Beautiful image of Deimos captured by the Hope Mission
On 19th July 2020, the United Arab Emirates’ Hope mission to Mars launched from Japan’s Tanegashima Space Center. Tasked with studying the global Martian atmosphere, Hope has a high orbit above the red planet that has allowed the spacecraft to capture a rare view of the far side of Mars’s outer moon, Deimos. The results were presented at the European Geosciences Union Meeting (EGU) in April this year.
In addition to the beautiful visuals of this tiny moon, Hope’s onboard instruments observed the wavelengths of light reflected from Deimos’s surface from infrared to the extreme ultraviolet. Measuring the intensity at different wavelengths gives a “spectrum” for Deimos over the observed range. This can provide clues about the moon’s composition, since different minerals absorb particular wavelengths that are then absent in the spectrum.
However, Hope saw a relatively flat spectrum, with no strong absorption at any wavelength. This is similar to what is seen when looking at the basaltic rocks that form the surface of Mars, and might suggest that Deimos formed from fragments ejected from Mars during a giant impact. The “impact scenario” is one of two main theories of the formation of the Martian moons, the other being that they are captured asteroids.
Watch: How did the moons of Mars form?
But while a flat spectrum may resemble observations of Mars, this is not sufficient to determine if the composition of Mars and its moons truly match. Kuramoto Kiyoshi, Principal Investigator of the MMX Science Working Team, notes that more observations are needed to identify the materials of Deimos.
From the new ultraviolet and thermal infrared spectra of Deimos taken by the Hope spacecraft, the Hope team speculates that this second Martian moon may have a basaltic composition: if this is true, it is more likely that Deimos was formed from debris ejected from Mars by an ancient huge asteroid impact. We have looked at the data presented at the EGU meeting and, as the Hope team notes, the spectral shape is not conclusively conducive of a basaltic composition, leaving open the possibility that Deimos has a carbonaceous meteorite composition. Further observations and spectral matching with various materials are important. Hope observations are very valuable because close observations of Deimos have been done so scarcely. Since the MMX spectrometers have different wavelength bands than those onboard Hope, combining those data will provide more definitive information on what material Deimos is made from.
Kuromoto Kiyoshi, MMX Science Working Team PI
Watch: What is a D-type asteroid?
MMX is equipped with a suite of scientific instruments designed to observe the Martian moons with a wide variety of techniques to decipher their composition. Kameda Shingo is the Principal Investigator for the two cameras onboard the MMX spacecraft, TENGOO and OROCHI. The cameras are sensitive to a different wavelength range than the instruments onboard Hope and will offer one of the first new views of the Martian moons.
The observations by Hope of Deimos add new information about the mysterious origins of the Martian moons. While Hope captured these observations in the extreme ultraviolet and thermal infrared, MMX will observe in the near ultraviolet, visible light, and near-infrared to give us complementary information. We will also get more detailed information on the moon topology. By adding together all these sources of knowledge, we hope to uncover the origin of the Martian moons.
Kameda Shingo, TENGOO/OROCHI PI
Also onboard the MMX spacecraft is the MMX InfraRed Spectrometer (MIRS) being developed at LESIA-Paris Observatory in partnerships with the French Space Agency, CNES. As the instrument name suggests, MIRS is tasked with analysing the light reflected from the Martian moons at near-infrared wavelengths. This range is particularly important for identifying materials that could pinpoint out the moons’ origins and compare both moon surfaces, explains MIRS Principal Investigator Antonella Barucci.
The images obtained by Hope mission are very exciting. The obtained spectra in the range far-infrared and those in the far-extreme UV will be complementary to those that will be obtained by MIRS. The spectral coverage of the MIRS imaging spectrometer from 0.9 to 3.6 µm will optimise the study of the Phobos and Deimos surface composition. In this range we have the best signatures to identify the presence of silicates, water and organics necessary to identify the origin of the two Martian moons. For Phobos, MIRS will allow us to obtain compositional maps, performed at different altitudes with compositional characterisation up to a few meters to select the most interesting sampling sites.
Antonella Barucci, MIRS PI
The MIRS unprecedented spatial resolution on Phobos will enable scientists to investigate the local compositional heterogeneity and detect presence of exogenous material. MIRS will also allow us to characterise the Deimos surface composition, which will be compared with that of Phobos.
The MIRS instrument together with the MMX payload and sample analysis will be able to give an answer to the origin of the Martian moons and be able to elucidate the process of the evolution of the Mars environment.
Another scientific instrument flying with MMX is MEGANE, the “Mars-moon Exploration with GAmma rays and NEutrons” which is being developed at the Johns Hopkins University Applied Physics Laboratory in partnership with the US Space Agency, NASA. Rather than reflected light, MEGANE will detect gamma rays and neutrons that are released from atoms on the surface of Phobos, identifying the moons’ chemical elements.
MEGANE Principal Investigator David Lawrence explains that detecting gamma rays and neutrons is a tough task, and the MMX spacecraft is expected to only pass close enough to Phobos for MEGANE’s measurements. However, this will allow the chemical composition of the Mars’s inner moon to be measured.
Hope has captured fantastic visible details of Deimos’s surface that have never before been seen — those photos are great!
David Lawrence, MEGANE PI
As far as MEGANE data go, it should provide a good down payment to help us understand the formation hypothesis. The reason is that one of the key pieces of information needed is the elemental composition of the two moons.
Our primary measurement will be to measure the elemental composition of Phobos. It is unlikely MEGANE will get composition information from Deimos, as the current mission plan does not have the spacecraft fly close enough to Deimos’s surface for MEGANE to collect robust data. A spacecraft altitude of roughly one Deimos radius (approximately 6km) is needed to even have a chance of measuring neutrons or gamma rays from Deimos
In addition to a thorough examination of the Martian moons from orbit, MMX will also land on Phobos and collect samples of material from the moon to bring back to Earth. At laboratories on the ground, an even more detailed analysis can begin to explore the moons’ history and that of the evolution of the Martian environment.
Hope has provided a tantalising glimpse of the amazing new vistas that await MMX when the spacecraft leaves Earth to explore the Martian moons. With a plethora of data that will be collected on the moons’ properties, we may finally be able to reveal their secrets.
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