APOD: Venus' Once Molten Surface (2013 Jun 23)

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APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by APOD Robot » Sun Jun 23, 2013 4:06 am

Image Venus' Once Molten Surface

Explanation: If you could look across Venus with radar eyes, what might you see? This computer reconstruction of the surface of Venus was created from data from the Magellan spacecraft. Magellan orbited Venus and used radar to map our neighboring planet's surface between 1990 and 1994. Magellan found many interesting surface features, including the large circular domes, typically 25-kilometers across, that are depicted above. Volcanism is thought to have created the domes, although the precise mechanism remains unknown. Venus' surface is so hot and hostile that no surface probe has lasted more than a few minutes.

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Re: APOD: Venus Once Molten Surface (2013 Jun 23)

Post by Beyond » Sun Jun 23, 2013 4:35 am

Venus... Hot stuff! :yes:
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by madtom1999 » Sun Jun 23, 2013 6:30 am

Just wondering if these might not be old meteorite scars. If the rock is so hot then it may be more like a non-newtonian fluid so impacts dont result in lots of ejecta and the energy released eventually results in these lava mounds.

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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Boomer12k » Sun Jun 23, 2013 8:10 am

Interesting...being so big...I wonder if they are lava flows...very viscus...slow building, slow flowing...so they spread and cool a tad, and build on each other.

Similar...on Earth...my state of Oregon...
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Sinan İpek » Sun Jun 23, 2013 8:14 am

Could they be some molten craters?

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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Ann » Sun Jun 23, 2013 10:11 am

I think it is important to remember that Venus is very different from the Earth mostly because it is much closer to the Sun. Therefore, what is true about meteorite impacts and craters on the Earth and the Moon may not be true about meteorite impacts on Venus.
http://www.economist.com/node/10205171 wrote:
Hakan Svedhem, of the European Space Agency, and his colleagues say that Earth and Venus probably started out much the same. The Earth's oceans teemed with plants and animals that converted most of its atmospheric carbon dioxide into carbonates and sank to the bottom as they died, to become sedimentary rocks. By contrast, Venus lost most of its liquid water. That is because Venus, being closer to the sun, started to warm up. This generated more water vapour in its atmosphere, further increasing the temperature in a runaway greenhouse effect.
Recently Swedish newspapers published articles about the findings by Japanese astronomers about Venus. According to an article in Sydsvenskan, May 31, 2013, the Japanese astronomers point out that the outer parts of the Earth cooled quickly, within 20 million years, allowing a lot of water to survive on the Earth. But for Venus this cooling process took much longer, because of Venus's greater proximity to the Sun. For Venus the cooling may have taken as much as 100 million years. By then, almost all the water of Venus had escaped into space.

I have translated the Swedish article into English, using Google translate and ironing out the most embarrassing mistakes. Here it is:
Why is Venus a lifeless and bone dry planet, while the Earth is full of life?

The reason, according to a new study, is that Venus cooled very slowly. When the planet ended up being solid all of its water had disappeared.

Earth, however, cooled very rapidly. Like any other planet the Earth was originally a molten and glowing mass, but during the course of only 20 million years the outer parts of it cooled and solidified.

Most of the planet's water was therefore left, and could eventually form the basis for life and its evolution.

In the new study, presented by researchers working at the University of Tokyo in Japan, the researches point out that Venus could have gone down the same route.

Venus and Earth are similar in size and are composed of roughly the same minerals.

Therefore, the prevailing hypothesis was that the two planets initially developed in much the same way - and that Venus somehow lost its water at a later time in its history.

But the new findings, based on a different model of planetary development, suggest that this is wrong.

According to the researchers, who report their findings in the journal Nature, Venus evolved completely differently from the Earth from the very beginning.

The critical factor was that Venus is much closer to the Sun.

The heat made the planet cool down relatively slowly.

Although it is not possible to calculate exactly how long the process lasted, it is quite possible that it took 100 million years before the magma to the surface cooled and became solid.

At that time, Venus had probably lost most of its water.

Originally the amount of water on Venus may have been the same as on the Earth Earth, but most of it disappeared into space during the slow cooling.

Therefore Venus today lifeless.
Okay. This is my point. If Venus cooled so slowly, perhaps an abiding "softness" of the crust affected the volcanism of the planet during much of its "childhood and youth", so that was quite different from the volcanism on the youthful Earth. Later, however, the presence of plate tectonics on the Earth and the lack of plate tectonics on Venus have caused volcanism to evolve very differently on the two planets.

Or so I think anyway. I am, of course, a complete amateur when it comes to the formation and evolution of Venus and the Earth. Still, I think that we should probably not base our judgment of the volcanism on Venus by what we know about the volcanism on the Earth.

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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by rr_carroll » Sun Jun 23, 2013 11:58 am

Is there vertical exaggeration in today's image? How much? I checked all the links in the text, hope I didn't overlook it.

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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Chris Peterson » Sun Jun 23, 2013 2:03 pm

madtom1999 wrote:Just wondering if these might not be old meteorite scars. If the rock is so hot then it may be more like a non-newtonian fluid so impacts dont result in lots of ejecta and the energy released eventually results in these lava mounds.
I don't think there is much difference between a dense fluid (non-newtonian or otherwise) and a solid in terms of what happens when a hypersonic impact occurs.

I can believe that, post-impact, there could be a difference in how craters evolve. However, there are clear impact craters on Venus, and they look about like craters everywhere. It's just that Venus has a new surface, so (like Earth) impact craters are rare. All evidence of the early bombardments has been erased.
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by stephen63 » Sun Jun 23, 2013 2:27 pm

"The atmospheric pressure at the surface of Venus is about 92 times that of the Earth, similar to the pressure found 910 metres below the surface of the ocean. The atmosphere has a mass of 4.8×1020 kg, about 93 times the mass of the Earth's total atmosphere. The density of the air at the surface is 67 kg/m3, which is 6.5% that of liquid water on Earth.[1] The pressure found on Venus's surface is high enough that the carbon dioxide is technically no longer a gas, but a supercritical fluid. This supercritical carbon dioxide forms a kind of sea that cover the entire surface of Venus. This sea of supercritical carbon dioxide transfer heat very efficiently, buffering the temperature changes between night and day (which last 56 terrestrial days)". - Wiki

Wouldn't this supercritical fluid shield the surface from a percentage of meteor strikes and how energy is transferred? Also, acting as a "sea", it seems to me that it would smooth the surface as well.

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Post by neufer » Sun Jun 23, 2013 3:35 pm

stephen63 wrote:
Wouldn't this supercritical fluid shield the surface from a percentage of meteor strikes and how energy is transferred?
  • For small meteor strikes but probably not large ones.
http://en.wikipedia.org/wiki/Burckle_Crater wrote:
Image
<<Burckle Crater is an undersea feature hypothesized to be an impact crater by the Holocene Impact Working Group. They considered that it likely was formed by a very-large-scale and relatively recent (c. 2800–3000 BCE) comet or meteorite impact event. It is estimated to be about 30 km in diameter, hence about 25 times larger than Meteor Crater. Burckle Crater is 3,800 m below the surface.

Its proposed location is to the east of Madagascar and west of Western Australia in the southern Indian ocean adjacent to the SW Indian Ocean Ridge. Its position was determined in 2006 by the same group using evidence of its existence from prehistoric chevron dune formations in Australia and Madagascar that allowed them to triangulate its location. But the theory that these chevron dunes are due to tsunamis has been challenged by geologists Jody Bourgeois and R. Weiss. Using a computer model to simulate a tsunami, they argue that the structures are more consistent with aeolian processes. The tsunamis origin of these chevrons is also disputed by other Earth scientists.

Unusual calcite (CaCO3) crystals, translucent carbon spherules, fragments of basaltic glass and native metals (native iron and nickel) are reported near the crater and associated with impact ejecta or hot water precipitates. Seawater at the depth of the crater is undersaturated with respect to calcite and rapid burial would be required for the preservation of those crystals.>>
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Chris Peterson » Sun Jun 23, 2013 4:27 pm

stephen63 wrote:"The atmospheric pressure at the surface of Venus is about 92 times that of the Earth, similar to the pressure found 910 metres below the surface of the ocean. The atmosphere has a mass of 4.8×1020 kg, about 93 times the mass of the Earth's total atmosphere. The density of the air at the surface is 67 kg/m3, which is 6.5% that of liquid water on Earth.[1] The pressure found on Venus's surface is high enough that the carbon dioxide is technically no longer a gas, but a supercritical fluid. This supercritical carbon dioxide forms a kind of sea that cover the entire surface of Venus. This sea of supercritical carbon dioxide transfer heat very efficiently, buffering the temperature changes between night and day (which last 56 terrestrial days)". - Wiki

Wouldn't this supercritical fluid shield the surface from a percentage of meteor strikes and how energy is transferred? Also, acting as a "sea", it seems to me that it would smooth the surface as well.
Well, even the ocean on Earth doesn't change the dynamics of a large impact substantially. The denser atmosphere of Venus will change the dynamics of a meteor, meaning that we might expect material to decelerate faster, break up higher, and lose its cosmic velocity before reaching the ground. Nevertheless, any object large enough to reach the ground still traveling at hypersonic speeds will make a crater very like those we see on any other body.

The main issue is that Venus was recently tectonically active. It has a new surface, and large impacts are rare in the modern Solar System. So we wouldn't expect to see many craters, even if most impactors made it to the surface. There just haven't been many of them since the surface formed.
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Very misleading image and caption

Post by geoffrey.landis » Sun Jun 23, 2013 5:28 pm

A very misleading image and caption, I'm afraid.

This is a radar image. The dramatic reds and yelows color it have nothing to do with the temperature, or that it is a "once molten" surface. (In fact, all of the rocky planets have a "once molten" surface.) The color in the image is chosen for artistic effect.

JPL usually gives a red/orange color to the Venus surface. This is because the atmosphere scatters the spectrum, and most of the blue is gone by the time the light reaches the surface, leaving a yellow-orange light, so if you could actually see it, it would be illuminated with orange-yellow light. Here's a Russian image of the surface, showing the color and also the reconstruction of what it would look like in "white" light: http://www.aerospaceweb.org/question/as ... urface.jpg
(I do have to note that the cameras were very poorly color calibrated, though.)

I don't have any idea why the most highly sloped surfaces in this radar reconstruction are colored as being yellower and brighter than more horizontal surfaces. It gives the visual impression of heat coming up from below, but this is inaccurate. (If anything, the lower altitudes should be redder and dimmer, not yellower and brighter, since there is less short wavelength light and less light total further down.)

The vertical in this image has been stretched, too, to make it look more dramatic.

Finally, the caption says that the "no" surface probes lasted longer than "a few minutes". In this case, the phrase "a few" should be translated as meaning "127".
Last edited by geoffrey.landis on Sun Jun 23, 2013 8:51 pm, edited 1 time in total.

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Re: Very misleading image and caption

Post by neufer » Sun Jun 23, 2013 6:35 pm

geoffrey.landis wrote:
A very misleading image and caption, I'm afraid...

I don't have any idea why the most highly sloped surfaces in this radar reconstruction are colored as being yellower and brighter than more horizontal surfaces. It gives the visual impression of heat coming up from below, but this is inaccurate. (If anything, the lower altitudes should be redder and dimmer, not yellower and brighter, since there is less short wavelength light and less light total further down.)

The vertical in this image has been stretched, too, to make it look more dramatic.

Finally, the caption says that the "no" surface probes lasted longer than "a few minutes".
In this case, the phrase "a few" should be translated as meaning "127".
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Re: Very misleading image and caption

Post by Chris Peterson » Sun Jun 23, 2013 9:25 pm

geoffrey.landis wrote:A very misleading image and caption, I'm afraid.
I disagree. That it is a reconstructed radar image is clearly stated. It shouldn't need to say that reflected radio signals were arbitrarily mapped to an orange intensity map.

It's a caption, that's all. There's always more that could be said, but space is limited. Plenty of links are always provided in order for those with sufficient interest to track down more details.
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by geckzilla » Mon Jun 24, 2013 1:33 am

It does look similar enough to some crusting over lava that some people probably thought that's what it was. The title helps steer the viewer away from it ("Once molten? You mean it's not molten anymore like the photo looks?") and then the caption completes the point. I guess some people still might not get it. Someone on Facebook told Frodo to throw the ring in it though and that was pretty funny.
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by geckzilla » Mon Jun 24, 2013 2:53 am

Ahhh, there we go. Now it's a quaint, grassy Venus.
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Beyond » Mon Jun 24, 2013 3:26 am

Looks like someone had some free time on their hands today. :mrgreen:
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Again: VERY misleading image and caption

Post by geoffrey.landis » Mon Jun 24, 2013 3:23 pm

Chris Peterson wrote:
geoffrey.landis wrote:A very misleading image and caption, I'm afraid.
I disagree. That it is a reconstructed radar image is clearly stated. It shouldn't need to say that reflected radio signals were arbitrarily mapped to an orange intensity map.
If they had chosen greens instead of reds for APOD, as shown in the recolored image by geckzilla, would you have just as calmly said "it's not misleading, any idiot should know that the colors are arbitrary"? The green image is just as accurate-- as you point out, the colors are arbitrarily mapped.

What does the word "once molten" means in the title here? Again: for EVERY planet that has a surface, that surface was "once molten." Earth. Mars. The moon. Mercury. Other than misleading the reader into thinking "oh, yes, I can see it was once molten, it's still glowing red hot", why is the word "once molten" used in the title? Why isn't every picture of, say, the moon on APOD labelled "the once molten surface of the moon..."

And why are the vertical surfaces brighter and yellower than the horizontal surfaces? This is the very characteristic of a glowing hot surface that is cooling by radiation. It looks nothing at all like an illuminated surface.

Summary: This image and caption are both horribly misleading. Venus does not glow yellow hot.

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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Old Tex 67 » Mon Jun 24, 2013 3:30 pm

The caption is misleading. The Soviet Venera 13 lasted about 127 minutes on the surface - something I have always considered a rather amazing engineering feat. That is m ore than a "few" minutes.

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Re: Again: VERY misleading image and caption

Post by Chris Peterson » Mon Jun 24, 2013 3:38 pm

geoffrey.landis wrote:If they had chosen greens instead of reds for APOD, as shown in the recolored image by geckzilla, would you have just as calmly said "it's not misleading, any idiot should know that the colors are arbitrary"?
Yes. The pseudocolor maps are chosen for various reasons. Sometimes it's purely aesthetic, sometimes there are more scientific reasons. This appears to be the map usually called "heat", and it is one of the most commonly used because that particular mapping maximizes the dynamic range we can see in a monochromatic image, which this is.
What does the word "once molten" means in the title here? Again: for EVERY planet that has a surface, that surface was "once molten." Earth. Mars. The moon. Mercury.
Only in one sense. Some planets show no evidence of having a molten surface, because they have been resurfaced by non-tectonic processes. This includes All of your examples above. Venus is exceptional in that it has been recently resurfaced by volcanism. So we are actually seeing a cooled, largely unmodified surface that was recently molten.
And why are the vertical surfaces brighter and yellower than the horizontal surfaces?
Because those surfaces have a different radar reflectivity, and when you apply the color map, that's the color that happens to result.
This is the very characteristic of a glowing hot surface that is cooling by radiation. It looks nothing at all like an illuminated surface.
And no such claim is being made. It appears that you are projecting your own biases and perceptions on the image and then complaining that you don't personally like the caption. Fine. But it isn't misleading.
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Chris Peterson » Mon Jun 24, 2013 3:49 pm

Old Tex 67 wrote:The caption is misleading. The Soviet Venera 13 lasted about 127 minutes on the surface - something I have always considered a rather amazing engineering feat. That is m ore than a "few" minutes.
In 127 minutes you are going to be struck dead by a massive coronary. I'm sure you're feeling very glad that you have more than just a "few" minutes left to live!

Jeez, the things people find to complain about!
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by neufer » Mon Jun 24, 2013 4:47 pm

Chris Peterson wrote:
Old Tex 67 wrote:
The caption is misleading. The Soviet Venera 13 lasted about 127 minutes on the surface
- something I have always considered a rather amazing engineering feat. That is more than a "few" minutes.
In 127 minutes you are going to be struck dead by a massive coronary.
I'm sure you're feeling very glad that you have more than just a "few" minutes left to live!
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The sign on the shop window states: "Back in a few minutes"
but the owners don't show up for over 2 hours :!:

I'm sure it would have been få better to have stated:
"No surface probe has lasted more than a few hours."
Chris Peterson wrote:
Jeez, the things people find to complain about!
The language used at APOD for instance :!:

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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Chris Peterson » Mon Jun 24, 2013 4:54 pm

neufer wrote:I'm sure it would have been få better to have stated:
"No surface probe has lasted more than a few hours."
Nice one.
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Beyond » Mon Jun 24, 2013 5:01 pm

Chris Peterson wrote:
neufer wrote:I'm sure it would have been få better to have stated:
"No surface probe has lasted more than a few hours."
Nice one.
Yes, it is.
Because if neufer had said a couple of hours... there would be comments that it actually lasted a few minutes longer than that. :mrgreen: :lol2:
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Re: APOD: Venus' Once Molten Surface (2013 Jun 23)

Post by Chris Peterson » Mon Jun 24, 2013 5:25 pm

Beyond wrote:
Chris Peterson wrote:
neufer wrote:I'm sure it would have been få better to have stated:
"No surface probe has lasted more than a few hours."
Nice one.
Yes, it is.
Because if neufer had said a couple of hours... there would be comments that it actually lasted a few minutes longer than that. :mrgreen: :lol2:
Well, yes. But I was referring to his bilingual pun.
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