Original Source: University of New South Wales, Sydney

January 18, 2002

Jupiter as a typical example of large planets around other stars

Image copyright: NASA

Research by UNSW astronomers indicates that Jupiter, the largest planet in our Solar System, is a typical example of the largest planets around other stars. This helps answer the question: Are there billions of other planetary systems like ours scattered through the Universe, or do we live in a unique system of planets?

Scientists at the Anglo-Australian Telescope and other astronomical observatories around the world have been scanning the sky for tell-tale signs of planets around nearby stars. So far these planet hunters have found 74 extra-solar planets orbiting 66 nearby stars (some stars have two known planets; one has three).

A new analysis of these planets by two UNSW astronomers gives us the clearest indication yet of where our own Solar System fits in the universe. According to Dr Charles Lineweaver, a researcher in UNSW's School of Physics, and Daniel Grether, an Honours student, Jupiter seems to be a typical planet - much more typical than indicated by previous analyses. In their paper, cited at this week's meeting of the American Astronomical Society and in the next issue of Science magazine, Dr Lineweaver and Mr Grether analysed the latest data on the masses and orbital periods of all the recently detected extra-solar planets. They carefully edited the data to correct for the limitations of the detection techniques, which are not yet able to detect Jupiter-sized planets.

"Although Jupiter-like planets taking 12 years to orbit their host star have not yet been detected, we were able to make a simple extrapolation of the trends identified in the current data," Dr Lineweaver said. "Correcting for the limitations of the detectors in a simple new way gave us the result that Jupiter is not an exceptional planet. Jupiter-like planets are 50 per cent more common than indicated by previous analyses. If someone like us were doing a similar survey from one of these other planets, using instruments as sensitive as ours, and looked at our Sun, they would not yet have found evidence of any of our planets. Planet hunters should begin to find Jupiter-like extra-solar planets within the next few years," he said.

The existence of the 74 planets has been inferred from 'wobbles' in the positions of the 66 host stars as each star and its planet, or planets, orbit their common centres of gravity. The bigger the planet and the shorter its 'year', or orbital period, the easier it is to detect, so only planets much bigger than Jupiter or in closer orbits than Jupiter have been detected so far. Jupiter is twice as massive as all other planets in our Solar System combined.

"Similar analyses to answer the question 'How typical is Earth?' cannot yet be done using this technique, but our larger estimate for the number of Jupiter-like planets suggests a similarly larger estimate for the number of Earth-like planets," Dr Lineweaver said.

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see also:

• Preprint of the paper