Not only did you understand what I was asking you just answered it simply in terms I can understand.
But this is just the beginning of the issue, as it assumes that things remain the same for the change in orbits. We know from venus and mars and our own global warming that climate can over-ride the direct relationship with systems that retain heat energy or systems that reflect it or let it escape.
The only conclusion we can make from the available data is that the "possible life band" around our sun encloses the orbit of the earth and extends to somewhere between here and venus on one side and from here to mars on the other, and that's a pretty big swath and a fairly large uncertainty eh?
There may also be a question that if venus had less gravity and mars had more if they would be able to support life.
Overall I agree that there are far more factors than just this one of distance from the sun. As was mentioned previously, Venus is .7 AU from the sun yet is hotter than Mercury which is .38, almost half the distance from the sun. Other factors than distance are certainly to be kept in mind.
I have to disagree with the idea of Venus supporting life if it had less gravity. Venus has a number of issues preventing it from providing a nurturing environment, for example, it has almost no discernible magnetic field to protect it from cosmic radiation or solar radiation. Venus already has lower gravity than the earth at .904 g. The composition of Venus seems more of a hindrance than gravity. The axial tilt of 177.36 degrees also is strongly against it. A sizable moon such as ours, would have remedied that in all probability.
A big problem far Venus has, for a while, been posited that the lack of plate tectonics prevent the planet from being able to cool down internally. Instead of a general steady tectonic movement as on earth, Venus has periods of massive upheaval. Venus also has the slowest rotational period of any of the major planets. That would mean about 117 earth days of sunlight followed by 117 earth days of night. The temperature fluctuations would be extreme to say the least.
I do agree with the argument that mars would be better suited with more gravity, since that would enable it to maintain an atmosphere. That gives us a potential survival band of .7 AU (about 107,000,000 km) to 1.5 AU (about 227,000,000 km)
Edited by EighteenDelta, : added paragraph
"Debate is an art form. It is about the winning of arguments. It is not about the discovery of truth. There are certain rules and procedures to debate that really have nothing to do with establishing fact — which creationists have mastered. Some of those rules are: never say anything positive about your own position because it can be attacked, but chip away at what appear to be the weaknesses in your opponent's position. They are good at that. I don't think I could beat the creationists at debate. I can tie them. But in courtrooms they are terrible, because in courtrooms you cannot give speeches. In a courtroom you have to answer direct questions about the positive status of your belief. We destroyed them in Arkansas. On the second day of the two-week trial we had our victory party!" -Stephen Jay Gould
I have to disagree with the idea of Venus supporting life if it had less gravity. ... Venus already has lower gravity than the earth at .904 g.
I am aware of this, however it also has too much atmosphere, and that is one of the reasons for the run-away greenhouse effect that causes it to be hotter than mercury. Thin atmosphere would reduce that temperature back down to something habitable.
Some people think it may have had life before the atmosphere went acidic:
The Earth is the only planet in the Solar System with liquid water on its surface now. This might suggest that the habitability zone of our own Solar System is very narrow. However we have direct evidence that liquid water used to exist on Mars, and very good indirect evidence that it also used to exist on Venus. Thus both of those planets at least were at one time in our Sun's habitability zone.
Venus's atmosphere is very different than Earth's. For one thing, there's a LOT more of it. The surface pressure on Venus is about 90 times higher than it is on Earth. The composition is also quite different:
... (so it could do with less atmosphere without loss of habitability), and life may already exist there:
quote:A Sulfur-Based Survival Strategy for Putative Phototrophic Life in the Venusian Atmosphere http://www.liebertonline.com/doi/abs/10.1089/153110704773600203
Several observations indicate that the cloud deck of the venusian atmosphere may provide a plausible refuge for microbial life. Having originated in a hot proto-ocean or been brought in by meteorites from Earth (or Mars), early life on Venus could have adapted to a dry, acidic atmospheric niche as the warming planet lost its oceans. The greatest obstacle for the survival of any organism in this niche may be high doses of ultraviolet (UV) radiation. Here we make the argument that such an organism may utilize sulfur allotropes present in the venusian atmosphere, particularly S8, as a UV sunscreen, as an energy-converting pigment, or as a means for converting UV light to lower frequencies that can be used for photosynthesis. Thus, life could exist today in the clouds of Venus.
What if that maximum distance of 152.5 million km was changed to 153 million km.
Ditto what RAZD said. You also have to remember that Earth has a big ass body of water to act as a buffer for any drastic changes in the weather.
Say that the energy received from the sun gets reduced somewhat dramatically at it's furthest point from the sun. Sure, we might experience colder winters, but the difference will not be so drastic that life on Earth will go meet their creator. At best, we'd see some species that can't adapt and go extinct while others taking over certain new niches.
Like I said before. The Earth have gone through many many ice ages before, some of them global. Armageddon never came despite of this.
Occasionally, owing to the deficiency of the English language, I have used he/him/his meaning he or she/him or her/his or her in order to avoid awkwardness of style.
He, him, and his are not intended as exclusively masculine pronouns. They may refer to either sex or to both sexes!
You see, more than just gravity and existence in the habitable zone of a star is neccesary for life. You need (as far as we know), liquid water, the correct chemicals, and an atmosphere. The moon is missing some of these, namely liquid water.