Asteroid 2018 XH passed by the Earth at a distance of about 14 773 000
km (38.5 times the average distance between the Earth and the Moon, or 9.87% of the distance between the Earth and the Sun), slightly before 9.25 am
GMT on Saturday 5 January 2019. There was no danger of
the asteroid hitting us, though were it to do so it would have
presented a significant threat. 2018 XH has an estimated
equivalent
diameter of 75-240 m (i.e. it is estimated that a spherical object
with
the same volume would be 75-240 m in diameter), and an object at the
upper end of this range would be predicted to be capable of
passing through the Earth's
atmosphere relatively intact, impacting the ground directly with an
explosion that would be about 29 400 times as powerful as the
Hiroshima
bomb. Such an impact would result in an impact crater over 3.5 km
in
diameter
and devastation on a global scale, as well as climatic effects that
would last years or even decades.
The calculated orbit of 2018 XH. JPL Small Body Database.
2018 XH was discovered on 3 December 2018 by the European Space Agency's Optical Ground Station on Tenerife in the Canary Islands. The
designation 2018 XH implies that it was the eighth asteroid
(asteroid H -
in numbering asteroids the letters A-Y, excluding I, are assigned
numbers from 1 to 24, so that H = 8) discovered in the first half of December 2018 (period
2018 X - the year being split into 24 half-months represented by letters).
2018 XH has an 615 day orbital period and an eccentric orbit
tilted at an angle of 1.23° to the plane of the Solar System, which
takes it from 0.99 AU from the Sun (i.e. 99% of the the average distance at
which the Earth orbits the Sun) to 1.84 AU from the Sun (i.e. 184% of
the
average distance at which the Earth orbits the Sun, more the distance at which 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). This means that close
encounters between the asteroid and Earth are extremely common, with the
last having occurred in May 2014 and the next predicted
in March 2024. 2018 XH also has occasional close encounter with the planet Mars, with the last having happened in January 2017. As an asteroid probably larger than 150 m in diameter
that occasionally comes within 0.05 AU of the Earth, 2018 XH is also
classified as a Potentially Hazardous Asteroid.
See also...
Follow Sciency Thoughts on Facebook.