More planets in 55 Cancri?

Here's a topic that doesn't seem to fit well with any of the forum descriptions, but would go nicely into an "Extrasolar systems" forum as in my proposal on the subject...

Can more planets fit into the 55 Cancri system between planets f and d? If this is possible, the Packed Planetary Systems hypothesis says that more planets will exist.

Results: you can get up to 2-3 planets in the gap. Beyond the orbit of planet d, there is a stable zone at 8.6-9 AU, but the main stability region extends outwards from about 10 AU. Looks like a very good target for further discoveries!

arXiv: A dynamical perspective on additional planets in 55 Cancri

Interesting, but the masses involved that they speak of are rather low. I'm going to guess we won't have any new planets from 55 Cnc for a long time. I hope I'm wrong, though.

55 Cancri: A Laboratory for Testing Numerous Conjectures about Planet Formation

Suggests that the planets of 55 Cancri may have formed in situ in a small, massive disc, with no or little migration between their formation location and their current locations. This can apparently explain the configuration with the two Saturn-mass planets between the orbits of the Jupiter-mass planets. The Uranus-mass planet 55 Cancri e is assumed to be an eroded gas giant. In addition, the model predicts that no planets exist in the 5 AU gap between planets f and d, in contrast to the Packed Planetary Systems hypothesis.

There's also a short discussion about Mu Arae.

I'm doing an add-on to Celestia of a fictional planetary system based on 55cnc system. But to do well I need some informations:

1st: Can the newly discovered planet f have an Earth-sized moon? Or at least a Mars-sized moon? What's the max moon mass permited?
2nd: The 2 or 3 planets between the F and D gap could be gas giants or only rocky planets? And the estimated max mass for each one of them?

If you give me the informations needed, I can do a very interesting copy of 55cnc with some more planets and moons.

I'll assume you mean mass, as opposed to size.

Diakonov wrote:1st: Can the newly discovered planet f have an Earth-sized moon? Or at least a Mars-Sized moon?

Judging by a well known Saturn-mass planet and it's array of moons (i.e. Saturn), probably not. Gas planets tend to form moons whose total mass is a small fraction of the gas planet's mass (I keep forgetting... was it 0.01%?).

55 Cnc f's hill sphere is ~0.0275 AU. Stable orbits are usually found out to a third this distance. So for 55 Cnc f, we can expect moons on stable orbits to have altitudes up to ~0.00915 AU.

Diakonov wrote:What's the max moon mass permited?

If the moon was captured, then it could be significantly higher than what the gas planet's circumplanetary disk would allow. Neptune/Triton for example.

Diakonov wrote:The 2 or 3 planets between the F and D gap could be gas planets or only rocky planets? And the estimated max mass for each one of them?

Well, we don't really know if there are a few planets between f and d. Some work has speculated that there may not be any at all. We won't know until continued radial velocity surveying confirms or disproves the existence of anything in there.

As such, if any planets exist in the gap, they might be of any (reasonable) mass. I would guess less than a Jupiter or two, or else they should have shown up in the 20 years of monitoring we've done on 55 Cancri A.

Until astronomers start detecting exomoons I guess it is all fairly speculative, even for Earth-size moons around massive gas giants. MOA-2007-BLG-192Lb system shows that super-Earths can form around (isolated) brown dwarfs. There's also a possible moon-forming disc around Fomalhaut b, but its properties are not well-constrained, even assuming it exists at all.

As far as I can see, there's no particular reason why Earth-size moons around 55 Cnc f would have been destroyed by tidal migration, but there's still the issue of formation. Since 55 Cnc's planets appear to have formed from a more massive protoplanetary disc than our own system, who knows.

(Perhaps the thread on the formation of the 55 Cancri system should be merged in here?)

Lazarus wrote:(Perhaps the thread on the formation of the 55 Cancri system should be merged in here?)

Merged.

About the gap between f and d: If there's any planet between the gap, in which distances a planet could be at a stable orbit other than 2AU, if the planet is up to 10 Earth mass? For example, could be there 3 planets with Earth-like mass in the gap?

Of course there could be. Radial velocity has not excluded such a scenario.

Or maybe the existence of this gap is due to the fact that 55cnc f migrated inward and 55cnc d migrated outward. So now there's the empty space. Or I may be wrong...

The Dynamical Architecture and Habitable Zones of the Quintuplet Planetary System 55 Cancri

Another study which concludes that terrestrial planets could still exist in the outer regions of the habitable zone.

Assuming they didn't form in situ (which I find the more likely case), I would think that there couldn't be much of anything else in the system at all, let alone something in the habitable zone. On a second slightly off-topic note i've thought perhaps that the .2 eccentricity is instead caused by 2 planets in 1:2 orbital resonance like in Gliese 876. Perhaps habitable planets can't be ruled out afterall. *whew*

P.S. What's this systemic thing that I keep hearing about?