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Last Updated: Wednesday, 4 October 2006, 17:01 GMT 18:01 UK
'Bulge' yields new planet class
Many of the planets are the size of Jupiter

Astronomers have discovered a new class of planets that take less than a day to whiz round their parent stars.

Observations with the Hubble Space Telescope revealed the existence of the planets, which orbit closer to their stars than any previously known.

Dr Kailash Sahu and colleagues report finding the planets in a faint, crowded star field in a region of the Milky Way known as the galactic bulge.

The team has published its findings in the scientific journal Nature.

It uncovered the existence of 16 planets in the category of close orbiters, taking between 0.4 and 3.2 days to go around their respective stars.

Many of the planets are the size of Jupiter, the largest planet in our Solar System. Two of the 16 have orbits of less than a day, creating a new category of "ultra-short" orbit exoplanets.

In addition, these worlds generally orbit stars that are somewhat lighter than the typical stars where extrasolar planets have been found before.

'Wobble' effect

Dr Sahu, from the Space Telescope Science Institute in Baltimore, US, and colleagues searched for the characteristic dips in a star's luminosity that occur as it is temporarily blocked by an orbiting planet.

They carried out back-up, confirmation measurements using the "wobble" method, in which they looked for a telltale oscillation, or wobble, in the light coming from a star as it is tugged by the gravitational attraction of a planet.

The researchers say that any planets that orbited at such a close distance to brighter, hotter stars would be destroyed by solar radiation.

Astronomers have spotted 202 extrasolar planets since the first was spotted in October 1995.

Astronomers announce details of new planets

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