It's a scientific fact
that the planet Earth will be hit by cataclysmic
asteroids in the future. Assuming we can see them coming,
what can we do to stop them? [MUSIC PLAYING] Space is swarming with lots
of really fast moving rocks, like the planet Earth, but also
like that 19-meter-wide wide chunk, that blazed across the
sky above the Russian town Chelyabinsk, in 2013,
exploding in the air and across Russian dash
cams, with the power of up to half a megaton of TNT. (RUSSIAN ACCENT) In post-Soviet
Russia, space explore you. Now, Russia does seem
to get hit a lot. The Tunguska event of
1908 was even bigger, when a 100-meter
space rock exploded to flatten 2,000 square
kilometers of forest in Siberia. Now, there were no recorded
fatalities in either case. Tunguskia was very isolated. And the Chelyabinsk asteroid
came in at a shallow angle, so it had lots of
atmosphere to burn up in. Had it been a direct hit, then a
city of over one million people would have been devastated. Now that's pretty lucky. But so far, we've
all been lucky. Impacts have tended to
happen in remote regions. But now that more
and more of the world is covered in urban areas, the
chance of a catastrophic impact is increasing rapidly. It's really not a matter
of if, just of when. So when can we expect
the next killer asteroid? And can we stop it? That depends on how
bad the situation is. Let's run through the
levels of catastrophe. OK. A rock less than 10
meters in diameter vaporizes harmlessly
in the atmosphere. This stuff isn't a problem. At least 40,000 tons of it rains
down on the Earth every year, mostly in the form of
pebbles and smaller. These are the shooting stars
that you see on a dark night. Meteors 20-100 meters in
size have the kinetic energy equivalent of a
thermonuclear explosion. And this is a city
killer on a direct hit. We expect something like this
once every century or so. Now, we just had one. But that does not mean we
won't get one tomorrow. For a rock around 500
meters in diameter, the strike will have
the energy equivalent of all currently operational
nuclear weapons in the world. This devastates a country
or makes a tsunami. Expect one of these at least
every 50,000 years or so. Of course, it gets
worse as you get bigger. At two to three
kilometers, the sky goes dark from the ejector,
and nuclear winter effects global climates. These happen every
couple of million years. Much larger than
this and the planet is showered in molten rock. Nuclear winter lasts decades. Oceans are acidified. And most life on Earth dies. An asteroid of this magnitude
probably killed the dinosaurs 65 million years ago,
hitting the Yucatan Peninsula with the power of a billion
megaton hydrogen bombs. Earth gets smacked this hard
every 100 million years or so. Now the chance of any one of
these killers on a given day is tiny. But small probabilities
have a way of adding up to a
certainty, over time. That means a big
one will hit again. And we can only stop it
if we know it's coming. There's been some good work. Astronomers around the
world have worked together as part of the
Spaceguard Program to find and track most of the
biggest, one kilometer plus, comets or asteroids that
cross Earth's orbit. Those are called Near
Earth Objects, or NEOs. Good news-- none are
coming close for centuries. There are a couple of
500 meter bad boys that have a very small chance of
hitting in the late 2100s, and the 300 meter
Apophis, who will buzz us inside the orbit of the
geosynchronous satellites in 2029 and 2036, but will
almost certainly not hit. So we've got some time. But what about the NEOs the size
of the Chelyabinsk or Tunguskia rocks, Potential city killers. We have no idea where
most of these are. These things are
very faint specks in the deep dark of space. And current monitoring programs
can only find a fraction. This is probably something
we want to deal with. There are efforts. The nonprofit B612
organization is fund raising to launch the
Sentinel infrared telescope, that will orbit the
sun and look outwards, tracking hundreds of
thousands of NEOs. They need $450 million. But that's less
than the box office take of the movie Armageddon. So you know, we either
pay to save the world, or pay to watch Bruce
Willis pretend to. And speaking of
Armageddon, what do we do if we spot an
incoming city killer, or for that matter, a planet
killer that we somehow missed? Is there even
anything we can do? Absolutely. But the approach is going to
depend on how fast we can act. Caught early, we have options. See, the Earth is
a very small target on the scale of
the solar system. And Earth itself is
moving pretty fast, traveling its own diameter
once every seven minutes. Let's say we catch this
killer rock at 10 years out. We need to slow it
down or speed it up so that it is behind
or in front of the Earth. That means making it arrive just
seven minutes later or seven minutes earlier. So divide seven
minutes by 10 years. We need to change its speed by
roughly one part in a million, and we save the world,
and get to have a parade. We can also nudge it by a
similar amount to the side. The further out we catch it,
the less we need to nudge it. There are a few different
ways to do this. Number one-- brute force. Just slam a heavy spaceship into
the NEO to knock it off course. This is kinetic impact. A one ton impact gives
the necessary one part to a million momentum change
needed to divert city killers. Now unfortunately,
this doesn't work for planet killers, which
are at least a million times more massive. Number two, nuke it, but miss. Yup, explode a nuke right next
to the rock and vaporize part of the surface. The pressure of the nuke, and
of the ejected asteroid bits, will push the NEO off target. A regular nuke would be
fine for smaller asteroids. But for a planet killer, you're
going to need a few 50 megaton Tsar bombs. Thanks again, Cold War. Number three, graffiti. Seriously, arm a spacecraft
with a cosmic-sized can of spray paint, and color one
side of the asteroid white. The sun's light will push harder
on the more reflective side, slowly pushing it just far
enough off course to miss us. A similar proposal
fixes a giant light sale to the side of the rock. Now for this option you're
going to have to catch it early. Number four, the weirdest
deflection option-- a gravitational tractor. Fly a 20 ton spacecraft
alongside the object for 10 years, and their mutual
gravity will pull the impactor off course. Options are great. In fact, I don't want to
attempt more than one, because once the
first one fails, it may be too late
to start again. The real trick is
getting politicians to agree to something that
involves scientific uncertainty and long term thinking. Hm, maybe we should do a
Kickstarter to save the world. OK, let's address the
worst case scenario. What if we catch this
thing at the last minute, or fail to act
for other reasons? The asteroid or comet is
heading straight for us. And we have a month
or two, at most. At this point, we can't
deflect a large impactor. We have to blow it up. Now people often say that
you shouldn't explode NEOs. You'll just get lots of
hard to track fragments. But at this point, tracking
isn't even that helpful. And lots of small bits are
much better than one big bit. My favorite idea so far is
the Hypervelocity Asteroid Intercept Vehicle. The idea is that you launch
a thermonuclear device at the rock, but you lead
with a very high speed kinetic impactor, that creates a
nice, deep crater for the nuke to explode in. This uses the nuke's energy
much more efficiently, sending shockwaves through the
asteroid, that will break it into much smaller pieces. That is, if you believe the
supercomputer simulations of HAIV team, a
one megaton H-bomb should break up a 500
meter asteroid nicely, although it depends on
the structure of the rock. A loose, gravitationally-bound
rubble pile is obliterated, while a single
rock will be fragmented. For a giant asteroid, you're
going to need a gigaton blast. And such devices don't exist. Should we build
one just for this? I don't know. But without question,
a better option would be to build the
infrastructure needed to detect and deflect all
dangerous objects much, much earlier. To me, this is amazing. We are a species
capable of defending our world from a
planet-killing meteor strike. Or we could be, soon. Science has given us
such incredible power-- among other things, to serve as
custodians of the planet Earth. But what does it take? Just a little support
from enough of us. Fund Sentinel. Petition our leaders. Study hard and do some mad
astronomy or rocket science. Check some links
in the description. And assuming no giant
asteroids hit in the meantime, I'll see you on the next
episode of "Space Time." In a recent episode we
talked about the origin of life and the Fermi paradox. And you guys had some
extremely interesting points. William George, and
a number of others, note that any civilization
advanced enough to colonize the galaxy would
also be advanced enough to choose not to do so. Now this may well
eliminate a number of potential galactic empires. But all of them,
with 100% efficiency? Great filter items based
on the presumed psychology or sociology of advanced species
aren't really compelling, because only one
such species needs to make a different choice
to not stay at home, and we have galaxy-wide
colonization. It may be that
advanced civilizations' psychos sociological
evolution converges on an extremely narrow range
of outlooks and motivations. But even in that case, there
are sure to be exceptions. 794651519, and a
number of others, point out that maybe
our definition of life is too restrictive. Does life have to be chemical? Does it have to be cellular? Well actually,
there's good reason to think that extraterrestrial
life might be chemical. From everything we've seen in
this universe, the arrangement of atoms into molecules
and molecular structures, via chemical bonds, seems
to be the process most able to support
extreme diversity and complexity of form. But even if life can
arise in other ways, that just increases
the number of lifeforms that we should be able to see. And so it makes the Fermi
paradox even more paradoxical. Sam Shields asks
whether Panspermia is suggesting that
life only arose on one planet in the Milky Way
before being spread everywhere. Well first let me note
that Panspermia is far from being an accepted theory. It's a cool one. And it might be true, which
is why we mentioned it. And yes, that's the
attraction of it. Life would only
have to arise once in the galaxy, which allows the
initial event of abiogenesis to be very unlikely, and
yet have life arise quickly on another planet. The big challenge is
getting life-infested rocks to spread through the galaxy. Stars are very far apart. There are ideas on
how this might happen. But it's not obvious
that it's possible. Now DivShadow, and
a number of others, told me that the Reapers wiped
out all advanced civilizations. Well, I choose the ending
where Shepard saves the galaxy.
Hey All, I just wanted to let you all know that I have stepped down as the lead designer/animator in order to pursue other opportunities. This was my final episode working on Space Time so I hope you all enjoy it!
I had a great time working on the show with Matt, Gabe and all the others who worked together to create an excellent program and I can honestly say that, I am truly proud and honored to have worked on it.
The praise and compliments from you all was easily my favorite part of working on the show, and I hope you all continue to support and love the show! I have passed the mantle onto a colleague of mine, and I assure you all, it is in good hands! (Although the amount of ponies MIGHT decrease hahaha
Cheers you all! May you all live long and prosper!