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In 2006, a group of scientists at the University of Hawaii detected a small asteroid circling the Earth, and kept track of it until it went out of orbit mid-2007. Later last week, these scientists – Mikael Granvik, Jeremie Vaubaillon, Robert Jedicke – published a paper stating that the Earth may have additional temporary moons at any given time. The paper, published in the science journal Icarus, also theoretically models the orbits of the secondary moons, and states that the research they did is consistent with the observations of the current secondary moon.
Another recent study at Cornell concludes that it is common for numerous small objects to enter the Earth’s orbit and become temporary moons at any given time. These objects are usually small asteroids, one to several meters in length.
“There are lots of asteroids in the solar system, so chances for the Earth to capture one at any time is, in a sense, not surprising,” explains Vauballion.
Sometimes, an asteroid on its way to the sun is “grabbed” by Earth’s gravitational pull. It orbits the Earth for nearly a year, and then it breaks out of its orbit and goes along its merry way. These objects are too small to do any damage to the Earth, though they do qualify as natural satellites like the Moon.
Although it may be reassuring that these asteroids can do no harm to our planet due to their miniscule sizes, scientists find it quite difficult to detect them for the same reason. Moreover, instruments cannot collect data because the secondary moons move too quickly when they come closer to Earth. There would not be enough time to send an observational satellite. Also, according to Granvik, “When coming closer in during their orbit, they are moving too fast to be detected, because the limited amount of photons is spread over too many pixels.”
Currently, the Large Synoptic Survey Telescope (LSST) is being constructed and will open in the northern mountains of Chile in 2005. The LSST will be able to detect these tiny moons and collect data.
Having astronauts visit asteroids and mine them of their assets is one of the astronomers’ ambitions. It may be possible to take further advantage of these secondary temporary satellites so astronauts would be able to visit one of them and then transport it (it would not be too difficult, considering the asteroid’s size) back to Earth for analysis.
Says Granvik, “We certainly hope that a space mission to a natural Earth satellite would someday materialize and have actually already started a collaboration with experts in spacecraft orbital mechanics to find out how a mission from the Earth to a temporary satellite could be accomplished.”
He, Vaubaillon, and Jedicke conclude their paper stating: “The scientific potential of being able to ﬁrst remotely characterize a meteoroid and then visit and bring it back to Earth would be unprecedented.”