How does a close flyby of a comet affect a planet? This is something we now have an answer for after comet Siding Spring flew by Mars last month.
Instruments from two NASA and one European spacecraft studied Mars before, during and after the comet flyby on October 19 and are now reporting back data on how the comet affected Mars' atmosphere.
Comet Siding Spring comes from the Oort Cloud, that part of space at the farthest edge of the solar system. Scientists believe that the icy objects that make up the Oort Cloud are remnants of the solar system's birth. It's theorized that the objects in the Oort cloud originally formed near the sun, but gravitational effects of the larger planets flung them to their current position.
The comet flew by Mars at a close distance, less than half the distance between Earth and our moon, so its effects on the planet were noticeable.
All three spacecrafts picked up details that showed that Siding Spring left behind debris that supercharged Mars' upper atmosphere with ions. This probably resulted in a spectacular meteor shower in Mars' skies. However, most impressively, this is the first time scientists have seen this sort of effect on any planet, including Earth.
"This historic event allowed us to observe the details of this fast-moving Oort Cloud comet in a way never before possible using our existing Mars missions," says Jim Green, director of NASA's Planetary Science Division. "Observing the effects on Mars of the comet's dust slamming into the upper atmosphere makes me very happy that we decided to put our spacecraft on the other side of Mars at the peak of the dust tail passage and out of harm's way."
NASA's Mars Atmosphere and Volatile Evolution (MAVEN) also studied the chemical composition of a sample of the comet's dust. The results showed that the dust consisted of eight different kinds of metal ions, including sodium, magnesium and iron. This is the first time we've ever directly measured the composition of dust from an Oort cloud comet.
NASA's Mars Reconnaissance Orbiter (MRO) imaged the comet, discovering that its nucleus is smaller than expected. The images confirmed previous Hubble Space Telescope findings, though, that Siding Spring's nucleus rotates every eight hours.
The European Space Agency's Mars Express spacecraft confirmed the presence of additional ions in Mars' upper atmosphere, its instruments picking up a huge change after the comet passed by. This was probably caused by the comet's particles burning up in Mars' atmosphere.
[Photo Credit: NASA/JPL]
