Posted on June 26, 2023

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Earthlings are ungrateful. Many consider the planet Mars to be a hostile and distant land, so it should be ignored. You are wrong. Instead, they should realize that it is the very stepping stone humanity needs to one day venture into space. You should therefore thank nature for bringing it to the place where it is, the way it is.

The basic advantages that Mars offers us humans, compared to the other planets of the solar system and compared to the planets of other systems that would not have the same configuration as our Earth/Mars pair, are related to mass and mass together the distance. More precisely, on the one hand it is the mass ratio between the two planets and the mass of Mars in absolute numbers; on the other hand, the distance from Mars to Earth and the distance from Mars to the Sun.

This week I will explain the advantages that the crowd offers.

As a reminder, Mars has a relatively small mass, one-tenth the mass of Earth, with a diameter half that of Earth (so about the same density), but an area equal to all of the nascent countries of ours planet corresponds to . This small mass is not “normal”. Given the likely homogeneity of the protoplanetary disk, Mars could have had the same mass as Earth or Venus. It should have had this mass even if Jupiter, which formed beyond the line of ice, had not reached this mass, as the astrophysicist Alessandro Morbidelli brilliantly showed us (the theory of the “great tack”) apex”) to enter this region of the inner Solar System (below the asteroid belt) while it was still forming (with some delay compared to the gas giants).

Luckily, after resonating with it, Saturn halted its descent towards the sun and guided it together into the outer system (beyond the asteroid belt). However, the damage from the incursion was already enormous, most of the material in the asteroid belt was turned upside down, scattered, absorbed, absorbed, most of the material that could have created a planet Mars the size of Earth. However, Jupiter hadn’t sunk into this region long enough to absorb all of the matter, and fortunately it had stayed there long enough for the remaining matter to be gravitated to a planet much less massive than Earth. Earth, but significantly more massive than the moon, which is exactly what we would need later.

In fact, this mass of Mars implies a gravity on the ground about a third of that we have on Earth (0.38 g) and an escape velocity of 5.03 km/s (compared to 11.2 km/s on Earth Earth).

The consequences in space travel are:

This weight is to be compared to that of the Starship with its SuperHeavy launch vehicle when it took off from Earth: 4000 tons (ie 200 tons for the structure for the SuperHeavy and 100 tons for the Starship and for the propellants 3400). tons for the SuperHeavy and 150 tons for the Starship – waiting to be refueled in orbit – plus 150 tons payload). It should also be compared to the weight of the 538 tons of the heaviest version of a loaded Falcon-9 or the 780 tons of an Ariane-5 on departure from Earth.

Clearly, the difficulties of landing and then exiting a “hypothetical Mars” Earth-mass planet would not compare to the difficulties encountered to lift off from Earth. Similarly, the desire to land on the unprepared soil of such a planet, and especially the desire to leave it, would pose almost insurmountable problems. Considering launch alone, it would be necessary to have a SuperHeavy-capable launch vehicle on-site to take to Mars, and the fuel (or laboratory capable) to supply it. to produce them from local resources in sufficient quantity and at sufficient speed).

It is therefore a machine much more powerful than the machine built into the spacecraft (with its SuperHeavy) that we would need from Earth. However, the launch test for the orbital flight of the integrated spacecraft has clearly shown that we have achieved the maximum of what is possible with our current means of propulsion. We can therefore only hope today to be able to carry out manned missions on our “real Mars” planet, since it has a much lower mass than Earth. To continue the argument, any mission to the surface of Venus (or any planet of the same mass) is in addition to the fact that you cannot get there due to the surface’s atmospheric pressure (90 bar) and temperature (450°C). descending, not possible ) would be completely out of the question, since we would not be able to leave it due to gravity. A mission on a “super-Earth” (larger than the mass of the earth by definition) would be completely out of the question.

After liftoff from Mars proper, it will then be much easier to reach orbit before interplanetary transport to Earth, since the astronauts will not have to pass the Max-Q test, which is the pinnacle of danger after leaving the surface of Earth (or any other planet with a dense atmosphere). Let’s remember that Max-Q is the maximum aerodynamic stress that we have to go through when the atmospheric pressure is still high enough that, depending on the speed already achieved, the density of the atmosphere imposes the most severe constraints on the structure of the rocket .

This voltage then decreases rapidly as a function of the reduction in air pressure, which in turn depends on altitude. In the Martian atmosphere, the Max-Q is much lower (not to say negligible) because the initial atmospheric pressure is already very low (615 pascals at “datum”, so here the equivalent of sea level), which is what we have in an altitude of about 30 km above the ground.

At this altitude, the Starship orbital crossed its Max-Q, no doubt contributing to its destabilization, which became evident a few kilometers higher. When the rocket leaving Mars reaches an altitude of 21 km above the datum, i. three tenths of a millibar), obviously almost nothing (and in any case, he would not have had to perform the delicate maneuver of dropping his launch vehicle, since this first step will not be necessary due to the lower gravity).

Once astronauts are on Mars, they are required to wear spacesuits and possibly a vest and radiation helmet in partially shielded surface habitats (like the transparent domes seen in many habitat projects) for all outdoor activities, unless of course they choose to for living under a thick shelter of regolith or rock. This is good, because the mass corresponding to this life support (equipped space suit) and radiation protection (vest and helmet) will be perfectly adapted to the muscular and bone capacity of the astronauts and will even benefit them in keeping bone tissue and muscles in good condition , while this would be totally intolerable on a planet with a mass and therefore a gravity equal to (or greater!) that of Earth.

Mars also has two major advantages for research, which result from its mass and thus its gravity. While this mass has allowed for much more advanced geological activity than on the lunar surface, it has not allowed for the development of significant tectonic activity like that on Earth.

Geological activity on primitive Mars enabled the geological transformation through diagenesis and metamorphosis that associated liquid water, while this water-associated evolution was almost nil on the moon, as our natural undermass satellite very soon became a dead star became. Mars began a geological history similar to Earth’s, with numerous early reactivations due to changes in the tilt of its axis of rotation on the ecliptic plane or due to strong volcanic eruptions. Fortunately for scientists, this activity slowed and almost stopped a few hundred million years after it began (about -3.5 billion years), while at the same time the atmosphere became extremely thin and surface water disappeared.

In the planet’s mantle, a lower amount of water, which is also related to Mars’ lower mass and therefore lower gravity compared to Earth, and thus Mars’ lower gravitational pull for ice-bearing comets, prevented the development of such strong convection movements are associated with such a thin one crust as connected on earth. As a result, the convection movements could only outline a very weak plate tectonics (Valles Marineris or Isis Planitia?) that allowed the almost complete preservation of a very ancient planetary surface spanning tens of millions of km2, while the same surfaces were observed on Earth from the very beginnings of life, now cover only a few tens of square kilometers in Australia and Greenland.

The only downside: the low mass of Mars did not allow the formation of a ferrous metal core at the center of the planet that was as pure and whose periphery was as clearly defined as at the center of the Earth, which did not allow efficient differential rotation enough to create protective global magnetic fields (if not at the very beginning of the earth’s history). Since the exhaustion of the atmosphere (approx. -4 billion years apart from incidents that are becoming increasingly rare), there is no longer any protection on earth against solar and galactic radiation. These conditions were obviously unfavorable to life.

Despite this last negative remark, Mars, because of its mass, represents an optimal laboratory to deduce what may have been the oldest surface of the earth and a place where the gravitational conditions should allow humans to live in acceptable conditions.

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