At present, it seems like we are alone in our solar system. How many earth-like planets would fit into the habitable zone of the solar system?

The orbits should be stable for quite a time, i.e. for life to evolve, let's say 4.6 billion years. The habitable zone may be estimated from 0.725 to 3.0 astronomical units, according to Wiki.

Could one use perturbation theory to answer this?

  • $\begingroup$ how far does earth-like go in your description? do you mean just rocky, or does the size have to be the same as well? (does earth-like also include sizes like mars, or not?) Or is the question more like "how many habitable planets could fit in the habitable zone?" $\endgroup$ Commented Feb 24, 2014 at 10:11
  • $\begingroup$ How nice, it's you, @usethedeathstar. I was interested in the last one... $\endgroup$
    – draks ...
    Commented Feb 24, 2014 at 21:49
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    $\begingroup$ This question will be extraordinarily difficult to answer, since the inner solar system behaves chaotic over timescales of more than 100 mllion years. For shorter time intervals there have been simulations with up to 42 co-orbital planets, and up to 210 planets in total. $\endgroup$
    – Gerald
    Commented Feb 24, 2014 at 22:29
  • $\begingroup$ Just for fun, here are a couple of things that Kepler found. $\endgroup$ Commented Sep 14, 2015 at 17:46
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    $\begingroup$ Sorry, a glitch deleted most of my comment above. It's not totally relevant to the question, but what I was going to say was that Kepler 444 (a K dwarf) appears to have 5 "Mars-sized" objects all between .04 and .08 AU and Kepler 90 (a F dwarf) has a Super-earth, Earth-sized planet, 3- Neptunes and 2- Jupiters from .07 to 1AU respectively. There is some weird stuff out there. $\endgroup$ Commented Sep 14, 2015 at 18:09

2 Answers 2


This question not only makes you think about the temperature, pressure but also the impact of gravity. Not moving away from topic, I must say that the region you are saying about is quite large in the view of metrics but quite short again if we really sense gravity.

The distance of a planet from the sun is maintained by gravity, but we must also not forget that distance between two planets is also controlled by the same. You must appreciate gravity because most of the features on earth are because of the same thing.

Now, if you want to calculate it more precisely you should know each and every postulates, theorems and properties shown by the space in nourishing our Earth for habitability.

Perturbation may give you an idea of adjustments, that how our earth is adjusting day by day for its decreasing distance from sun or increasing size of the sun. Talking according to theory of perturbation there may be more than 2-3 planets in the habitable zone. But still you cannot annoy the word "more" in that.

It shall depend mainly on the following factors : -

  • Size of Planets
  • Distance between each of them
  • Distance from sun accordingly
  • Their mass (priorly)
  • Speed of revolution around sun

I know this information is not much for your question but this is enough according to recent knowledge about space. We even don't know the drastic changes happening in the space....the dimensions of space or how vast it is....whether it is measurable or not.....and if yes then are the measurements precise. Each answer tackles you more to have questions....But don't stop, just keep asking!


Here's a blog post with an exploration of how many Earth-like planets you could pack into the habitable zone.

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    $\begingroup$ We tend to encourage answers which refer to an external link or article to Provide a link to the original page or answer and also Quote [only] the relevant portion. More info here - How to reference We try to make this a place where users can find answers instead of links to answers (like Google). In any case our policy is to Always be polite and have fun. $\endgroup$
    – harogaston
    Commented Aug 3, 2014 at 16:25

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