Martian moon could come from clashes with the native planet

Strange shapes and colors of the tiny Martian satellites Phobos and Deimos led scientists to think about their origin. The dark faces of these moons resemble primitive asteroids of the outer Solar system, allowing to assume that these asteroids just landed in the gravity network of Mars. But the shape and angles of the satellite orbits do not support this capture scenario. A fresh look at the data 20 years ago missions Mars Global Surveyour supports the idea that the satellites of Mars were formed after a large impact shook the planet and was thrown into the orbit of many stones.

This follows from a study published in the Journal of Geophysical Research: Planets American geophysical Union. According to the authors of the study, this data set contained important clues about what is Phobos, and it can be more similar in composition to the crust of Mars than it seems.

How did the satellites of Mars?

“The most interesting thing for me is to extract ideas from the old datasets, which were used not enough,” says Tim Glotch, a geologist from stony brook University in new York, the lead author of a new study.

Mark freis, a planetary scientist and curator for cosmic dust in Space center. Johnson at NASA, was not involved in the new study, says that the failure to explain the origin of two moons of a neighboring planet stems from poor understanding by scientists of the processes of lunar formation. Understanding this will allow to interpret the appearance of the other moons in the Solar system and beyond. The new study does not clarify the mystery, but it is a step in the right direction, he says.

“The question of the origin of Phobos and Deimos — funny mystery, because we have two competing hypotheses that are mutually exclusive,” says freis. “I would not have considered this as a final solution, but it will help to move the discussion forward.”

Strange objects

The debate about the origin of the satellites of Mars was divided scholars into camps for many years, from the earliest days of planetary science. In visible light the Phobos and Deimos look so much darker than the Mars, which lends weight to the hypothesis of capture.

Scientists are studying the mineral composition of objects, breaking the light they reflect, into its component colors using the spectrophotometer, and creating representative samples. Comparing the spectral samples of planetary surfaces with a library of spectra of known materials, they can determine the composition of distant objects. Most studies of the composition of asteroids studied spectra in visible light and near infrared light outside the visible spectrum humans.

In the visible and near-infrared light of Phobos and asteroids of a class D look like that their spectra almost without features, so they are dark. Asteroids D-class is almost as black as coal, because, like coal, contain carbon. This dark aspect of Phobos led to the hypothesis that this moon is a captured asteroid that flew too close to Mars.

But scientists studying the orbit Marcovich moons, say they could not be captured. Perhaps the moon was formed simultaneously with Mars or happened in a massive attack on the planet during her millennia of formation.

“If you ask people who understand orbital dynamics and understand why some bodies rotate so and not otherwise, they say that given the inclination and the details of the orbit of Phobos, with its capture almost impossible. Spectroscopy say one thing and dynamite else,” said Glatch.

Heat signatures

Glotch decided to look at the problem in a different light: in the mid-infrared, which is in the same range as the temperature of the body. He looked at the heat signatures of Phobos, made in 1998, a tool that he calls the cool thermometer on Board Mars Global Surveyor. This robotic machine has spent most of his life, staring at Mars, but also glanced at Phobos, passing near the moon.

Thermal energy, like visible light, can be divided into a spectrum of “colors”. Even objects that look black in visible light, can glow in a characteristic infrared spectrum. Although the Phobos is very cold, its heat range has a distinctive signature.

Glotch and his students compared the mid-infrared spectrum of Phobos recorded by the Mars Global Surveyer, with samples of meteorites that fell to Earth near lake Tagish in British Columbia. These meteorites, according to some scholars, were the fragments of the asteroid D-class. In the laboratory the samples were placed in a environment similar to the one in which is the Phobos — cold vacuum — heating them on the top and bottom to simulate abrupt changes of temperature in Sunny and shaded sides of the object in the vacuum of space.

“We found that in these wavelength ranges meteorite Tagilskogo lake is not similar to Phobos, and a whole lot more likely Phobos corresponds to basalt, a common volcanic rock that makes up a large part of the Martian crust,” says Glatch. “It made us believe that Phobos may be a legacy of the collision in the early history of Mars.”

The baked crust of the planet

The new study does not undertake to say that Phobos made entirely of the material of Mars, but the new results correlate with the fact that the moon contains some of the planet’s crust, possibly due to the merging of the debris from the planet with the remains of the impact facility.

Freis, who did not participate in the study, says that the meteorite Tagilskogo lake kind of unusual and maybe not the best example of an asteroid with a D-class to compare with Phobos. Freis added that the new study does not give a convincing answer, because Phobos is exposed to space weathering, which affects the reflected spectrum, and it is difficult to reproduce in the laboratory.

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