Every person of age in western society usually remembers where they were on the morning of 9/11. The visual power of seeing the flight United Airlines Flight 175 hit on live television the South Tower and left an indelible memory for a generation. For younger generations, we all remember March 2020 when, starting in Italy, the whole European continent went into lockdown. The US Capitol takeover on January 6th, 2021, was just as mesmerising, broadcasted with the feeling of perhaps seeing the end of the American experiment. Even this year, we remember the morning of January 24th, with the first images of Russian forces starting a full-out invasion of Ukraine. We remember those particular flashpoints in time with a deep sense of understanding that they indisputably constitute a tipping point, a fissure in the continuum. There was a “before”, and there will be an “after”, meaning that for better or worse, the paradigm changed. However, most tipping points are not necessarily memorable, far from that. For example, not many people can tell that it was only in 2022 that scientists published the first complete sequence of the human genome, something that will continue to revolutionise modern medicine in the coming decades. The same could be said of 1885, which seems randomly chosen. Nonetheless, it was in 1885 that Hans Adolf Edward Driesch created the first cloned animal with sea urchins. On July 15th, 1799, French soldiers spotted an interesting stone with three types of inscriptions during Napoleon’s Egypt campaign. This stele would later be known as the Rosetta Stone and, subsequently, be key in allowing the deciphering of Ancient Egyptian hieroglyphs. In turn, fuelling the discipline of Egyptology. Recently another tipping point has been reached, one that in the immediate will not change anything but in the long term may very well guard the human species against extinction.
Earth’s history is marked by large mass extinctions that destroy biodiversity on a large scale, which usually reshuffles which animal group became dominant among the survivors. The Permian-Triassic extinction, powered by super volcanoes in Siberia, allowed the dinosaurs to kickstart the development 251 million years ago by ending 95 per cent of life on the planet. However, their success was not guaranteed. The competition against one distant cousin group, the pseudosuchians, was particularly fierce, and the dinosaurs were not at their advantage. Today only the crocodilians subsist among the pseudosuchians. Indeed, 201 million years ago came the Triassic-Jurassic extinction, where once again volcanoes ushered global warming and ocean acidification resulting in the loss of three-quarters of all species on Earth. For reasons still not entirely explained, the dinosaurs emerged as the dominant group after the mass extinction’s recovery. For the next 136 million years, they would dominate the planet despite struggling in the oceans and air. At that time, the Tyrannosaurus Rex had become the apex predator, dominating all life in Northern America. It might have had the strongest known bite among all terrestrial animals and be a masterpiece of evolution, but even the mighty T-Rex could not survive what was to happen. Sixty-six million years ago, an asteroid of 10-15 kilometres hit the Earth on what is now the Yucatán Peninsula in south-eastern Mexico, close to the actual city of Cancun. The resulting crater is known as the Chicxulub crater. The impact was equivalent to detonating 10 billion WWII atomic bombs. The impact created tsunami-like earthquakes on land, literally ejecting dinosaurs in the air, and kilometres-high tsunamis on the Oceans, hitting every coastal region on Earth in the following days. The dinosaurs surviving that first apocalyptic choc were not at rest. Some debris was ejected so powerfully into the air that it escaped Earth’s gravitational pull and crashed elsewhere in the solar system. Other debris re-entered our surface, which ignited them, and started massive wildfires throughout the planet. Finally, after all that destruction, dust clouds in the atmosphere blocked the
sunlight, leading to temperature drops and preventing photosynthesis. Food chains collapsed, and just in a few decades, the Cretaceous–Paleogene extinction happened, and thus the age of dinosaurs came to an end. Or perhaps to a partial end, since some dinosaurs survived and their descendants still walk among us or rather fly. As the direct lineage of dinosaurs, birds are technically avian dinosaurs. Moreover, this fifth mass extinction allowed a new group of animals to reign over the planet, mammals. Among them is found homo sapiens, that is, us.
Therefore, it is understandable that we benefited from the asteroid that triggered the end of dinosaurs but are also weary not to suffer the same faith. According to a recent study by Avi Loeb and Amir Siraj, two renowned Harvard astrophysicists, the object that hit Earth was a long-period comet and we should expect a comparable object to hit the planet every 250 to 730 million years ago. That might appear as low odds, but the dinosaurs probably thought so too. Moreover, a smaller object could already cause some heavy damage. There is already an established precedent of that kind. On June 30th, 1908, an asteroid of 50-60 meters in diameter exploded while entering our atmosphere in a phenomenon known as a meteor air burst. The explosion took place approximately 5-10 km above the ground surface. The estimated energy released in the explosion was as much as 15 megatons of TNT, a thousand times more powerful than the 15 kilotons released by Little Boy, the atomic bomb dropped on Hiroshima in 1945. By chance, this situation, now known as the Tunguska event, took place in Eastern Siberia, a sparsely populated area. The number of casualties is unknown, but the reports of only three victims appear as a miracle, as estimations speak of 80 million trees flattened by the explosion. Had the Tunguska event taken place over London, at the time the most populated city with its seven million inhabitants, it would probably have been the deadliest catastrophe in human records and changed the course of history. This is even more true nowadays, with megacities like Tokyo, where forty million persons inhabit. Therefore, it is not a surprise that Stephen Hawking named an asteroid hitting Earth as the biggest danger to the planet, in his last book. It is thus inevitable that we will be hit again by a devastating asteroid. The only unknown variable is when. However, among all the possible dangers that threaten to end the human species this one has not been ignored, or at least is in the process of being taken care of.
It is unclear who first postulated the idea of planetary defence, meaning the human capacity to engineer systems capable of avoiding asteroid impacts on Earth. However, it is clear is that the first concrete efforts in the area are recent. In 1998 NASA was officially tasked to find at minimum 90 per cent of objects of 1 km or larger that could potentially pose a collision risk with the planet. The objective was completed, with 95 per cent of those dangerous asteroids found and no danger posed. In 2005, the US Congress extended that task but with smaller objects, 140m or larger within 30 million miles of the Earth with the deadline of having catalogued 90 per cent of them by 2020. An objective that remains ongoing to this day. Indeed, the smaller the objects, the more numerous they are, which ultimately makes the undertaking more difficult. In 2014 only 10 per cent of the goal had been accomplished, and that was despites considerable budget increases. As of today, 40 per cent of the objective is completed. Thus, to reach that goal, NASA established in 2016 the Planetary Defence Coordination Office (PDCO), something you might have seen in the movie Don’t Look Up. The PDCO is aimed at finding and cataloguing near-Earth objects, sounding the alarm if needed and creating in advance a response strategy for the US in case of an actual alarm. However, knowing what threats lure out there in space is only the first component of planetary defence.
Just like in the movies Armageddon and Deep Impact, the second part of planetary defence consists of sending a spaceship to the object to alter its course. Various methods have been proposed to deflect asteroids or comets, even some that appear in science fiction. For example, detonating a nuclear bomb is a real strategy that has been studied. Some propose to fragment the object into smaller ones, while others attempt more simply to make it deviate from its orbit. Nonetheless, none of those strategies had ever left the planning stage. That was until the Double Asteroid Redirection Test (DART). On November 24th, 2021, a Falcon 9 rocket left the Vanderberg Space Force Base in California, carrying the DART spacecraft, a small-sized box with one array of solar panels on each side. The satellite travelled in space to reach its destination, Dimorphos, the moon of a minor planet. On September 26th, 2022, DART intentionally crashed on Dimorphous, sending data to the Earth until its last breath. A
smaller satellite, of the size of a briefcase, detached from the DART before its impact to capture the aftermath of the impact. The mission was a success and constitutes humanity’s first accomplishment in deflecting the course of an asteroid. Hopefully, this will be remembered as a tipping point in our history.
Much remains to be done to have an effective planetary defence system. It will probably take at least a few decades for NASA to identify all the asteroids Congress asked them to. Beyond all the earth-based means of detection, the NEO Surveyor should be launched in 2026 to help with the task. It will be a space-based telescope specialised in detecting threatening asteroids. The impact of DART’s crash on Dimorphos will continue to be studied, with the European Space Agency expected to launch a probe to investigate it in the following years. More missions like DART can also be expected in the near future. Moreover, making the human species multi-planetary with the establishment of a permanent colony on another planet could significantly increase our chance of surviving massive catastrophes, something Elon Musk often mentions as the reason behind the creation of SpaceX. Nonetheless, it brings relief to know that this existential threat is on course to be tackled. Now to be safe, we just have to tackle; climate change, super volcanoes and the proliferation of nuclear weapons.