Mercury and pluto (planets)

Pluto

 Pluto was the last of all the planets to be discovered, and it was only found because it has a slight effect on the orbits of Neptune and Uranus. Pluto is the furthest out of all the planets, varying from 4730 to 7375 million km from the Sun. The Sun is so far from Pluto that if you could stand on the planet’s surface, the Sun would look no bigger than a star in Earth’s sky and shine no more brightly than the Moon does. 
A Pluto is tiny in comparison to the Earth, which is why it was so hard to find. Earth is five times bigger and 500 times as heavy. This illustration shows the relative sizes of the Earth and Pluto. Pluto’s orbit is so far from the Sun that it takes 248.54 years just to travel right around once. This means that a year on Pluto lasts almost three Earth centuries.
 A day, however, lasts just under a week. Pluto has a strange elliptical (oval) orbit which actually brings it closer to the Sun than Neptune for a year or two every few centuries. Unlike all the other planets which orbit on exactly the same plane (level) as the Earth,Pluto’s orbit cuts across diagonally. While studying a photo of Pluto in 1978, American astronomer James Christy noticed a bump. 

This turned out to be a large moon, which was later named Charon. Charon is about half the size of Pluto and they orbit one another, locked together like a weightlifter’s dumbbells. Charon always stays in the same place in Pluto’s sky, looking three times as big as our Moon Unlike the other outer planets, Pluto is made from rock. But the rock is covered in water, ice and a thin layer of frozen methan Daytime temperatures on Pluto’s surface are -220°C or less, so the surface is thought to be coated in frozen methane. 

 This picture of Pluto is entirely imaginary, since it is so small and so far away that even photographs from the Hubble space telescope show no more detail on Pluto’s surface than you could see on the surface of a billiard ball. However, a twinkling of starlight around the edge of the planet shows that it must have some kind of atmosphere. Pluto was discovered on 18 February 1930 by young American astronomer Clyde Tombaugh.
 The largest moon in the Solar System is Jupiter’s moon Ganymede. The smallest moons are rocky lumps just a few kilometres across, rather like asteroids. 

 Mercury 

Mercury is the nearest planet to the Sun - during its orbit it is between 45.9 and 69.7 million km away. Mercury is the fastest orbiting of all the planets, getting around the Sun in just 88 days.once, so a Mercury day lasts nearly 59 times. Mercury takes 58.6 days to rotate as long as ours. Temperatures on Mercury veer from -180°C at night to over 430°C during the day (enough to melt lead). 
The crust and mantle are made largely of rock, but the core (75 percent of its diameter) is solid iron. Mercury’s dusty surface is pocketed by craters made by space debris crashing into it .Mercury is a tiny planet with a thin atmosphere and a solid core. With barely 20 percent of Earth’s mass, Mercury is so small that its gravity can only hold on to a very thin atmosphere of sodium vapour. 
Mercury is so small that its core has cooled and become solid (unlike Earths). 
As this happened, Mercury shrank and its surface wrinkled like the skin of an old apple. Craters on Mercury discovered by the USAs Mariner space probe have names like Bach, Beethoven, Wagner, Shakespeare and Tolstoy. 
Mercury gets very close to the Sun and speeds up so much that the Sun seems to go backwards in the sky.
 Mercury is a planet of yellow dust, as deeply dented with craters as the Moon. It does have small polar icecaps, but the ice is pure acid. The largest feature on Mercury is a huge impact crater called the Caloris Basin, which is about 1300 km across and 2 km deep. Mercury’s surface is covered with impact craters. Most were formed by the impact of debris left over from the birth of the Solar System, about 4 billion years ago.