Astronomers combined the power of the 8-meter Gemini South telescope in
Chile with an extremely high-resolution camera to scrutinize the star
TRAPPIST-1. Previous observations of the star, which is only about 8%
the mass of our Sun, revealed dips in the star’s light output that would
be expected if several Earth-sized planets orbited the star. However,
the situation would be greatly complicated if, upon closer examination,
the star was found to have a yet-unseen stellar companion.
No such companion was found with Gemini, which essentially seals the case for multiple Earth-sized planets orbiting TRAPPIST-1.
Steve Howell of NASA’s Ames Research Center led the extremely
high-resolution observations using the Differential Speckle Survey
Instrument (DSSI), an instrument he has used before at both Gemini
telescopes to probe other exoplanetary systems. The new observations
reinforced the hypothesis that several Earth-sized planets are
responsible for the fluctuations in the star’s brightness. “By finding
no additional stellar companions in the star’s vicinity we confirm that a
family of smallish planets orbit this star,” says Howell. “Using Gemini
we can see closer to this star than the orbit of Mercury to our Sun.
Gemini with DSSI is unique in being able to do this, bar none.”
The research, led by Howell, is published in the September 13th issue of The Astrophysical Journal Letters.
TRAPPIST-1 is what astronomers call a late M-type star; stars which are
small, ultra-cool (compared to most stars), and faint. Late M stars are
so faint that the only specimens we can observe are relatively close-by
in space and, as the Gemini observations demonstrate, allow astronomers
to probe very close to these stars in the search for companions.
“While no current telescope can actually image an Earth-size planet
around another star, even if orbiting a nearby star such as TRAPPIST-1,
our instrument on Gemini allows us to detect close companion stars and
even brown dwarfs.” says Elliott Horch, [Southern Connecticut State
University] co-author of the paper. “Such observations validate not only
the existence of exoplanets, but their small size as well.”
M stars are of great interest to astronomers today as their diminutive
size allows easier detection of small, Earth-size planets. The intrinsic
faintness of M stars means that potentially habitable planets will have
short orbital periods, on the order of weeks. Such planets will be the
targets of detailed study by both ground- and space-based telescopes,
studies that will attempt to measure the composition of their
atmospheres and see if they are indeed Earth-like beyond just their
size.
The discovery of TRAPPIST-1’s likely exoplanet pedigree began late in
2015 with data from the TRAPPIST (the TRansiting Planets and
PlanetesImals Small Telescope) project. This work, published in the 12
May 2016 issue of the journal Nature, and led by Michael Gillon,
observed TRAPPIST-1 over 62 nights. During that period, the star was
found to fluctuate in a manner that is consistent with at least three
Earth-sized planets orbiting and periodically eclipsing and blocking
part of the star’s light from our view on the Earth. While work is still
ongoing to refine the total number of planets, two of them appear to
orbit in 1.5 and 2.4 days and are so close that they receive four and
two times the radiation that our Earth receives from the Sun,
respectively. The third planet is more difficult to characterize, having
possible orbital periods between 4 to 73 days. However, this third
planet’s most likely period, 18 days, would place this world well within
the system’s habitable-zone where liquid water could exist on its
surface.
The Gemini observations, made with the DSSI instrument, were made during
a temporary visit of the instrument at the Gemini South telescope in
Chile.
“Gemini’s flourishing Visitor Instrument program is producing superb
results in all areas of astronomy,” said Chris Davis, a program director
at the U.S. National Science Foundation, one of the agencies that funds
the International Gemini Observatory and which also provided initial
funding for DSSI. “The DSSI observations of the TRAPPIST-1 system of
exoplanets is just one example. The instrument team and their
collaborators deserve credit for building such a versatile and
productive instrument and also for making it available to all of
Gemini’s users."
The DSSI instrument on Gemini provides a unique capability to
characterize the environment around exoplanetary systems. The instrument
provides extreme-resolution images by taking multiple extremely short
(60 millisecond) exposures of a star to capture fine detail and “freeze”
the turbulence caused by the Earth’s atmosphere. By combining the
images and removing the momentary distortions caused by the Earth’s
atmosphere, the final images yield a resolution equal to what the
telescope would produce if it was in space. With this technique, called
speckle interferometry, astronomers can see details at, or very near,
the theoretical limit of the 8-meter Gemini mirror yielding the
highest-resolution single telescope images available to astronomers. The
available resolution is like being able to separate an automobile’s two
headlights at a distance of about 2000 miles.
Science Contacts:
Dr. Steve B. Howell
Project Scientist, NASA K2 Mission
NASA Ames Research Center
Email: steve.b.howell@nasa.gov
Desk: 650.604.4238
Cel: 520.461.6925
Dr. Elliott P. Horch
Professor of Physics, Southern Connecticut State University
Email: horche2@southernct.edu
Desk: 203-392-6393
Cell: 203-214-4310
Media Contacts:
Peter Michaud
Gemini Observatory
Hilo, Hawai‘i
Email: pmichaud@gemini.edu
Desk: (56) 51-2205-628
Available (in Chile) until 9/12/16
Manuel Paredes
Gemini Observatory
Gemini South Base Facility, La Serena, Chile
Email: mparedes@gemini.edu
Cell: (56) 51-2205-671
Source: Gemini Observatory
