Before it was flown by for the first time in 1964 by the American probe Mariner 4, little was known about the planet Mars. The discovery of an cold, arid world did not reduce the time or money devoted to the search for life or traces of life on the planet. Although some 40 probes have been sent to Mars, the American mission InSight will be the first to provide planetologists with precise information on its geological structure, a witness of its entire history. To discuss further, the CNES has invited Philippe Lognonné, professor at the University of Paris Diderot and planetologist at the IPGP (Paris Institute of Earth Physics), and Francis Rocard, head of solar system exploration programs at the CNES. Join them tonight, June 17th, at 7:30pm at the Café du Pont Neuf in Paris.
This article was originally published in French: Ce que Mars ne nous a pas encore dit. It was translated to English by Abby Tabor.
Mars: Much Like Earth
Since the end of the 19th century, and thanks to observation of its satellites Phobos and Deimos, we know the mass of Mars. Since 1997 and the Pathfinder probe, we know even more about its rotation. But, as Francis Rocard, head of Solar System Exploration programs at the CNES explains, “We have very little information about the internal composition of Mars. There are plenty of models, but we still can’t verify them.” The instruments of the InSight probe will, thus, be able to determine with unequaled precision geological characteristics such as the thickness of the Martian crust, the diameter and composition of the core, and details of the planet’s seismic activity.
Just like Venus, Mercury and the Earth, Mars is a terrestrial, or rocky, planet. Studying the internal structure of Mars could tell us more about the formation of its neighbors and, in particular, our planet. “That’s the goal of comparative planetology,” France Rocard points out. “It’s about understanding why these planets that formed from the same materials are so different today.” The Earth, for example, is the only rocky planet in the Solar System that currently has a system of plate tectonics, a major factor that determines, in particular, how fast the planet cools. Nothing today lets us state with any certainty whether Mars experienced such a geological phenomenon.
Yet, for the planetologist Philippe Lognonné of the IPGP, geology brings part of the answer to the question of life on Mars. “In the lifetime of a planet, there is a window of surface temperatures between 0°C and 100°C that is very favorable for the appearance and the development of life. So, it’s essential to know the geological history of a planet to know when this window occurred and for how long it lasted.” Planets are hot objects surrounded by the cold and the emptiness of space: they are, thus, constantly losing heat. Since Mars is smaller than Earth, it cooled faster. “Mars had significant geological activity for 500 million years,” Philippe Lognonné points out. “Following that, the volcanic activity quickly came to a halt.” Today, it is a cold, dry desert, but we know that liquid water flowed on its surface, and that the planet probably had a denser atmosphere, as well as a global magnetic field: Mars foreshadows the destiny of the Earth.
High Precision Instruments
SEIS (Seismic Experiment for Interior Structure) is the main instrument onboard the probe InSight, which won NASA’s call for offers. Provided by the CNES, with the participation of the Paris Institute of Earth Physics (IPGP) and other international laboratories, the seismometer can measure quakes of magnitude greater than 4.5 at any point on the surface of Mars. Studying the propagation of seismic waves, linked to geological activity as well as meteorite impacts, should help understand the internal composition of the planet.
Another instrument called HP³ (Heat Flow and Physical Properties Package), developed by the German space agency, will allow the probe to measure heat flows up to 5 meters into the Martian ground, over the course of two years. “It’s like trying find the power of a motor,” explains Philippe Lognonné. “We measure how quickly the planet is losing heat.”
The major difficulty of space technology is to produce instruments that are, at the same time, very precise and able to stand up to the extreme conditions of their transport and the local environment once they arrive. So, for SEIS, the challenge was the following: to create a device capable of sensing the faintest quakes, but that can be protected from impacts and vibrations during the interplanetary trip. Placed on the ground by the probe’s mechanical arm, designed for this purpose and equipped with a camera, SEIS will then have to be covered by a protective shield developed by the Jet Propulsion Laboratory. The seismometer will be exposed to hostile winds and to a significant temperature variation (from 20°C during the day to -120°C at night).
A seismometer on the Red Planet, at last?
Space exploration is a risky business. If everything goes as planned during the InSight mission, a functional seismometer will be in a position to tell scientists what’s going on inside the planet, for the very first time. It’s not for lack of earlier attempts, though. The first in a series of disappointments, the most convincing failure remains that of the two Viking probes sent by NASA to the red planet in 1975. On Viking I, the instrument never became active. On Viking II, the seismometer was attached to the lander: “All we were able to measure was the Martian wind,” Francis Rocard says. If the strength of the planet’s winds was little known beforehand, this was definitely not the case after the Viking mission. One understands why InSight’s seismometer needs to be placed directly on the surface of Mars.
The CNES-NASA cooperation is the result of the long maturation period of SEIS. The renewed effort in seismological studies of Mars goes back to the middle of the 1990s with the Russian probe Mars96, which was to bring a seismometer, but, unfortunately, never reached its objective, following a launcher dysfunction. Today destined for the InSight mission, SEIS was originally thought up for the Netlander project, developped by the CNES and its European and American partners between 1998 and 2003, then abandonned for its high cost. The program had planned to send 4 probes, which would have created a network of sensors: by crossing the data from several seismometers, higher quality measurements can be obtained. « After the loss of Mars96, we wanted to move to the next level and establish this network with Netlander, » explains Philippe Lognonné. « We’re getting back to something more modest with InSight. »
It is not news that space programs are costly, and seismology is generally not a priority. « The main objective of space agencies concerning the planet Mars is still to find out more about Martian life. Geology only tells us about this subject indirectly, » confirms Francis Rocard. The InSight mission is part of NASA’s Discovery program, which explains certain of its characteristics : fixed budget and maximum efficiency. For example, the probe will reuse the model of the Phoenix lander that successfully touched down on Mars in 2008. Last year, SEIS was already at an advanced stage of design. For seismology, patience has paid off.
The SEIS seismometer should be delivered in a year, and the launch of the Atlas V transporting the probe is planned for March 2016. After six months of travel, the lander should touch down in the volcanic region of Elysium Planitita, not far from where the rover Curiosity tread on the Martian ground in August 2012. The InSight mission is off to a good start to accomplish a first in the exploration of the Red Planet: collect, for the first time, clues indispensable to understanding the geology of Mars and contribute to a better understanding of the formation of rocky planets like the Earth. The CNES, the Bar des sciences and MyScienceWork invite you to come debate and discuss Martian seismology, tonight June 17th at 7 :30pm at the Café du Pont Neuf or via the hashtag #CnesTweetUp.