It was a task that required centimetre precision. Over the last few weeks, researchers from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) have measured every rock shown in the images of the InSight landing site and used the radiometer that is part of the Heat Flow and Physical Properties Package (HP³) experiment to analyse the dust on the surface of Mars, in order to determine the ideal point for deploying the InSight mission's instruments. This work has been performed in cooperation with colleagues from the United States and France. Scientists at the Jet Propulsion Laboratory (JPL) in California have created an accurate laboratory simulation of InSight's surrounding area based on the analysis, and have tested the deployment manoeuvres using a replica of the NASA lander. Now that the seismometer has been successfully positioned in front of the lander, exploration of the Martian interior has begun. The Mars mole, which was developed by DLR, will be positioned approximately one metre to the east of the seismometer in late January 2019. A four-person team from DLR's Microgravity User Support Center (MUSC) in Cologne will remain in California over Christmas and New Year to control and monitor the HP3 experiment.
"We are very happy with InSight's flat and sandy landing site," says Tilman Spohn, Principal Investigator for the HP3 experiment, from the DLR Institute of Planetary Research in Berlin. "Following intensive analysis of the geological conditions, with major contributions from many DLR researchers on the HP3 team, we can finally breathe a sigh of relief. As there are no large rocks within the working area of the robotic arm, or fragments that suggest the presence of large rocks beneath the surface, we found selecting a place to set HP3 down much easier than we expected." This point is around 1.6 metres from the lander, as far away as possible. This prevents shadows that would interfere with the temperature measurements conducted by HP3.
When selecting and testing potential deployment locations, the researchers had to ensure that the sensitive tether connecting the instruments on the ground to the lander would not get caught or rub on sharp edges. The even, largely rock-free surface proved helpful in this respect. "We think that InSight landed in a sand-filled meteorite crater on 26 November 2018," says HP3 scientist Matthias Grott, explaining the geological conditions. "This should make it easier for the Mars mole to penetrate up to five metres deep in order to measure temperature and heat flow." The scientists are looking forward to late January, when they will discover the conditions that the Mars mole finds beneath the planet's surface. "We have seen some large stones beneath the lander, which may, of course, go deeper," says the DLR planetary researcher, explaining why there is still a certain amount of trepidation.
Christmas in California and warming up in the minus 90-degrees-Celsius Martian night
At present, the HP3 instrument is still on the InSight lander's platform. The scientists have already started operating the experiment's radiometer, measuring the surface temperature on Mars, among other readings. This will later be compared with the temperature measurements conducted by the mole underground. "We are currently calibrating our 'Mars thermometer', and initial data shows that, as expected, nights are very cold at the landing site on the Elysium Planitia plain, at around minus 90 degrees Celsius. During the day, the uppermost layer of sand reaches approximately 15 degrees Celsius in the midday sun," says HP3 Operations Manager Christian Krause from DLR MUSC. "Over the New Year, we will continue to make further preparations for the deployment of HP3. We are carrying out test runs for preheating the mole's motor and the cable for suspending the instrument. We will take a short break on Christmas Eve and Christmas Day, but then we will go straight back to work."
At the end of January 2019, the operations team under Christian Krause will command the hammering of the mole into the Martian soil, which is expected to take several weeks. Once the target depth has been reached, the temperature and heat flow data will be received and processed at the DLR control centre in Cologne and then evaluated by scientists at the DLR Institute of Planetary Research. The temperature sensors will provide data about the temperature gradient in the subsurface for a total of two years. Together with thermal conductivity, researchers will be able to calculate how much heat is still being emitted from the Martian interior and draw conclusions about how the interior of Mars formed, how active it is today, whether it still has a hot liquid core, and what sets the Earth apart from Mars.
Putting the SEIS seismometer into operation
Before this, however, the Seismic Experiment for Interior Structure (SEIS), a seismometer designed and constructed under the leadership of the Centre national d'études spatiales (CNES), the French space agency, was successfully deployed from the lander on the morning of 20 December 2018 (CET). The first images show the instrument in position exactly 1.64 metres in front of the lander. "The seismometer will allow us to study ground movements of the Red Planet caused by marsquakes or meteorite impacts in detail," says DLR planetary researcher Martin Knapmeyer, who is involved in the SEIS experiment. "By analysing how seismic waves travel through the different layers of the planet, we seismologists are able to deduce the depth of these layers and establish what they are made of, similar to a medical ultrasound scan." After the first tests in January, a windproof and temperature-sensing cover will be placed over SEIS to protect its sensitive sensors from disturbances caused by wind or temperature variations.
The HP3 instrument on the NASA InSight mission
The InSight mission is being conducted by JPL in Pasadena, California, on behalf of NASA’s Science Mission Directorate. The InSight mission is part of the NASA Discovery programme. DLR has contributed to the mission with its HP3 experiment. The DLR Institute of Planetary Research, which was responsible for developing the experiment in collaboration with the DLR Institutes of Space Systems, Optical Sensor Systems, Space Operations and Astronaut Training, Composite Structures and Adaptive Systems, System Dynamics and Control, and Robotics and Mechatronics, is directing the experiment. The following industry partners are also involved: Astronika (Poland) and the CBK Space Research Centre (Poland), Magson (Germany) and Sonaca (Belgium), and Astro- und Feinwerktechnik Adlershof GmbH (Germany). The Space Research Institute at the Austrian Academy of Science and the University of Kaiserslautern are scientific partners in the project. The DLR MUSC operates HP3. In addition, the DLR Space Administration has used funding from the German Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie; BMWi) to support the contribution of the Max Planck Institute for Solar System Research to the SEIS instrument.
Detailed information about the InSight mission and the HP3 experiment can be found on DLR's special mission site, which has in-depth background articles, as well as in the mission booklet, and on DLR's Twitter channels.