What are the chances of an asteroid hitting the Earth?

Bill Read looks at the latest research into the potential threat from Near Earth Objects

Mention the words "meteor" or "asteroid" and everyone probably thinks of Hollywood disaster movies such as Armageddon or Deep Impact. But how much of these films are based on fact? Is there a real danger of an asteroid hitting the Earth? The answer is yes - there is a risk. In fact, the Earth is being bombarded with pieces of rock and metal every day. Most pieces are very small and burn up in the atmosphere as shooting stars, while larger pieces occasionally reach the ground as meteorites. The real danger comes from larger pieces of debris, known as Near Earth Objects (NEOs), which measure between 10 and 300 metres across and are believed to have originated from an asteroid belt between Mars and Jupiter.

When an NEO hits the Earth, it brings about widespread devastation, loss of life and possible climate change. It is believed that an NEO hitting the Earth 65 million years ago may have brought about the extinction of the dinosaurs. The last collision occurred in 1908, when a 100 metre-wide NEO crashed into an uninhabited region of Siberia called Tunguska, causing an explosion that burned an area of 2,000sq km. It is inevitable that, sooner or later, another impact will occur.

It is not known how many NEOs are currently in existence but, thanks to the introduction of new Earth- and space-based telescopes, more are being discovered all the time. In 1975 a total of 70 had been discovered but, in 2007, the latest statistics from NASA revised this figure to a much larger 4,559.

Once a new NEO is detected, the next stage is to determine where it is going and what orbit it is following. From this, a probability can be calculated of the likelihood of an NEO hitting the Earth; in most cases it is extremely low.

If an NEO is detected heading for Earth, the good news is that there are feasible methods to avert a collision. However, fans of Armageddon may be disappointed to learn that none of them involve sending Bruce Willis into space to try to imbed a nuclear bomb in an approaching meteorite. Trying to explode an NEO is not a wise countermeasure, as it will only result in the Earth being hit by several objects rather than just one.

The effective way to deal with an approaching NEO, according to scientists, is not to destroy it but to deflect it away from a collision course. This can be achieved either by speeding it up, so that it does not collide with the Earth but instead passes in front of it, or to slow it down so that it passes behind. The deflection does not have to be large, as a small course change will build into a large one over time.

A simple way to change the speed of an NEO is either to ram a spacecraft into it or hit it with an explosive device (a method known as kinetic energy deflection). However, for the best effect, the explosive device would have to be nuclear and runs the risk of breaking up the asteroid. Also, politicians and many other people and organisations are not keen on the idea of anyone deploying nuclear weapons in space.

A second, more complicated approach is that of low-thrust deflection, which consists of methods that continue to affect the speed of an NEO over time. These include attaching a solar electric propulsion unit to the NEO to push it or using "gravitational coupling", in which a spaceship flies close to an NEO and diverts it by using its own gravitational pull. Other ideas include altering the orbit of an NEO by reducing the amount of sunlight reflected off its surface, by either flying a reflector close to it or even (in the case of smaller NEOs) by painting its surface black. Alternatively, the speed of the NEO could be adjusted by firing lasers at it or even by attaching solar sails to pull it faster.

The practicality of sending unmanned missions to asteroids has already been proved. In 2005, the Japanese Space Agency's Hayabusa mission collected samples from the asteroid Itokowa. On 4 July 2005, NASA crashed a craft into the comet Tempel 1 on its Deep Impact Mission. However, space agencies are suffering from budgetary constraints for future missions. To succeed, it is vital that potentially dangerous NEOs are detected in plenty of time so that a deflection can be carried out well in advance - ideally 20 years - before a potential collision. In March 2007, NASA admitted that it had insufficient funds to find all the NEOs that might pose a threat to Earth, let alone prepare any countermeasures.

Of all the NEOs currently detected, one in particular is causing scientists concern. The object in question is the 280 metre-wide asteroid MN4 (now renamed Aphophis after the Greek name for the Ancient Egyptian god of darkness and chaos), which will have a very close approach (within 30,000km) to Earth on 13 April 2029. The probability of a collision varies according to different calculations but could be between 1 in 3,600 and 1 in 5,500. Additional radar observations in 2013 may alter this figure. However, if Aphophis flies through a particular "keyhole" in space in 2029, it greatly increases the likelihood (to 1 in 2,000) of the NEO hitting the Earth on the next encounter in 2036. If this were to happen, Aphophis would hit the Earth at a speed of 20km per second, releasing around 1,000 megatons of energy and causing huge loss of life and long-term effects on the environment. Deflecting Aphophis is feasible but action needs to be taken earlier rather than later.

One opportunity to intercept Aphophis using the kinetic energy deflection approach is the 2011 Don Quijote mission organised by the European Space Agency (ESA). The mission will comprise two unmanned spacecraft: Sancho, which could reach the asteroid in 2015 and go into orbit around it to study its composition, and an impactor, Hidalgo, which would leave Earth in 2015 and could be used to crash into the asteroid in 2017.

Whether Don Quijote goes to Aphopsis has yet to be decided; if it does, then ESA might save the world.

Bill Read is features editor of 'Aerospace International' magazine

Alan Bennett criticised the lack of fairness in British society encapsulated by the private school system
peopleBut he does like Stewart Lee
David Moyes and Louis van Gaal
Arts and Entertainment
Sheridan Smith as Cilla Black and Ed Stoppard as her manager Brian Epstein
tvCilla Episode 2 review: Grit under the glamour in part two of biopic series starring Sheridan Smith
Life and Style
Alan Turing, who was convicted of gross indecency in 1952, was granted a royal pardon last year
Have you tried new the Independent Digital Edition apps?
Life and Style
Arts and Entertainment
Tennis player Andy Murray's mum Judy has been paired with Anton du Beke for Strictly Come Dancing. 'I'm absolutely delighted,' she said.
tvJudy Murray 'struggling' to let Anton Du Beke take control on Strictly
Life and Style
Vote with your wallet: the app can help shoppers feel more informed about items on sale
lifeNew app reveals political leanings of food companies
Arts and Entertainment
The cover of Dark Side of the Moon
musicCan 'The Endless River' carry on the tradition? See for yourself
New Zealand fly-half Aaron Cruden pictured in The Zookeeper's Son on a late-night drinking session
Arts and Entertainment
Worldwide ticket sales for The Lion King musical surpassed $6.2bn ($3.8bn) this summer
tvMusical is biggest grossing show or film in history
A new app has been launched that enables people to have a cuddle from a stranger
voicesMaybe the new app will make it more normal to reach out to strangers
Arts and Entertainment
Salmond told a Scottish television chat show in 2001that he would also sit in front of a mirror and say things like,
tvCelebrity Trekkies from Alex Salmond to Barack Obama
Life and Style
food + drink
Rob Merrick's Lobby Journalists were playing Ed Balls' Labour Party MPs. The match is an annual event which takes place ahead of the opening of the party conference
newsRob Merrick insistes 'Ed will be hurting much more than me'
A cabin crew member photographed the devastation after one flight
Life and Style
Carol O'Brien, whose son Rob suffered many years of depression
healthOne mother's story of how London charity Maytree helped her son with his depression
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
iJobs Job Widget
iJobs Student

Year 6 Teacher

£100 - £120 per day: Randstad Education Hull: Randstad Education are currently...

Year 1 Teacher

£90 - £120 per day: Randstad Education Hull: Year 1 Primary Supply Teachers ne...

Early Years Teacher

£90 - £120 per day: Randstad Education Hull: Early Years supply teachers neede...

Primary Teacher Plymouth

£23500 - £40000 per annum: Randstad Education Plymouth: ***KS1 & KS2 Teachers ...

Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

Day In a Page

Secret politics of the weekly shop

The politics of the weekly shop

New app reveals political leanings of food companies
Beam me up, Scottie!

Beam me up, Scottie!

Celebrity Trekkies from Alex Salmond to Barack Obama
Beware Wet Paint: The ICA's latest ambitious exhibition

Beware Wet Paint

The ICA's latest ambitious exhibition
Pink Floyd have produced some of rock's greatest ever album covers

Pink Floyd have produced some of rock's greatest ever album covers

Can 'The Endless River' carry on the tradition?
Sanctuary for the suicidal

Sanctuary for the suicidal

One mother's story of how London charity Maytree helped her son with his depression
A roller-coaster tale from the 'voice of a generation'

Not That Kind of Girl:

A roller-coaster tale from 'voice of a generation' Lena Dunham
London is not bedlam or a cradle of vice. In fact it, as much as anywhere, deserves independence

London is not bedlam or a cradle of vice

In fact it, as much as anywhere, deserves independence
Vivienne Westwood 'didn’t want' relationship with Malcolm McLaren

Vivienne Westwood 'didn’t want' relationship with McLaren

Designer 'felt pressured' into going out with Sex Pistols manager
Jourdan Dunn: Model mother

Model mother

Jordan Dunn became one of the best-paid models in the world
Apple still coolest brand – despite U2 PR disaster

Apple still the coolest brand

Despite PR disaster of free U2 album
Scottish referendum: The Yes vote was the love that dared speak its name, but it was not to be

Despite the result, this is the end of the status quo

Boyd Tonkin on the fall-out from the Scottish referendum
Manolo Blahnik: The high priest of heels talks flats, Englishness, and why he loves Mary Beard

Manolo Blahnik: Flats, Englishness, and Mary Beard

The shoe designer who has been dubbed 'the patron saint of the stiletto'
The Beatles biographer reveals exclusive original manuscripts of some of the best pop songs ever written

Scrambled eggs and LSD

Behind The Beatles' lyrics - thanks to Hunter Davis's original manuscript copies
'Normcore' fashion: Blending in is the new standing out in latest catwalk non-trend

'Normcore': Blending in is the new standing out

Just when fashion was in grave danger of running out of trends, it only went and invented the non-trend. Rebecca Gonsalves investigates
Dance’s new leading ladies fight back: How female vocalists are now writing their own hits

New leading ladies of dance fight back

How female vocalists are now writing their own hits