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Decepticon
I'm looking for earth based radar mapping of Venus.

I've had a hard time finding much. I clearly remember seeing images in books as a child.

Any help would be great!
JRehling
QUOTE (Decepticon @ Mar 6 2006, 06:43 PM) *
I'm looking for earth based radar mapping of Venus.

I've had a hard time finding much. I clearly remember seeing images in books as a child.

Any help would be great!


http://www.gps.caltech.edu/~margot/venus/aogbt.html

http://www.nrao.edu/pr/2001/gbtfirstsci/
(almost identical content to the first link)

http://www.nasm.si.edu/ceps/etp/venus/venusimg/P15.JPEG
Decepticon
WOW!

I didn't expect the images so clear!
JRehling
QUOTE (Decepticon @ Mar 6 2006, 07:25 PM) *
WOW!

I didn't expect the images so clear!


Compared to spacecraft flyby/orbiter standards... what terrestrial observations of Venus lack in proximity, they make up for in the size of the antennas. And those observations can be made when Venus is almost at conjunction, and thus considerably closer to the Earth than Venus or Mars ever is for a telescopic observation. Quite simply, radar observations of Venus are of considerably higher resolution than any other Earth-based observations of any planet could be.
edstrick
The only fly in this pudding is that there is a weird near-synchronicity between the rotation period of Venus and the position of inferior conjunctions with Earth. Very-Very nearly the same hemisphere of Venus faces Earth each conjunction! It's not quite exact, but it is improbably close. They've tried to see if the small tidal pull of Earth on Venus at inferior conjuction was more than vanishingly small and might explain this cooincidence, but it seems to be unlikely. The best idea I've heard so far is that the gods must be crazy.
helvick
QUOTE (edstrick @ Mar 7 2006, 08:58 AM) *
The best idea I've heard so far is that the gods must be crazy.

And are the same crazy Gods responsible for the very slow rotation of Venus? Or is there a plausible\likely explanation for it just happening that way?
edstrick
Last I heard they figure it's just coincidence.
Decepticon
The best one I've heard so far is "Venus was a Comet!" Straight from the wHoGland Funny Farm. biggrin.gif
Jeff7
Venus is made from people! Peeeoopllle!!!!!
AlexBlackwell
QUOTE (helvick @ Mar 7 2006, 09:46 AM) *
And are the same crazy Gods responsible for the very slow rotation of Venus? Or is there a plausible\likely explanation for it just happening that way?

Correia and Laskar have published some interesting work on this.
Decepticon
I once heard a theory that a violent impact hit Venus against it's natural spin causing it to rotate the opposite way.

What ever it was it must have been a big bugger.
AndyG
QUOTE (Decepticon @ Mar 7 2006, 11:16 PM) *
I once heard a theory that a violent impact hit Venus against it's natural spin causing it to rotate the opposite way.

What ever it was it must have been a big bugger.

Shame it didn't end up with a lovely (and life-on-Earth-supporting?) Moon like ours.

Andy
ljk4-1
QUOTE (AndyG @ Mar 8 2006, 04:24 AM) *
Shame it didn't end up with a lovely (and life-on-Earth-supporting?) Moon like ours.

Andy


I dunno - War of the Worlds could have happened coming from the
other direction.

Or in a parallel universe, it is the inhabitants of Venus who wonder
what might have been if only Earth weren't a barren wasteland.
JRehling
QUOTE (AlexBlackwell @ Mar 7 2006, 01:02 PM) *
Correia and Laskar have published some interesting work on this.


I've tried about six of those links, and they are all dead.


QUOTE (JRehling @ Mar 8 2006, 08:10 AM) *
I've tried about six of those links, and they are all dead.


However, a summary/abstract appears here:
http://physicsweb.org/articles/news/05/6/6

The low inclination and extremely low angular momentum always made impact-based explanations unlikely. It's pretty hard to smash things together and get things to balance out that neatly. C&L's work seems to conclude that from first principles, that with an atmosphere that thick, the planet's rotation is going to be driven by the atmosphere. Presumably (what the abstract/summary doesn't say), the huge thermal input from the Sun is another part of the story. Saturn, Uranus, and Neptune have bigger atmospheres, but they don't have daysides lit by a Sun measuring a full degree in the sky -- they have two+ orders of magnitude less solar input.

I don't know if anyone has ever looked at this angle, but with Grinspoon, et al, proposing that Venus may have lacked those bright clouds for much of its history, it may have formerly had particulalry large thermal tides if it had an albedo as low as, say, Mars or Earth's continents. If you imagine an atmosphere sticking out tens of km (?) farther on the dayside than the nightside, that's a lot of friction working against rotation.
AlexBlackwell
QUOTE (JRehling @ Mar 8 2006, 04:10 PM) *
I've tried about six of those links, and they are all dead.

Ouch. I know it worked back in 2002; in fact, I believe I referenced it over in Yahoo! planetary_sciences at the time biggrin.gif

Try Laskar's page, though I believe these may be preprints instead of the final versions that were on Corriea's page. If you need the the final versions, John, let me know.
BruceMoomaw
In reality, it wouldn't make a tinker's damn to Venus' chances of sustaining life whether it had a large moon or not -- its death warrant was signed the moment it formed close enough to the Sun to activate the "moist greenhouse" effect that stripped it of all its initial water and so allowed its volcanically released CO2 to build up and produce a huge blanket with a killer greenhouse effect.

Kevin Zahnle has an interesting new LPSC abstract ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2359.pdf ) in which he claims that an Earthlike planet like Dune -- which started out with less water than Earth, but not NO water -- would actually be capable of sustaining a small biosphere much closer to the Sun than a planet which started out with a large water supply, because its moist-greenhouse effect would be minimal. However, he doesn't explain how that small initial amount of water could lock up most of the planet's CO2 in carbonate rocks, and thus why that planet wouldn't simply proceed to Venus' final fate much more directly. (Come to think of it, didn't we learn in the first Dune book that the planet actually had quite a bit of water overall, but the Little Makers sealed most of it off underground and prevented it from reaching the surface? If so, then before the Sandworms evolved -- since the Little Makers are their larval stage -- the planet must have been relatively wet and friendly. Kind of a reverse-Gaia effect.)
Bob Shaw
Bruce:

The Gaia effect - shorn of it's New Age mystical baggage - is just a handy catch all for homeostatic systems on a planetary environmental scale, so the Little Makers and the Sand Worms on Dune are simply ensuring that their environment suits their own needs, and in turn that environment has allowed them to fit it's paramaters. No real mystery there - except to the over-mystically inclined. Venus, however, is possibly a homeostatic system which has suffered catastrophic feedback and collapse to a more-or-less steady state which is quite inimical to life, and as such stands as a grim warning to us all regarding the changes we are wreaking on our own planet. Should we make the discovery of death (as opposed to the absence of life) on Venus then it should, I hope, have a profound effect on how we act here. I confess that I am rather concerned by our current effects on the Earth, not so much in terms of a few islands being drowned as a profound alteration to the whole environment (for example, as a result of clathrate decomposition in what was once tundra) and it'd be nice to have some changes made here and there before it's too late!

Bob Shaw
AndyG
QUOTE (Bob Shaw @ Mar 9 2006, 03:09 PM) *
Venus, however, is possibly a homeostatic system which has suffered catastrophic feedback and collapse to a more-or-less steady state which is quite inimical to life...

Perhaps on the surface - maybe not higher up the atmospheric column.

But that collapse of a system: is it due solely, as Bruce suggests, to the insolation received by the planet, or is it a deeper issue? If Venus had had a large Moon for example, and a higher rotation rate, and therefore more active tides and subsequent tectonic activity more akin to that of the Earth, wouldn't that have buried - sorry, sequestrated, to use the modern word ;-) - the excess CO2 efficiently?

The early Venus received 1800 watts per square metre compared to our 1380 today - that's not a huge difference compared to other locales in the Solar System. A spun-up Venus with a Moon might have been a suitable place for early life as well as the Earth.

(Perhaps I'm just hankering for the pre-probe SF Venus - dinosaurs wandering among the swampy jungles of our twin planet...)

Andy
ljk4-1
QUOTE (AndyG @ Mar 9 2006, 11:01 AM) *
(Perhaps I'm just hankering for the pre-probe SF Venus - dinosaurs wandering among the swampy jungles of our twin planet...)

Andy


So did the Soviets in the 1960s - they designed Venera 4 to float if it
came down upon a Venusian ocean!

http://www.hightechscience.org/venera-4_spacecraft_model.htm

http://www.kolumbus.fi/jimenez/photos/avaruus2000/
Decepticon
^Thanks for those Links!

Those models are so cool. cool.gif
Gsnorgathon
QUOTE (Bob Shaw @ Mar 9 2006, 03:09 PM) *
...
Should we make the discovery of death (as opposed to the absence of life) on Venus
...

Bob - that's absolute genius. I'd say it's beautiful, but somehow that doesn't seem quite the right word.
JTN
Going back to the subject of planetary radar: although they don't add much to the links already posted re Venus specifically, the following have some good material (eye candy!) for other objects:
http://www.naic.edu/~pradar/pradar.htm
http://www.naic.edu/~nolan/radar/
(more by Googling arecibo planetary radar or just "planetary radar")
Decepticon
Great links!

Going threw each one.
DonPMitchell
QUOTE (ljk4-1 @ Mar 9 2006, 09:10 AM) *
So did the Soviets in the 1960s - they designed Venera 4 to float if it
came down upon a Venusian ocean!


Russian scientists mostly believed in the greenhouse theory. In the Venera-1 articles in Pravda, it describes a surface that is so hot that the rocks are "red hot". That must have been the official line from Keldysh. Lebedinsky did seem to believe in the ionospheric model, and proposed some varations of his own. He also believed in life on Mars, and installed a Sinton-band methane detector on Mars-1.

Actually, the Soviet radioastronomer Korol'kov was the first to measure microwave limb darkening of Venus (before Mariner-2), which he also interpreted as supporting the hot-surface theory.

The landers were made to float just as a contingancy.
BruceMoomaw
Yes -- remember that they were extensively insulated, which is why Venera-4 was standing up quite nicely to 280 deg C at the time air pressure crushed its hull.
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