Are Breathable Desert Planets Unrealistic?

[Beamer]

16 minutes ago, Spacescifi said:

 

What do you mean that Titan and venus are not desert worlds?

 

Do they have oceans of carbox dioxide?

 

I think titan has lots of ice but I think it's carbon dioxide ice or something not water.

Venus rains acid, so you may get pools of the stuff but it is so hot I doubt it would make any standing bodies of liquid last.

Jupiter, Saturn, and Uranus are rumored to have oceans of hydrogen which sounds cool... but trying to reach it sounds suicidal because of the 500 mph winds you would encounter on the way down and stormy atmosphere.

Titan has lakes, rivers and clouds, they're just not made of water but of methane. Although rain was not directly observed AFAIK, if there are clouds, rivers and lakes it stands to reason there's a rain cycle involved. On Titan, the 'ground' is mostly made of water ice, the methane cycle plays on top of that.

Venus of course has clouds. It also has a rain cycle, although the general consensus is it never reaches the surface in liquid form. However since there have been suggestions about life in Venus' atmosphere I didn't want to outright group it with desert worlds. Its atmosphere is so dense and material-rich you could argue its a biome by itself where life could conceivably persist and perhaps even originate. But looking purely at the surface you could certainly argue its a desert world, it doesn't change the odds all that much

The gas and ice giants are just nasty. As beautiful as Clarke could make it sound, I don't think there are ever stable enough conditions for life to get a foothold. It's not that the materials are not there, but its all so turbulent that if you were to 'inject' some form of life that could survive in the local conditions where you injected it, it wouldn't take more than a day for it to end up in conditions that would outright kill it.

 

[kerbiloid]

24 minutes ago, Beamer said:

Titan has lakes, rivers and clouds, they're just not made of water but of methane.

They are very extra-shallow and get frozen to the very bottom, unlike the terrestrial ones.

[JoeSchmuckatelli]

1 hour ago, Beamer said:

Earth has technically been a desert world at several periods in its past (after the start of life).

There are a couple of definitions of a 'desert'. The biological one is typically centered around the hostility to life. Needless to say if you take this definition it would be unlikely as the definition itself is specifically centered around "hostility to life".

The geological one typically mentions the lack of precipitation caused by extreme heat or cold and/or the absence of abundant surface water. By this definition, Antarctica is a desert, and the entire Earth was a desert planet the few times in its past when it froze over completely. Of course life was quite simple during those times and it's possible biogenesis couldn't occur on such a world, but once life gets a foothold it is very good at hanging on.

 

 

I know of 'Snowball Earth' - but did not think it happened more than once since the PreCambrian.  Also, when the life was constrained to water and had not colonized land yet, I don't know how we'd call that barren terrain.  'Desert' seems inapt.  Absent lichens &etc. the land was certainly without soil.  

If we're simply using 'desert' to mean a landform with a certain amount of annual rainfall, then yeah, parts could be described as 'desert' or 'tropical' without having any plant or animal life.  Once life started colonizing land, however, all bets were off.

I think the key is that 'desert' =/= 'lifeless'.  It just requires hardier life than the easy, warm and wet places.  Bacteria still colonize glaciers.  There are plants in the Atacama that survive only on whisps of Marine Fog.

Even glaciers have a microbiome — including unique bacteria (nature.com)

Atacama Desert Plants - Gardenerdy

The Earth's deep reservoir of life in its oceans is a huge bonus, as is the water that wafts about through the atmosphere.

What strikes me, though, is how freaking early we think life colonized this rock.  Literally almost as soon as it was cool enough to have rocks, we start finding bacteria.  (perhaps a bit of exaggeration on my part... but):

Quote

 

It is thought that the Earth coalesced from material in orbit around the Sun at roughly 4,543 Ma, and may have been struck by another planet called Theia shortly after it formed, splitting off material that formed the Moon (see Giant impact hypothesis). A stable crust was apparently in place by 4,433 Ma, since zircon crystals from Western Australia have been dated at 4,404 ± 8 Ma.

...

A specific date for the origin of life has not been determined. Carbon found in 3.8 billion-year-old rocks (Archean Eon) from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have been found in Western Australia.^[15] Probable fossils 100 million years older have been found in the same area. However, there is evidence that life could have evolved over 4.280 billion years ago

 

Precambrian - Wikipedia

[kerbiloid]

29 minutes ago, JoeSchmuckatelli said:

I don't know how we'd call that barren terrain.  'Desert' seems inapt.

https://en.wikipedia.org/wiki/Weathering_rind

[JoeSchmuckatelli]

2 minutes ago, kerbiloid said:

https://en.wikipedia.org/wiki/Weathering_rind

Cool - I've seen that, but never knew it had a name!

 

[Beamer]

4 hours ago, JoeSchmuckatelli said:

I know of 'Snowball Earth' - but did not think it happened more than once since the PreCambrian.  Also, when the life was constrained to water and had not colonized land yet, I don't know how we'd call that barren terrain.

Depending on who you ask, it may have happened one or multiple times during the Proterozoic eon. Not since the Precambrian no, but the first land life emerged well before that (In fact I think by now they've pushed it back to 2.7 billion years ago which would put it well into the Archean eon). Snowball Earth is a bit of a bad name, the important part about these periods is that enough potable water is locked in ice that there is no precipitation. That doesn't necessarily mean that the entire earth is covered in snow and ice. There may still be open stretches of ocean and land, as long as the temperature is low enough.

If it happened again I think complex life would stand a pretty good chance. The oceans under the polar caps are full of life happy as pigs in mud. Thermal vents have complex life forms around them. Plant seeds and fungal spores might survive long periods of freezing. Hot water springs might even provide small biomes for fresh water aquatic life. I don't think we'd have to go back all the way to single cellular life after such a period, but your garden variety mammals would definitely be out of the picture for a while :s

When it comes to human-like intelligent life though, who knows. I certainly believe we would try. We can create energy from the sun, wind, geothermal, plenty of energy to create our own biomes. Food would be an issue, it would all have to come from hydroponic gardens (lab grown meat?). If it happened 'right now' we'd be in trouble but 100 years, 200 years from now? I think it would still beat living on Mars

To tie it all back to the original question, I think it would be unlikely for complex life to evolve and thrive on a desert planet. Once it's started on a planet to the extent it has on present day earth however, I can certainly see it surviving their planet turning into a desert, especially if it's the space-faring type of life from sci-fi books and movies rather than just microbes or 'cow and chicken'.

Edited November 27, 2022 by Beamer
million, billion, what's the difference? :D

[sevenperforce]

On 11/27/2022 at 1:04 PM, Spacescifi said:

I think titan has lots of ice but I think it's carbon dioxide ice or something not water.

Titan has lakes and rivers and rainclouds.

Of course these lakes and rivers and rain clouds are all full of liquid methane, not liquid water, but that’s beside the point.

On 11/27/2022 at 1:04 PM, Spacescifi said:

Jupiter, Saturn, and Uranus are rumored to have oceans of hydrogen which sounds cool... but trying to reach it sounds suicidal because of the 500 mph winds you would encounter on the way down and stormy atmosphere.

Jupiter, Saturn, Uranus, and Neptune are gas giants. Gas giants do not have oceans anywhere; they are so heavy that the gases which compose them transition gradually through supercriticality, so there is never any sharp surface transition (like the transition between air and liquid/solid like on Earth, Mars, Venus, and Titan).

It should be noted that Uranus and Neptune are also commonly referred to as ice giants. Ice giants are still gas giants and there is nothing particularly icy about them since they are extremely hot. But unlike the “classic” hot gas giants, they just are composed mostly of heavier elements.

It is believed that during the formation of stellar systems, the largest accretors suck up the majority of the hydrogen and helium in the protoplanetary disc, achieving a substantial amount of internal heat production through Kelvin-Hemholtz contraction. These form the gas giants, which rob the rest of the protoplanetary accretors the opportunity to grow in mass. Slightly smaller accretors are able to capture heavier elements in the hot disc and grow to significant size, but cannot hang onto hot hydrogen and helium and thus stop growing out at much lower masses. These smaller giants will be either completely ejected from the system or will be flung into more distant orbits, where they cool relative to the gas giants. 

[JoeSchmuckatelli]

4 minutes ago, sevenperforce said:

t is believed that during the formation of stellar systems, the largest accretors suck up the majority of the hydrogen and helium in the protoplanetary disc, achieving a substantial amount of internal heat production through Kelvin-Hemholtz contraction. These form the gas giants, which rob the rest of the protoplanetary accretors the opportunity to grow in mass. Slightly smaller accretors are able to capture heavier elements in the hot disc and grow to significant size, but cannot hang onto hot hydrogen and helium and thus stop growing out at much lower masses. These smaller giants will be either completely ejected from the system or will be flung into more distant orbits, where they cool relative to the gas giants. 

I've read that in relation to all the Hot Jupiter's we've found.  Aren't they still debating on why our system has distant Gas Giants?  I know there is one talk about the 3:2 Jupiter-Saturn relationship and migration... but has there been anything new lately?

[sevenperforce]

On 11/27/2022 at 6:42 PM, Beamer said:

To tie it all back to the original question, I think it would be unlikely for complex life to evolve and thrive on a desert planet. Once it's started on a planet to the extent it has on present day earth however, I can certainly see it surviving their planet turning into a desert, especially if it's the space-faring type of life from sci-fi books and movies rather than just microbes or 'cow and chicken'.

One of the problems with the OP (and with science fiction in general) is that there’s a disconnect between what ecosystems could exist and how ecosystems form.

Even the deserts of Earth (the Sahara, Antarctica, etc.) weren’t always deserts.

By the way, @Beamer, are you new? You seem uncommonly smart and I’m not sure why I haven’t interacted with you before.

8 minutes ago, JoeSchmuckatelli said:

Aren't they still debating on why our system has distant Gas Giants?  I know there is one talk about the 3:2 Jupiter-Saturn relationship and migration... but has there been anything new lately?

The best working hypothesis is that they formed close and got themselves ejected into more distant orbits by any number of interactions, but there are other possibilities. 

[Beamer]

Just now, sevenperforce said:

By the way, @Beamer, are you new? You seem uncommonly smart and I’m not sure why I haven’t interacted with you before.

Not all that new, but off an on. Lately I've been doing a round of XCOM2 (sometimes you want to kill some LGM the old-fashioned way ), which drastically reduces the amount of time I spend posting in the "What did you do in KSP today?" thread, which in turn gives me more time to sleuth the science forums for interesting topics.