I have New Scientist edition 25 September 2010 in front of me, talking about several interesting topics (including the importance of happiness and sexy daisies in Africa). However, what catches my attention right now is an article by Battersby et al titled ‘Cosmic Coincidences: Ten improbable events that paved the way for our existence’, which – as it goes – tells me how coincidence is a big factor that shapes the Earth into a living planet habitable for human (and rabbits, and dolphins, and also dinosaurs in the past). And then cometh the Moon, my favourite planetary object.
I’ve learned for quite some time that the Moon was actually not ‘captured’ by the Earth’s orbit, but rather was ‘made’ by the Earth because of a massive impact a long long time ago. But I didn’t realise how important is the role of the Moon until now. I will copy some paragraph from the article, written by David Shiga (p. 39).
The solar system in which the infant Earth found itself was an unsettled environment, filled with lumps of rock whizzing around on irregular orbits. Some 4.5 billion years ago one of these, a Mars-sized body, clobbered our planet. The result was a comprehensive rearrangement. Some of the impacting material stuck, while the rest was blasted into orbit along with bits of Earth excavated by the collision, where it formed the moon.
It does not sound a particularly propitious event. But luckily, it resulted in a satellite that is anomalously big in comparison to its parent planet. There is nothing else like it in the solar system, where satellites are relatively small bodies that either accreted slowly from orbiting debris or were captured in passing. Elsewhere it seems a similar story. Giant collisions in other solar systems would produce abundant dust visible to the infrared Spitzer Space Telescope, but although a few such dusty systems have been found, collisions big enough to produce something like the moon seem to happen in only 5 to 10 per cent of solar systems – with the number of instances where this has actually happened considerably smaller even than that (The Astrophysical Journal, vol 670, 0516).
Why does this matter? Because the moon’s size provides a steadying gravitational hand that helps to stabilise the tilt, or “obliquity”, of Earth’s axis. That prevents wild changes in the pattern of solar heating on the planet’s surface that could lead to extreme climate swings, including frequent periods where the whole planet freezes over. That’s a big deal for us. “Conditions might be bad for complex land-based life if there were no moon and obliquity varied significantly,” says David Spiegel, a planetary scientist at Princeton University.
Earth might still have spawned life without its outside moon – even with a frozen surface, the water beneath could offer a decent habitat for sea creatures, Spiegel says. It’s just unlikely that we would be around to appreciate it. ~ David Shiga
Over the last few years, I’ve been always thinking and seeing the Moon as a source of guidance. I understand that my belief might be originated from the ancient civilisations around the world that referred to the Moon as a sacred object. Now I see that such notion might not be far off at all. Instead of just merely being ‘seized’ by Mother Earth as she strolled along the cosmic path, the Moon was actually sent by the Earth herself to guard her. And for billions of years, she has done the job well. She provides the force to stabilise life on Earth while she the Moon Maiden remains barren.
I start to really see the Moon as our major sentinel now.
Pic: Orange Moon