Astronomers to use huge flower in space for exoplanet hunting

To better characterise planets beyond the solar system, scientists have developed huge flower-shaped disks for better function that will give the most precise and clear data in discovering more Earth-like exoplanets in the universe. Named as “starshades,” the disks, working in space with a separate flying telescope, can block the light from a parent star to dim exoplanets to be observed and studied.

Distance is the most common challenge for astronomers to study Earth-like alien planets, which are up to 10 billion times dimmer than the stars they orbit. A starshade, or an external occulter, is capable to counteract the dimness of the planets through blocking the light from a star, the same way how people place their hand over the sun light to help see other objects in the sky.

The starshades were built in a variety of sizes. A common disk would be about 100 feet, or 30 metres wide, that would fly tens of thousands of miles from its partner telescope. But at any size, the starshade would have flower petal-like protrusions with a softer edge, which will allow less bending of light and a darker shadow.

However, scientists are still testing the technology on Earth before sending one to space. NASA wants to assure that before spending billions for putting the disks in space, serious testing should be performed to verify that the starshade concept would work.

"The unique architecture of the starshade — namely, the size and separation needed — make it difficult to test cheaply," said Anthony Harness, a graduate student at the University of Colorado, Boulder, told Space.com. Harness is currently working with a team of experts from the aerospace company Northrop Grumman, to test the concept of starshades in dry lake beds and on mountaintops.

The team has already performed several starshade tests on dry lake beds in the desert. Harness and his colleagues simulated the stellar light through an extremely bright light source as the "star," while a far dimmer LED light served as the "planet."

"The whole purpose of these tests [was] to demonstrate we can get a billion times contrast," Harness said. For the results, the starshade has successfully blocked the light, which allowed the team to observe the simulated planet.

NASA has also performed another study, called Exo-S, to evaluate a potential one billion dollar starshade space telescope mission. The Exo-S team used a small telescope on the ground, with a starshade hung on a short distance away.

At first, the team planned to hang the starshade from a zeppelin, but the telescope was not able to get necessary precision as the airship was difficult to control. The team then turned to reusable rockets for the next tests.

For the new idea, two telescopes will be placed on the ground. One will be used to work for the necessary science, while the other will point infrared lights on the rocket to position it precisely.

However, with the challenges in testing the concept of starshade, Harness said that the team will succeed. The team believes that "starshades are the only near-term solution for characterising and determining the habitability of an Earth-like planet," Harness stated.

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