UC Santa Cruz astronomers have received three major grants from the Heising-Simons Foundation for projects related to direct imaging of planets around other stars.
In recent decades, astronomers have discovered thousands of planets outside our solar system, called exoplanets. The vast majority of these have been detected indirectly using methods that rely on precise measurements of the light from their host stars.
Direct imaging of exoplanets is much more difficult because the faint light from a planet tends to be hidden in the glare of the bright star around which it orbits. But it is potentially a powerful approach for studying exoplanets because it enables the use of spectroscopy to analyze the light from a planet for clues to its chemical composition and other properties.
Direct imaging and spectroscopy of exoplanets has the potential to characterize Earth-like planets around other stars and possibly even detect signs of life on them.
“With the next generation of ground-based telescopes, we could potentially image a rocky planet in the habitable zone of a nearby M-dwarf star, but current technology is not there yet,” said Rebecca Jensen-Clem, assistant professor of astronomy and astrophysics at UC Santa Cruz.
Adaptive Optics
Jensen-Clem is part of a multi-university team of astronomers that has been funded by the Heising-Simons Foundation to advance the technologies for a new era of exoplanet direct imaging and spectroscopy. Her part of the project, funded by a $995,000 grant to UC Santa Cruz, will involve work at UCSC’s Laboratory for Adaptive Optics and at the W. M. Keck Observatory in Hawaii.
Adaptive optics (AO) is a critical technology for direct imaging of exoplanets, and UC Santa Cruz has played a leading role in its development. AO systems sharpen the images obtained by ground-based telescopes by removing the blurring effects of turbulence in the Earth’s atmosphere. AO systems can also be used to control image distortions introduced by the telescope itself, such as slight misalignments of mirror segments in large telescopes like those at Keck Observatory that use segmented primary mirrors.
“When we’re trying to image exoplanets, we need to correct every possible source of distortions,” Jensen-Clem explained. “This initiative is a series of related projects to advance adaptive optics technology, not only to improve the performance of current telescopes, but also because we will need this technology for the next generation of giant, 30-meter class telescopes.”
Another project in this initiative is being led by Steph Sallum, currently a postdoctoral fellow at UC Santa Cruz, who will be joining the astronomy faculty at UC Irvine in July.
SCALES
Meanwhile, Andrew Skemer, associate professor of astronomy and astrophysics, is developing a new instrument for the Keck Telescopes that will be dedicated to exoplanet spectroscopy. A $1 million grant from the Heising-Simons Foundation is funding Skemer’s team to complete the design stage and purchase or fabricate several critical components for the instrument, called the Santa Cruz Array of Lenslets for Exoplanet Spectroscopy (SCALES).
SCALES is designed to maximize the ability of astronomers to detect and characterize directly-imaged exoplanets in the thermal infrared wavelengths where they peak in brightness. Skemer explained that directly imaged planets are far enough away from their host stars that they slowly cool off over time.
“The exoplanets we aim to detect and characterize with direct imaging tend to be relatively cold and emit the majority of their light in the thermal infrared,” he said. “By operating at longer wavelengths than existing spectrographs of this kind, SCALES will extend the wavelength range we use to characterize exoplanets, and will also discover new exoplanets that are not detectable with near-infrared instruments.”
PEAS
The third project, funded by a $400,000 Heising-Simons grant, is led by Emily Martin, a postdoctoral fellow working with Skemer, and it will be based at UC’s Lick Observatory on Mt. Hamilton. Both Martin and Sallum are UCSC Chancellor's Postdoctoral Fellows as well as National Science Foundation Postdoctoral Fellows. Martin’s goal is to perform spectroscopic observations of solar system planets as if they were distant exoplanets, producing an atlas for use in interpreting exoplanet observations and designing future exoplanet instruments.
Because they are so far away, directly imaged exoplanets appear as point sources of light. Martin is developing a novel instrument, called the Planet as Exoplanet Analog Spectrograph (PEAS), which will take the light from a planet such as Jupiter and effectively turn it into a point source for spectroscopic analysis.
“We can then compare the results of our analyses with what we already know about the planets in our solar system from space missions that have actually sent probes to those planets and done direct measurements,” Martin explained.
As Skemer put it, “PEAS will tell us if we’re doing it right.”
Although these projects are very different from one another, they will all provide critical new knowledge and capabilities needed to discover and understand the full diversity of planets to be found beyond our solar system.
