The planet Mars has two moons, Phobos and Deimos. Many researchers are fascinated with trying to know how and where Mars's moons came from and this resulted to two main theories about Mars's moons: Asteroid Capture Theory and Large Impact Theory. Explorations have been done on the moons of Mars but more information is needed. Yet, researchers believe that an in-situ exploration (sending a probe to land) is needed to grab some soil and rocks for further study.

Mars's Moons

Mars's moons, Phobos and Deimos, share many characteristics with two types of asteroids common in the belt: C- and D-type asteroids. Moreover, by the looks of Phobos and Deimos, we can easily assume that they are both captured objects from the Asteroid Belt, that maybe there was a collision that sent them off into the direction where Mars's gravitational pull would confine them. Many questions still lie with whether they are captured asteroid and their circular orbits over the history of the solar system.

Asteroid Capture Theory

The Large Impact Theory brings upon the idea that Mars has suffered a large collision. Just like how the Earth's moon is the result of an immpact between our infant planet and a planetisimal named Theia. With this theory, astronomers suggest that the composition of Phobos and Deimos may have originated from Mars itself, so therefore this must have happened, but we can only truly say that up until today this is only a theory.

Large Impact Theory

<figure><img src="https://www.thoughtco.com/thmb/39J90v01kmOAOt3Iv0iCmddfkaM=/768x0/filters:no_upscale():max_bytes(150000):strip_icc():format(webp)/gaspra_deimos_phobos-58b84b1d3df78c060e692756.jpg" srcset="https://www.thoughtco.com/thmb/3c16Fu_4KjukmJ8248TjAeS5ONg=/300x0/filters:no_upscale():max_bytes(150000):strip_icc():format(webp)/gaspra_deimos_phobos-58b84b1d3df78c060e692756.jpg 300w, https://www.thoughtco.com/thmb/poiLPXlvD_hVD-AklYuIg9ze0ZQ=/417x0/filters:no_upscale():max_bytes(150000):strip_icc():format(webp)/gaspra_deimos_phobos-58b84b1d3df78c060e692756.jpg 417w, https://www.thoughtco.com/thmb/9dVdOa-r5YbHktPRjC3iH32Upz0=/534x0/filters:no_upscale():max_bytes(150000):strip_icc():format(webp)/gaspra_deimos_phobos-58b84b1d3df78c060e692756.jpg 534w, https://www.thoughtco.com/thmb/39J90v01kmOAOt3Iv0iCmddfkaM=/768x0/filters:no_upscale():max_bytes(150000):strip_icc():format(webp)/gaspra_deimos_phobos-58b84b1d3df78c060e692756.jpg 768w" alt="Asteroids Pictures Gallery - Gaspra, Deimos and Phobos" width="721" height="551"><figcaption dir="auto">NASA, Jet Propulsion Laboratory</figcaption></figure><div>
Updated January 10, 2020
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<a href="https://www.thoughtco.com/things-you-should-know-about-mars-3073200" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1" dir="ltr">Mars</a> has always fascinated humans. The Red Planet holds many mysteries, which our landers and probes are helping scientists solve. Among them is the question of where the two Martian moons came from and how they got there. Phobos and Deimos look more like asteroids than moons, and that has caused many planetary scientists to look for their origin somewhere else in the solar system. Others maintain that those moons may have formed when Mars did or are the result of some catastrophic event early in the history of the solar system. Chances are good that when the first missions land on Phobos, rock samples will tell a more definitive story about these mysterious companion moons.
<h2 dir="ltr"> Asteroid Capture Theory </h2>
One clue about the origins of Phobos and Deimos lies in their makeup. Both have many characteristics in common with two types of asteroids common in the belt: C- and D-type asteroids. These are carbonaceous (meaning they are rich in the element carbon, which bonds easily with other elements). Also, judging by the look of Phobos, it's easy to assume that it and its sister moon Deimos&nbsp;are both&nbsp;captured objects from the <a href="https://www.thoughtco.com/asteroids-and-the-asteroid-belt-3073446" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1" dir="ltr">Asteroid Belt</a>. This is not an unlikely scenario.&nbsp;After all asteroids break free from the belt all the time. This happens as a result of collisions, gravitational perturbations, and other random interactions that affect an asteroid's orbit and send it off in a new direction.&nbsp;Then, should one of them stray too close to a planet, like Mars, the planet's gravitational pull could confine the interloper to a new orbit.&nbsp;

If these ARE captured asteroids, then there are many questions about how they could have settled into such circular orbits over the history of the solar system. It's possible that Phobos and Deimos could have been a binary pair, bound together by gravity when they were captured. Over time, they would have separated into their current orbits.&nbsp;

It's possible that early Mars was surrounded by many of these types of asteroids. They could have been the result of a collision between Mars and another solar system body in the early history of the planets. If this did happen, it could explain why Phobos's composition is closer to the makeup of Mars's surface than that of an asteroid from space.&nbsp;
<h2 dir="ltr"> Large Impact Theory </h2>
That brings up the idea that Mars suffered a large collision very early in its history. This is similar to the idea that Earth's <a href="https://www.thoughtco.com/all-about-the-moon-3073237" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1" dir="ltr">Moon</a>&nbsp;is the result of an impact between our infant planet and a planetesimal named Theia.&nbsp;In both cases, such an impact caused a large amount of mass to be <a href="https://www.thoughtco.com/astronomy-4133558" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="2" dir="ltr">ejected into outer space</a>. Both impacts would have sent a&nbsp;hot, plasma-like material into a concentric orbit about the&nbsp;infant planets. For Earth, the ring of&nbsp;molten rock eventually gathered together and formed the Moon.&nbsp;

Despite the look of Phobos and Deimos, some astronomers have suggested that perhaps these tiny orbs formed in a similar way around Mars. Perhaps the best evidence for an asteroidal origin is the presence of a mineral called phyllosilicates on the surface of Phobos. It's common on the surface of Mars, an indication that Phobos formed from the Martian substrate.

However, composition argument isn't the only indication that Phobos and Deimos may have originated from Mars itself. There is also the question of their orbits. They're nearly circular. They are also very near to Mars' equator. Captured asteroids likely wouldn't settle into such precise orbits, but material splashed out during an impact and then accreted over time could explain the orbits of the <a href="https://www.liveabout.com/mars-in-birth-chart-206496" data-component="link" data-source="inlineLink" data-type="externalLink" data-ordinal="1" rel="nofollow noopener" dir="ltr">two moons</a>.
<h2 dir="ltr"> Exploration of Phobos and Deimos </h2>
During the past decades of Mars exploration, various spacecraft have looked at both moons in some detail. But, more information is needed. The best way to get it is to do an in-situ exploration.&nbsp;That means "send a probe to land on one or both of these moons". To do it right, planetary scientists would send a lander to grab some soil and rocks and return it to Earth for study). Alternatively, when humans start to explore Mars in person, part of a mission could be diverted to land people on the moons to do a more nuanced geological study. Either one would satisfy people's urge to know just how those moons came to be where they are in orbit around Mars.&nbsp;
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Mars has two moons: Phobos and Deimos. Planetary scientists debate about whether they formed in an ancient collision, or could be captured asteroids.

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<a data-component="link" data-ordinal="1" data-source="inlineLink" data-type="internalLink" dir="ltr" href="https://www.thoughtco.com/things-you-should-know-about-mars-3073200">Mars </a>has always fascinated humans. The Red Planet holds many mysteries, which our landers and probes are helping scientists solve. Among them is the question of where the two Martian moons came from and how they got there. Phobos and Deimos look more like asteroids than moons, and that has caused many planetary scientists to look for their origin somewhere else in the solar system. Others maintain that those moons may have formed when Mars did or are the result of some catastrophic event early in the history of the solar system. Chances are good that when the first missions land on Phobos, rock samples will tell a more definitive story about these mysterious companion moons.

One clue about the origins of Phobos and Deimos lies in their makeup. Both have many characteristics in common with two types of asteroids common in the belt: C- and D-type asteroids. These are carbonaceous (meaning they are rich in the element carbon, which bonds easily with other elements). Also, judging by the look of Phobos, it's easy to assume that it and its sister moon Deimos are both captured objects from the <a data-component="link" data-ordinal="1" data-source="inlineLink" data-type="internalLink" dir="ltr" href="https://www.thoughtco.com/asteroids-and-the-asteroid-belt-3073446">Asteroid Belt </a>. This is not an unlikely scenario. After all asteroids break free from the belt all the time. This happens as a result of collisions, gravitational perturbations, and other random interactions that affect an asteroid's orbit and send it off in a new direction. Then, should one of them stray too close to a planet, like Mars, the planet's gravitational pull could confine the interloper to a new orbit.

If these ARE captured asteroids, then there are many questions about how they could have settled into such circular orbits over the history of the solar system. It's possible that Phobos and Deimos could have been a binary pair, bound together by gravity when they were captured. Over time, they would have separated into their current orbits.

It's possible that early Mars was surrounded by many of these types of asteroids. They could have been the result of a collision between Mars and another solar system body in the early history of the planets. If this did happen, it could explain why Phobos's composition is closer to the makeup of Mars's surface than that of an asteroid from space.

That brings up the idea that Mars suffered a large collision very early in its history. This is similar to the idea that Earth's <a data-component="link" data-ordinal="1" data-source="inlineLink" data-type="internalLink" dir="ltr" href="https://www.thoughtco.com/all-about-the-moon-3073237">Moon </a> is the result of an impact between our infant planet and a planetesimal named Theia. In both cases, such an impact caused a large amount of mass to be <a data-component="link" data-ordinal="2" data-source="inlineLink" data-type="internalLink" dir="ltr" href="https://www.thoughtco.com/astronomy-4133558">ejected into outer space </a>. Both impacts would have sent a hot, plasma-like material into a concentric orbit about the infant planets. For Earth, the ring of molten rock eventually gathered together and formed the Moon.

Despite the look of Phobos and Deimos, some astronomers have suggested that perhaps these tiny orbs formed in a similar way around Mars. Perhaps the best evidence for an asteroidal origin is the presence of a mineral called phyllosilicates on the surface of Phobos. It's common on the surface of Mars, an indication that Phobos formed from the Martian substrate.

However, composition argument isn't the only indication that Phobos and Deimos may have originated from Mars itself. There is also the question of their orbits. They're nearly circular. They are also very near to Mars' equator. Captured asteroids likely wouldn't settle into such precise orbits, but material splashed out during an impact and then accreted over time could explain the orbits of the <a data-component="link" data-ordinal="1" data-source="inlineLink" data-type="externalLink" dir="ltr" href="https://www.liveabout.com/mars-in-birth-chart-206496" rel="nofollow noopener">two moons </a>.

During the past decades of Mars exploration, various spacecraft have looked at both moons in some detail. But, more information is needed. The best way to get it is to do an in-situ exploration. That means "send a probe to land on one or both of these moons". To do it right, planetary scientists would send a lander to grab some soil and rocks and return it to Earth for study). Alternatively, when humans start to explore Mars in person, part of a mission could be diverted to land people on the moons to do a more nuanced geological study. Either one would satisfy people's urge to know just how those moons came to be where they are in orbit around Mars.

How Did Mars Get its Moons?

Mars's Moons

Asteroid Capture Theory

Large Impact Theory

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