Even a heap of scrap can delight the eye. Assuming it is natural space junk. Plenty of cosmic debris can be seen in the sky these days as the Perseids peak around August 12th. A few dozen of these shooting stars will then dart across the firmament every hour. Behind the tracers are dust grains originating from comet 109P/Swift-Tuttle. The US astronomers Lewis Swift and Horace Parnell Tuttle found it independently in the summer of 1862. The comet eventually became as bright as North Star, and its 60 full moon diameter tail caught the eye. He then disappeared into the depths of space and was only rediscovered in 1992 by a Japanese amateur stargazer.
Swift-Tuttle orbits the Sun on its orbit, coming particularly close to it every 133 years. The deep-frozen core of the comet, made up of ice, gases, dust and porous rock, heats up. Tiny particles splinter from it and form a kind of sandy track. Every time the earth rushes through it on its annual orbit around the sun, it unleashes a more or less violent bombardment of the crumbs. Such a tiny meteoroid enters the atmosphere at a speed of 216,000 kilometers per hour and creates a plasma channel at an altitude of about 80 kilometers by friction with the air particles. “Atomic processes take place inside, a meteor flashes,” says Marco Sproviero from the observation group at the Deutsches Museum. Only the larger chunks survive the ride through the atmosphere and reach the ground, where they are occasionally found as meteorites. A good 5,000 tons of cosmic material reach earth in this way every year.
To see the natural spectacle of the Perseids with your own eyes next weekend, Sproviero has a few tips ready. “The best time is the night of August 13,” he says. You should look for a dark place with as little stray light as possible and a good view of the horizon. While the Perseids all appear to come from the constellation Perseus – a perspective effect created by the movement of the Earth – they show up across the sky. You should also have a sleeping mat and warm drinks with you. According to Sproviero, the conditions this year are particularly favorable, because the narrow crescent of the waning moon only rises towards morning and its light does not bother us any further. If the weather plays along, nothing stands in the way of the cosmic fireworks – and you don’t have to be afraid that the sky will fall on your head.
Earth nearly collided with an asteroid
It was different on July 13, as it became known belatedly. It was close. An asteroid about 40 meters wide sped past Earth. It came from the direction of the brilliantly bright sun and therefore could not be detected by terrestrial telescopes. Two days later, a telescope in South Africa spotted the chunk. Calculations show that the rendezvous in space was dangerous: The celestial body called “2023 NT1” had passed our planet at a distance of one hundred thousand kilometers, about a quarter of the distance to the moon. What appears to be a reassuring amount on a human scale is, astronomically speaking, just a hair’s breadth.
If the asteroid’s trajectory had deviated by just a few tens of thousands of kilometers, it could have caused a collision and, in the worst case, an explosion over populated areas. The pressure wave would have caused considerable damage in a large city. The consequences of such a cosmic crash became clear ten years ago. At that time, a 20-meter asteroid burst near the Russian city of Chelyabinsk. Buildings were damaged, 1500 people injured.
In order to recognize such dangers at an early stage and to better assess them, researchers like Detlef Koschny are scouring space with automated observation programs. “So far we only know half a percent of potentially dangerous objects between 30 and 100 meters in diameter,” says the scientist at the Technical University of Munich. Koschny and his colleagues estimate the total number of these celestial bodies at around two million. In order to increase the detection rate, the European space agency Esa is currently working on the “Fly Eye” company: In a few years, the Flyeye telescope with extreme wide-angle optics and 16 cameras should be able to discover vagrant debris from the summit of Monte Mufara in Sicily from a size of 40 meters. Other similar observatories around the world are being planned.