the dilemma of the habitable zone
Here’s yet another idea that gets the Intelligent Design and creationist crowd excited. The Habitable Zone. It’s the zone around a star in which the temperature is right for liquid water and relatively mild global climate. Move the planet a bit closer to the star and it will be too hot to support life. Move it farther back and the planet with freeze to an icy ball, too cold for living things to exist. According to creationists, the fact that Earth is in the habitable zone must mean that there’s something or someone responsible for the narrow range of temperatures we experience. There’s no way we can thread a cosmic needle by pure and simple chance.
But the habitable zone is a concept that applies only to the living things of this planet. Alien life could be a lot tougher. For example, it’s plausible for some alien bacteria to use liquid ethane instead of water as a solvent and live in -250F weather. Heat is a bigger problem because very few usable solvents can stay liquid at very high temperatures, but alien life forms could just do what animals on our planet do when it gets too hot for their tastes. They could hide in a cooler, darker place where the heat can’t reach them and it’s cold enough for water to stay in its liquid form. In both cases, the planets they inhabit could be out what we think is the habitable zone of a given star. But then again, the habitable zone is supposed to be a quick and dirty rule, not an authoritative ruling on the possibility of life for an extrasolar world.
On top of that, habitable zones are actually measured in hundreds of millions of miles. A little closer and a little farther are relative terms. For our solar system, the habitable zone would be between the orbits of Venus and Mars. That’s a band some 200 million miles wide. Our 12,700 mile wide planet has a whole lot of room to wander and still host life. If we include an alien that can use super-chilled liquids in our estimates, the habitable zone swells to over a billion miles. As you can see this is a pretty vague concept based on woefully incomplete knowledge.
However, this didn’t stop the concept’s creators from making a galactic variant. Apparently, a galaxy also has a habitable belt around its midsection. Too close to the galactic center and the radiation from the black hole and colliding, hyperactive stars will doom all life on a planet. Too far away and there wouldn’t be enough metal to form rocky worlds in the dark recesses of the galaxy. I can understand that you wouldn’t want to be too close to the galactic center. After all, there’s a supermassive black hole there and whipping around it are large, chaotic stars. Stellar explosions are common and huge gamma ray bursts could fry an otherwise habitable planet into a lifeless rock.
There’s also a problem with the chemical composition of planets on the edge of a galaxy. Stars migrate, moving around as they spin and when tugs from other stars, nebulae and black holes pull and push them around. Supernovae, which make metals in the final moments of their lives, scatter the atoms they produce across thousands of light years. The entire galaxy will be awash in all sorts of gases and metals given a little time. Relatively speaking of course.
So what are the chances that Earth is in the right spot in the galaxy and in the right spot around its parent star to host life by chance alone? Actually, very good when we consider that our star can safely wander in a swath over 25,000 light years wide (that’s 150 quadrillion miles) and our planet has an almost 80 million mile margin of error either way, conservatively speaking. There is a little disclaimer though. Different temperatures would drive the evolution of different kinds of life so while we wouldn’t survive being more than 80 million miles closer to or farther from the Sun, other living creatures could.
I might be missing the point of the “habitable zone” concept, but it seems almost tautologous to me.
If life is going to emerge on a particular planet, it will emerge in a form compatible with the conditions on that planet. If it’s very hot, life (if it emerges at all) will be able to thrive under those conditions; if it’s very cold, subjected to intense radiation, etc., the same will apply. And if that life form starts thinking about “habitable zones,” it will decide that they consist of conditions like those on its planet. If earth differs substantially from those conditions, then they will decide that it probably does not support life. (The jury is still out on whether or not earth supports *intelligent* life.)
One of my favorite books as a kid was “Dragon’s Egg” (http://en.wikipedia.org/wiki/Dragon%27s_Egg) by Robert Forward, which told the story of life on the surface of a neutron star. That’s one heck of a habitable zone! :-)
Well yes and no. The habitable zone is based on chemistry and different chemistry requires different temperature ranges to support it. Life on Earth is made of carbon, hydrogen and oxygen with some phosphorous and trace metals added. Since this kind of chemistry needs a certain temperature range to work, a planet with the same temperatures as Earth should be able to host Earth-like life.
But here we run into the problem you illustrated and I mentioned in the post. Alien life can have different chemistry and if it does, the habitable zone becomes a circular argument.
I just want to poin out tha the earth is only about 93 million miles from the sun, so a 200 million mile habitable zone is wrong. I found this while looking for the actual size of the HZ, so if I wasnt aware of the earth sun distance, I may have used that figure. Just being nit-picky, not trying to be a jerk.
the earth is only about 93 million miles from the sun, so a 200 million mile habitable zone is wrong.
As noted in the post, the habitable zone extends beyond Earth in this solar system. It isn’t based on what planets are inhabited, but at what distance you could have liquid water and chemical reactions that life as we know it needs.
I think the concept of the habitable zone is too narrow and misleading when ourown solar system is suppose to be an example. mars is about twice earths average distance but its a smaller planet with lesser gravity and has largely cooled down within its interior meaning the core doesnt produce a vialble magnetic field like earht does which helps protect agains6t the solar radiations and solar storms from the sun.eventually the suns solar radiation stripped mars of most of its atmosphere into space and perhaps most of its water which also might have been frozen over.
If mars is geologically dead and doesnt have plate tectonics like earth does, no more new gasses such as carbon dioxide are being added to the atmosphere. the current evidence shows mars was once more habitable like earth especially when the sun has been slowly warming and growing brighter since it was born and if mars is outide the habitable zone it shouldn’t have evidence of running water.
if you go to the most extreme places on earth there is some form of life but i really want to know about the climatic and weather effects of moving earth closaer to or further from the sun. the distribution of our worlds landmasses with the mountain rainges and al across the globe greatly effects global weather patterns as the regions closer to the equator warm up and distribute heat towards the polar regions and the position of landmasses effecting ocean and atmospheric circulations greeatly effect local climats such as places in europe being warmer due to the gulf stream than similar latitudes in america or places deep in siberia being far colder than the north pole in the dead of winter due to land warming up and cooling down much quicker than ocean areas.
on venus, why is the planet the way it is??? it is slightly closer than earth but that cannot explain enough since its rotation is opposite our rel\sulting in daylengths lasting several of our months which allow heat to build up tremendously and the atmosphere composed primarily of CO2 at 90x earths pressure forming a powerful greenhous effect. theres no water on venus to recycle the CO2 back into carbonate rocksand the effetc of venus rotation theres no internal dynamo in its core to form a magnetic field but the exact results of this on venus being the way it is i am very uncertain. However, venus unlike earth doesnt have plate tectonics but astronomers and planetary geologist i read suspect that internal heat builds up until in pratically melts through the surface which is made easier with the already hot surface. I heard that the vast quantities of water have some influence on our planets tectonism like the crustal rocks saturated with water while being subducted along oceanic trenches lowers the melting point of the crustal block.
Something must’ve happened in venus’s past for it to be the way it is. if earth was the same distance we shortan its days and the heat buildup isnt as bad. we put earth a bit farther and increas its day and the planet may be able to compensate. I know there are limits but even if earth froze over, some life would exsist in the seas especially around hydrothermal vents and on the surface most likely near the equator perhaps some seasons if ice free water with plants