Pluto is no longer known as a planet. In fact it is smaller than the Moon, and is now called a dwarf planet. It’s surface temperature is about -200C, and it is mostly covered with solid nitrogen. And it is turning slightly red in colour, but no-one knows why.
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This NASA article provides some explanation for why Pluto is reddening.
http://www.nasa.gov/mission_pages/hubble/science/pluto-20100204.html
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Many thanks Laurel, I will study this site and make a new post for my students.
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Thanks Laurel for putting me straight in this matter, and if you have any information on why Pluto is reddening then it would be most appreciated.
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Unfortunately, you are presenting only one side of an ongoing debate as truth. Please do not blindly accept the controversial demotion of Pluto, which was done by only four percent of the International Astronomical Union, most of whom are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. Stern and like-minded scientists favor a broader planet definition that includes any non-self-luminous spheroidal body in orbit around a star. The spherical part is important because objects become spherical when they attain a state known as hydrostatic equilibrium, meaning they are large enough for their own gravity to pull them into a round shape. This is a characteristic of planets and not of shapeless asteroids and Kuiper Belt Objects. Pluto meets this criterion and is therefore a planet. At the very least, you should note that there is an ongoing debate rather than portraying one side as fact when it is only one interpretation of fact.
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