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Thursday, 25 November, 1999, 15:52 GMT
We saw it too, say astronomers
The new world has been called a The new world has been called a "hot Jupiter" (Artist's impression)

By BBC News Online Science Editor Dr David Whitehouse

Another group of astronomers have come forward to say that they too have made observations of the planet seen orbiting the star HD 209458, which is 150 light-years from Earth.

Renowned planet hunters Geoffrey Marcy and Paul Butler made the dramatic announcement last week that they had seen a dimming in the light coming from HD 209458 and said it was caused by a planet passing in front of the star. They proclaimed the observation as the first visual - albeit indirect - proof of a planet outside our Solar System.

It certainly seemed to fit with previous work which had detected a wobble in the star's motion caused by a body the size of Jupiter circling in a very close orbit every 3.5 days.

Now a separate team of astronomers from the US and Switzerland have reported that they scrutinised HD 209458 in August and September and witnessed the same phenomenon.

The team includes David Charbonneau and David Latham from the Harvard-Smithsonian Center for Astrophysics, Massachusetts, Timothy Brown from the National Center for Atmospheric research, Colorado, and Michel Mayor from the Geneva Observatory.

Important details

Several times during their observing run, they noticed that HD 209458, a star very similar to our Sun, dimmed slightly for about two hours every 3.5 days.

Like Marcy and Butler, The US-Swiss team believe the reduction in light was caused by a planet passing in front of the star.

And from their observations, it has been possible, they say, to calculate the most accurate parameters yet obtained for a planet circling another sun.

The planet would seem to be fractionally larger than Jupiter, the largest world in our Solar System. It has a "year" of 3.5 days and orbits HD 209458 at an inclination of 87 degrees.

It has a density less than that of Saturn, the least dense planet in our Solar System, and an atmospheric temperature of 1,000 C.

What of life?

This means that it would not be hot enough to lose much of its atmosphere into space. These observations, Marcy and Butler's research, and the British work which has detected light from a so-called exoplanet orbiting the nearby star Tau Bootes, have propelled planetary astronomy into a new era.

For the first time, astronomers are gathering the parameters of planets outside our Solar System and are thus able to make predictions about their properties.

In the last three years, astronomers have discovered more worlds than in all of previous human history. And the indications are that many more will be found because our galaxy, and the Universe, is quite obviously teeming with planets.

But what of life? Nobody knows, but because the only life we know of (ourselves) lives on a planet, everyone would agree that we must extend our detection techniques and look for other Earths.

With new instruments and satellite observatories on the drawing board, this could happen within a decade.

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See also:
15 Nov 99 |  Sci/Tech
Extrasolar planet detected
22 Nov 99 |  Sci/Tech
Light detected from distant planet
22 Sep 99 |  Sci/Tech
'Earth-sized planet' in deep space

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