Wednesday, 2 April 2014

Asteroid 2009 FD passes the Earth.

Asteroid 2009 FD passed the Earth at a distance of roughly 15 100 000 km (a little over 39 times the average distance between the Earth and the Moon) at about 9.10 am GMT on Tuesday 1 April 2014. There was no danger of the asteroid hitting us, though were it to do so it would be likely to cause severe problems. 2009 FD is calculated to be 472 m in diameter, and an object of this size would be expected to punch straight through the Earth's atmosphere, impacting directly into the ground, an impact which would result in an explosion over 17 650 times as large as that caused by the Hiroshima bomb, creating a crater over 7 km in diameter and climatic effects that could last for decades.

Image of 2009 FD captured by the Very Large Telescope on 1 January 2014. The elongate structures are actually stationary stars, they appear drawn out as the telescope was tracking the asteroid during a shot with a long exposure time. European Southern Observatory.

2009 FD was discovered by the Observatorio Astronómico de La Sagra in southern Spain on 16 March 2009. The designation 2009 FD implies that it was the fourth object (object D) discovered in the second half of March 2009 (period 2009 F).

2009 FD has an 1.25 year orbital period and an eccentric orbit that takes it from 0.59 AU from the Sun (i.e. 59% of the average distance at which the Earth orbits the Sun, inside the orbit of Venus) to 1.75 AU from the Sun (i.e. 127% of the average distance at which the Earth orbits the Sun, outside the orbit of 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).

The calculated orbit of 2009 FD. JPL Small Body Database Browser.

This short orbital period and Earth-crossing orbital path means that 2009 FD makes frequent close passes of the Earth, the most recent having occurred on 24 October 2010, and the next being predicted for 29 October 2015. It also makes frequent close approaches to the planets Venus and Mars, the most recent of which occurred on 3 August 2013, when 2009 FD came within 11 600 000 km of Mars, and the next is predicted to happen on 6 May 2017, when 2009 FD will come within 10 810 000 km of Mars. These close encounters with planets raise the possibility of 2009 FD being nudged onto a slightly different course by tidal energy, making its long-term danger to the Earth harder to predict.

The large size and frequent close proximity to Earth of 2009 FD have made it a subject of considerable interest to astronomers, with its future trajectory being calculated for several centuries ahead, calculations that have been updated several times following detailed observations of the asteroid. In January 2011 it was estimated by JPL that there was a 1 in 435 chance of 2009 FD impacting the Earth in 2185, though this possibility has now been ruled out. There is currently considered to be a 1 in 667 change that 2009 will impact the Earth on 30 March 2190.

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