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Hank: Here on SciShow Space, we’re big fans of Jupiter’s moon Europa. I mean, who wouldn’t be? It’s a weird-looking world with a bunch of crazy, colorful cracks, a thin atmosphere of oxygen, and probably a deep ocean of liquid water beneath its surface, too. If there’s life elsewhere in our solar system, Europa’s a really good place to find it.

So, back in June, we were excited to tell you about NASA’s plans for a mission that would involve dozens of close flybys of Europa, with a space probe known as Clipper. And that’s still happening. But since then, Congress has thrown a wrench into those plans. It has mandated that NASA add a lander to the mission, and launch both the probe and the lander by 2022. Which is a really cool idea! Seriously, as ideas go, this is one of the better ones that Congress has had. Kind of.

But adding a lander is going to make the mission much more complicated. And expensive. That’s creating a lot of problems for the space agency, and from last week’s meeting of NASA’s Outer Planets Assessment Group, it sounds like they still aren’t quite sure how to solve some of them. No one has ever sent a probe to study Europa specifically, but we’ve learned a lot about it from probes like Galileo and telescopes like Hubble. We know that it’s an active world, with plumes of water vapor that probably come from geysers and, of course, there’s that liquid ocean that might be hiding under the crust.

But that’s the thing: all this activity is probably happening on Europa. We still don’t know for sure. So the Clipper probe’s main mission has been to analyze the moon’s atmosphere, surface, and subsurface, to help us figure out exactly what’s going on, and whether life could survive there. The original idea was that, if NASA decided to send a lander -- or even a rover -- to Europa in the future, scientists would be able to use the images and data from Clipper to find possible landing sites.

At least, that was the original plan. But back in December, Congress passed its new budget for the space agency. And it turns out, NASA’s getting about 175 million dollars specifically for the Europa mission. The mission just has to include a lander, and both probe and lander have to launch by 2022, on the Space Launch System that NASA’s in the process of developing. Now, of course, having a lander on Europa will teach us a lot more about the moon than we could ever get from a few fly-bys. But adding a lander is going to be really, really hard.

The first problem is that we... just aren’t prepared to land on Europa yet. For example, we don’t know enough about Europa’s surface to pick a good landing site. I mean, nobody wants our lander to touch down on a bunch of rock spikes or something that we won’t know about until it’s too late. Plus, the lander will probably have about 10 days of power, starting from the moment it touches down. So, to get the most out of the mission, we’ll want a spot where we can answer the most questions in a very short amount of time. But since we’ll be sending the probe and the lander at the same time, we won’t have much time to find a promising place to land. What will probably happen is that, for the first few months or years of the mission, Clipper will scout out the surface until scientists find a good site, and then release the lander.

But another issue is: landers are heavy. The Space Launch System is designed to carry huge payloads -- up to 70 metric tons -- into low Earth orbit. But the SLS can only send a small amount of stuff on a fast-track straight to Jupiter. When you take into account all the fuel that Clipper’s going to need to help it make a soft landing, that’ll add about 8,000 kilograms to the mission. So the heavier probe-lander combo will have to take a slower route, using some of the inner planets to slingshot its way into Jupiter’s orbit. In the end, Congress has given NASA a challenge -- a big one. But we can do it! We can get to Europa, and land a probe on its crazy, frozen surface. And we’ll learn a whole lot about the moon no matter what happens. But when it comes to how they science up a solution to this challenge, NASA definitely has their work cut out for them.

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