How big a telescope would we need to see Earth-like planets around other stars?

Hello,
You asked how big a telescope we would need to see
Earth sized planets around nearby stars. A quick
answer is that a telescope the size of Keck (10 meters)
in space might hope to image Earth sized planets -
and would certainly be able to resolve Jupiter sized
planets around nearby stars. Jupiter is about one billion
times fainter than the Sun, or about 27th magnitude in
visible wavelengths. However, by observing in infrared
wavelengths we gain a lot! There, Jupiter is only about
10,000 times fainter than the sun.
Although Keck is able to see objects that are 27th
magnitude on Earth (with a bit of work!) the Earth's
atmosphere smears out the light from the star the planet
is orbiting. That smeared up light swallows the light
from the planet (which is close by) making the planet
unobservable.
There are at least 3 techniques that are being explored
that would enable the direct observation of planets
around nearby stars from Earth. These would have to be
fairly massive planets (at least in the beginning) but
offer the hope of observing extrasolar planets - perhaps
within the next 10 years.

I hope this helps answer your question!

-With Regards,
Debra Fischer

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