Night after night, the sky sends quiet clues. A star brightens, dims, and shifts by a fraction, just enough to show that a hidden world may be circling in the dark. At the European Southern Observatory’s (ESO) La Silla site in Chile, CSEM’s technology will help astronomers catch the tiniest movements in starlight, the kind that point to planets not so different from our own.
For thirty years, the University of Geneva (UNIGE) has led the search for exoplanets, i.e. planets orbiting other stars beyond our solar system. The same team that shared the 2019 Nobel Prize in Physics for discovering the first exoplanet now leads the Near Infrared Planet Searcher (NIRPS), a next-generation spectrograph mounted on ESO’s telescope at La Silla. The NIRPS project measures the tiniest wobbles in a star’s light, a telltale sign of an orbiting planet, using a method known as radial velocity.
Detecting signals this small means the instrument must stay perfectly steady. Even a slight change in air temperature can affect the readings. That is where CSEM comes in. UNIGE commissioned CSEM to build a custom laser frequency comb (LFC): a reference light source so stable it is expected to keep the spectrograph precisely calibrated for years, enabling astronomers to trust every measurement.
Developed in close collaboration with UNIGE, CSEM’s LFC produces a stream of light made up of thousands of evenly spaced colors, like millimeter markings on a ruler but made of light. Astronomers line up a star’s light against this reference pattern to see if it has shifted slightly over time. Those tiny shifts reveal whether the star is moving toward or away from Earth, with precision down to just a few centimeters per second.
“For NIRPS, the spacing of these marks is set at 15 GHz, which gives a smooth, stable reference across a wide measurement range,” says Christopher Bonzon, Manager for Laser Technologies, CSEM. “When starlight passes through the spectrograph, these fixed intervals act like landmarks, making even minute changes visible and pointing to the possible presence of a planet.” It is expected to give the NIRPS instrument a precise reference to align every observation, year after year. Moreover, the system has been designed to run autonomously in the thin air and wide temperature swings of the Atacama plateau, checking its own performance, and flagging anything unusual.
“The installation of CSEM’s laser frequency comb at La Silla marks a significant step in extending Swiss precision beyond Earth-based laboratories. While CSEM’s and NIRPS’ teams are still in the process of fully integrating the comb into routine scientific observations, the system has already demonstrated the kind of promising stability required for long-term calibration,” explains Prof. François Bouchy, Co‑Principal Investigator, NIRPS Consortium, UNIGE. As integration progresses, this platform positions NIRPS to detect fainter and subtler signals, paving the way for discoveries of smaller, cooler, and potentially inhabited planets.
CSEM and UNIGE have transformed a laboratory concept into a system now installed at one of the world’s leading optical observatories. Beyond astronomy, the same precision technology opens opportunities in fields that require exact light measurements, such as telecommunications and advanced sensing. For CSEM, this project reflects a core commitment: precision, reliability, and a driving partnership for progress, on Earth and far beyond.
The laser frequency comb developed by CSEM is essential for achieving the high performance and long-term reliability we need for the NIRPS spectrograph. Together, we hope to make new discoveries and advance exoplanet science.
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