I If Jupiter had a 5th large moon until "recently", would we know?

[xpell]

TL;DR Summary

If Jupiter had had another large moon and lost it relatively recently (e.g. 1 billion yeas or so), would we be able to realize it nowadays? How?

Hi! I'm fascinated by the apparent "concentration" of the four large Galilean moons in a barely 1.5 million km "strip", and the vast, "empty" distance to the next moons (moonlets?) Out of a purely aesthetic sense of horror vacui, I've always wondered if there was at least another Jovian moon (or more) beween Callisto (orbital radius = 1,883,000 km) and the very tiny Themisto (7,405,000 km) or more possibly the Himalia Group (starting at 11.2 million km.)

I'm aware that the large "Jupiter system" is thought to have had several "generations" of moons that spiraled into the planet during or shortly after its formation, and that this process tended to favor the final stabilization of moons relatively close to the planet ---in that "strip." But I'm wondering if additional moons could have formed and survived beyond Callisto, only to be lost later by whatever reason (Impact? Orbital instability? A passing object that expelled it/them to the outer confines of the solar system or wherever?)

Whatever. My question is: if Jupiter had had a fifth moon and lost it in relatively recent astronomical times (let's say 1 billion years or so), would we be able to realize it nowadays? How, please?

 

[DaveC426913]

I think it's not about "realizing" it; it's about some proponent creating an hypothesis and then a simulation that shows it's possible. But possible merely means it's not impossible.

That something is not impossible is not really evidence that it may have happened.

It would need some sort of corroborating evidence to support it.

I'm not sure what evidence you could get without the hypothesis including an existing culprit somewhere in the system. Perhaps an analysis of elemental ratios seem to match Jupiter or his children or somesuch.

Even my logic is hypothetical.

 

[xpell]

Hi, Dave, thank you very much. Yes, I fully agree that:

But possible merely means it's not impossible. That something is not impossible is not really evidence that it may have happened. It would need some sort of corroborating evidence to support it. (...) Even my logic is hypothetical.

Indeed. However, my question (in my mind, at least...) was more like, "If it had happened, do we have the tools to learn or deduct that it did? What are those tools? Or would it be immediately obvious because this-and-that?"

 

[DaveC426913]

Indeed. However, my question (in my mind, at least...) was more like, "If it had happened, do we have the tools to learn or deduct that it did? What are those tools? Or would it be immediately obvious because this-and-that?"

That is indeed the question I attempted to answer, including a suggestion of some of the tools.

It's not as simple as 'did it happen'. Most celestial science is about 'This may have happened. Let's make a model to see if it makes sense, and look for more evidence.' You never know for certain, you just have a strong, well-supported theory. If it's compelling enough - and answers more question than it raises - then it has taken its first steps toward an accepted theory.

Compare to a similar (but unrelated) deep history hypothesis such as The Giant Impact Hypothesis of Earth's childhood for some ideas about how we look for evidence to bolster such concepts. (It was first proposed by Darwin in 1898 - and it's still "just" an hypothesis (i.e. not widely accepted.)TL;DR: No there is no immediate smoking gun that would tell us there used to be a fifth Galilaen moon. It would need a hypothesis that is then supported with evidence. That would take years of research and analysis.

 

[xpell]

TL;DR: No there is no immediate smoking gun that would tell us there used to be a fifth Galilaen moon.

Thank you again, Dave. This part was especially important for me. I didn't want to pass for an ignorant just by asking, "Hey, what if that big guy had another moon or a couple of them?" and be slammed with an avalanche of, "Are you silly?! That is totally impossible because of this obvious thing!" answers. Now I know that I can ask.