A new study from Rensselaer Polytechnic Institute (RPI) and NASA reveals that a radically different telescope design could accelerate the search for potentially habitable worlds beyond our solar system.  

The design solves a longstanding problem in exoplanet detection: resolving an Earth-sized planet from a Sun-sized star at a distance of 30 light-years would require a space telescope with a 20-meter diameter circular mirror, which is out of reach with current technology. 

The study proposes, instead, a telescope with a rectangular mirror, 20 meters long but only one meter wide, that can be rotated to capture multiple images of the same star from different orientations. The design ensures that exoplanets can be resolved from their host stars regardless of how they're oriented relative to our own solar system, and it is small enough to be launched using existing rocket technology. 

The study, led by RPI astrophysics professor Heidi Newberg, Ph.D., demonstrates that the design could achieve one of the primary science goals of NASA's proposed Habitable Worlds Observatory (HWO) mission — finding at least 25 habitable exoplanets and detecting atmospheric biosignatures — in approximately 3.5 years. The proposal has considerable advantages over other HWO plans, which require significant technology development before becoming feasible. 

“I think a lot of people want to find another Earth,” Newberg said. “This is the most straightforward way to find Earth 2.0.” 

An engineering problem 

To date, most exoplanets have been observed indirectly, by sensing the dimming of a star’s light as a planet passes in front of it. NASA’s proposed HWO mission aims to image exoplanets directly, with an eye toward detecting signs of life like oxygen and methane in their atmospheres. 

But doing so represents a formidable engineering challenge. Even under the best circumstances, stars appear millions of times brighter to us than their orbiting planets. Resolving an exoplanet from its host star is kind of like trying to spot a firefly sitting on a stadium floodlight from thousands of miles away.  

A traditional space telescope would need to have an enormous 20-meter circular mirror to pull off the feat. By comparison the James Webb Space Telescope, representing the current limit of our telescope launch capabilities, has a diameter of just 6.5 meters. 

Scientists planning the HWO have explored alternative approaches, like launching a telescope with a separate craft positioned thousands of kilometers away to block out the light of targeted stars. But those approaches introduce new engineering challenges that strain our current capabilities to the breaking point.  

Working smarter, not harder 

Newberg and her colleagues, including NASA astronomer Richard K. Barry, propose a much simpler approach: a rectangular mirror, 20 meters long but only one meter wide. Such a mirror is small enough to fit in existing launch systems, like the Falcon Heavy vehicle. 

The rectangular design works by taking two images of each target star system: one with the telescope oriented in one direction, and another with the mirror rotated 90 degrees. This approach allows the telescope to detect planets at virtually any position around their host stars, overcoming the limitation of having high resolution along only the long axis of the mirror. 

“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,” Newberg writes in a Frontiers editorial accompanying the peer-reviewed study. “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.” 

The approach represents a much more efficient pathway toward identifying promising exoplanets that could then become the targets of future, more complex missions. 

The study appears in the journal Frontiers in Astronomy and Space Sciences and was supported by NASA's Innovative Advanced Concepts program. A high-resolution version of the concept art of the telescope is available here.