Daniel Brown: On September 4, 2024, astronomers discovered an asteroid with a diameter of one meter heading towards Earth. The space rock would burn up harmlessly in the atmosphere near the Philippines later that day, officials announced. Nevertheless, it produced a spectacular fireball that was shared in videos posted to social media.
The object, known as RW1, was only the ninth asteroid spotted before the impact. But what about much larger, more dangerous asteroids? Could our warning systems detect all the asteroids that could threaten us on the ground?
Asteroid impacts have affected every major body in the solar system. They determine their appearance, change their chemical abundance and – in the case of our own planet at least – helped trigger the formation of life.
But these same events can also disrupt ecosystems and wipe out life, as they did 66 million years ago when a 10 km space rock contributed to the extinction of the dinosaurs (excluding birds).
Asteroids are the material left over from the formation of our solar system that is not incorporated into planets and moons. They come in all shapes and sizes. Their paths are determined by gravity and can be predicted to some extent.
Of particular interest are the objects that are close to Earth’s orbit, so-called Near Earth Objects (NEOs). As of September 2024, we know of approximately 36,000 such objects, ranging in size from a few meters to several kilometers.
But statistical models predict that nearly 1 billion such objects should exist, and we know very few of them.
We have been monitoring these asteroids since the 1980s and have mounted more detailed studies of them since the 1990s. The studies use telescopes to observe the entire sky each night and then compare images of the same region on different dates.
Astronomers are interested in whether anything has moved relative to the stars in the same part of the sky from one night to the next. Anything that moves could be an asteroid.
By observing its positions over time, team members can determine the exact path. This in turn allows them to predict where it will be in the future, although collecting and analyzing such data is a time-consuming process that requires patience.
It is made even more challenging by the fact that there are many more smaller objects than larger ones. Some of these smaller objects are nonetheless large enough to wreak havoc on Earth, so we still need to keep an eye on them. They are also quite faint and therefore more difficult to see with telescopes.
It can be difficult to predict the paths of smaller objects far into the future. This is because they have gravitational interactions with all other objects in the solar system. Even a small force of gravity on a smaller object can change its future trajectory in unpredictable ways over time.
Funding is crucial in this effort to detect dangerous asteroids and predict their path. In 2023, NASA has allocated $90 million (£69 million) to the hunt for near-Earth objects (NEOs). Several missions are being developed to detect dangerous objects from space, for example the Sutter Ultra project and NASA’s NEOsurveyor infrared telescope mission.
There are even space missions to explore realistic scenarios for changing the paths of asteroids, such as the Dart mission. Dart crashed onto an asteroid’s moon so scientists could measure the changes in its path.
This showed that it was indeed possible in principle to change the course of an asteroid by colliding with a spacecraft. But we are still far from a concrete solution that can be used in the case of a large asteroid that really threatens the Earth.
Detection programs create a huge amount of image data every day, which is challenging for astronomers to process quickly. However, AI could help: advanced algorithms could automate the process to a greater extent. Citizen science projects can also make the task of sifting through the data accessible to the public.
Our current efforts are working, as evidenced by the detection of the relatively small asteroid RW1. It was only discovered shortly before it hit Earth, but gives us hope that we are on the right track.
Asteroids smaller than 25 meters in diameter usually burn up before they can cause damage. But objects with a diameter of 25 to 1,000 meters are large enough to penetrate our atmosphere and cause local damage.
The extent of this damage depends on the properties of the object and the area where it will impact. But a 450-foot asteroid could cause widespread destruction if it hit a city.
Fortunately, collisions with asteroids of this size are less common than with smaller objects. An object with a diameter of 140 meters should hit the Earth every 2000 years.
Statistical models suggest that by 2023 we will know of 38% of all existing near-Earth objects with a size of 140 meters or larger. With the new American Vera Rubin 8.5m telescope, we hope to increase this share to roughly 60% by 2025. NASA’s NEOsurveyor infrared telescope could identify 76% of asteroids 140 meters or larger by 2027.
Asteroids larger than 1 kilometer have the potential to cause damage on a global scale, similar to the damage that helped wipe out the dinosaurs. These asteroids are much rarer, but easier to spot. Since 2011, we think we have detected 98% of these objects.
Less reassuring is the fact that we currently have no realistic proposal to move the path – even though missions like Dart are a start. We may eventually be able to compile a nearly complete list of all possible asteroids that could cause global impacts on Earth.
It is much less likely that we will ever detect every object that could cause local damage on Earth, such as destroying a city. We can only continue to monitor what is happening out there, by creating an early warning system that allows us to prepare and respond.
Daniel Brown, Lecturer in Astronomy, Nottingham Trent University
This article is republished from The conversation under a Creative Commons license. Read the original article.
