If Pandemics and Climate Change Aren’t Enough of a Threat There is Always Errant Asteroids

Elon Musk created SpaceX, his rocket company, to save humanity from an extinction event by making us an interplanetary species. He was thinking about a nuclear holocaust or an asteroid strike like the one that purportedly ended the reign of the dinosaurs on Earth around 66 million years ago. Musk isn’t alone in having concerns about a future space rock striking the planet with devastating effects.

NASA has created the Planetary Defense Coordination Office to begin providing for a planetary-wide defence strategy that includes:

• the early detection of hazardous objects between 30 to 50 metres (100 to 165 feet) in diameter coming within 9 million kilometres (5 million miles) of Earth’s orbit.
• the tracking and characterization of these objects and the issuance of warnings of potential planetary impacts.
• strategizing and developing technologies to mitigate future impacts.
• coordinating the U.S. government’s planning in response to an actual impact threat.

NASA’s Jet Propulsion Laboratory in Pasadena, California, is helping in this strategy by managing the agency’s near-Earth object study which tracks comets and space rocks in our orbital neighbourhood. The agency is also using the NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer) satellite to survey Earth’s close neighbours and has identified more than 26,000 objects so far. A future NASA satellite, the NEO Surveyor, will be deployed to find even more potential space rock threats.

NASA is joined by organizations like the International Astronomical Union (IAU), a body of academics and researchers from 90 countries that are employing several Earth-based observatories and space telescopes to track potential impactors.

Then there is B612, a non-profit organization created by two former NASA astronauts, Dr. Edward Lu, an astrophysicist, who flew on three space missions during the construction of the International Space Station, and his partner, Rusty Schweickart, who served on the crew of Apollo 9. The work they are doing is less about detection and more about developing defences. Why? Because B612 sees the planet’s vulnerability to space rock impactors.

Fortunately, most space rocks that enter our atmosphere are small and burn up harmlessly from friction and heat. About every five years, however, Earth intercepts one of at least 6 metres (20 feet) in diameter, that either detonates in the atmosphere or makes it to the planet’s surface. The vast majority of these fall into the ocean arriving unnoticed.

About once a century a larger space rock collides with Earth measuring up to hundreds of metres in diameter. If one of these were to strike an urban area the energy and shockwave produced would be more powerful than the largest hydrogen bomb ever tested.

Finally, about every 15 million years we see a space rock equivalent to a dinosaur killer. These are rocks with the potential to wipe out much of life on Earth.

A recent study describes a period in Earth’s history in which city-sized asteroids struck our planet at frequency rates far greater than anything recent in the geological record. Between 2.5 and 3.5 billion years ago, these space rocks, the size of cities and larger continuously pummeled Earth. These were rocks equivalent or greater in size than the asteroid of the Cretaceous-Paleogene event that formed the Chicxulub Crater in the Yucatan. We still see evidence of these impactors on the lunar surface which was equally bombarded during that period and also received post-impact debris expelled into space from Earth. The remaining evidence here are spherules, molten glassy globs embedded in ancient rocks. The rest has worn away over time.

So how can we defend the planet from a future space rock strike as menacing as the one that took out the dinosaurs? NASA and JPL have a plan that will begin to unfold this fall with the launch of the Double Asteroid Redirection Test (DART).

DART will target a companion moonlet of the near-Earth asteroid, Didymos. The asteroid spans 780 metres (2,500 feet). Its moonlet is 160 metres (over 500 feet), more typical, states NASA, of the types of rocks that have struck Earth in the past. DART will crash into the moonlet. It is a kinetic energy weapon that will intercept its target in September 2022 with the asteroid about 11 million kilometres (6.8 million miles) from Earth. The impact speed will be 6.6 kilometres (4.1 miles) per second and the results should be captured by DART’s onboard camera with the signal beamed to Earth. In addition, Earth-based telescopes will monitor post-impact results which NASA hopes will show a small change to the moonlet’s orbit increasing it by several minutes.

As critical as DART will be in the evolving plan to defend Earth, it only works on potential impactors we can detect while still far away. We know of at least one recent space rock, however, that arrived here on Earth virtually undetected. That was the estimated 17-metre (56-foot) space rock that weighed 10,000 metric tons and travelled at a speed of 17.88 kilometres (11.11 miles) per second before exploding and breaking up over the Russian city of Chelyabinsk in February 2013. It came out of nowhere and had never been tracked because its orbit was atypical.

Another concern we will need to address is probably still decades away when commercial space mining operations begin to exploit the potential riches found within space rocks. Asteroid mining is seen as being worth tens of trillions of dollars.

An unintended consequence could be the altering of the orbit of one of these asteroids during a mining operation. What miners will need to ensure is they don’t cause a change that could send pieces or the entire asteroid on a collision course with Earth. Because the most likely mining candidates will be near-Earth asteroids and not those in the Asteroid Belt between Mars and Jupiter, the risks of such an accident are that much greater.

That risk is the subject of a conference paper presented at the 7th IAA Planetary Defense Conference, held in April of this year, in Vienna, Austria, where authors Aaron Boley and Michael Byers, from the University of British Columbia, describe a need to actively manage asteroid orbits as a precautionary principle.