Penelope Wilson
Penelope Wilson
April 21, 2020 ·  5 min read

As Comet ATLAS crumbles away, Comet SWAN arrives to take its place for sky-watchers

The last comet that came reasonably close to the earth was Comet 46P/Wirtanen in 2018, but the show was a bummer since the comet was blurred out by high pollution areas. Comet ATLAS became the next buzz after it was discovered on Dec. 28, 2019, by the robotic survey Asteroid Terrestrial-impact Last Alert System, where it got the name ATLAS [1].

Also known as Comet C/2019 Y4, there was a huge buzz that this comet is going to be the first naked-eye friendly ball of dust and ice to be seen in decades as it descended closer to the earth. It was estimated that it would be 0.781 astronomical units (117 million kilometers) at its closest distance from the earth, which is about 303 times the distance of the moon from the earth.

Astronomers discovered about 94 comets in 2019, but the ATLAS stood out because it was the only one with the potential to be seen clearly in the earth’s sky. They were super-excited because, at a distance of 0.25 AU from the sun, which is within the orbit of Mercury, Atlas was certainly going to heat up and became exceedingly bright, so much that it could be possible to spot even the faint tail with the unaided eye [2].

There was a lot of speculation about Atlas when it was first found. The comet was traveling in similar galactic trajectories with the Great Comet of 1843 and was believed to be a fragment from the larger celestial body.

Atlas was expected to appear in its most visible form any time between late April and early May. To the unaided eye and small telescopes, people hoped to see a large, extremely bright slow-moving star making its way across the sky. To powerful stargazing equipment, you could see the slowly unfurling long banner of ghostly bright light.

And then, ATLAS fragmented before the big period

Comets are some of the most unpredictable bodies in the universe, and you can never be too certain with them. They may get too close to the sun and explode from their nuclei into smaller pieces, and that’s exactly what our precious ATLAS did.

“This thing could turn out to be completely spectacular and just put on a show for a couple of months,” said Larry Denneau, Co-PI and senior software engineer at the ATLAS observatory. “Or it could be like Comet ISON, which was supposed to be spectacular, as bright as the full moon. It got so close to the sun that it was wiped out immediately. So, we don’t know. It’s hard to make predictions. The current projections show it brightening greater than the models might indicate and that’s great, but these things are really fussy. It’s dangerous to make grandiose predictions about them.”

Well, you can’t blame us for wanting too much. Reports from Space.com on April 6 suggested that ATLAS’s brightness journey had “hit a wall” as of March 17 [3]. In the first week of April, the comet evidently began to drop in brightness and this became an alarming development to astronomers.

Several images captured by observers showed the nucleus of the comet beginning to fragment, and on April 11, it was confirmed that it had broken into at least three pieces [4]. ATLAS is on its way to fading completely by the time it reaches the sun at the end of May.

An image captured by astronomers at the Institute of Astronomy of the Bulgarian Academy of Sciences shows the multiple parts of the comet as the fragments began to separate.

Comet Swan to the rescue

I always like to think of celestial bodies as entities with emotions (weird, I know but it makes them seem more appealing). When we had a planet trifecta with the moon this April, when Jupiter, Saturn, and Mars lined up in the sky, I liked to think they were visiting with sick sister Earth.

Right on April 11, the same day it was confirmed that Comet ATLAS has disintegrated, Comet SWAN came into view. It’s just cute to think that ATLAS couldn’t hold up and knew it was going to disappoint the millions of us who’d been waiting, and so it held out until SWAN came along.

An amateur astronomer, Michael Mattiazzo was comparing data from NASA’s Solar and Heliospheric Observatory (SOHO) when he discovered SWAN. The comet was detected by the SOHO’s Solar Wind Anisotropies, and hence, the name SWAN (and another cute thought, Mattiazzo lives in Swan Hill, Victoria, Australia).

The instrument was designed to pick up hydrogen emissions around the solar system, but SWAN was emitting a considerable amount of hydrogen in the form of ice and was flagged by the instrument.

Could SWAN be the bright star ATLAS didn’t get to be?

If you’re on the south of the equator, you’d be able to see the relatively small comet as it advances closer to the earth. The best viewing date is estimated to be May 12, when it will pass closest to the earth at a very safe distance of 51.8 million miles (83.3 million kilometers).

The current estimated magnitude of Comet SWAN (C/2020 F8) is 10.68 (JPL), and people are wondering if it will heat up as much as ATLAS did.

While Swan is not significantly showing signs of aggressive fire-packing like its predecessor (yet), researchers believe that it might get bright enough to be seen with the unaided eye in the final week of May, according to Space.com [1]. It will be at its closest point to the sun (perihelion) on May 27, and before it moves out of sight, it could heat up and become incredibly bright.

Again, it’s important not to get our hopes up so much. Comets are great at disappointing people, and there a high chance SWAN would disappear/disintegrate just as suddenly as it appeared.

References:

  1. “As Comet ATLAS crumbles away, Comet SWAN arrives to take its place for skywatchers.” Space.
  2. “A Bright Comet Is Approaching Earth. Here’s How You Can See It Now.” Thrillist
  3. “Bright Comet ATLAS could blaze into view this month.” Space
  4. “Comet Atlas is falling apart, new photos confirm.” Space.
  5. “Asteroid Terrestrial-impact Last Alert System”. Atlas.
  6. “SOHO: Spying on the Sun.” Space.