Mars does have an atmosphere, though some of it has been lost over the course of billions of years. The planet has become evidence of large-scale climate change, losing much of its once-thick atmosphere to having one 100-times thinner than that on Earth, with about 1% of its density. Scientists continue to study the composition of the planet's atmosphere and its volume to determine whether there may once have been life on the fourth planet from the sun, and if it could ever sustain life as we know it again.
What Is The Martian Atmosphere Made Of?
Martian atmosphere is comprised mainly of carbon dioxide (95%). The remainder of the elements are nitrogen (2.7%), argon (1.6%), oxygen (0.13%), carbon monoxide (0.08%), and minor levels of water, nitrogen oxide, neon, hydrogen-deuterium-oxygen, krypton, and xenon.
Carbon dioxide makes up the greatest portion of the Martian atmosphere. The planet becomes so cold in winter months, carbon dioxide ice caps form on the poles but when they are exposed to heat those caps undergo sublimation and return to gas form. Because carbon dioxide transforms from gas to solid form regularly, the atmospheric composition can change from year to year as the element condenses or sublimes. The levels of carbon dioxide on the Red Planet exceed those on Earth due to a lack of plant life, which helps convert the carbon dioxide into oxygen.
Though it accounts for just 2.7% of the atmosphere on Mars, many scientists believe there may be higher levels of nitrogen on the planet as some of it may be hidden and stored as nitrate salt within the planet's red soil. Those amounts of solid nitrogen have not been measured, however.
There is more argon in the atmosphere of Mars than any other planet, and its levels are constant because the gas does not condense. Despite its actual amounts remaining steady, the relative levels of argon in the atmosphere may fluctuate as carbon dioxide moves in and out of the atmosphere via condensation.
What Is Mars Like?
The Red Planet is a cold, desert-like environment with dry riverbeds and minerals that form only with liquid water. These elements of the planet's make-up lead scientists to believe Mars once had a thick enough atmosphere to retain heat, which would have permitted water to flow on its surface similar to Earth. As the atmosphere faded, the climate of Mars transformed into a frozen and dessicated land, and water is scarce or non-existent. It's atmosphere is now so thin, it could not sustain life.
With a thin atmosphere and its distance from the sun, the Red Planet is cold, with average temperatures hovering around -80 degrees Fahrenheit or -60 degrees Celsius and notable cold snaps reaching -195 F (-125 C) near the poles and midday heat climbing to 70F, or 20C, near its equator.
How Was The Atmosphere Lost?
It is difficult to estimate just how much of Mars' atmosphere was lost, because scientists are unable to solve the mystery of how thick it was in ancient times. While studies indicate it was healthy enough to keep the planet warm and water flowing, there is no evidence as to just how much atmosphere Mars once had.
Scientists have looked at isotopes of oxygen on the planet for some clue. Lighter isotopes escape into space faster than heavier ones, and the Red Planet has rich levels of heavier oxygen isotopes. These amounts can help estimate how much more atmosphere once existed if scientists work with the assumption the amounts of light and heavy oxygen isotopes on Mars were once similar to Earth.
Some believe the atmosphere may have been compromised by a devastating impact from a small body, which could have stripped way many isotopes and left behind a thinner atmospheric layer.
Leading theories for the reason of atmosphere loss is that the planet's light gravity and lack of a magnetic field left its ancient atmosphere susceptible to pressure from strong solar winds, which carry a consistent stream of particles from the sun. Pressure from the sun pulled lighter isotopes from the atmosphere, thinning it out.
In 2013, NASA's MAVEN mission measured the rate Mars' atmosphere was being stripped away by solar winds, which would have provided data to infer the rate it had lost the rest of its atmospheric layer through history. The findings indicated Mars loses approximately 100 grams, or 0.25 pounds, of its atmosphere every second. When solar flares occur, that rate increases by about 20 times. Scientists estimate when the atmosphere was at its thickest, the same levels of solar winds would have stripped it away faster.
What Is The Importance Of The Martian Atmosphere?
The atmosphere on Mars may be much thinner than on Earth, but it remains intact enough to cause weather, clouds, and wind. Often during spring and summer, weather patterns cause giant dust devils, kicking up the oxidized iron dust that covers its surface, giving Mars its signature red hue. One theory as to the cause of the dust storms is that the airborne particles, which are considered a permanent part of the atmosphere, absorb sunlight and cause warmer pockets of air to flow through cold regions, which generates strong wind. These winds lift more dust from the ground into the air, heating the atmosphere more, creating more wind and dust.
The high levels of carbon dioxide in the atmosphere create Martian snowflakes, which are actually small particles that form together and create a fog-like effect. The planet's poles are also covered in ice caps, but these are also largely comprised of carbon dioxide rather than water.