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NASA
An asteroid zooms past the Earth in this artist's impression -- but how many space rocks are captured by Earth's gravity?
By Irene Klotz
Discovery
Earth's gravity may not have the gravitas of Jupiter, but the planet regularly plucks small asteroids passing by and pins them into orbit. The mini-moons don't stay for long. Within a year or so they resume their looping, twisting paths like crazy straws around the sun. But others arrive to take their place.
Simulations show that two asteroids the size of dishwashers and a dozen half-meter (1.6 feet) in diameter are orbiting Earth at any given time. Every 50 years or so something the size of a dump truck arrives. So far, there's been just one confirmed sighting.
"We'd eventually like to see a mission to a mini-moon," astronomer Robert Jedicke, with the University of Hawaii, said this week at a workshop in Huntsville, Ala., to discuss proposals for two spare Hubble-class spy telescopes donated to NASA by the National Reconnaissance Office.
PICTURES: Asteroids and Near-Earth Objects
Jedicke would like to use one of the telescopes to hunt for near-Earth objects, including mini-moons, which could be captured whole and brought to the ground for study.
"It's the Rosetta stone of the solar system. You bring back a chunk of material that's never been processed through the atmosphere, that's not been sitting on the ground. It's going to be a tremendous wealth of information about how the solar system formed -- even more so if you can bring back more than one and get different types of material," Jedicke told Discovery News.
"The great thing is you don't have to go very far," he added. "These things are sitting there right in geocentric orbit and they're relatively easy to get to."
But hard to find.
A paper published last year showed that, in theory, a cloud of temporarily captured asteroids circles Earth at all times, but that the largest object is just about a meter (3 feet) in diameter.
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"These are really difficult to detect with current technology," said astronomer Paul Chodas, with NASA's Near Earth Object program at the Jet Propulsion Laboratory in Pasadena, Calif.
So far, the only confirmed captured asteroid that orbited Earth was RH120, which most recently visited from September 2006 to June 2007. Initially, the object was suspected of being a spent upper-stage motor from an Apollo rocket, but follow-up observations by ground-based radars determined the object was not metallic.
"There is great interest in tracking these Temporarily Captured Objects (TCOs), because for a short time they are easily accessible for both scientific study and, possibly, eventually, resource utilization," Chodas wrote in an email to Discovery News.
In addition to being small, mini-moons are difficult to find because they only hang around for a relatively short time, between six and 18 months.
"We would want to discover one of these as soon after capture (by Earth’s gravity) as possible to have enough time to get a spacecraft out there, and then still have time to study the object before it escapes back into heliocentric orbit," Chodas said.
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In addition to science, there is economic interest in asteroids. Two U.S. firms, Planetary Resources and Deep Space Industries, announced plans last year to mine asteroids for raw materials. Both companies are developing precursor missions to scout potential targets.
"Maybe you're not going to mine a half-meter diameter wide asteroid, but you can test out your techniques on it," Jedicke said.
Hunting mini-moons wouldn't be the telescope's only job.
"It would be best asteroid survey ever of the entire solar system," Jedicke said.
"That survey could be used to build up a very deep image of the sky in that region which could be used to look for supernova, gamma ray bursts, asteroid collisions -- basically anything that changes, this survey would find," he said.
A list of proposals for the donated telescopes is expected to be presented to NASA managers next week.
Leave a Comment:
Mini-moons, meh. I like big moons and I can not lie.
These other brothers can't deny.
When an asteroid comes from inner solar space
And a round thing in yo face
you get sprung!
Yes, I've been saying something like this for years. How about they park a rocket-taxi at the space station and when one of these guys comes along, the taxi goes out and brings it back to the space station. It would not take much to bring one of these meter sized rocks back. But it would take some ingenuity about how to bring it back. How about a claw mounted on the nose of the rocket that would grab the rock and hold onto it as the rocket returns to the space station.
Or, since it appears these rocks hang out in a certain area around the earth, we should send a taxi out there with a good radar system and have it map out the area and then bring back a good sample. This would serve a double purpose, as it appears this area is not one that has been explored. Wouldn't it be way cool to be able to watch a live feed of a taxi-rocket sneaking up and grabbing one of them or even just going out there and doing what robo-car is doing on mars: taking samples, zapping with lasers, etc. The lag time of our signals is fairly short for this areas compared to mars, so it would lots easier to manipulate the grabbers, samplers, etc.
This is mickey mouse level work compared to putting the robo-car on mars, so let's get on it. This is too fun to pass up and the science from this relatively small project could be enormous. The more I think on this, the more I wonder why we haven't done something like this.
I hope they get funding to bring one closer. Even a small one 3 ft across is a multi ton mass and it's probably spinning. It would be a great practice run for something bigger, rich in resources.
ED-2874315
a mini moon would weigh nothing in space, though it would have mass. In order to have weight, it would need to be stationary in earth's gravitational field.Mass has to do with the amount of matter in some object, and determines how hard it is to push something around. Weight is how big the force of gravity is that is acting on some object. An object has the same mass no-matter where it is. So a very small object would not need much effort at all.