# How many Mars sized planets can form and remain stable in the habitable zone of a Sun-like star?

By Mars sized I mean with masses between 0.10 (M) and 0.25 (M), the planets need to have independent orbits around the star. We can assume the habitable zone stretches from 0.70 AU, to 1.5 AU for a typical G type star like the Sun. I don't know if adding a gas giant to the system will cause instabilities, but I think they are important for perturbing comets and other volatiles to terrestrial planets.

• No idea of the actual answer, but here is a simulation you can play with. stefanom.org/spc Commented Sep 11, 2016 at 15:27
• Can't calculate it now, but I dare to say that for Sun-like star you can't get very different results. Sun-like star would form from solar-system-like disk, leaving similar protoplanetary disk... I guess 4. give or take. Commented Sep 11, 2016 at 16:25
• I managed to find an interesting planetary system generator called StarGen, Though I haven't been able to generate what I want just yet, not sure how accurate the systems are either. If anyone wants to try it here is the link, fast-times.eldacur.com/StarGen/RunStarGen.html Commented Sep 13, 2016 at 16:07

.7 to 1.5 A.U.?

Venus is .72 A.U., earth is 1 A.U. and Mars is 1.52 A.U. So judging by our solar system, 3 planets are possible.

Smaller bodies at a star planet L4 and L5 are stable if the smaller bodies are 1/25 the mass (or less) of the larger planet. And 0.04 (M⊕) lies below the 0.10 (M⊕) boundary you suggest. Unless the larger planet is 4 times the mass of the earth, then it could have a Mars sized trailing as well as a leading Trojan.

Would a planet 4 times earth's mass destabilize the other planets within the habitable Goldilocks zone? Sorry, I don't know. If a super earth is possible, I could see a super earth with two Mars sized trojans as well as two other Mars sized bodies in other star centered orbits. So my guess is up to 4 Mars sized bodies and a super earth are doable within a sun like star's Goldilocks zone.

Edit: JDługosz suggested double planets are possible. I believe this is true.

So I think 6 are possible. Here's a pic:

At 1.5 A.U. is a super earth with a Mars like moon. Also at 1.5 A.U. are two Mars sized Trojans.

At 1 A.U. is a single Mars sized body. I want to keep this guy small so he doesn't destabilize the super earth trojans.

At .7 A.U. is a double planetoid, each Mars sized. This might be far enough from the 1.5 A.U. orbit that a more massive double planetoid won't destabilize the trojans.

Speaking of Mars sized moons, that raises the possibility of one of my favorite settings: A Gas Giant In Earth Like Orbit (GIELO) and an Earth Like Moon (ELM). I talk about GIELO and ELM on my ZRVTO post.

• Super-earth trojans? I thought they were all mars sized. Commented Sep 12, 2016 at 16:48
• The super earth and it's Mars sized moon needs to total a mass 25 times (or more) massive than each Trojan mass. Or else the L4 and L5 Trojans aren't in a stable orbit. Commented Sep 12, 2016 at 17:42
• Ok, I missed that; thought the primary was a Giant. Commented Sep 12, 2016 at 17:45

Based on the series of essays Building the Ultimate Solar System, one of his “super” systems comes to mind.

3 stable orbits of different radii. Maybe need a wider spacing if we play more tricks, but you can push the far end of the zone by using greenhouse effects.

Each orbit might contain 2 bodies 60° apart, being in each other’s trojen points.

Or, each body might actually be a double planet! So that’s 6 to 12 bodies.

The presence of additional giant planets will mess that up. HopDavid’s variation uses a giant with a habitable moon to get 3 in one orbit, but that means the other orbits can’t share so much and I still worry about the eccentricity being pumped up. So ditch the giant completely and put 2 to 4 Mars bodies in each orbit.

• Trojans more than 1/25 mass aren't stable. Moreover a planet in a neighboring orbit orbit can destabilize Trojans. Jupiter can hold on to its Trojans because it's the big frog in our solar system swamp. So in my opinion two Trojans max. Double planets isn't a possibility I had considered through. I might edit my answer to reflect that possibility. Commented Sep 12, 2016 at 15:38
• Ok, I reread the article. Part 4 isn’t clear on its own but in part 5 the illustrations/examples indicate 2 sharing an orbit, not 3, of equal-mass bodies. Commented Sep 12, 2016 at 16:44
• What do you mean by "giant"? A Saturn or Jupiter would undoubtedly destabilize the lower orbits. But something 4 earth masses? Possibly, but at the moment I'm betting 4 earth masses at 1.5 A.U. wouldn't be that destructive. Commented Sep 12, 2016 at 17:48