Shocking Results

Sarah Stewart

"Nobody as a little child thinks, I'm going to grow up and have a lab full of cannons."

As a kid, planetary scientist Sarah Stewart spent her free time reading science fiction novels. Now, much like her favorite sci-fi authors, she is a world-builder — pursuing research that helps us better understand our own planet.

Planets are created from collisions between space rocks. Stewart uses massive guns to mimic these impacts. Her Shock Compression Laboratory at UC Davis contains two cannons that launch small projectiles at speeds more than 6,000 mph. The projectiles are about the size of cardboard toilet paper tubes. When they hit their target — usually small disks of rock or ice — the powerful crunch reproduces the extreme temperatures and pressures reached during planetary collisions.


Stewart and her students use impact experiments to build realistic computer simulations of growing planets. Their models help explain how planets form in our solar system and elsewhere in the universe.

Recently, Stewart and graduate student Simon Lock came up with a new theory of the moon’s origins. They propose the moon formed from the Earth when the Earth was vaporized by a planet-planet collision.

"Picture the Earth. Then imagine heating it up so much it has a vapor atmosphere. Now it is spinning so quickly that the whole thing cannot rotate all together and instead spreads out to form a disk around the original planet. When you do that, you’ve made a new planetary object that we call a synestia."

About Sarah Stewart

Stewart is a professor in the Department of Earth and Planetary Sciences and was recently honored with a MacArthur "Genius Grant." She was born in Taiwan, where her father was stationed with the U.S. Air Force. She earned a bachelor's degree from Harvard and a doctorate from Caltech. Stewart was a professor at Harvard from 2003 to 2014 before joining UC Davis.