NASA’s InSight Lander Gives First Look at Mars Interior, Yielding a Big Surprise

Science

The Wall Street Journal 22 July, 2021 - 01:00pm 68 views

NASA-funded researchers said Thursday they had mapped the interior of Mars, using seismic data collected by the agency’s Mars InSight lander to reveal a planet with a molten core whose size and composition came as major surprises.

The interior map—the first ever created of another planet—shows that the internal structure of Mars differs dramatically from Earth’s. Mars has a thicker crust and a thinner underlying mantle layer as well as a core that is bigger, less dense and more liquid than the researchers had expected.

The scientists said their findings, which were described in three papers published Thursday in the journal Science, suggest that Mars formed millions of years before Earth, when the sun was still condensing from a cloud of glowing gas.

“It gives us our first sample of the inside of another rocky planet like Earth, built out of the same materials but very, very different,” Sanne Cottaar, a seismologist at the U.K.’s University of Cambridge, said of the new research. “It is impressive.”

Dr. Cottaar, who wasn’t involved in the new research, called the findings “a major leap forward in planetary seismology.”

travel through the planet, the strength and frequency of their reflections reveal the planet’s structure.

travel through the planet, the strength and frequency of their reflections reveal the planet’s structure.

travel through the planet, the strength and frequency of their reflections reveal the planet’s structure.

The new in-depth portrait of Mars was assembled by an international team of more than 40 scientists working at research centers from Pasadena to Moscow.

The scientists peered into the innards of the red planet using French-built seismometers on board the space agency’s $828 million InSight lander, which in 2018 landed on a smooth plain along the Martian equator called Elysium Planitia.

The instruments captured detailed information about hundreds of marsquakes, including the way the vibrations caused by the alien temblors were reflected and refracted by subsurface layers to reveal their positions and densities.

“The clues don’t lie on the surface,” said Amir Khan, a geophysicist at the University of Zurich in Switzerland and a member of the research team. “You have to look inside for the fundamental building blocks that make a planet: the crust, the mantle, the core and the separation of materials that happens as the planet forms.”

The InSight lander has recorded more than 700 marsquakes since beginning operations in February 2019, fewer and less intense than the scientists had expected.

Even the strongest of them, registering at about magnitude 4.0, would barely rattle the windows on Earth. The largest quake on Earth in 2020—a magnitude 7.8 temblor that struck Perryville, Alaska—was about 6,000 times more powerful than the biggest marsquake recorded by InSight.

Mars is so seismically stable that InSight’s sensors were able to detect tiny shivers from faults thousands of kilometers away, the scientists said. “It is a testament to the quietness of Mars,” said team leader Mark Panning, InSight project scientist at NASA’s Jet Propulsion Laboratory in Southern California. “You would never get that quiet on Earth because, no matter where you go, the oceans are always making seismic noise.”

The research showed that the core of Mars has a radius of nearly 1,137 miles (1,830 kilometers) and extends about midway to the planet’s surface. As best as the scientists can tell, the molten core isn’t very dense and likely contains a mixture of light elements such as hydrogen, oxygen, carbon and sulfur.

Less layered than Earth's mantle, without a layer of the mineral bridgmanite.

Liquid core containing mixture of lighter volatile elements.

Spins creating the earth’s magnetic field.

Hot, dense semi-solid rock, cooler and more rigid near the surface.

1. Crust, 14-44 miles

2. Mantle, 990 miles

Less layered than Earth's mantle, without a layer of the mineral bridgmanite.

Liquid core containing mixture of lighter volatile elements.

1. Crust, 0-60 miles

2. Mantle, 1,800 miles

Hot, dense semi-solid rock, cooler and more rigid near the surface.

3. Liquid outer core, 1,370 miles

Spins creating the earth’s magnetic field.

1. Crust, 14-44 miles

2. Mantle, 990 miles

Less layered than Earth's mantle, without a layer of the mineral bridgmanite.

3. Liquid core, 1,137 miles

Liquid core containing mixture of lighter volatile elements.

1. Crust, 0-60 miles

2. Mantle, 1,800 miles

Hot, dense semi-solid rock, cooler and more rigid near the surface.

3. Liquid outer core, 1,370 miles

Spins creating the earth’s magnetic field.

4. Solid inner core, 780 miles

Wrapped around the core is a relatively thin mantle, composed perhaps of just two or three rocky layers. These are topped by an unusually thick and rigid outer shell of upper mantle and crust, called the lithosphere, which the scientists said seems to be two or three times thicker than a similar formation on Earth. The crust itself was found to have a thickness of between 14 and 44 miles (24 and 72 kilometers).

But Mars might not have given up all its structural secrets. The scientists discovered that the rocky soil beneath the lander dissipates seismic energy, meaning that the 794-pound, solar-powered craft may be located within a vast seismic “shadow” where some marsquakes might elude detection.

The new findings from InSight come as NASA’s six-wheeled Perseverance rover prepared to collect its first samples of Martian rock at its landing site, located 2,100 miles from InSight in the Jezero crater. Plans call for the $2.7 billion rover to collect up to 43 samples that might contain chemical traces of ancient microbial life—if any ever existed on the now-barren planet—for eventual transport back to Earth.

InSight has been struggling in recent months, as wind-whipped Martian dust collected on its solar panels and cut their ability to generate electrical power. In May, NASA engineers directed the probe’s digging tool to pile sand on the lander’s deck so that the wind would blow it across the solar panels and, like a whisk broom, sweep away the dust.

“We dump sand on ourselves to get rid of dust,” Dr. Panning said, adding that the fix seemed to be working.

The lander recently was granted a two-year extension for scientific work, now lasting until the end of 2022.

Write to Robert Lee Hotz at sciencejournal@wsj.com

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Read full article at The Wall Street Journal

Thickness and structure of the martian crust from InSight seismic data

Science Magazine 22 July, 2021 - 02:01pm

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Because of the lack of direct seismic observations, the interior structure of Mars has been a mystery. Khan et al., Knapmeyer-Endrun et al., and Stähler et al. used recently detected marsquakes from the seismometer deployed during the InSight mission to map the interior of Mars (see the Perspective by Cottaar and Koelemeijer). Mars likely has a 24- to 72-kilometer-thick crust with a very deep lithosphere close to 500 kilometers. Similar to the Earth, a low-velocity layer probably exists beneath the lithosphere. The crust of Mars is likely highly enriched in radioactive elements that help to heat this layer at the expense of the interior. The core of Mars is liquid and large, ∼1830 kilometers, which means that the mantle has only one rocky layer rather than two like the Earth has. These results provide a preliminary structure of Mars that helps to constrain the different theories explaining the chemistry and internal dynamics of the planet.

Science, abf2966, abf8966, abi7730, this issue p. 434, p. 438, p. 443 see also abj8914, p. 388

A planet’s crust bears witness to the history of planetary formation and evolution, but for Mars, no absolute measurement of crustal thickness has been available. Here, we determine the structure of the crust beneath the InSight landing site on Mars using both marsquake recordings and the ambient wavefield. By analyzing seismic phases that are reflected and converted at subsurface interfaces, we find that the observations are consistent with models with at least two and possibly three interfaces. If the second interface is the boundary of the crust, the thickness is 20 ± 5 kilometers, whereas if the third interface is the boundary, the thickness is 39 ± 8 kilometers. Global maps of gravity and topography allow extrapolation of this point measurement to the whole planet, showing that the average thickness of the martian crust lies between 24 and 72 kilometers. Independent bulk composition and geodynamic constraints show that the thicker model is consistent with the abundances of crustal heat-producing elements observed for the shallow surface, whereas the thinner model requires greater concentration at depth.

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By Brigitte Knapmeyer-Endrun, Mark P. Panning, Felix Bissig, Rakshit Joshi, Amir Khan, Doyeon Kim, Vedran Lekić, Benoit Tauzin, Saikiran Tharimena, Matthieu Plasman, Nicolas Compaire, Raphael F. Garcia, Ludovic Margerin, Martin Schimmel, Éléonore Stutzmann, Nicholas Schmerr, Ebru Bozdağ, Ana-Catalina Plesa, Mark A. Wieczorek, Adrien Broquet, Daniele Antonangeli, Scott M. McLennan, Henri Samuel, Chloé Michaut, Lu Pan, Suzanne E. Smrekar, Catherine L. Johnson, Nienke Brinkman, Anna Mittelholz, Attilio Rivoldini, Paul M. Davis, Philippe Lognonné, Baptiste Pinot, John-Robert Scholz, Simon Stähler, Martin Knapmeyer, Martin van Driel, Domenico Giardini, W. Bruce Banerdt

Data from the InSight mission on Mars help constrain the structure and properties of the martian mantle.

By Brigitte Knapmeyer-Endrun, Mark P. Panning, Felix Bissig, Rakshit Joshi, Amir Khan, Doyeon Kim, Vedran Lekić, Benoit Tauzin, Saikiran Tharimena, Matthieu Plasman, Nicolas Compaire, Raphael F. Garcia, Ludovic Margerin, Martin Schimmel, Éléonore Stutzmann, Nicholas Schmerr, Ebru Bozdağ, Ana-Catalina Plesa, Mark A. Wieczorek, Adrien Broquet, Daniele Antonangeli, Scott M. McLennan, Henri Samuel, Chloé Michaut, Lu Pan, Suzanne E. Smrekar, Catherine L. Johnson, Nienke Brinkman, Anna Mittelholz, Attilio Rivoldini, Paul M. Davis, Philippe Lognonné, Baptiste Pinot, John-Robert Scholz, Simon Stähler, Martin Knapmeyer, Martin van Driel, Domenico Giardini, W. Bruce Banerdt

Data from the InSight mission on Mars help constrain the structure and properties of the martian mantle.

Scientists finally know what’s inside Mars

The Independent 22 July, 2021 - 01:05pm

Scientists have finally been able to understand the crust underneath the surface of Mars.

The research represents the first time that humanity has been able to start mapping the interior of another planet beyond our own Earth.

The new research relied on data taken from Nasa’s InSight mission, which has been looking for Marsquakes that reverberate across its surface.

Using information about those quakes, researchers are able to understand what might be lurking beneath the Martian surface.

Beneath the InSight landing site, the crust is either approximately 20 kilometres or 39 kilometres thick, according to an international research team led by geophysicist Dr Brigitte Knapmeyer-Endrun at the University of Cologne’s Institute of Geology and Mineralogy and Dr Mark Panning at Jet Propulsion Laboratory, California Institute of Technology (Caltech).

Studying a planet’s interior layers - its crust, mantle and core - can reveal key insights into its formation and evolution, as well as uncovering any geomagnetic and tectonic activity.

Deep interior regions can be probed by measuring the waves that travel through the planet after seismic events like a quake.

The internal characteristics of Earth have been surveyed using such methods.

In the past, only relative differences in the thickness of Mars could be estimated, and additional assumptions were required to obtain absolute thicknesses. These values showed large scatter, depending on which assumptions were made.

Seismology replaces these assumptions with a direct measurement at the landing site, and calibrates the crustal thickness for the entire planet.

The independent data also allows researchers to estimate the density of the crust.

Dr Knapmeyer-Endrun, lead author of the paper published in Science, said: “What seismology can measure are mainly velocity contrasts. These are differences in the propagation velocity of seismic waves in different materials.

“Very similar to optics, we can observe phenomena like reflection and refraction.

“Regarding the crust, we also benefit from the fact that crust and mantle are made of different rocks, with a strong velocity jump between them.”

The crust’s structure can be determined precisely based on these jumps.

According to the data, at the InSight landing site the top layer is about eight kilometres thick, with a margin of two kilometres either way.

Below that, another layer follows to about 20 kilometres, with a margin of five kilometres.

Dr Knapmeyer-Endrun said: “It is possible that the mantle starts under this layer, which would indicate a surprisingly thin crust, even compared to the continental crust on Earth.

“Beneath Cologne, for example, the Earth’s crust is about 30 kilometres thick.”

There is a third layer on Mars, which would make the crust under the landing site around 39 kilometres thick, with a margin of eight kilometres.

That would be consistent with previous findings, but the signal from this layer is not essential to match existing data, the experts said.

In both cases they are unable to rule out the possibility that the entire crust is made of the same material known from surface measurements and from Martian meteorites.

The data suggests the uppermost layer is made up of an unexpectedly porous rock. There could also be other rock types at greater depths than the basalts seen at the surface.

The single, independent measurement of crustal thickness at the InSight landing site is sufficient to map the crust across the entire planet.

Measurements from satellites orbiting Mars provide a very clear picture of the planet’s gravity field, allowing the scientists to compare relative differences in crustal thickness to the measurement taken at the landing site.

The combination of this data provides an accurate map.

Data on the present-day structure of Mars can also provide information on how the planet evolved.

In a separate study, Simon Stahler of ETH Zurich and colleagues used the faint seismic signals reflected off the Martian core-mantle boundary to investigate the planet’s core.

They found that the relatively large liquid metal core has a radius of nearly 1,830 kilometres and begins roughly halfway between the surface and the centre of the planet, suggesting the mantle consists of only one rocky layer, rather than two, like in Earth.

The findings indicate that the iron-nickel core is less dense than previously thought and enriched in lighter elements.

ESA & MPS for OSIRIS Team

NASA data reveals details of the core, mantle and crust of Mars

Daily Mail 22 July, 2021 - 01:00pm

By Ryan Morrison For Mailonline

The inner structure of the planet Mars has been revealed thanks to the NASA InSight lander, showing the size of the core, mantle and crust for the first time.

Using data on 'marsquakes' experienced by the NASA robot, were able to find evidence of three layers of crust stretching down 41 miles below the surface.

Each layer of the crust has a slightly different makeup, and just below the crust is the mantle, which goes down as far as 500 miles, with the rest an iron-nickel core. 

The findings were published in three studies using NASA InSight data, from the University of Cologne, the California Institute of Technology and ETH Zurich.

Using data on 'marsquakes' experienced by the NASA robot, were able to find evidence of three layers of crust stretching down 41 miles below the surface

The inner structure of the planet Mars has been revealed thanks to the NASA InSight lander, showing the size of the core, mantle and crust for the first time

The findings were published in three studies using NASA InSight data, from the University of Cologne, the California Institute of Technology and ETH Zurich 

Marsquakes are the shaking of the surface or interior of the planet, caused by the sudden release of energy in the planet's interior. 

On Earth this is from plate tectonics and on Mars it could be hotspoots.

These could be at sites like Olympus Mons or the Tharsis Montes. 

Hundreds of marsquakes were detected in two years of the NASA InSight robot operating on Mars.

The first marsquake was measured and recorded by InSight on April 6, 2019.

The InSight Mars lander operated on the Red Planet from May 5, 2018 until February 2021 when dust covered the solar powers preventing it from charging. 

Its objectives were to place a seismometer on the surface to measure seismic activity - marsquakes - and produce 3D models of the planet's interior. 

Researchers have reported preliminary findings from the mission and for the first time have begun to map the interior of a planet other than the Earth.

Beneath the InSight landing site, the crust is either 12 miles or 24 miles thick, according tot he team led by the University of Cologne, working with NASA JPL. 

Studying a planet's interior layers - its crust, mantle and core - can reveal insights into its formation and evolution, as well as uncovering any geomagnetic and tectonic activity, the team, including researchers from Caltech, explained.

Deep interior regions can be probed by measuring the waves that travel through the planet after seismic events like a quake.

The internal characteristics of Earth have been surveyed using such methods, revealing the size, structure and make-up of the core and mantle.

In the past, only relative differences in the thickness of Mars could be estimated, and additional assumptions were required to obtain absolute thicknesses. 

These values showed large scatter, depending on which assumptions were made.

Seismology replaces these assumptions with a direct measurement at the landing site, and calibrates the crustal thickness for the entire planet.

The independent data also allows researchers to estimate the density of the crust, revealing it is potentially split into three distinct sections.

Dr Knapmeyer-Endrun, lead author of the paper published in Science, said: 'What seismology can measure are mainly velocity contrasts. These are differences in the propagation velocity of seismic waves in different materials.

The InSight Mars lander operated on the Red Planet from May 5, 2018 until February 2021 when dust covered the solar powers preventing it from charging

The two largest quakes detected by NASA's InSight appear to have originated in a region of Mars called Cerberus Fossae (pictured here by the Mars Reconnaissance Orbiter)

'Very similar to optics, we can observe phenomena like reflection and refraction.

'Regarding the crust, we also benefit from the fact that crust and mantle are made of different rocks, with a strong velocity jump between them.'

The crust's structure can be determined precisely based on these jumps, and according to the data the top layer is about five miles thick. 

Below that, another layer follows to about 12 miles, according to Dr Knapmeyer-Endrun, who said: 'It is possible that the mantle starts under this layer, which would indicate a surprisingly thin crust, even compared to the continental crust on Earth.

This is an artist impression of SEIS, a highly sensitive seismometer that was used to detect marsquakes from the Red Planet's surface for the first time

Volcanos on Mars could still be active, researchers claim, saying that it could mean life on the Red Planet was active within the past 30,000 years.

University of Arizona's Lunar and Planetary Laboratory and the Planetary Science Institute discovered unknown volcanic deposits in satellite images of the planet.

The team said these images showed evidence of eruptions in the past 50,000 years, in the Elysium Planitia region, about 1,000 miles from the NASA InSight lander.

Most volcanism on the Red Planet occurred between three and four billion years ago, with smaller eruptions in isolated locations continuing up to three million years ago.

They say this evidence 'absolutely raises the possibility that there could still be volcanic activity on Mars' and of habitable conditions under the Martian surface.  

'This may be the youngest volcanic deposit yet documented on Mars,' said lead study author David Horvath, adding that 'if we were to compress Mars' geologic history into a single day, this would have occurred in the very last second.' 

'Beneath Cologne, for example, the Earth's crust is about 30km (18.6 miles) thick.'

There is a third layer on Mars, which would make the crust under the landing site around 24 miles thick, consistent with previous findings.

But the signal from this layer is not essential to match existing data, the experts said.

In both cases they are unable to rule out the possibility that the entire crust is made of the same material known from surface measurements and Martian meteorites.

The data suggests the uppermost layer is made up of an unexpectedly porous rock. 

There could also be other rock types at greater depths than the basalts seen at the surface, the authors said.

The single, independent measurement of crustal thickness at the InSight landing site is sufficient to map the crust across the entire planet.

Measurements from satellites orbiting Mars provide a very clear picture of the planet's gravity field, allowing the scientists to compare relative differences in crustal thickness to the measurement taken at the landing site.

The combination of this data provides an accurate map, which could also provide information on how the planet evolved into the dusty, lifeless world it is today. 

The crustal thickness of Mars is particularly interesting because the crust formed at an early formation stage from the remnants of a molten mantle. 

Thus, data on its present-day structure can also provide information on how Mars evolved. In addition, a more precise understanding of the evolution of Mars helps to decipher how early differentiation processes unfolded in the solar system and why Mars, Earth, and other planets are so different today. 

InSight's super-sensitive seismometer, known as SEIS, has recorded more than 480 marsquakes

Its objectives were to place a seismometer on the surface to measure seismic activity - marsquakes - and produce 3D models of the planet's interior

In a separate study, Simon Stahler of ETH Zurich used the faint seismic signals reflected off the Martian core-mantle boundary to investigate the planet's core.

They found that the relatively large liquid metal core has a radius of nearly 1,140 miles, beginning roughly halfway between the surface and the centre of the planet, suggesting the mantle consists of only one rocky layer, rather than two, like in Earth.

The findings indicate that the iron-nickel core is less dense than previously thought and enriched in lighter elements. 

'Direct seismic observations on Mars represent a major leap forward in planetary seismology,' the team said. 

'Over the coming years, as more marsquakes are measured, scientists will refine these models of the red planet and reveal more of Mars' enigmatic mysteries.' 

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NASA craft provides an insight into Mars’ interior – Physics World

physicsworld.com 22 July, 2021 - 01:00pm

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The interior of Mars has been mapped with seismic waves for the first time revealing tantalising details about how Mars may have formed across billions of years. The work was done by NASA’s Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport (Insight) craft that landed in Elysium Planitia, close to the Martian equator, in November 2018. Since then, its seismometer has detected more than 500 marsquakes produced by tectonic stresses, albeit none stronger than magnitude 4 on the Richter scale.

The quakes send seismic waves reverberating through the interior of the red planet. Their strength and their velocity depends upon the composition of the material they are passing through, and hence they provide a window into Mars’ inner structure. Now three new papers show that Mars’ interior has crucial differences to Earth’s. “Mars is smaller and therefore cools faster than Earth,” says Amir Khan of the Institute of Geophysics at ETH Zurich, who is the lead author of one of the papers that studied the upper mantle.

This heat escape is exacerbated by the lack of a bridgmanite layer in Mars’ lower mantle. Bridgmanite is the most common mineral on Earth, but because it is buried 660 km below the surface where the temperatures and pressures are high enough for it to form, it is rarely seen. However, the seismic data collected by InSight implies that Mars lacks a bridgmanite layer. “Bridgmanite acts as a barrier to convection inside Earth,” says Simon Stähler, also of ETH Zurich and lead author of a paper that describes Mars’ core and lower mantle. Rising mantle plumes have their progression slowed by this layer, reducing the exchange of heat between the core and the surface.

Mars’ surface lies on top of a crust that is, on average, thicker than Earth’s crust, and is composed of several layers according to Brigitte Knapmeyer-Endrun, who is the lead author of a seismic study that shows two, or possibly three, crustal layers. The uppermost layer extends to a depth between 6 and 11 km, while a second layer goes down between 15 and 25 km. A third layer, if it exists, would then extend to 39 km below the surface at InSight’s location, but the measurements made so far are unable to distinguish between the two- and three-layer scenarios.

“The rather low seismic velocities that we find for the uppermost layer is probably due to a significant amount of porosity, which could mean rocks that have been fractured due to repeated meteorite impacts, and chemical alteration,” Knapmeyer-Endrun told Physics World. The other layers are probably less fractured and altered but could have a different composition.

Earth’s crust also has multiple layers, but is much thinner on average, being “roughly 30 km thick below continents but only 7 km thick beneath oceans,” says Sanne Cottaar, who is a global seismologist from the University of Cambridge. “The differences [between Earth and Mars’ interior] have much to do with Mars having a single, stable lid, while Earth has plate tectonics.”

InSight’s initial results have provided a rough guide to the interior of Mars, and it is also the first time that a rocky planet other than Earth has had its interior mapped in such fashion. Further detections of seismic waves will provide greater resolution, and the results can be fed into models of how Mars – and indeed other planets – formed and developed.

“Mars presents unique questions,” says Cottaar. “There’s the mystery of the early magnetic field that died, the strange topography where the southern hemisphere is high and the northern hemisphere is low, and the very localised volcanism. The new constraints provided by the seismic data can now be used to model whether these are caused by Mars’ thermal and dynamical history.”

The three papers are published in Science.

Keith Cooper is a science writer based in the UK

Physics World represents a key part of IOP Publishing's mission to communicate world-class research and innovation to the widest possible audience. The website forms part of the Physics World portfolio, a collection of online, digital and print information services for the global scientific community.

Scientists Just ‘Looked’ Inside Mars. Here’s What They Found

WIRED 22 July, 2021 - 01:00pm

While humans have been struggling to control the Covid-19 pandemic, baking in record heat, and trying to figure out how not to run out of water, our spacecraft on Mars have been enjoying a rather more tranquil existence. (Not needing to breathe helps.) Parked on the Martian surface, the InSight lander is listening for marsquakes, while the Perseverance rover is rolling around in search of life.

This week, scientists are dropping an Olympus Mons of findings from the two brave robots. In three papers published today in the journal Science—each authored by dozens of scientists from around the world—researchers detail the clever ways they used InSight’s seismometer to peer deep into the Red Planet, giving them an unprecedented understanding of its crust, mantle, and core. It’s the first time scientists have mapped the interior of a planet other than Earth. And yesterday, another group of scientists held a press conference to announce early research results from Perseverance, and the next steps the rover will take to explore the surface of Jezero Crater, once a lake that could have been home to ancient microbial life.

Scientists still have a lot to learn about the Red Planet. “It's built from similar building blocks as our own planet, but Mars looks very different,” says University of Cambridge global seismologist Sanne Cottaar, who penned a perspective paper in Science on the three new studies. “There's lots of evidence that its evolution has been very different. And now forming this image of the layering of the planet will give us the tools to work out how this formed, how Mars came to be.”

Curiosities abound when comparing the two. Why, for instance, does Earth have a magnetic field, but Mars’ seems to have disappeared? Why are so many volcanoes spread all over Earth, while volcanoes are more localized—and bigger—on Mars? (At 374 miles in diameter and 16 miles high, Olympus Mons is the biggest known volcano in the solar system.) Its formation must have been cataclysmic, but the surface of Mars is now quiet; unlike Earth, it doesn’t seem to be volcanically active. (In May, though, scientists presented evidence of what they say is recent activity.) Only by peeking under the surface can scientists better understand these planetary oddities—and in doing so, better understand Earth’s own quirks as a fellow rocky planet.

But before we dive into today’s avalanche of scientific literature, we need a crash course on the workings of both Mars and its InSight observer. Compared to Earth, the Red Planet is geologically quite calm. Because our planet has plate tectonics—huge slabs of land that shift over the underlying mantle—the surface is positively popping with activity like volcanoes and catastrophic earthquakes. Mars lacks plate tectonics; it doesn’t have a plated surface, because its core formed and cooled off rapidly during its early days. Today it shakes with much smaller quakes that may come from the contracting of the planet as it continues to cool.

The InSight lander’s job is to detect these quakes with its seismometer, which it’s been doing since February 2019. The instrument provides scientists with extremely rich seismic data on two phenomena in particular: the P-waves and S-waves that marsquakes produce. “P-waves are compressional waves, like sound in air, and they are the fastest waves that we see moving through any planetary body,” says University of Cologne seismologist Brigitte Knapmeyer-Endrun, lead author on the paper that modeled Mars’ crust. “And then we have the secondary waves, the S-waves, the shear waves. The motion is more like if you pluck a string on a guitar and it swings.”

Critically, these S-waves are slower than P-waves, so when a quake pops off, they arrive at InSight’s seismometer a bit later. “This difference between the arrival of the P and S waves can give you an idea about what's the location of the quake; how far it was away from your station,” says Knapmeyer-Endrun. The waves also differ in what mediums they can travel through, versus which ones they bounce off of. P-waves move through solids, liquids, and gases, while S-waves only travel through solids.

By analyzing the waves that reach InSight’s seismometer, scientists can get an idea of the composition of Mars’ insides. Since S-waves can’t travel through the liquid core, all of their energy bounces off the boundary between core and mantle. Think of it like binary code for computers: Just as two elements—ones and zeros—can combine to produce extremely complex programming, so too can two kinds of waves combine to produce a sophisticated picture of the Red Planet’s guts. “We also look at differences in arrival times, and then we can say, ‘OK, this tells us something about the thickness of the layer,’” says Knapmeyer-Endrun.

Using this technique, she and her colleagues were able to estimate the thickness of the crust. Previously, scientists had used satellites flying overhead to measure the differences in gravity and topography across the planet, and they had taken a stab at the crust’s thickness that way, landing on an estimate of a global average of 110 kilometers. “Now, with our measurements from inside, we can say that that's definitely too much,” says Knapmeyer-Endrun. They now think the maximum figure for average thickness is 72 kilometers.

The researchers found the core density to be surprisingly low, at only about 6 grams per cubic centimeter, which is much lower than what they’d expected of an iron-rich center. “It’s still a bit of a mystery how the core is so light,” Stähler says. There must be lighter elements present, though exactly what those may be is unclear. He and his team eventually hope to detect P-waves produced by a marsquake originating directly across the planet from where InSight is parked. Since they can pierce through the core-mantle boundary, they will carry information about the core’s composition to the lander's receiver. But for that to happen, Stähler says, “Mars has to play along and give us this one quake on the other side of the planet.”

In Stähler’s team’s paper, they report a core radius of 1,830 kilometers. Another team, led by ETH Zürich geophysicist Amir Khan, found that this size is so large it leaves little room for an Earth-like lower mantle, a layer that acts as a heat-trapping blanket around the core. Earth’s mantle is divided into two parts, with a so-called transition zone in between; the upper and lower levels are composed of different minerals. “The mantle of Mars is—can I say flippantly—a slightly simpler version of the mantle of Earth, simply in terms of the mineralogy,” says Khan, lead author on the paper describing the mantle.

Previous estimates of the core’s radius using geochemical and geophysical data hinted at the absence of a lower mantle, but scientists needed InSight’s seismological readings to confirm it. Without this layer, the Martian core likely cooled much more readily than Earth’s. This is key to understanding the evolution of the Red Planet, and in particular why it lost its magnetic field, a barrier that would have protected the atmosphere—and potential life—from harsh solar winds. Creating a magnetic field requires a temperature gradient between the outer and inner core, high enough to create circulating currents that churn the core’s liquid and give rise to a magnetic field. But the core cooled so fast that these convection currents died out.

Khan’s analysis also shows that Mars has a thick lithosphere, the rigid and cold part of the mantle. This might be a clue as to why the Red Planet doesn’t have the plate tectonics that drive the frenzy of volcanism on Earth. “If you have a very thick lithosphere, it's going to be very difficult to break this thing up and create the exact equivalent of plate tectonics on Earth,” says Khan. “Maybe Mars had it very early on, but it's certainly shut down now.”

While InSight eavesdrops on the interior vibrations of Mars, Perseverance has been rolling around its dusty surface looking for signs of ancient life in the rocks, scoping out places to collect regolith samples, and learning about Jezero’s geological history. “Exploration is not a sprint, it’s a marathon,” said Thomas Zurbuchen, NASA’s associate administrator of science, who opened the press conference on Wednesday that highlighted early advances from the rover’s first few months in its new home. “Perseverance is one step in a long legacy of carefully planned Mars exploration that links robotic and human exploration for the time to come.”

The scientists at the press briefing laid out what Perseverance has been up to on its road trip so far. “The challenge is figuring out exactly where we want to go and how we’re going to fit everything into our schedule,” said Vivian Sun, a systems engineer at NASA’s Jet Propulsion Laboratory. Sun said they decided to detour Perseverance about 3,000 feet south of its landing site to extract its first rock samples, which will be stored in the belly of the rover and later cached on the planet’s surface for a future return mission that will ferry them to Earth.

Perseverance is equipped with a 7-foot arm carrying a suite of new gadgets, including the Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE, that has already demonstrated the conversion of small amounts of atmospheric carbon dioxide into oxygen. The arm also includes sensors to assess the present climate and high-resolution cameras to take pictures of the rover's surroundings. “We’re getting photobombed by dust devils,” said Caltech geochemist Ken Farley, and large wind gusts that, to him, appear very Earth-like.

Some of the rocks in the images resemble hardened lake mud, which might indicate a good place to search for fossilized biosignatures—signs of former life. The team is also interested in figuring out whether the rocks in the crater are of sedimentary or volcanic origin; if the latter, they can be radiometrically dated to better understand the geologic timeline of the materials Perseverance is collecting. Farley says the most surprising observation they’ve made so far is evidence of flash flooding and varying water levels, suggesting that in the past the crater went through several phases of drying out and filling back up with liquid water.

With its newly designed AI-powered software, Perseverance also broke the record for the longest time a rover has ever driven itself on Mars—on only its second day of driving solo. “Autonomous driving is now just about as fast as human-directed driving,” said Olivier Toupet, a JPL roboticist. While humans can remotely steer Perseverance around 100 feet per day, carefully maneuvering it around obstacles, the AI software allows for increased agility. It creates a three-dimensional mapping of the surface while the rover is driving, so it can update and optimize its route in real time. Toupet said the longest autonomous Martian drive so far has been about 350 feet, and they expect Perseverance to quadruple that distance within the next few weeks.

After its southern detour, Perseverance will trek northwest to the site of an ancient river delta that once fed water into Jezero Crater. Then it will fully ramp up its use of instruments on the robotic arm to discover the elemental composition, mineralogy, shape, and texture of the nearby Martian rocks, information that will help scientists learn about the basin’s past water flow.

A few thousand miles away, InSight will continue to record quakes and reveal the inner workings of the first rocky planet, other than our own, that scientists have been able to characterize with seismology. “It’s a very young field for humanity,” Cottaar says. “We’ve been looking up at the stars much longer than we’ve been looking beneath our feet.”

Ever wondered what's at the heart of Mars? Now we know

ABC News 22 July, 2021 - 01:00pm

But for researchers working on NASA's InSight mission, these seismic vibrations offer tantalising clues about what Mars looks like on the inside.  

Using data collated over several years, researchers have mapped the planet's crust, mantle and core for the first time — and they look quite different to Earth's interior, according to three studies published today in Science.

Unlike Earth, Mars' liquid core takes up nearly half of its interior, leaving little room for the planet's upper layers.

The findings challenge previous ideas about what lies beneath the planet's surface, according to Suzanne Smrekar, study coauthor and the mission's deputy principal investigator from NASA's Jet Propulsion Laboratory.

"This information helps us understand the overall history and evolution of Mars, from the very earliest days of the planet's formation to the present day," she said.

The InSight lander touched down on Mars at the end of 2018 on a volcanic plain known as Elysium Planitia.

While other Mars missions have focused on finding out what's happening on the planet's surface, InSight's goal is to work out what lies beneath. 

In February 2020, InSight's seismometer picked up 174 marsquakes — vibrations that travel below the surface, similar to earthquakes on our own planet.

Studying how these internal wobbles travel can offer clues about the planet's inner structure, right down the to its liquid core, said Katarina Miljkovic, a planetary scientist at Curtin University who is also involved in NASA's InSight mission. 

"These marsquakes can tell us about what the interior structure actually looks like," said Dr Miljkovic, who was not involved in the three new studies. 

NASA's InSight researchers analysed marsquake data collected by InSight's seismometer in 2019. 

When they studied faint marsquake signals that had bounced off the planet's core, they discovered that it had a radius of 1,830 kilometres.

The huge liquid core takes up nearly half of the planet's interior.

It's also a melting pot of iron, nickel, and light elements like sulphur, making it less dense than the team expected.  

The core's massive size suggests the planet's mantle — the layer that sits between the core and crust — is relatively thin and is made up of just one rocky layer rather than two, like Earth's.

This finding throws water on the idea that there was a layer at the base of the mantle that pushes hot molten rock to the surface, which was once thought to be the driving force behind Mars' huge volcanoes. 

"That idea is out the door," Dr Smrekar said.

"These ideas about the thickness of the layers have really major impacts for understanding how processes are happening inside the planet."

Using data from eight marsquakes, the researchers were able dive 800 kilometres below the surface for a closer look at Mars' mantle.

They hit upon a thick rocky layer lying almost 500 kilometres deep and found that seismic waves associated with marsquakes slow down as they travel through this mantle layer. 

Mars' mantle also lacked a mineral found in Earth's called bridgmanite, which has an insulating effect. 

This suggests that Mars' core might have cooled more rapidly in its early days than Earth's did.

The team were also able to measure the Red Planet's crust — its outermost layer.

Across the planet, Mars' crust is about 24 to 72 kilometres thick on average — slightly thinner than previous estimates, which which fell somewhere between 33 and 81 kilometres. 

For perspective, Earth's crust is around 15 to 20 kilometres thick.

"Most estimates of the crustal thickness have been larger than the value that we're finding," Dr Smrekar said. 

They also found that Mars' crust is made up of two or possibly even three distinct layers, indicating that it could be made up of different types of rock rather than just one, as previously thought. 

Another surprise was that the crust was rich in radioactive elements like uranium and thorium that heat up the planet's outer shell. 

"This thinner crust is at the edge of what we thought was possible in terms of the concentrations of these elements," Dr Smrekar said.

"We're going to have to go back and rethink how those elements get concentrated into the crust that formed initially."

Dr Miljkovic said that the new findings were crucial in building a more accurate picture of the Red Planet's insides.

"It's telling the story about the planet's structure that we really didn't know much about in the past," Dr Miljkovic said. 

"We had some idea of how thick the crust was and that there was a core. But [the findings] put a little bit more precision to where the layers are in the interior."

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Dr Smrekar said the new results indicate there is still so much to learn about how Mars became the planet is today. 

"We have to train ourselves to recognise all these different signatures in seismic waves" she said. 

"All these things help us gain new information about the variability inside the planet."

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NASA's InSight Reveals the Deep Interior of Mars – NASA’s Mars Exploration Program

NASA Mars Exploration 21 July, 2021 - 07:00pm

Before NASA’s InSight spacecraft touched down on Mars in 2018, the rovers and orbiters studying the Red Planet concentrated on its surface. The stationary lander’s seismometer has changed that, revealing details about the planet’s deep interior for the first time.

Three papers based on the seismometer’s data were published today in Science, providing details on the depth and composition of Mars’ crust, mantle, and core, including confirmation that the planet’s center is molten. Earth’s outer core is molten, while its inner core is solid; scientists will continue to use InSight’s data to determine whether the same holds true for Mars.

“When we first started putting together the concept of the mission more than a decade ago, the information in these papers is what we hoped to get at the end,” said InSight’s principal investigator Bruce Banerdt of NASA’s Jet Propulsion Laboratory in Southern California, which leads the mission. “This represents the culmination of all the work and worry over the past decade.”

InSight’s seismometer, called the Seismic Experiment for Interior Structure (SEIS), has recorded 733 distinct marsquakes. About 35 of those – all between magnitudes 3.0 and 4.0 – provided the data for the three papers. The ultrasensitive seismometer enables scientists to “hear” seismic events from hundreds to thousands of miles away.

Seismic waves vary in speed and shape when traveling through different materials inside a planet. Those variations on Mars have given seismologists a way to study the planet’s inner structure. In turn, what the scientists learn about Mars can help improve the understanding of how all rocky planets – including Earth – formed.

Like Earth, Mars heated up as it formed from the dust and larger clumps of meteoritic material orbiting the Sun that helped to shape our early solar system. Over the first tens of millions of years, the planet separated into three distinct layers – the crust, mantle, and core – in a process called differentiation. Part of InSight’s mission was to measure the depth, size, and structure of these three layers.

Each of the papers in Science focuses on a different layer. The scientists found the crust was thinner than expected and may have two or even three sub-layers. It goes as deep as 12 miles (20 kilometers) if there are two sub-layers, or 23 miles (37 kilometers) if there are three.

Beneath that is the mantle, which extends 969 miles (1,560 kilometers) below the surface.

At the heart of Mars is the core, which has a radius of 1,137 miles (1,830 kilometers). Confirming the size of the molten core was especially exciting for the team. “This study is a once-in-a-lifetime chance,” said Simon Stähler of the Swiss research university ETH Zurich, lead author of the core paper. “It took scientists hundreds of years to measure Earth’s core; after the Apollo missions, it took them 40 years to measure the Moon’s core. InSight took just two years to measure Mars’ core.”

The earthquakes most people feel come from faults caused by tectonic plates shifting. Unlike Earth, Mars has no tectonic plates; its crust is instead like one giant plate. But faults, or rock fractures, still form in the Martian crust due to stresses caused by the slight shrinking of the planet as it continues to cool.

InSight scientists spend much of their time searching for bursts of vibration in seismograms, where the tiniest wiggle on a line can represent a quake or, for that matter, noise created by wind. If seismogram wiggles follow certain known patterns (and if the wind is not gusting at the same time), there’s a chance they could be a quake.

The initial wiggles are primary, or P, waves, which are followed by secondary, or S, waves. These waves can also show up again later in the seismogram after reflecting off layers inside the planet.

“What we’re looking for is an echo,” said Amir Khan of ETH Zurich, lead author of the paper on the mantle. “We’re detecting a direct sound – the quake – and then listening for an echo off a reflector deep underground.”

These echoes can even help scientists find changes within a single layer, like the sub-layers within the crust.

“Layering within the crust is something we see all the time on Earth,” said Brigitte Knapmeyer-Endrun of the University of Cologne, lead author on the paper about the crust. “A seismogram’s wiggles can reveal properties like a change in porosity or a more fractured layer.”

One surprise is that all of InSight’s most significant quakes appear to have come from one area, Cerberus Fossae, a region volcanically active enough that lava may have flowed there within the last few million years. Orbiting spacecraft have spotted the tracks of boulders that may have rolled down steep slopes after being shaken loose by marsquakes.

Curiously, no quakes have been detected from more prominent volcanic regions, like Tharsis, home to three of the biggest volcanoes on Mars. But it’s possible many quakes – including larger ones – are occurring that InSight can’t detect. That’s because of shadow zones caused by the core refracting seismic waves away from certain areas, preventing a quake’s echo from reaching InSight.

These results are only the beginning. Scientists now have hard data to refine their models of Mars and its formation, and SEIS detects new marsquakes every day. While InSight’s energy level is being managed, its seismometer is still listening and scientists are hopeful they’ll detect a quake bigger than 4.0.

“We’d still love to see the big one,” said JPL’s Mark Panning, co-lead author of the paper on the crust. “We have to do lots of careful processing to pull the things we want from this data. Having a bigger event would make all of this easier.”

Panning and other InSight scientists will share their findings at 9 a.m. PDT (12 p.m. EDT) on July 23 in a livestreamed discussion on NASA Television, the NASA app, the agency’s website, and multiple agency social media platforms, including the JPL YouTube and Facebook channels.

JPL manages InSight for NASA’s Science Mission Directorate. InSight is part of NASA’s Discovery Program, managed by the agency’s Marshall Space Flight Center in Huntsville, Alabama. Lockheed Martin Space in Denver built the InSight spacecraft, including its cruise stage and lander, and supports spacecraft operations for the mission.

Managed by the Mars Exploration Program and the Jet Propulsion Laboratory for NASA’s Science Mission Directorate

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