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.
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..
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.