A new space telescope is preparing to survey the Sun’s closest stellar neighbors, Alpha Centauri A and B, for planets that might resemble our own. This focused mission, a departure from broad galactic surveys, will apply a novel optical technique to detect worlds within the habitable zones of these stars, which are just over 4 light-years away. If successful, the project could identify the nearest potentially habitable exoplanets, opening a new chapter in the search for life beyond Earth and identifying targets close enough for future study.
The mission, named TOLIMAN, is designed as a low-cost and agile project specifically to overcome the immense technological hurdles of spotting small, rocky worlds so close to their bright host stars. By concentrating on the Alpha Centauri system, scientists aim to fill a significant blind spot in astronomical knowledge; while thousands of distant exoplanets have been discovered, humanity knows very little about the planets orbiting the stars in its own cosmic backyard. The project brings together a global collaboration of researchers and engineers to achieve its ambitious goals, with a scheduled launch in 2026 for a three-year observing campaign.
A Precise Search in a Crowded System
The primary scientific objective of the TOLIMAN mission is to discover planets with masses comparable to Earth’s within the habitable zones of Alpha Centauri A and B. The habitable zone, often called the “Goldilocks zone,” is the region around a star where conditions might be right for liquid water to exist on a planet’s surface. The Alpha Centauri system is a triple-star system, but the mission’s focus is on its two Sun-like stars, A and B, which are tantalizingly close at just 4.3 light-years away. This proximity makes them prime candidates for a targeted search, as any planets found there would be the closest to our solar system.
The method TOLIMAN will use is called astrometry, which involves making extremely fine measurements of a star’s position in the sky. If a planet is orbiting a star, its gravitational force will cause the star to “wobble” slightly. Detecting this minuscule, periodic movement is the tell-tale sign of an orbiting world. This technique is sensitive enough to reveal not only the presence of a planet but also its mass and key orbital parameters, such as its path and inclination. For the Alpha Centauri stars, the mission is designed to be sensitive enough to detect planets down to one Earth mass.
Innovative Optics for a Difficult Task
Finding an Earth-sized planet next to a star is an extraordinary challenge. The faint signal of a planet is easily lost in the overwhelming glare of its host star. To overcome this, the TOLIMAN telescope incorporates a groundbreaking optical design centered on a diffractive pupil lens. This specialized mirror is etched with a complex pattern that intentionally spreads the incoming starlight, transforming the star’s focused point of light into a delicate, flower-like pattern on the telescope’s sensor.
While spreading out the light may seem counterintuitive, this innovative approach makes the task of detecting a planet’s signature easier. The intricate fringe pattern created by the diffractive optic is highly sensitive to tiny shifts in the star’s position. By analyzing changes in this pattern, scientists can measure the star’s wobble with a precision of about 2.5 micro-arcseconds, a signal consistent with an Earth-mass planet in the habitable zone of Alpha Centauri A. This clever optical strategy is pivotal to the mission’s performance, allowing a relatively small, 30cm-diameter telescope to achieve results that would otherwise require a much larger and more expensive instrument.
Embedding a Spectrometer
In addition to its primary optical function, the diffractive pupil mask also carries an embedded spectrometer that will measure the color of the starlight. This capability helps the science team monitor and calibrate for stellar activity—natural variations and sunspot cycles on the host stars—that could otherwise mimic the signal of a planet and degrade the data’s sensitivity. The combination of the unique optical architecture and signal encoding is crucial, as the planet’s signal is expected to be incredibly small, representing just a millionth of a single pixel on the detector.
A Global Partnership for Discovery
The TOLIMAN mission is an international effort led by scientists at the University of Sydney’s School of Physics. The project receives its primary funding from Breakthrough Initiatives, a suite of science programs dedicated to investigating fundamental questions about life in the universe. Dr. Pete Worden, the Executive Director of Breakthrough Initiatives, has noted that our nearest stellar neighbors are proving to be extraordinarily interesting and that the TOLIMAN mission represents a huge step toward discovering if they host life-supporting planets.
Several other key partners are providing essential expertise and technology. NASA’s Jet Propulsion Laboratory is contributing to the scientific goals, while Saber Astronautics in Australia is also a core partner. In 2023, the Bulgarian aerospace manufacturer EnduroSat joined the collaboration to provide its satellite technology for the mission. The mission has also received funding from the Australian Research Council and the SmartSat NSW Node Demonstrator grant scheme. This global collaboration unites scientific leaders and aerospace innovators to focus on a single, compelling target.
The Neighborhood and Beyond
Project leader Professor Peter Tuthill of the University of Sydney has highlighted a paradox in modern astronomy: researchers have found thousands of planets across the galaxy but remain largely ignorant about our immediate celestial neighborhood. The TOLIMAN mission was conceived to address this “blind spot,” as the planets it may find would be the most accessible for follow-up observation and, eventually, perhaps even robotic exploration. The name TOLIMAN is derived from the ancient Arabic name for Alpha Centauri, reflecting the mission’s focused goal.
Once launched into its planned 550km sun-synchronous low Earth orbit, the satellite will conduct its observational campaign for three years, downlinking data to the University of Sydney. While the primary goal is the thorough examination of Alpha Centauri A and B, the mission’s scope extends to other stars within 10 parsecs (about 32.6 light-years) of the Sun. This establishes TOLIMAN as a pioneering mission for exoplanetary discovery in the solar neighborhood, paving the way for future large-scale instruments designed to characterize these nearby worlds in detail.