Updated: March 21, 2021 8:04:51 pm
On March 21, the largest asteroid predicted to pass by Earth in 2021 will be at its closest. It won’t come closer than 2 million km to Earth, but it will present a valuable scientific opportunity for astronomers who can get a good look at a rocky relic that formed at the dawn of our Solar System.
It is called 2001 FO32. There is no threat of a collision with our planet now or for centuries to come.
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Speed & distance
Scientists know its orbital path around the Sun very accurately, since it was discovered 20 years ago and has been tracked ever since.
For comparison, when it is at its closest, the distance of 2 million km is equal to 5¼ times the distance from Earth to the Moon. Still, that distance is close in astronomical terms, which is why 2001 FO32 has been designated a “potentially hazardous asteroid”.
During this approach, 2001 FO32 will pass by at about 124,000 kph – faster than the speed at which most asteroids encounter Earth. The reason for the asteroid’s unusually speedy close approach is its highly eccentric orbit around the Sun, an orbit that is tilted 39° to Earth’s orbital plane. This orbit takes the asteroid closer to the Sun than Mercury, and twice as far from the Sun as Mars.
As 2001 FO32 makes its inner solar system journey, the asteroid picks up speed. In a statement announcing the upcoming approach, NASA likened the asteroid’s picking up of speed to a skateboarder rolling down a halfpipe. Later, the asteroid slows after being flung back out into deep space and swinging back toward the Sun. It completes one orbit every 810 days (about 2¼ years).
After its brief visit, 2001 FO32 will continue its lonely voyage, not coming this close to Earth again until 2052, when it will pass by at about seven lunar distances, or 2.8 million km.
Even if it is at the smaller end of the scale, 2001 FO32 will still be the largest asteroid to pass this close to our planet in 2021. The last notably large asteroid close approach was that of 1998 OR2 on April 29, 2020. While 2001 FO32 is somewhat smaller than 1998 OR2, it will be three times nearer to Earth.
Studying the visitor
The March 21 encounter will provide an opportunity for astronomers to get a more precise understanding of the asteroid’s size and albedo (i.e. how bright, or reflective, its surface is), and a rough idea of its composition.
When sunlight hits an asteroid’s surface, minerals in the rock absorb some wavelengths while reflecting others. By studying the spectrum of light reflecting off the surface, astronomers can measure the chemical “fingerprints” of the minerals on the surface of the asteroid.
Over 95% of near-Earth asteroids the size of 2001 FO32 or larger have been discovered, tracked, and catalogued. None of the large asteroids in the catalogue has any chance of impacting Earth over the next century, and it is extremely unlikely that any of the remaining undiscovered asteroids of this size could impact Earth, either. Still, efforts continue to discover all asteroids that could pose an impact hazard.
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