What are the largest near-Earth objects?

What is the largest asteroid and comet considered a near-Earth object? What is their size?

Doug Kaupa

Council Bluffs, Iowa

Doomsday impactors are a staple of modern science fiction. The most famous real-life example of an impact wiping out much of life on Earth is, of course, the object that wiped out the dinosaurs around 66 million years ago.

Fortunately, events of this magnitude are quite rare, occurring about once every few hundred million years. But the possibility is there, so space agencies around the world have taken to monitoring the skies for Near-Earth Objects (NEOs). These objects are comets and asteroids whose orbits take them within 1.3 astronomical units (AU; where 1 AU is the average distance between the Earth and the Sun) from our star.

On that note, the larger comets and asteroids tend to stay far enough away that we have very little to worry about. The largest asteroid considered NEO is 1036 Ganymed. This asteroid is about 23 miles (37 kilometers) in diameter. With a closest solar approach of 1.24 AU, 1036 Ganymed is just within the minimum distance to categorize it as NEO.

The largest comet in the sky today is 109P/Swift-Tuttle. At 16 miles (26 km), Swift-Tuttle is about twice the size of the object that would have wiped out the dinosaurs. However, this comet poses little threat to us, as it makes its closest solar approach at 0.95 AU every 133 years. And, in fact, we have him to thank for the Perseid meteor shower.

It’s actually the little guys we need to be more concerned about because they’re more likely to go unnoticed. The closest encounter to Earth on record with a known NEO was with 2020 VT4, which passed just 232 miles (375 km) above the Earth’s surface on November 13, 2020. The asteroid was only spotted after making its closest approach. The previous closest asteroid, 2020 HQ, flew by Earth just three months before 2020 VT4; he too was not seen before his close passage.

Caitlyn Buongiorno

Associate Editor

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