Figure 1. 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). Full Resolution JPEG
Figure 2. An artistic conception of the Jupiter-like exoplanet, 51 Eri
b, seen in the near-infrared light that shows the hot layers deep in its
atmosphere glowing through clouds. Because of its young age, this young
cousin of our own Jupiter is still hot and carries information on the
way it was formed 20 million years ago. Credits: Danielle Futselaar & Franck Marchis, SETI Institute. Full Resolution JPEG
The simulated fly-by of the 51 Eridani star and planet system begins with the view of the
sky showing the location of the star near the constellation Orion visible in the northern hemisphere winter.
The young star 51 Eridani is 100 light-years from the Sun and a Jupiter-like planet is
directly imaged in the infrared in an orbit similar in size to the Sun-Saturn distance.
The star also has indirect evidence of belts of rocky debris orbiting closer and farther
to the the star than the new planet. The fly-by ends with a view back toward the Sun from
the newly discovered planet.Credits: J. Patience & J. Cornelison (ASU). Fly-by video in AVI (600MB)
The Gemini Planet Imager utilizes an integral field spectrograph, an
instrument capable of taking images at multiple wavelengths – or colors –
of infrared light simultaneously, in order to search for young
self-luminous planets around nearby stars. The left side of the
animation shows the GPI images of the nearby star 51 Eridani in order of
increasing wavelength from 1.5 to 1.8 microns. The images have been
processed to suppress the light from 51 Eridani, revealing the exoplanet
51 Eridani b (indicated) which is approximately a million times fainter
than the parent star. The bright regions to the left and right of the
masked star are artifacts from the image processing algorithm, and can
be distinguished from real astrophysical signals based on their
brightness and position as a function of wavelength. The spectrum of 51
Eridani b, on the right side of the animation, shows how the brightness
of the planet varies as a function of wavelength. If the atmosphere was
entirely transmissive, the brightness would be approximately constant as
a function of wavelength. This is not the case for 51 Eridani b, the
atmosphere of which contains both water (H2O) and methane (CH4).
Over the spectral range of this GPI dataset, water absorbs photons
between 1.5 and 1.6 microns, and methane absorbs between 1.6 and 1.8
microns. This leads to a strong peak in the brightness of the exoplanet
at 1.6 microns, the wavelength at which absorption by both water and
methane is weakest.Robert De Rosa (UC Berkeley), Christian Marois (NRC Herzberg, University of Victoria).
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.
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.
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.
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.
