Stable planetary orbits around the sun?

[Moontanman]

I think we have four already. Venus, Earth, Mars and the Moon.

 

I guess you could look at it like that but since the Earth and the Moon both share the same orbit they don't represent two different orbits.

 

Michael

[Eclogite]

You asked how many planets, capable of sustaining life, could orbit around the sun. The moon assuredly orbits around the sun (with some minor fluctuations dut to its gravitational interaction with the Earth). If it were large enough to retain an atmosphere then it too could support life.

[Qfwfq]

Er, strictly, the centre of mass of the Earth-Moon system counts as one orbit around the sun. While it makes sense to consider Earth's trajectory as a slightly perturbed orbit, it doesn't make sense to consider them both in this way, counting them as two orbits.

[Eclogite]

But to repeat, the op asked for the number of planets, not the number of orbits.:eek2:

[TheFaithfulStone]

How about this one.

 

stargen

 

Fun to play with. There are a couple of more out and about. I haven't been able to find one to do binary star obits yet.

 

Celestia theoretically does some orbital mechanics plotting, but again with the figuring it out.

 

tfs

[CraigD]

I think Boerseun’s earlier post is on target to answer the question “how many Earth-sized planets could orbit around our sun closely enough to sustain life?”

But the four that was created, was created with the available matter and heavy elements that was left over after the solar wind started blowing. There simply isn't enough sizable matter left to build another planet …

It’s less a question of orbital dynamics, than one of available material.

… and the only stuff left (the asteroid belt) that could conceivably do the job, is denied the opportunity because of Jupiter's proximity.

Even this understates the situation – the total mass of the Asteroid belt is estimated to be roughly [math]3.5 \times 10^{21} \, \mbox{kg}[/math], less than 0.1% of Earth’s mass of about [math]6 \times 10^{24} \, \mbox{kg}[/math], not even enough for a decent moon - Earth’s nice, big one is about [math]7.3 \times 10^{22} \, \mbox{kg}[/math].

 

The only source of unused planet-making material appears to be that in the distant Kuiper belt. Due to the difficulty of observing cold, dark objects at such a distance, estimates vary considerable, but most arrive at a figure between 0.3 and 1.2 times Earth’s mass – enough for an exactly Earth-sized planet, but with no plausible mechanism for gathering and accreting it all in the inner solar system.

 

Moontanman’s original question was not, however, “how many Earth-sized planets could orbit around our sun closely enough to sustain life?”, but (italics mine)

… how many eath sized planets could orbit around a sun like star in close enough to sustain life?

, which can be interpreted in several ways, including:

 

What sort of planetary systems can evolve from substantially different pre-stellar nebulae than our solar system’s that still produce stars like our Sun?

 

How, given not terribly unlikely random-ish events other than those that occurred in our solar system, might a pre-stellar nebulae about the same as ours have developed substantially differently?

 

Answering the first question, it’s not unreasonable to conclude from current theory and observation that a Sun-like star can form from a nebulae several times less or more massive than ours. One substantially more massive might result in a system much like ours, but with more Earth-like inner planets – 4, 5, 6 or more, rather than 3 – or, paradoxically, might result in the formation of more and/or larger giant planets, “sweeping” the proto-planetary nebulae more thoroughly so that fewer or no Earth-like inner planets formed, or gravitationally churning the inner solar system so it formed only small bodies. One substantially less massive might result in fewer or no Earth-like planets, or might result in less massive and/or fewer giant planets, and a much “dirtier” system forming many more Earth-size planets.

 

Minor events early in the system’s formation might have major consequences later on. For instance, if Jupiter or one of the other giants’ rocky core had been slammed and fragmented early in its formation, delaying its development into huge, space-cleaning body, more material might have been available for inner planet formation. Or, had the hypothesized Mars-size body, “Theia”, of the widely accepted ”big whack” theory for the formation of the Moon, experienced appropriate impacts or other orbit-changing events, it might be a 4th Earth-like planet now, rather than having impacted Earth 4.5 billion years ago, and the Earth, without its Moon, would likely now be distinctly un-Earth-like.

 

Some models suggest that, had the solar system formed only one giant planet, or had Jupiter been relatively much larger than the other giants, it might have spiraled in to then stabilized in an orbit much closer to the Sun, in which case, several of its great moons might today be Earth-like (though not planets).

 

Ultimately, all this speculation, and much recent data from astronomical searches for extra-solar planet system, supports the view that the formation of planetary systems is as variable as the most complicated games of chance – or, to use a fashionable term, that it is chaotic. Like many chaotic systems, planet formation seems resistant to simple, elegant predictive theories, requiring rather prediction and explanation by exceedingly sophisticated and computationally intense computer modeling.