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Several Jupiter sized exoplanets found to have only weak Earth likegravity (Forwarded)



 
 
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Old June 7th 07, 07:00 PM posted to sci.astro
Andrew Yee
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Default Several Jupiter sized exoplanets found to have only weak Earth likegravity (Forwarded)

Press and Media Relations
University of Warwick
Coventry, UK

For further details please contact:

John Southworth, Department of Physics, University of Warwick
Tel: +44 (0)2476 574329

Peter Dunn, Press & Media Relations Manager, University of Warwick
Tel: 024 76 523708

2nd May 2007

Several Jupiter sized planets found to have only weak Earth like gravity

Astrophysicists at the University of Warwick have found that several
Jupiter sized gas giants beyond our solar system have surface gravities
much closer in strength to Earth than the intense gravity of Jupiter.

The University of Warwick team, Dr John Southworth, Dr Peter Wheatley and
Giles Sams are the first people to calculate accurate measures of the
surface gravity of all 14 known gas giant planets beyond our solar system
that can be observed transiting (moving across the face of) their star.
They created a new method which enabled the Warwick researchers to deduce
the surface gravity of all 14 of these gas giants using a technique which
is both simpler and ten times more accurate than an older method that had
only produced a rough estimate for just one of the gas giants -- HD 209458.

All but one of these 14 known gas giant planets that can be seen
transiting their star have a planetary radius bigger than Jupiter.
Intriguingly the one older surface gravity estimate available, for HD
209458, suggested it had a surface gravity of only 9.43 to 9.7 ms**-2 .
Despite being bigger than Jupiter this would give it a surface gravity
closer to Earth's at 9.8 ms**-2 or our own solar system's smaller gas
giants (Saturn 8.96 ms**-2, Uranus 8.69 ms**-2 and Neptune 11.15 ms**-2 )
rather than Jupiter at 24.79 ms**-2 .

On carrying out their more accurate measurement of all 14 of these gas
giants the Warwick team have discovered that the surface gravity of HD
209458 is not an anomaly. Despite all but one of the gas giants (HD
149026) being bigger than Jupiter all but one of them turned out to have
surface gravities that are much lower than Jupiter's. Only OGLE-TR-113 was
found to have a surface gravity higher than Jupiter's.

In fact they found that 4 of these planets actually have surface gravities
close to or lower than that of Earth's or our own solar system's "smaller"
gas giants rather than Jupiter's much more intense gravity. A further 4
had surface gravities around half to two thirds that of Jupiter's. For the
planet for which there was already a rough estimate of surface gravity
(HD209458b) they actually found an even lower surface gravity of 9.28
ms**-2 (error factor of plus or minus 0.15 ms**-2). A full table of their
findings now follows:

Surface gravity values for the known transiting extra-solar planets.


Planet Surface gravity Margin of 12 Stone man
in ms**-2 error would weigh*

HD 189733 21.5 +/- 3.5 26.33
HD 209458 9.28 +/- 0.15 11.35
OGLE-TR-10 4.5 +/- 2.1 5.47
OGLE-TR-56 17.9 +/- 1.9 21.89
OGLE-TR-111 13.3 +/- 4.2 16.31
TrES-1 16.1 +/- 1.0 19.72
WASP-1 10.6 +/- 1.7 13.02
HAT-P-1 7.1 +/- 1.1 8.65
XO-1 13.3 +/- 2.5 16.26
HD 149026 16.4 +/- 2.5 20.00
OGLE-TR-113 28.3 +/- 4.4 34.61
OGLE-TR-132 18.0 +/- 6.0 21.96
TrES-2 20.7 +/- 2.6 25.34
WASP-2 20.1 +/- 2.7 24.53

University of Warwick researcher John Southworth said: "This research
gives us a sense of the sheer variety of types of planet to be found
beyond our Solar System. An understanding of the surface gravity of these
worlds also gives us a clearer picture of the rate of in the evaporation
of planetary atmospheres."

Full paper online at
http://uk.arxiv.org/PS_cache/arxiv/p...704.1570v1.pdf

* this last column in the table gives the weight that man who was 12 stone
[76.2 kg or 168 lb] on the surface of the Earth would be if he stood the
surface of each of those gas giant worlds ... That is just before he sunk
into the gaseous atmosphere and was suffocated and roasted to death of
course ...


 




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