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NASA’s InSight Lander Made the First Ever Direct Observation of Another Planet’s Core

Cold dead rock, indeed.

By Cassidy Ward
Neil Degrasse Tyson: We'll Never Get to Mars

If you take a minute to think about it, it’s weird that we know anything about the Earth’s core. It is necessarily obscured from our view, and the conditions that far down are so hot and so high-pressured that digging becomes impossible. There is an underground horizon beyond which humanity and our machines cannot pass, unless you’re Luke Perry.

In the SYFY original movie Descent (streaming now on Peacock!), the Ring of Fire — a loop of increased tectonic activity lining the Pacific — starts dumping magma onto the surface and a team of scientists including Dr. Jake Rollins (Perry) must brave a mission to the Earth’s core to save the world from destruction. An active core is a critical component of our cozy planet, but it comes with the occasional natural disaster built in. That’s the cost of planetary paradise.

RELATED: Earth’s inner core might have its own innermost core

Mars, by contrast, might seem like a cold dead rock in the blackness of space, but that isn’t quite true. Just ask NASA’s Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) lander. The spacecraft launched May 5, 2018, and entered service on Mars six months later. It spent the next four years listening for marsquakes, in the hope of directly measuring the Martian core.

An image of NASA’s InSight Mars lander's seismometer on the Red Planet’s surface

On Earth, scientists use the behavior of seismic waves to infer information about the planet’s core. To get an idea of how that works, rap your knuckles against a countertop and pay attention to the sound, then put your ear to the counter and knock again. There’s a pretty stark difference between the way sound travels through the counter and through the open air. When an earthquake happens, seismic waves travel through the planet, encountering different materials and conditions along the way.

Scientists can look at the way the waves move through the Earth — are they slowing down or changing direction — to figure out what the Earth is made of. But we can only do that because we have seismic instruments deployed all over the planet. The InSight mission offered the first opportunity to take what we’ve learned about geology directly to another world.

RELATED: Mars’ tiny moon Deimos might be a fractured piece of the red planet itself

While InSight is now retired, having lost contact with Earth on December 15, 2022, scientists still have years of data to sift through. Recently, scientists confirmed that InSight succeeded in the first direct measurements of another planet’s core. The findings were published in the Proceedings of the National Academy of Sciences.

Measurements came from two quakes which occurred on August 25 and September 18 of 2021. That was well into InSight’s mission and scientists had had time to acclimate themselves to the measurements, which contributed to the detection. It also helped that one of the quakes was triggered by a meteoroid, which provided a clear point of origin. Both quakes occurred on the opposite side of the planet from InSight, which was crucial for measuring the planet’s core.

Each tremor sends out waves in all directions, but InSight could only pick up on the waves pointed its way. That means if a quake was too nearby, the waves wouldn’t travel through the core before hitting InSight. But when the quakes are far away, like the two identified in the paper, they travel through a considerable portion of the interior before hitting InSight’s detectors. Measurements of these two quakes revealed that Mars has a liquid-iron core which is smaller and denser than scientists anticipated.

This might be the first direct observation of the Martian core, but it likely won’t be the last. Researchers are still digging through all of the data InSight sent back and there’s no telling what else we might learn.

In the meantime, catch Descent, streaming now on Peacock.

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