☄ Wild 2 81P/Wild 2

How to follow comet Wild 2 live

The panel above recomputes the position of Wild 2 every second in your browser: its distance from the Sun and from Earth, its position in the sky (right ascension and declination), and a live countdown to the next perihelion. It runs on the same kind of engine observatories use, a Kepler solver applied to the JPL osculating orbital elements, so the numbers are not a static snapshot, they keep ticking.

Just below, the top-down map of the Solar System shows exactly where Wild 2 is right now among the planets. You can fast-forward time with the day slider, zoom and pan, compare its distance to another body with a click, and press "Next event" to jump straight to perihelion. It is the most direct way to grasp the orbit of Wild 2 with no math at all.

Comet fact sheet

About Wild 2

81P/Wild 2 -- pronounced "Vild 2", honouring Swiss astronomer Paul Wild -- is a short-period comet that spent most of its known existence in a more distant orbit with perihelion beyond Saturn. A close Jupiter encounter in September 1974 drastically reshuffled its orbit and brought it into the inner Solar System, where it was discovered just four years later. Its nucleus measures about 5.5 km across -- relatively large for a short-period comet.

The Stardust mission was the first to return physical samples from a Solar System body beyond the Moon. Analysis of the collected material revealed over a hundred organic compounds, including the amino acid glycine -- the first confirmed in cometary material -- and high-temperature minerals that challenged established models of how the primitive Solar System mixed and redistributed its material.

History and discovery

Paul Wild discovered the comet on January 6, 1978, at the Astronomical Observatory of Bern, Switzerland, using a 40 cm Schmidt camera. It was the fifth comet found by Wild in his career. The name "Wild 2" distinguishes this object from other comets discovered by the same astronomer. In the official periodic designation, the "2" in 81P/Wild 2 is part of the discoverer's name, not a sequential number.

The reason the comet was only found in 1978 -- despite existing for billions of years -- is that its previous orbit kept perihelion beyond Saturn, too far to develop visible cometary activity or be detected in surveys of the era. The gravitational encounter with Jupiter in September 1974 shrank perihelion from 4.9 AU to 1.49 AU, placing Wild 2 in a Mars-crossing orbit accessible to both ground observers and spacecraft. Wild 2 had completed only five orbits on its current path when Stardust visited in 2004 -- making it a pristine object whose surface had been only minimally altered by solar heating.

Orbit and returns

After the 1974 perturbation, 81P/Wild 2 settled into an orbit with eccentricity 0.5391 and inclination of only 3.24 degrees relative to the ecliptic -- one of the lowest among short-period comets. Perihelion is at 1.5936 AU and aphelion at 5.3 AU near Jupiter. The orbital period is about 6.4 years.

The orbit is considered relatively stable on short timescales. Future close Jupiter approaches could reshape it again, but no close encounter is forecast in the coming decades.

Nucleus, coma and tail

The nucleus of Wild 2 measures roughly 5.5 km across and displays topography unusual for a comet. Stardust images at 14 metres per pixel revealed structures not previously seen on any comet: circular craters with well-defined rims (rather than the diffuse edges expected in very porous material), pinnacles up to 100 m tall, and depressions up to 150 m deep with nearly vertical walls -- structures that require the nucleus material to have sufficient mechanical strength to sustain them against even the comet's weak gravity.

The coma of Wild 2 is modest under normal conditions. The presence of more than a hundred well-collimated gas and dust jets was a surprise: most comets have a few active jets, but Wild 2 displayed dozens of distinct emission sources distributed across its surface, creating a structured, dense coma that complicated spacecraft navigation during the flyby.

How to observe

81P/Wild 2 is not a spectacular visual comet. With perihelion at 1.59 AU it remains relatively far from the Sun, and typical brightness at perihelion ranges between magnitude 9 and 12, requiring a telescope of at least 100 to 200 mm aperture. It is not naked-eye visible.

The comet is preferentially located in the constellation Pisces and adjacent areas in recent returns. To locate Wild 2 in the sky, consult updated ephemerides near the predicted 2029 perihelion. The best observing window is four to six weeks around perihelion when brightness peaks. Telescopes from 150 mm under dark skies should detect the diffuse coma.

Missions and notable observations

The Stardust mission (launched February 1999) was the first to return physical samples from a Solar System body beyond the Moon. The Wild 2 flyby occurred on January 2, 2004, at a distance of 236 km. The return capsule landed in Utah, USA, on January 15, 2006. Mission milestones:

Sample analysis -- conducted by more than 200 scientists worldwide -- revealed over a hundred organic compounds including glycine (the simplest amino acid), methylamine, and ethylamine. Surprisingly, the samples also contained high-temperature crystalline silicates: olivine (forsterite) and pyroxene, minerals that form above 1,000 K -- temperatures incompatible with the cold outer Solar System. This indicates transport of hot material from the inner protoplanetary disk to the outer regions where comets form.

Trivia and records

• The detection of glycine in Stardust samples was announced in August 2009, after years of careful analysis to rule out terrestrial contamination. The carbon isotopic composition confirmed the extraterrestrial origin.
• The aerogel used to capture particles has a density of only 0.003 g/cm3 -- about 40 times less dense than air -- yet it decelerates high-velocity particles gradually, leaving characteristic carrot-shaped tracks up to 10 cm long.
• Captured particles were travelling at roughly 6.1 km/s at impact with the aerogel; some left tracks up to 10 cm long in the material.
• After delivering its samples, the Stardust spacecraft was redirected to fly past comet Tempel 1 in February 2011 -- the mission was renamed Stardust-NExT (New Exploration of Tempel).
• The Wild 2 nucleus shows craters with well-defined rims and pinnacles up to 100 m tall -- structures that only persist if the nucleus material has sufficient mechanical strength to support them against even the comet's weak gravity.
• Wild 2 had completed only five orbits on its current path before Stardust visited -- making it far less weathered by the Sun than typical short-period comets, better preserving its primitive material.
• The Stardust mission cost approximately 212 million dollars and was the first NASA Discovery mission to return extraterrestrial material to Earth since the Apollo missions.

Other comets

See the full comet catalogue.