At 10 microns, the wavelength at which water vapor in a planet’s atmosphere shines brightest, a sun-like star remains a million times brighter than an Earth-sized companion. That difference has long been the optical barrier interposed between astronomers and directly imaging nearby worlds that are habitable. Now, Heidi Newberg at Rensselaer Polytechnic Institute and colleagues contend that the solution does not lie in making a telescope larger, but in morphing it.
Classic space telescopes, from Hubble to the James Webb Space Telescope (JWST), use about circular mirrors. JWST’s segmented 6.5‑meter gold-coated primary mirror already strained the boundaries of what could be folded onto a rocket fairing. To see an Earth twin 30 light-years distant at 10 microns, optics theory in this case, the Rayleigh criterion requires an aperture of almost 20 meters. A round mirror of such dimensions would be an engineering and launch hassle, demanding extraordinary folding mechanisms and record deployment accuracy.
The alternative rectangular one suggested by Newberg’s group is 1 by 20 meters. Although its collecting area is in fact smaller than JWST’s roughly 20 square meters as opposed to JWST’s 25.4 its extended axis provides the vital 20‑meter baseline to allow the angular resolution to distinguish planet light from starlight. By rotating the mirror between observations, the telescope can align its long axis with the star–planet orientation in multiple directions, ensuring that no matter where a planet sits in its orbit, the light from star and planet can be disentangled.
This design sidesteps some of the most daunting barriers faced by other next-generation concepts. Interferometric arrays of several spacecraft, for instance, would involve keeping separations to accuracies on the scale of a molecule’s thickness something beyond the capabilities of today’s formation-flying technology. Starshade missions, where a distinct tens‑of‑meters-wide occulting disk is flown tens of thousands of kilometers ahead of a telescope, call for vast fuel reserves to reposition between targets. Even offers to utilize shorter, observable wavelengths face the issue that a sun-like star is over 10 billion times brighter than its planet at that spectrum, overpowering coronagraphs.
Work in the mid-infrared not only enhances contrast but also addresses the thermal emission of potentially inhabited planets, where biosignature gases such as water vapor, carbon dioxide, methane, and oxygen create characteristic absorption features. JWST’s Mid-Infrared Instrument has already shown to be capable of sensing water vapor in the atmospheres of hot, massive exoplanets, but it is too small an aperture to detect an Earth analog around a sun-like star at the needed distances.
The dimensions of the rectangular mirror are compatible with current heavy-lift rockets like SpaceX’s Falcon Heavy, obviating the need for conceptual launch systems. Such a telescope, according to the team’s modeling, could, in theory, discover half of all Earth-like planets around sun-like stars within 30 light-years within three years. Since there are approximately 60 such stars in that volume, and with a one-in-one occurrence rate of an Earth-like world, the survey would provide about 30 top candidates for follow-up.
These follow-ups might consist of atmospheric spectroscopy to look for oxygen created by photosynthesis, or methane in disequilibrium with other gases possible indicators of biological activity. The design complies with the science objectives of NASA’s Habitable Worlds Observatory concept, which is to directly image at least 25 potentially habitable exoplanets and characterize their atmospheres. But unlike other HWO architectures that are dependent on untested technology, the rectangular design is based on current materials, deployment systems, and infrared detector technology.
In the context of exoplanet discovery in general, the technique provides a direct-imaging counterpoint to transit surveys such as TESS and radial velocity campaigns with ultra-stable spectrographs such as EXPRES and ESPRESSO. Those methods are great for discovering planets but frequently can’t tell us about atmospheres or surface states. Direct imaging at high thermal infrared resolution fills that gap, giving both detection and the first hints of habitability.
Newberg is candid about the attraction: “I think a lot of people want to find another Earth. This is the most straightforward way to find Earth 2.0.”
