subject: An antidote to chaos [print this page] An antidote to chaosAn antidote to chaos
One previous theory had suggested that the Earth was spinning so rapidly when it formed that the Moon broke off from a small bulge, like a stone from a sling.
Another said that the Earth and Moon formed as a double planet in much the same way as stars very often originate in pairs called binaries.
According to a third hypothesis, the Moon originated somewhere else and was later captured by the Earth.
Wherever it came from, the Moon is large enough to act as the Earth's stabilizer.
Its importance in that role became clear in the early 1990s, when scientists got to grips with the effects of chaos in the Solar System.
In this context, chaos means erratic and unpredictable alterations in the orbits of planets due to complicated interactions between them, via gravity.
Not only can the shape of an orbit be affected by chaos, but also the tilt of a planet's axis of rotation, in relation to its orbit.
This orientation governs the timing and intensity of the seasons.
Thus the Earth's North Pole is at present tilted by 23.4 degrees, towards the Sun in the northern summer, and away in winter.
Jacques Laskar of the Bureau des Longitudes in Paris was a pioneer in the study of planetary chaos.
He found many fascinating effects, including the possibility that Mercury may one day collide with Venus, and he drew special attention to chaotic influences on the orientations of the planets.
The giant planets are scarcely affected, but the tilt of Mars for example, which at present is similar to the Earth's, can vary between 0 and 60 degrees.
With a large tilt, summers on Mars would be much warmer than now, but the winters desperately cold.
Some high-latitude gullies on that planet have been interpreted as the products of slurries of melt-water similar to those seen on Green land in summer.
'All of the inner planets must have known a powerfully chaotic episode in the course of their history, ' Laskar said.
'In the absence of the Moon, the orientation of the Earth would have been very unstable, which without doubt would have strongly frustrated the evolution of life.'
