How Long is a Day on Venus? We Finally Know the Exact Answer – Universe Today

Venus, aka. Earth’s “Sister Planet,” has at all times been shrouded in thriller for astronomers. Despite being planet Earth’s closest neighbor, scientists remained blind to what Venus’ floor even appeared like for effectively into the 20th century, due to its extremely dense and opaque ambiance. Even in the age of robotic area exploration, its floor has been all however inaccessible to probes and landers.
And so the mysteries of Venus have endured, not the least of which has to do with a few of its most simple traits – like its inside mass distribution and variations in the size of a day. Thanks to observations carried out by a staff led from UCLA, who repeatedly bounced radar off the planet’s floor for the previous 15 years, scientists now know the exact size of a day on Venus, the tilt of its axis, and the dimension of its core.

The staff’s examine, titled “Spin state and moment of inertia of Venus,” lately appeared in the journal Nature Astronomy. The staff was led by Jean-Luc Margot, a Professor of Earth and planetary sciences and astrophysics at UCLA. He was joined by researchers from Cornell University, NASA’s Jet Propulsion Laboratory (JPL), and the National Radio Astronomy Observatory‘s (NRAO) Green Bank Observatory.
Radar measurements of Venus’ floor, used to find out its fee of spin and axial tilt. Credit: Jean-Luc Margot/UCLA and NASATo recap, Venus and Earth are appropriately thought of siblings, seeing as how they’re comparable in dimension, composition, mass, and density. In spite of that, the separate evolutionary paths they’ve adopted have resulted in extensively completely different outcomes. Whereas Earth has an environment that may keep temperatures conducive to life, Venus has a tremendous-dense ambiance that is poisonous and sizzling sufficient to soften lead!
In order to grasp why and the way our two planets had such divergent histories, scientists must know the fundamentals – like what number of hours there are in a Venusian day. Knowing this will yield useful details about a planet’s spin, orientation, inside construction, and mass distribution. Having exact measurements for these traits will finally shed mild on the formation and volcanic historical past of the planet, in addition to how its floor advanced over time.
Precise knowledge is additionally essential to planning missions to the floor since a planet’s rotation can throw off touchdown makes an attempt by as a lot as 30 km (~18.5 mi). “Venus is our sister planet, and yet these fundamental properties have remained unknown,” mentioned Margot in a UCLA Newsroom launch. “Without these measurements, we’re essentially flying blind.”
To acquire correct estimates on Venus’ rotation, Margot and his colleagues used the 70-meter (230 ft) radio antenna at the Goldstone Deep Space Communications Complex, which is situated in the Mojave Desert and is a part of NASA’s Deep Space Network (DSN). Between 2006 and 2020, the staff carried out 21 separate measurements of Venus’s floor by bouncing radio indicators off Venus’ floor that have been then obtained by Goldstone and Green Bank.
The Goldstone Deep Space Communications Complex, located in the Mojave Desert in California. Credit: NASAAs Margot defined, the course of is just like shining a mild (the radio dish) on hundreds of thousands of tiny reflectors (the planet’s panorama) and measuring the reflections to get a sense of how briskly its transferring:
“We use Venus as a giant disco ball. We illuminate it with an extremely powerful flashlight — about 100,000 times brighter than your typical flashlight. And if we track the reflections from the disco ball, we can infer properties about the spin [state].”
The complicated manner Venus displays the radio indicators causes them to erratically brighten and dim earlier than they’re obtained again on Earth. The Goldstone antenna intercepts the return sign first, adopted by the Green Bank antenna about 20 seconds later. The precise timing of the delay permits scientists to understand how rapidly Venus is spinning whereas the specific window of time through which the echoes are most comparable permits them to gauge the planet’s axial tilt.
What they discovered was somewhat fascinating. For starters, they discovered that a mean day on Venus lasts 243.022 Earth days – the equal of about two-thirds of a yr on Earth. What’s extra, the outcomes confirmed that Venus’ fee of rotation seems to be altering all the time. This was indicated in how every particular person radar measurement could be smaller or bigger than a earlier one, and by a distinction of at the least 20 minutes per measurement.
These variations, that are in all probability what led to earlier estimates being inconsistent, are seemingly the results of Venus’ heavy ambiance. As it rotates round the planet, it is more likely to trade a lot of momentum with the floor, inflicting its rotation to hurry up and decelerate. The identical phenomenon occurs on Earth, however the decrease density of our ambiance implies that there is solely a distinction of a millisecond per day.

Margot and his colleagues additionally obtained much more exact measurements of Venus’ axial tilt, which is tilted at 2.6392 levels (in comparison with Earth’s 23 diploma-tilt). Their measurements enhance over earlier measurements by a issue of 10 and likewise revealed the fee at which the orientation of Venus’ axis modifications over time. On Earth, the precession of our axial tilt takes about 26,000 years to finish a single cycle, whereas Venus’ takes about 29,000 years.
What’s extra, these exact measurements allowed the staff to measure Venus’ core and decide that it is about 3,500 km (2,175 mi) in diameter. This is just like Earth’s, which is an estimated 3,485 km (2,165 mi) in diameter, although they can not say whether or not it’s liquid or strong simply but. Earth’s magnetic subject is the results of a dynamo impact created by Earth’s molten outer core rotating about its strong inside core.
For this purpose, figuring out the state of Venus’ core is important to understanding if the absence of a world magnetic subject contributed to Venus’ evolution. Obtaining correct measurements with this technique presents many challenges, not the least of which is the distinctive timing it takes to make sure that Venus and Earth are correctly positioned.
At the identical time, each observatories need to be working completely to make sure that they intercept the return indicators reliably. “We found that it’s actually challenging to get everything to work just right in a 30-second period,” mentioned Margot. “Most of the time, we get some data. But it’s unusual that we get all the data that we’re hoping to get.”
Jupiter’s moons Europa (left) and Ganymede (proper.) Both moons seemingly have subsurface oceans. Credit: NASADespite the challenges, Margot and his colleagues plan to proceed learning Venus utilizing this radio-echo method. With every sign that is bounced again from its floor, researchers are in a position to be taught a bit extra about its floor, formation, and sophisticated historical past. This information won’t solely enable us to crack the thriller of our “Sister Planet,” however drastically enhance our understanding of how liveable planets can transition to veritable hellholes!
Similarly, Margot and his staff hope to make use of this identical technique to check Jupiter’s moons Europa and Ganymede. For a long time, astronomers have strongly suspected that these moons comprise huge heat water oceans of their inside (significantly Europa). Ground-based radar measurements of those moons are anticipated to fortify the case for inside oceans and reveal how thick their icy shells are – each of which can inform future missions to seek for life there.
This analysis was carried out with assist supplied by NASA JPL and the National Science Foundation (NSF).
Further Reading: UCLA Newsroom, Nature Astronomy
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