A major part of finding extraterrestrial life is to be able to profile the atmosphere of any planets outside of our solar system. This is not an easy task, as these planets are usually found through the slight darkening of their star as they pass in front of it (transition). 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. This is a major issue that the upcoming Habitable Exoplanet Imaging Mission (HabEx, also called the Habitable Worlds Observatory, or HWO) hopes to address using a range of technologies, including a coronagraph that should block out most of the stellar glare.
While this solves much of the issue, there are still a range of issues which the new field of astrophotonics seeks to address, as detailed in a recent paper by Nemanja Jovanovic and colleagues. This involves not only profiling chemical compositions, but also increasing the precision when monitoring for planet transit events using e.g. semiconductors-based laser frequency combs. These are generally combined with a spectral flattener, which in experimental on-chip form are significantly less bulky than previous setups, to the point where they don’t necessarily have to be Earth-based.
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. 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 coronograph.
Although probably not as exciting a subject as pretty pictures of remote galactic phenomena, the field of astrophotonics could provide us with something that’s possibly far more exciting, in the form of being able to perform remote spectroscopy on an exoplanet’s atmosphere and more, along with recording details about its orbit and the like that are far beyond our capabilities today.
(Heading image: Artist’s concept of an Earth-like planet in the habitable zone of its star. Credit: NASA Ames/JPL-Caltech/T. Pyle)