By Simon O'Toole, Australian Astronomical Observatory
An asteroid named 2012 DA14 will come within 27,700 kilometres of Earth early on Saturday morning Australian time (around 6:30am AEDT). At this distance the asteroid will pass within the orbits of several geostationary satellites. Should we be worried? Alert but not alarmed is probably a better approach.
We do not know of any large asteroid that will impact the surface of Earth in the next few hundred years.
The threat of asteroidal impact on Earth is a real one and should be taken seriously. Every hour of every day, many hundreds of meteors hit Earth. Most are the size of a grain of rice or smaller. Approximately once a week, a meteor the size of a car enters the atmosphere.
But the reality is far from romantic. The geological record is littered with the debris of previous asteroidal impacts; there are many craters still visible in Australia. The most famous crater is at Chicxulub in Mexico, caused by an asteroid whose impact is believed to have wiped out the dinosaurs. The larger the body, the greater the damage caused.
We haven't had a major impact for many thousands of years, unless you count the Tunguska event in 1908, but there have been some near misses. In the last two years, there have been several instances of these so-called Near-Earth Objects swinging dramatically close by the planet.
Extinction level events such as the Chicxulub impact are caused by objects with diameter greater than one kilometre. At 45 metres in diameter, 2012 DA14 wouldn't leave a scratch, and there would be no major damage if it did collide with Earth. Even at its closest approach, the asteroid will even be visible with the naked eye.
One of the larger Near-Earth Objects – and one that has garnered a lot of media attention recently – is Apophis. This asteroid – named for the god of darkness and chaos in ancient Egyptian religion – is fast becoming our favourite celestial Doomsday object.
Its size estimate has just been revised up to 325 metres by new observations with the Herschel Space Telescope and it will come within 31,300 kilometres of Earth on April 13, 2029. Before you ask: yes, April 13 in that year falls on a Friday.
Apophis just passed by on January 10, about 14 million kilometres away. Using new observations, NASA confirmed that at its next close approach, the asteroid will not collide with Earth in 2036 either.
The probability of impact with Earth was recently revised from one in 250,000 to less than one in a million. You're more likely to be struck by lightning.
There have been some alarming reports of Apophis possibly destroying satellites in 2029.
The orbits of some geostationary satellites are at a similar distances to Apophis' closest approach (out to about 42,000 kilometres from Earth) – but the chances of a collision occurring are tiny in such a large volume of space.
So do we know all of the dangerous objects out there? Sadly, the answer is no, although we think we've found 96% of the biggest, but only 30% of those that could still cause serious mayhem.
To find the remainder, last year the not-for-profit organisation the B612 Foundation announced plans to build a privately-funded space telescope, called the Sentinel Mission. While this name evokes a famous Arthur C. Clarke short story for many, this mission is far from science fiction.
Sentinel is an infrared telescope designed to find and track asteroids greater than 50 metres in diameter that threaten Earth. It will be inserted into an orbit around the sun in 2017.
The telescope will discover more asteroids in one month than all other telescopes combined. Donors are jumping on board and links with large aerospace companies have been forged. Significant progress is being made, but for now we have to rely on ground-based observations.
In many ways it is a shame that the fear of Earth-killing asteroids steals most of the headlines, since 2013 will bring two of the most exciting celestial objects of recent times to our skies, Comet PANSTARRS and Comet ISON.
The former object will be at its brightest in March this year, and may be as bright as Venus. Comet ISON has the potential to be even more exciting, with many headlines screaming “Comet to be brighter than the Full Moon!”, although don't believe everything you read.
Despite the misleading headlines, the comet will probably be very bright, and therefore make for excellent viewing.
The internet is a funny place though, so don't be surprised to hear that Comet ISON or PANSTARRS will impact Earth and it's all being hushed up in a giant conspiracy.
You heard it here first, folks.
Simon O'Toole has previously received funding from the Australian Research Council and the Science and Technology Facilities Council (UK).