There are a lot of weird planets out  there, like one that could be packed full of diamond, or the one that’s  probably half covered in lava.

Oh wait. Those are actually the same planet.

Behold, an artist’s rendition of 55 Cancri e, also officially known as Janssen… or Janssen if you’re American. And this space tourist’s dream  vacation is a little bit mysterious, because the half covered in lava  isn’t the half you might expect. [♪ INTRO] Janssen is located about 41  light years away from Earth, orbiting a star called Copernicus…aka 55 Cancri A. But that orbit is super tight.

Janssen’s year is less than 18 hours long. Which makes it very, very hot. Temperatures on one half of the planet  reach at least 2,500 degrees Celsius.

And might be as high as 3,500 degrees! That’s over seven times hotter than Venus. And it’s hot enough for the rocky  surface to melt into an ocean of lava.

Meanwhile, on the opposite side, it’s  around a brisk 1,100 degrees Celsius. Technically hot enough to melt copper, but cool enough for much of  the surface to stay solid. Now, a two-faced planet  with an ocean of liquid rock might sound weird on its own.

But there’s more. You might expect the side that’s  covered in lava to be the side that’s directly facing the star. But Janssen’s hotter half is a little off-center.

And scientists don’t know why. One possible explanation is that  Janssen has a thick atmosphere, made up of gasses like nitrogen or oxygen, that could help move some of  those intense temperatures around. Another hypothesis is that, unlike  every other planet we’ve found that close to its star, Janssen  isn’t locked into a position where one half of its surface experiences  perpetual day, and the other perpetual night.

Instead, it could be like Mercury,  where it rotates at just the right speed so that every two trips around its  star, every part of its surface gets to go through three whole  days and three whole nights. And since it takes time for rock to both  heat up and cool down, that slow rotation would explain why Janssen’s lava ocean  isn’t pointed directly at Copernicus. It would also mean that some of the  magma evaporates from the surface during the day, and comes back  down as fiery rain at night.

Yikes. To understand this mystery, astronomers  have already targeted Janssen with the James Webb Space Telescope. Because lucky for humanity,  the planet is close enough that we can take a detailed  peek at its atmosphere.

From previous observations, we know  that there aren’t significant amounts of water vapor, carbon  monoxide, or carbon dioxide. And if the Webb reveals  signs of nitrogen or oxygen, that would point to a “thick”  atmosphere causing Janssen’s heat shift. But if we see a super thin atmosphere  of vaporized minerals instead, then we can be pretty sure the  lava rain scenario is right.

Based on some early results,  lava rain might be the winner. And along with giving us that terrifying visual, the Webb may also tell us what’s  going on below Janssen’s atmosphere. Remember those diamonds earlier?

Astronomers have debated whether  or not this world is “carbon-rich”. A closer look from the Webb  may provide more evidence that there really is a bunch of  diamond deep beneath the surface. Either way, Janssen is shaping up to be a pretty cool target for future space tourists.

Well, not cool cool. You know what I mean. This episode is brought to you by our  very cool supporters on Patreon!

They may not be half covered in lava, but we wouldn’t get to talk about  awesome exoplanets without them. And if you’re watching this  video and thinking to yourself, “Self, I want to be that cool”, you can  head on over to Patreon.com/SciShow to check out how to support the channel, and  all the perks we’ve got waiting for you. Thanks for watching! [♪ OUTRO]