“Our fate seems closely dependent on the nearest and greatest of the gas giants”by Philip Ball / July 19, 2016 / Leave a comment
It’s not easy to get very excited about NASA’s Juno spacecraft mission to Jupiter, which entered orbit successfully around the giant planet on 4th July after a five- year voyage. Unlike the New Horizons mission unveiling the eye-popping mysteries of Pluto, or the European Space Agency’s Rosetta mission which landed a probe on a comet, Juno seems to be going into well-charted territory. Jupiter can be seen without too much effort even in amateur telescopes, and its bleary red eye—a storm three times the size of the Earth—is a familiar sight, no matter how glorious its baroque swirls.
And Juno’s objectives—to investigate the composition of Jupiter’s atmosphere and interior, and study its magnetic field—sound like stolidly unglamorous planetary science. Of course, this is all a build-up to my saying that you should not shrug off Juno as the prosaic face of space exploration. Truly, though, we might be in for some spectacular sights and surprises from this low-key mission. For one thing, Jupiter is really the key to the entire solar system. Easily the most massive of the planets, it is primarily a ball of gaseous hydrogen and helium—the same stuff from which the Sun is made. If Jupiter were only twice as massive, it wouldn’t be formally a planet at all, but one of the intriguing objects called sub- brown dwarfs or rogue planets: halfway between planet and star, made from gravitational collapse of their own gas clouds rather than the offspring of some parent star. At thirteen times the mass of Jupiter, such bodies become genuine brown dwarfs: quasi-stars dense enough to ignite nuclear fusion reactions and emit a dull glow.
Jupiter is thought to have changed its orbit somewhat over the lifetime of the solar system, and these wanderings gave rise to the asteroid belt and limited the size of Mars—and maybe of the Earth and Venus too. Jupiter’s huge mass makes it a gravitational magnet for comets: some, like Comet Shoemaker-Levy 9 in 1994, smash into the planet, but more are dispatched like slingshots to the outer solar system before they can collide with Earth. It’s possible that this might have helped life here to develop; but Jupiter’s gravity is also capable of nudging the asteroids towards the Sun, raising the possibility of their hitting our planet on the way. Either way, our fate seems closely dependent on the nearest and greatest of the gas giants.