Discovering Exoplanets Using Starshade

Exoplanets are planets not in our solar system. Most exoplanets orbit other stars, but there are rogue planets out there, planets that don’t orbit a specific star but do orbit the centre of our galaxy. At the time of writing, over 5,000 exoplanets have been discovered, and astronomers expect that number to keep increasing.

There are different ways to discover exoplanets. One way is to measure the drop in a star’s intensity as a large planet passes in front of the star. This is called the transit method. Another way is to take a photo of a star thought to have its own solar system, but that isn’t always revealing. Stars are so bright that any planets in orbit around them get lost in the star’s glare.

Canadian planetary scientist Dr. Sara Seager is working with NASA on another way to find and study exoplanets. Dr. Seager’s particular goal is to find Earth-like exoplanets and, hopefully, some signs of microbial life.

Dr. Seager was born in Toronto, Ontario. She completed her B.Sc. at the University of Toronto and her Ph.D. at Harvard. She is currently on staff with the Massachusetts Institute of Technology as a Professor of Physics, Professor of Planetary Science, and a Professor of Aeronautics and Astronautics. Dr. Seager is also the current Honorary President of the Royal Astronomical Society of Canada.


Dr. Sara Seager. Credit NASA Exoplanet Exploration

The technology that Dr. Seager is involved with is called Starshade. Starshade is just that, a shade to cover a star. A shade attached to a telescope will be launched into space and programmed to image a star with known or potential exoplanets. The shade detaches itself from the telescope. Then the shade unfolds, much like a flower unfolds, to a width of about 50 metres. Then Starshade positions itself in a line with the telescope and the target star. The distance between Starshade and the telescope will be up to 50,000 kilometres.

With the brightness blocked, the exoplanets come into view. Instruments on the telescope will study the atmospheres of the exoplanets, yielding information such as the gases present. The types of gases will tell us whether life could be present.

The system is simple, although all technology has its benefits and challenges. For example, one benefit is, because so much of the starlight is blocked, the telescope doesn’t need an elaborate optics system. One challenge is dealing with the diffraction of starlight around Starshade (diffraction is the bending of light around an edge). Too much diffraction means the shadow made by Starshade may not be dark enough, which means it might be more difficult to see the exoplanets.

The program, called New Worlds, is still in its research and funding stage, so a launch date is not available yet.

Once Starshade positions itself between a star and Starshade’s telescope, any exoplanets pop into view. This artist’s conception of Starshade is not to scale. Credit: NASA and Northrop Grumman

This video from JPL shows how it will work.