4 The objects that orbit the Sun fall into two regions the inner and outer solar systems The inner solar system is a warm area close to the Sun and it contains four small planets that are mostly made of rock Mercury Venus Earth and Mars There are various other smaller worlds Earth’s Moon and the tiny satellites moons of Mars plus the asteroids most of which lie in a belt beyond Mars The outer solar system in contrast is cold and dominated by gas and ice rather than rock It contains four giant planets Jupiter Saturn Uranus and Neptune They are spread over a much wider area and surrounded by a variety of smaller moons and comets The Sun right is a huge ball of exploding gas much larger than any planet Like all heavy objects it produces a pull called gravity This stops fast-moving objects from flying off into space and instead traps them in circular or oval paths called orbits THE SOLAR SYSTEM BALL OF FIRE Get ready to blast off on the trip of a lifetime We’re off on a mission to explore the worlds of the inner solar system Mercury Venus and Mars as well as our own planet Earth and its Moon The solar system consists of our nearest star the Sun and everything that circles around it The Local Neighborhood
5 NEED TO KNOW Our tour of the solar system will start with Mercury the planet closest to the Sun From there we will travel away from the Sun visiting Venus Earth and the Moon before moving on to Mars and the asteroid belt Each of the astronomical bodies we’ll visit is a world in its own right with its own days seasons and years its own unique features and its own hazards It’s going to be a fun trip but it could also be a dangerous one TOUR OF THE PLANETS You’ll need strong sun block for your trip to Mercury and Venus and warm clothes for visiting chilly Mars Earth is 93 million miles 150 million km from the Sun this is one astronomical unit or AU Mercury and Venus are closer to the Sun than the Earth but Mars is farther away When measured in astronomical units the distances from the Sun are as follows Mercury 0 4 AU Venus 0 7 AU Mars 1 5 AU asteroid belt 2 8 AU MARS 1 5 AU FROM SUN EARTH’S MOON 238,855 MILES 384,400 KM FROM EARTH EARTH 1 AU FROM SUN MERCURY 0 4 AU FROM SUN VENUS 0 7 AU FROM SUN ASTEROID BELT 2 8 AU FROM SUN
Mercury is a special world in many ways it’s the smallest of the planets and the fastest moving It’s also the closest to the Sun and suffers the biggest variations in temperature As a result Mercury is a parched airless ball of cratered rock Despite the daytime heat it’s not the best vacation spot Mercury D i a m et er 3,029 miles 4,875 km Mass 0 0 5 x E a r t h D a y 5 8 6 E a r t h d a y s Y e a r 8 8 E a r t h d a y s Mercury is similar in appearance to Earth’s Moon It is heavily cratered with regions of smooth plains and has no natural satellites Unlike the Moon it has a large iron core which generates a weak magnetic field about 1 percent as strong as that of the Earth Mercury races round the Sun at about 31 miles 50 km per second so you’ll need a fast spacecraft to keep up with it Although it orbits the Sun in just 88 days it takes a surprisingly long 58 6 days to spin on its axis As a result most parts of the planet have a day and a night that both last for an entire Mercury year During the baking days temperatures on the side facing the Sun can reach 806 F 430 C while at night it plunges to a frozen 274 F 170 C SPEEDY PLANET 6
7 WEIRD TERRAIN An area where shockwaves from the Caloris smash met up on the other side of Mercury and shook the landscape to pieces DISCOVERY RUPES This huge cliff 404 miles 650 km long and 1 2 miles 2 km high is one of many such cliffs on Mercury which are known as rupes They seem to mark places where the planet’s crust has been pulled apart and jammed back together THE SPIDER Dozens of mysterious cracks stretch out like a spider’s legs around this crater see below POLAR ICE Astronomers believe that craters at Mercury’s poles may contain deep-frozen ice dumped by comet crashes DEEP IMPACT At 833 miles 1,340 km across Mercury’s Caloris Basin is one of the biggest impact craters in the solar system But although it’s wide it’s not very deep the asteroid collision that created it was so powerful that it cracked the planet’s crust and allowed molten rock to erupt and fill in the center Today the most impressive features are the surrounding rings of mountains and the ray-like ridges which formed where rocks from the impact were blasted out across the nearby surface The surface of the Caloris Basin is covered with lava flows and rocky ridges NOT TO MISS
