We interview Juan Luis Cano, coordinator of the ESA’s Planetary Defense Office
NASA has raised to 3.1% the probability of the asteroid 2024 YR4 hitting our planet. The ESA’s Near-Earth Object Coordination Center has also adjusted its calculations upwards, estimating a 2.8% chance of impact on December 22, 2032.
Let’s not lose sight of the fact that the odds are still in our favor. 1 in 32 means there is a 96.9% chance that the asteroid will pass us by. But as astronomers have incorporated new data and observations to calculate its trajectory, the chances of impact have been increasing. Why is this happening? We asked Juan Luis Cano, ESA’s Planetary Defense Coordinator
The busiest man at ESA
Trained as an aeronautical engineer, Juan Luis Cano specialized in orbital mechanics and celestial mechanics, which are the basis for calculating the movement of objects in outer space. Twenty years ago he was part of the Don Quijote project, a European Space Agency mission to deflect an asteroid with a kinetic impactor.
Led by the Spanish company Deimos, Don Quijote did not prosper, but it was a precursor to the DART probe of NASA, which successfully diverted the asteroid Dimorphos, and the HERA probe of ESA, launched later to analyze the impact.
As coordinator of the Information Service of the Office of Planetary Defense of the ESA, Cano is especially busy these days. For the first time, the action protocols for planetary defense established in 2018 have been activated, which means coordinating as many observatories as possible to follow the asteroid closely.
“These protocols were established after the UN promoted the creation of the International Asteroid Warning Network and the Space Mission Planning Advisory Group,” says Cano. ”It is the first time they have been officially invoked, although this asteroid is the most relevant in the last 20 years, after Apophis at the end of 2004.”
For the moment, the Space Mission Planning Advisory Group (SMPAG) has decided to wait until May to assess, based on new and more definitive observations, whether the asteroid still poses a real danger.
Why the probability of impact has increased
As they obtain more data and observations of 2024 YR4, astronomers reduce the uncertainty of its trajectory, but their calculations remain focused on the probability of impact with the Earth, which does not change in size.
If the Earth remains within the zone of uncertainty, the probability of impact increases because the uncertainty becomes smaller, but our planet is still in the middle. “It’s like going through the next round in a championship,” explains Juan Luis Cano. “You don’t know if you’re going to win, but as you go from 32 teams to 16, your chances increase.”
It can also happen that the probability distribution “slips” and the Earth moves away from the central part of the graph, which is what happened when the estimate dropped from 2.3% to 2.1% a few days ago before rising again.
European scientists use the Torino scale to categorize the risk posed by near-Earth asteroids and comets. With a rating of 3 out of 10, 2024 YR4 exceeds the 1% probability threshold of causing localized destruction on Earth. However, new observations are likely to reduce that estimate to zero.
This is what happened with the asteroid Apophis. Apophis reached level 4 on the Torino scale, the highest ever recorded. But astronomers extended their observation arc and ruled out an impact a few days later.
Now the OSIRIS-APEX probe from NASA is heading towards it to study it when it passes just 38,000 km from Earth. It is the same spacecraft that collected samples from the asteroid Bennu, which shows the growing importance of missions to these small bodies close to Earth.
Cano is betting that the Earth will fall outside the probability distribution when we have data from Webb and other observatories in the coming weeks.
What is the protocol to follow in both cases?
There are things that astronomers know for sure about 2024 YR4, such as the plane in which it moves and the strip of the Earth in which it could fall, if necessary: a “corridor” that extends through the eastern Pacific Ocean, northern South America, the Atlantic Ocean, Africa, the Arabian Sea and southern Asia.
Others are more complicated. The asteroid was discovered as it approached the Earth and is now moving away, so with each passing day it becomes fainter and harder to see. By April, not even the Great Canary Telescope (10 meters in diameter) will be able to detect it.
There is also no precise measurement of its size because its albedo, the amount of light that its body reflects, is unknown. It could be a highly reflective 40-meter object or a very dark 90-meter object.
To be on the safe side, astronomers have reserved hours of emergency use of the powerful James Webb Space Telescope. The Webb will be able to observe the asteroid until May and will be able to obtain a more precise measurement of its size and temperature.
It is crucial to be able to discern whether it is at the lower or upper end of the estimated size range in order to be able to assess the consequences of its improbable but possible impact. Although it is too small to wipe out human civilization, the asteroid could devastate a major city, especially if it explodes in the air.
As for its destructive capacity: “We can’t talk about a single value, but a range from about 5 to 50 megatons, depending on whether the object measures 40 or 100 meters,” says Juan Luis Cano. “The larger the diameter, the more the volume and potential impact energy are multiplied. So there is no exact figure until we know its diameter better.”
And what would we do if it finally heads for Earth? “If the object is less than 50 meters, it is considered preferable to evacuate the impact zone; if it is larger, a deflection mission would be considered,” explains Cano. “Even so, we think that, with a 90% probability, the impact will be definitively ruled out in May.”
