A NASA telescope in early development should be able to detect light bouncing off the surface of oceans on alien planets, vital information in the hunt for alien life. The Habitable Worlds Observatory is currently earmarked for launch in the 2040s. It will sport an advanced coronagraph, a device that can block out much of the light emanating from other stars.
This will allow us to take images of potentially habitable Earth-like worlds outside our solar system for the first time. NASA’s huge Nancy Grace Roman Space Telescope is about to launch Eleanor Cornish and Tyler Robinson at the University of Arizona have assessed whether the telescope would be able to spot oceans on these planets. Even though its images will be basic, with each world appearing as a single pixel, the pair found that light reflecting off the oceans – known as glint – should be noticeable when the planet is at certain angles around its star.
The study shows the glint will be detectable when the angle of the planet relative to its star and Earth, known as its phase angle, is greater than 120 degrees – meaning the light will bounce off the planet towards Earth, rather than out into space. The glint will cause the brightness of the planet to increase slightly. How much the planet brightens in its orbit should tell us how much of the surface is covered by water, revealing whether it is a water world entirely encased in an ocean or partially covered by land like Earth.
Sophia Vaughan at the Max Planck Institute for Astronomy in Germany says it might not just be oceans that the Habitable Worlds Observatory can detect. Other features on the planet, such as clouds, vegetation or even rainbows, might affect the nature of the light that is reflected to Earth. A rainbow would slightly focus the light of the planet, she says, “and you can possibly see that”.
All of this information will be crucial to astronomers as they finalise designs for the Habitable Worlds Observatory in the coming years.
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