Mars doesn’t have plate tectonics like Earth. Instead, its quakes are generated by the movement of magma deep below its surface, the slow cooling of the planet and shockwaves created by tiny meteorites hammering the planet.
Despite all this activity it took Nasa’s InSight probe two long months of listening before it detected the first faint rumblings from the red planet. On April 6, the probe’s seismometer registered what was later confirmed as the first ever marsquake detected by human instruments.
But measuring the rumblings of a planet that – at its closest – remains almost 34 million miles away, requires an almost unimaginable amount of patience. Twice a day, a team in Switzerland receives seismic data from the InSight probe, where they perform an initial analysis.
For Renee Weber, planetary scientist on the Mars InSight seismology team, this meant obsessively checking her email at the start of the day in the hope that a signal had been detected overnight. “Before I even can get out of bed in the morning, every day I get my phone and I look at my email like ‘Maybe today's the day! Are we going to get that quake? Is it going to be now? How about now?’” she says.
She wasn’t alone in her anticipation. “It was quite tantalising when [the probe landed] and potentially seeing [a signal] any day,” says Tom Pike, an engineer at Imperial College London who lead the team that designed and built silicon sensors for the UK portion of the seismometer. “Then weeks went by and we didn't see one, then more weeks went by – more than a hundred sols (Martian days) on the planet, and more than two months since deployed, before we saw a clear signal.”
Fifty years after seismometers placed by astronauts during the Apollo missions first detected moonquakes, and forty years after the Viking landers seismometers disappointed by being too wind-buffeted to definitively detect quakes on Mars, the InSight lander is actively detecting the very faintest vibrations on another world.
The team knew about these signals within hours of their first detection, but spent a few weeks analysis the findings before releasing the data on April 23, shortly before InSight principle investigator Bruce Banerdt announced the findings on stage at a meeting of the Seismological Society of America in Seattle. “This is just the start of Mars seismology,” says Philippe Lognonné, part of the Mars InSight team at the Institute of Earth Physics in Paris and a veteran of missions to explore Mars’ seismic activity.
The signal was also recorded in audio form – the first time we’ve ever been able to hear the inner workings of Mars. In a clip posted to Nasa’s Twitter account, you can hear the background whirl of the Martian wind that merges into a growing warble – the sound of an marsquake. The sharp chirrup at the end of the clip, that has been sped up by a factor of 60, is the sound of the lander maneuvering its camera to scan the sky.
That long, slow build up is similar to recordings of lunar earthquakes and may have something to do with the fact that the surface of Mars is so exposed to meteorite attacks thanks to its thin atmosphere. Over billions of years, meteorite impacts have shattered the top surface of Mars. “It moves like a cracked mirror producing a whole wave of vibrations,” explains Pike. That broad crackling wave may be the seismic signature of dry shattered rocks, unlike the more cohesive movement of intact and wet surface rocks on Earth.
Understanding what caused the quake, however, will take more time and comparisons with other seismic events. “We don't know quiet at the moment in terms of a source – it could be an impact, it could be from the planet itself – but whatever it is, it's causing vibrations inside the planet,” says Pike.
“A big part of figuring out what’s noise and what's signal is just monitoring the background for an extended period of time,” says Weber, explaining that the team needs to figure out whether the probe is picking up on the wind, weather and robotic movements instead of detecting real seismic signals.
Mars InSight has the most sensitive portable seismometer ever designed. When the spacecraft was in Colorado for testing, it picked up the crash of waves in both the Atlantic and Pacific Oceans. And when Pike was testing sensors in Oxford he noticed very distinct signals happened every Sunday at the same time. After a bit of analysis, he was able to track the location of one of the signals to a nearby church with a bell tower.
The seismometer wasn’t picking up the sounds of the bells, but instead the vibration of the church’s spire. “The bell tower like a great big stick in the ground going backwards and forwards,” he says. “It's a really nice seismic source.”
After identifying the first church, Pike was able to locate roughly another dozen churches, calling up to confirm their bell-ringing schedule and even identifying when muffled bells were used for remembrance services one morning. “We were spying on every bellringer's activity while we were testing,” he says. “They were concerned. They actually had the Oxford Bellringers Association look into it.”
But on Mars, there is nothing as familiar as a church bell tower. Every new seismic signal will have to be investigated for hints about its source. “We're really just really just starting to ask questions like, ‘What is this? It looks weird. It wasn't what we were expecting,’” Weber says.
This article was originally published by WIRED UK
