When people think of cosmic objects hitting Earth, their minds typically jump to calamities like the meteor that killed off the dinosaurs some 66 million years ago. However, the Earth is actually bombarded by about 100 tons of cosmic debris per day; the vast majority of it is just so small it is insignificant and burns up in the atmosphere. When the objects become bigger though, there are no robust defence systems currently protecting against these potential threats — this is the problem Professor Philip Lubin in the Department of Physics at UC Santa Barbara is trying to solve.
Lubin began this research in 2015 before shelving it for five years and then resuming it during the pandemic. His work, along with that of his co researcher, Alexander Cohen, and various students assisting him, culminated in the project titled PI (π), or Pulverize It. The project proposes a way to break up incoming objects, instead of just deflecting them as past efforts have sought to do. The basic concept involves using penetrator rods in order to fragment the incoming asteroid or comet. The key is not to have all the fragments miss Earth but for them to be so small that they burn up in the atmosphere and the shock blasts are decorrelated (or spread out), making them so they pose little threat to life on the ground.
Lubin offers the analogy of a bulletproof vest, where the vest “will take the damage from a bullet and spread it out over a significant region so that it doesn’t hurt you too much.” What PI would do is “break the bullet — or the asteroid — up into pieces, so each piece hits a different part of the atmosphere and the atmosphere then acts like our bulletproof vest.”
This method has the advantage of being able to wait until much later to deal with an incoming problem. Deflection requires many months, if not years of work on detection and then changing the path of the object. PI would theoretically allow threats to be mitigated on a scale of minutes or days, depending on the size of the threat.
“It is just a matter of time. It’s not a matter of if, it’s a matter of when,” Lubin said, emphasizing the importance of planning ahead. “Someday, those kinds of objects will hit us.” In the last 113 years, two meteors have been large enough to cause serious damage to the Earth, according to Lubin. A forested region in Siberia was decimated by a meteor in 1908 in what is known as the Tunguska Event. More recently in 2013, a meteor shattered over Chelyabinsk, Russia. Despite breaking apart in the atmosphere, the resulting shock wave was enough to cause major destruction, though not killing anyone.
While Earth faces no current threats from asteroids or comets, a few asteroids are scheduled to make a close flyby in the coming decades. On Friday the 13th of April 2029, the asteroid 99942 Apophis — which boasts a diameter of 370 meters and carries the equivalent energy of all the nuclear weapons on Earth — will pass within geosynchronous orbit, according to NASA. That is less than 32,000 kilometers, or 20,000 miles, away from the Earth’s surface, closer than some of the planet’s satellites. In 2135 the asteroid 101955 Bennu, 490 meters in diameter, will also come close to the planet.
Both of these asteroids are returners, meaning they will continue to pass by Earth every number of years. This opens up the possibility of the asteroids going through a gravitational keyhole, meaning that if an object passes by the Earth, the planet’s gravity could affect the object’s trajectory so that it will hit Earth on a future trip.
It is worth noting that neither Apophis or Bennu are extinction level threats. For reference, the asteroid that killed the dinosaurs was approximately 10 kilometers wide. PI would allow a meteor the size of Apophis to be mitigated 10 days prior to impact, while about 60 days would be necessary to allay Bennu from hitting the planet in its current form. Smaller asteroids like the one that exploded above Chelyabinsk could be dealt with a mere 100 seconds prior to impact.
Lubin’s work and that of his students is ongoing. The paper is currently being peer reviewed and students are continuing their work coding and designing simulations for various scenarios. Part of a team featuring several UCSB students and one high schooler, fourth-years Dharv Patel, a Physics major and Astronomy minor, and Hannah Shabtian, who is majoring in Earth Science with Geophysics Emphasis and minoring in Astronomy and Planetary Sciences and Iranian Studies, work to “create simulations for various burst scenarios to assess what parameters would best mitigate the damage caused by the resulting pressure waves.” Meanwhile fourth-year Physics major Jeeya Khetia is “designing penetrators that could be used in these simulations.”
With the work of PI, Lubin hopes to put in place “the ultimate environmental project” and protect Earth from the previously uncontrollable threats from the skies.