KAREN PERCY: To the far extremes of the solar system now. Is it a rock? Is it an icy mass? Or is it a planet? A team of German astronomers has for the first time measured the so-called 10th planet. In findings that have been published in the science journal Nature, they've determined that the icy, rocky object discovered last year is larger than Pluto. As a result our smallest, most distant planet in the solar system could be, well, on the outer.
Jennifer Macey reports.
JENNIFER MACEY: Last year, on the outer edges of the solar system, a massive ball of ice and dust was discovered by a team of American astronomers.
Now scientists have measured its size. At roughly 3,000 kilometres in diameter, the object known as 2003 UB313 is about 700 kilometres bigger than Pluto.
So does it qualify as a planet? Yes, says Frank Bertoldi, a professor of Astronomy from Bonn University in Germany.FRANK BERTOLDI: Now, Pluto really belongs to the Kuiper Belt, it's not the classical kind of planet in the outer solar system. So do you want to take away the title of planet from Pluto?
I'd be against that, just out of, let's say, cultural respect. But then, to be more consistent, you also have to restore that title then to objects that are larger than Pluto and part of the same family out there.JENNIFER MACEY: When UB313 was first discovered in July 2005 by US astronomer Michael Brown, its size was uncertain because it reflects the same amount of light as Pluto.
German astronomers overcame this problem by measuring the amount of heat it radiated using a special telescope in southern Spain.
Professor Bertoldi says UB313 takes twice as long as Pluto to orbit the sun.FRANK BERTOLDI: And it's 97 times the distance between the sun and earth, so it's really far out there. It's the most distant solar system object we know of.
JENNIFER MACEY: In the interim the object has been dubbed Xena, after the television series, and its moon, which was also discovered last year, is known as Gabrielle. Official names will be decided this year by the International Astronomical Union.
FRANK BERTOLDI: We'd certainly get another name. This funny name, 2003 UB313, it's not very pretty. I guess Mike Bonner's made a suggestion for a name. He doesn't reveal it to anybody, except for the International Astronomical Union, who now have to decide whether, first of all, this is a planet, and second that name is good.
JENNIFER MACEY: Is it Xena?
FRANK BERTOLDI: No, it will definitely not be Xena, nor Lila, nor UB313.
JENNIFER MACEY: But astronomers around the world are split on how to define a planet, and a committee has been set up to resolve the issue.
Professor Fred Watson, the astronomer in charge of the Anglo-Australian Observatory in Coonabarabran, believes UB313 should not be defined as a planet.FRED WATSON: It's a thing called a Kuiper Belt object, and the Kuiper Belt is a kind of outer asteroid belt that sits beyond the orbit of Neptune, something like 30 to 50 times the earth's orbital distance from the sun, away from the sun.
And it's made up of probably 70,000 rocky and icy objects which are almost certainly the debris left over from the formation of the solar system about four-and-a-half billion years ago.
These are things that were never… came together to form planets, so they never really coalesced, and they never have been processed by heat, which makes them very interesting.JENNIFER MACEY: Dr Scott Shepherd is a fellow at the Carnegie Institute in Washington who's following the debate for the journal Nature.
His personal preference is that neither UB313 nor Pluto should be considered planets.SCOTT SHEPHERD: My personal belief is that we should go with the scientific route and anything that has similar formation, evolutionary history, should kind of be grouped together as an ensemble, and so that would leave us with only the eight major planets, and that would drop Pluto from the list.
JENNIFER MACEY: However, both Professor Watson and Professor Bertoldi believe Pluto should retain its ranking as the ninth planet for historical and cultural reasons.
And what will the addition or loss of a new planet mean for astrologers? Professor Bertoldi is confident that they too will cope.FRANK BERTOLID: They'd adjust their horoscopes a little bit (laughs).
KAREN PERCY: Professor Frank Bertoldi from the University of Bonn in Germany, ending Jennifer Macey's report.
source: http://www.abc.net.au/cgi-bin/common/printfriendly.pl?http://www.abc.net.au/worldtoday/content/2006/s1560680.htm 3feb2006
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