New Exoplanet Hunter Directly Images Alien Worlds
Gemini Planet Imager's 'first light' image of Beta Pictoris b, an exoplanet orbiting the star Beta Pictoris.
Gemini Planet Imager’s 'first light' image of the light scattered by a disk of dust orbiting the young star HR4796A.
A new instrument, attached to one of the most powerful telescopes in the world, has opened its infrared eye for the first time, taking snapshots of a nearby planet orbiting another star and a ring of proto-planetary stellar dust.
The sophisticated car-sized instrument, called the Gemini Planet Imager (GPI), is attached to the 8-meter Gemini South telescope in Chile and represents a new era in exoplanetary discovery. The GPI, which has been in development since 2003, is capable of not only resolving the dim light from an exoplanet orbiting close to its parent star; it can also analyze the planet’s atmospheric composition and temperature.
The majority of ground-based exoplanet surveys watch for stars’ “wobbles” to betray the gravitational presence of massive exoplanets in orbit -- known as the “radial velocity technique.” Another powerful technique for discovering smaller exoplanets in tight orbits around their star is employed by NASA’s Kepler space telescope. As an exoplanet passes in front of its host star, a small dip in brightness can be detected by Kepler’s sensitive optics – this is known as a "transit."
Other methods for exoplanetary detection are possible (such as microlensing), but the “Holy Grail” for astronomers is to use a powerful telescope to directly image star systems, picking out tiny dots of light in orbit. This feat has been achieved a handful of times (most notably the 2008 Hubble and Keck/Gemini announcements of directly imaging exoplanets around the stars Fomalhaut and HR 8799) its wholesale use as an effective exoplanet-hunting tool has been limited by technology, a limit that the GPI has now dramatically lifted.
Through the ingenious combination of adaptive optics -- a laser system used on some observatories that can actively counteract the blurring effects of turbulence in the Earth’s atmosphere -- and an active obscuring coronagraph perfectly covering the star (to counteract the glaring effect of the starlight), GPI has the power to distinguish star from exoplanet to unparalleled precision.
“Most planets that we know about to date are only known because of indirect methods that tell us a planet is there, a bit about its orbit and mass, but not much else,” said Bruce Macintosh of the Lawrence Livermore National Laboratory, who led the team that developed GPI. “With GPI we directly image planets around stars -- it’s a bit like being able to dissect the system and really dive into the planet’s atmospheric makeup and characteristics.”
Speaking at the 223rd American Astronomical Society meeting in Washington D.C. on Tuesday, Macintosh showcased images from the GPI’s “first light” campaign in November.
“Even these early first-light images are almost a factor of 10 better than the previous generation of instruments,” he said in a Gemini Observatory press release. “In one minute, we are seeing planets that used to take us an hour to detect.”
In a stunning image of the Beta Pictoris system, located some 63.4 light-years from Earth, the GPI clearly picked out the known exoplanet Beta Pictoris b and measured the world’s spectrum for the first time. This is akin to trying to photograph a firefly buzzing around a streetlamp thousands of miles away and measuring the spectrum of the chemicals providing the luminescence in the firefly’s tail.
In addition to imaging Beta Pictoris, GPI turned to the young star HR4796A, located 237 light-years away, which is surrounded by a ring of proto-planetary dust (above). Using the instrument’s polarization filter, astronomers were able to see the full detail of the ring.
A little closer to home, the GPI also focused on Europa, Jupiter’s enigmatic icy moon, and resolved surface features that closely matched observations by flyby missions.
One of the first projects the GPI will undertake is a three-year search campaign with the goal of observing 600 young and bright stars in the southern sky, writes SETI Institute astronomer and member of the GPI development team Franck Marchis in a recent GPI blog update.
“In two decades, thanks to sophisticated instruments like GPI, stargazers will no longer see stars as simple twinkling specks of light, but also as worlds surrounded by planets,” Marchis added.
Comparison of Europa observed with Gemini Planet Imager in K1 band on the right and visible albedo visualization based on a composite map made from Galileo SSI and Voyager 1 and 2 data (from USGS) on the left.(Jan 7, 2014 10:30 AM ET // by Ian O'Neill)
