Mars
Known as “The Red Planet,” Mars looks like a bright red dot in the night sky. It is the fourth planet from the Sun and the friendliest one, with a dry, rocky surface that may prove useful to humans in the future.
Nomenclature
Mars gets its name from the Roman god of war because of its bloody, red appearance in the night sky. The easily-visible red dot has been friends with humans throughout history, from the Egyptians naming it “Her Deshur,” which translates to “the red one,” up until today, where it’s known as “The Red Planet” to most.
Why So Red?
To answer this question, we have to look at the chemistry on Mars. The Red Planet gives off such a bright red color because on its surface, iron minerals in the Martian dirt oxidize, or rust. When you combine iron with enough oxygen, you can get iron (III) oxide, which gives off a reddish tinge. This is similar to a bike or a pipe on Earth becoming rusty over time after being left outside. However, we do not know exactly where the oxygen came from that oxidized the Martian soil. It could have come from when Mars was young with water, when rainstorms could have pounded the soil with water as well as oxygen detached from the water molecules. Or, sunlight could have broken down molecules in the Martian atmosphere over time, producing oxidants such as ozone and hydrogen peroxide that could have reacted with the soil. Or perhaps dust storms have broken apart quartz crystals in the soil, which contain oxygen, which could then react with the nearby iron.
A Watery Past
One of the most intriguing things about Mars is that it may have once looked similar to Earth. Not only does the rusted soil suggest the possibility of water, but the land features sprawling over the Martian surface prove that Mars once had a surface flowing with water. In 1972, NASA’s Mariner 9 mission orbited Mars and sent back photos revealing a surface of riverbeds. Further exploration has found river valley networks, deltas, lake beds, and rocks and minerals that could only have formed in liquid water. All of these features reveal that liquid water used to inhabit Mars.
Ancient river valley networks on Mars
A delta on Earth compared to a dried up delta found on Mars
The landing location of the Curiosity rover in the Gale crater, a crater now known to once have been filled with water.
The Mars rovers have been extremely useful in teaching us the history of liquid water on Mars. NASA’s Curiosity rover landed in the Gale crater on Mars in 2012 at the foot of a layered mountain to begin its exploration over the dry surface. The Gale Crater was chosen as the landing sight because of it holds many signs that water existed over Mars’ history. Evidence suggests that around 3.5 billion years ago, the 96 mile crater held a lake of water. The rover observed an alluvial fan at the spot where it landed, which likely formed by water-carried sediments as well as layers at the base of the mountain, called Mount Sharp, with clay and sulfates, which both need water to form. A unique part of the Curiosity rover is that its payload can identify ingredients of life, such as organic compounds, which are built by the life-stimulating element: carbon. The exploratory rover drilled into the mudstone of four different areas in the Gale Crater and then analyzed the samples using SAM, which heats the rocks up to 500 degrees Celsius (900 degrees Fahrenheit) to release the organic compounds. SAM found small organic compounds and organic carbon concentrations of 10 parts per million, which is 100 times greater than prior detection of organic carbon on the Martian surface. Although these discoveries do not confirm life on Mars since we do not know the source of the organic molecules, it is a great motivator to stay on the path of Martian exploration.
NASA’s Curiosity rover takes a selfie.
The alluvial fan at Gale Crater indicates the place where sediment was deposited onto flatter land by a stream flowing downhill.
The layers forming the base of Mount Sharp.
Martian Missions Timeline
There have been around 50 missions so far that ventured to the Red Planet, and the number is bound to grow in the future with the appeal of a planet that is known to once have liquid water flowing on its surface. Out of all of the space missions, those that go to Mars may be the most significant, given that Mars is one of the few places we know where life may have existed and may be able to exist in the solar system. While past missions have given us unprecedented information about the Red Planet, present and future Martian missions may determine the future of humanity. Below are the most successful and impactful missions to the Red Planet to date, with NASA dominating the majority of them, especially today.
Mariners 4, 6, 7
All of the Mariner missions by NASA were designed to successfully fly by Mars with Mariner 4 taking the first photos of another planet from space in 1965. Mariners 6 and 7 were sent as a dual mission to Mars in 1969 to study the surface and atmosphere of Mars during close flybys.
The first close up image ever taken of Mars was taken by the Mariner 4 spacecraft.
The 11 foot tall Mariner 6 spacecraft.
Mariner 9
Mariner 9 was launched in 1971 and beat the Soviet Mars 2 to become the first spacecraft to orbit another planet. The 22 foot long orbiter mapped 85% of the Maritan surface and sent back more than 7,000 pictures.
A mosaic created by putting together multiple images taken of the Martian surface by Mariner 9.
Mariner 9
Mars 3
The Soviet Union’s Mars 3 was the first successful Mars landing, touching the surface in 1971. The soviet spacecraft landed during a dust storm and returned data for only about 20 seconds, taking a partial image from the Martian surface that is messy with no identifiable features.
Illustration of Mars 3 on the surface of Mars.
What was supposed to be the first image of Mars’ surface turned out to be fuzzy with indistinguishable features. Although some say you can make out a skyline, mountains, and clouds, the most likely truth is that no valuable information was transmitted during the short broadcast.
Vikings 1 and 2
The world finally received clear pictures of the Martian surface when Viking 1 successfully touched down on the surface on July 20, 1976. Viking 2 also successfully landed in September of the same year. Viking 1 and Viking 2 both included Mars landers and orbiters so the orbiters could create global maps from above while the landers examined the surface up close. Viking 1 landed on Chryse Planitia (Greek for “Golden Plain”) in Mars’ norther equatorial region and Viking 2 landed in a large impact basin named Utopia Planitia (Greek and Latin for “Nowhere Land Plain”). The high resolution cameras onboard the Viking orbiters created global surface maps and found that the Martian surface is really just made up of northern low-elevation plains and southern cratered highlands. On the surface, the landers found Martian soil to consist of iron-rich clay and conducted chemical analyses of the soil to look for life.
Carl Sagan standing with a model of the Viking 1 lander in Death Valley, California.
The first clear photograph of the surface of Mars, taken by the Viking 1 lander.
Mars Pathfinder
This NASA mission entailed the landing of the Pathfinder lander along with the Sojourner Rover on the surface of Mars in July 1997. Pathfinder demonstrated a new type of landing technique that was assisted by a parachute to slow the descent through the atmosphere before a large system of airbags inflated 8 seconds before the impact with the surface. Sojourner was the first rover to explore the Martian surface, spending 83 days observing the terrain, snapping photographs, and making atmospheric and chemical measurements. The rover confirmed predictions that ancient floods brought the variety of rocks seen at the landing site and Ares Vallis was once a flood channel.
An image taken of the small Sojourner rover after rolling out of the lander. The first two exploration targets would be the large rock at the top right dubbed Yogi (found to be volcanic) and the rock to the rover’s left named Barnacle Bill.
Pathfinder used its dual-camera Mastcam-Z imager to capture the Santa Cruz hill about 1.5 miles away from the landsite. All of this scenery lies inside the Jezero Crater.
Mars Global Surveyor
NASA’s Mars Global Surveyor arrived at Mars in September 1997 and mapped the planet from pole to pole as well as studied its atmosphere and interior, sending more than 240,000 images to Earth. The most exciting findings were the ancient signs of liquid water from gullies and debris flows that suggest the flow of water and the observance of repeatable weather patterns such as regular dust storms. The Mars Orbiter Camera aboard the spacecraft also helped to scout landing sites for the rovers as well as the Phoenix lander.
Mars Global Surveyor
The eerie image of a face on Mars taken by the Viking 1 orbiter in 1976 (left) was retaken with more detail by the Mars Global Surveyor in 2001 (right).
Mars Odyssey
Arriving at the Red Planet in 2001, the Mars Odyssey orbiter continues to operate today and is NASA’s longest-lasting spacecraft at Mars. Its primary mission was to make a global map of the quantity and distribution of chemical elements and minerals that make up the surface of Mars, which was completed successfully by 2004. In the process of mapping, Odyssey made several discoveries such as the identification of large amounts of hydrogen in the soil, indicating the presence of ice under the surface and the discovery of salt deposits in 200 locations, which were left behind in places where water used to be abundant. In addition to mapping, Odyssey acts as a relay for landers and rovers on the surface. The THEMIS camera (Thermal Emission Imaging System) on board the orbiter had returned more than 188,000 thermal-infrared images and more than 208,000 visible-light images by 2016, and 21,000 images were put together to create the most accurate Mars map ever made according to NASA.
Mars Odyssey
An incredibly detailed image of the “Grand Canyon of Mars” taken by THEMIS as part of the global Mars map. The red rectangle represents the location of another full resolution image, emphasizing the stunning capabilities of this camera.
Mars Exploration Rover
The success of the Sojourner rover compelled NASA to send more rovers to find more clues about the history of water on Mars and to learn more about the planet in general. The Mars Exploration Rover mission consisted of two twin rovers named Spirit and Opportunity that were each the size of a small golf cart, much larger than the Sojourner rover, which was about the size of a microwave oven. In 2004, Spirit landed in the Gusev Crater, which is thought to have once held water because of what looks like several large rivers flowing into the crater. Opportunity was chosen to land on the other side of Mars at a flat area called Meridiani Planum, where a mineral called grey hematite, often found in the presence of water, was thought to exist. The Spirit rover found rocks that were very rich in key chemicals and formed when Mars was warm and wet, found soil that contained 90% pure silica, usually existing in hot springs or steam vents where life like microbes can thrive, and came across an ancient volcano that erupted likely from the interaction of basaltic lava and water. Meanwhile, Opportunity was making discoveries of its own, such as the water-based, blueberry-looking mineral called hematite at the rover’s landing spot, the colored veins of gypsum in rocks in the Endeavor Crater, likely formed from water flowing through underground fractures in them, leaving calcium behind, and signs of the friendliest conditions for ancient life at the same crater, where clay minerals formed in neutral-pH water. Unfortunately, Spirit’s journey came to an end when it got stuck in soft soil in 2009 and used all of its energy trying to escape, but Opportunity worked for nearly 15 years on Mars before being declared dead in 2019 after losing signal during a dust storm.
The structure of both the Spirit and Opportunity rovers since they are nearly identical. Opportunity was the longest-functioning rover that has ever traversed the red surface.
During Opportunity’s life on Mars, it studied the geology of more than 100 craters, studying how they form and erode with time. This shows Opportunity’s path from crater to crater after landing.
Mars Reconnaissance Orbiter
Another NASA mission shot off to the Red Planet in 2005 and the spacecraft began orbiting it in 2006. This new spacecraft carried the most powerful high-resolution camera ever sent to Mars. With this camera, NASA found a landing spot for the Mars Curiosity rover and even imaged a comet called Comet Siding Spring in 2014. Another notable finding was recurring slope lineae or crater streaks that may have formed from briny (salty) surface water slowly flowing down the slope of the craters. The spacecraft served as a communication relay for the Opportunity rover and serves as a relay for the Curiosity rover today. Although the mission was initially designed for two years at Mars, the formidable orbiter continues to take pictures today.
Mars Reconnaissance Orbiter
An image taken by the Mars Reconnaissance Orbiter of recurring slope lineae, the dark-toned features that appear in early spring and are thought to originate from downslope flowing water or granular material.
Mars Phoenix
The Mars Phoenix stationary lander was sent by NASA in 2007 to fulfill the mission of its lost brother, the Mars Polar Lander, which unexpectedly lost communication as it touched down on the surface. Phoenix was sent to the polar regions of Mars to attempt to uncover water ice and look for signs of microbial life. The lander successfully found and studied ice beneath the Martian surface using its robotic arm and portable laboratory. The chemical perchlorate was also found at the landing site, which could have been an energy source for microbes in the past.
Illustration of the Phoenix lander at work on the Martian surface.
Mars 2020 Mission
The continuing success of the Mars rover programs like Curiosity led to the even more ambitious introduction of the Mars rover, Perseverance, as well as the first interplanetary helicopter, Ingenuity. The rover was based on Curiosity’s rover configuration and is about the size of a car. The main goal of Perseverance was to seek ancient life and collect samples of rock and regolith (broken soil and rock) for a possible return to Earth. The Ingenuity helicopter was a late addition to the project that was relatively low-cost. After its main goal of conducting flights was successful, Ingenuity acted as a scouting partner for the rover, observing the terrain ahead on Perseverance’s path.
The image taken by NASA’s Phoenix Mars lander of frozen water beneath the Martian surface on the 21st and 25th days of the mission.
Mars Science Laboratory/Curiosity
NASA’s Mars Science Laboratory mission set down the large 10-foot-long rover, Curiosity, on the surface of Mars at the Gale Crater in 2012. This new rover is twice as long and five times as heavy as Spirit and Opportunity. The purpose of the mission was to search for signs of ancient habitable environments inside the crater, which is known to have once held a lake of water. Curiosity’s unique set of instruments allow it to collect and analyze soil and atmospheric samples, taking close-up pictures with very fine detail and using a spectrometer to determine the amounts of different elements in the soil samples. The landing site at Gale Crater is about the size of Connecticut and Rhode Island combined, leaving a lot of space for exploration. This special rover was the first to actually drill into a Martian rock (a rock named John Klein), discovering geological and mineralogical evidence for liquid water and other key ingredients for life as well as determining the age of another rock to be 4.2 billion years with only 80 million years of exposure to the surface. Some other major findings include the discovery of organic compounds, which are essential for life, methane on the surface, implying the existence of microbes, and multiple land features that indicate the flow or soaking of water in the past. Today, Curiosity continues its ascent up the 5.5 kilometer (3-mile) Mount Sharp at the center of the Gale Crater that it started in 2014, uncovering more and more of the planet’s watery history as it goes.
Curiosity descended to Mars using a parachute until the last seconds before landing, when rockets were fired allowing the system to hover in the Martian air as a tether lowered the rover down to the surface. After Curiosity landed, the tether was cut and the landing system crash landed a distance away from the rover.
NASA’s Mars Rover team posing around the one-ton Curiosity rover.
Explore the 360-degree panorama taken as the Curiosity rover was perched on the lower slopes of Mount Sharp in 2019.
Mars Insight
It may seem like a bit of a stretch, but InSight is short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport. This outlines the purpose of the mission, which was to investigate the interior structure of Mars. The lander’s goals were to gather data about the crust, mantle, and core of Mars as well as find out how a rocky body can form and evolve to become a planet like Mars. Insight used three tools to carry out its investigations: a seismometer, its RISE tool (Rotation and Interior Structure Experiment), and a heat flow probe.
Checking Mars’ Pulse
The seismometer, called SEIS (Seismic Experiment for Interior Structure) can be thought to measure the “heartbeat” of the planet, detecting seismic waves or vibrations coming from deep beneath the surface on which it sits. This ultra-sensitive tool detected meteor impacts, weather phenomena like dust devils, marsquakes, and can even sense tremors smaller than a hydrogen atom. SEIS studied the interior structure of Mars by listening to a hose of different variations in seismic waves, which change as they pass through different materials. Although the probe was only hammered 1.1 feet out of the 5 feet is what supposed to be inserted into the Martian surface due to clumping of soil, some significant discoveries were still made. The tool found that the crust is thinner than it was believed to be and that Mars has a molten core, which is surprisingly large. It also found “ghosts” of Mars’ magnetic field, which died about four billion years ago, suggesting that it may have been stronger than believed.
Measuring Mars’ Reflexes
The RISE instrument, on the other hand, how much Mars’ north pole wobbles as it revolves around the Sun and the Sun pushes and pulls it in its orbit by keeping track of the exact location of InSight within even a few inches. By reflecting signals sent to the lander from Earth back to Earth, RISE measures the “Doppler shift” in frequency or how much the wavelengths are measured to stretch if Mars is moving away from Earth or shrink if is Mars moving toward Earth. By tracking how the lander is moving in space, the wobble of Mars can be determined. A planet with liquid in its core will wobble more than one that is solid in its core. Therefore, how much Mars wobbles can tell us whether the core is molten or solid. Although the SEIS’ analysis of seismic waves that vibrated through Mars after a meteorite helped conclude that Mars has a molten metal core, tracking Mars’ wobble suggested a core size of about 1,835 kilometers (1,140 miles).
Taking Mars’ Temperature
Finally, the heat probe on board InSight was designed almost 5 meters or 16 feet into the surface to measure heat from the planet’s interior to uncover how much heat is leaving the body of the planet. A tether embedded with sensors is attached to the mole, which is the tool that burrowed down into the soil and can send out a pulse of heat to the above sensors to watch how the heat pulse decreases with time. A quick decay in the pulse indicates crust material that is a good conductor of heat, like metal, while a slow decay indicates material that is a poor conductor. However, due to a lack of friction needed to dig, the heat probe only made it 14 inches into the ground before being stuck. The team learned about the soil properties of Mars from this failure, which could be useful for future missions.
A diagram of the many different instruments onboard the InSight lander, including the heat probe, and RISE and SEIS instruments.
Scientist spent almost two years using InSight’s robotic arm to help the heat probe dig into the surface, but the effort was finally called off in January 2021.