This diagram shows the shape and size of the orbit of Comet Wild 2. The comet's orbit is shown in aqua. The orbits of Jupiter, Mars, and Earth are also shown. Click on image for full size (6K GIF) Image courtesy NASA/JPL.

Comet Wild 2 is a short-period comet that orbits the Sun once every 6.39 years. A Swiss astronomer named Paul Wild discovered it on January 6, 1978. Wild 2 is pronounced "Vilt 2". The comet comes about as close to the Sun as the planet Mars, and loops about as far away as the planet Jupiter. The comet's nucleus is about 5 km (3 miles) across, so Wild 2 is not an especially large comet.

Astronomers routinely calculate the positions of newly discovered comets at earlier times to make sure someone hasn't re-discovered a previously known comet. The scientists made a surprising discovery when they calculated the orbit of Wild 2 backwards in time to the years before its discovery. They realized that on September 10, 1974, the comet passed very close to Jupiter and had its orbit substantially altered by that giant planet's gravity. Before 1974, Wild's orbit was in the outer solar system, ranging between Jupiter's and Uranus' distance from the Sun. So, until recently, Wild 2 had never come very close to the Sun.

Since Wild 2 has only taken a few swings near the heat of the Sun, most of its ices have not been melted away. Apparently Wild 2 has been kept in cold storage since the early days of our Solar System, which makes it a very interesting comet to study. Studies of Wild 2 may help scientists understand what the materials that originally formed our Solar System were like.

Because Wild 2 (which is also known as Comet 81P/Wild 2) is in such a pristine condition, scientists chose it as the target of a space mission called Stardust. The Stardust spacecraft flew by Wild 2 in January 2004 and captured some tiny particles from the comet. It will return those particles to Earth in 2006, giving scientists their first sample of cometary materials that may shed light on the history and evolution of our Solar System. Stardust also shot the best images ever taken of the nucleus of a comet during its flyby.