National Aeronautics and Space Administration Logo
Follow this link to skip to the main content NASA Banner
Solar System Exploration
News & Events
A Giant Planet Embedded in the Magnetosphere of its Star
A Giant Planet Embedded in the Magnetosphere of its Star
28 Nov 2006
(Source: National Center of Scientific Research (CNRS))

Using the ESPaDOnS spectropolarimeter1 installed on the Canada-France-Hawaii telescope2 (Mauna Kea, Hawaii), an international team of researchers, led by two french astronomers (LESIA, Observatoire de Paris and LATT, Observatoire Midi-Pyr?n?es), has just discovered a magnetic field on tau Bootis, a star orbited by a giant planet on a close-in orbit: the first ever detection of this kind! Up to now, only indirect clues pointed to the presence of magnetic fields on stars hosting giant extra-solar planets. This result opens major prospects, in particular the study of the interaction between the planet and the magnetosphere of its star. This discovery is published in a Letter to the Journal MNRAS (Monthly Notices of Royal Astronomical Society).

The catalogue of extrasolar planets is growing continuously, containing today more than 200 objects, and the detection of these exoplanets has almost become a routine. But what are the characteristics of the stellar hosts, how can we explain the formation of these planetary systems, or why are some of these giant exoplanets, which are called 'hot jupiters', migrating down to very close-in orbits? Astrophysicists suspect the magnetic field to play a crucial role in some of these questions. However, although indirect effects of magnetic fields have already been detected on stars hosting giant extrasolar planets, no direct measurement had ever been done until now.

This first measurement of a magnetic field in a planet-hosting star has been obtained by an international team of astronomers with the ESPaDOnS spectropolarimeter located on the Canada-France-Hawaii telescope. They detected the magnetic field of tau Bootis, a one billion year old star, having a mass of one and a half solar masses and located at nearly 50 light years from the Earth. This cool and weakly active star, orbited by a giant planet with 4.4 Jupiter masses on a very close-in orbit at 0.049 AU (i.e. 5% of the Sun-Earth distance), possesses a magnetic field of a few gauss, just a little more than the Sun's, but showing a more complex structure.

Moreover, astronomers have also measured the level of differential rotation of the star, a crucial parameter in the generation of magnetic fields. In the present case, the matter located at the equator rotates 18% faster than that located at the poles, leading by one full turn in approximately 15 days. By comparing the differential rotation of the star with the revolution of the giant extrasolar planet, astronomers have noticed that the planet is synchronized with stellar material located at about 45 degrees. This observation suggests very complex interactions between the magnetosphere of the star and its companion, perhaps similar to the interaction of the magnetosphere of Jupiter with its satellite Io, giving rise to the so-called "Io torus".

The data collected for this study are not sufficient to describe precisely these interactions, but this first measurement is opening new prospects for detailed studies of star-planet systems.

Press release written by Cyrille Baudouin, with the support of SF2A (Soci?t? Fran?aise d'Astronomie et d'Astrophysique)

Notes: (1) ESPaDOnS is a collaborative project funded by France (CNRS/INSU, Minist?re de la Recherche, LATT - Observatoire Midi Pyr?n?es, Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique - Observatoire de Paris), Canada ((NSERC), CFHT and ESA (ESTEC/RSSD). (2) CFHT is operated by the National Research Council of Canada, the Institut National des Sciences de l?Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

News Archive Search  Go!
Show  results per page
Awards and Recognition   Solar System Exploration Roadmap   Contact Us   Site Map   Print This Page
NASA Official: Kristen Erickson
Advisory: Dr. James Green, Director of Planetary Science
Outreach Manager: Alice Wessen
Curator/Editor: Phil Davis
Science Writer: Autumn Burdick
Producer: Greg Baerg
Webmaster: David Martin
> NASA Science Mission Directorate
> Budgets, Strategic Plans and Accountability Reports
> Equal Employment Opportunity Data
   Posted Pursuant to the No Fear Act
> Information-Dissemination Policies and Inventories
> Freedom of Information Act
> Privacy Policy & Important Notices
> Inspector General Hotline
> Office of the Inspector General
> NASA Communications Policy
> NASA Advisory Council
> Open Government at NASA
Last Updated: 28 Nov 2006