An Opening In Earths Crust Through Which Lava Flows Into The Solar System: Mercury

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Into The Solar System: Mercury

Mercury is the smallest planet in the Solar System and the closest planet to the Sun. With a diameter of just over 3,000 miles, this little planet is only about 1/3 the size of Earth and only about 40% larger than Earth’s moon. On a scale where Earth is the size of a baseball, Mercury would be about the size of a golf ball.

Mercury has a very elongated orbit that takes the planet about 28.5 million miles from the Sun at its closest approach, known as PERIHELION, and as far away as 43 million miles at its farthest, known as APHELION. At perihelion, the Sun would appear nearly three times larger and about eleven times brighter when viewed from the surface of Mercury than what we see from the surface of Earth (but the sky on Mercury would be black because Mercury has no air). Mercury is so close to the Sun that it’s usually obscured by it, making Mercury difficult to study from the Earth even though the little planet is only about 48 to 50 million miles from the Earth at its closest approach.

Traveling at a speed of approximately 108,000 miles per hour, Mercury completes one orbit around the Sun in about 88 Earth-days. The Earth travels about 66,000 miles per hour, and completes one orbit around the Sun every 365 days. Mercury completes more than four orbits of the Sun in one Earth-year. In contrast to this short year, days and nights on Mercury are very long. Mercury turns slowly on its axis, taking about 59 Earth-days to complete a single rotation. Mercury only completes three rotations on its axis over the course of two orbits around the Sun. This means that three days on Mercury last two Mercurian-years.

Mercury was the name of the Roman messenger god who carried messages and performed errands for other gods. Mercury was also the god responsible for watching over trade, commerce, travelers and merchants. Mercury was often associated with peace and prosperity, and was also considered a god of the winds because of his speed. Because Mercury orbits the Sun faster than any other planet in the Solar System, ancient civilizations, including Mayans, Egyptians, Greeks and Romans, envisioned this speeding “star” as a messenger god in their religions and myths.

Mercury’s surface temperatures vary dramatically, from over 800 degrees Fahrenheit on the side facing the Sun to about minus 300 degrees Fahrenheit on the side facing away. This range in surface temperature between Mercury’s sunlit-side and dark-side is the most extreme for any planet in the Solar System. Mercury simultaneously broils and freezes… literally! A major contributor to this cycle of extreme heat and cold is the fact that Mercury is too small to retain a significant atmosphere. Mercury does have an atmosphere, but it’s so thin – only about 1-trillionth the density of Earth’s atmosphere – that it’s practically non-existent. This thin atmosphere prevents Mercury from retaining and circulating heat around the planet. So as the little planet rotates, the side no longer exposed to the Sun cools dramatically while the side facing the Sun roasts.

Mercury’s thin atmosphere contains traces of elements from the solar wind and gases that have been baked out of the planet’s crust and surface rocks. A planet retains its atmosphere with its gravitational pull. Mercury does not have sufficient mass to retain – by gravitational pull – a substantial atmosphere. Mercury’s surface gravity is only about 1/3 of the Earth’s. This means that a person who weighs 100 pounds on Earth would only weigh about 38 pounds on Mercury. Also, a planet as close to the Sun as Mercury is even less likely to retain a thick atmosphere than a more distant planet like Earth because it’s constantly being blasted by solar radiation. Charged particles emitted by the Sun are scorching the planet, and this atomic debris does manage to accumulate, but the intense heat combined with Mercury’s weak gravity allows the gases to escape.

Mercury is composed of about 70% iron and about 30% silicate material. It’s believed that most of Mercury’s iron is concentrated in its core. This core, the densest of any of the planets in the Solar System, accounts for about 75% of Mercury’s volume. This means that Mercury’s core is proportionally larger than any other planet in the Solar System. This core may be responsible for creating Mercury’s weak – less than 1% as strong as Earth’s – but still detectable magnetic field. This magnetic field is an indication that Mercury’s core contains molten iron and is not completely solid. The fluid interior could – like Earth’s core – act like a molten conductor. As Mercury spins on its axis, the molten iron in the core could generate the magnetic field that surrounds the small planet.

The Earth has a very conductive core that is composed of iron and nickel. This core is very hot, but its material doesn’t vaporize because of tremendous pressure inside the Earth. The material in the very center of the Earth’s core is under a pressure so great that it has raised the melting point of this material so high that it won’t melt, even though it’s being subjected to intense heat. The pressure is so powerful that the metal is actually compressed into a solid inner core. Further from the center, the pressure drops and the metal becomes a liquid outer core. This liquid outer core enveloping the solid inner core flows and moves through the process of convection and the effect of the rotation of the planet. The heat and motion of such a large amount of conductive material is what generates the Earth’s magnetic field. The process is known as the DYNAMO EFFECT. The heat of the Earth’s solid inner core causes convection currents in the liquid outer core surrounding it, and the Earth’s rotational movement turns the core about an axis and causes it to behave like an electrical generator. Electricity and magnetism arise from the core where swirling currents of molten iron generate electric and magnetic fields. A planet’s magnetic field occupies an area of space around the planet called the MAGNETOSPHERE, which deflects the solar wind and protects the planet.

Mercury is small because it formed so close to the Sun where solid material was not abundant, and what little solid material was available was mostly metallic. This is why Mercury has such a large metallic core. Mercury formed from high-temperature minerals – metals and silicates – that could survive high temperatures. But a planet as small as Mercury should have lost most of its internal heat a long time ago, so any molten iron in Mercury’s core should’ve cooled and solidified by now. And if a planet’s iron core is not molten, then it can’t generate a magnetic field. Mercury should not have a magnetic field because its iron core should be solid and it rotates too slowly on its axis.

Mercury’s magnetic field may be due to remnant magnetism “frozen” into a solid core. Or Mercury’s dense core could be surrounded by a thin shell of iron enriched with elements such as sulfur that have lowered its melting point, which would allow the iron to remain in a liquid state and allow Mercury to generate a magnetic field.

Geologically, Mercury is an inactive world that actually has more in common with Earth’s moon than the other seven planets. Mercury has a crust of silicate rock and a rocky mantle. The planet’s surface is covered with a thin layer of fine dust and is heavily scarred with craters of all sizes, some old and degraded and others that are fairly young. When an object approaches Mercury, with virtually no atmosphere to slow it down or break it up, the object strikes the planet’s surface intact and at full speed. Mercury’s craters are different from the craters found on Earth’s moon, appearing flatter with thinner rims due to Mercury’s stronger gravitational pull. But like the moon’s craters, Mercury’s craters remain virtually intact because there is no liquid water on the surface or a thick enough atmosphere to erode them.

One of Mercury’s most notable features, as well as its largest structural feature, is the Caloris Basin. Stretching about as wide as the state of Texas from rim to rim, the Caloris Basin probably formed as a result of a powerful impact from an asteroid. The basin’s interior is fractured and ridged, and the middle of the basin contains a formation known as the spider, which consists of over 100 narrow troughs that radiate out from a central region. The basin is surrounded by a ring of mountains called Caloris Montes, which rise about one mile above the surrounding surface. Beyond the mountains are areas littered with rocks ejected by the impact itself. The impact that created Caloris was so strong that its shock waves were probably felt on the opposite side of the planet, resulting in a hilly terrain.

Craters on Mercury are separated by lava-flooded plains, ridges, valleys, mountains and banks of cliffs up to two miles high and over 300 miles long. No other planet or moon in the Solar System features such a vast number of winding cliffs that snake hundreds of miles across the surface. These lines of cliffs crisscrossing Mercury’s surface preserve a record of fault activity early in the planet’s history. These cliffs were probably created when Mercury began to cool after its formation. They indicate that when Mercury’s interior cooled, it shrank. This shrinking caused Mercury’s crust to buckle, and the cliffs and ridges were produced by compression as the crust crumpled around the shrinking interior.

Mercury’s surface also bears the imprint of a series of thrust faults, where sections of the crust overlap each other. Like the cliffs, the thrust faults originated from the contraction of the crust as Mercury cooled. But some of the faults may be the result of tidal stresses. Mercury is controlled by tidal forces generated by the Sun. Being so close to the Sun, the Sun’s gravity has probably distorted Mercury’s shape and created some of the faults in Mercury’s crust. The friction of these forces is also responsible for Mercury’s slow rotation.

Mercury’s surface also preserves a history of volcanism, with plains that were probably created by cooling lava. Smoother plains, which appear to be solidified lava flows that covered older terrain, are the youngest and cover about 40% of the planet’s surface. There is also evidence of water-ice at Mercury’s polar regions. Impact craters at the poles contain areas shrouded in permanent shadow that could preserve ice for long periods of time.

A NASA spacecraft designated Mariner 10, launched November 3, 1973, became the first spacecraft to study two planets. With Mercury as its primary target, Mariner 10 performed a fly-by of the planet Venus in February of 1974, passing within 3,300 miles of Venus and taking about 6,800 pictures. This fly-by of Venus allowed Mariner 10 to use the planet’s gravity to bend its flight-path to Mercury.

Mariner 10 used the gravitational pull of the planet Venus to give itself a boost in the direction of the planet Mercury. After the spacecraft’s first encounter with Mercury in March of 1974, it went into a permanent orbit around the Sun, which brought Mariner 10 back to Mercury in September and then again in March of 1975. Contact was lost with Mariner 10 a little over a week after its third pass of Mercury, but it’s still orbiting the Sun and making close approaches to Mercury about every six months. The only real problem with Mariner 10’s three fly-bys of Mercury was that the same portion of the little planet was in sunlight during every pass, so the whole planet’s surface could not be mapped.

Mariner 10 weighed about 1,109 pounds and was equipped with protective blankets and a sunshade made of Teflon-coated glass fiber cloth. The spacecraft was built to survive not only the extreme cold temperatures of space, but also the extreme heat from being so close to the Sun. Mariner 10 was equipped with instruments to study the atmospheric, surface and physical characteristics of Mercury and Venus. Two solar panels were attached to the top of the spacecraft. With its solar panels extended, Mariner 10 had a wingspan of about 25 feet.

Mariner 10 took thousands of photographs of Mercury and mapped about half of the planet’s surface. Mariner 10 confirmed Mercury’s mass and rotational period, and discovered Mercury’s magnetic field, the Caloris Basin, the planet’s system of cliffs and plains, and its thin atmosphere, and also discovered that Mercury is shaped more like a sphere than the Earth is.

On August 3, 2004, NASA’s Messenger (MErcury Surface Space ENvironment GEochemistry and Ranging) spacecraft was launched on a journey to Mercury. Messenger’s objectives included constructing a detailed map of Mercury’s surface, determining the chemical composition of Mercury’s surface, studying the planet’s geological history, examining the behavior and determining the origin of Mercury’s magnetic field, determining the size and state of Mercury’s core, and studying the nature of Mercury’s atmosphere. The spacecraft was shaped like a flat box. It was equipped with a semi-cylindrical thermal shade for protection against the Sun, two solar panel wings to provide power – for each row of solar cells there were two rows of mirrors to reflect and dissipate heat – a nickel-hydrogen battery for power storage, a large velocity adjust (LVA) thruster and a series of small thrusters to adjust its flight-path and attitude. Messenger was also equipped with propellant tanks and their associated plumbing, star-trackers and five science instruments mounted on the spacecraft’s exterior. Messengers mission was to spend at least one year studying Mercury from orbit.

In August of 2005, Messenger flew by the Earth for a gravity assist. In December of that same year, Messenger fired its large thruster for more than eight minutes to put itself on course for a Venus fly-by in October of 2006. A second Venus fly-by occurred in June of 2007, which put Messenger on course for a series of Mercury fly-bys in January of 2008.

Because Mercury is so close to the Sun, the Sun’s gravitational pull causes spacecrafts to accelerate as they approach the tiny planet. This required Messenger to slow down enough to be captured by Mercury’s weak gravitational pull. So over the course of the mission’s first five years, Messenger flew by Mercury three times, with each fly-by using Mercury’s gravity to slow itself down enough to achieve orbit around the planet by March of 2011.

During the Mercury fly-bys, Messenger gave humanity a global view of Mercury, revealing evidence of past volcanic activity, which most likely has concealed evidence of Mercury’s early history. Messenger also observed radiating impact craters, obtained evidence of a shifting liquid core inside the planet that generates its magnetic field, and discovered water vapor within Mercury’s exosphere. Because of these fly-bys, about 90% of Mercury’s surface was imaged and analyzed.

On March 18, 2011, after traveling for over six-and-a-half years, Messenger became the first spacecraft to achieve orbit around the planet Mercury. To accomplish this, Messenger pointed its large thruster close to its direction of travel and fired it for almost fourteen minutes, and the other thrusters for an addition minute. This maneuver slowed the spacecraft by about 1,929 miles per hour and allowed Mercury’s gravitational pull to capture it into orbit. If Messenger had done nothing, then Mercury’s gravity would have deflected its motion and the spacecraft would have just flown past the planet. Instead, Messenger slowed down and inserted itself into a twelve-hour orbit around the closest planet to the Sun. This simply means that Messenger went into an orbit that carried it around Mercury once every twelve-hours. The primary science phase of Messenger’s mission began the following month, on April 4, when the spacecraft started mapping Mercury’s surface.

One of Mariner 10’s discoveries during its first fly-by of Mercury was bursts of energetic particles in Mercury’s magnetosphere. No such events were observed by Messenger during its fly-bys of the planet in 2008 and 2009. But since achieving orbit, Messenger began observing these energetic-bursts on an almost daily basis.

Messenger discovered that large portions of Mercury’s surface are covered with dried lava, and that Mercury’s magnetic field is offset to the north of the center of the planet. Messenger also discovered that the rocks on the surface of Mercury do not contain much iron, and that there are high concentrations of magnesium and calcium on the night-side of the planet. Messenger also discovered that Mercury’s core is a little bigger that originally thought, perhaps accounting for up to 85% of the planet’s volume. Images from Messenger taken of Mercury in late 2011 and 2012 confirmed that there are deposits of water-ice on Mercury around the planet’s north and south poles in regions permanently shaded from the Sun. It’s been estimated that there could be between 100-billion and 1-trillion tons of water-ice on the planet closest to the Sun. Messenger also discovered deposits of what appear to be a mixture of frozen water and what might be organic materials.

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