How to Survive an Asteroid Attack

April 25, 2015

6-minute read

Imagine a massive rock the size of a house is hurtling towards Earth – what do you do? Duck and cover? Head to an underground shelter? Call Bruce Willis? Ask Science explains how to survive an asteroid attack.

144 EE How to Survive an Astreroid Attack

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Hi I’m Dr. Sabrina Stierwalt, and I’m Ask Science bringing you Quick and Dirty Tips to help you make sense of science.

Asteroids are chunks of metal and rock that zip around our solar system. Some are small, while others are the size of many football fields. There are millions of them, but do they really pose a threat?

The short answer is: Yes!

So let’s explore what we can do to protect ourselves from these giant space rocks.

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What Is an Asteroid?

Astronomers believe that most asteroids are likely failed planets, or smaller pieces that never grew large enough to become planets of their own when our solar system formed 4.6 billion years ago.

Asteroids can have their own moons – some even have two! Asteroids are almost always irregularly shaped and can be heavily cratered, suggesting their histories were full of collisions. Most asteroids (that we know of) orbit the Sun in the asteroid belt, the region of space between Mars and Jupiter, and many others, called Jupiter Trojans, hang out in Jupiter’s orbit.

Ceres, the largest known asteroid, measures 950 kilometers (approximately 590 miles or about the size of Texas) and is so big that it is also classified as a dwarf planet. Ceres constitutes about one third of the total mass of the asteroid belt. In February 2015, the Dawn spacecraft sent back to Earth the closest picture we have to date of Ceres on the probe’s approach to the asteroid. The image revealed bright spots on the asteroid’s surface that astronomers have not yet been able to explain.

How Many Asteroids Are Near Earth?

There are populations of asteroids elsewhere in the solar system, sometimes called “orbital families,” including about 10,000 near Earth asteroids or NEAs. These rocks are in orbits (or paths) around the Sun that are either close to or cross the Earth’s orbit.

A subset of these asteroids, called potentially hazardous asteroids, or PHAs, come within 5 million miles of Earth’s orbit and are believed to be big enough (more than 100 meters) to cause regional damage should they impact Earth.

This means they pose a possible impact threat should something (like the gravitational nudge from a previous Earth flyby) knock them slightly off course.

Should an impact occur, the potential for devastation on our planet depends heavily on the size of the asteroid involved in the collision. If the asteroid is the size of a car, then we likely have nothing to worry about. Such a relatively small asteroid would get incinerated by the Earth’s atmosphere upon arrival and would result in a gorgeous shooting star. In fact, NASA only tracks NEAs that are larger than 1 kilometer (0.6 miles).

The latest asteroid statistics come from NASA’s space-based WISE mission which surveyed the entire sky at infrared wavelengths. Dr. Amy Mainzer and her team determined there to be 981 NEAs that are larger than 1 kilometer in size (including about 70 that have yet to be found).

Previous Asteroid Impacts

The only large asteroid impact for which we have firsthand accounts occurred in 1908 in an area of Siberia called Tunguska. Not a single person is thought to have been seriously hurt, but that is thanks mostly due to the remote location of the impact. Instead, 80 million trees were felled. Even at an estimated weight of 220 million pounds, the Tunguska asteroid was mostly detonated in the atmosphere just above Siberia.

Thus, at ground zero, or the precise location of the impact, rather than producing a large impact crater, trees were left standing but without limbs or bark. This means the shock waves produced by the impact were so fast that they removed the trees’ branches before the branches could carry their momentum through to the rest of the tree!

An asteroid impact is also believed to have eliminated the (non-avian) dinosaurs. The father/son physicist/geologist team of Luis and Walter Alvarez first proposed an impact had occurred around the right time based on their investigations of layers of rock. Although some geologists feel the link is still open for debate, most agree that the large Chicxulub Crater in Mexico’s Yucatan Peninsula is likely associated with the mass extinction.

See also: What Physics Recently Discovered About the Big Bang

An asteroid that hit an ocean would create devastating tsunamis, while impact on land or in shallower bodies of water would stir up enough dust and ash into the atmosphere to block sunlight. The ensuing cold, dark, dusty conditions (known as “impact winter”) would likely cause mass extinction and may be the reason humans and dinosaurs never got to coexist.

What America Is Doing to Monitor Asteroids

Unfortunately, once an asteroid hits, there is not much you can do other than hope you are not in the wrong place at the wrong time. Luckily, we have the technology to prevent an impact. NASA uses radar, optical, and infrared searches to track near-Earth asteroids that are either larger than 1 kilometer in size or are otherwise on trajectories with high impact likelihoods.

One such asteroid is Apophis, which caused a moment of panic back in 2004 when its measured orbital parameters indicated an impact with Earth in April of 2029. As astronomers continued to monitor the asteroid and honed their models of its orbit, however, they were able to rule out a possibility of an impact in 2029. At that time Apophis will instead travel beneath our communication satellites on its closest passage yet.

Depending on the trajectory of Apophis at that time, astronomers will know whether or not we need to prepare for a direct (although unlikely) impact with Earth on its next orbital pass in 2036.

How Can We Deflect Asteroids?

So what do we do if we find an asteroid on path to hit Earth?

Some suggest the brute force method of blowing the rock up with some kind of bomb. Unfortunately, the size, speed, and trajectories of the resulting pieces would be nearly impossible to control and thus potentially could create a whole new set of problems. However, vaporizing an asteroid into dust may be the best option if time is short.

Another approach would be instead to nudge the asteroid off its path so that it just misses our planet. This nudging, called a gravitational tractor, can be done with rocket boosters attached to the asteroid or by placing an object near the asteroid that can coax the asteroid off course with its gravitational pull.

A third way would be to paint one side of the asteroid and therefore change its “albedo” or how much light its surface reflects. Darker surfaces absorb more light than lighter ones (it’s why we are better off wearing white clothes in the summertime rather than black or navy), and the resulting force difference due to the hot versus cold sides can actually affect the asteroid enough to push it off course. This force imbalance is known as the Yarkovsky effect and has been measured for asteroids from the Sun’s incident radiation.

Another important piece of the prevention puzzle is to continue sending space missions to gather information on asteroids so we can better understand their sizes, shapes, and structural and chemical compositions. Knowing a few asteroids in depth allows predictions of similar parameters for asteroids where we don’t have as much information. Such studies also help us to better understand how to deflect any asteroids headed toward Earth, should we find one.

Lucky for all of us, there are scientists, like my friend and colleague Dr. Patrick Taylor, who just attended the Planetary Defense Conference in Rome where scientists, engineers, and disaster-response experts all get together to discuss how to find and characterize asteroids that may be hazardous to Earth, as well as how to take action against any potential threats.

Dr. Taylor says:

“The best way to protect the Earth is to find all of the potentially hazardous near-Earth asteroids that can cause catastrophic regional damage. Detailed characterization with optical, infrared, and radar telescopes can then determine if the asteroid poses a risk and guide us in how to react, whether with a deflection mission or through coordinated emergency response prior to and post impact.”

Worst comes to worst, we can always call on Bruce Willis and his team.

Until next time, this is Dr. Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science.

I want to give huge thanks to all of you science fans for tuning in each week. As I announced last week, there is a change coming to Ask Science. Starting in May, new episodes will be released on Monday evenings instead of Fridays. I hope this new schedule will give you more time to satisfy your scientific curiosity during the week and maybe free up some weekend time for going outside!