Tonight (Wednesday July 12, 2017 at 9/8 Central), the CBS television network premiers the first episode of a new series called Salvation. Its a drama - part science fiction and part political thriller - about an asteroid discovered on a collision course with Earth. In the show, we have just six months before impact.
I am very pleased to let yall know that I am the science consultant for the show! Its my first big-time consultation (Ive done quite a few before, but usually for one-offs, pilots that never get made, and oh, yeah, a big Hollywood movie where I literally changed one word in the script).
Ive seen the first episode (you can watch the first 15 minutes here) and I have to say, its pretty good. Lots of intrigue and, while I wont spoil anything, I will say that there are plenty of twists and turns to the plot as story unfolds. Its been a lot of fun to come up with real (or near-real) solutions to some of the plot points the characters find themselves in. In some cases, I did as best I could to be as realistic and scientifically accurate as possible, but thats not always the way it works out. As any science consultant will tell you, the story must come first! If the science needs to be bent a little bit to make that happen, well, you cant be too stiff, or else youll break.
Im OK with that, because without a story youve got nothing. Let science add what it can where it can, and dont sweat it too much if you have to lean more on the fiction side of science fiction.
[Credit: CBS]
With that in mind, and in honor of the Salvation premier, I thought it would be fun to make a short list of ten facts, trivia, and misconceptions people have about asteroids and asteroid impacts. Some of these will tie directly into the show, so read this and keep it in mind when you watch the premier tonight (at 9/8 Central, remember, and check your local listings). How did we do? Leave comments below! And for more info about the show, follow SalvationCBS on Twitter.
So:
1) Mostly, asteroids spend their time in the Main Belt. Mostly.
Asteroids are chunks of rock, metal, or a mixture of both. Theres no real lower limit to their size its weird to call something the size of a basketball an asteroid, but there you go and the biggest (Ceres and Vesta) are so large theyre called protoplanets.
The vast majority orbit the Sun between the orbits of Mars and Jupiter, far from Earth. But not all of them do. Some share Jupiters orbit, for example, and are called Trojan asteroids. Others have looping elliptical orbits, usually yanked into those paths by Jupiters mighty gravity.
[The main belt asteroid Vesta as seen by the Dawn spacecraft. Credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA]
Others pass close to the Earth. We call those near-Earth asteroids, or NEAs, because sometimes astronomers lack imagination when it comes to etymological coinagement. They come in lots of different groups, generally classified by the semi-major axis of their orbit (the long diameter of an ellipse divided by two, analogous to a circles radius).
If the semi-major axis of an asteroids orbit is greater than Earths distance from the Sun, we call it an Apollo asteroid (named after the asteroid 1862 Apollo, the first of its kind to be found). If the semi-major axis is less than Earths distance to the Sun, its an Aten asteroid. There are also Amors (which have orbits that keep them at least just outside Earths orbit), Atiras (also called Apohele asteroids), which stay well inside Earths orbit, and some others. There may even be asteroids that stay inside Mercurys orbit, called Vulcanoids, but they are currently theoretical; none has been seen.
Which brings us to
2) An asteroid on an impact course may not come from deep space. It may be a neighbor thats getting too friendly.
In 2004, an asteroid was discovered, later named Apophis. It was found to be an NEA, on an orbit just about 0.9 Earth years long. Its an Aten with an orbit that crosses ours, and it was soon discovered that in the year 2029 it will pass so close to Earth it will be under our geosynchronous satellites! Itll pass no less than 31,000 kilometers over our surface. A close call, but a clean miss.
But theres more. During that encounter, Earths gravity will bend the orbit of Apophis. For a while it wasnt clear how much. But it was quickly found that if it passed at exactly the right distance (going through a region of space astronomers call a keyhole), its orbit would change just enough that seven years later, in 2036, it would impact the Earth!
That caused a lot of concern, obviously. However, more recent observations show conclusively that it will miss the keyhole, and will therefore miss the Earth in 2036 by a substantial margin. Phew! But it was a wake-up call that not all asteroid threats come from far away, and that the keyhole is an important concept in asteroid science.
In Salvation, the asteroid comes from deep space. Thats not impossible, but there are other ones we need to keep our eyes on. But then, how do we find them? Well
3) Asteroids arent usually discovered by people. Theyre found in automated surveys.
It used to be that astronomers found asteroids literally by drawing maps by hand, then noting which stars moved (the name asteroid, after all, means star-like). The first, Ceres, was discovered that way!
Then we invented photography, and asteroids betrayed their existence by their motion around the Sun, leaving little streaks in the images.
Now, though, we have electronic detectors and telescopes that can see wide swaths of the sky. This means we can survey huge chunks of celestial real estate, looking for things that move and that can be done using software that is much faster than humans.
The vast majority of asteroids are now found this way. The Wide-field Infrared Survey Explorer, or WISE, was a space telescope designed in part to look for asteroids, catching their warm glow in infrared. It found quite a few before the mission ended; it was so successful it was revived and renamed to NEOWISE, for Near-Earth Object WISE.
[WISE image of the asteroid Santa Claus. Yes, seriously. Credit: NASA/JPL-Caltech/UCLA]
New observatories are coming online now and in the near future that will find tremendous numbers of asteroids, too.
But how many are there? Well
4) There are billions of asteroids. But the asteroid belt is actually pretty empty.
The main asteroid belt has over a million asteroids bigger than 1 km across, and there are likely more than a billion 100 meters across. Despite that, the main belt is mostly empty space! The total volume of asteroids is less than the Earths Moon, and theres a huge amount of space out there, more than a quintillion square kilometers (and vastly more if you include the volume, not the area, of space available).
Its also not clear how many NEAs there are. Well over 16,000 are known, and there are probably about 1000 a kilometer or more in size (statistics indicate weve found 90% of those already). There are probably a million NEAs bigger than about 40 meters in size out there. Weve only discovered about 1% of them.
That sounds scary, but were looking for them! Thats the first step in preventing them hitting us, after all.
Speaking of which
5) An asteroid doesnt have to physically hit the ground to be a big problem.
Sure, youve seen movies where some gigantic asteroids slams into the Earth, creating devastation and all kinds of horribleness. But really big asteroids are very rare (the one in Salvation is big enough that very few like it exist). The smaller they are, the more common they are.
Really small ones just burn up in Earths atmosphere. Were hit by about 100 tons of material every day, most smaller than a grain of sand! When that happens, we see a shooting star, or more technically a meteor.
If an asteroid is mostly metal, than it can get through the atmosphere and hit the ground hard enough to do real damage if its bigger than roughly 20 meters in size or so. The one that carved out Meteor Crater in Arizona was probably 30-50 meters across.
If its rock, then its more fragile, and wont hit the ground; itll disintegrate high up in the atmosphere. But thats still a problem! Salvation opens (no spoilers) discussing the asteroid that blew up in the air over the Russian city of Chelyabinsk in 2013. That was a real event. The asteroid was rocky, and about 19 meters in diameter. Its power was tied to its kinetic energy, the energy of motion. That depends on the asteroids mass and its velocity (actually the velocity squared), and it was moving fast, about 20 kilometers per second. All that energy was released as the asteroid was stopped by Earths air, and the result was an explosion equivalent to 500,000 tons of TNT. Thats the same as a small atomic bomb.
Thats why astronomers are so intent on finding these things and preventing them from hitting us. But how do we do that?
6) Blowing up an asteroid is NOT the best way to prevent an impact. It may even be the worst.
In the movies, they usually try to blow up the asteroid, creating a cloud of zillions of little rocks that burn up harmlessly in the atmosphere.
But thats a terrible idea. First of all, that doesnt help. As I said, the kinetic energy of an asteroid (and thus its impact energy) depends on its mass and velocity. If you blow it up and all the pieces still hit, you havent changed the impact energy at all! Youve just spread it around. For a really big asteroid that doesnt help, and in fact could make things worse, creating damage over a larger area.
So, you might think blowing it up is a better idea if the asteroid is still far away, letting it disperse. But, nope. Explosions are hard to get right, and you might create several somewhat smaller pieces still on a collision course. Now, you dont have one problem, you have many. And if you use a nuke, now you have many radioactive problems.
A better idea is to try to nudge it into a path that misses the Earth. There are lots of ways of doing this. Perhaps the best is whats called a gravity tractor, a small spacecraft that uses its tiny gravity to slowly tug an asteroid into a new orbit (you can find more technical detail here). But that takes a long time. If the clock is running out, you can simply slam a spacecraft into the asteroid, whats called a kinetic impact, to try to change its velocity enough to miss, us as well (without breaking it up!). Most likely youd need both a kinetic impactor and a gravity tug to make sure the asteroid misses.
There are lots of other techniques being discussed now. The problem is, none has been tested very well. Thats something Id actually like to see NASA do; fund a series of missions to try different methods on asteroids to see what works best, and what we need to do to iron the kinks out.
By the way, the B612 Foundation is a group of astronomers, engineers, and astronauts dedicated to characterizing the asteroid threat and doing something about it. Many other groups exist as well. Like I said, we take this threat seriously.
One thing well need to know in advance is what the asteroid is made of. They can be full of surprises! For example
7) Some asteroids are not much more than piles of rubble.
You probably think of asteroids as being monolithic, literally one big chunk of stuff. But weve learned thats not always the case.
A rocky asteroid orbiting the Sun isnt alone; there are lots of other asteroids out there. Over billions of years, a typical asteroid will suffer many impacts from those other rocks. If the collision is high speed, and the intruder big enough, they can both shatter. But a small rock moving relatively slowly will hit the bigger one hard, but not hard enough to disrupt it. Instead, the impact can create cracks in the big one that can run very deep. After lots of such encounters, the asteroid can be so riddled with fissures its really nothing more than a pile of rubble held together by its own gravity (and other weak forces).
Weve actually found several asteroids like this. Its possible this structure would affect how we try to deflect it, and what happens should one hit Earth, so astronomers are very intently studying these weird objects.
Speaking of weird
8) Most asteroids arent round. Some are shaped like bowling pins!
In movies, asteroids are usually depicted as round. Lots of them are! Especially if theyre big; their gravity can be strong enough to shape them into a sphere. Think of it this way: Imagine a mountain on Earth. If it gets too big the rock inside it isnt strong enough to support it against gravity, so it collapses. It smooths out. Now imagine a million mountains all over the Earth like that: They all collapse, flattening out. The overall shape that would form is a sphere.
But most asteroids are way too small for their gravity to be strong enough to do that. So they come in all kinds of shapes. Many weve seen up close are elongated, like potatoes. Some are even shaped like bowling pins, or like cartoon dog bones! Those may be formed when two small asteroids impact at slow enough speed that they stick together. Its also possible that over time, various forces can spin an asteroid up, making it rotate faster and faster, until it breaks apart. Then the pieces can reform, creating a dumbbell shape. We see that in many of the comets weve visited with spacecraft; comets and asteroids are very similar.
There are other things that can result from this breakup, too. For example
9) Many asteroids have moons.
Some asteroids have come close enough to Earth recently that astronomers have pinged them with radar. Using sophisticated techniques they can learn a lot about them that way, including their size, how fast they spin, and whether theyre alone.
Yup: Just like planets, asteroids can have moons! In fact, something like 16% of NEAs larger than about 200 meters across have small companions. They may form when a bigger asteroid spins up and breaks apart, or undergoes a smallish impact that sends debris into space around it.
[The asteroid 1998 QE2 imaged by radar shows the motion of its small moon. Credit: NASA/JPL-Caltech/GSSR]
An asteroid with a moon provides incredibly useful information: by measuring how long it takes the moon to orbit, the mass of the big asteroid can be found (because the gravity of the asteroid depends on its mass, and its that gravity that controls the orbit of the moon). Thats nearly impossible to determine otherwise. Thats one way we know that many asteroids are rubble piles; they have way too little mass for a solid rock their size. Theyre full of holes!
But thats not all theyre full of. In fact
10) Asteroids are a threat. But they can also be oursalvation.
We almost always hear about asteroids in terms of how harmful they are if they impact Earth. But theyre not all doom and gloom!
Many asteroids have water ice inside them. Weve detected it in several, and its possible quite a few have ice and other useful substances in them.
Useful? Yup. Humans need water to survive, of course, but you can also use electricity (supplied by solar panels, say) to break water molecules up into oxygen and hydrogen. Oxygen is rather useful for breathing, and hydrogen is great as a fuel. So, right there, you have three critical components to inhabiting space!
Scientists are very interested on figuring out whether we can harvest asteroids for materials. If you can mine them and store those materials, they can become space depots, floating way stations for astronauts exploring deep space. Water is very heavy, so launching it into space is difficult and expensive. If its already there, you can save a huge amount of effort and money.
They also have metals in them that are useful for building spaceships and structures, too. They could very well be one-stop shopping places for future astronauts. Some private companies have even been started in the hopes of doing this!
I love this idea. It makes space travel far easier, and can provide humanity with the tools and raw materials needed to not only explore space, but to stay there.
If we do nothing, eventually a large enough asteroid will hit us, and could do a lot of damage; destroying a city, collapsing our civilization, or even causing our extinction.
[Someday, some human will have this view. Credit: Erik Wernquist, from his magnificent short film "Wanderers".]
By learning how to divert asteroids we can prevent this from happening. By tapping into asteroids as a resource we can simultaneously ensure humanity wont get wiped out by any single cause. If we become a true space faring race our future will be long indeed, and will include seeing us stepping foot on other planets, hopefully to live there. Permanently.
Extinction, or salvation? The choice is ours.
[Top image credit: Shuttertstock / solarseven]
The rest is here:
Ten things you don't know about asteroids (and impacts thereof) - SYFY WIRE (blog)
