ASTR-401 Lessons

4.4: Mars - Visiting the Red Planet

You may have noticed that the area around the Astronomy Tower looks different from its usual appearance. I have charmed it to look like the surface of Mars.  Imagine that we are all travelling in a spaceship and are finally reaching our destination - the Red Planet. We’re going to exit the ship and walk around on the surface of the planet. As you can see, we’re already quite close to Mars now, and we’re going to fly around it looking for the best place to land.

Mars was named after the Roman god of war because of its reddish-orange colour, caused by the rust (iron oxide) on its surface. Its mean radius is just about 3390 kilometres, its mean density is approximately four times that of water, and its mass is 0.107 times that of Earth. It is bigger than Mercury but less dense, so its surface gravity is about the same as Mercury’s – that is, 0.38 times that of Earth. From the image below you can see how big Mars is compared to Earth.

Mars vs Earth

Source: here

 

Surface Features

Mars

Source: here

From this true colour picture of Mars, you can see that a lot of it is reddish-orange, but the southern hemisphere is darker than the northern one. The white regions on the Martian poles are the polar caps. Water ice makes up about 70% of each of the polar caps, though the northern one gets covered by a layer of dry ice (frozen carbon dioxide) to a depth of about one metre in the northern winter. In the summer, the dry ice sublimes – that is, it turns into gas without passing through the liquid phase. The southern polar cap is covered by about eight metres of dry ice all year round.

A striking feature of the terrain on Mars is the amazing difference between the planet’s northern and southern hemispheres. The northern hemisphere is made up mostly of rolling volcanic plains (large fields covered with lava or ash) not unlike the Moon – indeed, this similarity was key to their identification as lava-flow features. Much larger than their counterparts on the Earth or Moon, these extensive lava plains were formed by eruptions involving enormous volumes of material. They are covered with blocks of volcanic rock, as well as with boulders blasted out of impact areas by infalling meteoroids, as the Martian atmosphere is too thin to offer much resistance to incoming debris. Conversely, the southern hemisphere consists of heavily cratered highlands lying some five kilometres above the level of the lowland north. Most of the dark regions visible from Earth are mountainous regions in the south, as seen below. It is suggested that because of the cratering in the south that the northern hemisphere’s surface is much younger: three billion years compared to the four billion year old surface of the south. 

Martian Mountain

Source: here

It is assumed that the southern hemisphere is the original crust of the planet. How most of the northern hemisphere could have been subsequently flooded with lava remains a mystery. Oh, look! We can already see some interesting features of Mars! Let's take a closer look and admire the beauty of this planet.

Mars with major geological features labelled

Source: here

 

The Tharsis Bulge

The major geological feature on the planet is the Tharsis bulge. Roughly the size of North America, Tharsis lies on the equator and rises some ten kilometres higher than the rest of the Martian surface. To its east lies the Chryse Planitia (the “Plains of Isis,” an Egyptian Goddess), a series of wide depressions hundreds of kilometres across and up to three kilometres deep. If we wished to extend the idea of ‘continents’ from Earth and Venus to Mars, we would conclude that Tharsis is the only continent on the Martian surface. However, as on Venus, there is no sign of plate tectonics on Mars – the ‘continent’ of Tharsis is not drifting as its earthly counterparts are.

 

Olympus Mons

The tallest volcano on Mars, called Olympus Mons, is about two and a half times as tall as Mount Everest. It is also the tallest known mountain in the Solar System! Olympus Mons is a shield volcano that is 25 kilometres (16 miles) high. Shield volcanoes have gently sloping sides and are known to erupt fluid, basaltic lava.

 

Mount Everest compared to the Olympus Mons

Source: here

 

The Hellas Basin

Almost diagonally opposite to Tharsis, in the southern hemisphere, lies the Hellas Basin, which contains the lowest point on Mars. This feature is some 3000 kilometres across, the floor of the basin lying nearly nine kilometres below the basin’s rim and over six kilometres below the average level of the planet’s surface. Its shape and structure allow us to identify the Hellas Basin as an impact feature. The formation of the Hellas Basin must have caused a major redistribution of the young Martian crust – perhaps even enough to account for a substantial portion of the highlands around it. The impact probably occurred very early on in Martian history – some four billion years ago – during the heavy bombardment that accompanied the formation of the terrestrial planets.

 

The Borealis Basin

The giant Borealis Basin around the Martian north pole may be the result of one of the largest known impacts in the solar system. Recent research based on simulations of the collision and detailed data from Muggle spacecraft missions (Mars Global Surveyor and Mars Reconnaissance Orbiter) suggests that the basin has formed when a giant celestial object some 2000 kilometres across – twice the size of the largest known asteroid, Ceres – dealt a grazing blow to the planet during its formation stages. The collision could also explain why the northern hemisphere of Mars is so distinctive from (and much lower than) the south.

 

The Mariner Valley

A particularly prominent feature associated with the Tharsis bulge is a great “canyon” known as Valles Marineris (the Mariner Valley). This feature is not really a canyon in the terrestrial sense because running water played no part in its formation. It is theorised that it was formed by the same crustal forces that caused the entire Tharsis region to bulge outward, making the surface split and crack. The resulting cracks, called tectonic fractures, are found all around the Tharsis bulge. Valles Marineris is the largest of them, and studies suggest that the Valles Marineris range is around 3.5 billion years old.

Valles Marineris runs for almost 4000 kilometres along the Martian equator, about 1/5th of the way around the planet. At its widest point, it is some 120 kilometres across, and it is as deep as seven kilometres in places. Like many Martian surface features, it simply dwarfs all Earthly competition. The Grand Canyon in Arizona, USA, Earth, would easily fit into one of its smaller side cracks. Valles Marineris is so large that it can even be seen from Earth. In fact, it was one of the few “canals” observed by 19th-century astronomers, who named the feature Coprates Canal at the time. We’re flying over it now; take a close look.

The Mariner Valley

Source: here

 

What’s it Like on Mars?

Now that we’ve finished discussing Mars’s surface features, we turn to the conditions on this fascinating planet. It’s usually cold there; the average temperature is -63 degrees Celsius or -82 degrees Fahrenheit. During the winter, the temperature can drop as low as -143 degrees Celsius or -226 degrees Fahrenheit on the south pole, whereas it can occasionally rise as high as 35 degrees Celsius or 95 degrees Fahrenheit right at the equator at noon.

The atmosphere is much thinner than that of the Earth: on average it exerts only 0.00628 times as much pressure as Earth’s, and even the greatest atmospheric pressure, in Hellas Planitia, is only about twice as great as that average. It is made up of about 96% carbon dioxide, almost 2% of argon and nitrogen, and traces of oxygen and carbon monoxide.

Although the atmosphere is thin, it can raise dust from the surface of the planet because the wind can reach speeds of over 160 kilometres (100 miles) per hour. Some of these storms cover only a small area, but occasionally there are gigantic storms that cover the entire planet – the largest dust storms in the solar system.

Aside from dust, the surface of Mars has a lot of rocks and, like the Moon, it is covered with craters. Not all of its surface is reddish; some of it is greenish-brown, giving rise to the false belief that these were areas of vegetation, even though these colours are actually caused by minerals.

Landforms visible on Mars suggest that there once was liquid water on the surface, but since the planet has no magnetic field, solar radiation stripped away any atmosphere that existed. The atmosphere is now too thin to retain water in liquid form – when it gets warm enough, water ice sublimes directly into water vapour. Nevertheless, some water was found under the ice of the south polar cap in July 2018. 

 

Exploration of Mars

The conditions on Mars, although certainly not as comfortable as those on Earth, are much more habitable than on Venus, meaning that a manned mission to the planet in the near future is a distinct possibility. To prepare for it, Muggles have sent many unmanned missions there; dozens of orbiting space probes have already been sent to Mars by the United States, the Soviet Union, Europe, and India. There are also several robotic rovers on the surface, all sent by NASA.

Spirit and Opportunity were sent to the Red Planet in 2003. Their mission was to explore the Martian surface to better understand the geology, surface, and climate of our neighbour planet and to find out if there had ever been water there. The robots parachuted onto Mars, where they rolled across the face of the planet guided by human controllers back on Earth. Though their original mission was only supposed to last 90 days, both rovers continued exploring and reporting for several years. Spirit only got deactivated in 2010 and Opportunity lasted until June 2018, when a global dust storm blocked the sunlight that the rover needed to continue in operation. The dust storm ended in October, and NASA made many attempts to revive the rover before finally pronouncing it dead on February 13, 2019.  Both rovers found strong evidence that there was once water on the surface of Mars.

The Curiosity rover, which landed on Mars in the fall of 2012, continued the missions started by Spirit and Opportunity. Curiosity is almost eight times larger than Spirit or Opportunity and carries a vast array of scientific instruments. While its primary mission is the exploration and study of the Martian climate and surface, it has also been searching for evidence of life now that we have discovered evidence of water on Mars. Like its sister rovers, Curiosity has also outlasted its original mission deadline of 687 days (a Martian year) and continues to send back photographs and data to this day.  In 2021, another rover called Perseverance landed on Mars, carrying with it a helicopter called Ingenuity that has made several flights despite Mars’s thin atmosphere.

Ah, here is the perfect place to land: right beside the rover Curiosity. Before we exit the spaceship, we’re all going to prepare ourselves to experience the reduced gravity of Mars. I asked the Potions professor to prepare a mixture of Billywig venom and Wideye Potion, which makes you lighter without feeling dizzy.  Each of you, take one vial and drink its contents, then put on one of these spacesuits, on which a Lightening Charm has been cast. Now let’s all exit the spaceship and walk about on the surface. Jump as high as you can. Despite the extra weight of the spacesuit, you can all jump considerably higher than you could on… oh no! A sandstorm is approaching! Quick, run back into the spaceship! We have to take off before it hits us or we’ll be stranded without power, possibly for months! You, Johnny, hurry up or we’ll have to leave without you! Okay, we’re all here. No time for a countdown. Liftoff! Whew! We just made it. That concludes this leg of the tour. When we next board it, we will be on our way to Jupiter through a somewhat unconventional route.

The rover Curiosity on the surface of Mars

Source: here

 

Life on Mars

Is there life on Mars? Was there ever life on Mars? Several discoveries were once considered evidence of life, or at least past life, but there is no definite proof that there was or wasn’t life on Mars. We just don’t know, but if robots don’t provide the answer, perhaps human explorers will. If you train hard enough, you may be able to become one of those explorers.

Humans may eventually colonise Mars. They will have a number of problems to solve first, though - the cold, the thin atmosphere with almost no oxygen, deadly radiation from the Sun, and perchlorates in the soil that are toxic to plants as well as humans among other things. But with enough ingenuity (and I don’t mean helicopters) they may be able to pull it off.

For magical people, some of these problems could be solved with the usage of spells or potions. The Warming Charm might help with the cold or the Bubble-Head Charm could allow us to breathe on the surface of Mars for some time. Unfortunately, there are still many problems that we cannot deal with, so for now we will wait for new Muggle and magical technology.

 

Planetary Motion and Apparent Magnitude

As nice as it is to pretend to travel to Mars, we still have to learn more about that fascinating planet right here in this classroom, in particular when it comes to its motion and brightness. Mars revolves around the Sun in approximately 1.88 Earth years. Its perihelion (the point in the orbit of a planet at which it is closest to the Sun) is 1.382 astronomical units and its aphelion (the point in the orbit of a planet most distant from the Sun) is 1.666 astronomical units. It rotates around its axis in 24 hours, 37 minutes and 22 seconds, or about 1.026 Earth days. Its axis of rotation is tilted by 25.19 degrees from the plane of its orbit; this means that its seasons are much like Earth’s, only colder.

When Mars and the Sun are close together in the sky, we say that Mars is in conjunction. The apparent magnitude of Mars when it’s in conjunction can get as faint as +1.86, and its angular diameter as seen from Earth can get as low as 3.5 arcseconds, so a ground-based telescope without adaptive optics can see very few features on the planet when this is the case. 

When Mars and the Sun are on opposite sides of the Earth, we say that Mars is in opposition. When it’s near opposition, it appears to move backwards in the sky (that is, from west to east). During this time, it is closer to the Earth than at any other point, but its distance from our planet isn’t the same each time it’s in opposition because of the eccentricity of Mars’s orbit, and, to a lesser extent, that of Earth. When Mars is in opposition, it can be considered “favorable” or “unfavorable” opposition, depending on whether the planet is at or near perihelion or aphelion, respectively. When in favorable opposition, the planet is only about 54 million kilometres from Earth, has an apparent magnitude of -2.98, and has an angular diameter of about 25 arcseconds, making this the best time to look at Mars through a telescope. Conversely, when Mars is in unfavorable opposition, it is nearly twice as far away from Earth and its apparent magnitude is closer to -1.4.

 

A.M.E.

Now that we know how Mars moves, we have enough information to be able to say when its magical effect on us is at its greatest. The optical albedo of Mars is 0.25 and its magical albedo is a little lower because there are some rocks on the surface. The A.M.E. is the greatest when Mars is in favourable opposition, because it is the nearest it gets both to the Sun and Earth and, therefore, looks bigger. The Sun’s magic would interfere destructively with Mars’s magic except that when Mars is far enough above the horizon, the Sun is far enough below that its magic can’t interfere. That’s the best time to view Mars but the worst time to meet an enemy more powerful than you because, as we learned in Year One, that planet’s reflected magic increases one’s anger. When is it safest to meet a powerful enemy? One would think that it’s when Mars is in conjunction, but remember, the Sun’s magic now interferes constructively with Mars’s magic, doubling it. Mars’s magic is still less powerful than it is at other times, but there is a time when it’s even safer to meet a powerful enemy, and you don’t have to know what Mars’s A.M.E. is to figure out when that time is. Think about it before doing the quiz.

Aside from the quiz, there is an essay in which you will be exploring Mars and, hopefully, saving the lives of your fellow explorers.

Original lessons written by Professors Polgara and Gagarina.

Portions of this lesson written by Professor Plumb.