Is Astrophotonics The Key To Discovering Alien Life?

By John Oncea, Editor

Astrophotonics has the potential to revolutionize exoplanet research and, quite possibly, help discover alien life.

I’m not gonna lie – my head about exploded when discussing what to write about this month with all-around good guy Geoff Tecza and he suggested a technology that could be key to finding alien life. I mean, I’m definitely going to look into anything that might help me track down Gordon Shumway.

What Geoff was talking about was astrophotonics, a rapidly developing field that uses photonic technologies to improve the collection and processing of light and is helping astronomers detect and characterize exoplanets and other planets. And, of course, might help find Alf.

The Rise Of Astrophotonics

Astrophysical research requires a broad foundation of knowledge in fundamental physics and, at the same time, familiarity with astronomical data and phenomenology. The application of astrophysical research has confirmed the existence of over 5,400 exoplanets orbiting distant stars.

These planets, according to a team of researchers led by Nemanja Jovanovic, come in a variety of sizes and compositions, as to the configurations of the systems they reside in, the great majority of which do not resemble our solar system.

Some of those 5,400+ planets, such as 51 Pegasi b which was confirmed as an exoplanet in 1995, were discovered using the wobble method which measures changes in a star’s radial velocity. “The wavelengths of starlight are alternately squeezed and stretched as a star moves slightly closer, then slightly farther away from us,” explains Exoplanet Exploration. “Those gyrations are caused by gravitational tugs, this way and that, from orbiting planets.”

NASA’s Kepler Space Telescope brought with it a new method of planet hunting. “Kepler settled into an Earth-trailing orbit, then fixed its gaze on a small patch of sky, Exoplanet Exploration writes. “It stared at that patch for four years.”

What Kepler found was 150,000 stars, revealed when Kepler caught tiny dips in the amount of light coming from individual stars, caused by planets crossing in front of them, a process called the transit method. Once detected, the planet's orbital size can be calculated from the period (how long it takes the planet to orbit once around the star) and the mass of the star. NASA’s Transiting Exoplanet Survey Satellite employs the same technique, as do the Spitzer and Hubble space telescopes which have discovered exoplanets and revealed more information about what they’re like.

Next up, NASA’s James Webb space telescope which has several powerful spectrographs that can be used to look at newly forming planetary systems and identify the unique signatures of molecules in space. “It's a technique known as ‘transit spectroscopy,’ when light from a star travels through the atmosphere of an orbiting planet and reaches our telescopes – in space or on the ground – and tells about where it's been,” Exoplanet Exploration writes. By using this technique, Hubble detected helium and water vapor in exoplanet atmospheres and more detailed profiles of exoplanet atmospheres are expected.

“Unfortunately, only a handful of the known planets have been characterized spectroscopically thus far, leaving a gaping void in our understanding of planetary formation processes and planetary types,” writes Jovanovic’s research team. “To make progress, astronomers studying exoplanets will need new and innovative technical solutions.” This includes astrophotonics, which replaces the bulk optics of traditional instruments, such as lenses, mirrors, and diffraction gratings, with devices embedded within waveguides.

Not So Fast, There Are Some Problems

“Although spectroscopy is the ideal way to profile the chemical composure of such a planet, having a massive, extremely bright star right next to the planet is more than enough to completely overpower the faint light reflecting off the planet’s surface and through its atmosphere,” writes Hackaday. “This is a major issue that the upcoming Habitable Exoplanet Imaging Mission hopes to address using a range of technologies, including a coronagraph that should block out most of the stellar glare.”

While the use of a coronagraph should solve that issue, others need to be addressed. These include accurately measuring the chemical makeup of a planet's atmosphere and improving the precision of detecting planet transit events. To achieve this, researchers are using semiconductor-based laser frequency combs, which are combined with a spectral flattener to create a more compact and efficient system. With this technology, it may be possible to detect exoplanets from space rather than just from Earth.

“For profiling a planet’s spectrum, waveguide devices called photonic lanterns are used that provide an adiabatic transition of multimoded input into single-mode outputs for use by subsequent instruments,” Hackaday writes. “Such a photonic lantern is part of the SCExAO testbed at the Subaru telescope in Hawai’i, along with a photonic nulling device called GLINT. The purpose of GLINT is as the device type suggests there to reduce the impact of photonic noise from the star’s light that will still leak past the coronagraph.”

While it may provide beautiful images of distant celestial objects, astrophotonics brings something far more exciting: the ability to conduct remote spectroscopy on the atmosphere of exoplanets and gather data about their orbit and other details that are currently beyond our technological capabilities.

Technologies, Instruments, And Applications

Astrophotonics is where observational, theoretical, and computational techniques meet the emission, transmission, processing, and detection of light writes Jonathan Hawthorn, Federation Fellow, Professor of Physics at the University of Sydney.

While the rate of advance made in astrophotonics during the past decade has “been astonishing,” Hawthorn writes, “The next 10 years will see the development of concepts that are currently in their infancy such as space photonics, integration of photonic spectrographs into large high-resolution wide bandwidth replicated spectrographs, arrayed waveguides acting as dispersers but with a much smaller footprint than classical dispersive elements (diffraction gratings), further development of OH suppression into a commonplace major instrument, fiber scramblers to stabilize the illumination from a fiber for precise radial velocity work (e.g. exoplanet detection), frequency combs, optical circulators, ring resonator filters, forked gratings, sub-lambda gratings, spatial light modulators, and more.”

Many of the biggest technological advancements in the coming decade and beyond will be spurred by the need for smaller instrument solutions for the next generation of extremely large telescopes. While astrophotonics has numerous applications in astronomy, the devices developed through this field also can be applied in other areas such as communication and medicine.

“Historically, photonics’ primary application has been in the telecommunications industry. Astrophotonics takes photonics such as optical fibers and planar waveguides and uses them for astronomical purposes,” Hawthorn writes. “Many of the technologies that have been developed by astrophotonics researchers are a direct result of a problem faced by the astronomical and astrophysics community. As a result, the fields are intimately intertwined.”

The cost of increasing telescope size and the implementation of photonic functions in new instrument designs are the two main drivers behind photonics technologies in astronomy. To detect fainter or more distant targets with higher spatial and spectral resolution, telescopes need to be larger, which leads to larger and more expensive optics and components. However, astrophotonics can break this cost cycle by miniaturizing instruments, enabling multiplexing on a much larger scale, and making technological advancements and photonic functions possible in astronomical instrumentation that were not previously available.

Now, Let’s Find Alien Life

As alluded to above, astrophotonic technologies are already being used by researchers in observatories to detect and even characterize the properties of exoplanets. For instance, writes Vice, “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.”

Work is underway to integrate complex photonics devices into and solve scalability problems associated with astronomical instruments, a process 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.”

Jovanovic added that doing this can be inefficient, but the process is gradually improving as different technologies are integrated. That said, there is still extensive data lost.

As these inefficiencies are resolved certain astrophotonic technologies will come to the forefront in the search for alien 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,” Vice writes. “Photonics could also help to miniaturize astronomical instruments on spacecraft, potentially allowing for much more scientifically productive missions.”

 

Jovanovic and his team have been exploring techniques that might be useful to the Habitable Worlds Observatory. Still in the conceptual stage, the Habitable World Observatory – if greenlit – “Would seek to find a few dozen worlds that are similar to Earth, and that also orbit stars similar to the Sun.”

“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.”