The time it takes to circle the star once is only 16 hours. It's the second-hottest exoplanet ever found, and the shortest ever seen for a gas giant.
The planet is doomed. The star brings it ever closer because it is already hot and losing its atmosphere. The star will eventually consume it.
TESS is the transiting exoplanet survey satellite and the star is called TOI-2109 TESS scans the sky for bright stars. If a planet passes in front of the star, it dims the star's light. The amount of the star dims depends on the size of the planet and the length of the transit.
The constellation of Hercules is about 860 light years away from Earth, and is larger and more massive than the Sun. It's also hotter than the Sun, which is what we call an F-type star.
The planet, called TOI-2109b, is cooking. TESS data shows it is 1.35 times the diameter of Jupiter and 1.5 million kilometers above the star's surface. The distance from the Earth to the Sun is 1%. The planet is being prepared. The planet's temperature at its cloud tops is about 3,360C, according to observations from the ground. It was very bad.
The planet is so hot that when it passes behind its host star, a secondary drop in brightness is seen by TESS because the star blocks the planet. The planet's glow contributes to the total light seen from the system.
The planet's mass can be found because it tugs on the star with its gravity and makes a circle. Sometimes the star is moving towards us and sometimes it is away. The mass of the planet is about 5 times that of Jupiter.
I chuckled when I saw that. If you add more mass to a planet like Jupiter, it will shrink because of the weird quantum mechanical mechanism called degeneracy. We see this with massive exoplanets where they have more mass than Jupiter but are smaller.
Why is TOI-2109b bigger? It puffed up from the star's heat. When you heat a gas, it expands. The planet is so hot it's inflated.
It's so hot that it's likely losing atmosphere to space. We think of heat on a scale as motion on a tiny scale. The hotter the gas, the faster it jiggles. The material at the top of TOI-2190b's atmosphere is so hot that it can escape the planet's intense gravity and look like a comet.
It gets worse for this planet. The planet is so close to the star that it can distort the planet into an egg shape, and the star can raise bulges in the planet as it rotates. The bulge raised in the star pulls the planet backwards a bit because it spins a bit slower than the planet's. That means that the planet is close to its star all the time.
If true, the planet's speed will increase, which will mean it will have a reduced period. The TESS observations give a very accurate orbital period of 0.67247414 0.00000028 days, with an accuracy of just 25 milliseconds. TESS may be able to see that part of the sky next year, because complex mathematical calculations show TOI-2109b's orbital period should shorten by almost one second per year.
That's amazing. If this planet is getting closer to its star via tides, we may be able to see it soon.
It means the planet is doomed. The planet is close to that star. It will get closer and closer to the star. Bye bye at that point. If TOI-2109b gets too close to the star, it will get torn apart by its gravity, but it has enough mass that it can hold itself together.
The star is bright enough to be easily observed with a ground-based telescope, so we can keep an eye on it. A planet like this is a great place to observe and understand what the planet is doing to its star. It will likely be millions of years before it plummets to its doom, but there is a lot more to learn.
