Photo by: NASA

NASA

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.

April 08, 2021

The oxygen and hydrogen get together and make water.

All these water molecules (in the form of ice) get caught up in the formation of new stars, new solar systems, and new planets.

This Hubble Space Telescope photograph showcases the majestic spiral galaxy UGC 2885, located 232 million light-years away in the northern constellation Perseus. The galaxy is 2.5 times wider than our Milky Way and contains 10 times as many stars.

Photo by: NASA/ESA/B. Holwerda (University of Louisville)

NASA/ESA/B. Holwerda (University of Louisville)

This Hubble Space Telescope photograph showcases the majestic spiral galaxy UGC 2885, located 232 million light-years away in the northern constellation Perseus. The galaxy is 2.5 times wider than our Milky Way and contains 10 times as many stars.

Like, for instance, the Earth.

Viewed from space, the most striking feature of our planet is the water. In both liquid and frozen form, it covers 75% of the Earth's surface. It fills the sky with clouds. Water is practically everywhere on Earth, from inside the planet's rocky crust to inside the cells of the human body.

Photo by: NASA

NASA

Viewed from space, the most striking feature of our planet is the water. In both liquid and frozen form, it covers 75% of the Earth's surface. It fills the sky with clouds. Water is practically everywhere on Earth, from inside the planet's rocky crust to inside the cells of the human body.

According to new research, a lot more ice than we originally thought may have contributed to the infant Earth, helping it grow in its first few million years of existence. At first, when our planet was only 1% of its current size, it grew only by accumulating little bits of ice and carbon. Once it got a little heftier, however, is started collecting more serious rocks.

But once our planet grew warmer, that initial cache of ice melted and made its way to the surface where we can enjoy those lovely ocean views today.

And if it happened here, it could happen anywhere. Since water is so dang common in the universe, anywhere you have the same conditions that led to the Earth (and even Venus and Mars, as those planets were also born with a lot of water), then you’ll likely end up with a liquid-coated planetary surface.

On Feb. 5, 1974, NASA's Mariner 10 mission took this first close-up photo of Venus.
Made using an ultraviolet filter in its imaging system, the photo has been color-enhanced to bring out Venus's cloudy atmosphere as the human eye would see it.

Photo by: NASA

NASA

On Feb. 5, 1974, NASA's Mariner 10 mission took this first close-up photo of Venus.
Made using an ultraviolet filter in its imaging system, the photo has been color-enhanced to bring out Venus's cloudy atmosphere as the human eye would see it.

And since you never know exactly how much water you’re going to get in any random solar system, sometimes Earth-like planets may end up a little drier than our world, and sometimes a little wetter.

And sometimes a lot wetter.

It’s not only possible for Earth-like planets to be completely engulfed in liquid water oceans, they might be outright normal.

The Bahamas as seen from STS-52 in November 1992.

Photo by: NASA

NASA

The Bahamas as seen from STS-52 in November 1992.

This has huge implications for the search for life outside the Earth. Right now, we’re targeting our searches for planets that look like our own and life that looks like us.

But nature is much more clever than we are, and life might take on a much more varied character than we’re used to. Of course, all of this is speculative right now: we have absolutely no evidence for any kind of life outside the Earth, and all our searches are coming up empty.

And maybe they’re coming up empty because we’re looking in all the wrong places. Earth-like planets with a mixture of wet oceans and dry continents might be relatively rare, and the most common forms of life in the galaxy may be purely aquatic (and presumably not very good at building fires, rockets, and radio emitters).

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

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.

NASA is Going Back to Venus. Here’s Why You Should Care.

Recently NASA announced two brand-spanking new missions to our sister planet, Venus. This is the first time in over 40 years that Americans have led a mission to that enigmatic planet. What do they hope to find? Clues to our past…and answers to our future.

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.

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.

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?

Why Pluto Isn’t a Planet, but (Maybe) Should Be

What, exactly, is a “planet”? For ancient astronomers it was pretty easy. When they stared up at the night sky, they saw a) the sun, b) the moon, c) a lot of fixed stars, d) a few wandering points of light. Those vagabonds were the planets. Indeed, our word planet comes from the Greek word for “wanderer”.

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.

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.

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.

Ingenuity Takes First Flight on Mars

In a historic first, Ingenuity successfully flew on the Red Planet. The Mars helicopter was in the air for about 40 seconds.
Related To: