Click to viewEver since the International Astronomical UniondemotedPluto to a gnome planet ( does it even deserve a capital “ P ” ? ? ? ) in 2006 , astronomers around the human race have been at odds to describe just what they mean when they say the Word of God “ planet . ” For the mo , the solar system is holding steady with eight of them , but latterly last week grounds returned from the Mercury MESSENGER delegacy showed that the smallest planet left is shrinking . One has to wonder : how long will it be before Mercury getsplutoed ?
Mercury is about twice as large as pluto , but still is the smallest object called a “ satellite ” orbiting the Sun . The question is : how much smaller will it get ? It will never get anywhere near as modest as the former ninth major planet , but will theIAUsee fit to break it too as it continues squinch ? Only meter will assure .
Meanwhile , Mercury ’s molten branding iron kernel continues to cool , shrinking the planet from the inside . pocket-sized particles of solid iron ‘ snow ’ rain down toward the ever - widening hearty center . But even as the solid grows it ’s denser than the liquid and so takes up less quad . This has been going on probably for million of long time and over time the shrinkage has cause Mercury ’s crust to crumple and fold up on itself , as seen here ( that y - influence fracture in the left side of the effigy is a huge fracture in the rock . The whole picture is about 200 kilometers wide of the mark ):
( fromNASA )
On the veracious hand side of the image , the craters with the soft - look rim appear to be old encroachment catchment basin that have been fill in with lava , indicating the Mercury once had some serious volcanoes exploding on its surface . Why did the vent die off ? Mercury cooled off . Just like on Mars and the Moon , Mercury was fiery when it first fare into being , but lost its heat in the just about 4.5 billion years since , silencing is volcanic activity . globe is chill in a similar way and in a few billion age it will get too moth-eaten for volcanoes too . When it does it will go quiet always .
seed : Science , NASA , viaLA Times
Pluto
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