InSight’s Instrument Deployment Camera (IDC) acquired this image of the HP3 experiment on Sol 99, March 8, 2019.
Credit: NASA/JPL-Caltech

Mixed news from the “mole” probe onboard NASA’s Mars InSight – part of Germany’s HP3 (Heat and Physical Properties Package) instrument.

It began hammering into the surface of Mars on February 28. However, the device may have come up against a rock or something else that is proving highly resistant beneath the surface. The researchers are now analyzing the data before it can continue hammering.

InSight’s Instrument Deployment Camera (IDC) acquired this image showing the HP3 experiment and SEIS seismometer (Seismic Experiment for Interior Structures) on Sol 99, March 8, 2019.
Credit: NASA/JPL-Caltech

The mole had come about three-quarters of the way out of its housing structure before stopping. Data also suggests that the device is at a 15-degree tilt.

Pause the hammering

“The team has therefore decided to pause the hammering for about two weeks to allow the situation to be analyzed more closely and jointly come up with strategies for overcoming the obstacle,” explains Tilman Spohn of the  German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Institute of Planetary Research and principal investigator of the HP3 experiment.

The HP3 team has commanded a large number of images to be taken by the cameras on the InSight lander and its robotic arm.

Play it safe

“Some of the images we already have, indicate that part of the mole is actually visible,” Spohn reports. “The consensus is that the mole is about 30 centimeters in the regolith and probably still 7 centimeters in the tube of the support structure. It is approximately pointing 15° away from the vertical and has undergone either some rotation or precession of its rotation axis.”

The instrument remains healthy. But the team wants to play it safe and get all the evidence that could become available including seismic data together to assist the mole overcome the obstacle (or to get through a possible layer of gravel). “Once we have all the data, we will decide on how to proceed best,” Spohn explains.

Components of the HP3 heat flow probe. Top left: the radiometer (RAD), which is used to measure the radiation temperature (roughly equivalent to the ground temperature) of the surface. Right: the casing with the mole penetrometer, the temperature measuring cable (TEM-P) and the data cable (ET) connected to the lander. In addition, the casing contains an optical length meter for determining the length of the temperature measuring cable that has been pulled from the casing. The mole contains the TEM-A active thermal conductivity sensor and the STATIL tiltmeter. Bottom left: the electronic control unit, known as the back end electronics (BEE), which remains on the lander and is connected to the probe via the ET.
Credit: DLR


Design heritage

The mole penetrometer was developed at the DLR Institute of Space Systems. It draws upon earlier developments at DLR and in Russia. An earlier version of the probe was built at the former DLR Institute of Space Simulation in Cologne as a sample collector for the Beagle II lander – flown as part of the Mars Express mission – which crashed onto the Martian surface in 2003. The hammering mechanism for the HP3 mole was developed by Astronika in Warsaw, Poland.



Phobos eclipse

Meanwhile, Spohn says there’s excellent news concerning the Mars moon, Phobos.

“We just got the data from the first Phobos eclipse observation and the cooling by the shadow passing through the fields of view of the radiometer in about 30 seconds is clearly visible,” Spohn notes. “So the team is happy and is rejoicing about the first eclipse on Mars ever observed with a radiometer.”

Set of three images shows views three seconds apart as the larger of Mars’ two moons, Phobos, passed directly in front of the sun as seen by NASA’s Mars rover Curiosity on Aug. 20, 2013.
Credit: NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M Univ.

The Radiometer (RAD) is mounted underneath the platform of the lander and monitors the area beside the lander where HP3 is installed.

The team will analyze the RAD data and come up with a model of the uppermost millimeters or so of the Mars surface material. This measurement is called the thermal inertia. This quantity depends on the thermal conductivity of the near surface material, its density and its heat capacity.

“So, it is part of our efforts to measure the geophysical parameters of Mars,” Spohn says.

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