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Mars ‘Mole’ takes a break

(5 March 2019 - DLR) As part of NASA’s InSight mission, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) developed a penetrometer designed to dig three to five metres below the surface of Mars and measure the heat emanating from the planet’s interior.

After the Mars ‘Mole’ began hammering into the ground on Thursday 28 February, the probe, which is part of DLR’s HP3 (Heat and Physical Properties Package) instrument, came about three-quarters of the way out of its housing structure before stopping. Data also suggests that the 'Mole' is at a 15-degree tilt.

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The housing of the HP3 experiment moved slightly during hammering (courtesy: NASA/JPL-Caltech/DLR)

“The team has therefore decided to pause the hammering for about two weeks to allow the situation to be analysed more closely and jointly come up with strategies for overcoming the obstacle,” writes Tilman Spohn of the DLR Institute of Planetary Research, Principal Investigator of the HP3 experiment, on his InSight mission blog. The researchers suspect that the Mole has hit a rock or some gravel. The team had hoped that there would be relatively few rocks beneath the soil, as images of the landing site show only a few on the surface near the landing module. In principle, the Mars Mole has been designed to push smaller stones aside, and proved capable of such a feat in tests conducted before it was launched for Mars.

All of the data received show that the Mole is continuing to work as expected: after heating up by 28 degrees Celsius during the hammering process, it measured how quickly heat dissipated into the soil as it cooled down. This property, known as thermal conductivity, helps to determine the heat flow from deep inside the planet. Once the Mole is deep enough, it will be possible to calculate the heat flow with greater accuracy.

The researchers will carry out more measurements this week in order to gauge the thermal conductivity of the upper layer of the Martian soil (regolith) more precisely. In addition, the radiometer on InSight’s deck will be used to analyse temperature changes in the soil caused as Phobos, one of Mars’ moons, moves in front of the Sun. Phobos’ shadow will cross the radiometer’s field of view three times this week, rather like an eclipse of the Sun on Earth, and the instrument will measure the result.

The InSight mission is being carried out by NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, on behalf of the agency’s Science Mission Directorate. InSight is part of NASA’s Discovery Program. DLR is contributing the Heat Flow and Physical Properties Package (HP³) experiment to the mission. The scientific leadership lies with the DLR Institute of Planetary Research, which was also in charge of developing and implementing the experiment in collaboration with the DLR Institutes of Space Systems, Optical Sensor Systems, Space Operations and Atronaut Training, Composite Structures and Adaptive Systems, and System Dynamics and Control, as well as the Institute of Robotics and Mechatronics. Participating industrial partners are Astronika and the CBK Space Research Centre, Magson GmbH and Sonaca SA, the Leibniz Institute of Photonic Technology (IPHT) as well as Astro- und Feinwerktechnik Adlershof GmbH. Scientific partners are the ÖAW Space Research Institute at the Austrian Academy of Sciences and the University of Kaiserslautern. The DLR Microgravity User Support Center (MUSC) in Cologne is responsible for HP³ operations. In addition, the DLR Space Administration, with funding from the German Federal Ministry for Economic Affairs and Energy, supported a contribution by the Max Planck Institute for Solar System Research to the French main instrument SEIS (Seismic Experiment for Interior Structure).