 | |
| Discovery[1] | |
|---|---|
| Discovered by | Paul Wild |
| Discovery site | Zimmerwald, Switzerland |
| Discovery date | 6 January 1978 |
| Designations | |
| P/1978 A2; P/1983 S1 | |
| 1978 XI; 1984 XIV; 1990 XXVIII | |
| Orbital characteristics[3][4] | |
| Epoch | 17 October 2024 (JD 2460600.5) |
| Observation arc | 46.67 years |
| Number of observations | 7,963 |
| Aphelion | 5.307 AU |
| Perihelion | 1.597 AU |
| Semi-major axis | 3.452 AU |
| Eccentricity | 0.53739 |
| Orbital period | 6.414 years |
| Inclination | 3.237° |
| 136.09° | |
| Argument of periapsis | 41.568° |
| Mean anomaly | 103.17° |
| Last perihelion | 15 December 2022 |
| Next perihelion | 14 May 2029[2] |
| TJupiter | 2.879 |
| EarthMOID | 0.601 AU |
| JupiterMOID | 0.012 AU |
| Physical characteristics[3][5][6] | |
| Dimensions | 5.5 km × 4.0 km × 3.3 km (3.4 mi × 2.5 mi × 2.1 mi) |
| Mass | 2.3 x 1013 kg (5.1 x 1013 lb)[a] |
Meandensity | 0.6 g/cm3 (37 lb/cu ft) |
| Comet total magnitude (M1) | 9.8 |
| Comet nuclear magnitude (M2) | 12.9 |
Comet81P/Wild, also known asWild 2 (pronounced "vilt two") (/ˈvɪlt/VILT), is acomet with a period of 6.4 years named after Swiss astronomerPaul Wild, who discovered it on January 6, 1978, using a 40-cmSchmidt telescope atZimmerwald, Switzerland.[1]
For most of its 4.5 billion-year lifetime, Wild 2 probably had a more distant andcircular orbit. In September 1974, it passed within 1.0 million km (0.62 million mi) of the planetJupiter, the strong gravitational pull of whichperturbed the comet'sorbit and brought it into theinner Solar System.[7] Itsorbital period changed from 43 years to about 6 years,[7] and itsperihelion is now about 1.59 AU (238 million km).[4]
Prior to its encounter with Jupiter in 1974, the comet had an orbital period of around 43 years with an aphelion at around 25 AU and a perihelion of just under 5 AU. The encounter reduced the aphelion and perihelion to its present value of around 5 and 1.5 AU, respectively.[8]
NASA'sStardust Mission launched aspacecraft, namedStardust, on February 7, 1999. It flew by Wild 2 on January 2, 2004, and collected particle samples from the comet'scoma, which were returned to Earth along withinterstellar dust it collected during the journey. Seventy-two close-up shots were taken of Wild 2 byStardust. They revealed a surface riddled with flat-bottomed depressions, with sheer walls and other features that range from very small to up to 2 km (1.2 mi) across. These features are believed to be caused by impact craters or gas vents. DuringStardust's flyby, at least 10 gas vents were active. The comet itself has a diameter of 5 km (3.1 mi).
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.[9] NASA is collaborating withThe 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,[10] 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 asolivine,anorthite anddiopside were found,[11] 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 theStardust sample return mission by van Boekel et al.:[12]
Results from a study reported in the September 19, 2008 issue of the journalScience 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.[14] 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 theUniversity of Arizona discovered evidence of the presence of liquid water. They found iron andcopper 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. Eithercollisions orradiogenic heating might have provided the necessary energy source.[16]
On August 14, 2014, scientists announced the collection of possibleinterstellar dust particles from theStardust spacecraft since returning to Earth in 2006.[17][18][19][20]
| The Inward Migration of 81P | |||||||
| Year (epoch) | Semi-major axis (AU) | Perihelion (AU) | Aphelion (AU) | ||||
|---|---|---|---|---|---|---|---|
| 1965 | 13 | 4.95[7] | 21[b] | ||||
| 1978[4] | 3.36 | 1.49 | 5.24 | ||||
Wild 2 has a similar name to other objects:
| Numbered comets | ||
|---|---|---|
| Previous 80P/Peters–Hartley | 81P/Wild | Next 82P/Gehrels |
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