Current plans for flagship telescopes in the 2040s are focused on answering a simple question - are we alone? Our best telescopes to date, such as the James Webb Space Telescope (JWST) have only given us tantalizing glimpses into the atmospheres or other worlds, but not enough to truly determine whether or not life as we know it exists there. Astronomers have been waiting for technology to catch up to their dreams of what is possible in terms of new types of telescopes, and recently the W.M. Keck Institute for Space Studies released a report detailing the Large Interferometer For Exoplanets (LIFE) mission, which they hope will help provide a definitive answer to that simple question.

Exoplanets are hard to take pictures of. For one thing - they are typically very close to their host star, which is also billions of times brighter than them. One solution to that problem is to use a device called a coronagraph, which physically blocks the star's light, allowing the telescope to capture only (reflected) light coming from the planet itself. This is the technique planned for use in NASA’s Habitable World Observatory (HWO), and it's effective at capturing visible and ultraviolet light.

But there’s another type of light that’s particularly useful for hunting habitable exoplanets - mid-infrared. At these wavelengths, which monitor emitted heat, the contrast between the planet and star drops dramatically, allowing telescopes to directly observe (non-reflected) thermal light from the planet directly. But perhaps more importantly, the mid-infrared is a gold mine of potential spectral biosignatures, including ozone, methane, water, carbon dioxide, and even phosphine, a potential “capstone” biosignature in some contexts.

Fraser interviews Dr. Daniel Angerhausen about the LIFE telescope.

Building a system to capture this light is no easy feat, though. The JWST is already designed to capture infrared light, but even it was too small to effectively isolate exoplanets at the resolution required to provide a detailed picture of their atmosphere. In fact, any space telescope big enough to do so would be too bulky to fit on a rocket. So the LIFE designers suggest an alternative - formation-flying null interferometry.

Essentially they want to launch multiple spacecraft and fly them in a precise, untethered formation tens to hundreds of meters apart. They then beam the light they collect to a central collecting spacecraft, allowing it to do some fancy optical tricks to both “null” the light from the central star while also boosting the heat signature of the planet itself.

That sounds great in theory, but in practice it’s been notoriously tricky to build. LIFE isn’t the first proposed space interferometer - in fact two missions this century (Terrestrial Planet Finder-Interferometer from NASA and Darwin from ESA) have already been cancelled because the technology just wasn’t ready yet. According to the new report, though, our engineering skills have recently caught up with our imagination.

Fraser talks about the limits of the HWO

Breakthroughs in astrophotonics have shrunk what would once be a bench-sized optical instrument down to the form factor of a microchip. And the commercial space launch industry is continuing to push down launch costs for all sorts of missions. The report notes that formation flying, one of the trickiest parts of the proposed LIFE mission, is planned for a few technology demonstration missions, such as SEIRIOS and SunRISE, which will fly CubeSats in formation, in the coming years.

As the technology matures, the likelihood of the LIFE mission actually being technologically feasible improves. But what about that other life hunting mission - the HWO? The report points out that LIFE and HWO are actually great tag-team partners and look at completely separate pieces of the same puzzle. HWO will focus on visible/ultraviolet light, while LIFE will measure thermal emission in the mid-infrared to derive a planet's temperature, radius, and atmospheric composition. Combining data from both missions is critical to eliminate “false positives” where something that might look like a biosignature is actually caused by an abiotic process.

HWO is planned to launch in the 2040s, but is still undergoing its design phase. LIFE is also in development, and while the two may launch in similar timeframes, LIFE’s primary goal is to provide complementary data to HWO. The report points out that, in order to spread the funding around evenly, the LIFE project should be an international collaboration rather than reliant on a single funding source.

If the LIFE project is funded, hopefully HWO will be too. But even if not, we are finally getting to a point where we can build a system that can help us find the proof that we are not alone, and if that isn’t inspiring enough to fund these programs, it's unclear what would be.

Learn More:

S. P. Quanz et al - Exploring Exoplanets with Interferometry

UT - The Next Generation LIFE Telescope Could Detect Some Intriguing Biosignatures

UT - The LIFE Telescope Passed its First Test: It Detected Biosignatures on Earth.

UT - Future Telescopes Could Detect Life Managing their Planet Atmospheres