by Staff Writers
Paris (AFP) Oct 22, 2014
Astronomers using an ultra-sensitive telescope in the Chilean desert said Wednesday they had mapped hundreds of comets orbiting a star 63 light years from Earth.
The feat marks the most complete census of so-called exocomets, or comets in other solar systems, they said.
Comets are familiar to us on Earth, for they shed a coat of ice and dust as they near the Sun, which is reflected as a spectacular "tail" in the solar rays.
Astrophysicists, though, are keen on them for other reasons.
Comets are believed to be ancient remnants left from the building of our Solar System some 4.6 billion years ago.
Previous work has found that other stars, too, have comets.
But it has been extremely difficult to get a more detailed picture.
Comets are tiny relative to the size of their sun, and their "tail" is swamped by the starlight, which makes it hard to identify them and calculate their orbit.
Reporting in the journal Nature, a French-led team pored over nearly 1,000 observations of a youthful star, Beta Pictoris, that were made over a period of eight years.
The images were taken with a highly-sensitive instrument, HARPS, at the European Southern Observatory's La Silla facility in Chile's bone-dry Atacama desert.
Out of these observations, the team identified a total 493 comets, the most ever netted in an extra-solar probe.
The comets comprise two distinct families, similar to the way that comets in our own Solar System fall into different categories, the astronomers found.
One is a group of "old" exocomets whose orbits have been skewed by the gravitational pull of a massive planet -- a gas giant called Beta Pictoris b that orbits the star at a distance of about a billion kilometres (600 million miles).
These comets may have been stripped of their ice after coming too close, or too often, to the star, according to the study.
The other is a newer group of comets, which appear to be from the breakup of larger objects.
Beta Pictoris is a mere kid in terms of solar ageing.
It is only about 20 million years old, and is surrounded by a huge disc of gas and dust -- the materials from which planets, asteroids and comets are formed.
That makes it a "remarkable" window for observing some of the mechanisms that form a solar system, said lead investigator Flavien Kiefer of the Paris Institute of Astrophysics.
"Beta Pictoris is a very exciting target," Kiefer said. "The detailed observations of its exocomets give us clues to help understand what processes occur in this kind of young planetary system."
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