Welcome to Exoplanet Radio, I'm Tony Darnell.
One of the most exciting exoplanetary systems discovered so far,
and one we've talked about many times on Exoplanet Radio, is Trappist-1,
a system of seven planets, all of them rocky and more or less Earth-sized,
and about three of them are in the habitable zone of the star.
But new observations from an amazing space
telescope have just discovered a system that rivals it.
Habitable zones and Earth-sized are words we
hear a lot when we talk about other star systems
because those words outline a hope that life might exist on their planets.
Life could possibly arise under many scenarios,
and it's entirely possible that life may well survive without it.
But based on our experience, here, on Earth, life needs liquid water.
And if a planet might have it, then we are naturally interested.
Trappist-1 has held our attention for a
long time because it has so many rocky worlds,
orbiting a star that may allow some of them to have liquid water.
The promise of life is too great to ignore,
so we turn our most powerful telescopes to this system whenever possible.
Now, there's a new system on the block.
The Transiting Exoplanet Survey Satellite, or TESS,
has brought us the discovery of a system
that is every bit as interesting as Trappist-1.
Known as TOI-700 because it is the "700th TESS
Object of Interest" catalogued by the mission,
is a system that contains four worlds,
all presumed to be rocky based on the parameters
measured from the planets as they transit the star.
The four planets are imaginatively named b, b,
d, and e, with d and e being the most interesting.
So, what's the system like?
Well, like Trappist-1, all of these planets are very close to their star.
They all have orbits measured in days, the longest being TOI-700d at 28 days.
The reason we're seeing so many systems with short orbits like this
is that our transit measuring space
telescopes don't stare at the system long enough
to get planets that take a long time to go around their star.
Those types of planets are probably out there,
but we haven't seen them yet because we don't look at them long enough.
TESS, for example, only looks at one region of the
sky for 27 days before it moves on to another sector.
The star TOI-700 is a small, cool, M-dwarf star
located about 100 light years away in the southern constellation Dorado.
The innermost planet, TOI-700b, is about 90%
Earth's size and orbits the star every 10 days.
TOI-700c is huge, over 2.5 times bigger than
Earth and completes an orbit every 16 days.
These planets are probably tidally locked,
which means they spin only once per orbit,
such that one side always faces the star, just like
one side of the moon is always turned toward Earth.
In fact, all of these planets are so close, they may all be tidally locked.
TOI-700e resides in what astronomers are calling the "optimistic habitable zone."
Now, this is a term we've not mentioned before,
but it refers to a range of distances from a star
where liquid water could have existed at some point in a planet's history.
Compare this to what we usually refer to as a habitable zone
where liquid water could have existed over most of the planet's lifetime.
TOI-700e orbits in the optimistic habitable zone
and TOI-700d, the most promising for
habitability because it lies just a little farther out,
orbits once over 28 days.
Planet e is closer to the star, but because it was
found a year after the others, it's designated with E.
Like TRAPPIST-1, this system is full of promise.
Follow-up study of the TOI-700 system with
space and ground-based observatories is ongoing,
and with each new observation, our anticipation
of what we might learn about habitable exoplanets
and life elsewhere grows.
Exoplanet radio is produced by Deep Astronomy.
The music is by Geodesium and available at Loch Ness Productions.com.
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