Is there life on Europa? We take a look at Greenland and Antarctica to find out more about life on Jupiter’s icy moon.

Further reading:

Life on Venus claim faces strongest challenge yet

Stanford researchers’ explanation for formation of abundant features on Europa bodes well for search for extraterrestrial life

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

Today we’re going to learn about the potential of life on Europa, a moon of Jupiter! To do that we’ll need to look at some extreme life on Earth too.

Back in September 2020, we talked about potential signs of life in the atmosphere of Venus, which excited me a whole lot. As a follow-up to that episode, further studies suggest that signs of phosphine detected in Venus’s atmosphere, which might be produced by life, may actually just be sulfur dioxide (not a sign of life). But while it’s not looking likely that phosphine is actually found in Venus’s atmosphere, so far no studies can completely rule it out. So, maybe.

Venus isn’t the only part of our solar system where life might exist outside of Earth, though. Astronomers have been speculating about Europa for a long time. The planet Jupiter is a gas giant that has at least 80 moons, but Europa is the one that’s closest to the planet. It’s only a little bit smaller than our own moon.

Europa has an atmosphere, mostly made up of oxygen but so thin that if you could magically appear on the moon, you wouldn’t be able to breathe. Also, you would freeze to death almost immediately. It’s a dense moon, so astronomers think it’s probably mostly made up of silicate rock, which is what Earth is mostly made up of, along with Mars, Venus, Mercury, and a lot of moons.

If you’ve ever looked at our moon through a telescope or binoculars, you know it has lots of impact craters on its surface caused by asteroid strikes in the past. Europa doesn’t have very many craters—in fact, its surface is incredibly smooth except for what look like cracks all over it. It’s mostly pale in color, but the cracks are reddish-orange or brown.

The cause of the cracks has been a mystery ever since astronomers got the first good look at Europa. Many astronomers think these cracks are where warm material from below the surface erupted through the crust, sort of like what happens where lava oozes up on Earth and forms oceanic ridges. But on Europa, the material breaking through the crust isn’t lava, it’s ice—but ice that isn’t as cold as the surface ice. You know you’re on a cold, cold moon when ice that’s close to freezing instead of way below freezing can act like lava. The surface of Europa is about 110 kelvin at the equator and even colder at the poles. That’s -260 F or -160 C.

The exciting thing is that researchers are pretty sure the surface of Europa is icy but that the crust lies over a deep saltwater ocean that covers the entire moon. Yes, an ocean! As Europa orbits Jupiter, the planet’s gravity pulls at the moon, while the smaller gravity fields of the other nearest moons also pull on Europa in other directions. This push and pull causes tides that help warm the ocean and keep it from freezing solid. The brown coloration in the moon’s cracks may be due to mineral salts from the water that get leached up through the cracks after warm ice breaks through, assuming that’s what is actually happening to cause the cracks. Astronomers even have images of Europa taken by space probes that show what look like water plumes erupting through the surface and shooting up an estimated 120 miles high, or 200 km.

But new studies suggest that the water plumes might not be from the ocean. They might be from pockets of water that form within the crust itself, which grow larger until they burst out through the crust. This is even more exciting when it comes to potential life on the moon, because it suggests that the crust isn’t just a big block of ice. It’s a dynamic system that might harbor life instead of all potential life on Europa being restricted to the ocean. But to learn more about Europa, we have to come back to Earth and examine the island of Greenland.

Most of Greenland is covered with a permanent ice sheet like the ones found in Antarctica, but it’s a lot easier to study than Antarctica. One feature seen in the ice sheet is something called a double ridge, shaped sort of like a capital letter M. It’s caused when the ice fractures around pressurized water that forms inside the ice sheet and refreezes. This is caused when water from streams and lakes on the surface finds its way into the ice. The double ridge can look like a crack. New pictures of the cracks on Europa’s surface look just like Greenland’s double ridges, but much bigger.

My explanation of all this is extremely clumsy, because this is a really complex mechanism. Researchers only figured it out because some of the team had been studying Greenland’s double ridges for a completely different project, and noticed the similarities. There’s a link in the show notes to an article about this phenomenon if you want to learn more.

The Greenland ice sheet is over a mile thick. In 1966, the U.S. Army drilled into the ice to see what was under it, and the answer is dirt, as you might have expected. They took a 15-foot, or 4.5 meter, core sample and stuck it in a freezer, where everyone promptly forgot about it for 51 years. At some point it ended up in Denmark, where someone noticed it in 2017.

In 2019, the frozen core sample was finally studied by scientists. They expected to find mostly sand and rock. Instead, it was full of beautifully fossilized leaves and other plant material.

The main reason scientists were so surprised to find leaves and soil instead of just rock is that ice is really heavy, and it moves—slowly, but a mile-thick sheet of ice cannot be stopped. If you listened to the recent episode in the main feed about the rewilding of Scotland, you may remember that Scotland doesn’t have a lot of fossils from the Pleistocene because it was covered in glaciers that scoured the soil and everything in it down to bedrock, destroying everything in its path. But this hasn’t happened in Greenland, even though the sample was taken from an area only about 800 miles, or 1,290 km, from the North Pole.

Where the ice sheet now is, there used to be a forest. Obviously, the ice sheet hasn’t always covered Greenland. Research is ongoing, but a study of the sediment published in 2021 indicates that Greenland was ice free within the last million years, and possibly as recently as a few hundred thousand years.

All this is interesting, but it’s very different from Europa, whose ice sheets have probably been in place almost from the moon’s formation. What kind of life can live on, in, or under ice sheets?

On Earth, at least, a lot of organisms live on glaciers. Most are tiny or microscopic, including a type of algae that grows on top of ice, bacteria that live pretty much everywhere, including inside ice crystals, and microbes of various kinds. But there are some larger organisms, including glacial copepods, snow fleas, glacial midges, and the ice worms we talked about in episode 185 that live on glaciers in the Pacific Northwest.

Most likely, life on Europa will be tiny too. Researchers hypothesize that there could be microbial life living deep within the ice or in the pockets of melted water that develop inside it. There might be microbial mats or algae-type organisms that live on the underside of the ice, anchored there but able to extract nutrients from the ocean water.

But obviously, Europa’s ocean is where most life will probably be found, assuming it’s there. While there’s no environment quite like Europa’s to be found on Earth, since Earth is so close to the sun and nice and warm in comparison, parts of the deep sea are somewhat similar. Lots of animals live around hydrothermal vents, where volcanic activity breaks through the ocean floor and superheats water in small areas. Invertebrates of all kinds have adapted to live between boiling hot water and frigid deep-sea water, where absolutely no sunlight has ever reached. Animals like giant tube worms can grow nearly 10 feet long, or 3 meters, and don’t actually eat anything. Instead, they have symbiotic bacteria that provide them with all the nutrients they need while in turn, the bacteria get a safe place to live.

When the intensely heated, mineral-rich water of a hydrothermal vent comes in contact with cold water, it causes all sorts of chemical reactions. That’s what fuels most of the life around the vents. There are even some fish that live around hydrothermal vents, including the cutthroat eel that can grow over 5 feet long, or 1.6 meters. They’re bottom-dwelling deep-sea eels that live worldwide, but they spend time around hydrothermal vents to eat some of the other animals that live there exclusively. There’s even a type of bacteria found at one vent off the coast of Mexico that uses the faint light emitted by lava deep within the vent for photosynthesis. All other known photosynthesizing organisms use the sun as a light source.

Scientists think that Europa has hydrothermal vents similar to the ones on Earth. Since at least some researchers think life on Earth got its start around hydrothermal vents, it wouldn’t be surprising if life forms also live around Europa’s vents. But that doesn’t mean that life could only live around the vents.

In 2018, a team of scientists in Antarctica bored through the ice sheet and took a sample from the sea floor far below the ice to see if anything liv...