Venus’ thick atmosphere speeds up the planet’s spin

The way the air flows over mountains changes the entire planet’s rotation speed


PUSH AND PULL  New research has shown that Venus’ thick atmosphere, shown here in an image from the Japanese space agency’s Akatsuki spacecraft, can speed up the planet’s rotation.

Damia Bouic, DARTS, ISAS, JAXA

Time is out of joint on Venus. The planet’s thick air, which spins much faster than the solid globe, may push against the flanks of mountains and change Venus’ rotation rate.

Computer simulations show that the thick Venusian atmosphere, whipping around the planet at 100 meters per second, exerts enough push against a mountain on one side and suction on the other side to speed the planet’s rotation rate by about two minutes each Venus day, according to a study in Nature Geoscience June 18.

That’s not much, considering that the planet rotates just once every 243 Earth days. By comparison, Venus’ atmosphere rotates about once every four Earth days. Precise measurements of the planet’s rotation rate have varied by about seven minutes, however. The push and pull of the air over the mountains could help explain the mismatch, with some other force — possibly the gravitational influence of the sun — slowing the planet’s spin back down.

Venus's atmosphere
DRAW BACK The motion of Venus’ atmosphere over mountains on the planet’s surface raises a bow-shaped wave that stretches from pole to pole in this image from Akatsuki. PLANET-C
The simulations by UCLA planetary scientist Thomas Navarro and colleagues are the first to account for a 10,000-kilometer-long wave in Venus’ cloud tops , spotted in 2015 by the Japanese space agency’s Akatsuki spacecraft (SN: 2/18/17, p. 5) . Similar waves are launched into the atmosphere on Earth when air flows over a mountain, but they normally dissipate quickly as opposing winds break them up. Venus’ atmosphere rotates so much faster than the planet and in such a uniform direction that the waves could persist for a long time.

“This work is very interesting,” says planetary scientist Tetsuya Fukuhara of Rikkyo University in Tokyo, one of the researchers who discovered the atmosphere wave. The work helps explain where the wave comes from and addresses how Venus’ surface features affect the atmosphere, “which is the most important issue in the Venus atmospheric science.”

More detailed measurements of Venus’ rotation, possibly taken with a future lander (SN: 3/3/18, p. 14), could eventually help reveal details of Venus’ interior, such as the size of its core.

“Venus is the closest thing to Earth that we know of,” Navarro says, and yet its hot, thick, toxic atmosphere makes it utterly alien. “We’d like to know what’s inside.”

Lisa Grossman is the astronomy writer. She has a degree in astronomy from Cornell University and a graduate certificate in science writing from University of California, Santa Cruz. She lives near Boston.

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