46 | New Scientist | 25 January 2020
asteroids are common, which seems likely,
we need to study and test the effects of a
kinetic impactor more carefully.
NASA is on the job with the Double Asteroid
Redirect Test (DART) probe. DART is due to
launch next year to the asteroid Didymos,
where it will deliberately crash into the
asteroid’s 150-metre moonlet, nicknamed
Didymoon. That is expected to change
Didymoon’s orbit enough for the effects
to be visible from Earth. Once we know how
crashing into an asteroid (or, in this case, an
asteroid moon) affects its motion, we will
be much better equipped to build a kinetic
impactor – and guarantee it works.Chodas has good news and bad news.
The good news is that the kinetic impactor
missions have hit 2019 PDC, and the bulk
of the asteroid is no longer on course to hit
Earth. The bad news is that a fragment about
60 metres across remains on its original
trajectory. That isn’t all: contact has been
lost with the Recon 1 spacecraft, probably
owing to collision with debris. The resulting
lack of information is compounded by the
asteroid now being behind the sun, making
it impossible to observe from Earth. Our
options are limited. It is now 3 September
2024, and as the collision time approaches,
the momentum needed to disrupt the
fragment’s trajectory sufficiently to avoidEarth rises. But given the asteroid’s small
size, any disruption is likely to break it apart,
causing a repeat of today’s scenario. A radical
proposal is raised for a deliberately robust
collision, shattering the rock into such small
pieces that no damage to Earth’s surface
will result. That means a nuclear device is
needed. The legality of such a launch sparks
heated debates. Meanwhile, time ticks on.Ultimately, a disastrous asteroid strike of
this sort remains very unlikely. But we should
still be prepared. That means working on more
mission concepts (see “They just might work”,
above), building more telescopes to look for
asteroids and maybe moving them into orbit
so that they can operate 24/7. For Chodas, that
also means running more “what if ” scenarios,
testing the limits of our contingency planning.
“In each one of these exercises, we go a little
deeper into interesting details and we are
forced to think about issues that we haven’t
thought about before,” he says.
This most recent scenario, for instance,
brought home to him the scale of the
disaster response required. “Evacuating a
large metropolitan area, of course, would be a
daunting task,” he says. “What was eye-opening
for me was how long that would take.” As for
how life resumes on the day after the sky falls
in, that is beyond his remit. “That’s something
that FEMA [the US Federal EmergencyManagement Agency] would address after
the fact, like they do for other disasters.”
But thanks to planetary defence research,
the chances of such a clean-up ever being
necessary are pretty slim. “If we try hard
enough,” says Mainzer, “it’s something
that we can cross off our list of worries.”
An asteroid probably won’t kill us all.
But it would be good to know for sure.A last-ditch nuclear strike on the asteroid
remnant has been cancelled for lack of
time. The collision has been inevitable for
weeks. Last night, the Arecibo Observatory
in Puerto Rico confirmed the space rock
would explode above Central Park, New
York, in 10 days’ time, after approaching
Manhattan at an angle of 29 degrees south
of due east. By a quirk of fate, that matches
the orientation of many of the island’s
streets, giving any life forms in the city an
uninterrupted view of the incoming fireball.
The 9/11 attacks damaged an area of
around 16 acres; 2019 PDC is expected
to render 20,480 acres uninhabitable.
The evacuations begin immediately. ❚Leah Crane is a reporter
for New Scientist based
in Chicago. She tweets
@ downhereonearthTwo methods are considered the most
credible ways of helping us divert
asteroids on a collision course with Earth
(see main story), but other, wackier,
ideas are also being taken seriously.
The simplest would be to paint one side
of an asteroid white or silver. The painted
part would then reflect more sunlight
and the energy imparted by the extra
light bouncing off that surface could
change the asteroid’s trajectory.
Alternatively, we could attach
engines to an asteroid and turn it into
a spacecraft, or use high-powered
lasers that could vaporise rock. While
demolishing an entire asteroid with a
laser is unlikely to be possible, the puff of
dust jetting off the surface could act like a
thruster, allowing us to push it off course.
Such ideas could work, but are untested
and would probably take decades or
require technology we don’t yet have,
so they aren’t part of any official plan.THEY JUST
MIGHT WORK With the right
preparation,
apocalypse
can be avertedALAN
POWDRILL/GET
TY
IMAG
ES