Source: The National

This week our planet will cut across a vast swarm of meteors, including some big enough to wipe out a major city with the violence of a nuclear weapon.

Known as the Taurid Complex, the cosmic debris has already been implicated in the Tunguska Event of June 30, 1908, when a huge meteor exploded over Siberia unleashing the power of 1,000 Hiroshima atomic bombs.

Now Earth is about to make its closest approach to the same swarm since June 1975, when instruments put on the moon by the Apollo missions detected enormous numbers of meteors pummelling our nearest celestial neighbour for several days.

Exactly what will happen over the coming days is unknown, but astronomers around the world are preparing to observe the contents of the Taurid Complex as the planet sweeps through.

The plan is to peer into the cloud of debris looking for meteors similar in size to the 100-metre wide object responsible for the Tunguska Event.

By determining the orbit of such objects, astronomers believe they can identify those on a collision course Earth early enough to take action against them.

They also hope to test the theory that the Taurid Complex is just the remnant of a colossal comet-like object that entered the solar system thousands of years ago and whose disintegration still poses a threat to our planet.

Scientists have long accepted that Earth has been struck many times by comets and asteroids over its 4.5 billion year history.

The most notorious impact is the so-called K-T extinction event of 66 million years ago, when an object 10 kilometres across smashed into the Gulf of Mexico.

The resulting global fires and ecological devastation drove the dinosaurs into extinction along with at least 75 per cent of species Earth.

Such an event could happen again if a new comet entered the solar system on a collision course with the planet.

While no object capable of global devastation has yet been identified, some astronomers believe the Taurid Complex may harbour meteors capable of repeating the Tunguska Event of 1908.

Hurtling in at over 100,000kph, the giant meteor was torn apart as it entered the Earth’s atmosphere. Eye-witnesses reported feeling the heat of the fireball, and being knocked off their feet by the blast, which devastated thousands of square kilometres of Siberia near the Tunguska River.

Gale-force winds struck towns across Russia, while seismic stations from the United States to Java in Indonesia detected a massive disturbance that shook the whole planet.

Because it took place over a remote part of the world, there were no casualties. If repeated over a more densely populated region or near a coast, however, the resulting blast or tsunami would be catastrophic.

Concern that the Tunguska Event could re-occur has been mounting for decades. In 1947 astronomers at Britain’s Jodrell Bank radio telescope near Manchester discovered a shower of meteors which Earth encountered at the same time each year as the Tunguska object.

These are now thought to be debris shed by a 5km-wide chunk of ice and dust first observed in 1786. Known as Encke’s Comet, its orbit brings it closer to the searing heat of the sun than Mercury, making it potentially unstable.

Historians have also uncovered evidence that a medieval report of a “flaming torch” that “split the moon in two” one evening in late June 1178 may have been the result of an Taurid Complex object entering the Earth’s atmosphere in the same part of the sky.

During the 1980s, British astronomers Dr Victor Clube and Dr Bill Napier of the University of Oxford argued that the best explanation for all these events was that a giant comet around 100km across entered the solar system and has been breaking apart ever since, leaving a vast trail of debris through which Earth passes each year on its way around the Sun.

Most of these encounters result in nothing more than some small meteors entering Earth’s atmosphere during daylight and burning up harmlessly.

However, some of the debris is predicted to form huge swarms gathered together by the combined gravity of Earth and Jupiter.

This so-called Taurid Resonant Swarm is expected to harbour much more debris and potentially Tunguska-sized objects posing a significant impact risk to Earth.

Support for the existence of the TRS emerged in 2015, when a team of European astronomers predicted an encounter with part of the swarm and recorded over 140 fireballs shooting through the Earth’s atmosphere.

The team, led by Dr Pavel Spurny of the Ondrejov Observatory in the Czech Republic, also found evidence that the swarm contains two objects code-named 2015 TX24 and 2005 UR.

At 200 or 300 metres across, both are far more massive than the Tunguska object. Entering the atmosphere at huge speeds, even their disintegration in mid-air would trigger a blast capable of wiping out a large city.

Reporting their findings in the journal Astronomy and Astrophysics in 2017, the team concluded that the risk of such events makes detailed observation of the TRS “extremely important”.

This week’s close encounter gives astronomers their best chance yet to find out what lurks inside the swarm.

If Tunguska-scale objects are found, astronomers will add them to their watch-list of Potentially Hazardous Objects, which currently numbers over 1,900 comets and asteroids on orbits that could pose a threat to Earth.

Precision observations plus the laws of celestial mechanics allow astronomers to predict any impact decades into the future – giving plenty of time to take action.

Among the methods for averting disaster are the use of rockets embedded into the object or blasts from so-called enhanced radiation weapons – better known as neutron bombs – to nudge it off-course.

This week’s observations are essential for estimating the risk of cosmic impacts. While controversy still surrounds the role of the TCS in future Tunguska events, one thing astronomers do agree on is that forewarned is forearmed.