An extraordinary celestial event may occur soon, but many will miss it. The Kepler-89 system, the only known place outside our Solar System to have seen two exoplanets eclipsing each other, is expected to present a similar occurrence again. This event would align four celestial bodies: Earth, the star Kepler-89 A, and two of its planets, Kepler-89Ad and Kepler-89Ae.
The alignment of three or more celestial bodies is called a syzygy. This phenomenon can be likened to solar eclipses in our own Solar System. Observations from 2010 captured the outer planet of Kepler-89 A eclipsing another, marking an important discovery. Teruyuki Hirano from the Tokyo Institute of Technology, who was part of the original team, estimates that this event could happen again in April, although the exact timing remains uncertain due to various factors affecting the planets’ movements.
However, there is a challenge. No observatory is currently set to monitor the event in April. The European Space Agency’s CHEOPS telescope cannot observe it, and the team was unsuccessful in securing time with the Hubble Space Telescope. Hirano noted that the star is best observed in summer, complicating ground-based observations.
Despite these challenges, this event is significant for understanding distant planetary systems. Planet-planet eclipses provide an opportunity to measure the relationship between the orbits of planets, offering insights that are hard to achieve otherwise. The Kepler-89 system, discovered by NASA’s Kepler nearly twenty years ago, may soon not be unique in having eclipsing planets, as advancements in exoplanet research continue. A new mission, PLATO, is set to launch next year, potentially discovering more planets in our nearby cosmos. If this April event isn’t observed, the team will plan for the next opportunity.
