Astronomers have been predicting a “storm” from the Tau-Herculid meteor shower for years. The rare and long-awaited phenomenon could happen next week, with the possibility of thousands of “shooting stars” per hour, if the researchers’ projections are confirmed.
If all goes well, the meteors should hit our atmosphere at a speed of 16 km/s, which is considered low. Thus, the light lines can travel slowly and long, staying in the sky longer.
The peak of the possible storm is forecast to occur between Monday and Tuesday (May 30-31). The phenomenon will be better observed from the Northern Hemisphere, but the possibility of it generating a beautiful spectacle in Brazilian skies is not ruled out.
Tau-Herculids is formed by debris from comet 73P/Schwassmann-Wachmann 3 (SW3), which is breaking up. Every year at this time, between late May and early June, Earth crosses the trail of dust and small rocks it left behind on previous passes.
Typically, this shower is more discreet, with two or three meteors per hour. “It was more intense in 1930, when it was seen for the first time. Afterwards, it became very weak”, says amateur astronomer Lauriston Trindade, a member of Bramon (Brazilian Meteor Monitoring Network).
Storm or rain?
Engraving depicts the commotion caused by the Leonids meteor storm in 1833
It has been almost 200 years since we witnessed a phenomenon of this type and intensity. The last one happened in 1833, in the Leonids rain — which created panic in the United States (imagine, at that time, waking up at dawn with thousands of lights streaking the sky; was it the end of the world?).
“Storm” is the term for a meteor shower that features an unusual, extremely intense outbreak. They usually arise after a fragmentation of their “parent” asteroid or comet — a process that leaves a dense cloud of ejected particles into space.
“Over time, this cloud disperses in the orbit of the parent body, forming the annual meteor showers. So, the more recent the fragmentation, the denser the cloud, and the more intense the meteor storm generated by it”, explains to Bramon.
Two nuclei of Comet 73P with tails, recorded by telescope on a pass by Earth
Image: Michael Jaeger
Destruction of a comet
Comet SW3 was discovered in 1930 by German observers Arnold Schwassmann and Arno Arthur Wachmann. It was calculated to have a core about 1.5km in diameter—relatively small—and orbit the Sun every 5.4 years.
But it disappeared from our skies for decades, only to be seen again in 1979, with a normal appearance.
In 1995, however, its brightness suddenly increased: it was about 600 times brighter, becoming visible even to the naked eye. Until then, it was just a speck on telescopes.
“A month later, astronomers discovered that the nucleus had broken up into some large blocks during the trip. The observations indicated at least four large fragments, two of which were in the clear process of disintegration”, recalls Trindade.
In 2006, when it was heated on its return to the interior of the Solar System, the situation worsened: in March, there were already eight fragments; in April, dozens; in May, almost 70, along an immense trail.
The largest of them remain in orbit, acting as a multiple nucleus. Eventually, the comet may completely disintegrate and become unobservable.
Infrared image shows comet 73P shattered; at least 36 fragments can be seen in a trail
“The ruptures generated fragments of different sizes; an immense amount of dust was thrown into space. Calculations indicate that on the night of May 30th to 31st, the Earth will vertically cross a dense region of debris”, believes Bramon.
When these small rocks hit the Earth’s atmosphere at high speed, they are literally burned and vaporized by friction, generating the luminous phenomenon called a meteor (the popular “shooting stars”).
Uncertainties about the phenomenon
Since the 1995 fragmentation, astronomers have performed calculations to predict this storm. “The great difficulty in predicting meteor dates and rates is precisely to know what the particle ejection velocity was during the breakup of large blocks”, explains Trindade.
Studies indicate that, this year, Earth will pass through the cloud of debris left by comet 73P in five previous passes: 1892, 1930, 1941, 1979 and 1995 (when the breakup occurred).
“All expectations indicate that it will be a very high activity. But we know that there are chances that the calculations will fail, because it is something unprecedented and we don’t have enough data”, he adds.
The show is not yet guaranteed. According to NASA, it will be an “all or nothing” moment: if, during the breakup of the comet, the particles were ejected from the nucleus at a speed of at least 354 km/h, we will have a beautiful storm. Otherwise, they won’t hit our atmosphere — that is, we won’t see meteors.
“It is not possible to predict with precision. It could be that nothing happens, it could be a light, intense rain, and even a meteor storm, a rare and inspiring spectacle”, says Marcelo de Cicco, astronomer coordinator of Exoss, project Collaborative Meteor Research.
How to observe
Despite its name, the radiant (point where meteors appear to converge) of the Tau-Herculids is the constellation Boieiro, known for the bright stars Arcturus and Vega.
Just find it, heading northwest and look carefully around you. A compass or astronomy app (like Stellarium, Star Walk, Star Chart, Sky Safari, and SkyView) can help.
The best places on the planet to follow the phenomenon are Mexico and the United States. The bad news for us is that, here in the southern hemisphere, the radiant will be very close to the horizon, making observation a little difficult. In Brazil, we can see between 10% and 50% of meteors — the further north of the country, the more chances.
“It seems little, but if the best scenarios are confirmed, this could mean tens of thousands of meteors per hour, which would be spectacular”, highlights Trindade. The good news is that the moon in the new phase, without brightness, will make the sky darker. Thus, even the least intense meteors can be observed.
The recommendations are the same for all rains: look for a place with less light pollution, with a good field of vision, get comfortable and wait, looking at the entire area around the radiant. The phenomenon is visible to the naked eye, without the need for any special equipment.
According to Bramon, at least three outbreaks of Tau-Herulds should occur:
May 31, 12:10 am ET: Earth will cross the debris trails left by the comet in 1892 and 1941. Up to 50 meteors are expected per hour. May 31, 2:10 am: Earth will hit the 1979 trail and also the dense cloud thrown up by the 1995 rupture. As it is the first time in history that we have interacted with these particles, the time may vary (and even not occur). Basic modeling indicates a rate of 600 to 700 meteors per hour. “However, considering that in 1995 the comet broke into several pieces, the intensity of this outbreak could reach up to 10,000, or perhaps 100,000 meteors per hour during the maximum”, believes Bramon, optimistically. : Earth will meet the trail left in the 1930s pass. The intensity will be much lower, with about three meteors per hour.
Outbreaks are unpredictable and short-lived, so keep an eye out. “Because of the uncertainty of the orbital position of the other pieces of comet SW3, we recommend that observations be made in the period from May 28 to June 1, always at dawn, with the possibility of seeing many meteors coming from the Northwest direction, close by to the radiant”, emphasizes de Cicco.