The researchers found that the core density was surprisingly low, only about 6 grams per cubic centimeter, much lower than they expected from the iron-rich center. “It is still a mystery why the core is so light,” says Stehler. Lighter elements should be present, although it is not clear exactly what they might be. He and his team ultimately hope to detect the P-waves generated by an earthquake striking right across the planet where InSight is parked. Since they can penetrate the core-mantle boundary, they will transmit information about the composition of the core to the lander’s receiver. But for this, according to Stehler, “Mars must play along with us and cause one earthquake on the other side of the planet.”
In an article by the Stehler group, they report that the radius of the core is 1,830 kilometers. Another group, led by ETH Zürich geophysicist Amir Khan, found that the size is so large that it leaves little room for the Earth’s lower mantle, a layer that acts as an insulating blanket around the core. The mantle of the Earth is divided into two parts, between which is the so-called transition zone; the upper and lower levels are composed of different minerals. “The mantle of Mars is – one might say lightly – it is a slightly simpler version of the mantle of the Earth, simply from a mineralogical standpoint,” says Khan, lead author of the article describing the mantle.
Previous estimates of the core radius using geochemical and geophysical data hinted at the absence of the lower mantle, but scientists required InSight seismic data to confirm this. Without this layer, the core of Mars probably cooled much faster than the core of the Earth. This is the key to understanding the evolution of the Red Planet and, in particular, why it lost its magnetic field, a barrier that would protect the atmosphere – and potential life – from harsh solar winds. Creating a magnetic field requires a temperature gradient between the outer and inner cores high enough to create circulating currents that agitate the core fluid and induce a magnetic field. But the core cooled down so quickly that these convection currents were extinguished.
Khan’s analysis also shows that Mars has a thick lithosphere, a hard and cold part of the mantle. This may be a clue as to why the Red Planet lacks plate tectonics, which is driving the volcanic madness on Earth. “If you have a very thick lithosphere, it will be very difficult to break it up and create the exact equivalent of plate tectonics on Earth,” says Khan. “Maybe Mars had it very early, but it is definitely off now.”
While InSight eavesdrops on Mars’ internal wobbles, Perseverance has rolled across its dusty surface looking for signs of ancient life in the rocks, looking for sites 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 assistant administrator for science, who opened Wednesday’s press conference highlighting the rover’s early successes in its first few months at its new home. “Perseverance is one step in a long legacy of carefully planned Mars exploration that links human and robotic exploration for the future.”
Scientists at a press briefing talked about what Perseverance was at the moment. “The challenge is to figure out exactly where we want to go and how we’re going to fit everything into our schedule,” said Vivian Sun, systems engineer at NASA’s Jet Propulsion Laboratory. Sun said they decided to circle Perseverance about 3,000 feet south of the landing site to retrieve the first rock samples, which would be stored in the rover’s belly and then stored in a cache on the planet’s surface for a future return mission that would take them to The earth. …