Cold Planet: Unraveling the Weak Greenhouse Effects on Mars

The greenhouse effect is important for warming planets’ surfaces by trapping heat through gases like CO₂, methane (CH₄), and water vapor (H₂O). Greenhouse gases absorb infrared radiation from planets and re-radiate it. The greenhouse effect can maintain a suitable temperature for life.

The greenhouse effect isn’t the same on all planets and differs considerably based on the thickness and composition of a planet’s atmosphere.

In comparison to other planets, Mars is colder due to its greater distance from the Sun and weak greenhouse effect. Mars’s lower mass and gravity make it difficult to retain a thick atmosphere. The lack of a strong magnetic field allows solar wind to strip away atmospheric gases.

Its thin atmosphere primarily consists of CO₂ and lacks sufficient density to trap heat effectively. The limited greenhouse effect on Mars results from the absence of substantial amounts of other greenhouse gases like water vapor and methane and due to the low atmospheric pressure.

Unlike Mars, Venus experiences a runaway greenhouse effect due to its dense CO₂-rich atmosphere. This leads to extreme temperatures. Due to the runaway greenhouse effect, Venus experiences hotter temperatures than Mercury.

Understanding the weak and runaway greenhouse effects on planets can help us evaluate the temperatures of planets and potential liquid water existence. This can give an insight into the habitable zone in the solar system.

The Greenhouse Effect

Image-1. The Greenhouse Effect (Image Credit: Climate Central).

The greenhouse effect is a natural process that warms the planet’s surfaces. When the Sun’s energy reaches the planet, some of it is reflected back to space, and the rest is absorbed. Absorbed energy warms the planets.

The planets then emit this energy in the form of infrared radiation. Greenhouse gases in the atmosphere absorb and re-radiate some of this infrared radiation, trapping heat and warming the planet.

Without this process, the Earth’s average temperature would be much colder, making it inhospitable for most forms of life. According to scientists, the average temperature of Earth would drop from 14˚C to as low as –18˚C, without the greenhouse effect.

Some of the greenhouse gasses can be listed as:

Carbon Dioxide (CO₂):

Sources are burning fossil fuels, deforestation, and various industrial processes. Throughout Earth’s history, whenever the amount of CO2 in the atmosphere has increased, the overall temperature of Earth has also increased. Thus, there is a proportional relationship between the amount of CO2 in the Earth’s atmosphere and the temperature of the planet.

Methane (CH₄):

Sources are agriculture, landfills, natural gas extraction, and wetlands.

Water Vapor (H₂O):

Sources are evaporation from oceans, lakes, and rivers. This is the most abundant greenhouse gas, but its concentration in the atmosphere is primarily controlled by natural processes.

The greenhouse effect accounts for the trapping of long-wave thermal infrared energy within the atmosphere of planets which increases the planet’s overall temperature.

The more greenhouse gases there are in the atmosphere, the more thermal energy radiated by the planet’s surfaces will be trapped within its atmosphere and, consequently, the hotter the climate of the planet will become.

Why is Mars So Cold?

Image-2. Atmosphere of Mars. (Image Credit: NASA).

Mars is significantly colder than Earth due to several factors, including its distance from the Sun, its thin atmosphere, and the limited greenhouse effect.

Average surface temperatures on Mars range from about -60 degrees Celsius at the poles during winter to about 20 degrees Celsius at the equator during summer.

Distance from the Sun:

Mars is about 1.5 times farther from the Sun than Earth, receiving less solar energy. This reduced solar energy input causes lower temperatures.

Thin Atmosphere:

Mars has a very thin atmosphere, composed mainly of carbon dioxide (CO₂) with traces of other gases like nitrogen and argon. The atmospheric pressure on the surface of Mars is less than 1% of Earth’s. Less atmospheric pressure makes it insufficient to trap heat effectively. The thin atmosphere of Mars is unable to keep heat effectively.

Mars’s atmosphere lacks the density and variety of greenhouse gases needed to create a significant greenhouse effect. Consequently, Mars experiences extreme temperature variations and remains much colder overall.

There is still a minor greenhouse effect on Mars, primarily driven by CO₂. However, it is much weaker than the greenhouse effect on Earth due to the low atmospheric pressure and lack of other significant greenhouse gases like water vapor and methane.

Even though Mars’s atmosphere is composed mostly of carbon dioxide since its atmosphere is so thin, the greenhouse effect is almost ineffective on Mars.

Earth’s atmosphere is thick and rich in a mix of greenhouse gases, including CO₂, water vapor, methane, and nitrous oxide. This allows Earth to trap heat effectively, maintaining a stable and warm climate suitable for life.

On Earth, gases like methane (CH₄) and nitrous oxide (N₂O) also contribute to the greenhouse effect. Mars has trace amounts of these gases. These are insufficient to cause the strong greenhouse effect.

Surface Reflectivity (Albedo):

The surface of Mars has a higher albedo compared to Earth. In other words, it reflects more sunlight back into space. This reflection contributes to lower surface temperatures.

Thin Atmosphere of the Mars

Image-3. Crater on Mars. (Image Credit: Mars Exploration Rover Mission, Cornell, JPL, NASA).

Mars’s thin atmosphere is the result of several factors related to its size, gravity, magnetic field, geological activity, and past impacts:

Low Gravity Mass and Gravity:

Mars is smaller and less massive than Earth. Mars has only about 11% of Earth’s mass. This lower mass results in weaker gravity. Weaker gravity makes it harder for Mars to retain a thick atmosphere.

Due to its lower mass and density, Mars has a gravitational force that is weaker than Earth’s. This weaker gravity has some impacts on Mars, including the thin atmosphere.

Magnetic Field and Atmospheric Protection:

Earth’s magnetic field protects its atmosphere from being eroded by solar wind. The solar wind is a stream of charged particles emitted by the Sun. Mars lacks a strong global magnetic field. This makes its atmosphere vulnerable to solar wind stripping.

Solar Wind:

The Sun constantly emits a stream of charged particles called the solar wind. Mars, unlike Earth, lacks a strong global magnetic field to deflect this solar wind. Over time, the solar wind is thought to have stripped away much of the Martian atmosphere.

Scientists believe Mars once had a thicker atmosphere, but over time, it was stripped away by the solar wind due to Mars’ weak magnetic field. This loss of atmosphere reduced the greenhouse effect.

Runaway Greenhouse Effect on Venus

Venus is an example of a planet that has experienced a runaway greenhouse effect. Runaway greenhouse effect leads to extreme conditions and temperatures. A runaway greenhouse effect is a scenario where a planet’s atmosphere traps too much heat.

Greenhouse gases, like carbon dioxide, build up in such vast quantities that they trap way too much heat. The planet can’t radiate this heat back out to space.

Venus has an incredibly thick and dense atmosphere consisting of 96% carbon dioxide. Carbon dioxide traps a significant amount of radiated thermal energy within the atmosphere of the planet. This is what primarily causes extremely hot temperatures.

Its atmosphere is filled with carbon dioxide. This results in a surface hotter than Mercury! Scientists believe a similar process might have happened on Mars in the past, but Mars lost most of its atmosphere over time. Mars is currently a cold planet.

As an MoEP Astroarcheolgy Research Team (ARK), we will continue to evaluate the habitability conditions of planets in the next article. Keep following us!