New "Minor Planet" Found in Solar System

Brian Handwerk
for National Geographic News

August 19, 2008

The solar system as we know it is a bit more crowded due to the recent discovery of an intriguing new "minor planet."

The object, dubbed 2006 SQ372, is a kind of tailless comet that's currently some two billion miles (three billion kilometers) from Earth, a bit closer to the sun than Neptune.

But the lump of ice and rock is moving on a long, elliptical orbit that will take it on a round-trip journey lasting about 22,500 years.

At its peak distance, the body will be about 150 billion miles (241 billion kilometers) from Earth—1,600 times farther than the distance between Earth and the sun.

Visitor From the Oort Cloud?

Scientists first sighted the unusual object in 2006 while scanning the skies for distant supernovae that help measure the ongoing expansion of the universe.

Based on data collected between 2005 and 2007, Andrew Becker of the University of Washington and colleagues charted the object's unusual orbit—an ellipse four times as long as it is wide.

The object appears to be a comet that does not get close enough to the sun for its ice to evaporate and form a tail.

"Currently it's in a transient orbit right now, an unstable orbit," Becker said.

"It's close to the orbits of Uranus and Neptune, and we think that in a couple of hundred million years, one of those planets will scatter it."

Becker's team believes 2006 SQ372 probably came from the inner edges of the Oort cloud, a theoretical region of asteroid-like bodies several trillion miles away that is believed to be the source of many known comets.

The scientists think the body was bounced into the Oort cloud from the inner solar system during planet formation some 4.5 billion years ago.

An unusual event—such as a star passing by—later perturbed the object and flung it into its current, irregular orbit.

Becker and colleagues announced their research in Chicago, Illinois, last week at a symposium called "The Sloan Digital Sky Survey: Asteroids to Cosmology."

Object in Trouble

Mike Brown, an astronomer at the California Institute of Technology, is one of the discoverers of Sedna, a planetlike body found in 2003 that may be the first object seen from the inner Oort cloud.

Brown said that 2006 SQ372 is a very interesting object but not necessarily one that comes from the inner Oort cloud.

"It may have formed from debris just beyond Neptune [in the Kuiper belt] and been 'kicked' into it's distant orbit by a planet like Neptune or Uranus," Brown said.

"I think a perfectly reasonable explanation is that it's like many of the Kuiper belt objects that have eccentric orbits."

Brown added that, although 2006 SQ372 travels more than twice as far from the sun as Sedna, it also gets closer to the sun and thus likely has interactions with Neptune.

"Sedna is distant and never comes close to any giant planets, so it's been in the same orbit for maybe four billion years," Brown said.

"Every time [2006 SQ372] comes into the inner solar system, it's in trouble and has a very good chance of being deflected by a planet," he said. "This is not its original orbit since the early days of the solar system."

Chad Trujillo of the Gemini Observatory in Hawaii said that although many objects with similarly eccentric orbits probably exist, actually finding one is an accomplishment.

"I think most researchers in the field expect there to be many such objects out there, so it is not the presence of the object that is surprising, it is more the fact that is was actually discovered," he said.

Objects on an extreme elliptical orbit like 2006 SQ372's are rarely in visible locales close to the sun, so spotting them requires a lucky look in the right place at the right time.

"What this really points [out] and what is really exciting," Trujillo said, "is the huge number of undiscovered objects on similar—or even more extreme—orbits that are just too faint for us to see."