SN Ares Supernova Will Return Twice in 70 Years

The explosion happened once. Earth gets to watch it three times. A team led by Conor Larison of the Space Telescope Science Institute reports the discovery of SN Ares, a supernova that detonated about 8.8 billion years ago, when the universe was 4.9 billion years old. They spotted it in August 2025, in near-infrared images the James Webb Space Telescope took of the galaxy cluster MACS J0308.9+2645. The discovery paper was posted to the arXiv preprint server on October 23, 2026, so it hasn't yet passed peer review, and every number in it should be read with that label attached.

The cluster is the instrument. A galaxy cluster that massive bends the light of the galaxies behind it, magnifying them and splitting them into multiple images, a phenomenon called gravitational lensing. Each image's light takes a slightly different path around the cluster, so the images arrive at different times — sometimes hours apart, sometimes decades. Ares is the extreme case. The team's analysis, run through three separate lens models, says two more images of the same supernova are still in transit and will appear in about 73 and 76 years.

The supernova itself sets a record of a different kind. Webb's spectroscopy shows helium and hydrogen signatures, the marks of a star that had shed most of its outer hydrogen layer before exploding — a Type IIb supernova. At a redshift of z=1.276, the team says it's the highest-redshift member of its class ever identified spectroscopically. That's the measurement that makes Ares more than a curiosity: it's a well-characterized explosion, not just a bright smudge.

The delay is the prize. Because the gap between image arrivals is set by the geometry of the paths and the expansion of space itself, timing a lensed supernova's return gives a direct handle on the Hubble constant, the universe's expansion rate — one of the most contested numbers in cosmology. The team writes that at an assumed timeline of 70 years, the SN Ares system has by far the highest predicted delays of any discovered lensed supernova system so far. A return caught on schedule, seven decades from now, could be timed precisely enough to yield one of the sharpest single measurements of that rate.

Nobody on the discovery team will run that observation. That's the strange, honest core of this paper: it's a bequest. The team's own next step is nearer-term — additional spectroscopic redshift measurements planned for early 2027, to pin down the lens properties and sharpen the arrival predictions they're handing forward. After that, the work belongs to astronomers who are currently in school, or not yet born, using instruments that haven't been designed.

Lensed supernovae have form here. Hubble spotted the multiply imaged Supernova Requiem in the MACS J0138 cluster in 2016, with a fourth image expected in 2035, and Webb later found a second lensed supernova in the same galaxy — the first system known to produce more than one. Ares stretches that same trick across a human lifetime. The universe, it turns out, keeps receipts. It just delivers some of them very, very late.