Mercury 101 | National Geographic

– The planet
Mercury is named afterthe messenger of the Roman gods,because even the ancients could seehow swift and fleeting it is in the sky. But it wasn’t until
recently that scientistsbegan unraveling Mercury’s many mysteries. Mercury is the smallest
planet in our solar system. It’s diameter currently
measures just over 3,000 miles,about the size of the
continental United States. Like Earth, Mercury is
a terrestrial planetwith three main layers, a
core, a mantle, and a crust. Only Mercury’s crust
has no tectonic plates. Also, its iron core is
enormous by comparison,making up 85% of its radius,while Earth’s inner and outer coreaccount for just 55%. Because of the core’s exceptional size,it’s had a surprising influenceon Mercury’s overall size,
by causing it to shrink. The hot iron core has
slowly cooled and contractedover the planet’s 4. 5 billion years. In doing so, it pulled
Mercury’s surface inward,and has caused the
planet to shrink radiallyby more than four miles. This shrinking planet is also
the planet closest to the sun,orbiting our solar
system’s star at an averagedistance of roughly 36 million miles. Such proximity affects
Mercury’s atmosphere,or rather, the lack of one. It only has a very thin exosphere,which is traditionally the outermost layerof a planet’s atmosphere. This exosphere is made of oxygen, sodium,hydrogen, helium, and potassium,all whipped up from the planet’s surfaceby solar winds. The lack of atmosphere and
close proximity to the sunalso makes Mercury a planet of extremes. The surface temperature can climbto 800 degrees Fahrenheit
during the daytime,and fall to 290 degrees
below zero at night. Mercury’s proximity to
the sun is also the reasonbehind it’s ago old reputation
of being swift and fleeting. The sun’s gravity pulls harder on Mercurythan any other planet,
and like all planets,Mercury travels in an elliptical orbit,slowing down when it’s
father away from the sun,and accelerating as it draws closer. Clocking in at an average speedof over 100,000 miles per hour,Mercury slings around
the sun in just 88 days. From Earth, Mercury is
difficult to observebecause it’s fleeting
and so close to the sun. And so far, it’s only been
visited by two spacecraft,NASA’s Mariner 10 and Messenger. Those missions gave us
much of what we know today,but future ventures are in the workswith high hopes of revealingmore of Mercury’s secrets.