Sky survey yields new cosmic haul

Astronomers looking through the data from the Sloan Digital Sky Survey, the world's largest survey of galaxies, have found a new haul of objects closer to home - including one with a potentially exotic origin.

By searching through a survey region known as Stripe 82, a team led by Dr Andrew Becker of the University of Washington, has discovered almost 50 new asteroid-sized bodies in the outer regions of our Solar System.

As part of a search for supernovae - exploding stars in distant galaxies - the robotic Sloan telescope in New Mexico revisited this area of the southern sky every three days.

By comparing images taken on different nights, the Washington team was able to detect the asteroids as they moved across the sky.

"It's probably a mixture of ice and rock, rather like a comet"
Dr Andrew Becker, University of Washington

As team member Dr Lynne Jones pointed out: "If you can find things that explode, you can also find things that move, but you need different tools to look for them."

While most of the newly discovered objects are normal members of the Kuiper belt, a large band of icy bodies stretching beyond the orbit of Neptune, there were also surprises.

The team discovered two Neptunian Trojans, asteroids which share the same orbit as the outermost giant planet.

"Jupiter has plenty of trojans," Dr Becker told me, "and we knew that Neptune must have a similar population of objects. Surprisingly, not many had been found before this survey."

The team's prize find is an object given the temporary designation of 2006 SQ372. This icy body is currently roughly two billion miles away, just closer to the Sun than Neptune, but is beginning a journey that will take it out to a distance of 150 billion miles from the Earth.

Unpredictable fate

The new object is only 30-60 miles across, and not a normal asteroid: "It's probably a mixture of ice and rock, rather like a comet although it never comes close enough to the Sun to develop a tail," said Dr Becker.

The new object's orbit is also unusual; only one other object - Sedna, discovered in 2003 - might come from the same region of the Solar System.

Dr Becker told me that simulations carried out by a third member of the team, Nathan Kaib, show that 2006 SQ372 won't stay in its current orbit for long (by astronomical standards at least).

"Sedna is in a stable orbit, and has probably been there for billions of years, but in more than half of our simulations our new object got too close to either Uranus or Neptune within 180 million years," he explained.

An interaction with either of its large neighbours would send 2006 SQ372 spinning in a random direction, leaving its fate impossible to predict.

In the meantime, Sedna and 2006 SQ372 might represent the first two known objects to have come from the inner edge of the Oort cloud, a vast reservoir of cometary material believed to exist right on the edge of the Solar System.

Only further study will confirm if this really is the new object's home, but in the meantime the discoverers are thinking of a permanent name, presenting Dr Becker with a dilemma.

"It will end up with the name of either a centaur, or a mythological name associated with the underworld or creation," he pondered.

"I would certainly prefer the underworld scenario! Too much heavy metal music in my iPod!"

RELATED INTERNET LINKS
Sloan Digital Sky Survey
Galaxy Zoo
The Sky at Night
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