What Are the Origin of Mars’ Moons?

It’s always interesting to hypothesize about where various moons come from. In some cases, the creation of a moon is easy to determine, but with the origin of Mars’ moons, that is not the case. With some planets, it’s pretty obvious that a moon was formed due to an impact, such is believed to be the case with Earth’s moon, but what about its next-door neighbor, Mars? The origin of Mars’ moons don’t appear to come from this type of source, and there’s one main reason that astronomers theorize this: the composition of the moons.

origin of mars' moons
Photo Credit: Justin Cowart aquired by India’s Mars Orbiter Mission

What Are Mars’ Moons Made out of?

The composition of Mars’ moons put them in a category that astronomers call “C-Type asteroids”. These are the most common type of asteroids in the Solar System, making up for over 80% of all asteroids, especially those in the outer part of the asteroid belt. The “C” in the name stands for carbon and refers to the predominant material found throughout the moons surface.

Astronomers are far more certain about the material composition of the larger, innermost moon. This is for a few reasons, and not just because there is more surface area to explore. Stickney, the large crater, allows for the investigation of the fine dust and boulders that the impact left behind, which allows for the scientists to further conclude that this moon is very likely made up of a carbonaceous material.

Stickney crater
Photo Credit: NASA

It is a little more difficult to ascertain the material of the smaller, outermost moon. Due to its size, its gravitational pull is much, much weaker. This presents a problem. Typically, when small meteors hit the surface, surface material is thrown up and it returns down, creating the dusty and rocky features that make up the barren moons that you are used to seeing.

It is believed that this small moon’s gravity is so low that the ejected material simply doesn’t come back down, leaving its surface much smoother, but this makes it more troublesome to be certain that it is also the same carbonaceous material, though scientists are pretty sure that it is, based on the similarities to the other moon.

origin of Mars' moons
Photo Credit: NASA

Discovering the Origin of Mars’ Moons

The truth is that the origins of these moons still remain a debate among astronomers to this day. Many believe that, in some way, they originated in the nearby asteroid belt. The question is when they came to Mars’ side. Some astronomers believe that these moons came to the planet after it had formed and established its gravitational pull, dragging the asteroids out of the belt on their own. Others believe that the asteroids had already drifted out around the time that Mars was beginning to form and came along for the ride with Mars’ formation. The true origins still remain controversial.

Quick Facts About Mars’ Moons

Mars' Moons
Photo Credit: PlanetVolumes

Compared to Earth’s moon, Mars’ moons are a mere fraction in size. Unlike Earth’s moon, they cannot be seen by the naked eye in the night sky. If you wish to see them, you need to use a telescope and you need to have a good sense of where to be looking. This is because these moons are incredibly small.

The larger, innermost moon has a radius of just over 11 kilometers. The smaller, outermost moon is approximately half the size of the larger moon with a radius of approximately 6 kilometers. Compare both of these to Earth’s moon which has a radius of 1,736 kilometers, and you may see why Mars’ moons are so difficult to find in the night sky.

Mars' Moons
Photo Credit: NASA

Why are Mars’ Moons Such an Odd Shape?

One of the most notable aspects of these moons is the fact that they, very clearly, do not look the way that other moons do. One moon is a bit warped in shape, oblong and unnatural, while the other is strange and square-like. This is because the gravity on these moons is so low, due to their size and lack of mass, that they cannot pull their own material into a perfectly spherical shape the way that most other moons can. The larger, innermost moon ends up being somewhat oblong in shape, being likened to a potato. The smaller, outermost moon is closer to a square.

Phobos
Photo Credit: NASA
Demios
Photo Credit: NASA

An Imminent Problem

Another unique aspect of these moons is the fact that the larger moon is, in relative terms, quickly being drawn closer to Mars. It is a known fact that this moon is orbiting Mars only about 6,000 kilometers away, which is closer than any other moon orbits its planet. At a rate of approximately two meters per century, it only getting closer. While this may not seem like much at first, this is a noticeable speed in terms of planetary movement. This also means that in approximately 50 million years, this moon is going to collide with Mars, either breaking down entirely in a massive collision or breaking into smaller pieces and forming a ring.

A Quick Guide to Dwarf Planets

When most people talk about the solar system, they’re thinking of the big guys—large planets like Jupiter and Neptune

However, there are also smaller planets, called dwarf planets in the solar system. 

dwarf planets
Photo Credit: Guillermo Ferla

These dwarf planets are much farther away, and have some slightly different characteristics. Let’s go over what they are and why they can’t be considered true planets!

What Are Dwarf Planets?

This concept was integrated into the world of astrology in August 2006, when the International Astronomical Union decided that Pluto was no longer a planet and changed its title. While it was no longer the farthest planet from the sun, it was still part of the solar system as a dwarf planet.

According to the IAU, dwarf planets have to meet both the basic requirements to be a planet:

  1. They must orbit a star
  2. They must have enough mass to have a spherical (or nearly spherical) shape through hydrostatic equilibrium. 

However, those aren’t the only requirements they have to meet. In addition to those requirements, they also have to meet the following criteria:

  • Can’t be a satellite of a planet or another stellar body
  • Must share the vicinity of the orbit with other objects

As long as a planet meets those four criteria, you’ve got a dwarf planet on your hands. 

Currently Known Dwarf Planets

The whole dwarf planet thing started one year before Pluto got kicked out of the solar system (not literally, just technically speaking). 

This is when a celestial body called Eris was found. 

Scientists began to debate whether Eris should be added as the tenth planet in the solar system, or whether it deserved its own classification. 

As you can tell, they decided on the latter. However, that also meant that they had to re-examine Pluto’s classification, naming it as a dwarf planet too. 

Once this classification was established, it paved the way for scientists to identify and classify other dwarf planets. Today, there are five known dwarf planets: 

  1. Ceres
  2. Pluto
  3. Haumea
  4. Makemake
  5. Eris

Let’s take a closer look at each of them. 

Ceres

Ceres is the dwarf planet closest to the sun. It’s a trans-Neptunian object, with a distance of 413,690,250 km from the sun, and was the first visited by NASA’s Dawn space probe. Before being a dwarf planet, until 2006, it was classified as an asteroid.

Pluto

Pluto is a frozen dwarf planet, whose average temperature sits at -240 ºC. This dwarf planet can, at times, can be closer to the sun than Neptune due to its orbit. 

Pluto
Photo Credit: NASA

Haumea

Haumea is similar in size to Pluto and is the fourth in the solar system when it comes to dwarf planets. It was discovered in 2003, but it didn’t get classified as a dwarf planet until after Pluto. 

This planet is shaped like a rugby ball, and half a decade ago, it was discovered that it was the first known Kuiper belt object to have rings. In case you’re not clear on where Kuiper is, that’s the same belt that Pluto is located in!

Makemake

Makemake is a plutoid object smaller than Pluto. However, it’s the second brightest plutoid in the Kuiper belt, as seen from Earth. 

Eris

Eris is the fifth and last dwarf planet. That means that it’s the furthest from the sun. It’s also the largest known dwarf planet to date.

dwarf planets
Photo Credit: Alexander Andrews

Dwarf Planets, a Recent Concept

Astronomers who study space constantly decid to adopt a new terms. That’s how they managed to regroup celestial bodies such as Pluto!

Despite their smaller stature, dwarf planets are still important parts of our solar system. They also are just one more step on the road to many more discoveries about outer space. 

The Former Farthest Planet from the Sun: Pluto

The solar system hasn’t always been what we know of today. As scientists have made new discoveries, they’ve had to make some adjustments including what planets make it up. 

NASA image of Pluto
Photo Credit: NASA

You see, until just over 10 years ago, Pluto was considered the ninth planet and the farthest planet from the sun

However, more recently, scientists and astronomers have changed their tune, and today, Pluto isn’t considered a planet at all. Read on and find out what happened to Pluto and what its current characteristics are like.

What’s the Deal With Pluto?

Pluto is located in the Kuiper belt and is smaller than the moon. It’s said to be composed of a blanket of frozen water, as well as methane ice and nitrogen frost. The terrain of the planet consists of rocky mountains, valleys, plains, and a glacier.

As you might have guessed from that description, this planet is pretty cold. The average temperature of this dwarf planet is about -240ºC, cooling more at that time of year when the sun is further away. It even gets red, methane snow!

Despite that, when Pluto’s orbit brings it close to the sun, the ice on its surface can turn to gas. During these times, it can actually be closer to the sun than Neptune. 

Is Pluto a Planet?

While Pluto is no longer considered to be the farthest planet from the sun, it is still a part of the solar system, just as a dwarf planet.Previously, Pluto was the farthest planet from the sun, but in 2006 Pluto was determined to be a dwarf planet and was no longer considered a planet. The solar system went from having 9 to 8 planets, causing a before and after in astronomy.

So, what happened?

One year earlier, scientists discovered the dwarf planet Eris. When they did so, they realized that Pluto actually fit the same classification as Eris. 

As a result, scientists were faced with two choices: 

  1. Classify Eris as the 10th planet in the solar system
  2. Remove Pluto from the solar system

As you now know, International Astronomical Union (IAU) went with the second option.

farthest planet from the sun
Photo Credit: Andy Holmes

The Difference between Planets and Dwarf Planets

The IAU didn’t just randomly decide to eliminate Pluto from the solar system. When they made that decision, they had to come up with a new way of classifying spacial bodies. 

What the IAU said is that planets have to meet two requirements: 

  1. Orbit around a star without being a star or moon of a planet
  2. Have a mass that’s large enough to reach hydrostatic equilibrium (or, in simpler terms, take a spherical shape)

The problem is that both Pluto and Eris met these requirements, as did many other celestial objects! In order to prevent confusion, a resolution issued on August 24, 2006, added a new characteristic that planets had to meet. 

Under this resolution, the IAU said that in order to be a planet, in addition to meeting the two previous requirements, the bodies must have cleared the vicinity of their orbit of other celestial bodies.

In contrast, dwarf planets could share the vicinity of their orbit with other objects. 

To make things even clearer, the IAU also affirmed that the objects that orbit the sun beyond Neptune are trans-Neptunian objects. These are considered plutoids, or dwarf planets that are farther from the sun than Neptune, the farthest planet from the sun.

The Farthest Dwarf Planet from the Sun

What you might now be curious about is what the farthest dwarf planet is from the sun. 

Let us give you a hint: it’s not Pluto!

Eris is farther away from the sun than Pluto, making it the farthest dwarf planet from the sun. However, beyond Eris is another planetary object called 90377 Sedna.

The jury is still out on whether or not this object could be considered a dwarf planet or not. 

Photo Credit: Andy Holmes

From Planet to Dwarf Planet

Although Pluto was once considered a planet, today, it’s been redefined as a dwarf planet. Now it’s a dwarf planet, the second farthest from the sun.

Although it is no longer the farthest planet from the sun, Pluto is still worth knowing about. It’s just the start of us discovering even more about our solar system and outer space!