MERCURY

MERCURY

Mercury is the planet closest to the Sun. It is also the fastest-moving planet, whizzing round the sun in just 88 days. Being close to the Sun, Mercury gets extremely hot. Its surface is covered in thousands of craters, making it look rather like a moon.

How big is Mercury?

Mercury is the smallest of the rocky, Earth-like planets. With a diameter of only 4,880 kilometres, it is less than half the size of the Earth. The planet Pluto, a deep-frozen ball of rock and ice, is even smaller.

What is strange about Mercury’s orbit?

Most planets have a nearly circular orbit, or path, around the Sun. Mercury, however, has an oval orbit. At times it travels as far as 70 million kilometres away from the Sun. At others, it gets as close as 46 millions kilometres.

Why does Mercury get so hot?

As it travels around the Sun, Mercury spins so slowly on its axis that a point on its surface stays in the Sun for nearly six Earth-month at a time. With the Sun so close and shining for so long, surface temperatures on Mercury soar to 430°C- hot enough to melt metals such as tin and lead.

What has shaped Mercury’s surface?

Billions of years ago, all the planets were bombarded by huge meteorites. On Earth, most craters made up by the meteorites have been worn away by the action of the weather. Mercury has no weather because it has almost atmosphere. So all the craters that formed ages ago remain, and the whole planet is covered with them. A huge one, called the Calories Basin, was made by a giant meteorite that send shock waves throughout the planet.

What is Mercury made of?

Like the Earth and the other rocky planets, Mercury is made up of different layers. Underneath a rocky crust there is a rocky mantle, and at the centre, a huge metal core. The shrinking of the core has caused great ridges, up to 3 kilometres high, to appear on the surface.

Have any space probes visited Mercury?

Only one space probe has flown to study Mercury. Named Mariner 10, it flew to the planet in 1974, after visiting Venus. Its picture revealed for the first time that Mercury looked rather like some parts of the Moon. Mariner 10 flew past Mercury twice more. On the last occasion, in March 1975, it skimmed only about 300 kilometres above the surface.

MERCURY DATA

Diameter at equator: 4880km

Mass : 0.06 times Earth’s mass

Average distance from the Sun : 58 millions km

Minimum distance from the Earth : 91 millions km

Length of day : 59 Earth-days

Length of year : 88 Earth-days

Temperature : -185°C to 430°C

Satellites : 0

VENUS

VENUS

Venus is the planet whose orbit comes closest to Earth. We often see it shining in the western sky after sunset, which is why it is known as the Evening Star. Venus is a near twin of Earth in size, but it is waterless world with a scorching climate.

Why does Venus change shape?

From Earth, Venus seems to change its shape and size as time goes by. This is because it orbits closer to the Sun than Earth. When it is on the far side of the Sun, we see it as a small circle. As it moves closer to Earth, it gets bigger, but it as a part-circle. Finally, it is just a thin crescent.

What is the surface of Venus like?

Space probes have shown that great plains cover much of Venus’ surface. There are two big highland regions, which we can think of as continents. One is found in the north, and is called Ishtar Terra. The other lies near the equator, and is called Aphrodite Terra.

Why is Venus so cloudy?

We cannot see Venus’ surface from Earth because of thick clouds in its atmosphere. These clouds are not like the clouds we find on Earth, which are made up of tiny water droplets. Venus’ clouds are made up of tiny droplets of sulphuric acid, one of the strongest acids we know. The sulphur has found its way into the atmosphere from the many volcanoes that have erupted on Venus over the years.

How can we see through Venus’ clouds?

Space probes can see through Venus’ clouds and show us what the planet’s surface is like. But they do not ‘see’ in ordinary light. They ‘see’ with radar beams, because radar beams can go straight through the clouds. The most successful radar probe, name Magellan, mapped the whole planet between 1990 and 1992.

What is Venus made of?

Venus is nearly the same size as Earth, and is probably similar in make-up. It has a hard rocky crust, but no great oceans as Earth has. Venus is far too hot for water to remain in liquid form. Beneath the crust is a mantle of heavier rock, and at the centre is a metal core, which may b partly liquid.

Why is Venus so hot?

The average temperature in Venus is more than twice as hot as an oven set on ‘high’. This is because its atmosphere contains mainly carbon dioxide – a heavy gas that trap heat. Over the years it has caused the atmosphere to trap more and more heat, as a greenhouse does. The cloud layers trap the heat too, making the temperature reach a scorching 480°C.

VENUS DATA

Diameter at equator : 12,100 km

Average distance from Sun : 108 million km

Minimum distance from Earth : 42 million km

Turns on axis : 243 Earth-days

Circles Sun : 225 Earth-days

Surface temperature : 480°C

Satellites : 0

THE PLANETS

THE PLANETS

The nine planets are the most important members of the Sun’s family. In order of distance from the Sun , they are Mercury , Venus , Earth , Mars , Jupiter , Saturn , Uranus , Neptune and Pluto. The first four are small rocky bodies. The next four are giants , made up mainly of gas . Pluto is a tiny ball of rock and ice.

Which is the biggest planet?

Jupiter is by far the largest of the planets. It has more mass than all other planets put together. It measures nearly 143,000 kilometres across, which is 11 times bigger than Earth. Even though it is so big, it takes less than 10 hours for it to spin round once. This means that its surface round at a speed of 45,000 kilometres an hour. This is 30 times faster than Earth spins.

Which planets have rings?

Once it was thought that Saturn was the only planet that had rings around it because they were the only one that can be seen through a telescope. But close up photographs taken by the Voyager space probes have shown us that the other three gas giants- Jupiter, Uranus and Neptune-have rings too. The rings around the these other planets are much thinner , narrower , and darker than Saturn’s.

Why is Uranus sometimes called ‘new’?

Astronomers have been studying the planets for thousand of years. They have watched the way they move, or ‘wander’ across the night sky, unlike the stars. But the ancient astronomers could only see five planets in the night sky. It was not until 1781 that someone built a telescope powerful enough to spot another planet, which came to be called Uranus. Uranus was the first of three ‘new’ planets to be discovered. Neptune was discovered in 1846, and Pluto in 1930.

What is special about Saturn?

Two things are outstanding about Saturn. One is obvious when you look at the planet through telescope. The planet is surrounded by a set of bright, shining rings. Many people think that these make Saturn the most beautiful object in the Solar System. The other special thing about Saturn is that it is the lightest(least dense) of all the planets. It is lighter even than water. This means that if you could place it in huge bowl of water, it would float.

Which planet is furthest from the sun?
As far as we know, the most distant planet from the Sun is Pluto, the last ‘new’ planet to be discovered after Neptune. But Pluto is not always the furthest away. For 20 years between 1979 and 1999, Neptune was further still because during this time Pluto was travelling inside Neptune’s orbit. Neptune will become the furthest planet again in a little over 200 years’ time. Pluto travels more than 7000 million kilometres away from the Sun. It takes nearly 248 Earth-years to circle the Sun once.

URANUS

URANUS

Uranus is the third biggest planet, and is four times bigger across than Earth. It is so far from the Earth that it is barely visible with the naked eye. Because of this it was not discovered until 1700s, with the help of a telescope

Who discovered Uranus?

In March 1781, an English astronomer named William Herschel was looking at the sky through a telescope. He spied what he thought must be a new comet. But it was actually a new planet. Until then, astronomers knew of only six planets. The new planet, which was late called Uranus , turned out to be twice as far away from the Sun as Saturn.

Why is Uranus sometimes called the topsy-turvy planet?

All planets spin as they orbit the Sun. We say they spin round their axis (an imaginary line that goes through their north and south poles). In most planets the axis is nearly upright as the planet spins. But Uranus spins on an axis at right-angle to normal, so it is as if Uranus is lying on its side. This means that, at times in its orbits, Uranus’ poles point straight at the Sun. As a result, they become hotter than the rest of the planet, instead of always being colder, as on Earth.

How many rings does Uranus have?

Astronomers use to think that Saturn was the only planet that had rings circling it. But, in 1977, they discovered that Uranus had rings too. There are about 11 main rings, made up of bits of rock up to a metre across, which whizz round the planet at high speed. The particles in some of the rings are kept in place by tiny ‘shepherd’ moons.


Which probe has visited Uranus?

We can find out very little about Uranus through telescopes because it is so far away. Most of what we know comes from Voyager 2 space probe, which visited Uranus in 1986. Voyager 2 had earlier visited Jupiter(1979) and Saturn(1981). It has now gone far beyond the planets, and will soon leave the Solar System and begin a journey to the stars.

What is Uranus made of?

Uranus has a thick atmosphere of hydrogen, helium and methane ice, and a mantle of water, ammonia and methane ice. At the centre there is an iron silicate core.
What is Uranus’ moons like?
We can only see the five largest of Uranus’ moons from Earth – Miranda, Ariel, Umbriel, Titania and Oberon. Ten smaller moons were discovered by Voyager 2. The large moons are great balls of rock and ice, pitted with craters, and with long cracks in their surface. Titania is the biggest moon. It is about 1,600 kilometres across.

What is special about Miranda?

Miranda is the smallest moon that can be seen from Earth, with a diameter of only about 500 kilometres. Close-up photographs show it to be the most interesting moon of all. Its surface is a patchwork of different kinds of landscape – craters, grooves, cliffs and valleys. Astronomers think that, ages ago, Miranda shattered into pieces when it collided with another body. Then the pieces came together to create the landscape we see today.

URANUS DATA

Diameter at equators : 51,000 km

Average distance from Sun : 2,870 million km

Minimum distance from Earth : 2,600 million km

Turns on axis : 17 hours 14 minutes

Circles Sun : 84 Earth-years

Temperature at cloud tops : -200°C

Satellites : 15

SATURN

SATURN

Saturn is the biggest planet, after Jupiter. Like Jupiter, it is a giant ball of gas. Saturn is a favourite planet among astronomers because of its shining rings. The rings appear to change shape year by year as the planet makes its way round the Sun.

What are Saturn ‘s rings made of?

Saturn is surrounded by many rings, but only three can be seen from Earth. The other rings were discovered by space probes. The rings look like solid sheets, but they are not. They are made up of millions upon millions of bits of ice, whizzing round the planet at high speed. The bits vary in size from specks of dust to large chunks. In places, the rings are less than 50 metres thick.

Why is Saturn so cloudy?

Saturn is a very cloudy planet. The clouds form into bands parallel to the equator because the planet is spinning round so fast. These bands are not as easy to see as they are on Jupiter because of the haze that tops the atmosphere. There seem to be three main cloud layers of Saturn, located at different level, with clear areas in between. The upper layers of cloud are made up of ammonia and ammonium compounds. At the lowest level, the clouds seem to be made up of water and ice particles, like the clouds wa have on Earth.

What’s Saturn like inside?

Saturn is a gas giant, which means that it is composed mainly of gas and iquid gas. Its cloudy atmosphere is made up almost entirely of hydrogen and helium. Below that lies a vast, deep ocean of liquid hydrogen. Deeper down is a layer of hydrogen in the form of a liquid metal. At the centre of the planet, there is a small core of rock.

What are Saturn’s moons like?

Saturn has at least 18 moons – more than other planet. Only five have a diameter greater than 1,000 kilometres – Tethys, Dione, Rhea, Titan and Lapetus. The smallest, Pan, is only about 20 kilometres across. Biggest by far is Titan. With a diameter of 5,140 kilometres, it is the second largest moon in the whole Solar System, and the only one that has a thick atmosphere.

What is Titan’s surface like?

Titan’s thick atmosphere is made up mainly of nitrogen gas. It is orange in colour and full of hazy clouds that stop us seeing what its surface is like. Astronomers reckon that it may be covered with great lakes or seas of liquid methane, and there may be land areas covered with methane ice and snow. In 2004, the Cassini space probe will drop a landing probe(Huygens) on to the surface, which should tell us what conditions are like there.

SATURN DATA

Diameter of equator : 120,000 km

Diameter of visible rings : 270,000 km

Average distance from Sun : 1,427 million km

Minimum distance from Earth : 1,200 million km

Turns of axis : 10 hours 40 minutes

Circles Sun : 29.5 Earth-day

Temperature at cloud tops : -170°C

Satellites : 18 known

JUPITER

JUPITER

Jupiter is a giant among the planets. All the others could fit into it room to spare, and it could swallow more than 1,300 bodies the size of Earth. Jupiter is a gassy planet, made up mainly of hydrogen. Its stormy atmosphere is full of clouds. Jupiter travels through space with a large family of moons, some as big as planet.

What is Jupiter made of?

Jupiter is a great ball of gas and liquid gas. Its atmosphere is more than 1,000 kilometres deep and is made up of mainly of hydrogen, with some helium. It is full of ice, ammonia and ammonium compounds. At the bottom of the atmosphere the great pressure turns the hydrogen into a liquid. Deeper down, rapidly increasing pressure turns the hydrogen into a kind of liquid metal. Right at the centre, there is a small core of rock.

How many moons does Jupiter have?

Jupiter has at least 16 moons. We can see the four biggest with binoculars. The Italian astronomer Galileo discovered them in 1610, so they are known as Galilean moons. In order of distance from Jupiter, they are Io, Europa, Ganymede and Callisto. With a diameter of 5,262 kilometres, Ganymede is the largest of Jupiter’s moons and, at roughly the same size as planet Mercury, is the biggest moon in the Solar System. The smallest of Jupiter’s moons, Leda, is about 15 kilometres across.

What’s special about Io?

Io has been nicknamed the ‘pizza moon’ because it is so colourful. It is a very unusual moon because it has active volcanoes on it. These pour out liquid sulphur, which is a rich yellow-orange, giving Io its brilliant and varies colours. The Voyager 1 probe discovered Io’s volcanoes when it flew past Jupiter in 1979.

What is the Great Red Spot?

The most prominent feature on Jupiter’s surface is a large red oval region called the Great Red Spot. Astronomers did not know what it was until space probes looked at it is a gigantic swirling storm, rather like a huge hurricane on Earth. It measures about 40,000 kilometres across – three times the size of Earth.

Which probes have visited Jupiter?

Pioneer 10 flew past Jupiter in 1973 and took the first close-up photographs of its colourful atmosphere. Pioneer 11 followed the next year, and travelled on to Saturn. Voyagers 1 and 2 flew past in 1979, sending back astounding pictures and information. In 1995, the Galileo probe went into orbit round Jupiter after dropping a probe into its atmosphere.

JUPITER DATA

Diameter at equator : 142,800 km

Average distance from Sun : 778 million km

Minimum distance from Earth : 590 million km

Turns on axis : 9 hours 50 minutes

Circles Sun : 11.9 Earth-years

Temperature at cloud tops : -150°C

Satellites : 16 known

MARS

MARS

Small and red in colour, Mars is more like earth than any other planet .People once believed that intelligent beings lived on mars- but space probes have shown that they no Martians, and no other life on the planet. It is too cold, and the atmosphere is too thin for life to exist.

Why Mars is called the ‘Red Planet’?

Astronomers call Mars the red planet because of is colour. Its surface is reddish- orange. This colour comes from the rust-like iron minerals in the surface rock and soil.

How is Mars made up?

Mars is a rocky planet and it has a similar make-up to Earth. It has a hard crust, a rocky mantle and an iron core. Its atmosphere, however, is very much thinner than Earth’s. The atmospheric pressure on Mars is only about a hundredth of what is it on Earth. The main gas in the Martian atmosphere is carbon dioxide, instead of nitrogen and oxygen, as on Earth. There is very little moisture in the atmosphere, and no oceans, lakes or rivers. Around the cold poles, the moisture freezes to form the planet’s ice caps. Although Mars is similar to Earth in some ways, it is a lot smaller.

Does Mars have moons?

Mars has two small moons, Phobos and Deimos. Phobos is the larger, but is less than 30 kilometres across. Astronomers believe they were once asteroids, captured by Mars’ gravity.
Which space probes explored Mars?
In 1965, Mariner 4 flew past and sent back pictures. Mariner 6 and 7 also flew past, and, in 1997, the Pathfinder dropped landers onto the surface. In 1997, the Pathfinders probe landed, carrying a small vehicle called Sojourner, which investigated the surrounding rocks.

What is Mars’ surface like?

Mars’ surface is dotted with vast deserts, craters and volcanoes. The highest volcano, Olympus Mons, is nearly 30 kilometres high. There is also a gash in the surface over 4,000 kilometres long and 7 kilometres deep in places. It has been called Mars’ Grand Canyon, but it proper name is Mariner Valley. Smaller valleys look as if they have been made by flowing water, so astronomers think that Mars may once have had rivers and seas.

MARS DATA

Diameter at equator : 6,787 km

Average distance from the Sun : 228 million km

Minimum distance from Earth : 56 million km

Turns on axis : 24 hours 37 minutes

Circles Sun : 687 Earth-days

Surface temperature : -110°C to 0°C

Satellites : 2

THE MOON

THE MOON

Any object, or satellites, which orbits a planet is called a moon. Our Moon circles Earth once a month and is Earth’s nearest neighbour in space. We can see it clearly through telescope, and astronauts have explored it on foot. It is a small body – about a quarter the diameter of Earth. It has no atmosphere, no weather and no life.

How did the Moon form?

Most astronomers think that the Moon formed after another large body smashed into Earth thousand of millions of years ago. Material from Earth and the other body were flung into space. In time, this material came together to form the Moon. This explains why Moon rocks are different from rocks on Earth.

When did astronauts land on the Moon?

The first astronauts landed on the Moon on July 20, 1969. They were Edwin Aldrin and Neil Armstrong, the crew of the lunar landing module of the Apollo 11 spacecraft. Armstrong was the first person to stand on the Moon. There are five more lunar landings – one more in 1969, two in 1971, and two in 1972.

What made the Moon’s craters?

The surface of the Moon is covered with many thousands of pits, or craters. They have been made by meteorites raining down from outer space. Most large craters have stepped, or terraced, walls and mountain peaks in the middle. The largest craters are more than 200 kilometres across. Some young craters have bright streaks , or rays, coming from them, while only the tips of some old ‘ghost’ craters can be seen.

Where are the Moon’s seas?

Early astronomers thought that the dark areas we see on the Moon might be seas. They called them ‘maria’, the Latin word foe ‘seas’. We know now that they are vast dusty plains, but we still call them seas. Most seas are found on the side of the Moon that always faces us, the near side. There are only one or two small seas on the opposite side, the far side.

Why does the Moon change shape?

The Moon seems to change shape because we can only see the parts of it that are lit by the Sun. At New Moon, the unlit side faces Earth and it is invisible. Gradually, as the Moon circles Earth, we see more and more of the sunlit side, until Full Moon. Then we gradually see less and less, until it disappears. There are 29.5 days between one new moon and the next.

MOON DATA

Diameter at equator : 3,476 km

Minimum distance from Earth : 356,000 km

Time to circle Earth : 27.3 Earth-days

Surface temperature : -170°C to 110°C