meteorites

seismic-data-shows-mars-is-often-pummeled-by-planet-shaking-meteorites

Seismic data shows Mars is often pummeled by planet-shaking meteorites

astronomy, Impacts, Mars, meteorites, planetary science, Science, seismology / /

Brace for impact —

Seismic information now allows us to make a planet-wide estimate of impact rates.

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One of the craters identified seismically, then confirmed through orbital images.

Enlarge / One of the craters identified seismically, then confirmed through orbital images.

Mars trembles with marsquakes, but not all of them are driven by phenomena that occur beneath the surface—many are the aftermath of meteorite strikes.

Meteorites crash down to Mars every day. After analyzing data from NASA’s InSight lander, an international team of researchers noticed that its seismometer, SEIS, detected six nearby seismic events. These were linked to the same acoustic atmospheric signal that meteorites generate when whizzing through the atmosphere of Mars. Further investigation identified all six as part of an entirely new class of quakes known as VF (very high frequency) events.

The collisions that generate VF marsquakes occur in fractions of a second, much less time than the few seconds it takes tectonic processes to cause quakes similar in size. This is some of the key seismological data that has helped us understand the occurrence of earthquakes caused by meteoric impacts on Mars. This is also the first time seismic data was used to determine how frequently impact craters are formed.

“Although a non-impact origin cannot be definitively excluded for each VF event, we show that the VF class as a whole is plausibly caused by meteorite impacts,” the researchers said in a study recently published in Nature.

Seismic shift

Scientists had typically determined the approximate meteorite impact rate on Mars by comparing the frequency of craters on its surface to the expected rate of impacts calculated using counts of lunar craters that were left behind by meteorites. Models of the lunar cratering rate were then adjusted to fit Martian conditions.

Looking to the Moon as a basis for comparison was not ideal, as Mars is especially prone to being hit by meteorites. The red planet is not only a more massive body that has greater gravitational pull, but it is located near the asteroid belt.

Another issue is that lunar craters are often better preserved than Martian craters because there is no place in the Solar System dustier than Mars. Craters in orbital images are often partly obscured by dust, which makes them difficult to identify. Sandstorms can complicate matters by covering craters in more dust and debris (something that cannot occur on the Moon due to the absence of wind).

InSight deployed its SEIS instrument after it landed in the Elysium Planitia region of Mars. In addition to detecting tectonic activity, the seismometer can potentially determine the impact rate through seismic data. When meteorites strike Mars, they produce seismic waves just like tectonic marsquakes do, and the waves can be detected by seismometers when they travel through the mantle and crust. An immense quake picked up by SEIS was linked to a crater 150 meters (492 feet) wide. SEIS would later detect five more marsquakes that were all associated with an acoustic signal (detected by a different sensor on InSight) that is a telltale sign of a falling meteorite.

A huge impact

Something else stood out about the six impact-driven marsquakes detected with seismic data. Because of the velocity of meteorites (over 3,000 meters or 9,842 feet per second), these events happened faster than any other type of marsquake, even faster than quakes in the high frequency (HF) class. That’s how they earned their own classification: very high frequency, or VF, quakes. When the InSight team used the Mars Reconnaissance Orbiter’s (MRO) Context Camera (CTX) to image the locations of the events picked up by SEIS, there were new craters present in the images.

There are additional seismic events that haven’t been assigned to craters yet. They are thought to be small craters formed by meteorites about the size of basketballs, which are extremely difficult to see in orbital images from MRO.

The researchers were able to use SEIS data to estimate the diameters of craters based on distance from InSight (according to how long it took seismic waves to reach the spacecraft) and the magnitude of the VF marsquakes associated with them. They were also able to derive the frequency of quakes picked up by SEIS. Once a frequency estimate based on the data was applied to the entire surface area of Mars, they estimated that around 280 to 360 VF quakes occur each year.

“The case is strong that the unique VF marsquake class is consistent with impacts,” they said in the same study. “It is, therefore, worthwhile considering the implications of attributing all VF events to meteoroid impacts.”

Their detection has added to the estimated number of impact craters on Mars since many could not be seen from space before. What can VF impacts tell us? The impact rate on a planet or moon is important for determining the age of that object’s surface. Using impacts has helped us determine that the surface of Venus is constantly being renewed by volcanic activity, while most of the surface of Mars has not been covered in lava for billions of years.

Figuring out the rate of meteorite impacts can also help protect spacecraft and, someday, maybe Martian astronauts, from potential hazards. The study suggests that there are periods where impacts are more or less frequent, so it might be possible to predict when the sky is a bit more likely to be clear of falling space rocks—and when it isn’t. Meteorites are not much of a danger to Earth since most of them burn up in the atmosphere. Mars has a much thinner atmosphere that more can make it through, and there is no umbrella for a meteor shower.

Nature Astronomy, 2024. DOI: 10.1038/s41550-024-02301-z

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a-giant-meteorite-has-been-lost-in-the-desert-since-1916—here’s-how-we-might-find-it

A giant meteorite has been lost in the desert since 1916—here’s how we might find it

astrophysics, Chinguetti meteorite, geophysics, meteorites, Physics, Science / /

“This story has everything…” —

A tale of “sand dunes, a guy named Gaston, secret aeromagnetic surveys, and camel drivers.”

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Chinguetti slice at the National Museum of Natural History

Enlarge / Chinguetti slice at the National Museum of Natural History. A larger meteorite reported in 1916 hasn’t been spotted since.

In 1916, a French consular official reported finding a giant “iron hill” deep in the Sahara desert, roughly 45 kilometers (28 miles) from Chinguetti, Mauritania—purportedly a meteorite (technically a mesosiderite) some 40 meters (130 feet) tall and 100 meters (330 feet) long. He brought back a small fragment, but the meteorite hasn’t been found again since, despite the efforts of multiple expeditions, calling its very existence into question.

Three British researchers have conducted their own analysis and proposed a means of determining once and for all whether the Chinguetti meteorite really exists, detailing their findings in a new preprint posted to the physics arXiv. They contend that they have narrowed down the likely locations where the meteorite might be buried under high sand dunes and are currently awaiting access to data from a magnetometer survey of the region in hopes of either finding the mysterious missing meteorite or confirming that it likely never existed.

Captain Gaston Ripert was in charge of the Chinguetti camel corps. One day he overheard a conversation among the chameliers (camel drivers) about an unusual iron hill in the desert. He convinced a local chief to guide him there one night, taking Ripert on a 10-hour camel ride along a “disorienting” route, making a few detours along the way. He may even have been literally blindfolded, depending on how one interprets the French phrase en aveugle, which can mean either “blind” (i.e. without a compass) or “blindfolded.” The 4-kilogram fragment Ripert collected was later analyzed by noted geologist Alfred Lacroix, who considered it a significant discovery. But when others failed to locate the larger Chinguetti meteorite, people started to doubt Ripert’s story.

“I know that the general opinion is that the stone does not exist; that to some, I am purely and simply an imposter who picked up a metallic specimen,” Ripert wrote to French naturalist Theodore Monod in 1934. “That to others, I am a simpleton who mistook a sandstone outcrop for an enormous meteorite. I shall do nothing to disabuse them, I know only what I saw.”

Encouraged by a separate report of local blacksmiths claiming to recover iron from a giant block somewhere east or southeast of Chinguetti, Monod intermittently searched for the meteorite several times over the ensuing decades, to no avail. A pilot named Jacques Gallouédec thought he spotted a dark silhouette in the Saharan dunes in the 1980s. But neither Monod nor a second expedition in the late 1990s—documented by the UK’s Channel 4—could find anything. Monod concluded in 1989 that Ripert had likely mistakenly identified a sedimentary rock “with no trace of metal” as a meteorite.

Still, as Rutgers University physicist Matt Buckley noted on Bluesky, “This story has everything: giant unexplained meteorites, sand dunes, a guy named Gaston, ductile nickel needles, secret aeromagnetic surveys, and camel drivers.” So naturally, it intrigued Stephen Warren of Imperial College London, Oxford University’s Ekaterini Protopapa, and Robert Warren, who began their own search for the mysterious missing meteorite in 2020.

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