Department Colloquium: Tuesday, February 15, 2022 - Don’t Look Up - A Physicist’s View of Planetary Defense

Event Date: 

Tuesday, February 15, 2022 - 3:45pm

Event Date Details: 

This will be Zoom streamed event only.

Event Location: 

  • Zoom Only
  • Physics Department Colloquium

Don’t Look Up
A Physicist’s View of Planetary Defense

Philip Lubin
Physics Dept, UC Santa Barbara

Planetary defense is like taxes. You would rather not deal with it but you know that if you do not, someday something bad is going to happen to you. Think of the IRS like an asteroid or a comet. It is out there waiting to hit you with an audit.  Eventually it will come for you. Traditional methods, including ones we have worked on previously, involve deflection of the threat by various means. The problem with deflection is that it is an extremely poor use of interception launch mass. Deflection is fine is you have a lot of time to “sit back and assess” and you get the orbital parameters precisely enough (not so easy). In several recent papers we taken a radically different approach to planetary defense that uses energy not momentum transfer, allowing for extremely short mitigation time scales. The method involves an array of small hypervelocity kinetic penetrators that pulverize and disassemble an asteroid or small comet. This effectively mitigates the threat using the Earth’s atmosphere to dissipate the energy in the fragment cloud.  The approach will work in extended time scale interdiction modes where there is a large warning time, as well as in short interdiction time scenarios with intercepts of minutes to days before impact. In longer time intercept scenarios, the disassembled asteroid fragments cloud spreads and the fragments largely miss the Earth. In short intercept scenarios, the asteroid fragments of maximum ~10-meter diameter allow the Earth's atmosphere to act as a "beam dump" where the fragments either burn up in the atmosphere and/or air burst, with the primary channel of energy going into spatially and temporally de-correlated shock waves. This approach represents an extremely rapid response, testable, and deployable approach with a logical roadmap of development and testing. This allows for effective defense against asteroids in the 20-1000m diameter class and could virtually eliminate the threat of mass destruction caused by these threats. As an example, with only a 1m/s internal disruption, a 5 hours prior to impact intercept of a 50m diameter asteroid (~10Mt yield, similar to Tunguska), a 1 day prior to impact intercept of 100m diameter asteroid (~100Mt yield), or a 10 day prior to impact intercept of Apophis (~350m diameter, ~ 4 Gt yield) would mitigate these threats. Mitigation of a 1km diameter threat with a 60-day intercept is also viable. We show that a 20m diameter asteroid (~0.5Mt, similar to Chelyabinsk) can be mitigated with a 100 second prior to impact intercept with a 10m/s disruption and 1000 second prior to impact with a 1m/s disruption. Zero-time intercept of 20m class objects are possible due to atmospheric dispersion effects. We also show that extension to nuclear penetrators allow for relatively short term mitigation of 10km existential (planet killer) threats such as in a recent movie. Having such a capability would allow humanity for the first time to take control over its destiny relative to asteroid and comet impacts.  Apologies for  those die-hards who want to take on an “asteroid the size of Texas” – time to move off planet.



Philip Lubin is a professor of Physics at UC Santa Barbara whose primary research has been
focused on studies of the early universe in the millimeter wavelengths bands as well as
applications of directed energy for planetary defense and relativistic propulsion. His group has
designed, developed and fielded more than two dozen ground based and balloon borne
missions and helped develop two major cosmology satellites. Among other accomplishments
his group first detected the horizon scale fluctuations in the Cosmic Microwave Background
from both their South Pole and balloon borne systems twenty years ago and their latest results,
along with an international teams of ESA and NASA researchers, are from the Planck
cosmology mission which have mapped in exquisite detail the structures of the early universe.
He is a co-I on the Planck mission. His group has worked on applications of directed energy
systems for both small scale single launcher solutions as well as large standoff systems for
planetary defense and on applications to allow small interstellar probes to achieve relativistic
speeds for the first interstellar missions. He is co-recipient of the 2006 Gruber Prize in
Cosmology along with the COBE science team for their groundbreaking work in cosmology as
well as the 2018 Gruber Prize in Cosmology along with the Planck science team for their
determination of fundamental cosmological parameter. He has published more than 450 papers.

Philip Lubin, Physics Dept, UC Santa Barbara