Magazine article New Statesman (1996)

A Long Way from Alpha Centauri

Magazine article New Statesman (1996)

A Long Way from Alpha Centauri

Article excerpt

Just when you think that you're getting to know your neighbours, everything changes. And sadly there's very little we can do about it.

In the past couple of weeks, not only have we realised that there's a planet in the star system next door, but it turns out the moon and the earth may not be what we thought. You spend 200,000 years getting to know your surroundings and then--barn--suddenly everything is wrong.

"Barn" is the appropriate word here. One of the things we have learned is that the cosmic collision that created the moon may also have created the earth.

The received wisdom has long been that a Mars-sized planet known as Theia collided with the young earth 4.5 billion years ago, and the resulting debris came together to form the moon. Two new papers have destroyed this neat story. It turns out that other types of creation scenario become possible when you think to consider the influence of the sun on the rotation of the newly formed earth and moon.

So, it could be that a tiny projectile hit a fast-spinning young earth and threw out enough debris to coalesce into the moon, slowing earth's rotation to its present rate. Equally plausible is the idea that two fast-spinning, half-earth-sized lumps of rock collided and merged to become our slow-spinning earth, again with debris forming a moon.

Both of these ideas resolve a nagging flaw in the Theia idea. The Apollo missions brought back lunar rocks that show the moon to be geologically more similar to earth than the original impact story would allow. The thing is, with the new fast-spin scenario allowed, anything is possible. Researchers expect a slew of hypotheses over the next few months; we have to admit we have no idea now how the earth or the moon formed.

As if that weren't humbling enough, it turns out we'd missed an earth-sized planet that is orbiting our nearest star system, Alpha Centauri. …

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