- Artist’s rendering of HR 8799c at an early stage in the evolution of the planetary system, showing the planet, a disk of gas and dust, rocky inner planets, and HR 8799. Credit: Dunlap Institute for Astronomy & Astrophysics; Mediafarm.
MOLECULES DETECTED IN DISTANT PLANETARY ATMOSPHERE
A team of astronomers, including Travis Barman (Lowell Observatory), have made the most detailed examination yet of the atmosphere of a Jupiter-sized planet beyond our Solar System.
According to Quinn Konopacky, an astronomer with the Dunlap Institute for Astronomy & Astrophysics, University of Toronto, and lead author of the study, “We have been able to observe this planet in unprecedented detail because of the advanced instrumentation we are using on the Keck II telescope, our ground-breaking observing and data processing techniques, and because of the nature of the planetary system.” The paper presenting this breakthrough discovery is being published in the journal Science on March 21, 2013.
The team, using the OSIRIS instrument at the Keck II observatory, has uncovered the chemical fingerprints of specific molecules, revealing a cloudy atmosphere containing water vapor and carbon monoxide. “With this level of detail,” says co-author Travis Barman, “we can compare the amount of carbon to the amount of oxygen present in the atmosphere, and this chemical mix provides clues as to how the planetary system formed.”
There has been considerable uncertainty about how planets in other solar systems formed, with two leading models, called core accretion and gravitational instability. When stars form, a planet-forming disk surrounds them. In the first scenario, planets form gradually as solid cores slowly grow big enough to start acquiring gas from the disk. In the latter scenario, planets form almost instantly as the disk collapses on itself. Planetary properties, like the composition of a planet’s atmosphere, are clues as to whether a system formed according to one model or the other. “This is the sharpest spectrum ever obtained of an extrasolar planet,” said co-author Bruce Macintosh, an astronomer at the Lawrence Livermore National Laboratory. “This shows the power of directly imaging a planetary system – the exquisite resolution afforded by these new observations has allowed us to really begin to probe planet formation”.
Although the planet’s atmosphere shows clear evidence of water vapor, that signature is weaker than would be expected if the planet shared the composition of its parent star. Instead, the planet has a high ratio of carbon to oxygen – a fingerprint of its formation in the gaseous disk tens of millions of years ago. As the gas cooled with time, grains of water ice formed, depleting the remaining gas of oxygen. Planetary formation then began when ice and solids collected into planetary cores. “Once the solid cores grew large enough, their gravity quickly attracted surrounding gas to become the massive planets we see today”, said Konopacky. “Since that gas had lost some of its oxygen, the planet ends up with less oxygen and less water than if it had formed through a gravitational instability.”
“Spectral information of this quality not only provides clues about the formation of the HR8799 planets but also provides the guidance we need to improve our theoretical understanding of exoplanet atmospheres and their early evolution,” comments Barman. “The timing of this work could not be better as it comes on the heels of new instruments that will image dozens more exoplanets, orbiting other stars, that we can study in similar detail”.
The planet is one of four gas giants known to orbit a star called HR 8799, 130 light-years from Earth. The authors and their collaborators previously discovered this planet, designated HR 8799c, and its three companions back in 2008 and 2010. Unlike most other planetary systems, whose presence is inferred by their effects on their parent star, the HR8799 planets can be individually seen. “We can directly image the planets around HR 8799 because they are all large, young, and far from their parent star. This makes the system an excellent laboratory for studying exoplanet atmospheres,” says coauthor Christian Marois, an astronomer at the National Research Council of Canada. “Since its discovery, this system just keeps on surprising us!”
Although the planet does have water vapor, it’s incredibly hostile to life – like Jupiter, it has no solid surface, and it has a temperature of more than a thousand degrees as it glows with the energy leftover from its original formation.
The study of these super-sized planets will continue, taking advantage of a recent upgrade to the OSIRIS instrument (developed at the Dunlap Institute) and access to the Keck Observatory provided by support from NASA and NExScI. “These future observations will tell us much more about the planets in this system,” says Konopacky. “And the more we learn about this distant planetary system, the more we learn about our own.”
▪ Science article posted early and AAAS release: http://www.sciencemag.org/content/early/2013/03/13/science.1232003.full
▪ Artist’s rendering of HR 8799c at an early stage in the evolution of the planetary system, showing the planet, a disk of gas and dust, rocky inner planets, and HR 8799. Credit: Dunlap Institute for Astronomy & Astrophysics; Mediafarm.
▪ Supporting images of the HR 8799 system also available upon request.
Dr. Travis Barman, Astronomer
Tom Vitron, Media and Communications Coordinator
p: (928) 233-3260, (928) 853-5233 cell
About Lowell Observatory: Lowell Observatory is a private, non-profit research institution founded in 1894 by Percival Lowell. The Observatory has been the site of many important findings including the discovery of the large recessional velocities (redshift) of galaxies by Vesto Slipher in 1912-1914 (a result that led ultimately to the realization the universe is expanding), and the discovery of Pluto by Clyde Tombaugh in 1930. Today, Lowell’s 20 astronomers use ground-based telescopes around the world, telescopes in space, and NASA planetary spacecraft to conduct research in diverse areas of astronomy and planetary science. The Observatory welcomes about 80,000 visitors each year to its Mars Hill campus in Flagstaff, Arizona for a variety of tours, telescope viewing, and special programs. Lowell Observatory currently has four research telescopes at its Anderson Mesa dark-sky site east of Flagstaff, and recently completed its four-meter class research telescope, the Discovery Channel Telescope. For more information: www.lowell.edu.