ABOUT 4.5 billion years ago, a gigantic cloud of dust and gas floating through space collapsed in on itself, going on to form the sun, the planets and everything else in our solar system. That we are reasonably certain of this fact is a triumph for science, but our cosmic neighbourhood has so many more secrets for us to reveal.
Take what seems like, on face value, a pretty easy question: how did the planets get to where they are today? We know that the most obvious answer, that they formed where they currently sit, is wrong, because the two outermost planets, Uranus and Neptune, are too large to have developed at the thin edge of the solar system鈥檚 protoplanetary disc.
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That is why many astronomers favour a scenario in which Jupiter, the largest planet, throws itself about the early solar system, knocking all the other planets here and there until things settle down. There are a few varieties of this idea: Jumping Jupiter, Grand Tack and the Nice model (named for the French city, not its pleasantness). All of them have issues, but on a broad scale, they produce the solar system as we know it today.
鈥淎n ancient meteorite seems to show signs of a Jupiter-driven mix-up in the early solar system鈥�
These models, nice as they might be, are built on a whole heap of necessary assumptions, simply because we can鈥檛 go back in time and see if the maths checks out. But now, researchers have done the next best thing, discovering an ancient meteorite that seems to have telltale signs that a Jupiter-driven mix-up really occurred.
If this piece of the cosmic puzzle has finally fallen into place, there are still many looking for a home. Finding signs of past or present聽life on another planet or moon would be incredible, but little green microbes aren鈥檛 the only game in town. How planets put themselves together is another favourite head-scratcher (little by little or big bits all at once are the main options) and theorists are always dreaming up new ones, such as the question of whether the moon is hiding secret signs of ancient black holes.
If you are impatient for answers, remember that many of these things happened billions of years ago, so waiting a little longer won鈥檛 hurt.
