The Scariest Exoplanets We Know About

Full disclosure here:

I'm not a scientist. Just a deep space enjoyer who has spent enough time reading about exoplanets to know that Earth is apparently playing this whole "being a planet" thing on easy mode.

Earth has problems.

Hurricanes.

Volcanoes.

Earthquakes.

Michigan winter deciding it's going to be 52 degrees on Tuesday and -4 by Thursday.

But in the grand scheme of planets?

We got ridiculously lucky.

Because once you start looking outside our Solar System, you very quickly discover that nature has been personally offended by the existence of life.

Planets where it may rain molten iron.

Planets covered in magma.

Planets darker than coal.

A planet so hot that molecules basically give up.

And one poor bastard that is actively spiraling toward its own star.

There are thousands of confirmed exoplanets now, and many of them aren't really "places" in the way we normally imagine planets. Some are enormous balls of gas practically touching their stars. Some have temperatures high enough to vaporize rock and metal. Some orbit stellar corpses.

Sources: NASA Science · NASA Science 2 · NASA Science 3

So, naturally, I want to talk about the worst ones.

All of the images below are my take on what each would look like based off their landscape, weather patterns, descriptions from NASA's website, and various other artists' renditions.

I had to learn Photoshop for this, so you are now legally required to appreciate them.

So when I say something like "iron rain," there is actual science behind that.

But nobody has a GoPro sitting on WASP-76 b.

WASP-76 b: It Might Literally Rain Iron

Okay.

Glass rain is pretty bad.

Sources: NASA

How about iron?

WASP-76 b is an ultra-hot gas giant orbiting extremely close to its star.

Its year lasts about 1.8 Earth days.

Sources: NASA Science

You could celebrate New Year's, sleep, spend the next day recovering, and basically be preparing for New Year's again.

The planet is expected to be tidally locked, meaning one side permanently faces its star while the other sits in perpetual night.

And that creates one of the most ridiculous weather systems we've discovered.

The dayside gets above 2,400 degrees Celsius.

That's hot enough to vaporize iron.

Strong atmospheric circulation carries material toward the cooler nightside, and observations have found a strange imbalance in the iron signature around the planet: gaseous iron appears where the atmosphere moves from day toward night, while the returning side doesn't show the same signal.

The iron cools enough to condense out before making the trip back.

In other words:

Iron rain.

Scientists are still studying the details of exactly how the planet's atmosphere circulates, so "it rains iron" shouldn't be interpreted as somebody physically holding a bucket outside and checking.

But iron condensation on the nightside is a serious scientific explanation for what we're observing.

Sources: European Southern Observatory · Nature

Just picture that environment for a second.

Behind you is permanent daylight.

The star is cooking the atmosphere hard enough to turn your car into vapor in a millisecond.

Ahead of you is permanent night.

You move toward the darkness.

Things cool down.

The vapor starts condensing.

And metal begins falling from the sky.

I would like to remind everyone that Earth has water rain.

We complain about it.

Sometimes I think we need perspective.

KELT-9 b: A Planet So Hot That Chemistry Starts Breaking

KELT-9 b reaches roughly 4,300 degrees Celsius on its dayside.

For comparison, that is hotter than the surfaces of many actual stars.

We've apparently found a planet that looked at stars and decided it wanted in.

The atmosphere is so hot that hydrogen molecules can literally be ripped apart on the dayside.

Atmospheric circulation carries those separated hydrogen atoms around toward the nightside, where the slightly lower temperature can allow them to recombine into molecules.

Then they travel back around.

And get ripped apart again.

I don't think "weather" feels like the correct word anymore.

The planet is almost three times Jupiter's mass and takes only about a day and a half to complete an orbit. Its host is an incredibly hot A-type star blasting the planet with intense radiation. NASA lists KELT-9 b as one of the hottest exoplanets ever discovered.

Sources: NASA Science · NASA Science 2 · Oxford Research Archive

Imagine putting Jupiter next to a gigantic cosmic blowtorch.

Then leaving it there.

That's basically KELT-9 b.

Very cool.

Extremely unfortunate.

55 Cancri e: The Planet With a Magma Ocean

Gas giants are easy nightmare fuel because you can always say:

"Well, technically I couldn't stand on it anyway."

That's fine. Let’s put some ground under your feet.

Meet 55 Cancri e.

Also called Janssen.

It's a super-Earth almost twice Earth's diameter, located about 41 light-years away.

And its year lasts less than 18 hours.

The planet orbits only around 1.4 million miles from its star.

Mercury, for comparison, is tens of millions of miles from our Sun.

Sources: NASA Science · NASA Science 2

55 Cancri e is basically sitting in the front row.

Its surface is thought to be molten.

Not:

"There are some volcanoes."

Not:

"There's an especially spicy lava lake."

The entire surface is lava. I. love. it.

NASA's James Webb Space Telescope has also found what is currently some of the best evidence that this rocky world may actually have an atmosphere containing things like carbon monoxide or carbon dioxide.

And here's the really good part.

Scientists think that atmosphere may be continually replenished by gases bubbling out of the magma below.

So this is potentially a planet where the ground is molten and the atmosphere is continuously being burped out by a global lava ocean.

Wonderful.

Webb measured the dayside at around 1,540 degrees Celsius.

Brutal.

But it's actually cooler than scientists would expect if the molten surface were completely bare.

One of the best explanations is that an atmosphere is taking some of that heat and redistributing it toward the nightside.

NASA even notes that depending on the atmospheric conditions, this world could potentially have short-lived clouds made of tiny droplets of lava condensed from the air.

Sources: NASA Science · Nature · NASA Science 2

Lava clouds. :)

Rock is only solid because Earth happens to exist at temperatures where rock is solid.

Heat it enough and suddenly the substance we make mountains, buildings and countertops out of becomes an ocean.

Our definition of "ground" is temperature-dependent.

TrES-2 b: The Planet That Basically Doesn't Reflect Light

This one fascinates me for completely different reasons.

TrES-2 b isn't covered in a global lava ocean.

It doesn't have the most violent weather on this list.

It's just...

dark.

Really dark.

TrES-2 b is one of the darkest planets ever discovered orbiting another star.

It reflects less light than coal.

NASA describes the atmosphere as so dark that if you were somehow flying through it, you would effectively be flying blind. Some models suggest the scorching atmosphere might produce an extremely faint deep-red glow.

So imagine a Jupiter-sized planet.

Almost completely black.

Sitting right beside a star.

Barely reflecting any of that light back into space.

And somewhere underneath that darkness, the atmosphere may have a faint red furnace glow of its own.

Obviously, the planet wouldn't look like a perfectly black circle in every wavelength. "Dark" here specifically refers to how little visible light it reflects.

Sources: NASA Science · Harvard-Smithsonian Center for Astrophysics

But that almost makes it creepier to me.

Stars are throwing ridiculous amounts of light at this thing.

And TrES-2 b just eats it.

WASP-12 b: Currently Being Murdered by Its Star

WASP-12 b gets an award for the most existentially terrible situation.

It takes only about 1.1 Earth days to orbit its star.

The planet is so close that enormous tidal forces are distorting it away from a normal sphere.

NASA describes it as being stretched toward an egg-like shape.

Its outer atmosphere has expanded so far that material is escaping the planet and being pulled toward its star.

Sources: NASA Science · NASA Science 2

Studies have repeatedly found WASP-12 b's orbital period shrinking by roughly 30 milliseconds per year.

That number sounds small, but for a planet that's cruising.

The corresponding orbital-decay timescale is measured in only a few million years. More recent measurements continue to support a rapid decay rate around 30 milliseconds per year.

Sources: Research paper · CaltechAUTHORS

A few million years sounds like forever to us.

Planetarily speaking?

That's basically a terminal diagnosis.

The star and planet exchange tidal energy.

The orbit shrinks.

The planet moves closer.

The interaction gets increasingly ugly.

Sources: arXiv · Research paper

Eventually, WASP-12 b loses.

There is no clever orbital maneuver coming.

Gravity has already filed the paperwork.

PSR B1257+12: Planets Orbiting a Stellar Corpse

And then we have PSR B1257+12.

Technically, this isn't one hostile planet.

It's an entire hostile planetary system.

These planets orbit a pulsar.

A pulsar is what you can end up with after a massive star explodes as a supernova and its core collapses into a neutron star.

We're talking about roughly a star's worth of mass crammed into something around the size of a city.

Then spin it really, really fast, add enormous magnetic fields, and blast radiation into space in thin beams.

Congratulations.

Pulsar.

Interestingly, planets around PSR B1257+12 were the first confirmed exoplanets ever discovered.

Which is incredibly funny to me.

Humanity spent centuries wondering whether other stars have planets and when we finally found one the answer we received was "Yes. They’re orbiting a stellar corpse."

Couldn't ease us into it.

NASA's artist concept shows three planets around the pulsar, with intense charged-particle radiation potentially producing massive auroral displays in their skies. Current thinking suggests these worlds probably formed from material left behind after the original star's destruction rather than surviving the supernova as intact planets.

Sources: NASA Science · NASA Science 2 · NASA

A star dies violently.

It blows itself apart.

The center collapses into an object so dense that ordinary matter basically loses the argument.

Debris gathers around the remains.

And eventually:

Planets.

There's something deeply unsettling about imagining the sky from one of these worlds.

Instead of our familiar Sun, your system is centered on an ultra-dense stellar remnant spinning through the darkness and sweeping radiation through space like a lighthouse.

Sources: NASA Science

It's beautiful.

It's horrifying.

It's exactly the kind of thing the universe seems to make just because physics technically allows it.

The Scariest Part Is That These Aren't Even the Weirdest Planets That Exist

Here's what gets me about all of this.

Before we discovered exoplanets, it was very easy to accidentally imagine that planetary systems probably looked vaguely like ours.

Rocky planets near the star.

Gas giants farther out.

Maybe some icy stuff in the outskirts.

...Nice.

Then we started finding exoplanets.

And the universe responded:

lol.

Hot Jupiters practically touching their stars.

Super-Earths with no real equivalent in our Solar System.

Planets orbiting multiple stars.

Planets orbiting dead stars.

Planets losing their atmospheres.

Planets spiraling into their stars.

Rocky worlds covered in molten oceans.

Gas giants hot enough to destroy molecules.

Sources: NASA Science · NASA Science 2 · NASA Science 3 · NASA Science 4 · NASA Science 5 · NASA Science 6

The lesson from exoplanet astronomy so far seems to be that if gravity, chemistry and orbital mechanics permit something to exist...

the universe will eventually try it.

And we've barely started looking.

That's the part that really breaks my brain.

These aren't necessarily the scariest planets that exist.

They're the scary planets we've managed to find.

Our detection methods are heavily biased.

Big planets close to their stars are easier for us to detect because they block more starlight, tug harder on their stars and produce stronger signals.

Sources: NASA Science · NASA Science 2

There are hundreds of billions of stars in the Milky Way.

We have characterized the atmospheres of a laughably tiny fraction of their planets.

Sources: NASA Science · NASA Science 2 · NASA Science 3

There could be completely different categories of planetary nightmare sitting 10,000 light-years away that we've never even imagined.

Maybe a world far more hostile than anything here.

Maybe something genuinely beautiful.

Maybe something looking back.

We don't know.

And that's the neat part.

Earth Is Starting to Look Pretty Good

After touring some of the galaxy's worst vacation destinations, I've developed a renewed appreciation for Earth.

Our atmosphere isn't currently evaporating.

Sources: NASA Science

Our Sun isn't pulling chunks off us.

Our ocean is water.

Our rain is also water.

The rocks mostly remain rocks.

Molecules generally stay assembled.

And our star has not exploded and collapsed into a rapidly spinning neutron star yet.

Sources: NASA Science · NASA Science 2 · NASA Science 3

Not bad.

None of this requires magic.

None of it requires breaking physics.

It's just physics operating under conditions so ridiculous that the result sounds made up.

And somewhere out there, orbiting one of the hundreds of billions of stars in our galaxy, is almost certainly something even stranger.

Sources: NASA Science