Mars' moon Phobos may hold evidence of the ancient Martian atmosphere

New research has been published that shows Phobos, one of the moons orbiting Mars, circles the planet through a stream of charged atoms and molecules from the Martian atmosphere. NASA says many of these charged particles, or ions, are of oxygen, carbon, nitrogen, and argon. They have been escaping from the Martian atmosphere for billions of years as Mars shed its atmosphere.Scientists believe that some ions have smashed into the surface of Phobos and could be preserved in its uppermost layer. NASA suggests that if soil was gathered from Phobos and analyzed in labs on Earth, scientists could learn essential information about the evolution of the Martian atmosphere. Scientists know that Mars once had an atmosphere that was thick enough to support liquid water on its surface, but today the Red Planet's atmosphere is less than one percent of the density of the atmosphere on Earth.

Scientists have known for a long time that the Martian atmosphere escaped to space, and with the new research, it now knows that some of that atmosphere ended up on Phobos. Mars has two moons that orbit very close to the planet, including Phobos and Deimos. Phobos orbits about 60 times closer to Mars than the moon orbits Earth.

Phobos is an oddly shaped moon marred by craters 100 times smaller in diameter than the Earth's moon. One of the mysteries about Mars is where its two closely orbiting moons came from. Some suggest that both Phobos and Deimos might be asteroids captured by the gravity of Mars.

Others believe they are natural satellites created from the debris resulting from Mars colliding with something early in its formation, similar to how scientists believe our moon was formed. Phobos is tidally locked with Mars, with the planet only seeing one side meaning the rocks on the near side of Phobos have been pelted with atoms and molecules from the Martian atmosphere for millennia.