Astronomers have forecasted a rare alignment of two planets and their star in the Kepler-89 system for April 1, 2026, but the event may pass unobserved due to denied telescope access. This exosyzygy, first identified in 2010, offers a unique chance to study planetary orbits, yet complications in scheduling have thwarted observation efforts. Researchers remain optimistic about the prediction while planning for future opportunities.
In 2010, Teruyuki Hirano and his team at the Tokyo Institute of Technology analyzed data from NASA's Kepler space telescope and detected the first known exosyzygy—a straight-line alignment of three celestial bodies around a star outside our solar system. The discovery involved the star Kepler-89, which hosts four planets, and revealed two of them transiting the star simultaneously, briefly increasing the observed light as they aligned from Earth's perspective.
By 2013, the researchers had predicted the next such alignment would occur on April 1, 2026, lasting approximately two hours. Hirano recalls the amusement in presentations: “When I made a presentation in meetings, it was always fun to say: ‘The next event will take place on April 1 2026, and I’m not joking’.”
As the date nears, Hirano's team sought observation time on the Hubble Space Telescope and the European Space Agency's CHEOPS mission, but both applications were rejected. Reviewers deemed the observations unlikely to yield new insights beyond confirming existing data. The system's complex planetary orbits, influenced by factors like planet masses and dynamical interactions, add uncertainty. Hirano notes: “We found that the event would likely happen in 2026, but it would depend on many factors including the true planet masses, dynamical interactions among planets and presence [or] absence of outer, additional, planets in the system.” Recent calculations still indicate a strong possibility for 2026.
Observing the event could provide valuable details on planetary masses and system dynamics. Without access, Hirano plans to model the subsequent alignment. This missed opportunity highlights challenges in allocating scarce telescope resources for rare astronomical phenomena.