IT COULD easily be the plot for a Hollywood disaster movie. Last February, a young dental surgeon called Jaime Nomen was sailing along the Mediterranean coast of Spain, checking images on his laptop from an observatory 600 kilometres away. Suddenly he spotted a speck of light speeding through the constellation Boötes. Nomen knew exactly what it was.
He alerted the in Cambridge, Massachusetts, which collects information about asteroids and comets. Telescopes around the world swung into action, checking the new asteroid’s orbit. The result was sensational: was on near-collision course with the Earth.
On 15 February 2013, the errant rock will skim Earth just 25,000 kilometres above our heads – that’s 500 times nearer than the much-publicised asteroid Apophis came earlier this month, and even closer than Apophis will get on its much-hyped return in 2029. Asteroid 2012 DA14 will fly inside the ring of communications satellites in geosynchronous orbit but sail safely above the orbits of the International Space Station and the Hubble space telescope.
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“I’m not easily surprised by close-Earth approaches any more,” says Don Yeomans, who heads in Pasadena, California. “But this one will be a record close approach by a known object of this size.”
From the fleeting glimpses they have had, astronomers reckon 2012 DA14 is 45 metres across – similar in size to the space projectile that exploded over the uninhabited Tunguska region of Siberia in 1908, ripping up 80 million trees across 2000 square kilometres. While there is no chance that 2012 DA14 will hit Earth (see diagram), this closest of encounters raises important questions. Will we actually be able to spot the next asteroid with our name on it? And what, if anything, can we do about it?
Vital effort
The discovery of 2012 DA14 is all the more amazing because it was , whose observatory in the dark mountains at La Sagra near Granada, Spain, comprises three small telescopes equipped with off-the-shelf cameras. Motivated and skilled teams of amateurs like Nomen’s are vital for asteroid-spotting. The La Sagra team turns up around 15 near-Earth objects (NEOs) each year, a tiny but crucial fraction of the bigger teams’ hauls. “Even the large surveys can’t cover the whole of the sky all the time, and modern amateur-scale equipment rivals the best professional equipment of only 15 to 20 years ago,” explains Steve Larson, who heads the . The world’s most prolific asteroid-hunters, Larson’s team has bagged over 4200 NEOs using two telescopes in Arizona and one at in Australia. “We very much applaud the efforts of Nomen’s group,” he says.
One discovery made by the Catalina survey shows the value of asteroid-hunting. In 2008, it made the very first prediction that a space rock the size of a truck was about to wallop Earth. The asteroid, named 2008 TC3, was expected to hit north Sudan within a day. Astronomers alerted the Pentagon and even the White House. Right on schedule, an airline pilot saw a fireball over Sudan as the asteroid exploded with the force of a kiloton of TNT. And a few months later, scientists recovered a batch of fresh meteorites scattered over the desert – the equivalent of a “sample return mission” for a NEO. “2008 TC3 was the most exciting discovery we’ve made,” says Larson.
However, there is a region of sky that remains poorly watched. The sky over the south pole never rises above the horizon for telescopes in the northern hemisphere, so is off limits even to the (Pan-STARRS), which is twice the size of its predecessors and is based on the summit of Haleakala mountain in Maui, Hawaii. The Siding Spring telescope near Coonabarabran is the only instrument that could spot a dangerous asteroid approaching from this most southerly patch of sky – but the Catalina project cut its funding in mid-2012. When the solitary astronomer still on duty there, Rob McNaught, visited the UK last September, the Siding Spring Survey shut down for a month, leaving a totally blind spot in our monitoring capabilities.
That hole will be plugged in a few years’ time by the (LSST) on Cerro Pachón mountain in Chile. At 8.3 metres in diameter, its mirror is one the biggest in the world, and it will pick up asteroids far smaller than Pan-STARRS can see. Uniquely among such large telescopes, the LSST will scan the sky to pick out the faintest objects, from the solar system to the edge of the universe.
“LSST will decrease the risk of unexpected collision with Earth by a factor of 10 to 100 compared to existing surveys,” anticipates its director, Tony Tyson. His team has already cast the giant glass mirror and blasted off the top of the mountain peak to create a level base. The telescope is expected to see “first light” in 2019, and will then begin a survey of NEOs lasting 10 years. “Once LSST comes online, it will be the big dog and dominate the ground-based NEO survey discoveries,” says Yeomans.
That’s all well and good, but taking the hunt for asteroids into space would be even better. Telescopes on Earth can only look for asteroids at night, limiting their surveys to the region of space away from the sun. This leaves us blind to any dangerous space rocks that approach us from inside Earth’s orbit. What’s more, small asteroids that are too faint to see at visible wavelengths glow brightly in the infrared against the cold, dark background of space – but Earth’s atmosphere blocks many infrared wavelengths. That’s why a private consortium is planning to build and launch an asteroid-hunting .
Small but dangerous
Sentinel will be modelled on the Spitzer telescope – Hubble’s infrared brother – and on the Kepler telescope that’s currently seeking out planets around other stars. If money can be raised to fund it, Sentinel will launch around 2018 and will orbit the sun near Venus. “It will be much more effective at finding the smaller, yet still dangerous, asteroids,” says ex-astronaut Ed Lu, a veteran of missions on the space shuttle and the International Space Station. He set up the B612 Foundation with Apollo 9 astronaut Rusty Schweickart and Piet Hut of the Institute of Advanced Study in Princeton, New Jersey, who first suggested that cosmic impacts cause mass extinctions of life on Earth. They are aiming to raise Sentinel’s $400 million cost – considerably less than NASA’s Kepler mission – through private donations.
The foundation believes it can keep the price tag down for several reasons. Not only are infrared systems and computers becoming cheaper, but Sentinel will be launched on a private rocket built by the company SpaceX.
If B612 can secure funding – and it’s a big if – Sentinel will be the best way to discover NEOs and will provide much better estimates of the sizes of the objects it finds. And when it comes to asteroids, size is everything. The asteroid that wiped out the dinosaurs was about 10 kilometres across; anything bigger than 1 kilometre could cause a global catastrophe.
Fortunately, there is good news on that front, thanks to the sterling efforts of the NEO-hunters so far. “We’ve discovered about 94 per cent of the largest near-Earth asteroids,” says Yeomans, “and none of these represent a credible threat for the next 100 years.”
So the focus is on objects that could devastate a whole region were they to hit. These potentially hazardous asteroids (PHAs) are bigger than 140 metres across. Larson says that only 1350 PHAs have been discovered out of an estimated total of 30,000. The LSST survey in Chile will increase that measly discovery rate to 75 per cent.
As for smaller, Tunguska-sized objects, we know the orbits of only about one in 100 of them. A Sentinel map, if we get one, would contain more than half of them and will warn us years – if not decades – in advance of an impending cosmic strike. How then do we protect ourselves?
Well, that all depends on how long we have. “The longer the time, the more gentle the nudge that’s needed to mitigate an Earth impact,” says Larson.
The best approach, says Lu, is a concerted campaign of deflection, with one major wallop followed by a smaller nudge to fine-tune the asteroid’s path. There is a precedent for such a “kinetic impactor”. In 2005, NASA’s Deep Impact mission whacked comet Tempel 1 with a lump of copper, although its goal was simply to find out what the comet is made of.
“One major wallop, followed by a smaller nudge to fine-tune the asteroid’s path, will mitigate an impact”
The European Space Agency is planning a similar mission to Didymos, the larger of a pair of nearby asteroids. Due for launch around 2020, the will carry an impactor to smack into the 800-metre-wide asteroid, and a second spacecraft to observe the results.
“The impact should produce a change in the orbital period that can be noticed, both from ground-based and space observations,” says AIDA’s planner Andrés Gálvez. “This will give us assurance in case we need to use a kinetic impactor at relatively short notice – though I hope we do not.”
For a secondary deflection, Lu recommends a gravity tractor – which he says can be built with existing technology. Here, a spacecraft comes so close to an asteroid that they feel each other’s gravity. Rockets on the spacecraft propel it gently away from the space rock; the mutual gravitational bond pulls the asteroid along, like a dog on a lead, out of harm’s way. It should work regardless of how fast the asteroid is spinning or what it is made of.
Even more imaginative ideas have been bandied around, such as fitting a rocket on an asteroid; using a “mass-driver” to fling matter out of the asteroid and so propel it the other way; focusing sunlight on the asteroid’s surface to vaporise its rocks and again force the asteroid to move; or even to “paintball” the surface white, so the pressure of sunlight will gradually force the asteroid away from its threatening orbit. “These are all in the realm of science fiction for now,” concludes Lu.
If we happen to be faced with a Tunguska-style airburst rather than a global disaster, deflection might not even be necessary. “A 40-metre object would need to pass over populated areas before it would cause major concern,” says Yeomans. “Policymakers would have to decide whether to deflect it (if there’s time), to take the hit (it would more than likely hit harmlessly in an ocean or an unpopulated area), or whether to evacuate the threatened area.” Coping with an asteroid impact would then move into the much more familiar territory of disaster mitigation – akin to dealing with predicted hurricanes, earthquakes or volcanic eruptions.
Might we still be taken unawares by the Big One, perhaps a comet zipping in unannounced from the outer parts of the solar system? A subcommittee of the United Nations is working on an action plan for an international response. Ironically, its next meeting will take place when asteroid 2012 DA14 is whizzing over our heads.
Meanwhile, NASA has contingency plans for a global threat, a version of the Bruce Willis solution: to nuke an asteroid with our name on it. “For such a last-minute mission, without warning times of 10 to 20 years, a disruption using nuclear explosive devices is the only technically and economically viable option,” says of Iowa State University in Ames. On NASA’s behalf, his is designing a nuclear missile that will blow a dangerous asteroid or comet apart.
There is always a worry that the shrapnel from the explosion could cause just as much damage as the original object. But Wie says the blast will pulverise and disperse the asteroid: “If we have a warning time of at least a few months, the size of the debris cloud will be much larger than the Earth,” he says. His calculations show that less than 0.1 per cent of the object will end up hitting our planet.
To blow the asteroid apart, the nuclear device has to explode inside it, not on the surface. So Wie’s spacecraft comes in two parts: a front section that blasts out a crater, and a nuclear section that explodes deep within the crater. He is planning a test mission – which he is calling Deep Impact 2 – to smash a spacecraft, minus nuclear explosive, into a small asteroid.
The forbids countries from deploying nuclear weapons in space. But Wie doesn’t foresee any real objections if his system is ever needed in earnest. “If we have a real impact threat with short warning time,” he predicts, “I don’t think there will be a legal problem!”
