Astronomers may have discovered almost 4,000 planets beyond our Solar System so far, but trying to image these worlds is a bit like trying to get a good look at a fly buzzing around the Sun. Described as the world's largest and most advanced superconducting camera, a new instrument dubbed DARKNESS is designed to filter out the blinding light of host stars to see orbiting exoplanets in more detail than ever before.

To date, the bulk of the exoplanet haul has been found using the transit method, where dips in a star's light can indicate that an exoplanet is passing in front of it. More details can then be figured out by measuring the wavelength of that light, letting astronomers infer what the planet and its atmosphere are made up of. Even so, the bright starlight can easily hide planets from view.

"Taking a picture of an exoplanet is extremely challenging because the star is much brighter than the planet, and the planet is very close to the star," says Ben Mazin, lead researcher on the team.

That's where the new instrument comes in. The DARK-speckle Near-infrared Energy-resolved Superconducting Spectrophotometer (DARKNESS) is designed to take images with much higher contrast ratios, allowing astronomers to spot extremely faint planets around bright stars.

Boasting 10,000 pixels, DARKNESS is an integral field spectrograph that uses Microwave Kinetic Inductance Detectors. That allows it to determine the wavelength and arrival time of each individual photon, meaning planets can be picked out from the background noise more clearly. At the same time, the instrument can also clean up distortion introduced as the light passes through the Earth's atmosphere, allowing the image to have a higher contrast ratio.

"This technology will lower the contrast floor so that we can detect fainter planets," says Mazin. "We hope to approach the photon noise limit, which will give us contrast ratios close to 10-8, allowing us to see planets 100 million times fainter than the star. At those contrast levels, we can see some planets in reflected light, which opens up a whole new domain of planets to explore. The really exciting thing is that this is a technology pathfinder for the next generation of telescopes."

The current version of DARKNESS is designed for the 200-inch Hale telescope housed at Palomar Observatory, where the instrument has been tested several times. In future, the researchers plan to adapt it for use by other telescopes.

"Our hope is that one day we will be able to build an instrument for the Thirty Meter Telescope planned for Mauna Kea on the island of Hawaii or La Palma," says Mazin. "With that, we'll be able to take pictures of planets in the habitable zones of nearby low mass stars and look for life in their atmospheres. That's the long-term goal and this is an important step toward that."

The research was published in the journal Publications of the Astronomical Society of the Pacific.

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