World astronomers have declared that Pluto is no longer a major planet under new guidelines. It is now considered a "dwarf planet".
History From its discovery in 1930 until 2006, Pluto was counted as the Solar System's ninth planet. In the late 20th and early 21st centuries, however, many objects similar to Pluto were discovered in the outer solar system, notably Eris, which is 27% more massive than Pluto.
On August 24, 2006 the International Astronomical Union (IAU) defined the term "planet" for the first time. This definition excluded Pluto, which the IAU reclassified as a member of the new category called dwarf planets along with Eris and Ceres. So now Pluto is just the second-largest known dwarf planet in the Solar System (after Eris).
IAU Decision (August 24, 2006)
According to the International Astronomical Union's 2006 redefinition of planet, there are three main conditions for an object to be called a 'planet'.
1. The object must be in orbit around the Sun.
2. The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should pull it into a shape of hydrostatic equilibrium.
3. It must have cleared the neighborhood around its orbit. Pluto fails to meet the third condition.
The IAU further resolved that Pluto be classified in the simultaneously created dwarf planet category, and that it act as prototype for a yet-to-be-named category of trans-Neptunian objects, in which it would be separately, but concurrently, classified. Prior to this decision several other definitions had been proposed, some of which might have ruled out planetary status for Earth or Mercury or may have classified several of the asteroids as planets. This version was democratically chosen in a successful attempt at avoiding these non-traditional results.
See related link for the IAU official reason.
Pluto is no longer a planet but there are dwarf planet Pluto is considered a dwarf planet
Yes. Earth receives radiation. The atmosphere acts as a filter. The atmosphere of Mars is thinner than Earth. Mars receives radiation also.
OK, wait... humans can't live on Saturn, Jupiter, Uranus, Mercury, the sun, pluto, or neptune. Heres why:
Saturn: The gases and the atmoshpere are too overwhelming. Plus its cold.
Jupiter:The gases are poisionous and its far away from the sun.
Mercury: Its too close to the sun, and its too small
The sun: Well obviously you'd be burned alive
Neptune: Its way to far away from the sun... You'd freeze to death
Pluto:Its too small and really really really really cold!
As for Mars... I guess you could live there but really who's gonna travel through space just to get to mars where you might have a chance of starting a civilzation. I think the government needs to stop paying money to the NASA program. Because we have alot more issues and alot more things to accomplish than to go into space.