Astronomers from the University of Texas at Austin want to build a telescope on the moon.
Scientists already proposed that idea to NASA years ago, to no avail.
This telescope, nicknamed the “Ultimately Large Telescope,” could be different.
In 2008, a group of astronomers from around the world came to NASA with a wild idea: Why not put a giant telescope on the moon?
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The unbelievably large telescope, called the Lunar Liquid Mirror Telescope (LLMT), would have used a large spinning mirror made of liquid and be placed on one of the moon’s poles to study the earliest stars born in the universe.
The telescope was ahead of its time—so much so that NASA scrapped the idea because there wasn't enough supporting evidence for the existence of the ancient stars the telescope planned to study. But now, more than a decade later, astronomers from the University of Texas at Austin have resurrected the telescope and propose to build a new LLMT, nicknamed the “Ultimately Large Telescope.”
The defining feature of the telescope would be a 328-foot-wide mirror made of liquid. Because the silver-coated glass mirrors used in traditional telescope designs are both heavy, expensive, and fragile, the team is looking to use a lighter, more transportable liquid mirror instead.
The mirror would consist of a spinning basin of liquid, topped by another layer of reflective liquid. The telescope would sit stationary inside a crater at either of the moon’s poles and be operated remotely, receiving power from a solar panel power station nearby.
A mirror made from liquid may not be as bizarre as it sounds. One of the largest telescopes in the world, the Large Zenith Telescope (LZT) in British Columbia, Canada, is a liquid-mirror telescope. Although its 20-foot diameter would be dwarfed by the LLMT, the LZT packs a considerable punch for its price. The Canadian liquid-mirror telescope cost less than $1 million to build, which is a fraction of the price of equivalently sized solid-mirror telescopes.
"It's so simple," Ermanno F. Borra, a professor of physics who has studied liquid-mirror telescopes since 1992, told NASA. "Isaac Newton knew that any liquid, if put into a shallow container and set spinning, naturally assumes a parabolic shape—the same shape needed by a telescope mirror to bring starlight to a focus. This could be the key to making a giant lunar observatory."
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The LZT, like most liquid-mirror telescopes on Earth, uses mercury as its reflective liquid. Mercury, which is a metallic liquid at room temperature, reflects almost 75 percent of the light it receives, making it almost as effective as silver-coated mirrors. However, mercury would be unusable on the surface of the moon. It would quickly turn to solid from the moon’s frigid temperatures and would easily evaporate when exposed to lunar vacuum.
One solution may be organic compounds known as ionic liquid salts. As Borra explained to NASA, ionic liquids evaporation rates are nearly zero and can remain liquid at the very low temperatures you would find inside a crater of the moon. Ionic salts are also much less dense than mercury and closer to the density of water, giving them a significant weight advantage. One big drawback? Ionic liquid salts aren't highly reflective alone. To remedy this, engineers could coat the liquid with a thin layer of silver only nanometers thick.
The astronomers, led by Anna Schauer, a NASA Hubble Fellow, hope to study some of the first stars formed after the Big Bang, more than 13 billion years ago. These stars, born from the hydrogen and helium gasses that clouded the early universe, are likely 10 to 100 times larger than our sun and would be found in the furthest reaches of the observable universe.
"We live in a universe of stars," Volker Bromm, a professor of astronomy at the University of Texas, said in a press release. He continued:
"It is a key question how star formation got going early in cosmic history. The emergence of the first stars marks a crucial transition in the history of the universe, when the primordial conditions set by the Big Bang gave way to an ever-increasing cosmic complexity, eventually bringing life to planets, life, and intelligent beings like us."
Throughout history, astronomers have built bigger and better telescopes to peer deeper into the universe, and in effect, further back in time. The James Webb Space Telescope (JWST), considered by many to be the Hubble Space Telescope’s successor, will soon be launched into space to observe the formation of the universe’s first galaxies. However, even this technological marvel won't be able to view the dim stars Bromm and his colleagues are searching for.
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This led Schauer to reanimate the telescope proposal scrapped by NASA more than a decade before. The scientists investigated the ability for the new Ultimately Large Telescope to study the first stars and will publish their results in the upcoming issue of The Astrophysical Journal.
"This moment of first light lies beyond the capabilities of current or near-future telescopes," said Bromm. "It is therefore important to think about the 'ultimate' telescope, one that is capable of directly observing those elusive first stars at the edge of time."
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