There are various reasons for all this activity, including geopolitical posturing and the search for lunar resources, such as water-ice at the lunar poles, which can be extracted and turned into hydrogen and oxygen propellant for rockets. However, science is also sure to be a major beneficiary.

The moon still has much to tell us about the origin and evolution of the solar system. It also has scientific value as a platform for observational astronomy.

The potential role for astronomy on Earth’s natural satellite was discussed at a Royal Society meeting earlier this year. The meeting itself had, in part, been sparked by the enhanced access to the lunar surface now in prospect.

Far Side Benefits

Several types of astronomy would benefit. The most obvious is radio astronomy, which can be conducted from the side of the moon that always faces away from Earth—the far side.

The lunar far side is permanently shielded from the radio signals generated by humans on Earth. During the lunar night, it is also protected from the sun. These characteristics make it probably the most “radio-quiet” location in the whole solar system as no other planet or moon has a side that permanently faces away from the Earth. It is therefore ideally suited for radio astronomy.

Radio waves are a form of electromagnetic energy—as are, for example, infrared, ultraviolet, and visible-light waves. They are defined by having different wavelengths in the electromagnetic spectrum.

Radio waves with wavelengths longer than about 15 meters are blocked by Earth’s ionosphere. But radio waves at these wavelengths reach the moon’s surface unimpeded. For astronomy, this is the last unexplored region of the electromagnetic spectrum, and it is best studied from the lunar far side.

Observations of the cosmos at these wavelengths come under the umbrella of “low-frequency radio astronomy.” These wavelengths are uniquely able to probe the structure of the early universe, especially the cosmic “dark ages”—an era before the first galaxies formed.

At that time, most of the matter in the universe, excluding the mysterious dark matter, was in the form of neutral hydrogen atoms. These emit and absorb radiation with a characteristic wavelength of 21 centimeters. Radio astronomers have been using this property to study hydrogen clouds in our own galaxy—the Milky Way—since the 1950s.

Because the universe is constantly expanding, the 21-centimeter signal generated by hydrogen in the early universe has been shifted to much longer wavelengths. As a result, hydrogen from the cosmic “dark ages” will appear to us with wavelengths greater than 10 meters. The lunar far side may be the only place where we can study this.

The astronomer Jack Burns provided a good summary of the relevant science background at the recent Royal Society meeting, calling the far side of the moon a “pristine, quiet platform to conduct low-radio-frequency observations of the early Universe’s Dark Ages, as well as space weather and magnetospheres associated with habitable exoplanets.”

Signals From Other Stars

As Burns says, another potential application of far side radio astronomy is trying to detect radio waves from charged particles trapped by magnetic fields—magnetospheres—of planets orbiting other stars.

This would help to assess how capable these exoplanets are of hosting life. Radio waves from exoplanet magnetospheres would probably have wavelengths greater than 100 meters, so they would require a radio-quiet environment in space. Again, the far side of the moon will be the best location.

A similar argument can be made for 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 serendipitous discoveries of new phenomena.

We should get an indication of the potential of these observations when NASA’s LuSEE-Night mission lands on the lunar far side in 2025 or 2026.

Crater Depths

The moon also offers opportunities for other types of astronomy as well. Astronomers have lots of experience with optical and infrared telescopes operating in free space, such as the Hubble telescope and JWST. However, the stability of the lunar surface may confer advantages for these types of instruments.

Moreover, there are craters at the lunar poles that receive no sunlight. Telescopes that observe the universe at infrared wavelengths are very sensitive to heat and therefore have to operate at low temperatures. JWST, for example, needs a huge sunshield to protect it from the sun’s rays. On the moon, a natural crater rim could provide this shielding for free.

The moon’s low gravity may also enable the construction of much larger telescopes than is feasible for free-flying satellites. These considerations have led the astronomer Jean-Pierre Maillard to suggest that the moon may be the future of infrared astronomy.

The cold, stable environment of permanently shadowed craters may also have advantages for the next generation of instruments to detect gravitational waves—“ripples” in space-time caused by processes such as exploding stars and colliding black holes.

Moreover, for billions of years the moon has been bombarded by charged particles from the sun—solar wind—and galactic cosmic rays. The lunar surface may contain a rich record of these processes. Studying them could yield insights into the evolution of both the sun and the Milky Way.

For all these reasons, astronomy stands to benefit from the current renaissance in lunar exploration. In particular, astronomy is likely to benefit from the infrastructure built up on the moon as lunar exploration proceeds. This will include both transportation infrastructure—rockets, landers, and other vehicles—to access the surface, as well as humans and robots on-site to construct and maintain astronomical instruments.

But there is also a tension here: human activities on the lunar far side may create unwanted radio interference, and plans to extract water-ice from shadowed craters might make it difficult for those same craters to be used for astronomy. As my colleagues and I recently argued, we will need to ensure that lunar locations that are uniquely valuable for astronomy are protected in this new age of lunar exploration.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Image Credit: NASA / Ernie Wright

The problem is that even the nearest stars are a very long way away, and enormous engineering efforts will be required to reach them on timescales that are relevant to us. But with research in areas such as nuclear fusion and nanotechnology advancing rapidly, we may not be as far away from constructing small, fast interstellar space probes as we think.

Scientific and societal case

There’s a lot at stake. If we ever found evidence suggesting that life might exist on a planet orbiting a nearby star, we would most likely need to go there to get definitive proof and learn more about its underlying biochemistry and evolutionary history. This would require transporting sophisticated scientific instruments across interstellar space.

But there are other reasons, too, such as the cultural rewards we would get from the unprecedented expansion of human experience. And should it turn out that life is rare in our galaxy, it would offer opportunities for us humans to colonize other worlds. This would allow us to spread and diversify through the cosmos, greatly increasing the long-term survival chances of Homo sapiens and our evolutionary descendants.

Five spacecraft — Pioneers 10 and 11, Voyagers 1 and 2, and New Horizons — are currently leaving the solar system for interstellar space. However, they will cease to function many millennia before they approach another star, should they ever get to one at all.

Clearly, if starships are to ever become a practical reality, they will need to be based on far more energetic propulsion technologies than the chemical rockets and gravitational sling shots past giant planets that we use currently.

To reach a nearby star on a timescale of decades rather than millennia, a spacecraft would have to travel at a significant fraction — ideally about 10% — of the speed of light (the Voyager probes are traveling at about 0.005%). Such speeds are certainly possible in principle — and we wouldn’t have to invent new physics such as “warp drives,” a hypothetical propulsion technology to travel faster than light, or “wormholes” in space, as portrayed in the movie Interstellar.

Top rocket-design contenders

Over the years, scientists have worked out a number of propulsion designs that might be able to accelerate space vehicles to these velocities (I outline several in this journal article). While many of these designs would be difficult to construct today, as nanotechnology progresses and scientific payloads can be made ever smaller and lighter, the energies required to accelerate them to the required velocities will decrease.

The most well thought through interstellar propulsion concept is the nuclear rocket, which would use the energy released when fusing together or splitting up atomic nuclei for propulsion.

Spacecraft using “light-sails” pushed by lasers based in the solar system are also a possibility. However, for scientifically useful payloads this would probably require lasers concentrating more power than the current electrical generating capacity of the entire world. We would probably need to construct vast solar arrays in space to gather the necessary energy from the sun to power these lasers.

Another proposed design is an antimatter rocket. Every sub-atomic particle has an antimatter companion that is virtually identical to itself, but with the opposite charge. When a particle and its antiparticle meet, they annihilate each other while releasing a huge amount of energy that could be used for propulsion. However, we currently cannot produce and store enough antimatter for this to work.

Interstellar ramjets, fusion rockets using enormous electromagnetic fields as a ram scoop to collect and compress interstellar hydrogen for a fusion drive are another possibility, but these would probably be yet harder to construct.

The most well developed proposal for rapid interstellar travel is the nuclear-fusion rocket concept described in the Project Daedalus study, conducted by the British Interplanetary Society in the late 1970s. This rocket would be capable of accelerating a 450 tonne payload to about 12% of the speed of light (which would get to the nearest star in about 36 years). The concept is currently being revisited and updated by the ongoing Project Icarus study. Unlike Daedalus, Icarus will be designed to slow down at its destination, permitting scientific instruments to make detailed measurements of the target star and planets.

All current starship concepts are designed to be built in space. They would be too large and potentially dangerous to launch from Earth. What’s more, to get enough energy to propel them we would need to learn to collect and manage large amounts of sunlight or mine rare nuclear isotopes for nuclear fusion from other planets. This means that interstellar space travel is only likely to become practical once humanity has become a spacefaring species.

The road to the stars therefore begins here — by gradually building up our capabilities. We need to progressively move on from the International Space Station to building outposts and colonies on the Moon and Mars (as already envisaged in the Global Exploration Roadmap). We then need to begin mining asteroids for raw materials. Then, perhaps sometime in the middle of the 22nd century, we may be prepared for the great leap across interstellar space and reap the scientific and cultural rewards that will result.

Ian Crawford, Professor of Planetary Science and Astrobiology, Birkbeck, University of London

Disclosure Statement: Ian Crawford is a scientific consultant for Project Icarus.

This article was originally published on The Conversation. Read the original article.

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