Cosmic Sailing to an Ocean World: A Deep Dive into Europa Clipper

Article October 19, 2024

On Monday October 14^th (four days later than it was originally scheduled thanks to Hurricane Milton), a Falcon Heavy rocket lifted off from Cape Canaveral, Florida, bearing precious cargo—Europa Clipper, the most massive interplanetary spacecraft ever designed by NASA, specially built to explore one of the most intriguing places of our solar system.

The moon Europa as seen by NASA’s Juno spacecraft. Credit: NASA

The launch was just the beginning of a loooooong trip, with the spacecraft arriving at the Jupiter system in 2030. The target is Jupiter’s moon Europa. And planetary scientists are, to put it mildly, excited. What’s so intriguing about this moon and this mission? Let’s deep dive!

Under the Sea

I’mma just state it up front: we think Europa is one of the best bets in the solar system to have developed life. That’s why we want to know more. So let’s get to know this moon a little better.

Three of the four Galilean moons (Ganymede is not in view) as seen by the Hubble Telescope. Credit: NASA/ESA/STScI/AURA

When Galileo became the first person to point a telescope at Jupiter in 1610, he saw four points of light around the planet and named them the Medicean Stars, after his patrons. Today we know these objects as the Galilean Moons of Jupiter: Ganymede, Callisto, Io, and Europa.

Europa is the smallest of them, being just slightly smaller than our own Moon. And at first glance (when seen up close) it does not look like a moon. Europa is actually credited with having one of the smoothest surfaces in the solar system, very different from the tortured, pockmarked surfaces we usually think of with moons. Europa’s surface is constantly changing and renewing. Craters and dimples don’t last long here.

That’s because this surface isn’t rock at all. It’s ice. And that ice is always shifting and moving, kind of like plate tectonics on Earth only, you know, waaaaay faster. That movement is being driven by what’s under the ice, what so intrigues us about this moon: the Europan ocean. We think there is over twice as much water under the surface of Europa than on the surface of Earth. That’s…a lot of water.

An artist’s illustration of what astronomers think the interior of Europa may look like. Credit: NASA/JPL-Caltech/Michael Carrol

If you’re wondering how an ice moon so far from the Sun could harbor so much liquid water under its surface, fair question. The answer is that it’s Jupiter’s fault. Jupiter’s gravity pulls and tugs on its moons, especially the closer-in ones, similar to how our Moon pulls at Earth and causes tides in the ocean. Only Jupiter causes tides in the very rocks of its moons, grinding them together and generating frictional heat deep in their interiors. On Io this manifests as nonstop volcanic activity as that moon tries to relieve the pressure all that internal heat is building up. On Europa that internal heat serves to warm a thick layer of what otherwise would be ice and keep it liquid.

This, research is showing, is actually a common thing amongst outer solar system moons. Many of them appear to have layers of liquid water under their surfaces. Of course, we get very excited when we find liquid water because life as we know it needs it to survive. That said, not all of these ocean moons get us worked up. Life needs other things besides liquid water, and we suspect that most of these underground oceans lack those other ingredients and are sterile.

Not Europa though. We have reasons to believe that this ocean just might have all the right ingredients, and that it can support life. And we really want to know for sure.

The Rocket Race

So that’s why we bothered building a spacecraft to study Europa. But boy getting that spacecraft launched was no easy task! The mission got caught up in the politics that unfortunately sometimes come with NASA’s position as a government agency. That position means that from time to time NASA receives commands from Congress that are not necessarily being driven by what makes sense for a mission’s science or engineering goals.

One big issue was the rocket. In 2017, Congress dictated two requirements to NASA regarding Clipper: it had to launch by 2025 and it had to launch on an SLS rocket. This was A Problem. SLS rockets are excessively expensive and get built very, very slowly. And Project Artemis has first dibs on any coming off the assembly line (also by Congressional decree). That meant there wasn’t going to be a spare SLS for Clipper to launch on before 2025.

Europa Clipper launches successfully aboard a SpaceX Falcon Heavy rocket. Credit: NASA TV

NASA was either going to have to launch later than that or not launch on SLS. Either of those options would have the space agency violating legal requirements put in place by the legislative body of the United States. Preferring not to become an outlaw organization, NASA spent years trying to convince Congress to let it seek out alternative launch options. Somehow it still took until 2021 for Congress to finally approve Clipper’s launch aboard a SpaceX Falcon Heavy instead.

Enter Clipper

Clipper is large. At over 7,000 lbs without counting its propellant, it’s the most massive spacecraft NASA has ever sent on an interplanetary mission. With its twin solar panels fully extended, the spacecraft has a wingspan of a hundred feet, making it longer than a tennis court. It needs that panel real estate too. Jupiter is about as far we can send a spacecraft from the Sun and still have it rely on solar power, and it takes some large panels to soak up enough rays to do it.

The spacecraft itself is 16 feet tall and loaded for bear. It’s a scientific Swiss army knife, carrying no less than nine different science instruments representing the most sensitive investigative array ever sent to the outer solar system.

Diagram showing a representative orbit for Clipper around Jupiter with a Europa encounter. The colored circles indicate where the radiation is most powerful, with darker colors indicating more radiation danger. Credit: NASA/JPL-Caltech — An artist’s illustration of the Europa Clipper spacecraft. Credit: NASA

Clipper will be able to scan Europa in far, mid and near infrared, in ultraviolet, in visible, and in radar. It will measure magnetic fields, plasma fields, surface composition, gravitational pull, and collect dust ejected off of Europa’s surface for internal analysis. Given a little extra payload capacity it probably would have been able to cook a nice Beef Wellington while it was at it.

One thing Clipper will likely not be able to do is tell if there actually is life under the surface of Europa. Its job is to find out if Europa is capable of supporting life. If there is life, it is stuck under several miles of rock-hard ice. Europa does not seem to be doing us the favor of spitting bits of its oceans out in plumes like Saturn’s moon Enceladus (although some possible faint plume detections have been made, they’ve been inconclusive).

That said, it has been suggested that if there is microbial life, and if it can somehow make its way to the surface, and it just happens to be on one of the pieces of dust blasted off the surface, and Clipper just happens to pick that dust up and look at it with its Surface Dust Analyzer, the Dust Analyzer would be able to register it as biological. There’s a lot of ifs in that statement though.

Jupiter: Home of Radioactive Death

Another thing Clipper will not be doing is orbiting Europa. After all, we don’t want to immediately fry it in the bands of radioactive death that circle Jupiter. The liquid metallic hydrogen making up parts of Jupiter’s core generate one of the strongest magnetic fields humans have ever seen, ably assisted by the materials being ejected into it by the volcanos of Io.

Mix in charged particles emitted by the Sun and you get bands of extreme radiation that would cook a spacecraft that tried to set up shop there, no matter how well we built it. And of course, Europa is in the middle of all of this (yes, radiation like this is bad for life, but again any life on Europa is under miles of ice, which is a handy natural radiation shield).

Clipper will, instead, be orbiting Jupiter on a big, elliptical path that will take it into Europa’s vicinity as frequently as is plausible and safe. Over the four years the spacecraft is expected to last, it is due to fly by Europa 49 times. Each time it does Clipper will be exposed to enough radiation to kill a human several times over. Jupiter doesn’t mess around, y’all.

Looking Towards the End

It may seem dumb to talk about how this mission will end when it only just began, but it’s such a cool ending I can’t help it. Since we suspect Europa may be capable of supporting life, we can’t dispose of Clipper at the end of its mission in 2034 in any way that might cause it to hit Europa. But we can smack it hard into Jupiter’s biggest moon, Ganymede!

The Europa Clipper and JUICE spacecraft will have their missions to the Jupiter system overlap, and may make it possible for them to team up. Credit: ESA

Besides being just awesome, this would have a major side benefit. Clipper could, of course, keep taking close-up readings of Ganymede right up until the end (we always wring the very last drop of science out of our dying spacecraft). But Clipper won’t be the only one there.

The ESA’s Jupiter Icy Moons Explorer (JUICE!) will also be there exploring, well, the icy moons of Jupiter. This includes Europa, but it also includes Ganymede. If NASA and the ESA can time it right, JUICE could witness Clipper’s death dive and examine the extremely fresh impact zone on Ganymede’s surface created as a result (and fresh impact zones, if you weren’t aware, can be absolute goldmines for studying what’s under the surface). Now that is what you call teamwork!

On the Road

With the launch behind it, Clipper has fully extended its solar panel wings and is soaring along on its long trip through the black to reach its destination. It’s got a whole new world to explore when it gets there. Godspeed Clipper!