I Fraction of solar systems with an Earth-moon configuration?

[Buzz Bloom]

TL;DR Summary

What is the expected fraction of solar systems which include an Earth sized planet having an Earth's moon sized moon?

Although I have over the years seen reports about simulations of the the Earth's moon's origin by a variety of possible mechanisms, none of these reports have ever reported the probability of such events. What is a reasonable estimate of the fraction of solar systems that have a planet of a size somewhat similar to the Earth's, and this planet has a moon somewhat similar in size to that of the Earth's moon? I am hoping someone here at the PFs will be able to help me find out this information.

 

[Ophiolite]

This 2018 paper, The role of multiple giant impacts in the formation of the Earth-Moon system, focuses on an alternative moon formation through repeated large impacts. However, it references several prior studies that include the probability of moon formation. I have not delved into those references to extract any numbers - I'll leave that to you - but Brasser et al. (2013) mention a 2% - 8% probability based on N-body simulations.

This paper, Kaib & Cowan (2018), The Feeding Zone of Terrestrial Planets and Insight into Moon Formation, examines the continuing problem of of near identical isotope signatures for the Moon and the Earth, noting "Our work suggests that there is still no scenario for the Moon’s origin that explains its isotopic composition with a high probability event." That rather throws the whole thing up in the air.

 

[Buzz Bloom]

"Our work suggests that there is still no scenario for the Moon’s origin that explains its isotopic composition with a high probability event." That rather throws the whole thing up in the air.

Hi Ophiolite:

Thank you very much for your post.

My interest is not about our moon's origin, but about the relative frequency that a configuration of a planet and moon somewhat similar to the Earth and it's moon has occurred in the Milky Way galaxy.

Regards,
Buzz

 

[Ophiolite]

Hi Ophiolite:

Thank you very much for your post.

My interest is not about our moon's origin, but about the relative frequency that a configuration of a planet and moon somewhat similar to the Earth and it's moon has occurred in the Milky Way galaxy.

Regards,
Buzz

I understand, but that can only be determined if we understand the origin of the moon. If we know how the moon formed we can estimate how likely such an event is. The two papers I linked and the references within contain estimates that address that question. You will need to sift through them to find some of the plausible answers to your question.

There may be a study out there that provides a direct answer, but it is likely to be outdated. The answers - as good as we can currently get - can be found through the links I provided.

 

[Buzz Bloom]

I understand, but that can only be determined if we understand the origin of the moon. If we know how the moon formed we can estimate how likely such an event is. The two papers I linked and the references within contain estimates that address that question. You will need to sift through them to find some of the plausible answers to your question.

Hi Ophiolite:

The problem for my purpose with considering the specifics of the moon's origin is that the attempts to simulate the moon's origin varies with the different ideas about how Earth and moon minerals must match. My interest is independent of composition. For example if there have been say five models for how the moon formed (but with different compositions), and each model produced an estimate of how likely that model results in a moon-sized satellite becoming the Earth's moon, then the sum of these five likelihoods would be close to the estimate that I am seeking.

Regards,
Buzz

 

[Ophiolite]

For example if there have been say five models for how the moon formed (but with different compositions), and each model produced an estimate of how likely that model results in a moon-sized satellite becoming the Earth's moon, then the sum of these five likelihoods would be close to the estimate that I am seeking.

That is not valid. Using that approach you would also need to factor in the probability that any specific estimate is valid and since that is an open question (as per my second link) the exercise would be meaningless.

May I ask the reason you are seeking the estimate? That may provide insight as to a viable alternative.

Edit: In the meantime you may find this paper by Malamud et al (2019), Collisional formation of detectable exomoons of super-terrestrial exoplanets, useful.

And this one by Barr (2016), Formation of exomoons: a solar system perspective .

 

[Buzz Bloom]

May I ask the reason you are seeking the estimate?

Hi Ophiolite:

I have had an controversial idea for several decades now related to Drake's Equation.

https://en.wikipedia.org/wiki/Drake_equation​

f_l = the fraction of planets that could support life that actually develop life at some point​

This controversial idea is that in order for life to evolve on a planet, the planet must have a moon large enough to make significant tides.

Regards,
Buzz

 

[Ophiolite]

Hi Ophiolite:

I have had an controversial idea for several decades now related to Drake's Equation.

https://en.wikipedia.org/wiki/Drake_equation​

f_l = the fraction of planets that could support life that actually develop life at some point​

This controversial idea is that in order for life to evolve on a planet, the planet must have a moon large enough to make significant tides.

Regards,
Buzz

Thank you for that. The idea is not that controversial. It's been out there for decades also. I think the consensus is that it may have had a role, but minor. (One is still going to get solar tides.) As originally proposed, as I recall, it related more to abiogenesis than evolution. The switch of attention to black smokers as the seat of abiogenesis reduced interest in the concept.

Keep in mind that the Drake equation was devised as an agenda for the SETI meeting at Green Bank observatory. It works well as an outline of what we need to investigate, but there are too many unknowns - even today - to produce a meaningful number.

 

[Nik_2213]

Tangential to this, getting such a comparatively large Moon with respect to Earth seems low probability. Venus' odd spin and Mars' mega-basin suggest such outcomes are more likely. Is Mercury the remnant core of a stray impactor ?
D'uh...
IMHO, getting a Moon-sized moon of a habitable zone super-earth / neptune-ish / gas-giant seems more likely. Especially as such big planets may migrate...

Which, perhaps, puts yet-another possibility into the 'Where Are They' question: if super-Earth's are common in or at the outer edges of habitable zones, their mega-moons' internal heat supplemented by tidal stirring, then NOT seeing such a big planet's Doppler / transit in Sol System would suggest there's nothing of interest here, folks, move along, move along...

We've come to the hunt the other way around...

FWIW, would Jupiter's and Saturn's 'Grand Tack' have destabilised, ingested or ejected a 'Super Earth' ??
D'uh...

It's a long, long time ago, circa Van de Kamp's era, but I remember reading in 'Icarus' about a very early attempt to simulate planetary formation. The algorithm was 'obviously' nonsense, as it produced zoos of planets totally unlike our familiar set. IIRC, there were even gas-giants close in !
;-)