[Music throughout] Narrator: NASA’s TESS mission has found its first
Earth-size world in its star’s habitable zone. This means
the planet, called TOI 700 d, has the potential for liquid
water on its surface. TESS stares at patches of sky
for long stretches, recording light from thousands of stars.
Some of these stars have planets that cross, or transit, in front of them.
TESS sees these events as tiny, regular dimmings of the
host stars. One star where TESS saw transits is
TOI 700. It’s a red dwarf about 40% the mass
and size of our Sun and roughly half its temperature.
One set of transits announced the presence of a planet close to the star,
called TOI 700 b. Another set
revealed a second planet, named TOI 700 c, a little farther out.
The deeper, shorter transit means the planet is larger than the first,
and the plane of its orbit is slightly tipped. A final set
of transits showed TOI 700 d orbiting even farther out.
TESS observed this system for nearly 11 months
and saw each planet transit multiple times. Scientists
determined that the inner and outer planets are almost Earth-size and may be
rocky. The middle world is more than twice as large and most likely
made of gas. All three may be tidally locked, rotating
just once each orbit, so the same side always faces the star.
But most importantly, TOI 700 d is
within the star’s habitable zone. Scientists wanted
independent confirmation of TOI 700 d, so they monitored
its star with NASA’s Spitzer Space Telescope. Spitzer saw a clear
transit from the outer planet, affirming its existence and improving
scientists’ certainty of the planet’s size.
TOI 700 d is one of only a few Earth-size planets found in
potential habitable zones. Others include discoveries by Kepler
and several planets in the TRAPPIST-1 system.
Because TOI 700 is bright and nearby, the planets are good
candidates for precise mass measurements by ground-based telescopes.
Future missions may also tell us if the worlds have atmospheres.
But scientists need to know what kinds of signals to look for.
Researchers at NASA’s Goddard Space Flight Center created models of the planet
to explore its potential conditions. One version is a
water-covered world with an atmosphere similar to early Mars but denser.
Another looks like a completely dry version of today’s Earth.
Both models have vastly different surface temperatures.
Light passing through their atmospheres creates distinct signals
because different molecules are present. By simulating
these data now, scientists can make predictions for real future observations
and narrow the range of TOI 700 d’s possible
conditions. We still have much to learn about the TOI
700 system. but thanks to TESS. Spitzer. and the work of
many scientists, we’re beginning to form a picture of its exciting
new worlds. [Explore: Solar system & beyond]
[NASA]