The following information is adapted from: http://www.exploringmars.com/science/ataglance.html. Mars is the 4th planet from the Sun. It orbits around the Sun between the Earth and the asteroid belt. It is about one and a half times as far from the Sun as the Earth. Mars is a little more than half the size of Earth, and has two small moons, which are basically asteroids captured in its gravitational pull. The atmosphere is very thin, having about 1/180 the atmospheric pressure of the Earth. It is chiefly composed of Carbon Dioxide (95.3%), Nitrogen (2.7%), and Argon (1.6%). Mars has a reddish-orange color caused by the iron-rich minerals in its soil. A fine-grained reddish dust blankets the planet and can be lifted into the atmosphere when blown by the wind. Martian dust storms range from small dust devils to an occasional spectacular event that shrouds the entire planet for months! On the surface, there are many intriguing features such as volcanoes and canyons. The highest point on the planet is Olympus Mons, a huge shield volcano about 26 km (16 miles) high and 600 km (370 mi) across, about the same size area as the state of Arizona. The canyon system of Valles Marineris is the largest and deepest known in the solar system. It extends more than 4,000 km (2,500 miles) and reaches depths of 5 to 10 km (3 to 6 miles) below the surface. Finally, Mars has polar caps composed primarily of frozen carbon dioxide and water ice that grow and shrink with the changing Martian seasons.

Humans have been observing Mars since ancient times. Around 400 BC the Babylonians started studying astronomy. They originally named the planet they saw Nergal, which means king of conflict. Later, the name Mars came from the Roman god of war.

People knew that the planets were not the same as the stars since they traveled differently across the night sky. However, no one could explain their unique motion. The problem stemmed from the early belief that we lived in a geocentric universe. This means we thought the Earth was located at the center of the universe. In 1543, Nicolaus Copernicus wrote a book that stated that the Sun was at the center of our solar system (heliocentric). As scientists realized that the Sun was at the center and the planets revolved around it, they began to learn more about Mars. In 1576, the Danish astronomer Tycho Brahe — using only his naked eyes and a few crude instruments — calculated that Mars is roughly 200,000,000 kilometers from the sun. Much to the advancement of technology, Galileo invented the telescope in the early 1600s, which became crucial to further discoveries about the Red Planet. Another important discovery was made by Johannes Kepler in 1609. He discovered that all of the planets orbited around the Sun in ellipses as opposed to perfect circles — knowledge which Sir Isaac Newton used half a century later in explaining the physics of planetary motion. Later in the 17th century, Christiaan Huygens and Giovanni Cassini calculate that a Martian day is around 24 hours and 40 minutes long.

Many of the mysteries surrounding Mars were uncovered throughout the 18th and 19th centuries. Giancomo Miraldi discovered that Mars has polar ice caps in 1704, and in 1809, Honore Flaugergues observed yellow clouds on the surface of Mars. In 1877, Giovanni Schiaparelli discovered that Mars has two moons, which he named Phobos and Deimos after the horses of the Greek war god Ares.

Fun Fact: The yellow clouds that Honore Flaugergues observed actually turned out to be dust storms. (http://www.exploringmars.com/history/1800.html)

Eventually, there became a point when there was not lot more to learn about Mars by just using telescopes from Earth. With the engineering development of large rockets in the 1950s and 1960s, it became possible to send probes to Mars in order to explore the planet up close. From 1960 through the present day, there have been many Mars exploration missions sent by the United States and Russia. The first successful mission to Mars was the Mariner 4 spacecraft, which was launched by the United States on November 28, 1964. Seven and a half months later, the craft did a flyby of Mars, taking pictures of the surface and measurements of the magnetic field, atmosphere, and radiation of Mars. Mariner 6 and 7 flew past Mars in 1969 taking even more, detailed pictures of the planet's surface. While all previous missions had just flown past Mars, the Mariner 9 mission, in 1971, became the first spacecraft to ever orbit a planet other than Earth. Mariner 9 was the last of the Mariner series. Mariner missions 1, 2, 3, 5 and 8 were not mentioned because they were actually missions that failed for one reason or another (e.g., some did not even get off of the ground successfully, while another failed en route, and another got to Mars just to stop working once there).

The next spacecrafts to reach the Red Planet — and the first to successfully land on the surface of Mars — were the Viking spacecrafts that were both launched in 1975. Both Viking 1 and Viking 2 were each comprised of an orbiter and a lander. The purpose of orbiters was to gather high resolution images of the surface and perform further studies of Mars from space. The purpose of the landers was to study the soil and atmosphere of Mars and to search for any signs of life on the planet. The Viking missions were very successful, and taught scientists a lot about the surface of Mars.

Figure 3. The 1997 Pathfinder mission with the Sojourner Rover click for copyright

After the Viking missions, it wasn't until 1997 that another American spacecraft successfully reached Mars. That year the Mars Global Surveyor and the Mars Pathfinder reached the Red Planet. The Mars Global Surveyor photographed the Martian surface as well as measured the gravity and the magnetic field of the planet. The Mars Pathfinder was another successful mission. The Mars Pathfinder mission consisted of a lander and a small robotic rover, called Sojourner, whose purpose is to investigate the structure of the Martian atmosphere, weather and geology. Pathfinder landed on the surface of Mars, and the Sojourner rover left the lander and drove around the Martian surface. The rover took samples of rocks and tested them for signs of water and life. Figure 3 shows the Pathfinder lander with its three triangular solar panels and the small Sojourner rover.

In early 2004, two rovers landed on the surface of Mars. They were named Opportunity and Spirit. These rovers will be discussed in more detail in the Lesson 2 of the Mission to Mars unit.

Despite all these successful missions, there have been even more failures. Many vehicles lose contact with Earth, crash into Mars, or even miss Mars altogether. Engineers are constantly trying to find better and more reliable ways to explore Mars. While getting to Mars successfully is very difficult, it is this challenge that makes getting there so exciting.

So why do we care so much about Mars anyway? What makes it worth spending millions of dollars to send a spacecraft there? Well, the most intriguing aspect of Mars is that out of all the other planets in our solar system, besides Earth, it is the one that is most likely to have life on it or to have supported life at one time. Despite the fact that humans cannot live on Mars since the atmosphere is too thin and does not contain oxygen, Mars very well could have water on it, which is an important key when it comes to supporting life. There have been meteorites found on Earth that came from Mars which contain potential signs of very basic life. While there are many fanciful stories about little green men on Mars, most scientists believe that if there is life on Mars, it exists on a very simple level such as single celled organisms and bacteria.

Mars is also the most hospitable planet to humans other than Earth. Mercury is so close to the Sun that the radiation and heat make it a very hostile environment. While Venus is the closest planet to Earth, it has a thick atmosphere of sulfuric acid that is poisonous and creates a very hot and high pressure atmosphere. Jupiter, Saturn, Uranus and Neptune are all gas giants, which means there is no solid surface to stand on or the surface is under incredible atmospheric pressure. Pluto is far too cold and distant to make it a good candidate for exploration. This leaves Mars as the only logical candidate for exploration. It is relatively close and has a fairly friendly environment with the potential for life.

Aside from the prospect of life, an understanding about the origin of our solar system can be gained by visiting Mars. The scientific information taken from Mars can be compared to Earth in order to make conclusions about the solar system. Mars has changed a lot over time. Evidence suggests that Mars used to be warmer — with volcanoes and possibly rivers. What happened to make Mars the cold desert it is today? If we can answer this question about Mars, we can predict what might be in store for the future of Earth. Clearly, there are many mysteries about Mars that have not yet been solved.

One of the most basic reasons for visiting Mars is just for the sake of exploring. Humans are naturally curious, and a distant planet represents one of the most intriguing explorations. Mars is very different from Earth, and there is so much we have yet to learn about it. The challenge and excitement of exploring other planets — coupled with the potential for new information and how it relates to Earth and the rest of the solar system — makes Mars a very tempting place to visit.

Figure 4. What a future airplane on Mars might look like. click for copyright

The future of Martian exploration is very exciting. The next planned mission is the Mars Reconnaissance Orbiter, expected to launch in 2005, which will take high-resolution pictures of the Martian surface. These images will be used to determine the best landing points for future landers. The Mars Reconnaissance Orbiter is also equipped with a sounding device that can locate water under the surface of the planet. Talk about advances in technology! 18th century explorers probably never have imagined such sophisticated engineering feats. Following the Mars Reconnaissance Orbiter, there will be a series of robotic rovers that will explore the polar ice caps as well as search for life and water beneath the surface. There are even plans to send airplanes or airships to Mars that can explore the atmosphere. This is a difficult and thrilling engineering challenge since the thin Mars air requires that special aircraft will have to be designed to cope with these conditions. Figure 4 is an artist's rendition of what such an airplane might look like.

Figure 5. A vision of future human exploration of Mars. click for copyright

Beyond the year 2015, there are plans to send a vehicle that can pick up samples of the Martian surface and then bring them back to Earth to be analyzed. The most exciting and ambitious mission involves taking humans to Mars, which is incredibly difficult since it takes six months just to get there! Once there, they will have to land safely, find a place to live and work, and then strategize a way to get back to Earth. One of the most difficult challenges is having enough food, water and oxygen for a mission that will most likely last a couple of years. Currently, there are mock Martian habitats on Earth that simulate living on Mars, but scientists and engineers are continuously researching ways to keep people alive in the harsh Martian environment for extended periods of time. This involves recycling water and oxygen and growing food on the planet in special greenhouses. In order to put humans on Mars, there are many engineering challenges to overcome; but, as technology improves, it is only a matter of time before there are manned missions and even permanent residence on Mars (see Figure 5).

Discussion Question/Answer: Solicit, integrate, and summarize student responses.

• Ask the students what they know about Mars. How do scientists research Mars? (Answer: They should come up with things like telescopes and spacecraft.)
• A way to describe Mars is to compare it to Earth. Is it bigger or smaller? (Answer: It is a little more than half the size of Earth).
• Is it further or closer to the Sun? (Answer: Further)
• Are there oceans? (Answer: No)
• Are there moons? (Answer: Yes, there are two.)
• Is it colder/warmer? (Answer: Colder)
• What have they seen about Mars in movies and television? How much of this is true and how much is fantasy?

Voting: Ask a true/false question and have students vote by holding thumbs up for true and thumbs down for false. Count the number of true and false, and write the number on the board. Give the right answer.

• Have the students vote on whether or not there is life on Mars. (Answer: We do not know yet. That is why engineers are working hard at developing rovers and satellites to answer these unknown questions.)

Discussion Question/Answer: Solicit, integrate, and summarize student responses.

• Why do we want to go to Mars? (Answers: Figure out more about our solar system and how it was formed; determine if there is water on Mars; conclude whether or not there is/was life on Mars; or just to explore.)

Community Debate: In teams, have the students write/perform a short play or debate about Mars missions. The setting is a town meeting about a relevant issue. The people present are: an engineer, a manager of the industry, a local politician and various citizens. Possible scenarios include:

• Should we try to send humans to Mars? Why or why not?
• What information do we need to gather about Mars before we can send humans there?

Numbered Heads: Have the students on each team pick numbers (or number off) so each member has a different number. Ask the students a question (give them a time frame for solving it, if desired). The members of each team should work together to answer the question. Everyone on the team must know the answer. Call a number at random. Students with that number should raise their hands to give the answer. If not all the students with that number raise their hands, allow the teams to work a little longer. Ask the students:

• Where did Mars get its name? (Answer: The Roman god of War)
• Nicolaus Copernicus theorized that the solar system was not geocentric, but heliocentric. What do geocentric and heliocentric mean? (Answer: heliocentric means Sun centered; geocentric means Earth centered.)
• Is the Martian day longer or shorter than the Earth day? (Answer: longer by about 40 minutes.)
• Is Mars closer or further from the Sun than the Earth? (Answer: Mars is further.)
• What is the name of the giant volcano on Mars? (Answer: Olympus Mons)

Question/Answer Revisited: solicit, integrate, and summarize student responses.

• Revisit the questions in the Pre-Lesson Assessment. Determine what they have learned to be true and false about Mars. How does this differ from the Hollywood view of Mars?