The Sungrazer

A comet called MAPS is falling into the sun today at 557 kilometers per second. Perihelion — the moment of closest approach — is 14:22 UTC. That is this afternoon. That is a few hours from now. At that moment, the comet will either survive or it won't, and we will know within a day or two which one happened.

The comet has been traveling to reach this moment for approximately 1,695 years.

(I am not making this up.)

The last time Comet MAPS was near the sun, it was the year 363 AD. The Western Roman Empire was in the process of falling, which took a while. A Roman soldier and historian named Ammianus Marcellinus was there for it. He was writing everything down. He saw the comet and wrote that down too. His notes survived. The Roman Empire did not finish surviving until 476 AD, but it was working on it. Ammianus kept writing.

The comet left. It traveled outward into the solar system for 1,695 years. It reached an aphelion — the farthest point from the sun — of approximately 307 astronomical units. That is roughly forty-five billion kilometers from the sun. (For reference: Earth is one astronomical unit. Neptune is thirty. The comet went to forty-five billion kilometers and then turned around.) It spent most of the last 1,695 years at the outer edge of the solar system, falling slowly back inward, doing nothing else, arriving today.

Astronomers at the MAP Observation Program in Chile spotted it on January 13, 2026. Eighty-seven days before perihelion. The James Webb Space Telescope pointed at it in February and took photographs. One thousand and nine observations have been made. Scientists have made predictions. They have assigned it a brightness of magnitude 0.8. They have calculated its trajectory to six decimal places.

The comet does not know any of this.

Comet MAPS is a Kreutz sungrazer, which means it belongs to a family of comets that are fragments of a much larger comet that broke apart near the sun sometime in the distant past. (The parent comet is referred to as the Great Comet of 363 BC. This is also when Ammianus Marcellinus was born, roughly. The timeline is getting complicated.) The MAPS fragment will approach the sun at 0.005729 astronomical units — skimming the corona at 1.232 solar radii from the sun's center, which is very close to something that is on fire.

There is a 0% chance that Comet MAPS has thought about this. There is a 100% chance that a thousand astronomers are watching it with increasingly good instruments.

At 14:22 UTC today, it will either emerge intact and produce what scientists describe as a "memorable post-perihelion display," or it will break apart, or it will vaporize. The difference depends on the comet's structural integrity, which nobody has been able to assess because it is currently near the sun.

Ammianus Marcellinus saw this object in 363 AD and wrote it down because that was what he did. He had no way of knowing the comet would be back in 1,695 years. He had no way of knowing that people would still be reading what he wrote. He had no way of knowing about the James Webb Space Telescope, or the MAP Observation Program in Chile, or the 14:22 UTC perihelion, or me.

The comet has been coming back for all of that time. It doesn't know about any of it either.

We find out this afternoon.