My Science School

Have you ever wondered how the night sky would appear from the Red Planet? Some say it would be pretty similar to that on a clear Earth night, but with one key difference - instead of just one moon, you would see two. One might resemble a bright star and the other, a pale space potato! And through a telescope they look nothing like our Moon; they are highly uneven masses covered with lumps, bumps and huge craters. But like our Moon, they always show the same face to their planet. Meet Deimos and Phobos, the only natural satellites of Mars!

Only around 12 kilometres wide, Deimos is the smaller of the two. It takes a little more than 30 hours to complete an orbit around Mars. Phobos measures 22 kilometres across (for comparison, the diameter of our Moon is 3,474 kilometres). However, it orbits very close to Mars, and takes only about eight hours to complete a revolution!

Unfortunately for Phobos, it is coming closer and closer to Mars - its orbital distance is reducing by about 1.8 centimetres every year. At this rate, one day it will either crash into the Red Planet, or get pulled apart by the gravitational effect of Mars and form a ring of debris around it. Either way, this will be a spectacular event. But we will have to wait 50 million years more to see it happen!

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Perseverance pays! Maybe that was what the American astronomer, Asaph Hall, felt after he discovered the Martian moons in 1877!

Asaph Hall was just 33 years old when he joined the prestigious U.S. Naval Observatory (USNO) in Washington, D.C. in 1862 as an astronomer. Though the very next year he was made the Professor of Mathematics in the USNO, Hall retained an active interest in the study of planets, moons, stars and their orbits. The year 1877 brought Mars especially close to the Sun and the Earth in a rare phenomenon called the “perihelic opposition.” During this time, Hall was in charge of his observatory’s 26-inch refracting telescope (telescope that uses lens for magnification), the world’s largest during that time, and he decided to use it in his search for Martian moons.

Initially it must have been quite frustrating for Hall, because after catching a glimpse of what appeared to be a moon on the 10th of August he could not find it again. He was about to give up. But his wife, Angeline Stickney (who was also a mathematician), motivated him to keep trying. Finally on the night of 12 August 1877, Hall discovered Deimos, and on 18 August 1877, Phobos! The biggest feature on Phobos, a nine-kilometre-wide impact crater, was named “Stickney” in the light of Hall’s wife’s contribution to the discovery of the two Martian moons.

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The formation of Valles Marineris was a puzzle that left many scientists scratching their heads. Erosion by an ancient melting glacier? Tectonic action? Volcanic activity? Theories were many. But what everyone agreed upon was that the story of this canyon system was closely tied to the history of the Tharsis region!

Around four billion years ago, when Mars was at its ‘volcanic’ best, enormous quantities of magma collected underneath its north western part. The ground swelled up to form the Tharsis bulge. Over the years, as more and more lava spilled out, volcanoes grew in size to become giants like the Olympus Mons, Ascraeus Mons, Pavonis Mons and Arsia Mons. Finally, the pressure build-up was so great that it cracked the Martian crust! These fractures expanded in time, forming the system of chasmata that we know as the Valles Marineris - this is the commonly accepted theory today.

These cracks also released the water stored below the Martian surface. The escaping fluid washed away the sides of the chasmata making it still wider. The channels found in chaotic terrain on the eastern end of Valles Marineris may be the result of such flooding events. But we still don’t have all the details. Was it a single large flood episode followed by smaller ones later, or a series of floods within a short period of time? Nobody knows!

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Scientists say there may be mainly two factors that help Martian volcanoes grow enormous.

One, Mars has a weak gravitational pull (which is only about one-third that of the Earth’s) and a thin atmosphere. Magma, or the molten material under a planet’s surface before it becomes lava, contains not only melted minerals but also gases trapped within it. As magma approaches the surface, the effects of low atmospheric pressure helps gas bubbles expand faster. This pushes out huge quantities of hot ash and other debris in a large explosion called a Plinian eruption. The low gravity also makes it easier for magma to collect under the Martian surface in magma chambers, larger and deeper than those found on the Earth. So when a volcano erupts on Mars, there is more lava produced and the low gravity keeps it flowing for longer periods.

Two, Mars does not have any active tectonic plates. The Earth’s crust (along with the upper mantle) is in the form of huge jigsaw-puzzle-like pieces known as tectonic plates. As these plates gradually move, their boundaries (which are points of weakness) may get aligned above areas of the underlying mantle that are hotter than the surrounding regions, permitting magma to move up and form volcanoes. When the plates move again the flow is cut off. In Mars, however, there is hardly any tectonic movement. So lava is able to continuously flow and pile up at a single location.

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Did you think that the area occupied by Olympus Mons (300,000 square kilometres) was unimaginably big? Wait till you hear how much of Martian land the shield volcano Alba Mons covers. At least 5.7 million square kilometres! That’s more than half the size of Europe!

With respect to area, Alba Mons may be the largest volcano on Mars. But it stands only 6.8 kilometres tall; that is hardly one-third the height of Olympus Mons! You can guess looking at its dimensions that this volcano has a very gentle slope. With an average slope of just 0.5 degrees even at its steepest northern side, this “mountain” looks nothing like the ones we have here on the Earth!

In reality, until 2007 Alba Mons (Latin for “white mountain”) used to be called Alba Patera (Latin for “white saucer”) because of the white clouds found around the volcanic craters of the mountain. Today, Alba Patera refers only to the two calderas (hollowed out regions found on top of volcanoes after an eruption), the larger of which is more than 100 kilometres wide. They are relatively shallow though - only about one kilometre deep! Curved fault lines, called Tantalus Fossae and Alba Fossae, run on the eastern and western sides of the volcano. We can also find evidence of lava flows and surface water run-off around it.

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If you focus a telescope on the Red Planet on a clear Martian “sol,” you will see near its centre, a dark scar stretching over nearly half its face. This is Valles Marineris, the largest canyon system on Mars.

In Latin its name means “Mariner valley.” But Valles Marineris is quite unlike any of the river valleys we see on the Earth. Nearly seven kilometres deep, it surpasses the world’s deepest gorge, the Yarlung Tsangpo Grand Canyon in Tibet, China, by close to a kilometre. At certain points it may be as deep as 10 kilometres, and as wide as 200 kilometres! It is also more than 4,000 kilometres long; this is nearly double the distance between Kochi and Delhi! For comparison, the famous Grand Canyon in Arizona, USA, is only 446 kilometres long, 29 kilometres at its widest and 1.9 kilometres at its deepest.

Valles Marineris runs below the Martian equator on the eastern side of the Tharsis bulge and Chryse Planitia, a circular plain where the U.S. National Aeronautics and Space Administration’s (NASA) Viking 1 spacecraft landed in 1976. This fascinating canyon system is made up of a number of chasmata (its singular form is chasma), or deep and steep-sided fractures on the Martian surface. It starts with a chaotic system (a rough terrain with cracks, ridges and plains mixed together) on the east, and ends in a region of crisscrossing valleys, called Noctis Labyrinthus, on its west.

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When dust storms rage around Mars, they cover the globe in a rusty haze, blocking the planet from our view. But when the dust starts settling, what do we get to see first? The majestic peak of the tallest mountain on the planet! Meet Olympus Mons, a shield volcano, and the largest volcano in our solar system!

Simply put, a “shield” volcano is one that looks like an ancient warrior’s round shield. It is wider rather than tall, and has very gentle slopes. This is because the lava erupting out of this volcano is not very thick. It keeps flowing down the sides, and the volcano gradually grows wider over the years.

It probably took Olympus Mons more than a billion years to reach its present size. Spread over an area of 300,000 square kilometres, Olympus Mons is almost as big as our state of Maharashtra! Its volume is almost 100 times that of the biggest volcano on the Earth, Mauna Loa in Hawaii.

The average slope of Olympus Mons is only about three degrees. This means that to climb to a point just one metre higher on the mountain you will have to walk a little more than 20 metres! Imagine climbing to its summit which is almost 21 kilometres above the Martian surface!

Even the tallest mountain on our planet, Mount Everest in the China-Nepal border, is only 8.8 kilometres high.

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The short answer is - yes! In fact, Mars was volcanically very active around three to four billion years ago. The largest volcano discovered in our entire solar system is also said to be found on Mars!

Most of the major, known volcanoes are concentrated in two areas of the planet - Tharsis and Elysium volcanic regions. With a diameter that is roughly 4,000 kilometres, Tharsis bulge is by far the biggest volcanic region on Mars. It is home to 12 large volcanoes, including Ascraeus Mons, Pavonis Mons and Arsia Mons. Together, these three volcanoes standing in a line on the crest of the bulge is known as the Tharsis Montes. (“Mons” is a Latin word meaning “mountains,” and its plural is “Montes.”)

On the western side of the Tharsis bulge we can find Olympus Mons, the tallest mountain and volcano on Mars; and on its northern side, Alba Mons, or Alba Patera, the largest volcano on the planet in terms of area covered. Compared to the Tharsis region, the Elysium is smaller - it is only about 2,000 km wide. Its three main volcanoes are Elysium Mons, Hecates Tholus and Albor Tholus. (In Latin, “tholus” means a “dome.”) It was in the Elysium region that scientists found the “youngest” volcanic deposits on the planet, indicative of Mars having had volcanic activity as recently as 53,000 years ago!

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Somewhere around four billion years ago, volcanism started picking up on Mars. Scientists say that most part of the Tharsis bulge, the largest volcanic region in Mars, must have formed by 3.7 Gya (in Geology, Gya means Giga years ago, or billion years ago). But this was by no means the end of volcanic activity in the region, or on the planet. Lava and ash from newer eruptions continued to bury the older volcanoes over the years - it is said that the base of certain smaller, but ancient, volcanoes in the Tharsis region, called Tharsis tholi, lie about four kilometres below the current Martian surface! Intense volcanic activity on Mars continued till about 3 billion years ago, which was then followed by smaller isolated eruptions. It was believed until recently that volcanoes on Mars are presently inactive.

But thanks to the photographs taken by the European Space Agency’s (ESA) Mars Express Orbiter in 2004, scientists have evidence that Olympus Mons, the largest volcano on Mars, erupted somewhere between 1.1- and 2 million years ago. This meant that the mountain was quite young, in geological terms, and may still be active! More exciting news came this year with scientists finding a dark area in the Elysium region of Mars, something that might be a relatively fresh volcanic deposit of ash and rock. Based on this, scientists now believe that the Red Planet may have been volcanically active as recently as 53,000 years ago!

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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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