Colorful thermal images help reveal the origins of a doomed Martian moon

Views Mars' largest moon Phobos captured by NASA's 2001 Mars Odyssey orbiter
Views Mars’ largest moon Phobos captured by NASA’s 2001 Mars Odyssey orbiter.  (Credit: NASA/JPL-Caltech/ASU/SSI).

NASA has released new images of the Martian moon Phobos that could shed light on the origin of the enigmatic satellite. Scientists are currently unsure whether the barren moon is an asteroid that was captured by the Red Planet’s gravitational pull, or if the world coalesced from debris cast out after a dramatic collision between Mars and another solar system object in the distant past.

Phobos, which boasts a radius of over 11 km (6.8 mi), is the largest Martian moon by a significant margin, however, it still pales in comparison to other solar system satellites, such as Earth’s Moon, or Saturnian Enceladus.

The troubled world is drawing ever closer to the Red Planet at a rate of six feet (1.8 m) per century, and is destined to end its life either by colliding with Mars in roughly 50 million years, or by being torn apart by its gravity. Whilst this may sound like an eternity to us, it is little more than the blink of an eye in astronomical terms. Should the latter scenario come to pass, the debris that once formed the moon would likely settle to form a ring around the fourth rock from the Sun.

The newly released images of Phobos were captured by NASA’s 2001 Mars Odyssey spacecraft, which has been collecting data and snapping images of the Martian system since its arrival in 2001. It also acts as a a vital communications relay between other robotic explorers braving the surface of Mars, and their handlers back on Earth.

Odyssey’s latest photo shoot happened while Phobos was in a “full moon” phase relative to the spacecraft. This means that, at the time that the data was captured, the Sun was positioned directly behind the orbiter, fully illuminating the Martian satellite.

“This new image is a kind of temperature bullseye – warmest in the middle and gradually cooler moving out,” says Jeffrey Plaut, Odyssey project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “Each Phobos observation is done from a slightly different angle or time of day, providing a new kind of data.”

While shots of the moon that are illuminated from the side are more useful in discerning Phobos’s surface texture and features, full-moon observations are invaluable for scientists trying to figure out what a celestial body is made of.

Different minerals and metals reflect and radiate different amounts of heat. Scientists can look at the thermal images obtained by Odyssey to gain a better understanding of abundances of certain materials on the moon, and to see how thoroughly they are mixed in with other minerals.

Annotated images of Phobos displaying temperature and date captured

On April 24, 2019, NASA scientists commanded the orbiter to use its Thermal Emission Imaging System (THEMIS), to take detailed surface temperature measurements of Phobos.

This information in turn could help reveal whether the moon is simply a large asteroid or is made from material cast off from the Red Planet itself. The data harvested by Odyssey is not enough to definitively confirm the origin of the moon on its own, but it is a step in the right direction.

Phobos is set to be visited by another robotic mission in the near future – JAXA’S Martian Moons eXploration (MMX) mission. Unlike Odyssey, MMX will have the capability to land on the moon, and retrieve a sample for return to Earth. The mission is currently slated for launch in 2024, with an eye to returning to Earth in 2029.

Looking even further to the future, scientists have even considered the prospect of putting human boots on the surface of the alien world as the prelude to an eventual crewed mission to Mars itself.

“By studying the surface features, we’re learning where the rockiest spots on Phobos are and where the fine, fluffy dust is,” comments Joshua Bandfield, THEMIS co-investigator and senior research scientist at the Space Sciences Institute in Boulder, Colorado. “Identifying landing hazards and understanding the space environment could help future missions to land on the surface.”

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