The moon still has much to tell us about the origin and development of the solar system. It also has scientific value as a platform for observational astronomy
By Ian Crawford, Professor of Planetary Sciences and Astrobiology, Birkbeck, University of London, Honorary Associate Professor, UCL
Lunar exploration is undergoing a renaissance. Dozens of tasks, organized by many space agencies - and increasingly also by commercial companies - are planned to reach the moon by the end of this decade. Most will involve small robotic spacecraft, but NASA's ambitious Artemis program aims to return humans to the lunar surface by mid-decade, and the Chinese also have a similarly ambitious plan.
There are various reasons for all this activity, including geopolitical competitions and the search for lunar resources, such as Water-ice at the lunar poles, which can be extracted and turned into hydrogen and oxygen fuel for rockets. However, science should be the main beneficiary.
To the moon There is still much to tell us On the origin and development of the solar system. It also has scientific value as a platform for observational astronomy.
The potential role of the Earth's natural satellite as a platform for placing telescopes is discussed At a meeting of the Royal Society earlier this year. The meeting itself took place, in part, thanks to the improved lunar approach now expected.
Side benefits are far
Some areas of astronomy will benefit. The most prominent field is radio astronomy, which can be performed from the side of the Moon that always faces away from Earth.
The far side of the moon is permanently shielded from the radio signals generated by humans on Earth, and during the lunar night it is also shielded from the sun. These characteristics make it probable to the "quietest place on the radio" in the entire solar system, for no other planet or moon has a side which is permanently hidden from the earth. It is therefore ideally suited for radio astronomy.
Radio waves are a type of electromagnetic energy - like, for example, infrared waves, ultraviolet and visible light. All these types of radiation are defined by different wavelengths in the electromagnetic spectrum.
Radio waves whose wavelengths are longer than about 15 meters are blocked by the ionosphere of the earth. But radio waves at these wavelengths reach the surface of the moon without interference. For astronomers, this is the last unexplored region of the electromagnetic spectrum, and it can best be explored from the far side of the Moon.
Observations of the universe at these wavelengths come under the umbrella of "low frequency radio astronomy". These wavelengths are uniquely capable of probing the structure of the early universe, particularly the “The Middle Ages"The Cosmic - an era that occurred before the formation of the first galaxies.
At that age most of the matter in the universe, except the dark matter The mysterious, was in the form of neutral hydrogen atoms. These atoms emit and absorb radiation with a characteristic wavelength of 21 cm. Radio astronomers have been using this feature to study hydrogen clouds in our Milky Way Galaxy since the XNUMXs.
Because the universe is constantly expanding, the 21 cm wavelength signal produced by hydrogen in the early universe was shifted to much longer wavelengths. As a result, hydrogen from the cosmic "middle ages" will appear before us at wavelengths greater than 10 meters. The far side of the moon may be the only place we can explore this.
Astronomer Jack Burns provided a good summary of The scientific background relevant at the last meeting of the Royal Society, and called the far side of the moon "a pristine and quiet platform for making low radio frequency observations of the dark ages of the early universe, as well as space weather and magnetospheres associated with habitable exoplanets."
Signals from other stars
As Burns says, another potential application of radio astronomy on the far side is trying to detect radio waves from charged particles trapped in magnetic fields - Magnetospheres – of planets orbiting other stars.
This will help assess how capable these planets are of hosting life. Radio waves from the magnetospheres of extrasolar planets will likely have wavelengths greater than 100 meters, so they will need a radio quiet environment in space. Again, the far side of the moon would be the best location.
A similar argument can be made regarding Attempts to detect signals from intelligent aliens. And by opening up an unexplored part of the radio spectrum, there is also the possibility of making random discoveries of new phenomena.
We should get an indication of the potential of these observations when NASA's LuSEE-Night mission It will land on the far side of the moon in 2025 or 2026.
The depth of the crater
The Moon also offers opportunities for other types of astronomy. Astronomers have extensive experience with optical and infrared telescopes operating in free space, such as Hubble telescope ו– Web. However, the stability of the lunar surface may provide advantages for such devices.
Furthermore, there are Makhteshim At the lunar poles that do not receive sunlight. Telescopes that observe the universe at infrared wavelengths are very sensitive to heat and therefore need to operate at low temperatures. James Webb, for example, needs a huge sun visor that protects him from the sun's rays. On the Moon, a natural crater rim can provide this shielding for free.
The moon's low gravity may also allow it Building much larger telescopes than is possible with satellites. These considerations led the astronomer Jean-Pierre Millard to suggest that the moon might be The future of infrared astronomy.
The cold and stable environment of permanently shadowed craters may also have advantages for the next generation of detection instruments Gravitational waves - "ripples" in space-time caused by processes such as exploding stars and colliding black holes.
Furthermore, for billions of years the Moon has been bombarded by charged particles from the Sun - the solar wind - and galactic cosmic rays. The lunar surface may contain Rich documentation of these processes. Their investigation may yield insights into the evolution of the Sun and the Milky Way.
For all these reasons, astronomy stands to benefit from the current renaissance in lunar exploration. In particular, astronomy may benefit from the infrastructure that will be built on the moon as lunar exploration progresses. This will include both transportation infrastructure – rockets, landers and other vehicles – to access the surface, as well as humans and robots on site to build and maintain astronomical instruments.
But there's also tension here: Human activity on the far side of the moon could create unwanted radio interference, and plans to extract water ice from shadowy craters could make those craters difficult to use for astronomy. As my colleagues and I They claimed Finally, we will need to ensure that lunar sites of unique astronomical value are protected in this new era of lunar exploration.
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