This is Exoplanet Radio, I'm Tony Darnell.
Human beings have discovered over 5,500 exoplanets.
Over 80% of them have orbits shorter than
50 days, which would place them at over twice
as close to their star as Mercury is to the Sun.
Some are even closer.
Some observations from tests, however, have
found one with an orbit of 82 days and another
measured in hundreds of days.
Why are we finding so many toasty worlds so close to the star?
There are likely just as many planets
farther out from their star that orbit with periods
measured in hundreds of days, like the
Earth does, but the reason we've seen so many of
these types of planets comes down to the
limits of our telescopes and how we are observing
with them.
Two of the most popular ways of finding
exoplanets right now are the transit and radial velocity
methods.
To use them, we have to actually watch the
planet move around the star, or between us
and the star, and waiting around for that to happen is expensive.
Telescopes are in high demand, and to stare
at a star for hundreds of days hoping to see
a planet go around is not practical with the way telescope time is allocated.
So we are only getting good data from planets
that whizz around their star in a short time.
But of course, astronomers realize that that's not the whole picture.
There are no doubt many long-period exoplanets
out there, we just have to deploy an observing
system capable of finding them.
More on that in a minute.
Back to TESS, the Transiting Exoplanet Survey satellite.
It only looks at an area of the sky for
about a month before it moves on to other parts
of the sky.
The idea was to sacrifice getting complete
orbits of planets for partial ones, all the
while imaging the entire sky and flagging
potential transits as "objects of interest"
for further study by other telescopes.
TESS has amassed thousands of objects of interest, or TOIs, since its launch.
One of them, TOI 4600, is a rare system
containing two long-period planets orbiting a nearby
star that is 815 light-years from Earth.
The test team discovered that the star hosts
an interplanet with an orbit of 82 days, similar
to that of Mercury, while the outer planet
circles every 482 days, placing its distance
from the star somewhere between the orbits of Earth and Mars.
Both planets are likely gas giants, similar
to Jupiter and Saturn, though the composition
of the interplanet may be more of a mix of gas and ice.
The two planets bridge the gap between "hot jupiters"
the toasty, short-orbit planets that
make up the majority of exoplanet discoveries,
and the colder, longer-period gas giants like
the ones in our solar system.
Astronomers found the longer-period planet
by stacking up data from past searches of
the sky to build up the light curve.
Tests has scanned the entire sky once already.
They also looked at the system using
ground-based telescopes to get a fuller picture of the system
What TESS is really good at, though, is for short searches over a wide area of sky.
This method of observing is great for getting those short-period exoplanets.
An ideal scenario would be to look at the entire sky for a long time.
Luckily, we have just such a program
starting very soon with the Vera Rubin telescope.
It will survey the entire sky several times
a week looking for all sorts of things, one
of them being exoplanet transits.
And it will do it for years, allowing
astronomers to build a deep view of the heavens over a
long time, seeing dips in brightness across the heavens.
Our window to more worlds around other stars is about to get a lot bigger.
Exoplanet Radio is produced by Deep Astronomy.
Music is by Geodesium and available at Loch Ness Productions.com.
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