Using data from NASA's Transiting Exoplanet Survey Satellite, scientists have identified an Earth-size world, called TOI 700 e, orbiting within the habitable zone of its star -- the range of distances where liquid water could occur on a planet's surface. The world is 95% Earth's size and likely rocky.
From: NASA/Goddard Space Flight Center
January 10, 2023 -- Astronomers
previously discovered three planets in this system, called TOI 700 b, c, and d.
Planet d also orbits in the habitable zone. But scientists needed an additional
year of TESS observations to discover TOI 700 e.
"This is one of
only a few systems with multiple, small, habitable-zone planets that we know
of," said Emily Gilbert, a postdoctoral fellow at NASA's Jet Propulsion
Laboratory in Southern California who led the work. "That makes the TOI
700 system an exciting prospect for additional follow up. Planet e is about 10%
smaller than planet d, so the system also shows how additional TESS
observations help us find smaller and smaller worlds."
Gilbert presented the
result on behalf of her team at the 241st meeting of the American Astronomical
Association in Seattle. A paper about the newly discovered planet was accepted
by The Astrophysical Journal Letters.
TOI 700 is a small,
cool M dwarf star located around 100 light-years away in the southern
constellation Dorado. In 2020, Gilbert and others announced the discovery of
the Earth-size, habitable-zone planet d, which is on a 37-day orbit, along with
two other worlds.
The innermost planet,
TOI 700 b, is about 90% Earth's size and orbits the star every 10 days. TOI 700
c is over 2.5 times bigger than Earth and completes an orbit every 16 days. The
planets are probably tidally locked, which means they spin only once per orbit
such that one side always faces the star, just as one side of the Moon is
always turned toward Earth.
TESS monitors large
swaths of the sky, called sectors, for approximately 27 days at a time. These
long stares allow the satellite to track changes in stellar brightness caused
by a planet crossing in front of its star from our perspective, an event called
a transit. The mission used this strategy to observe the southern sky starting
in 2018, before turning to the northern sky. In 2020, it returned to the
southern sky for additional observations. The extra year of data allowed the
team to refine the original planet sizes, which are about 10% smaller than
initial calculations.
"If the star was a
little closer or the planet a little bigger, we might have been able to spot
TOI 700 e in the first year of TESS data," said Ben Hord, a doctoral
candidate at the University of Maryland, College Park and a graduate researcher
at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "But the
signal was so faint that we needed the additional year of transit observations
to identify it."
TOI 700 e, which may
also be tidally locked, takes 28 days to orbit its star, placing planet e
between planets c and d in the so-called optimistic habitable zone.
Scientists define the
optimistic habitable zone as the range of distances from a star where liquid
surface water could be present at some point in a planet's history. This area
extends to either side of the conservative habitable zone, the range where
researchers hypothesize liquid water could exist over most of the planet's
lifetime. TOI 700 d orbits in this region.
Finding other systems
with Earth-size worlds in this region helps planetary scientists learn more
about the history of our own solar system.
Follow-up study of the
TOI 700 system with space- and ground-based observatories is ongoing, Gilbert
said, and may yield further insights into this rare system.
"TESS just
completed its second year of northern sky observations," said Allison
Youngblood, a research astrophysicist and the TESS deputy project scientist at
Goddard. "We're looking forward to the other exciting discoveries hidden
in the mission's treasure trove of data.
https://www.sciencedaily.com/releases/2023/01/230110151046.htm
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