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Mars Days Shortening as Spin Speeds Up, NASA’s InSight Reveals Leave a comment


Data collected by the InSight Lander on Mars before its untimely demise this past December may have revealed some of the planet’s curious behavior. Scientists studying Mars recently revealed that the planet’s rotation may be increasing while its core is causing it to wobble.

NASA announced the results in a press release yesterday, while the detailed findings were published in a Nature paper this past June. The researchers, led by Sébastien Le Maistre from the Royal Observatory of Belgium, found that Mars’ days are shortening by a fraction of a millisecond every year as the planet’s rotation accelerates. The team used data collected by the lander’s Rotation and Interior Structure Experiment, also known as RISE, during InSight’s first 900 Martian days to study the planet’s movement throughout time.

“What we’re looking for are variations that are just a few tens of centimeters over the course of a Martian year,”said Le Maistre, who is also a principal investigator on RISE, in the press release. “It takes a very long time and a lot of data to accumulate before we can even see these variations.”

RISE offered insights into Mars’ rotation and wobble as scientists beamed radio signals from NASA’s Deep Space Network at the lander. RISE would then reflect those waves back to Earth, allowing scientists to precisely track the position of the lander and, subsequently, Mars’ movement. With this, Le Bastien and his team calculated that Mars’ rotation is seeing an annual increase in rotation of 4 milliarcseconds per year. For reference, one arcsecond is 0.0002 degrees, while a milliarcsecond is one thousandth of an arcsecond. Suffice it to say the acceleration is incredibly minute, and the researchers still aren’t clear on what may be causing it.

The researchers also used RISE to reveal information on Mars’ inner geology, with Le Maistre and his colleagues deducing that Mars holds a molten metal core at its center that sloshes as the planet spins, causing it to wobble. The team also compared readings from the experiment to two different sets of data from InSight’s onboard seismometer. Using the different sets of data, Le Maistre and his colleagues found that the molten core has a radius somewhere between 1,112 and 1,150 miles (1,789 and 1,850 kilometers); Mars itself has a radius of approximately 2,110 miles (3,396 kilometers).

“It’s a historic experiment,” said Le Maistre in the release. “We have spent a lot of time and energy preparing for the experiment and anticipating these discoveries. But despite this, we were still surprised along the way—and it’s not over, since RISE still has a lot to reveal about Mars.”

InSight has offered NASA and scientists an unprecedented suite of geophysical Martian data, as well as the first direct observations of another planet’s core according to NASA’s Jet Propulsion Laboratory. During it’s lifetime, InSight spent over four years collecting geologic data on Mars. InSight recorded data on over 1,000 earthquakes on Mars—which are referred to as “marsquakes”—and in May 2022, the lander detected the biggest marsquake during its time, clocking in at a magnitude 5. Later that year, NASA announced that InSight had detected the energy of meteoroids slamming into the Mars’ surface, with the event sounding like a “bloop” to InSight.


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