Asteroid 2021 DW1 passes the Earth.

Asteroid 2021 DW1 passed by the Earth at a distance of about 570 000 km (1.48 times the average distance between the Earth and the Moon, or 0.38% of the distance between the Earth and the Sun), slightly before 9.00 am GMT on Thursday 4 March 2021. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2021 DW1 has an estimated equivalent diameter of 17-55 m (i.e. it is estimated that a spherical object with the same volume would be 17-55 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) between 25 and 8 km above the ground, with only fragmentary material reaching the Earth's surface.

 

120 second image of 2021 DW1 taken with the Elena Planetwave 17" Telescope at Ceccano in Italy on 1 December 2020. The asteroid is the small point at the centre of the image, indicated by the white arrow, 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.

2021 DW1 was first detected on 16 February 2021 (16 days before its closest approach to the Earth), by the University of Hawaii's PANSTARRS telescope. The designation 2021 DW1 implies that it was the 47th asteroid (asteroid W1 - in numbering asteroids the letters A-Z, 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 = 25, A2 = 49, etc., which means that W1 = (25 x 1) + 22 = 47) discovered in the second half of February 2021 (period 2020 S; the year being split into 24 half-months represented by the letters A-Y, with I being excluded).

 

The closest approach of 2021 DW1 to the Earth on 4 March 2021. JPL Small Body Database.

2021 DW1 has a 552 day (1.51 year) orbital period, with an elliptical orbit tilted at an angle of 7.14° to the plain of the Solar System which takes in to 0.99 AU from the Sun (99% of the distance at which the Earth orbits the Sun) and out to 1.64 AU (164% of the distance at which the Earth orbits the Sun, and more than the distance at which the planet Mars orbits the Sun). 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). This means that Asteroid 2021 DW1 has regular close encounters with the Earth, with the thought to have happened in February 2018, and the next predicted for December 2023.

 

The orbit and current position of 2021 DW1. The Sky Live 3D Solar System Simulator.

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