Every year the U.S. government and the scientific establishment spend quite a bit of money looking for “Earth-like” worlds orbiting distant suns. This is of course a bit of a fraud on those of us contributing the money to do so. The gullible public and media’s minds go immediately to visions of cities filled with little green men flying around in zero-gravity airships. As any reputable scientist would tell you however, that is not quite what is meant by “Earth-like”. What they are saying is ‘roughly the same size as the Earth, roughly the same distance from their sun as Earth, and said sun being roughly of the same type as Earth’s sun. So what’s so fraudulent about that? Well, it overlooks the “miracle” of Earth; what makes Earth, so far as has been found, unique.
Let’s start with a few of those “roughlys” in our own solar system. There are two other planets circling the Sun with us that are roughly the same size as Earth and roughly similar in distance from it. Of course I’m referring to Mars and Venus. Mars is about 53% of the diameter of Earth[2]; Venus around 94%. Mars’ and Venus’ orbits are around 150% and 72% of Earth’s respectively. Were we being observed from one of those distant “Earth-like” worlds they would say that there were three “Earth-like” worlds in our solar system.
We however would hardly consider Mars and Venus Earth-like. Mars effectively has no breathable atmosphere, less than 1% of Earth’s air pressure. In its average temperature of 80 degrees below zero (Fahrenheit), water, were there any, would be solid ice. On the other hand Venus’ atmosphere is around 92 times as dense as Earth’s. Its average surface temperature is 865° F. Needless to say liquid water is impossible there.
Breathable air and liquid water are essential to life as we know it.
Why don’t Mars and Venus have them? Let’s consider first of all that if the positions of Mars and Venus were reversed, the newly positioned Venus would be considerably hotter than the old Mars and the new Mars would be considerably colder than the old Venus. Why? Atmosphere. Atmosphere traps heat. And Mars is just slightly too small to have sufficient gravity to have held onto the atmosphere that undoubtedly it once had. Venus, only a bit larger, has a crushing atmosphere and blazing temperatures. Its size, its gravity, is sufficient to have retained its atmosphere; in fact far too much of it to be truly “Earth-like”.
But wait? Didn’t I just say that Earth is slightly larger than Venus? How is it that Venus’ gravity retained an extremely dense atmosphere and Earth didn’t? The answer is the true miracle of Earth, the Moon. The Moon is over 70% as large as the planet Mercury and is in fact almost half again the size of the (former) planet Pluto; it’s about half the diameter of Mars. In fact, judging by diameter, it is a planet in its own right. As it is only around 380,000 miles from Earth, the Earth/Moon pair should rightly be thought of as twin planets. And what has having another planet this close to the Earth done to it? Among other things over the eons the Moon has dragged away much of Earth’s atmosphere, leaving just sufficient air to trap just enough heat to keep water liquid.
So what are the odds of that? A planet of just the right size at just the right distance from just the right type of star and this planet is one of a pair, a twin planetary system. If the little green men come from worlds like ours they must be very rare indeed.
Air and water, essential to life. Let’s think for a moment about our air, our atmosphere. Almost all of it is contained in the troposphere; that’s the 7 mile thick layer that our weather occurs in (although only the first mile or so is dense enough to breathe). To us, crawling along the Earth’s surface, this seems an immense mass. It is in fact an incredibly thin film over the surface of the planet. Every junior high school student learned that, despite Earth’s soaring mountains and deep oceanic trenches, if the Earth were reduced to its size it would be smoother than a pool ball. Were that pool ball dipped in very thin paint, that would be our atmosphere. Another way of thinking of it is to imagine a stack of 20 decks of playing cards. If we were to slide an extra card in at the top and bottom they would be our atmosphere; very thin and, as we are learning, very fragile. If that coating of paint were twice as thick, if two cards instead of one were added to the top and bottom of the stack, our planet would be uninhabitable. The Moon; thank the Moon.
And water; what a remarkable thing that is. So simple, composed only of two hydrogen and one oxygen atoms yet able to contribute so much to our carbon-based life. Water also has remarkable heat transferring properties absorbing and releasing heat in ways that make life possible. [3] The inventor William Lear, who gave us among other things the Lear jet and 8-track tape player, thought that if he could find a substance with better heat-transferring properties than water he could devise a modern steam engine more efficient than the internal combustion engines that drive most of our cars. After years of experimentation he came up with a substance he called Learium III which, as he admitted, “mixes well with scotch”. [4] It was water. If there were a better liquid for storing and releasing heat Bill Lear couldn’t find it. And why do we have an abundance of liquid water? Mars doesn’t have it (not enough atmosphere); Venus neither (too much). Thank the Moon
And how did this remarkable thing, this Moon, come about? Various theories for the origin of the Moon have been proposed but the currently favored one [5] is that shortly after the Earth’s formation a Mars-sized planet collided with it. Large portions of the Earth were ejected and this matter coalesced into the Moon which settled into orbit around the Earth. While startling that seems simple enough, but think about it.
The Earth could have just shattered and dispersed but it didn’t.
The ejected material could have had such velocity that it just kept on going, but it didn’t.
The ejected matter could have drifted around and then come crashing back into the Earth, but it didn’t.
The ejected matter could have been insufficient to make the planet-sized Moon with all the attendant consequences noted above, but that wasn’t the case.
Instead a planet-sized pile of debris was ejected from a planetary collision and this debris coalesced into a planet that settled into orbit around the Earth; quite a coincidence and just what we needed.
The Moon, Earth’s miracle.
[1] This bizarre fact and others from http://www.newsoftheweird.com/archive/nw060319.html
[4] “Popular Mechanics” August 1972. http://books.google.com/books?id=NNQDAAAAMBAJ&lpg=PA116&ots=uIIoh1HIgJ&dq=learium%20iii&pg=PA116#v=onepage&q=learium%20iii&f=true
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