An early warning system for meteorite impacts capable of destroying whole cities is on alert this week as the Earth passes through a vast trail of cosmic debris.
Astronomers are focusing their attention on the constellation Ara in a patch of sky lying due south after sunset in the Emirates. Calculations show this is likely to give the best view of the contents of the so-called Taurid Complex, a trail of material left by a giant comet that disintegrated after entering the solar system thousands of years ago.
They are searching for signs of meteors similar to the 100-metre object which plunged through the Earth’s atmosphere in June 1908 and exploded over Siberia with the violence of 1,000 Hiroshima atomic bombs.
Known as the Tunguska Event, it flattened thousands of square kilometres of forest near the Tunguska River in Siberia. If such an event occurred over a city, the resulting blast-wave would be devastating.
When a far smaller meteor exploded high over central Russia in February 2013, the blast was equivalent to the detonation of 500,000 tonnes of TNT. Despite being only 20m across, the meteor shook buildings, blew out windows and caused over 1600 casualties with injuries ranging from cuts from flying glass, temporary deafness and sunburn from the intense light of the explosion.
Astronomers hope this week’s observations of the Taurid Complex will give more insight into how likely such events are.
It is also being seen as a test of a network of telescopes designed to detect small but potentially dangerous meteors soon enough to issue alerts to those likely to be affected.
Funded by Nasa, the Asteroid Terrestrial-impact Last Alert System (ATLAS) currently consists of two telescopes on the Hawaiian islands in the mid-Pacific. Further instruments will be added over the next few years.
Unlike standard telescopes, the ATLAS instruments scan the entire sky every 48 hours, and use computers to spot faint, fast-moving objects heading for the Earth.
This allows them to detect meteors as small as that which exploded over Russia in 2013 and calculate their trajectory – giving up to a week’s warning of where they will strike.
The network scored its first success last month, when it spotted an incoming meteor just 4 metres wide while it was still 500,000 km from the Earth – even further away than the moon.
Code-named 2019MO, the object exploded over the Caribbean near the island of Puerto Rico on 22 June with the violence of 4,000 tonnes of TNT. All the debris is thought to have plunged into the sea, but weather satellites monitoring the area witnessed the blast high in the atmosphere.
Despite coinciding with the Earth’s passage through the Taurid Complex, 2019MO isn’t thought to be part of that meteor swarm. Instead, astronomer believe it originated in the asteroid belt, the vast disc of rubble between the orbits of Mars and Jupiter.
Even so, the event has provided a “dry run” for the impact warning system now being rolled out across the globe.
Next year astronomers will begin using a huge telescope capable of spotting Tunguska-sized objects months or even years before they encounter the Earth.
Based in the Andes of central Chile, the Large Synoptic Survey Telescope (LSST) has a mirror 8.4 metres across that will photograph the entire sky every few nights. By comparing images over successive nights, computers will be able to catalogue over 90 per cent of objects capable of posing a major threat to the Earth over the next decade or so.
But finding dangerous asteroids is only the start. NASA and the European Space Agency (ESA) are now working on the first-ever mission to defend the Earth against cosmic disaster.
Called the Asteroid Impact and Deflection Assessment (AIDA) mission, it involves firing a 500kg probe into a small asteroid to see whether it’s possible to nudge dangerous objects away from the Earth.
Under current plans, in June 2021 NASA will launch a probe towards Didymos, a mountain-sized asteroid with a 160-metre wide companion in orbit around it.
Impacting at around 24,000 km/h, the probe will leave the smaller companion intact, but slightly alter its orbit. A second probe built by ESA will then travel out to Didymos and send landers down to the surface of its companion to examine the effects of the impact.
The data will give astronomers insights into the effectiveness of nudging asteroids as a method for averting impacts with the Earth.
In an ESA video explaining the mission astrophysicist - and former Queen guitarist – Dr Brian May conceded that the mission “will be really, really hard”, but will help humans avoid the fate of the dinosaurs, who were driven into extinction by the impact of a giant asteroid 66 million years ago (see box).
“Could we prevent an asteroid hitting planet Earth? The dinosaurs couldn’t - but we humans have the benefit of knowledge and science on our side," said Dr May.
Robert Matthews is Visiting Professor of Science at Aston University, Birmingham, UK