Thick atmosphere boosts how fast Venus spins | Science News for Students

Thick atmosphere boosts how fast Venus spins

Planet’s rotational speed can change based on how air flows over mountain tops
Jul 23, 2018 — 6:45 am EST
Venus atmosphere

With help from its thick atmosphere, the speed at which Venus spins changes. This planet close-up was taken by the Japanese space agency’s Akatsuki spacecraft.

Damia Bouic, DARTS, ISAS, JAXA

Time gets tricky on Venus. The planet has extremely thick air, which flows much more rapidly than the rate at which the solid planet spins. As that thick atmosphere pushes against the planet’s mountains, it can change how quickly Venus spins, scientists now report.

Researchers used a computer to simulate the movements of that thick atmosphere. It whips around at 100 meters per second (around 224 miles per hour). Those winds exert enough push against mountains on one side of the planet — and suction on the other side — to alter the speed of the planet’s rotation. The thick atmosphere increases the rotation rate by up to about two minutes each day. Each Venus day, that is. And each day on this planet is 243 times longer than one on Earth.

Two minutes is not much in a rotation that lasts almost 350,000 Earth minutes. Venus’ atmosphere, by contrast, rotates about once every four Earth days (5,760 Earth minutes).

There also must be some other force slowing the planet’s spin back down. If not it would continue to just spin faster and faster. What might that other force be? Researchers suspect it could be the sun’s gravitational influence.

The researchers reported their calculation in the July issue of Nature Geoscience.

Then there’s that mighty wave

Precise measurements of the rotational period (day length) on Venus have varied by up to seven minutes. The push and pull of the air over the planet’s mountains could help explain this mismatch.

A wave in the atmosphere of Venus
As the atmosphere moves over mountains on the surface of Venus, an arched wave forms, which extends from pole to pole. This image from the Akatsuki spacecraft shows the wave.
PLANET-C

Thomas Navarro and his colleagues wanted to better understand the differences in the planet’s spin. Navarro is a planetary scientist at the University of California, Los Angeles. He was part of a team that developed the computer model to study the thick Venusian atmosphere and how it affects the planet’s spin. Their results are the first to explain a bizarre wave found atop the planet’s clouds. That wave is 10,000 kilometers (6,200 miles) long, extending from pole to pole.

The Japanese space agency’s Akatsuki spacecraft first spotted that wave in 2015. Similar waves ripple through Earth’s atmosphere when air flows over a mountain. But those Earth waves normally dissipate quickly. Opposing winds break them up. Not so on Venus. Its atmosphere rotates far faster around the planet — and in only one direction. So once formed, such waves can persist for a long time.

“This work is very interesting,” says Tetsuya Fukuhara. He is a planetary scientist at Rikkyo University in Tokyo, Japan. He also is among the researchers who discovered those waves in the atmosphere of Venus. The new work, he says, helps explain where the wave comes from. It also addresses how surface features on Venus affect its atmosphere. That “is the most important issue in the Venus atmospheric science,” he says.

Scientists hope to get even more detailed measurements of Venus’ rotation. That could help them better understand how the atmosphere influences it. Those measurements could be taken with a future lander. And, they could eventually help reveal details of the planet’s interior, such as the size of its core.

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

Power Words

(for more about Power Words, click here)

alien     A non-native organism. (in astronomy) Life on or from a distant world.

atmosphere     The envelope of gases surrounding Earth or another planet.

cloud     A plume of molecules or particles, such as water droplets, that move under the action of an outside force, such as wind, radiation or water currents. (in atmospheric science) A mass of airborne water droplets and ice crystals that travel as a plume, usually high in Earth’s atmosphere. Its movement is driven by winds. 

colleague     Someone who works with another; a co-worker or team member.

computer model     A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

core     Something — usually round-shaped — in the center of an object. (in geology) A planet’s innermost layer. Or, a long, tube-like sample drilled down into ice, soil or rock. Cores allow scientists to examine layers of sediment, dissolved chemicals, rock and fossils to see how the environment at one location changed through hundreds to thousands of years or more.

force     Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

geoscience     Any of a number of sciences, like geology or atmospheric science, concerned with better understanding Earth. People who work in this field are known as geoscientists.

lander     A special, small vehicle designed to ferry humans or scientific equipment between a spacecraft and the celestial body they will explore.

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood. The solar system includes eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

simulate     (n. simulation) To deceive in some way by imitating the form or function of something. (in computing) To try and imitate the conditions, functions or appearance of something. Computer programs that do this are referred to as simulations or computer models.

sun     The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.

toxic     Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.

Venus     The second planet out from the sun, it has a rocky core, just as Earth does. Venus lost most of its water long ago. The sun’s ultraviolet radiation broke apart those water molecules, allowing their hydrogen atoms to escape into space. Volcanoes on the planet’s surface spewed high levels of carbon dioxide, which built up in the planet’s atmosphere. Today the air pressure at the planet’s surface is 100 times greater than on Earth, and the atmosphere now keeps the surface of Venus a brutal 460° Celsius (860° Fahrenheit).

wave     A disturbance or variation that travels through space and matter in a regular, oscillating fashion.

Citation

Journal:​ ​​T. Navarro, G. Schubert and S. Lebonnois. Atmospheric mountain wave generation on Venus and its influence on the solid planet’s rotation rate. Nature Geoscience. Vol. 11, July 2018, p. 487. doi: 10.1038.s41561-018-0157-x.