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Mercury
Kenneth J Timms
Physics 1040 Sec. 002
Spring 2015
Mercury is the first planet in our solar system and is the closest to the Sun out of the nine
planets within our solar system. It is only 57,900,000 kilometers or 36,000,000 miles from the
sun (Source #3). This close proximity to the sun creates an extreme atmosphere upon the planet’s
surface. Mercury is now known as the smallest planet in our solar system, this is due to the latest
declassification of Pluto from a planet to a dwarf planet. Mercury is a terrestrial planet. There are
only four terrestrial planets in our Solar system, Mercury, Venus, Earth, and Mars. A terrestrial
planet is composed of rocky material and are solid in composure. Terrestrial planets have a
higher density and most are known to have a core. The opposing planets in our Solar system are
known as Jovian planets which simply means no solid surface.
How big is Mercury? In comparison to the rest of the planets in our Solar System
Mercury is the smallest planet. Mercury is slightly larger than Earth’s moon. It is composed of
heavier materials unlike the Moon and would weigh much more than the Moon. Mercury’s
surface is much like the moon’s surface, it has many craters caused by the bombardment of
meteorites. One of the largest is known as the Caloris Basin which was caused by a meteorite
with the size of approximately 100 kilometers (Source #6). When the massive meteorite hit the
surface of Mercury it sent shockwaves that produced jumbled hills and valleys. It is thought that
due to the Caloris impact, lava flows flowed into craters and basins and smoothed out the floors.
Like Earth, Mercury has three main layers to the planet, a crust, a mantle, and core.
Mercury’s three layers are a rocky silicate crust, a solid rocky silicate mantle and a hot liquid
iorn-nickle core. Scientist believe that the core makes up for approximately 75% of the diameter
of the planet. However they believe that the core has hardened over time, this would explain the
slowing of Mercury’s rotation over time. The surface of Mercury provides a poor reflection of
light due to its rough, porous, and dark-colored rock. (Source #4)
There is no single person who has been credited with the discovery of Mercury. Mercury
is one of the five planets that can be seen in the night sky without using a telescope or binoculars.
The planet Mercury has been known since ancient times and was observed for thousands of years
by people of many different cultures. One of the earliest records of Mercury comes from the
Sumerians around 3,000 B.C. Since Mercury never travels far from the sun in the sky, it is more
difficult to see and was probably discovered later than brighter planets like Venus, Mars, Jupiter
and Saturn (Source #2).
How did Mercury get its name? The Romans believed that gods and goddesses were
responsible for everything on Earth and the Universe. The Romans knew of only seven bright
objects in the sky: the Sun, the Moon, and the five brightest planets. They named them after their
most important gods. Because Mercury was the fastest planet as it moved around the Sun, it was
named after the Roman messenger god Mercury. Mercury was known as the son of Jupiter in
Roman mythology, he wore wings upon his helmet and shoes. He could travel very quickly from
place to place. The planet Mercury has the quickest orbit around the sun this is how the two are
related and how the planet got its name. (Source #1)
Mercury has a unique orbit that sets it apart from all the other planets in our Solar system.
The planet has the second highest eccentricity only second to the dwarf planet Pluto. Mercury
does not return to exactly the same point in space at the end of each orbit. Instead Mercury is
some small distance ahead in its orbit from its location of the year previous. Mercury’s
precession, as this orbital change is called, amounts to about 570 arc seconds per century. Almost
all of the precession is due to gravitational interactions with the other planets, however there are
43 arc seconds that cannot be explained by this mechanism. This little fact, even as small as it is,
contradicts Kepler’s law of orbital motion. Einstein was able to explain this anomaly centuries
later. His theory of relativity predicts that huge masses, like the Sun, actually bends the space
around them. (Source #1)
Mercury’s Orbit
Rotation on its axis (‘day”)
Rotation speed at equator
Rotational direction
58.65 Earth days
10.9 km/hr (6.8 mph)
Prograde (counterclockwise when
viewed from above the Northern pole)
Sidereal period (“year”)
87.97 Earth days, or two-thirds of an
orbit
Orbital velocity
47.9 km/s (29.9 miles per second)
Sunlight travel time (average)
3 minutes 20 seconds to reach
Mercury
Average distant from the Sun
57,909,175 km, 35,984,076 miles, or
0.387 AU
Perihelion
46.0 million km, 28.58 million miles, or
.31 AU
Aphelion
69.82 million km, 43.38 million miles,
or 0.47 AU
Orbital Eccentricity
0.206 A
Orbital inclination to the ecliptic
7.01 degrees
Obliquity (inclination of equator to
0 degrees (Some argue that it is 180
orbit)
degrees)
Table: Source #1
Mercury being the smallest planet of our Solar System has the lowest gravitational force
at the surface followed closely by Mars. The mass of Mercury is also the smallest of the Solar
system. In comparison it is only about 0.055 of Earths size, or 3.30 x 10 to the power of 23.
Although that seems like a very large number it is not, on an astronomical level. The
gravitational force that is felt on Mercury is quite a bit less than that felt here on Earth.
Mercury’s gravity of 3.70 m/s squared is slightly larger than one third of Earth’s gravity. Which
means that a two hundred pound man on Earth only weighs seventy-six pounds on Mercury. The
difference in daily temperatures on Mercury stand alone in our Universe. Mercury’s average
daytime temperature is 400 degrees Celsius or 752 degrees Fahrenheit, compared to the night
time temperature of -170 degrees Celsius or -274 degrees Fahrenheit. This is the extreme of both
ends of the spectrum. No other planet experiences such a difference in temperature. The
atmosphere on Mercury is also quite extreme. It is mostly composed of oxygen about 42% but it
also has a high amount of Hydrogen (22%) and Sodium (29%). These factors combined, extreme
temperature and heavy gases, prevent much life from being able to inhabit the planet as we can
tell. Mercury also has no moons or satellites in its orbit. The only other planet to have no moons
or satellites is Venus. (Source #3)
Mercury’s location in our Solar system being in such close proximity to the Sun makes it
difficult to observe and study. There has been very limited spacecraft missions sent to Mercury.
The first was Mariner 10, it was able to only fly by the planet twice, once in 1974 and the second
was a year later in 1975. Although Mariner 10 was the first to visit Mercury it provide little
informative for the science community on the planet. Less than half the planet was able to be
seen by the spacecraft. It took another thirty years before any other spacecraft was sent to reexamine the planet again. In August of 2004 MESSENGER lifted off from Cape Canaveral Air
Force Station located in Florida, on a three-stage Boeing Delta II expendable launch vehicle.
MESSENGER in an acronym for MErcury Surface, Space ENviroment, GEochemistry, and
Range. MESSENGER's path on the way to Mercury took it past Venus twice, once in 2006 and
the second time in 2007. Each pass by Venus took MESSENGER closer to the planet than ever
before the second pass was within 338 kilometers (210 miles). In 2008 and 2009 MESSENGER
made its first two fly byes of Mercury. In March of 2011 MESSENGER entered Mercury’s orbit.
MESSENGER's first extended mission began on March 18, 2012, and ended one year later.
MESSENGER is now in its second extended mission, which is scheduled to conclude in March
2015. (Sources #4 and #5)
This picture is an artist rendition of MESSENGER orbiting Mercury.
MESSENGER has provided the picture below along with another approximate 150,000 other
pictures of Mercury. The picture provides only a glimpse of the surface.
With the advancement in technology I believe that we will be able to visit and revisit
every planet and moon within our Solar System. With mercury I hope that we can find a better
understanding of the origin of our Solar System and that of the Galaxy also. I believe that there is
other life out there and it would be arrogant not to believe so. I believe that if we can explore and
study the polar caps on Mercury along with the deep canyon of Caloris Basin, we might find an
answer if life was ever there. I think that space exploration is going to be fundamental to the
continuous existence of mankind. As we continue to grow as a population the need for expansion
is going to be critical.