Rhaedas

I found a 6 page PDF discussing exactly what you're talking about, using the Hubble to look for planets around the Centauri system. On page 5, they show an example of what a Jupiter sized planet would look like, given the Hubble's abilities. Rather small...we could detect its presence, and take measurements of what it's made of...but no big pictures.

Detection of Planets with the Hubble Space Telescope Advanced ...

And this is the closest star system...

Now, if we were to create a huge array of space telescopes, consisting of 100s of hubble sized scopes spread out, then we'd bump up our abilities to see things. But still...it's a long way to other stars.

auto-da-fe

Interesting.

We have been able to send vessels outside our planetary system. Presumably, we could do the same with an HST - like telescope. That would put us considerably closer, and we may eventually be able to get good pictures. I wonder how long the telescope would have to travel towards AC before we could really start seeing some detailes?

fando

Hmm... Rhaedas must be figuring for only one physical telescope lens. That's not the whole story; there's reason to be more optimistic: Optical Interferometry.

Essentially, what optical interferometry allows is a much larger effective telescope diameter by combinding two telescopes into one larger scope of a diameter equal to the distance between them. For instance, the Keck telescopes (each 10 meters in diameter) are separated by 90 meters. Optical interferometry allows these two scopes to be treated as one single scope 90 meters accross. (There's more to the technical story, but this is basically it in a nutshell.) That's roughly an order of magnitude improvement on the theoretical resolution limit!

What this means is that once the technology is mature enough, we will be able to construct telescope arrays with an effective diameter limited only by our present engineering capabilities. (Imagine kilometer-sized effective telescopes, even orbit-sized!) And with such vast power, it is conceivable that we will be able to directly resolve Earth-sized planets around other stars.

Mageth

We have been able to send vessels outside our planetary system.

Only just barely.

Presumably, we could do the same with an HST - like telescope. That would put us considerably closer, and we may eventually be able to get good pictures. I wonder how long the telescope would have to travel towards AC before we could really start seeing some detailes?

At the speed we can currently send craft into space, a long, long time.

Rhaedas

I would say that we'd have to get within the system to begin to get "clear" pictures of what's there.

Here we begin to discuss the scale of things again. The Voyager spacecrafts are averaging around 16-17 km/s in speed. That's about 536 million kms in one year. To go 4.5 lys at that speed it would take about 80,000 years.

Abacus

A long, long time meaning tens of thousands of years.

fando

Whoa there you guys, there's really no need to leave our system to see what's out there. A combination of optical interferometry and spectroscopy has the potential to reveal a gold mine of information about extrasolar planets. Among that info is likely to be a very good answer to the frequency and quality (complexity) of life in the universe.

auto-da-fe

Why? Why do we have to be within the system that we are looking at? With the HST we are able to see galaxy formations, and stars so far away that it is approaching the begining of time. Why can we not get say, 1/1000th of the distance closer to AC and see if there are planets? I'm not talking about being able to read the street signs, only to be able to see it well enough to know wether or not it has clouds.

Rhaedas

fando: yeah, I was talking about that with the arrays...but I wasn't clear enough on the math to try and figure out how much better it was. I still question visual pictures, but certainly our ability to explore would increase significantly.

Now, if we can just get into space cheaply...

Shadowy Man

A star with the radius of the sun (6.96x10^10 cm) at 3 light years away would subtend 0.005 arcseconds, an order of magnitude smaller than the HST can do at 500nm.

An earth-sized planet at the same distance is 2 orders of magnitude smaller!!

So, a single telescope would need to be 1000 times bigger than HST - and that would only give you the resolving power, you'd still have to see the small planet in the glare of the bright star.

As fando points out, you'll need to use interferometric techniques to improve the resolving power. And the glare can be abated in several ways - coronography, aperture masks, etc.