Take a close look at these images, do you recognize anything? What differences and
similarities do you see? Some of you may be surprised to find out that these images are
in fact of two different objects, one a satellite and one a planet.
On the right, we can recognize the Moon. But It would be reasonable to assume the left
image is also a picture of the Moon just from a different angle. However, it is not the Moon
but instead the mysterious planet Mercury. So how can a planet and the Moon look so similar?
Looking at these objects they could be mistaken as twins. Both grey with craters
pockmarking their surfaces from countless bombardments of meteorites during their
formation and throughout their lives. A difference to note between the craters we
see on Mercury and those on the Moon are, however, the rays surrounding the craters.
Crater rays are formed from dust and other crushed material that is thrown onto the
surface from the impact sight. These light streaks exploding out from the
central crater are much more prominent on Mercury’s surface than on the lunar
surface. Suggesting that the rays are mainly made up of finer-grained material.
One explanation for this is that the rayed craters on Mercury are younger
and therefore less eroded by space than the ones we see on the Moon.
We see so many impact craters on their surfaces because neither of them have thick atmospheres,
they actually have very thin unprotective atmospheres,
called exospheres, leaving their surfaces unprotected from the ravages of space.
During its formation, the solar system was a hot and volatile place. Many
celestial bodies still have or show evidence of volcanic activity. Both
the surfaces of the Moon and Mercury indicate previous volcanic activity,
and this can be seen in what appears to be more craters but that are actually dormant volcanoes.
Unlike the mountainous volcanoes we see on Earth, many of the volcanic structures
found on Mercury are likely from lava oozing out of vents in the crust.
Over time this lava spread out and settled over Its surface. On the far side of the Moon, we see
steep-sided domes that indicate similar volcanic activity may have occurred here as well. Moreover,
the familiar dark regions on the face of the Moon are vast plains of once-liquid rock and lava.
While it is clear neither the Moon nor Mercury have liquid water, there is evidence of ice on
both their surfaces. NASA’s MESSENGER mission discovered, that despite the heat on Mercury,
there is hydrogen in amounts consistent with frozen water at its North and South poles.
These ice deposits exist in perpetual shadows where sunlight never reaches.
Recent investigations of the Moon’s Shackleton Crater by NASA’s Lunar Reconnaissance Orbiter
suggest that there may be ice on the floor of the crater, also only surviving in perpetual shadows.
Ironically, despite the Moon being far colder, Mercury has larger stores of ice on its surface.
Exploring more of their surfaces we find even more similarities between the Moon and
Mercury with very similar surface compositions. Both objects’ crusts contain large amounts of
oxygen and silicon that form mineral silicates. Traces of elements such as aluminium and titanium
give the Moon’s surface a reflective quality, and we find this to be true as well with Mercury.
While there are many similarities between the surfaces of these bodies, as we dig deeper,
we find many characteristics that distinguish these objects. Both appear grey to the naked eye,
but with advanced telescopes, astronomers can digitally enhance their natural colour. When
this is done to Mercury, we see the planet come to life with blues, yellows, and bits of orange.
However, when this enhancement process is done to the Moon we still see mainly greys and browns.
The colour of any object, a planet, a rock, or a vegetable, is determined by
what it is made of. Though the surfaces of these objects have similar compositions,
their true colours reveal that their overall compositions are more different than alike.
Another key difference between these fraternal twins comes down
to the basics. Mercury is larger with a diameter of 3032 miles, which is 4,879 km,
while the Moon’s diameter is 2159 miles, which is 3,474 km.
While at surface level the Moon and Mercury may look very similar,
they do have many key differences. Studying their differences and similarities give us great
insights into the formation of planets and other objects in our solar system.
So we have it, the moon and Mercury aren't so similar after all. I really
hope you enjoyed this video, if you did, then tap the like button and subscribe.