An asteroid colliding with Earth could have devastating consequences, but with enough warning time and if the asteroid is not too large, the best strategy for avoiding such a catastrophe would be to deflect the asteroid’s path. According to a 2010 report by the National Research Council, the best deflection method would be to intercept the asteroid with high-speed spacecraft before it reaches Earth. Researchers at Lawrence Livermore have been studying the effectiveness of this strategy, called kinetic impact, through three-dimensional simulations of the impact process.
In a paper published in the January 14, 2016, online edition of the journal Icarus, Livermore’s planetary defense researchers show that the effectiveness of asteroid deflection by kinetic impact depends on various asteroid characteristics, including material strength, porosity, rotation, and shape. By simulating an array of initial conditions for an asteroid of constant size, researchers quantified how asteroid characteristics affect the success of kinetic impact deflection.
“Asteroids are naturally diverse, and researchers have little direct information about their mechanical properties,” says Livermore researcher Megan Syal, lead author on the paper. “This study emphasizes the important role of asteroid characterization research, which is needed to constrain the different types of conditions that could be encountered at potential deflection targets.” This work, which includes contributions from Livermore co-authors Mike Owen and Paul Miller and other team members, has provided new information for designing future kinetic-impact missions.
Contact: Megan Syal (925) 423-0435 (syal1@llnl.gov).
Livermore analytical chemists Mike Kristo and Ruth Kips, in collaboration with researchers from the Australian Nuclear Science and Technology Organisation, wrote an overview that describes how nuclear forensics supports law enforcement and national security investigations. The article, which was featured on the cover of the February 2, 2016, issue of Analytical Chemistry, includes examples of how investigators use multiple types of scientific analysis to capture a material’s key forensic signatures.
“This work shows how a material’s ‘signatures’—characteristics such as isotopic abundances, elemental concentrations, physical and chemical forms, and physical dimensions—can be used to link a radioactive material to individuals, locations, or processes,” says Kristo. Their article highlights a pair of cases in which the capture of highly enriched uranium specimens by law enforcement officials in two countries and the subsequent analysis of the material by scientists established a link between the cases. The team’s research also showed that while the samples may well have a similar origin, they were probably not created at the same time.
The International Atomic Energy Agency maintains the Incident and Trafficking Database (ITDB) to record incidents of nuclear and other radioactive material outside of regulatory control. According to the ITDB, between 1993 and 2013, 16 confirmed incidents involved the unauthorized possession of highly enriched uranium or plutonium. The authors note that because no single nuclear forensics signature exists to identify all unknown nuclear materials, information needs to be gathered through multiple analytical techniques.
Contact: Mike Kristo (925) 422-7714 (kristo2@llnl.gov).
Livermore researchers have measured the carbon-14 (14C) isotope produced by cosmic rays in the stratosphere and found its production rate is lower than most previous estimates. The team, led by Kristie Boering of the University of California at Berkeley, measured the 14C content of carbon dioxide collected by high-altitude balloon flights in 2003, 2004, and 2005, and estimated the contemporary production of 14C in the stratosphere from cosmic rays. The research appears in the February 29, 2016, issue of the journal Geophysical Research Letters.
Atmospheric testing of nuclear weapons in the 1950s and 1960s injected massive amounts of 14C into the stratosphere, which hid the natural production of the isotope. Since weapons-generated 14C has mostly dissipated from the atmosphere, the team’s measurements indicate that natural 14C production is lower than most previous estimates. Livermore scientist Philip Cameron-Smith, a co-author on the paper, says, “We confirmed our analysis by using IMPACT—an atmospheric chemistry-transport model—to simulate 14C on Livermore’s supercomputers.”
According to Cameron-Smith, “This work will improve our understanding of the carbon cycle on Earth, including how to distinguish the effects of natural processes from fossil-fuel burning and how quickly atmospheric carbon flows in and out of the biosphere, water, and soil.” The lead author of the paper was Lawrence Scholar Amadu Kanu, and additional authors include Livermore’s Tom Guilderson and Dan Bergmann as well as researchers from the University of California at Berkeley, the University of Miami, and the National Center for Atmospheric Research.
Contact: Philip Cameron-Smith (925) 423-6634 (cameronsmith1@llnl.gov).