'Asteroid Day' is a good time to learn about the threat of space rocks

We only know of around one percent of the asteroids lurking in our solar system

On June 30th, 1908, more than 770 square miles of remote Russian forest were obliterated from the face of the Earth when a relatively small meteor, estimated at only around 400 feet across, unleashed 15 megatons of energy above the Stony Tunguska River. One hundred and nine years later, humanity knows precious little more about the dangers that lurk within our solar system than we did in 1908. But a recently founded "global day of education" aims to bring the existential threat that space rocks pose to the forefront of our collective consciousness.

"Asteroid Day" is a UN-sanctioned event held every June 30th, the anniversary of the Tunguska incident, since 2014. That was when former Queen guitarist and now astrophysicist Dr. Brian May teamed up with Rusty Schweickart and Dr. Ed Lu, a pair of former NASA astronauts and current proprietors of the B612 Foundation, along with Danica Remy and film director Grigorij Richters, to form the Asteroid Day Foundation (the ADF).

While the B612 group seeks to ultimately develop methods of deflecting dangerous asteroids before they stray into Earth's path, Asteroid Day works to simply increase our ability to detect incoming threats before it's too late. Specifically, the ADF advocates for improving our asteroid-spotting capabilities by a factor of 100, which would enable astronomers to more quickly identify and track hundreds of thousands of the estimated one million near-Earth objects (NEOs) that are floating around our neck of the galaxy, rather than the thousand or so that we currently do.

"The more we learn about asteroid impacts, the clearer it became that the human race has been living on borrowed time," May noted during a 2014 press conference. "Asteroid Day and the 100X Declaration are ways for the public to contribute to an awareness of the Earth's vulnerability and the realization that Asteroids hit Earth all the time."

Science Museum

Brian May and Grig Richters at the Science Museum, London - Image: Max Alexander

Asteroid Day festivities are largely decentralized. Hundreds of independently organized events are hosted in museums, schools, theaters and libraries across 72 countries and five continents under the Asteroid Day banner. In the three years that the event has been held, the number of events has doubled annually, from 250 the first year to 500 last year. This year, the ADF estimates that there will be closer to 1,000 gatherings going on. These include a number of regional events, such as a panel discussion being held at Imperial College in London, planetarium shows at the University of Nebraska, and "Asteroid Day walks" held in various cities throughout Pakistan. Additionally, the ADF is teaming with Discovery Channel to air a 24-hour livestream of asteroid-centric content.

Even NASA is getting in on the fun. As part of a star-packed astronomers' panel being held at the University of Arizona, researchers from NASA's OSIRIS-REx mission ("Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer") will be discussing their efforts to acquire and return to Earth the first physical samples of an asteroid.

This mission is part of NASA's New Frontiers program, which has already sent spacecraft to investigate Jupiter (the Juno mission) and Pluto (the New Horizons mission). "In this case it's actually an asteroid sample return. Specifically, a near-Earth asteroid that's carbonaceous to boot," explained Dr. Bashar Rizk, OCAMS instrument scientist at University of Arizona's Lunar and Planetary Laboratory. "This means that it has implications not just for the origin of the solar system, but for the origin of life."

The asteroid they chose, Bennu, isn't just scientifically interesting; "it is one of the most hazardous asteroids that we know about," Rizk continued. "And the factors, the physical mechanism to determine whether it's going to continue to be hazardous in the future, are one of the five major things that we want to go there and study."

As of the publication of this story, the 20-foot-long OSIRIS-REx spacecraft is in orbit around the sun, awaiting the moment when Earth's and Bennu's orbits overlap and then using the planet's gravity well to slingshot to within range of the asteroid. This should be sometime in September.

Once the spacecraft and the asteroid are within visual range, approximately 1 million miles from each other, the OSIRIS will spend the following two years mapping and surveying the asteroid with its suite of visual cameras and lidar sensors. They'll examine the space rock's surface in microscopic detail, determine its chemical composition and plot out a safe space for the spacecraft to get close enough to collect a sample from it.

The OSIRIS-REx has a clever means of doing this: It will extend a boom arm, dubbed the Touch-and-Go Sample Acquisition Mechanism (TAGSAM), which will "phoof" the surface with a puff of nitrogen, stirring up anywhere from a few ounces to a few pounds of material for collection. Anything the TAGSAM grabs will be loaded into a return capsule and blasted back toward Earth on a 2.5-year return journey. The rest of the OSRIS will return to its solar orbit, and, depending on how much fuel it has left, could be repurposed for future survey missions.

"The samples that we get from Bennu will inform primarily origin-of-the-solar-system or origin-of-life kinds of questions," Rizk explained. "So they'll be very interesting to us in terms of their precise chemical state and their heterogeneity (or lack thereof), the presentation that they have, the geological aspects that we find here on the asteroid, and everything that they can tell us about that asteroid's history."

The OSIRIS-REx mission may well tell us where we came from, but it's also doing important work to help ensure we stay here. While the 1,600-foot-diameter Bennu asteroid isn't big enough to wipe out life on Earth, should it hit, which it may do in the late 22nd century, the impact would still mess us up real bad.

Given that the Tunguska meteor, a quarter the size of this one, managed to wipe out a patch of land the size of the Cleveland metro area, Bennu could conceivably take out the better part of an entire state. The human cost alone would be utterly catastrophic.

Luckily, Bennu, like other asteroids, is subject to non-gravitational forces such as the Yarkovsky effect. That's when the side of the asteroid facing a star absorbs solar radiation and heats up. As the asteroid rotates, the absorbed energy is emitted as thermal photons, which generate momentum, redirecting the object ever so slightly as it travels through space.

"This object we believe came from the main [asteroid belt] and was part of a specific asteroid family which maybe is related to the breakup of one larger object sometime in the past," Rizk said. "Once the smaller objects became subjected to non-gravitational effects, they would have migrated to one of the residences with Jupiter's orbit in the asteroid belt that would tend to kick objects out."

When that happens, asteroids will either be shunted out of the solar system entirely or fly into the sun unless their trajectories are influenced by another celestial object. "Sometime in the past, [Bennu] has just probably had some encounter with the Earth ... because its orbit is so closely tied to the Earth," he continued.

This close proximity could eventually prove beneficial. "Near-Earth asteroids are the place to go if you want resources for a large space endeavor," Rizk figures. "So if you want to build solar-power satellites in space, or if you want to colonize the L4 or L5 points in your Earth-moon system, or go out and start a colony of the L2 point ... you're not going to be able to launch the resources that you want for such a project from the Earth itself, because it costs too much."

Instead, Rizk envisions future space explorers using passing asteroids as celestial gas stations. "The nearest asteroids have the ideal combination of potential resources both in terms of volatiles and metals and all the rest of the stuff we need -- oxygen -- and accessibility." And since the latest federal budget has effectively killed NASA's asteroid redirect mission, it's not like we're going to be making artificial near-Earth objects of our own anytime soon.