DART Mission is on its way to stop a killer asteroid
Sooner or later, it was bound to happen. On 30 June 1908, Moscow escaped destruction by three
hours and four thousand kilometers - a margin invisibly small by the standards of the universe.
Again, on 12 February 1947, yet another Russian city had a still narrower escape, when the second
great meteorite of the twentieth century detonated less than four hundred kilometers
from Vladivostok, with an explosion rivaling that of the newly invented uranium bomb.
In those days, there was nothing that men could do to protect themselves against the last random
shots in the cosmic bombardment that had once scarred the face of the Moon. The meteorites of
1908 and 1947 had struck uninhabited wilderness; but by the end of the twenty-first century,
there was no region left on Earth that could be safely used for celestial target practice.
The human race had spread from pole to pole. And so, inevitably.
At 09.46 GMT on the morning of 11 September, in the exceptionally beautiful summer of the year
2077, most of the inhabitants of Europe saw a dazzling fireball appear in the eastern sky.
Within seconds it was brighter than the sun, and as it moved across the heavens - at first in
utter silence - it left behind it a churning column of dust and smoke.
Somewhere above Austria it began to disintegrate, producing a series of concussions so violent that
more than a million people had their hearing permanently damaged. They were the lucky ones.
Moving at fifty kilometers a second, a thousand tons of rock and metal impacted
on the plains of northern Italy, destroying in a few flaming moments
the labor of centuries. The cities of Padua and Verona were wiped from the face of the earth;
and the last glories of Venice sank forever beneath the sea as the waters of the Adriatic
came—thundering landwards after the hammer-blow from space.
Six hundred thousand people died, and the total damage was more than a trillion dollars. But the
loss to art, to history, to science - to the whole human race, for the rest of time - was beyond
all computation. It was as if a great war had been fought and lost in a single morning;
and few could draw much pleasure from the fact that, as the dust of destruction slowly settled,
for months the whole world witnessed the most splendid dawns and sunsets since Krakatoa.
After the initial shock, mankind reacted with a determination and a unity that no earlier
age could have shown. Such a disaster, it was realized, might not occur again for a thousand
years—but it might occur tomorrow. And the next time, the consequences could be even worse.
Very well; there would be no next time. A hundred years earlier a much poorer world,
with far feebler resources, had squandered its wealth attempting to destroy weapons launched,
suicidally, by mankind against itself. The effort had never been successful, but the
skills acquired then had not been forgotten. Now they could be used for a far nobler purpose,
and on an infinitely vaster stage. No meteorite large enough to cause catastrophe would ever
again be allowed to breach the defenses of Earth. So began Project SPACEGUARD. Fifty years later -
and in a way that none of its designers could ever have anticipated - it justified its existence.
How do you say? This thing never happened? Yes, in fact, it is only the realistic prediction
of a future catastrophe of cosmic origin that we owe to the sublime imagination of Arthur Clarke.
But now try to hear this…
It's a cold and serene morning in Chelyabinsk, the populous capital of the province of the same name
in the southern Urals close to the border with Kazakhstan. It's 9:20 a.m. on February 15, 2013,
and the sun has just peeped over the horizon. Slowly the city is emerging from its nocturnal
torpor and the numerous security cameras scattered around the city bear witness
to the lazy start of a normal working day. Only a few notice a tiny light that is lighting
up in the sky, about twenty degrees high and just to the left of the Sun.
Then it is a matter of seconds: the glow becomes more and more intense until it turns
into an impressive fireball brighter than the Sun. The video cameras at the crossroads of the streets
capture the dark shadows of houses, trees, and cars that almost magically emerge from nowhere
in that morning of pale sunshine and accompany the sudden and mysterious flash with their
rapid movement. No less impressive are the images collected by the numerous "dashcams" on board the
cars, tiny cameras that many insurance companies in Russia require to be placed on the dashboard of
the cars to witness the dynamics of any accidents. This circumstance has guaranteed to the
Chelyabinsk events incredible media coverage: there are really numerous
videos of that dazzling light that sets the sky of Western Siberia on fire.
"Hey, guys, just a moment before we continue... BE sure to join the Insane
Curiosity Channel... Click on the bell, you will help us to make products of ever-higher quality!"
After the initial moment of general bewilderment, some comments can be heard in the videos,
sometimes accompanied by some shy laughter. It is still unclear what has happened and a witty
remark helps to dilute the uncertainty. The concrete evidence that it was not
a collective illusion is the presence of a thick and persistent whitish trail in the sky,
a trail that for some stretches seems to double and that testifies that something really happened.
The worst, however, is yet to come. Just as passers-by are beginning to exchange
their first impressions, a powerful shock wave is already rushing towards the ground and about a
minute and a half later the flash hits Chelyabinsk and the surrounding region. It is really
impressive to listen to the roar recorded in the numerous videos that capture the smoke trail.
Even more impressive are the sounds of shattered glass, collapsing windows, alarm sirens, and
the screams of terror that immediately follow the roar. Internal cameras show sturdy warehouse doors
being ripped off like twigs, office workers being thrown from one side of the room to the other by
an invisible hand, groups of panicked people not knowing whether to go outside or stay inside the
building. Those few who have kept their video camera on now point it towards the buildings and
frame the windows shattered by the shock wave and the fragments of glass scattered everywhere.
Unfortunately, the count of the wounded begins, mostly hit by the shards of glass hurled with
force like deadly bullets. Agency flashes initially speak of a few dozen, but soon
the tens become hundreds. The final balance, according to the most reliable evaluations,
will be of more than 1500 people injured, a couple of them quite seriously, so much
so that they will have to be hospitalized in a better equipped hospital in Moscow.
In the following hours, the first estimates of material damage also arrived. Authorities speak
of as much as one square kilometer of glass windows shattered, and damages for a hundred
million euros. Estimates are surely destined to rise, given that the shock wave did not affect
only that populous city. Also in other cities of the region, although to a lesser degree, damage
to numerous buildings is reported. What happened, in short, is a disaster of truly historic scope.
The size of the meteoroid was initially underestimated by Russian scientists,
who for a couple of days have spoken of a mass of a dozen tons. Within a week, however,
NASA has increased the estimate up to assume the fall, far more disturbing, an object of twenty
meters in diameter weighing about 11000 tons! After the disintegration over Chelyabinsk,
the fragments have continued the flight taking the ground in a rather large area,
a hundred kilometers to the west ... Is this fantasy too? No! This - you
will surely remember - is a cosmic accident that really happened! And if instead of 20
meters in diameter they had been twice as large, it would have been another Tunguska,
with the aggravating factor of the explosion over a city and not in the Siberian tundra desert...
All this to say that we are not talking about science fiction.
The impact of a small or large asteroid is a real danger that we must absolutely avoid.
An asteroid passing relatively close to Earth is a more common event than most people think.
Every year, dozens of asteroids large enough to cause regional devastation like
Tunguska to pass within eight million miles of our planet, the distance that NASA says begins
to make an asteroid potentially dangerous. And on average, one or two space rocks large
enough to have a catastrophic impact on an entire continent cross that boundary...
In 1998, the U.S. Congress ordered NASA to detect and characterize at least 90 percent
of potentially hazardous asteroids larger than one kilometer in diameter. Seven years later,
the space agency was tasked with finding 90% of nearby asteroids larger than 150 meters...
Which it has done, but which still leaves large margins of risk due to the impossibility
of keeping track of thousands of ever-changing trajectories due to gravitational interactions.
At some point in its future, Earth will be in danger of an impact large enough to wipe out a
city, or worse. And if humans are still around when that day comes, it will be prudent to have
a plan to protect the planet. Don't you think? That's why NASA has launched just these days a
spacecraft intended to test the possibility of deflecting a killer asteroid through
a strong impact! A mission that started quietly, but is probably to be considered
among the most important of recent years. The Dart spacecraft - an acronym that stands
for Double Asteroid Redirection Test - took off on November 24 from the base of Vanderberg
in California with a Falcon 9 rocket of Space X. In the following hours, the vehicle deployed its
solar panels, heading toward the encounter with the double asteroid Didymos that will take place
between late September and early October 2022. Didymos is an Apollo-class near-Earth asteroid.
Discovered in 1996, it is an average of 246 million kilometers from the Sun,
but given its high orbital eccentricity, it may come close to Earth's orbit.
In 2003, a small satellite was identified around Didymos and given the name Dimorphos.
The two components of the system, 1.18 km apart, are about 750 and 170 m in size. The satellite
orbits the main body in 11 hours and 54 minutes. Astronomers examined several candidate targets,
but opted for the choice of a double asteroid for two reasons. The first concerns
safety ... Changing with an impact the orbit of Dimorphos will not be able to disturb the orbit
of Didymos up to bring it on a path intersecting with the Earth. The second reason is that it
will be easier, taking as absolute reference the main asteroid, to measure the eventual
deviations of the satellite due to the impact. Anyway... After a long pursuit, Dart will arrive
at its destination when the target will be at 11 million kilometers from Earth,
and the probe will be impacted on Dimorphos at the speed of 6 kilometers per second. Everything
will be documented by the onboard camera, which will send images up to just before the crash.
The nice thing is that there will also be a witness ... About ten days before his sacrifice,
in fact, DART will release LiciaCube, a small satellite made by the Italian Space Agency.
Licia will be positioned close to the binary system (but at a safe distance)
and will immortalize all phases of the impact thanks to its two onboard cameras.
From Earth also the eyes of several telescopes will be focused on Dimorphos and Didymos:
to assess the success of the mission, in fact, it will be necessary to observe the motion of
the two asteroids and detect changes in the orbit, For NASA the mission will have been
successful if the orbital period of Dimorphos will be lengthened by at least 73 seconds,
although in reality, we expect a variation of several minutes.
Success, however, would not mean that Earth would automatically be protected from rogue asteroids.
DART, no doubt, represents an important step forward. But the path to a comprehensive
planetary defense plan is a long and winding one, and we have only just begun to travel it.
It will be a long wait for us until next fall... Always hoping that Dimorphos is not inhabited!