Radiation astronomy/Comets

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This image shows Comet 67P/Churyumov-Gerasimenko. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/ UPM/DASP/IDA.
This image shows Comet 67P/Churyumov-Gerasimenko rotated around a vertical axis from the right. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/ UPM/DASP/IDA.

The image at the right is an optical astronomy image of the comet 67P/Churyumov-Gerasimenko. Rosetta's OSIRIS narrow-angle camera made the image on 3 August 2014 from a distance of 285 km. The image resolution is 5.3 metres/pixel.

The left image is rotated 90° from the right. The location of the right image is the front view of the left side just out of view in the left image. The object rotates by the right hand rule from the left image to the right.

Note that due to the evaporation of volatiles, the surface of the rocky object appears pitted or cratered.

Cyans[edit]

Recent changes in Comet Lulin's greenish coma and tails are shown in these two panels taken on January 31st (top) and February 4th (bottom) 2009. In both views the comet has an apparent antitail to the left of the coma of dust. Credit: Joseph Brimacombe, Cairns, Australia.
Sweeping slowly through northern skies, the comet PanSTARRS C/2012 K1 posed for this telescopic portrait on June 2nd in the constellation Ursa Major. Credit: Alessandro Falesiedi.

Perhaps the most prominent cyan planetary source is Uranus, which has only been visited by the space probe Voyager 2. More recent images come from the Hubble Space Telescope in orbit around Earth.

Methane possesses prominent absorption bands in the visible and near-infrared (IR) making Uranus aquamarine or cyan in color.[1]

“During the Halley Monitoring Program at La Silla from Feb.17 to Apr.17,1986 ... In the light of the neutral CN-radical a continuous formation and expansion of [cyan] gas-shells could be observed.”[2] “The gas-expansion velocity decreases with increasing heliocentric distance from 1 km/s in early March to 0.8 km/s in April.”[2]

Shown at right, "Lulin's green color comes from the gases that make up its Jupiter-sized atmosphere. Jets spewing from the comet's nucleus contain cyanogen (CN: a poisonous gas found in many comets) and diatomic carbon (C2). Both substances glow green when illuminated by sunlight"[3]

The electric blue glow of electricity results from the spectral emission of the excited ionized atoms (or excited molecules) of air (mostly oxygen and nitrogen) falling back to unexcited states, which happens to produce an abundance of electric blue light. This is the reason electrical sparks in air, including lightning, appear electric blue. It is a coincidence that the color of Cherenkov radiation and light emitted by ionized air are a very similar blue despite their very different methods of production.

On the right is a visual image of comet PanSTARRS C/2012 K1.

"Now within the inner solar system, the icy body from the Oort cloud sports two tails, a lighter broad dust tail and crooked ion tail extending below and right. The comet's condensed greenish coma makes a nice contrast with the spiky yellowish background star above. NGC 3319 appears at the upper left of the frame that spans almost twice the apparent diameter of the full Moon."[4]

Sun-grazing comets[edit]

Comet Lovejoy survives it sun-grazing cruise around the Sun and back into space (Dec. 15-16, 2011). Credit: https://www.youtube.com/user/SDOmission2009.{{free media}}

"Sun-grazing comets almost never re-emerge, but their sublimative destruction near the sun has only recently been observed directly, while chromospheric impacts have not yet been seen, nor impact theory developed."[5] "[N]uclei are ... destroyed by ablation or explosion ... in the chromosphere, producing flare-like events with cometary abundance spectra."[5]

"The death of a comet at r ~ Rʘ has been seen directly only very recently (Schrijver et al 2011) using the SDO AIA XUV instrument. This recorded sublimative destruction of Comet C/2011 N3 as it crossed the solar disk very near periheloin q = 1.139Rʘ."[5]

"The phenomenon of flare induced sunquakes - waves in the photosphere - discovered by Kosovichev and Zharkova (1998) and now widely studied (e.g. Kosovichev 2006) should also result from the momentum impulse delivered by a cometary impact."[5]

Comet Bennett 1970 II[edit]

The velocities of the cyan molecule as produced in the head of comet Bennett 1970 II have been measured.[6]

Comet Borrelly[edit]

This image reveals dust being ejected from the nucleus of comet Borrelly. Credit: NASA/JPL.
Comet Borrelly is imaged by Deep Space 1 revealing no surface ice. Credit: NASA/JPL.

"A typical comet nucleus has an albedo of 0.04.[7]

"This image, taken by Deep Space 1 on September 22, 2001, has been enhanced to reveal dust being ejected from the nucleus of comet Borrelly. As a result, the nucleus, which is about eight kilometers (about five miles) long, is bright white in the image. The main dust jet is directed towards the bottom left of the frame, around 35 degrees away from the comet-Sun line. The jet emerges as actually comprised of at least three smaller features. This active region as a whole is at least three kilometers (less than two miles) long."[8]

"Another, smaller, jet feature is seen on the tip of the nucleus on the lower right-hand limb. Dust also seems to be ejected from there into the night-side hemisphere, probably from the dayside hemisphere. The expansion of the gas and dust mixture into the vacuum of space has swept some material around the body of the nucleus so that it appears above the night-side hemisphere. The night-side of the nucleus could not be seen, of course."[8]

"The line between day and night on the comet is towards the upper right. This representation shows a faint ring of brightness separated from the terminator by a dark, unlit area. It is possible that this is a crater rim, seen in grazing illumination, which is just about to cross into darkness as the comet rotates. The direction to the Sun is directly downwards."[8]

On the left is a close-up picture of comet Borelly. The right portion is a topographic relief map of the cometary nucleus.

"Comets are sometimes described as "dirty snowballs," but a close flyby of one by NASA's Deep Space 1 spacecraft last fall detected no frozen water on its surface."[9]

"The spectrum suggests that the surface is hot and dry. It is surprising that we saw no traces of water ice."[10]

"We know the ice is there. It's just well-hidden. Either the surface has been dried out by solar heating and maturation or perhaps the very dark soot-like material that covers Borrelly's surface masks any trace of surface ice."[10]

"The Deep Space 1 science team released pictures and other initial findings days after the spacecraft flew within 2,171 kilometers (1,349 miles) of the comet's solid nucleus on September 22, 2001."[9]

"Comet Borrelly is in the inner solar system right now, and it's hot, between 26 and 71 degrees Celsius (80 and 161 degrees Fahrenheit), so any water ice on the surface would change quickly to a gas. As the components evaporate, they leave behind a crust, like the crust left behind by dirty snow."[11]

"It seems to be covered in this dark material, which has been loosely connected with biological material. This suggests that comets might be a transport mechanism for bringing the building blocks of life to Earth."[11]

"It's remarkable how much information Deep Space 1 was able to gather at the comet, particularly given that this was a bonus assignment for the probe."[12]

Comet 67P/Churyumov-Gerasimenko[edit]

This is an image of the nucleus of Comet 67P/Churyumov-Gerasimenko by Rosetta. Credit: ESA Rosetta Mission.{{free media}}
Single frame Rosetta spacecrast NAVCAM image of Comet 67P/C-G was taken on 6 March from a distance of 82.9 km to the comet. Credit: ESA/Rosetta/NAVCAM.{{free media}}
Images taken by the Rosetta navigation camera (NAVCAM) on 19 September 2014 at 28.6 km (17.8 mi) from the centre of comet 67P/Churyumov–Gerasimenko. Credit: ESA/Rosetta/NAVCAM.{{free media}}
Four-image montage comprises images taken by Rosetta's navigation camera from a distance of 9.8 km from the centre of comet 67P/C-G – about 7.8 km from the surface. Credit: ESA/Rosetta/NAVCAM.{{free media}}
Image is taken by Rosetta's navigation camera from a distance of 9.8 km from the centre of comet 67P/C-G Credit: ESA/Rosetta/NAVCAM.{{free media}}

"The short period comets have orbital periods <20 years and low inclination. Their orbits are controlled by Jupiter and thus they are also called Jupiter Family comets. [...] Because the orbit crosses that of Jupiter, the comet will have gravitational interactions with this massive planet. The objects orbit will gradually change from these interactions and eventually the object will either be thrown out of the Solar System or collide with a planet or the Sun."[13]

Perihleion distance in AU = 1.243, eccentricity = 0.641, inclination = 7.0, and orbital period in years = 2.745.[14]

Comet Halley[edit]

This is a photograph taken in 1910 during the passage of Halley's comet. Credit: The Yerkes Observatory.

“During the Halley Monitoring Program at La Silla from Feb.17 to Apr.17,1986 ... In the light of the neutral CN-radical a continuous formation and expansion of [cyan] gas-shells could be observed.”[2]

“The gas-expansion velocity decreases with increasing heliocentric distance from 1 km/s in early March to 0.8 km/s in April.”[2]

The 1910 approach, which came into naked-eye view around 10 April[15] and came to perihelion on 20 April,[15] was notable for several reasons: it was the first approach of which photographs exist, and the first for which spectroscopic data were obtained.[16] Furthermore, the comet made a relatively close approach of 0.15AU,[15] making it a spectacular sight. Indeed, on 19 May, the Earth actually passed through the tail of the comet.[17][18] One of the substances discovered in the tail by spectroscopic analysis was the toxic gas cyanogen,[19] which led astronomer Camille Flammarion to claim that, when Earth passed through the tail, the gas "would impregnate the atmosphere and possibly snuff out all life on the planet."[20] His pronouncement led to panicked buying of gas masks and quack "anti-comet pills" and "anti-comet umbrellas" by the public.[21] In reality, as other astronomers were quick to point out, the gas is so diffuse that the world suffered no ill effects from the passage through the tail.[20]

"It is quite possible that [faint streamers preceding the main tail and lying nearly in the prolonged radius vector] may have touched the Earth, probably between May 19.0 and May 19.5, [1910,] but the Earth must have passed considerably to the south of the main portion of the tail [of Halley's comet]."[22]

A magnetohydrodynamics (MHD) and chemical comet-coma model is applied to describe and analyze the plasma flow, magnetic field, and ion abundances in Comet Halley.[23] A comparison of model results is made with the data from the Giotto mission.[23]

Orionid meteor showers[edit]

"The Orionid meteor shower [leftover bits of Halley's Comet] is scheduled to reach its maximum before sunrise on Sunday morning (Oct. 21 [2012]). This will be an excellent year to look for the Orionids, since the moon will set around 11 p.m. local time on Saturday night (Oct. 20) and will not be a hindrance at all ... The orbit of Halley's Comet closely approaches the Earth's orbit at two places. One point is in the early part of May producing a meteor display known as the Eta Aquarids. The other point comes in the middle to latter part of October, producing the Orionids."[24]

103P/Hartley (Hartley 2)[edit]

Comet Hartley 2 is taken by NASA on November 4, 2010, by Deep Impact spacecraft Credit: JPL/NASA.{{free media}}

In November 2007 the JPL team targeted Deep Impact toward Comet 103P/Hartley (Hartley 2); however, this would require an extra two years of travel for Deep Impact (including earth gravity assists in December 2007 and December 2008).[25] On May 28, 2010, a burn of 11.3 seconds was conducted, to enable the June 27 Earth fly-by to be optimized for the transit to Hartley 2 and fly-by on November 4. The velocity change was 0.1 m/s (0.33 ft/s).[26]

On November 4, 2010, the Deep Impact extended mission (EPOXI) returned images from comet Hartley 2.[27] EPOXI came within 700 kilometers (430 mi) of the comet, returning detailed photographs of the "peanut" shaped cometary nucleus and several bright jets. The probe's medium-resolution instrument captured the photographs.[27]

17P/Holmes[edit]

The image shows Comet 17P/Holmes. Credit: Johnpane.{{free media}}
Comet Holmes (17P/Holmes) in 2007 shows a blue ion tail on the right. Credit: Ivan Eder.
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).

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."[28]

"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."[28]

"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."[28]

"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."[28]

"The horizontal line seen in the contrast-enhanced picture is a trail of debris that travels along with the comet in its orbit."[28]

"The Spitzer picture was taken with the spacecraft's multiband imaging photometer at an infrared wavelength of 24 microns."[28]

Comet C/2018 Y1 Iwamoto[edit]

This is an animation of photographs of C/2018 Y1 Iwamoto with the RASA 8" - Rowe-Ackermann Schmidt Astrograph. Credit: Michael Jäger.{{fairuse}}

"A beautiful Valentine's Day comet [sped] past Earth [last night]. Known as the Valentine's Day comet C/2018Y1 Iwamoto, it's the first binocular comet of 2019, which means its green glow will be visible to the human eye through a pair of binoculars."[29]

"Travelling at roughly 238,000 kilometres per hour (or 148,000 miles per hour), the comet has just passed the sun and will be heading closer to Earth throughout Thursday 14th February."[29]

"It will be visible throughout the day but the best views will occur after dark. You can track exactly where the comet is in the sky using this online tool."[29]

"This particular bright green comet was only discovered recently by astronomer Masayuki Iwamoto".[29]

Comet Kohoutek 1973 XII[edit]

The neutral cyan coma of comet Kohoutek 1973 XII is measured.[30]

Comet Lovejoy[edit]

Comet Lovejoy has a blue ion tail leading away off to the left. Credit: NASA/Dan Burbank.
Comet Lovejoy is detected in STEREO/SECCHI's EUVI-A imager's 17.1-nm wavelength. Credit: STEREO/SECCHI image courtesy NASA/NRL.

At right is Comet Lovejoy as detected in STEREO/SECCHI's EUVI-A imager's 17.1-nm wavelength. "The comet is clearly visible racing away from the Sun, leaving a wiggly-tail in its wake! Why the wiggles? We're not sure -- we need to start studying that when we get all of the spacecraft data from STEREO-B this weekend. However, we think there may some kind of helical motion going on, or perhaps there's a projection affect and we're seeing tail material magnetically "clinging" to coronal loops and moving with them. There are other possibilities too, though, and we will certainly investigate those! We should have equivalent images from the STEREO-A spacecraft which we will also get this weekend. When we pair these together, and throw in the SDO images too, we should be able to get an incredibly unique 3-D picture of how this comet is reacting the the intense coronal heat and magnetic loops."[31]

Comet Lulin[edit]

Recent changes in Comet Lulin's greenish coma and tails are shown in these two panels taken on January 31st (top) and February 4th (bottom) 2009. In both views the comet has an apparent antitail to the left of the coma of dust. Credit: Joseph Brimacombe, Cairns, Australia.

Shown at the right "Lulin's green color comes from the gases that make up its Jupiter-sized atmosphere. Jets spewing from the comet's nucleus contain cyanogen (CN: a poisonous gas found in many comets) and diatomic carbon (C2). Both substances glow green when illuminated by sunlight".[3]

Comet McNaught[edit]

McNaught Comet is captured in visual color with a Canon 350D...EF50...F2...25 sec. Credit: Davewhite7.

Comet PanSTARRS C/2012 K1[edit]

Sweeping slowly through northern skies, the comet PanSTARRS C/2012 K1 posed for this telescopic portrait on June 2nd in the constellation Ursa Major. Credit: Alessandro Falesiedi.

On the right is a visual image of comet PanSTARRS C/2012 K1.

"Now within the inner solar system, the icy body from the Oort cloud sports two tails, a lighter broad dust tail and crooked ion tail extending below and right. The comet's condensed greenish coma makes a nice contrast with the spiky yellowish background star above. NGC 3319 appears at the upper left of the frame that spans almost twice the apparent diameter of the full Moon."[4]

Comet Schwassmann-Wachmann I (P/SW-1)[edit]

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.

"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)."[32]

"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."[32]

"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."[32]

Comet C/2013 A1 Siding Spring[edit]

"A comet that flew close to Mars showered the red planet with fine cometary dust, according to observations by a trio of spacecraft."[33]

"Comet C/2013 A1 Siding Spring passed within 139,500 kilometres of the red planet on 19 October, the closest a comet has ever been seen to come to a planet without actually colliding with it. To avoid being damaged by the comet dust, all spacecraft orbiting Mars moved to the far side of the planet for 20 minutes while the comet dust was at its most intense, but this did not prevent them from studying the effects it had on Mars’ atmosphere."[33]

“They call this comet encounter a once-in-a-lifetime event, but it’s more like once in a million years.”[34]

"The European Space Agency’s Mars Express spacecraft detected an increase in electrons in Mars’ upper atmosphere, partly ionising it. This was attributed to fine cometary dust penetrating the atmosphere, which led to a meteor storm of thousands of meteors per hour. The increase in electrons led to the creation of a temporary new layer of charged particles in the ionosphere, which runs from an altitude of 120 kilometres to several hundred kilometres above. This is the first time such an event has been seen, even on Earth the extra density of electrons was measured to be five to ten times higher than normal by NASA’s Mars Reconnaissance Orbiter. Another NASA spacecraft, MAVEN, which also observed the new layer in the ionosphere, will monitor for any long-term events as it goes about its regular duties of studying Mars’ atmosphere."[33]

"MAVEN’s Imaging Ultraviolet Spectrograph was able to ascertain the species of ions that flooded into the ionosphere from the comet, the first time a comet that has come direct from the distant Oort Cloud has been sampled in this way. It detected the signal of magnesium, iron and sodium ions following the meteor shower, a signal that dominated Mars’ ultraviolet spectrum for hours afterwards, taking two days to dissipate."[33]

"The results show that dust from the comet, which has a nucleus two kilometres across, according to high resolution images from the Mars Reconnaissance Orbiter, had a dramatic effect on Mars’ atmosphere."[33]

“Observing the effects on Mars of the comet’s dust slamming into the upper atmosphere makes me very happy that we decided to put our spacecraft on the other side of Mars at the peak of the dust tail passage and out of harm’s way.”[35]

Comet Swan[edit]

This is a real color composite image of Comet Swan. Credit: Ginger Mayfield.

"Comet Swan recently made a swing through the inner solar and emerged in the evening sky. Astronomy enthusiast Ginger Mayfield recorded the blue-green color of the comet's nucleus and a tenuous tail in this composite created from multiple images taken on October 26 from Divide, Colorado."[36]

Comet West 1976 VI[edit]

Visual photograph of Comet West in early March 1976 shows red gases coming off the comet's head and multicolor dust tail. Credit: Peter Stättmayer (Munich Public Observatory) and ESO.

The physical parameters of the neutral cyan coma of comet West (1975n) have been measured.[37]

Solar binary[edit]

The Sun-Jupiter binary may serve to establish an upper limit for interstellar cometary capture when three bodies are extremely unequal in mass, such as the Sun, Jupiter, and a third body (potential comet) at a large distance from the binary.[38] The basic problem with a capture scenario even from passage through “a cloud of some 10 million years, or from a medium enveloping the solar system, is the low relative velocity [~0.5 km s-1] required between the solar system and the cometary medium.”[39] The capture of interstellar comets by Saturn, Uranus, and Neptune together cause about as many captures as Jupiter alone.[39]

Exploratory astronomy[edit]

"Deep Space 1 was launched in October 1998 as part of NASA's New Millennium Program, which is managed by JPL for NASA's Office of Space Science, Washington, D.C. The California Institute of Technology manages JPL for NASA."[8]

"Deep Space 1 completed its primary mission testing ion propulsion and 11 other advanced, high-risk technologies in September 1999. NASA extended the mission, taking advantage of the ion propulsion and other systems to undertake this chancy but exciting, and ultimately successful, encounter with the comet."[8]

Exocomets[edit]

The first exocomets were detected in 1987[40][41] around Beta Pictoris, a very young A-type main-sequence star. There are now a total of 11 stars around which exocomets have been observed or suspected.[42][43][44][45]

All discovered exocometary systems (Beta Pictoris, HR 10,[42] 51 Ophiuchi, HR 2174,[43] 49 Ceti, 5 Vulpeculae, 2 Andromedae, HD 21620, HD 42111, HD 110411,[44][46] and more recently HD 172555[45]) are around very young A-type stars.

A gaseous cloud around 49 Ceti has been attributed to the collisions of comets in that planetary system.[47]

Interstellar comets[edit]

This shows the hyperbolic path of extrasolar object ʻOumuamua, the first confirmed interstellar object, discovered in 2017. Credit: Tomruen.{{free media}}
Comet Machholz 1 (96P/Machholz) is viewed by STEREO-A (April 2007). Credit: NASA.
Comet Hyakutake (C/1996 B2) might be an interstellar object captured by the Solar System. Credit: E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria.{{free media}}

An interstellar object is an astronomical object that is located in interstellar space including objects that are on an interstellar trajectory but are temporarily passing close to a star, such as certain asteroids and comets (including exocomets[48][49])

The image on the right shows `Oumuamua's hyperbolic trajectory across the full solar system, with annual markers, and planet positions on 1/1/2018.

"A newly discovered comet is screaming away from Earth, and based on its weird orbital trajectory might be the first comet ever observed to come from interstellar space. A sky-surveying telescope in Hawaii spotted the fast-moving object, now called C/2017 U1, on 18 October, after its closest approach to the sun. The following week, astronomers made 34 separate observations of the object and found it has a strange trajectory that doesn't appear to circle the sun."[50]

ʻOumuamua showed no signs of a cometary coma despite its close approach to the Sun, but underwent non-gravitational acceleration which is seen in many icy comets,[51][52] although other reasons have been suggested.[53][54][55]

The object could be a remnant of a disintegrated interstellar comet (or exocomet).[56][57]

It is possible for objects orbiting a star to be ejected due to interaction with a third massive body, such a process was initiated in early 1980s when C/1980 E1, initially gravitationally bound to the Sun, passed near Jupiter and was accelerated sufficiently to reach escape velocity from the Solar System, changing its orbit from elliptical to hyperbolic and making it the most eccentric known object at the time, with an eccentricity of 1.057.[58] It is headed for interstellar space.

Asteroid (514107) 2015 BZ509 may be a former interstellar object, captured some 4.5 billion years ago, as evidenced by its co-orbital motion with Jupiter and its retrograde orbit around the Sun.[59]

An interstellar comet can probably, on rare occasions, be captured into a heliocentric orbit while passing through the Solar System. Computer simulations show that Jupiter is the only planet massive enough to capture one, and that this can be expected to occur once every sixty million years.[60] Comets Machholz 1 and Comet Hyakutake C/1996 B2 are possible examples of such comets, as they have atypical chemical makeups for comets in the Solar System.[61][62]

Current models of Oort cloud formation predict that more comets are ejected into interstellar space than are retained in the Oort cloud, with estimates varying from 3 to 100 times as many.[49] Other simulations suggest that 90–99% of comets are ejected.[63] There is no reason to believe comets formed in other star systems would not be similarly scattered.[48]

A more recent estimate, following the detection of 'Oumuamua, predicts that "The steady-state population of similar, ~100 m scale interstellar objects inside the orbit of Neptune is ~1×104, each with a residence time of ~10 years."[64]

There should be hundreds of 'Oumuamua-size interstellar objects in the Solar System, based on calculated orbital characteristics, with known examples: 2011 SP25, 2017 RR2, 2017 SV13, and 2018 TL6.[65] These are all orbiting the sun, but with unusual orbits, and are assumed to have been trapped at some occasion.

References[edit]

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