The red planet Mars, located fourth from Earth’s sun, has two small moons: Phoebe and Deimos. It’s also not like Earth’s moons: small and irregularly shaped, astronomers have long believed that they are likely captured asteroids that were pulled into Mars’ orbit by the red planet’s gravity and then held there indefinitely as temporary satellites. This makes sense given Mars’ proximity to the asteroid belt.
However, a new report from Hope, the United Arab Emirates-sent into orbit around the red planet, offered the first highly detailed image of Deimos, and Hope’s data caused scientists to reevaluate that assumption.
Deimos may not have been a captured asteroid, but rather a chunk of Mars that broke away from the planet at some point in its history.
During the March 10 flyby of Deimos, the Hope mission team scanned the planet’s surface using instruments that detected light waves ranging from infrared to extreme ultraviolet, Nature reports. Using spectrometry, scientists were able to analyze the readings and learn about the type of elements on the planet’s surface. All of Hope’s instruments showed a flat spectrum, meaning that Deimos is composed of the same minerals seen on Mars — as opposed to the carbon-rich rocks found in asteroids. This suggests a completely different origin than theorized.
Spectrographic analyzes of this type are a common means of elucidating the composition, and thus the origin, of various bodies in the Solar System. The geological history of each body in the Solar System is unique—so much so that scientists have been able to establish beyond doubt that some of the small meteorites that hit Earth millions or billions of years ago originated on Mars. 175 such Martian meteorites have been discovered on Earth, including one that may hold evidence of past life on Mars.
The scientists involved in the study noted that the composition of Deimos did not resemble the carbon-rich nature of the asteroids that dominate the asteroid belt. “If there was carbon or organic matter, we would see spikes at specific wavelengths,” Hesa Al Matroushi, lead scientist on the Emirates Mars Mission (EMM), told Nature. Al Matroushi first reported the findings on April 24 at the European Geosciences Union meeting in Vienna.
Thus, using spectrometry, it became clear to scientists that Deimos was probably not a captured asteroid, but a piece of Mars that broke away from the planet at some point in its history. If indeed Deimos is composed of the same minerals found on Mars, it opens the door to a new hypothesis: that Deimos, and possibly its sister moon Phoebe, formed after a large celestial object collided with Mars, washing away part of the Martian surface. material in process. This is not an unprecedented theory, as a similarly catastrophic impact from a much larger celestial body was what created the Earth-Moon system more than 4 billion years ago.
Of course, as The New York Times reported, it’s not yet entirely clear how Deimos was formed from Mars. In other words, this theory claims that before Deimos was Deimos – as opposed to Deimos being an asteroid – that Deimos was originally part of Mars.
The Mars probe on Deimos is historic for another reason. Deimos is tidally locked with Mars, meaning that the same side of Deimos always faces the same side of Mars. This means that previous probes that visited Mars studied only one side of Deimos’ surface – up to Hope. Hope was launched in mid-2020 and reached Mars in early 2021. Hope was originally designed to study the Martian atmosphere; it completed that mission and still had extra fuel, so mission engineers decided to move the spacecraft to the region around Deimos so they could learn more about the moon.
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As mentioned, this is not the first probe to study Deimos. In 1976, NASA’s Viking 2 orbiter approached within 19 miles of Deimos’ surface, although its cameras and other equipment were much more primitive than Hope’s. Viking 2, like every spacecraft before Hope, was unable to receive information about the side of Deimos not facing the Martian surface. Although Hope did not hold the record for being the closest spacecraft to Deimos, it easily captures the most information.
The new data on Deimos comes at an exciting time for Mars research. Earlier this month, data from the InSight probe’s seismograph provided new data on what the Martian core looks like. Last year, the journal Nature Astronomy suggested that life could once have flourished in Martian regoliths (that is, the loose dust and rocks on top of Mars’ main bedrock layer). That paper suggested that if said life released methane gas, it might have altered the planet’s climate so much that it could no longer sustain it. (However, the life forms in question would have resembled Earth’s microbes.) And last year, scientists found water on nuclides, or Martian meteorites, that crashed into Earth about 11 million years ago, though whether or not the water originated on Mars is debated.
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