posted on Apr, 21 2008 @ 05:58 PM
If the Earth's rotation slowed down gradually over millions of years, and this is the most likely scenario, it would be a very different story. If
the Earth slowed down to one rotation every year, called synchronous rotation, every area on Earth would be in either sunlight or darkness for one
year. This would be similar to what the Moon goes through where for two weeks the front side of the Moon is illuminated by the Sun followed by the
front side being in darkness for two weeks.
But what if the Earth stopped rotating completely? In that case, one half the Earth would be in daylight for half the year while the other side would
be in darkness. The second half of the year it would be reversed. Temperature variations would be far more extreme then they are now. The temperature
gradient would affect the wind circulation also. Air would move from the equator to the poles rather then in wind systems parallel to the equator as
they are now.
Even stranger would be the change in the Sun's position in the sky. In the above scenario, Sun would just have a seasonal motion up and down the sky
towards the south due to the orbit of the Earth and its axial tilt. You would see the elevation of the Sun increase or decrease in the sky just as we
now see the elevation of the Sun change from a single point on the Earth due to the Earth's daily rotation.
As an example, say we live at 30 degrees North latitude. In the Summer, at a longitude where the Sun was exactly overhead, it would slide gradually to
the horizon as Fall approached, but since the Sun has moved 90 degrees in its orbit, it would now be due west. As Winter approached, you would now be
located on the dark side of the Earth. You would have to move to a longitude 180 degrees around the Earth to see the Sun 1/2 way up the sky because in
the Winter, the Sun is 50 degrees south of its summer location in the sky.
There would be other effects of the Earth's rotation slowing also. The magnetic field of the Earth is generated by a dynamo effect that involves its
rotation. If the Earth stopped rotating, the magnetic field would no longer be regenerated and it would decay away to some low, residual value due to
the very small component which is 'fossilized' in its iron-rich rocks. There would be no more 'northern lights' and the Van Allen radiation belts
would probably vanish, as would our protection from cosmic rays and other high-energy particles. Losing this protection would cause serious health
Be glad for our Earthly rotation, without it we would be much worse off!
A planet will lose it's atmosphere if the atoms within it overcome the escape speed needed to escape the planet's gravitational pull...
Let's compare Earth and Mars. Earth's mass is almost ten times that of Mars. That means if the two planets were the same size, the surface gravity
would be ten times greater. But, of course, Mars is actually smaller. It is about half the size of Earth. Putting those two together, the surface
gravity on Mars is a little less than half the surface gravity on Earth. Simply put, Mars has less strength holding the atmosphere in place.
So why does Mars have an atmosphere at all? Let's talk escape velocity. Escape velocity is the amount of speed any object, wheter it is a spaceship
or a baseball or an air molecule, needs in order to completely leave the gravitational influence of the planet. Once again, escape velocity is
dependent on the mass and the starting distance. (If you start farther away, you don't need as much starting speed to escape) When we run the
numbers, we see that the escape velocity from the surface of Mars is about 5.0 kilometers per second, less than half Earth's escape velocity of 11.2
km/s. Now, air molecules don't all move at the same speed. It's like a cup of hot cocoa. The really fast stuff flies off, leaving the slower stuff
behind. (That's why hot cocoa cools down so fast if you leave it uncovered. All the "hot" particles go flying away.) In the case of Mars, that
means a lot more of the atmosphere had "escape velocity," but not all of it. So, some of it (the slower, heavier molecules) stayed behind. Also, if
the temperature increases, we get more fast particles and lose more air than if it is colder.
Let's take a quick look at the Moon: Its escape velocity is only 2.38 km/s. With such a low escape velocity, you wouldn't expect it to hold barely
any atmosphere. And voila! we see it is virtually airless.
thus earth doesn't move and voila atmosphere starts to escape because gravity is dead