Several exoplanets have been discovered that may harbor alien life

The argument

This argument rests on what has become observable about planets outside our own solar system. The analysis developed in recent years allows planets in outer solar systems to be detected at all — a capability that did not previously exist — and it also allows a good deal to be inferred about them once found. Spectrography can be used to predict the composition of a planet, distinguishing a gas giant of the kind represented by Jupiter and Saturn from a rocky planet. The same methods establish the planet's orbit around its star. Those two determinations matter because together they bear on whether a planet could support life. Composition matters because a rocky planet offers a surface, whereas a gas giant does not. Orbit matters because it fixes how much energy the planet receives, and therefore the temperatures prevailing at its surface. The case of interest is a planet whose orbit lies inside what is called the Goldilocks zone — the band of distances from a star within which water can exist in the liquid state, being neither frozen by remoteness nor boiled away by proximity. Several exoplanets have been identified that meet these conditions. The conclusion drawn from them is deliberately limited. It is not that life has been detected, nor that any particular world is inhabited; nothing observed amounts to proof. It is that the conditions associated with life are not confined to our own system but recur among the planets we have been able to examine, and that we have examined only a small sample. Planets which may harbour alien life therefore appear to be common rather than exceptional. On that basis aliens probably do exist, even though we do not yet have proof of alien life.

Context

The advance in space exploration with telescopes or other instruments either on Earth or in Space allowed the detection of several planets on many Stars.

Premises

Counter-arguments

The analysis conducted so far only proves that some planets might be compatible with life but does not say anything with respect of actual presence of a life-form or which is its state (whether primordial or intelligent).

Rejecting the premises

[Rejecting P1] The detection methods described establish far less than the premise implies: transit and radial-velocity data yield size, mass and orbit, and atmospheric spectroscopy has so far been achieved for a small number of mostly large, hot planets — so "predicting composition" overstates what is currently measurable for rocky worlds. [Rejecting P2] The habitable zone is defined by the possibility of surface liquid water given a suitable atmosphere, which is a screening criterion rather than a finding about a planet — a world in that zone may be airless, tidally locked or dry, so counting such planets supports the claim that suitable locations are common, not that any of them harbours life.

Further reading

Nasa site on exoplanets exploration: https://exoplanets.nasa.gov