(Sen) - Its not surprising that many people think the sky never changes but this couldn’t be further from the truth. There are stars varying in brightness even exploding, planets moving across the sky and meteor showers bringing life to a seemingly static background. There are even dark, silent predators out there in the guise of asteroids which pass close by the Earth, sometimes a little too close for comfort.
The truth is, there are plenty of lumps of space rock out there in the solar system and whilst we know about the orbit of many of them, there are others that are previously undiscovered that just surprise seem to pop up out of nowhere and surprise us! Back in December 2005, astronomer Robert McMillan of the Spacewatch Program near Tucson Arizona discovered an asteroid now known as 2005 YU55 and this month, it will spin by the Earth at a distance of just 325,500km, that’s even closer than the Moon. Click here to view the projected flight path of the asteroid.
Studies with the Arecibo radio dish have since shown the asteroid to be nearly spherical in shape and about 400 metres in diameter which means if it were to hit Earth then it might very well be game over for humans. BUT the good news is that it won’t hit the Earth and there is no chance of that happening even within the next 100 years when it returns to our vicinity.
Astronomers around the world are counting down to the moment of closest approach which will be at 23:28 UT on November 8. As it approaches, telescopes of all sizes will be trained on the interloper hoping to catch a close-up glimpse of it although, unfortunately a telescope will be needed as its brightness (magnitude 11) will be far too low for the unaided eye to detect.
Whilst its not unusual for interplanetary rocks to ‘interact’ with Earth, its not often that we get rocks of this size so close to the Earth indeed the next object of this calibre is due in 2028 and will pass even closer at just over 220,000km. Now with all these rocks flying around space you would think a fragile place like Earth is pretty vulnerable. It seems we have someone looking out for us, the mighty planet Jupiter. Thanks to Jupiter’s massive gravitational pull, it tends to sweep up much of the debris floating around the Solar System, as we saw back in July 1994 when Comet Shoemaker Levy 9 got dragged into the gravitational well of Jupiter. The comet nucleus got broken up into about 20 pieces and each one met its demise when it was pulled on to a collision course with the planet. It seems that Jupiter is somewhat of a celestial hoover sweeping up wayward rocks and protecting the inner Solar System.
Those rocks that do get through are of course a risk to us here on Earth but for the most part, impacts are unlikely. When you remember that most asteroids are no bigger than 1km in size and the Earth is 12,700km across the chances of a collision are pretty slim. However there has been evidence of asteroid impacts in our history. One of the most well known is Meteor Crater in Arizona which was created by a meteor striking Earth at 42,000 km per hour over 50,000 years ago. The crater still maintains a classical crater shape even with the erosive effects of the weather and measures 1.2km in diameter by 168 metres deep.
Even more well known is the infamous event that is believed to have caused the extinction of the dinosaurs. Its thought the Chicxulub crater (180km in diameter) is the site of an asteroid impact that took place 64 million years ago at the end of the Cretaceous Period. From studying this ancient buried crater underneath the Yucatan Peninsula its estimated that the object that bought about the demise of the dinosaurs was 10km across and delivered 96 teratons of TNT.
Whether or not there is anything we could do to deflect any potential impactor depends heavily on having plenty of warning and that means, finding them early enough. Fortunately there are a number of projects that are keeping eyes peeled on the sky for unknown intruders; LINEAR (run by NASA and MIT) and Spaceguard (privately operated and based in the UK). There are also amateur astronomers all over the World that keep an eye on the sky, constantly checking familiar patches to see if there are any unusual specks of light.
If one does get discovered which has our name on it, is there really anything we can do, assuming we find it early enough? Well there are a number of possibilities. We might launch an explosive device to detonate just above the surface and nudge the asteroid into a slightly different orbit. Give it a tiny nudge early enough and that will turn into a big change shift in its path by the time it gets to us. Alternatively perhaps detonate on the surface or even inside the asteroid and cause it to break up into many tiny pieces. The latter idea of breaking up a threatening asteroid by blowing it up from the inside was the subject of the 1998 blockbuster Armageddon. This may just mean the Earth will get hit by lots of little pieces rather than one big one. This might mean our atmosphere could burn up the smaller pieces or they might miss completely. Other more wacky ideas involve fitting solar sails to allow the constant stream of solar wind to adjust the orbit or fix rocket motors and literally drive it away from Earth.
For the moment though, we don’t need to worry. There is nothing we know of that is heading on a collision course. Fortunately, the physics that articulates how orbits work is very well understood so as long as we can get enough observations of an object then we can accurately calculate its path. In the case of 2005 YU55 there is no risk, quite the contrary, astronomers are pretty excited at the prospect of a ring side seat to witness one of the rather more deadly yet somehow enigmatic objects in the Universe.