Comet 29P suffers the brightest explosion in recent years – Sky & Telescope

Martin Mobberley captured this image of the bright explosion of Comet 29P / Schwassmann-Wachmann at around 9:50 a.m. UT on September 29.
Martin mobberley

A comet infamous for its explosive personality has been exploding almost continuously since September 25. The brightness of comet 29P / Schwassmann-Wachmann is steadily increasing and it now appears as a small magnitude 11 object easily seen in telescopes 8 inches and larger. If you’ve never seen a comet disguise itself as a star-like planetary nebula, don’t pass up the opportunity – watch it soon. As the explosion evolves, the coma’s coma will expand but also fade.

Localization map of comet 29P / Schwassmann-Wachmann
This map plots the movement of comet 29P / Schwassmann-Wachmann at night until October 9. Posts are nightly at 11 p.m. EDT. Limiting magnitude, orientation (north up for all maps), and field of view are displayed in the upper left corner. The bright star, labeled 27 (its magnitude) is Iota (ι) Aurigae.
MegaStar, used with permission

The timing and location couldn’t be better, with the comet just 1.3 ° south-southeast of the visually-friendly star Iota (ι) Aurigae and standing on the threshold of a large viewing window. Best viewing begins around 10:30 p.m. in local daylight and lasts until dawn. I caught 29P on Tuesday night September 28 at 10:15 p.m. CDT, 45 minutes before the last quarter of the moon rose.

Composite photo of previous comet explosion: conflagration, expansion and fade
This composite photo shows the fascinating evolution of comet 29P / S-W1 from a previous light explosion from June 16, 2013 (bottom left) to July 28, 2013. The comet generally exhibits a characteristic horseshoe shape or spiraling as it evolves because we see the lateral explosion on a hemisphere. 29P appears to be running slowly with a possible period of 57 days.
Damien fishing

Although at only 12 ° elevation, I spotted the suspected comet in my 15 inch Dob even at the lowest magnification of 64 ×. With just a glance it looked exactly like a star, but with sidelong vision I could see a small, faint coma enveloping the shiny false core. Fortunately or not, 29P was involved with a magnitude 13 star some 12 ″ east at the time. When I looked again just before moonrise, he had parted.

Due to the low elevation I couldn’t make out more detail, just a bright, super-compact coma with a degree of condensation (DC) of 8 on a scale of 0 to 9, from least concentrated to most concentrated. I am as eager as you are to get the bezel out for another look. The comet may continue to ignite and brighten or begin its inevitable dimming. Seeing the night-to-night changes in a celestial object is one of the reasons comets are so fun to watch.

Map showing comet's orbit
Comet 29P / Schwassmann-Wachmann orbits beyond Jupiter with a perihelion of 5.7 au and an aphelia of 6.3 au
Courtesy of Richard Miles

Many comets have explosions, but 29P is unique because there are an average of 7.3 explosions per year! Typically two or three per occurrence are visible in amateur telescopes. Normally a magnitude 16 object, an explosion can cause this comet to go from darkness to a magnitude as bright as 10. It orbits a little beyond Jupiter with a period of 14.7 years, and like comets, it orbits a little beyond Jupiter. is huge with a diameter of 60.4 ± 7.4 kilometers. Frankly, seeing any comet at such an incredible distance is not only amazing, but an indication of how powerful the current explosion is.

Richard Miles, with the British Astronomical Association (BAA), is the project leader for MISSION 29P, a clearinghouse devoted to news and observations of the comet in the hope of better understanding the underlying cause of its tumultuous explosions. Miles suspects that the object may have suffered four successive explosions, “each subsequent event triggering the next” during the current push. Another good resource for current comet events is the comet mailing list.

Close-up of comet 29P on September 28, 2021
This photo, taken on September 28, closely resembles the current visual appearance of the comet in a medium-sized telescope at high magnification.
Richard Miles

Water ice, an important volatile that stimulates the activity of many comets, is practically inert at a distance of 29P. Instead, the vaporization of carbon monoxide ice appears to be the primary driver of its regular explosions. Based on data obtained largely by amateur astronomers, Miles describes the explosions as cryovolcanoes that explode explosively after carbon monoxide and methane, under pressure under the comet’s crust, melt, mix and release energy. Solar heating causes the crust to break above these points, explosively releasing gases and a million tons of dust and debris all at once. Consider popping the cork of a bottle of champagne. Because 29P is a large comet, its gravity temporarily closes the “wound” until another cycle begins.

As described in the September 2021 issue of Sky and Telescope magazine, there is currently a campaign to observe this comet. We encourage you to share your observations on page 29P / SW 1 Observations.

I wish you clear skies so that you can witness the delicious and informative volatility of 29P!


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