This Year, James Webb will Take a Close Look at a Lava World

The James Webb Space Telescope is gearing up to be an exoplanet extraordinaire. Among many other missions and targets, astronomers plan to use the observatory, now in its final stages of preparations to study…well, a world where it might rain lava.

August 25, 2022

Meet 55 Cancri e. This planet orbits a star about 41 light-years away. The parent star, 55 Cancri is similar in size and age to the Sun, and the planet itself sits in a rocky world. When it was first discovered, it was a candidate for a potential Earth 2.0 – after all, rocky planets around sun-like stars are relatively rare.

A couple of issues with that, however. 55 Cancri e is about eight times more massive, and almost twice as wide, as our planet. That classifies it as a “super-earth.” Second, it’s close to its parent star. Very close.

It orbits a mere 2.3 kilometers from its star on average. That’s only about 1.5% of the distance between the Earth and the Sun. to put that in perspective, 55 Cancri e orbits its star about 20 times closer than Mercury, and Mercury is a dead world constantly blasted by the Sun’s radiation.

NASA/JPL-Caltech

The surface temperatures on 55 Cancri e are hot enough for it to…well, not have a surface. It’s so hot that the rocks that make up its crust melt under its parent star’s glare, turning the world into a permanent pool of lava. The planet has such a tight orbit that an entire year lasts only 17 hours.

Astronomers have known about 55 Cancri e since its initial discovery in 2004. So why is Webb taking a look?

Well, something funny is going on with this lava world. Astronomers had long assumed that this planet is tidally locked, meaning that it always presents the same face towards its parent star as it goes about its orbit, much like the Moon does to the Earth. In that scenario, the amount of heat coming off the day side should stay the same throughout its orbit.

But observations with NASA’s Spitzer Space Telescope have shown that the total amount of heat coming from the day side changes with time and that the hottest part of the planet is offset from the center of the day side.

One way to explain this observation is that 55 Cancri e has an atmosphere. On the Earth, our atmosphere circulates warm and cool air, keeping our nightside warm. But 55 Cancri e is way too hot for a gaseous atmosphere like our own. Instead, astronomers suspect that the dayside is so hot that the heat doesn’t just melt rocks, it vaporizes them, creating a thick haze that circulates the world. When it reaches the nightside, the vaporized rock cools off and condenses, falling like solid rain back onto the surface. There is circulates back through the lava oceans to the dayside where the cycle repeats itself.

It's an insane version of our weather system and a wild idea. But current observatories aren’t powerful enough to detect the presence of an atmosphere, which is where Webb will come in. During the observatory’s first campaign, astronomers hope to get a solid analysis of the planet, trying to understand one of the wildest places in the galaxy.

See the Latest Photos from JWST

Groundbreaking New Images of Jupiter Exceed NASA's Expectations

NASA’s James Webb Space Telescope captured new images of Jupiter revealing never-before-seen details of the planet.

Paul M. Sutter

Paul M. Sutter is an astrophysicist at Stony Brook University and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space.

Next Up

Got You! Astronomers Find an Especially Sneaky Black Hole

Black holes are tricky creatures. Since ancient times the practice of astronomy has been to point our eyes and instruments at all the glowing things in the skies above us. But black holes are defined by the fact that nothing, not even light, can escape their gravitational clutches. So how you do see something that is completely, totally black?

What We’ve Already Learned From James Webb? (Hint: it’s a lot)

That was worth the wait. Just a quick handful of months since its historic launch on Christmas Day, the James Webb Space Telescope has flown to its observing position, unfolded its delicate instruments and ultra-sized mirror, and run through a suite of checks and alignments and calibrations. The team at NASA behind the telescopes released their first batch of images from the science runs, and besides being gorgeous, they're powerful.

Why Astronomers Care About Super-Old Galaxies?

A long time ago, our universe was dark.It was just 380,000 years after the big bang. Up until that age, our entire observable cosmos was less than a millionth of its present size. All the material in the universe was compressed into that tiny volume, forcing it to heat up and become a plasma. But as the universe expanded and cooled, eventually the plasma changed into a neutral gas as the first atoms formed.

The Perseid Meteor Shower Reaches its Peak

Stargazers rejoice! The annual Perseid meteor shower is upon us. Here's what you need to know...(updated August 11, 2022)

A Guide to this August’s Best Astronomy Attractions

Learn more about the exciting things happening in the night sky this month! From the rings of Saturn to the most popular meteor shower of the year, August 2022 has us stargazing all month.

Jupiter Makes Its Closest Approach to Earth in Nearly 60 Years

The last time Jupiter appeared this large and bright in the sky was in October 1963.

How Astronomers Use a Trick of Gravity to See the Most Distant Objects in the Universe

Let’s say you’re an astronomer (work with me here) and you want to take a picture of something incredibly, deeply far away. You know, the typical business of astronomy.

How Exoplanets Became the Next Big Thing in Astronomy

To date, we know of over 5,000 planets outside the solar system. And astronomers suspect that there may be *checks notes* around a trillion more in our galaxy alone. The search for exoplanets is one of the hottest topics in astronomy, with expensive telescopes and giant collaborations all searching for the holy grail of the 21st century: an Earth 2.0, a habitable world like our own.

Scientists Watch as Stars Quake

The European Space Agency’s Gaia spacecraft has managed to watch stars tremble, their light subtly changing as starquakes ripple through their surfaces. Which is pretty cool, because Gaia wasn’t even designed to do it.

Astronomers May Have Found a Rare “Free-Floating” Black Hole

How do you see a perfectly black object in the middle of a pitch-dark night? It sounds like the start of an annoying riddle, but it’s really the question faced by astronomers when they want to search for black holes.

Related To: