Sunday 16 May 2021

Asteroid 2021 JR3 passes the Earth.

Asteroid 2021 JR3 passed by the Earth at a distance of about 779 900 km (2.03 times the average distance between the Earth and the Moon, or 0.52% of the distance between the Earth and the Sun), slightly after 1.55 am GMT on Wednesday 12 May 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 JR3 has an estimated equivalent diameter of 19-61 m (i.e. it is estimated that a spherical object with the same volume would be 19-61 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) betwenn 35 and 5 km above the ground, with only fragmentary material reaching the Earth's surface.

Asteroid 2021 JR3 imaged on 11 May 2021 from London, England. Image is a single three minute exposure. Asteroid is the point indicated by the red lines, which has moved only slightly over the course of the image gathering, while the longer lines are stars that have moved considerably in the same time.  Northolt Branch Observatories/Facebook.

2021 JR3 was discovered on 9 May 2021 (two days before its closest approach to the Earth) by the the Hungarian GINOP KHK dedicated meteor camera system. The designation 2021 JR3 implies that the asteroid was the 92nd object (asteroid R3 - 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 R3 = (25 x 3) + 17 = 92) discovered in the first half of May 2021 (period 2021 J - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).

The relative positions of 2021 JR3 and the Earth on 12 May 2021. JPL Small Body Database.

2021 JR3 has a 1352 day (3.70 year) orbital period, with an elliptical orbit tilted at an angle of 0.96° to the plain of the Solar System which takes in to 0.74 AU from the Sun (74% of the distance at which the Earth orbits the Sun, and slightly outside the orbit of the planet Venua) and out to 4.04 AU (404% of the distance at which the Earth orbits the Sun, and considerably more than twice 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). 

The orbit and current position of 2021 JR3. The Sky Live 3D Solar System Simulator.

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