Colliding Worlds

Velikovsky’s distinctly different construction of Earth’s past.  This edition published by Sphere Books 1972.

Velikovsky’s distinctly different construction of Earth’s past. This edition published by Sphere Books 1972.

One of the best-known facts arising from modern astronomy is that the day will come when our Sun will expand to become a red giant, consuming the inner planets of the Solar System and, beyond any doubt, ending all life on Earth.  But it won’t happen for another five billion years or so, when the hydrogen in the Sun’s core is eventually depleted.  So there’s nothing for us to worry about since Earth and the other rocky planets will continue safely in their comfortable orbits in the meantime.

Or maybe not.  Research shows that planetary orbits in the inner Solar System could well be disturbed by catastrophic events long before anyone needs to worry about the Sun starting to expand.  In On The Dynamical Stability of the Solar System (The Astrophysical Journal, August 2008), Konstantin Batygin and Gregory Laughlin carried out computer simulations which showed that, although the orbits of the outer planets are likely to be fairly stable in the long term, the same can’t be said for our close neighbours.  Or indeed for the Earth itself.

Depending on the particular gravitational interactions that occur, Mercury and Venus may collide in considerably less than a billion years and, even before that, Mars might be thrown clear of the Solar System entirely.  Any of this would destabilise Earth’s orbit and, in any event, in only around three billion years, Venus or Mars (if it’s still here) could end up colliding with us.  Not to worry, though – we’ve got at least 40 million years to go before anything drastic is even remotely likely, and actually the strong probability is that nothing much at all will happen anyway before the Sun turns nasty.

But the possibility is there, and writers have often pondered on situations where planets careering around the Solar System cause mayhem on the Earth.  Perhaps the most memorable, and not intended to be science fiction, was Immanuel Velikovsky’s 1950 book Worlds in Collision.  He argued that Venus was ejected from Jupiter around 3,500 years ago, passing near Earth and disrupting our orbit.  Then Mars, displaced by Venus, approached us a few centuries later.  All of this is said to explain the disasters on Earth that appear in various myths and legends around the world.

Velikovsky’s ideas were pretty well torn to pieces by the scientific community at the time (and since) since they seem to defy the laws of physics.  However, in his 1980 book Cosmos, Carl Sagan made the valid point that the worst aspect of this affair was not that Velikovsky was wrong, but that some scientists attempted to suppress his work.  Even when it seems very strange, any hypothesis deserves to be considered on its merits.

Of course, science fiction itself can have a field day with the threat of other planets crashing into the Earth.  The 1951 film When Worlds Collide, based on a 1933 novel by Edwin Balmer and Philip Wylie, shows the desperate attempts to build a spacecraft to escape from a doomed Earth, since that offers the only hope for humanity, albeit only an extremely small  and carefully selected part of it.  The rest of the human race is inevitably wiped out.

And there’s the nub of the matter – sooner or later, the Earth may suffer from a catastrophe which ends life here.  Even disregarding disasters generated by mankind itself, an asteroid collision could possibly deal the final blow far sooner than any of the events described by Batygin and Laughlin.

Having said that, there’s a presumption, even amongst people who deride our current efforts to get humanity into space, or actively oppose the drive for manned space flight, that eventually the human race will indeed expand into the cosmos.  It’s probably more widely accepted than we think, and the truth is that only in that way will our species’ long-term future be really assured.

Richard Hayes, Assistant Editor (Odyssey)

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