asteroid : orbit leader from Earth

Thursday, July 28th 2011. | Science News

Astronomers studying observations taken by NASA’s Wide-field Infrared Survey Explorer (WISE) mission have discovered the first known “Trojan” asteroid orbiting the sun along with Earth, the agency reported Wednesday. “It’s as though Earth is playing follow the leader,” said Amy Mainzer, the principal investigator of NEOWISE at NASA’s Jet Propulsion Laboratory. “Earth always is chasing this asteroid around.”

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 asteroid is roughly 1,000 feet in diameter. The object is about 50 million miles 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. An animation showing the orbit is available at: Mars rover to land at Gale Crater. NASA’s next Mars rover will land at the foot of a layered mountain inside the planet’s Gale Crater. “Mars is firmly in our sights,” said NASA Administrator Charles Bolden. “Curiosity not only will return a wealth of important science data, but it will serve as a precursor mission for human exploration to the Red Planet.”

The target crater spans 96 miles in diameter and holds a mountain rising higher from the crater floor than Mount Rainier rises above Seattle. Gale is about the combined area of Connecticut and Rhode Island. Layering in the mound suggests it is the surviving remnant of an extensive sequence of deposits. The crater is named for Australian astronomer Walter F. Gale. In 2006, more than 100 scientists began to consider about 30 potential landing sites during worldwide workshops. Four candidates were selected in 2008 – and whittled down to Gale. The car-sized Mars Science Laboratory – dubbed “Curiosity” – is scheduled to launch late this year and land in August 2012.

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