The solar wind consists of a relentless stream of charged particles that are thrown from the Sun at extremely high speeds, sweeping the solar system in their wake. It has been detected beyond Pluto’s orbit by the Voyager 1 probe and caused Mars to lose much of its atmosphere millions of years ago. But could the solar wind completely sweep away the Earth’s atmosphere? To answer this question, let’s first see what the solar wind is exactly and what happened on Mars (and other bodies and planets) to see what could happen on Earth.
The photosphere is the region of the sun that we normally understand as its surface. This region has a temperature of several thousand degrees and as a consequence it emits electromagnetic radiation, light , constantly. But the Sun does not end there, because surrounding this photosphere and extending millions of kilometers above it is the solar corona , a much more diffuse and less dense region in which the plasma reaches temperatures of several million degrees .
These temperatures are not reached by the same mechanism as inside the star, where nuclear fusion reactions release huge amounts of energy, bringing the core of the Sun to about fifteen million degrees. In the solar corona, these temperatures are a consequence of the intense magnetic fields that run through it, which excite and accelerate the charged particles found there.
As the temperature of any substance is determined by the kinetic energy of its particles , and therefore by its speed, these very high temperatures will imply very high speeds. In this way, the particles that make up the solar corona usually move at several hundred kilometers per second . Certainly incredible speeds, but still less than the escape velocity of the Sun at that height, which is around 400 or 500 kilometers per second. This escape velocity is the speed that a particle, or any other body, would need to completely escape from the Sun’s gravity. Well, although most particles do not manage to escape, there will be a small percentage that have enough speed to do so. . These particles will constitute the solar wind. They are mostly electrons and protons , charged and relatively light particles. However, there will also be among these ions of oxygen, silicon and even iron, among others.
This constant flow of matter causes the Sun to lose part of its mass every moment, at a rate of more than a million tons of material per second . Enough to lose a mass equivalent to that of the Earth every 150 million years. Despite this, the mass of the Sun is so great, millions of times that of our planet, that the Sun has lost less than a thousandth of its mass to the solar wind since it formed.
This solar wind moves away from the Sun at speeds that can reach several hundred kilometers per second , interacting with everything in its path. When it reaches the Earth, it is, for example , responsible for the auroras that are observed in the polar regions . It was also responsible for almost completely wiping out the Martian atmosphere . In the origins of the solar system, Mars was not very different from Earth. A substantial atmosphere surrounded it and liquid water ran over its surface , forming rivers, lakes and seas.
However, after several hundred million years and due to its smaller size, the core of Mars cooled and its magnetic field lost strength. This magnetic field is the one that protected Mars and any other planet from the influence of the solar wind . Since this wind is made up of charged particles, magnetic fields are able to deflect them. Losing its magnetic field, the solar wind was able to bombard the Red Planet’s surface, blowing away its atmosphere in the process. With the loss of the atmosphere , the pressure and temperature that made the presence of liquid water possible disappeared, and with it all hope that Mars would develop a rich biosphere like that of Earth.
But could something like this happen to Earth? The answer is of course yes , it could, but too long in the future for us to worry. As the Earth is considerably larger than Mars, with a volume almost 7 times greater , it has much more material in its core and is able to retain the heat that keeps it molten longer. This has been enough to keep the Earth’s core and mantle warm to this day , allowing the convection of material that ultimately creates the Earth’s magnetic field. It will also be enough to last several hundred or billion years more, helped in part by the disintegration of radioactive elements, which helps keep the interior of our planet at a high temperature.
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S. Yokoo et al, 2022, Stratification in planetary cores by liquid immiscibility in Fe-S-H. Nat Commun 13, 644, https://doi.org/10.1038/s41467-022-28274-z