Frequency Shifts. Mars Lander serves up a surprise : The Red Planet is spinning faster.

For reasons unknown, the spin of Mars is speeding up. In a paper published in June in the journal Nature, scientists working on NASA's InSight Lander mission on Mars reported findings gleaned from tiny shifts in the frequencies of radio transmissions between Earth and InSight.

The measurements showed the expected undulations of the planet's rotation, quickest during winter and summer and slowest during spring and fall, as the distribution of frozen carbon dioxide in the ice caps shifted with the seasons.

WHEN including the NASA Viking mission's Doppler measurements from 47 years ago, the scientists found a slight speeding up in the spin of Mars, which has led to a shortening of a Martian day by about 1.5 millionths of a second per Martian year.

'' It was a surprise,'' Bruce Banerdt, the principal investigator for the InSight mission, said. '' We did not expect to see that at all.''

It is known that one of the Martian moons, Phobos, is gradually falling, and that indeed is speeding up the rotation of Mars, but that is not big enough to explain what was observed.

Dr. Banerdt said that the most likely cause was a long term accumulation of ice at the poles. [ Kenneth Chang ].


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