Everything we thought we knew about the Martian moon Deimos could be wrong

Everything we thought we knew about the Martian moon Deimos could be wrong

The red planet Mars, fourth from Earth’s sun, has two small moons: Phobos and Deimos. Neither is Earth’s moon: small and irregularly shaped, astronomers have long believed that they were more likely captured asteroids, pulled into Mars’ orbit by the red planet’s gravity and held there indefinitely as makeshift moons become. That makes sense given Mars’ proximity to the asteroid belt.

But a new report from Hope, an orbiter sent by the United Arab Emirates around the red planet, offered the first highly detailed image of Deimos – and Hope’s data have prompted scientists to reevaluate that assumption.

Deimos was probably not a captured asteroid but a piece of Mars that broke off the planet at some point in its history.

During a Deimos flyby mission on March 10, the Hope mission team scanned the planet’s surface with instruments that Nature says detected light waves ranging from the infrared to the extreme ultraviolet. Using spectrometry, scientists were able to analyze the readings and learn about the types of elements on the planet’s surface. Instruments on board Hope all showed a flat spectrum in their readings, meaning Deimos is composed of the same minerals seen on Mars — as opposed to the carbon-rich rocks discovered in asteroids. This points to a very different origin than theorized.

These types of spectrographic analyzes are a common means of finding out the composition, and hence the origin, of various bodies in the solar system. The geological history of every body in the solar system is unique – so much so that scientists have been able to determine without a doubt that some small meteorites that impacted Earth millions or billions of years ago originated on Mars. 175 such Martian meteorites have been discovered on Earth, including one that may have contained evidence of past life on Mars.

Scientists involved in the study said the composition of Deimos does not resemble the carbon-rich nature of the asteroids that dominate the asteroid belt. “If there were carbon or organic matter, we would see spikes in certain wavelengths,” Hessa Al Matroushi, senior scientist for the Emirates Mars Mission (EMM), told Nature. Al Matroushi first reported these results on April 24 at the European Geosciences Union meeting in Vienna.

So, through spectrometry, scientists realized that Deimos was probably not a captured asteroid, but a piece of Mars that broke off the planet at some point in its history. If Deimos is indeed composed of the same minerals found on Mars, it opens the door to a new hypothesis: that Deimos and possibly its sister moon Phobos formed after a large celestial object collided with Mars and shed some of the Martian surface material in process. This is not an unprecedented theory, as a similarly cataclysmic impact from a much larger celestial body created the Earth-Moon system over 4 billion years ago.

Of course, as the New York Times reported, it’s not yet clear with certainty how Deimos formed from Mars. In other words, this theory holds that Deimos was originally part of Mars before Deimos was Deimos – as opposed to Deimos being an asteroid.

The Mars probe to Deimos is historic for another reason. Deimos is tidally connected to Mars, meaning that the same side of Deimos always faces the same side of Mars. This means that previous probes that visited Mars only studied one side of Deimos’ surface – up to Hope. Hope was launched in mid-2020 and reached Mars in early 2021. Originally, Hope was supposed to study the Martian atmosphere; It completed that mission and still had extra fuel, so mission engineers decided to take the spacecraft to the Deimos region so they could learn more about the moon.

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As mentioned, this isn’t the first probe to explore Deimos. In 1976, NASA’s Viking 2 orbiter came within 19 miles of the surface of Deimos, though its cameras and other equipment were much more primitive than Hope’s. Viking 2 was also – like every starship before Hope – unable to acquire information about the side of Deimos that does not face the Martian surface. Though Hope hasn’t set a record for being the starship that came closest to Deimos, it’s by far the one that’s captured the most information.

The new data on Deimos comes at an exciting time for Mars studies. Earlier this month, data from the InSight probe’s seismograph provided novel data on what the core of Mars looks like. Last year, an article in the journal Nature Astronomy suggested that life may have once thrived in Martian regoliths (ie the loose dust and rock on the main rock strata of Mars). This paper suggested that if said life emits methane gas, it may have altered the planet’s climate so much that it could no longer endure it. (The life forms in question would have resembled Earth microbes, however.) And last year, scientists found water on nightlites, or Martian meteors, that struck Earth about 11 million years ago, though there’s debate as to whether or not the water came from Mars.

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