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Mars’ Increasing Rotation Speed and Shrinking Days Baffle Scientists

Rover on Mars'

Discoveries from NASA’s InSight lander

Recent findings from NASA’s InSight lander shed light on the intriguing trend of Mars’ day getting shorter. Currently, a day on Mars, known as a “sol,” lasts for 24 hours and 37 minutes. However, advanced measurements with an accuracy of a fraction of a millisecond have revealed a gradual speeding up of the planet’s rotation rate.

“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,” said aerospace engineer Sebastien Le Maistre of the Royal Observatory of Belgium, a lead scientist on the study.

Although the exact cause remains uncertain, planetary scientists suggest that the phenomenon could be attributed to the redistribution of Mars’ mass. Similar to an ice skater pulling in their arms to spin faster, the redistribution of mass on Mars may be influenced by factors such as the accumulation of ice on the polar caps or the slow rebound of the planet’s surface from the weight of past glaciers. These discoveries provide valuable insights into the dynamic nature of Mars and its geologic history.


The Doppler Shift Puzzle

NASA’s Deep Space Network, which consists of three radio antennas situated across the globe for interplanetary communication, directed a powerful radio signal towards Mars. This signal was received by InSight’s RISE (Rotation and Interior Structure Experiment) instrument and then bounced back to Earth.

An interesting phenomenon known as the Doppler shift occurs during this process. The Doppler shift is similar to what happens when the siren of an approaching emergency vehicle gradually increases in pitch and then decreases as it moves away. In the case of InSight, as it rotates into the view of the hemisphere on Mars, the radio signal emitted undergoes a Doppler shift towards higher frequencies.

Conversely, when InSight is on the hemisphere rotating out of view, the signal experiences a Doppler shift towards shorter frequencies. The measurement of this Doppler shift is crucial for accurately determining the length of a day on Mars to the level of fractions of a millisecond. However, this task is far from simple due to the precise dependence on the planet’s rate of rotation.

“What we’re looking for are variations that are just a few tens of centimeters over the course of a Martian year [687 Earth days],” said Le Maistre, who is also RISE’s principal investigator. “It takes a very long time and a lot of data to accumulate before we can even see these variations.”

These findings, acknowledged by experts such as Sebastien Le Maistre, signify a remarkable milestone in the ongoing exploration of Mars and contribute to our knowledge of the planet’s rotation. The potential implications of this new information could pave the way for future understanding of not only Mars but also other planets in our solar system and beyond.

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