First profile of a foreign planetary system

Three-planetary system studied around the star HR 8799

HR 8799: The first image of a foreign planetary system created by the Keck Observatory © C. Marois (NRC-HIA), IDPS survey and Keck Observatory
Read out

Are multi-planetary systems like the solar system an exception or the rule in the cosmos? That's not clear yet. However, astronomers have now for the first time analyzed and described one of the few known systems with more than one planet in more detail. Now published in the journal "Astronomy & Astrophysics", the study helps to better understand extrasolar planets and their laws.

In recent years, extrasolar planets are always discovered. So far, however, only a few cases are known in which several planets orbit a star together. One of them is the three-planetary system around the star HR 8799. Astronomers of the Keck Observatory on Hawaii in September 2008 succeeded in directly imaging the young star and its planets for the first time. The system is located 130 light-years from Earth in the constellation Pegasus.

Three planets around young star

But whether planetary systems such as HR 8799 or the solar system are the exception or the rule, is not yet known. "We simply do not know too many other planetary systems, " explains Professor Alexander Krivov of the Friedrich Schiller University Jena. "Our own solar system has been relatively well researched. However, we have hardly any possibilities for comparison. "The team of astronomers at the University of Jena now succeeded in detailing the multi-planetary system around the star HR 8799 for the first time.

For their study of the star HR 8799 and its system, the scientists combined all existing data and information about the star and the three orbiting planets. Also the observation data of two belts of asteroids, comets and dust in the same system flowed into the Jenaer investigations.

Computer model matches observation data

"All data was collected at very different times and using different methods, " reports Martin Reidemeister. Together with his colleagues, the doctoral student analyzed all this information in detail. "Using a computer model, we simulated whether the data was even plausible, " says the physicist. "This allowed us to determine many parameters quite accurately." Display

Jupiter-sized gas giants in resonance

One of these sizes is the age of the system. "The figures in the literature vary between 30 million and a billion years, " says Krivov. "An enormous amount of time, which we were able to significantly reduce to 30 to 50 million years with our analysis." The scientists were also able to determine the mass of the planets and the alignment of their orbits relatively reliably with their simulation analyzes.

Accordingly, the planets could have fivefold, sevenfold, and yet another sevenfold masses of Jupiter from the inside to the outside. However, this would only be stable if its orbit plane were inclined no more than approximately 20 degrees from the line of sight of the observations from the earth. In addition, the model revealed that the stable orbits could bring about a 4: 2: 1 resonance in the motion of the three planets.

Asteroid girdle inside and outside

The astronomers also describe the position of the asteroid and dust belts in the system more precisely: for example, an asteroid belt holds about ten astronomical units (AU) within the innermost planet, and another forms a kind of "Kuiperergrum" and framing the system outside of the very first planet at about 100 AU away from the central star. The masses of the two belts protect the researchers to 1 x 10-5 earth masses for the inner and 4 x 10-2 for the outer ring.

"We have found many similarities, but also quite a number of differences with our solar system, " reports Krivov. "Our analyzes should help to better understand how other planetary systems are organized overall." Maybe this will eventually discover other planetary systems where life is possible.

(University of Jena, 21.08.2009 - NPO)