Stanford's starshade satellite casts an artificial eclipse to spot exoplanets
It might sound like the evil plan of a Bond villain, but a team from Stanford is planning to create an artificial eclipse with a light-blocking satellite. Thankfully though, the Sun's rays aren't the target of the system: instead, the shade will block out distant stars, allowing a telescope on its partner satellite to get a clearer look at exoplanets that might be orbiting them.
Exoplanets have been discovered by the thousands in recent years, and most of them have been found through occlusion, where regular dips in the light from a star indicates an orbiting planet has passed in front of it. But while the brightness of the star is useful in that situation, the glare makes it hard for astronomers to observe the planets directly.
"With indirect measurements, you can detect objects near a star and figure out their orbit period and distance from the star," says Simone D'Amico, lead researcher on the project. "This is all important information, but with direct observation you could characterize the chemical composition of the planet and potentially observe signs of biological activity – life."
To solve the problem, the Stanford team is proposing a project called the Miniaturized Distributed Occulter/Telescope (mDOT). This duo would include a 100-kg (220-lb) microsatellite carrying the starshade, and a 10-kg (22-lb) nanosatellite equipped with a small telescope.
At launch, the shade would be folded up tight, before unfurling in high Earth orbit to its full width of 3 m (10 ft). Its flower-like shape has a very specific purpose, allowing it to cast the darkest shadow possible onto its companion satellite with the telescope that is orbiting less than 1,000 km (620 mi) away.
"With this special geometric shape, you can get the light diffracting around the starshade to cancel itself out," says Adam Koenig, a graduate student on the project. "Then, you get a very, very deep shadow right in the center. The shadow is deep enough that the light from the star won't interfere with observations of a nearby planet."
To throw shade with such precision is a delicate dance, requiring exact positioning of the two satellites. The best view comes at the point in their orbit where the two are moving the slowest relative to each other, which gives the researchers about an hour of viewing time of the target planets. After that, the duo can drift apart until they're needed to line up again.
Getting the two to tango so perfectly would be too much for human control to manage given the communication delay, but the research lab is focused on developing systems for spacecraft to fly in formation autonomously.
While mDOT won't be able to spot Earth-sized planets, it could help study dust clouds or Jupiter-like giants. But its primary objective is to be a low-cost demonstration of the starshade technique, to help set the stage for an eventual larger-scale mission.
Source: Stanford University