Lawrence Livermore National Laboratory



Theory for Crater Formation on Martian Moon

Physicists at Lawrence Livermore have demonstrated for the first time how an asteroid or comet impact could have created Stickney Crater on the Martian moon Phobos without obliterating the moon in the process. The dominant surface feature on Mars’s largest moon, Stickney Crater spans 9 kilometers, stretching nearly halfway across Phobos. However, understanding the massive crater’s formation has proven elusive until now.

“We have demonstrated, in a three-dimensional simulation, that the crater can be created without destroying the moon if the proper porosity and resolution are used,” says Megan Bruck Syal, a member of the Laboratory’s planetary defense team and lead author of research published in the October 24, 2016, edition of Geophysical Research Letters. The study showed that a range of possible solutions exists for the size and speed of the impactor, but Syal says one possible scenario is an object 250 meters across traveling close to 6 kilometers per second.

The research served as a benchmarking exercise for the team, which uses a Livermore-developed open-source code called Spheral to simulate various methods of deflecting potentially hazardous Earthbound asteroids. Bruck Syal points out, “Something as big and fast as what caused Stickney Crater would have a devastating effect on Earth. If NASA sees a potentially hazardous asteroid coming our way, it will be essential to make sure we are able to deflect it. We will only have one shot at it, and the consequences could not be higher. We do this type of benchmarking research to make sure our codes are right when they will be needed most.”
Contact: Megan Bruck Syal (925) 423-0435 (syal1@llnl.gov).

Measuring Radiation Dose from Cancer Treatment

Lawrence Livermore scientists have developed a new technique using gene-expression analysis to measure internal radiation dose in cancer patients receiving targeted radiation therapy. Although dosimeters can be used to measure radiation dose externally, more precise dosimeters to assess internal dose do not exist.

In a paper published in the August 24, 2016, edition of Radiation Research, the Lawrence Livermore team—with collaborators at Purdue University, the University of California (UC) at San Francisco, UC Davis, and Houston Methodist Research Institute—describes a technique to characterize internal exposure by using gene-expression assays to monitor changes at the molecular level. This sort of biological approach to measuring physical dosimetry is known as biodosimetry. The method was used to compare calculated internal dose with the modulation of selected RNA transcripts.

“This is a novel study, using whole blood collected from patients treated with a radiopharmaceutical, to characterize biomarkers that may be useful for better cancer treatment and biodosimetry,” says coauthor Matt Coleman, a Livermore biologist and adjunct professor at UC Davis. “Our data indicate that RNA transcripts, which have been previously identified as biomarkers of external exposures in whole blood and radiotherapy patients, also are good early indicators of internal exposure.” The technique also may be a valuable tool for first responders to triage individuals after a nuclear accident or for astronauts to monitor space radiation exposure while traveling to Mars.
Contact: Matt Coleman (925) 423-7687 (coleman16@llnl.gov).

Metamaterials Shrink When Heated

Livermore engineers, working with researchers from the University of Southern California, the Massachusetts Institute of Technology, Singapore University of Technology and Design, and the University of California at Los Angeles, have created three-dimensionally printed, lightweight materials exhibiting negative thermal expansion, that is, a tendency to shrink when heated. The materials are metamaterials—composites whose properties heavily rely upon their internal structure—and are described in a paper published in the October 21, 2016, edition of Physical Review Letters.

Researchers note the study may be the first experimental demonstration showing large tunability of negative thermal expansion in three Cartesian directions of microlattice structures. Printed from a polymer or polymer–copper composite that can flex inward, the microlattice structure contracts when exposed to heat over a range of tens to hundreds of degrees. Principal investigator Chris Spadaccini says, “Our metamaterials have thermomechanical properties not achievable in conventional bulk materials.”

The metamaterials consist of beams surrounded by void space. When heated, some beams expand more than the others, causing the connecting points between each unit cell to pull inward and making the overall mircrolattice contract. Thermal expansion also can be zero or positive, depending on how the geometry and topology of the structure are engineered. Possible applications for such metamaterials include securing parts that tend to move out of alignment under varying heat loads, such as microchips and high-precision optical mounts.
Contact: Chris Spadaccini (925) 423-3185 (spadaccini2@llnl.gov).