Camera Can Differentiate Between Exoplanet Light and Nearby Starlight

A new superconducting camera will be used in the search for exoplanets that could contain or support life. The camera’s high-contrast imaging capabilities will help overcome the challenges inherent in distinguishing the light of a planet from the light of the star that it orbits.

DARKNESS (the DARK-speckle Near-infrared Energy-resolving Superconducting Spectrophotometer) is a 10,000-pixel integral field spectrograph designed to overcome the limitations of traditional semiconductor detectors. It employs IR microwave kinetic inductance detectors (MKIDs) for high-contrast imaging. The photon counting and simultaneous low-resolution spectroscopy provided by the MKIDs will enable real-time speckle control techniques and postprocessing speckle suppression at frame rates capable of resolving the atmospheric speckles that currently limit high-contrast imaging from the ground.

DARKNESS (the DARK-speckle Near-infrared Energy-resolving Superconducting Spectrophotometer) can detect planets around the nearest stars. Courtesy of UCSB.

The scientific team includes researchers from the University of California Santa Barbara (UCSB), the California Institute of Technology (Caltech), and the Jet Propulsion Laboratory.

DARKNESS will be used in conjunction with a large telescope and an adaptive optics system to enable direct imaging of planets around nearby stars. It has been designed for the 200-in. (5.1-m) Hale telescope at the Palomar Observatory near San Diego.

“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,” UCSB professor Benjamin Mazin said. “This technology will lower the contrast floor so that we can detect fainter planets.”

The camera can take the equivalent of thousands of frames per second without any read noise or dark current. It also has the ability to determine the wavelength and arrival time of every photon, important for distinguishing a planet from refracted light.

DARKNESS acts as both the science camera and a focal plane wavefront sensor, measuring the light and then sending a signal back to a rubber mirror that can form into a new shape at a rate of 2000× a second. This process suppresses the starlight and cleans up the atmospheric distortion that causes stars to twinkle, enabling higher contrast ratios between the star and the planet.

Professor Ben Mazin, physicist at the University of California Santa Barbara. Courtesy of Sonia Fernandez.
“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," Mazin said. "At those contrast levels, we can see some planets in reflected light, which opens up a whole new domain of planets to explore.”

DARKNESS is now operational behind the PALM-3000 extreme adaptive optics system and the Stellar Double Coronagraph at Palomar Observatory. During the past year and a half, the team has employed DARKNESS on four runs at Palomar to work out bugs. The researchers will return in this month to take more data on certain planets and to demonstrate their progress in improving the contrast ratio.

“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 [Spain]," Mazin said. "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 Publications of the Astronomical Society of the Pacific (doi:10.1088/1538-3873/aab5e7).