14. January 2021
InSight mission – exploring the interior of Mars

The Mars 'Mole' has reached the end of its jour­ney

HP3 on the Martian surface
HP3 on the Mar­tian sur­face
Image 1/6, Credit: NASA/JPL-Caltech/DLR

HP3 on the Martian surface

DLR’s HP3 Mars ‘Mole’ on the Mar­tian sur­face, af­ter be­ing re­leased by the robot­ic arm of the In­Sight lan­der.
Artist’s impression of the NASA InSight lander on the Martian surface
Artist’s im­pres­sion of the NASA In­Sight lan­der on the Mar­tian sur­face
Image 2/6, Credit: NASA/JPL-Caltech

Artist’s impression of the NASA InSight lander on the Martian surface

Launched on 5 May 2018, NASA’s In­Sight space­craft land­ed on 26 Novem­ber 2018 just north of the Mar­tian equa­tor, and de­ploy its so­lar pan­els. SEIS, an in­stru­ment for record­ing seis­mic waves (left of im­age), and HP3, an in­stru­ment de­vel­oped by DLR to mea­sure the ther­mal con­duc­tiv­i­ty of the Mar­tian re­golith and the heat flow from the in­te­ri­or of the plan­et (right of im­age), have been placed on the plan­et's sur­face.
DLR Mars 'Mole' after having moved backwards
DLR Mars 'Mole' af­ter hav­ing moved back­wards
Image 3/6, Credit: NASA/JPL

DLR Mars 'Mole' after having moved backwards

This overview im­age shows al­most half the length of the DLR Mars Mole pro­trud­ing from the re­golith af­ter its sur­pris­ing back­ward move­ment in au­tumn 2019.
Video: In­Sight's arm cam­era stares in­to the pit
Video 4/6, Credit: NASA/JPL-Caltech

Video: InSight's arm camera stares into the pit

Credit: NASA/JPL-Caltech
Length: 00:00:07
The shad­ow of NASA In­Sight's robot­ic arm moves over DLR’s heat probe, or 'Mole', on 3 Novem­ber 2019, the 333rd Mar­tian day, or sol, of the mis­sion.
The HP3 experiment
The HP3 ex­per­i­ment
Image 5/6, Credit: NASA / JPL-Caltech

The HP3 experiment

The Ger­man Aerospace Cen­ter (Deutsches Zen­trum für Luft- und Raum­fahrt; DLR) con­tribut­ed the HP3 ex­per­i­ment for NASA's In­Sight mis­sion. HP3 stands for ‘Heat Flow and Phys­i­cal Prop­er­ties Pack­age’; it was de­vel­oped pri­mar­i­ly at the DLR In­sti­tute of Plan­e­tary Re­search. A pen­etrom­e­ter ca­pa­ble of ham­mer­ing it­self five me­tres deep in­to the Mar­tian sub­sur­face was in­tend­ed to mea­sure the ther­mal con­duc­tiv­i­ty of the soil be­neath the land­ing site and de­ter­mine the amount of heat flow­ing from the in­te­ri­or of Mars to the sur­face. The ex­per­i­ment was de­signed to run for two years. The main com­po­nents of HP3 are the 'Mole' and a rib­bon ca­ble fit­ted with tem­per­a­ture sen­sors, which the Mole was de­signed to pull be­hind it in­to the sub­sur­face.
Testing the InSight arm, as it presses onto soil in the laboratory
Test­ing the In­Sight arm, as it press­es on­to soil in the lab­o­ra­to­ry
Image 6/6, Credit: NASA/JPL-Caltech

Testing the InSight arm, as it presses onto soil in the laboratory

In a JPL lab­o­ra­to­ry, a test mod­el of the In­Sight robot­ic arm push­es its scoop against the sur­face near the test mod­el of the self-ham­mer­ing Mars ‘Mole’. DLR re­searchers had hoped that this type of pres­sure on the Mar­tian soil would help the ‘Mole’ to dig, as it in­creas­es the fric­tion from the sur­round­ing soil.
  • Even backfilling with Martian soil could not help the heat-flow sensor to dig any deeper.
  • Five hundred final blows of the hammer did not result in any visible progress.
  • The InSight mission is continuing with other experiments.
  • Focus: Space, Mars, exploration

For two years, the Mars 'Mole' has endeavoured to dig ever deeper into the Martian soil. Now its journey has come to an end. Until recently, scientists and engineers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and the Jet Propulsion Laboratory (JPL) had been working to get the mole to dig to a target depth of five metres. The DLR Mole, which travelled to Mars on board the NASA InSight lander, was designed to measure temperature and heat flow beneath the surface of Mars. In recent months, the InSight team at JPL in Pasadena, California, used InSight's robotic arm to get the Mole back beneath the surface and backfill the cavities beside it with Martian soil. It was thought that the additional lateral friction would allow the Mole to advance further. Unfortunately, despite careful preparations, another 500 hammer blows conducted on Saturday 9 January did not result in any visible progress.

The Mole is part of the Heat Flow and Physical Properties Package (HP3) experiment. It is essentially a 40-centimetre-long penetrometer – like a self-hammering nail – with a diameter of 2.7 centimetres. It was designed to pull a ribbon cable fitted with temperature sensors behind it. These sensors were intended to measure heat flowing from the interior of the planet to the surface. To do this, the Mole needed to burrow to a depth of at least three metres. Almost two years ago, on 28 February 2019, having been set down on the Martian soil, the Mole was activated for the first time within its housing, and began to hammer its way underground.

Almost two years of running through every possible option

"We did absolutely everything that we could, but Mars and our plucky Mole were simply not a good fit," says Tilman Spohn of the DLR Institute of Planetary Research. Spohn is the Principal Investigator for the HP3 experiment, which was developed by DLR and various partners. He is now also the Executive Director of the International Space Science Institute in Bern, Switzerland. “Fortunately, we have gained a lot of experience that can help future Mars missions get beneath the surface," says Spohn. Interest in exploring the planet's subsurface remains high. Due to harmful aspects of solar radiation, very little of which is filtered out by the thin Martian atmosphere, the surface of the planet is rather inhospitable for potential lifeforms. However, suspecting that microbial life may be viable in the subsurface, researchers believe that life could once have been present on Mars and may even exist there today.

To find out how the robotic arm of the InSight lander could help the Mole dig, JPL – which is conducting the InSight mission on behalf of NASA – carried out numerous experiments in its 'Indoor Mars Yard'. Among other findings, the researchers established how the scoop on the robotic arm could apply pressure to and alongside the Mole. "The Mole was developed based on soil analysis by NASA rovers such as Spirit and Opportunity," says JPL scientist Troy Hudson. "But after the landing, we found that the soil in this area is completely different to anything that we have seen before." The DLR Test Laboratory in Bremen also conducted research into the reasons why the Mole had come to a standstill.

Ongoing measurements by parts of the experiment

"Given the many years of planning, development and construction that have gone into our heat-flow experiment, we are naturally disappointed that not all of HP3's components are working as we had expected," says Professor Heike Rauer, Director of the DLR Institute of Planetary Research in Berlin-Adlershof. "However, HP3 will at least be able to provide us with temperature measurements from the top layer of the Martian surface. While this is not all that we had been hoping for, it will nevertheless help us to gain new knowledge about Mars. This planet remains a difficult neighbour to explore. We will continue trying to unlock the mysteries of Mars, so as to find out whether life ever actually existed there. The next experiments are already being developed."

HP3 is one of several scientific experiments on board the InSight lander, which recently had its mission extended by two years to December 2022. Another experiment is the French seismometer SEIS, which continues to record Marsquakes and local tremors caused by atmospheric phenomena. Furthermore, a radio wave experiment is collecting data about the position and orientation of the planet's axis of rotation to provide insights into whether the core of Mars is liquid or solid. At the same time, weather sensors provide detailed meteorological data. HP3 will now continue as a partial experiment.

Exploring the inside of Mars

You can find more details about the InSight mission and the HP3 experiment on DLR's special mission site, which has in-depth background articles, as well as by searching the hashtag #MarsMaulwurf, which was used on the DLR Twitter channel. Professor Tilman Spohn also reported on the activities of the Mars Mole in his blog posts.

Contact
  • Andreas Schütz
    DLR Spokesper­son, Head of Me­dia Re­la­tions
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 2203 601-2474
    Fax: +49 2203 601-3249
    Linder Höhe
    51147 Cologne
    Contact
  • Katja Lenz
    Ed­i­tor
    Ger­man Aerospace Cen­ter (DLR)
    Me­dia Re­la­tions
    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 2203 601-5401
    Linder Höhe
    51147 Cologne
    Contact
  • Ulrich Köhler
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin
    Contact
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