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Caitlin: When your lander leaves a crater on Mars, you might need to change things the next time around. In October, the first mission of the ExoMars program arrived at the Red Planet, and things didn’t go exactly as planned. The mission is a joint project between the European Space Agency and Roscosmos, the Russian space agency, and it had two parts: an orbiter and a lander.

The plan was for the Trace Gas Orbiter, or TGO, to orbit Mars and search for methane — a possible byproduct of life — in its atmosphere. Then, while the TGO was in orbit, the Schiaparelli lander would land on the planet’s surface to test out technology for the second ExoMars mission: a rover, which is set to launch in 2020.

The good news is that the TGO is still orbiting Mars, and everything is going well! Unfortunately, the lander had a rougher time. With only 50 seconds until landing, we lost contact with it... and then it crashed into the surface. Right after the crash, we knew the parachutes had deployed early and that there were issues with the thrusters, but we didn’t know what caused them. But now, thanks to data the lander sent to the TGO while it was descending, we think we know what went wrong!

Even though it was still way above the surface, apparently Schiaparelli thought it was underground. The problem was caused by software issues and problems merging the data from different sensors. First, just after the parachute was deployed, the Inertial Measurement Unit, which measures the rotation rates of the lander, maxed out. It measured the highest possible reading it could, which it shouldn’t have. Then, when that bad data was merged into the navigation system, it caused the computer to calculate that the lander had a negative altitude — in other words, that it was underground.

In reality, the lander was about 3.7 kilometers above the surface. Thinking it had missed a bunch of landing procedures, the computer basically freaked out. The parachute was ejected early, and then the thrusters — which were supposed to fire for 30 seconds to slow the lander down — only fired for three seconds. Schiaparelli even switched on its instruments, all ready to take readings about Mars’ weather and magnetic field! Unfortunately, we got a crater instead. The lander crashed into the ground at over 300 kilometers an hour.

This is only a preliminary analysis, and the investigation won’t officially finish until early next year. But it seems pretty clear what happened. The 2020 ExoMars rover will use a lot of the same software as the lander, so it’s especially important to make sure whatever happened with Schiaparelli is fixed before launch.

Thankfully, as far as spacecraft problems go, software issues are pretty easy to solve. So hopefully, in about four years, the ESA’s first rover will be on Mars! During its descent, Schiaparelli sent back information about processes like deceleration and parachute deployment that will help the rover, and TGO is still alive and well in orbit around Mars. So despite the crash, the first part of the ExoMars mission was a success.

Meanwhile, while one mission is starting, another is ending. After almost 20 years, the Cassini probe is getting ready to finish its mission to investigate Saturn and its moons! Way back in 1997, Cassini launched from Cape Canaveral, Florida, and it arrived at Saturn seven years later in 2004. Since then, it’s returned thousands of images, dropped the Huygens probe onto Saturn’s moon Titan, found evidence of an ocean on Enceladus, and more.

Now, the probe is running out of fuel, and it’s time to say goodbye. On Wednesday, Cassini began the first part of its Grand Finale - what NASA is calling its “Ring-Grazing Orbits.” From now until the end of April, the spacecraft will dive through Saturn’s rings 20 times and collect particles and gases, which will help us learn more about what the rings are made of.

It will start by skimming through some of the faint outer rings before moving closer to Saturn, passing through the main ring system and getting only 90,000 kilometers away from the planet’s cloud tops. Along the way, it will take the most comprehensive, detailed scans of the rings’ structure ever. And while it’s exploring the rings, Cassini will also get our best look at some of Saturn’s smaller moons, like Atlas and Pandora.

They have average radii only of about 15 and 40 kilometers, respectively, so it’s almost impossible to observe them using telescopes on or near Earth. But after this part of the mission ends in April, the real Grand Finale starts, and it’s time to say goodbye to Cassini! The probe will sling around Saturn’s moon Titan to start 22 more dives between Saturn and its rings, getting as close as 1628 kilometers away from the cloud tops. Then, on September 15th, it will make the final dive into Saturn’s atmosphere.

On the way down, it will learn about the planet’s atmosphere, gravity, and composition, sending back the last bit of science before it finally falls silent. Right up until the very end, Cassini will be delivering our best information about Saturn yet. We’ll miss you, little spacecraft!

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