And it turns out, there’s bacteria living inside the methane hydrate ice.They’re called methanotrophs, and they eat the methane.So if something like methane hydrate could form on a frigid world, like Saturn’s moon Enceladus, then that could mean there’s a chance life might exist in the ice.
Thanks to Brilliant for supporting this SciShow video! As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow.
Ever since astronomers discovered worlds beyond Earth, they’ve been trying to find life on them. Most were willing to bet that they’d find it on planets that look like Earth - rocky with liquid water flowing on the surface. Not too hot, not too cold - Goldilocks conditions. And all those frozen-over worlds out there? Eh, those’ll be big wastelands.
But scientists are learning that icy environments might actually have benefits for some forms of life. In fact, some researchers now think that life might even thrive on icy worlds… not in spite of the ice, but because of it.
One perk of ice is that it can form a shield against dangerous radiation. Radiation is a catch-all term for things like light and high-energy particles that move energy from one place to another. And there’s a bunch of it in space, coming from extreme sources like supernovas and neutron star mergers, but also regular ol’ stars like our Sun. Some radiation is fine and dandy. Your basic visible sunlight helps warm the Earth and is used by plants to make their own food. But the super energetic stuff is bad news. Those particles can barrel through a lot of materials and damage molecules like DNA, or in the case of other worlds, prevent the building blocks of life from ever forming.
Here on Earth, we’re pretty safe from this destructive radiation. Our planet has a magnetic field that deflects most of it, and the atmosphere absorbs many of the particles that manage to slip through. But not all worlds have a magnetic field, or a respectable atmosphere. In places like these, harmful radiation could make life all but impossible… unless they had some other kind of shield.
And that’s why some astronomers are interested in ice. Like our atmosphere, ice is really good at absorbing radiation. For example, Jupiter’s moon Europa has an ocean covered by an ice shell that’s between 15 to 25 kilometers thick. And scientists found that all that high-energy radiation coming from space would only penetrate, like, 20 centimeters of the stuff, max. So it’s safe to say life as we know it would be plenty protected, at least from that particular threat.
Granted, that might not seem like an ideal habitat. But here on Earth, we have found microbes surviving under kilometers of Antarctic ice. They surround themselves in a kind of antifreeze mucus to keep from freezing solid, and subsist on nutrients that flow through pores in the ice. It’s not exactly a glamorous lifestyle, but on a world without an atmosphere or magnetic field, life under an ice sheet might be as good as it gets.
And if you’re wondering if NASA has plans to hunt for signs of life beneath the Europan ice, the answer is…yes! The Europa Clipper mission is currently scheduled to launch in 2024. Meanwhile, the European Space Agency has already launched Juice, which originally got its name from the acronym JUpiter ICy moons Explorer. Europa will be the first icy moon it visits. We’ve just gotta wait until 2032. But if you’re hoping for a mission to the Europan surface… or under the surface… well, there’s nothing official in the pipeline just yet.
In the meantime, some scientists have begun wondering if extraterrestrial life could actually exist within the ice on distant worlds. Not just under it, but inside it. That’s because it actually happens here on Earth. Scientists made this discovery in the Sea of Japan, where there are whole sheets of a type of ice called methane hydrate. It looks like regular ice, but if you could zoom in and see its crystal structure, you’d see a bunch of methane mixed in amongst the water molecules. In the Sea of Japan, it forms near vents on the seafloor that pump out methane. As the water freezes, it traps some of this methane within it. And it turns out, there’s bacteria living inside the methane hydrate ice. They’re called methanotrophs, and they eat the methane.
So if something like methane If methane hydrate forms quickly enough, it can trap little bubbles of oil and saltwater, as well as tiny lifeforms. In 2015, a team of scientists were surprised to find organisms living off the oil within the bubbles of ice. This could mean that beyond Earth, methane hydrates and other icy blends may exist on comets, moons, and planets, and could potentially host life.
Ice can not only support life living within and below it, but in some cases, it could also be the key to supporting life above it. On Earth, oceans usually have a depth of less than four kilometers, but on some exoplanets, astronomers predict that there are oceans thousands of kilometers deep. This means that a big icy slab is sandwiched between the planet’s rocky interior and its liquid ocean. If salty nutrients from the planet’s rocky interior can’t get to the liquid ocean, it could be detrimental to any life forms that exist there.
However, according to a paper published in 2022, ice may be the key to moving these nutrients from the planet’s rocky interior to its oceans. On Earth, when saltwater freezes, the salt gets kicked out as ice crystals form, resulting in freshwater ice. But on exoplanets, the alien conditions form ice with a different crystal shape that can store salt. This means that the temperature difference between the upper and lower layers of ice causes it to churn, moving the salty stuff up until it reaches the base of the liquid ocean and delivers its nutrients.
So, ice may be the key to making some watery worlds fertile and life could exist in places we never imagined possible. The next time you hear the phrase “habitable planet”, don’t just picture a world like Earth - picture a giant ball of ice or a world so watery, it makes ice below its liquid ocean.
If you’re interested in learning more about astrophysics, check out the free 30 day trial and 20% off an annual premium Brilliant subscription at Brilliant.org/SciShow or in the link in the description.