[Home] [Headlines] [Latest Articles] [Latest Comments] [Post] [Sign-in] [Mail] [Setup] [Help]
Status: Not Logged In; Sign In
|
Science/Tech See other Science/Tech Articles Title: Earth's Traveling Companion There's something deeply intriguing about the interplanetary objects known as Trojan asteroids. The great French dynamicist Joseph-Louis Lagrange predicted in 1772 that small bodies might be sharing Jupiter's orbit, in gravitationally stable sweet spots (now called Lagrange points) located ahead of and behind the planet by 60°. But it wasn't until 1906 that the first of these, 588 Achilles, was spotted. Today more than 4,800 Jupiter Trojans are known, with roughly two-thirds in the preceding "Greek camp" (L4) and a third in the trailing "Trojan camp" (L5). Earth's Trojan asteroid Not much to look at, the asteroid 2010 TK7 nonetheless represents Earth's first Trojan asteoid. NASA's WISE spacecraft captured the view at top in October 2010 at the infrared wavelength of 4 microns. Then, in April 2011, a follow-up image was recorded by the Canada-France-Hawaii Telescope in Hawaii. M. Connors & P. Wiegert (top); C. Veillet (bottom) Within the past two decades, astronomers have found four Trojan asteroids sharing the orbit of Mars and seven accompanying Neptune. They've looked for companions to Earth as well, but the geometry is all wrong: Earth's Trojans would spend most of their time in the daylight sky. But the odds tipped back in observers' favor with the 2009 launch of NASA's Wide-field Infrared Survey Explorer (WISE), which recorded big swaths of sky 90° away from the Sun. Late last year, astronomers Martin Connors (Athabasca University) and Paul Wiegert (University of California, Los Angeles) picked through the spacecraft's scans and identified one object, designated 2010 TK7, that seemed to have an Earthlike orbit. Follow-up was needed, but that wasn't possible until this past April, when it was swept up by two observers in Hawaii. Their suspicions confirmed, Connors, Wiegert, and Christian Veillet (Canada-France-Hawaii Telescope) report the discovery in July 28th's Nature. This little body is tied to Earth's preceding Lagrange point. But if you're imagining it circling the Sun in lock step with our planet, think again. The orbit of L4 is distinctly eccentric (0.19) and inclined (21°). In fact, it's never actually at L4. Instead, it vacillates widely (almost widely) in a 400-year-long epicyclic pattern that at times brings it relatively near Earth (though still many times the Moon's distance) and at others places it on the far side of the Sun from us, near the L3 point. Orbit of asteroid 2010 TK7 The WISE spacecraft photographed a small asteroid, designated 2010 TK7, that is locked in a resonance with Earth. This plot, shows the range of separation between the asteroid and Earth over a 400-year period. (The red line is its average orbit.) M. Connors & others / Nature In fact, its motion is a little hard to fathom in a static representation. So Wiegert has cooked up some very instructive animations to help us all out. A 10-MB Windows .avi file is here, and a 7-MB Quicktime .mov version is here. (He's got some other nice graphics and details about 2010 TK7 on this website.) Earth's little buddy is so wide ranging that it might even occasionally spend some time resonating around the distant L3 point. In fact, gravitational influences from Jupiter make the orbit chaotic, and there's no why to know with certainty where L4 was or will be when its orbit is tracked for more than 10,000 years. Unfortunately, even though Earth probably has other Trojans in its entourage, WISE won't be able to see them. The spacecraft ran out of its cryogenic coolant last October, and on February 17th principal investigator Ned Wright sent a command to turn off WISE's transmitter for good. Word is that the spacecraft will remain in hibernation, awaiting a possible wake-up call in the future. Post Comment Private Reply Ignore Thread
|
||
|
[Home]
[Headlines]
[Latest Articles]
[Latest Comments]
[Post]
[Sign-in]
[Mail]
[Setup]
[Help]
|
||