Asteroid 2007 AG passed by the Earth at a distance of about 8 747 000
km (22.7 times the average distance between the Earth and the Moon, or 5.85% of the distance between the Earth and the Sun), slightly before
11.45 pm
GMT on Tuesday 26 December 2017. There was no danger of
the asteroid hitting us, though were it to do so it would have
presented a significant threat. 2007 AG has an estimated
equivalent
diameter of 180-570 m (i.e. it is estimated that a spherical object
with
the same volume would be 180-570 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 1 175 000 to 8 825 000 times as powerful as the
Hiroshima
bomb. Such an impact would result in an impact crater 2.5-8.0 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 2007 AG. Minor Planet Center.
2007 AG was discovered on 8 January 2007 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 2007 AG
implies that the asteroid was the seventh object (object G) discovered in the first half of January 2007 (period 2007 G).
2007 AG has a 223 day orbital period, with an elliptical orbit tilted at
an angle of 11.9° to the plain of the Solar System which takes in to
0.45 AU from the Sun (45% of the distance at which the Earth orbits the
Sun; slightly outside the orbit of the planet Mercury) and out to 0.99 AU (99% of the distance at which the Earth orbits the Sun). This means that close
encounters between the asteroid and Earth are fairly common, with the
last thought to have happened in January 2015 and the next predicted
in December 2020. Although it does cross the Earth's
orbit and is briefly
further from the Sun on each cycle, 2007 AG spends most of its time
closer to the Sun than we are, and is therefore classified as an Aten
Group Asteroid. As an asteroid probably larger than 150 m in diameter
that occasionally comes within 0.05 AU of the Earth, 2007 AG4 is also
classified as a Potentially Hazardous Asteroid.
2007 AG also
has frequent close encounters with the planets Mercury, which it is
thought to have last passed in February this year, and is next predicted to
pass in January 2025, and Venus, which it is next predicted to pass in June 2059. 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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