For many years scientists have studied our own solar system and modern technology allows them to look deeper and deeper into space. Knowing the Sun is only one of a few billion stars in the Milky Way galaxy, I can imagine scientists also started studying other planetary systems… at least enough to know how many planetary systems (like our solar system) reside in our galaxy.

Is there any information available that would be able to (at least "indicate") how many planetary systems reside in our galaxy?

  • $\begingroup$ I think this should be changed to 'How many star systems are in our galaxy?' There is only one solar system - the system surrounding the sun. That's what solar means. $\endgroup$
    – Beno
    Commented Mar 5, 2014 at 4:00
  • $\begingroup$ @Beno Valid point... edited my question to reflect that. Tnx $\endgroup$
    – e-sushi
    Commented Mar 5, 2014 at 13:44
  • 2
    $\begingroup$ I've edited the question to use "planetary system" instead of "star system", as that seems to be the intent. See Wikipedia for the difference: Star system vs. Planetary system. This doesn't affect the answers in any way. It just makes the question more accurate. $\endgroup$
    – called2voyage
    Commented Mar 5, 2014 at 13:53
  • $\begingroup$ @called2voyage Even better! Where would we be without smart mods like you? Much appreciated... thanks. $\endgroup$
    – e-sushi
    Commented Mar 5, 2014 at 14:05

2 Answers 2


A good, but hard question to answer - as you stated, only an indication could be provided. But, there is some information available from the number of exoplanetary systems found 'locally', according to the NASA web page How many solar systems are in our galaxy?:

So far, astronomers have found more than 500 solar systems and are discovering new ones every year. Given how many they have found in our own neighborhood of the Milky Way galaxy, scientists estimate that there may be tens of billions of solar systems in our galaxy, perhaps even as many as 100 billion.

Another estimate from the article 160 Billion Alien Planets May Exist in Our Milky Way Galaxy (Hall, 2012), particularly with their quote from a scientist:

"This statistical study tells us that planets around stars are the rule, rather than the exception," said study lead author Arnaud Cassan of the Paris Institute of Astrophysics. "From now on, we should see our galaxy populated not only with billions of bright stars, but imagine them surrounded by as many hidden extrasolar worlds."

An important caveat from the NASA site is that exoplanetary observations are still in its infancy - so over time, this estimate is likely to improve.


According to observations by the Kepler space telescope and other ground based observations, it seems that about 5% of the stars in our galaxy have giant gas planets, similar to Jupiter (but often larger). Smaller planets are difficult to detect, but it is estimated that 40% of the stars have small planets orbiting them.

All in all it is said that on average, 1.6 planets are orbiting each star. So almost all stars form a kind of solar system with planets. However, there is still a lot of uncertainty regarding the numbers, since small planets are very, very hard to detect. And other aspects of solar systems, like our asteroid belt, Kuiper belt and Oort cloud are hard to detect even in our own solar system.

But my own opinion is that it is reasonable to assume that we live in a pretty average solar system (because the odds are obviously suggesting this). So I think that almost every star will have a solar system with a couple of planets, some rocky, some gas giants, plus stuff like comets, asteroids and so on.

Source: Wikipedia Extrasolar planets


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