Humans have stretched Earth’s resources to the limit, and ever-expanding populations now require new technologies — such as genetically engineered crops and alternative energy sources — to survive.
What would happen to this delicate balance if the planet’s climate changed slightly due to a smaller-sized asteroid or comet impact — an event just large enough to cause crop failures or reduce atmospheric ozone?
That’s what planetary scientist Elisabetta Pierazzo hopes to discover through research that has been funded under a new grant from the NASA Astrobiology: Exobiology and Evolutionary Biology Program.
Pierazzo, a senior scientist at the Tucson-based Planetary Science Institute, will use general circulation models (GCMs) of the Earth’s atmosphere to analyze the effects of impactors between 300 meters and 2 kilometers in diameter. This project is a collaborative partnership between PSI and the National Center for Atmospheric Research (NCAR), Pierazzo emphasized. NCAR scientists will provide the computer code and support for the atmospheric modeling parts of the project.
Atmospheric chemistry models are now being coupled to atmospheric GCMs, Pierazzo noted. This makes it possible to interactively evaluate the effects of atmospheric perturbations, such as those associated with an impact event, on the overall physical and chemical state of the atmosphere.
Pierazzo, an expert in modeling impact events, will determine the amount of dust and/or water that would be ejected from impacts of various types and sizes and how high the ejecta would rise in the atmosphere. Then she will run an atmospheric model that accounts for this extra material and the changes in atmospheric dynamics and chemistry.
”We’re trying to find out the threshold for significant effects on climate and how long those effects will last,” she said.
Destruction of ozone, for instance, would allow more ultraviolet radiation to reach the ground, potentially affecting the DNA of every living organism. Dust could alter weather patterns, with devastating effects on food supplies. “Even slight changes in the atmospheric circulation might affect weather patterns and agriculture,” she said.
”The Spaceguard Survey is getting close to its goal of finding ninety percent of the Near Earth Objects larger than one kilometer in diameter,” Pierazzo said. “But there are many more smaller objects out there than larger ones, so we still have a large potential threat that we haven’t resolved.”
A smaller object between 500 meters and 1 kilometer in diameter might be spotted months in advance or maybe only days, depending on its trajectory, she said. Or it might be seen only at the last minute or not at all, if its trajectory is close to the sun.
While attempts have been made to model large impacts, such as the Chicxulub meteorite that may have killed off the dinosaurs, GCMs are so sensitive to current conditions that they may not be able to withstand the introduction of Chicxulub-sized perturbations, Pierazzo said.
”We want to start with smaller impactors and then move on to larger ones,” she said. “Eventually the idea would be to try to model the effects of a Chicxulub-sized impact.”
”This project is going to be a learning experience because we really don’t know what to expect,” Pierazzo added. “There might be climatic effects we haven’t anticipated, or maybe we’ll find impacts of this size are not a big deal as far as climate is concerned. We just don’t know yet.”
Other researchers working with Pierazzo on the project are: Rolando Garcia, Charles Bardeen, Doug Kinnison, and Daniel Marsh, of NCAR; Natalia Artemieva, of PSI; and H. Jay Melosh and Tamara Goldin, of the University of Arizona.