InSight’s heat probe will dig 16 feet beneath the surface of Mars

Having placed its seismometer onto the Martian surface and covered it with a heat shield to keep it safe, NASA’s InSight mission has moved on to deploying its second instrument. New images from the lander have confirmed that on February 12, InSight succeeded in setting the Heat Flow and Physical Properties Package (HP3) instrument onto the surface.

The HP3 is equipped with a scary-sounding “self-hammering spike” which will delve up to 16 feet down into the soil and rock below the planet’s surface. This is considerably deeper than previous missions to Mars, which dug 8.6 inches down in the case of Viking 1m and 7 inches down in the case of Phoenix. The HP3 achieves this using a long vertical metal tube which contains a sharp spike called a mole which will be pushed into the soil. The cord which attaches to the mole has heat sensors to measure the temperature of the subsurface, and the mole itself has sensors to measure the thermal conductivity of the soil.

InSight will use this instrument to learn about temperatures on Mars by measuring thermal conductivity every 19 inches as the probe moves beneath the ground. Because of heat from friction caused by the drilling, the probe has to pause and cool down for a couple of days before a measurement can be taken. Once it is at a stable temperature, the probe is gradually warmed up to 50 degrees Fahrenheit (10 degrees Celsius) over the course of a day, and the temperature sensors measure how long it takes for the soil to conduct that heat.

“Our probe is designed to measure heat coming from the inside of Mars,” InSight Deputy Principal Investigator Sue Smrekar of NASA’s Jet Propulsion Laboratory in Pasadena, California said in a statement. “That’s why we want to get it below ground. Temperature changes on the surface, both from the seasons and the day-night cycle, could add ‘noise’ to our data.”

The biggest problem that could arise is that the mole could hit a rock beneath the surface which would prevent it from being able to burrow deep enough. If there is a rock at less than 10 feet (3 meters) down then there will be considerable noise in the temperature data which would take several years to filter out. But the researchers are optimistic that this will not happen, as the landing site had no surface rocks so hopefully there won’t be large rocks beneath.