Artist’s rendering of the planetary system HR 8799 at an early stage in its
evolution, showing the planet HR 8799c, a disk of gas and dust, and
interior planets. Credit: Image courtesty of Dunlap Institute for Astronomy & Astrophysics; Mediafarm.
One
of the discovery images of the system obtained at the Keck II telescope
using the adaptive optics system and NIRC2 Near-Infrared Imager. The
rectangle indicates the field-of-view of the OSIRIS instrument for
planet C. Credit: Image courtesy of NRC-HIA, C. Marois and Keck Observatory.
KAMUELA, HI – A team of international scientists
using the W. M. Keck Observatory has made the most detailed examination
yet of the atmosphere of a Jupiter-size planet beyond our Solar System.
According to lead author Quinn Konopacky, an astronomer with the
Dunlap Institute for Astronomy & Astrophysics, University of Toronto
and a former Lawrence Livermore National Laboratory (LLNL) postdoc, “We
have been able to observe this planet in unprecedented detail because
of Keck Observatory’s advanced instrumentation, our ground-breaking
observing and data processing techniques, and because of the nature of
the planetary system.” The paper appears online March 14th in Science
Express, and March 22nd in the journal Science.
“This is the sharpest spectrum ever obtained of an extrasolar planet,” said co-author Bruce Macintosh, an astronomer at LLNL. “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.”
“This is the sharpest spectrum ever obtained of an extrasolar planet,” said co-author Bruce Macintosh, an astronomer at LLNL. “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.”
The team, using the OSIRIS instrument fitted on the mighty Keck II
telescope on the summit of Mauna Kea, Hawaii, has uncovered the chemical
fingerprints of specific molecules, revealing a cloudy atmosphere
containing water vapor and carbon monoxide. “With this level of detail,”
says coauthor Travis Barman, an astronomer at the Lowell Observatory,
“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 uncertainty about how planets in other solar systems
formed, with two leading models, called core accretion and gravitational
instability. When stars form, they are surrounded by a planet-forming
disk. In the first scenario, planets form gradually as solid cores
slowly grow big enough to start absorbing gas from the disk. In the
latter, planets form almost instantly as parts of the disk collapse on
themselves. 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.
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 form, depleting the remaining gas of oxygen. Planetary
formation began when ice and solids collected into planetary cores—very
similar to how our solar system formed.
“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.”
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 very far from their parent star. This makes the
system an excellent laboratory for studying exoplanet atmospheres,” said
coauthor Christian Marois, an astronomer at the National Research
Council of Canada and another former LLNL postdoc. “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 Fahrenheit as it glows with the energy of
its original formation. Still, this discovery provides clues as to the
possibility of other Earth-like planets in other solar systems. “The
fact that the HR8799 giant planets may have formed the same way our own
giant planets did is a good sign—that same process also made the rocky
planets close to the Sun,” said Dr. Macintosh.
The HR 8799 four planet system:
All four planets are more massive than any in our Solar System, with masses three to seven times that of Jupiter. Their orbits are similarly large when compared to our system. The system is believed to be young, of the order of 30 million years. HR 8799c orbits 40 times farther from its parent star than the Earth orbits from the Sun; in our Solar System that would put it beyond the realm of Neptune.
All four planets are more massive than any in our Solar System, with masses three to seven times that of Jupiter. Their orbits are similarly large when compared to our system. The system is believed to be young, of the order of 30 million years. HR 8799c orbits 40 times farther from its parent star than the Earth orbits from the Sun; in our Solar System that would put it beyond the realm of Neptune.
The OSIRIS instrument:
The team analyzed the distant giant’s atmosphere using a high-resolution imaging spectrograph called OSIRIS. Just as Keck’s adaptive optics technology gives astronomers a sharp image of HR 8799c, OSIRIS enables an extremely detailed analysis of the spectrum of the light from the planet—much more detailed than ever before—and allows astronomers to separate the star’s light from the planet’s. This in turn provides a more detailed understanding of the composition of the gas giant’s atmosphere.
The team analyzed the distant giant’s atmosphere using a high-resolution imaging spectrograph called OSIRIS. Just as Keck’s adaptive optics technology gives astronomers a sharp image of HR 8799c, OSIRIS enables an extremely detailed analysis of the spectrum of the light from the planet—much more detailed than ever before—and allows astronomers to separate the star’s light from the planet’s. This in turn provides a more detailed understanding of the composition of the gas giant’s atmosphere.
The telescope’s adaptive optics system corrects for distortion caused
by the Earth’s atmosphere, making the infrared view through Keck II
sharper than through the Hubble Space Telescope.
The W. M. Keck Observatory operates the largest, most scientifically
productive telescopes on Earth. The two, 10-meter optical/infrared
telescopes on the summit of Mauna Kea on the Island of Hawaii feature a
suite of advanced instruments including imagers, multi-object
spectrographs, high-resolution spectrographs, integral-field
spectroscopy and a world-leading laser guide star adaptive optics
system. The Observatory is a private 501(c) 3 non-profit organization
and a scientific partnership of the California Institute of Technology,
the University of California and NASA.
Contact: Anne M. Stark
Phone: (925) 422-9799
E-mail: stark8@llnl.gov
Media Contact:
Steve Jefferson
Communications Officer
W. M. Keck Observatory Contact
Phone: (808) 881-3827
E-mail: sjefferson@keck.hawaii.edu
Source: W. M. Keck Observatory
