Where is the largest known canyon?
On Mars! There is no running water to wear away the rocky landscape on Mars, so huge valleys can survive for millions of years. A system of enormous canyons called the Valles Marineris (Mariner Valleys) was discovered by the space probe Mariner 9. It is more than 4,000 km long, and four times as deep as the Grand Canyon in the USA. Scientists think that these valleys were caused by erosion (wearing-away). During storms the gritty Martian dust is blasted by winds reaching up to 450 km/h, wearing away the softer rock.
Which are the outer planets?
Uranus, Neptune and Pluto are the outer planets. They are so far away that they were discovered only when powerful telescopes were developed. Pluto, the smallest and most remote of the planets, is on the edge of deep space. It was only discovered in 1930, as a result of mathematical calculations to find out why Neptune’s orbit was being disturbed by an unknown body. Pluto has an oval orbit that occasionally takes it inside the orbit of Neptune. As recently as 1978 scientists found that Pluto, which is only 2,284 km across has an even smaller companion planet or Moon called Charon.
What are the rings of Saturn?
Shining rings of billions of tiny chips of ice, rock and dust surround Saturn. The rings reflect light strongly and can be clearly seen through a telescope from the Earth. It was first thought that Saturn had three wide rings, but it is now known that the rings are actually made of thousands of narrow ringlets. The rings are only 100 m thick, but they extend into space for 76,000 km. the material in the rings was probably captured by Saturn’s gravity when the Solar System was forming, or it might be the remains of a moon that has broken up. Recently space probes discovered that some of the rings are braided, or twisted, but so far there is no explanation for this strange effect.
What makes Neptune blue?
Neptune is covered with a blue ocean of liquid methane gas. It is a very cold place – at the farthest part of its orbit it is 4,000 million km from the Sun. its surface temperature drops to – 210 degree Celsius. Neptune is made of hydrogen, helium and methane, and probably has a rocky core. It takes an amazing 164.8 years to travel just once around the Sun.
Neptune was first identified in 1846 when astronomers found that an unidentified planet was disturbing the orbit of Uranus. Neptune has huge storms and one of these, the Great Dark Spot, was larger than the Earth.
The Red Planet
Mars is covered by a stony desert that contains lots of iron oxide, making it appear a rusty-red colour. At one time Mars had an atmosphere containing oxygen, and it has valleys through which water may have flowed. Now the water and oxygen are locked up in the rusty iron deposits, and the planet has hardly any atmosphere.
Mars has small polar ice-caps that grow larger during the Martian winter. These probably contain water and frozen carbon dioxide. It is possible that there is enough water in these ice-caps to support a human space mission to Mars.