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Is Earth unique, or are there other planets with life in the Milky Way? To answer this question and many others, astronomers need larger and more sensitive observatories than anything we currently have. For that reason, the Center for Astrophysics | Harvard & Smithsonian is collaborating with a number of other institutions around the world to create the Giant Magellan Telescope (GMT), currently under construction in Chile. The GMT will consist of seven large mirrors acting in concert as one giant telescope 80 feet across. That large size provides an unprecedented view of the sky and the ability to detect the chemical composition of exoplanet atmospheres. Like NASA’s Hubble Space Telescope, the GMT will be a powerful tool across the field of astronomy, providing insights into the formation of planets, the structure of galaxies, and the evolution of the universe itself.

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This artistic depiction shows what the Giant Magellan Telescope will look like when construction is completed. The finished GMT will have seven mirrors working together to focus light from distant stars and galaxies.

Credit: CfA

The Telescope and the Science

If we want to see things that are small, faint, very distant, or some combination of those, we need large and sensitive telescopes. The size of a telescope is related to its resolution — how well it can pick out details in an astronomical system — and the amount of light it can collect. The Giant Magellan Telescope will excel in both of these regards: when completed, it will have 368 square meters (nearly 4000 square feet) of mirrors to collect light. The telescope’s instruments will create images and analyze the spectrum of objects in both visible and infrared light.

The seven GMT mirrors are each 8.4 meters in diameter, arranged approximately in a hexagonal pattern. These mirrors reflect the light from astronomical sources onto secondary mirrors, which will be equipped with “adaptive optics” to correct for fluctuations in Earth’s atmosphere. The telescope is under construction on Cerro Las Campanas, a mountain in Chile, where the weather is dry and clear for more than 300 nights of the year. Together, the location, mirrors, and adaptive optics will give the GMT a resolution ten times better than that of the Hubble Space Telescope.

Even with such observational power, Earth-size exoplanets are too small for astronomers to get direct images for many of them, and even then they’ll appear as points of light. However, the GMT will bring several powerful abilities to study exoplanets. The first of these is the GMT-Consortium Large Earth Finder (G-CLEF) spectrograph, developed by CfA | Harvard & Smithsonian researchers and designed to measure the spectrum of light very precisely.

G-CLEF will be able to measure the slight wobble of a star created by the gravitational pull of an orbiting planet, which will allow astronomers to determine the mass of that planet. Current measurements of exoplanet masses are mostly limited to large worlds orbiting close in, but G-CLEF will enable to the GMT to measure masses for Earth-class planets, including possibly those in the habitable zone where liquid water could exist on the planet’s surface. The G-CLEF spectrograph will also be able to detect many important molecules in the atmospheres of exoplanets, including those created by life on Earth, such as molecular oxygen (O2).

The GMT will also study protoplanets, the progenitors of planets, to understand how worlds like ours form and what chemicals are present at their birth. In addition, astronomers will use the observatory to look for supernovas in distant galaxies, the destruction of stars by black holes, and binary white dwarfs and black holes that produce gravitational waves. The unparalleled light-collection abilities of the GMT will enable astronomers to search for the earliest galaxies in the cosmos to understand how they formed, as well as find the faintest and darkest galaxies. The GMT will be one of the most powerful telescopes in the world when completed, bringing us a wealth of new knowledge about the universe and its contents.