Close pass of ‘swarm’ calls for close observation

An oncoming swarm of meteors – one blamed for perhaps the most famed Earth encounter since the time of the dinosaurs – may statistically pose a more immediate risk for Earth and its inhabitants than previously believed. That fact, according to Western researchers, makes its observation all the more important.

“Observation of events like these allows us to understand the risks we face – our research is a call for observers to go out and observe,” Earth Sciences PhD candidate David Clark said. “The more we observe, the more we understand, just as the more we don’t observe, the things that don’ happen that we think might, the more we understand, as well.”

When considering catalysts for catastrophic collision with our planet, the go-to list is short: near-Earth objects (e.g. asteroids and meteoroids) and interlopers from the outer solar system (e.g. comets). Nearly 90 per cent of near-Earth objects have been catalogued in recent years; work is ongoing to chart the more-difficult-to-spot visitors from outside the solar system.

However, a third catalyst for catastrophe exists, one that doesn’t get near the attention, and looms large this summer, according to Western researchers.

The Taurid swarm is a theorized dense cluster of objects within the known Taurid meteoroid stream. Every year from September-November, the Earth passes through this broad stream of debris left by Comet Encke. The dust associated with the comet hits the Earth’s atmosphere at 65,000 mph and burns up, creating the Taurid meteor shower. Most years the shower is weak and only a few Taurid meteors can be seen each night. Other years, the Taurids can put on a show.

Clark explained that early work around the swarm had more of an “exploding-space-rocks-of-doom” feel that turned people off to its study. That is unfortunate, he continued, saying that by emphasizing the sensational over the science, the swarm maybe didn’t get the attention it needed.

It wasn’t until 2015, when measurements of the Taurid encounter offered real insights. That researchers began to take serious note.

This year, Earth might be in store for a closer – and, potentially more damaging – encounter. And researchers are looking to our past to eye our future.

Special to Western NewsHistoric photo of Tunguska damage (1929).

Most space junkies know about the Tunguska Event.

On June 30, 1908, in a remote part of Russia, a fireball was seen streaking across the daytime sky. Within moments, something exploded in the atmosphere above Siberia’s Podkamennaya Tunguska River. It released enough energy to kill reindeer and flatten trees for kilometers around the blast site.

Previously, Physics and Astronomy professor Peter Brown, along with colleagues from the Los Alamos National Laboratory, showed that the tree-fall pattern in Siberia was consistent with an asteroid coming from the same area in the sky as the Taurid meteor swarm. At a presentation of the American Geophysical Union last year, Brown called for a special observation campaign to search for Tunguska-class or larger objects embedded in the Taurids.

Now widely known as The Tunguska Event, it has been immortalized in popular culture by everyone from Thomas Pynchon and Isaac Asimov to The X-Files and The Simpsons. It was considered a one-in-1,000-year event assuming a random distribution of events over time.

However, if Western researchers are correct, the hypothesized might of the Taurid swarm may heighten the possibility of a cluster of large impacts like Tunguska over a shorter period of time. For example, a one-in-a-thousand-year event might be far more frequent than believed.

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For their study, Clark, Brown and Physics and Astronomy professor Paul Wiegert simulated a large collection of 100-metre diameter meteoroids (like the one that triggered the Tunguska Event) with orbits similar to the Taurid swarm. They calculated the positions of the objects forward for 1,000 years.

By analyzing, each object’s position and motion over time, the astronomers calculated two optimal viewing times and telescope pointing locations for the Taurid swarm to properly investigate its overall risk potential.

According to Western Meteor Physics Group data analysis, the Earth will approach within 30 million km of the centre of the Taurid swarm this summer. That may not seem close when compared to your daily commute, but in the expanse of space, it is a close call – the closest such encounter since 1975.

“It keeps reminding us these things can happen, and let’s be honest, they will happen,” Clark said. “We don’t know if it will be in a thousand years, a hundred years, or tomorrow. It reminds people of how small and exposed we are in the cosmos.”

Western calculations also show that this will be the best viewing time of the Taurid swarm until the early 2030s.

“There has been great interest in the space community since we shared our results at the recent Planetary Defense Conference in Washington, D.C.,” Clark said. “There is strong meteoric and near-Earth object evidence supporting the Taurid swarm and its potential existential risks. But this summer brings a unique opportunity to observe and quantify these objects.”

Taurid meteors can be seen any time the constellation Taurus is above the horizon during the months of September, October, and November. The best time to look for Taurids is after midnight, when Taurus is high in the sky, and when the sky is dark and clear, with no moonlight to mask the fainter meteors. Given the behavior of past Taurid swarms, increased fireball activity may be seen during the last week of October and the first two weeks of November.

Members of the Western Meteor Physics Group plan to observe the Taurid swarm using the Canada–France–Hawaii Telescope at the University of Hawaii in August.

The study, The 2019 Taurid resonant swarm: prospects for ground detection of small NEOs, was recently published within the open-access community arXiv and has been accepted for publication in Monthly Notices of the Royal Astronomical Society.