NASA’s Mars Odyssey orbiter is Mars’ longest-living visitor. For 16 years the orbiter has circled the red planet with its Thermal Emission Imaging System (THEMIS) almost always focused straight down. But that changed recently. On September 29, the orbiter swung around and captured this image of the Martian moon Phobos.

Phobos in infrared

You’re looking at the first infrared imagery ever captured of Phobos. But this wasn’t the first time the orbiter’s team looked away from Mars. Back in 2014, the mission’s team rotated the spacecraft to observe Comet Siding Spring during its close encounter in 2014. The team used what they learned from the comet observation to get a look at Phobos.

What’s so special about this infrared image? First, let’s take a closer look.

Phobos surface tempeartures

The temperature scale is in Kelvin and ranges from 130 K (minus 226 degrees Fahrenheit) in the purple color to 270 K (26 degrees Fahrenheit) in the red color. Examining how the moon’s surface warms and cools throughout the day can tell us what the surface is made up. Is it rocky or dusty?

THEMIS Deputy Principal Investigator Victoria Hamilton explains. “As you go from predawn area to morning area you get to watch the heating behavior. If it heats up very quickly, it’s likely not very rocky but dusty instead.”

Knowing the stuff Phobos is made of gives us clues about the small moon’s origin. Information gleaned from this infrared image, and future THEMIS observations may help answer this origin question. Is Phobos a captured asteroid? Or, a 14-mile across chunk of Mars that was knocked into the sky after a much larger impact?

The image above was a test. Odyssey’s team wanted to see if they could safely capture an image of the Martian moon without anything going wrong with the spacecraft or its primary mission. Now, the team is planning a series of observations to look at Phobos and Mars’ smaller moon Deimos.

Here’s Mars Odyssey Project Scientist Jeffery Plaut on why Phobos is a particularly interesting target for future observations. “There is heightened interest in Phobos because of the possibility that future astronauts could perhaps use it as an outpost.”

Any future outpost would not last forever, though. That’s because Phobos is slowly being pulled apart by Mars’ gravity. Ok, slowly is an understatement. NASA estimates it’ll take 30 to 50 million years to completely break up. I’m sure we’ll have already mined it or something by then.

Image credits: NASA

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