Say It Ain’t So! Comets ATLAS And Borisov Commence To Crumble

These photos from the 0.6-m Ningbo Education Xinjiang Telescope show a possible fragmentation of ATLAS’s core. The photo are color-coded to better distinguish detail in the comet. Quanzhi Ye and Qicheng Zhang

No, no, no. Please don’t let it happen. It appears that the nucleus of Comet ATLAS, the one predicted to brighten to naked-eye visibility next month, may be breaking apart and breaking our hearts.

In late March, Comet ATLAS shows a small, bright, round “nucleus”. A breakup in early April shows a fuzzy, more elongated nucleus. José Chambó Bris (left) and Gianluca Masi

The comet had been brightening rapidly as it headed sunward the past couple months … until recently. In the past week it lost steam and plateaued. That’s not all. In an Astronomical Telegram astronomers Quanzhi Ye (University of Maryland) and Qicheng Zhang (Caltech) report that photographs on April 5th revealed that the comet’s false nucleus had changed from a compact, star-like object to an elongated, lentil-like appearance “as would be expected from a major disruption of the nucleus” as reported in an Astronomical Telegram. A second team of astronomers using the Liverpool Telescope in the Canary Islands  confirmed the first team’s results.

Spectacular jets of vaporizing ice and dust shoot from the nucleus of Comet 67P/Churyumov-Gerasimenko taken by the European Space Agency’s orbiting Rosetta probe several years back. The comet measures about 2.5 miles (4 km) across. The tiny spots are dust grains released from vaporizing ice. ESA/Rosetta/NAVCAM

The nucleus is the heart of the comet, the rotating ball of ice and dust that partially vaporizes in sunlight to create the comet’s fuzzy head and swept-back tail. Either a fragment broke off the nucleus or the entire body is crumbling, causing it to spread apart and appear elongated in photos. Other observers have noted a slight drop in ATLAS’s brightness as well as an unexpected shift in its direction of movement caused by “non-gravitational” forces. Fragmentation exposes fresh icy material to sunlight which then vaporizes rapidly. The expanding gases give the comet a push like a rocket engine and set it off on a slightly different path.

Astronomers warned us this might happen. When fresh comets that hail from the edge of the solar system approach the sun they’re often quick to brighten as pristine ices swiftly vaporize. But then as they draw closer to the sun they crack under the stresses of heating and jetting. That appears to be happening now with Comet ATLAS and could mean its swift demise. Those in the know expect the nucleus to expand and become more diffuse until the comet fades away.

Photos taken in an 11-inch telescope by Australian amateur astronomer Michael Mattiazzo clearly show how Comet Elenin faded after its nucleus disintegrated. The left image was taken on August 3, 2011 when the comet was steadily brightening; the right on September 14 after the breakup. Michael Mattiazzo

Or not. Perhaps enough of the nucleus will survive to continue the journey and put on a modest show next month. We’ll just have to wait and see. Right now the full moon is out making the comet difficult to view, but a dark, moonless “window” opens up as soon as Thursday the 9th at the end of evening twilight. I’ll update you on the comet’s appearance and chances for survival later this week. Use this pdf map to spot it. Binoculars may still show it faintly but I recommend a 6-inch or larger telescope for a happy look. I will post a new map for you after full moon.

Nick Haigh of England compiled 682 10-second exposures taken with his 12-inch telescope on April 6 to reveal that Comet Atlas’s nucleus has broken into at least three pieces. Nick Haigh

In 2011 Comet Elenin, another visitor from the distant deeps, self-destructed only a couple weeks before its closest passage to the sun. Comets are inherently fragile entities made of porous ice and dust. Although solar heating and gravitational tugs from the sun and planets can play a role in a comet’s breakup, spin might be the main culprit. Jets of gas blasting away from the comet can cause it to spin faster and faster, stressing the icy body until it develops cracks that lead to a breakup.

Photos from the Hubble Space Telescope show how the core of comet 2I/Borisov went from single to double as a piece broke off in late March. 
Jewitt et al. / The Astronomers Telegram

Comet ATLAS isn’t the only one suffering from internal fractures. On March 23rd, 28th and 30th, Hubble Space Telescope photos revealed that the interstellar comet 2I/Borisov’s core had also become elongated. Comet Borisov is the first comet ever discovered belonging to another solar system to pay a visit to our own. Instead of a single bright spot the photos show two, small fuzzy object about 112 miles (180 km) apart. A third tiny fragment was found later in the images. It’s unknown whether the entire nucleus is busting up or if it’s just a few fragments breaking off the main body.

Comet 2I/Borisov, the first interstellar comet discovered, made its closest approach to Earth in late December 2019 at a distance of 180 million miles (290 million km). NASA, ESA, and D. Jewitt (UCLA)

Fragility is what makes comets so lovely to observe but it’s also their Achilles Heel.

5 Responses

  1. Edward M Boll

    Taking the average brightness of recorded observations from yesterday it appears that Atlas may have brightened a bit from magnitude 9.8 to 9.6. That probably doesn’t mean much except for the fact that we know it’s still out there.

  2. Edward M Boll

    This comet May not be done yet. After reports of seeing it at magnitude 10, the last reports put it back to about magnitude 9 again.

    1. astrobob

      Hi Edward,

      Hmmmm … that nucleus is pretty busted up but I’m still willing to be optimistic.

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