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Close encounter: Giant asteroid slipped by Earth last week, evading detection

In a shocking turn of events, an asteroid larger than the Leaning Tower of Pisa made an exceptionally close approach to Earth, slipping unnoticed past NASA’s monitoring systems. This giant asteroid, designated 2023 NT1, managed to avoid detection until two days after it had already whizzed past our planet.

The asteroid reached a startlingly close distance of around 62,000 miles from Earth. To put it in context, this is roughly a quarter of the distance between Earth and the Moon, a strikingly short distance in astronomical terms. 

However, due to the unfortunate alignment with the sun, the asteroid was masked by sunlight, thereby evading early detection.

Flying under the asteroid detection radar

The asteroid, now moving away from Earth at an impressive speed of 25,000 miles per hour, boasts a diameter of up to 200 feet. 

This size distinction places 2023 NT1 as larger than the 60-foot Chelyabinsk meteor that famously crashed into Earth’s atmosphere in 2013, resulting in injuries to over 1,600 people.

Based on information provided by NASA and the International Astronomical Union, the close encounter with 2023 NT1 occurred at 10:12 UTC on July 13. 

However, ATLAS South Africa didn’t make the first recorded observation until two days later. Specialists specifically designed this four-telescope system to detect potentially hazardous asteroids.

Was the asteroid potentially hazardous?

In a social media discussion about the incident, amateur astronomer Tony Dunn speculated that, with a diameter of up to 200 feet, 2023 NT1 could be larger than the asteroid believed to have created the Meteor Crater in Arizona.

This significant landmark near Flagstaff, spanning around 3,900 feet in diameter, is attributed to a collision that occurred approximately 50,000 years ago.

Although 2023 NT1’s approach to our planet was alarmingly close, it is not technically classified as “potentially hazardous.”

The criteria for this designation require the asteroid to come within 0.05 astronomical units (roughly 4.65 million miles) of Earth and be larger than 459 feet in diameter. While 2023 NT1 meets the proximity requirement, its size falls short of the designated threat threshold.

The sun’s glare obscured NT1

Despite its innocuous passage this time around, 2023 NT1’s close flyby underscores the ongoing challenge in detecting some asteroids, particularly those obscured by the sun’s glare.

For example, the Chelyabinsk meteor of 2013 remained undetected due to its radiant point’s proximity to the sun. The meteor eventually exploded in a spectacular fireball, releasing an energy equivalent to 500,000 tons of TNT and sending a shockwave twice around the globe.

In light of such incidents, there are proactive measures underway to mitigate future threats. The European Space Agency plans to launch its NEOMIR orbiting observatory around 2030 as one such initiative. Designers created this observatory to act as an early warning system, detecting and monitoring any asteroid approaching Earth from the direction of the sun.

Positioned at the L1 Lagrange point, a stable point in space between Earth and the sun, NEOMIR’s infrared telescope aims to identify asteroids 65 feet and larger that are currently masked by sunlight.

Planetary defense 

Such efforts are part of the broader conversation around planetary defense, a topic that has gained substantial attention following NASA’s successful Double Asteroid Redirection Test (DART) mission last September. During this mission, the DART spacecraft intentionally crashed into Dimorphos, an asteroid moonlet in the double-asteroid system of Didymos, marking humanity’s first successful planetary defense test.

Despite these advancements, there are some asteroid types that may prove difficult, if not impossible, to deflect using current techniques, as indicated by recent studies. “Rubble pile” asteroids, like Itokawa, consist of boulders and rocks loosely clustered together.

Due to their structure, these asteroids could potentially absorb the energy of an impact and continue on their trajectory, posing challenges to future mitigation strategies.

More about asteroid detection

Asteroid detection involves the use of various observational technologies and techniques to identify and track asteroids, particularly those that may pose a threat to Earth (also known as Near-Earth Objects, or NEOs). 

Ground-based telescopes

Ground-based telescopes typically use charge-coupled devices (CCDs) to record images of the sky. Scientists then use software to compare images taken at different times and look for objects that have moved. The key ground-based facilities include the Catalina Sky Survey in the United States and the Pan-STARRS telescope in Hawaii.

Space-based detection

Space-based detectors offer several advantages over ground-based ones. They can observe the sky continuously, aren’t affected by the Earth’s weather or daylight, and can detect objects that are faint or close to the sun, which are difficult to observe from Earth. 

NASA’s Near-Earth Object Observations (NEOO) program uses a space-based infrared telescope called NEOWISE to detect asteroids. Development is also underway for the NEO Surveillance Mission (NEOSM), previously known as the Near-Earth Object Camera (NEOCam).

Efforts are also underway to improve asteroid detection capabilities. For instance, the Large Synoptic Survey Telescope (LSST), renamed as Vera C. Rubin Observatory, which is under construction in Chile, will have a much larger field of view than existing telescopes. When it becomes operational, scientists expect it to significantly improve asteroid detection.

Scientists use data from these telescopes and detectors to calculate the orbits of detected asteroids and assess whether they pose a threat to Earth. The Minor Planet Center in Massachusetts is the global repository for such information.

Detection remains a challenge

However, even with these resources, asteroid detection remains a significant challenge. Many asteroids are very small or dark, making them difficult to spot, and the vastness of space means that there are many areas to search.

Additionally, predicting the exact path of an asteroid is difficult due to the gravitational influence of other celestial bodies and the so-called Yarkovsky effect, where an asteroid’s trajectory can be subtly altered by the radiation of heat from its surface.

Scientists and engineers continue to develop new technologies and techniques to improve asteroid detection, including better algorithms for processing images, new types of sensors, and proposals for new space-based telescopes. The goal is to find potentially hazardous asteroids as early as possible, providing time to take action if necessary.


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