What makes some meteor showers continue for days, while the "Unicorn shower" can be shorter than one hour?

Question

The Washington Post's One hundred meteors in 15 minutes? ‘Short-lived outburst’ of shooting stars forecast for Thursday night. says:

A “short-lived outburst” is forecast for Thursday evening around 11:50 p.m. Eastern.

and later:

The prediction of an outburst comes from NASA research scientist Peter Jenniskens and Finnish Fireball Network’s Esko Lyytinen and was published in MeteorNews. The pair specialize in sniffing out meteor outbursts and storms, expertly calculating the orbits of various celestial bodies that give rise to meteor showers. Scientists still haven’t pinned down the object depositing the debris anticipated to trigger this display.

However, outbursts in 1925, 1935, 1985 and 1995 offered enough information for the team to produce a model. It indicates the close passage of a dense pocket of spaceborne debris. That narrow but potent debris stream is likely to manifest in a 15-to-40-minute-long barrage of meteors around 11:50 p.m. Eastern on Thursday, according to the researchers.

What will it look like? Jenniskens and Lyytinen indicate events in 1985 and 1995 produced 700 and 400 meteors per hour and wrote that this event could emit anywhere from around 100 per hour to even more than 1,000 per hour, the latter considered a meteor “storm.”

The outburst is calculated to last a fraction of an hour, so those numbers can be sliced in half. And because the radiant point of the meteors will be comparatively low in the sky, we can trim off a bit more.

The linked Meteor News article LIKELY ALPHA MONOCEROTIDS (AMO#246) OUTBURST ON THE MORNING OF NOVEMBER 22, 2019 gives orbital elements derived by different groups of astronomers that can be used to predict the time of maximum.

But what is it that makes this debris trail so narrow that the shower is predicted to last less than one hour while other showers can sometimes extend for several days?

Probably mostly depends on the age and original size of the comet which generates this particle trail. — Carl Witthoft, Nov 21 '19 at 16:39
They discuss this under RESULTS in METEOR OUTBURSTS FROM LONG-PERIOD COMET DUST TRAILS and Jenniskens has a review article On the dynamics of meteoroid streams. — Keith McClary, Dec 22 '19 at 03:55
TRACING THE DUST TRAILS OF COMET 67P/CHURYUMOV-GERASIMENKO from ESA. Five minutes, but I think I will re-watch at 0.25 speed. — Keith McClary, Dec 22 '19 at 21:06
@KeithMcClary I think I will re-watch with headphones and the lights out and pretend I'm back in college. Seriously though, these are really helpful, thank you! — uhoh, Dec 22 '19 at 23:51
ESA has actually imaged these trails but I can't find any orbital dynamics explanation of why the trails should form behind the comet like this (other than numerical simulations). I may have to do-the-math. — Keith McClary, Dec 23 '19 at 19:17
@KeithMcClary just to double check, these links are for 67P but the comet causing the predicted 15-minute meteor is an unknown long period comet, proposed to be comet C / 539 W1. Earth moves only about 27,000 km in 15 minutes, I'm trying to understand how trail that may be hundreds of years old could possibly be only 27,000 km wide, and hasn't spread out. — uhoh, Dec 23 '19 at 23:56
"Indeed, the meteoroid distribution in the a Monocerotid stream resembles known dust trails of short-period comets, except where we expect differences. Similar are the width of the stream and the shape of the stream cross section as well as the range of particle sizes et al. The width of (Sykes 1990). the stream reflects the mean ejection velocity, which is a function of perihelion distance and the size of the parent nucleus. Both are not necessarily different when comparing a long-period comet to the population of short-period comets.", according to: ... — Keith McClary, Dec 24 '19 at 03:35
... The Detection of a Dust Trail in the Orbit of an Earth-threatening Long-Period Comet. My understanding is that the grains take different orbits depending on their ejection velocity, so they may be spread out in width at the apogee, but they return to the same point where they were ejected (but at different times).The writers' expectations seem plausible to me (for the first return), I don't know if they are based on calculations. — Keith McClary, Dec 24 '19 at 03:36
"...but they return to the same point..." Ah! Now I am starting to get the beginning of an idea of where this is going! — uhoh, Dec 24 '19 at 03:39

score 2 · Accepted Answer · answered Nov 21 '19 at 23:09

It sounds like this effect:

... in addition to the usual shower on August 12th, there might be an extra surge of meteors on August 11th caused by a filament of dust newly drifting across Earth's orbit.
The filament, like all the rest of the dust in the Perseid cloud, comes from Comet Swift-Tuttle. The difference is, the filament is relatively young. It boiled off the comet during the Civil War, in 1862. Other dust in the cloud is older (perhaps thousands of years old), more dispersed, and responsible for the month-long shower that peaks on August 12th. The filament will eventually disperse, too, but for now it retains some of its original ribbon-shape.

The 2004 Perseid Meteor Shower NASA

What makes some meteor showers continue for days, while the "Unicorn shower" can be shorter than one hour?

1 Answers1

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