Kiruna, 2008-02-20

Press release

New results on planets around other stars to be published in Nature

Planeten HD 209458b

Illustration of the planet HD 209458b passing in front of the star, with outflowing hydrogen atoms in a comet-like tail.
Credit: Jörgen Medman, KRAUZ & Co, NASA (JPL-Caltech, STEREO, STScl.)
The image as a CMYK tiff fil [67 MB]

In Thursday's issue of Nature, scientists at the Swedish Institute of Space Physics present a new explanation for hot hydrogen atoms observed at extrasolar planets.

During the last 20 years, hundreds of extrasolar planet have been discovered - planets orbiting other stars. Some of these planets pass in front of the star. This allows us to gain information about the planet's atmosphere by observing how it attenuates the light from the star. In 2003 the Hubble telescope observed the planet HD 209458b and saw hydrogen atoms with high velocity. This has been explained as a loss of atmosphere due to the high temperature of the planet.

Scientists at the Swedish Institute of Space Physics now present a new explanation of the fast hydrogen atoms. That they are the result of the interaction between the stellar wind (a flow of charged particles) and the planet's atmosphere. A process that we have observed in the solar system. This introduces a completely new method to study stellar winds. Making it possible to observe from Earth the space environment near extrasolar planets.

The results are presented in the February 21 issue of Nature, and is a cooperation with scientists from France, Italy, Austria, and Switzerland:
Energetic neutral atoms as the explanation for the high velocity hydrogen around HD 209458b, M. Holmström, A. Ekenbäck, F. Selsis, T. Penz, H. Lammer, and P. Wurz, Nature, 451, 970–972, 2008.

Web pages:
The Swedish Institute of Space Physics:

More information:
Docent Mats Holmström, IRF, tel. +46-980-79186, e-post: matsh*
Rick McGregor, Information officer, IRF, tel. +46-980-79178, rick*

webmaster*, 2008-02-25

The Swedish Institute of Space Physics (IRF) is a governmental research institute which conducts research and postgraduate education in atmospheric physics, space physics and space technology. Measurements are made in the atmosphere, ionosphere, magnetosphere and around other planets with the help of ground-based equipment (including radar), stratospheric balloons and satellites. IRF was established (as Kiruna Geophysical Observatory) in 1957 and its first satellite instrument was launched in 1968. The head office is in Kiruna (geographic coordinates 67.84° N, 20.41° E) and IRF also has offices in Umeå, Uppsala and Lund.

Institutet för rymdfysik, IRF, är ett statligt forskningsinstitut under Utbildningsdepartementet. IRF bedriver grundforskning och forskarutbildning i rymdfysik, atmosfärsfysik och rymdteknik. Mätningar görs i atmosfären, jonosfären, magnetosfären och runt andra planeter med hjälp av ballonger, markbaserad utrustning (bl a radar) och satelliter. För närvarande har IRF instrument ombord på satelliter i bana runt tre planeter, jorden, Mars och Saturnus. IRF har ca 100 anställda och bedriver verksamhet i Kiruna (huvudkontoret), Umeå, Uppsala och Lund.