NASA’s Transiting Exoplanet Survey Satellite (TESS) has discovered its first Earth-size planet in its star’s habitable
zone, the range of distances where conditions may be just right to allow the
presence of liquid water on the surface. Scientists confirmed the find, called
TOI 700 d, using NASA’s Spitzer Space Telescope and have modeled the planet’s potential environments to help
inform future observations.
TOI
700 d is one of only a few Earth-size planets discovered in a star's habitable
zone so far. Others include several planets in the TRAPPIST-1 system and other worlds discovered by NASA’s Kepler Space Telescope.
“TESS
was designed and launched specifically to find Earth-sized planets orbiting
nearby stars,” said Paul Hertz, astrophysics division director at NASA
Headquarters in Washington. “Planets around nearby stars are easiest to
follow-up with larger telescopes in space and on Earth. Discovering TOI 700 d
is a key science finding for TESS. Confirming the planet’s size and
habitable zone status with Spitzer is another win for Spitzer as it approaches
the end of science operations this January."
NASA's Transiting Exoplanet Survey
Satellite (TESS) has discovered its first Earth-size planet in its star's
habitable zone, the range of distances where conditions may be just right to
allow the presence of liquid water on the surface. Scientists confirmed the
find, called TOI 700 d, using NASA's Spitzer Space Telescope and have modeled
the planet's potential environments to help inform future observations.
Credits: NASA's Goddard Space Flight
Center
TESS monitors large
swaths of the sky, called sectors, for 27 days at a time. This long stare
allows the satellite to track changes in stellar brightness caused by an
orbiting planet crossing in front of its star from our perspective, an event
called a transit.
TOI 700 is a small, cool
M dwarf star located just over 100 light-years away in the southern constellation Dorado. It’s roughly 40% of
the Sun’s mass and size and about half its surface temperature. The star
appears in 11 of the 13 sectors TESS observed during the mission’s first year,
and scientists caught multiple transits by its three planets.
The star was originally
misclassified in the TESS database as being more similar to our Sun, which
meant the planets appeared larger and hotter than they really are. Several
researchers, including Alton Spencer, a high school student working with
members of the TESS team, identified the error.
“When we corrected the
star’s parameters, the sizes of its planets dropped, and we realized the
outermost one was about the size of Earth and in the habitable zone,” said
Emily Gilbert, a graduate student at the University of Chicago. “Additionally, in 11
months of data we saw no flares from the star, which improves the chances TOI
700 d is habitable and makes it easier to model its atmospheric and surface
conditions.”
Gilbert and other
researchers presented the findings at the 235th meeting of the American Astronomical Society in Honolulu, and
three papers — one of which Gilbert led — have been submitted to scientific journals.
The innermost planet,
called TOI 700 b, is almost exactly Earth-size, is probably rocky and completes
an orbit every 10 days. The middle planet, TOI 700 c, is 2.6 times larger than
Earth — between the sizes of Earth and Neptune — orbits every 16 days and is
likely a gas-dominated world. TOI 700 d, the outermost known planet in the
system and the only one in the habitable zone, measures 20% larger than Earth,
orbits every 37 days and receives from its star 86% of the energy that the Sun
provides to Earth. All of the planets are thought to be tidally locked to their
star, which means they rotate once per orbit so that one side is constantly
bathed in daylight.
A team of scientists led
by Joseph Rodriguez, an astronomer at the Center for Astrophysics | Harvard & Smithsonian in Cambridge,
Massachusetts, requested follow-up observations with Spitzer to confirm TOI 700
d.
“Given the impact of
this discovery — that it is TESS’s first habitable-zone Earth-size planet — we
really wanted our understanding of this system to be as concrete as possible,”
Rodriguez said. “Spitzer saw TOI 700 d transit exactly when we expected it to.
It’s a great addition to the legacy of a mission that helped confirm two of the
TRAPPIST-1 planets and identify five more.”
The Spitzer data
increased scientists’ confidence that TOI 700 d is a real planet and sharpened
their measurements of its orbital period by 56% and its size by 38%. It also
ruled out other possible astrophysical causes of the transit signal, such as
the presence of a smaller, dimmer companion star in the system.
Rodriguez and his
colleagues also used follow-up observations from a 1-meter ground-based
telescope in the global Las Cumbres Observatory network to improve
scientists’ confidence in the orbital period and size of TOI 700 c by 30% and
36%, respectively.
Because TOI 700 is
bright, nearby, and shows no sign of stellar flares, the system is a prime
candidate for precise mass measurements by current ground-based observatories.
These measurements could confirm scientists’ estimates that the inner and outer
planets are rocky and the middle planet is made of gas.
Future missions may be
able to identify whether the planets have atmospheres and, if so, even
determine their compositions.
While the exact
conditions on TOI 700 d are unknown, scientists can use current information,
like the planet’s size and the type of star it orbits, to generate computer
models and make predictions. Researchers at NASA’s Goddard Space Flight Center
in Greenbelt, Maryland, modeled 20 potential environments of TOI 700 d to gauge
if any version would result in surface temperatures and pressures suitable for
habitability.
Their 3D climate models
examined a variety of surface types and atmospheric compositions typically
associated with what scientists regard to be potentially habitable worlds.
Because TOI 700 d is tidally locked to its star, the planet’s cloud formations
and wind patterns may be strikingly different from Earth’s.
One simulation included
an ocean-covered TOI 700 d with a dense, carbon-dioxide-dominated atmosphere
similar to what scientists suspect surrounded Mars when it was young. The model
atmosphere contains a deep layer of clouds on the star-facing side. Another
model depicts TOI 700 d as a cloudless, all-land version of modern Earth, where
winds flow away from the night side of the planet and converge on the point
directly facing the star.
When starlight passes
through a planet’s atmosphere, it interacts with molecules like carbon dioxide
and nitrogen to produce distinct signals, called spectral lines. The modeling
team, led by Gabrielle Engelmann-Suissa, a Universities Space Research Association visiting research
assistant at Goddard, produced simulated spectra for the 20 modeled versions of
TOI 700 d.
“Someday, when we have
real spectra from TOI 700 d, we can backtrack, match them to the closest
simulated spectrum, and then match that to a model,” Engelmann-Suissa said.
“It’s exciting because no matter what we find out about the planet, it’s going
to look completely different from what we have here on Earth.”
TESS is a NASA
Astrophysics Explorer mission led and operated by MIT in Cambridge,
Massachusetts, and managed by NASA's Goddard Space Flight Center. Additional
partners include Northrop Grumman, based in Falls Church, Virginia; NASA’s Ames
Research Center in California’s Silicon Valley; the Harvard-Smithsonian Center
for Astrophysics in Cambridge, Massachusetts; MIT’s Lincoln Laboratory; and the
Space Telescope Science Institute in Baltimore. More than a dozen universities,
research institutes and observatories worldwide are participants in the
mission.
The Jet Propulsion
Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission
for NASA's Science Mission Directorate in Washington. Science operations are
conducted at the Spitzer Science Center at Caltech in Pasadena. Space operations
are based at Lockheed Martin Space in Littleton, Colorado. Data are archived at
the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for
NASA.
The modeling work was
funded through the Sellers Exoplanet Environments Collaboration at Goddard, a
multidisciplinary collaboration that brings together experts to build
comprehensive and sophisticated computer models to better analyze current and
future exoplanet observations.
Banner image: The three planets of the
TOI 700 system orbit a small, cool M dwarf star. TOI 700 d is the first
Earth-size habitable-zone world discovered by TESS. Credit:
NASA's Goddard Space Flight Center
Last Updated: Jan. 7,
2020
Editor: Rob Garner
No comments:
Post a Comment