Astro Bob: Listen to space rocks hit Mars
NASA's InSight lander has detected several meteoroid impacts, one of which left a string of craters and a big "bloop-bloop!"
Mars gets hit by meteorites just like Earth. NASA's Curiosity, Spirit and Opportunity rovers have discovered 15 meteorites to date on the Martian surface, most of them irons. We know they're meteorites both from appearance and by analyzing the light they reflect with an instrument called a spectrometer . If the reflected light matches that from a similar meteorite found on Earth we can confirm its origin. Materials absorb and reflect different wavelengths of light in specific ways, imprinting it with clues to their composition.
Provided the space rocks are big enough, we can detect their impacts by the seismic waves they create. In news shared Monday, Sept. 19, NASA reports that its InSight lander has detected seismic waves from four space rocks that crashed on Mars in 2020 and 2021. This marks the first time seismic and acoustic waves from an impact have been detected on the planet and the first since the probe touched down there in 2018.
The space rocks (called meteoroids) slammed into the crust between 53 and 180 miles (85 and 290 km) from the lander's location in a region of Mars called Elysium Planitia, a broad plain that straddles the planet's equator.
The first of the four made the most dramatic entrance, entering the atmosphere Sept. 5, 2021, and exploding into at least three fragments. Each shard punched out its own crater one after another in succession, creating a dramatic impact train. To hear just the meteoroid impact sound, cue the video above to the 0:55-second mark.
Sometime later, NASA’s Mars Reconnaissance Orbiter flew over the estimated impact site and photographed three darkened spots on the surface. Next, the orbiter’s team used the craft's high-resolution camera to get a color close-up of the triple impact.
“After three years of InSight waiting to detect an impact, those craters looked beautiful,” said Ingrid Daubar of Brown University, a co-author of the recent paper on the discovery and a specialist in Mars impacts.
Scientists then combed through earlier seismometer data and were able to confirm three additional earlier meteorite strikes that occurred on May 27, 2020; Feb. 18, 2021; and Aug. 31, 2021. That may sound like a lot of activity, but it's actually much less than expected.
Mars orbits near the main asteroid belt which is rich in rocky projectiles available to pelt the poor planet. Also, the Martian atmosphere is just 1 percent as thick as Earth's, so much more material should be able to pass through without disintegrating.
Over the past four years, InSight has detected over 1,300 marsquakes with the goal of investigating the interior structure and composition of Mars. It's also measuring the amount of heat flowing through the planet's interior, tectonic processes and of course, meteorite impacts.
Mars' internal plumbing fascinates planetary scientists because they hope it will shed light on the processes that formed the terrestrial planets. Most marsquakes are caused by subsurface rocks cracking from heat and pressure. Studying how the resulting seismic waves change as they move through different material provides scientists a way to study Mars’ crust, mantle and core. Even the meteorite impacts, which registered no more than 2.0 on the Richter Scale, can provide information about the Martian crust.
InSight’s team suspects that other impacts may have been obscured by noise from wind or by seasonal changes in the atmosphere. But now that we know what to look for, scientists expect to find more impact signatures hiding in the data. Knowing how often impacts occur today will help us to estimate the ages of different parts of Mars — the more craters we see, the older the surface.
Sadly, InSight days, called Sols on Mars, are numbered. Dust buildup on the solar panels is already reducing its power and will eventually lead to the probe shutting down. Its demise is expected between October this year and January 2023.
Keep those space rocks coming!