Here’s a Planetary Society report on the making of one of the seven mirrors for the Giant Magellan Telescope, which should become operational in 2020.
From the caption:
After spending three months cooling, the GMT’s third mirror was removed from its rotating furnace on Dec. 6, 2013 and unveiled at the University of Arizona Steward Observatory Mirror Lab. It will take another three years for the mirror to be polished to extremely high precision. If the finished mirror were enlarged to cover the continental U.S., the peak-to-valley variance in smoothness would only be a half-inch.
The GMT’s seven 8.4 meter mirrors and adaptive optics system will give it ten times the resolution and sensitivity of the Hubble Space Telescope. It will be able to measure the mass of exoplanets and determine the composition of their atmospheres.
If life exists on one of the 1,000 currently known exoplanets, the GMT may be able to see indicators of life like ozone and chlorophyll in the exoplanet’s atmosphere. Such a game-changing discovery could tell us Earth is not the only planet in the Universe with life.