Asteroid 2019 SX8 passed by the Earth at a distance of about 381 200
km (0.99 times the average distance between the Earth and the Moon, or
0.25% of the distance between the Earth and the Sun), at about 7.50 am
GMT on Saturday 28 September 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 SX8 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) in the atmosphere more than 32 km above the ground, with only fragmentary material
reaching the Earth's surface.
The calculated orbit of 2019 SX8. JPL Small Body Database.
2019 SX8 was discovered on 30 September 2019 (two days 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 SX8
implies that the asteroid was the 215th object (asteroid X8 -
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 X8 = 23 + (24 X 8) = 215) discovered in the second half of September 2019 (period 2010 S).
2019 SX8 has a 704 day orbital period and an eccentric orbit
tilted at an angle of 4.50° to the plane of the Solar System, which
takes it from 0.95 AU from the Sun (i.e. 95% of he average distance at
which the Earth orbits the Sun) to 2.15 AU from the Sun (i.e. 215% of
the
average distance at which the Earth orbits the Sun, and further from the Sun as 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). This means that 2019 SX8 occasionally comes close to the Earth, with the last such encounter having happened in October 2017, and the next predicted for June 2021. 2019 SX8 also has occasional close encounters with the planet Mars, with the last having happened in January 1971.
See also...
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