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A Scope That Takes Mirror Size to the Max

Astronomers have peered into their crystal ball and seen a lot of glass: a telescope with a 30- to 50-meter mirror, on which the largest telescopes being built today would fit like so many crackers on a plate. At the Maximum-Aperture Telescope (MAXAT) workshop in Madison, Wisconsin, last week, they discussed the feasibility and scientific justification for a mammoth ground-based telescope costing up to $1 billion. Now the enthusiasts hope to win over their colleagues, especially those who will prepare U.S. astronomy's official list of spending priorities for 2000 to 2010.

The largest telescopes being built today, with mirrors spanning 8 to 10 meters, will lose much of their sparkle over that period if the proposed Next Generation Space Telescope (NGST) is launched, boasting a 4- to 8-meter mirror and the distortion-free seeing of space. But MAXAT could surpass the light-gathering power of NGST by 15- to 150-fold. That would open new vistas, especially in the near-infrared part of the spectrum, where astronomers can best correct for atmospheric blurring. MAXAT could take high-resolution spectra of distant galaxies and "decompose them into their building blocks," says Frank Bash of the University of Texas, Austin. The giant scope also might spy the first supernovae ever to explode, study the life histories of stars, and spot planets around other stars. If NGST gets off the ground, MAXAT would complement it, say advocates. "Once NGST is flying, this is the next obvious facility," says Matt Mountain, director of the multinational Gemini 8-Meter Telescopes.

The biggest challenge would not be MAXAT's gargantuan mirror, which would be a mosaic of hundreds of segments. Developing the adaptive optics controls that would adjust the telescope's optics to compensate for Earth's rippling blanket of air will be more demanding. But cost is likely to be the biggest hurdle of all. Workshop participants said NASA and the National Science Foundation are unlikely to foot the bill alone--especially with NGST in the pipeline. "Our feeling was that this would have to be a world telescope," Mountain says.

Astronomers in Europe already are thinking along the same lines--or even grander ones. Roberto Gilmozzi of the European Southern Observatory in Garching, Germany, for example is pushing his vision of a 100-meter behemoth, dubbed OWL for "overwhelmingly large."