💰 Hundreds of millions missing to finish the GMT, the future giant telescope

The Giant Magellan Telescope (GMT) is one of the largest telescopes ever imagined. Yet, after years of work and more than a billion dollars already spent, its completion still depends on additional funding.

The optical design of the GMT is unique. Instead of a giant mirror composed of many segments, like its competitors, it uses seven primary mirrors of 28 feet (8.4 m) each, the largest ever made. This configuration offers a major advantage for adaptive optics, which corrects atmospheric disturbances.


Adaptive optics relies on seven deformable secondary mirrors, each 3.3 feet (1 m) in diameter and only 0.08 inches (2 mm) thick. Behind each mirror, about 700 small magnets, actuated by electromagnetic coils, reshape them thousands of times per second. This system cancels atmospheric blur and delivers images of exceptional sharpness.

Thanks to this technology, the GMT will be able to study exoplanets in the habitable zone of their stars. The G-CLEF instrument will detect their transit in front of their sun, while the GMag-AOx coronagraph will block starlight to analyze the planets' light.

At the other extreme, the observatory will observe distant galaxies, located 10 or 11 billion light-years away. Astronomer Gwen Rudie explains that the GMT will allow mapping for the first time the gas around these galaxies, thus linking the birth and death sites of stars to gas flows.

On the construction site, the foundations are already dug in Chile, while in Illinois, the 128-foot (39 m) high, 2,866-short-ton (2,600 t) support structure is being assembled. But the main obstacle is funding. The National Science Foundation (NSF) has capped its budget for extremely large telescopes at $1.6 billion, insufficient to support both the GMT and the Thirty Meter Telescope. The consortium president, Daniel Jaffe, indicates that 40% of the components are already in fabrication and that the consortium must be expanded to raise the more than $2 billion needed.


With a bit of luck, the three giants — GMT, ELT and TMT — will be operational by the mid-2030s. In collaboration with observatories like Rubin and the James Webb Space Telescope, they promise to transform our understanding of the Universe. Jaffe hopes that the GMT will begin its scientific observations in the 2030s, after final approval from the U.S. Congress.