Don. Edwards wrote:I don't think we can assume Venus is pristine by any account. Something hit it millions if not billions of years ago and flipped it over on its axis. The impactor simply didn't hit at the right angle to create a moon, or it was too small, but large enough to the damage it did. It is looking more and more like each and every inner planet has had at least one or more very big impacts.
Apparently not. Believe it or not, it turns out the 'upsidedownness' is most likely caused by solar tides acting on the dense atmosphere. (don't ask how, it's pretty complicated and I only understand the general gist of it. But I've seen some papers on it though and the analysis did seem fairly convincing).
I still think if you could exchange the planets before the impactor that hit Earth and made the moon you could still get a planet much the same as Earth is now moon and all. It?€™s what they are made of that would determine this in the long run. Venus and Earth are made of the same stuff basically and in the same proportions.
I disagree. You'd have a planet with less metal in its core for starters, since most of the impactor's is down there too. And it'd have more volatiles too, since a good chunk of them wouldn't have been vapourised when the planet melted in the impact. And you'd have a less massive world too, obviously. Any one of those changes - particularly that early on - would result in a totally different environment today. The atmosphere would be massively different too. Sure, it'd still be a rocky planet about 6000 km in radius, but that's about where the similarity would end.
Although there seems to be some reason Venus?€™ core isn?€™t generating a magnetic field. Maybe that ancient impactor had something to do with it. We may never know.
Actually we do have a pretty good idea why it doesn't have one. It's largely down to the slow rotation - there's just not enough rotational energy to make a dynamo. And also, the core is most likely completely molten and stably stratified, which means there's no inner core forming to make convection currents in there.
What I meant by "Wrong" is that something hit and turned Venus over on itself.
I think the "wrong" part is the idea that something hit Venus. That simply isn't supported by the evidence, which is that the solar tides on the atmosphere are what tilted the planet (I'd throw a scientific paper reference at you, but all my papers are in boxes and I have no idea where that one is. If you're really interested I'll see if I can dig it up).
It?€™s just like Uranus this case. Something went horribly wrong there as well. These planets didn't just form this way. They formed much like all the others did. But they are now in there present form due to interactions with other shall we say rouge bodies that moved in our early solar system. It even looks like tiny Pluto gets to join this club as well.
Well, the 'standard way' that planets would form is exactly along the plane of the sun's rotational equator, with no tilt at all. But we all know that no planet is like that, so saying that's the 'right way' is misleading. The fact is that the protoplanets got whacked around by impactors large and small, tipped over by tides, realigned by moons, and whathaveyou. It's pretty meaningless to talk about "normal" in this or any other solar system, beyond talking about how things generally orbit the same way around the sun. The point is that each planet is unique - despite their common origins. You can't just pick one and say "that's what a "normal" or "right" planet is supposed to be" because that's a totally arbitrary definition.
Yes we often think in Terran terms. How else are we to think, we are Terrans. We aren't Venusians or Martians for that matter, although there are some on the fringe that think we are.
Just because we're Terrans doesn't mean we have to be limited to thinking that we're the norm. If there's anything I learned from all my years of learning geology and astronomy and planetary science, it's that our planet is most definitely NOT the norm.
The challenge is to climb outside that mental box and see each planet as a unique world, and that our world isn't really any more or less unique than the others.
At this point in time all we have to compare are really three terrestrial worlds in our own system. I don't count Mercury as it doesn't really show any sign of being truly geologically active as the other are and it doesn?€™t have an atmosphere at the present time.
But that's a completely arbitrary definition. Why should you ignore a bona fide planet just because it doesn't have a thick atmosphere (actually it has a trace atmosphere of trapped helium and sodium ions)? I'd say we have a LOT of terrestrial worlds in our system - I'd count all the inner planets, our moon, Jupiter's Galileans, Titan, Enceladus, all of Saturn's other classical moons, Uranus' five main moons, Triton, Pluto, Charon, Ceres, and a bunch of the big KBOs. They're all worlds with their own character and individuality, and all bring something unique to the table. Mercury has its contraction scarps, Venus has its atmosphere and 'jiggly' geology, Earth has its MORs and tectonism and life, Mars has its hemispherical dichotomy and huge volcanoes and rift valleys, the Moon has it's origin and maria, Io has its permanent volcanism, Europa it's cracks and oceans, Ganymede it's sulci, and so on. We've got a hell of a lot to compare and examine here, and all of those worlds - even our own - have things that continue to baffle us.
It?€™s really too bad we can't see back in time and see all the planets that formed in the early solar system. We know there were more planets then there are now. There was an additions Mars size planet orbiting close to the Earth. How many others were there? It would be great if maybe a few of them managed to stay in the outer solar system and weren?€™t fully ejected. Maybe we can find an inner solar system time capsule out there waiting to answer many questions.
Well, we're looking at the survivors of the process in the inner system. I'm sure Mars itself was probably just another mars-sized body wandering around the inner system at some point, it just happens to be the one that survived.
All of this is really just conjecture at this point anyway. We need to see a vast number of terrestrial planets around other stars before we can really know any of this for sure. Unfortunately we have a very long wait on our hands. I just hope that before I die we find our first truly Earth like planet. But I am not holding my breath.
I think we'll find another habitable planet in the next 10-20 years. It'll probably be very far away though. But I think we have a lot more terrestrial variety in our own system than you give credit for.
. Venus is probably a more ideal candidate for a terrestrial planet than Earth is - at least you're looking at a bona fide, untainted planet with Venus. Earth however is this mishmash of whatever was here first and a mars-sized impactor. Its chemistry, density and future evolution were irrevocably changed when that body slammed into it to melt its entire surface and ultimately create the very unusual moon we have today.