I was just reading this article and this sentence stood out.
https://www.bbc.co.uk/news/science-environment-49648746
“Water has been detected on other planets but they have been either too big or too hot to support life.”
The hot bit is obvious but how might a planet being too big affect its ability to support life?
In: Physics
I think this is probably just wrong.
I guess they mean “life as we know it” because what might theoretically the absolute limit for life in general is quite a hazy concept but probably very far from what we might imagine.
For life in theory you just need some energy gradient that enables a pattern to copy itself (imperfectly). Strictly speaking even chemistry is not a hard requirement for life, let alone organic chemistry.
To claim that a planet would be to big to support any sort of life is making a lot of unfounded assumptions and even our sort of life might be quite a bit more flexible than you would think.
Gas giant planets can have water, but life as we know it can’t live on a gas giant planet (at least not as far as we know). Gas giant planets don’t have a well-defined surface, so it’s hard to imagine a lot of kinds of terrestrial life living on them.
On the other hand, somebody in 1989 would have said it was hard to imagine a gas giant planet orbiting its parent star in a few days. And yet, we’ve found many such planets.
You might be interested in reading Mission of Gravity by Hal Clement.. it’s sci fi and the setting is a huge planet with extreme gravity. (I recommend his other writings too such as Needle and Ice World). His work is somewhat dated but still very good.
Pressure and gravity basically you might only be able to exist as a tiny bacteria, also water planets may have difficulty with sunlight penetrating deep enough into the water to generate any light where the potential living organisms are – https://youtu.be/tz47XLhwtzQ
As planets get bigger, their gravity increases substantially. At a certain point it becomes impossible for humans to survive somewhere if the gravity is too strong. Some bacteria could survive at several thousand times earth’s gravity, but we can only survive at a few times earth’s gravity.
Not sure that’s the reason but bigger planet maybe means more mass, then more gravity. But I don’t see why life could find ways to develop with way more gravity, so the reason must be something else.
Maybe related to atmosphere
I think a better wording would be “unlikely to support higher life”. That’s enough for us to rather focus our efforts on more likely candidates.
Sure, I could find a lost penguin in the Sahara desert, but it’s not the smart place to look until all other places has been searched.
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