I first learned of the potential threat of asteroids when I read Arthur C. Clarke’s Rendezvous with Rama. As with all of Sir Arthur’s novels it is a book full of hope, speculation, wonder, and hard science. We travel with the crew of the exploration vessel Endeavour as it encounters a massive space vehicle from parts unknown that is just passing through our solar system. It’s a fabulous book and I pick it up from time to time and re-read it. It’s a thoroughly enjoyable yarn.
The book begins on a bit of a grim note, however. It briefly mentions the Tunguska event of 30 June 1908 when a meteor or comet slammed into the Earth’s atmosphere and exploded with several megatons of energy high above the Siberian taiga. The airburst flattened millions of trees and devastated almost 2100 square kilometers of an unpopulated region.
Clarke goes on and describes a fictional event in the year 2077, when a large asteroid enters the atmosphere somewhere high above the Mediterranean Sea. Crossing the sky, it leaves a trail of devastation across southern Europe and northern Africa before it impacts northern Italy. I read this book in high school and the scenario left a deep impression on me. When the Chelyabinsk meteor and its shockwave struck in February of 2013 Clarke’s book immediately came to mind.
Clarke suggested that one of the remedies to avoid potential disaster was to use powerful arrays of optical telescopes and radars to catalog the many asteroids that cross Earth’s path. In the novel he called this observational campaign Project Spaceguard. It is one such telescope array that discovers the object Rama and drives the plot forward.
The Earth has been struck by asteroids many times. Evidence of this can be seen in places like Meteor Crater, Arizona. Earlier impacts include the devastating Chicxulub impact that wiped out the dinosaurs 65 million years ago. Perhaps lesser known is the Eltanin impact that struck the Pacific Ocean 2.5 million years ago. The Eltanin asteroid was 4 kilometers in diameter and left a crater 35 kilometers across on the ocean floor. It led to large tsunamis and was perhaps the trigger for an ice age. If an Eltanin happened tomorrow it would be a global catastrophe.
Since Clarke’s novel a number of efforts have been made to actively catalog near-Earth objects (NEOs). In a nod to Sir Arthur these efforts are collectively referred to as Project Spaceguard. Many scientists, amateur astronomers, and even governmental agencies around the world have become involved. This includes many notable writers, cosmonauts, astronauts, artists, and celebrities. Detection of a threatening asteroid would give us some lead time to prepare either for a disaster or, better yet, to put the energies and technologies of humanity forward to deflect a NEO. An asteroid strike is the only type of natural disaster that could potentially be prevented.
International Asteroid Day is an attempt to raise awareness of the hazard of NEOs. It also seeks to explore possible mitigation methods which could literally save the planet. Many activities related to the International Asteroid Day and Project Spaceguard are led by the B612 Foundation. One of the founders of the B612 Foundation is Apollo 9 astronaut Rusty Schweikart. He and Brian May…who is both a celebrated guitarist for Queen as well as a PhD astrophysicist…helped establish Asteroid Day. According to the B612 Foundation’s website there is a working group in place that has three primary goals:
1. Employ available technology to detect and track Near-Earth Asteroids that threaten human populations via governments and private and philanthropic organisations.
2. A rapid hundred-fold acceleration of the discovery and tracking of Near-Earth Asteroids to 100,000 per year within the next ten years.
3. Global adoption of Asteroid Day, heightening awareness of the asteroid hazard and our efforts to prevent impacts, on June 30 – with United Nations recognition.
Activity on these three tasks has been robust and the third action item has been achieved. There are many ongoing events and activities around the world today. There are also links and interesting interviews and videos at Asteroid Day.
It should be noted that in recent years various exploration craft have visited both asteroids and comets. This small armada includes the Deep Impact mission, the Rosetta orbiter and Philae lander, NEAR-Shoemaker, and the Dawn spacecraft that is currently orbiting Ceres. In addition, the OSIRIS-REX craft is on its way to asteroid Bennu. The spacecraft’s acronym stands for: Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer. That’s a mouthful!
The “Security” part of that title is based on the fact that this mission will extensively study the asteroid to learn about its composition and interaction with its surroundings, including the Yarkovsky Effect. Bennu was chosen in part due to the fact that it has a 1-in-1800 chance of impacting the Earth when it passes nearby in the year 2170.
In flight to a distant worldlet and on the hunt, OSIRIS-REX has used its camera systems to search for NEOs. It should arrive at Bennu in August of 2018. A sample probe will be returned to Earth by September of 2023. The samples could shed light on the composition of asteroids. It may also give us some idea as how to thwart an asteroid should we ever detect one on a path to hit us.
According to NASA’s JPL website other scientific objectives of the mission include:
- Return and analyze a sample of pristine carbonaceous regolith in an amount sufficient to study the nature, history, and distribution of its constituent minerals and organic material.
- Map the global properties, chemistry, and mineralogy of a primitive carbonaceous asteroid to characterize its geologic and dynamic history and provide context for the returned samples.
- Document the texture, morphology, geochemistry, and spectral properties of the regolith at the sampling site in situ at scales down to millimeters.
- Measure the Yarkovsky Effect on a potentially hazardous asteroid and constrain the asteroid properties that contribute to this effect.
- Characterize the integrated global properties of a primitive carbonaceous asteroid to allow for direct comparison with ground-based telescopic data of the entire asteroid population.
The Yarkovsky Effect is of interest and definitely falls under the “Security” part of the OSIRIS-REX mission. First described in 1900 by Ivan Yarkovsky, the theory relates the thermal effects of sunlight falling on a rotating body in space to tiny forces that are generated on the object’s center of mass. Over time these tiny forces could nudge even a large asteroid into a different orbit. Scientists have studied the idea that by changing the areal coverage or location of sunlight on the surface of an asteroid its course could be adjusted. Given enough of a warning a spacecraft could be sent out to intercept the asteroid. A crew or robots (or both) could paint absorptive material onto an asteroid or deploy reflectors that might increase the level of solar radiation that strikes its surface. These alterations could change the asteroid’s orbit just enough for it to miss Earth.
This is not science fiction. The Deep Impact mission voyaged to the comet Tempel-1 and arrived in 2005. It launched an impactor into the comet. The impactor was a semi-autonomous vehicle that could maneuver and return telemetry and images to Earth. On July 4th 2005 it hit Tempel-1 at a high rate of speed and released the energy equivalent of 5 tons of dynamite. Careful study showed that the comet’s course was altered slightly, with a 10 centimeter adjustment to its perihelion, or closest point of its orbit to the Sun. Follow-on studies by NASA and other organizations have indicated that an impactor strike of this type is perhaps the most mature technology currently available to successfully deflect an inbound asteroid.
So we live in an amazing age. Rather than fearing this hazard, people around the globe are staring it in the face, pooling resources, and coming up with competent strategies. We even have an International Asteroid Day. I think Sir Arthur would approve.