Whenever you can, look up at the sky tonight and tomorrow night. There is a good chance that you will be treated to some free cosmic fireworks courtesy the Perseids meteor shower, which peaks this time of the year. Strong activity has been predicted for 11-13 August, and one can expect about 60-100 meteors per hour for on a clear night.
“In general, the Perseids are simply one of the most reliable annual meteor showers and always produce plenty of nice meteors to see, especially when the moon is absent from the sky, as is the case for the peak of this year’s Perseid shower,” David Asher, a noted meteor astronomer and a senior member of the International Meteor Organisation, Belgium, told The Wire.
One does not need any expensive equipment like powerful telescopes or advanced binoculars to enjoy this meteor display. As such, meteor phenomena are the most democratic astronomical events of all because everyone can enjoy the cosmic fireworks in full glory in equal measure.
“Every meteoroid stream is unique. However, the Perseids are interesting in several ways,” said Galina Ryabova, a top meteor expert based at the Tomsk State University, Siberia. “As far as I know, this stream or shower was the first which was associated with its comet, 109P/Swift-Tuttle. The first complete mathematical model for a meteoroid stream was constructed just for the Perseids.”
The meteor shower occurs when Earth, in its orbit around the Sun, passes through a cloud of dust and debris left behind by the Swift-Tuttle comet. The planet’s gravitational pull ‘sweeps up’ some of the debris towards itself, precipitating the shower over its skies as seen from the ground.
Scientists at the International Meteor Organisation compile meteor observations of various annual showers every year. Such records are compared and calibrated for better clarity and accuracy in observations.
“This hardly was possible without a long series of observations of the Perseids activity, including the outbursts. The meteor outburst, i.e. abrupt spike of enhanced activity, happens when Earth in its motion meets a compaction or a dense filament in the stream” Ryabova explained. She has worked extensively in meteoroid dynamics and modelling.
In August 1993, the Perseids showed unusually enhanced activity, which was later identified as a direct effect of an orbital resonance of the Perseids stream with Jupiter and Saturn.
“The Perseid stream was the first and only stream where three-body resonance seems to exist, as it was shown in 2016, and this can led to meteor outbursts or storms in the future” Ryabova said.
From an orbital point of view, the Perseids is the first meteoroid stream to show a stable three-body resonance with Jupiter and Saturn. This is similar to the famous three-body resonance found by the French astronomer and mathematician Pierre-Simon Laplace in 1799, between three Galilean moons of Jupiter – Ganymede, Europa and Io. The resonance is born of the fact that the moons’ orbital periods are in the ratio 1:2:4.
The orbital period of the Perseids, about 120 years, is roughly four-times that of Saturn’s period (i.e. 4 × 30 years) and 10-times that of Jupiter’s (10 × 12 years). It is this periodicity that makes the resonance tick like clockwork.
“A resonance can create a dense filament in the stream. This place, of heightened dust density, is dangerous for spacecrafts,” Ryabova explained.
Scientists and engineers monitor the dust influx, strength and densities of the Perseids with great interest because of the potential threat they pose to satellites and space instruments. During the 1993 meteor outburst, Olympus, a communication satellite launched by the European Space Agency, was hit by an energetic Perseid meteor, killing the four-year-old, $850-million mission. Landsat-5, an imaging satellite managed jointly by NASA and the US Geological Survey, lost gyro stability during the peak of the Perseids in 2009. These examples show the strength, energy and activity levels of the Perseid meteors. As a result, it is important that scientists continuously monitor the activity levels of the Perseids.
For non-scientists, the Perseid meteor shower peaks always promise to be spectacular for the naked eye. They offer learning opportunities for children, amateur astronomers and citizen scientists. All of them can spend the night counting meteors, taking pictures and, with the right tools, create processed statistical data that can be submitted to the International Meteor Organisation. Such data enriches the organisation’s existing database and helps with future research and meteor studies in this area.
Meteors have also become more interesting from the POV of exoplanet astronomy. As the Kepler and TESS space probes continue to demonstrate, there are millions upon millions of planets beyond our Solar System. To learn how they formed, scientists first try to understand how our own planetary neighbourhood formed. To this end, comets and meteors are understood to contain materials leftover from the formation of the Sun and the planets, and they could hold clues to the links between the Solar System and exoplanets.
“Meteors enable us to study the building blocks of the Solar System, and by learning about them we can learn about why our planetary system looks the way it does,” said Tom Barclay, an exoplanetary scientist at the NASA headquarters in Washington, D.C.
From a recreational, educational and research POV, observing the Perseids can be a valuable and rewarding experience. So wherever you are this weekend, if you have access to a clear night sky, do set out for a while, look up and enjoy.
Aswin Sekhar is an Indian astrophysicist working at the University of Oslo, Norway.