It turns out Uranus has a cosmic companion as it circles the sun from nearly 1.8 billion miles away. Scientists have detected a Trojan, an asteroid-like object that shares a planet’s orbit, moving ahead of the ice giant.
The discovery of 2011 QF99, reported last week in the journal Science. was found almost by accident.
Mike Alexandersen, a doctoral student in astronomy at the University of British Columbia in Vancouver wasn’t looking for a Trojan. Nor was he studying Uranus.
He and his colleagues were surveying the transneptunian region of the outer solar system, hoping to see what kinds of orbits the objects there followed.
As Alexandersen and the team examined images snapped using the Canada-France-Hawaii telescope during 2011 and 2012, they noticed one object that moved across the field of vision more quickly than the others.
That part wasn’t a surprise. But seeing something that moved the way 2011 QF99 did was a shocker.
Over the course of a year of observations, they realized that this space rock was traveling in an orbit very much like that of Uranus.
“It was, in fact, a Trojan,” said Alexandersen, who added that the team members “were certainly not anticipating finding something as cool as this.”
Chunks that float around in the zone of the giant planets are called Centaurs. Those that make it into the inner solar system, heating and vaporizing in the sun’s heat, are known as comets.
Trojans get captured in particular locations in a planet’s orbit where gravity from the sun and gravity from the planet interact to lock them in place.
Some Trojans — around Mars, Neptune and especially Jupiter — are permanently bound to their planets, and have been for billions of years. Others, like 2011 QF99 and Earth’s Trojan 2010 TK7, are temporarily trapped in their orbits.
