For decades, scientists have turned their gaze towards Mars, employing powerful telescopes, sophisticated orbiting spacecraft, and intrepid landers and rovers to explore the enigmatic Red Planet. This relentless exploration has painted a detailed picture of Mars, revealing fascinating similarities and stark differences when compared to our home, Earth.
Planetary Basics: Size, Mass, and Gravity
One of the most fundamental differences between Mars and Earth is size. Mars is significantly smaller, with its diameter at the equator being approximately half that of Earth. This size disparity extends to circumference and volume, with Mars’s circumference also roughly half of Earth’s and its volume a mere 15% of Earth’s. Imagine cracking Earth open – you could fit about 6.5 Mars-sized planets inside!
Beyond size, Mars is also less dense than Earth. While occupying only 15% of Earth’s volume, Mars possesses only about 11% of Earth’s mass. This lower density has a direct impact on gravity. The gravitational pull on the Martian surface is only 38% as strong as Earth’s gravity.
Earth and Mars Size Comparison: Depicting the size difference between Earth and Mars, highlighting Earth’s larger size and blue oceans in contrast to Mars’s smaller, reddish appearance. Source: NASA
If you were to stand on Mars, your mass would remain unchanged, but your weight would be significantly less – only 38% of your Earth weight. This is because weight is the force of gravity acting upon mass. Less gravity, less weight, even with the same amount of matter.
Two Rocky Worlds: Terrains and Geological Features
Both Earth and Mars are classified as rocky planets, sharing a composition rich in iron-based rocks on their surfaces. Mars earns its nickname, the “Red Planet,” from the prevalence of red iron oxides, or rust, coloring its landscape.
Both planets boast impressive geological features like mountains and canyons, but Mars takes these features to a colossal scale. Olympus Mons, the largest Martian mountain, dwarfs Mount Everest, standing three times taller and claiming the title of the tallest known mountain in our solar system.
Olympus Mons 3D Render: A three-dimensional view of Olympus Mons, illustrating its massive caldera, steep cliffs, and the extensive volcanic slopes that make it the solar system’s largest volcano. Source: Public domain image by NASA via National Science Foundation
Valles Marineris, Mars’s grand canyon, is equally awe-inspiring. Plunging four times deeper than the Grand Canyon on Earth, Valles Marineris is the deepest known canyon in our solar system, a testament to Mars’s dramatic geological history.
Mars also harbors volcanoes, though unlike Earth, these Martian giants are currently dormant.
Curiosity Rover Selfie on Mars: A selfie of NASA’s Curiosity rover on the Martian surface, showing the red soil, grey rocks, and the rover’s robust wheels adapted for Martian terrain. Source: NASA/JPL-Caltech
Days and Years: Time’s Pace on Different Planets
Earth spins on its axis, completing one rotation in approximately 24 hours, which defines our day. Interestingly, an Earth day is slightly shorter than 24 hours, actually lasting 23 hours and 56 minutes.
Mars rotates a bit slower, resulting in a slightly longer day. A Martian day, called a sol, lasts 24 hours and 37 minutes.
Planets also orbit the Sun, and the time for one complete orbit defines a year. Earth completes one revolution around the Sun in about 365 days, defining an Earth year. To be precise, an Earth year is 365 and a quarter days, necessitating leap years every four years to keep our calendar aligned with Earth’s seasons.
Mars, being farther from the Sun, has a larger orbit than Earth and moves slower in its solar system journey. Consequently, a Martian year is significantly longer, lasting 669 sols, equivalent to 687 Earth days.
Earth and Mars Orbits: An orbital diagram illustrating the paths of Earth and Mars around the Sun, highlighting the concepts of opposition and conjunction in their orbits. Source: Let’s Talk Science using an image by NASA
Atmosphere: Breathing and Density
The atmosphere, the gaseous envelope surrounding a planet, is another key differentiator. Earth’s atmosphere, the air we breathe, is composed primarily of 78% nitrogen and 20% oxygen, with trace amounts of other gases like carbon dioxide (around 0.04%).
The Martian atmosphere is drastically different and unbreathable for humans. It is overwhelmingly dominated by carbon dioxide (96%) and contains a minuscule amount of oxygen (0.145%). Furthermore, the Martian atmosphere is remarkably “thin,” about 100 times less dense than Earth’s, offering minimal protection from solar radiation and having significant implications for temperature regulation.
Climate: Temperature and Seasons
Both Earth and Mars experience four seasons due to their axial tilts. However, because a Martian year is nearly twice as long as an Earth year, each Martian season stretches out for a much longer duration.
The climate on Mars is considerably colder, drier, and more extreme than any environment on Earth. Earth’s average temperature hovers around a comfortable 14°C (57°F). In stark contrast, Mars endures an average temperature of a frigid -63°C (-81°F). This extreme cold stems from Mars’s greater distance from the Sun and its thin atmosphere, which poorly retains heat.
Water: Presence and State
Water, essential for life as we know it, exists in abundance on Earth, covering 71% of our planet’s surface as a vast liquid ocean. Mars also possesses water, but its cold temperatures and thin atmosphere prevent liquid water from persisting stably on the surface.
Evidence suggests the intermittent presence of salty liquid water flows on the Martian surface, occurring when temperatures briefly rise above -23°C (-9°F). Like Earth, Mars has water ice in its polar ice caps and subsurface ice. Trace amounts of water vapor and ice crystals also exist in the Martian atmosphere, forming clouds.
Mars Polar Ice Cap: A view of the Martian north polar ice cap, showing the swirling cloud formations above and the layered ice structure with some land exposed due to seasonal melting. Source: NASA
Precipitation, like rain and snow, is common on Earth. Mars also experiences snowfall, albeit in a surprising form. Carbon dioxide ice clouds can produce snow made of frozen carbon dioxide, reaching the Martian surface. Water ice clouds can also generate snow, but this water-ice snow typically sublimates into vapor in the thin atmosphere before reaching the ground.
Wind is a significant weather element on both planets. Mars’s dry surface makes dust storms a frequent occurrence. Strong winds, driven by uneven atmospheric heating, lift dust particles, sometimes escalating into planet-wide dust storms that can dramatically reshape the Martian surface. Smaller dust devils, similar to those on Earth, also occur due to localized swirling winds.
Martian Dust Devil: A photograph capturing a large dust devil on Mars, illustrating its impressive height and width as it sweeps across the Martian landscape. Source: NASA/JPL-Caltech
By the Numbers: Earth vs. Mars – Key Properties
| Property | Earth | Mars |
|---|---|---|
| Diameter¹ | 12,756 km | 6,792 km |
| Circumference² | 40,075 km | 21,339 km |
| Surface area | 5.10 × 10⁸ km² | 1.44 × 10⁸ km² |
| Volume | 1.08 × 10¹² km³ | 1.63 × 10¹¹ km³ |
| Mass | 5.97 × 10²⁴ kg | 6.42 × 10²³ kg |
| Average Density | 5,514 kg/m³ | 3,933 kg/m³ |
| Surface Gravity³ | 9.81 m/s² | 3.71 m/s² |
| Minimum Temperature | -88 °C | -140 °C |
| Maximum Temperature⁴ | 58 °C | 30 °C |
| Closest Distance to Sun (perihelion)⁵ | 1.47 × 10⁸ km | 2.07 × 10⁸ km |
| Farthest Distance from Sun (aphelion)⁶ | 1.52 × 10⁸ km | 2.49 × 10⁸ km |
| Orbital Distance | 9.40 × 10⁸ km | 1.43 × 10⁹ km |
| Average Orbital Velocity | 107,218 km/h | 86,677 km/h |
| Day Length | 24 hours | 24 hours, 37 minutes |
| Year Length | 365.25 days | 687 Earth days |
| Axial Tilt⁷ | 23.5° | 25.2° |
| Number of Moons | 1 | 2 (Deimos, Phobos) |
| Planetary Magnetic Field⁸ | Yes | No |
| Closest Distance to Earth | N/A | 55.6 × 10⁶ km |
| Farthest Distance from Earth | N/A | 401 × 10⁶ km |
Table adapted from: Mars Facts | All About Mars – NASA’s Mars Exploration Program
¹ Rounded to the nearest whole number
² Measured as gravitational acceleration at the planet’s surface
³ Maximum temperature on Mars is during summer at the equator when the Sun is directly overhead.
⁴ Earth’s orbit is nearly circular; Mars’ orbit is more elliptical.
⁵ Tilted axis of rotation causes seasons on both planets.
⁶ No magnetic field on Mars and a thin atmosphere mean less protection from solar radiation.
In conclusion, while Earth and Mars share the classification of rocky planets and exhibit some intriguing similarities, the differences between these celestial bodies are profound. From size and gravity to atmosphere and climate, Mars presents a starkly different environment compared to our vibrant, life-sustaining Earth. Continued exploration will undoubtedly reveal even more about these fascinating planetary neighbors and our place within the cosmos.
