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View Full Version : Bad Astronomy at work--Help Please.



NASA Fan
2004-Mar-31, 02:51 AM
I overheard someone make a comment today that sounded wrong, and I wanted to make sure that I am right and that he is wrong. Can someone help me please.

This guy claimed to another person in his group that he had heard somewhere that the Earth is located in the one spot in our universe that works. If the Earth had been 10 miles closer to the Sun it would be too warm for life to survive, and if it was 10 miles further away it would be too cold for life to survive.

It just does not sound right to me. The Earth is about 93 million miles from the sun, I just can't see 10 miles making a difference.

Could someone let me know if I am right or wrong please.

Thanks for your help.

Brady Yoon
2004-Mar-31, 03:01 AM
This is definitely wrong. You are seeing some bad astronomy for sure.
1. If this was true, we would already be dead because our orbit is slightly elliptical.
2. This is also bogus because the Earth's orbit is getting slightly larger all the time because the sun loses mass from its nuclear reactions, and (to a much lesser extent) its solar wind.
10 miles is around the average cruising height of a jet plane. If the Earth is that sensitive to changes, how did life survive the ice ages and asteroid impacts, which substantially decreased the amount of solar radiation. If the person meant 10 million miles instead of 10 miles, that would have made more sense...

Ut
2004-Mar-31, 03:01 AM
This individual is talking about the sun's habitable zone, which is an area surrounding a star in which liquid water can exist. The idea's a little...sketchy, so to speak, but it makes for a good illustration at times.

The guy's flat out wrong in the details, though. The Earth doesn't stay the same distance from the sun throught its orbit, and the distance varies by more than 10 miles. I'm sure someone who wouldn't have to reteach themselves the geometry of an ellipse would have more details.

AGN Fuel
2004-Mar-31, 03:35 AM
This individual is talking about the sun's habitable zone, which is an area surrounding a star in which liquid water can exist. The idea's a little...sketchy, so to speak, but it makes for a good illustration at times.

The guy's flat out wrong in the details, though. The Earth doesn't stay the same distance from the sun throught its orbit, and the distance varies by more than 10 miles. I'm sure someone who wouldn't have to reteach themselves the geometry of an ellipse would have more details.

The difference between perihelion & aphelion is far greater than 10 kilometres. The sentiment is OK (although only 'perfect spot is the universe' is going a bit far!), but his numbers are way off.

JohnOwens
2004-Mar-31, 04:29 AM
The guy's flat out wrong in the details, though. The Earth doesn't stay the same distance from the sun throught its orbit, and the distance varies by more than 10 miles. I'm sure someone who wouldn't have to reteach themselves the geometry of an ellipse would have more details.
You rang? :wink:
Actually, I didn't even have to go to the elliptical a,b,e stuff, just checked the Earth (http://en.wikipedia.org/wiki/Earth) page on the Wikipedia (although I was looking for values of a and e when I went there). Difference between the two is about 5,000,000 km, or 3,100,000 miles. A little bit more than 10 miles there. :wink:

NASA Fan
2004-Mar-31, 04:43 AM
Thank you so much--I thought that I was right.

Fortunately I will probably never see this guy again, so I will not have to argue the point.

Thanks again for setting my mind at ease.

Maksutov
2004-Mar-31, 07:36 AM
I overheard someone make a comment today that sounded wrong, and I wanted to make sure that I am right and that he is wrong. Can someone help me please.

This guy claimed to another person in his group that he had heard somewhere that the Earth is located in the one spot in our universe that works. If the Earth had been 10 miles closer to the Sun it would be too warm for life to survive, and if it was 10 miles further away it would be too cold for life to survive.

It just does not sound right to me. The Earth is about 93 million miles from the sun, I just can't see 10 miles making a difference.

Could someone let me know if I am right or wrong please.

Thanks for your help.

BTW, I've heard that one too. It's usually a thinly veiled ID argument that gets the whole cause and effect thing backwards. #-o

kenneth rodman
2004-Mar-31, 08:37 AM
"The habitable zone first encompassed the orbits of Venus to Mars, planets close enough to the sun for solar energy to drive the chemistry of life but not so close as to boil off water or break down the organic molecules on which life depends. "

thats an older definition by the way

Kaptain K
2004-Mar-31, 11:54 AM
If Mars were as large as Earth and Venus had a large moon, they would probably both be habitable.

milli360
2004-Mar-31, 11:59 AM
If Mars were as large as Earth and Venus had a large moon, they would probably both be habitable.
Wouldn't Mars need a large moon too? :)

Kaptain K
2004-Mar-31, 12:10 PM
You had to ask, didn't you? The honest answer is "I don't know".

Eroica
2004-Mar-31, 02:01 PM
If Mars were as large as Earth and Venus had a large moon, they would probably both be habitable.
Could you explain the Venus part, please? I thought Venus was just so close to the Sun, it suffered a runaway greenhouse effect. How would a large moon prevent this?

daver
2004-Mar-31, 05:47 PM
If Mars were as large as Earth and Venus had a large moon, they would probably both be habitable.
Could you explain the Venus part, please? I thought Venus was just so close to the Sun, it suffered a runaway greenhouse effect. How would a large moon prevent this?

Good question. I'd heard that a lot of the crust got blasted out to form the moon, so the earth is relatively thin-skinned and hence subject to plate tectonics. The long-term carbon cycle has carbon dioxide in the atmosphere being converted to calcium carbonate which accumulates on the ocean bottom; plate tectonics eventually causes these carbonates to be subducted down into the earth where the heat and pressure release the carbon dioxide which eventually makes its way into the atmosphere again.

Now, it seems to me that if Venus isn't subject to subduction, that the calcium carbonates would accumulate on the ocean floor (assuming that early Venus had oceans); the net effect would be that the amount of CO2 in its atmosphere would continually decline, eliminating the CO2 component of greenhouse gasses. So, it seems to me that having a thicker skin would help, not hurt.

Maybe what's going on is that, because of the relatively thick skin, early Venus went through binges--volcanic pressure would build up until there would be a catastrophic resurfacing--lots of eruptions, over the entire planet, boiling the oceans, releasing scads of CO2. The planet might recover from a few of these episodes when the sun was relatively young, but eventually the sun would get hot enough that the super greenhouse produced by all the water vapor and CO2 would raise the surface temperature high enough that more water would evaporate than condense. This would start the runaway greenhouse, and bye-bye hydrosphere. From that point on, there's nothing to take the CO2 out of the atmosphere, so any that had been sequestered in the rocks is flushed into the atmosphere in subsequent volcanic events.

So, maybe the theory goes that if Venus had a thinner crust, the vulcanism would have been milder, and no single event would have triggered a runaway greenhouse. On the other hand, earth has been subject to massive volcanic events (the Deccan Traps, for instance); if one of these had occurred after the Sun had gotten sufficiently bright, Venus would still be toast. The earth has supposedly had other non-volcanic greenhouse events--there was some speculation that one of the extinction events was caused by something like a methane clathrate-induced greenhouse, i think. Venus gets twice the insolation that Earth does; I'd think that there's a good chance that, no matter what, Venus would be toast by now, regardless.

daver
2004-Mar-31, 05:53 PM
If Mars were as large as Earth and Venus had a large moon, they would probably both be habitable.
Wouldn't Mars need a large moon too? :)

I don't know if a large moon would make as much difference to Mars. It seems like it would be subject to periodic "snowball Mars" scenarios; periodic catastrophic vulcanism might help to break it out of those.

JohnOwens
2004-Mar-31, 10:30 PM
If Mars were as large as Earth and Venus had a large moon, they would probably both be habitable.
Could you explain the Venus part, please? I thought Venus was just so close to the Sun, it suffered a runaway greenhouse effect. How would a large moon prevent this?
I know there used to be a hypothesis that the Moon, back when it was much closer to Earth, was responsible for stripping off a considerable portion of our atmosphere so we didn't end up like Venus. I think that idea's been pretty much dismissed since somewhere between one and three decades ago, but I'm not sure.

stu
2004-Apr-01, 09:56 PM
I read an article a year or so back in Astronomy Magazine that Earth's habitable zone was between about 0.9 AU and 1.4 AU. So, we're relatively close to the inner edge, but we could be almost as far away as Mars and still be habitable for humanoid life.