Updated Model Puts Earth On the Edge of the Habitable Zone 264
cylonlover writes with news of an update to the model used for calculating the habitable zone around stars shifting things out a bit. From the article: "Researchers at Penn state have developed a new method for calculating the habitable zone (original paper, PDF) around stars. The computer model based on new greenhouse gas databases provides a tool to better estimate which extrasolar planets with sufficient atmospheric pressure might be able to maintain liquid water on their surface. The new model indicates that some of the nearly 300 possible Earth-like planets previously identified might be too close to their stars to to be habitable. It also places the Solar System's habitable zone between 0.99 AU (92 million mi, 148 million km) and 1.70 AU (158 million mi, 254 million km) from the Sun. Since the Earth orbits the Sun at an average distance of one AU, this puts us at the very edge of the habitable zone."
Re:Different Stars.... different habitable zones? (Score:5, Informative)
They adjust the "habitable zone" for each star already.
Re:Different Stars.... different habitable zones? (Score:5, Informative)
Re:GW solution (Score:2, Informative)
You probably mean more like our entire combined worldwide nuclear arsenal all going off at once in a single location.
Even then, I doubt it would have enough effect. The earth has been hit by countless enormous hunks of rock during its creation, each with power in the multitudes of times greater than our arsenal, and they didn't manage to move the world.
Wow (Score:5, Informative)
The whole "Earth is fine-tuned for life" stuff has been debunked for ages (but still circulates thanks to creationists), but it's pretty amazing to consider our planet could be more than 1.5 times as far out as it is now, and still remain habitable.
Also, note that the Earth's perihelion places us at 0.983AU. If these numbers are correct, our orbit actually leaves the habitable zone for a brief period every year.
Re:GW solution (Score:5, Informative)
A few hundred well-placed nuclear bombs ought to do it.
If the goal is a nuclear winter, sure. If you're trying to move the planet... how can I put this as succinctly as possible: If we detonated every nuke we had on one side of the planet, we'd succeed only in leaving one side of the planet uninhabitable. It wouldn't move the planet by any appreciable amount. The subsequent earthquakes would probably do more, by affecting spin. People seem to forget in orbital mechanics, to move in one direction, you have to displace an equal amount of mass x energy in the opposite direction. All a nuke would do is move the air around and leave a hole in the ground. Nothing would be ejected into space, and therefore, no movement.
I know you're trying to be funny, but after awhile, I get tired of the "a nuke is powerful enough to do anything!" thinking. I blame Bruce Willis.
{something} is amazing! (Score:5, Informative)
Re:GW solution (Score:5, Informative)
Niven's way ahead of you. It's a simple matter of knocking Uranus into a cometary orbit and using its gravity to move Earth further out.
Re:GW solution (Score:5, Informative)
I get tired of the "a nuke is powerful enough to do anything!" thinking. I blame Bruce Willis.
My Organic instructor was a real math geek, one day she demonstrated that a quarter inch of rain falling on Manhattan resulted in the same release of energy as the atomic bomb dropped on Hiroshima, she was good at estimating cube roots of 4 digit numbers in her head too.
Re:GW solution (Score:5, Informative)
I thought the same thing, and then I thought: Not Niven, he wouldn't write something so dumb. So I googled and found this:
(source [orbiter-forum.com]) I don't think that would pass proper physics audit, but... there have been stupider ideas in scifi books.
Easy calculation (Score:5, Informative)
Hmm, not in my definition of "few hundred". The calculation is actually easy to make:
The earth is about 1,5E11 m away from the Sun, let's say that 1% is the variation that we want, so we get it to 1,515E11 m. So the difference in energy that we need is GMm(1/R1-1/R2) \approx 5E31 J; quite a lot.
The best (or worst, depending on your point of view) nuke we ever exploded is the Tsar Bomba [wikipedia.org], which was 57 megatons or better 2,4E17 J.
So if we managed to use this energy with 100% efficiency (which we obviously can't) to move the Earth, we would need 10^14 nukes. Well, guess we're stuck here.
Re:But for Terraforming? (Score:5, Informative)
Alas, you are wrong about Venus. It has a negligible magnetic field (likely due to no core convection) and cosmic rays and the soloar wind freely interact with the upper atmosphere causing hydrogen loss. As well, if Venus was a black body and had no incoming radiation it would take on the order of 600+ years to cool off.
Re:GW solution (Score:1, Informative)
what's dumb about it, the orbital mechanics were worked out. or maybe you didn't like his novel fusion drive?
anyway, during a war the sun was turned into a red giant by deliberate collision with giant asteroids. the earth was left in orbit around jupiter and Uranus moreover was used to pull Ganymede into Jupiter to ignite it in fusion so the Earth would have new star
Re:GW solution (Score:4, Informative)
Well, if you consider 98.8+% to be "significantly smaller" than 100%, then you're correct.
Otherwise, you might want to recheck your numbers....
Re:Wow (Score:5, Informative)
You do realize that the habitable zone has been moving out over the life of the solar system? The Sun converts hydrogen to helium, helium is more dense, increasing the density of the Sun causing it to burn hotter. Estimates are that some billion years ago the Sun was 25% cooler which would have shrunk the habitable zone quite a bit, perhaps to the point where Venus was habitable. Also with the Sun getting hotter, in perhaps half a billion years the oceans will boil and the Earth will be much more similar to Venus.
Re:GW solution (Score:5, Informative)
Not directly related, but the XKCD "What If" scenario on just changing the rotation of the earth enough to avoid having leap-seconds would require 50,000 4m diameter rocky asteroids hitting the earth every second.
http://what-if.xkcd.com/26/ [xkcd.com]
Back-of-a-fag-packet calculations that every nuclear and non-nuclear explosion in the history of civilisation wouldn't give enough oomph to move us more than a few km away from the sun (although that didn't stop anyone making films about it). http://www.imdb.com/title/tt0054790/ [imdb.com]
Re:Mars (Score:5, Informative)
Mars had liquid water at some point and is outside the habitable zone, for some definitions of habitable zone. So it is entirely possible that planets with liquid water can exist outside the habitable zone.
Am I correct in assuming that the liquid which must have flowed on Mars doesn't necessarily have to be water, or has there been proof that the liquid was specifically water? That's a real question by the way, I'm not trying to be sarcastic. If anyone knows, I'd appreciate an answer.
The presence of water is proven on Mars. The existence of minerals that only form in the presence of water is proven on the surface of Mars. Massive liquid-based erosion is proven on the surface of Mars. Its reasonable to assume they're all related. And, frankly, the fact that water is found damn near everywhere in the solar system where it hasn't been torn apart by radiation, or heat makes is really implausible that there wouldn't have been water on Mars -- water that got there the same way it got to Earth, during a period of time in which Mars was more conducive to surface water than Earth.
IMO, the whole "finding water on Mars" thing is more akin to the "seeing a giant squid alive in the ocean". Everyone knows its there, but scientists just like to see things with their own eyes. The search is the fun part, so... search away.