My Science School

Isn’t it curious how most of the Martian northern hemisphere is a low-lying flat terrain, while the southern side, dotted with craters, lies one to two kilometres higher than it? To explain this scientists have come up with a theory - the northern plains is one large impact basin called the Borealis Basin, or the North Polar Basin.

The Borealis Basin is elliptical in shape, approximately 10,600 kilometres at its widest, and covers almost one-third of the Red Planet. Like the southern highlands it contains craters too but far fewer in number. Utopia Planitia, which is presently the largest impact basin on Mars, is also located within it. Despite these craters, Borealis Basin is considered one of the flattest regions in our solar system.

It is believed that the Borealis Basin was created when a massive body crashed into Mars billions of years ago. Such an event can explain why the crust is thicker in the southern highlands as compared to the northern plains. Mars’ moons, Deimos and Phobos, could have also been formed from the debris of the impact. (But this too is just a theory, as the origin of Martian moons is a mystery to date.) This means that the impacting object would have to be one-fiftieth as heavy as Mars, and almost 1,900 kilometres wide to produce such a huge crater!

Nevertheless if this theory is proven true, the Borealis Basin would become the largest impact crater in our solar system!

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“Utopia,” is a combination of two Greek words meaning “not” and “place.” It was created by Sir Thomas More in 1516 to name a fictional and remote island in his book. Now, the Utopia on Mars may be far, far away. But it is neither an island, nor imaginary! It is an impact crater in Mars’ northern hemisphere, and the flat terrain inside it is called Utopia Planitia.

With an estimated width of almost 3,300 kilometres, the Utopia Planitia is believed to be the largest impact basin found to date on Mars, as well as in our solar system. But that is not its only speciality. Some areas in Utopia Planitia have curiously-shaped shallow depressions, called scallops, which may be clues to the presence of water-ice beneath the surface.

We have also found polygon-shaped fracture patterns on the basin floor, the origins of which continue to puzzle scientists. They may have been formed when the once-hot volcanic surface cooled down, contracted and cracked. Another theory is that loose deposits of dust, soil and small pieces of rock forming the surface material shrunk over time and created these troughs. We can see such polygonal patterns inside certain other Martian impact basins as well. What is even more surprising is that we can also find them here on Earth, in the Arctic regions, where ground becomes frozen!

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What can be so special about a planet’s orbit? Well, three things, to be precise!

Firstly, the eccentricity. Like all planets, Mars’ orbit is elliptical (or elongated), with the Sun located to one side of the ellipse. At its perihelion (point in its trajectory where the planet is closest to the Sun), Mars and the Sun are separated by 206.6 million kilometres. But at its aphelion (the point where it is farthest away from the Sun), this distance increases to 249.2 million kilometres - quite a large leap! This is because of the extreme eccentricity of the Martian orbit, second only to Mercury’s when compared to those of other planets in our solar system!

Secondly, the Martian orbit may not have always been this ‘eccentric!’ Looking at evidence, scientists say that there was a time in the Red Planet’s history when it used to follow a near-circular path around the Sun, similar to the Earth’s. The gravitational pull from the giant planets gradually gave the movement its current shape. Thirdly, it is the only terrestrial planet in our solar system to take more time than the Earth to complete a full orbit. A Martian year is 687-days long, nearly twice as long as a year on Earth. But this probably comes as no surprise as the average distance between Mars and the Sun is 1.5 times that between the Earth and the Sun!

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Yes. And they literally fell from the sky for us. In the form of meteorites!

Most meteorites are remnants of ancient space rock that are at least 4.5 billion years old. That was why scientists were puzzled when they came across volcanic rocks that were definitely from space, but only about 1.3 billion years old - quite young, astronomically speaking! Fortunately, the US National Aeronautics and Space Administration’s (NASA) Viking spacecraft that landed on Mars in 1976 helped us clear that mystery. Using specialized instruments on the Viking landers, scientists were able to get key information about the Martian surface and atmosphere. When they compared it with the chemical composition of the minerals and gases trapped in the strangely-young meteorites, they had their answer - the rocks were from Mars! The age of the meteorites was also consistent with the time when Mars was in its volcanic phase.

But how did these rocks get to the Earth? Scientists believe that the very same space rocks that crashed into Mars to create its craters also sent Martian rocks flying into space. These newly-formed debris then wandered around in space for millions of years until they were pulled in by the Earth’s gravitational force. As on date, we have identified around 300 Martian meteorites. Maybe there are many more, waiting in remote corners of the Earth, for you to find and name one day!

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In the southern highlands of Mars lies a massive impact crater. About 2,300 kilometres wide, it is one of the largest in our solar system. With a basin floor lying more than seven kilometres below the Martian surface level, it is the lowest region on the planet. This is the Hellas crater, and the plain inside it is Hellas Planitia. Hellas is the Greek word for “Greece,” and Planitia is Latin for a “flat surface”.

To astronomers of the late 1800s looking through their low-powered telescopes, Hellas was a huge light-coloured region that stood out against the rest of Mars’ dark-coloured southern side. They mistook the paler area for a continent, and the darker part for seas!

Scientists believe that the Hellas crater was formed when a large space rock hit Mars around 4 billion years ago. The crash was so massive that the debris can be found up to two kilometres beyond the walls of the crater!

Radar images taken by the National Aeronautics and Space Administration’s (NASA) Mars Reconnaissance Orbiter indicate that there may be water-ice in Hellas Planitia hidden under a thin layer of dirt and rock. We can also find sand dunes in the basin with squiggly lines on its sides. These are linear gullies, believed to have been created by blocks of dry ice (frozen carbon dioxide) rolling down the dune slopes!

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“Terra” is a Latin word meaning “earth” that found its way to the English dictionary in the 15th century. So in simple terms, a terrestrial planet is an Earth-like planet in size and composition!

In our solar system, the first four planets - Mercury, Venus, Earth and Mars - are called terrestrial, as they are dense and made up of mainly silicate (minerals containing silicon and oxygen) rocks and metals. The remaining four outer planets - Jupiter, Saturn, Uranus and Neptune - are called giant planets; the first two are gas giants and the last two are ice giants.

Mars, like all other terrestrial planets, has a core, a mantle and a crust. The metallic core is dense, consisting mainly of iron. The mantle, the layer above it, contains silicates. Millions of years ago, fierce volcanic activity covered the Martian crust with lava flows that solidified into iron-rich basaltic rock. As time went by, iron in the rock reacted with the atmosphere, became iron oxide, and gave Mars its characteristic reddish colour!

Though we are yet to see any eruptions on the planet, we don’t know for sure whether Mars’ ‘volcanic’ days are behind it or not! Its surface still has many volcanoes including the Olympus Mons, which is the largest volcano, and the highest mountain discovered till date in our solar system.

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The ice caps on the Martian northern and southern Polar Regions, called Planum Boreum and Planum Australe respectively, are made up of - you guessed it - ice. But not just any ice. Only about 70 per cent of it is water in solid form. The rest is solidified carbon dioxide - called dry ice - and dust!

During the cold and dark winters on a Martian pole, nearly one-sixth of the atmosphere freezes and deposits on the permanent ice cap to form a metre-thick layer of dry ice. Months later when spring arrives bringing sunlight to the poles, the dry ice sublimes (or, directly turns from solid to gas). By summer, most of the carbon dioxide layer on the North Pole vanishes leaving behind a water-ice cap. But the South Pole has a permanent cover of dry ice and water-ice beneath this temporary layer.

Beneath the residual ice caps lies a formation called polar layered deposits, which are nothing but sheets of ice and dust stacked one on top of the other, like the pages of a book. Scientists say that since these deposits are the result of seasonal cycles and dust storms, they can give us clues about how Martian climate used to be in the past. Polar layered deposits rest on frozen ground made up of loose sand, dust and water-ice. In the north, this surface is called north polar basal unit, and in the south, Dorsa Argentea Formation.

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Planning a trip to Mars? Better carry all your blankets along! Because the Red Planet is a much colder place than the Earth.

Near the equator, summer afternoons can be a pleasant 20 degrees Celsius. But don’t let that fool you. At night you may get a freezing minus 73 degrees Celsius! For comparison, the freezers we have at home, even the very best ones, can only go up to minus 23 degrees Celsius. Winters are worse, with temperatures at the poles dropping down to minus 125 degrees Celsius. In fact, the average temperature on Mars is around minus 60 degrees Celsius compared to our planet’s 15!

There are more than a few reasons for this Martian ‘coldness.’ One, the average distance between the Sun and Mars is almost 50 per cent more than that between the Sun and the Earth. So the amount of sunlight reaching the Red Planet is lesser, only about 43 per cent of what we get here. Two, Mars has a more elliptical orbit when compared to the Earth, which periodically takes it closer to, and farther from the Sun. During this second phase, Mars’ axial tilt keeps its south pole further away from the Sun, making southern winters quite extreme. Three, the Martian atmosphere is very thin, only one-hundredth as dense as the Earth’s. So it cannot store heat and act like a “thermal blanket” for Mars.

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For Mars observers, 1877 was a special year. The Sun and Mars aligned on opposite sides of the Earth (a phenomenon called “opposition”), while Mars came closest to the Sun in its orbit. This “perihelic opposition,” where Mars appeared at its biggest and brightest phase, gave astronomers the perfect opportunity to study the planet. During this period, an Italian astronomer started mapping the surface of Mars. He was the director of the Brera observatory (in Milan, Italy), and his name was Giovanni Virginio Schiaparelli.

Schiaparelli called the light-and dark-coloured areas on the Martian surface “continents” and “seas,” respectively, and the inter-connected lines he saw through his telescope, “canali.” There were almost 40 such canali on his map, and he named them after well-known rivers on the Earth.

“Canali” was an Italian word that meant “channels” or “grooves,” features that could be natural to a planet’s topography. However, when “canali” was translated to English, it became “canals,” meaning artificial water-ways! This led many to imagine there were intelligent beings on Mars who had constructed these magnificent 40-odd “canals!”

Though most astronomers of those times could not spot Schiaparelli’s canali, it remained a hotly-debated topic in academic circles, until proof emerged that the lines Schiaparelli saw were optical illusions. Nevertheless, the concept of intelligent life on Mars was immensely popular, and continued to inspire countless works of science fiction.

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Fresh grass of spring, sun in summer, falling leaves of autumn and snow in winter - change of seasons make our planet beautiful, doesn’t it? Like the Earth, Mars too has all four seasons, thanks to its “axial tilt” (25.2 degrees, compared to the Earth’s 23.4 degrees). But Martian seasons are nothing like the ones we have on the Earth! To know why, we must understand two things about Mars’ orbit.

One, the planet takes 687 days to complete a full orbit, about twice the time the Earth does. Therefore Martian seasons are also nearly twice as long. Two, while the Earth has a near-circular orbit, Mars’ orbit is more elliptical, or elongated, in shape with the Sun located at one of its two foci. As a result, during a certain period of the Martian year, the red planet is close to the Sun, and in another, it is far away. It so happens that Mars’ southern hemisphere is always tilted towards the Sun during the first phase, and away from the Sun in the second. This makes summers in the southern hemisphere warmer, and winters, colder.

The temperature differences between the northern and southern halves are so extreme that they generate winds often strong enough to sweep up fine dust from the surface and become massive dust storms.

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Polar Regions, southern highlands, and northern plains. Do they sound like remote regions of the Earth? Or do they remind you of a fictional terrain made for books, like Tolkien’s Middle-earth? In reality, they are the names given to three distinct regions on the Martian surface!

Similar to the Earth’s Polar Regions, Martian poles also have ice caps. Surface temperatures are the lowest here compared to anywhere else on the planet. The ice cap on the south lies at a higher level than the north, and is also colder. In fact, a large portion of Mars’ southern side lies on higher ground compared to the north (by one to three kilometres), which gives it the name, southern highlands. Here, we can find a lot of craters created by the impact of meteors that are said to have bombarded the planet nearly 4 billion years ago.

The northern part of Mars, however, has far fewer craters even though it covers nearly one-third of the planet. The flat terrain of the low-lying northern plains is said to have been created by lava flows. The iron-rich dust and sand on the plains give it a pale appearance. Decades ago when telescopes were far less powerful than the ones we have today, astronomers mistook the northern plains for continents, and the dark-coloured southern highlands, for oceans!

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Our ancestors spent centuries observing the positions and movements of Mars. And yet, how the planet looked up-close remained a mystery. But an amazing invention in the hands of a talented Italian astronomer-cum-scientist changed that!

Galileo Galilei started observing Mars in 1610 using a low-power telescope he himself made. Though he could not make out any details of the Martian surface, this was the first time anyone was seeing Mars through a telescope. It also inspired many astronomers to follow in Galileo’s footsteps, and by 1659 we had our first sketch of the Martian surface! This drawing, made by Christiaan Huygens (a Dutch scientist), clearly shows Mars’ characteristic “dark spot” - a region called Syrtis Major Planum.

Huygens also determined the size of Mars, and the time it takes for it to complete a full rotation about its axis. In 1666, an Italian astronomer-cum-engineer, Giovanni Domenico Cassini, gave a better estimate; he said a day on Mars is 24-hours-and-40-minutes long, which is just three minutes more than the actual duration! He is also credited with the discovery of Mars’ polar ice caps.

By the 19th century, we had a better understanding of Mars’ topography. Detailed maps and more accurate estimates of Mars’ rotational period and size could be made, thanks to more powerful telescopes.

In fact, it was the U.S. Naval Observatory’s refracting telescope (the world’s largest one during that time) that helped the American astronomer, Asaph Hall, discover the two moons of Mars, Deimos and Phobos, in 1877.

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To someone who has read the book of fiction, The Martian, or seen its movie version, a Martian storm seems rather terrifying. As the astronaut’s equipment goes flying in the wind, it injures him badly. His camp gets damaged too. In reality, are the winds on Mars that powerful? There are two things you should know.

One, because of its low gravitational pull - amounting to just one-third that on the Earth - Mars has a much thinner atmosphere. It is hardly one-hundredth as dense as the Earth’s atmosphere! That means, to move anything around, Martian winds have to blow very fast.

Two, winds on Mars generally blow at a speed of 16 to 32 kilometres per hour. This is influenced by many factors, such as temperature variations, atmospheric circulation patterns (large-scale movement of air by which heat is redistributed across the planet), and landscape. Often winds gather enough speed to sweep up Mars’ fine red dust and become dust storms. Some are intense enough to be spotted through telescopes here on the Earth! Moderately big dust storms, covering continent-size areas, occur annually. But once every few years, they grow really massive and blow across the entire planet, blanketing it in dust for weeks. Even so, maximum wind speeds on Mars are only about 100 kilometres per hour!

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Did you know that ancient Egyptians were excellent star-gazers? It is said that they prepared the oldest map of the skies, known as the Senenmut star map, in 1534 BCE. And in this map, we can find one of the earliest records of “Her Desher,” or “the red one!” Mars is also depicted in the tomb of an Egyptian pharaoh, Seti I, and on the ceiling of Ramesseum, the memorial temple of Ramesses the Great. What is even more impressive is how the ancient astronomers of Egypt were aware of the forward-reverse-forward path tracked by Mars on the night sky (called apparent retrograde motion) as early as the 2nd millennium BCE!

Closer home, the earliest records of Mars observations can be traced back to the period before the Zhou Dynasty rule in China, sometime around 1045 BCE. By around 6th century BCE, the astronomers of Babylonia also started observing the movement of planets across the night sky, and developing calculations to predict planetary positions more accurately. They even knew how long it takes Mars to complete a full orbit. Up until this period, the Greeks, who had associated Mars with Ares, their god of war, had given no further attention to planetary observations. This was to remain so until the times of Plato and Aristotle.

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Martian soil is a farmer’s nightmare! The reason? It has no organic content. It is not aerated either. Instead, all it contains is mineral matter, largely in the form of sand, the product of weathering of volcanic rocks. Mars is also extremely dry. Scientists say the trace amount of water in the soil, about 2 per cent, may have been absorbed from the atmosphere.

The Martian surface layer is made up of fine dust. Rich in iron oxides, or rust, this dusty layer gives the planet its unique red colour! Though similar iron-rich soils can also be found on the Earth, it is limited to certain places. Not so, on Mars. Dust storms sweep across it occasionally, transporting fine dust all over the planet. So the Martian surface layer is largely homogenous, like a huge desert.

Photographs of steep slopes, such as those of hills, craters and troughs, often reveal thin dark lines on the Martian surface. Sometimes, these “streaks” start small and gradually grow until they are hundreds of meters in length! They may grow lighter in colour with time, and even follow the edges of rocks and boulders blocking their path to get to the other side. What are these strange lines? Are they flow paths of water, or growth of organisms? No one knows for sure. Scientists think they may just be hidden darker layers of soil that are revealed by dust avalanches or spinning columns of dust, called dust devils.

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