Rare exoplanet alignment set for 2026 – but we are likely to miss it

An extraordinary and rare celestial event – an alignment of two distant planets and their star, predicted to take place on 1 April 2026 – will probably go unseen by humanity because astronomers have been denied telescope time to observe it.

The event is a syzygy, an alignment of three celestial bodies in a row, but because it will take place outside our solar system, it has been dubbed an exosyzygy, similar to the term exoplanet. The only known example of this took place in 2010 and was discovered by Teruyuki Hirano at the Tokyo Institute of Technology, Japan, and his colleagues by analysing data from NASA’s Kepler space telescope.

Kepler discovered planets by watching stars and looking for a dip in their light, caused by a planet passing in front, or transiting. Hirano’s team looked at a star called Kepler-89 and saw a signal that suggested two planets passing in front of the star at the same time, then, surprisingly, the amount of light momentarily increasing. This could only occur if the two planets were aligned with their star, as viewed from Earth, creating the exosyzygy.

In 2013, the team predicted that the next such alignment around Kepler-89 would probably take place on April Fool’s Day 2026 and last for around 2 hours. “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’,” says Hirano.

Now, this date is fast approaching. Hirano and his colleagues applied for observation time with both the Hubble Space Telescope and the European Space Agency’s CHEOPS telescope, but were unsuccessful, in part because reviewers felt that a new observation may only confirm what was known before. Hirano says there are still unanswered questions around the prediction because the orbits of the planets around Kepler-89 – the star has four in total – is “so complicated”.

“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” says Hirano. “Our latest calculation still suggests that there is a good chance of the event happening in 2026.”

Besides witnessing a rare event, Hirano says the observation would allow the team to gain more information about the system, such as the mass of the planets. But if no telescope is made available, he won’t give up and he plans to calculate when the next alignment will occur.