Những bức ảnh mới nhất từ tàu vũ trụ Hope cho thấy hai mặt trăng nhỏ của sao Hỏa có thể không bị các tiểu hành tinh bắt giữ như suy nghĩ trước đây. Nhưng nhiều câu hỏi vẫn còn.
Vào ngày 10 tháng 3 năm 2023, tàu vũ trụ Hope đã đi qua trong phạm vi 62 dặm (100 km) từ mặt trăng Deimos của sao Hỏa, chụp được 27 bức ảnh (bao gồm cả bức ảnh ở trên) trong suốt 25 phút bay ngang qua. Sứ mệnh sao Hỏa của Emirates
Stunning new views of Deimos, one of Mars’ two strange moons, hint at questions about how the martian moons formed in the first place — and why they are still in orbit around Mars today. These questions have perplexed scientists since the discovery of the martian moons Phobos and Deimos almost 150 years ago.
The latest photographs are from the United Arab Emirates’ Hope spacecraft, a robotic probe that has been orbiting the Red Planet since 2021. On March 10, the Hope obiter made its first of several proposed flybys of the smaller moon Deimos, which is only 7.7 miles (12.4 kilometers) wide. Following the flyby, Hope sent back photographs of Deimos’ farside, which has never been seen up-close before.
Hope got as close to Deimos as anyone (or anything) is likely going to get for a while. “This was approximately 100 kilometers [62 miles] up, and I don’t believe we will get that close again,” Hessa Al Matroushi, the science lead for the Emirates Mars Mission, tells Astronomy.
Emirates Mars Mission
During additional flybys of Deimos planned for later this year, “we’re going to get to around 200 kilometers [124 miles], and that’s still pretty good data,” she says. “That will help us understand the moon.”
Are Phobos and Deimos captured asteroids?
The mission to take the new photos of Deimos, with Mars looming large in the background, allowed the probe’s two spectrometers to record crucial data about the moon’s composition.
These initial readings are preliminary and will be refined in later flybys. But they suggest Deimos is made of rocky material similar to Mars itself, and not the carbon-rich rock that would be expected if Deimos was a captured asteroid, as scientists once suspected.
That supports theories that both Deimos and Phobos — Mars’ larger moon, which is nearly 17 miles (27 km) across at its widest point — formed in orbit when a large object, perhaps a dwarf planet, struck Mars in the distant past. If confirmed, that would put to rest long-standing theories that both Phobos and Deimos are asteroids that have been captured by Mars’ gravity.
But many questions remain, including whether Phobos has the same composition as Deimos. Both Martian moons are also small and irregularly shaped, which supports the idea they are captured asteroids; and both are optically very dark, unlike Mars itself, which suggests they may have a different origin than the Red Planet.
Understanding the origins of Phobos and Deimos
The spectrometer aboard Hope captured unprecedented spectral data of nearly the entire surface of Deimos, revealing surface temperature variations as well as clues about the small martian moon’s composition and physical properties.
Emirates Mars Mission
The two moons of Mars, Phobos and Deimos, were discovered in 1877 by the American astronomer Asaph Hall using the 26-inch refractor telescope at the U.S. Naval Observatory in Washington D.C.
Hall named the martian moons after the charioteers of the war god Ares — the Greek version of Mars. As described in Homer’s Iliad, Deimos personified the dread felt before a battle, and Phobos personified the panic felt during battle. (Some sources suggest Deimos and Phobos were actually the horses of Ares, possibly because he also had a horse named Phobos.)
The moons of Mars have been enigmas since their discovery. Phobos has a low orbit, about 3,700 miles (6,000 km) above the martian surface, and it zips across the martian sky in just four hours. But Deimos orbits much farther out, at a distance of some 14,500 miles (23,500 km), and it circles the Red Planet almost as fast as Mars rotates.
Both moons are tidally locked to Mars, so they always present the same face to the rusty world. Phobos and Deimos occasionally transit between Mars and the Sun, but neither is large enough to completely eclipse it. Both moons are roughly potato-shaped, not spherical like Earth’s Moon, which gives strength to the idea that they’re captured asteroids. But the idea they were originally part of the Red Planet has always been a possibility, says Abigail Fraeman, a planetary scientist at NASA’s Jet Propulsion Laboratory.
The impact theory suggests both Phobos and Deimos formed when an object the size of Ceres smashed into the martian protoplanet; and that Phobos may periodically break apart into a ring of dust, from which it reforms. The moons might also be remnants of a larger martian moon that broke up in the past; or they might have both formed from rings; or maybe they formed alongside Mars from the protoplanetary disk around the Sun. Scientists just don’t know for sure.
“This is one of the big, outstanding mysteries in planetary science,” Fraeman tells Astronomy. “However they formed, there are broad implications for our understanding of the solar system.”
MMX: A new mission to explore Mars’ moons
Fraeman is one of more than a dozen American scientists who will soon study Phobos and Deimos as part of the Martian Moons Exploration Mission (MMX), a robotic probe scheduled to launch in 2024 and arrive at the Red Planet a year later.
MMX is being led by the Japanese space agency JAXA, with participation by space agencies from several other nations. NASA has engaged the Applied Physics Laboratory at Johns Hopkins University to build a gamma-ray and neutron spectrometer called MEGANE for the probe. And last month, NASA announced 10 American scientists who will work on the MMX mission.
Kế hoạch là để tàu thăm dò MMX lần đầu tiên đến thăm cả Phobos và Deimos. Sau đó, nó sẽ cố gắng hạ cánh xuống Phobos, thu thập các mẫu từ bề mặt mặt trăng và đưa các mẫu đó trở lại Trái đất vào năm 2029. Các nhà khoa học Mỹ sẽ nằm trong số những người có cơ hội phân tích các mẫu.
Công việc riêng của Fraeman sẽ là điều tra thành phần của các mặt trăng trên sao Hỏa bằng cách sử dụng các phép đo được thực hiện bởi các thiết bị trên tàu thăm dò MMX. Các nhà khoa học khác sẽ nghiên cứu động lực quỹ đạo của các mặt trăng để tìm kiếm manh mối về cả thành phần và cấu trúc của chúng. Và vẫn còn nhiều nhà nghiên cứu sẽ nghiên cứu bề mặt của các mặt trăng — mà các bức ảnh cho thấy có nhiều miệng núi lửa, nhưng vẫn có vẻ mịn hơn dự kiến — cũng như các đặc tính vật lý nhiệt của các mặt trăng, điều này có thể giúp giải thích tại sao Phobos và Deimos trông giống như vậy.
Fraeman nói: “Không có ý tưởng nào giải thích được tất cả những quan sát mà chúng tôi đã thực hiện. “Vì vậy, có điều gì đó mà chúng tôi chưa hiểu rõ, về cách kết hợp các quan sát lại với nhau, hoặc một điều khác mà chúng tôi chưa nghĩ đến… các mặt trăng của sao Hỏa rất thú vị.”
