This image from NASA captures the Orionid meteors observed on October 13, 2015.

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Jet Propulsion Laboratory/NASA/AP

In the upcoming weeks, astronomers will focus their attention on an asteroid measuring up to the size of a football field, analyzing how likely it could potentially impact Earth in 2032.

At present, the chances for such a collision are estimated at 2.1%, equivalent to roughly 1 in 47. However, as astronomers refine the orbital predictions for the asteroid known as 2024 YR4, these odds are expected to diminish to negligible levels. (There is even a slimmer chance that it may impact the moon.)

This article elaborates on how astronomers identify, categorize, and monitor these celestial bodies, along with the measures that can be taken to mitigate potential impacts on Earth.

Defining “Near-Earth Objects”

Near-Earth Objects (NEOs) are asteroids or comets that have been nudged closer to our planet’s orbit by the gravitational pull of nearby celestial bodies. These remnants, consisting of rock, metal, or ice, originate from the formation of our solar system approximately 4.6 billion years ago.

While most NEOs are too small to pose any risk, larger ones could result in significant localized destruction, akin to the 2013 Chelyabinsk meteor that caused extensive damage and injuries across a large area. The impact from larger NEOs, like the asteroid believed to have exterminated the dinosaurs around 65 million years ago, has the potential to be catastrophic for human life.

Finding NEOs

Each night, astronomers from the U.S., Europe, and Asia utilize a global network of large ground-based telescopes to photograph the night sky. These sky surveys commonly employ “wide field” telescopes that capture an extensive area of the sky at once, explained Larry Denneau, a researcher from the University of Hawaii’s Institute for Astronomy, which operates NASA’s Asteroid Terrestrial-impact Last Alert System (ATLAS).

“Our goal is to cover as much of the sky as we can,” he mentioned, emphasizing that the focus isn’t on the furthest reaches of the universe but rather on detecting any unexpected movements against the backdrop of stars indicating a previously unnoticed NEO.

As objects approach Earth, they seem to move more quickly than those further away. “Think of it like a train speeding past you at a railway crossing,” Carson Fuls, director of the Catalina Sky Survey at the University of Arizona, illustrated. “A distant train would appear to move slowly in comparison, just like a nearby asteroid would move faster than a distant one, even if they are traveling at the same speed.”

ATLAS uses four telescopes that constantly capture images of the sky after dark. Denneau’s team was the first to detect 2024 YR4 using a remotely operated telescope in Chile. “These are high-resolution images that return to our base in Honolulu, where we analyze them to identify star-like objects that are moving,” he elaborated.

Images showing the path of 2024 YR4 across the sky.
JPL/NASA Center for Near-Earth Object Studies
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JPL/NASA Center for Near-Earth Object Studies

Utilizing advanced computer algorithms, researchers significantly streamline the analysis process. “We categorize the data into two bins: the credible detections and the outliers, with some cases falling in between,” Denneau explained.

“This operation is conducted for hundreds of footprints recorded by each telescope nightly,” he added.

The Catalina Sky Survey includes three observing telescopes. The one with the broadest field of view captures more than half of the visible sky simultaneously, according to Fuls.

The challenge lies in the fact that astronomers are analyzing a 2D image, making it difficult to ascertain exact distances. “We can begin estimating distances once we observe the object’s orbit,” he further elaborated.

Determining Size and Distance of NEOs

While optical telescopes excel in spotting NEOs, radio telescopes are the best tool for measuring distance, according to Anne Virkki, a research fellow at the University of Helsinki. “Radar helps us glean the third dimension, which is crucial,” she highlighted.

Radio telescopes utilize large dishes to capture radio waves emitted by celestial bodies, allowing astronomers to bounce radar signals off NEOs for size determination, although 2024 YR4’s distance makes this impossible now.

A radar image of asteroid 2014 JO25 captured by the Arecibo Observatory/NASA/NSF in Puerto Rico on April 17, 2017.
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By evaluating the brightness of an asteroid and how it changes over time, astronomers can infer its shape, rotation speed, and composition. However, without understanding its reflectivity, this analysis remains largely speculative, Fuls admitted. The process resembles piecing together a jigsaw puzzle. “We begin by mapping out the orbit and then deduce conclusions about its distance and size,” he noted.

Assessing Risks of Earth Impacts

Once an object is visualized, it is cross-referenced with an existing database to confirm its identity. This process takes around 10 minutes, according to Fuls. If it is recognized as new, subsequent observers escalate the findings, placing it on a list for future observation to verify its movement within an hour or so.

If the object is validated as a new discovery, it is reported to the Minor Planet Center, managed by the International Astronomical Union.

“Considering the limited movement observed over a 30-minute window, we can predict if the object will come close to Earth,” Denneau stated.

However, astronomers encounter a significant limitation: detecting an object approaching from behind the sun is often impossible for optical telescopes to resolve through the sun’s blinding glare. This is how the Chelyabinsk meteor went undetected prior to its impact. “The Chelyabinsk meteor approached from the solar side,” Denneau recalls. “No telescope was able to register it before it struck.”

Contingency Planning for Potential Impacts

The course of action depends on the object’s size. In cases where the object presents a substantial risk, with a likelihood of at least 1% of hitting Earth, it is reported to the International Asteroid Warning Network (IAWN), created in 2013 for global observation of potentially hazardous space objects. IAWN has issued its inaugural Potential Asteroid Impact Notification concerning 2024 YR4, aiming to alert the astronomical community to gather information to determine if an impact is feasible.

Astronomers follow up with further observations to acquire more details about the object’s size, composition, and potential threat to Earth.

Enthusiasts organized under the International Occultation Timing Association (IOTA) frequently use their telescopes and advanced cameras to monitor for sudden reductions in light from distant stars as asteroids or comets pass in front of them, a phenomenon known as occultation. Their collective measurements from different locations assist in sizing the asteroid.

“Some amateur astronomers operate at remarkably high levels and utilize advanced tools,” noted Kelly Fast, acting planetary defense officer for NASA’s Planetary Defense Coordination Office. “They significantly contribute additional observations once a new object is observed.”

Aggregating all available data allows astronomers to generate something similar to the National Hurricane Center’s forecasts that predict tropical storm trajectories.

“We visualize a cone of probability indicating where the object might be, and the cone shrinks as we gather more observations,” Fuls clarified.

You can also think of it as a “cloud” that may extend hundreds or thousands of miles wide, with some portions intersecting Earth in 2032, Denneau added.

However, time is critical. Soon, 2024 YR4 will fade from view, making it invisible to even the largest telescopes, and it’s already too far away for radar measurements. If not detected soon, astronomers will have to wait until 2028 to observe it again, just four years before it may reach Earth.

“We need the asteroid to move further along its orbit for more data, which will help pinpoint its trajectory,” he voiced. “This will allow us to narrow down its potential path more effectively.”

Possibilities for Impact Prevention

NASA’s DART mission (“Double Asteroid Redirection Test“) successfully impacted the asteroid Dimorphos about 7 million miles away, slightly adjusting its orbit. Although Dimorphos posed no threat to Earth, the mission aimed to establish the feasibility of redirecting an asteroid on a collision course with our planet. The mission was deemed successful.

Thus, it is feasible to redirect an asteroid, but multiple factors come into play.

Primarily, the object must be solid enough to apply force effectively against it. Therefore, determining its composition is essential. “Is it rocky? Does it contain significant metals? Is it a rubble pile or a solid mass?” pondered NASA’s Fast. “This information is vital.”

Nevertheless, executing space missions requires significant planning and often years of preparation. In situations like 2024 YR4, astronomers may have several years to devise a strategy for sending a spacecraft to engage a hazardous object. However, such opportunities may not always arise.

A 2023 NASA report indicates that very few of the largest asteroids that could cause extensive destruction—like the one that resulted in the extinction of the dinosaurs—are still unidentified or untracked. Moreover, NASA has located around 95% of the smaller yet dangerous objects capable of “mass devastation [and] the potential to destabilize civilizations.”

In terms of size, 2024 YR4 is estimated to range between 40 to 90 meters (approximately 130 to 300 feet) in diameter, which places it in a category below two of NASA’s classifications: those larger than 50 meters (165 feet) could lead to “local devastation,” of which only an estimated 7% have been discovered; and those larger than 140 meters (460 feet)—40% remain undiscovered—could potentially cause lethal impacts over metropolitan regions with significant casualties.

Is there any positive outcome?

Certainly! Currently, the likelihood of 2024 YR4 colliding with Earth appears minimal. While an impact could cause significant local damage if it were to strike a populated area, it is not categorized as a planet-wide threat!