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65 Articles

Astronomer Royal

INTERVIEW BIO Martin Rees Renowned Astronomer Royal Martin Rees is best known for his work on some of the most exotic and extreme objects in the cosmos: black holes, quasars, gamma ray bursts and the early universe. He’s written several books, has received numerous prestigious academic awards, he was the president of the Royal Astronomical Society and even has a seat in the UK's House of Lords, as Baron Rees of Ludlow What, in your mind, is the greatest unanswered question of the solar system? Whether there is life somewhere away from the Earth. There may be simple life on Mars, but the most interesting place to search would be the oceans under the ice of Europa and Enceladus. Do you think Pluto's demotion to a dwarf planet was an…

Astronomer Royal

Birth of the SOLAR SYSTEM

Around 4.5 billion years ago, our Sun and all the other objects that orbit around it were born from an enormous cloud of interstellar gas and dust, similar to the glowing emission nebulae we see scattered across today’s night sky. Astronomers have understood this basic picture of the birth of the Solar System for a long time, but the details of just how the process happened have only become clear much more recently – and now new theories, discoveries and computer models are showing that the story is still far from complete. Today, it seems that not only did the planets form in a far more sudden and dynamic way than previously suspected, but also that the young Solar System was rather different from that we know now. The so-called…

Birth of the SOLAR SYSTEM

LIFE in the SOLAR SYSTEM

On the north-eastern border of the vast Vatnajökull glacier, Iceland, lies the Kverkfjöll mountain range, where a string of active volcanoes pepper the bleak, Icelandic landscape. Deep under the mountains, searing-hot magma gathers in cavernous chambers. Heat escaping from the chambers warms the glacial ice overhead, sculpting it into a spectacular ice cave some 2.8 kilometres (1.7 miles) long. The melted water crafts lakes that would freeze were it not for the hydrothermal energy escaping from the seething molten rock below. These hot, acidic lakes may not seem like the most hospitable of places, but bacteria have made a home here. Ian Crawford, professor of planetary science and astrobiology at Birbeck, University of London, studies these hardy organisms. “Part of my work is sampling the water from these boiling, acidic…

LIFE in the SOLAR SYSTEM

Planetary habitats

Mars The Red Planet is very dry, has a thin atmosphere and once had running water on its surface. At the very least, it could have been a viable habitat for extremophile life Venus We probably don’t need to look as far as the crushing pressure and heat of Venus’ surface: its clouds could be a perfect environment for acid-loving organisms Pluto The dwarf planet is probably one of the most unlikely candidates for life in the Solar System and yet, scientists won't rule out the potential of its icy oceans…

Planetary habitats

All about… THE SUN

At about 150 million kilometres (93 million miles) from Earth lies a giant incandescent ball of gas weighing in at almost 2,000 trillion trillion kilograms and emitting power equivalent to 1 million times the annual power consumption of the United States in a single second. Since the dawn of Earth, 4.6 billion years ago, it has been the one ever-present object in the sky, basking our world and those around us in energy and light – and providing the means through which environments, and ultimately life, can flourish. We see it every day and rely on its energy to keep our planet ticking, but what exactly is this giant nuclear reactor at the centre of the Solar System that we call the Sun? Over 5 billion years ago, a vast…

All about… THE SUN

Solar wind and the Earth Solar storms are violent outbursts of activity on the Sun that interfere with the Earth’s magnetic field and inundate our planet with particles. They are the result of outpourings of energy from the Sun, either in the form of a Coronal Mass Ejection (CME) or a solar flare. The former is a release of a large amount of material, mostly plasma, from the Sun, while the latter is a sudden release of electromagnetic radiation commonly associated with a sunspot. While no direct connection has been found between CMEs and solar flares, both are responsible for causing solar storms on Earth. The reason why these two events occur is due to the Sun’s atmosphere and its turbulent interior, with all of its components playing a part…

The solar cycle

“Solar cycles have been observed for centuries, but a method of counting them was not devised until 1848” 10 years of the Sun These X-ray images were taken by Japan’s Yohkoh Solar Observatory and show the changes in the Sun’s corona over a ten-year cycle between 30 August 1991 and 6 September 2001 The Scientist’s view How we understand solar cycles “Sun-Earth interaction is complex, and we haven’t discovered all the consequences of solar cycle variation on Earth’s environment. We saw a large amount of geomagnetic activity driven by recurring fast solar wind streams during the recent solar minimum. A surprising departure from the consistently low activity we’d come to expect from previous minima, especially considering the record low level of sunspots. These new observations deepen our understanding of how…

The solar cycle

The SOHO mission

Interview SOHO project scientist Bernhard Fleck tells us why studying the Sun is important to Earth 1. Understand life “The Sun provides the energy for all life on Earth. It seems quite natural that we are curious to know more about the star from which we live.” 2. Understand climate “Solar radiation is the dominant energy input into the terrestrial ecosystem. The Sun provides a natural influence on the Earth’s atmosphere and climate. To understand mankind’s roles in climate change, the Sun’s impact must be understood.” 3. Predict space weather “Our Sun is very dynamic and produces the largest eruptions in the Solar System. These solar storms can reach our planet and adversely affect technologies such as satellites and power grids. Space weather becomes increasingly important as our society depends…

The SOHO mission

Observing the Sun

Observations of the Sun have been used for both scientific and religious observations for millennia. Civilisations have used the Sun to keep an accurate count of days, months and years since at least 300BC, while scientists such as Galileo studied the Sun through telescopes to discern some of its characteristics. At the Chankillo archaeological site in Peru can be found the oldest solar observatory in the Americas, a group of 2,300yearold structures used to track the motion of the Sun known as the Thirteen Towers. These towers provide a rudimentary solar calendar through which the Sun can be traced. The towers, each between 75 and 125 square metres (807 and 1,345 square feet) in size, run from north to west along a ridge along a low hill. From an observation…

Observing the Sun

The history of observing the Sun

400BC The world’s oldest solar observatory, the Thirteen Towers of Chankillo, is built in Peru to track the motion of the Sun 350BC Aristotle uses a camera obscura to project an image of the Sun and observe a partial eclipse. 1612 Galileo Galilei uses his telescope to make one of the first observations of sunspots on the surface of the Sun. 1749 Daily observations of the Sun begin at the Zurich Observatory in Switzerland. 1849 New observatories around the world allow continuous observations of sunspots to be made 2006 The Japanese telescope Hinode is launched to study the magnetic fields and atmosphere of the Sun. 2010 NASA launches the Solar Dynamics Observatory, its primary goal being to study the influence of the Sun near Earth. 2018 NASA’s new Sun-observing telescope…

The history of observing the Sun

Different ways to observe the Sun

On Earth we perceive the Sun to be a yellow ball of gas in the sky but, like anything as hot as the Sun, it is actually closer to being white hot when viewed from space. There are several telescopes currently observing the Sun but the large majority of our images come from the STEREO telescope and the SOHO observatory, both in orbit around the Sun. By viewing the Sun in different wavelengths we can study its different characteristics and see some of its main features in a different light. Ultraviolet Images of the Sun in ultraviolet light are between wavelengths of about 19.5 and 30.4 nanometres. Such an image of the Sun is at the lower end of this scale, and allows us to see where the lower part…

Different ways to observe the Sun

FUSION POWER SUN

The Sun is a huge ball of blazing gas, with a visible surface roughly 1.4 million kilometres (870,000 miles) across. In a single second it pumps out energy equivalent to what could be generated by 2 billion large Earth power stations in a year, making use of a process that scientists have only been able to harness for a fraction of a second in Earth-based laboratories: nuclear fusion. Fusion is the process of joining together the atomic nuclei of light elements to build the nuclei of heavier ones. All atoms consist of a nucleus (a tiny, positively charged core that accounts for the vast majority of their mass) surrounded by a cloud of orbiting electrons (lightweight, negatively charged particles). In comparison to the entire atom, the nucleus is about the…

FUSION POWER SUN

Fission versus Fusion

Fission Nuclear fission is the most familiar form of nuclear reaction here on Earth, but it is very different from fusion. Fission involves the release of energy from the splitting apart of a heavy atomic nucleus whose configuration of protons and neutrons have left it unstable or ‘radioactive’ – it produces one or more lighter nuclei along with other subatomic particles or excess energy. Fission happens regularly in nature, but can also be triggered artificially, which is the principle behind nuclear power stations and, unfortunately, atomic bombs as well. Fusion Unlike fission, fusion is very unfamiliar to us on Earth – it only happens naturally in the extreme conditions of stars, although scientists can replicate it in experiments. Fusion is the forging together of lighter atomic nuclei to make heavier…

Fission versus Fusion

Proton-proton chain fusion

Colliding protons Stripped of their electrons in the heart of the Sun, exposed hydrogen nuclei are simply individual positively charged protons. At intense temperatures and pressures, they are forced together, overcoming forces of electromagnetic repulsion Colliding protons Stripped of their electrons in the heart of the Sun, exposed hydrogen nuclei are simply individual positively charged protons. At intense temperatures and pressures, they are forced together, overcoming forces of electromagnetic repulsion Beta-plus decay In order for the bonded pair of particles to remain stable, one proton transforms almost instantly into a neutron, shedding its positive charge as a small positron particle. This immediately collides with an electron and generates a burst of gamma-ray energy Building a nucleus The resulting stable deuterium nucleus now fuses with a second proton, releasing another burst…

Proton-proton chain fusion

How did our Sun form?

1. Origins of a star Our Sun and its planets were born when a hydrogenrich cloud of interstellar gas and dust began to slowly collapse around 5 billion years ago. 2. Flattening out As the cloud grew denser, it span faster. Collisions within the cloud tended to even out its rotation, resulting in a flattened disc with a large central bulge. 3. Condensing Sun As the central region of the ‘protostellar nebula’ grew more massive, its gravity began to pull in more material, gradually condensing and heating up. 4. Protostar At first, the Sun shone by radiating energy generated by its own gravitational contraction. It was a large, warm ball of gas surrounded by a ring of debris. 5. Ignition! The Sun continued to grow smaller and denser, until its…

How did our Sun form?

The Sun’s twin star

“ HIP 56948 has physical properties and a chemical composition identical to that of the Sun” Since the dawn of mankind our Sun has been regarded as unique. In ancient times it was thought to be the only star in existence, responsible for determining the day and night cycles on Earth. In the modern era we know it to be the heart and soul of the Solar System but it has long been regarded as one-of-a-kind in its composition and size. Now, however, it appears that our Sun could just be one of many similar stars in the Milky Way alone, providing a key piece of evidence to the belief that life could be lurking elsewhere in the universe. The Sun is about 4.6 billion years old, born from a…

The Sun’s twin star

The universe’s Sun-like stars

The Sun Radius: 696,000km Distance: 150 million km Surface temp: 5,778 K Age: 4.57 billion years HIP 56948 Radius: 1.14 Suns Distance: 210 light years Surface temp: 5,748 K Age: 3.6 billion years 18 Scorpii Radius: 1.01 Suns Distance: 45.3 light years Surface temp: 5,433 K Age: 4.7 billion years HD 143436 Radius: Unknown Distance: 142 light years Surface temp: 5,768 K Age: 3.8 billion years HD 44594 Radius: 1.0 Suns Distance: 82 light years Surface temp: 5,840 K Age: 4.1 billion years HD 98618 Radius: 1.0 Suns Distance: 126 light years Surface temp: 5,843 K Age: 4.21 billion years…

The universe’s Sun-like stars

All about EARTH

Like the TV show says, the Earth is indeed the third ‘rock’ from the Sun – it’s also the largest of our Solar System’s four terrestrial planets, the fifth-largest planet and the densest planet overall. It’s called an oblate spheroid – it’s flattened at the poles, but bulgy at the equator, thanks to forces from the Earth’s rotation. The bulge means that the furthest point from the centre of the Earth to the surface is located in Ecuador. The Earth has a density of 5.52 grams per cubic centimetre, a mass of 5.98 x 1024 kilograms and a circumference of 40,075 kilometres (25,000 miles). Earth rotates on its axis once approximately every 24 hours, although the length of a true solar day (measured from noon to noon) always varies slightly…

All about EARTH

Earth inside and out

You may think you know all there is to know about Earth, but we take the wonders of our home planet for granted sometimes. It’s unique because it’s the only planet that has all of the elements needed to support life. It’s also incredibly diverse, from the vast array of geographic features to the millions of plant and animal species. If you want to explore the unknown, there’s no need to look to the stars; we’re always discovering something new about our own planet. But let’s start with the basics. Along with the other planets, the Earth formed from the solar nebula – a cloud of dust and gas left over from the Sun’s formation – about 4.54 billion years ago. It may have taken between 10 and 20 million…

Earth inside and out

“ Some plates have hot spots – areas of volcanic activity under the mantle within the plate, where volcanoes form” While we typically divide the Earth into crust, mantle and core, there are other ways of differentiating the outer layers. The lithosphere comprises both the crust and part of the upper mantle – specifically, the part that is rigid but has elasticity and becomes brittle over thousands of years. Underneath is the asthenosphere, a deeper part of the mantle that behaves like a viscous fluid. The lithosphere is divided into tectonic plates, pieces that are about 100 kilometres (62 miles) thick and move on top of the flowing asthenosphere. There are seven major plates: African, Antarctic, Eurasian, Indo-Australian, North American, Pacific and South American. These include the continents and the…

Surface features

Desert Deserts get so little precipitation that they can’t support much life, but there are desert-dwelling plants and animals. A true desert gets less than 400mm (16in) of rainfall per year. They make up about one-third of the Earth’s land surface. Rainforest Rainforests have very high levels of rainfall, usually a minimum of 1,750mm (68in) each year. They cover 5% of the Earth and are the source of about 25% of our natural medicines, and home to millions of species of plants and animals. Oceans Saline or saltwater makes up about 71% of the Earth’s surface. No other observable planet has as much water on its surface. The total volume of saltwater on Earth is approximately 1.3 billion cubic kilometres (311 million cubic miles). Ice caps Ice caps and glaciers…

Surface features

Why is there life on Earth?

Water Although other planets have been found to have water, none have as much as Earth. Sometimes our water mass, including the oceans and freshwater sources, is known as the hydrosphere. Without such plentiful sources, the water cycle could not function and there wouldn't be enough oxygen to support life. Human bodies comprise about 70 per cent water, and life on Earth needs it to survive. Astronomers have coined the term ‘Goldilocks Zone’ to describe star systems that theoretically have planets with atmospheres capable of retaining water. All known forms of life require liquid water, so this has become the gold standard for finding life on other planets. They may also be called circumstellar habitable zones (CHZ). But a planet needs more than just water – other bodies within our…

Why is there life on Earth?

5 kingdoms of life

Animalia The animal, or Animalia, kingdom (also called Metazoa), includes about 1,000,000 multicellular, heterotrophic species. Plantae Kingdom plant, or Plantae, includes everything from multicellular flowers to mosses. There are about 250,000 plant species Fungi Fungi include around 100,000 identified species. The Fungi kingdom includes mushrooms, yeasts and moulds. Protista The Protista kingdom has 250,000 species which don’t have much in common with each other, apart from not belonging elsewhere. Monera The Monera kingdom is made up of species such as algae and bacteria. There are approximately 10,000 species in this kingdom.…

5 kingdoms of life

Observing Earth

Until we were able to get far enough away from our planet to view it, the only way we could infer things about it was by exploring its relationship to other heavenly bodies. And for a long time, what we believed was wrong. Many ancient cultures, for example, believed that the Earth was the centre of the universe. This was based on two observations: the stars and other planets appeared to revolve around the Earth, and to a person on Earth, the planet seemed to be perfectly at rest. Once we were able to better observe other bodies, we began to learn the truth about our home planet. Then we developed the technology to take pictures of the Earth from space. The first such image was taken by a rocket,…

Observing Earth

8 stunning Earth landmarks

Largest rainforest One in ten of the world’s known species live in the Amazon rainforest. Biggest active volcano Mauna Loa in Hawaii is the largest active volcano on Earth in terms of volume and area. Tallest waterfall Situated in Venezuela, Angel Falls stands at 979m and is the world’s highest uninterrupted waterfall. Biggest crater With a 300km diameter, the Vredefort crater in South Africa near Johannesburg is Earth’s largest known impact crater. Deepest canyon The Tsangpo Canyon in Tibet can reach depths of over 6,000m. Biggest ice sheet The East Antarctic Ice Sheet is the largest ice sheet on the planet and is home to the South Pole. Largest glacier Antarctica’s Lambert Glacier is about 100km wide, over 400km long and about 2,500m deep. Highest mountain At 8,848m tall, Mount…

8 stunning Earth landmarks

On 4 November 2011, six triumphant men from across the world returned to Earth and emerged from a windowless isolation chamber to elated cheers. They had – in theory at least – been to Mars and back on a journey that had taken them away from their friends and families for 520 days. During that time, three crew members had spent 30 days on the Red Planet, having detached from their mother ship to explore the Martian surface, removed soil and rock samples and planted three flags; one each for the Chinese, Russian and European space agencies. Their time away proved tough. The mission affected their sleep patterns, with one crew member’s body falling into a 25-hour day cycle. And although they had books, DVDs and the videogame Guitar Hero…

Hervé Stevenin

Hervé Stevenin leads ESA’s Neutral Buoyancy Facility Operations. With more than 20 years of training experience, he is a spacewalk instructor for European astronauts. Why is underwater training useful for astronauts? Astronauts have to perform EVAs and so we need an environment of weightlessness. Although we can use reduced gravity aircraft, they only give astronauts 23 seconds of pure weightlessness or microgravity. This is not appropriate for EVAs because they are six hours long and astronauts have to work on modules and in a complex environment. So we use an underwater environment to simulate the weightlessness and the astronauts feel like they are in a controlled buoyancy How closely can simulation match real life? The astronauts can work in a big water tank, into which we submerge big modules of…

Loredana Bessone

Loredana was hired by ESA for a student job in 1990 and within a few years had begun work on human space flight. She went on to develop astronaut operational skills training including ESA’s CAVES. What were you looking for when you developed CAVES? I was looking for an environment very similar to that which astronauts would encounter during human space flight so I wanted isolation, confinement, limited resources and difficult communication. There had to be real risk to create stressors that are typical on human space flight and a real mission that would allow astronauts to work together effectively and safely as an international team. How can you be sure simulations match real life experiences? CAVES is a good analog. If anything, it can be even worse in a…

Loredana Bessone

Desert RATS training

Located by a 2-million-year-old lava flow near Flagstaff, Arizona, Desert RATS conducts annual missions, with an emphasis on testing roving and spacewalks. They test for optimum crew sizes and the science that can be conducted on Mars, the Moon or other rocky bodies. It has experimented with backpacks and arm-mounted computers and it has introduced cutting edge robots. It has also experimented with surface networking and spacesuits that can use speech recognition to control suit parameters or the movement of robots. Any technology trialled one year is refined and tried again the next. The six-legged ATHLETE all-terrain vehicle has been chopped back to three legs, for example, and retested.…

Desert RATS training

Where in the world?

1. Desert RATS Flagstaff, Arizona Desert Research and Technology Studies (Desert RATS) makes use of the Black Point Lava Flow site in Arizona which shares a host of environmental and terrain similarities with Mars, the Moon and near-Earth asteroids. As well as understanding how rovers can cope with craters, slopes, dust storms and volcanic ash fields, it also looks at the tasks that would be better suited to humans such as sample collection. 2. In-Situ Resource Utilisation Mauna Kea, Hawaii When astronauts in the future land on the Moon, they would, ideally, be able to produce their own oxygen from lunar rocks and soil. This dormant volcano has proven to be a perfect simulation of the Moon’s polar regions. Scientists have studied the effectiveness of rovers to produce oxygen in…

Where in the world?

All about… THE MOON

Because we can easily discern features on the Moon with the naked eye, it has been a sense of wonder to us since ancient times. The Moon is the brightest object in our sky after the Sun, and influences everything from our oceans to our calendars. It’s always been ‘the Moon’ because we didn’t know that there were any others. Once Galileo discovered in 1610 that Jupiter had satellites, we’ve used the word ‘moon’ to describe celestial bodies that orbit larger bodies, which orbit stars. Since the Moon has always been so present, it might not seem worth studying. Yet there’s a reason why we continue to return to it – we still have plenty to learn from our satellite. The Moon is the fifth-largest and second-densest satellite in the…

All about… THE MOON

The Moon inside and out

Although the Moon may seem like a solid rock, it’s actually differentiated like the Earth; it has a core, a mantle and a crust. The Moon’s structure likely came from the fractional crystallisation of a magma ocean that once covered the Moon. This probably happened not long after the Moon was formed, about 4.5 billion years ago. This means that as the magma ocean cooled, its composition changed as the different minerals within the melt crystallised into solids. The denser materials sank, forming the mantle, while less dense materials floated on top and formed the crust. We believe that the core is probably very small, with a radius about 20 per cent the total size of the Moon. By contrast, most differentiated celestial bodies have cores about 50 per cent…

The Moon inside and out

The landscape of the Moon is dominated by three main features: maria, terrae and craters. The basalt maria appear dark due to their high iron content and are much more prevalent on the near side of the Moon. Other volcanic features located on the surface of the Moon include domes and rilles. Domes are shield volcanoes that are round and wide with gentle slopes, while rilles are twisting sinuous formations caused by channels of flowing lava. The lighter areas on the Moon are called terrae (terra is singular), or lunar highlands. They are made up of anorthosite, the type of igneous rock that dominates the overall crust of the Moon. While this type of rock can be located in some places on Earth, it’s not generally found on the surface…

Exploring the Moon: the past

Apollo 11 21 July 1969 NASA astronauts Buzz Aldrin and Neil Armstrong became the first humans to set foot on another body in space when they landed on the Moon in 1969. This mission ended the race to the Moon between the United States and the USSR. Apollo 12 19 November 1969 The second spacecraft to land on the Moon, Apollo 12 used a Doppler effect radar technique to precisely land the spacecraft within walking distance of the Surveyor 3 probe, which had landed on the lunar surface about two years prior. Apollo 14 5 February 1971 The commander on board the third spacecraft to land on the Moon was Alan Shepard, who, a decade earlier on 5 May 1961, had become the second person in space after Yuri Gagarin…

Exploring the Moon: the past

Exploring the Moon: present and future

Although there hasn’t been a manned mission to the Moon since 1972 and there were no soft landings at all until 1966, we’re still exploring our satellite. Currently the Lunar Reconnaissance Orbiter (LRO) is still circling the Moon. It launched on 18 June 2009, and became the first NASA mission to the Moon in more than a decade. The LRO is meant to be a precursor to future manned missions, and was originally designed to spend just a year in orbit. However, the mission was extended several times. It was designed to extensively map the Moon in high resolution, explore the potential of ice in the polar regions, study the deep space radiation, and continue to map the surface of the Moon. The other current NASA mission is ARTEMIS, an…

Exploring the Moon: present and future

Current and future missions

Luna-Glob Russia This Russian Federal Space Agency programme is scheduled to be the first of a series of missions, with the ultimate goal of creating a robotic base on the Moon. Its goals include gathering seismic activity, studying cosmic rays, and studying the origin of the Moon. Chang’e 2 China This Chinese probe was launched on 1 October 2010 and left lunar orbit in November to go on an extended mission. Chang’e 2 was designed to study future landing sites Kaguya Japan Also known as SELENE, this Japanese orbiter was launched on 14 September 2007 and circled the Moon before impacting on 10 June 2009. Kaguya measured the Moon’s gravity, studied the surface and sought information on the Moon’s history. LADEE USA NASA plans to launch the Lunar Atmosphere and…

Current and future missions

Explore… The Moon

The Moon’s diameter is 27 per cent of Earth’s, which is freakishly large. Jupiter’s moon Ganymede is larger in absolute terms, but compared to its parent planet it is just a speck, with less than a fiftieth of the diameter. The disproportionate size of the Moon reflects its unusual origins. Most other moons are captured asteroids, or leftover material from the ball of dust and gas that coalesced to form the Solar System. But the Moon is made from the rubble of another planet, called Theia, that collided with Earth around 4.5 billion years ago. When it was first formed, the Moon may have been ten times closer to Earth than it is today and would have caused tides on Earth several kilometres high. Over billions of years, the gravitational…

Explore… The Moon

All about MERCURY

Every planet is unique, but Mercury is a planet of paradoxes and extremes, and that’s just based on what we know so far. It’s the innermost planet, the smallest planet and has the most eccentric orbit. We’ve known about its existence since the third millennium BC, when the Sumerians wrote about it. But they thought that it was two separate planets – a morning star and an evening star – because that’s just about the only time you can see it due to its closeness to the Sun. The Greeks knew it was just one planet, and even that it orbited the Sun (long before acknowledging that the Earth did, too). Galileo could see Mercury with his telescope, but couldn’t observe much. This little planet has a diameter that’s 38…

All about MERCURY

Mercury inside and out

Mercury contains about 30 per cent silicate materials and 70 per cent metals. Although it’s so small, this make-up also means that it’s incredibly dense at 5.427 grams per cubic centimetre, only a little bit less than the Earth’s mean density. The Earth’s density is due to gravitational compression, but Mercury has such a weak gravitational field in comparison to the Earth’s. That’s why scientists have decided that its density must be due to a large, iron-rich core. Mercury has a higher concentration of iron in its core than any other major planet in the Solar System. Some believe that this huge core is due to what was going on with the Sun while Mercury was forming. If Mercury formed before the energy output from the Sun stabilised, it may…

Mercury inside and out

The surface of Mercury is not very well understood, but mapping by Mariner 10 and Messenger has revealed numerous craters and plains regions, crisscrossed with compression folds and escarpments. Not long after it formed, the planet was hit heavily and often in at least two waves by large asteroids and comets, which caused its extremely cratered surface. Couple this with periods of strong volcanic activity, which resulted in the smooth plains, and you have a very hilly surface. Mercury can reach 427 degrees Celsius (800 degrees Fahrenheit), and there’s a big difference between the temperature at the equator and the temperature at its poles. It has the most temperature variations of any planet in the Solar System, getting as low as -183 degrees Celsius (-297 degrees Fahrenheit). There may be…

All About…VENUS

“ Venus rotates clockwise, making a Venusian sidereal day last the equivalent of 243 days on Earth” Venus, named after the Roman goddess of love and beauty, is a study in contradictions. It was likely first observed by the Mayans around 650 AD, helping them to create a very accurate calendar. It’s well-known to us because of its apparent magnitude, or brightness, in our sky – the secondbrightest after our own Moon. It’s most visible at sunrise and sunset, and like Mercury was thought of as two different planets by the Ancient Egyptians – Morning Star and Evening Star. It’s the second-closest planet to the Sun, the closest planet to Earth, and the sixth-biggest planet in the Solar System. Venus is often described as the Earth’s ‘twin’ or ‘sister planet’.…

All About…VENUS

Venus inside and out

While our knowledge of Venus’s internal makeup is mostly based on speculation, we do know that it does not include a dynamo, like Earth’s. A dynamo is a convecting, rotating fluid that conducts electricity and is responsible for a planet’s magnetic field. Venus may have a liquid outer core and that conducts electricity, but does not convect and rotates too slowly to produce a dynamo. The Earth has a dynamo in part because its liquid core is hotter on the bottom than on the top, creating convection. Venus’s core may be all one temperature. But why? Some astronomers believe that Venus was subject to an unknown event on its surface, which caused an end to plate tectonics on the surface and led to a cooling of the core. Venus’s core…

Venus inside and out

Everything that we’ve learned about Venus’s surface is from radar, because the atmospheric pressure is too great for a probe to survive longer than an hour. But Magellan has mapped most of the surface, and showed that Venus has a lot of interesting surface features. It has a relatively flat surface, with about 13 kilometres (eight miles) between the lowest point and the highest point. Most of them fall into one of three categories: highlands, deposition plains and lowlands. There are also some mountain ranges, with the highest one, Maxwell Montes at 11 kilometres (6.8 miles). The highlands comprise about ten per cent of the planet’s overall surface area, and there are two main ‘continents's – Ishtar Terra and Aphrodite Terra. The deposition plains (formed from lava flows) cover over…

Mountains, volcanoes and craters

Maxwell Montes Maxwell Montes is the tallest mountain range on Venus, reaching 11 kilometres (6.8 miles) above the mean planetary radius. By comparison, the tallest mountain on Earth, Mount Everest, is 8.8 kilometres (5.5 miles) tall. Although this is a computergenerated image, it was formed using data from the Magellan spacecraft. The arachnoids Spider-web like formations crawl across the surface of Venus. Arachnoids are formations of unknown origin that look like concentric circles of cracked crust. They can cover as much as 200 kilometres (124 miles). Mead Crater A crater almost as big as the largest crater on Earth. Mead Crater, named after anthropologist Margaret Mead, is the largest impact crater on Venus’s surface. It’s 280 kilometres (170 miles) wide, just 20 kilometres shy of Earth’s widest crater Vredfort. It…

Mountains, volcanoes and craters

SURVIVING ON MARS

Stranded on Mars. That’s the fate that befalls one unfortunate astronaut in the novel and film The Martian. With no way to contact home, he must rely on his skills and the equipment available to stay alive in the face of deadly Martian elements. While the film and book are both works of fiction, it is true that going to Mars will be the most dangerous crewed space mission ever attempted. There are dust storms, radiation, an unbreathable atmosphere, fierce coldness and low gravity to contend with, while the astronauts themselves will have to constantly be in top physical and mental condition in the most challenging of environments. Should anything go wrong, it is an 18-month wait for a new launch back home, and then a further eight months travel…

SURVIVING ON MARS

One-way ticket to Mars

What training will you need to be able to survive on Mars? Ryan McDonald: Perhaps the most important aspect of training is spending up to three months each year conducting a mission in one of the simulation outposts. During these simulations we are continually subject to surprises, obstacles and intensive struggles with the intention of ensuring that only the most committed stick through to the end, since there is no turning back once you are on Mars. Hannah Earnshaw: We will need to have all the skills necessary to run the settlement ourselves, as well as to respond to any emergency without help from Earth as a message could take up to 40 minutes to receive a reply. We will need training in engineering, farming and medicine, as well as…

One-way ticket to Mars

JUPITER PLANET KILLER

There are many things we know about Jupiter. It is a huge gas giant with a mass equivalent of 317.8 Earths. It is twice as massive as every other planet in the Solar System combined. It has four large moons and a number of smaller ones, and it spins at an incredible rate, which means a day lasts less than around ten hours. But there are also some things about Jupiter, which continue to surprise us. Who would have thought, for example, that this mass of hydrogen and helium could potentially have been a wrecking ball, helping to shape the entire Solar System as we know it today? As it stands, the eight planets appear to be in regular, fixed orbits around the Sun. Mercury is closest, followed by Venus,…

JUPITER PLANET KILLER

The making of gas planets

Bottom-up model 1 The start of a planetary system Dust grains in orbit around a young star begin to coalesce into planetesimals. The clumping occurs through nongravitational forces 2 Growing into planets The size of the planetesimals begins to increase, moving in orbits, to form the planetary embryos. 3 The making of a gas giant Before the gas in the disk disappears, the planetesimals drag gas envelopes onto themselves that gives them their puffy layers. 4 Planetary scatter Some of the gas giants scatter and, due to their sheer size, accrete remaining planetesimals and embryos. Top-down model 1 In the beginning A disk of gas and dust – known as a protoplanetary disk – is made around a young central star. 2 Unstable dust Gravitational instabilities in the disk form…

The making of gas planets

Mars is smaller than expected When the Sun's protoplanetary disk is simulated on a computer, it shows Mars as larger than it is due to a greater level of mass near the planet's orbit. The Grand Tack Hypothesis supposes Jupiter absorbed much of this mass. The asteroid belt's object mix The existence of icy objects and dry, rocky objects within the asteroid belt has challenged astronomers. The Grand Tack claims Jupiter's outward migration pushed the belt in, and deflected icy objects toward the Sun. Earth has the “right” amount of water on its surface The classical model of the Solar System's formation shows Earth with too much or too little water. The Grand Tack supposes C-type, icy asteroids were the source of water. The asteroid belt doesn't have as much…

All about… SATURN

Gas giant Saturn is the second-largest planet in the Solar System behind Jupiter and the sixth planet from the Sun. As such, it is the most distant planet that is easily visible with the naked eye from Earth. From here, it looks like a bright yellowish point. That doesn’t mean that you’ll be able to see the rings, though – you will need at least some strong binoculars if you hope to see them. Saturn is more than 95 times more massive than the Earth, although it has just one-eighth the density. In fact, with a density of just 0.687 grams per cubic centimetre (0.397 ounces per cubic inch), it is less dense than water, meaning that it would float in an ocean if there were one big enough to…

All about… SATURN

The major moons

Mimas ”That’s no moon!” But in this case it is. Mimas is known for its appearance, which is similar to the Star Wars Death Star because of an extremely large impact crater (140km or 87 miles in diameter) in its northern hemisphere known as Herschel. It is a heavily cratered planet with a surface area that’s about the same as Spain’s. Enceladus Enceladus is the sixth-largest moon of Saturn and is believed to have ice water under its frozen surface. The moon is unique because it’s one of just three in the Solar System that has active eruptions – in this case, gigantic ice geysers that shoot out into space. This water ice contributes to the matter in Saturn’s rings as well as falling as snow on the moon itself.…

The major moons

Saturn inside and out

Saturn is one of the gas giants because it has no solid surface and it’s mostly composed of gas. But it does have a rocky core, which is similar in composition to the Earth’s. Comprising iron, nickel and silicate rock, it is estimated to be somewhere between 10 and 20 times the size of the Earth’s core. Surrounding the core, there’s a layer of ice made of ammonia and other elements, then a layer of highly pressurised metallic hydrogen, and finally molecular hydrogen that changes from a liquid to a gas. The outer layers of the planet are different types of ice, including ammonia, ammonium hydrosulphide and water. The cloud cover is mostly coloured yellow by ammonia, and there’s a mild weather system. Density, pressure and temperature all increase as…

Saturn inside and out

The composition of Saturn’s clouds depends on where you are in the atmosphere. The pressure increases and temperatures drop as you travel further down through the layers and towards the planet’s core. At the upper cloud layer, the clouds are made up of ammonia ice, followed by water ice clouds with a layer of ammonium hydrosulphide ice mixed in, and then the bottom layer is ammonia mixed in water droplets. Much like fellow gas giant Jupiter, Saturn has bands of clouds that are divided into zones and belts. The zones are the lighter-coloured areas and the bands are darker, with the orange and reddish hues coming from sulphuric compounds. The darker clouds tend to be thinner and lower, while the lighter ones are denser and higher. The bands of clouds…

The ring system

Although Saturn isn’t the only planet in our Solar System with a system of rings, it’s the only one with a system this big. There are billions of tiny particles, mostly ice but with some rocky material, too. Despite the fact that they increase Saturn’s brightness, we weren’t even aware of its ring system until Galileo observed them via telescope. He was confused a few years later when the rings seemed to disappear, not knowing that they just weren’t visible with his telescope when the Earth is on the same plane as Saturn. By the 1800s we knew that the rings were just that – not moons, not a single disc, but many rings comprising tiny particles. Saturn’s ring system is divided into rings, arcs, divisions and gaps. The first…

The ring system

All about… URANUS

While William Herschel officially discovered Uranus in 1781, he wasn’t the first to observe it. Others thought it was a star and Herschel himself called it a ‘comet’ before deciding that it was, in fact, a planet – and the first one discovered by telescope. Although Uranus can be seen from Earth with the naked eye, it’s so dim and has such a slow orbit compared to the other known planets that it didn’t register as one. It just looks like a faint pinpoint of greenish or bluish light. Uranus’s acceptance as a new planet overturned beliefs that had been held for millennia about the size of our Solar System, and kicked off a flurry of planetary discovery. But despite Uranus’s significance, we haven’t spent much time visiting the planet.…

All about… URANUS

Uranus inside and out

The term ‘gas giant’ implies that Uranus is solely composed of gases, but studies indicate that it actually has a core of silicate rock, encased in ices and topped with a gaseous layer. The core must be very small, since Uranus is the second-least dense planet. It likely takes up only 20 per cent of the planet’s radius. The ice mantle surrounding the core is fluid, with volatiles like methane, ammonia and water. In fact, this electrically conducive fluid is often called an ammonia-water ocean. The outer layer is mostly helium and hydrogen. Uranus is also much cooler inside than the other gas giants – it’s actually the coldest planet in the Solar System. Neptune radiates 2.61 times the heat that Uranus does. We aren’t sure why Uranus is so…

Uranus inside and out

Moons and rings

Spin of the rings Discovering the Uranian ring system was a real surprise for astronomers. Since the planet is on its side, we have the opportunity to view the rings in a completely different way than we have for the rings of Jupiter and Saturn. Most of the rings were identified in 1977, with Voyager 2 and later the Hubble Telescope bringing the total to its current number of 13. Many of these rings are not quite in the plane of Uranus’s equator, and most of them are not exactly circular. Unlike the rings of Jupiter, most of Uranus’s rings comprise mostly microscopic particles of water ice and an unknown material – not dust. And in comparison to Saturn’s rings, Uranus’s rings are very dark. The brightness seems to vary…

Moons and rings

Discovering the rings

When William Herschel discovered Uranus, he also claimed to see a faint ring around the planet. It seems unlikely he was truly able to see anything, however. The ring system was officially discovered by a team working with the Kuiper Airborne Observatory (KAO). In 1977 and 1978, the team found a total of nine rings around Uranus. KAO was the first airborne astronomical research observatory, based at the NASA Ames Research Center in California. A military jet aircraft was modified to carry a 91.5cm (36in) reflecting telescope used to conduct infrared astronomy. Why a telescope on a plane? The aircraft was used to fly above 13,716m (45,000ft). This altitude is above the layer of water vapour in the Earth’s atmosphere that absorbs infrared radiation, allowing the team to use the…

Discovering the rings

All About… NEPTUNE

Each planet is unique, and Neptune’s claim to fame is being the first planet to be discovered not by observation, but by prediction. French astronomer Alexis Bouvard spent a lot of time closely observing the orbit of Uranus, and detected a gravitational perturbation that he deduced could only be explained by the existence of another planet. From his observations, other astronomers calculated the location of Neptune. To be fair, Galileo actually spotted Neptune more than 200 years before, but since he thought it was a star, he didn’t get the credit. There’s still some debate over who did deserve the credit – French astronomer Urbain Le Verrier or British astronomer John Couch Adams – and some sources include a third astronomer, Johann Galle of Germany. At any rate, Galle was…

All About… NEPTUNE

Neptune inside and out

Like Uranus, Neptune is a gas giant but not solely comprising gases. Its core contains silicate rock, iron and nickel and is a little larger than planet Earth. Neptune’s core is also under great pressure (twice as much pressure as the Earth’s core) and about 5,100 degrees Celsius (9,200 degrees Fahrenheit). The mantle surrounding the core is icy, but that’s a relative term when it comes to planet temperatures because it’s actually a hot, dense liquid. Made of methane, ammonia, and water, the mantle is electrically conductive and its temperature ranges between 1,700 degrees Celsius (3,100 degrees Fahrenheit) and 4,700 degrees Celsius (8,500 degrees Fahrenheit). The mantle may also consist of additional layers, including a layer of ionised water (with electrically charged hydrogen and oxygen) and a deeper layer of…

Neptune inside and out

Supersonic winds and storms

Neptune’s massive winds and storms set it apart from Uranus. Most of the winds blow in retrograde rotation (opposite the planet’s rotation), but the general pattern is prograde rotation (in the direction of the planet) in the higher latitudes and retrograde rotation in the lower latitudes. The winds reach almost 2,000 kilometres per hour (1,240 miles per hour) – nearly supersonic speeds. On Voyager 2’s flyby in 1989, it observed a massive anti-cyclonic storm that was 13,000 by 6,600 kilometres (8,700 by 4,100 miles) in size. The storm was dubbed the Great Dark Spot. It wasn’t present when the Hubble Space Telescope viewed the planet five years later, but another storm was found and given the name. Neptune also has other large storms named the Scooter and the Small Dark…

Supersonic winds and storms

Moons and rings

Neptune has 13 known moons. Triton is by far the largest moon, comprising more than 99 per cent of the total mass in orbit around the planet. It has a diameter of 2,705 kilometres (1,700 miles) and is the only spheroid moon. Triton was probably a dwarf planet in the Kuiper belt before being captured by Neptune’s orbit. Astronomers believe it was captured instead of forming as a satellite because it has a retrograde orbit – it circles Neptune opposite of the planet’s rotation. Triton has an irregular orbit, and is the second known moon (along with Saturn’s moon Titan) to have an atmosphere. The atmosphere mostly comprises nitrogen, with some trace amounts of carbon monoxide and methane. It is also one of the coldest objects in the Solar System.…

Moons and rings

PLUTO OUR LAST FRONTIER

It has been on a breathtaking journey 4.8 billion kilometres (3 billion miles) long. It has taken nineand-a-half years. And it has cost $700 million (£460 million). But for patient astronomers working on the New Horizons mission, the spacecraft which is about to make the first-ever reconnaissance of Pluto is more than worth its half-ton weight in gold. Launched on 19 January 2006, New Horizons is set to spend this summer flying by Pluto and its five known moons. It is already the closest man-made object to Pluto, but very soon it will be within a space whisker and scientists are very excited about the possible discoveries it will enable them to make. “Imagine the explorers of old who crossed the oceans,” says Dr Alan Stern, the principal investigator of…

PLUTO OUR LAST FRONTIER

Is Pluto still a planet?

YES Dr William B McKinnon, professor at the Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St Louis “ Pluto is a planet. But it is a small, ordwarf, planet. It is the exemplar of an entirely new class of planets, the other classes being the rocky terrestrial planets and the gas giants. All of the dwarf planets we know of so far are made of ice and rock, and most reside in the Kuiper belt, beyond Neptune. But the idea that dwarf planets are not planets is linguistically sloppy and a bit silly. Planetary scientists study bodies, not just masses and orbits, and a world with five moons, an atmosphere and hints of a complex history, is planet enough for most…

Is Pluto still a planet?

Pluto: the missing pieces

01 How Pluto fits in Dr Harold Weaver, New Horizons project scientist, The Johns Hopkins University Applied Physics Laboratory “I want to transform Pluto from a pixellated blob into a world with complexity and diversity. What does Pluto’s landscape really look like? Are there high mountains and deep valleys? Are there cryovolcanic vents hinting at interior activity? And how do Pluto and its moons compare to other bodies in the Solar System?” 02 Pluto’s actual size Dr Marc Buie, astronomer, Southwest Research Institute “The simplest thing I want to learn is the actual size of Pluto. However, I also really want to see how geologic and surface processes on Pluto relate to the known albedo patterns. Are they connected or are they independent?” 03 The atmospheric make-up Dr Randy Gladstone,…

Pluto: the missing pieces

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