MARS' ORBIT AND ITS MOONS: Mars is the fourth planet from the sun (one after Earth) and takes 687 Earth days to orbit the sun once, while rotating on a tilted axis of 25.19O. That means that if a 30-year-old lived on Mars, he/she would only be 15 Martian years old! A day on Mars is slightly longer than an Earth day, being 24 hours and 37 minutes. Mars' orbit is the shape of an ellipse (as of all planets) – it is 20% closer to the sun in the winter than in summer, and its orbiting speed can change - when it is close to the Sun, it moves swiftly, when it is further out, it moves more slowly due to the reduced gravity. As a result of this, a Martian spring is 52 days longer than a Martian autumn. It normally hurtles through space at a rate of 24 kilometres per second. It has 2 small moons - Phobos and Deimos, believed by astronomers to formerly be part of the Asteroid Belt, and then captured by Mar's gravitational pull. Phobos is the larger moon, though its dimensions are only 27 kilometres, by 22 kilometres, by 19 kilometres, while Deimos' are 15 kilometres, by 12 kilometres, by 10 kilometres. Phobos is heavily cratered, while Deimos is smooth and darker.
Phobos moves speedily - it whizzes around the
planet in only seven and a half-hours, while
Deimos takes six hours longer than Mars does
to rotate on its axis once, hence it looks as
though Deimos is moving in the opposite
direction! Phobos orbits Mars at a distance
of 9330 kilometres from Mars' centre, while
Deimos circles the planet at a distance of
23,500 kilometres from its centre. These moons are very irregular in shape, and have been compared to giant potatoes!
MISSIONS TO MARS
HUMAN EXPLORATION: Even sophisticated telescopes on Earth can not reveal much, because of the atmosphere. Humans have been long fascinated with Mars, though successful flights to the harsh planet have only been made since the mid 20th century. Even so, unmanned probes and orbiters so far have made the only flights. Traveling to Mars is not as easy as it seems - the planets don't stay in one position, but move around the Sun. Therefore the shuttle must be aimed at where Mars would be when the craft would arrive (approximately 200 days), as a difference of just 1 kilometre per hour could be disastrous.
MARINER 3: On November the 5th, 1964, NASA launched the Mariner 3, though a shell covering the spacecraft failed to come off in space, hence none of its instruments could work and unfortunately it missed its destination by a great distance.
MARINER 4: However, NASA was still determined. By November the 28th, 1964 they had prepared another craft – the Mariner 4, which actually was due to be launched a few days after Mariner 3, but its launch was postponed due to the shell problem, so that engineers could design a new type of shell. It was wonderfully successful – the 264.5 kg (575 pounds) spacecraft consisting of 138,000 pieces, to which solar panels were attached, carried eight scientific instruments and was sent to study the planet’s radiation and magnetic field. One of the instruments was a television camera that would take the first close up pictures of Mars. The 21 and a half pictures taken with primitive technology, at a distance of 6118 miles (approximately 9788 kilometres) during the Mariner 4’s encounter with Mars, weren’t very clear compared to pictures taken by later probes, though were at least fifty times clearer than images via a telescope on Earth. A photograph took up to eight hours to transmit, at a rate of only 8.3 bits per second!
MARINERS 6 AND 7: Later in February and March of 1969, Mariners 6 and 7 were launched. (Mariner 5 was bound for Venus). Both weighed 900 pounds (414 kg) and carried expanded scientific instruments and greatly improved data - transmission capabilities, a maximum capacity of 16,200 bits per second. Their purpose was to examine the Martian surface condition and gather evidence as to whether life on Mars actually existed. Mariner 6 and 7 also featured advanced television systems – a single photograph would contain 3.9 million bits of data, compared to just 250,000 in a Mariner 4 picture. Pictures of Mars from about 3,200 kilometres showed some relatively flat areas speckled with shallow craters, others heavily cratered with many craters measuring 50 to 80 kilometres in diameter. Also, there were wavy areas containing a chaos of small ridges and valleys. Despite the fact that only 20% of the entire surface of Mars had been photographed close-up, a scientist studying the results made a sweeping statement that Mars was "uninteresting", as a result of indications of poor prospects for life.
MARINERS 8 AND 9: In 1971, Mariners 8 and 9 were launched. But not everything went right. These two spacecraft were designed as orbital spacecraft that would travel to Mars and orbit the planet, taking thousands of photographs and examining the atmosphere, temperature and surface. On May the 8th, 1971, Mariner 8 took off to Mars. The launch vehicle was a two -stage rocket consisting of an Atlas upper stage (famous for its use in propelling John Glenn into space to become the first American to orbit the Earth), and a Centaur upper stage. The Centaur was a cryogenic rocket, using extremely cold liquid hydrogen and oxygen for its propellants. During liftoff, the Atlas performed well, however the Centaur failed to ignite, causing the mission to be ruined. Twenty - two days later, on May the 30th, 1971 at 6:23 p.m., the next attempt came. This time, both rocket stages worked perfectly and the
974-pound (448-kg) orbital probe, Mariner 9
was on its journey to Mars. It was launched
from Cape Kennedy in Florida when Mars
was approximately 101 million kilometres
from Earth. Unfortunately, a new problem
arose, not with the Mariner 9, but with
Mars; two months before the orbital probe
was to orbit the planet, a massive storm
began in a region in the southern hemisphere
and spread until the whole planet was
surrounded in dust. When the spacecraft
entered its orbit of 1,600 kilometres on
November 9, the storm was still in its fury and
so dense that nothing could be seen, beside four
darkish spots on the surface. Therefore,
scientists decided to direct the two cameras
at the two moons, Phobos and Deimos, revealing
their irregular shape and cratered surface. Fortunately, by the end of 1971, the storm began to subside and the surface of Mars opened for inspection. The planet was filled with magnificent sights and appeared to be a dynamic world with amazing landforms. Although volcanic activity was not observed, the fact was not surprising to scientists as volcanoes on Earth can lie dormant for hundreds of years. The strong probability that water existed on Mars reinforced scientists' hopes of life on Mars.
VIKING 1 AND 2 - THE SEARCH FOR EXTRA TERRESTRIAL: It was time to send probes to the Martian surface...
NASA was already hard at work, even when the Mariner 9 was in orbit, on a new Mars exploring spacecraft that would land on Mars - the Viking 1 and 2. NASA had accomplished this feat before when astronauts landed on the moon. However, the Apollo 11 commander Neil Armstrong had the advantage of making on-the-spot decisions and altering landing plans to fit unexpected situations, while the Viking lander would not be under human control. It would have to make its own landing decisions - a radio "Help!" message would take 35 - 40 minutes to reach Earth, even while traveling at the speed of light. There would be two Viking spacecraft, so that if one failed, the other one could complete the job. The two Viking spacecraft comprised to parts - an orbiter and a lander.
THE VIKING ORBITERS: The orbiter would serve as the "bus" to transport the lander to Mars and would relay the data back to Earth. There were four windmill-like solar panels to generate electricity from sunlight. Communications with Earth and the Viking probes would be accomplished through the use of three separate radio antennas. One would be a high-gain steerable two-way antenna that would have to point directly at the Earth to work and could transmit up to 16,000 bits of data per second. A second would be an omnidirectional (meaning in all directions) antenna for reestablishing radio contact with Earth in an emergency. However, this antenna sent signals in all directions, so it could only be used when the Viking was still near the Earth as the signals get weaker as they spread. The third antenna was used to receive messages from the lander on Mars and to send it back to Earth via the high-gain antenna. Two tracking sensors would lock on the position of the Sun and the star Canopus. If the two stars weren't in their proper places, small nitrogen jets at the ends of the solar panels would correct the Viking's position. When the spacecraft was at the right distance, a large braking rocket engine would ignite, providing sufficient thrust to stop the Viking spacecraft, permitting Mars' gravitational pull to put it into orbit. The orbital spacecraft would have a pair of 1500 millimetre focal-length lens television cameras for scanning landing areas and mapping the whole surface of Mars. The water vapour detector would be a spectroscope, which breaks light up into its components so those wavelengths can be measured. Water vapour in the atmosphere would filter out certain waves, and the orbiter would respond to these. An infrared mapping device would measure Martian surface temperatures, polar ice cap temperatures, and the temperature in the clouds.
THE VIKING LANDERS: The Viking landers would have to pass through an atmosphere before landing, therefore it would have to withstand the air friction. Moreover, the entire lander would have to be sterilised to prevent any Earth microorganisms from "hitching" a ride to Mars. The lander was constructed of aluminum and titanium metal alloys, providing support for scientific experiments, communication and other equipment. Three folding legs were mounted on the bottom of the probe, and at the end would be 30 centimetre circular footpads. Surrounding the lander would be its two-part bioshell, which prevented Earth microorganisms from 'nesting' inside the Viking lander. Prior to the landing, the lower half of the bioshell would be discarded, and an aeroshell would protect the lander during the entry of the Martian atmosphere. A cork-like material covering the aluminum would burn off during intense heating, carrying away the majority of the excess heat. A parachute would be ejected at just the right moment to slow down the lander. Finally, the touchdown would be accomplished by a set of three rocket engines, burning hydrazine propellant, and providing a total of 7800 newtons of thrust. The unique 18 nozzles per engine would spread out the thrust to protect the surface of Mars and any possible "Martians". Radar devices would accurately calculate the elevation of the lander as it came down. Viking instruments included a television station, a miniature weather station, automatic chemical laboratories, an arm and a scoop for digging Martian soil, a conveyor system, a magnetic particle sensor, and a seismometer for measuring quakes (Marsquakes).
LIFTOFF! At 5:22 p.m., August 20, 1975, the mighty Titan III Centaur rocket launched the Viking 1 on its journey to Mars. On September 9, 1975, Viking 2 was launched. The voyage of the two went very smoothly, besides a few minor exceptions. Viking 2 had battery charging problems, but engineers were able to radio instructions to the probe. A short time after Viking 1 was in orbit (the next year), scientists and engineers decided that the selected landing site was too rough, therefore the landing had to be delayed until July the 20th, 1976 - and the new landing area was the Chryse Planitia region in the northern hemisphere. (The residents of America were slightly disappointed because delaying the landing would meant that they couldn't celebrate the two-hundredth anniversary of America, the 4th of July 1976 by landing a spacecraft on another world). Scientists on Earth watched with great excitement and frustration as the Viking 1 began the long, arcing fall to the surface. Even traveling at the speed of light, the radio signals took up to nineteen minutes to reach Earth, hence what scientists and engineers saw had happened nineteen minutes ago, so if a problem arose, it was already too late and it was all over. The last sixty seconds of touchdown was to be handled by the three hydrazine rocket engines, as the parachute was thrown overboard. Viking 1 touched down on Mars at 8:12 a.m., and 56 million kilometres away on Earth, the jubilant NASA workers cheered. However, the "smooth, safe" landing site was actually littered with rocks of all sizes, one nicknamed "Big Joe" could have tumbled onto the lander and flipped it over. Meanwhile, back in space, Viking 2 went into orbit on August 7, and touched down on September 3, 1976 in the Utopia Planitia region, 6,400 kilometres west of the Viking 1 landing site. Although the two landing sites resembled each other in many ways, there were also many differences. When the search for life began eight days after Viking 1 landed, scientists mistakably believed that there was life on Mars, due to exotic chemical reactions that only mimicked life. The Viking landers also looked at the huge volcanoes, craters, canyons, and twisting water-cut channels. At one point, the Viking 2 orbiter was instructed to change orbits in order to study the polar ice caps, confirming the theory of water ice in the northern ice cap. Although they were only supposed to last a few months on Mars, they lasted much longer. The Viking 2 orbiter finally ran out of fuel on July 25, 1978, and the Viking 1 orbiter in the late summer of 1980. Without attitude control fuel, the probes could no longer point in the correct position to send data to Earth. The Viking 1 stubbornly worked until November 1982, until it suddenly fell silent.
THE PATHFINDER AND SOJOURNER PROBES: The year 1997 marked the return to the red planet. For nearly twenty years, every Mars mission had ended in failure. The two Russian Phobos craft failed, the US Mars Observer exploded as it prepared to enter orbit, and the Russian Mars '96 craft did not escape the Earth's gravity. But finally, on July the 4th 1997 (American Independence Day), the Pathfinder probe landed on Mars, carrying a small six-wheeled vehicle - Sojourner to study nearby rocks. The Pathfinder landed in a panorama of rolling hills
and scattered rocks of all
sizes and textures. The
microwave-sized Sojourner
spent nearly three months
analyzing the surface and
rocks, until the battery went
flat. The Mars Global
Surveyor reached Mars in
September 1997 and its
ongoing mission is to
accurately map the entire planet. Its modern, high-resolution cameras, lasers and radar devices can spot objects less than one metre across from its position in orbit! It might even be able to see the Pathfinder probe on the surface! More space journeys have been planned for the future, including a mission to return rock samples and the ultimate one to land astronauts on Mars. Scientists are ambitious to establish a space station on Mars in the next 30 years!
INTERESTING FACTS/FEATURES
- An American astronomer, Asaph Hall got fed up with studying Mars one night, and decided to go to bed. However, his domineering wife bullied him to stay up and that night he discovered the red planet's two moons. He named them Phobos and Deimos after the sons of the Roman god of war - the god of fear and terror!
- Water may actually exist in the form of ice at the poles.
- Most of the ice at the poles consists of frozen carbon dioxide or "dry ice"!
- In 1996, microscopic fossils on Mars showed what may be could miniature viruses.
- The two moons may have formerly been asteroids and then captured by Mars" gravitational pull.
- From the planet, the Martian sky appears to be yellowish-pinkish, as a result of the particles containing iron oxide in the atmosphere, which absorb most of the blue light.
- In the seventeenth century, Johannes Kepler "predicted" that Mars had two satellites (moons) because Earth had one and Jupiter had four! (only the four Galiliean moons were known at that time).
- There is a gigantic canyon, Valles Marineris, far larger than the Grand Canyon in America, 4,000 kilometres long and 8 kilometres deep, forming a huge gash in the planet's surface.
CONCLUSION
Mars is an astonishing planet, a land
filled with secrets we have not yet
discovered. However one day, we
may be able to know much more
about it, and spacecraft journeys
may just be like current local bus
services. Perhaps a long time ago,
liquid water existed on Mars, but it all evaporated into space? We may just be an insignificant corner of the universe, or the only unique, hospitable place where life exists. To us, the universe is immeasurable, as we are just beginning to discover its wonderful secrets and exploring the planet most similar to Earth...
...Mars.
