Transcript: Life on Pluto?

The search for life on planets within our solar system other than Earth has a long and spotty history. A hundred years ago, the obvious candidate was Mars where some astronomers such as Giovanni Schiaperelli and Percival Lowell were certain they were observing a large network of alien-created canals on the surface of that world. To this day, we have no idea what they were looking at since nothing even close to what they claimed to have observed exists on that planet.

The best guess is that they were seeing optical illusions caused by their own telescopes. We now know that civilization on Mars at any time in its past is an utter impossibility for many reasons, lack of a substantial long-term atmosphere being a good one. High levels of sterilizing solar radiation on the surface due to the lack of a substantial magnetosphere would be another.

But what is possible on Mars is the past existence of microbial life early in its history and a lingering possibility that if you go deep enough into the liquid water aquifers thought to still exist on Mars you may still find holdouts of simple life on the red planet. But what none of the canal-spotting astronomers of old expected was that Mars, just a century later, would no longer be the best candidate for a second source of life in our solar system.

Given that all life on earth requires liquid water to exist, it's a good bet that this is true anywhere else in the universe -- though there are other, theoretical ways for it to happen. And the best sources for liquid water in our solar system, and perhaps the universe at large, may not be big ocean planets like Earth. These are probably somewhat rare. Instead, it's the smaller icy bodies of our solar system that may hold the best chances for developing life.

As we've explored our solar system, we have found no other ocean planets. Mars may have been one long ago, but that ocean is long gone and locked up in ice. Even earth is not so stable in that regard, having gone through numerous great ice ages where the planet's surface came close to freezing over. But we have found, potentially, other alternative oceans on not just one world in the solar system but quite a few including the moons Enceladus, Titan and Europa that could all harbor subsurface liquid oceans that might hold life that in theory could be complex perhaps similar to the life that exists on earth near deep-ocean geothermal vents.

But now we can add one more potential extraterrestrial ocean to that list. And, before the New Horizons flyby, it was probably the most unlikely body to be considered for life in our solar system. It's Pluto, and it would be hard to understate that this tiny world is one bizarre place and the more we study the data returned by the New Horizon's probe, the worse it gets.

There are two remarkable things going on at Pluto. Unknown geologic processes that have led to water ice mountain ranges and what may be complex prebiotic organic chemistry going on in the thin atmosphere of that world. Prebiotic means just that, chemistry that is a precursor to life rather than actually being life. But it's interesting to see at this little world because by all rights it should be completely dead but it's not, it more resembles Titan with its hydrocarbon rain than any other world in our solar system.

Interesting organic chemistry aside, the geologic processes going on at Pluto are not well understood but one possibility is that beneath the surface of the planet exists a liquid water ocean kept warm by radioactive decay in the planet's core. This creates an interesting mix, prebiotic chemistry in the atmosphere and liquid water under the surface existing on the same world opens up a lot of possibilities.

It's going to be a long while before we have a proper understanding of Pluto and it's equally strange and interesting moon Charon, but what is becoming clear is that the most interesting places as far as the potential for life are concerned may be the cold, seemingly frozen worlds far outside the habitability zones of stars. In fact, with the addition of Pluto to the possible list, there are now more worlds that could theoretically harbor life in our solar system outside the sun's habitable zone than within it.