Could Venus be shifting gear?

Feb 10, 2012
Venus Express in orbit since 2006 around our nearest planetary neighbour. Credits: ESA

(PhysOrg.com) -- ESA’s Venus Express spacecraft has discovered that our cloud-covered neighbour spins a little slower than previously measured. Peering through the dense atmosphere in the infrared, the orbiter found surface features were not quite where they should be.

Using the VIRTIS instrument at infrared wavelengths to penetrate the thick cloud cover, scientists studied surface features and discovered that some were displaced by up to 20 km from where they should be given the accepted rotation rate as measured by NASA’s Magellan orbiter in the early 1990s.

These detailed measurements from orbit are helping scientists determine whether Venus has a solid or liquid core, which will help our understanding of the planet’s creation and how it evolved.

If Venus has a solid core, its mass must be more concentrated towards the centre. In this case, the planet’s rotation would react less to external forces.

This video is not supported by your browser at this time.
This animation shows Venus, a planet very similar to Earth in mass and size, but with a crushing atmosphere, sulphuric acid clouds and surface temperatures in excess of 460ºC. Venus Express is helping scientists to understand how a planet with similar physical characteristics to Earth evolved in a way so fundamentally different. Credits: ESA - C. Carreau

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.

In the 1980s and 1990s, the Venera and Magellan orbiters made radar maps of the surface of Venus, long shrouded in mystery as well as a dense, crushing and poisonous atmosphere. These maps gave us our first detailed global view of this unique and hostile world.

Over its four-year mission, Magellan was able to watch features rotate under the spacecraft, allowing scientists to determine the length of the day on Venus as being equal to 243.0185 Earth days. .

However, surface features seen by Venus Express some 16 years later could only be lined up with those observed by Magellan if the length of the Venus day is on average 6.5 minutes longer than Magellan measured.

Topographic maps from Magellan and Venus Express clearly show the shift in surface features. At infrared wavelengths Venus Express was able to peer through the dense atmosphere and map surface features observed from both Earth-based radar imaging and with the Russian Venera 15 and 16 missions as well as NASA’s Magellan spacecraft. By comparing the currently accepted rotation rate value for the planet from the Magellan mission, scientists discovered a ‘shift’ in surface features of up to 20 km caused by what they believe is a change in the rotation rate of the planet. Credits: NASA/JPL/Magellan/P. Ford/ESA/Venus Express/P. Drossart/G. Piccioni

This also agrees with the most recent long-duration radar measurements from Earth.

“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.

Scientists, including Özgur Karatekin of the Royal Observatory of Belgium, looked at the possibility of short-term random variations in the length of a Venus day, but concluded these should average themselves out over longer timescales.

On the other hand, other 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. 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.

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

While further study is needed, it’s clear that Express is penetrating far deeper into the mysteries of this enigmatic planet then anyone dreamed.

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Shootist
1 / 5 (16) Feb 10, 2012
OK Boffins,

more than 90 times the pressure of Earth


Which is fine and good, except that 90Bar is found at a depth of 2700 ft, in the world's oceans (1 BAR increase ever 30 feet). The average depth of the planetary ocean is 3800 ft.

So actually, the densest part of Earth's "atmosphere", the Ocean, is significantly denser than the Venusian "atmosphere".

Where is this gedanken incorrect?
antialias_physorg
4.7 / 5 (13) Feb 10, 2012
Where is this gedanken incorrect?

Oceans aren't atmosphere.

http://en.wikiped...mosphere

Quote:
An atmosphere ... is a layer of gases


Atmospheric pressure for a planet is always with respect to the surface. From the same link:
Atmospheric pressure is the force per unit area that is always applied perpendicularly to a surface by the surrounding gas
GeoGeo
5 / 5 (4) Feb 10, 2012
Earth's atmosphere does not include its oceans.
The atmosphere, biosphere, hyrdosphere / cryosphere, and lithosphere are each different and unique from one another. The atmosphere consists of the exosphere, thermosphere, mesosphere, stratosphere and the troposphere. You don't see the Earth's atmosphere including pressures found in the lithosphere so why would you include pressures found in the Earth's hydrosphere?

"The most important of those forces is due to the dense atmosphere more than 90 times the pressure of Earths and high-speed weather systems."

So actually, the densest part of the Venusian atmosphere is 90 times the pressure of Earth's atmosphere.
axemaster
1.5 / 5 (6) Feb 10, 2012
If Venus has a solid core, its mass must be more concentrated towards the centre. In this case, the planets rotation would react less to external forces.

This is wrong. If the mass were concentrated at the center, the moment of inertia would be lower and the rotation would be easier to change.
barakn
5 / 5 (8) Feb 10, 2012
If Venus has a solid core, its mass must be more concentrated towards the centre. In this case, the planets rotation would react less to external forces.

This is wrong. If the mass were concentrated at the center, the moment of inertia would be lower and the rotation would be easier to change.
No. If the core is solid, then the core and mantle/crust are coupled, rendering the moment of inertia much higher than if we were discussing the moment of inertia of the mantle/crust only.
ccr5Delta32
1.6 / 5 (5) Feb 10, 2012
That's 24 seconds per earth year .That seems a ridiculous rate of change for a planet if considered like a rigid body angular momentum being conserved ,the energy needed would be beyond by any measure an effect of atmospheric causes .
Not a rigid body .If I was pressed I would suggest loose crust like an egg shell but also the possibility something was overlooked or indeed underlooked in the data acquisition
Sanescience
1.3 / 5 (6) Feb 10, 2012
Wonder if Venus rotates slow enough that it will become tidal locked with the sun.
MarkyMark
not rated yet Feb 11, 2012
If Venus has a solid core, its mass must be more concentrated towards the centre. In this case, the planets rotation would react less to external forces.

This is wrong. If the mass were concentrated at the center, the moment of inertia would be lower and the rotation would be easier to change.
Heh and what makes you say that then? Do you have full access to current data on Venus? And are you at least as qualified as those who are reserching this?
Shootist
1 / 5 (4) Feb 11, 2012
Where is this gedanken incorrect?

Oceans aren't atmosphere.

http://en.wikiped...mosphere

Quote:
An atmosphere ... is a layer of gases


Atmospheric pressure for a planet is always with respect to the surface. From the same link:
Atmospheric pressure is the force per unit area that is always applied perpendicularly to a surface by the surrounding gas


fluid (gas liquid) the equations are not the same?
antialias_physorg
4 / 5 (4) Feb 11, 2012
If you want to argue that way: then why stop at liquid? Why are you exempting pressure in the solid parts of the planet?

Just admit you misunderstood what 'atmosphere' means or misread the sentence. No shame in that.
packrat
2.3 / 5 (3) Feb 12, 2012
This might be an silly question to some of you but I'm going to ask it anyway. Since Venus is closer to the sun and deeper in the sun's gravity well couldn't that make it's time run slightly slower than ours based on the positions? Or would the difference be a lot smaller than that?
antialias_physorg
3.7 / 5 (3) Feb 12, 2012
Yes: Venus is deeper in the suns gravity well and therfore it's time would run slower (immeasurably so). However you have to look at the total gravity you experience on Venus - and for that the gravity of Venus itself is MUCH more important than that of the sun. Gravity on Venus' surface is less than on Earth so time would be going faster if you were on Venus.

But again: at these gravity levels the difference is just incredibly tiny.
nkalanaga
5 / 5 (2) Feb 14, 2012
Sanescience and ccrDelta32: The atmosphere is a significant factor in the rotation of Venus. It's unlikely that it will ever be tidally locked. Whether the atmosphere could be responsible for the observed changes is another, but it is known that minor changes in ocean and atmospheric currents on Earth can affect rotation speed. Our changes aren't nearly as great as those on Venus, but, then, our atmosphere is much thinner, and the ocean currents are strongly affected by the continents. It's hard to get all of the water going the same direction.

"Venus has altogether escaped capture into a resonance because thermal atmospheric tides counteract its interior tides (Correia & Laskar 2003).

Long term evolution of the spin of Venus - I. Theory.
Alexandre C.M. Correia, Jacques Laskar and Olivier N¶eron de Surgy

www.imcce.fr/Equi...2002.pdf
www.imcce.fr/Equi...2002.pdf
Sanescience
1 / 5 (2) Feb 24, 2012
Neat. I like how the question is disapproved but the answer is voted up. There will be no questions! Only answers! heh.