No planet outside of Earth has been more visited than Mars. More than fifty missions have reached it with mixed success. Currently, eight spacecraft orbit the planet and, on the surface, three autonomous vehicles operate normally: the Curiosity and Perseverance rovers, from the NASAand the Zhurong rover), sent by the CNSA, China. There is also a small helicopter that makes flights over the Martian surface and a fixed station, InSight, which provides data on the deep interior of Mars.
All these missions have been possible thanks to the common effort of thousands of scientists, engineers, technicians and specialists in the most diverse branches of knowledge. Today, in Hablando con Científicos, we have Fernando Rull, one of the people who, with his work, make possible the missions capable of sailing through space and reaching Mars to study the planet.
Fernando Rull is principal investigator of the Raman instrument of the ExoMars mission, a mission that unfortunately currently has an uncertain future due to the war in Ukraine, is responsible for the calibration system of SuperCam, a multiple instrument that is on the rover Perseverance, and is director of the group ERICA.
Mars was once a very different planet from the current one, there was abundant liquid water as evidenced by the beds of ancient rivers, deep canyons excavated by water, remains of lakes and seas whose bottoms are now dry and dusty deserts. At the moment there is no liquid water on the Martian surface, because, for it to exist, there must be a temperature above the freezing point and there must also be an atmospheric pressure high enough so that the water does not evaporate. Although certain places and times of the year the temperature can exceed 0ºC, the atmosphere is so tenuous that it does not allow the existence of water in a liquid state on the surface. Understanding what the environment was like in those distant wet times and what happened afterwards makes the study of dry river, lake or sea beds a very interesting objective for Martian missions.
That is the reason why Jezero crater was chosen as the landing site for the Perseverance rover. Jezero has a diameter close to 50 kilometers and contained a lake in ancient times. As it happens in terrestrial lakes, Jezero must have accumulated a significant volume of sediments during its existence, sediments that preserve data on past history, among them, perhaps, if there was life, signs that reveal its existence.
One of the most important instruments in Perseverance is SuperCam, which, as Fernando Rull comments during the interview, is actually a collection of techniques integrated into a single instrument. It contains a Raman spectrometer, a pulsed laser, an infrared sensor, imaging cameras, and a microphone. Part of the analysis carried out with SuperCam is based on a pulsed laser that, when focused on a rock, excites the atoms that make it up and emits light that is analyzed with the Raman spectrometer. Thus, it is possible to determine the chemical composition and the type of minerals that exist in the rock.
SuperCam can increase the intensity of the laser to the point of producing in the chosen sample a release of plasma, that is to say a charged gas whose emission allows to reveal the elemental chemical composition of the sample.
The built-in microphone in SuperCam has made it possible to record and analyze the sound emitted by the small Ingenuity helicopter while it was flying over the Martian terrain. The sound that is very different from that recorded on Earth because the weak atmospheric density dampens sound transmission. Analysis of the differences between the same source of sound on Earth and Mars reveals unknown facts about the way sounds are transmitted on the Red Planet. Firing the SuperCam’s built-in laser also produces a sound that is being analysed.
The multiplicity of techniques incorporated into SuperCam required a significant calibration effort, says Fernando Rull, because in addition to correctly calibrating each instrument separately to ensure that the measurements on Mars were correct, cross-calibrations between the different elements had to be carried out to be sure that the results of the analyzes were consistent. To carry out these calibrations, various materials existing on Earth were used, but which are known to exist on Mars as well. A meteorite of Martian origin has also been used, a part of which has traveled with the “return home” ship.
Fernando Rull is also principal investigator of the Raman instrument of the ExoMars mission of the ESAa mission that, unfortunately, has suffered launch delays due to the pandemic and, now, has an uncertain future due to the problems that have arisen with Russia over the war in Ukraine.
I invite you to listen to Fernando Rull, Professor of Crystallography and Mineralogy at the University of Valladolid, principal investigator of the ExoMars Raman instrument, head of the SuperCam calibration system at Mars 2020 and director of the group ERICA.