This prototype starshade concept uses origami principles to unfold as large as possible.
Credit: NASA
A recent study published in the journal Nature lays out an intriguing concept for finding hard-to-spy exoplanets, especially those in the same overall category as Earth: a giant sunshade held in orbit to block confounding light and allow a clear image to be captured from below.
The idea itself dates back to 1962, with the paper “The Beginnings and Future of Space Astronomy.” At the time, the idea wasn’t technologically possible, but other researchers continued to develop the concept for decades, coming up with more detailed designs and requirements for the fabrication, launch, and use of a great big flat thing in space.
The idea has seen real work from NASA’s JPL through its Starshade project, though it has yet to launch a test shade, and even its largest proposed project is still smaller than the starshade proposed in this paper, whose diameter is around 100 meters.
The reason this paper requires a larger starshade than JPL’s concepts is that it seeks to apply the idea of a starshade to ground-based telescopes, rather than confining it to space telescopes. For instance, NASA’s Habitable Worlds Observatory proposes to use a starshade in concert with a new space observatory.
The starshade concept, together with a proposed space telescope designed specifically to work with it.
Credit: NASA
With a much larger starshade, though, it might be possible to use ground-based instruments like the Extremely Large Telescope (ELT), the Thirty Meter Telescope (TMT), or the Giant Magellan Telescope (GMT) more effectively, too.
The problem with capturing images of exoplanets, especially those thought to be most likely to host life, is that they are absurdly small and dim compared to their host stars. Even to the extent that modern telescopes can be powerful enough to resolve real information about a planet at that distance, they still can’t get to see the planet for all the glare from its over-bright host star.
This is why virtually all exoplanet detections have been “transits,” or the capture of the silhouette of an exoplanet against the backdrop of its host star. This makes the planet much easier to spot, as a dark blob on a bright background, but it also carries only partial information about the planet itself.
The Giant Magellan Telescope that could find an Earth-like planet, someday.
Credit: GMTO Corporation
Size and mass can often be discerned, but more nuanced information about its atmosphere or other life-relevant characteristics is hard to discern from such a simple outline. That’s why direct imaging of exoplanets is much more desirable, since real images would provide much more useful insights.
With a starshade, it would be possible to block the light of the host star from entering the telescope, meaning it could no longer wash out the relatively dim exoplanet beside it.
Though a roughly 100-meter-scale starshade is an ambitious idea, it also offers the upside of not requiring the design and launch of a brand-new space observatory. That fact alone might make the extra expense of the bigger shade worth it, and lead to real observations more cheaply and quickly than the above-mentioned Habitable Worlds Observatory project.
