Trying a new thing - I'll be semi-regularly posting science news. If people want to discuss it, that's great, I'll try to answer any questions, especially for deeper understanding, as best I can and hope others will as well. Otherwise, I hope everyone gets something out of the initial post.


In the past, we've found evidence of many large planets circling other stars, but not small ones. The main way we look for planets is to look at the motion of stars.

Physics interlude: although we think of planets as circling stationary stars, this isn't quite true. In a simple system with one star and one planet, they both circle the same point. This point is their center of mass. When you are dealing with two objects with different masses, this point will be closer to the larger object. In the case of the Sun and the Earth, the Sun is so much larger that the center of mass is actually within the Sun and not that far from the center. With 3 or more objects, moving around, the situation gets more complex, but the basic idea stays the same.

Because the wobble, actually the orbit of the star around the system's center of mass) is small with relatively small planets, this is only really useful for finding large planets. This technique has found more than 100 Jupiter-sized (318 times as massive as the Earth) or larger planets. Exciting as it is to find these planets, they aren't suitable for life as we know it, or anything close. There was excitement when a planet of the appropriate sort to sheild an Earth-sized planet from meteors and allow life to start, but no evidence of smaller planets.

The excitement with the latest round of discoveries is that they are so much smaller than have been found in the past. With new telescopes, wobbles of a few miles per hour tens of light years away have now been detected. At least 3 small planets (14, 15, and 20 times the size of the Earth) tens of light years away (50, 41, and 33) have been found. One of these planets has 3 at least three other planets (large ones). These planets are still too large to be Earth-like, but finding them gives hope both that there are smaller planets and that we have a chance at spottign them.

So until we find more than one small planet in a system, it probably won't be likely to have life?

Thanks. I'll be looking for the next one.

To have life as we know it, you need a relativley small planet (smaller than has yet been found). A larger planet helps by sheltering the smaller planet.

Oh ok. I think I was reading it wrong or something.

Thanks, Methos! A planet only 33 light years away seems relatively close to us when you consider that other stars (and planets?) are millions or billions of light years away. Assuming that that planet had intelligent life on it 33 years ago and was technolically capable of transmitting a radio signal to us at that time, what does it take for us to pick up that signal and why haven't we?

33 light years is quite close. Something I didn't mention (indeed, no article I have read on these recent discoveries has mentioned it) is that there is a good reason these planets are so close. The closer the star, the smaller a movement you can see.

I doubt there is any life at a similar technological level to us on planets in those particular solar systems because I agree we would likely have heard something. There are a lot of reasons why we wouldn't have, though. These reasons go for more distant planets, as well.

First, we first communicated by radio little over 100 years ago (1895), and we didn't start broadcasting enough and stong enough signals that they were likely to be picked up until much later. Add to that that with increasing use of cable, we are putting less and less electromagnetic radiation out there, and you realize that there is likely actually a fairly short stage in a societies existance where all this electromagnet junk is being put out there.

Of course, that would assume we were looking for a certain frequency. We can't look for every frequence aliens might have chosen to communicate at.

So what do we do? We look at and around 1420 MHz, a frequency that has 2 benefits. (1) It is in a region that passes through space and the atmospher fairly easily (but there's a wide range (about 1000-10000 MHz, if I remember correctly) that meets this condition. (2) it corresponds to a frequency emitted by hydrogen. We've made the bet that aliens will think that this is significant and use it to communicate with us. Of course, since it corresponds to something natural, there are lots of meaningless signals (meaningless in the search for life, anyway - the most recent signals found at this frequency seem extremely unlikely to be aliens, but are likely some previously undiscovered phenomenon).

Of course, they don't just have to think it is a significant frequency. They have to use it for broadcast. Would they? Well, lets think in reverse - would they see us (a civilization that has decided the frequency is significant)?
Since about 1960, it has been against international regulations to broadcast anywhere near 1420 MHz because radio astronomers don't want a lot of interference while looking for hydrogen (or aliens for that matter). That rules out them picking up any terrestrial noise. I'm pretty sure we also don't broadcast any signals at this wavelength intended for them. Even targetting at a single distant star would cost an enormous sum. Using a beacon that would broadcast in all directions with enough strength to reach other solar systems (especially more distant ones) would use an amount of energy that would solve all the world's energy problems.

Finally (and this applies more to distant stars than the nearby ones) we only spend a very small amount of time looking at each star for alien signals.



I'd love to find alien life, but the deck is stacked against us unless it is plentiful.