We should be categorical here: the question if we are alone in the Universe remains yet unanswered. Nevertheless, several government bodies are now publicizing the issue with enormous coverage by the mass-media, and these facts has also motivated my attention to the problem from a scientific perspective.
Source: https://www.dni.gov/files/ODNI/documents/assessments/Prelimary-Assessment-UAP-20210625.pdf
Are the Unidentified Aerial Phenomena (or UAPs) — or formerly known as Unidentified Flying Objects (or UFOs) — spacecrafts of extraterrestrial civilizations? This question cannot be yet answered, for obvious reasons, but we can speculate and brainstorm on the challenge of deploying a spacecraft to travel interstellar distances.
Of course, a major branch of such a challenge is materials science. The design and selection of materials to compose a light-speed-fast-moving (or higher?) object relies on the mind of a meticulous alien materials scientist or engineer.
I imagine that if the aliens were planning to build a spacecraft, they will face the same challenges we have to build our own spacecraft and probes. The criteria to select a material to compose a spacecraft has been precisely summarized by Miria M. Finckenor, a scientist working at NASA’s Marshall Space Center.
Which kind of metallic alloys (if they are metallic alloys!) the aliens are using in their spaceships? First answer to this question is: it must be lightweight, have good strength and ductility and most important… it has to be radiation tolerant.
Well, interstellar travel will subject such a spaceship to huge amounts of stellar-radiation, not only in our solar system, but everywhere in the galaxy and in the universe. For example, thermonuclear instabilities in the Sun’s corona are known to be the source of huge amounts of light ions (protons and He) that travel throughout the solar system up to the heliopause. Although not very high fluxes in normal solar activity conditions, the energy is so high (a couple of MeVs) that can cause damage in the crystal structure of most materials we know.
I remain skeptical about us being visited by alien civilizations. The technical and scientific challenges are so huge, that we as humans not even yet started to deeply address. If these aliens are able to travel astronomical distances in short period of time I would be glad to know the status of their knowledge on materials science. Perhaps someone could ship me a sample of their spacecraft material?
Extraordinary discoveries require extraordinary evidence…
Materials at Extremes 