On Christmas Eve last year Mars moved.
An exquisitely sensitive seismometer on NASA’s Inspection lander dutifully recorded the noise of seismic vibrations and then sent the data back to Earth the next day, a gift of science.
The inspection of the scholars was busy celebrating the holidays. When they studied the tremor in detail at the beginning of January, they observed more than a thousand different marches that students of the space station recorded on their mission to the interior of the red planet.
“The seismic event was obvious, and it was a big seismic event,” said Mark Panning, project scientist for the mission. “And we were excited right away.”
In a scientific paper published on Thursday, scientists using data from two NASA spacecraft show that the seismic event was not a crash of rocks from the red planet’s interior. But the waves were sent out from the space rock hitting Mars. The discovery will give scientists a better understanding of what’s inside Mars and remind us that like Earth, Mars is also hit by meteors.
Mars lacks plate tectonics, the sliding pieces of crust that make up Earth’s surface. However, estuaries do occur, driven by other tectonic pressures such as the shrinking and cracking of the red planet’s crust as it cools. The greatest limits of the earth are by modest standards.
They recorded the December earthquake as one of the most powerful on record, at a magnitude of 4. However, it did not occur in the tectonically active region where most of the major tremors were observed.
Most importantly, the Christmas Eve seismic event was the first time that surface waves – vibrations through the outer crust of rocks on the surface of Mars – have been detected. For all the rest of the mars, the seismometers examined only observed what are known as body waves, vibrations traveling through the interior of the planet.
The epicenter is no closer — more than a thousand miles from the Inspect — to the mystery. The motion suggested that it was not only great but light.
“It was difficult to determine why we had surface waves,” said Philippe Lognonne, a professor at the University of Paris who serves as the principal investigator for the seismometer.
This mystery remained until two months later, when scientists on another NASA spacecraft – the Mars Reconnaissance Orbiter – discovered this seismic event after all the known movements.
Rather, it was a space rock to hit Mars.
It wasn’t a small space rock either, estimated to be somewhere between 15 and 40 feet in diameter, said Liliya Posiolova, orbital science operations lead at the Malin Space Science System in San Diego, which built and operates the two Mars Reconnaissance Orbiter cameras.
The impact released energy equivalent to somewhere between 2.5 and 10 kilobytes of TNT, Dr Posiolova said. (The atomic bomb dropped on Hiroshima at the end of World War II was equivalent to 15 kilotons of TNT.) It left a crater wider than a football field.
During a NASA news conference on Thursday, Ingrid Daubar, a planetary scientist at Brown University who leads the impact science task force Observer, said this large meteor enters Earth once a year.
“We see them almost regularly,” Dr. Daubar said. “But because Earth has a thicker atmosphere, asteroids of that size burn up and are generally pretty harmless.”
Scientists including Dr. Panning, Dr. Lognonné, Dr. Posiolova and Dr. Daubar reported the findings in two articles published Thursday in the journal Science.
When Insight — a probe of Interior Exploration using Seismic, Geodesy and Heat Transport probes — landed in November 2018, scientists expected to observe not only the tides, but also a few meteor impacts throughout the year. But for more than three years they have seen no meteor strike at all in the seismic data.
That indicated a failure in the knowledge of the Martian crust and in computer models simulating the expected seismic signals.
Last month, scientists reported identifying four small meteors within two miles of Insight, accompanied by screeching sounds as rocks entered the Martian atmosphere.
Now, too, the larger meteors are farther away.
In early February, Dr. Posiolova and other scientists were working to get a three-dimensional, stereo image of Mars. A few years ago they had one image of the country, and now they were getting another image from a slightly different angle.
The second image, however, includes a large spot, a dust-disturbed blast zone more than 10 miles outside that was not in the first image.
It was so large that it was seen in the daily global weather pictures taken by another camera on the orbiter. “So we’re pretty much starting to go from that February image,” said Dr. Posiolova, lead author of one of the science papers.
Spotted on 25 Dec. but not on the 24th of Dec.
He said he remembered in the back of his mind that Insight mentioned one of his major seismic events on Christmas Eve. And he said: “Is it so?”
Higher-resolution images showed the meteor carved a crater about 500 feet wide in the center of the blast zone and also kicked up water ice from the lower surface. It is the closest to the Martian equinox that ice has ever been spotted.
When the seismic signals from the meteor impact were definitive, the Survey scientists went back through their data to see if there were any previous meteor impacts.
In fact, the magnitude 4.2 shock appeared similar to the seismic event three months earlier, on Sept. 18. So the orbiting cameras looked around that epicenter, located about 4,600 miles from Insight, and there spotted a crater about 426 feet in diameter.
Dr. Posiolova said these are by far the two largest new craters the orbiter has spotted in 16 years of studying Mars. The two combine to be referred to differently, Dr. Panning said; it was fortunate that it had happened in a few months except by an accidental accident.
Correlating seismic signals with newly carved craters provides a sharper view of the planet’s internal structure. Dr. Lognonné likened the film to him. Mars Reconnaissance Orbiter images while Insight is recording sound.
“You can understand a film better than with just sound or image,” he said.
Dr. Lognonné said that the current models work well for the Mars crust, but not so much for the deep mantle. “This is the only data to get more information about the interior of Mars,” he said.
One possible surprise is that surface waves appear to travel at about the same speed through the crust of the Northern Hemisphere as they do in the Southern Hemisphere.
The topography of the northern half of Mars—which was once overshadowed by the ocean—is much lower than the southern mountains. The velocity data suggests that the crustal rocks in both hemispheres are of similar density. On Earth, the crust beneath the oceans is denser than the crust of the continents.
“We are beginning to unravel the mystery of this dichotomy,” said Doyeon Kim, a planetary scientist at the Swiss Federal Institute of Technology in Zurich and author of the Science paper describing Insight’s findings.
The Science Panels are the latest discoveries from a busy year for the Inspection mission even as the spacecraft perishes due to dust accumulating on the solar panels, cutting off the energy supply.
In a NASA news conference Bruce Banerdt, the mission’s principal investigator, said that the expectation is that space will be silent in the next four to eight weeks. “It is miserable,” said he, to be contemplated.
A regional dust storm in the southern hemisphere did not directly pass Insight, but kicked up more dust into the atmosphere that eventually settled on solar panels, further reducing power output, Dr. Banerdt said.
“The seismometer has been off for several weeks,” he said. “We are now working on the seismometer again, only one day out of four at this point to maintain our power. But even in this relatively small advantage, batteries are still slow and infrequent.
In another paper published in the journal Nature Astronomy on Thursday, scientists examined seismic data to study the Cerberus Fossae, a highly fractured region, 750 miles long, where most of Mars’ seismic sounds originate.
Magma heat from the volcanic region to the west warms the crust there, said Simon C. Stähler, a seismologist also at the Swiss Federal Institute of Technology and lead author of the Nature Astronomy paper.
“You’re basically creating this weakness, the weakness of this place, which allows the movement to happen,” he said.
Observing scientists also study a magnitude-4.7 eclipse in May, the largest detected during the mission. That one seems to be the actual marsquarian, because no crater has been seen near the epicenter, which lies near the Cerberus Fossae.
When the Observatory closes, there will again be no seismometers operating anywhere else in the Solar System. But the park seismometer built for Insight has been moved to the far side of the moon in a few years, and NASA’s Dragonfly mission to Titan, Saturn’s largest moon, will also carry a seismometer.
“Planetary seismology is an ongoing field,” Dr. Panning said.
#violent #shook #surface #Mars #Space