Photo by: NASA

NASA

Do Giant Water Worlds Host Alien Life?

We all wish we could find an Earth 2.0 – a planet about the size of our own, made of roughly the same chemical mixture, orbiting a sun-like star at just the right distance so that all its water doesn’t evaporate or freeze.

September 15, 2021

We want to find an Earth 2.0 because it would be a prime candidate to host Life 2.0. Life originated on our planet, and so if we want to know how common life is in the universe, our safest bet is to find out how common Earth-like worlds are.

But the safest bet isn’t always the most rewarding one.

It turns out that Earth-like worlds are relatively rare (or at least, difficult to detect with our current methods). A much more common planet is known as a “mini-Neptune”, which as the name implies is a slightly smaller version of the giant planet found in our own solar system.

You might think that giant, gassy globes would be the last place to look for life, but the creativity and imagination of astronomers knows no bounds. One group has proposed that a certain type of mini-Neptune might be rich in liquid water oceans…and rich in life.

Photo by: NASA

NASA

They’re called Hycean worlds. It’s pronounced “HI-shun” because it’s a portmanteau of “hydrogren” and “ocean”. The gist is that a giant planet might have a sufficiently thick hydrogen atmosphere (like, a thousand times thicker than the Earth’s) that it acts like the lid of a pressure cooker, keeping liquid water on the surface nice and contained for billions of years.

And since giant planets tend to have a lot of everything, Hycean worlds could contain enough water to completely engulf themselves in a world-girdling ocean.

The Hycean worlds could have any distance from their star. Close up, things would get hot and steamy, like a Louisiana swamp. Worlds more distant from their star might more resemble the Arctic.

Either way, as long as there’s liquid water, there’s the potential for life. And here’s the wild thing about (still hypothetical) Hycean worlds: it might be easier to detect life on those worlds and Earth-like ones.

Photo by: NASA

NASA

It all comes down to that thick and juicy atmosphere. It’s extremely difficult to directly observe planets orbiting other stars. Instead, we wait for the planets to cross the face of their parent star, causing a mini-eclipse and dimming the light that we see on Earth. During that crossing event, a tiny fraction of the starlight passes through the alien planet’s atmosphere.

All the chemicals and molecules and elements in that atmosphere change the nature of light, which is something we can observe from the Earth. We can then look for chemical signs of life, like lots of oxygen or methane. And since Hycean worlds have truly gigantic atmospheres, and we know where some candidates are already (unlike Earth 2.0), we have a chance of measuring this with the soon-to-launch James Webb Space Telescope.

As early as next year, we might be getting signals from some watery friends.

Dive Deeper into the Cosmos

Journey Through the Cosmos in an All-New Season of How the Universe Works

The new season premieres March 24 on Science Channel and streams on discovery+.

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

The Nobel Prize Fell Into a Black Hole (and That’s a Good Thing)

The 2020 Nobel Prize in Physics is being awarded to scientists to have dedicated their careers to the study of black holes.

When We’ll Know if NASA’s Asteroid Impact Test was a Success

Recently NASA’s DART mission succeeded in its primary goal, which was to slam a spacecraft face-first into an asteroid. For science. The intention of the mission was to test if we could actually redirect an asteroid and send it into a different orbit. But how and when will we know if it worked?

What Screaming Black Holes are Telling Us

In 2002, NASA’s orbiting X-ray observatory, the Chandra telescope, mapped out the movements of hot gas in a cluster of galaxies sitting 250 million light-years away.

Watch NASA's Asteroid-Crashing DART Mission Make Impact

NASA sent a spacecraft on a mission to crash into an asteroid, so how did it go?Updated 9/26/22

Want to Name a Planet? Now’s Your Chance

Read on to learn about this rare opportunity to name a distant world observed by the James Webb Telescope.

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.

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.

Watch the Super Flower Blood Moon Total Lunar Eclipse

Those located in the Americas, Europe, or Africa can see this rare total lunar eclipse during the night of May 15, 2022.

Six Planets are Retrograde, What Does that Mean for You?

Spoiler alert: It's an optical illusion.

NASA’s $10 Billion Space Telescope Hit by Micrometeoroid

NASA’s new James Webb Space Telescope (JWST) was recently hit by a micrometeoroid. One of the 18 golden mirror segments on the telescope was hit, causing some minor damage.

Related To: