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A 100 meter rotating floating mirror telescope on the moon? Yes please.



In the years to come, some truly amazing next generation telescopes will gather their first lights. Between space telescopes as James Webb and Nancy Grace Romanand terrestrial telescopes such as the Extremely Large Telescope (ELT) and the Giant Magellan Telescope (GMT), astronomers will be able to study aspects of the universe that were previously inaccessible.

For example, there are Population III stars, which are the first stars formed in the universe. These stars cannot be observed in visible light, and even the next generation of facilities (like those mentioned above) will not be able to see them. But according to a team led by NASA Hubble Fellow Anna Schauer, the solution could be to build what she has named the “Ultimately Large Telescope”

; (ULT) on the Moon.

This idea, which was stored by NASA a decade ago, was put forward by Schauer and her colleagues from the University of Texas at Austin in a recent article to be published in an upcoming issue of The Astrophysical Journal. It requires a floating mirror telescope measuring 100 m (~ 330 ft) in diameter and powered by a solar panel that acts autonomously on the moon’s surface and transmits data to a satellite in orbit.

Artist Impressions of the Lunar Liquid-Mirror Telescope LLMT) Credit: Steward Observatory / University of Arizona

Professor Volker Bromm, a theorist from UT Austin and co-author on paper, has studied the first stars that formed in our universe for decades. As he explained in a recent press release from the McDonald Observatory (supervised by UT Austin):

“Throughout the history of astronomy, telescopes have become more powerful, allowing us to study sources from successively earlier cosmic times – ever closer to the Big Bang. The upcoming James Webb Space Telescope [JWST] when the time when galaxies were first formed. ”

“But the theory predicts that there was an even earlier time when galaxies did not yet exist, but where individual stars were first formed – the elusive Population III stars. This moment of ‘very first light’ is beyond the capabilities of the powerful JWST and instead needs an ‘ultimate’ telescope. ”

The current scientific consensus is that the Population III stars formed a few hundred million years after the Big Bang (over 13 billion years ago). These stars, unlike those found today, were composed of hydrogen and helium and relatively short-lived (a few million years). Within the nuclei of these giant stars, heavier elements formed and became part of their outer layers, which were then blown off when these stars died.

The artist’s rendering of a starship starting from a lunar base. Credit: SpaceX

This process allowed the creation of heavy metals and silicates, which would allow the formation of the planets. It also meant that all subsequent generations of stars had higher metal content (aka. Metallicity), which astronomers use to determine the age of the stars. By studying Population III stars, astronomers revealed much about the evolution of our universe.

Unfortunately, these stars formed during what is known as the cosmic “dark ages,” when the universe was filled with clouds of gas obscuring visible and infrared light. This makes Population III stars invisible in all but parts of the near-infrared and radio spectrum, which are currently inaccessible to even our most advanced instruments.

Fortunately, calculations performed by Schauer and her colleagues show that a floating mirror telescope operating from the Moon’s surface is capable of studying these stars. The concept, originally known as the Lunar Liquid-Mirror Telescope (LLMT), was first proposed in 2008 by a team led by Roger Angel – Regents’ Professor of Astronomy and Optical Sciences at the University of Arizona.

After reviewing this proposal shortly thereafter, NASA chose not to pursue the project. According to Niv Drory, senior researcher at the McDonald Observatory and co-author of the paper, the supporting science of the earliest stars did not exist at the time. However, subsequent research into Population III stars and NASA’s plans to return to the Moon (Project Artemis) makes this proposal possible again.

https://royalsociety.org/-/media/events/2020/03/astronomy-moon/Observatory_on_the_moon-web.jpg?w=400
The artist’s concept of astronomy is performed on the surface of the Moon. Credit: NASA

Similar to LLMT, ULT would rely on liquids instead of coated glass (making it much cheaper to transport to the moon. One type of liquid will be arranged in a spinning vessel, while another metallic liquid (such as mercury, which is reflective) will would rotate continuously to keep the surface of the liquid in the proper parabolic shape to act as a mirror.

Similar to what NASA, ESA, China and other space agencies are planning – to build a lunar base in the South Pole-Aitken basin – the telescope would be located at the Moon’s polar regions (north or south). Within one of the many permanently shady craters in these regions, the OCT would be free of radio or atmospheric interference.

On top of that, it would be able to stare at the same spot of sky continuously and gather as much light in the near-infrared spectrum as possible. As Bromm summed up:

“We live in a universe of stars. It is a key question how star formation began early in cosmic history. The emergence of the first stars marks a decisive transition in the history of the universe, as the original conditions set by the Big Bang gave way to an ever-increasing cosmic complexity and eventually brought life to planets, life and intelligent beings like us.

“This moment of first light is beyond the capabilities of current or near future telescopes. It is therefore important to think of the ‘ultimate’ telescope, one that is able to directly observe the elusive first stars at the edge of time.

In this illustration, an astronaut gently climbs down the ladder and carefully places his foot on the Moon. Image credit: NASA

The Ultimate Light Telescope is one of many proposals for a lunar observatory. For example, several recommendations have been made for radio observatories to be located on the other side of the Moon. The lack of interference from terrestrial sources would not only be ideal for observing the unseen parts of the cosmos, but also in the search for extraterrestrial intelligence.

In addition, Dr. Karan Jani and Prof. Abraham Loeb – from the Laser Interferometer Gravitational Observatory (LIGO) and the Harvard-Smithsonian Center for Astrophysics (CfA), respectively – suggested that the moon would also be an ideal location for a gravitational-wave Lunar Observatory for Cosmology ( GLOC).

NASA also plans to send a small satellite called the Dark Age Polarimetry Pathfinder (DAPPER) to lunar orbit in the coming years. This joint project between UC Boulder and the National Radio Astronomy Observatory (NRAO) will build on previous work by the Wilkinson Microwave Anisotropy Probe (WMAP) to explore the early universe.

These and other proposals will have their chance to be implemented in the coming years. In addition to returning to the astronauts for the Moon in 2024, the long-term goal is with Project Artemis is to establish a program of “sustainable exploration of the moon.” Once this infrastructure is in place, permanent facilities can be built to help advance the science of space exploration!

Further reading: McDonald Observatory, arXiv


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