A team of Canadian scientists has discovered that Uranus – like Earth, Mars, Jupiter and Neptune — has a travelling companion on its path around the Sun.
Astronomers from British Columbia detected the icy space rock, about 60 kilometres in diameter, and noted that it runs along Uranus’s orbit but is ahead by about 60 degrees.
It’s the first such "Trojan" object discovered accompanying Uranus.
Labelled 2011 QF99, the space rock is predicted to stay in position for 700,000 years before its orbit decays slightly. Eventually, it will escape Uranus’s pull and fly off on its own into the outer solar system.
The Trojan looks like an asteroid, but its makeup is similar to a comet.
Its discovery was published last week in the journal Science. The scientific team comprised doctoral students Mike Alexandersen and Sarah Greenstreet and professor Brett Gladman of the University of British Columbia, researchers J.J. Kavelaars and Stephen Gwyn of the National Research Council of Canada, and Jean-Marc Petit of France.
They used the Canada-France-Hawaii telescope on Hawaii Island to spot the orbiting rock.
Some 6,000 space rocks are known to follow Jupiter, the most of any planet. Earth shares its orbit with a tiny asteroid called 2010 TK7, discovered in 2010 also by a Canadian team.
Trojan objects interest scientists because they may hold material left over from the formation of the solar system, Athabasca University astronomer Martin Connors told CBC News in 2011.
While meteorites also contain such material, they typically have wandered long distances and scientists can never be quite sure where they came from.