It has become a long agony, and it is also a long goodbye that NASA is paying to one of its Martian missions. Insight is perhaps one of the least spectacular and celebrated but it has nevertheless contributed, in almost four years, to deepen the knowledge of Mars in some of its less studied aspects: earthquakes (or “martemoti”, if you prefer) and in general the subsoil. Its large solar panels are now obscured by the dust that has settled on them over the past few months. The energy it obtains, over 200 million kilometers from the Sun, is less than a fifth of the original one. Soon Insight will go out, as he continues, with the last drops of energy, to listen to the beating heart of Mars to steal the last secrets.
A seismometer su Mars
Taking off on May 5, 2018 from California, Insight landed on November 26 of the same year in Elysium Planitia, a few degrees from the equator. In the following weeks, with her arm, she deposited her equipment on the ground. In particular, the Seis seismometer, with which she made us listen to the sound of the Martian wind, collecting the vibrations of the air. And then she started the work she traveled hundreds of millions of miles for. On April 6, 2019, the announcement: her instrument detected for the first time a seismic shock on another planet https://www.nature.com/articles/d41586-019-01330-3. It had already happened with the Moon: the seismometers placed on our satellite by various Apollo missions have picked up some “lunamotes” due not to plate tectonics, as in the case of the Earth, but to the tidal forces triggered by the gravitational force of our planet. Mars, we discovered thanks to Insight, is an even different story. Not even Martian earthquakes have a similar origin to that of Earth, there is no evidence of a plate tectonics that moves continents like rafts on a sea of magma, but rather they are the “creak” of a planet that cools and in doing so it breaks rocks and creates cracks like faults.
Mars is an arid, uninhabited but not so silent place. At least not for a sensitive girl like Insight. She found herself having to pick up signals through a great din generated by the wind, the dust devils, small whirlwinds, from a sandstorm. Then there are the impacts from micrometeorites, which must be included in a different category, but still useful for understanding what is under the surface. From all this noise, the signs of more than 1,300 tremors have emerged, most of them are micro-movements, with some, notable, exceptions.
The Seis seismometer, placed by Insight with its robotic arm. Credit: NASA / JPL-Caltech.
Due “big one”
It came at the very end, when the energies of Insight were already almost at the bottom of a rapid decline. The most powerful tremor ever recorded occurred on May 4, 2022, and corresponds to the fifth degree of magnitude. On Earth it would be a powerful phenomenon, sure, but not entirely exceptional. On Mars, it represents roughly the maximum that scientists expected from this mission. And they were lucky: “Since we placed our seismometer in December 2018 we have been waiting for ‘the big one’ – said Bruce Banerdt, principal investigator of InSight at the Jet propulsion laboratory in Pasadena, leading the mission – certainly this shock us will allow you to take an unprecedented look inside the planet. Scientists will analyze this data for years ”.
There is another page in Insight’s diary that is hard to forget. On December 24, 2022, the lander’s legs trembled again. A shock of just over magnitude 4. A relevant phenomenon, but not exceptional. Analyzing the data, however, the seismologists realized that it was not due to an internal movement of the planet. Instead, it was due to the impact with a meteoroid, a small asteroid between 5 and 12 meters in size. If it had fallen to Earth it would have been consumed by burning in the atmosphere, but the Martian one is much thinner and more rarefied, not enough to act as a shield.
The crater left by the meteorite that fell on Mars on December 24, 2021, photographed by the NASA probe Mars reconnaissance orbiter. The impact generated a magnitude 4 earthquake recorded by Insight. Credits: NASA / JPL-Caltech / University of Arizona
Subsoil ultrasound: crust, mantle and core
The waves that Insight’s Seis seismometer was able to record are not just a statistic. The analysis of how they propagate and bounce from one end of the planet to the other allows us to describe the “medium” through which they travel, that is, the layers of the planet itself. From three studies, published in July 2021 in the journal Science thanks to the data collected by Insight, they described its “onion” structure, from the surface to the core https://mars.nasa.gov/news/8996/nasas-insight-reveals-the-deep-interior-of- mars /? site = insight. At the same time, they allow to refine the models that try to describe how the planets of the solar system were formed.
We now know, for example, that the Martian crust, the “skin”, the most superficial layer, is thinner than expected, from 24 to 72 kilometers. It has a mantle, up to over 1,500 kilometers deep and finally a core, much less dense than expected. It is liquid, unlike the terrestrial one, solid and covered with a fluid outer part. These differences could be what makes Mars so different from our home. The movement of the fluid mass of the Earth’s outer core, in fact, is considered the origin of our magnetic field. Mars does not have a magnetic field (it has lost it in the course of its history) but some traces are known of it. It therefore does not have the shield from solar radiation and storms, the same ones that over billions of years could have wiped out much of its atmosphere and made it the icy desert we know today, bombarded by radiation and meteorites. A difficult place to colonize on which, however, there was once liquid water, and perhaps for a while there was life.
The drawing shows Insight’s work in capturing the seismic waves generated by “martemoti” or by the impacts of meteorites
To testify how much distance there is between science and science fiction, just think of the difficulties encountered in using another tool, called “the mole” (“the mole”). A tube to be buried up to five meters deep to record the temperature of the subsoil. Without a drill, the mole was pushed with some kind of hammer. The ground, however, is too soft and after just ten centimeters the progress has stopped. The attempts to straighten it and compact the soil around it were useless. In January 2021 it was decided to give up, after almost two years of trying to dig a hole from hundreds of thousands of kilometers away.
Choked with dust
Insight had just arrived a couple of months ago when, on the same line as the equator but a few thousand kilometers away, another probe, the Opportunity rover, ended its mission. The great sandstorm that enveloped almost the entire red planet was fatal, preventing it from collecting light with solar panels, dusted and blinded by red earth. The same fate is now falling to Insight. He had already had some problem of this type in 2021. Solved brilliantly by NASA engineers who, with the mechanical arm, dropped some sand next to the panels and this, carried by the wind, swept away some of that that had accumulated https://mars.nasa.gov/news/8959/nasas-insight-mars-lander-gets-a-power-boost/?site=insight. He earned the lander a few more months, but now, really, it doesn’t seem to be able to do it anymore. The first phase of its mission had ended in 2020, NASA had extended it until December 2022. Apparently, the end of the line has arrived for Insight.
To save energy and continue as long as possible with scientific activity, NASA has decided to leave only the seismometer activated, turning off everything else. Rooms included. We hang on to the hope that the wind, the same one that has covered it with dust, will give it back some vitality, sweeping away some of the dirt. But nobody believes it. So we are preparing to say goodbye, “farewell” Insight, who listened to the beat of Mars and made us peek inside a planet so similar yet so different from ours.
