A long stare at stars

NASA's satellite linkPfeilExtern.gifKEPLER has started its science program on May 12, 2009. The satellite had been launched successfully on March 6 from Cape Canaveral (Fig. 1). Its primary mission is to search for planets around other stars and to detect the first Earth-size planet in another planetary system. Scientists at the Max-Planck-Institut fuer Astrophysik are using the satellite's results for a completely different subject: They want to find out about the internal structure of stars.

Fig. 1: Launch of the KEPLER satellite on March 6 by a Delta II Rocket from the spaceport at Cape Canaveral

Fig. 2: Image of the Cygnus region in the Milky Way, overlaid with the constellations of Cygnus, Lyra and Aquila and the CCD mosaic of KEPLER

Fig. 3: The first image of the KEPLER field as observed on May 12. The mosaic of CCDs is clearly visible.

KEPLER's mission is quite different from other space activities: The satellite flies in an Earth-trailing orbit with a period of 372.5 days and will observe the same star field in the constellation of Cygnus (Fig. 2) for the next 3.5 years continuously. This field is exceptionally large, 105 square degrees, and contains over 100.000 stars. The telescope has a mirror of 1.4 m diameter and a CCD camera with 95 million pixels, consisting of a mosaic of 42 CCDs. On May 12, after the successful commissioning of the satellite and the completed readiness review the first image of the target field was taken (Fig. 3).

The planet search is done with the transit method: When a planet's orbit is in the line of sight to a star, the planet will periodically transit in front of that star, thereby reducing its brightness by a tiny fraction. This reduction in brightness is extremely small (of order milli-magnitudes) and can be detected only with high-precision photometry from space. It is hoped that over the 3.5 years mission duration several hundreds of planets will be found, up to 50 of them could be similar to Earth.

As a secondary science goal, small brightness variations of stars will also be observed. These are due to thousands of oscillations which take place in a star at the same time. They allow to determine stellar properties of stars, such as its mass, its age and its internal structure. This method of asteroseismology has already been used successfully to learn about our Sun and several other bright stars. With KEPLER more accurate measurements for stars of very different types will allow to deepen our knowledge about stellar struture. Scientists interested in this part of the mission are organized in the linkPfeilExtern.gifKEPLER Asteroseismic Science Consortium (KASC), a US-European group of specialists in asteroseismology.

At the Max-Planck-Institut fuer Astrophysik Martin Asplund, Achim Weiss, Aldo Serenelli and PhD student Victor Silva are members of KASC. Together with Jerome Ballot (Toulouse, formerly MPA) they have successfully submitted a plan for observing stars in two stellar clusters within KEPLER's field of observation. From the analysis of the oscillations the team, and in particular V. Silva, want to learn more about the properties of convective energy transport at the center of stars. Since the Sun does not have such a core, more massive stars have to be observed. Because the stars in a cluster are all of the same age and chemical composition, analyzing many of them allows to determine how convective core properties change with mass, and it is hoped that this will lead to better theoretical models, as they are computed at MPA. Convection is one of the biggest uncertainties in stellar evolution theory.

On June 18 the first science data are expected. Then the work of analyzing and modelling begins.


The interested public can help to support young scientists involved in the mission. There is a linkPfeilExtern.gifnon-profit organization, where everybody can "adopt" a star of the KEPLER field for a small donation. The linkPfeilExtern.gifKEPLER target list is available in Google Sky. The donor receives a personalized "certificate of adoption" by email, and the entries for the star they selected are updated with an "Adopted by" tag in both Google Sky and a text version of the target list. After planets begin to be discovered, those who adopted a planet-hosting star will be notified by email with information about where they can learn more about the discovery (making this an effective public outreach program), and featured on a special section of the website. The donations will be used, for example, to allow young scientists to attend scientific workshops and meetings concerned with KEPLER results.


Kepler is a NASA Discovery mission. NASA's Ames Research Center is the home organization of the Science Principal Investigator and is responsible for the ground system development, mission operations and science data analysis. Kepler mission development is managed by JPL. Ball Aerospace & Technologies Corp., Boulder, Colo., is responsible for developing the Kepler flight system and supporting mission operations.
More information about the Kepler mission is at linkPfeilExtern.gifhttp://www.nasa.gov/kepler.

For more information, please, contact:

Dr. Achim Weiss
Max Planck Institute for Astrophysics
Phone: +49 89 30000-2213
Fax: +49 89 30000-3569
Email: aweissmpa-garching.mpg.de