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The thing that stood out to me was the second rung of the ladder, the Moon. Having a large companion satellite is not a prerequisite for life (probably), so how

The thing that stood out to me was the second rung of the ladder, the Moon. Having a large companion satellite is not a prerequisite for life (probably), so how would aliens without one bridge this gap? It seems like it would take a lot more physical theory beyond simple geometry to get there.

defrost 3y ago
If you can find a copy I can recommend The Tragedy of the Moon which covers such questions (from a 1973 perspective), also raising the advantages to land based life moving from the oceans with the assistance (or forcing) of the tides and tidal zones. As a sub thread bonus I've got a sneaking suspicion Terence Tao read this collection of essays about the same time he met Paul Erdős in Australia in the early 1980s. https://en.wikipedia.org/wiki/The_Tragedy_of_the_Moon https://en.wikipedia.org/wiki/The_Tragedy_of_the_Moon
jaggederest 3y ago
> Having a large companion satellite is not a prerequisite for life (probably) I don't know, there's a sibling comment to this one that brings up some proposed benefits to having a moon. It's possible that the foundation of life itself relied on having tidal variation of some kind, since AFAIK the equivalent of early amino acids were formed in tidal pools cut off from the main ocean and cooked under the stress of UV and evaporation. Obviously not something we'll know for sure until/unless we find other organic life, but it's interesting to think about something like having a large orbital influence being a requirement. Plug that into the fermi equation with observed planets with a moon >0.2% the size of the parent body and it has a definite damping effect on the probability of observing complex life. Edit: Also shocked I had to revise my numbers, the moon is only 1.2% of the weight of the earth. I thought it was something more like 10% - so you can probably put "tides too strong to allow life" under the other side of that fermi equation factor as well!
- ahazred8ta 3y ago
  they may have found Darwin's 'warm little pond' - http://www.nature.com/nchem/journal/vaop/ncurrent/full/nchem.2202.html http://www.nature.com/nchem/journal/vaop/ncurrent/full/nchem... Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism
chongli 3y ago
Aliens might live on a planet without a large moon but it’s pretty unlikely for their planet to be the only object in orbit around their star. The easy way to measure the Earth-Sun distance today is to use radar to precisely measure our distance from Venus and triangulate our position from that. Aliens with radar could do the same trick using other objects in their home planetary system. But even before radar, we had parallax methods for figuring this stuff out. Radar just brings the error down into the low parts-per-billion territory.

defrost 3y ago

If you can find a copy I can recommend The Tragedy of the Moon which covers such questions (from a 1973 perspective), also raising the advantages to land based life moving from the oceans with the assistance (or forcing) of the tides and tidal zones. As a sub thread bonus I've got a sneaking suspicion Terence Tao read this collection of essays about the same time he met Paul Erdős in Australia in the early 1980s. https://en.wikipedia.org/wiki/The_Tragedy_of_the_Moon https://en.wikipedia.org/wiki/The_Tragedy_of_the_Moon

jaggederest 3y ago

> Having a large companion satellite is not a prerequisite for life (probably) I don't know, there's a sibling comment to this one that brings up some proposed benefits to having a moon. It's possible that the foundation of life itself relied on having tidal variation of some kind, since AFAIK the equivalent of early amino acids were formed in tidal pools cut off from the main ocean and cooked under the stress of UV and evaporation. Obviously not something we'll know for sure until/unless we find other organic life, but it's interesting to think about something like having a large orbital influence being a requirement. Plug that into the fermi equation with observed planets with a moon >0.2% the size of the parent body and it has a definite damping effect on the probability of observing complex life. Edit: Also shocked I had to revise my numbers, the moon is only 1.2% of the weight of the earth. I thought it was something more like 10% - so you can probably put "tides too strong to allow life" under the other side of that fermi equation factor as well!

ahazred8ta 3y ago
they may have found Darwin's 'warm little pond' - http://www.nature.com/nchem/journal/vaop/ncurrent/full/nchem.2202.html http://www.nature.com/nchem/journal/vaop/ncurrent/full/nchem... Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism

chongli 3y ago

Aliens might live on a planet without a large moon but it’s pretty unlikely for their planet to be the only object in orbit around their star. The easy way to measure the Earth-Sun distance today is to use radar to precisely measure our distance from Venus and triangulate our position from that. Aliens with radar could do the same trick using other objects in their home planetary system. But even before radar, we had parallax methods for figuring this stuff out. Radar just brings the error down into the low parts-per-billion territory.