spaceSpace and Physics

How Phobos Got Its Giant Crater


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockOct 14 2016, 10:26 UTC

The Stickney Crater as seen by the Viking Probe. Viking Project/JPL/NASA

Phobos, the largest of the two moons of Mars, is an incredible and mysterious object. But thanks to a very sophisticated simulation, we might have uncovered a few of its secrets.

Researchers from the Planetary Defence team at Lawrence Livermore National Laboratory (LLNL) in California looked at how the moon's largest crater, the Stickney crater, formed. The crater is 9 kilometers (5.6 miles) across, almost half the size of Phobos, which is only 22 kilometers (13.6 miles) across.


Previous attempts at simulating the impact couldn’t really explain this impressive feature, but the new approach – published in Geophysical Research Letters – suggests one likely scenario is an impact between the Martian moon and a 250-meter-wide (820 feet) object moving at 6 kilometers (3.7 miles) per second.

"We've demonstrated that you can create this crater without destroying the moon if you use the proper porosity and resolution in a 3D simulation," said lead author Megan Bruck Syal in a statement.

"There aren't many places with the computational resources to accomplish the resolution study we conducted."


The study also looked at the grooved terrain of the moon. It was previously suggested that they were cracks formed after the impact, but the simulation doesn’t support that hypothesis. According to the researchers, the grooves could have formed by slow-rolling boulders after the impact.

Another alternative hypothesis suggests that the grooves are due to Mars’ gravity slowly tearing Phobos apart. The moon gets 2 meters (6 feet) closer every 100 years, and it will either collide with Mars or turn into a ring system within 30 to 50 million years.

The simulation is interesting in its own right, but it is part of something bigger. The computer code was also used by the researchers to simulate the most effective way to deflect asteroids.


"Something as big and fast as what caused the Stickney crater would have a devastating effect on Earth," Syal said.

"If NASA sees a potentially hazardous asteroid coming our way, it will be essential to make sure we're able to deflect it. We'll only have one shot at it, and the consequences couldn't be higher."

This type of research is crucial to improving the code, although let’s hope we will never have to use it.

spaceSpace and Physics
  • tag
  • Mars,

  • Phobos,

  • Stickney Crater