(ORDO NEWS) — It is believed that volcanic eruptions on the Red Planet have long ceased. But the latest data shows that they can resume at any moment. Judging by the tremors of the Martian crust, there are pockets of liquid magma in it.
The past of all the rocky worlds of the solar system was hot. Mercury, Venus, Earth and Mars abound with traces of ancient eruptions.
But the key word here is “ancient”. Of all the planets, active volcanoes are known only on Earth. The “planets” clause is important, because in fact the most volcanically active body in the solar system is Jupiter’s moon Io.
True, if we have not seen active volcanoes, this does not mean that they do not exist. No planet other than the Earth has been properly studied by volcanologists. There is, for example, indirect evidence that fire-breathing mountains may be on Venus.
But it is difficult to catch them behind the eruption, if only because the surface of this planet is always covered with dense clouds. It is easier to study Mars, at least it is clearly visible from orbit.
Just four years ago (in 2018), thanks to the InSight probe, the first decent seismograph was launched on the Red Planet. It was he who brought intriguing data, which we will discuss below. But first, let’s tell you how Martian volcanoes differ from terrestrial ones and where they come from.
Where do volcanoes come from?
Two hundred years ago, naturalists thought the Earth was liquid inside. It turned out that a thin solid crust separates us from the ocean of liquid magma. And volcanic vents are just holes in the crust.
This idea has migrated into popular culture and to this day confuses people. In fact, with volcanoes, the situation is not at all so simple. To be more precise: firstly, it’s not at all simple, and secondly, it’s not at all like that.
The mantle of the planet (not only ours), although hot, is solid, and not liquid at all (the temperature of the Earth’s upper mantle, for example, is about 1300 – 1500 C).
Yes, it is mobile, but the speed of mantle flows is a few centimeters, or even millimeters, per year. At about the same rate, the concrete pillars of a poorly built bridge can “leak”.
For magma to form, the solid matter of the mantle (or crust) must melt. Magma, by the way, is also not quite a liquid. It is a mixture of liquid melt, crystals and gases.
It can be compared to carbonated semolina. Volcanic lava is magma that has erupted onto the surface. Under each active volcano there is a reservoir of magma – a magma chamber.
How to melt the substance of the upper mantle? The obvious way is to heat it above its melting point. An ascending flow of matter from the lower mantle, and even from the very boundary of the core, the mantle plume, will cope well with this.
The lower mantle is hotter than the upper, so the “newcomer” brings with it additional heat that melts the surrounding rocks. It is believed that such a plume warms the centers of Hawaiian volcanoes.
You can also not look for additional heat, but simply lower its melting point so that it melts at its usual temperature. To this, in turn, there are two ways. The first is to reduce the pressure on the substance. When the deep masses of the mantle rise to the surface, where the pressure is less, they melt.
This is how magma is formed under the volcanoes of the mid-ocean ridges, in the place of powerful ascending flows of mantle matter. The second way is to remember the ancient advertising slogan and “just add water.”
A mixture of mantle matter with water melts at a temperature at which a dry mantle would remain solid. Therefore, there is a Pacific ring of fire at the edges of the Pacific lithospheric plate, where water-saturated rocks of the seabed sink into the mantle.
Terrestrial volcanoes often live for thousands of years, sometimes hundreds of thousands of years. But not millions of years.
The movement of tectonic plates will not allow the magma chamber to exist for a long time in one place. It will move the focus away from the mantle plume heater or shift the point of water inflow into the mantle.
But on Mars, according to scientists, there are no moving lithospheric plates. And most likely never was. Therefore, magma chambers can be extremely durable.
Meteorites of Martian origin show that the same volcano could wake up from time to time for nearly a hundred million years! And with each eruption, throw out new masses of lava and ash.
Adding to this low gravity (38% of the Earth), we will understand why the highest volcanoes in the solar system are on Mars. The most grandiose of them is Olympus. This giant with a base diameter of 540 kilometers can hardly even be called a mountain.
It cannot be fully seen from the surface: most of Olympus will always be hidden behind the horizon. The height of this colossus exceeds 21 kilometers, if you count from the foot.
And above the conditional local “sea level” the giant rises more than 24 kilometers! Other Martian volcanoes are not as grandiose as Mount Olympus, but they are also impressive.
However, all traces of Martian eruptions are very ancient. The youngest of them are over two million years old. How do we know their age? By counting meteorite craters. Experts know (at least in theory) how often meteorites of one size or another fall on the Red Planet.
Since erosion on Mars is weak, the craters are almost not destroyed. If there are few of them on some part of the surface and they are small, then this part is young. The method is not very accurate, but convenient.
Until recently, there was no evidence that there were active volcanoes on Mars. Moreover, it seemed most likely that they did not exist. All planets gradually cool down, wasting their internal heat.
On Mars, which is almost ten times smaller than the Earth, this process has gone very far. And where there is little underground heat, it is difficult to expect the melting of the mantle.
By the way, many experts believe that numerous deep cracks in the planet’s crust are just a consequence of cooling. The planet shrinks, shrinks, and its crust cracks.
But the latest data cast doubt on both the “restrained, Nordic” disposition of Mars and the origin of the cracks.
Crack in theory
In 2021, an interesting article was published in Icarus magazine. Astronomers have discovered something very similar to fresh volcanic deposits in images from the Mars Reconnaissance Orbiter. This is a dark spot around one of the so-called furrows of Cerberus – deep cracks in the crust of Mars.
The sunspot is almost symmetrical and is not elongated in the direction of the prevailing winds. So it is difficult to attribute its origin to the whims of Aeolus.
Deposits have a high heat capacity: they heat up slowly and cool down just as slowly. Combined with the color, this makes one suspect that they are composed of the volcanic mineral pyroxene.
Similar structures have been found more than once on the Moon and Mercury and are usually considered to be volcanic.
But, unlike its twins on other celestial bodies, the Martian spot is very young. He is from 50 to 200 thousand years old. Even on Earth with its moving plates, volcanoes of this age can be active, and even more so on Mars.
Sweet shiver of discovery
The authors of the article in Icarus immediately noted that it was in the region of the Cerberus furrows that the epicenters of the strongest marsquakes recorded by the InSight seismograph were located. And now a new paper has appeared in the journal Nature Astronomy.
Scientists have analyzed data on many quakes, since more than 1300 of them have already been recorded. Experts have identified a special class of shaking of Mars: low-frequency ones. By the nature of the signal, they are quite similar to the events familiar to terrestrial seismologists.
It can be hoped that the cause of such tremors is not in the crackling of the shrinking crust and not in the rare falls of meteorites, but in the geological activity of Mars.
For 18 out of 24 such low-frequency tremors, it was possible to determine the distance between the seismograph and the epicenter.
And it coincided (within the margin of error) with the distance to the furrows of Cerberus. That is, to the very place where fresh volcanic deposits or something very similar was found.
But that’s not all. Judging by the speed of seismic waves, they passed through a liquid or almost liquid medium. The mantle, we recall, is solid. And the bark is also hard. What then can be liquid? Magma.
There appears to be a magma chamber beneath the bottom of at least one of Cerberus’ furrows. And if so, then the crack itself, most likely, was formed as a result of a volcanic catastrophe, and not a gradual cracking of the cooling crust.
And the most important thing is that as long as the magma remains liquid, it can be erupted to the surface. A Martian volcano may wake up and declare itself.
Two independent pieces of evidence – images from orbit and seismograms from the surface – that’s a lot. But scientists take the notion of “established fact” very seriously.
The press service can force them to make a big statement for the release, but in their own circle they do not rush to conclusions, slowly and meticulously accumulating arguments for and against.
Perhaps one day a whole network of seismographs will appear on Mars, instruments will measure the flow of underground heat at different points on the planet, and rock samples from the edges of that very crack will be studied by rovers, or even delivered to earthly laboratories.
And then it will be possible to say for sure whether there is a magma chamber there. Well, or we are very lucky, and the orbiters will photograph the eruption process.
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