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There are still quite a lot of unsolved mysteries in our neighbourhood, the Solar System. Astronomers know very little, for instance, about the so-called ‘transneptunian objects’: a ring of asteroid-type bodies located beyond planet Neptune. Dutch astronomer Gerald Kuiper predicted the existence of this ‘belt’ fifty years ago — it is therefore named the ‘Kuiper belt’ — but the first detection of one of its constituent bodies only happened in 1992. Further surveys have provided an estimate of how many objects are actually there: possibly 10,000 bodies with a diameter larger than 300 kilometres, and maybe three million larger than 30 kilometres in diameter. Only 300 of them have been observed so far. The list of pending questions about them is very long: what’s their precise origin and composition? Which of the comets that periodically visit the Earth are ‘Kuiper objects’? ESA’s next infrared space telescope, the Herschel Space Observatory — formerly called ‘FIRST’ — will help to provide the answers, astronomers gathered in Toledo (Spain) said yesterday.
Large infrared telescopes are the only ones able to give direct information about the size and chemical composition of the Kuiper belt objects. The new generation of ground-based giant infrared telescopes are now starting their study, but the Earth’s atmosphere blocks most of the infrared light from astronomical objects and therefore a large infrared space telescope, such as ESA’s ‘Herschel’, is needed. ‘Herschel’ will be launched in February 2007; more than 200 astronomers from all over the world are gathered this week in Toledo to discuss its ‘scientific agenda’.
"The study of the transneptunian objects will give us many clues to understand how the Solar System was formed", said Solar System expert Emmanuel Lellouch (Observatoire de Paris-Meudon, France). "Now we know very little about them".
Astronomers think these objects are probably like comets: an aggregate of dust grains mixed with ices — their surfaces are only heated to minus 230 degrees Celsius by the very feeble distant Sun.
In the Solar System there are three ‘reservoirs’ of minor bodies: the ‘Main belt’ or ‘asteroid belt’, between Mars and Jupiter; the Kuiper belt; and the ‘Oort Cloud’ surrounding the whole Solar System.
The comets that ‘visit’ the Earth for the first time come from the Oort Cloud, which was made out of left-over material after the formation of the gaseous planets — Jupiter, Saturn, Neptune and Uranus. But the ‘periodic’ comets — that come at precise intervals of time — are originated in the Kuiper belt. Unlike those coming from the Oort Cloud, these periodic comets might reflect the original chemical composition of the interstellar cloud that provided the material to make the whole Solar System (4.6 billion years ago).
"The high sensitivity of the Herschel Space Observatory will allow us to study in detail these periodic comets, and determine precisely their chemical composition", said Dominique BockelÈe-Morvan from the Observatoire de Paris-Meudon in France.
Comets are mostly made of water. Finding out the isotopic composition of this water will help astronomers, among other things, to trace the origin of water in the Solar System planets, such as our own planet.
* "The Promise of FIRST" workshop
* ESA Science Herschel home page
* FIRST science homepage
[Image 1:] Neptune in Primary Colors. Clouds elevated above most of the methane absorption appear white, while the very highest clouds tend to be yellow-red as seen in the bright feature at the top of the image.
[Image 2:] Another ice-making machine in the Solar System? A Jupiter-like planet evolves in a disk of gas and dust around a young star, in computer model of the process devised by Pawel Artymowicz of Stockholm University.
[Image 3:] A near-infrared NICMOS image of Saturn.