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The length of a Martian day is shortening by three-quarters of a millisecond each year as the planet rotates, according to new results from NASA’s InSight (Interior Exploration Using Seismic Investigations, Geodesy, and Heat Transport) mission.
A standard sol, or sol, is 24 hours and 37 minutes long, but measuring this length of day with an accuracy of a fraction of a millisecond revealed that the planet’s rotation rate is accelerating by an insignificant amount. Planetary scientists aren’t entirely sure why this happens, but it’s likely related to the redistribution of Martian mass, which can have an effect on the planet’s rotation like a snowboarder pulling his arms to spin faster. Experts think this redistribution may be caused by ice accumulating on Mars’ polar caps, or by the surface itself slowly bouncing back from settling under the weight of massive glaciers that once housed Mars. tropical latitudes During the most recent ice ages in the world It ended about 400,000 years ago.
To get these incredibly accurate measurements of Mars’ rotation rate, study scientists used radio waves.
“It’s a landmark experiment,” said Sebastien Le Maistre, a planetary scientist at the Royal Belgian Observatory and lead author of a new paper on the findings. statement. “We spent a lot of time and energy preparing for the experiment and anticipating these discoveries.”
Related: Scientists pay tribute to the scientific legacy of NASA’s Mars Insight lander
NASA has fired a strong radio signal towards Mars Deep Space Network, consisting of three radio antennas around the world that are used to communicate with interplanetary missions. The radio signal was then received by InSight’s RISE (Rotation and Internal Structure Experiment) instrument and returned to Earth. Adds the rotation of Mars a Doppler shift these reflected radio waves.
Doppler shift is the same effect that causes an emergency car siren to get louder as it approaches a listener before falling again as it drives away. Similarly, when InSight is in the orbiting hemisphere of Mars in view, the radio signal it sends is converted to higher frequencies, and when InSight is in the orbiting hemisphere of Mars out of view, the signal is Doppler converted to shorter frequencies. This Doppler shift is entirely dependent on the rate of rotation, and harnessing it to measure the length of a day on planet Earth—with an accuracy of fractions of a millisecond—is no small task.
“What we’re looking for are differences of only a few tens of centimeters over the course of a Martian year [687 Earth days]said Le Maistre, who is also the principal investigator for RISE. “It takes a very long time and a lot of data to accumulate before we can even see these differences.”
The experiment used data from InSight’s first 900 days on Mars, and concluded that Mars’ rotation is accelerating by 0.76 milliseconds per year – the most accurate measurement of Mars’ rotational period ever.
Mars core
RISE is also working on the interior of the Red Planet, measuring the volume of Mars’ molten core.
Although the planet’s core cannot be accessed for direct observation, scientists can gauge the potential size and state of Mars’ mantle and core by tracking how radio data from RISE changes as Mars wobbles on its axis. This oscillation is a result of the molten iron in the core. Previously, InSight had already confirmed that the core of Mars is On the big sideUsing seismic waves from the swamps that ripple across the planet. Now, RISE has managed to improve on this measurement.
The interior of Mars, like Earth, is differentiated into different layers.
There is the crust on which the surface sits. Beneath it is the mantle, which contains Earth on molten magma but is assumed to be completely solid on Mars. This is because it is expected to cool down as heat escapes away faster than it does on Earth, which is an order of magnitude greater. Beneath the mantle is a molten metallic core of liquid iron — the volume of this molten core is the one Le Maistre’s team measured using RISE.
RISE data indicated that the molten Martian core has a diameter of 2,280 miles (3,670 kilometers). This can be compared to Mars as a whole, which has a diameter of 4,212 miles (6,779 kilometers). However there is a legal note. If the mantle is not completely solid, and is already molten at the bottom, this molten portion will rotate independently of the solid portion. This means that the core may be about 400 km smaller than the RISE data indicate.
The RISE data also found that the core is not perfectly spherical, but rather lumpy, with what Le Maistre’s team described as an “internal mass anomaly.”
“The RISE data indicate that the shape of the core cannot be explained by its rotation alone,” Attilo Revoldini of the Royal Observatory of Belgium said in the release. “This shape requires regions of slightly higher or lower density buried deep within the mantle.”
vision I ran out of energy And She finished her mission It’s December 2022, but there’s still plenty of data from the mission, and from RISE in particular, to analyze.
These were the results published In June in the journal Nature.
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