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NASA’s InSight Has a Thermometer for Mars

Ambitious climbers, forget Mt. Everest. Dream about Mars.

The Red Planet has some of the tallest mountains in the
solar system. They include Olympus Mons, a volcano nearly three times the
height of Everest. It borders a region called the Tharsis plateau, where three
equally awe-inspiring volcanoes dominate the landscape.

But what geologic processes created these features on the
Martian surface? Scientists have long
wondered — and may soon know more.

NASA and DLR (German Aerospace Center) plan to take the
planet’s temperature for the first time ever, measuring how heat flows out of
the planet and drives this inspiring geology. Detecting this escaping heat will
be a crucial part of a mission called InSight (Interior Exploration
using Seismic Investigations, Geodesy and Heat Transport), managed by NASA’s
Jet Propulsion Laboratory in Pasadena, California.

InSight will be the first mission to study Mars’ deep
interior, using its Heat Flow and
Physical Properties Package (HP3)
instrument to measure heat as it is
conducted from the interior to the planet’s surface. This energy was in part captured
when Mars formed more than 4 billion years ago, preserving a record of its
creation. That energy is also due to the decay of radioactive elements in the
rocky interior.

The way heat moves through a planet’s mantle and crust
determines what surface features it will have, said Sue Smrekar of JPL, the
mission’s deputy principal investigator and the deputy lead for HP3.

“Most of the planet’s geology is a result of
heat,” Smrekar said. “Volcanic eruptions in the ancient past were
driven by the flow of this heat, pushing up and constructing the towering mountains
Mars is famous for.”

A mole for Mars

While scientists have modeled the interior structure of
Mars, InSight will provide the first opportunity to find ground truth — by
literally looking below the ground.

HP3, built and operated by DLR, will be placed on the
Martian surface after InSight lands on Nov. 26, 2018. A probe called a mole
will pummel the ground, burying itself and dragging a tether behind it.
Temperature sensors embedded in this tether will measure the natural internal heat
of Mars.

That’s no easy task. The mole has to burrow deep enough to
escape the wide temperature swings of the Martian surface. Even the spacecraft’s
own “body heat” could affect HP3’s super-sensitive readings.

“If the mole gets stuck higher up than expected, we
can still measure the temperature variation,” said HP3 investigation lead Tilman
Spohn of DLR. “Our data will have more noise, but we can subtract out daily
and seasonal weather variations by comparing it with ground-temperature measurements.”

In addition to burrowing, the mole will give off heat
pulses. Scientists will study how quickly the mole warms the surrounding rock,
allowing them to figure out how well heat is conducted by the rock grains at
the landing site. Densely packed grains conduct heat better — an important piece
of the equation for determining Mars’ internal energy.

Cooking up a new
planet

For an example of planetary heat flow, imagine a pot of
water on a stove.

As water heats, it expands, becomes less dense, and rises.
The cooler, denser water sinks to the bottom, where it heats up. This cycling of
cool to hot is called convection. The same thing happens inside a planet, churning
rock over millions of years.

Just as expanding bubbles can push off a pot lid, volcanoes
are lids being blown off the top of a world. They shape a planet’s surface in
the process. Most of the atmosphere on rocky planets forms as volcanoes expel
gas from deep below. Some of Mars’ biggest dry river beds are believed to have
formed when the Tharsis volcanoes spewed gas into the atmosphere. That gas
contained water vapor, which cooled into liquid and may have formed the
channels surrounding Tharsis.

The smaller the planet, the faster it loses its original
heat. Since Mars is only one-third the size of Earth, most of its heat was lost
early in its history. Most Martian geologic activity, including volcanism,
occurred in the planet’s first billion years.

“We want to know what drove the early volcanism and
climate change on Mars,” Spohn said. “How much heat did Mars start
with? How much was left to drive its volcanism?”

NASA’s orbiters have given scientists a “macro”
view of the planet, allowing them to study Martian geology from above. HP3will offer a first look at the inside of Mars.

“Planets are kind of like an engine, driven by heat
that moves their internal parts around,” Smrekar said. “With HP3,
we’ll be lifting the hood on Mars’ engine for the first time.”

What scientists learn during the InSight mission won’t
just apply to Mars. It will teach them how all rocky planets formed –
including Earth, its Moon and even planets in other solar systems.

More information about InSight is at:

https://mars.nasa.gov/insight

JPL, a division of Caltech
in Pasadena, California, manages InSight for NASA’s Science Mission Directorate
in Washington. InSight is part of NASA’s Discovery Program, managed by the
agency’s Marshall Space Flight Center in Huntsville, Alabama. The InSight
spacecraft, including cruise stage and lander, was built and tested by Lockheed
Martin Space in Denver.

News Media Contact

Andrew Good
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-2433
andrew.c.good@jpl.nasa.gov

2018-205

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