The search for deadly asteroids that could slam into Earth
must be speeded up 100-fold to help protect the future of life on Earth,
according to an influential group of scientists, astronauts and rock stars.
The call for action comes as experts around the world take
part in Asteroid Day, an event on Tuesday marked by a series of talks and
debates aimed at raising awareness of the existential threat posed by hurtling
rocks from the heavens.
Lord Rees, the astronomer royal, and Brian May, from the
rock group Queen, added their names to the 100X declaration, which calls for a
rapid acceleration in human efforts to find and track potentially dangerous
asteroids. Other signatories including Peter Gabriel, Richard Dawkins, Brian
Cox and Eileen Collins, the first female commander of Nasa’s space shuttle.
“The aim is to ramp up public awareness and the awareness of
governments to the fact that we are under threat from a meteor strike,” May
told the Guardian. “It’s been made light of, and we’ve seen some great films,
like Bruce Willis saving the day, but it is a very serious threat.”
Asteroid Day falls on the anniversary of an asteroid strike
in 1908 that saw a 40 metre-wide lump of space rock enter the atmosphere over
Tunguska in Siberia at about 33,500 miles per hour. The rock exploded mid-air
and released the energy of a large hydrogen bomb, which flattened 2000 sq km of
conifer forest.
Were an asteroid of the same size to slam into the
atmosphere over London, the blast could destroy much of the capital within the
M25. People in cities as far away as Oxford could be burned by the intense heat
released in the explosion. In Scotland, the same blast would still have the
force to blow peoples’ hats off.
From observations with ground-based telescopes, researchers
know that of the million or so asteroids that could one day strike Earth, only
about 10,000 are known and tracked. That means we are in the dark about 99% of
the asteroids that have the potential to crash into the planet.
“They are clearly a threat and for the first time it is
possible for us to do something to reduce that threat,” Lord Rees told the
Guardian.
“It is now feasible to do a survey of all the potentially
Earth-crossing asteroids above 50m in diameter, and objects like that impact
Earth about once per century. One could then check their orbits to see if any
are on a collision course with Earth and within 20-30 years have technology to
divert any that are on course,” he added.
Huge asteroids several kilometres across are expected to hit
Earth every ten million years or so. These can cause destruction on a global
scale. A ten kilometre-wide space rock that crashed into what is now Mexico
triggered a global catastrophe 68 million years ago which brought the reign of
the dinosaurs to an end.
Since most of the Earth’s surface is covered by water,
asteroids are more likely to arrive over the oceans. But these can be the worst
impact sites for asteroids of about 300 metres wide. If one landed in the
mid-Atlantic, it would produce a tsunami wave that could devastate cities on
the east coast of the US, and along the coast of Europe.
“We know the rough numbers, we just don’t know when a
particular asteroid is going to hit. If we are going to take precautions, we
need to know the orbits of all of these bodies,” Rees said.
“The first thing is to do the survey to find out if there
are any asteroids which seem to be on course with a high probability of hitting
within the next 50 years. If we knew there was one on course to hit the Earth
in next 50 years, that would focus minds on the technology.”
One mission, proposed by Nasa, aims to catalogue two thirds
of the asteroids and other “near earth objects” that are larger than 140m and
come close to Earth’s orbit. The NEOCam mission would use an infra-red camera
to garner information on asteroid size, shape, rotation and composition. A
private mission called Sentinel, which would put an another infra-red telescope
in space, is being led by Ed Lu, a former space shuttle astronaut.
Scientists are actively looking at ways to protect Earth
from any asteroids that do turn out to be on a collision course. One strategy
is to crash a massive spacecraft into the asteroid and change its trajectory.
Another option is a “gravity tractor”. In this scenario, a spacecraft flies
alongside an inbound asteroid for long enough that its minuscule gravitational
tug diverts the asteroid enough to pass Earth safely. Both could run into
problems in a real situation, though: if the nudge does not work as expected,
the asteroid may miss one city only to hit another.
The option to lob nuclear warheads at an incoming asteroid
is appealing to Hollywood, but less so to many scientists, including May, who
has a PhD in astrophysics.
“Blowing it up is probably not the greatest option, because
you have a lot of fragments to deal with then, and it becomes rather random,
but deflecting it one way or another seems to be an option,” he said.
“It’s absolutely possible there’s something out there of the
magnitude that would wipe out a major city of the world, and that’s a very big
thing: you’re talking about a human disaster on a vast scale.
“This is about saving us all. All the people on the planet,
all the creatures on the planet, everything which we have built up and might be
proud of. It’s a kind of insurance if you like,” he said.
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