There are a lot of giant asteroids out in space, and it’s just a matter of time before another one finds a bullseye on Earth. What can we do about it?
Article as posted on Medium written by: A.S. Deller
Managing the Existential Threat of Asteroids
Our Earth has been struck by asteroids countless times, mostly during the period immediately following our solar system’s formation — thankfully, when there was no life on the planet.
But numerous giant hunks of space rock have hit us in the billions of years since those early days.
Often the terms “asteroid” and “meteoroid” are conflated. They do, in fact, have different definitions. An asteroid is a very large chunk of rock and metal orbiting the Sun, while meteoroids are considerably smaller. When a meteoroid vaporizes in our atmosphere (creating that characteristic “shooting star” trail), it’s called a meteor. And when it makes it through the atmosphere and actually crashed into the Earth’s surface, we call it a meteorite.
The actual size range that classifies something as an asteroid rather than a meteoroid doesn’t have an exact lower limit, with the smallest usually considered “boulder-sized”. The largest known asteroid at this time is Ceres, at nearly 600 miles in diameter. Ceres lies in the asteroid belt between Mars and Jupiter and is such a large body that we also categorize it as a dwarf planet.
Meteor Crater, Arizona. At over 1 km (.74 miles) across, this crater was made by a meteor only 50 meters (160 ft) in diameter. CREDIT: NASA
When a meteor or meteorite hits our atmosphere or surface, it is generally not a threat to many people, and certainly would never be an extinction-level threat. One of the more recent and publicized of such occurrences happened over the Ural region of Russia on February 15, 2013, known as the Chelyabinsk meteor. This began as a 20-ton asteroid but burned off most of that mass in the atmosphere before exploding at an altitude of 18.5 miles with the energy of roughly 30 Hiroshima bombs. The shockwave blew out windows in six regional cities, injuring 1500 people.
This was the largest such meteor explosion since the larger Tunguska event in 1908 which flattened nearly 800 square miles of forest in Siberia. Without the benefit of modern technology to analyze the event, it is still unknown if the Tunguska explosion was caused by an asteroid or a comet, though based on the destruction it is estimated the object was anywhere from 200 to 600 feet in diameter.
There are about 175 known asteroid impact craters on Earth at this time. Arizona’s Meteor Crater (not so original a name, I know) was created about 50,000 years ago, while it is believed the gigantic crater off the Yucatan Peninsula was made 65 million years ago and accounts for the ultimate extinction of the dinosaurs.
This image, taken by NASA’s Near Earth Asteroid Rendezvous mission in 2000, shows a close-up view of Eros, an asteroid with an orbit that takes it somewhat close to Earth. Credits: NASA/JHUAPL
The European Space Agency’s GAIA spacecraft recently sent new data, and it included the locations of over 14,000 asteroids. The below video displays the orbits of the 200 brightest objects:
That’s quite an impressive bowl of spaghetti, isn’t it? It’s actually far denser a concentration than that. There are tens of millions of asteroids (2 million larger than 3,000 feet in diameter) inside the Solar System, and in the Oort cloud that surrounds our Solar System, there could be more than 8 billion objects.
So, knowing that there are a lot of big ones out there, what are the odds one of those things hits us?
Meteorites (small chunks of rock and metal that make it through the atmosphere and cause no damage): 500 impacts per year
Car-sized object (hits the atmosphere and vaporizes or explodes): Once per year
Football field-sized object (makes it through the atmosphere to make a big impact): Once every 5,000 years
Extinction-level event: Once every few million years
9 asteroids and 4 comets visits by spacecraft. The largest seen here is Lutetia, which at 100 km across (62 miles) would completely cover an area larger than the city of Los Angeles. CREDIT: NASA
So what can we do about it?
There a few built-in defenses we have: One, our thick atmosphere creates a lot of friction for objects falling into Earth’s gravity well. Small meteors burn up and others explode from the heat. And two, our Moon acts like a satellite broom, sweeping up meteors that pass close enough for its own gravity to grab them. Three, before meteors from the asteroid belt or the Oort Cloud can get to us, they have to get past all those other satellite brooms in our system, including the massive gravitational pulls of Saturn and Jupiter.
But what happens when something gets through all that? Something big?
When we talk about asteroids, we’re talking about a force of nature. We’re at the whim of the universe when it comes to when something comes at us which has the mass to cause significant destruction. Luckily, our current technology allows us to find and track the largest such objects. So far, over 95% of asteroids in and around our Solar System on the scale of the ones that killed the dinosaurs have been found. However, as these near-Earth objects (NEOs) get smaller, they are more difficult to spot, and only about a fifth of the potentially highly destructive football-field-sized objects have been found.
A lot of smart folks (rocket scientists included!) have been working hard to devise effective methods to deflect incoming NEOs for decades now. There are several possibilities:
Kinetic Impacter: Send a massive spacecraft to collide with the NEO and knock it off-course.
Gravity Tractor: Send a massive spacecraft to within a very near distance of the NEO, and use said spacecraft’s large mass to slowly change the NEO’s course via gravitational pull.
One of the techniques we’re putting forward is to use a contactless deflection of an asteroid through laser ablation. Where we are having a moderately sized or small sized spacecraft with an onboard laser system and that laser would shoot against the asteroid while the absorbed heat of the laser beam would enable the sublimation of the material. This sublimation immediately transforms the rocky asteroid into a big plume of hot gas and ejector from the illuminated spot. That’s enough to sublimate the surface creating a plume of ejector that is very much like a rocket exhaust in standard methods of rocket propulsion. And it’s that plume of ejector that acts against the asteroid over a long period of time to gently nudge it away, so gently push it away. — Alison Gibbings, 2013 Planetary Defense Conference
There is one inherent problem with these three methods of deflecting an asteroid:
If we had years of warning time before a possible impact, then we could coordinate with space agencies to try to divert the asteroid. You need to have a warning time of many years to be successful at diverting an asteroid. It also depends on the size. In our exercises, we have worked with five to 10 years of warning time, which is sufficient to deflect an asteroid away. — Paul Chodas, manager of the Center for Near-Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory, Newsweek
And then, much like one of the staple solutions seen in movies such as Armageddon, we have our current option of last resort.
Blast Deflection: Send NASA’s proposed Hypervelocity Asteroid Intercept Vehicle to the asteroid, where robotic machinery excavates a crater into its face, places a nuclear device, and detonates it with the aim of breaking the asteroid up into a cloud of much smaller (relatively harmless) objects.
The Planetary Defense Coordination Office at NASA published this timeline to illustrate what goes into the entire process:
NASA and other space agencies were actually able to practice near-Earth tracking of a 50 meter asteroid (TC4) which passed by Earth at a distance of about 27,000 miles.
There is something called the Torino scale which rates the probability of an object’s impact and the destruction it might cause:
CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1724705
For a while, in the early 2000s, the asteroid labeled 99942 Apophis was at a level 4 on the Torino scale. More recent and accurate observations have lowered Apophis to a 0 on the scale. Apophis will pass by Earth on April 13, 2029, but most likely not strike us.
This [image] shows the distance between the Apophis asteroid and Earth at the time of the asteroid’s closest approach. The blue dots are the many man-made satellites that orbit our planet, and the pink represents the International Space Station. (NASA Image Library)
At this time, there are no asteroids or comets that have been found or are being tracked that rank higher than a 0 on the Torino scale.
Thanks to the brilliant minds at NASA and other space agencies around the world, the chances that we actually see potential dangerous impacters with enough advance warning fairly good. Additionally, we have some technical capabilities that might allow us to defend ourselves if (and when) we do find ourselves playing a real-life game of ASTEROIDS.