The largest volcano on Mars may sit above a 1,000-mile magma pool. Could Olympus Mons erupt again?

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An enormous plume of magma is slowly but steadily rising underneath Mars and could one day provoke an eruption of the solar system's tallest volcano.

a red and blue textured map of a planet surface with some craters circles with red circles.
The gravity map of Mars, showing the variable mass distribution in the planet's interior. The Tharsis region is just right of center, with the three volcanoes Ascraeus, Arsia and Pavonis Mons in a diagonal line and Olympus Mons to their left. The black circles are impact craters larger than 62 miles (100 kilometers). The Tharsis bulge has a high gravity signal (in red); surrounding it is a low-gravity signal (in blue) of an underlying magma plume. (Image credit: Root et al.)

An enormous plume of magma over a thousand miles across is slowly but steadily rising underneath Mars' Tharsis volcanic region and could one day provoke a mighty eruption from the solar system's tallest mountain, Olympus Mons.

At 13.6 miles (21.9 kilometers) tall, Olympus Mons climbs so high into the Martian sky that its caldera pokes out of Mars' atmosphere and into space. Olympus Mons is joined by three other large volcanoes in the Tharsis region: Ascraeus Mons, Arsia Mons and Pavonis Mons. All of these volcanoes have been dormant for millions of years, but that could be changing, new research suggests.

"Mars might still have active movements happening inside it, affecting and possibly making new volcanic features on the surface," Bart Root, an assistant professor at the Delft University of Technology in the Netherlands, said in a statement. Root presented his team's discovery at the Europlanet Science Congress last week in Berlin.

The four volcanoes stand on the Tharsis bulge, a gigantic swelling on the side of Mars that is 3,000 miles (5,000 km) across and 4 miles (7 km) above its surroundings, not including the height of the volcanoes atop it.

By carefully studying minute variations in the orbits of several satellites around Mars — such as Mars Express, the Mars Reconnaissance Orbiter and the ExoMars Trace Gas Orbiter — Root and his colleagues were able to map the Red Planet's gravitational field. They found regions where the gravity was stronger and regions where the gravity was weaker. 

Related: Magma on Mars may be bubbling underground right now

Combined with seismic measurements of the thickness and flexibility of the planet's crust, mantle and deep interior made by NASA's Mars InSight mission, the new findings reveal the complexities of the distribution of mass within Mars. Rather than being divided into neat layers like an onion, Mars' interior is lumpier, with various density anomalies.

Root's team found that beneath Tharsis is a vast region of weaker gravity, caused by a 1,100-mile-wide (1,750 km) region of lower density at a depth of 680 miles (1,100 km). They interpreted it as a huge plume of magma that's slowly working its way up from the planet's interior, to perhaps one day power the Tharsis volcanoes again. 

However, this mantle plume is not the only oddity that Root's team found from the gravity map. They also discovered more than 20 mysterious subsurface structures of various sizes — including one that resembles a dog — beneath Mars' northern hemisphere, where an ancient ocean once filled the lowlands. Unlike the mantle plume underneath Tharsis, these northern features are denser than their surroundings and have a strong gravitational pull. These structures are not visible from Mars' surface; they are buried deep beneath the sediments laid down by the ocean.

"These dense structures could be volcanic in origin or could be compact material due to ancient impacts," Root said. "There seems to be no trace of them at the surface. However, through gravity data, we have a tantalizing glimpse into the older history of the northern hemisphere of Mars."

Among the several gravity anomalies in the northern hemisphere is one that looks a bit like a dog (on the right).  (Image credit: Root et al.)
Related Stories:

—Mars may still be volcanically active, study finds

—Giant Mars mountain Olympus Mons may once have been a volcanic island

—Life on Mars could have thrived near active volcanoes and an ancient mile-deep lake 

A new mission would be required to learn more about these mysterious features. Root is part of a team proposing the Martian Quantum Gravity (MaQuls) mission, which would map Mars' gravity field in detail from orbit.

"Observations with MaQuls would enable us to better explore the subsurface of Mars," Lisa Wörner, a researcher at the German Aerospace Center, said in the statement. "This would help us to find out more about these mysterious hidden features and study ongoing mantle convection, as well as understand dynamics surface processes like atmospheric seasonal changes and the detection of groundwater reservoirs."

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Keith Cooper
Keith Cooper
Contributing writer

Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He's the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.

27 Comments Comment from the forums
  • Inmymind
    Admin said:
    A low-density, weak-gravity region has been found below Olympus Mons and the Tharsis volcanoes, while Mars' northern hemisphere is littered with puzzling high-gravity structures beneath the surface.

    The largest volcano on Mars may sit above a 1,000-mile magma pool. Could Olympus Mons erupt again? : Read more
    If Olympus Mons were to erupt, how high could its volcanic plug go? Phobos and Deimos would have originally fitted snugly into magma chambers of its caldera, the heavier former now slowly falling back to Mars, and the lighter latter now moving further away.
    (https://universemagazine.com/en/doomed-moon-and-the-solar-systems-largest-volcano-caught-in-the-same-frame/)
    Reply
  • Inmymind
    Inmymind said:
    If Olympus Mons were to erupt, how high could its volcanic plug go? Phobos and Deimos would have originally fitted snugly into magma chambers of its caldera, the heavier former now slowly falling back to Mars, and the lighter latter now moving further away.
    (https://universemagazine.com/en/doomed-moon-and-the-solar-systems-largest-volcano-caught-in-the-same-frame/)
    (I provided the link solely for the image showing scale and position. If Phobos and Deimos were volcanic plugs that might better explain the grooves with semi-circular hollows imo..)
    Reply
  • billslugg
    It is not possible to put into orbit any satellite launched from the planet using a single impulse. There must be at least two, one to get you up there and one to get it to orbital velocity. Combining the two vectors in a surface launch won't work. A tenet of orbital mechanics is the satellite always returns to the same spot in space. In the case of a satellite shot into orbit from the ground, it would attempt to return to that spot and crash into
    Mars. Another way to do it would be a three body interaction to circularize the orbit. It is possible but unlikely.
    Reply
  • Inmymind
    billslugg said:
    It is not possible to put into orbit any satellite launched from the planet using a single impulse. There must be at least two, one to get you up there and one to get it to orbital velocity. Combining the two vectors in a surface launch won't work. A tenet of orbital mechanics is the satellite always returns to the same spot in space. In the case of a satellite shot into orbit from the ground, it would attempt to return to that spot and crash into
    Mars. Another way to do it would be a three body interaction to circularize the orbit. It is possible but unlikely.
    Thanks Bill, but does that apply to non-circular orbits? Phobos is predicted to crash into Mars because its orbit is more spiral than circular, (and Deimos to carry on drifting away).
    Reply
  • Torbjorn Larsson
    Interesting finds, Let's hope they get their gravitational mapper!

    Olympus Mons is a shield volcano, with any eruptions tending to flow easily long distances.

    Active shield volcanoes experience near-continuous eruptive activity over extremely long periods of time, resulting in the gradual build-up of edifices that can reach extremely large dimensions.
    https://en.wikipedia.org/wiki/Shield_volcano
    The origins of Phobos and Deimos are open questions, though their equatorial orbits hint at early impact moon formation as our own Moon had.
    Reply
  • Unclear Engineer
    Inmymind said:
    Thanks Bill, but does that apply to non-circular orbits? Phobos is predicted to crash into Mars because its orbit is more spiral than circular, (and Deimos to carry on drifting away).
    Answering for Bill, yes, it applies to elliptical orbits, too.

    Think of it this way - draw a circle for the planet's surface. Pick a spot on the circle and draw any ellipse passing through that spot, with one of the ellipse's foci at the center of the circle. Part of that ellipse will be inside the circle. So, an elliptical orbit that has some part of it on or under the ground will be a crash orbit.

    To get something off the surface and into a non-crashing orbit, we use rockets that fire for multiple minutes, first pushing mostly upward, but turning to the side and pushing more parallel to the Earth's surface once they get high enough to be mostly out of the atmosphere, so that there is little drag against fast flight.

    Trying to do that with a big gun sitting on the surface (or a volcano shooting its plug skyward) won't make a satellite that can stay in orbit, because all the gun can do is put the projectile on one of those elliptical orbits that are partly underground. It would take a projectile that has its own rocket motor that could fire when the projectile reached peak altitude, so that its velocity parallel to the surface would increase enough to raise the lowest part of the elliptical orbit to some altitude above ground level, actually above atmosphere level.

    "Spiral orbits" are not elliptical only because there is some force being applied that slows the satellite down (or speeds it up) in a more or less continuous manner, such as drag from a very thin atmosphere. But, there are other ways to make spirals. For instance, the Earth's Moon is spiraling (very very slowly) away from Earth because of tidal forces between the Earth and the Moon. Effectively, the tides in the ocean are working to transfer energy from Earth's rotation to the Moon's orbital velocity, increasing the Moon's altitude while slowing the Earth's rotation.

    What is happening with Mar's moons I do not know. But, with 2 of them, it is a 3-body problem that can have all sorts of counter-intuitive solutions.
    Reply
  • Inmymind
    Torbjorn Larsson said:
    Interesting finds, Let's hope they get their gravitational mapper!

    Olympus Mons is a shield volcano, with any eruptions tending to flow easily long distances.


    https://en.wikipedia.org/wiki/Shield_volcano
    The origins of Phobos and Deimos are open questions, though their equatorial orbits hint at early impact moon formation as our own Moon had.

    Unclear Engineer said:
    Answering for Bill, yes, it applies to elliptical orbits, too.

    Think of it this way - draw a circle for the planet's surface. Pick a spot on the circle and draw any ellipse passing through that spot, with one of the ellipse's foci at the center of the circle. Part of that ellipse will be inside the circle. So, an elliptical orbit that has some part of it on or under the ground will be a crash orbit.

    To get something off the surface and into a non-crashing orbit, we use rockets that fire for multiple minutes, first pushing mostly upward, but turning to the side and pushing more parallel to the Earth's surface once they get high enough to be mostly out of the atmosphere, so that there is little drag against fast flight.

    Trying to do that with a big gun sitting on the surface (or a volcano shooting its plug skyward) won't make a satellite that can stay in orbit, because all the gun can do is put the projectile on one of those elliptical orbits that are partly underground. It would take a projectile that has its own rocket motor that could fire when the projectile reached peak altitude, so that its velocity parallel to the surface would increase enough to raise the lowest part of the elliptical orbit to some altitude above ground level, actually above atmosphere level.

    "Spiral orbits" are not elliptical only because there is some force being applied that slows the satellite down (or speeds it up) in a more or less continuous manner, such as drag from a very thin atmosphere. But, there are other ways to make spirals. For instance, the Earth's Moon is spiraling (very very slowly) away from Earth because of tidal forces between the Earth and the Moon. Effectively, the tides in the ocean are working to transfer energy from Earth's rotation to the Moon's orbital velocity, increasing the Moon's altitude while slowing the Earth's rotation.

    What is happening with Mar's moons I do not know. But, with 2 of them, it is a 3-body problem that can have all sorts of counter-intuitive solutions.
    Thanks. The orbits of Phobos and Deimos are described as nearly circular, hence my wording as spiral, rather than elliptical. If Deimos had escape speed could it achieve a spiralling orbit away from Mars? If so would there not be a threshold for Phobos to spiral back to Mars? One thing is for sure - both of those opposite spirallings are happening somehow!
    Reply
  • Unclear Engineer
    If a satellite has "escape velocity", it does not complete even one orbit around the bigger body. So, nothing that has made even one complete orbit has escape velocity.

    But, that doesn't mean that it cannot get more energy from somewhere and increase its velocity until it does escape. But, last I read, Earth's moon is not projected to ever escape.

    Mars having one moon spiraling in and the other spiraling out seems to me to indicate that they are interchanging energy with each other in some fashion. They do have gravitational effects on each other as they have different orbital periods.

    Mars does not have the liquid ocean that the Earth has, so it does not have the strong tidal effects that oceans can create on orbiting moons. However, there are still "tides" in the rock of the planets to some degree, so that might have some smaller effect on transferring energy to a moon.

    The inner moon orbits faster than Mars rotates, while the outer moon orbits a little slower than Mars rotates, see https://en.wikipedia.org/wiki/Moons_of_Mars which says:

    "The motions of Phobos and Deimos would appear very different from that of Earth's Moon. Speedy Phobos rises in the west, sets in the east, and rises again in just eleven hours, while Deimos, being only just outside synchronous orbit, rises as expected in the east but very slowly. Despite its 30-hour orbit, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars."

    and

    "Both moons are tidally locked, always presenting the same face towards Mars. Since Phobos orbits Mars faster than the planet itself rotates, tidal forces are slowly but steadily decreasing its orbital radius. At some point in the future, when it falls within the Roche limit, Phobos will be broken up by these tidal forces and either crash into Mars or form a ring. Several strings of craters on the Martian surface, inclined further from the equator the older they are, suggest that there may have been other small moons that suffered the fate expected of Phobos, and that the Martian crust as a whole shifted between these events. Deimos, on the other hand, is far enough away that its orbit is being slowly boosted instead, akin to Earth's Moon."

    But, it may also be the faster orbiting Phobos that is boosting the slower orbiting Deimos as it repeatedly passes below it. And that may also be slowing Phobos.
    Reply
  • billslugg
    Inmymind said:
    Thanks Bill, but does that apply to non-circular orbits? Phobos is predicted to crash into Mars because its orbit is more spiral than circular, (and Deimos to carry on drifting away).
    We are talking two different things. I am talking about launching a projectile from the surface of a sphere, neglecting air friction and third bodies. The only way to do it is to launch it from top of a mountain and send it exactly horizontal. In that case it could orbit in a circular orbit. At the end of each orbit it would hit the top of the mountain it was launched from. Air friction on Mars would make this short lived. A volcano would send the plug straight up and it would fall straight down.

    The "spiraling Phobos" situation is where a moon is destined to continually lose energy somehow and spiral into its planet.
    Reply
  • Inmymind
    billslugg said:
    We are talking two different things. I am talking about launching a projectile from the surface of a sphere, neglecting air friction and third bodies. The only way to do it is to launch it from top of a mountain and send it exactly horizontal. In that case it could orbit in a circular orbit. At the end of each orbit it would hit the top of the mountain it was launched from. Air friction on Mars would make this short lived. A volcano would send the plug straight up and it would fall straight down.

    The "spiraling Phobos" situation is where a moon is destined to continually lose energy somehow and spiral into its planet.
    I found this useful (hope it's reliable) :-

    https://api.www.labxchange.org/api/v1/xblocks/lb:HarvardX:2baac4d9:html:1/storage/Orbits-cbf678ae2f1144f62424e6a4c5dca427.png
    Taken from
    https://www.labxchange.org/library/items/lb:HarvardX:2baac4d9:html:1
    ("A thought experiment typically used to understand orbits is Newton’s cannonball, illustrated below. In this experiment, Newton thought about what would happen if you shoot a cannonball horizontally from the top of a tall mountain at varying speeds. We ignore air resistance and friction acting on the cannonball. When the ball is fired with a low initial speed, it won’t travel far horizontally before falling to the ground on Earth - this corresponds to the light green trajectory in the figure. The ball still feels the gravitational pull of the Earth and thus falls toward the Earth, but the ground curves away from the ball. Let’s now consider what happens if the cannon is fired at a sufficiently high speed, such that the ground curves away from the ball just as much as the ball falls. In this situation (the orange trajectory), the ball will never hit the ground.")

    "This is a circular orbit. The orange line shows the special case of a circular orbit, which only occurs for a specific initial velocity of the cannonball. If the initial velocity is greater or less than this speed, but still sufficiently high not to fall to the surface, the orbits become elliptical (red and yellow paths, respectively). If we continue to increase the initial velocity at which the cannonball is fired, eventually it will have enough energy to escape the gravitational pull of the Earth. The minimum velocity sufficient for this case is called the escape velocity "
    Escape velocity, I read is a scalar quantity - does that imply that it is the speed that is important and not the direction of launch? When it comes to the image, the scenario I have in mind is one where (applying back to Mars) Phobos might have been very, very slightly short of the speed required to reach the orange circular orbit, but greater than would have resulted in the yellow elliptical one, with real forces causing its slow downward spiral. Maybe for Deimos the converse of this situation might apply.

    Just a few thoughts which might be well off the mark.
    Reply