Asteroid 2019 UU1 passed by the Earth at a distance of about 225 900
km (0.59 times the average distance between the Earth and the Moon, or
0.15% of the distance between the Earth and the Sun), slightly after 6.20 am
GMT on Friday 18 October 2019. There was no danger of
the asteroid hitting us, though were it to do so it would not have
presented a significant threat. 2019 UU1 has an estimated
equivalent
diameter of 2-5 m (i.e. it is estimated that a spherical object
with
the same volume would be 2-5 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) in the atmosphere
more than 40 km above the ground, with only fragmentary material
reaching the Earth's surface.
The calculated orbit of 2019 UU1. JPL Small Body Database.
2019 UU1 was discovered on 19 October 2019 (the day after its closest encounter with 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 2019 UU1
implies that the asteroid was the 44th object (asteroid L -
in numbering asteroids the letters A-Y, excluding I, are assigned
numbers from 1 to 24, 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 U1 = (24 x 1) + 20 = 44) discovered in the second half of October 2019 (period 2010 U).
2019 UU1 has a 399 day orbital period and an eccentric orbit
tilted at an angle of 1.26° to the plane of the Solar System, which
takes it from 0.81 AU from the Sun (i.e. 81% of he average distance at
which the Earth orbits the Sun) to 1.31 AU from the Sun (i.e. 131% of
the
average distance at which the Earth 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 2019 UU1 occasionally comes close to the Earth, with the
last such encounter having happened in January this year, and the next
predicted for October 2020. 2019 UU1 also has occasional close encounters
with the planet Venus, with the last having happened in June 2017, and Mars, which it last came close to in April 2035.
See also...
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