When you think of a planet that could be crawling with aliens, you and hundreds of scientists probably imagine an Earth-ish terrestrial planet with liquid water oceans and just enough starlight to spawn life. That idea is now being put on ice.
Alien hunters usually seek what they consider low-hanging fruit in the hunt for extraterrestrials, which is why rocky planets orbiting within the habitable zones of their stars get so much attention. Researchers Mansavi Lingam and Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics and Harvard Insitute for Theory and Computation want to look beyond life as Earthlings know it and dive into the liquid water oceans on icy moons. In their recent study Subsurface Exolife, they argue that worlds like Enceladus, Europa, Ganymede, and Titan are far more likely to be floating around in the universe than Earth doppelgangers.
Lingam and Loeb believe that planets in the habitable zone are too often assumed to be potential breeding grounds for life when killer radiation and poisonous atmospheres would make survival on the surface impossible. This is why it’s unlikely that anything alive is more likely to be swimming in the depths of a strange ocean than creeping around above water on frozen orbs, even though the complexity of that life (like the stromatolites and creepy blind life forms thriving around undersea hot-water vents) could be limited by how much light can reach so far into the abyss. Sending out a spacecraft that can drill through the ice and probe for organisms will be the only way to find out if the moon in question doesn’t have vaporous plumes like those that originate in the hydrothermal vents of Enceladus.
For anyone who still thinks there’s a better chance of finding something with 16 legs and a feeding tube (or even just bacteria) lurking on a rocky planet, just look at our solar system.
We’re not the only terrestrial planet in the sun’s habitable zone just because our species is the only intelligent life we know of anywhere. Earth is actually an anomaly. If a spacecraft from a distant planet were to wander over here and investigate what would be considered potentially habitable planets without any previous knowledge of our existence, those would include Venus and Mars—and no, the prospect of humans colonizing Mars in the future doesn’t count. Never mind where these planets are located, because Venus is swirling with clouds of sulfuric acid in a toxic carbon dioxide atmosphere, and billions of years of getting radiation-bombed means the atmosphere of Mars has been everything but obliterated.
“Since planets with subsurface oceans are more common than rocky planets in the habitable zone, why do we find ourselves on the latter?” Lingam and Loeb ask. “The reason most likely stems from the fact that 'we' refers to an intelligent, conscious and technological species.”
So maybe we won’t be finding any civilizations planning intergalactic domination on these planets, but microbial life outside our planet still qualifies as alien.
(via Universe Today)