Astronomers determine the length of a day on Venus

Shane McGlaun - May 4, 2021, 7:54am CDT
Astronomers determine the length of a day on Venus

Venus is a difficult planet to study, even though it’s right next door to Earth. One of the challenges in learning more about Venus is that the planet is covered in a veil of extremely thick clouds, and its surface is blasted with acid rain and temperatures hot enough to liquefy lead. Astronomers have used earth-based observations to learn some of the most fundamental properties of Venus.

Over the last decade and a half, the team of researchers from UCLA has repeatedly bounced radar signals off the surface of Venus. The radar observations have allowed the team to determine the precise length of a day on Venus, the tilt of its axis, and the size of its planetary core. Earth and Venus do have a lot in common, with both being rocky planets of nearly the same size, mass, and density.

However, the way the two planets have evolved is vastly different. One of the fundamental things scientists need to know to understand how the evolutionary history of the planets diverged was how many hours are in a Venusian day. Scientists also note that precise data on the planet was needed because any future landing in temps on the surface can be off by as much as 30 kilometers.

Radar measurements show that an average day on Venus lasts 243.0226 Earth days, about two-thirds of a year here on Earth. Another critical bit of knowledge learned is that the rotation rate of Venous is constantly changing. Scientists say the value measured at one time will be a bit larger or smaller than the previous value. The team has estimated the length of the day from each of the individual measurements, and they observed differences of at least 20 minutes.

Researchers say that likely explains why past estimates didn’t agree with one another. The heavy atmosphere of Venus is believed to be responsible for the variation. The heavy atmosphere sloshes around the planet, exchanging a lot of momentum with the solid ground speeding up and slowing down the planet’s rotation.

Venus tips to one side by precisely 2.6392 degrees, according to the researchers. The measurement is an improvement on previous estimates in terms of accuracy by a factor of 10. Scientists were able to determine the rate of the orientation of Venus’s spin axis changes known as precession. On Earth, precession takes about 26,000 years to cycle around one time, while Venus takes about 29,000 years.


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