"Armageddon" as a scenario: Who at the UN is raising the alarm about the asteroid threat?

The United Nations official had been training for that moment, going through simulations and table-top exercises in her Vienna offices, housed in a gray, nondescript 1970s concrete building next to the Danube River.

Aarti Halla-Maine, a British lawyer with experience in the satellite industry, had to go through the scenario step by step. As director of the United Nations Office for Outer Space Affairs (UNOOSA), she had to know exactly what to do if, and that's a big if, she received information that a large asteroid was on a possible collision course with Earth. Or, as she says with a laugh: "Armageddon."

In such an event, Halla-Maine is the person responsible for immediately informing the UN Secretary-General. He would then forward her message to all 193 member states - practically every government in the world.

Warning about asteroid threats is not a common part of the job. Yet a little over a year ago, Halla-Maine found herself in just such a situation. In between trips, a colleague pulled her aside in the office. “This wasn’t a simulation or a drill,” she recalls. “It was real.”

On December 27, 2024, a robotic telescope in Chile spotted a distant object hurtling through space, initially estimated to be the size of a small building. This in itself is not unusual, as scientists typically track an asteroid at that time to more accurately assess its likelihood of impacting Earth. The information was also not secret, so word of the asteroid had been circulating in the public domain even before Halla-Maine got involved.

But in this case, the asteroid, vaguely named 2024 YR4, began to be seen as a growing threat. The estimated probability of impact gradually increased over the next three weeks, as additional observatories tracked it and new calculations were made. The initial estimate of less than a 0,05 percent chance of hitting Earth increased to more than a one percent chance of impact in 2032.

This, combined with its size, meant that asteroid 2024 YR4 met the criteria for UNOOSA to issue its first global warning since the United Nations established cooperation on planetary defense in 2013. Although the probability was very low, practically a 99 percent chance of not hitting, the situation was considered significant because, due to the size and speed of the asteroid, a possible collision with Earth would release energy many times greater than that dropped on Hiroshima. It could destroy an entire city, or even an entire region.

By that time, in late January 2025, Romana Kofler, a program officer, was already working late into the night. At UNOOSA, she is in charge of planetary defense (an asteroid in the asteroid belt is named after her). Kofler was in contact with the International Asteroid Warning Network, a UN-backed body that brings together astronomers, members of NASA and its European counterpart, the ESA, as well as experts who calculate the orbits and trajectories of space objects.

“We had been preparing for this through simulations, but this was reality,” says Kofler. “The adrenaline kicked in.”

After informing Halla-Maine, they drafted a letter together and sent it to UN Secretary-General Antonio Guterres. “We drafted it very quickly. This was the first real-time test of an international response,” Halla-Maine said.

Real threats

The threat posed by objects from space is far from theoretical. In 2013, a meteor exploded over Chelyabinsk, Russia. The event, caused by a rock about 20 meters in diameter, released energy equivalent to 500 kilotons of TNT, creating a shock wave that shattered windows in thousands of residential buildings. More than 1.200 people were injured by shards of glass and debris. The fireball shone 30 times brighter than the Sun, causing instant skin burns and demonstrating that even smaller space objects can cause mass casualties without warning.

For a brief period last year, asteroid 2024 YR4 posed the most significant near-term threat since the discovery of Apophis in 2004, which made headlines when it was rated a four on the Torino Impact Hazard Scale, but was later downgraded after observations showed it posed no threat for at least a century. The Torino scale ranges from zero, when there is no risk, to 10, when a collision is certain and poses a threat to the survival of civilization as we know it.

On that scale, 2024 YR4 has reached level three, and its discovery has activated another UN-backed body, the Space Mission Planning Advisory Group, tasked with developing ways to protect Earth. One option is to deflect the asteroid by colliding with an interceptor spacecraft, a technique that was successfully tested on another asteroid by NASA's Dart mission in 2022.

UNOOSA's day-to-day work doesn't always revolve around crises. Pronounced "Junosa," it's one of the United Nations' lesser-known agencies. It's also not big: 35 staff members work out of the modest Vienna International Centre, far from the busier UN hubs in Geneva and New York.

It was founded in the late 1950s, at the dawn of the space age, when the then-infant United Nations decided to establish a body with the “desire,” as it put it, to prevent political rivalries from Earth from being transferred to space. Today, the office’s small team manages an extraordinarily wide range of responsibilities, as governments and companies increasingly seek to operate in space.

After 25 years in the commercial sector and a move into the sprawling and bureaucratic UN system, Halla-Maine spends much of her time traveling around the world to conferences and has numerous responsibilities, including promoting international law and regulation in an increasingly congested and competitive space environment.

The agency runs the Space for All program, which helps countries without their own space capabilities access the benefits of being in orbit. Its disaster and emergency response program, UN-Spider, provides countries affected by natural disasters with access to satellite imagery.

However, UNOOSA's role as the official registry of satellites launched into Earth orbit has become more important. As the number of satellites exceeds 10.000, and many more are planned for launch, the space closest to Earth is becoming an increasingly congested and risky zone of traffic.

The agency thus found itself in the role of an informal "hotline" for potential satellite collisions - a task that becomes frighteningly complex when it comes to satellites from countries that do not have diplomatic relations.

Holla-Maine recalls an incident in June last year, when the Malaysian Space Agency contacted UNOOSA over the weekend after one of its satellites, unable to maneuver, was on a collision course with a North Korean satellite. The distance between them was just 75 meters, Holla-Maine says - the situation was "extremely tense."

Without official two-way communication with Pyongyang, the Hall-Maine team had to send all the information to North Korean email addresses that they knew would not respond. “The most you can do is send all the notes and information to all the official contacts you have,” she says. And then, without any response, the North Korean satellite suddenly moved. “They moved off-track without us actually having any bilateral communication.”

Whether it's raising the alarm about an asteroid that could destroy a city, providing satellite imagery for flood relief in Morocco, or preventing a collision in Earth's orbit, the "small team" in Vienna is achieving much more than one might expect, says Halla-Maine. "Having worked for a long time under staff and budget constraints has forced us to be extremely efficient," she adds.

The asteroid 2024 YR4 alert has served as a useful test of UNOOSA's relatively new role in planetary defense. For now, the asteroid is still being monitored. Although the probability of an impact with Earth peaked at more than three percent in February last year, it has since fallen to negligible levels.

“Suddenly,” says Halla-Maine, “he was no longer a threat.”