Living in a denser atmosphere

[sailorhathor]

This relates to my last question, which was here.

I believe I have settled on a planet for my human-like aliens to come from - Tau Ceti f. This choice brings up a whole new set of questions based on this information:

Assuming that Tau Ceti f is a terrestrial planet, it would likely be at least 2.3 times larger in size than the Earth. Assuming an

Comments

[beccastareyes]

The no land, all water thing comes from this:

Tau Ceti f is 2.3 times bigger than Earth in radius. If we assume it's made of the same things in proportion, that means it has 2.3^3 = 12 times as much water. Let's assume the same proportion of water ends up at the surface. The surface area of the planet is 2.3^2 or 5.3 times as much area. That means that 12 times as much water would be about 2.3 times deeper. Then add in that gravity would be stronger (so you'd end up with smaller mountains and shallower oceans), and the water would cover most of the ground.)

Now, there's assumptions in that. Tau Ceti f may have had less (ore more) water mixed in with it. More might be stuck in the deeper layers of the planet*. A factor of 2.3 deeper oceans is everything is equal means you can probably turn knobs to get the water down.

(Incidentally, the gravity would be about 2.3 times heavier*, which would make it harder to fly.)

As for the atmosphere, a lot depends on what you pack it with. Earth has a few percent of its atmosphere filled with greenhouse gases (water vapor is most of it, and carbon dioxide is the next big one, but at only 0.04%). The scale isn't linear, since some gases are better at warming than others, but our few percent provides about 30 degrees C of warming. So you could imagine if you make the atmosphere even slightly more dense but add all CO2, that would do more than adding air.

(For reference, Earth's average temperature is around 15 degrees C.)

For people, it depends on how big a change. Humans tend to be more sensitive to oxygen amounts rather than overall density. (I recall reading about underwater research stations that operate by packing a lot more gas in the station, so it matches the pressure of the water outside. You can't go to the surface without hours of preparation to avoid 'the bends', but you can comfortably go in and out of the water without worrying about even an airlock. An astronomy professor of mine did that to test living conditions in a small, isolated station as a study in crewed spaceflight.

(My guess is the sky would be lighter -- our air is what creates our blue sky. Again, it depends on how dense.)

* The Earth's mantle has more water than all of our oceans.
** Again, this is assuming the same density of Earth.

[sailorhathor]

Thank you! I'm researching other planetary possibilities because the gravity seems like it's going to be more trouble than it's worth. There's always something with these alien planets. :P :D

[beccastareyes]

Keep in mind, that we've only just barely got the ability to see Earth-sized planets*, so unless there's a planet already there, you can probably assume one is possible.

* As in, you need exactly the right star, the right telescope, and the right alignment to see one, while for Jupiter-sized planets we can see those easily unless conditions are wrong (a star that's active or the wrong alignment of a planet.)