The month of July 2021 was a historic one, with two groups of civilians taking off toward space. The first group, Virgin Galactic, was led by its founder Richard Branson, and the second group, Blue Origin, was led by its owner Jeff Bezos.
The third member of the billionaire space club, Elon Musk, who is CEO of SpaceX, has yet to travel to space himself, but in September 2016, he announced a plan to launch a crewed mission to Mars by the year 2024.
What being on Mars is really like
When seen from Earth, Mars is the brightest object in the sky, behind only the Sun, Moon, and the planet Venus. Mars is named for the Roman god of war, which in Greek is Ares.
Mars has an equatorial radius of 2,110 miles (3,396 km), while Earth has an equatorial radius of 3,963 miles (6,378 km), making Earth almost twice as large as Mars. However, 71 percent of Earth's surface is covered by oceans, and the two polar areas are largely uninhabitable, while Mars has no detectable surface liquid water. That makes the actual inhabitable surface area of the two planets surprisingly similar. Mars has a surface area of around 55,900,000 square miles (144,780,335 sq km) while Earth has a land surface area of around 57,900,000 square miles (149,960,311 sq km).
Mars is much less dense than Earth, having only around 11 percent of Earth's mass. Less mass also means that Mars has only around 38 percent of Earth's surface gravity, so a person weighing 220 pounds (100 kg) on Earth would weigh only 84 pounds (38 kg) on Mars. Sign me up!
While the possibility of weighing less on Mars is appealing, astronauts have demonstrated that prolonged periods of time spent in less-than-Earth gravity can have detrimental effects on the body, including loss of muscle mass, bone density, and organ function. Even eyesight has been shown to be negatively affected by low gravity.
Mars rotates once around its axis every 24 hours 39 minutes and 36 seconds, making a Martian day, or sol, very similar in length to that of an Earth day. Mars completes one revolution around the Sun every 687 days, making a Martian year almost twice as long as an Earth year.
Seasons on Earth are caused by the fact that Earth's axis is tipped 23.5 degrees to the plane of the ecliptic. Mars' axis is currently almost identically tipped, at 25.19 degrees, meaning that it too has four seasons, but they are each twice as long due to the length of Mars' year.
Each of Mars' seasons is much cooler than they are on Earth because Mars lies an average of 143 million miles (230 million km) away from the Sun, while Earth is only 93 million miles (150 million km) away. While Earth's north pole points to the star Polaris, or the North Star, Mars' north pole points to a spot in the sky that's about midway between Deneb, in the constellation Cygnus the Swan, and Alderamin, in the constellation Cepheus the King
Surface temperatures on Mars range from a low of −225 °F (−143 °C) during winter at the polar caps to 95 °F (35 °C) during equatorial summer. However, because Mars's atmosphere is around 100 times thinner than Earth's, Mars can't retain any heat energy, so even in the Martian equatorial summer, nights dip to a chilly -100 °F (-73 °C). Due to its distance from the Sun, Mars receives just 43 percent the amount of sunlight as Earth.
Like Earth, Mars' orbit is elliptical rather than circular. It makes its closest approach to the Sun, or perihelion when it is summer in Mars' Southern Hemisphere and winter in its Northern Hemisphere. Mars is at aphelion, or its farthest point from the Sun when it is winter in the Southern Hemisphere and summer in the Northern Hemisphere. This causes summer temperatures in the south to be much warmer than summer temperatures in the north by up as much as 54 °F (30 °C).
The surface of Mars
Due to Mars' colder temperatures, it is home to more elements having low boiling points than the Earth — elements such as chlorine, phosphorus magnesium, sodium potassium, and sulfur. Some of these elements are vital for the growing of plants.
The most abundant elements in Mars' crust are silicon, oxygen, iron, magnesium, aluminum, calcium, and potassium. On average, the Martian crust is around 31 miles (50 k) deep, while on Earth, the average crust is 25 miles (40 k) deep. Mars' red-orange appearance is caused by ferric (iron(III)) oxide, also known as rust, covering its surface.
Unlike Earth, Mars doesn't have a global magnetic field while parts of Mars' crust are magnetized. Indeed, billions of years ago Mars may have experienced the same magnetic polarity reversals that occur on Earth.
The Martian atmosphere is comprised of:
- 95.97% carbon dioxide
- 1.93% argon
- 1.89% nitrogen
- 0.146% oxygen
and less than one-tenth of one percent of the elements carbon monoxide, water vapor, nitrogen oxide, neon, hydrogen-deuterium oxide, krypton, and xenon.
The surface of Mars is marked by what is called the Martian dichotomy, and it refers to differences in the thickness of the crust between the planet's Northern and Southern hemispheres. The crust of the Martian Northern Hemisphere is about 20 miles (32 km) thick, while the Southern Hemisphere crust is around 36 miles (58 km) thick. The surface of the Northern Hemisphere of Mars is primarily flat, while the surface of the Southern Hemisphere is pitted and cratered by ancient impacts.
A theory proposed in 1980 was that the Northern Hemisphere had been struck by an object up to two-thirds the size of Earth's Moon, and this unleashed lava flows resulting in the flat appearance. Today, Mars is not geologically active, with its last lava flows dating back 20 million years ago.
Because Mars is smaller than the Earth, and it has much less mass, it should attract fewer objects that could impact it. However, Mars' next-door neighbor in the Solar System is the Main Asteroid Belt, which contains lots of dangerous objects, and Mars is also in the firing line of comets that have been captured by the gravity of its massive neighbor, Jupiter.
Up to 60 percent of the Martian surface shows asteroid and comet impacts. The enormous impact basin located in Mars' Northern Hemisphere, Borealis Basin, is 6,600 by 5,300 miles (10,600 by 8,500 km) in size, suggesting that four billion years ago, Mars was struck by a Pluto-sized object. This event is thought to be the cause of the Martian hemispheric dichotomy, and to have created the smooth basin that covers 40 percent of the planet.
Mars' lower gravity might be responsible for the fact that it has both the largest volcano/highest mountain of any planet in the Solar System, Olympus Mons. It is thought to be around 16 miles (26 km) high.
Mars is also home to one of the largest canyons in the Solar System, Valles Marineris, which reaches a depth of 6 miles (10 km) and is about 2,500 miles (4,000 km) long. It extends across one-fifth of the planet's circumference and has been theorized to mark a boundary between two tectonic plates.
Elsewhere on the planet, deltas and alluvial fans look as though they were carved by water runoff from precipitation, suggesting that at some point in Mars' past, it had a warmer and wetter climate. Mineral and sediment evidence points to crater lakes having been spread across a large portion of the Martian surface.
During each pole's Martian winter, it is in continuous darkness and cold, causing 25 to 30 percent of the Martian atmosphere to freeze into slabs of CO2, or dry ice. When one of the poles warms during its Summer, the frozen CO2 goes directly from a solid to a gas, which along with water ice, forms large clouds in Mars' atmosphere.
Water on Mars
Large quantities of liquid water can't exist on the surface of Mars due to the planet's low atmospheric pressure of .095 pounds per square inch (psi) compared to 14.7 psi on Earth. However, Mars' two polar ice caps appear to be partly comprised of water ice, with the south polar ice cap thought to contain enough water to cover Mars to a depth of 36 feet (11 m).
In November 2008, the Mars Reconnaissance Orbiter detected permafrost stretching from the Martian poles down to a latitude of 60 degrees. In September 2015, NASA announced that, based on spectrometer readings, it had found conclusive evidence of water flowing in the very shallow subsurface of dark streaks that frequently appear on slopes during the Martian summer, when temperatures are above -31 degrees F (−23 degrees C).
In an astounding finding in November 2016, NASA reported that it found an amount of underground ice equivalent to the volume of water in Lake Superior in the Utopia Planitia region of Mars.
Near Mars' northern polar ice cap, at 73 degrees north latitude, lies Korolev Crater, named for Sergei Korolev who is considered the father of the Russian space program. Korolev Crater is 50.6 miles (81.4 km) in diameter and 1.1 miles (1.8 km) deep, and in December 2018, the Mars Express orbiter found the crater to be filled with around 530 cubic miles (2,200 cubic km) of water ice.
Day and night on Mars
Standing on Mars, if you looked up into the night sky, you would see not one, but two moons - Phobos and Deimos. They were first discovered in 1877 by American astronomer Asaph Hall. In Greek mythology, Deimos was the god of dread and terror and Phobos was the personification of fear and panic. Both Martian moons are far smaller than Earth's Moon, with Phobos being only 14 miles across (22 km), and Deimos being only around 7 miles (12 km) across.
Neither moon is as spherical as Earth's Moon, and their irregular shape supports the theory that both moons are captured asteroids. If you were standing on Mars, you would see Phobos rise in the west and set in the east, and it would rise again just 11 hours later.
Deimos is in an almost synchronous orbit, meaning that it orbits once around the planet in the same amount of time as Mars makes one rotation. Deimos rises in the east, but it crosses the Martian sky very slowly, taking 2.7 days between its rise and set.
Visits to Mars
The first spacecraft to visit Mars was Mariner 4, which was launched by NASA on November 28, 1964. It made its closest approach to Mars on July 15, 1965, and it captured the first images of another planet from deep space.
In December 1971, the Soviet Mars 3 mission achieved a soft landing on Mars, however, contact with the spacecraft was lost just seconds after touchdown.
On July 20, 1976, NASA's Viking 1 spacecraft made the first successful landing on the Martian surface. On July 4, 1997, NASA's Mars Pathfinder spacecraft landed on Mars, and the next day Pathfinder released Sojourner, the first robotic rover on Mars.
On December 25, 2003, the European Space Agency (ESA) spacecraft Mars Express visited Mars, followed a month later by NASA's two Mars Exploration Rovers - Spirit and Opportunity which landed on the planet. Incredibly, Spirit continued operating for six years, until March 22, 2010, while Opportunity continued working for a staggering 14 years, ceasing on June 10, 2018.
On August 6, 2012, NASA landed its Curiosity rover to examine Mars' climate and geology. On September 24, 2014, India's Space Research Organization (ISRO) placed its Mars Orbiter Mission spacecraft into orbit around Mars.
On February 9, 2021, the United Arab Emirates placed a spacecraft, the Hope orbiter, into Mars orbit, and just a day later, China's Tianwen-1 spacecraft joined it in orbit. A week later, on February 18, 2021, NASA landed its Perseverance rover on Mars, which successfully released its Ingenuity helicopter.
On April 19, 2021, Ingenuity took off vertically, hovered, and landed, becoming the first aircraft to complete a powered, controlled flight on a planet other than Earth.
On May 14, 2021, China's Tianwen-1 successfully landed on Mars and released its Zhurong rover, which successfully deployed on May 22, 2021, making China the second country to successfully deploy a rover on Mars.
Earth's relationship to Mars
Mars was well known to the ancient Sumerian and Egyptian astronomers. By 400 BCE, the Greek philosopher Aristotle made note that Mars disappeared behind the Moon, demonstrating that it must be farther away than the Moon. Greek astronomer Ptolemy, who lived in Alexandria, Egypt, analyzed the motion of Mars, and his writings became the definitive work on the subject for the next 1,400 years.
During the 1600s, the Danish astronomer Tycho Brahe measured the diurnal parallax of Mars, which the German mathematician Johannes Kepler then used to calculate the distance from Earth to Mars.
The first person to view Mars through a telescope was Italian astronomer Galileo Galilei, in 1610. The first person to draw a map of the planet was the Dutch astronomer Christiaan Huygens, and the Italian astronomer Giovanni Schiaparelli improved upon that map during a period when Earth and Mars were close together on September 5, 1877.
It was Schiaparelli who observed features on the surface of Mars which he called canali, meaning "lines", however, when translated into English, those lines became "canals". It was Schiaparelli who first began giving names from Greek mythology to features on Mars. Today, albedo features, meaning light and dark features that can be seen by Earth-based telescopes, tend to be named for mythological beings, while craters larger than 37 miles (60 km) across are often named for people who have contributed to the study of Mars or science fiction authors.
Craters on Mars that are smaller than 37 miles (60 km) are often named for towns around Earth. Large valleys on Mars receive names having the word "star" in various languages, while many small valleys are named for Earth's rivers.
Before you pack your bags for a trip to Mars, consider that Mars will not be easily habitable due to its lack of a magnetic field and its extremely thin atmosphere, which won't provide adequate protection from the solar wind. Mars' lack of atmospheric pressure means that it can't retain water in a liquid form, and it will instead sublime directly from a solid to a gas.
Unless you bring along friends, you might be lonely on Mars. Analyses by the Spirit, Opportunity, Phoenix, and Curiosity rovers have so far failed to detect any life on Mars. However, on June 7, 2018, NASA announced that its Curiosity rover had discovered organic compounds in sedimentary rocks that date to three billion years ago. This means that some of the chemical building blocks necessary for life were present on Mars at some point in time.
In July 2018, scientists discovered the first known stable body of liquid water on Mars. It is a subglacial lake that lies almost a mile (1.5 km) beneath the surface at the base of the southern polar ice cap, and it is about 12 miles (20 km) wide. These lakes may remain liquid because of high concentrations of toxic perchlorate salts.
At the time of writing, there are eight spacecraft in orbit around Mars including the 2001 Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, MAVEN, Mars Orbiter Mission, ExoMars Trace Gas Orbiter, the Hope orbiter, and the Tianwen-1 orbiter. There are six rovers currently on Mars' surface: the Mars Science Laboratory Curiosity rover, the InSight lander, the Perseverance rover, the Ingenuity helicopter, the Tianwen-1 lander, and the Zhurong rover.
In October 2016, then-president Barack Obama reiterated the U.S.'s intention to send humans to Mars sometime in the 2030s. The 2017 NASA Authorization Act instructed NASA to get humans near or onto the surface of Mars by the early 2030s.
Due to their complicated relative motions, it takes Earth and Mars a long time to reach their closest point to one another, 60,000 years to be exact. The two planets achieved that closeness on August 27, 2003, when they came within 34,646,419 miles (55,758,006 km) of one another. Before that, their closest approach was on September 12, 57,617 BCE, and their next close approach will be on August 24, 2208.
You might want to take along some reading material with you on your trip to Mars. The planet has made an appearance in a number of science fiction works including, H.G. Wells' 1898 The War of the Worlds, Edgar Rice Burroughs' Barsoom series of books, and a number of stories written during the 1960s by Robert A. Heinlein, including the classic, Stranger in a Strange Land.
Perhaps the strangest mention of Mars in writing appears in Chapter 19 of Jonathan Swift's 1726 classic Gulliver's Travels. There, Swift describes the two moons of Mars. The only problem with that description was that it was 150 years before Phobos and Deimos were discovered by Asaph Hall.