Alien Landers: Extreme Explorers Hall of Fame

Three European Space Agency (ESA) missions are due to send down robotic ‘spaceprobes’ when they arrive at their alien destinations. Since these craft will be going where no one has gone before, how can scientists be sure what it will be like down there? How do you ensure that your spaceprobe is prepared for anything?

Extreme Explorers' Hall of Fame
This artist’s impression shows the Rosetta Lander anchored to the comet’s surface with instruments, legs and solar panels. Credit: ESA 2001. Illustration by Medialab

Experts take every precaution to ensure that these probes will not burn up entering an alien atmosphere, or meet a spectacular, untimely end via a crash landing on inhospitable terrain. These probes expect the worst. For example, the Huygens probe, which is currently on its journey to Titan, Saturn’s largest moon, on-board the Cassini spacecraft, can withstand temperatures of up to 18 000°C in the shockwave in front of the heat shield. This is about three times the Sun’s surface temperature. Why? The heat generated as Huygens travels through Titan’s thick atmosphere will be immense.

Jean-Pierre Lebreton, Huygens Project Scientist, says "Things will get interesting once Cassini draws close to Saturn. We’ll get the best views of Saturn and Titan that we ever had. We’ll also observe Titan to verify that our models are correct. If we find the atmospheric density is different from what we expected, we could consider slightly changing the angle at which Huygens enters to protect it from overheating or the parachute deploying wrongly. However, late changes may bring new risks."


Extreme Explorers' Hall of Fame
Huygens parachutes onto Titan. ESA’s Huygens probe descends through Titan’s mysterious atmosphere to unveil the hidden surface (artist’s impression) Credit: ESA


Scientists designed Rosetta’s landing gear to cope with most nasty surprises as soon as it touches down on Comet Wirtanen in 2011. Two harpoons will anchor the probe to the surface. The self-adjusting landing gear will ensure that it stays upright, even on a slope. The lander’s feet will drill into the ground. These devices will help counteract the fact that there is no gravity on a comet.

What’s Next

Observations of Mars, Titan, and Comet Wirtanen will continue frantically while the spacecrafts approach their final destination. In this way, scientists will be able to make last-minute adjustments to the timing of the landing. Information from other space missions and ground-based observations will increase scientists’ understanding about the targets of the missions. In Rosetta’s case, this will help to determine the comet’s probable size and speed of rotation. These will help improve our ‘models’ for comet behaviour. However, for Rosetta, they may come too late. "We’ll just have to see if the models we’re using are good enough" says Schwehm.

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