Mercury

Saturday 31 December 2016 - 13:07:22 Posted by  Bobby

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mercury3

 Mercury is the innermost planet of our Solar System. Its orbit is not as circular as most of the other planets; in fact it is quite elliptical. The closest it comes to the sun is around 28.5 million miles while the farthest point of its orbit is 43.3 million miles.

Caloris Basin

calorisbasin

 The huge, multiringed Caloris Basin impact crater is about 840 miles across. The Asteroid that caused it was about 60 miles wide. The resulting seismic waves traversed Mercury, shattering the surface on the other side, before traveling back to cause fracturing and landslides.

Cratered World

mercurycrater

 Mercury is a dry, rocky world reminiscent of Earth's Moon. It has a very old surface, much of which is very heavily cratered, rather like the lunar highland. The remaining area is younger; it consists of more lightly cratered plains of solidified volcanic lava, somewhat similar to the lunar maria.

Brahms Crater

brahmscrater

 This bowl-shaped crater is 60 miles across and was formed when an asteroid hit Mercury about 3-5 billion years ago. It has a prominent central mountainous peak and inner walls that have slipped inward due to structural weakness and the influence of gravity.

"The Hot One"

mercuryhotone

 The planet has been given many different names from different cultures and languages. Mercury was the Roman god of commerce, and also a messenger for other gods. His speediness as a messenger is reflected in Mercury's rapid appearance and disappearance in the morning and evening skies.

 Mercury has been connected in German legends with the god Wodin, and in Norse legends with Odin. The Greek name for Mercury translate as "the gleaming," and it's Hebrew name translates as "the star of the hot one" -- "the hot one" is the Sun, in reference to the fact the planet never strays far from the Sun in the sky.

Extreme Conditions

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 It used to be thought that Mercury was in "tidal lock" with the Sun, meaning that it kept the same face turned toward the Sun at all times-- just like the moon does with Earth. But in the nineteen-sixties, scientist used huge radio dishes to bounce radio waves off Mercury's surface (i.e. radar). By analyzing the reflected waves, they could determine its rotation speed. They were astonished to find that the planet rotates 3 times for every 2 orbits around the sun. It's slow rotation on its axis-- one Mercury "day" -- takes 58.7 Earth days, while it takes 88 Earth days to complete one orbit-- one Mercury year. (A "day" can also be defined as the rotation time needed for the Sun to appear in the same spot in the sky on the meridian, called a solar day - due to Mercury's long day and shortish year, this means that one solar day on Mercury is 176 Earth days long, twice as long as its year.)

 Mercury's orbit is inclined at an angle of just on 7 degrees to the ecliptic-- the plane of Earth's orbit, and it has almost no axial tilt. Its proximity to the Sun means that parts of its surface get very hot, with a maximum in the equatorial regions of around 554 degrees fahrenheit. By contrast, in the deep shadows of craters near the poles, the temperature is a frigid minus 292 degrees fahrenheit, giving the planet the greatest temperature range in the Solar System. The range is mainly due to the lack of an atmosphere, as atmospheres work to smooth out heat distribution. (Venus actually is slightly hotter, even though it is further from the Sun, due to the runaway greenhouse effect in its atmosphere.)

Rocky World

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 Mercury is one of the Solar System's four terrestrial planets, a category that also includes Venus, Earth, and Mars. The planet is thought to be composed of around 30% rocky material (in its crust and mantle), and around 70% metallic material (in the form of a very large iron core). It has the second highest density in the Solar System, after Earth. (In fact, if compression of Earth's bulk due to its gravity is removed from the equation, Mercury actually has a higher density.) The core is believed to comprise around 40% of Mercury's total volume, compared to around 17% for Earth. The mantle is around 372 miles thick, and on top of that is the crust, around 60 to 125 miles in depth. Scientists think that Mercury was struck by another small planet billions of years ago, but smashed away much of the rocky mantle and crust, leaving only the thin remnants we see today.

 Although definitely considered a planet under both the Old and New classifications, Mercury is so small that it is actually smaller than 2 of The Solar System's moons-- Titan (Saturn's largest moon) and Ganymede  (Jupiter's largest moon). In fact, Mercury closely resembles Earth's moon, with smooth plains and countless craters. The large crater count indicates that its surface is very old; that is, it hasn't been geologically active for a very long time (as any such activity would have wiped away many of the craters).
 
Like Earth's Moon, Mercury shows abundant evidence of a period of intense bombardment by asteroids and comets around 3.8 billion years ago. There was also a lot of volcanic activity on the planet's surface, which flooded low-lying areas with magma, forming the vast plains.

 Mercury Statistics

Discovered Known from antiquity
Average distance from the Sun 36.0 million miles (57.9 million km) 0.39 AU
Equatorial diameter 3,032 miles (4,879 km)
Axial tilt
Axial rotation period (sidereal) 58.65 days (prograde)
Orbital period (in Earth days) 87.97 days
Mass (Earth=1) 0.055
Volume (Earth=1) 0.056
Surface gravity (Earth=1) 0.38
Average density (water=1) 5.43
Surface atmospheric pressure (Earth=1) 0
Escape velocity 2.8 miles/s (4.3 km/s)
Orbital eccentricity 0.206
Highest suface temperature 800°F (430°C)
Lowest surface temperature -280°F (-170°C)
Sunlight strength 450-1040% Earth's
Albedo (reflectivity) 11%
Number of satellites 0

 Mercury Timeline

4.5 billion years ago
An asteroid collides with a still-forming Mercury sending chunks of the planet hurtling through space.
3rd millennium BCE
Mercury is known to the Sumerians, who call it Ubu-idim-gud-ud.
Up to 6th Century BCE
The planet Mercury has two names, as it was not realized it could alternately appear on one side of the Sun and then the other. It was called Hermes when in the evening sky, but was known as Apollo in honor of the Roman god of the Sun when it appeared in the morning.
5th Century BCE
Pythagoras is credited for pointing out that Hermes and Apollo were one and the same planet.
4th Century BCE
Heraclitus of Ephesus (ca. 535-475 BCE) believed that Mercury and Venus orbited the Sun, not earth.
265 BCE
Greek scientists begin studies of mercury in the morning and evening skies.
12th Century
A transit is expected but not seen, leading the Moroccan astronomer Alpetragius to conclude that Mercury emits its own light.
807 CE
At the time of Charlemagne, Annales Loiselianos states "the star Mercury was seen in the Sun like a small black spot, a little above the center of that very body, and it was seen by us for 8 days." (However it was clearly a sunspot due to its visible size.)
1610
Galileo Galilei, the Italian astronomer, makes the first telescopic observation of Mercury.
1644
Johannes Hevelius discovers the phases of Mercury.
1676
Sir Edmund Halley travels to an island in the South Atlantic to create an atlas of southern stars. While there, he attempts to observe the transit of Mercury in 1677 but bad weather made the sightings virtually impossible.
1800s
Astronomers realize that the physics of the day could not correctly predict Mercury's orbital path.
1915
Albert Einstein uses his new theory of gravity, General Relativity, to correctly predict Mercury's orbit - and explains the reason for previous errors: Mercury is so close to the Sun that its orbit is affected by the warp in space created by the Sun's powerful gravitational field.
1965
After believing for centuries that the same side of Mercury always faced the Sun, astronomers discover the planet rotates three times for every two orbits.
1974/1975
NASA's Mariner 10 spacecraft photographs about half of Mercury's surface. The spacecraft makes three flybys. Mariner 10 takes first photograph of Mercury in detail on March 29.
1991
Scientists, using earth-based radar to study Mercury, find signs of ice tucked in permanently shadowed areas of craters in the planet's polar regions.
2003
Mercury makes a rare pass - a transit - across the face of the Sun as seen from Earth. On average, there are 13 transits of Mercury each century.
2004
NASA'S MESSENGER spacecraft is launched on a long circuitous trek to Mercury, and should enter orbit in 2011 for a one-year mission to the least-explored of the Solar System's inner planets.
The future - 2011
BepiColumbo is a future mission that will be a collaboration of Japan and the European Space Agency (Esa). It will consist of two probes, one to study Mercury's surface and the other to study its magnetosphere. The launch is planned for 2013.

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