Mars vs Earth: A Cosmic Comparison

Comparing Earth and Mars highlights just how different, yet strangely similar, the two neighboring planets are. The Mars vs Earth comparison reveals that while Mars is significantly smaller—having only about half the diameter of Earth and just 11% of its mass—its land surface area is remarkably close to Earth's. This is because Earth is covered roughly 71% by oceans, leaving its continents to make up a landmass almost equal to the entire dry, dusty surface of Mars. For future explorers and settlers, this means there is as much new land to map, explore, and potentially inhabit on Mars as exists on all the continents of Earth combined.

The most immediate difference a human would feel is the gravity. Mars' lower mass translates to a surface gravity of just 38% of Earth's standard pull. While this would make heavy lifting incredibly easy and allow for athletic feats impossible on Earth, the long-term medical implications for bone density and muscle atrophy are severe. This difference in gravity also dictates the planet's ability to hold onto an atmosphere. Earth's strong gravity keeps our thick, protective blanket of nitrogen and oxygen close to the surface. Mars' weaker gravity allowed its ancient, thicker atmosphere to be slowly stripped away by solar winds over billions of years, leaving the frigid, near-vacuum of primarily carbon dioxide that exists today.

Interestingly, the axial tilts of the two planets are surprisingly similar. Earth sits at a 23.5-degree tilt, while Mars is tilted at 25.2 degrees. This means that, just like Earth, Mars experiences four distinct seasons. However, because the Martian year (the time it takes to complete one orbit around the Sun) is 687 Earth days, these seasons last nearly twice as long. A Martian winter can be brutally long and incredibly cold, freezing a portion of the carbon dioxide atmosphere out of the sky to fall as dry ice snow at the poles.

Finally, the temperature profiles are drastically different. Earth enjoys a comfortable average surface temperature bolstered by a strong greenhouse effect that traps the sun's heat. Mars, with its incredibly thin atmosphere, fails to retain heat. While a summer day at the Martian equator might briefly reach a comfortable 70°F (20°C), the temperature plummets precipitously as soon as the sun goes down, often dropping well below -100°F (-73°C) overnight. This extreme thermal cycling, combined with the lack of liquid water and a breathable atmosphere, underscores the immense technological challenges facing any permanent human settlement.

Atmosphere: The Most Critical Difference

Of all the differences in the Mars vs Earth comparison, the atmospheric difference is the most immediately life-threatening. Earth's atmosphere is a thick, life-sustaining blanket of 78% nitrogen and 21% oxygen, with a surface pressure of 101,325 Pascals. Mars' atmosphere is a wispy, unbreathable veil of 95.3% carbon dioxide with a surface pressure of just 610 Pascals — less than 1% of Earth's. This means that even if the Martian atmosphere were made of pure oxygen, it would still be too thin to breathe. This atmospheric difference also means Mars cannot retain heat, has no protection from UV radiation, and cannot support liquid water on its surface for more than moments before it boils away or freezes.

Magnetic Fields: An Invisible Shield

One of the most consequential invisible differences between Earth and Mars is the presence of a global magnetic field. Earth's iron core generates a powerful magnetosphere that deflects the solar wind — a constant stream of charged particles from the Sun — away from our atmosphere and surface. This shield protects us from radiation and prevents the solar wind from stripping away our atmosphere. Mars lost its global magnetic field approximately 4 billion years ago when its smaller iron core cooled and solidified. Without this protection, the solar wind has been slowly eroding the Martian atmosphere for billions of years, and the surface is continuously bombarded with radiation. This is one of the primary reasons why Mars is inhospitable today despite evidence of a warmer, wetter past.

Mars vs Earth: Extended Data Table