Outer solar system's busy, busy, busy

From: http://www.abc.net.au/science/news/stories/s1696218.htm

Judy Skatssoon ABC Science Online. Aug 1, 2006

Researchers say they have found the first evidence that the frozen outer reaches of our solar system could be littered with many more objects than we think.

Astronomers have been trying to get a picture of the region, known as the Kuiper belt, because it is believed to contain debris from the birth of our solar system and so could tell us how planetary systems form.

About 1000 large bodies, including Pluto and the recently discovered Xena, have been located in the Kuiper belt so far.

But smaller objects have evaded detection as they are about 15 billion kilometres from the Sun, making it impossible to see them even with a powerful instrument like the Hubble Space Telescope.

Now an Australian team from the University of New South Wales (http://www.unsw.edu.au/) (UNSW) and the Anglo-Australian Observatory (http://www.aao.gov.au/) (AAO) has used optical fibre technology to detect signs of smaller Kuiper belt objects for the first time.

The wink of a star

They did this by observing split-second 'winking', or darkening, of stars which suggests a Kuiper belt object is passing in front, or occulting the star.

UNSW student George Georgevits presented his research at a recent workshop attended by international Kuiper belt experts in Italy.

His colleague Associate Professor Michael Ashley of UNSW says the observations offer the first evidence the Kuiper belt contains many more relics of the infant solar system than estimated.

"Basically our observation showed that that are many more, maybe five or 10 times as many, of the smaller objects than theory predicted," he says.

Ashley says Georgevits and fellow researcher Dr Will Saunders of the AAO found evidence of many objects ranging in size from 300 metres to one kilometre across using a 6DF instrument on the UK Schmidt telescope at Siding Spring.

The 6DF, which uses fibre optics, monitored 100 stars simultaneously over two weeks, the equivalent of 7000 star hours, or watching a single star every night for 3 years.

"We've got 100 fibres, each one of which is positioned on a star and then we feed the fibres into a high speed camera," he says.

A fraction of what's out there

Ashley says it's been suggested there are around 100 billion objects in the belt, but the latest observations suggest this could represent only a fraction of what's there.

"We saw at least 100 very definite [occultations] and as ... you look for smaller, less significant events we could have seen up to 1000," he says.

The Kuiper belt community has greeted the news with some scepticsm. Some critics say that the apparent dimming of the stars may be due to effects in the Earth's atmosphere.

Ashley says the scientists took pains to rule out other possible causes for dips in stars, including moths in the telescope.