why not build a scope big enough to view extrasolar planets?

im wondering, besides costs, is there any reason why some organization could not put a 20 or 50 meter scope into space to look for extrasolar planets? are their physical limitations that prevent this rather than monetary ones?

Nope, you hit the nail on the head about cost! Besides, you wouldn't need a 50 meter scope in space for that. The ability to 'see' through a vaccuum means a scope in space can be a third the size of its terrestrial-bound counterpart.

In your example, a scope that big would let you see such planets way beyond the need to see them! I mean, is it the signs for planets, or habitable environments you want to look for with such a huge scope? If you were to successfully get such a huge scope into orbit to look for the environment part, you'd only be able to go about a couple light years away at best. And so far, no planets of any kind have been found that close. That's is what makes our sun so unique - of about 10 close stellar neighbours, it ranks practically 1st in the standings for main sequence and planet harbouring capabilities.

Seanie.

so a huge scope like that wouldnt do away with the indirect methods of searching for extra solar planets , like finding a tiny wobble in the star,or an overall dimming of the star? or perhaps when a planet with those methods is detected, the giant scope could be aimed in that direction?

Well, for distant solar candidates, that what they look for. There have been a few instances where larger planets have been directly observed, but they are very close (I think Formalhaut's companian is a good example, as it is only 25 lightyears away). For closer ones, yes, optically there is a good chance to 'see' the planet. More distant objects, it is indirect methods of detection that is needed.

When it comes right down to it the ultimate observatory is a spaceship, even a robotic one, if we ever get around to building any before we kill ourselves off. Nothing is ever going to be as good as the range of possibilities offered by observation from interplanetary distances, or better yet from orbit.

What we need is a fleet of AI-piloted deep space rangers flitting (relatively speaking) from star to star and reporting their results using high powered directional transmissions (possibly laser). We'd certainly lose a few along the way and they would all eventually come to a sticky end far from home, but the fleet as a whole would return enough data to keep the scientists busy for a thousand years once they started reporting in.

thats a really cool idea!!!