As the Earth orbits the Sun, it passes through dust and debris left by comets and asteroids. This waste results in meteor showers, which can be one of nature’s most amazing spectacles.
Most meteor showers are predictable and are repeated annually when the Earth traverses a particular runway of debris.
From time to time, however, the Earth passes through a particularly narrow and dense group of ruins. This translates into a meteorite storm, which sends thousands of shooting stars across the sky every hour.
Artistic print of the Lions meteorite storm of 1833. Adolf Vollmy (April 1888)
A minor rain called Tau Herculids could create a meteor storm for observers in America next week. But while some websites promise “the most powerful meteor storm of generations,” astronomers are a little more cautious.
Presentation of comet SW3
The story begins with a comet named 73P / Schwassmann-Wachmann 3 (for short for comet SW3). First discovered in 1930, it is responsible for a light meteor shower called Tau Herculids, which today appears to radiate from a point of about ten degrees from the bright star Arcturus.
In 1995, comet SW3 suddenly and unexpectedly illuminated. Over the course of a few months, a series of explosions were observed. The comet had fragmented catastrophically, releasing large amounts of dust, gas and debris.
By 2006 (two orbits later), comet SW3 had disintegrated further, into several bright fragments accompanied by many smaller pieces.
Fragments of Comet 73P seen by the Hubble Space Telescope in 2006. NASA, ESA, H. Weaver (APL / JHU), M. Mutchler, and Z. Levay (STScI)
Is the Earth colliding?
This year, Earth will cross the orbit of comet SW3 in late May.
Detailed computer modeling suggests that debris has spread along the comet’s orbit like huge thin tentacles in space.
Has the debris spread far enough to find the Earth? It depends on how much debris was ejected in 1995 and how quickly this debris was thrown out when the comet was disposed of. But the pieces of dust and debris are so small that we can’t see them until we run into them. So how do we get an idea of what might happen next week?
Could history be repeated?
Our current understanding of meteor showers began 150 years ago with an event quite similar to the history of SW3.
In 1772 a comet called 3D / Biela was discovered. It was a short-period comet, like SW3, that returned every 6.6 years.
In 1846, the comet began to behave strangely. Observers saw that his head had split in two, and some described an “arc of cometary matter” between the pieces.
Sketch of Comet 3D / Biela in February 1846, after splitting into (at least) two pieces. Edmund Weiß
On the comet’s next return, in 1852, the two fragments had clearly separated and both were fluctuating unpredictably in brightness.
The comet was never seen again.
But in late November 1872, an unexpected meteor storm engulfed the northern skies, striking observers at speeds of more than 3,000 meteors per hour.
The meteorite storm of 1872. Amedee Guillemin
The meteorite storm occurred when the Earth crossed the 3D / Biela orbit: it was where the comet itself should have been two months earlier. A second storm, weaker than the first, occurred in 1885, when the Earth rediscovered the comet’s remains.
3D / Biela had disintegrated into rubble, but the two large meteorite storms it produced served as a suitable wake.
A dying comet, which crumbles before our eyes, and an associated meteor shower, usually almost imperceptible with the background noise. Are we about to see history repeat itself with Comet SW3?
What does this suggest for the Tau Herculids?
The main difference between the events of 1872 and this year’s Tau Herculids lies in the time of the Earth’s crossing of the comet’s orbits. In 1872, the Earth crossed the orbit of Biela a few months after the comet arrived, traversing backward material where the comet would have been.
In contrast, the encounter between the Earth and the SW3 debris stream next week occurs several months before the comet reaches the crossing point. Therefore, the debris must have spread in front of the comet for a meteorite storm to occur.
Could the debris have spread far enough to find the Earth? Some models suggest that we will see a strong screen from the shower, others suggest that the waste will fall short.
Don’t count your meteors before they blink!
Whatever happens, next week’s rain observations will greatly improve our understanding of how comet fragmentation events happen.
Calculations show that the Earth will cross the SW3 orbit around 3 pm on May 31 (AEST). If the debris arrives long enough for the Earth to find it, an explosion of the Tau Herculids is likely, but it will only last an hour or two.
From Australia, the show (if any) will end before it gets dark enough to see what happens.
For Australian observers, the radiant Tau Herculids is low in the northern sky around 19:00 local time. Museums Victoria / stellarium
However, observers from North and South America will have a seat next to the ring.
They are more likely to see a moderate display of slow-moving meteors than a large storm. That would be a great result, but it could be a little disappointing.
However, there is a possibility that the shower will make a truly spectacular display. Astronomers are traveling around the world, just in case.
What about Australian observers?
There is also a small chance that any activity will last longer than expected, or even arrive a little late. Even if you’re in Australia, it’s worth looking up the night of May 31st, in case you can see a snippet of a dying comet!
The 1995 garbage stream is just one of many established by the comet in recent decades.
During the morning of May 31, around 4 a.m. (AEST), the Earth will cross the comet’s passage debris in 1892 around the Sun. Later that night, around 8 pm, May 31 (AEST), the Earth will cross the remnants left by the comet in 1897.
However, the remnants of these visits will have spread over time, so we hope that only a few meteors will appreciate our sky from these currents. But, as always, we may be wrong: the only way to know is to go out and see him!
At midnight (local time), the radiant Tau Herculids will have moved across the northwest sky, seen from all over Australia. Victoria / Stellarium Museums