Photo by: NASA/ Exoplanet Exploration Program

NASA/ Exoplanet Exploration Program

Meet WASP-127b, the Fluffiest Planet in the Galaxy

Take a planet with the mass of, say, Saturn. You know, pretty big, but not ridiculously big. Just…normal big.

November 15, 2021

Now take that planet and move it closer to its parent star. No, closer. Nope, not close enough. Closer than the Earth orbits around the Sun. Closer than Venus. Yeah, go all the way: move that planet so that it’s less than a quarter of the orbit the Mercury.

An orbit that close is going to make the planet just a little bit hot. Over 2,000 degrees Fahrenheit hot. That’s hotter than any object in the solar system, by far.

That’s WASP-127b, a planet 525 light-years away from us.

WASP-127b is like any other massive planet: it’s made of almost entirely of the gasses hydrogen and helium. And what do gasses do when they get hot? They expand. Like a hot air balloon, WASP-127b has puffed out to become the fluffiest known planet in the galaxy. Despite only having a fraction of the mass of Jupiter, it’s 30% wider than the biggest planet in our solar system.

And like all the other weird exoplanets (planets outside the solar system) out there, the more we study it the weirder it gets.

Recently, a team of astronomers used a combination of instruments, including the Hubble Space Telescope and the ESPRESSO spectrograph at the European Observatory’s Very Large Telescope in Chile.



Hubble space telescope.

Photo by: jamesbenet


Hubble space telescope.

They found sodium. The same sodium that’s in your table salt is hanging out in the atmosphere of this alien world, at a much lower altitude than the astronomers expected. Who salted up this puffball and why is anybody’s guess.

And there are clouds. The astronomers found signals of water vapor that appeared in infrared light, but not in visible light. Since the water vapor signal came from deep in the atmosphere, this meant that there was something higher up that screened out visible light but let infrared light pass through.

That’s exactly what clouds do. So WASP-127b, this giant puffy planet orbiting way too close to its parent star, has clouds. The astronomers weren’t able to tell what the clouds are made of, how much they cover the planet, or what the weekend weather outlook is, which just adds to the mystery.

Oh, you want some more? Sure. The astronomers found that WASP-127b orbits its parent star the wrong way – its star spins one way while the planet orbits the other. Also, it has a really janky orbit, tilted far away from the plane of the rest of the planetary system. The astronomers suspect that there might be another, undiscovered planet in the system, and its gravitational influence is to blame for the weird orbital dynamics.

In short, WASP-127b is a hot mess of a planet, but at least it’s an interesting hot mess.

Dive Deeper into the Cosmos

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

Why Charting the Most Extreme Objects in the Solar System Matters

So the astronomers called it “FarFarOut”, which is mostly a joke because the last time they found such a distant object it they nicknamed it “FarOut”, and this new world is much, much, farther out.

The First Exoplanet Found…Outside the Galaxy!

This new planet has had a pretty rough life.

Yet Another Exoplanet That You’ll Never Want to Visit

Ready for an exotic vacation? How about…really exotic? Tired of tropical beaches or snow-covered mountains? Let’s go…out of this world.

Watch Out! Amateur Astronomer Watches as Jupiter Gets Whacked

Jupiter is the OG best friend in the solar system. It finds all the tiny little comets and asteroids heading for the vulnerable inner planets and takes one for the team, chewing up the dangerous rocks in its thick atmosphere. It happened again just recently, and this time an amateur astronomer caught it in the act.

It’s Time to Return to the Land of the Ice Giants

30 years--It’s been over 30 years since the Voyager 2’s historic flyby of Uranus and Neptune, the outermost and most mysterious planets in the solar system. It’s time to go back.

What Is a “Super Earth” and Why Do We Care?

Super Earths are super cool, and you should really know about them. In short, they are planets slightly bigger than the Earth (hence the name). And the cool part? They might be a home for life, and they’re way easier to study than regular Earths.

Celebrate the I Heart Pluto Festival, An Ode to the Beloved Planet

Yes, we said "planet." Clyde Tombaugh discovered Pluto at Lowell Observatory in Flagstaff, Arizona during the month of February in 1930.Last year on the 90th Anniversary of the discovery, the observatory held its first I Heart Pluto Festival. This year you can be a part of the action.

All Hail Ganymede, King of the Moons

NASA’s Juno probe, the supremely awesome Jupiter orbiter, recently captured some stunning images of Ganymede, the largest moon of Jupiter, during the orbiter’s 34th trip around the giant.

A Jupiter-Sized Exoplanet Orbiting Two Stars

One of my favorite things about exoplanet systems is just how weird they can get. It seems that every few months we are treated to another surprise. This time around, NASA's TESS observatory delivered a planet almost three times more massive than Jupiter orbiting around not one, but two stars. As an added bonus: that planet orbits its twin suns closer than the Earth does around the sun. Who wants to take a trip?

How Common are Water Worlds in the Galaxy?

If Kevin Costner wanted to make a sequel, he’s got plenty of opportunities. Water is by far the most common molecule in the universe. It’s made of two parts hydrogen and one part oxygen. Hydrogen is element number 1 (both on the period table and in abundance), and has been hanging around since the first 15 minutes of the Big Bang. Oxygen is forged in the hearts of sun-like stars, and spreads around when those stars die and turn themselves inside out. And since sun-like stars are also very popular, oxygen gets quite a boost.
Related To: