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Heat Flow and Physical Properties Probe (HP3)

NSSDCA ID: 2018-042A-02

Mission Name: InSight
Principal Investigator:Dr. Tilmann Spohn


The Heat Flow and Physical Properties Probe (HP3) instrument is designed to constrain models of the thermal state of the martian interior by measuring the thermal gradient and thermal conductivity of the regolith, giving an estimate of the surface heat flow at the lander location. It also includes a radiometer (RAD) that measures surface temperatures and thermal properties.

The HPS consists of a tether with a mole at one end. The mole is a 40-cm tube with a self-contained electro-mechanical hammering system designed to penetrate up to 5 meters into the martian regolith, pulling the tether behind it. The tether holds platinum resistance temperature detectors along its length, which will measure the subsurface temperature with a resolution of 35 cm. The mole will act as a heat source, measurements of the temperature with time will allow determination of the thermal conductivity. Tiltmeters in the tether will be used to determine the attitude of the probes in the ground. Total mass of the instrument is about 3 kg, using a maximum of 2 W power while hammering.

The HP3 was be deployed on the surface using the 2.4 meter long robotic arm within 30 sols (martian days) of landing, situated a distance from the lander to minimize effects of the lander shadowing the surface. The HP3 mole began its hammering cycle, planned to bring it initially 50 cm into the regolith, but the mole was unable to penetrate to the desired depth. After exhausting all available options, it was announced on 14 January 2021 that the efforts to burrow deeper into the surface were terminated. The cause of the failure to reach the required depths is not known.

The original plan, after reaching 50 cm depth, called for 48 hours of heat dissipation and 24 hours of thermal conductivity measurements. The mole would then hammer another 50 cm and the procedure repeated until a depth of 5 m was reached or the mole could not penetrate any further. Long term monitoring was to begin with measurements every hour until the end of the mission.

Alternate Names

  • INSIGHT/HeatFlowandPhysicalPropertiesProbe(HP3)
  • Mole
  • urn:nasa:pds:context:instrument:hp3.insight
  • urn:nasa:pds:context:instrument:radiometer.insight

Facts in Brief

Mass: 3 kg
Power (avg): 2 W


  • Planetary Science: Geology and Geophysics

Additional Information

Questions and comments about this experiment can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Dr. Tilmann SpohnPrincipal InvestigatorUniversitat

Selected References

  • Spohn, T., et al., The Heat Flow and Physical Properties Package (HP3) for the InSight Mission, Space Sci. Rev., 214, 96, doi:10.1007/s11214-018-0531-4, 2018.
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