Sciency Thoughts: Asteroid 2023 HW3 passes the Earth.

Wednesday 26 April 2023

Asteroid 2023 HW3 passes the Earth.

Asteroid 2023 HW3 passed by the Earth distance of about 209 000 km (54% of the the average distance between the Earth and the Moon or 0.14% of the distance between the Earth and the Sun), with a velocity of about 15.06 km per second, slightly before 7.35 am GMT on Sunday 23 April 2023. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2023 HW3 has an estimated equivalent diameter of 3-10 m (i.e. it is estimated that a spherical object with the same volume would be 3-10 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) more than 31 km above the ground, with only fragmentary material reaching the Earth's surface.

The relative positions of 2023 HW3, the Earth, and the Moon at 7.00 am on Sunday 23 April 2023. JPL Small Body Database.

2023 HW3 was discovered on 22 April 2023 (the day before its closest approach to the Earth) by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2023 HW3 implies that the asteroid was the 97th object (asteroid W3 - 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 = 26, A2 = 51, etc., which means that W3 = (25 x 3) + 22 = 97) discovered in the second half of April 2023 (period 2023 H - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).

2023 HW3 is calculated to have a 973 day (2.66 year) orbital period, with an elliptical orbit tilted at an angle of 19.1° to the plain of the Solar System which takes in to 0.92 AU from the Sun (92% of the distance at which the Earth orbits the Sun) and out to 2.92 AU (2.92 times the distance at which the Earth orbits the Sun, or almost twice the distance at which the planet Mars orbits). 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).