NASA decides to send robotic seismologist to Mars

[Nipuna]

Peter Aldhous, San Francisco bureau chief

Do Marsquakes rock the Red Planet? How big is its core? These and other questions should be answered by the next mission in NASA's Discovery programme, which aims to put top-quality science into space on a shoestring budget - in relative terms, at least.

The $425 million InSight mission, to be run from NASA's Jet Propulsion Laboratory in Pasadena, California, was chosen today as the next Discovery-class mission - edging out competing proposals to float a craft on a sea of methane and ethane on Saturn's moon Titan, and to land repeatedly on a comet.

Previous Discovery missions include Dawn, which after a rendezvous with the asteroid Vesta is now heading for the dwarf planet Ceres, and Kepler, a space telescope that has bagged an impressive haul of new extrasolar planets.

Based on the same lander used for the earlier Phoenix mission, which studied water ice in the Martian Arctic, InSight will instead be sent to near the planet's equator, arriving in September 2016.

It will carry three main instruments, including a seismometer called SEIS that will be placed onto the planet's surface. A previous attempt to record seismic activity on Mars, during the 1976 Viking 2 mission, failed because the seismometer was on the lander's legs, where it was buffeted by wind.

A probe called HP3, meanwhile, will burrow about 5 metres down into the surface, recording flows of heat from the planet's interior. Back on the lander, an instrument called RISE will measure the planet's wobbles on its axis in response to the Sun's gravity by measuring the Doppler shift of radio communications with Earth.

Putting these measurements together should provide a better picture of how Mars formed and has evolved, and reveal the current behaviour of its internal structures. For example, project scientists hope to discover the cause of landslides that have been spotted from space. Asks Jim Green, NASA's director of planetary science: "Are those occurring because of quakes, or melting?"

The decision to go with InSight over the Titan Mare Explorer will leave NASA without a craft studying the outer solar system from 2017, when the Cassini orbiter is due to crash into Saturn's atmosphere.

According to NASA science chief John Grunsfeld, in scientific terms there was little to choose between InSight and its two rivals. However, the Mars mission looked like a surer bet to stick within its budget. In the current fiscal environment, preventing cost overruns is crucial, Grunsfeld told reporters in a teleconference to announce the decision: "Otherwise, the Discovery programme gets stretched out and there are fewer opportunities."