by Graham Pierrepoint
Most of us, as it goes, are blissfully unaware of the often small rocks which hurtle past the Earth at mind boggling speed every few days. Thankfully so! However, if you turn your eyes skywards on the evening of April 19th, you will be treated to the sight of the biggest and brightest asteroid to have neighbored Earth in over a decade – around 13 years, to be more precise.
Stargazers will be able to see Asteroid 2014 JO25, to give the rock its full name, come within 1.8 million km - almost 1.1 million miles - roughly four and a half times the distance to the Moon - of our little blue planet. Even though this is a very close approach for an asteroid of this size, NASA advise that there is no chance of this particular boulder clashing with Earth. Nevertheless, 2014 JO25 has made it onto the infamous list of PHAs (Potentially Hazardous Asteroids) – a comprehensive roster of those galactic space boulders which are deemed large enough and pass close enough to Earth to be considered somewhat worrisome. To officially warrant concern, asteroids must be at least 100-150 meters (330-490 feet) in diameter and pass less than 0.05 a.u (7.5 million km / 4.6 million miles) from our planet. To date, we know of 1,786 PHAs, but don’t worry, no known PHA is expected to collide with Earth for at least the next century.
Asteroid 2014 JO25 was first spotted in May 2014 by astronomers at the Catalina Sky Survey (CSS) near Tucson, Arizona. CSS is a NASA-run project and is in collaboration with the state university.
Dimensions taken by NASA's NEOWISE mission suggest Asteroid 2014 JO25 measures about 650m (nearly 2000ft) across. It is thought to be about twice as reflective as the moon and is predicted to brighten to magnitude 11 on Wednesday night. This means that even amateur astronomers should be able to see the asteroid with any small optical telescope for at least a couple of nights before it fades from sight. Because of the proximity and projected trajectory of the asteroid, astronomers expect this event to be a once in a lifetime chance to study this it. NASA, for example, is planning to use the Goldstone Solar System Radar in California to obtain detailed radar images of the asteroid’s surface.
The asteroid should be visible to most people low in the evening sky on Tuesday 18th. This is the closest 2014 JO25 has come to Earth in about 400 years and is the closest it will come for another 500 - but we won’t have to wait too long for our next close shave. The next comparable space rock to zoom past our little world will be when the 800-meter-wide (half-mile-wide) asteroid 1999 AN10 flies by at 380,000 km (236,000 miles, or roughly one lunar distance) in 2027. So keep your telescopes handy – and get set to look to the skies!