 or −0.37 R[25]

K2-33b is the youngest confirmed transiting exoplanet.

The discoveries of K2-33b and V830 Tau b are most notable for explaining how close-in planets form, an open question in the field of exoplanets since the discovery of the first exoplanet, 51 Pegasi b, in 1995. Given the young ages of these exoplanets, several theories of planetary migration can be ruled out because they take too long to form close-in planets. The most plausible formation scenario for K2-33b is that it formed further away from its star, then migrated inwards through the protoplanetary disk, although it remains a possibility that the planet formed in place.[25][26]

"The question we are answering is: Did those planets take a long time to get into those hot orbits, or could they have been there from a very early stage? We are saying, at least in this one case, that they can indeed be there at a very early stage."[28]

NASA's Kepler spacecraft began its "Second Light" mission from 23 August to 13 November 2014, collecting data from the core of Upper Scorpius, which included K2-33.[25] The exoplanet was simultaneously discovered by two independent research groups.[26][25]

The star K2-33 was studied on days in late January, February, and March 2016. The observations were made with the Immersion Grating Infrared Spectrometer (IGRINS) on the 2.7-m Harlan J. Smith Telescope at the McDonald Observatory.[25] After observing the respective transits, which for K2-33b occurred roughly every 5 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic 5-day transits.[28]

HD 95086 b[edit]

This image from ESO's Very Large Telescope (VLT) shows the newly discovered planet HD95086 b, next to its parent star. Credit: ESO/J. Rameau.{{free media}}

"This image from ESO's Very Large Telescope (VLT) shows the newly discovered planet HD95086 b, next to its parent star. The observations were made using NACO, the adaptative optics instrument for the VLT in infrared light, and using a technique called differential imaging, which improves the contrast between the planet and its dazzling host star. The star itself has been removed from the picture during processing to enhance the view of the faint exoplanet and its position is marked. The exoplanet appears at the lower left."[29]

"The blue circle is the size of the orbit of Neptune in the Solar System."[29]

"The star HD 95086 has similar properties to Beta Pictoris and HR 8799 around which giant planets have previously been imaged at separations between 8 and 68 astronomical units. These stars are all young, more massive than the Sun, and surrounded by a debris disc."[29]

HIP 78530 b[edit]

Between 2000 and 2001, the ADONIS: ADaptive Optics Near Infrared System system at the ESO 3.6 m Telescope in Chile detected a faint object in the vicinity of HIP 78530, reported in 2005 and 2007.[30]

A random selection of ninety-one stars in the Upper Scorpius association provided a sample of stars to be observed using the Near Infrared Imager and Spectrometer (NIRI) and Altitude conjugate Adaptive Optics for the Infrared (ALTAIR) adaptive optics system at the Gemini Observatory for direct imaging including HIP 78530, first imaged by the camera on May 24, 2008.[30] This initial image revealed the presence of the same faint object within the vicinity of HIP 78530.[30]

Follow-up imaging took place on July 2, 2009 and August 30, 2010 using the same instruments, with additional follow-up data recovered in the spring and summer of 2010, with the data used to filter out pixelated portions of the images and improve the images' quality to suggest that the faint object in the image was near the star HIP 78530, was a brown dwarf or planet.[30]

HIP 78530 b is most likely a brown dwarf, a massive object that is large enough to fuse deuterium but not large enough to ignite and become a star, but HIP 78530 b's characteristics blend the line between whether or not it is a brown dwarf or a planet.[30]

  1. semimajor axis = 710 (± 60)[31] AU
  2. orbital period = ~12000[30] y
  3. mass = 23.04 (± 4)[31] MJ
  4. surface gravity = -2.55 (± 0.13)[30] g
  5. temperature = 2800 (± 200)[30] K

HIP 78530 is a bright, blue B-type main sequence star in the Upper Scorpius association, a loose star cluster composed of stars with a common origin.[30] The star is estimated to be approximately 2.5 times the mass of the Sun, with an age of the Upper Scorpius group of approximately 11 million years old.[32]

Its effective temperature is estimated at 10,500 K[31] less than twice the effective temperature of the Sun.[33]

HIP 78530 has an apparent magnitude of 7.18.[31] It is incredibly faint, if visible at all, as seen from the unaided eye of an observer on Earth.[34]

V830 Tau b[edit]

The hot Jupiter exoplanet V830 Tau b is the youngest known exoplanet with an age of around 2 million years (around the time that humans evolved on Earth).[35]

Technology[edit]

The North telescope of the Gemini Observatory directly imaged the HIP 78530 system. Credit: Mailseth.
Gemini South is on Cerro Pachón in Chile. Credit: Denys.{{free media}}
Comparison is of nominal sizes of primary mirrors of notable optical telescopes. Credit: Cmglee.{{free media}}
Gemini Planet Imager (GPI) image is of a planet orbiting a distant star known as 51 Eridani. Credits: J. Rameau (Univ. of Montreal) and C. Marois (NRC Herzberg, Canada).

In the lower image on the right, the bright central star 51 Eridani has been mostly removed by a hardware and software mask to enable the detection of the exoplanet (labelled "b") that is one millionth as bright.

Both Gemini telescopes employ sophisticated state-of-the-art adaptive optics systems: Gemini-N routinely uses the ALTAIR system, built in Canada, which achieves a 30%-45% Strehl ratio on a 22.5-arcsecond-square field and can feed NIRI, NIFS or GNIRS;[36] it can use natural or laser guide stars. In conjunction with NIRI it was responsible for the discovery of HR 8799 b.

At Gemini-S the Gemini Multi-Conjugate Adaptive Optics System (GeMS) may be used with the FLAMINGOS-2 near-infrared imager and spectrometry, or the Gemini South Adaptive Optics Imager (GSAOI), which provides uniform, diffraction-limited image quality to arcminute-scale fields of view, GeMS achieved first light on December 16, 2011.[37] Using a constellation of five laser guide stars, it achieved Full width at half maximum (FWHM) of 0.08 arc-seconds in the H band over a field of 87 arc-seconds square.

The detectors in each instrument have recently been upgraded with Hamamatsu Photonics devices, which significantly improve performance in the far red part of the optical spectrum (700–1,000 nm).[38]

Near-infrared imaging and spectroscopy are provided by the NIRI, NIFS, GNIRS, FLAMINGOS-2, and GSAOI instruments.[39]

The Gemini Planet Imager (GPI) is a high contrast imaging instrument that was built for the Gemini South Telescope that achieves high contrast at small angular separations, allowing for the direct imaging and integral field spectroscopy of extrasolar planets around nearby stars.[40][41]

See also[edit]

References[edit]

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  3. A Strange Lonely Planet Found Without a Star. Science Daily. 9 October 2013.
  4. Institute for Astronomy (2013-10-09). A Strange Lonely Planet Found without a Star. University of Hawaii.
  5. Michael Liu (October 10, 2013). Young planet, six times more massive than Jupiter, found hanging alone without a star.
  6. Niall Deacon (October 10, 2013). Young planet, six times more massive than Jupiter, found hanging alone without a star.
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  40. Bruce Macintosh, James Graham, David Palmer, Rene Doyon, Don Gavel, James Larkin, Ben Oppenheimer, Leslie Saddlemyer, J. Kent Wallace, Brian Bauman, Julia Evans, Darren Erikson, Katie Morzinski, Donald Phillion, Lisa Poyneer, Anand Sivaramakrishnan, Remi Soummer, Simon Thibault, Jean-Pierre Veran (June 2006). "The Gemini Planet Imager". Proceedings of SPIE. Astronomical Telescopes 6272: 62720L-62720L-12. doi:10.1117/12.672430. 
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External links[edit]