Even though we are in a relatively quiet area of the Universe, cosmic dynamics inevitably expose Earth to certain dangers. Among these threats are near-Earth objects; asteroids and comets whose orbit is close to that of the Earth. To deal with these potential dangers, space agencies try to detect and monitor them as best they can. To complement this strategy, scientists meet frequently to participate in impact simulations. Recently, one of these sessions was held, involving a scenario in which an asteroid heading towards Earth was not discovered until six months before it arrived. Experts concluded that it was impossible to avoid the impact in such a short period of time.
A group of experts from US and European space agencies participated in a week-long exercise led by NASA in which they were confronted with a hypothetical scenario: an asteroid 35 million kilometers away was approaching the planet and could strike within six months.
With each passing day, participants learned more about the asteroid’s size, path, and chances of impact. Then they had to cooperate and use their technological knowledge to see if anything could be done to stop the space rock. The experts failed. The group determined that none of the existing technologies could prevent the hypothetical asteroid from hitting given the six-month delay in the simulation. In this alternate reality, the asteroid crashed in Eastern Europe.
To our knowledge, no asteroid currently poses a threat to Earth in this way. But it is estimated that two-thirds of asteroids 140m or larger – large enough to cause significant havoc – remain to be discovered. This is why NASA and other agencies are trying to prepare for such a situation.
” These exercises ultimately help the planetary defense community communicate with each other and with our governments to ensure that we are all coordinated if a potential impact threat is identified in the future. Says Lindley Johnson, head of planetary defense at NASA.
Six months: too short a time to avoid an impact
The fictional asteroid in the simulation was called 2021PDC. In the NASA scenario, it was first “spotted” on April 19, when it was thought to have a 5% chance of hitting our planet on October 20, six months after the date of its discovery. . But the second day of the exercise took place on May 2, when new impact trajectory calculations showed that 2021PDC would almost certainly hit Europe or North Africa.
Participants in the simulation envisioned various missions in which spacecraft might try to destroy the asteroid or divert it from its path. But they concluded that such missions could not take off in the short time before the asteroid impact. ” If we were faced with the hypothetical real-life 2021PDC scenario, we wouldn’t be able to launch a spacecraft in such a short time frame with current capabilities. », Specify the participants.
They also considered trying to detonate or disrupt the asteroid using a nuclear explosive device. ” Deploying a nuclear disruption mission could dramatically reduce the risk of impact damage “. Nonetheless, the simulation stipulated that 2021PDC could be between 35 and 800m in size, so the likelihood that a nuclear weapon could breach was uncertain.
The third day of the exercise was June 30 and the future of Earth looked grim: the impact trajectory of 2021PDC showed it was heading towards Eastern Europe. By day 4, which advanced rapidly to a week before the asteroid impact, there was a 99% chance that the asteroid would strike near the border between Germany, the Czech Republic and Austria. The explosion would bring as much energy as a large nuclear bomb. All that could be done was to evacuate the affected areas in advance.
Near-Earth objects: what threats to the Earth?
It’s tempting to assume that in the real world, astronomers would spot a 2021PDC-like asteroid on much longer than six months’ notice. But the human ability to monitor near-Earth objects (NEO) is sadly incomplete. Any rock in space with an orbit that takes it within 200 million kilometers of the Sun is considered an NEO. But Johnson said in July that NASA believed ” that we only found about a third of the asteroid population that could pose a risk of impact on Earth “.
Of course, humanity is hoping to avoid a surprise like that of the dinosaurs 65 million years ago, when an asteroid 10 km in diameter crashed into our planet. But in recent years, scientists have missed many large and potentially dangerous objects that have come close. Comet Neowise, a piece of space ice 5 km in diameter, passed 103 million km from Earth in July. No one knew this comet existed until a NASA space telescope discovered it four months ago.
In 2013, a meteor about 20 m in diameter entered the atmosphere at a speed of 64,000 km / h. It exploded over Chelyabinsk, Russia, without warning, sending a shock wave that shattered windows and damaged buildings across the region. More than 1,400 people were injured.
And in 2019, an asteroid 130 m in diameter passed within 72,000 km of Earth. NASA had almost no information on this. Indeed, currently the only way scientists can track an NEO is to point one of Earth’s few powerful telescopes in the right direction at the right time.
To solve this problem, NASA announced two years ago that it would launch a new space telescope dedicated to monitoring dangerous asteroids. This telescope, called “Near-Earth Object Monitoring Mission” (Near-Earth Object Surveillance Mission), as well as the Test-Bed Telescope, recently launched by the European Space Agency, and the Flyeye telescope under construction in Italy, should ultimately increase the number of NEOs that we can detect and track.