Tuesday 3 May 2016

Asteroid 2016 GD241 passes the Earth.

Asteroid 2016 GD241 passed by the Earth at a distance of 7 643 000 km (19.9 times the average distance between the Earth and the Moon, or 5.12% of the average distance between the Earth and the Sun), slightly before 4.30 am GMT on Moday 2 May 2016. There was no danger of the asteroid hitting us, though had it done so it would have presented a considerable threat. 2016 GD241 has an estimated equivalent diameter of 99-310 m (i.e. a spherical body with the same mass would be 99-310 m in diameter), and an object of this size would pass through the atmosphere and directly impact the ground with a force of about 3.5-25 megatons (about 200-1500 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater 1-1.5 km across, and resulting in global climatic problems that could last for years or even decades.

The calculated orbit of 2016 GD241. JPL Small Body Database.

2016 GD241 was discovered on 14 April 2016 (18 days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2016 GD241 implies that it was the 6029th asteroid (asteroid D241) discovered in the first half of April 2016 (period 2016G).

2016 GD241 has a 663 day orbital period and an eccentric orbit tilted at an angle of 11.7° to the plane of the Solar System, which takes it from 0.34 AU from the Sun (i.e. 34% of the average distance at which the Earth orbits the Sun, inside the orbit of the planet Mercury) to 2.63 AU from the Sun (i.e. 263% 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 2012 this year and the next predicted inmay 2163. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2016 GD241 is also classified as a Potentially Hazardous Asteroid. 

2016 GD241 also has frequent close encounters with the planets Mercury (which it is predicted to pass next on 21 June this year) and Venus (which it last came close to in December 1921). 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.
 
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