Two years ago, NASA’s Insight spacecraft landed on the surface of Mars, aiming to clue the planet’s interior from the tremors of distant earthquakes and release deep heat from its soil. Mars, it turned out, had other ideas. Its sticky soil has failed the Insight’s heat test, and thunderous winds have deafened its sensitive seismometer in recent months. The most mysterious thing is that large marshes have not been plowed on this planet which can disperse their light from the depths.
Despite these hurdles, a precious clutch of small-but-obvious quakes has enabled the Insight team to see signs of boundaries down the cliff, tens and hundreds of kilometers below. They are clues to the creation of the planet billions of years ago, when it was a hot ball of heavy elements such as magma and iron to form a core, while light rocks sprang out of the mantle to form the crust’s lid.
The result, in an online meeting of the American Geophysical Union (AGU) this month with some debating, the planet’s crust is surprisingly thin, compared to the mantle cooler, and its large iron core is still molten. The findings suggest that in its infancy, Mars efficiently shed heat — perhaps through a layer of shallow rock and subduction — similar to plate tectonics on Earth. “This could be evidence for a more dynamic crust formation in the early days of Mars,” says Stephen Mojzsis, a planetary scientist at the University of Colorado, Boulder, who is unaffected with the mission.
The evidence is barely won. At the start of the mission, the winds for the seismometers of the Insights were quite calm, placed in a small dome on the surface to hear a multitude of small earthquakes – about 500 in total. But since June, winds have shaken the surface vigorously, but all but a handful of new earthquakes. Still, disappointingly, the winds have not been strong enough to sweep through the dust that is deepening the craft’s solar panels and foreshadowing the end of the mission over the next few years. Seismometers are still running nonstop, but power shortages have forced the team to close a weather station while using the lander’s robotic arm. “We’re starting to feel the effects”, says Bruce Baindet, Insight’s lead investigator and a geophysicist at NASA’s Jet Propulsion Laboratory.
Meanwhile, the heat probe, about the length of a paper towel tube, gets stuck in the soil that narrows instead of collapses as the rod tried to delimit. Mission engineers have used the robot’s arm to carry out the investigation and are scattering dirt from above. In the next month or two, they will try to investigate once more so that the bureau can be moved inside. “If that doesn’t work, we’ll say it one day and accept the disappointment.”
Perhaps the biggest disappointment is the lack of large swamps compared to 4.5. The seismic waves of a large earthquake travel more deeply, reflecting the core and mantle boundaries and even circling the planet on its surface. Multiple echoes of a major earthquake can enable a seismic station just like Insight to locate the source of the earthquake. But above magnitude 4, Mars has been curiously silent – a clear violation of the scaling laws that apply to Earth and the Moon, where 100 magnitude 3 events correspond to 10 magnitude 4 earthquakes, and so on. “It’s a bit weird,” says Simon Steller, an seismologist on the team at ETE Zurich. It may simply be that Mars defects are not sufficient to sustain large attacks, or that its crust is not quite brittle.
But two medium quakes with intensities of 3.7 and 3.3 have proved to be treasures. Detecting Cerberus Fossae, deep fragmentation in the crust 1600 kilometers east of the landing site, which was suspected to be seismically active, Quakers sent one-two punch of compressive pressure (P) waves, followed by shear (S) waves. Had to face. Obstacle towards lander. Some waves were confined to the crust; Others are reflected from the top of the mantle. The crust in the travel time of P and S waves hints at the thickness of the crust and suggests individual layers within it, Brigitte Notmeyer-Andrén, an seismologist at the University of Cologne, said in an AGU presentation. Steven Haq, a planetary scientist at Case Western Reserve University, said the top layer could reflect the contents of the planet’s first billion years of intense asteroid bombardment.
20 or 37 kilometers thick, depending on whether the reflection correctly traces the apex, martial crusts appear to be thinner than Earth’s continental crust – a surprise. Researchers thought that Mars, a small planet with low internal heat, would form a thick layer, with heat escaping through limited conduction and volcanic bouts. (Although Mars is volcanically dead today, the giant volcano dots its surface.) A thin crust, however, may mean that Mars was losing efficiently, rather than recycling its initial crust, only Instead of making it, perhaps through a rudimentary form of plate tectonics. Mojjis says.
A handful of distant lakes, located at a distance of about 4000 kilometers, provided another clue. Those waves travel deep through the mantle and interact with the mantle transition zone, a layer where the pressure mineral transforms olivine into a wadslite. By analyzing the travel time of waves passing upward, downward, and through the transition zone, the team located its depth – and found it to be more than expected, a sign of a cooler mantle. This calm for Mantle today suggests that convection-rotating motions, which drive tectonic plates on Earth, and carry heat from the mantle to the surface – will probably begin work on this soon, Quancheng Huang, a PHD. Students at the University of Maryland, College Park, who presented some results at the AGU meeting. “Plate tectonics is a very effective way of cooling a planet.”
A third science experiment is still deep in the Insight probe, which uses a small Doppler variation in radio transmissions sent from the probe to Earth to detect slight flaws in the planet’s spin. The size and continuity of the planet’s iron core affects debris, as much as raw eggs are separated from cooked ones. “We had something like 350 hours of tracking,” says Varić Dehnt, a geophysicist at the Royal Observatory in Belgium. Preliminary results confirm that the core is liquid, with radii consistent with previous estimates measuring small changes of gravity by spacecraft, the country reported in its AGU poster. Those gravity estimates have found a core with a radius of about 1800 kilometers – which takes up more than half the diameter of the planet.
Rebecca Fisher, a mineral physicist and modeler at Harvard University, is not surprised at the signs of a liquid core. “It would be a huge surprise if it weren’t,” she says. Sulfur and other elements mixed with iron should help it stay molten during cooling, as salt prevents the icing. On Earth, convective motions in the molten outer core drive the magnetic dynamo. But on Mars, those speeds were discontinued long ago – and without a magnetic field, the planet’s atmosphere was sensitive to the sun’s cosmic rays and the leeches of water in space.
Bannard hopes to sharpen this fuzzy picture of the planet’s interior, and he thinks calm winds will soon become possible. After two Earth years, the first martyr year of the Inquisition is ending, and the first months of the mission are returning to calm. “We’re looking forward to a more complete event stack,” Banerdt says. And although the planet has not cooperated so far, perhaps the Big One is ready to kill Mars like a gong – a rebirth that will clear all the previous ones.