Asteroid (474231) 2001 HZ7 passed by the Earth at a distance of about 15 210 000
km (39.6 times the average distance between the Earth and the Moon, or 10.2% of the distance between the Earth and the Sun), slightly before 7.10 am
GMT on Saturday 1 April 2017. There was no danger of
the asteroid hitting us, though were it to do so it would have
presented a considerable threat .(474231) 2001 HZ7 has an estimated
equivalent
diameter of 210-650 m (i.e. it is estimated that a spherical object with
the same volume would be 210-650 m in diameter), and an object of this
size 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 17 500-760 000 000 times as powerful as the Hiroshima
bomb. Such an impact would result in an impact crater 3-8 km in
diameter
and devastation on a global scale, as well as climatic effects that
would last decades or even centuries.
The calculated orbit of (474231) 2001 HZ7. Minor Planet Center.
(474231) 2001 HZ7 was discovered on 21 April 2001 by the Massachusetts Institute of Technology's Lincoln Near Earth Asteroid Research Laboratory in Socorro, New Mexico. The designation 2001 HZ7 implies that it was the 200th asteroid
(asteroid Z7) discovered in the second half of April 2001 (period
2001 H), while the longer designation (474231) indicates that it was the 474 231st asteroid discovered
overall (asteroids are not given this longer designation immediately, to
ensure that numbered objects are genuine asteroids that have not been
previously described).
(474231) 2001 HZ7 has a 650 day orbital period and an eccentric orbit
tilted at an angle of 5.42° to the plane of the Solar System, which
takes it from 0.73 AU from the Sun (i.e. 73% of he average distance at
which the Earth orbits the Sun, slightly more than the distance at which the planet
Venus orbits the Sun) to 2.20 AU from the Sun (i.e. 220% of the
average distance at which the Earth orbits the Sun, and considerably
outside the orbit of 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 close
encounters between the asteroid and Earth are extremely common, with the
last having occurred in December 2009 and the next predicted
in October 2018 As an asteroid probably larger than 150 m in diameter
that occasionally comes within 0.05 AU of the Earth, (474231) 2001 HZ7 is also
classified as a Potentially Hazardous Asteroid.
(474231) 2001 HZ7 also
has frequent close encounters with the planets Venus, which it is
thought to have last passed in February this year, and is next predicted to
pass in November 2034, and Mars which it last came close to in May 1915 and
is next predicted to pass in November 2048. Asteroids
which make close passes to multiple planets are considered to be in
unstable orbits, and are often eventually knocked out of these orbits by
these encounters, either being knocked onto a new, more stable orbit,
dropped into the Sun, knocked out of the Solar System or occasionally
colliding with a planet.
See also...
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