recently have been spotted in more sociable arrangements, harboring small companions. And now, as seen in newly released images, a pair of chunky twins are caught waltzing through space in a manner never before seen.In a discovery that rocks what we know about asteroids, sort of, two hunks of stone and iron known collectively as 90 Antiope are spied against a black backdrop, circling each other every 16.5 hours while simultaneously zooming around the Sun in the outer reaches of the main Asteroid Belt, between Mars and Jupiter.
In another dazzling example of cosmic paparazzi, made possible with the latest in ground-based telescope technology, Asteroid 762 Pulcova has been spotted with a wee little companion, becoming only the third known asteroid to have what scientists call a moonlet.
With the Pulcova pairing, the smaller moonlet is only about one-tenth the size of the 90-mile- (145-kilometer-) wide main rock. So the little one gets the biggest workout, zipping around its larger companion about once every four days at a distance of 500 miles (800 kilometers).
But the larger Pulcova rock gets an orbital nudge, too.
"Like kids on a teeter-totter, the smaller kid must sit further from the pivot point to balance the bigger kid," explained William Merline of the Southwest Research Institute. "Same here. The primary asteroid is much larger and the central point for the orbit is very close to the center of the primary asteroid."
Their first date was a smash
The Antiope pair was probably created by a collision of larger rocks long ago, Merline told SPACE.com. Knowing that what was once thought to be a single asteroid is actually two; researchers can now use one to study the other. Their orbital characteristics will reveal the density of each, and hence shed light on what they are made of and whether they are solid rocks or more loosely packed piles of rubble.
Because collisions are thought to have played a big role in building the nine planets long ago, studying these newly found asteroid configurations will help researchers understand how the other planets formed, Merline said.
And having found four asteroid pairings already, at the dawn of our ability to actually see into the Asteroid Belt with such clarity, has researchers expecting there may be a lot of asteroidal commingling going on out there.
"It's getting to be kind of bewildering," said Christopher Dumas of the Jet Propulsion Laboratory. "Asteroids were once thought to be single, mountain-like chunks of material, perhaps smashed into 'flying rubble piles' by occasional collisions among themselves."
Dumas, who works with Merline, said one surprising aspect of the recent discoveries is that the rocks have had very low densities compared with the average asteroid.
"From the density we have a better clue of what the asteroid might be made from," Dumas said. "It appears that these objects seem to be either loosely packed fragments of an original asteroid that has been broken up during an impact (rubble-pile model) or very rich in water ice, or both."
How the paparazzi did it
The first asteroid-moon pair was spotted in 1993, by the
. The team named the companion Petit-Prince.Galileo had the advantage of being in space, where the view is clear. The asteroid pair 90 Antiope, on the other hand, was imaged using the Keck Observatory atop Mauna Kea, Hawaii. Pulcova and its moon were photographed by the Canada-France-Hawaii Telescope (CFHT), also on Mauna Kea.
In both cases, researchers used a technique called adaptive optics, which filters out distortion caused by Earth's atmosphere by analyzing the light and applying a computerized correction. Experts say the technique allows ground-based telescopes to rival the orbiting
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