WHAT IS THE SURFACE OF MARS LIKE?


Mars has one of the most dramatic surfaces of any planet in the Solar System. Enormous volcanoes dominate the landscape, the largest of which —Olympus Mons — is over 25 kilometres (15.5 miles) tall. This is three times larger than Mount Everest on Earth! The giant canyon Vales Mariners is long enough to stretch across the entire United States of America.



Mar’s surface is a dry, barren wasteland marked by old volcanoes and impact craters. The entire surface can be scoured by a single sand storm that hides it from observation for days at a time. Despite the formidable conditions, Mar’s surface is better understood by scientists than any other part of the Solar System, except our own planet, of course.



Mars is a small world. Its radius is half of the Earth’s and it has a mass that is less than one tenth. The Red Planet’s total surface area is about 28% of Earth. While that does not sound like a large world at all, it is nearly equivalent to all of the dry land on Earth. The surface is thought to be mostly basalt, covered by a fine layer of iron oxide dust that has the consistency of talcum powder. Iron oxide(rust as it is commonly called) gives the planet its characteristic red hue.



In the ancient past of the planet volcanoes were able to erupt for millions of years unabated. A single hotspot could dump molten rock on the surface for millenia because Mars lacks plate tectonics. The lack of tectonics means that the same rupture in the surface stayed open until there was no more pressure to force magma to the surface. Olympus Mons formed in this manner and is the largest mountain in the Solar System. It is three time taller than Mt. Everest. These runaway volcanic actions could also partially explain the deepest valley in the Solar System. Valles Marineris is thought to be the result of a collapse of the material between two hotspots and is also on Mars.




















CAN ANYBODY LIVE ON MARS?


As it exists today, Mars is a planet hostile to life. Unlike Earth, Mars has no ozone layer to protect life from the Sun’s lethal ultraviolet radiation. There is no breathable oxygen in the air, and giant dust storms are common around the planet. The first astronauts to live on Mars will probably do so in large domes that can contain an artificial, Earth-like atmosphere.



Earth is the only place that we know for certain supports life. Many claims have been made by observers who thought they saw evidence of life on Mars, but we now know they were tricked by the very difficult measurements. From Earth, even with our most powerful telescopes, we just cannot see enough detail on Mars to answer this question. We need a close-up look at the planet.



While robotic spacecraft have given us wonderful views, no humans have ever tried to journey to Mars, and no such missions will be attempted for many years. In fact, whoever will turn out to be the first people on Mars may be your age today, and when you are an adult, perhaps you will watch -- or even participate!-- as people make the first voyage to that planet.



In the meantime, NASA is working hard now to discover whether there is life on Mars. The United States and other countries have been sending spacecraft to orbit or land there since the 1960s, and each mission teaches us more about this fascinating planet. We have learned that even though Mars is more similar to Earth than anywhere else in the solar system, and therefore is a good place to look for life, it is still different from Earth in many ways.



A compass point to the North Pole on Earth because our whole planet acts like a giant magnet, but Mars does not act this way. Besides turning a compass needle, Earth's magnetic field turns away dangerous particles of space radiation. Without a magnetic field on Mars and with much, much less air than on Earth, more harmful space radiation reaches its surface. Although some measurements tell us there probably is water on Mars, there is far less than on Earth. And it is so cold there that most of the water is probably not liquid but rather is ice. Overall, Mars would be a pretty uncomfortable place to try to live!



Even if there were no life on Mars, it would be exciting to know whether there used to be life there. So in addition to looking for living bacteria, NASA will be searching for tiny fossils that might indicate life got a start early in Mars' history but, unlike on our home planet, it did not survive and evolve into larger life forms.



Many of the studies of Mars will involve robots, like the ones that have gone there before, but getting more advanced with each flight. Someday a spacecraft may pick up samples from Mars and bring them back to Earth where they can be studied in our best laboratories. Eventually, humans may make the daring journey, but many important problems have to be solved before trying such an expensive, difficult, and exciting voyage.




















IS THERE STILL WATER ON MARS?


When mars first formed it had a much thicker atmosphere than it does today. Because the planet’s gravity is not very strong, this atmosphere gradually escaped into space. The climate became increasingly cold, and all the water on Mars froze. Today, the water on Mars exists only as an icy, permafrost layer deep in the soil. Temperatures in Mars’ Polar Regions are so low that carbon dioxide in the atmosphere freezes, covering sheets of water ice with a layer of frosty crystals of dry ice.



Almost all water on Mars today exists as ice, though it also exists in small quantities as vapor in the atmosphere. What was thought to be low-volume liquid brines in shallow Martian soil, also called recurrent slope lineae, may be grains of flowing sand and dust slipping downhill to make dark streaks. The only place where water ice is visible at the surface is at the north polar ice cap. Abundant water ice is also present beneath the permanent carbon dioxide ice cap at the Martian South Pole and in the shallow subsurface at more temperate conditions. More than 21 million km3 of ice have been detected at or near the surface of Mars, enough to cover the whole planet to a depth of 35 meters (115 ft). Even more ice is likely to be locked away in the deep subsurface.



Some liquid water may occur transiently on the Martian surface today, but limited to traces of dissolved moisture from the atmosphere and thin films, which are challenging environments for known life. No large standing bodies of liquid water exist on the planet's surface, because the atmospheric pressure there averages just 600 pascals (0.087 psi), a figure slightly below the vapor pressure of water at its melting point; under average Martian conditions, pure water on the Martian surface would freeze or, if heated to above the melting point, would sublime to vapor. Before about 3.8 billion years ago, Mars may have had a denser atmosphere and higher surface temperatures, allowing vast amounts of liquid water on the surface, possibly including a large ocean that may have covered one-third of the planet. Water has also apparently flowed across the surface for short periods at various intervals more recently in Mars' history. On December 9, 2013, NASA reported that, based on evidence from the Curiosity rover studying Aeolis Palus, Gale Crater, contained an ancient freshwater lake that could have been a hospitable environment for microbial life.



Many lines of evidence indicate that water ice is abundant on Mars and it has played a significant role in the planet's geologic history. The present-day inventory of water on Mars can be estimated from spacecraft imagery, remote sensing techniques (spectroscopic measurements, radar, etc.), and surface investigations from landers and rovers. Geologic evidence of past water includes enormous outflow channels carved by floods, ancient river valley networks, deltas, and lakebeds; and the detection of rocks and minerals on the surface that could only have formed in liquid water. Numerous geomorphic features suggest the presence of ground ice (permafrost) and the movement of ice in glaciers, both in the recent past and present. Gullies and slope lineae along cliffs and crater walls suggest that flowing water continues to shape the surface of Mars, although to a far lesser degree than in the ancient past.



Although the surface of Mars was periodically wet and could have been hospitable to microbial life billions of years ago, the current environment at the surface is dry and subfreezing, probably presenting an insurmountable obstacle for living organisms. In addition, Mars lacks a thick atmosphere, ozone layer, and magnetic field, allowing solar and cosmic radiation to strike the surface unimpeded. The damaging effect of ionizing radiation on cellular structure is another one of the prime limiting factors on the survival of life on the surface. Therefore, the best potential locations for discovering life on Mars may be in subsurface environments. On November 22, 2016, NASA reported finding a large amount of underground ice on Mars; the volume of water detected is equivalent to the volume of water in Lake Superior. In July 2018, Italian scientists reported the discovery of a sub glacial lake on Mars, 1.5 km (0.93 mi) below the southern polar ice cap, and extending sideways about 20 km (12 mi), the first known stable body of water on the planet.


















WHAT IS TERRAFORMING?


Terraforming is the process of changing the environment of a planet to make it more like Earth. Many scientists have proposed terraforming Mars as a way of dealing with over-crowding on Earth. Nobody knows exactly how terraforming would work, and whether it would have a damaging effect on Mars’ natural environment, but in theory, Mars could be transformed into a second Earth, where many forms of life could live naturally. The diagrams to the right show how it could be done.



Terraforming or terraformation (literally, “Earth-shaping”) of a planet, moon, or other body is the hypothetical process of deliberately modifying its atmosphere, temperature, surface topography or ecology to be similar to the environment of Earth to make it habitable by Earth-like life.



The concept of terraforming developed from both science fiction and actual science. The term was coined by Jack Williamson in a science-fiction short story (“Collision Orbit”) published during 1942 in Astounding Science Fiction, but the concept may pre-date this work.



Even if the environment of a planet could be altered deliberately, the feasibility of creating an unconstrained planetary environment that mimics Earth on another planet has yet to be verified. Mars is usually considered to be the most likely candidate for terraforming. Much study has been done concerning the possibility of heating the planet and altering its atmosphere, and NASA has even hosted debates on the subject. Several potential methods of altering the climate of Mars may fall within humanity's technological capabilities, but at present the economic resources required to do so are far beyond that which any government or society is willing to allocate to it. The long timescales and practicality of terraforming is the subject of debate. Other unanswered questions relate to the ethics, logistics, economics, politics, and methodology of altering the environment of an extraterrestrial world.
















WHAT IS SPECIAL ABOUT THE METEORITE ALH84001?


The most convincing evidence for life on the red planet comes from a Martian meteorite that landed on Earth around 13,000 years ago. This meteorite contained microscopic structures that could have been formed by living organisms.



The general consensus now is that the original rock formed 4 billion years ago on Mars. It was eventually catapulted into space by an impact and wandered the solar system for millions of years before landing on Earth 13,000 years ago.



Over 50 other meteorites have been identified as coming from Mars, but ALH84001 is by far the oldest, with the next in age being just 1.3 billion years old. "That alone makes ALH84001 a very important sample," says Allan Treiman of the Lunar and Planetary Institute. "It’s our only hope to understand what Mars was like at this time period."



The first thing that struck researchers examining the meteorite was the presence of 300-micron-wide carbonate globules that make up 1% of the rock. Dave McKay from NASA’s Johnson Space Center and his colleagues determined that the carbonate most likely formed in the presence of water.



Although evidence for a wet ancient Mars has accumulated in the subsequent years, the claim that ALH84001 once sat in water was pretty revolutionary at the time, says Kathie Thomas-Keprta, also from the Johnson Space Center.



Inside the ALH84001 carbonates, McKay spotted odd features that resembled very small worm-like fossils, so he asked Thomas-Keprta to look at them more closely with electron microscopy. "I kind of thought he was crazy," she says. "I thought I would join the group and straighten them out."



In the end, she helped the team characterize the biomorphic features, as well as unusual grains of the mineral magnetite found in the meteorite. In a 1996 Science paper, these two phenomena – along with the chemical distribution in the globules and the detection of large organic molecules – were taken collectively as signatures of biological activity occurring long ago on Mars.














WHY IS MARS KNOWN AS THE RED PLANET?


Mars has been known as the red planet for thousands of years. The Ancient Romans named the planet Mars because it reminded them of their God of anger and war. Mars gets its striking colour from large amounts of iron oxide (rust) in its soil.



Even photos from spacecraft show that it’s a rusty red color. The hue comes from the fact that the surface is actually rusty, as in; it’s rich in iron oxide. Iron left out in the rain and will get covered with rust as the oxygen in the air and water reacts with the iron in the metal to create a film of iron oxide.



Mars’ iron oxide would have formed a long time ago, when the planet had more liquid water. This rusty material was transported around the planet in dust clouds, covering everything in a layer of rust. In fact, there are dust storms on Mars today that can rise up and consume the entire planet, obscuring the entire surface from our view. That dust really gets around.



But if you look closely at the surface of Mars, you’ll see that it can actually be many different colours. Some regions appear bright orange, while others look browner or even black. But if you average everything out, you get Mars’ familiar red colour.



If you dig down, like NASA’s Phoenix Lander did in 2008, you get below this oxidized layer to the rock and dirt beneath. You can see how the tracks from the Curiosity Rover get at this fresh material, just a few centimeters below the surface. It’s brown, not red.



And if you could stand on the surface of Mars and look around, what colour would the sky be? Fortunately, NASA’s Curiosity Rover is equipped with a full colour camera, and so we can see roughly what the human eye would see. The sky here is blue because of Raleigh scattering, where blue photons of light are scattered around by the atmosphere, so they appear to come from all directions. But on Mars, the opposite thing happens. The dust in the atmosphere scatters the red photons makes the sky appear red. We have something similar when there’s pollution or smoke in the air.



But here’s the strange part. On Mars, the sunsets appear blue. The dust absorbs and deflects the red light, so you see more of the blue photons streaming from the Sun. A sunset on Mars would be an amazing event to see with your own eyes. Let’s hope someone gets the chance to see it in the future.












DOES MARS HAVE AN ATMOSPHERE?


When mars first formed it had a very thick atmosphere. However, the gases have long since disappeared into space due to the planet’s weak gravity. Mars’ atmosphere is now very thin, and made mainly of carbon dioxide.



The atmosphere of Mars is the layer of gas surrounding Mars. It is primarily composed of carbon dioxide (95.32%), molecular nitrogen (2.6%) and argon (1.9%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen and other noble gases. The atmosphere of Mars is much thinner than Earth’s. The surface pressure is only about 610 Pascal’s (0.088 psi) which is less than 1% of the Earth’s value. The currently thin Martian atmosphere prohibits the existence of liquid water at the surface of Mars, but many studies suggest that the Martian atmosphere was much thicker in the past. The highest atmospheric density on Mars is equal to the density found 35 km above the Earth’s surface. The atmosphere of Mars has been losing mass to space throughout history, and the leakage of gases still continues today.



The atmosphere of Mars is colder than Earth’s. Owing to the larger distance from Sun, Mars receives less solar energy and has a lower effective temperature (about 210 K). The average surface emission temperature of Mars is just 215 K, which is comparable to inland Antarctica. The weaker greenhouse effect in the Martian atmosphere (5 °C, versus 33 °C on Earth) can be explained by the low abundance of other greenhouse gases. The daily range of temperature in the lower atmosphere is huge (can exceed 100 °C near the surface in some regions) due to the low thermal inertia. The temperature of the upper part of the Martian atmosphere is also significantly lower than Earth’s because of the absence of stratospheric ozone and the radiative cooling effect of carbon dioxide at higher altitudes.



Dust devils and dust storms are prevalent on Mars, which are sometimes observable by telescopes from Earth. Planet-encircling dust storms (global dust storms) occur on average every 5.5 earth years on Mars and can threaten the operation of Mars rovers. However, the mechanism responsible for the development of large dust storms is still not well understood.



The Martian atmosphere is an oxidizing atmosphere. The photochemical reactions in the atmosphere tend to oxidize the organic species and turn them into carbon dioxide or carbon monoxide. Although the most sensitive methane probe on the recently launched ExoMars Trace Gas Orbiter failed to find methane in the atmosphere over the whole Mars, several previous missions and ground-based telescope detected unexpected levels of methane in the Martian atmosphere, which may even be a bio signature for life on Mars. However, the interpretation of the measurements is still highly controversial and lacks a scientific consensus.










HAS THERE EVER BEEN LIFE ON MARS?


Of all the planets in the Solar System, Mars most resembles Earth. Its day is only slightly over 24 hours, and it is tilted at the same angle as our planet, meaning that seasons are very similar to ours. Early on in its history, Mars had water on its surface. Oceans formed, kept warm by volcanic activity, and primitive life may have started here. Today, freezing conditions on Mars, and the planet’s thin atmosphere, mean that life can no longer exist on the planet’s surface.



The search for life on Mars shouldn’t focus exclusively on the distant past, some researchers say. Four billion years ago, the Martian surface was apparently quite habitable, featuring rivers, lakes and even a deep ocean. Indeed, some astrobiologists view ancient Mars as an even better cradle for life than Earth was, and they suspect that life on our planet may have come here long ago aboard Mars rocks blasted into space by a powerful impact.



Things changed when Mars lost its global magnetic field. Charged particles streaming from the sun were then free to strip away the once-thick Martian atmosphere, and strip it they did. This process had transformed Mars into the cold, dry world we know today by about 3.7 billion years ago, observations by NASA's MAVEN orbiter suggest. (Earth still has its global magnetic field, explaining how our planet remains so livable.)



One of the most promising hiding places is the Martian underground. Though the Red Planet's surface has no liquid water these days — apart, possibly, from temporary flows on warm slopes now and again — there’s a likely lot of the wet stuff in buried aquifers. For example, observations by Europe’s Mars Express orbiter suggest that a big lake may lurk beneath the Red Planet’s South Pole.



Earth’s diverse residents advertise their presence in dramatic and obvious ways; an advanced alien civilization could probably figure out pretty quickly, just by scanning our atmosphere, that our planet is inhabited. 



We don’t see any such clear-cut evidence in the Martian air, but scientists have spotted some intriguing hints recently. For example, NASA's Curiosity rover has rolled through two plumes of methane inside the 96-mile-wide (154 kilometers) Gale Crater, which the six-wheeled robot has been exploring since its 2012 touchdown. The rover mission also determined that baseline methane concentrations in Gale's air go through cycles seasonally.



More than 90% of Earth's atmospheric methane is produced by microbes and other organisms, so it's possible the gas is a signature of modern Martian life.



But the jury is most definitely still out on that. Abiotic processes can generate methane, too; the reaction of hot water with certain types of rock is one example. And even if the Mars methane is biogenic, the creatures that created it could be long dead. Scientists think the Red Planet methane plumes leaked out from underground, and there's no telling how long the gas lay trapped down there before making its way to the surface.








ARE THERE CANALS ON MARS?


In the 19th century, the astronomer Giovanni Schiaparelli claimed that Mars was covered by a network of channels. Many people believed that these were canals created by an intelligent civilization to help carry water from the Polar Regions to drier areas around the Equator. Recent photographs of Mars have shown that there are many channels on the planet, but scientists believe these were created naturally by running water billions of years ago.



The space-heads among you have undoubtedly heard about the Curiosity rover's first significant discovery: the remnants of an ancient streambed on Mars, which would seem to indicate the presence of water in the planet's history. This jagged pile of alluvial rock and dust my not took like much, but it brings to mind one of my favorite pieces of Martian historical arcana.



For a time in the late 19th century, it was believed that there were canals on Mars. The Italian astronomer Giovanni Schiaparelli, who observed Mars in 1877, was the first to describe, name, and lovingly illustrate mysterious straight lines along its equatorial regions, which he called canal. Viewed with the telescopes of the day, in brief instances of still air amidst the optical strangeness of atmosphere, Mars was tough to figure. There are areas which appear darker or lighter (these are called Albedo features); to an enthusiastic observer, it was easy to speculate of continents, oceans, or even straight-line canals.



Beset by the same optical illusions, many astronomers seconded Schiaparelli's observations. The maps of the day show a Mars riven with peculiar webs and lines–lines which successive high-resolution mapping of the planet have definitively shown do not exist. The mechanism that caused this illusion appears to be internal: faced with a shifting landscape of foggy forms, glimpsed at through simple lenses of glass through the refractive index of Earth’s atmosphere, the human brain tends to impose order.



The persistence of belief in Martian canals is often attributed to a linguistic fluke, that the Italian canal, meaning "channel" (or watercourse, and not necessarily of unnatural origin), was mistranslated to the English "canal." I really love this narrative of language shaping reality, but unfortunately it's the astronomical equivalent of an urban legend. "Canal," in fact, was used in the earliest English accounts, and Schiaparelli made no move to correct the misunderstanding, if he was aware of it.










WHY ARE THERE SO MANY VOLCANOES ON VENUS?


          Venus is covered by hundreds of thousands of volcanoes. This is because the surface of the planet is a thin skin floating on hot molten rock. This lava is vented wherever possible, meaning that, unlike Earth, Venus has volcanoes everywhere. Most of these volcanoes are around 3km (2 miles) wide and 90m (395ft) high, but there are over 160 much larger than this. Some volcanoes on Venus are over 100km (60 miles) in diameter! The volcanic activity on Venus means that the surface of the planet is always changing.



          The surface of Venus is dominated by volcanic features and has more volcanoes than any other planet in the Solar System. It has a surface that is 90% basalt, and about 65% of the planet consists of a mosaic of volcanic lava plains, indicating that volcanism played a major role in shaping its surface. There are more than 1,000 volcanic structures and possible periodic resurfacing of Venus by floods of lava. The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Venus has an atmosphere rich in carbon dioxide, with a density that is 90 times greater than Earth's atmosphere.



          Even though there are over 1,600 major volcanoes on Venus, none are known to be erupting at present and most are probably long extinct. However, radar sounding by the Magellan probe revealed evidence for comparatively recent volcanic activity at Venus’s highest volcano Maat Mons, in the form of ash flows near the summit and on the northern flank. Although many lines of evidence suggest that Venus is likely to be volcanically active, present-day eruptions at Maat Mons have not been confirmed.






























WHY IS VENUS LIKE A GREENHOUSE?


          Less than 20% of sunlight falling on Venus breaks through the clouds. Despite this, Venus has the hottest surface temperature of any planet in the Solar System. This is because infrared radiation (heat) released from the planet cannot escape back into space. The atmosphere traps heat inside, like the glass in a green-house, meaning that the temperature is over 400°C (750°F), greater than it would he if Venus had no atmosphere.



          Greenhouse involving carbon dioxide and water vapor may have occurred on Venus. In this scenario, early Venus may have had a global ocean if the outgoing thermal radiation was below the Simpson-Nakajima limit but above the moist greenhouse limit. As the brightness of the early Sun increased, the amount of water vapor in the atmosphere increased, increasing the temperature and consequently increasing the evaporation of the ocean, leading eventually to the situation in which the oceans boiled, and all of the water vapor entered the atmosphere. This scenario helps to explain why there is little water vapor in the atmosphere of Venus today. If Venus initially formed with water, the greenhouse would have hydrated Venus’ stratosphere, and the water would have escaped to space. Some evidence for this scenario comes from the extremely high deuterium to hydrogen ratio in Venus' atmosphere, roughly 150 times that of Earth, since light hydrogen would escape from the atmosphere more readily than its heavier isotope, deuterium. Venus is sufficiently strongly heated by the Sun that water vapor can rise much higher in the atmosphere and be split into hydrogen and oxygen by ultraviolet light. The hydrogen can then escape from the atmosphere while the oxygen recombines or bonds to iron on the planet’s surface. The deficit of water on Venus due to the runaway greenhouse effect is thought to explain why Venus does not exhibit surface features consistent with plate tectonics, meaning it would be a stagnant lid planet. Carbon dioxide, the dominant greenhouse gas in the current Venusian atmosphere, owes its larger concentration to the weakness of carbon recycling as compared to Earth, where the carbon dioxide emitted from volcanoes is efficiently sub ducted into the Earth by plate tectonics on geologic time scales through the carbonate-silicate cycle, which requires precipitation to function.




























WHAT WAS THE MAGELLAN MISSION?


          The most detailed information about Venus was acquired by a space probe called Magellan. Launched in 1989, Magellan travelled to Earth's neighbour and spent three years building a complete map of the planet. Flying as low as 294km (183 miles) above the surface, Magellan bounced radar pulses off the solid ground beneath and sent the data back to Earth to he analyzed. It measured strips of land 24km (14 miles) wide and 10,000km (6000 miles) long each time it circled the planet, while its altimeter measured its height above the surface.



          The Magellan spacecraft was the first planetary explorer to be launched by a space shuttle when it was carried aloft by the shuttle Atlantis from Kennedy Space Center in Florida on May 4, 1989. Atlantis took Magellan into low Earth orbit, where it was released from the shuttle's cargo bay and fired by a solid-fuel motor called the Inertial Upper Stage (IUS) on its way to Venus. Magellan looped around the Sun one-and-a-half times before arriving at Venus on August 10, 1990. A solid-fuel motor on the spacecraft then fired, placing Magellan into a near-polar elliptical orbit around Venus.



          Spacecraft carried a sophisticated imaging radar, which was used to make the most highly detailed map of Venus ever captured during its four years in orbit around Venus from 1990 to 1994. After concluding its radar mapping, Magellan also made global maps of Venus's gravity field. Flight controllers then tested a new maneuvering technique called aero braking, which uses a planet's atmosphere to slow or steer a spacecraft. The spacecraft made a dramatic plunge into the thick, hot Venusian atmosphere on October 12, 1994, and was crushed by the pressure of Venus's atmosphere. Magellan's signal was lost at 10:02 Universal Time (3:02 a.m. Pacific Daylight Time) that day.



          The Magellan mission was divided up into "cycles" with each cycle lasting 243 days (the time necessary for Venus to rotate once under the Magellan orbit). The mission proceeded as follows:



Magellan Assembly



          On May 4, 1989, the Magellan spacecraft was deployed from the shuttle. The spacecraft is topped by a 3.7-meter (12-foot) diameter dish-shaped antenna that was a spare part left over from the Voyager program. The long, white, horn-shaped antenna, attached just to the left of the dish antenna, is the altimeter antenna that gathers data concerning the surface height of features on Venus. Most of the spacecraft is wrapped in reflective white thermal blankets that protect its sensitive instruments from solar radiation. 



Deployment



          The Magellan spacecraft's deployment from the shuttle Atlantis' cargo bay was captured by an astronaut with a hand-held camera pointed through the shuttle's aft flight deck windows. Deployment occurred in the early evening of May 4, 1989, after Atlantis had carried Magellan and its Inertial Upper Stage (IUS) booster rocket, into low Earth orbit. Once the shuttle was safely away from the spacecraft, the IUS ignited and placed Magellan on course for its 15-month journey to Venus.



Magellan Orbiting Venus



          On August 10, 1990, Magellan entered into orbit about Venus, as depicted in this artist's view. During its 243-day primary mission, referred to as Cycle 1, the spacecraft mapped well over 80 percent of the planet with its high-resolution Synthetic Aperture Radar (SAR). The spacecraft returned more digital data in the first cycle than all previous U.S. planetary missions combined.




















HOW CAN WE SEE PAST VENUS’ CLOUDS?


          Venus’ atmosphere is formed from clouds of carbon dioxide, nitrogen and sulphuric acid. This heavy layer of clouds is over 30km (18 miles) deep in some places, meaning that no part of the planet’s surface can be seen with the naked eye. Only since the 1970s have scientists been able to “look” past these clouds to see the solid ground beneath. This has mainly been done with equipment mounted on space probes. Radar technology allows probes to record the geography of the planet, and to produce a map of surface features.



          The clouds of Venus are its defining characteristic. We can see the surface of Mars and Mercury, but the surface of Venus is shrouded by thick clouds. For most of history, astronomers had no idea what was beneath those clouds, and they imagined a tropical world with overgrown vegetation and constant rainfall. They couldn’t have been more wrong.



          The climate of Venus isn’t tropical at all; it’s hellish. Temperatures on the surface of Venus approach 475°C and the atmospheric pressure is 93 times what you experience here on Earth. To experience that kind of pressure, you would need to swim down 1 km beneath the surface of the ocean. Venus’ atmosphere is made almost entirely of carbon dioxide, and not the oxygen/nitrogen mix we have here on Earth.



          The clouds we see on Venus are made up of sulfur dioxide and drops of sulfuric acid. They reflect about 75% of the sunlight that falls on them, and are completely opaque. It’s these clouds that block our view to the surface of Venus. Beneath these clouds, only a fraction of sunlight reaches the surface. If you could stand on the surface of Venus, everything would look dimly lit, with a maximum visibility of about 3 km.



          The upper cloud deck of Venus is between 60-70 km altitudes. This is the part of Venus that we see in telescopes and visible light photographs of the planet. The clouds on Venus rain sulfuric acid. This rain never reaches the ground, however. The high temperatures evaporate the sulfuric acid drops, causing them to rise up again into the clouds again.



          Venus spacecraft have detected lightning on Venus, coming out of the clouds with a similar process to what we have on Earth. The first bursts of lightning were detected by the Soviet Venera probes and later confirmed by ESA’s Venus Express spacecraft.




















WHY IS VENUS A KILLER PLANET?


          Early astronomers claimed that Venus was Earth’s sister planet. They believed that the light and dark areas they saw on the planet through their telescopes were oceans and continents. Modern astronomy has proved that nothing could be further from the truth! The light and dark areas are Venus’ suffocating atmosphere — a layer of clouds containing sulphuric acid released by volcanic eruptions. The temperature on Venus can rise to 464°C (867°F), and the heavy layers of cloud make the air pressure on the surface over 100 times that of Earth.



          Venus is the second planet from the Sun and our closest planetary neighbor. Similar in structure and size to Earth, Venus spins slowly in the opposite direction from most planets. Its thick atmosphere traps heat in a runaway greenhouse effect, making it the hottest planet in our solar system with surface temperatures hot enough to melt lead. Glimpses below the clouds reveal volcanoes and deformed mountains.



          Had Venus drawn slightly luckier tickets in the cosmic lottery, our solar system could host two habitable planets today, according to recent simulations from a group of NASA researchers. Instead, our neighbor is a desolate place—and might give us a terrifying glimpse of our own future.



          Planetary scientists have traditionally viewed Venus's hellish temperatures, carbon dioxide-saturated atmosphere, and congealed crust as the inevitable outcome of its place in the solar system. Sitting too close to the sun, the hapless planet was doomed from birth to be burnt to a crisp. In recent years, however, an alternative possibility has thrown some shade at this simple story. Given the right starting conditions, cloud cover could have protected Venus from the barrage of sunlight and kept it balmy and wet for billions of years, according to simulations presented this week at a planetary science conference in Switzerland. In this scenario, Venus may have actually been the solar system’s first habitable planet… until some unknown catastrophe smothered it in carbon dioxide. While our carbon emissions probably couldn’t completely fry the Earth in quite the same way, the transformation of Venus may still hold an important moral for humanity.



          “If there was life on Venus, they only had one home,” says Colin Goldblatt, a planetary scientist at the University of Victoria in Canada, “and that home isn't very good anymore.”


















HOW DO CRATERS FORM?


          Craters are the most widespread landforms in the solar system. Craters are found on all of the terrestrial planets—Mercury, Venus, Earth and Mars. The surfaces of asteroids and the rocky, ice covered moons of the outer gas planets are cratered as well. The craters left by impacting objects can reveal information about the age of a planet's surface and the nature and composition of the planet's surface at the time the crater was formed.



MERCURY AND THE MOON



          Impact craters dominate the surfaces of Mercury and the Earth's Moon. Both bodies lack liquid water on their surfaces that would erode impact craters over time. They also lack an atmosphere which, on planets like the Earth and Venus, could disintegrate meteoroids before they impact the surface. However, old craters can be eroded by new impact events. Mercury and the Moon have very old surfaces. One of the youngest large craters on the Moon is Tycho, which was formed about 109 million years ago.



EARTH



          Liquid water, wind and other erosional forces erase impact craters on the Earth. There are still many craters on Earth which are visible from space. Some craters in areas of low rainfall (i.e. where little erosion occurs) are relatively intact, such as this crater - Meteor Crater in Arizona, U.S.A.



MARS



          Mars has experienced significant bombardment. The southern hemisphere is more heavily cratered than the northern hemisphere. Winds are the main erosional force on Mars and windblown dust and soil erode craters over time. The structure of some Martian impact craters, such as the one pictured here at left, provide evidence that suggests the presence of water or ice in the surface at the time the impact occurred.



ASTEROIDS



          Asteroids are rocky and usually heavily cratered due to a long history of impacts with other asteroids and possibly comets. Old impact craters on asteroids have beem deformed and erased by newer impact craters. Alternatively, impact events can disintegrate asteroids into smaller pieces. This asteroid, Mathilde, is interesting because of the large size of the impact craters on its surface. Despite the obvious intensity of the impacts, the asteroid was not destroyed. Scientists believe the asteroid must be  uncommonly dense to have withstood such bombardment.



PLANETARY SATELLITES



          The outer gas planets do not have solid surfaces, but their moons do. Most of these moons are rocky, icy worlds with a variety of surface features and compositions. Most of them are cratered, such as Europa, one of the Galilean satellites of Jupiter. Europa's surface is thought to consist of a thick layer of ice overlaying a liquid water ocean.



IMPACT WITH JUPITER



          Terrestrial planets aren't the only ones that are hit by meteors, comets and asteroids. The planets known as gas giants, such as Jupiter, don't have a solid surface to keep a record of impacts. However, the impact of comet Shoemaker-Levy in 1993 left visible holes in the cloud tops of Jupiter. The effects of these holes began to fade after only a few months, but it was the first time humans observed a major collision between two objects in our solar system.