Is Venus’ Rotation Slowing Down?

by Nancy Atkinson on February 10, 2012

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New measurements from ESA’s Venus Express spacecraft shows that Venus’ rotation rate is about 6.5 minutes slower than previous measurements taken 16 years ago by the Magellan spacecraft. Using infrared instruments to peer through the planet’s dense atmosphere, Venus Express found surface features weren’t where the scientists expected them to be.

“When the two maps did not align, I first thought there was a mistake in my calculations as Magellan measured the value very accurately, but we have checked every possible error we could think of,” said Nils Müller, a planetary scientist at the DLR German Aerospace Centre, lead author of a research paper investigating the rotation.

Venus Express in orbit since 2006 around our nearest planetary neighbor. Credits: ESA

Using the VIRTIS infrared instrument, scientists discovered that some surface features were displaced by up to 20 km from where they should be given the accepted rotation rate as measured by the Magellan orbiter in the early 1990s.

Over its four-year mission, Magellan determined the length of the day on Venus as being equal to 243.0185 Earth days. But the data from Venus Express indicate the length of the Venus day is on average 6.5 minutes longer.

What could cause the planet to slow down? One possibility may be the raging weather on Venus. Recent atmospheric models have shown that the planet could have weather cycles stretching over decades, which could lead to equally long-term changes in the rotation period. The most important of those forces is due to the dense atmosphere – more than 90 times the pressure of Earth’s and high-speed weather systems, which are believed to change the planet’s rotation rate through friction with the surface.

Earth experiences a similar effect, where it is largely caused by wind and tides. The length of an Earth day can change by roughly a millisecond and depends seasonally with wind patterns and temperatures over the course of a year.

But a change of 6.5 minutes over a little more than a decade is a huge variation.

Other effects could also be at work, including exchanges of angular momentum between Venus and the Earth when the two planets are relatively close to each other. But the scientists are still working to figure out the reason for the slow down.

These detailed measurements from orbit are also helping scientists determine whether Venus has a solid or liquid core, which will help our understanding how the planet formed and evolved. If Venus has a solid core, its mass must be more concentrated towards the center. In this case, the planet’s rotation would react less to external forces.

“An accurate value for Venus’ rotation rate will help in planning future missions, because precise information will be needed to select potential landing sites,” said Håkan Svedhem, ESA’s Venus Express project scientist.

Venus Express will keep monitoring the planet to determine if the rate of rotation continues to change.

Source: ESA

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Anonymous February 10, 2012 at 2:46 PM

That’s quite large! At that rate one would think Magellan would have detected a slow down over the course of its mission. If weather is a cause I suppose Magellan might have performed its mission during a ‘lull’ in the storm.

I love news about Venus… we never hear enough about her.

balarneystone February 10, 2012 at 4:11 PM

I am not qualified to understand all this, but maybe the speed of rotation is the same but the surface features used as a guage have moved. Did they think to check if there is a possibilty of tectonic plate movement. This would cause the surface features to be in a different spot than they were in the 90′s also.

Anonymous February 10, 2012 at 5:29 PM

A 20km shift in two decades would be quite some tectonic plate movement. It wasn’t clear from the article just how uniform the apparent shift in surfaces features is; if it was uniform, then it seems that the cause must be a slowdown in rotation. Otherwise, then there could be some wild and exciting things going on under the surface.

Anonymous February 10, 2012 at 8:13 PM

Here is part of the abstract from the Nils Müller paper:

“This deviation is sufficiently large to affect estimates of surface emissivity from infrared imaging. A revised period of rotation of Venus of 243.023 ± 0.002 d aligns the two data sets. This period of rotation agrees with pre-Magellan estimates but is significantly different from the commonly accepted value of 243.0185 ± 0.0001 d estimated from Magellan radar images. It is possible that this discrepancy stems from a length of day variation with the value of 243.023 ± 0.002 d representing the average of the rotation period over 16 years.”

Since the Magellan and Venus express data does indeed align that should mean that the shifts are uniform. I assume the 20 km “shifts” were only at the equator.

What also sticks out is that the Venus Express data ‘jives’ with pre-Magellan data (probably taken from Venera, Pioneer and/or Arecibo radar).

Anonymous February 10, 2012 at 10:09 PM

So do we think Venus is actually slowing, that Magellan miscalculated their rotation rate, or that Magellan placed all their surface maps a few miles to the left of where they really were?

Anonymous February 10, 2012 at 11:41 PM

I can’t believe Magellan miscalculated it yet it did strike me as odd. Maybe that retrograde rotation has them all confused (just joking of course).

BTW I forgot to add the link to the abstract http://www.sciencedirect.com/science/article/pii/S0019103511003782

The article itself is $ 31.50 to download and read.

Anonymous February 10, 2012 at 9:47 PM

It’s my understanding that Venus is known for having little to no active plate tectonics at all.
Pepper is right, if they had enough activity to move those features by 6.5 minutes, Express would have found some new mountains and canyons, and everything wouldn’t have shifted in one uniform direction.

Jon Souter February 10, 2012 at 4:12 PM

The article, as one possibility, suggests interactions between Earth and Venus might have contributed to the slowdown. But, wouldn’t a similar but opposite effect then have been detected in the Earth’s rotation as a result of this?

Torbjörn Larsson February 10, 2012 at 7:54 PM

The main angular momentum of a planet would be the orbital angular momentum. If Venus’ rotational angular momentum couples to that there wouldn’t be much of an effect. There is, IIRC, a small outward drift of Earth as the inner system dissipates some orbital angular momentum.

And there is the Moon FWIW, which would make these things very lopsided.

liberty_rocks February 10, 2012 at 5:17 PM

OK. As another poster said, “I am not qualified to understand all this”.

However, Earth reaches 90 BAR at ~2700 ft below ocean surface. The average ocean depth is ~3800 ft.. Thus, the average pressure in the Oceans (greatly) exceeds Venusian atmospheric pressure.

How is it the planetary ocean hasn’t had the same effect as the Venusian atmosphere?

Torbjörn Larsson February 10, 2012 at 7:51 PM

Our oceans rotate with the planet, except for relatively small ocean currents.

Anonymous February 10, 2012 at 6:13 PM

creationisme mode on

that means the universe is not older than 6000 years, because if it was older than 6000 years venus would be tidally locked

creationisme mode off

Anonymous February 10, 2012 at 6:17 PM

I suspect there is a clock synchronization problem. A fluid dynamics on a rotating body will cause the energy of angular rotation to change. Since the angular momentum is constant for a closed system that should not be changing. A change in the angular periodicity then happens if there is some change in the moment of inertia of the system. A change of 6.5 minute over ten years is unexpectedly large.

LC

Torbjörn Larsson February 10, 2012 at 7:56 PM

The main rotational momentum exchange of Venus vs its environment, as of yet unexplained, is the superrotation of the upper atmosphere I think. (Or at least it would be before this.) One model for that is coupling to the solar wind, I hear. It seems there are several mysteries to solve, likely in one fell swoop.

And there are hypotheses that Venus slow and reversed rotation is caused by coupling to the Sun, another factor to consider here.

Anonymous February 10, 2012 at 11:46 PM

I have no doubt that there is some coupling, but how much energy would be required to slowed down that much and is the Sun able to provide that energy

Also where would that lost energy be directed at? Speeding up of the Sun? Moving the Orbit of Venus further from the Sun?

Torbjörn Larsson February 11, 2012 at 8:54 PM

Astrophysicists would like to know!

Bruce Thomas February 10, 2012 at 8:55 PM

I guess they would never really think that there was a simple misstake made

Anonymous February 10, 2012 at 10:44 PM

Ho, ho, these arrogant scientists, eh? They just cannot imagine they do not know it all…

No. “When the two maps did not align, I first thought there was a mistake in my calculations…” said Nils Müller. This is always the first thought of a good scientist. And usually the second and third thoughts too if you are going to publish something that you have measured but don’t understand.

Torbjörn Larsson February 11, 2012 at 8:58 PM

Clearly you didn’t read the article, so why comment at all?

‘Tis a mystery shrouded in Venusian mists…

Anonymous February 10, 2012 at 10:39 PM

The recent earthquake in Japan changed the length of the Earth’s day by about 1.7 milliseconds. A day is 86000 seconds long, so that is a change of about 20 parts per billion. The figures for Venus’ day are 243.023 days versus 243.0185, which is a change of about 0.0045 days, which is about 18 parts per million, or about a thousand times greater. Quakes on Venus are not the cause.

The seasonal variation in winds affects the Earth’s angular momentum, changing the length of day by a millisecond or so. Venus’ atmosphere is 100 times that of earth, and it has strong winds, so possibly the effect is a hundred times greater on Venus than on Earth. Assuming Venus and Earth are roughly the same size and density, this might give a hundred times the change in surface velocity on Venus. As the days on Venus are 243 times as long as days on earth, the fractional change in surface motion is then 24 300 times greater on Venus. However, we are averaging over a 16 year period, so most seasonal variations should have averaged out. If we divide by about 16 * 3/2 for the number of years on Venus, we almost get back to our thousand to one ratio.

6 minutes is about the time it takes for light to come from Venus to Earth. Maybe the difference is just where the clock was.

I expect they have thought of all of these already.

Torbjörn Larsson February 11, 2012 at 9:01 PM

It’s the OPERA effect again.

John Ackerman February 11, 2012 at 9:12 PM

Over 200,000 ‘small domes’ on Venus’ surface are jetting gaseous S8 at high velocity directly to 48 km altitude, where they crystallize to form the lower cloud layer. This high speed jetting amplifies the slow rotation of Venus (day~248 earth days) causing the high altitude wind which circles the entire planet in four earth days. The Pioneer Venus instruments could not detect S8, the normal form of sulfur at the temperature in the lower atmosphere, because the molecule is above the mass range of the mass spectrometer. The same high speed jetting results in a loss of angular momentum, which accounts for the slowing of the planet. This is one means by which a new (6000 year-old) planet cools. Creationists – that does not mean the Earth is 6,000 years old. Every terrestrial planet is created by a massive impact on Jupiter, so each has a unique age. the earth is about 3.9 billion years old, while Mars (and Mercury, its former solid core) are 4.56 billion years old. Pioneer Venus probes all agreed that Venus is radiating 250 times more energy than the Earth. See
acksblog.firmament-chaos.com for more.

Anonymous February 12, 2012 at 2:56 AM

Yeah, that sounds legit.

A minor nitpick – apart from everything I think migrating Jovian core theory might need some refining :)

Anonymous February 12, 2012 at 4:50 PM

The planets were created by impacts with Jupiter? That’s absurd.

magnus.nyborg February 18, 2012 at 9:03 PM

Sounds like personal theory to me.

chris George February 12, 2012 at 2:07 AM

sorry if this has been asked already but would this be a danger or any threat to the solar system as a whole or our planet? Or what could this change if anything at all, if it continues to slow?

Anonymous February 12, 2012 at 4:45 PM

It won’t affect us or any other body in the solar system in any way whatsoever.

If it continues to slow… well, eventually it would stop. That would be interesting. It would be tidally-locked with the Sun… I wonder if its atmosphere would be thick and fluid enough to transport heat around the night side of the planet and prevent itself from freezing into a giant glacier? Maybe the temperature would be comfortable enough for humans (even if the pressure and composition were not).

Anonymous February 13, 2012 at 7:44 PM

I’m thinking it’s a data/calculation error. That’s a pretty significant slowdown.

On the other hand, it it possible that the planet slows and speeds up cyclically? Is there something going on in the interior that could cause this? I would think this would cause a detectable wobble, but as Venus’ rotation is already so slow it may not matter. Maybe some simulations would help.

Weird and cool.

Paul Felix Schott February 18, 2012 at 4:12 PM

QUESTION
In the Heavens above signs of great wonders. How many will you need before you will Believe???
Venus rotation has shortened for 6,5 minutes. What’s causing the planet Venus to slow down? The same think that is going to slow the Planet Earth rotation down.

ANSWER
Thy Lord GOD that art in Heaven.
Read
Matthew 24: 1-51 the whole chapter

when you have done so go back and read Matthew 24:21and 22.
then LUKE 21:11

in your Heart you will know then.

GOD Bless You and Your Love ones
Give thanks to our Lord Jesus Christ every day.

The Lord’s Little Helper
Paul Felix Schott

Olaf2 February 18, 2012 at 6:04 PM

You are in the wrong forum.
The Bible talk is a different site, this one focusses on science. And “Godidit” is not an scientific answer.

Torbjörn Larsson February 18, 2012 at 8:19 PM

Creationists shouldn’t post on science sites.

magnus.nyborg February 18, 2012 at 9:01 PM

The Flying Spaghetti Monster once again proves you wrong.

Debbie Scarbrough February 20, 2012 at 4:32 PM

This may or may not be related but it instantly reminded me of a few things that happened last year. Clocks in Sicily mysteriously jumped ahead (20 minutes) and two weeks later they reported they may be doing a power grid experiment (US) and our clocks may change… up to 20 minutes fast (there’s that 20 minutes again). Interestingly enough, the clocks they can control might not change.

There have been noticeable time changes here on Earth. The Sun rose 2 days early in Greenland last year and was up for 18 minutes in Alaska days before it was supposed to be.

There have been a lot of changes and unusual events on Earth and on other planets. There are many videos showing TWO SUNS from all over the world. Most are sundogs but the videos from NYC, China, Thailand and Russia are hard to deny [but I'm sure some people will].

6/9/11, Clocks in Sicily Mysteriously Jump Ahead- http://www.italymag.co.uk/italy/time/clocks-sicily-mysteriously-jump-ahead

6/24/11, Power grid may disrupt clocks – http://www.physorg.com/news/2011-06-power-grid-disrupt-clocks.html

Two Suns
NYC – http://www.youtube.com/watch?v=6H-xP1k7YLY&feature=related
China – http://www.youtube.com/watch?v=a8fWUPlqwlQ
Thailand – http://www.youtube.com/watch?v=F-8Dn-GXZbM&feature=results_main&playnext=1&list=PL5B67E86A7981548B
Russia – http://www.youtube.com/watch?v=fh6hIwbzCcs

magnus.nyborg February 20, 2012 at 8:03 PM

Unsubstantiated personal opinions, violating the posting criteria on UT…

Anonymous February 11, 2012 at 12:26 AM

I won’t be buying anything from Elsevier…

Anonymous February 11, 2012 at 7:13 PM

Dang… I was hoping someone else would do it ;-)

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