Mars

Introduction to Mars

Mars, the fourth planet from the Sun, has fascinated humanity since ancient times. Named after the Roman god of war due to its blood-red appearance, Mars has been the subject of countless myths, scientific inquiries, and modern-day exploration missions. It's the most explored planet in our solar system other than Earth, with a fleet of orbiters, landers, and rovers currently studying its secrets.

Often called Earth's "sister planet," Mars shares several similarities with our home world. It has a 24-hour 37-minute day (called a "sol"), seasonal changes due to its axial tilt of 25.2 degrees (similar to Earth's 23.5 degrees), polar ice caps, and evidence of ancient rivers and lakes. These similarities have made Mars the prime target for the search for extraterrestrial life and humanity's first interplanetary settlement.

Mars orbits the Sun at an average distance of 228 million kilometers (142 million miles), about 1.5 times Earth's distance from the Sun. This places it in the outer edge of the habitable zone, where liquid water could theoretically exist on the surface under the right conditions. A year on Mars lasts 687 Earth days, nearly twice as long as an Earth year.

Physical Characteristics

Mars is a terrestrial planet with a thin atmosphere and a solid, rocky surface marked by impact craters, valleys, deserts, and polar ice caps. Though often compared to Earth, Mars is considerably smaller and less massive, which has profoundly affected its geological and atmospheric evolution.

Data: NASA Planetary Science

The planet's lower gravity (38% of Earth's) means that a person weighing 100 pounds on Earth would weigh only 38 pounds on Mars. This reduced gravity has significant implications for human colonization, as prolonged exposure could lead to muscle atrophy and bone loss similar to what astronauts experience on the International Space Station.

Mars has a distinct reddish appearance caused by iron oxide (rust) prevalent in its soil and dust. This iron-rich dust covers most of the planet's surface and is regularly lifted into the atmosphere by winds, sometimes creating global dust storms that can obscure the entire planet for months. The presence of iron oxide suggests that Mars once had a more oxygen-rich atmosphere and liquid water on its surface.

Surface Features

Mars boasts some of the most extreme geological features in the entire solar system. Its surface tells the story of a geologically active past, with massive volcanoes, a canyon system that dwarfs Earth's Grand Canyon, and evidence of catastrophic floods.

Olympus Mons

Olympus Mons is the largest volcano and the tallest mountain in the solar system. Rising 21.9 kilometers (13.6 miles) above the surrounding terrain—nearly three times the height of Mount Everest—this shield volcano has a base diameter of approximately 600 kilometers (374 miles), roughly the size of Arizona. If you stood at its edge, you couldn't see the summit because it would be beyond the horizon. The volcano's caldera (crater at the summit) is 80 kilometers wide and could fit the entire city of Los Angeles inside it.

Valles Marineris

Valles Marineris is the largest canyon system in the solar system, stretching over 4,000 kilometers (2,500 miles) across the Martian surface—roughly the distance from New York to Los Angeles. At its deepest, it plunges 7 kilometers (4.3 miles) below the surrounding plateau, making it four times deeper than the Grand Canyon. The canyon is so vast that if placed on Earth, it would stretch from the Atlantic to the Pacific Ocean. Scientists believe it formed as Mars cooled and its crust cracked, rather than by water erosion like Earth's Grand Canyon.

Polar Ice Caps

Mars has permanent ice caps at both poles, composed of water ice and frozen carbon dioxide (dry ice). The northern cap is primarily water ice about 1,000 kilometers across, while the southern cap has a layer of carbon dioxide ice over water ice. During winter, the polar caps extend toward the equator as carbon dioxide from the atmosphere freezes onto the surface; in summer, this dry ice sublimates back into the atmosphere. The water ice in these caps represents a potentially valuable resource for future human missions.

Hellas Basin

The Hellas Basin is one of the largest impact craters in the solar system, measuring 2,300 kilometers (1,430 miles) in diameter and 7 kilometers deep. Created by a massive asteroid impact about 4 billion years ago, the basin's floor is the lowest point on Mars. Atmospheric pressure at the bottom of Hellas is nearly twice that of the Martian average, making it one of the few places on Mars where liquid water could theoretically exist briefly on the surface.

The Moons of Mars: Phobos and Deimos

Mars has two small, irregularly shaped moons named after the Greek gods of fear (Phobos) and terror (Deimos), who were the sons of Ares (the Greek equivalent of Mars). Both moons were discovered in 1877 by American astronomer Asaph Hall and are thought to be captured asteroids from the nearby asteroid belt.

Phobos

Phobos is the larger of the two moons, measuring about 22 kilometers (14 miles) across. It orbits remarkably close to Mars—just 6,000 kilometers above the surface—completing an orbit in only 7 hours and 39 minutes. This means Phobos rises in the west and sets in the east, appearing to move backward across the Martian sky. Due to tidal forces, Phobos is slowly spiraling toward Mars and will either crash into the planet or break apart into a ring system in about 50 million years.

Phobos's most prominent feature is Stickney Crater, a 9-kilometer-wide impact crater that nearly shattered the moon. The crater is named after Chloe Angeline Stickney Hall, the wife of the astronomer who discovered the Martian moons.

Deimos

Deimos is the smaller and more distant of Mars's moons, measuring only about 12 kilometers (7.5 miles) across. It orbits at a distance of about 23,500 kilometers from Mars, taking 30 hours to complete one orbit. Unlike Phobos, Deimos is slowly moving away from Mars. From the Martian surface, Deimos appears as a bright star rather than a moon, and it takes about 2.7 days to cross the sky.

Atmosphere and Climate

Mars has an extremely thin atmosphere, with surface pressure less than 1% of Earth's. This thin atmosphere, combined with the lack of a global magnetic field, makes the Martian surface inhospitable to life as we know it and poses significant challenges for human exploration.

Atmospheric Composition

The Martian atmosphere is composed primarily of carbon dioxide (95.3%), with small amounts of nitrogen (2.7%), argon (1.6%), and trace amounts of oxygen (0.13%) and water vapor. This composition, combined with the low atmospheric pressure, means humans cannot breathe on Mars and would need pressurized habitats and spacesuits.

Temperature Extremes

Mars experiences dramatic temperature variations. Average surface temperature is about -60°C (-80°F), but this varies significantly by location and season. Near the equator on a summer day, temperatures can reach a relatively mild 20°C (68°F), while at the poles in winter, temperatures can plummet to -125°C (-195°F). The thin atmosphere cannot retain heat effectively, causing temperatures to drop dramatically after sunset.

Dust Storms

Mars is famous for its dust storms, which can range from small dust devils to planet-encircling events that last for months. Global dust storms occur roughly every few years, blocking sunlight and dramatically changing surface conditions. The 2018 global dust storm was so severe that it ended the mission of NASA's Opportunity rover after 15 years of exploration. These storms are powered by solar heating and can lift fine particles tens of kilometers into the atmosphere.

Blue Sunsets

While Earth's sunsets are red and orange, Martian sunsets are blue. This reversal occurs because Mars's atmosphere contains fine dust particles that scatter shorter blue wavelengths of light toward the observer as the sun sets. The phenomenon creates an ethereal, otherworldly scene that has been captured by multiple Mars rovers.

Water on Mars

The search for water on Mars has been one of the driving forces behind Mars exploration. Water is essential for life as we know it and would be crucial for supporting future human missions. Evidence suggests that Mars once had abundant liquid water on its surface billions of years ago.

Ancient Mars: A Watery World

Geological evidence indicates that Mars once had rivers, lakes, and possibly even an ocean covering much of its northern hemisphere. Valley networks resembling river drainage systems, ancient lake beds, and minerals that only form in the presence of water all point to a warmer, wetter Mars in the distant past. Scientists estimate that about 3.5 billion years ago, Mars may have had enough water to cover the entire planet in an ocean 100-1,500 meters deep.

Where Did the Water Go?

Mars lost most of its water over billions of years due to several factors. Without a global magnetic field to protect it, the solar wind gradually stripped away the planet's atmosphere, causing surface water to either evaporate into space or freeze. Today, most of Mars's water is locked in the polar ice caps as ice, or exists as subsurface ice and possibly liquid water deep underground.

Current Water Ice

The polar ice caps contain significant amounts of water ice. The northern cap alone contains enough water ice to cover the entire planet in a layer about 2 meters deep. In addition, the Mars Odyssey orbiter detected vast deposits of subsurface ice in the mid-latitudes, and the Phoenix lander directly confirmed the presence of water ice just centimeters below the surface near the north pole.

The Mystery of Recurring Slope Lineae

Dark streaks called recurring slope lineae (RSL) appear on some Martian slopes during warmer months and fade in cooler seasons. Initially thought to be evidence of flowing liquid water, recent studies suggest they may be caused by dry granular flows. However, the debate continues, and some scientists still believe small amounts of briny water could play a role in their formation.

Exploration History

Mars has been the target of more exploration missions than any other planet besides Earth. Since the 1960s, numerous spacecraft have been sent to study the Red Planet, with varying degrees of success. These missions have transformed our understanding of Mars from a mysterious red dot in the sky to a complex world with a rich geological history.

Historic Mars Missions

• Mariner 4 (1965): First successful Mars flyby; sent back 22 close-up images revealing a cratered, Moon-like surface
• Mariner 9 (1971): First spacecraft to orbit Mars; discovered Olympus Mons and Valles Marineris
• Viking 1 & 2 (1976): First successful Mars landers; conducted biological experiments searching for life
• Mars Pathfinder & Sojourner (1997): First successful rover mission; Sojourner operated for 83 sols
• Spirit & Opportunity (2004): Twin rovers designed for 90 sols; Spirit lasted 6 years, Opportunity an incredible 15 years
• Phoenix (2008): Landed near north pole; confirmed presence of water ice in Martian soil
• Curiosity (2012-present): Car-sized rover exploring Gale Crater; found evidence of ancient habitable environments
• InSight (2018-2022): First mission to study Mars's interior; detected marsquakes and the planet's "hum"
• Perseverance & Ingenuity (2021-present): Searching for biosignatures; Ingenuity achieved first powered flight on another planet

Opportunity's Final Message

One of the most poignant moments in Mars exploration came when the Opportunity rover sent its final transmission in June 2018 during a global dust storm. Mission controllers poetically interpreted the rover's last data transmission as "My battery is low and it's getting dark." After 15 years of exploration—far exceeding its planned 90-day mission—Opportunity had traveled over 45 kilometers (28 miles) and discovered compelling evidence of Mars's watery past.

Future Missions and Colonization

Mars stands at the forefront of humanity's space exploration ambitions. Multiple space agencies and private companies are developing missions to send humans to Mars within the next few decades, with the ultimate goal of establishing a permanent human presence on the Red Planet.

Upcoming Robotic Missions

Several robotic missions are planned for the coming years. NASA's Mars Sample Return mission, in collaboration with ESA, aims to bring Perseverance's collected samples back to Earth by the mid-2030s. This would be the first time samples from another planet have been returned to Earth for detailed laboratory analysis. China's Tianwen-3 mission also plans to return Mars samples, potentially arriving before NASA's mission.

Human Missions to Mars

NASA's Artemis program includes Mars as a long-term goal, with human missions potentially occurring in the late 2030s or 2040s. Meanwhile, SpaceX founder Elon Musk has set an ambitious goal of sending humans to Mars using the Starship rocket system, with eventual plans for a self-sustaining city on Mars. A crewed mission would take approximately 6-9 months each way, with astronauts likely staying on Mars for about 500 days until the planets align for a return journey.

Challenges of Mars Colonization

Establishing a human settlement on Mars presents enormous challenges:

• Radiation: Without a global magnetic field or thick atmosphere, Mars offers little protection from cosmic rays and solar radiation
• Life Support: Producing food, water, and oxygen from local resources (called ISRU - In-Situ Resource Utilization)
• Psychological Factors: Extended isolation, communication delays of up to 24 minutes, and the impossibility of quick return to Earth
• Lower Gravity: Long-term effects of living in 38% Earth gravity are unknown
• Dust: Fine, potentially toxic Martian dust could pose health risks if inhaled

Interesting Facts About Mars

Beyond the serious science, Mars is full of surprising and delightful details that make it endlessly fascinating.

• Perseverance's Secret Message: The Perseverance rover's wheel treads contain a hidden pattern that spells "JPL" in Morse code, leaving this message imprinted in the Martian soil with every rotation.
• A Piece of Aviation History: Attached to the Ingenuity helicopter is a small piece of fabric from the Wright Brothers' original 1903 Flyer, connecting humanity's first powered flight on Earth to its first powered flight on another planet.
• Mars Sounds: NASA's InSight lander detected a low-frequency "hum" emanating from Mars, as well as the first recorded marsquakes. You can listen to actual sounds from Mars recorded by Perseverance, including the eerie howl of Martian wind.
• The Face on Mars: In 1976, Viking 1 photographed a rock formation that resembled a humanoid face, sparking decades of conspiracy theories. Higher-resolution images later revealed it to be a natural mesa that only appeared face-like due to shadows.
• Martian Meteorites on Earth: We have pieces of Mars here on Earth! About 224 meteorites have been confirmed as originating from Mars, blasted off the surface by ancient impacts and eventually landing on Earth.
• Olympic-Sized Volcano: Olympus Mons is so large and its slopes so gradual that if you stood at its base, you wouldn't be able to see the summit—it would be beyond the horizon.
• Two Calendars: Scientists and engineers working on Mars missions often operate on "Mars time," shifting their schedules by about 40 minutes each day to stay synchronized with the Martian sol.
• Longer Than Earth's: Mars's orbit is more elliptical than Earth's, which means its distance from the Sun varies more significantly throughout its year, contributing to more dramatic seasonal changes.

External Resources

• NASA Mars Exploration Program - Official NASA Mars page with latest news and mission updates
• Mars on Wikipedia - Comprehensive encyclopedia article
• NASA Perseverance Rover - Current mission exploring Jezero Crater
• NASA Curiosity Rover - Exploring Gale Crater since 2012