On Friday, November 18th, 2016 at 6:31 pm, KarmaJolt said:
Short of getting a radio signal with video proof (that couldn't have been faked on Earth) sent from the exoplanet, I don't think there's a way to be 100% sure of any alien life on any exoplanet.
If it would take way too long to send an actual probe, it's all guessing.
We can - at least theoretically - interfer a fair bit of information about an exoplanet. And what is possible with current technology is not going to be the final word on the issue. I actually expect that in the future, we'll have reasonably good estimates on bulk properties of exoplanets and, if we're being lucky, atmospheric composition. As I said, atmospheric composition is a possible indicator for the makeup of a planet. The problem is that for planets that are more massive than Earth, and less massive than say, Neptune, you have a broad range of overlap for different planet types, inculding:
- 'gas giants' (more accurate would be 'fluid giant', the big point is that Neptune and Uranus have an interior of fluids, or 'ice', surrounded by an envelope of gas, whereas the gas giants proper like Jupiter and Saturn have a mantle of metallic, high pressure hydrogen).
- 'water planets' (rocky or metallic core, surrounded by a rocky mantle, surrounded by a very deep, planet-wide ocean, with the deeper parts possibly consisting of exotic high-pressure types of ice).
- failed gas giants with an envelope of helium (and little or no hydrogen).
- carbon planets (planets that have more carbon than oxygen, which would yield a geochemistry dominated by silico-carbides as opposed to silicon oxides as on Earth. These planets would be super-rich in hydrocarbons but bereft of liquid water due to the scarcity of oxygen).
- actual earth analogues (with a metallic core and a rocky mantle), but substantially larger than earth.
Unless we have more data, many planets discovered so far that are significantly more massive than Earth (say, five to ten times its mass) could fall in any one of these cathegories.