By: Natalie Wolchover, Life's Little Mysteries Staff Writer
Mikael Gravnik, a physicist at the University of Helsinki and lead author of the new paper, says 2006 RH120 was probably discovered because it was slightly larger than most of the other "temporary moons" that come traipsing through our planetary system. Most of the hobo moons are only about 1 meter wide.
"Objects of this size are too faint to be detected when being at a distance of, say, a few lunar distances from the Earth," Gravnik told Life's Little Mysteries."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."
These limitations mean we don't currently have a way of finding our second moons. But an observatory called the Large Synoptic Survey Telescope (LSST), planned to open in Chile in 2015, could change that.
"We hope that LSST will do something about this, but dedicated programs will without doubt be even better," Vauballion said. "Statistic study is still needed to see where and how to look for them."
NASA's Spaceguard Survey tracks the paths of all near-Earth objects (NEOs) in Earth's neighborhood that are larger than 0.6 miles (1 kilometer) in diameter, but the scientists are less concerned with bodies that are too small to pose a threat to Earth — as is the case when they're just 1 meter wide.
But if our distant, noncommittal moons don't threaten Earth, and are much too dim to act as nightlights, does it matter that they're there at all?
According to astronomers, it does. Some researchers say it might be possible to go and get one of these temporary moons and bring it back to Earth for analysis.
"When found, such an asteroid will immediately raise the question whether or not we should go, and I'm ready to bet that many astronomers will argue that we definitely have to go!" Vaubaillon said in an email. "The reason is simple: What astronomers would not want to have a full and intact (unaltered by any physical process) piece of space rock? Meteorites are all altered because they go through our atmosphere. The only piece of asteroid we have comes from the Japanese Hayabusa mission (a few grams at the very most). The comet grains the Stardust mission got back from comet Wild 2 were all altered."
Clark Chapman, senior scientist at the Southwest Research Institute in Boulder, Colo., said a lot could be learned from the retrieval of a temporary satellite. "No doubt it is true that temporarily captured NEOs would be comparatively easy to get to and get back from ― it wouldn't take an especially rocket, and round-trip times would be short," said Chapman, who is an expert on asteroid impact hazards.
Gravnik said, "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."