Friday, August 14, 2015

Astronomers Discover 'Young Jupiter' Exoplanet

Discovery image of 51 Eri b with the Gemini Planet Imager taken in the near-infrared light on December 18, 2014. The bright central star has been mostly removed by a hardware and software mask to enable the detection of the exoplanet one million times fainter. Credits: J. Rameau (UdeM) and C. Marois (NRC Herzberg).

Going beyond the discovery and imaging of a young Jupiter, astronomers using the Gemini Observatory's new Planet Imager (GPI) have probed a newly discovered world in unprecedented detail. What they found is a planet about two times the mass of Jupiter, and the most Solar System-like planet ever directly imaged around another star. The planet, known as 51 Eridani b, orbits its host star at about 13 times the Earth-Sun distance (equivalent to being between Saturn and Uranus in our Solar System). The system is located about 100 light years away. The Gemini data also provide scientists with the strongest-ever spectroscopic detection of methane in the atmosphere of a planet outside of our Solar System, adding to its similarities to giant planets in our Solar System.

"Many of the exoplanets astronomers have imaged before have atmospheres that look like very cool stars" said Bruce Macintosh, of Stanford University who led the construction of GPI and now leads the planet-hunting survey. "This one looks like a planet."

The research is published in the August 13, 2015 issue of the journal Science.

"This superb result is a clear demonstration of the remarkable imaging and spectroscopic capabilities of GPI," said Chris Davis, the US National Science Foundation (NSF) Astronomy Division program officer who oversees Gemini Observatory funding. "The exoplanet surveys now possible with Gemini will undoubtedly lead to a far better understanding of the numbers of gas giants orbiting neighboring stars, the characteristics of their atmospheres, and ultimately the way in which giant planets like Jupiter and Saturn are formed."

The discovery is part of the team's broader effort to find and characterize new planets called the GPI Exoplanet Survey (GPIES). The survey expects to explore over 600 stars that could host planetary systems; so far they've looked at almost a hundred stars. "This is exactly the kind of system we envisioned discovering when we designed GPI", says James Graham, professor at UC Berkeley and Project Scientist for GPI.

"GPI is capable of dissecting the light of exoplanets in unprecedented detail so we can now characterize other worlds like never before," says Christian Marois of the National Research Council of Canada (NRC). Marois, one of almost 90 researchers on the team, pioneered many of the observation strategies and data reduction techniques that played a critical role in the detection and analysis of the new planet. The light from the planet is very faint – a million times fainter than the star – but GPI can see it clearly. "The planet is so faint and located so close to its star, that it is also the first directly imaged exoplanet to be fully consistent with Solar System-like planet formation models," adds Marois.

The Gemini observations were also followed up by the W.M. Keck Observatory on Maunakea in Hawaii to verify the discovery.

GPI Instrument Scientist, Fredrik Rantakyro, added, "Since I was a child, I dreamed about planets around other stars and the possible lives that could be out there. As an astronomer, it's common to work with state-of-the-art telescopes but not to make your heart beat faster. This is exactly what happened with this dream-come-true discovery of this brother to Jupiter!"

51 Eridani is young – only 20 million years old – and this is exactly what made the direct detection of the planet possible. When planets coalesce, material falling into the planet releases energy and heats it up. Over the next hundred million years they radiate that energy away, mostly as infrared light, and gradually cool.

Discovery image of 51 Eri b with the Gemini Planet Imager taken in the near-infrared light on December 18, 2014. The bright central star has been mostly removed by a hardware and software mask to enable the detection of the exoplanet one million times fainter. Credits: J. Rameau (UdeM) and C. Marois (NRC Herzberg).
Discovery image of 51 Eri b with the Gemini Planet Imager taken in the near-infrared light on December 18, 2014. The bright central star has been mostly removed by a hardware and software mask to enable the detection of the exoplanet one million times fainter. Credits: J. Rameau (UdeM) and C. Marois (NRC Herzberg).

"51 Eri is one of the best stars for imaging young planets," said co-author Eric Nielsen, a postdoctoral researcher at Stanford University and the SETI Institute. "It's one of the very youngest stars this close to the Sun. 51 Eri was born 20 million years ago, 40 million years after the dinosaurs died out."

“The exploration of very young planetary systems that will evolve to look like our own has just begun,” said Didier Saumon of Los Alamos National Laboratory, whose role was theoretical modeling and data analysis for the project. “The Gemini Planet Imager is amazing new technology that has quickly discovered the first extrasolar analog of Jupiter, but much younger,” Saumon said.

"By targeting young stars, we can catch planets while they are hotter and brighter and can study how planets evolve over time," says Arizona State University (ASU) astrophysicist Jennifer Patience, an associate professor in the School of Earth and Space Exploration and part of the GPI Exoplanet Survey Team.

In addition to being what is likely the lowest-mass planet ever imaged, its atmosphere is also very cool – 430 degrees C (800 degrees Fahrenheit). It also features the strongest spectroscopic atmospheric methane signal, similar to the heavy methane dominated atmospheres of the gas giant planets in our Solar System.

The team plans to begin observing the planet again in late September, when it emerges from behind the sun, and hope to find that the planet has moved along its orbit: confirmation that it is, in fact, a planet.

"Next, we want to measure 51 Eridani b's orbit and take more detailed spectra to reveal its atmospheric chemistry. We really want to know the ratio of the heavier elements, carbon or oxygen, to the lightest, commonest element, hydrogen, in 51 Eridani b's atmosphere," Macintosh said. "Because Jupiter formed partially out of solid material, it has extra carbon and oxygen compared to the Sun. That same process—building-up from solid material—is how we think the Earth formed. If we see that 51 Eridani b is enhanced in carbon and oxygen, then we would know it formed the way that the Earth or Jupiter did."

GPI was installed on the 8-meter Gemini South Telescope in Chile in 2013, and its science operation began in 2014. It was designed specifically for discovering and analyzing faint, young planets orbiting bright stars by direct imaging. NASA's Kepler mission indirectly discovers planets by the loss of starlight when a planet blocks a star. The GPI team has studied almost 100 stars already.

GPI Exoplanet Survey (GPIES) is currently less than 20% through the 600 targets slated for observations during the 3-year campaign. The targets were selected because of their youth and relatively close proximity to our Solar System (within about 300 light years). The results of this survey will be remarkable, as it is probing a regime of exoplanet mass and separation that have never been properly surveyed before. It is expected to provide the first detailed census and demography of gas giant exoplanets, to find several multi-planet systems, and to perform detailed spectral characterization of many new exoplanets.

"Previous search methods couldn't find systems like our own, with small, rocky worlds close to their star and large, gas giants at large distances like Jupiter and Saturn," said James Larkin, a UCLA professor of physics and astronomy. "The search for large planets at large separations from their star is exactly the goal of GPI. These solar systems are likely much more similar to our own. GPI will reveal to us how common our solar system architecture truly is."

"This discovery is one of many imaging detections of exoplanets to come in the next few years," said Inseok Song, an associate professor in the department of physics and astronomy in the University of Georgia (UGA) Franklin College of Arts and Sciences and co-principal investigator on the GPI exoplanet survey team. "Unlike most of the currently known confirmed exoplanets, these GPI images of exoplanets allow us to examine planetary atmospheric information, which will eventually allow astronomers to examine biosignatures from mature planets during the next decade."

GPI was made possible with funding by the US National Science Foundation and Gemini partnership to support the work of an international team from the US and Canada. Lawrence Livermore National Laboratory constructed GPI's adaptive optics system and worked to match it to the Gemini telescope. Engineers with the National Research Council of Canada (NRC) designed and built GPI's optical-mechanical structure, and wrote the top level and mechanical control software. UCLA produced GPI's infrared spectrograph. The American Museum of Natural History developed starlight-blocking masks. JPL was responsible for a precision wavefront sensor. University of Montreal, the Space Telescope Science Institute, and other members of the GPI team produced the data analysis software.

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