Astronomers Propose Rectangular Telescope to Hunt Earth-Like Planets

Astronomers are exploring a space telescope with a long, narrow primary mirror instead of the usual round one. This high-aspect design (e.g. ~20 m by 1 m) has very high resolving power along its length, enough to separate a Sun–Earth pair at ~30 light-years in infrared light. A 2025 study shows this could allow direct imaging of nearby Earth-like exoplanets that current telescopes cannot see. The mirror can be folded compactly for launch using JWST-like mirror segments. By taking two images with the strip rotated 90°, the telescope can cover all possible planet–star orientations.

Design advantages of a rectangular mirror

According to a paper describing the new telescope concept, published in the journal Frontiers in Astronomy and Space Sciences, rectangular mirror concentrates its area in one direction, yielding much finer resolution along its length. For example, at 1 µm a 20×1 m mirror provides ~0.1″ resolution along its long axis, whereas a circular mirror of the same area would blur planets together.

Two pointings (rotating the strip 90°) cover all orbital angles. The 20×1 m strip has only ~20 m² area (vs. JWST's 25 m²). It folds compactly (two 10 m halves) to fit current rockets, and uses JWST-style mirror segments and mid-IR detectors, so no exotic technology is needed.

Searching for Earth-like planets

Directly imaging Earth-like planets requires enormous resolution and starlight suppression. The rectangular telescope can resolve planets much closer to their stars than a conventional mirror of the same size. In simulations, a 20×1 m infrared telescope could detect about 11 Earth-size habitable planets (measuring atmospheric ozone) in 1 year and ~27 in 3.5 years.

That meets NASA's goal of ~25 habitable worlds and implies finding roughly half of all Earth-like planets within ~30 light-years.