MARS (PLANET): CHARACTERISTICS, COMPOSITION, ORBIT, MOVEMENT - ARTE - 2025

Mars is the fourth most distant planet from the Sun and the last of the inner rocky planets in the solar system, along with Mercury, Venus, and Earth. Easily visible, Mars has always fascinated observers since prehistoric times with its reddish color and for this reason it was named after the Roman god of war.

Other ancient civilizations also associated this planet with their respective gods of war or with fateful events. For example, the ancient Sumerians called it Nergal, and it is also referred to in Mesopotamian texts as the star of the judgment of the dead. Likewise, Babylonian, Egyptian and Chinese astronomers left meticulous records of the movements of Mars.

Figure 1. A close-up of Mars. Source: Pixabay.

For their part, Mayan astronomers were interested in it, calculating its synodic period (the time it takes for it to return to the same point in the sky with respect to the Sun) with great accuracy and highlighting the planet's retrograde period.

In 1610, Galileo was the first to observe Mars through a telescope. With improvements in optical instruments came the discoveries, facilitated by the fact that, unlike Venus, there is no thick cloud layer that hinders visibility.

This is how they discovered the black point of Syrtis Major, a characteristic spot on the surface, the white polar layers, the famous channels of Mars and some periodic changes in the coloration of the planet, which made many think about the possible existence of life on the planet. red, at least from vegetation.

However, the information from the probes shows that the planet is desert and has a thin atmosphere. So far there is no evidence of life on Mars.

General characteristics

Mars is small, just one-tenth the mass of Earth, and about half the diameter.

Its axis of rotation is currently inclined about 25º (that of the Earth is at 23.6º). That is why it has seasons, but of different duration from Earth, because its orbital period is 1.88 years. So the Martian seasons last more or less twice as long as the terrestrial ones.

This inclination was not always the same. Some mathematical models of the orbit suggest that in the past it may have varied significantly, between 11º and 49º, bringing notable changes in the climate.

As for temperatures, they range between -140ºC and 21ºC. It is somewhat extreme, and the thin atmosphere contributes to that.

The striking polar caps on Mars are CO ₂, as is the content of the atmosphere. The atmospheric pressure is quite low, about one hundredth of the earth's.

Figure 2. Image of Mars through the Hubble Space Telescope showing one of the polar caps. Source: NASA / ESA, J. Bell (Cornell U.), and M. Wolff (Space Science Inst.) / Public domain, via Wikimedia Commons.

Despite the high CO ₂ content, the greenhouse effect on Mars is much less marked than on Venus.

Being desert the surface, sandstorms are frequent on Mars. A traveler would not find any liquid water or vegetation there, only rocks and sand.

The distinctive reddish color is due to the abundant iron oxides and although there is water on Mars, it is found underground, under the polar caps.

Interestingly, despite the abundance of iron on the surface, scientists say it is scarce in the interior, because the average density of Mars is the lowest among rocky planets: just 3,900 kg / m ³.

Since iron is the most abundant heavy element in the universe, low density means a shortage of iron, especially taking into account the absence of its own magnetic field.

Summary of the main physical characteristics of the planet

-Mass: 6.39 x 10 ²³ kg

-Equatorial radius: 3.4 x 10 ³ km

-Shape: slightly flattened.

-Average distance to the Sun: 228 million km.

- Inclination of the orbit: 1.85º with respect to the plane of the ecliptic.

-Temperature: -63 ºC, average on the surface.

-Gravity: 3.7 m / s ²

-Own magnetic field: No.

-Atmosphere: thin, mostly CO ₂.

-Density: 3940 kg / m ³

-Satellites: 2

-Rings: does not have.

Mars-Africa size comparison

The moons of Mars

Natural satellites are not abundant on the so-called inner planets, unlike the outer planets, which number them by the dozen. The red planet has two small moons called Phobos and Deimos, discovered by Asaph Hall in 1877.

The names of the Martian satellites originate in Greek mythology: Phobos - fear - was the son of Ares and Aphrodite, while Deimos - terror - was his twin brother and together they accompanied their father to war.

Figure 3. Deimos, the small, irregular satellite of Mars. The whitish areas are layers of regolith, a mineral dust similar to the one that covers the lunar surface. Source: Wikimedia Commons. NASA / JPL-caltech / University of Arizona / Public domain.

The moons of Mars are very small, much smaller than our majestic Moon. Their irregular shape makes one suspect that they are asteroids captured by the planet's gravity, even more so if one considers that Mars is very close to the asteroid belt.

The average diameter of Phobos is only 28 km, while that of Deimos is even smaller: 12 km.

Both are in synchronous rotation with Mars, which means that the period of rotation around the planet equals the period of rotation around its own axis. That is why they always show the same face to Mars.

In addition, Phobos is very fast, so much so that it goes up and down a few times during the Martian day, which lasts almost the same as the Earth day.

The orbits of the two satellites are very close to Mars, and also unstable. For this reason it is speculated that at some point they could crash against the surface, especially the fast Phobos, with just 9377 km away.

Figure 4. Animation with the orbits of Phobos and Deimos around Mars. Source: Giphy.

Translation movement

Mars orbits the Sun along an elliptical path whose period equals approximately 1.9 Earth years, or 687 days. All the orbits of the planets follow Kepler's laws and are therefore elliptical in shape, although some are more circular than others.

This is not the case of Mars, because the ellipse of its orbit is somewhat more accentuated than that of the Earth or that of Venus.

In this way, there are times when Mars is very far from the Sun, a distance called aphelion, while in others it is much closer: the perihelion. This circumstance also contributes to Mars having a fairly wide temperature range.

In the remote past, the orbit of Mars must have been much more circular than it is now, however gravitational interaction with other bodies in the solar system produced changes.

Figure 5. Orbits compared between Mars and Earth. Source: Wikimedia Commons. NASA / JPL-Caltech / MSSS / Public domain.

Mars motion data

The following data briefly describe the motion of Mars:

-Mean radius of the orbit: 2.28 x 10 ⁸ km

- Inclination of the orbit: 1.85º

-Eccentricity: 0.093

- Average orbital speed: 24.1 km / s

- Transfer period: 687 days.

- Rotation period: 24 hours, 37 minutes.

- Solar day: 24 hours, 39 minutes.

When and how to observe Mars

Mars is easily identifiable in the night sky by its reddish color. It is distinguished from the stars in that it does not blink or flicker when seen with the naked eye.

There is a lot of information on the web to find the best times to observe Mars, as well as applications for smartphones that indicate its position, whether it is visible or not in a certain place.

As the red planet is outside the orbit of the Earth, the best time to see it is when it is in opposition to the Sun (see figure 6). The planets whose orbit is external to the Earth's orbit are called superior planets and those that are not the inferior planets.

Figure 6. Conjunction and opposition of a superior planet. Source: Maran, S. Astronomy for Dummies.

Mercury and Venus are the lower planets, closer to the Sun than Earth itself, while the higher planets are all the others: Mars, Jupiter, Saturn, Uranus, and Neptune.

Only the higher planets have opposition and conjunction with the Sun, while the lower planets have two types of conjunction.

So, when Mars is in opposition to the Sun seen from Earth, it means that the Earth stands between the planet and the Sun King. Thus it is possible to see it bigger and higher in the sky, visible throughout the night, while the conjunction makes observation impossible. This is valid for all the higher planets.

Mars is in opposition to the Sun approximately every 26 months (2 years and 50 days). The last Mars opposition took place in July 2018; therefore it is expected to occur again in October 2020, when Mars passes through the constellation Pisces.

Figure 7. Oppositions of Mars from 1995 to 2003. The planet does not always look the same size, nor does it always show the same face to Earth. Source: Naked Eye Planets - NASA / JPL / Solar System Exploration - ESA-Hubble.

Mars through the telescope

To the telescope, Mars looks like a pink disk. With good weather conditions and depending on the equipment, you can see the polar caps and some grayish regions whose appearance varies according to the Martian season.

The planet does not always show the same face to the Earth, nor does it look the same size, as can be seen in the mosaic of photographs taken by the Hubble space telescope (see figure 7). The difference is due to the eccentricity of the Martian orbit.

In 2003 Mars was very close to Earth, 56 million kilometers away, while in 2020 the expected distance is 62 million kilometers. The 2003 approach was the largest in 60,000 years.

As for the satellites of Mars, they are too small to see with the naked eye or with binoculars. It takes a telescope of reasonable size and waiting for opposition to occur to distinguish them.

Even so, the brightness of the planet does not allow to see them, but there are devices that hide Mars in the instrument's objective, enhancing the tiny moons.

Rotational motion of Mars

The rotational motion of Mars is similar in duration to that of Earth, and the tilt of the axis was discovered by William Herschel. This causes Mars to experience seasons just like Earth, only longer.

In the northern hemisphere of Mars, winters are milder and occur when the Sun is in perihelion, therefore they are less cold and shorter; on the other hand, summers occur in aphelion and are cooler. In the southern hemisphere the opposite occurs; climate changes there are more extreme.

However, the presence of carbon dioxide is causing a slight but sustained increase in the temperature of Mars, according to the data collected by the sounding missions.

In hot weather, part of the carbon dioxide accumulated in the polar caps evaporates in the form of geysers and passes into the atmosphere. But at the opposite pole, carbon dioxide freezes and thickens the cap.

Figure 8. Animation showing the carbon dioxide cycle in the polar ice caps of Mars. Source: Wikimedia Commons.

Since Mars does not have its own magnetic field to protect it, some of the carbon dioxide scatters into space. The Mars Odyssey space mission recorded this extraordinary atmospheric cycle.

Composition

What is known about the composition of Mars comes from spectrometry carried out by exploration probes, as well as the analysis of Martian meteorites that have managed to reach Earth.

According to the information provided by these sources, the main elements on Mars are:

-Oxygen and silicon are the most abundant in the crust, along with iron, magnesium, calcium, aluminum and potassium.

-Carbon, oxygen and nitrogen in the atmosphere.

- Other elements were detected to a lesser extent: titanium, chromium, sulfur, phosphorus, manganese, sodium, chlorine and hydrogen.

So the elements found on Mars are the same as on Earth, but not in the same proportion. For example, in the mantle of Mars (see the section on internal structure below) there is much more iron, potassium and phosphorus than in their terrestrial equivalent.

For its part, sulfur is present in the nucleus and crust of Mars in a greater proportion than on Earth.

Methane on Mars

Methane is a gas that is usually the product of the decomposition of organic matter, which is why it is also known as "swamp gas".

It is a greenhouse gas, but scientists are eagerly looking for it on Mars, because it would be a good indication that life existed or still exists on the desert planet.

The kind of life scientists hope to find are not little green men, but bacteria, for example. Some species of terrestrial bacteria are known to produce methane as part of their metabolism, and others consume it.

NASA's Curiosity rover in 2019 carried out an unexpectedly high methane reading in the Martian crater Gale.

Figure 9. Curiosity, the robotic rover that explores the features of Mars, launched by NASA in 2012. Source: NASA via jpl.nasa.gov.

However, do not jump to conclusions, since methane can also be produced from chemical reactions between water and rocks, that is, purely chemical and geological processes.

Also, the measurements do not indicate how recent that methane is; However, if there was water on Mars as everything seems to indicate, there could also be life and some scientists believe that there is still life under the permafrost, the forever frozen layer of soil in the circumpolar regions.

If true, microbes may be found living there, which is why NASA created the Curiosity rover, which has among its objectives the search for life. And also a new rover vehicle that may be launched in 2020, based on Curiosity and known until now as Mars 2020.

Internal structure

Mars is a rocky planet, as are Mercury, Venus, and Earth. Therefore, it has a differentiated structure in:

- Nucleus, about 1,794 km in radius, composed of iron, nickel, sulfur and perhaps oxygen. The outermost part may be partially melted.

- Mantle, based on silicates.

- Bark, between 50 and 125 km thick, rich in basalts and iron oxides.

Figure 10. Comparative sections of the inner planets plus the Moon. Source: Wikimedia Commons

geology

Rovers are robotic vehicles controlled from Earth, thanks to which there is invaluable information on Martian geology.

There are basically two regions, divided by a huge step:

• Highlands in the south, with numerous old impact craters.
• Smooth plains in the north, with very few craters.

Since Mars has evidence of volcanism, astronomers believe that lava flows may have erased evidence of craters in the north, or perhaps a large ocean of liquid water was there in a remote time.

The abundance of craters is used as a criterion to establish three geological periods on Mars: Noeic, Hesperian and Amazonian.

The Amazonian period is the most recent, characterized by less craters but with intense volcanism. In the Noeic, however, the oldest, the vast northern ocean could have existed.

Mount Olympus is the largest volcano known so far in the entire solar system and is located precisely on Mars, near the equator. Evidence indicates that it was formed during the Amazonian period, about 100 million years ago.

In addition to craters and volcanoes, on Mars there are also many canyons, dunes, lava fields and old dry channels, through which liquid water perhaps flowed in ancient times.

Figure 11. Mars engulfed by a dust storm, images from the Mars Reconnaissance Orbiter. Sandstorms of planetary proportions are frequent on Mars, since the soil is sandy and desert. Source: NASA / JPL-Caltech / MSSS / Public domain.

Missions to Mars

Mars has been the target of numerous space missions, some destined to orbit the planet and others to land on its surface. Thanks to them you have a large amount of images and data to create a fairly accurate picture.

Mariner 4

It was the fourth probe of the Mariner mission, launched by NASA in 1964. Through it the first photographs of the planet's surface were obtained. It was also equipped with a magnetometer and other instruments, thanks to which it was determined that the magnetic field of Mars is almost non-existent.

Soviet Mars

This was a program of the former Soviet Union that lasted from 1960 to 1973, through which records of the Martian atmosphere, details of the ionosphere, information about gravity, magnetic field and numerous images of the planet's surface were obtained.

Viking

NASA's Viking program consisted of two probes: VIking I and Viking II designed to land directly on the planet. They were launched in 1975 with the mission of studying the geology and geochemistry of the planet, in addition to photographing the surface and looking for signs of life.

Both Viking I and Viking II had seismographs on board, but only Viking II was able to carry out successful tests, of which it was found that the seismic activity of Mars is much lower than that of Earth.

As for the meteorological tests, it was revealed that the atmosphere of Mars was composed mainly of carbon dioxide.

Pathfinder

It was launched in 1996 by NASA within the framework of Project Discovery. It had a robotic vehicle built with minimal expense, with which new designs for this class of vehicles were tested. She also managed to carry out numerous geological studies of the planet and acquire images of it.

Mars Global Surveyor (MGS)

It was a satellite that was in orbit of Mars from 1997 to 2006. It had on board a laser altimeter, with which light pulses were sent to the planet, which were then reflected. With this, it was possible to measure the height of the geographical features, which together with the images taken by the satellite cameras allowed to build a detailed map of the Martian surface.

This mission also brought evidence about the presence of water on Mars, hidden under the polar caps. The data suggest that liquid water flowed across the planet in the past.

The probe found no evidence of a dynamo effect capable of creating a magnetic field similar to that of Earth.

Mars Science Laboratory

This robotic space probe, better known as Curiosity, was launched in 2011 and reached the surface of Mars in August 2012. It is an explorer vehicle or rover whose mission is to investigate the climate, geology and possible conditions for a future manned mission.

Mars odyssey

This probe was launched by NASA in 2001 to map the planet's surface and carry out climatological studies. Thanks to their data, data were obtained on the carbon dioxide cycle described above. The Mars Odyssey cameras sent back images of the south polar cap, showing the dark marks from the compound's vaporization.

Mars Express

It is a mission of the European Space Agency launched in 2003 and so far it is active. Its objectives are to study the climate, geology, structure, atmosphere and geochemistry of Mars, in particular the past and present existence of water on the planet.

Mars Exploration Rovers

The robotic rovers Spirit and Opportunity were launched by NASA in 2004 to land in locations where water was suspected or may have existed. In principle, it would be a mission of only 90 days, however the vehicles remained in operation for longer than expected.

Opportunity stopped broadcasting in 2018 during a global sandstorm, but among the most prominent results are having found more evidence of water on Mars and that the planet once had ideal conditions to host life.

Mars Reconnaissance Orbiter

This satellite was launched in 2005 and is still operational in the orbit of the planet. Its mission is to study water on Mars and whether it has existed long enough for life to develop on the planet.

References

1. Freudendrich, C. How Mars Works. Recovered from: science.howstuffworks.com.
2. Hollar, S. The Solar System. The Inner Planets. Britannica Educational Publishing.
3. Maran, S. Astronomy for Dummies.
4. POT. Mars Reconnaissance Orbiter Mission Overview. Recovered from: mars.nasa.gov.
5. Powell, M. The Naked Eye Planets in the Night Sky (and how to identify them). Recovered from: nakedeyeplanets.com.
6. Seeds, M. 2011.The Solar System. Seventh Edition. Cengage Learning.
7. Strickland, A. The Curiosity rover detects the highest levels of methane on Mars. Recovered from: cnnespanol.cnn.com.
8. Wikipedia. Climate of Mars. Recovered from: es.wikipedia.org.
9. Wikipedia. Composition of Mars. Recovered from: es.wikipedia.org.
10. Wikipedia. Curiosity. Recovered from: es.wikipedia.org.
11. Wikipedia. Mars (planet). Recovered from: en.wikipedia.org.
12. Wikipedia. Mars (planet). Recovered from: es.wikipedia.org.