I’ve been searching all night and I can’t find any info. Anybody know where I can find out what the estimated number of planets in the whole universe is? Anyone know a good web page or book?
Muchos gracias, el smarto people.
Well, since the universe is generally assumed to be infinite, isn’t that impossible? I can’t recall a fixed estimation, but one often hears phrases like “millions and millions of galaxies”.
Not that that’s very precise, but hey, it’s a start.
I don’t think anyone knows if the universe is infinate, but if it is, I would imagine there would still be a finite ammount of matter. Surely someone somewhere has done a gross extrapolation to come up with an estimate.
No, the universe is not usually considered to be infinite. If you accept the big bang theory, it is indeed finite. I’ve heard estimates of 100 billion galaxies total and 400 billion stars per galaxy. I don’t remember an estimate of the number of planets per star, but there’s increasing evidence that they are common. Let’s say that there are 5 planets per star. That means there are a total of 200,000 times a billion times a billion planets in the univere. This is 2 times 10 to the 23 power, or 200 sextillion.
Friedo, are you trying to solve the Drake equation?
BTW, new planets are being formed in the universe everyday(well in a cosmic sense), so the answer would not stay the same anyway.
Not really, that’s a future project. 
I’m writing an article debunking some creationist psuedoscience, and they mention the estimated number of planets as 10[sup]23[/sup]. I think it’s a lot more than that, but I haven’t been able to find any actual evidence in any direction.
Right, but planets are always dying, too. So I think it would either stay at some sort of equilibrium, be increasing slightly (since the universe is likely expanding) or…something.
AFAIK, the generally held consensus is that we don’t know enough yet to make a good guess. The limits of our view are still pretty darned strict. We can only see roughly Jupiter-sized planets and larger and only in the immediate vicinity (relatively speaking). Even with planets that size, we can only see them their orbital plane just happens to be aligned just right relative to us. Smaller planets, like roughly Earth-size, are still beyond our ability, though plans are in works for new telescopes that will help.
For a good overview of the current state, I’d suggest the last issue of Scientific American - either Aug or Sep, I forget. The one with the picture of the Olympic athlete on the cover.
friedo,
I think that estimate of 10 to the 23rd power that you read is actually pretty good. I got twice that, but given all the uncertainties, anything within two orders of magnitude is pretty close. We don’t really have a good estimate on the number of planets per star, but look at how fast we’re finding Jupiter-sized planets around stars. I said 5 planets per star, but, heck, you can do this yourself. What is your own estimate, and how did you come up with it? You said that you think that there’s a lot more than that.
My estimate would have been the same as the fundies’, 10[sup]23[/sup]. Isn’t that scary. I figured 10 planets per star, 100 billion stars per galaxy, and 100 billion galaxies in the universe.
Carl Sagan did a similar estimate years before the recent slew of discoveries of gas giants outside the solar system. He was trying to estimate the number of “advanced technical civilizations in the Galaxy.” See Cosmos p. 299, ff.. He figured [ol][li]there are 400 billion stars in the Galaxy,[/li][li]1/3 of stars have planets,[/li][li]in star systems with planets, there is an average of 2 planets or moons suitable for life to evolve,[/li][li]on 1/3 of such planets, life actually does evolve,[/li][li]on 1% of planets where life evolves, at least one species will become advanced enough to achieve “communicative technical civilization”, by which he seems to mean the development of radio astronomy, and[/li]technical civilization will last only 10[sup]-8[/sup] of the planet’s lifetime[/ol]His best guess is that there are about 10 technical civilizations in our Galaxy at any given time. However, I think that his estimate #4 may be a gross overestimate (or maybe not, considering that life may have evolved on Mars independently), and #6 may be a gross underestimate (Sagan was paranoid about the coming nuclear holocaust).