THE DINOSAURS HAD NO WARNING OR CHANCE – DO WE? A “PLANETARY DEFENSE” VIEWPOINT

About 66 Ma, a ca. 10 km asteroid was on collision course with the Earth. Life on Earth was different from what it is today, but the impact of that asteroid, which caused the formation of the ca. 200-km-diameter Chicxulub impact structure, with by now well-known consequences (leading to a severe mass extinction), changed the situation for its future development considerably, setting the stage for the era of the mammals, which ultimately included us humans. The most iconic species that has fallen victim to the impact, the dinosaurs, literally had no chance.

Today, we have a technological society with a lot of relevant knowledge. Potentially dangerous asteroids are known, as is technology to possibly slightly alter the orbits of such near-Earth objects (NEOs), termed “planetary defense”. At conferences of the same name, “exercises” involved the (fictitious) discovery of NEOs on impact course. Two main options exist – a discovery several years before collision, which allows to use (future) technology to potentially alter the course of the NEO to avoid impact, or, a discovery with just weeks or days to spare, which just gives the chance to refine the calculations of the impact location, leaving possibly enough time to evacuate an area. This poses interesting challenges, as in the era of “fake news” (perceived or real), public communication may not be easy (are “experts” to be believed, or politicians, or international organizations?). In this context, other interesting questions arise. For example, how long before the collision would the dinosaurs have seen the incoming Chicxulub-impactor in the night sky, or even the day sky? Different eyes and vision aside, our recent work (Bazso and Koeberl, in prep.) indicates that this was surprisingly late. As the impactor was of carbonaceous-chondritic composition, it had a low albedo. Other factors include velocity and phase angle (relative to the sun). This yields night-sky visibilities at about lunar distance, and day-sky detection at a distance of less than that for geostationary satellites. This results in a “time to impact”, at a slow 15 km/s velocity, on the order of less than 10 and 0.5 hours, respectively. And this is for a fairly large asteroid. Thus, to wait and “see with one’s own eyes” leaves dangerously little time to do anything. So do we have better chances than the dinosaurs?