A tour of our solar system reveals a stunning diversity of worlds, from charbroiled Mercury and Venus to the frozen outer reaches of the Oort Cloud.
In between are a few tantalizing prospects for life beyond Earth – subterranean Mars, maybe, or the moons of giant planets with their hidden oceans – but so far, it’s just us.
“There’s nothing else in the solar system with lots of life on it,” said Mary Voytek, senior scientist for astrobiology at NASA Headquarters in Washington, D.C. “Otherwise, we would have likely detected it.”
Still, NASA continues searching the solar system for signs of life, past or present, and decades of investigation have begun to narrow down the possibilities. The broiling inner solar system seems unlikely (though the high-altitude clouds of Venus remain a possibility).
The same goes for the cloud-covered gas giants, with their crushing atmospheric pressures and seemingly bottomless depths – perhaps no solid surface at all, or if there is one, it’s no place for any living being.
The farthest provinces, with their dwarf planets and would-be comets locked in deep freeze, also seem a poor bet, though they can’t be ruled out. Same for dwarf planet Ceres in the asteroid belt, considered a possible “water world” either now or earlier in its history.
That brings us back to those tantalizing prospects. There’s Mars, now a cold, nearly airless desert, but once temperate and flowing with water.
And much hope remains out among the gas giants – not the big planets themselves, but their long list of moons. Jupiter’s Europa and Saturn’s Enceladus, despite their frozen, forbidding surfaces, are hiding vast oceans beneath the ice – among several moons with subsurface oceans.
Let’s begin the tour with our hottest planet.
Venus, a tantalizing target
Earth as an analog in search for life
Mars: Potentially habitable at some point
Ocean worlds: The moons of gas giants Credit:NASA
