Earlier this month, an object called WT1190F was spotted on a trajectory that will bring it right to Earth. It came here from far beyond the moon, and its hollow nature and cylindrical shape suggest that it's human-made and not an asteroid or meteorite. It won't cause any major problems on the ground, but there's still something troubling: Astronomers don't know what the heck it is, or why it's only now coming up on their radar.
Its trajectory is pretty easily understood. It's headed for an area of space over the Indian Ocean, where it will re-enter the atmosphere at 2:20 p.m. EDT on November 14. Most of it will burn up, according to Nature, but any leftover debris will make sea-fall about 40 miles off the coast of Sri Lanka.
"It's coming in fast and will get very hot - it's possible a few dense parts of say a rocket engine will survive to impact the ocean," Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, said in an email.
What's not understood right now, though, is what the object is. It's all but certainly human-made, and it has an unusual elliptical orbit that takes it twice as far out as the distance of the moon, and something bothered it enough to come back down to Earth. It's likely a rocket stage or panelling, as it's only three to seven feet long, and may have been up there for a long, long time. It could even be a piece of debris from the Apollo missions. McDowell says precovery images place the object back at least to 2012, which may have been around when its orbit changed due to perturbations from the moon. Its previous orbit isn't known.
"To fit the solar radiation pressure effects on its orbit you need to assume a high area-to-mass ratio - implying the thing is hollow, like an empty rocket stage would be," Mcdowell said. "So it has the right size and properties, and it is in an orbit which would be surprising for a natural object (whizzing around theEarth-Moon system) but where we know there are a bunch of pieces of space junk."
That it was discovered so late in the game is unusual but not unheard of. The United States is currently working on its next version of the "space fence," which will be able to detect most large pieces of space debris in near-Earth orbit. But unless WT1190F were at its perigee nearer Earth, the object might still have gone undetected due to its strange orbit.
McDowell has a few speculations on what it could be, based on things that might've been in the vicinity of the moon. He says there are 86 unaccounted for artificial objects in moon crossing orbits, most of them from lunar probes. There's still a chance it could be China's Chang'e-2 lunar mission or another lunar probe, or it could be the adapter panels from the Saturn V rockets that launched the Apollo missions. The adapter panels deployed into four pieces when the lunar module was ready to deploy, and they are presently mostly unaccounted for.
Astronomers will focus in on the object and track its movements, and some spectral information may be gathered to help identify it, and whether its from the beginnings of the space race or a more recent robotic mission. But there's only three weeks left to get an answer. After that, it may not be much more than a few chunks of metal rusting in the Indian Ocean.
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