Asteroid (231937) 2001 FO32 passes the Earth.

Asteroid (231937) 2001 FO32 passed by the Earth at a distance of about 2 017 000 km (5.25 times the average distance between the Earth and the Moon, or 1.35% of the distance between the Earth and the Sun), slightly after 4.00 pm GMT on Sunday 21 March 2021. There was no danger of the asteroid hitting us, though were it to do so it would have presented a considerable threat. (231937) 2001 FO32 has an estimated equivalent diameter of 540-1700 m (i.e. it is estimated that a spherical object with the same volume would be 540-1700 m in diameter), and an object of this size would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground directly with an explosion that would be more than 600 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater 8 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.

 

300 second image of (231937) 2001 FO32 taken with the Elena Planetwave 17" Telescope at Ceccano in Italy on Friday 19 March 2021. The asteroid is the small point at the centre of the image, the longer lines are stars, their elongation being caused by the telescope tracking the asteroid over the length of the exposure. Gianluca Masi/Virtual Telescope.

(231937) 2001 FO32 was discovered on 23 March 2001 by the Massachusetts Institute of Technology's Lincoln Near Earth Asteroid Research Laboratory in Socorro, New Mexico. The designation 2001 FO32 implies that it was the 814th asteroid (asteroid O32 - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 25, with a number added to the end each time the alphabet is ended, so that A = 1, A1 = 26, A2 = 51, etc., which means that O32 = (25 X 32) + 14 = 814) discovered in the second half of March 2001 (period 2001 F - the year being split into 24 half-months represented by the letters A-Y, with I being excluded),  while the designation implies that it was 231 937th asteroid ever discovered (asteroids are not given this longer designation immediately to avoid naming double or false sightings). 

 

The relative positions of (231937) 2001 FO32 and the Earth on 21 March 2021. JPL Small Body Database.

(231937) 2001 FO32 has an 810 day (2.22 year) orbital period, with an elliptical orbit tilted at an angle of 39.0° to the plain of the Solar System which takes in to 0.30 AU from the Sun (30% of the distance at which the Earth orbits the Sun, inside the orbit of the planet Mercury) and out to 3.11 AU (311% of the distance at which the Earth orbits the sun, and more than twice the orbit of the planet Mars). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, (231937) 2001 FO32 is also classified as a Potentially Hazardous Asteroid.

 

The orbit and current position of (231937) 2001 FO32. Minor Planet Center.

This means that (231937) 2001 FO32 has occasional close encounters with the Earth, with the last thought to have happened in March 2001 and the next predicted in April 2032. The asteroid also has occasional close encounters with the planets Mercury, which it last cam close to in January 2008 and is next predicted to pass in June 2084, and Venus, which it last came close to in February 1979, and is expected to pass again in June 2074. Asteroids which make close passes to multiple planets are considered to be in unstable orbits, and are often eventually knocked out of these orbits by these encounters, either being knocked onto a new, more stable orbit, dropped into the Sun, knocked out of the Solar System or occasionally colliding with a planet. 

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