The mysterious Pluto is the smallest and farthest planet.
It is smaller than the Moon and 12,000 times farther; therefore it is nearly impossible to see it.
To observe its surface from Earth is like to try to read the inscription on a stamp from a 65 km. distance.
In spite of that, astronomers made some remarkable discoveries about the planet and its satellite Charon.
The two of them, for instance, form a "binary planetary system", that is, the planet rotates synchronously with the orbit of its satellite.
Pluto is the planet with the longest year: it completes a full revolution around the Sun in 248 Earth years.
Since its time of discovery, in 1930, it has not completed half of its orbit, yet.
On it, spacemen should always keep lighted torches since there, it is always dark, even in broad daylight.
The Sun is so far away that the the planet gets very little heat: its surface temperature is of -230°C and in winter its rarefied atmosphere freezes on the soil.
Its day, fron dawn to dawn, lasts 153 hours.
Since 2006 Pluto has been reclassified as a "Dwarf Planet".
The International Congress LAU in Prague has made that resolution and the reason for it has been caused by its size, considered too small.
Improvements in space observations, in facts, are permitting to scientists to discover many other celestial bodies the same size of Pluto and hence the need to give rise to the "dwarf planet" category.
