As we discussed in the previous post, to increase our chance to find life, we should look for planets where we can find a liquid surface and near to these planets. We are unlikely to find life away from a liquid planet.
But the liquid does not mean water. At least not only water, but any liquid, including methane.
Of course, that planets with liquid water will be more likely to find life more similar to ourselves, but we must keep in mind that there may be forms of life that are completely different from ourselves, including some based on silicon rather than carbon.
If we was searching for simple lives like bacteria and viruses, we must include very cold planets in our portfolio. In our solar system all planets except Mercury must be included. A solid surface is not needed to allow these organisms to emerge, only a liquid surface that can be composed of gas under pressure, making Jupiter, Saturn and Uranus possible candidates as well.
So, when we was searching for extraterrestrial life outside our solar system, we need to consider not only planets with solid surface and liquid water but those with solid surface and any liquid surface and large gaseous planets, including those very cold to have liquid water and even those too hot too, if the pressure of your atmosphere can create a liquid surface somewhere on the planet.
To find places that can support intelligent life the prerequisites are a bit more restrictive. We will discuss this in our next post.
But the question is what to search for on those planets that may suggest that some life is living there?
Should we search for organic components in the atmosphere?
It may be a target, of course, but as we discussed in our previous post, these components can be made by chemical reactions inside the planet, but this quest excludes the possibility that we find life based on silicon or life forms completely different from what we know.
What to search for then?
Light is the answer.
On Earth we have bioluminescent organisms and the light they produce is totally different from sunlight. We have a lot of organisms that produce light, including some algae and the light reflected by the plants also differ from the sunlight.
The hard thing to do is that we need to separate the light reflected by the planet from its own star from that produced within the planet itself. If we find in the middle of the light reflected by the planet radiation of a quality or color different from that emitted by the star, that light can only be produced by the life inside the planet.
To do this, we need to compare the composition of the frequency of the light emitted by the star with the composition of the frequency of the light reflected by the planet and subtract the effect of its atmosphere and any solid and liquid surface that can exist in the planet and the difference is the effect of the life there. A simple and beautiful solution.
This is our best chance to search for life in outer space away from us and it should be our choice, at least before we can make space travel and go there to check, because it is easy to implement and is unquestionable and undoubtedly, being scientifically very solid.
To gain experience on it, we should try to use this technics to infer the presence of life on the planets and satellites in our own solar system, including the Earth where we know that the life exists.