More than a year after NASA’s Mars InSight lander touched down in ‘Homestead hollow,’ a sand-filled impact crater on the western side of a flat, smooth expanse of lava called Elysium Planitia, Mars is now serving up its meteorological secrets: marsquakes, swirling ‘dust devils,’ and the steady, low rumble of infrasound. The findings are detailed in a set of six papers published in the journal Nature Geoscience and the journal Nature Communications.
In this artist’s concept of NASA’s InSight lander on Mars, layers of the planet’s subsurface can be seen below and dust devils can be seen in the background. Image credit: Nicolas Sarter / IPGP.
InSight is the first mission dedicated to looking deep beneath the Martian surface. Among its science tools are a seismometer for detecting quakes, sensors for gauging wind and air pressure, a magnetometer, and a heat flow probe designed to take the planet’s temperature.
While the InSight team continues to work on getting the probe into the Martian surface as intended, the ultra-sensitive seismometer, called the Seismic Experiment for Interior Structure (SEIS), has enabled scientists to ‘hear’ multiple trembling events from hundreds to thousands of miles away.
Seismic waves are affected by the materials they move through, giving scientists a way to study the composition of the planet’s inner structure.
Mars can help the team better understand how all rocky planets, including Earth, first formed.
Marsquakes
Mars trembles more often — but also more mildly — than expected. SEIS has found more than 450 seismic signals to date, the vast majority of which are probably quakes (as opposed to data noise created by environmental factors, like wind).
The largest quake was about magnitude 4.0 in size — not quite large enough to travel down below the crust into the planet’s lower mantle and core.
“Those are the juiciest parts of the apple when it comes to studying the planet’s inner structure,” said InSight principal investigator Dr. Bruce Banerdt, a researcher at NASA’s Jet Propulsion Laboratory.
Scientists are ready for more: it took months after InSight’s landing in November 2018 before they recorded the first seismic event.
By the end of 2019, SEIS was detecting about two seismic signals a day, suggesting that InSight just happened to touch down at a particularly quiet time. Scientists still have their fingers crossed for the ‘Big One.’
Mars doesn’t have tectonic plates like Earth, but it does have volcanically active regions that can cause rumbles.
A pair of quakes was strongly linked to one such region, Cerberus Fossae, where scientists see boulders that may have been shaken down cliffsides.
Ancient floods there carved channels nearly 1,300 km (800 miles) long.
Lava flows then seeped into those channels within the past 10 million years — the blink of an eye in geologic time.
Some of these young lava flows show signs of having been fractured by quakes less than 2 million years ago.
“It’s just about the youngest tectonic feature on the planet,” said Dr. Matt Golombek, a planetary geologist at NASA’s Jet Propulsion Laboratory.
“The fact that we’re seeing evidence of shaking in this region isn’t a surprise, but it’s very cool.”
Magnetic Signals
Billions of years ago, Mars had a magnetic field. It is no longer present, but it left ghosts behind, magnetizing ancient rocks that are now between 61 m (200 feet) to several km below ground. InSight is equipped with a magnetometer — the first on the surface of Mars to detect magnetic signals.
The magnetometer has found that the signals at Homestead hollow are 10 times stronger than what was predicted based on data from orbiting spacecraft that study the area.
The measurements of these orbiters are averaged over a couple of hundred miles, whereas InSight’s measurements are more local.
“Because most surface rocks at InSight’s location are too young to have been magnetized by the planet’s former field, this magnetism must be coming from ancient rocks underground,” said Dr. Catherine Johnson, a planetary scientist at the University of British Columbia and the Planetary Science Institute.
“We’re combining these data with what we know from seismology and geology to understand the magnetized layers below InSight. How strong or deep would they have to be for us to detect this field?”
In addition, scientists are intrigued by how these signals change over time. The measurements vary by day and night; they also tend to pulse around midnight. Theories are still being formed as to what causes such changes, but one possibility is that they’re related to the solar wind interacting with the Martian atmosphere.
A cutaway view of Mars showing the InSight lander studying seismic activity. Image credit: J.T. Keane / Nature Geoscience.
Martian Winds
InSight measures wind speed, direction and air pressure nearly continuously, offering more data than previous landed missions.
The spacecraft’s weather sensors have detected thousands of passing whirlwinds, which are called dust devils when they pick up grit and become visible.
“This site has more whirlwinds than any other place we’ve landed on Mars while carrying weather sensors,” said Dr. Aymeric Spiga, an atmospheric scientist at Sorbonne University.
Despite all that activity and frequent imaging, InSight’s cameras have yet to see dust devils.
But SEIS can feel these whirlwinds pulling on the surface like a giant vacuum cleaner.
“Whirlwinds are perfect for subsurface seismic exploration,” said SEIS principal investigator Dr. Philippe Lognonné, a researcher in the Institut de Physique du Globe de Paris (IPGP).
Red Planet’s Core
InSight has two radios: one for regularly sending and receiving data, and a more powerful radio designed to measure the ‘wobble’ of Mars as it spins.
This X-band radio, also known as the Rotation and Interior Structure Experiment (RISE), can eventually reveal whether the planet’s core is solid or liquid.
A solid core would cause Mars to wobble less than a liquid one would.
This first year of data is just a start. Watching over a full Martian year (two Earth years) will give scientists a much better idea of the size and speed of the planet’s wobble.
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W.B. Banerdt et al. Initial results from the InSight mission on Mars. Nat. Geosci, published online February 24, 2020; doi: 10.1038/s41561-020-0544-y
C.L. Johnson et al. Crustal and time-varying magnetic fields at the InSight landing site on Mars. Nat. Geosci, published online February 24, 2020; doi: 10.1038/s41561-020-0537-x
D. Banfield et al. The atmosphere of Mars as observed by InSight. Nat. Geosci, published online February 24, 2020; doi: 10.1038/s41561-020-0534-0
D. Giardini et al. The seismicity of Mars. Nat. Geosci, published online February 24, 2020; doi: 10.1038/s41561-020-0539-8
P. Lognonné et al. Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data. Nat. Geosci, published online February 24, 2020; doi: 10.1038/s41561-020-0536-y
M. Golombek et al. 2020. Geology of the InSight landing site on Mars. Nat Commun 11, 1014; doi: 10.1038/s41467-020-14679-1
This article is based on text provided by the National Aeronautics and Space Administration.
