We're Going Back to Mars But We Will Not Be Landing a Spaceship Boat on Saturn's Moon

With Curiosity just starting to move around, NASA has already announced its next mission. We're going back to Mars in 2016 with a lander designed to drill into the core and give scientists some insight into the planet's formation. Fittingly, the mission is called InSight. The main question on deck is why Mars evolved so differently from the other terrestrial planets, namely Earth. Unfortunately, InSight's selection has also stopped our pursuit of other interesting questions in our solar system.

InSight was selected as part of NASA's Discovery program that has been funding focused missions under a fixed budget since 1992. The idea is to send more missions more often without seeing cost overruns at every turn. That means Discovery missions aren't flagship missions like the Mars Science Laboratory rover Curiosity that just landed on the red planet a couple of weeks ago. For the time being, InSight is capped at just $425 million. This budget means smaller missions that typically focus on achieving one goal or answering one question.

In the case of InSight, the question is about Mars' interior structure and core – the things we can't see from orbit. These questions are interesting in the case of Mars precisely because of what we can see from orbit. NASA's Mars Reconnaissance Orbiter has seen landslides on Mars. These could be due to melting ice or earthquakes, or they could be due to a release of inorganically derived methane escaping from the planet's molten core. There's no way to conclusively explain these landslides without looking inside the planet.

To see inside Mars, InSight will use a sort of drill, a long probe that will vibrate its way a few meters into the soil. At the same time, a robotic arm will take a seismometer from the lander's platform and deposit it on the surface to make measurements. This will be the first seismic data since 1976; two seismometers on the twin Viking landers both failed to return good data. It will help scientists answer another pressing question about Mars: why doesn't the planet have the same plates tectonic that have shaped our own? Is Mars an active planet or completely dead?

This mission will go a long way in helping us understand the role geology has played in Mars past habitability. If, of course, it was a habitable planet in the past; chemical evidence of past habitability is Curiosity's main mission.

Our general fascination with Mars played a big part in InSight's selection, but it wasn't the only factor. InSight will reuse the basic lander structure and some hardware that was sent to Mars on the Phoenix mission. Using proven hardware helped the team keep costs within the strict budgetary limits, and it was exactly the risk of using unproven technology that gave InSight the edge over its competitors. InSight beat a comet hopper mission and a sailing probe on Saturn's moon Titan.

The comet hopper, called CHopper, is a dual purpose lander and orbiter probe. Had it been selected, it would have launched in 2015 and spent two and a half years flying to comet 46P/Wirtanen. Once there, it would have settled on the surface for a brief stay, then launched into orbit around the comet before settling on its surface again. It would have go on like this, hopping around the comet, throughout the mission. In orbit it would have mapped the surface and watched for changes in the comet's activity as it approaches perihelion at a distance just outside the Earth's orbit.

During its brief stays on the comet's surface, CHopper would used it's proposed imager and infrared spectrometer to map the shape and composition of the surface. Also on the proposed instrument list were panoramic cameras and a heating experiment.

The sailing probe, the Titan Mare Explorer or TiME, was, well, a proposal for a probe to set sail on the methane seas on an outer moon. Do I need to explain how amazing a mission this would have been? I'm biased; I love Titan and have been hooping to see this mission fly for a while.

Titan is an interesting destination not because it's thought to hold life but because its methane rich environment has a lot of the chemicals that were abundant on the early Earth when life formed. It's a trait that has led some scientists to label the moon a pre-biotic world. The big question on Titan is about these chemicals and the vast oceans of frozen water – surface temperatures on Titan are in the -290ºF range. Could the chemical processes leading to life get started in this environment or is it just too cold? Another big question is about the moon's methane cycle. It's similar to Earth's water cycle, and studying how it plays out on another planet could teach us a lot about our own.

The TiME mission would have sent a boat-like probe into the cryogenic seas of Titan by parachute for a 96-day mission. Floating like a buoy and drifting around the seas, propelled by the winds and waves, TiME would have identified and studied the moon’s complex organic molecules and detailed its chemistry. It would have also taken a camera along to take pictures of the surface. Scientists expect we might see surface ripples, bubbles, and films set against the organ Titanic sky.

The mission would have launched sometime between 2016 and 2018, the best window for arrival on Titan before its north pole plunged into winter and out of direct radio contact with Earth. Once Earth sets below the horizon, the mission would need a communications relay satellite. That drives up the over all cost, making the mission harder to fit within the Discovery class.

The final decision came down to a return on investment. InSight promised the best return with minimum risk. We know a lot more about landing and working on Mars than we do about landing on Titan or comets. We also know more about Mars than Titan or comets. It would have been spectacular to further our knowledge of different bodies on the solar system. But it certainly won't hurt to learn more about one of our neighbours and, by extension, our own planet.