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Earth Could Collide With Other Planets
Everybody put on your helmet;
Smivs writes "Astronomers calculate there is a tiny chance that Mars or Venus could collide with Earth — though it would not happen for at least a billion years.
The finding comes from simulations to show how orbits of planets might evolve billions of years into the future. But the calculated chances of such events occurring are tiny. Writing in the journal Nature, a team led by Jacques Laskar shows there is also a chance Mercury could strike Venus and merge into a larger planet. Professor Laskar of the Paris Observatory and his colleagues also report that Mars might experience a close encounter with Jupiter — whose massive gravity could hurl the Red Planet out of our Solar System."
From TFAbstract, helpfully linked downstream:
It has been established that, owing to the proximity of a resonance with Jupiter, Mercury's eccentricity can be pumped to values large enough to allow collision with Venus within 5 Gyr (refs 1â"3). This conclusion, however, was established either with averaged equations1, 2 that are not appropriate near the collisions or with non-relativistic models in which the resonance effect is greatly enhanced by a decrease of the perihelion velocity of Mercury2, 3. In these previous studies, the Earth's orbit was essentially unaffected. Here we report numerical simulations of the evolution of the Solar System over 5 Gyr, including contributions from the Moon and general relativity.
The authors claim this is the first extended simulation set incorporating GR and avoiding the problematic averaging technique.
Ok, here's a question: Has this happened in the past?
It doesn't take long playing with simple, fun orbit simulators to see that while most planetesimals get glommed, a few get chucked. Escape velocity from the Sun at Mars distance is WAY MORE* (technological term) than Jupiter could perturb. Some things tossed could have 'very long' periods, but still not escape. THAT would be news.
And yes, I am a rocket scientist and yes, I HAVE done the math.
Vcircular * sqrt(2) = Vescape! 41% is too much, even for Jupiter.
Actually, this result is a big deal. First, the authors used powerful new techniques to solve some long-standing problems in these sorts of simulations. This has allowed them to run simulations far further into the future (or the past) than was possible before. Second, they included General Relativity and the affects of planetary satellites in their calculations, which improves the precision of their results. This has not been done before. Third, this work is the first to put a quantitative time scale on instability in the inner Solar System. Up until now we knew that the orbits of the inner planets were unstable, but we had no idea how long it would take for those instabilities to lead to major changes in orbital parameters. Finally, this result has profound implications for the stability of planetary systems in general, which affects the probability of their being Earth-like planets around other stars, and thus the chances of there being animal life out there. This is a major paper and may become the baseline for this entire sub-field. It certainly deserved to be published in Nature. It is too bad that the media chose to glom onto the sensationalist aspects of the story.
Just because you are paranoid does not mean that no-one is out to get you.