Hubble Confirms Comet ATLAS Has Shattered Into Pieces

Well, that’s a bummer. Comet C/2019 Y4 (ATLAS) was supposed to be the big sky show of 2020 — some forecasts had it brightening enough to be visible in daylight, which would have made it one of the more spectacular comets in decades. Instead, Hubble just delivered the astronomical equivalent of “it’s complicated.”

New images taken with the Hubble Space Telescope today show the comet has broken apart into at least three, possibly four, distinct fragments. This isn’t a rumor or a modeling prediction anymore — it’s a direct visual confirmation from the best telescope we have pointed straight at the thing.

What actually happened

Ground-based observers had already started flagging that ATLAS was behaving oddly a couple weeks back — its brightening curve stalled and its coma (the fuzzy atmosphere around the nucleus) started looking elongated and diffuse instead of tight and compact. That’s usually a bad sign for a comet’s structural integrity. Cometary nuclei are basically loosely bound dirty snowballs, and when one gets close enough to the Sun, the thermal stress and outgassing can be enough to crack it apart. Hubble’s resolution is what finally let us see it happen directly instead of inferring it from brightness curves.

The plan is to keep watching. Another Hubble observation is scheduled for April 23, just a few days out, which should tell us whether these fragments are stable chunks or whether they’re going to keep crumbling further. Fragmenting comets don’t always behave predictably — sometimes the pieces settle out and you get multiple smaller comets following roughly the same orbit, and sometimes the whole thing just disintegrates into a stream of debris over the following weeks.

So is the “great comet” dead

Functionally, yes, in terms of the naked-eye spectacle people were hoping for. A comet made of several smaller fragments generally doesn’t produce the same dramatic, unified coma and tail that made ATLAS such an exciting prospect back when it was first found in December. That’s not to say there’s nothing to see — this is still a legitimate scientific opportunity. Watching a comet break apart in near-real-time gives researchers a rare look at what these bodies are actually made of on the inside, since fragmentation exposes fresh material that’s never been heated by the Sun before.

There’s also a decent chance amateur astronomers with backyard telescopes will still be able to track the fragments over the coming weeks as ATLAS continues its pass through the inner solar system, even if it never becomes the naked-eye showpiece the early hype suggested. I’ll be curious to see what the April 23 follow-up shows — whether we’re looking at three or four stable pieces, or a comet that’s still actively falling apart.