To the relief of many (and maybe disappointment for some), the chances of an asteroid dubbed 2024 YR4 colliding with Earth in the year 2032 have diminished significantly since it was first reported – from a 3% chance of an Earth collision determined on February 18th, down to a mere 0.004% chance on February 25th. What changed these predictions and more importantly, how do scientists determine if asteroids should strike?
Projecting asteroid collision depends on whether we can see it in the darkness of space and if we can determine whether its orbit has any chance of intersecting with Earth’s orbit. The size of these asteroids, of course, is what makes them dangerous. Near-earth objects are defined as anything within 93 million miles of Earth. Anything over 500 feet in diameter in that range is considered potentially hazardous.
While there are likely millions of asteroids in our solar system, many should never reach Earth thanks to gravitational pressures that keep them in a specific orbit – like the Sun, the planets, and the largest asteroids in our solar system.
The process of detecting nearby asteroids takes place at the Minor Planet Center, which is responsible for recording and distributing positional measurements of minor planets, comets, and other natural satellites of our solar system. Located in the Smithsonian Astrophysical Observatory in Massachusetts, the center operates as a hub for a network of observational telescopes across the globe – some on Earth, others in space – that constitute the main work of detecting near-Earth asteroids. Once detectable, orbit updates are given by the Sentry system housed at NASA’s Center for Near Earth Objects in Pasadena, California.
One of the observational centers involved, called ATLAS, uses four telescopes to provide a full-sky view of near-Earth objects. It was this system that detected 2024 YR4 and the temporary second moon that orbited our moon for a few days in 2024.
Part of the challenge of detecting asteroids has to do with the object’s size and whether it can reflect any light. Asteroids in the dark are practically invisible; the sun is almost the only way we can really see them. And even then, asteroids outside the limit of our telescopes are virtually undetectable.
Therefore, an asteroid with a very large orbit that intersects Earth’s orbit could potentially catch us off-guard. This was the case in February 2013, when the Chelyabinsk meteor exploded in the skies above Russia. Fortunately, with the use of new technologies that can view the entire sky, like ATLAS, our chances of catching these asteroids before they become meteors are much higher than they were in 2013.
As new asteroids become detectable, scientists compute their orbits, which takes time and refinement based on new observations. This explains why the probability of 2024 YR4 has decreased so rapidly – the orbit of the object is clearer to us now than it was when we first noticed it.
Fortunately, new technologies will aid in the process. NASA intends to send a new satellite into space that will use an infrared telescope to detect heat radiated by near-earth asteroids. The Neo Surveyor will improve our scope to about 30 million miles and will be the closest thing we have to being able to see in the dark.
Learn more
- Has The Earth Ever Been Hit By Space Rocks?
- The importance of time when navigating deep space
- How Old Is Cosmic Dust?
Sources
Sentry: Earth Impact Monitoring
Asteroid Hazards, Part 2: The Challenge of Detection
Astrophysics Breakthrough: The Promise of Improved Asteroid Detection - Science Informed
Near-Earth Object Surveyor | NASA Jet Propulsion Laboratory (JPL)
Keeping an Eye on Space Rocks | NASA Jet Propulsion Laboratory (JPL)
