Mercury

 

 

 

Mercury

 

 

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Mercury is the planet closest to the Sun. Of all the planets, it has the most elliptical orbit, except for Pluto. Because of its elliptical orbit, Mercury's closest distance to the Sun is only 46 million km while its greatest distance is 70 million km. Another unique aspect of Mercury is its rotational and orbital period. Mercury rotates on its axis once every 58.9 days and circles the Sun once every 87.9 days. As a result Mercury rotates exactly three times around its axis for every two orbits around the Sun. If you wanted to stay up for a solar day on Mercury (sunrise to sunrise), you would be awake for two Mercurian years (a total of 176 Earth days.) Because Mercury is so close to the Sun, its surface temperature has the greatest temperature range of any planet or satellite in the solar system. The surface temperature reaches a maximum of 427 degrees Celsius on the side closest to the Sun, and -183 degrees Celsius on the night side. Mercury's atmosphere is tenuous and like a vacuum. The atmosphere is composed of sodium and potassium, which is probably derived from the surface. While Mercury does have an atmosphere, it does not have satellites.

Physically, Mercury is smaller than any other planet except Pluto, measuring about one-third the size of Earth. However, Mercury's density (5.4 g/cm3) is about the same as Earth's; therefore,Earth vs. Mercury in size.scientists assume that the planet has an enormous iron core that composes some 75 percent of Mercury's diameter (42 percent of the volume). The core is surrounded by a rocky mantle and crust only about 600 km thick. Aside from Earth, Mercury is the only terrestrial planet with a magnetic field. Although the magnetic field is considerably weaker than Earth's, its presence is strong evidence that the outer core is fluid at the present time.

Soon after the planet formed it nearly melted from decay of radioactive elements and the inward migration of iron that formed its enormous core. This led to the expansion of the planet and extensive fracturing of the surface which provided an exit for lava to reach the surface and form the smooth plains within and between the craters. At about the same time and like the other planets, Mercury was subjected to heavy bombarded by asteroidal and cometary debris left over from accretion of the solar system. During this early period of heavy bombardment, the 1300 km diameter Caloris basin was formed by collision of a gigantic asteroid with Mercury. The strong shock wave produced by the impact traveled through the planet to instantaneously form the hilly, lineated terrain on the opposite side of the planet. Afterward, eruption of lava within and surrounding the Caloris, and other large basins formed the smooth plains. Over the next half billion years the core and mantle began to cool, Mercury's radius decreased by about 2 to 4 km, and the crust was subjected to compressive stresses that resulted in a unique global system of fractures. As this occurred, volcanism ceased when compressive stresses in the lithosphere became trong enough to close off magma sources. Since that time, only occasional impacts of comets and asteroids have occurred.

In 1973, Mariner 10 was launched to make multiple flyby encounters of Venus and Mercury. Mariner 10 provided the first detailed data of Mercury, mapping 40-45% of the surface. The final flyby of Mercury by Mariner 10 occurred on March 16, 1975, ending close-range observations of the planet for over 30 years.

MESSENGER performed a successful Earth flyby a year after launch, on August 2, 2005, with the closest approach at 19:13 UTC.

 

The MESSENGER Probe

The MESSENGER probe was launched on August 3, 2004 at 06:15:56 UTC by NASA from Space Launch Complex 17B at the Cape Canaveral Air Force Station in Florida.

 

MESSENGER Spacecraft Reveals More Hidden Territory on Mercury

Mercury

WASHINGTON -- A NASA spacecraft gliding over the battered surface of Mercury for the second time this year has revealed more previously unseen real estate on the innermost planet. The probe also has produced several science firsts and is returning hundreds of new photos and measurements of the planet's surface, atmosphere and magnetic field.

The Mercury Surface, Space Environment, Geochemistry, and Ranging, or MESSENGER, spacecraft flew by Mercury shortly after 4:40 a.m. EDT, on Oct. 6. It completed a critical gravity assist to keep it on course to orbit Mercury in 2011 and unveiled 30 percent of Mercury's surface never before seen by a spacecraft.

 

"The region of Mercury's surface that we viewed at close range for the first time this month is bigger than the land area of South America," said Sean Solomon, principal investigator and director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington. "When combined with data from our first flyby and from Mariner 10, our latest coverage means that we have now seen about 95 percent of the planet."

 

The spacecraft's science instruments operated throughout the flyby. Cameras snapped more than 1,200 pictures of the surface, while topography beneath the spacecraft was profiled with a laser altimeter. The comparison of magnetosphere observations from the spacecraft's first flyby in January with data from Mercurythe probe's second pass has provided key new insight into the nature of Mercury's internal magnetic field and revealed new features of its magnetosphere. The magnetosphere is the volume surrounding Mercury that is controlled by the planet's magnetic field.

"The previous flybys by MESSENGER and Mariner 10 provided data only about Mercury's eastern hemisphere," explains Brian Anderson of the Johns Hopkins University Applied Physics Laboratory, known as APL, in Laurel, Md. "The most recent flyby gave us our first measurements on Mercury's western hemisphere, and with them we discovered that the planet's magnetic field is highly symmetric."

 

The probe's Mercury Laser Altimeter, or MLA, measured the planet's topography, allowing scientists, for the first time, to correlate high-resolution topography measurements with high-resolution images.

"The MLA collected altimetry in regions where images from MESSENGER and Mariner 10 data are available, and new images were obtained of the region sampled by the altimeter in January," said Maria Zuber, co-investigator and head of the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology. "These topographic measurements now improve considerably the ability to interpret surface geology."

The Mercury Atmospheric and Surface Composition Spectrometer observed Mercury's thin atmosphere, known as an exosphere. The instrument searched for emissions from sodium, calcium, magnesium, and hydrogen atoms. Observations of magnesium are the first detection of this chemical in Mercury's exosphere. Preliminary analysis suggests that the spatial distributions of sodium, calcium, and magnesium are different. Simultaneous observations of these spatial distributions, also a first for the spacecraft, have opened an unprecedented window into the interaction of Mercury's surface and exosphere.

 

Mercury- unseenOn January 14, 2008, MESSENGER became the first spacecraft to see the side of Mercury shown in this image (right). The first image transmitted back to Earth following the flyby of Mercury, and then released to the web within hours, shows the historic first look at the previously unseen side. This image shows a closer view of much of that territory.

Just above and to the left of center of this image is a small crater with a pronounced set of bright rays extending across Mercury's surface away from the crater. Bright rays are commonly made in a crater-forming explosion when an asteroid strikes the surface of an airless body like the Moon or Mercury. But rays fade with time as tiny meteoroids and particles from the solar wind strike the surface and darken the rays. The prominence of these rays implies that the small crater at the center of the ray pattern formed comparatively recently.

 

Mercury's CratersMESSENGER acquired this view (01.20.08) of Mercury’s surface illuminated obliquely from the right by the Sun. The unnamed crater (52 kilometers, or 31 miles, in diameter) in the center of the image displays a telephone-shaped collapse feature on its floor. Such a collapse feature, not seen on the floors of other craters in this image, could reflect past volcanic activity at and just below the surface of this particular crater. MESSENGER team members are examining closely the more than 1200 images returned from this flyby for other surface features that can provide clues to the geological history of the innermost planet.

The crater is located in the southern hemisphere of Mercury, on the side that was not viewed by Mariner 10 during any of its three flybys (1974-1975). This scene was imaged while MESSENGER was departing from Mercury from a distance of about 19,300 kilometers (12,000 miles), about 1 hour after the spacecraft's closest encounter with Mercury. The image is of a region approximately 236 kilometers (147 miles) across, and craters as small as 1.6 kilometers (1 mile) can be seen.

 

Mercury's big craterThis image (right) shows a bright crater with an extensive system of impact ejecta rays; the crater is also clearly visible on the southern portion of Mercury near the limb of the planet in the departure full-planet image. This impact crater and its associated system of rays were originally detected in 1969 as a “bright feature” in radar images at 12.5-centimeter wavelength obtained by the Goldstone Observatory in California. Subsequently, about a decade ago, radar images acquired by the Arecibo Observatory in Puerto Rico clearly revealed this feature to be a crater with a fresh system of rays of rough material radiating outward from it. This feature has been referred to simply as feature “A.” MESSENGER’s recent Mercury flyby provided the first spacecraft images of feature “A,” enabling this relatively young crater with its impressive set of rays to be seen here in close-up detail.

 

Mercury CratersThis dramatic image (left) was acquired about 56 minutes prior to MESSENGER’s closest approach during the mission’s recent Mercury flyby, as the spacecraft approached the planet's illuminated crescent. Prominent toward the horizon in this view of newly imaged terrain is a long cliff face. A small impact crater (about 30 kilometers, or 19 miles, in diameter) overlies this lengthy scarp. The scarp extends for over 400 kilometers (250 miles) and likely represents a sign of aging unique to Mercury among the planets in the Solar System. As time passes, the interior of a planet cools. However, the relative size of Mercury's central metallic core is larger than that of the other planets and hence has significantly affected the planet’s geologic evolution. The numerous long scarps on Mercury are believed to be the surface expression of faults formed in the rocks of Mercury's crust as the interior of the planet cooled and contracted. This contraction compressed the surface and thrust some sections of crust over others, creating long curving cliffs like the one shown here.

 

The nine images shown here (right) were taken from January 9 to 13, 2008, as MESSENGER closed to between 2.7 million kilometers and 9 images of Mercury760,000 kilometers (1.7 million miles and 470,000 miles) from Mercury.

At the beginning of the image sequence, Mercury was no more than a bright crescent in the blackness of space. As MESSENGER drew closer, surface features began to be resolved. The image from January 13 (bottom right) has the highest spatial resolution of this sequence (20 kilometers/pixel, 12 miles/pixel). In this image, bright markings are visible, and impact craters can be seen near the terminator (the line between Mercury's day side, to the left, and the night side to the right).

During MESSENGER's closest pass by Mercury yesterday, January 14, 2008, extensive scientific observations were executed. Today, the last of these planned observations will be completed, and at noon EST, the spacecraft will begin to transmit the data gathered during the flyby to Earth. This exciting new dataset will be used to address fundamental questions about the origin and evolution of the planet Mercury and our solar system. Currently, the MESSENGER team is anxiously awaiting the arrival of this dataset.

 

Mercury's CliffsAs the MESSENGER team continues to study the high-resolution images taken during the Mercury flyby encounter on January 14, 2008, scarps (cliffs) that extend for long distances are discovered. This frame shows a region of Mercury's surface previously unseen by spacecraft and a large scarp crossing vertically through the scene, on the far right of the image. This scarp is the northern continuation of the one seen in the NAC image released on January 16. The width of this image is about 200 kilometers (about 125 miles), showing that these scarps can be hundreds of kilometers long on Mercury.

The presence of many long and high scarps, as discovered from pictures from the Mariner 10 mission in 1974 and 1975, suggests a history for Mercury that is unlike that of any of the other planets in the solar system. These giant scarps are believed to have formed when Mercury’s interior cooled and the entire planet shrank slightly as a result. However, Mariner 10 was able to view less than half the planet, so the global extent of these scarps has been unknown. MESSENGER images, like this one, are providing the first high-resolution looks at many areas on Mercury's surface, and science team members are busy mapping these newly discovered scarps to see whether they are common everywhere on the planet.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

 

 

 

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Say Aah!

This high-resolution color image shows a 14-kilometer diameter crater that is relatively young, as indicated by the bright rays that cross the neighboring features. A dark "tongue" of impact melt, which has a bluer color than the nearby surface, appears to have flowed out of the crater.


Date acquired: May 16, 2011

 

 


Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

 

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Hovnatanian's Close-up

Hovnatanian crater was formed by an object that impacted at a very oblique angle, causing the crater to appear elliptical. Although impacts at most angles produce circular craters, impacts with incidence angles <15º (from the horizontal) will create elliptical craters. The rays of Hovnatanian form a "butterfly" pattern, which also indicates an oblique impact.


Date acquired: January 16, 2012

 

 

 

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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Happy New Year! (Finally!)

Shown here is the first MESSENGER image from 2012! Though this image was acquired on January 1, it wasn't downlinked from the spacecraft until this week. The spacecraft has two solid-state recorders, which enable data to be stored on the spacecraft, and the mission uses a system of priorities to determine which data are downlinked. Often images are sent back to Earth within a few days of being acquired but occasionally longer times between image acquisition and downlink occur.

Date acquired: January 18, 2012

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

 

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Moon–Mercury image comparison. (Left) The near side of the Moon, showing the dark volcanic areas (maria) composed of lava flows and the bright, heavily cratered highland crust. (Right) Mariner 10 view of Mercury showing that, unlike the Moon, there is no brightness contrast between the cratered terrain and the smooth plains. The Moon is about one-quarter of the diameter of Earth; Mercury is about one-third of the diameter of Earth.

 

 

 

Credit: Lick Observatory (left); NASA/Jet Propulsion Laboratory/U.S. Geological Survey (right)

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Have a Gander at Sander

This targeted image of Sander crater reveals that the bright portions of the floor consist of large numbers of shallow irregular depressions ("hollows"), giving an etched appearance to the surface.

Date acquired: September 29, 2011


Image Credit: Courtesy of AAAS/Science

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Pit(ch) Black

The Tolstoj basin is located in Mercury’s southern hemisphere, and is 355 km (220 miles) in diameter. This oblique image shows an elongate pit inside Tolstoj, a basin whose floor appears to have been flooded by lavas. The pit lacks the raised rim of an impact crater, and may have formed when magma withdrew from a shallow chamber, causing an unsupported area of the surface to collapse. The low-angle lighting in this image hides the floor of the pit, making it appear much deeper than it actually is. The pit is aligned approximately north-south.

Date acquired: January 11, 2012
Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

 

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Deep Impact

Although Mercury is replete with impact craters, it can be difficult to gauge their size in a meaningful way. This oblique image shows an unnamed crater that lies within the Rachmaninoff basin. It is a simple crater, characterized by its bowl-like shape, and lacks the central peak or peak ring of larger, complex craters. The famous Meteor Crater in Arizona, though also a simple crater, is five times smaller in diameter! (North is towards the upper left corner of the image.)

Date acquired: February 09, 2012

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/
Carnegie Institution of Washington

 

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Sleepy Hollows

 

A fresh impact crater. Hollows are present on a section of the crater wall that has slid partway down toward the floor.

MESSENGER has indeed proven Mercury unexpectedly rich in sulfur. That in itself is a surprise that's forcing scientists to rethink how Mercury was formed. The prevailing models suggest that either (1) very early in Solar System history, during the final sweep-up of the large planetesimals that formed the planets, a colossal impact tore off much of Mercury's rocky outer layering; or (2) a hot phase of the early Sun heated
up the surface enough to scorch off the outer layers. In either case, the elements with a low boiling point - volatiles like sulfur and potassium - would have been driven off.

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