A quick tour of the solar system
Page 4

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Mercury
It would take us a day and a quarter to get to Mercury from Venus, as it’s 31 million miles (50 million km) farther in towards the Sun. It is a smaller planet than Earth or Venus, only about half as big again as the Moon, so you’d be about a third of your Earth weight. Like the Moon, it has no atmosphere, and it’s covered with craters. No spacecraft has ever landed on Mercury so we don’t really know what it would be like to stand on its surface, but it is probably like the Moon only very much hotter, being so close to the Sun. The surface is so hot that lead would melt, though still not as hot as Venus whose clouds keep the heat in.

Mercury is the heaviest planet for its size in the solar system, so maybe there are useful metals to be found there. Perhaps one day there will be mines on Mercury to extract its mineral wealth. But there is no air on Mercury, so it would be best if the mining were carried out by robots.


Mars
To get to the rest of the solar system we now have to travel back past the Earth and outwards to Mars, the next planet out from the Earth. We’d have a journey time of at least two days to get out there – longer, if Mars were not conveniently placed at the time.

Of all the planets, Mars is the most Earthlike. Your first glance out of the window might make you think you had landed on a desert on Earth. There are orange rocks and maybe some sand dunes; and the sky is not black, but pale like that of Earth. But if you decided to take a sniff of the air, you’d be in for a terrible shock. For one thing, it’s bitterly cold – even on the hottest day, it’s about as cold as Antarctica and usually it’s much colder than that. And instead of getting a lungful of good air, you’d feel as if you were suffocating because there’s no oxygen there at all, just very thin carbon dioxide. Very soon your blood would begin to boil in the low air pressure, only a hundredth that on Earth. So you’d need to close the hatch and put your spacesuit on pretty sharpish. The only good thing is that because Mars is smaller than Earth, you would weigh only a third what you do on Earth.

Once suited up and outside, your external microphone might pick up an eerie noise. Even though the air is thin, the wind can blow quite fiercely and can whip up the dust. So you might hear the howling of the wind and the clicking of dust grains hitting your suit. If the wind really gets up there could be a dust devil – a mini-tornado – ripping across the landscape, picking up the dust as it goes. Here’s one seen from space. Sometimes there could even be a dense dust storm. You could also see thin clouds in the pinkish sky, particular in the early morning, when you might also see a slight frost on the ground.

It never rains or snows on Mars – the clouds are not dense enough. However, if you travel up the the north or south pole, you’d see ice caps a bit like those in the Arctic or Antarctic. These are not formed when snow falls, but because it’s so cold that the air itself freezes.

One thing the first explorers will do will be to dig down to see if there is water ice below the surface of Mars Pic g8. Many scientists believe that there is, but we might have to go there to be certain. So far, only robot probes have visited the planet. Some people also believe that there might be a simple form of life on Mars – nothing with arms and legs, but possibly just a sort of slime clinging to rocks deep below the surface. Mars at the moment is too cold for life as we know it, but there are signs that in the distant past, water flowed there. Look at these vast channels, for example. The picture shows an area about the size of Southern England from Cornwall to Kent, so these channels are both much bigger and wider than the Thames.

Mars today is a world of bitterly cold bone-dry deserts, extinct volcanoes and craters. In 2003, two robot probes named Spirit and Opportunity began exploring two small areas of the surface of Mars, and they have send back thousands of closeups as they explore. They are equipped with the means to drill into rocks and study them. So far they have covered several miles – but there is a very long way to go and there are plans to send many more probes there over the next few years to search for signs of life.

Asteroids
Before we can reach the next stop on our trip round the solar system we have to travel through the asteroid belt. The asteroids are chunks of rock left over from the formation of the solar system, billions of years ago. There were not enough of them to gather to form one big planet, so hundreds of thousands of them remain orbiting the Sun between Mars and the next planet out, Jupiter. You might think that a crossing of the asteroid belt would be hazardous, but the actual distances between even tiny asteroids are very great. In fact you would be unlikely to even see one during the crossing.

Click on any picture for a larger version that you may use in a school project


Mercury from space
Mercury from space


Mercury closeup
Mercury closeup







Mars from space
Mars from space

Dunes on Mars
Dunes on Mars










Dust devil on Mars
Dust devil on Mars
Martian dust storm
Martian dust storm
Clouds before Martian sunrise
Clouds before Martian sunrise
A frosty morning on Mars
A frosty morning on Mars
South Pole of Mars
South Pole of Mars
Water channels on Mars
Water channels on Mars
Olympus Mons
Olympus Mons
Martian rock with drill marks
Martian rock with drill marks
View from a hill from Spirit
View from a hill from Spirit


Asteroid Ida and its tiny companion Dactyl
Asteroid Ida and its tiny companion Dactyl