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The search for exoplanets is one of the hottest areas of astronomy right now.
And one main reason for that is because humans are dying to know if there
are other Earth-like planets out there… and whether or not they might host life.
But sometimes, researchers are interested in exploring the other end
of the spectrum: the planets that are nothing like Earth.
These planets can give us an idea what extremes are possible out there
in the universe, and offer us insight into how planets come to be
and how they evolve over time.
Some of the most fascinating planets are the incredibly hot ones.
So today, we’ll take a look at three of the most blistering-hot worlds ever found.
The first is a planet called TOI-2109b.
It’s a huge gas giant in the constellation Hercules, 855 light-years away.
The planet is five times the mass of Jupiter, but unlike our Jupiter, it orbits
extremely close to its star, which is just a little bit bigger and hotter than our Sun.
The planet circles its star at a distance of about 2.6 million kilometers.
Now, that sounds like a long way, but it’s basically a stone’s throw in astronomical terms.
That’s just under 5% of the distance between our Sun and its closest planet, Mercury.
It’s so close that its entire year is just 16 hours long.
When astronomers first discovered huge planets like this
so close to their stars, they were confused.
Because in the early days of planet formation in a stellar system,
it’s just too hot near the star for such a big planet to form.
The material needed for the core is too hot to be solid,
and the gas needed for the atmosphere is too hot to be captured.
So this planet, and others like it, must have formed farther out,
like Jupiter, but migrated inward.
And now, because of its proximity to its star,
the day side of this so-called ultrahot Jupiter is around 3300 degrees Celsius.
That’s at least a thousand degrees more than the night side of the planet.
And this temperature difference is believed to drive ferocious winds
across the planet, making the skies of this world a pretty horrific place.
But, while this planet gets almost hot enough to melt diamonds,
it’s not even the hottest planet out there.
That distinction goes to another giant, known as KELT-9b.
This planet orbits a star 670 light-years from Earth, and it’s also an ultrahot Jupiter.
It’s more than three times as massive as our Jupiter,
and its orbit is around twice as big as TOI-2109b’s.
Now, since it’s farther from its star, you might also expect it to be cooler.
But KELT-9b orbits an absurdly hot star.
The star burns white-hot, and at about 10,000 degrees Celsius,
it’s around twice as hot as our own Sun.
That gives KELT-9b a scorching temperature of 4,300 degrees Celsius.
It’s a planet hotter than most stars.
And that temperature would melt… pretty much anything.
Even high-tech hafnium carbide, the material on Earth
with the highest known melting point, would turn to mush on this planet.
It’s actually so hot that astronomers think molecules of hydrogen in its atmosphere
get ripped apart on the day side and reform on the slightly cooler night side.
This extreme cycle likely won’t go on for too long, though,
at least not in astronomical terms.
The searing heat is evaporating the material that makes up the planet.
And observations show that the intense radiation from its star seems
to be blasting away these evaporated gases, almost like a comet’s tail. ~
So, in a few hundred million years, the planet may be no more than a husk.
Now, it’s hard to beat KELT-9b when it comes to extremely hot planets.
But we’d be remiss if we didn’t give a little shoutout
to a hypothetical exoplanet known as Kepler 70b.
Astronomers found what could be the sign of a planet while they were observing
the star Kepler 70, in the constellation Cygnus.
They picked up some periodic dips in the star’s brightness, which is a pattern that
can happen as a planet passes in front of its star and blocks a little bit of light.
This is actually one of the most common ways astronomers discover exoplanets.
And in this case, these dips suggested that astronomers were possibly looking at
a gas giant circling its star so closely that it made a full orbit every six hours.
But measurements like these are really tricky.
Detecting a gas giant passing in front of a star is like detecting a mosquito
passing in front of a car headlight over a hundred kilometers away.
And follow-up studies using different detection methods have suggested that these
dips in Kepler 70’s brightness are just natural variations,
not the signature of a planet.
So the planet Kepler 70b likely doesn’t exist after all.
But if it did, it would be the hottest planet ever discovered,
at over 7000 degrees Celsius.
Now, none of the planets we’ve talked about today are even close
to being anything like… even near-habitable, but the existence of these extremes
gives us an idea about the variety of planets that can exist.
And they’re a reminder that we share this galaxy with some incredible worlds.
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