Author: Eric Malikyte
I’ve been saying it! Haven’t I been saying it?
Yes, folks, we’ve finally figured out with quite a bit of certainty, what Mars’ core is like.
And it’s liquid and molten baby!
The Power Marsquakes
Marsquakes are much, much fainter than they are here on Earth. In fact, those of us who grew up living in California would probably not consider them to be quakes at all. They’re much more in line with tremors.
NASA’s InSight, a stationary lander that reached Mars in 2018, has a built-in seismometer on it (which was made by the French) that has been measuring Marsquakes since its arrival.
In total, the domed device has detected an estimated 733 marsquakes so far. Only 35 of those marsquakes featured magnitudes of 3.0 to 4.0 on the Richter scale.
A large portion of these quakes originated from a volcanic region 1,600 kilometers away from an area where molten lava may have flowed just a few million years ago, and although this is just my inference [speculation alert] I believe this may suggest that the area in question is volcanically active.
As we explained in another video, seismic waves have been used to understand what Earth’s interior regions are like. But, on Earth, we have many seismic monitoring stations scattered around the world to help pick up those waves as they effectively ricochet around inside our planet…like a giant Earth-sized pinball machine…
Because of seismometers scattered around our planet, we know that the Earth is composed of four different layers. Three of those areas are solid and one is composed of molten metal that is nearly as hot as the surface of the sun! (More on this later).
But despite InSight only having the one seismometer, we now have a pretty good idea of Mars’ interior structure as well.
The Martian Interior Structure
A series of articles published last month described new data that reveal Mars’ interior structure.
Let’s break it down!
Beneath Mars’ freezing surface is a crust that is just about as thick as Earth’s.
However, the Martian mantle between the crust and the core is about half as thick as the Earth’s.
But the Martian core is another story.
The core is on the larger end of estimates made by scientists, though it is certainly not nearly as large as our planet’s core (but that’s an unfair comparison because our planet is nearly twice as big as Mars).
And yes, the core has been determined to be liquid and molten, [zoom in] just as I’ve been saying over the past 7 or so months!
But one thing that scientists are still unsure of is whether or not Mars’s core features a smaller solid interior core like Earth has.
But make no mistake, the work is no where near close to done. There is still so much left to understand about Mars’ interior regions.
Mark Panning from the Jet Propulsion Laboratory (or JPL) who was involved with studying the Martian crust says that the largest marsquakes they’ve detected thus far are so weak that we would barely even feel them here on Earth.
If Mars were to have a series of larger quakes, however, it would give scientists a much clearer picture of the planet’s interior.
Right now, the basic description given of the planet’s interior is fairly broad, kind of like a low-resolution photo. We can see the basic structure of the planet now, but the finer details are still largely unknown.
Our knowledge of Earth’s interior for example is far more extensive. We know that the deepest layer of our planet is a solid iron core that is roughly ball shaped and about 2,400 kilometers in diameter. The inner most solid iron core, while certainly solid, is still extremely hot! About 5,000 to 7,000 degrees Celsius! But the immense pressures ensure that the iron in the core doesn’t become molten.
This iron is not pure. Scientists suggest that it contains sulfur and nickel along with smaller amounts of other elements.
We already know that the outer core is made of molten iron, followed by the mantle, which is often misunderstood to be lava.
The mantle is actually composed of rock, but that rock is so hot that it flows under pressure featuring characteristics that have been compared to road tar (which is basically a blend of liquid asphalt and water).
One major gap in knowledge between what we know of the Earth’s mantle and what we know of Mars’, is the fact that we can divide Earth’s into two separate regions. The upper and lower mantle are separated by a boundary that lies some 750 kilometers beneath the Earth’s surface.
There are also currents within the mantle that have broken the crust into different blocks, what you and I know to be plates, something that we’re pretty sure doesn’t exist on Mars.
But, okay, if we don’t yet have a full understanding of Mars’ structure…what is the extent of our knowledge?
From Cartoon to Raw Numbers
The current measurements of Mars’ crust suggest that it reaches a depth of 20 to 37 kilometers. The mantle extends nearly 1,600 kilometers into the planet with a lightweight core with an estimated radius of 1,830 kilometers.
Mark Panning said this about the current limits of our understanding, “By going from cartoon understanding of what the inside of Mars looks like, putting real numbers on it … we are able to really expand the family tree of understanding how our solar system’s rocky planet(s) formed.”
It seems as though Panning is suggesting that we’ve finally graduated from having a very simplistic understanding of Mars’ interior.
But I would say that when compared with what we know about the Earth’s interior, there is still a massive gap of knowledge to fill in when it comes to the red planet’s nether regions. And I’d like to see more data expand upon this information.
While InSight has had its mission extended by another two years, it’s also been hit with a bit of a power crunch thanks to dust covering its solar panels. This is further complicated by Mars reaching the furthest point in its orbit from the warmth of the sun.
In fact, the only system that hasn’t been put on hiatus is InSight’s seismometer (well, I guess that’s lucky, isn’t it?).
So, I guess it’s not morbid at all to hope that “the big one” hits Mars sooner rather than later, so we can get a much clearer picture of its innards.
But what is the likelihood that this will happen to Mars? Well, I guess we’ll have to figure out exactly how geologically active a terrestrial planet like Mars can be, and what factors influence this.
The Seismic Activity of Rocky Planets
According to a paper presented at the 52nd Lunar and Planetary Science Conference of 2021 called “Constraints on the Martian Upper Mantle Structure from InSight Seismic Data” the seismicity of a terrestrial planet depends on the state of strain inside of it. This is influenced by the amount of strain that the planet has developed throughout its history or as the paper puts it “throughout the thermal evolution of the planet.”
This thermal evolution is governed by how the planet dissipates heat. Seismic activity results from this heat building up to the point where the built-up strain causes material failure. The “disturbance” is described by the paper as traveling from the source of that material failure through the planet as seismic waves.
This particular paper is only suggesting a “preliminary radial velocity model” for the upper mantle of Mars with numbers that are very much in line with other studies that came out around the same time.
Unfortunately, there is a major lack of data for seismic events on the red planet and we would have to know a lot more about the process that leads to a marsquake, or as the paper puts it, how heat builds inside the planet until that point of material failure is reached.
Right now, no marsquake we’ve detected has exceeded a 4.0 on the Richter scale. On Earth, a quake must be greater than 5.5 in magnitude before buildings start getting damaged.
Mars does not have plate tectonics and that fact could mean [speculation alert] that it doesn’t have nearly the same level of interior strain that Earth does. The paper considers all of the information it has presented on Mars’ interior to be perfunctory, which is defined in the dictionary to be an action that is carried out with a minimum of effort or reflection.
So, that’s what makes me take think that we’re still in the early days of understanding the complex inner workings of the red planet.
But if scientists like Panning are hopeful that larger scale marsquakes are possible, then I guess I’ll be hopeful too.
So, I guess the unsatisfying answer to all this is that we simply don’t know if or when a “big one” may happen on Mars.
Is it weird to hope for a major marsquake?
Seismic Station (15638870938).jpg by daryl_mitchell from Saskatoon, Saskatchewan, Canada, CC BY-SA 2.0 Generic, https://creativecommons.org/licenses/by-sa/2.0/deed.en
Earth-crust-cutaway-english.svg by Surachit – Self-made, based on the public domain image, CC BY-SA 3.0, https://creativecommons.org/licenses/by-sa/3.0
Estimated-field-and-flow-within-the-core-in-2015.jpg by Christopher C. Finlay, Julien Aubert, Nicolas Gillet – Christopher C. Finlay, Julien Aubert, Nicolas Gillet. “Gyre-driven decay of the Earth’s magnetic dipole ,” Nature Communications doi:10.1038/ncomms10422. CC BY 4.0, https://creativecommons.org/licenses/by/4.0
Earth poster.svg by Kelvinsong – Own work, CC BY-SA 3.0
LLSVP.gif by Sanne.cottaar – Own Work, CC BY-SA 4.0 International
Heat flow of the inner earth.jpg by Bkilli1 – Own work, CC BY-SA 3.0