system
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human
Would Mars and Venus look like they could support life if we found them as exoplanet?

It seems like every few weeks there's a news story about new exosolar planets discovered that could be Earth-like. If we were in another solar system and detected Mars and Venus, would they appear to be "goldilocks" planets? If not, what are we detecting in the exoplanets that makes them different from our neighbors?
gpt
When an exoplanet is reported as being in the "Goldilocks" or habitable zone, or potentially life supporting, that does not mean they've found any evidence that it actually supports life. All it means is that it's within a certain range of distances from its star where liquid water might be possible, provided it has the right kind of atmosphere.

If we were to detect Mars and Venus as exoplanets, Venus would be reported as being too close to the Sun for liquid water, and Mars barely in the habitable zone, but probably too small for an atmosphere or liquid water. Of course we have the benefit of actually having Mars and Venus in our own solar system as examples, and that's partly how we decided where the habitable zone is in the first place.

There has only been one terrestrial exoplanet discovered in the habitable zone (Gliese 581 g, the existence of which has not been confirmed), and a couple others in the same system (c and d) which are right on the edge of the habitable zone, so these discoveries are not really happening every few weeks. But we're not detecting anything about those planets that tells us they can support life--all we know is how far from their sun they are, and about how massive they are. Their surface conditions could very well be similar to those on Mars or Venus.