“We already knew of many asteroids, but they have all been baked by billions of years near the Sun,” says Karen Meech of the University of Hawaii’s Institute for Astronomy. “This one is the first uncooked asteroid we could observe: it has been preserved in the best freezer there is.”
C/2014 S3 (aka PANSTARRS) was formed about 4.5 billion years ago, close to Earth when it was formed. But PANSTARRS traveled far from the sun, "preserved in the deep freeze of the Oort Cloud for billions of years." Now it is headed back, and astronomers are excited to see what fresh frozen ancient asteroid looks like.
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Careful study of the light reflected by C/2014 S3 (PANSTARRS) indicates that it is typical of asteroids known as S-type, which are usually found in the inner asteroid main belt. It does not look like a typical comet, which are believed to form in the outer Solar System and are icy, rather than rocky. It appears that the material has undergone very little processing, indicating that it has been deep frozen for a very long time. The very weak comet-like activity associated with C/2014 S3 (PANSTARRS), which is consistent with the sublimation of water ice, is about a million times lower than active long-period comets at a similar distance from the Sun.
The authors conclude that this object is probably made of fresh inner Solar System material that has been stored in the Oort Cloud and is now making its way back into the inner Solar System.
The green circle in the lower right of this image marks the position of Earth's own trojan asteroid, discovered by researcher's involved with NASA's Wide-field Infrared Survey Explorer project.
What's a trojan asteroid? Glad you asked. The good news: It's not going to kill us all.
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Trojans are asteroids that share an orbit with a planet near stable points in front of or behind the planet. Because they constantly lead or follow in the same orbit as the planet, they never can collide with it. In our solar system, Trojans also share orbits with Neptune, Mars and Jupiter. Two of Saturn's moons share orbits with Trojans.
Scientists had predicted Earth should have Trojans, but they have been difficult to find because they are relatively small and appear near the sun from Earth's point of view.
The team's hunt resulted in two Trojan candidates. One called 2010 TK7 was confirmed as an Earth Trojan after follow-up observations with the Canada-France-Hawaii Telescope on Mauna Kea in Hawaii.
The asteroid is roughly 1,000 feet (300 meters) in diameter. It has an unusual orbit that traces a complex motion near a stable point in the plane of Earth's orbit, although the asteroid also moves above and below the plane. The object is about 50 million miles (80 million kilometers) from Earth. The asteroid's orbit is well-defined and for at least the next 100 years, it will not come closer to Earth than 15 million miles (24 million kilometers).