Concept design for a rectangular space telescope, modeled after the Diffractive Interfero Coronagraph Exoplanet Resolver (DICER), a notional infrared space observatory, and the James Webb Space Telescope. Credit: Leaf Swordy/Rensselaer Polytechnic Institute.
Finding Earth-like planets is nearly impossible because stars drown them out in brightness. Conventional telescope designs fall short, but a proposed rectangular infrared telescope could solve this. It might reveal dozens of promising worlds within 30 light-years, paving the way to spotting signs of life.
Origins of Life and Water’s Role
Earth is the only place we know of that harbors life, and every living thing here depends on liquid water to power essential chemical reactions. Simple, single-celled organisms have been around for nearly as long as the planet itself, but it took about three billion years before more complex, multicellular organisms evolved. Humans, by comparison, have existed for only a tiny fraction of Earth’s history—less than one ten-thousandth of its age.
This timeline suggests that life could arise fairly often on planets where liquid water is present, but intelligent beings capable of exploring the cosmos may be far less common. If we hope to discover life beyond Earth, we may need to reach out to it directly.
Limits of Space Travel and Search Targets
The challenge is that space is unimaginably vast, and the laws of physics prevent us from moving or communicating faster than the speed of light. That restriction means only the nearest stars to our sun could realistically be explored within a human lifetime, even with robotic probes. Among those, the best candidates are stars that closely resemble our sun in size and temperature. Such stars live long enough and remain stable enough to allow complex life to develop.
Currently, astronomers have identified approximately 60 sun-like stars within a distance of roughly 30 light-years from Earth. Planets circling these stars that are similar in size and temperature to Earth, where both solid ground and liquid water might exist, are considered the most promising places to look.
The Overwhelming Brightness of Stars
Observing an Earth-like exoplanet separately from the star it is orbiting around is a major challenge. Even in the best possible scenario, the star is a million times brighter than the planet; if the two objects are blurred together, there is no hope of detecting the planet.
Optics theory says that the best resolution one can get in telescope images depends on the size of the telescope and the wavelength of the observed light. Planets with liquid water give off the most light at wavelengths around 10 microns (the width of a thin human hair and 20 times the typical wavelength of visible light). At this wavelength, a telescope needs to collect light over a distance of at least 20 meters to have enough resolution to separate the Earth from the sun at a distance of 30 light-years.
Additionally, the telescope must be in space, because looking through the Earth’s atmosphere would blur the image too much. However, our largest space telescope – the James Webb Space Telescope (JWST) – is only 6.5 meters in diameter, and that telescope was extremely difficult to launch.
Alternative Telescope Concepts and Challenges
Because deploying a 20-meter space telescope seems out-of-reach with current technology, scientists have explored several alternative approaches. One involves launching multiple, smaller telescopes that maintain extremely accurate distances between them, so that the whole set acts as one telescope with a large diameter. But, maintaining the required spacecraft position accuracy (which must be precisely calibrated to the size of a typical molecule) is also currently infeasible.
Other proposals use shorter wavelength light, so that a smaller telescope can be used. However, in visible light a sun-like star is more than 10 billion times brighter than the Earth. It is beyond our current capability to block out enough starlight to be able to see the planet in this case, even if, in principle, the image has high enough resolution.
One idea for blocking the starlight involves flying a spacecraft called a ‘starshade’ that is tens of meters across, at a distance of tens of thousands of miles in front of the space telescope, so that it exactly blocks the light from the star while the light from a companion planet is not blocked. However, this plan requires that two spacecraft be launched (a telescope and a starshade). Furthermore, pointing the telescope at different stars would entail moving the starshade thousands of miles, using up prohibitively large quantities of fuel.
In our paper, we propose a more feasible alternative. We show that it is possible to find nearby, Earth-like planets orbiting sun-like stars with a telescope that is about the same size as JWST, operating at roughly the same infrared (10 micron) wavelength as JWST, with a mirror that is a one by 20 meter rectangle instead of a circle 6.5 meters in diameter.
With a mirror of this shape and size, we can separate a star from an exoplanet in the direction that the telescope mirror is 20 meters long. To find exoplanets at any position around a star, the mirror can be rotated so its long axis will sometimes align with the star and planet. We show that this design can in principle find half of all existing Earth-like planets orbiting sun-like stars within 30 light-years in less than three years. While our design will need further engineering and optimization before its capabilities are assured, there are no obvious requirements that need intense technological development, as is the case for other leading ideas.
Toward Earth 2.0: The Search for Life
If there is about one Earth-like planet orbiting the average sun-like star, then we would find around 30 promising planets. Follow-up study of these planets could identify those with atmospheres that suggest the presence of life, for example, oxygen that was formed through photosynthesis. For the most promising candidate, we could dispatch a probe that would eventually beam back images of the planet’s surface. The rectangular telescope could provide a straightforward path towards identifying our sister planet: Earth 2.0.
Reference: “The case for a rectangular format space telescope for finding exoplanets” by Heidi Jo Newberg, Leaf Swordy, Richard K. Barry, Marina Cousins, Kerrigan Nish, Sarah Rickborn and Sebastian Todeasa, 30 June 2025, Frontiers in Astronomy and Space Sciences.
