81P/Wild

81P/Wild

Comet Wild 2 (81P/Wild) nucleus in 2004
Discovery
Discovered by	Paul Wild
Discovery date	1978
Alternative designations	1978 XI; 1984 XIV; 1990 XXVIII
Orbital characteristics ^A
Epoch	March 6, 2006
Aphelion	5.308 AU
Perihelion	1.592 AU
Semi-major axis	3.45 AU
Eccentricity	0.5384
Orbital period	6.408 a
Inclination	3.2394°
Last perihelion	February 22, 2010[1]
Next perihelion	July 20, 2016[2][3]

Wild 2 from Earth

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.^[4]

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.^[5] Its orbital period changed from 43 years to about 6 years,^[5] and its perihelion is now about 1.59 astronomical unit (AU).^[6]

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 kg (5.1 lb)×10^13[9]

Exploration

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. 72 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 for the presence of liquid water. They have 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]}

Gallery

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  Photograph taken by Stardust spacecraft

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  Details of the plume jets

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  Red/green stereo anaglyph

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  Stardust Approach Image

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See also

Wild 2 has a similar name to other objects:

• 116P/Wild
• 1941 Wild (1931 TN₁)
• 63P/Wild
• 86P/Wild

References

1. Kinoshita, Kazuo (April 13, 2005). "81P past, present and future orbital elements". Comet Orbit. FC2.
2. Nakano, Syuichi (December 12, 2009). "81P/Wild 2 (NK 1861)". OAA Computing and Minor Planet Sections. Retrieved February 24, 2010.
3. Yeomans, Donald K.; Chamberlin, Alan B. "Horizons Ephemeris". JPL Solar System Dynamics. Retrieved February 22, 2011.
4. Wild, P. (1978). Marsden, B. G., ed. "Comet Wild (1978b)". IAU Circular. 3166 (1): 1. Bibcode:1978IAUC.3166....1W.
5. Kronk, Gary W. (2001–2005). "81P/Wild 2". Cometography.com. Retrieved October 23, 2008. (Cometography Home Page)
6. "81P/Wild – Orbital Elements". IAU Minor Planet Center, Harvard University. Retrieved May 26, 2011.
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. 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. Retrieved August 15, 2014.

External links

• NASA/JPL homepage for Stardust project
• Stardust@Home Volunteer Particle Analysis Project