The Martian moon Deimos, with the Red Planet in the background, was captured in imagery by the UAE’s Hope orbiter March 10. Credit: Emirates Mars Mission / MBRSC
The United Arab Emirates’ Hope orbiter has seen the far side of the Martian moon Deimos up close for the first time, collecting compositional data suggesting it could have formed from material that broke off of Mars long ago, challenging a theory that the rarely-observed moon may have been an asteroid captured by the planet’s gravity.
The Hope probe, known as Al Amal in Arabic, flew about 60 miles (100 kilometers) from Deimos on March 10. The Emirati spacecraft’s three science instruments observed Deimos during the encounter, with the probe’s camera recording stunning views of the moon passing across the sunlit side of Mars far below.
The flyby with Deimos was first time a spacecraft has taken detailed images of the side of Deimos facing away from Mars. Deimos is tidally locked with the Mars, meaning the same side of the moon always faces the Red Planet. NASA’s Mars Reconnaissance Orbiter has pointed its high-resolution telescope toward Deimos before, but it flies much closer to Mars, meaning it only saw one side of the moon.
Deimos is the smaller of Mars’ two moons. Phobos orbits closer to Mars, and has been more often observed by spacecraft exploring the Red Planet.
The UAE’s Hope spacecraft orbits farther from Mars, regularly passing near the orbit of Deimos more than 14,000 miles (23,000 kilometers) from the planet’s surface. Last year, ground teams commanded the Hope spacecraft to adjust its orbit to set up a series of close encounters with Deimos, an irregular-shaped object about 7.7 miles (12.4 kilometers) across.
“We are unsure of the origins of both Phobos and Deimos,” said Hessa AlMatroushi, science lead for the Emirates Mars Mission at the Mohammed Bin Rashid Space Center in Dubai. “One long-standing theory is that they are captured asteroids, but there are unresolved questions about their composition. How exactly they came to be in their current orbits is also an active area of study, and so any new information we can gain on the two moons, especially the more rarely observed Deimos, has the potential to unlock new understanding of Mars’ satellites.”
Images from the spacecraft’s main camera showed the far side of Deimos to be unexpectedly smooth, scientists said. The flyby March 10 was the closest any spacecraft has been to Deimos since NASA’s Viking 2 orbiter in the 1970s.
Funded by the Emirati government, the Hope probe was built by a joint team of Emirati and U.S. engineers at the Laboratory for Atmospheric and Space Physics, or LASP, at the University of Colorado at Boulder. U.S. and Emirati scientists also developed the mission’s three instruments, with teams from the MBRSC in Dubai collaborating with researchers at LASP, Arizona State University and the University of California, Berkeley.
Along with its set of spectacular imagery, the Hope spacecraft recorded the first extreme and far ultraviolet observations and thermal imagery of Deimos. The joint U.S.-Emirati science team presented the initial results from the Deimos encounter Monday at a meeting of the European Geosciences Union.
“The new observations challenge the longstanding theory that Mars’ moons are captured asteroids and instead point to a planetary origin,” tweeted Sarah Al Amiri, the UAE’s minister of state for advanced technology, chairperson of the UAE Space Agency, and former lead scientist on the Emirates Mars Mission.
Artist’s illustration of the Hope spacecraft at Mars. Credit: MBRSC
The Hope probe’s EMIRS instrument, an infrared spectrometer, measured thermal energy coming from Deimos. The measurements suggest the surface of Deimos is “rough at small scales and blanketed in fine regolith material, similar to Photos and Earth’s moon,” officials from the Laboratory for Atmospheric and Space Physics wrote in a press release.
The data also show Phobos and Deimos are composed of dark volcanic rock similar to the composition of Mars itself.
“The findings to date suggest that both of Mars’ satellites may have formed from debris left over from an impact on Mars,” said Christopher Edwards, EMIRS instrument scientist from Northern Arizona University, in a press release. “These early findings are exciting and have big implications for understanding the formation of moons in our solar system. Differentiating between the captured asteroid and coalesced Mars debris hypotheses is something to which EMM is well positioned to make significant contributions.”
The Hope spacecraft’s EMUS instrument, which measured ultraviolet sunlight reflected off Deimos, found “no strong signatures” of carbon minerals of organic materials, according to Justin Deighan, deputy science lead for the mission at LASP.
“These findings suggest that Deimos may not be a D-type asteroid, the kind we’d expect if Mars’ gravity had captured an asteroid into orbit,” Deighan said in a statement. “Thanks to the orbiter … we expect to build a better understanding of the origins and evolution of both Phobos and Deimos and to advance our fundamental understanding of these two moons of Mars.”
The Hope spacecraft will make additional flybys of Deimos to collect additional data on the Martian moon, which could provide more insight into its origin.
Originally designed for Martian weather and climate observations, the Hope spacecraft launched in July 2020 on a Japanese H-2A rocket and arrived in orbit around Mars in February 2021, become the Arab world’s first interplanetary probe. The probe is about the size of a small car, with two solar array wings to produce electrical power.
The Emirates Mars Mission was supposed to last at least two years after entering orbit in 2021. Al Amiri announced Monday the Hope mission’s scientific observations would be extended at least another year until 2024.
“The remarkable performance of the Mars Hope probe has supported a whole range of new observations in addition to meeting our originally stated science mission goals,” Al Amiri said. “In the circumstances, Hope exceeding all expectations, we are extending the Emirates Mars Mission for a further year.”
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