London, June 5 : Astronomers searching for distant supernovae to probe dark energy in the early universe have stumbled upon two relatively nearby objects between Uranus and Neptune that may shed light on the early solar system.
According to a report in New Scientist, the odd solar system bodies were found by Andrew Becker of the University of Washington in Seattle, US, along with his team of students.
While one lies in a nearly circular orbit between Uranus and Neptune, the other may have been kicked out to a much more distant, tilted orbit by a marauding planet that was lost to the solar system long ago.
Supernova surveys look for changes in faint light sources, but many of the faint objects that suddenly appear at a new spot in the sky are actually small bodies in the solar system.
Often, supernova researchers ignore these nearby objects, but Andrew Becker realized that the intruders might be interesting in themselves.
When he had undergraduate students mine the survey data, they found 14,000 asteroids in the inner solar system, including 1300 new objects.
Now, the team reports finding 14 previously unknown objects in the outer solar system in data collected by the ESSENCE supernova search from 2002 to 2007.
One prize object is 2003 UC414, which is about 100 kilometers across and travels on a nearly circular orbit near the midpoint between Uranus and Neptune.
"You'd think something in between those two planets would be relatively unstable," Becker told New Scientist.
Only two other objects have been found in the zone, and they don't appear to be in stable orbits.
But 2003 UC414 is close to two "islands of stability", where objects could orbit for a billion years.
But if more observations show it is stable, the discovery will cast doubt on the idea that Uranus and Neptune swapped places during an unstable phase early in the solar system's history.
According to Becker, such shuffling should have kicked out anything orbiting between them and after the rearrangement, it would have been difficult for an object to become trapped there in such a circular, stable orbit.
The other interesting object is 2004 VN112, which is thought to be about 300 km wide.
Its orbit is tilted 25 degree c to the plane of the solar system and is quite stretched out, ranging from 1.5 to 30 times Neptune's distance from the Sun.
"That orbit is essentially gravitationally detached from all the current members of the solar system", said Becker.
He suspects a "rogue planet" later lost from the solar system originally forced 2004 VN112 into the unusual orbit.