Discovery of a new planetary system

Article originally published in December 2008

One planet is good, 3 planets is a crowd!

A team of Canadian, American and British researchers photographed for the 1st time a distant planetary system similar to our Solar System around the star HR 8799. The feat was achieved using observations obtained at the Gemini North and Keck telescopes. The system consists of three planets that are still young enough to be hot and radiate in the infrared, because the system is only 60 million years old (compared to 5 billion years for our own Solar system)HR 8799, a star 1.5 times more massive than the Sun, is located at about 130 lightyears from the Sun, in the constellation Pegasus.

Figure 1 : vue d’artiste du système planétaire. Source : Gemini Observatory Artwork by Lynette Cook

Figure 1 : Artist view of HR 8799’s planetary system. Credit: Gemini Observatory, Artwork by Lynette Cook.

An analysis of the brightness of the 3 objects at several infrared wavelengths and at different epochs, shows that these planets have masses between 7 and 10 times that of Jupiter (fig. 1) and that they revolve around the central star. The outermost planet moves in an orbit just inside a debris disk very similar to the Kuiper belt in our Solar system, from which comets are coming from. In many ways, this solar system is similar to our own (fig. 2). 

“Obtaining images of several planets orbiting a star outside our solar system is a first,” says Christian Marois (Herzberg Institute of Astrophysics), the Quebec astrophysicist who is the leader of the research team. 

The three Quebecers in the team: René Doyon, Christian Marois and David Lafrenière, are behind the technique of angular differential imaging (IDA) a sophisticated image processing algorithm which, combined with the technology of adaptive optics has allowed a better detection of three planets around the star HR 8799.

Figure 2

Figure 2 : Schematic representation of the HR 8799 planetary system (left) and our solar system on the same scale (right).

This discovery is a crucial step towards this ultimate quest of detecting rocky planets like Earth. All the great telescopes of the world will now look at this star to learn more about this fascinating planetary system,” says René Doyon, co-author of the paper.

A previous study the Gemini Deep Planet Survey (GPDS)  on the Gemini North telescope, co-directed by René Doyon and David Lafrenière from 2004 to 2007, showed that the giant planets (like Jupiter) are rare around young stars at orbital separations beyond 10 astronomical units (AU), which is the distance between Saturn and the Sun.

Figure 3

Figure 3 : The star HR 8799 photographed by the Keck telescope (left). The same star after image processing with the IDA technique (right). The three planets are clearly indicated as red dots at approximately 1 pm, 5 pm and 10 pm. The three planets revolve counter clockwise at orbital distances of 25, 40 and 70 astronomical units (AU). An astronomical unit is the average distance between the Earth and the Sun.

“We looked very actively using the IDA technique around 85 young stars of masses  less than or equal to that of the sun and none of them showed any planets. The next step was to look around a lot more stars but also to turn to stars more massive than the Sun. This system is a true gift of nature. It is amazing that our first detection include not one, not two but three planets orbiting the same star!”, remarked enthusiastically René Doyon.

The observations of the star HR 8799 are part of a large scale study – International Deep Planet Survey (IDPS) – of 80 relatively young massive stars, surrounded by a disk of dust and located in the vicinity of the solar system. The study uses the Keck 10m and Gemini North 8m telescopes (both located in Hawaii) and one of the four European Southern Observatory – Very Large Telescope 8m telescope to obtain images of planets that look like giant Jupiter.

Christian Marois noted that this 1st detection occurs after only a few stars were probed. It could be that the existence of giant planets around massive stars is more common than we think. The observing campaign (IDPS) currently underway will address this issue.

Videos

Movie showing the orbits of the 3 planets around HR 8799

Video (made by Université de Montréal Forum) in which René Doyon explains the discovery (in French)

More information

Details of the discovery are published in the article Direct Imaging of Multiple Planets Orbiting the Star HR 8799, that appeared in the November 28, 2008 of the journal Science. In addition to Christian Marois (NRC Herzberg Institute of Astrophysics, Victoria, B.-C., Canada), David Lafrenière and René Doyon (Institute for research on exoplanets, Université de Montréal, CRAQ, Montréal, Qc, Canada), the team includes Bruce Macintosh (Lawrence Livermore National Laboratory, Livermore, Calif., US), Travis Barman (Lowell Observatory, Flagstaff, Ariz., US), Benjamin Zuckerman (Astronomy Dep’t, University of California, Los Angeles, Calif., US), Jennifer Patience (School of Physics, University of Exeter, Exeter, U.-K.), and Inseok Song (University of Georgia, Athens, GA, US).