My Science School

By mid-1900s the Martian-canal confusion had cleared completely, and scientists were convinced that Mars was a dry planet. Photographs taken by the U.S. National Aeronautics and Space Administration’s (NASA) Mariner 4 spacecraft in 1965 and other Mars missions after that had played a huge role in it. That was why everyone was puzzled when about a decade later, in 1972; NASA’s Mariner 9 sent back images of a Martian surface lined with grooves! These were no Martian-made canals like Lowell had predicted, or straight, crisscrossing canali like the ones Schiaparelli had sketched on his maps. They were winding channels carved into the surface of Mars, kilometres long, and very similar to the river-made features we see on the Earth, except that they were completely dry!

It clearly looked as if flowing water had created such terrains but Mars had no liquid water! In fact, its atmosphere is so thin and dry that any water poured on its surface will immediately freeze or evaporate. Gradually, as more and more evidence of its past was discovered, scientists understood that Mars might have been quite a different planet millions of years ago - with a denser atmosphere, it might have been warmer and wetter than it is today. This justifies the possibility that the Martian channels may have been created by floods!

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During the years he spent studying Mars and its “system of canals,” the American astronomer, Percival Lowell, popularized the idea of the presence of intelligent life on Mars through newspapers and his books Mars (1895), Mars and its Canals (1906), and Mars as the Abode of Life (1908). Even though his theories were ultimately proven false, Lowell made great contributions to the field of astronomy. The Lowell Observatory he established in Arizona, U.S.A, in 1894 is one among them.

Using the 24-inch refracting telescope installed in his observatory, Lowell observed not only Mars but also Venus. In the later years of his career, he focused his energies on finding Planet X, the imaginary tenth planet in our solar system that was believed to orbit beyond Neptune. Lowell never found his Planet X. But in 1930, nearly three decades after his death, Clyde Tombaugh, an astronomer working at Lowell’s observatory, discovered the dwarf planet, Pluto.

Though unintentional, another major contribution made by Lowell is in the field of literature! His ideas about extra-terrestrial life, aliens on a dying planet struggling to survive, excited the public, and inspired writers of science fiction to craft the bestsellers of those times. H. G. Wells’ 1897 novel, The War of the Worlds, is one such example!

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Solis Lacus, meaning “Lake of the Sun” in Latin, is a dark patch lying south of the canyon system, Valles Marineris. It is surrounded by a light-coloured region known as Thaumasia. This colour contrast, along with the way Solis Lacus seems to change in size and shape occasionally, gives it the appearance of the pupil of an eye. So it is also known as Oculus (which means “eye” in Latin), and more simply, the Eye of Mars!

Though Solis Lacus was first observed and sketched by a French-Italian astronomer, Jacques Maraldi, in 1704, it was the Italian astronomer, Giovanni Schiaparelli, who gave it its present name. But what had he seen in Solis Lacus that made him call it a lake where there was none?

During the late 1800s, astronomers were limited by the ability of their telescopes - their magnification power was low, compared to that of the telescopes of today. So Schiaparelli, who could see only light- and dark-coloured patches on Mars, thought the paler areas were continents and the darker areas were seas (“mare” in Latin) or lakes “lacus”)! The American astronomer, Percival Lowell, took this belief one step further. He thought he saw his Martian channels intersect in this dark area, and concluded that Solis Lacus was the capital city of Mars. Today we know that the changing shape of Solis Lacus is due to dust storms that frequently pass over this area.

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Have you heard the expression, “seeing is believing?” So even though many well-known scientists had questioned the existence of Martian canals, as far as some astronomers of the late 19th century were concerned, canals were what they saw on Mars!

The field of astronomy was also quite different back then. Observers had to manually focus their low-power telescopes on Mars, sometimes wait for hours for the image to become sharp, and make sketches to record what they saw.

Even though astrophotography (taking photographs of astronomical objects) was first attempted as early as in 1839, it had not become popular in astronomical research work till early 20th century.

The camera-equipped telescope installed in the Pic du Midi Observatory, France, in the summer of 1909 changed all that! A French astronomer, Count Aymar de la Baume Pluvinel, and his assistant, Fernand Baldet, observed Mars through the telescope and took photographs.

The images were so clear that they helped settle, once and for all, this three-decade-long canal controversy - there were no artificial canals on Mars! By this time, scientists studying the Martian atmosphere based on the way light interacted with it had also realised that Mars was a dry planet.

A clearer “picture” emerged when the U.S. National Aeronautics and Space Administration’s (NASA) Mariner 4 spacecraft took close-up photographs of the planet in 1965.

There were craters on Mars, but no canals!

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Though Schiaparelli’s canali and Lowell’s irrigation canals may have looked fascinating on paper, most astronomers were not able to see them through their telescopes.

To settle the debate about the existence of these canals, Edward Maunder, a British astronomer, and Joseph Evans, the headmaster of a prestigious school in England, conducted an experiment in 1903. With the help of a group of schoolboys, they were able to show that the lines astronomers seemed to have seen on Mars were most likely optical illusions, or the tricks our eyes play on us! (Have you noticed that when you look at closely-spaced markings placed just outside the limits of your vision, you are sometimes able to see them as lines?)

A.E. Douglass, Lowell’s assistant at his observatory, too began to grow concerned about the influence of these illusions on their astronomical observations. But Lowell continued to believe the canals he had seen on Mars were real, and Douglass eventually had to leave his job!

Meanwhile, Alfred Wallace (a British biologist and explorer famous for his theory of evolution by natural selection - an honour he shares with Charles Darwin) also dismissed Lowell’s theories about intelligent beings on Mars in his book Is Mars Habitable? published in 1907.

Soon after, even astronomers who had initially supported the canal theory, like Eugene Antoniadi, observed Mars through better telescopes, and argued that there were no canals on Mars.

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Mars has always been the subject of countless movies and books on extra-terrestrial life. But do you know what gave rise to this sci-fi trend? We have a simple translation mistake and an optical illusion to thank for that!

In 1877, about the same time when Asaph Hall was trying to find the Martian moons, an Italian astronomer, Giovanni Schiaparelli, was trying to map the Martian surface. He carefully marked the network of crisscrossing lines he saw through his telescope, and called them canali, Italian for “grooves.” But when it got translated to English, canali became “canals.” This made many think that Mars has, or once had residents intelligent enough to design and construct waterways!

Among them was a wealthy American astronomer, Percival Lowell. He established an observatory called the Lowell Observatory in Arizona, U.S.A, and dedicated around 15 years of his life to the study of these Martian canals. He also published many of his theories about Mars and life on the Red Planet (such as how Martians had built canals to transport melt water from the poles to water dry areas on the equator) which also shaped popular imagination. Though a few other astronomers too saw these “canals,”” many more did not, and this became a controversy of “astronomical” proportions! Today, we know that the lines Schiaparelli, Lowell and others saw were just optical illusions seen through low-power telescopes working at their limits of magnification.

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There are two reasons why people started believing that Martian moons may be artificial satellites. One was a scientific theory and the other, an April Fool’s day joke!

Astronomers and scientists observing Phobos in the late 1950s saw that the moon was slowly spiralling closer and closer to Mars. Back then, they did not have enough information to understand why Phobos was behaving this way. A famous Russian astrophysicist named losif Shklovsky came up with a possible explanation - if Phobos was capable of getting slowed down by Mars’ thin atmosphere, and then it should be having a very low density, meaning it might be hollow, and may even be an artificial satellite! The U.S. President’s scientific advisor at the time, Fred Singer, too seemed to support this argument, while also raising doubts about the accuracy of the measurements the theory was based on. But the “if’s” and “might be’s” in their statements were ignored by a few who were fascinated by the possibility of Phobos being the evidence of extra-terrestrial life on Mars!

At around the same time, an American space enthusiast and columnist, Walter Houston, published an article in the April Fool’s edition of a magazine. He wrote that the moons of Mars were actually space stations made by a group of super-intelligent Martians! Even though this was meant to be a joke, it soon became “viral!”

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If you look at the photographs of Deimos and Phobos you will notice one point in common - their colour. Both the Martian moons look dark in colour, darker than Mars. In fact, they are said to be two of the darkest bodies in our solar system. On closer inspection, scientists discovered that they are made up of a peculiar type of carbon-rich material and ice - a composition they share with the space rocks drifting in the main asteroid belt (that lies between the orbits of Mars and Jupiter) of our solar system. This gave rise to the idea that Deimos and Phobos may be two runaway asteroids that wandered too close to Mars! After all, asteroids do break out of the main asteroid belt occasionally due to collisions or Jupiter’s gravitational effects. And during their journey afterwards, if they happen to pass by a planet like Mars, they could easily get pulled into its orbit!

But in such a case, the orbits of these asteroids would be elliptical at first. It would take them many, many years to settle into the kind of near-circular orbits that the Martian moons now have. Also, the thin atmosphere of Mars would perhaps not be enough to slow down the asteroids before they could fall into orbit. All these points make the asteroid-capture theory unlikely, but not impossible!

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The question of the origin of the Martian moons is something that has been worrying scientists for decades. The asteroid-capture theory offers a likely explanation. But is it good enough to be true? Only under certain very unique circumstances, scientists say.

Another theory is that Deimos and Phobos formed after a large space rock - something big enough to create the major craters that we now see on Mars - crashed into Mars millions of years ago. The impact of the collision sent material flying out of the crater, and into an orbit around Mars. Over time this ejecta collected together and formed the Martian moons. The evidence for this theory is a mineral (a type of silicate) seen on Phobos’ surface; it is found on Mars too! This would also easily explain Deimos’ and Phobos’ orbits - their alignment with Mars’ equator, and their circular shape - something that asteroid-capture theory cannot fully justify. But this theory too has its drawbacks; scientists are not sure whether both Martian moons are old enough to have formed during the asteroid impact period.

This has led scientists to yet another possibility. What if Mars already had a moon long back which was broken up into Deimos and Phobos, maybe by an asteroid impact around 1- to 2.7 billion years ago? It is the latest in a long list of theories.

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The paths of Deimos and Phobos are nearly circular, and they both lie on the plane of Mars’ equator. They also show the same face to the Red Planet as they revolve around it. But there ends the similarity!

The average orbital distance of Deimos, the smaller of the two moons, is around 23,500 kilometres! So from Mars on a full-moon night, Deimos looks like a bright star, just about one-twelfth the size of our Moon (as seen from the Earth)! It takes around 30.3 hours to complete an orbit (lesser than the rotational period of Mars, 24.7 hours) and so it rises in the east and sets in the west.

In comparison, Phobos, with an orbital distance of nearly 9,400 kilometres, travels quite close to Mars. This is why, despite its (relatively) bigger size, Phobos is not visible from the polar regions of Mars! It makes Phobos quite fast too - its orbital period is only about 7.7 hours - and so, if you are standing on Mars, you will see Phobos rise from the west and set in the east twice a day! But an unfortunate side-effect of this proximity to Mars is that Phobos is slowly getting pulled closer to the planet, and will be destroyed within a span of 50 million years or so. Deimos, on the other hand, is moving further away from Mars, and will one day be lost in space!

Not very! The dimensions of Phobos are said to be 27 by 22 by 18 kilometres -quite an odd shape for a moon, isn’t it? This is why we simply say that it has an average diameter of around 22 kilometres! Its mass is around 11 quadrillion kilograms, nothing compared to the Earth’s 6 septillion kilograms.

Further, the gravitational pull on Phobos is only about 1/1700th that on the Earth. This means that if you weigh 50 kilograms on the Earth, on Phobos you will hardly weigh 30 grams - the “Earth weight” of six grapes!

With such a low gravity, Phobos does not have an atmosphere either. But why is this Martian moon so light? For one, Phobos has a low density, a little less than twice that of water. (For comparison, the Earth’s density is 5.5 times that of water!)

Back in the 1950s, there were even rumours that Phobos might be hollow within and may be an artificial satellite made up of sheet metal! But this was later disproved.

Today, scientists say that Phobos is not a solid body but one made up of pieces of rock. It is quite porous and may even have ice hidden beneath its surface!

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The first thing anybody would notice about this Martian moon is the large depression on the middle-western side of its face. An impact crater nearly nine kilometres wide, it covers nearly half the width of Phobos. This is Stickney, named in 1973 in honour of a mathematician, Angeline Stickney, for her contributions that led to the discovery of the Martian moons by her husband, Asaph Hall. The crater Stickney was first photographed by National Aeronautics and Space Administration’s (NASA) Mariner 9 spacecraft. Phobos has many more, smaller craters, and a few of them have been named either after astronomers, or characters in Johnathan Swift’s book Gulliver’s Travels!

The second thing about Phobos’ appearance is the large number of cuts and grooves on its surface. Some of them seem to spread out from Stickney. Scientists say they may have been created by material that was thrown out of the crater (called ejecta), when a space rock hit Phobos. Heavier ejecta may have rolled down the sides of the moon creating these grooves.

The third is the regolith making up Phobos’ surface. It literally flows around as this moon orbits Mars! What we know today about Phobos’ mysterious surface largely comes from the photographs taken during various missions to Mars. But this Martian moon definitely hides many more secrets beneath its surface. Hopefully at least some of them will be revealed to us when the Japanese MMX spacecraft reaches Phobos!

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Deimos, like Phobos, was named after a son of the Greek god of war, Ares (remember, planet Mars was named after the Roman god of war).

Legend has it that he accompanied his father and brother to battle - not a surprise considering that Deimos literally means “dread” while Phobos means “fear”! But thankfully his planetary namesake is not all that “dreadful” in size or form. With an average diameter of about 12 kilometres, and a mass of around 1.5 quadrillion kilograms, Deimos is tiny even when compared to its sibling-moon, Phobos!

Its irregular shaped body (having dimensions of 15 by 12 by 11 kilometres) seems to be made up of a carbon-rich material generally found on certain types of asteroids. Its surface is covered with a dry and loose layer of dust and broken rocks known as regolith (a combination of the Greek words for “blanket” and “rock”) which may be up to 100 metres thick.

Though Deimos has many impact craters, its surface is smoother than Phobos’. As on date, only two main features on it have been identified and named.

Both are impact craters said to be around three-kilometres wide. They are called Swift and Voltaire in honour of the famous Irish and French writers who wrote about the two Martian moons more than a century before their discovery! The remaining craters are much smaller in size.

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The story of the “first discovery” of Martian moons is a funny one! In 1609, the Italian astronomer and scientist, Galileo Galilei, started making telescopic observations of celestial bodies. He was quite good at it, because a year later, he became the very first person to see Mars and four of Jupiter’s largest moons through a telescope! It was during this time that Johannes Kepler, a famous German astronomer, received a letter from Galileo. It contained a coded message (back then, scientists used to regularly communicate with each other this way). To Kepler, it seemed to say “Mars has two moons.” But in reality, Galileo was talking about Saturn’s moons (which were later proven to be its rings)!

The next “clue” came in 1726 in Jonathan Swift’s book Gulliver’s Travels! If you have read it you probably remember the flying island, Laputa, and its astronomy-loving residents who “discover” the two moons of Mars! Maybe Swift was inspired by Kepler, or he simply made a guess based on the number of moons Mercury, Venus, the Earth and Jupiter were then known to have. Twenty-six years later, another writer too used this two-Martian-moons idea in his story, Micromegas, and his name was Voltaire.

These famous works of fiction popularized the concept of Mars having two moons well before they were actually discovered by Asaph Hall in 1877 - more than a century after their publication!

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Though the two moons of Mars were discovered in 1877, it took 92 years until we could get their close-up photographs! This again, thanks to Mariner 7, the U.S. National Aeronautics and Space Administration’s (NASA) spacecraft launched in 1969 to study Mars. Even in the following years, we did not have any Deimos or Phobos explorations - we had to be satisfied with their photographs taken during Mars missions such as those by NASA, the European Space Agency (ESA), and the Indian Space Research Organization (ISRO). But this is not to say that Martian moon exploration programmes were not planned.

Even as early as 1988, humans had dreamt of sending probes to Phobos, the larger of the two moons of Mars. The Soviet Union’s (present-day Russia) Phobos 1 and Phobos 2 were designed to do just that! But while Phobos 1 failed before it could reach its destination, contact with Phobos 2 was lost just before it could reach within 50 metres of the moon to release its landers. In 2011, the Russian Space Agency made plans to collect samples from Phobos during the Fobos-Grunt (meaning ‘Phobos-Ground’ in Russian) mission. Unfortunately that too failed during the launch stage.

But hope still remains in the form of Japanese Aerospace Exploration Agency’s (JAXA) Martian Moons Exploration (MMX for short)! This mission, developed along with ESA, the German Aerospace Centre (DLR), the (French) National Centre for Space Studies (CNES), and NASA, will be launched in 2024. It will hopefully collect many samples from Phobos, and also study Deimos and Mars remotely.

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