Comet 81P/Wild, also known as Wild 2 (pronounced "vilt two") (/ˈvɪlt/ VILT), is a comet named after Swiss astronomer Paul Wild, who discovered it on January 6, 1978, using a 40-cm Schmidt telescope at Zimmerwald, Switzerland.[5]

For most of its 4.5 billion-year lifetime, Wild 2 probably had a more distant and circular orbit. In September 1974, it passed within one million kilometers of the planet Jupiter, the strong gravitational pull of which perturbed the comet's orbit and brought it into the inner Solar System.[6] Its orbital period changed from 43 years to about 6 years,[6] and its perihelion is now about 1.59 astronomical unit (AU).[3]

Wild2 3
Comet Wild 2 (81P/Wild) nucleus in 2004
Discovered byPaul Wild
Discovery date1978
1978 XI; 1984 XIV;
Orbital characteristics A
EpochMarch 6, 2006
Aphelion5.308 AU
Perihelion1.592 AU
Semi-major axis3.45 AU
Orbital period6.408 a
Jupiter MOID0.012 AU (1,800,000 km)[4]
Last perihelionJuly 20, 2016[1]
February 22, 2010[2]
Next perihelionDecember 15, 2022[3]

Nucleus parameters

  • Dimensions: 5.5 km × 4.0 km × 3.3 km (3.4 mi × 2.5 mi × 2.1 mi)[7]
  • Density: 0.6 g/cm3 (37 lb/cu ft)[8]
  • Mass: 2.3 x 1013 kg (5.1 x 1013 lb)[9]


Comet 81P Wild 2010-01-17
Wild 2 from Earth
Animation of Stardust trajectory
Animation of Stardust 's trajectory from 7 February 1999 to 7 April 2011
   Stardust  ·   81P/Wild ·   Earth ·   5535 Annefrank  ·   Tempel 1

NASA's Stardust Mission launched a spacecraft, named Stardust, on February 7, 1999. It flew by Wild 2 on January 2, 2004, and collected particle samples from the comet's coma, which were returned to Earth along with interstellar dust it collected during the journey. Seventy-two close-up shots were taken of Wild 2 by Stardust. They revealed a surface riddled with flat-bottomed depressions, with sheer walls and other features that range from very small to up to 2 kilometres across. These features are believed to be caused by impact craters or gas vents. During Stardust's flyby, at least 10 gas vents were active. The comet itself has a diameter of 5 kilometres.

Stardust's "sample return canister" was reported to be in excellent condition when it landed in Utah, on January 15, 2006. A NASA team analyzed the particle capture cells and removed individual grains of comet and interstellar dust, then sent them to about 150 scientists around the globe.[10] NASA is collaborating with The Planetary Society who will run a project called "Stardust@Home", using volunteers to help locate particles on the Stardust Interstellar Dust Collector (SIDC).

As of 2006,[11] the composition of the dust has contained a wide range of organic compounds, including two that contain biologically usable nitrogen. Indigenous aliphatic hydrocarbons were found with longer chain lengths than those observed in the diffuse interstellar medium. No hydrous silicates or carbonate minerals were detected, which suggests a lack of aqueous processing of Wild 2 dust. Very few pure carbon (CHON) particles were found in the samples returned. A substantial amount of crystalline silicates such as olivine, anorthite and diopside were found,[12] materials only formed at high temperature. This is consistent with previous observations of crystalline silicates both in cometary tails and in circumstellar disks at large distances from the star. Possible explanations for this high temperature material at large distances from Sun were summarised before the Stardust sample return mission by van Boekel et al.:[13]

"Both in the Solar System and in circumstellar disks crystalline silicates are found at large distances from the star. The origin of these silicates is a matter of debate. Although in the hot inner-disk regions crystalline silicates can be produced by means of gas-phase condensation or thermal annealing, the typical grain temperatures in the outer-disk (2–20 au) regions are far below the glass temperature of silicates of approx 1,000 K. The crystals in these regions may have been transported outward through the disk or in an outward-flowing wind.[14] An alternative source of crystalline silicates in the outer disk regions is in situ annealing, for example by shocks or lightning. A third way to produce crystalline silicates is the collisional destruction of large parent bodies in which secondary processing has taken place. We can use the mineralogy of the dust to derive information about the nature of the primary and/or secondary processes the small-grain population has undergone."

Results from a study reported in the September 19, 2008 issue of the journal Science has revealed an oxygen isotope signature in the dust that suggests an unexpected mingling of rocky material between the center and edges of the Solar System. Despite the comet's birth in the icy reaches of outer space beyond Pluto, tiny crystals collected from its halo appear to have been forged in the hotter interior, much closer to the Sun.[15]

In April 2011, scientists from the University of Arizona discovered evidence of the presence of liquid water. They found iron and copper sulfide minerals that must have formed in the presence of water. The discovery is in conflict with the existing paradigm that comets never get warm enough to melt their icy bulk. Either collisions or radiogenic heating might have provided the necessary energy source.[16]

On August 14, 2014, scientists announced the collection of possible interstellar dust particles from the Stardust spacecraft since returning to Earth in 2006.[17][18][19][20]


The Inward Migration of 81P
1965 13 4.95[6] 21[a]
1978[3] 3.36 1.49 5.24
Wild2 3

Photograph taken by Stardust spacecraft

Comet wild 2 jet plumes

Details of the plume jets

Comet Wild2 Anaglyph

Red/green stereo anaglyph

Comet Wild2

Stardust Approach Image

Comet wild 2

See also

Wild 2 has a similar name to other objects:


  1. ^ In 1951, comet 81P [1978] was at aphelion 21AU from the Sun.[21]


  1. ^ Nakano, Syuichi (December 12, 2009). "81P/Wild 2 (NK 1861)". OAA Computing and Minor Planet Sections. Retrieved February 24, 2010.
  2. ^ Kinoshita, Kazuo (April 13, 2005). "81P past, present and future orbital elements". Comet Orbit. FC2.
  3. ^ a b c "81P/Wild Orbit". Minor Planet Center. Retrieved 2017-02-26.
  4. ^ "JPL Small-Body Database Browser: 81P/Wild 2" (last observation: 2016-06-26). Jet Propulsion Laboratory. Archived from the original on February 26, 2017.
  5. ^ Wild, P. (1978). Marsden, B. G., ed. "Comet Wild (1978b)". IAU Circular. 3166 (1): 1. Bibcode:1978IAUC.3166....1W.
  6. ^ a b c Kronk, Gary W. (2001–2005). "81P/Wild 2". Cometography.com. Retrieved October 23, 2008. (Cometography Home Page)
  7. ^ "Comet 81P/Wild 2". The Planetary Society. Archived from the original on January 6, 2009. Retrieved December 16, 2008.
  8. ^ Britt, D. T.; Consol-magno SJ, G. J.; Merline, W. J. (2006). "Small Body Density and Porosity: New Data, New Insights" (PDF). Lunar and Planetary Science XXXVII. Archived (PDF) from the original on December 17, 2008. Retrieved December 16, 2008.
  9. ^ Using the volume of an ellipsoid of 5.5×4.0×3.3 km * a rubble pile density of 0.6 g/cm³ yields a mass (m=d*v) of 2.28×1013 kg
  10. ^ Jeffs, William (January 18, 2006). "Scientists Confirm Comet Samples, Briefing Set Thursday". NASA. Archived from the original on March 9, 2008. Retrieved March 5, 2008.
  11. ^ McKeegan, K. D.; et al. "Light element isotopic compositions of cometary matter returned by the STARDUST mission" (PDF). Lawrence Livermore National Laboratory. Retrieved March 5, 2008.
  12. ^ Stricherz, Vince (March 13, 2006). "Comet from coldest spot in solar system has material from hottest places". University of Washington. Archived from the original on October 16, 2007. Retrieved March 5, 2008.
  13. ^ van Boekel, R.; et al. (2004). "The building blocks of planets within the 'terrestrial' region of protoplanetary disks". Nature. ukads.nottingham.ac.uk. 432 (7016): 479–482. Bibcode:2004Natur.432..479V. doi:10.1038/nature03088. PMID 15565147. Retrieved March 5, 2008.
  14. ^ Liffman, K.; Brown, M. (1995). "The motion and size sorting of particles ejected from a protostellar accretion disk". Icarus. elsevier.com/. 116: 275–290. Bibcode:1995Icar..116..275L. doi:10.1006/icar.1995.1126. Retrieved April 12, 2011.
  15. ^ University of Wisconsin-Madison (September 15, 2008). "Comet Dust Reveals Unexpected Mixing of Solar System". Newswise. Retrieved September 18, 2008.
  16. ^ LeBlanc, Cecile (April 7, 2011). "Evidence for liquid water on the surface of Comet Wild-2". Archived from the original on May 12, 2011. Retrieved April 7, 2011.
  17. ^ Agle, DC; Brown, Dwayne; Jeffs, William (August 14, 2014). "Stardust Discovers Potential Interstellar Space Particles". NASA. Retrieved August 14, 2014.
  18. ^ Dunn, Marcia (August 14, 2014). "Specks returned from space may be alien visitors". AP News. Retrieved August 14, 2014.
  19. ^ Hand, Eric (August 14, 2014). "Seven grains of interstellar dust reveal their secrets". Science. Retrieved August 14, 2014.
  20. ^ Westphal, Andrew J.; et al. (August 15, 2014). "Evidence for interstellar origin of seven dust particles collected by the Stardust spacecraft". Science. 345 (6198): 786–791. Bibcode:2014Sci...345..786W. doi:10.1126/science.1252496. PMID 25124433. Retrieved August 15, 2014.
  21. ^ Horizons output. "Comet 81P/Wild 2 [1978] (SAO/1978)". Retrieved 2017-02-26. (Observer Location:@Sun)

External links

Numbered comets
81P/Wild Next
2004 in science

The year 2004 in science and technology involved some significant events.


276P/Vorobjov (previously P/2012 T7 (VOROBJOV)) is a Jupiter-family comet discovered on 15 October 2012 by Tomáš Vorobjov on three 120-s images taken remotely using the 0.81-m f/7 Ritchey-Chretien Schulman Telescope located at the Mt. Lemmon SkyCenter via the Sierra Stars Observatory Network in the course of a minor-planet search survey undertaken as part of the International Astronomical Search Collaboration (IASC) school campaigns. After posting on the Minor Planet Center's NEOCP webpage, other observers have commented on the object's cometary appearance. The discovery was announced by the Minor Planet Center on 18 October, three days after the discovery.

5535 Annefrank

5535 Annefrank (), provisional designation 1942 EM, is a stony Florian asteroid and suspected contact binary from the inner asteroid belt, approximately 4.5 kilometers in diameter. It was used as a target to practice the flyby technique that the Stardust space probe would later use on the comet Wild 2.The asteroid was discovered 23 March 1942, by German astronomer Karl Reinmuth at Heidelberg Observatory in southwest Germany. It was named after Anne Frank, a victim of the Holocaust.


80P/Peters–Hartley is a periodic comet in the Solar System with an orbital period of 8.12 years.

It was originally discovered by Christian Heinrich Friedrich Peters of Capodimonte Observatory, Naples, Italy. There was insufficient data to accurately compute the orbit, and the comet was lost for well over a hundred years.

It was accidentally rediscovered by Malcolm Hartley at the UK Schmidt Telescope Unit, Siding Spring, Australia on a photographic plate exposed on 11 July 1982. He estimated its brightness at a magnitude of 15. The sighting was confirmed by the Perth Observatory, where M. C. Candy calculated the orbit and concluded that Hartley had indeed relocated the lost Peter's comet. I. Hasegawa and Syuichi Nakano had simultaneously reached the same conclusion.

It was observed at its next apparition in 1990 by R. H. McNaught of the Siding Spring observatory, who described as diffuse with a brightness of magnitude 14. It was subsequently observed in 1998, 2006 and 2014.


82P/Gehrels is a periodic comet that was discovered on October 27, 1975, by Tom Gehrels at the Palomar Mountain Observatory in California having a faint nuclear brightness of magnitude 17.Calculations based on the early sightings gave an estimated perihelion of 23 April 1975 and an orbital period of 8.11 years. It was observed by J. Gibson on its next predicted apparition in 1984, using the 122-cm Schmidt at Palomar, when he estimated the nuclear brightness at a very faint magnitude 20. It has since been observed in 1993, 2001 and 2010.The object has been identified as a quasi-Hilda comet, which means it is near a 3:2 mean-motion resonance with the planet Jupiter. It fits the definition of an Encke-type comet with (TJupiter > 3; a < aJupiter). It has an estimated diameter of 1.46 km.On 15 August 1970 the comet passed 0.00143 AU (214,000 km; 133,000 mi) from Jupiter.

C/2012 E2 (SWAN)

Comet C/2012 E2 (SWAN) was a Kreutz group sungrazing comet discovered by Vladimir Bezugly in publicly available images taken by the SWAN instrument (Solar Wind ANisotropies) on board the SOHO spacecraft. It is recognized for being the first Kreutz sungrazer observed in SWAN imagery.

C/2015 F3

Comet C/2015 F3 (SWAN) was discovered in March 2015 by Rob Matson, Vladimir Bezugly and Michael Matiazzo in near real time images taken by the SWAN instrument aboard the SOHO spacecraft. At discovery the comet was already shining at around 10th magnitude as it was already near perihelion

. Orbital studies revealed C/2015 F3 to be a related fragment to long periodic comets C/1988 A1 (Liller) and C/1996 Q1 (Tabur), which were already thought to have broken off each other at a previous perihelion passage. As of May 2015, Comet SWAN was fading rapidly, as both C/1988 A1 and C/1996 Q1 ultimately did. .

C/2015 F5 (SWAN-XingMing)

Comet C/2015 F5 (SWAN-XingMing) was discovered on March 29, 2015 in near real time SWAN images of the SOHO spacecraft, by Szymon Liwo and Worachate Boonplod. It was also independently discovered on April 4, 2015 by Guoyou Sun and Gao Xing at the XingMing observatory near Ürümqi, China. At discovery, the comet had just passed perihelion and was only 0,35 AU from the Sun, shining at about +10 mag. As of May 2015 the comet had faded below mag +13. The comet is periodic with an orbital period of about 61 years .


A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times the Earth's diameter, while the tail may stretch one astronomical unit. If sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures.

Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide. Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition.

Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma (the central part immediately surrounding the nucleus) and the tail (a typically linear section consisting of dust or gas blown out from the coma by the Sun's light pressure or outstreaming solar wind plasma). However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System. The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. In the early 21st century, the discovery of some minor bodies with long-period comet orbits, but characteristics of inner solar system asteroids, were called Manx comets. They are still classified as comets, such as C/2014 S3 (PANSTARRS). 27 Manx comets were found from 2013 to 2017.As of July 2018 there are 6,339 known comets, a number that is steadily increasing as they are discovered. However, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System (in the Oort cloud) is estimated to be one trillion. Roughly one comet per year is visible to the naked eye, though many of those are faint and unspectacular. Particularly bright examples are called "great comets". Comets have been visited by unmanned probes such as the European Space Agency's Rosetta, which became the first ever to land a robotic spacecraft on a comet, and NASA's Deep Impact, which blasted a crater on Comet Tempel 1 to study its interior.

Comet nucleus

The nucleus is the solid, central part of a comet, popularly termed a dirty snowball or an icy dirtball. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublimate and produce an atmosphere surrounding the nucleus known as the coma. The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun. A typical comet nucleus has an albedo of 0.04. This is blacker than coal, and may be caused by a covering of dust.Results from the Rosetta and Philae spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals. Further, the ALICE spectrograph on Rosetta determined that electrons (within 1 km (0.62 mi) above the comet nucleus) produced from photoionization of water molecules by solar radiation, and not photons from the Sun as thought earlier, are responsible for the degradation of water and carbon dioxide molecules released from the comet nucleus into its coma. On 30 July 2015, scientists reported that the Philae spacecraft, that landed on comet 67P/Churyumov-Gerasimenko in November 2014, detected at least 16 organic compounds, of which four (including acetamide, acetone, methyl isocyanate and propionaldehyde) were detected for the first time on a comet.


Gehlenite, (Ca2Al[AlSiO7]), is a sorosilicate, Al-rich endmember of the melilite complete solid solution series with akermanite.

The type locality is in the Monzoni Mountains, Fassa Valley in Trentino in Italy, and is named after Adolf Ferdinand Gehlen (1775–1815) by A.J. Fuchs in 1815.

Ivano Bertini

Ivano Bertini (born April, 1968, in Milan, Italy) is an Italian astronomer at the University of Padua.

List of Earth flybys

List of Earth flybys is a list of cases where spacecraft incidentally performed Earth flybys, typically for a gravity assist to another body.

List of missions to comets

As of 2013, the United States, Soviet Union, Japan and the European Space Agency have conducted missions to comets.

Paul Wild (Swiss astronomer)

Paul Wild (German: [ˈvɪlt]; 5 October 1925 – 2 July 2014) was a Swiss astronomer and director of the Astronomical Institute of the University of Bern, who discovered numerous comets, asteroids and supernovae.

Richard Zare

Richard Neil Zare (born November 19, 1939 in Cleveland, Ohio) is the Marguerite Blake Wilbur Professor in Natural Science and a Professor of Chemistry at Stanford University. Throughout his career, Zare has made a considerable impact in physical chemistry and analytical chemistry, particularly through the development of laser-induced fluorescence (LIF) and the study of chemical reactions at the molecular and nanoscale level. LIF is an extremely sensitive technique with applications ranging from analytical chemistry and molecular biology to astrophysics. One of its applications was the sequencing of the human genome.Zare is known for his enthusiasm for science and his exploration of new areas of research. He has mentored over 150 PhD students and postdoctoral researchers, of whom more than 49 are women or members of minorities. Zare is a strong advocate for women in science, and a fellow of the Association for Women in Science (AWIS) as of 2008.

Tempel 1

Tempel 1 (official designation: 9P/Tempel) is a periodic Jupiter-family comet discovered by Wilhelm Tempel in 1867. It completes an orbit of the Sun every 5.5 years. Tempel 1 was the target of the Deep Impact space mission, which photographed a deliberate high-speed impact upon the comet in 2005. It was re-visited by the Stardust spacecraft on February 14, 2011 and came back to perihelion in August 2016.

Uncrewed spacecraft

Uncrewed or unmanned spacecraft are spacecraft without people on board, used for robotic spaceflight. Uncrewed spacecraft may have varying levels of autonomy from human input; they may be remote controlled, remote guided or even autonomous, meaning they have a pre-programmed list of operations, which they will execute unless otherwise instructed. Many habitable spacecraft also have varying levels of robotic features. For example, the space stations Salyut 7 and Mir, and the ISS module Zarya were capable of remote guided station-keeping, and docking maneuvers with both resupply craft and new modules. The most common uncrewed spacecraft categories are robotic spacecraft, uncrewed resupply spacecraft, space probes and space observatories. Not every uncrewed spacecraft is a robotic spacecraft; for example, a reflector ball is a non-robotic uncrewed spacecraft.

Zimmerwald Observatory

The Zimmerwald Observatory (German: Observatorium Zimmerwald) is an astronomical observatory owned and operated by the AIUB, the Astronomical Institute of the University of Bern. Built in 1956, it is located at Zimmerwald, 10 kilometers south of Bern, Switzerland.

Numerous comets and asteroids have been discovered by Paul Wild (1925–2014) at Zimmerwald Observatory, most notably comet 81P/Wild, which was visited by NASA's Stardust space probe in 2004. The main belt asteroid 1775 Zimmerwald has been named after the location of the observatory.The 1-meter aperture ZIMLAT telescope was inaugurated in 1997.

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