Scientists have outlined a new approach to the search for alien life that emphasizes the role of “astrophotonics,” an emerging field that applies photonic technologies to astronomical instruments with the aim of developing unprecedented observational capabilities, reports a new study.
Photonics is a subfield of optics that is especially focused on the practical applications of light particles, known as photons, in science and technology. When merged with astronomy, photonic techniques can expose a variety of hidden insights in light captured from outer space, and can also help to make instruments smaller and more practical for space missions, among many other advantages.
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Astrophotonics is already revolutionizing our view of exoplanets, which are worlds that orbit other stars, and the field could provide vital support in the hunt for extraterrestrial life beyond Earth, according to a study published last week on the preprint server arXiv. The work was led by Nem Jovanovic, an astrophotonics expert at Caltech, who recently presented it at the SPIE Optics + Photonics Exhibition in San Diego.
“Because I have a photonics background, I’ve always been looking at ways of bringing photonics and these micro-components with really cool functionalities, into astronomy,” Jovanovic told Motherboard in a call. “It’s not trivial. It’s rather challenging because the astronomy requirements are extremely demanding.”
“However, there is a small community of people that do both fields, photonics and astronomy, and it’s growing over time,” he added. “The technology is becoming more advanced and we’re understanding that it can play a unique role in both astronomy but specifically exoplanet science.”
Indeed, many astrophotonic technologies have already been implemented into observatories that can detect exoplanets, and even characterize some of their properties. For instance, Jovanovic and his colleagues point to the increasingly common use of laser frequency combs, a photonic system that can detect minute changes in a star’s velocity caused by the gravitational tug of a nearby planet. Another example is the European Southern Observatory’s Gravity instrument at the Very Large Telescope in Chile, which achieves high resolution of all kinds of space phenomena, including exoplanets, by combining light from four 8-meter telescopes through a photonic interferometer.
But while some astrophotonic technologies are rapidly maturing, specialists have identified several areas of the field that require more focus and resources, which were recently compiled into an expansive roadmap, led by Jovanovic, published in JPhys Photonics. Experts are currently figuring out how to solve scalability problems and how to integrate complex photonics devices into astronomical instruments, which Jovanovic calls “hybridization.”
“Each photonic technology can give you some functionality, and some advantage and benefit, but it’s not clear that there’s any one photonic technology that can give you all of them at once,” he said. “What you end up having to do is use disparate materials and different fabrication processes—so you might use silicon optical fibers and silicon nitride photonics, or whatever—and you want to put them together. Every time there’s an interface between them, you need to somehow channel the light efficiently between them.”
“That can be inefficient these days,” Jovanovic continued. “It’s getting better. People are hybridizing more and more with different technologies but it’s still a massive source of loss, and in astronomy, we count every single photon. I think over the next decade, that will be one area that industry will naturally just make huge inroads into that we will benefit from.”
While the recent roadmap outlines broad trends in the field, the new arXiv preprint focuses specifically on astrophotonic technologies that are most relevant to the search for extraterrestrial life. These include spectrographs, which break up light into tiny prismatic parts, or devices used for “photonic nulling” that block out the glare of starlight so that astronomers can isolate the reflected glow of exoplanets. Photonics could also help to miniaturize astronomical instruments on spacecraft, potentially allowing for much more scientifically productive missions.
In particular, the team explored techniques that might be useful to the Habitable Worlds Observatory, a major concept mission that, if greenlit, would seek to find a few dozen worlds that are similar to Earth, and that also orbit stars similar to the Sun. While the first step is actually detecting these worlds, Jovanovic and his colleagues are already figuring out how photonics could help spot signs of life on them.
“I would love to see a photonic spectrograph in a decade from now with the performance characteristics needed for several astronomy projects, including the Habitable Worlds Observatory so that it could be a realistic payload on that mission,” Jovanovic said. “And that’s something that we’re working on here at Caltech, amongst many other things.”
“The universe is clearly a very complex place, with lots going on, and every new instrument we build, we discover more about the universe,” he concluded. “I’m motivated by discovering these things that are really at the limits of human knowledge.”
