The charm on Rebecca Jensen-Clem’s necklace measures just about an inch in width, made up of 36 silver hexagons intricately arranged to form a honeycomb pattern. In Hawaii at the Keck Observatory, an equal number of segments constitutes a mirror that stretches 33 feet, capturing reflections of unexplored worlds for her examination.
Jensen-Clem, an astronomer affiliated with the University of California, Santa Cruz, collaborates with the Keck Observatory to discover methods for identifying new planets while remaining on our home planet. This endeavor typically encounters numerous challenges: Wind, changes in atmospheric density and temperature, or even a misaligned telescope mirror can cause a star’s light to glare, obscuring visibility of surrounding objects, thus making any planets orbiting that star nearly invisible. Additionally, light that isn’t obscured by Earth’s atmosphere is often absorbed. This is why scientists exploring these remote worlds frequently rely on space telescopes that entirely bypass Earth’s troublesome atmosphere, such as the $10 billion James Webb Space Telescope.
However, alternative routes exist to navigate these obstacles. In her lab nestled among the redwoods, Jensen-Clem and her students test new technologies and software aimed at enhancing the clarity of Keck’s main honeycomb mirror and its smaller, “deformable” mirror. By utilizing data from atmospheric sensors, these deformable mirrors can rapidly alter their shape to correct distortions induced by Earth’s atmosphere in real-time.
This imaging strategy, known as adaptive optics, has been prevalent since the 1990s. Nevertheless, Jensen-Clem seeks to elevate the standard with extreme adaptive optics technologies, intended to achieve the highest image quality over a limited field of view. Her team specifically addresses challenges related to wind or the primary mirror itself. The objective is to focus starlight with such precision that a planet can be discernible even if its host star shines a million to a billion times brighter.
In April, she and her former collaborator Maaike van Kooten received honors as co-recipients of the Breakthrough Prize Foundation’s New Horizons in Physics Prize. The prize announcement indicates they were awarded this early-career research honor due to their potential “to enable the direct detection of the smallest exoplanets” through a suite of methods both women have diligently developed throughout their careers.
In July, Jensen-Clem was also recognized as a member of a newly formed committee for the Habitable Worlds Observatory, envisioned as a NASA space telescope that will search for signs of life in the universe throughout its operational life. She is charged with defining the scientific objectives of the mission by the decade’s conclusion.
“In adaptive optics, a significant amount of our time is devoted to simulations or experimental work,” Jensen-Clem notes. “It’s been a lengthy journey to recognize that I’ve genuinely improved conditions at the observatory in recent years.”
Jensen-Clem has always been intrigued by the more perplexing aspects of astronomy. In seventh grade, she developed an interest in the phenomenon of time dilation near a black hole after her father, an aerospace engineer, explained it to her. As she commenced her bachelor’s studies at MIT in 2008, she became captivated by how a distant star can appear to vanish—either abruptly or gradually, based on the type of object that obstructs it. “It wasn’t strictly exoplanet research, yet there was considerable overlap,” she reflects.
“When you simply look up at the night sky and observe twinkling stars, it’s a swift occurrence. Thus, we must also act rapidly.”
During this period, Jensen-Clem began laying the groundwork for one of her award-winning methods after her teaching assistant suggested she apply for an internship at NASA’s Jet Propulsion Laboratory. There, she contributed to a setup designed to optimize the alignment of a large mirror. Such mirrors are more challenging to realign compared to smaller, deformable mirrors, which have segments that adapt to Earth’s changing atmosphere.
“Back then, we were thinking, ‘Wouldn’t it be fantastic to install one of these at Keck Observatory?’” Jensen-Clem shares. The concept lingered. She even included it in a fellowship proposal while preparing to commence her graduate studies at Caltech. After years of development, Jensen-Clem successfully integrated the system—which employs a technology known as a Zernike wavefront sensor—on Keck’s primary mirror about a year ago. “My college intern work is finally complete,” she smiles.
The system, which is presently utilized for periodic recalibrations rather than ongoing adjustments, incorporates a uniquely designed glass plate that bends light rays from the mirror to reveal a distinct pattern. The detector can identify even the slightest misalignment in that pattern: if one hexagon is shifted too far back or forward, its brightness varies. Correcting even the most minute misalignment is critical, as “when studying a faint object, you become significantly more vulnerable to minor errors,” Jensen-Clem explains.
She is also focused on perfecting the craftsmanship of shaping Keck’s deformable mirror. This instrument, reflecting light rerouted from the primary mirror, is much smaller—only six inches in width—and is engineered to adjust as frequently as 2,000 times per second to counteract atmospheric turbulence and produce the clearest image possible. “When you merely look up at the night sky and watch stars twinkling, it occurs rapidly. Therefore, we must act quickly as well,” Jensen-Clem states.
Even with this high speed of adjustment, a lag persists. The deformable mirror typically lags about one millisecond behind the actual outdoor conditions at any particular moment. “If the [adaptive optics] system cannot keep pace, then the resolution will not be optimal,” van Kooten, Jensen-Clem’s former collaborator, currently with the National Research Council Canada, notes. This lag can be especially problematic on blustery nights.
Jensen-Clem initially thought it was an insurmountable obstacle. “The cause of that delay is that we need to conduct computations and then adjust the deformable mirror,” she clarifies. “Achieving these tasks instantaneously is impossible.”
However, while still a postdoctoral researcher at UC Berkeley, she encountered a paper that proposed a solution. The authors suggested that by employing prior measurements and basic algebra to forecast atmospheric changes, instead of trying to match them in real time, superior results could be obtained. Although she couldn’t test the theory at that time, joining UCSC and collaborating with Keck provided the ideal chance.
During this period, Jensen-Clem invited van Kooten to become part of her team at UCSC as a postdoc, given their mutual interest in the predictive software. “Initially, I didn’t have a place to stay, so she accommodated me in her guest room,” van Kooten recalls. “She’s exceedingly supportive at every level.”
After developing experimental software for trials at Keck, the team assessed the predictive model against the conventional adaptive optics, evaluating how effectively each method imaged an exoplanet without overwhelming starlight. They discovered that the predictive software managed to image even faint exoplanets two to three times more distinctly. The findings, published by Jensen-Clem in 2022, contributed to her recognition with the New Horizons in Physics Prize.
Thayne Currie, an astronomer at the University of Texas, San Antonio, remarks that these innovative techniques will be increasingly crucial as scientists construct larger and more advanced ground-based facilities to capture images of exoplanets—including future projects like the Extremely Large Telescope at the European Southern Observatory and the Giant Magellan Telescope in Chile. “We’re learning an incredible amount about the universe, propelled by technology advancements that are very new,” Currie asserts. “Dr. Jensen-Clem’s contributions exemplify that innovation.”
In May, one of Jensen-Clem’s graduate students returned to Hawaii to reinstall the predictive software at Keck. This time, the arrangement isn’t merely a trial; it is intended for permanent implementation. The new software has demonstrated its capability to refocus artificial starlight. Next, it will need to prove its efficacy with actual starlight.
And in approximately a year, Jensen-Clem and her students and colleagues will prepare for a deluge of observations from the European Space Agency’s Gaia mission, which has recently completed measuring the motion, temperature, and composition of billions of stars over a period of more than a decade.
When the project releases its upcoming data set—expected in December 2026—Jensen-Clem’s team intends to search for new exoplanetary systems utilizing clues like the variations in a star’s motion caused by the gravitational influence of orbiting planets. Once a system is identified, exoplanet photographers will then have the opportunity to capture the concealed planets using a new instrument at Keck designed to provide further insights into their atmospheres and temperatures.
A substantial volume of data will need to be analyzed, alongside an even greater influx of starlight to refocus. Fortunately, Jensen-Clem has dedicated more than a decade to honing the techniques she will require: “By this time next year,” she expresses, “we’ll be racing to apply all our adaptive optics strategies to these systems and identify as many of these objects as we can.”
Jenna Ahart is a science journalist focusing on the physical sciences.
