Mars is spinning faster and faster, shortening the length of its days.
The Red Planet's rotation is increasing by around 4 milliarcseconds per year. A milliarcsecond is a unit of angle, with one milliarcsecond being about the size of a 50 cent coin, seen from around 3,800 miles, the distance between the Washington Monument and the Eiffel Tower.
This means that the Martian day is shortening by a fraction of a millisecond per year, according to a paper published in the journal Nature. Current Mars days, also known as Sols, last 24 hours, 39 minutes and 35 seconds.
This finding was discovered using data from the Rotation and Interior Structure Experiment, or RISE instrument, on NASA's InSight Mars lander, which measured the rotation of Mars precisely, as well as detecting how the planet wobbles in its spin because of its molten metal core "sloshing" around.
"It's really cool to be able to get this latest measurement—and so precisely," said InSight's principal investigator, Bruce Banerdt of NASA's Jet Propulsion Laboratory in Southern California. "I've been involved in efforts to get a geophysical station like InSight onto Mars for a long time, and results like this make all those decades of work worth it."
Over the past few centuries, the Earth's rotation has actually been slowing down ever so slightly, although 2020 saw 28 of the shortest days since records began in the 1960s. The Earth completed a rotation 1.47 milliseconds shy of 24 hours on July 19, 2020, and on July 26, spun 1.50 milliseconds faster than 24 hours. The shortest-ever recorded day occurred on June 29, 2022, when a full rotation was completed in 1.59 milliseconds under 24 hours.
The reason for Earth's changes in speed is thought to possibly relate to small irregular movements in the the planet's geographical poles. Mars' faster rotation, however, remains a mystery, but is theorized to be to do with ice accumulation on the poles, or landmasses rising after being buried by ice causing a shift in the planet's mass.
In the paper, the authors describe how they discovered this change in rotation speed, as well as the true size of the Martian core, which was previously unknown.
"What we're looking for are variations that are just a few tens of centimeters over the course of a Martian year," the paper's lead author and RISE's principal investigator, Sebastien Le Maistre of the Royal Observatory of Belgium, said in the statement. "It takes a very long time and a lot of data to accumulate before we can even see these variations."
"It's a historic experiment. 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," he said.
The authors explain that using RISE measurements of the wobbling of the planet caused by its liquid core, they could measure that the core had a radius of around 1,140 miles. They then combined this data with other data of how seismic waves pass through the planet to determine that the core's size was likely 1,112 to 1,150 miles in radius, or about 2,224 to 2,300 miles in diameter, compared to the 4,212-mile diameter of the whole planet.
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Jess Thomson is a Newsweek Science Reporter based in London UK. Her focus is reporting on science, technology and healthcare. ... Read more
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