Mercury (planet)
Perihelion 0.307499 AU (46.00 million km) | | ||||||||||||
0.387098 AU (57.91 million km) | |||||||||||||
Eccentricity | 0.205630[4] | ||||||||||||
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115.88 d[4] | |||||||||||||
Average orbital speed | 47.36 km/s[4] | ||||||||||||
174.796° | |||||||||||||
Inclination |
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48.331° | |||||||||||||
29.124° | |||||||||||||
Satellites | None | ||||||||||||
Physical characteristics | |||||||||||||
Mean radius | |||||||||||||
Flattening | 0.0009[4] | ||||||||||||
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Volume |
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Mass |
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Mean density | 5.427 g/cm3[6] | ||||||||||||
Sidereal rotation period |
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Equatorial rotation velocity | 10.892 km/h (3.026 m/s) | ||||||||||||
2.04′ ± 0.08′ (to orbit)[9] (0.034°)[4] | |||||||||||||
North pole right ascension |
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North pole declination | 61.45°[4] | ||||||||||||
Albedo | |||||||||||||
Temperature | 437 K (164 °C) (blackbody temperature)[13] | ||||||||||||
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−2.48 to +7.25[15] | |||||||||||||
−0.4[16] | |||||||||||||
4.5–13″[4] | |||||||||||||
Atmosphere[4][17][18] | |||||||||||||
Surface pressure | trace (≲ 0.5 nPa) | ||||||||||||
Composition by volume | |||||||||||||
Objects |
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Mercury is the first planet from the Sun and the smallest in the Solar System. In English, it is named after the Roman god Mercurius (Mercury), god of commerce and communication, and the messenger of the gods. Mercury is classified as a terrestrial planet, with roughly the same surface gravity as Mars. The surface of Mercury is heavily cratered, as a result of countless impact events that have accumulated over billions of years. Its largest crater, Caloris Planitia, has a diameter of 1,550 km (960 mi) and one-third the diameter of the planet (4,880 km or 3,030 mi). Similarly to the Earth's Moon, Mercury's surface displays an expansive rupes system generated from thrust faults and bright ray systems formed by impact event remnants.
Mercury's
Combined with its high orbital eccentricity, the planet's surface has widely varying sunlight intensity and temperature, with the equatorial regions ranging from −170 °C (−270 °F) at night to 420 °C (790 °F) during sunlight. Due to the very small axial tilt, the planet's poles are permanently shadowed. This strongly suggests that water ice could be present in the craters. Above the planet's surface is an extremely tenuous exosphere and a faint magnetic field that is strong enough to deflect solar winds. Mercury has no natural satellite.
As of the early 2020s, many broad details of Mercury's geological history are still under investigation or pending data from space probes. Like other planets in the Solar System, Mercury was formed approximately 4.5 billion years ago. Its mantle is highly homogeneous, which suggests that Mercury had a magma ocean early in its history, like the Moon. According to current models, Mercury may have a solid silicate crust and mantle overlying a solid outer core, a deeper liquid core layer, and a solid inner core. There are many competing hypotheses about Mercury's origins and development, some of which incorporate collision with planetesimals and rock vaporization.
Nomenclature
The ancients knew Mercury by different names depending on whether it was an evening star or a morning star. By about 350 BC, the
Physical characteristics
Mercury is one of four
Internal structure
Mercury appears to have a solid silicate crust and mantle overlying a solid, metallic outer core layer, a deeper liquid core layer, and a solid inner core.[26][27] The composition of the iron-rich core remains uncertain, but it likely contains nickel, silicon and perhaps sulfur and carbon, plus trace amounts of other elements.[28] The planet's density is the second highest in the Solar System at 5.427 g/cm3, only slightly less than Earth's density of 5.515 g/cm3.[4] If the effect of gravitational compression were to be factored out from both planets, the materials of which Mercury is made would be denser than those of Earth, with an uncompressed density of 5.3 g/cm3 versus Earth's 4.4 g/cm3.[29] Mercury's density can be used to infer details of its inner structure. Although Earth's high density results appreciably from gravitational compression, particularly at the core, Mercury is much smaller and its inner regions are not as compressed. Therefore, for it to have such a high density, its core must be large and rich in iron.[30]
The radius of Mercury's core is estimated to be 2,020 ± 30 km (1,255 ± 19 mi), based on interior models constrained to be consistent with a
Mercury's core has a higher iron content than that of any other planet in the Solar System, and several theories have been proposed to explain this. The most widely accepted theory is that Mercury originally had a metal–silicate ratio similar to common
Alternatively, Mercury may have formed from the
Each hypothesis predicts a different surface composition, and two space missions have been tasked with making observations of this composition. The first MESSENGER, which ended in 2015, found higher-than-expected potassium and sulfur levels on the surface, suggesting that the giant impact hypothesis and vaporization of the crust and mantle did not occur because said potassium and sulfur would have been driven off by the extreme heat of these events.[44] BepiColombo, which will arrive at Mercury in 2025, will make observations to test these hypotheses.[45] The findings so far would seem to favor the third hypothesis; however, further analysis of the data is needed.[46]
Surface geology
Mercury's surface is similar in appearance to that of the Moon, showing extensive
The planet's mantle is chemically heterogeneous, suggesting the planet went through a
Names for features on Mercury come from a variety of sources and are set according to the
Impact basins and craters
Mercury was heavily bombarded by comets and
The largest known crater is Caloris Planitia, or Caloris Basin, with a diameter of 1,550 km (960 mi).[61] The impact that created the Caloris Basin was so powerful that it caused lava eruptions and left a concentric mountainous ring ~2 km (1.2 mi) tall surrounding the impact crater. The floor of the Caloris Basin is filled by a geologically distinct flat plain, broken up by ridges and fractures in a roughly polygonal pattern. It is not clear whether they were volcanic lava flows induced by the impact or a large sheet of impact melt.[59]
At the antipode of the Caloris Basin is a large region of unusual, hilly terrain known as the "Weird Terrain". One hypothesis for its origin is that shock waves generated during the Caloris impact traveled around Mercury, converging at the basin's antipode (180 degrees away). The resulting high stresses fractured the surface.[62] Alternatively, it has been suggested that this terrain formed as a result of the convergence of ejecta at this basin's antipode.[63]
Overall, 46 impact basins have been identified.
Plains
There are two geologically distinct plains regions on Mercury.[59][66] Gently rolling, hilly plains in the regions between craters are Mercury's oldest visible surfaces,[59] predating the heavily cratered terrain. These inter-crater plains appear to have obliterated many earlier craters, and show a general paucity of smaller craters below about 30 km (19 mi) in diameter.[66]
Smooth plains are widespread flat areas that fill depressions of various sizes and bear a strong resemblance to lunar maria. Unlike lunar maria, the smooth plains of Mercury have the same albedo as the older inter-crater plains. Despite a lack of unequivocally volcanic characteristics, the localisation and rounded, lobate shape of these plains strongly support volcanic origins.[59] All the smooth plains of Mercury formed significantly later than the Caloris basin, as evidenced by appreciably smaller crater densities than on the Caloris ejecta blanket.[59]
Compressional features
An unusual feature of Mercury's surface is the numerous compression folds, or
Volcanism
There is evidence for pyroclastic flows on Mercury from low-profile shield volcanoes.[72][73][74] Fifty-one pyroclastic deposits have been identified,[75] where 90% of them are found within impact craters.[75] A study of the degradation state of the impact craters that host pyroclastic deposits suggests that pyroclastic activity occurred on Mercury over a prolonged interval.[75]
A "rimless depression" inside the southwest rim of the Caloris Basin consists of at least nine overlapping volcanic vents, each individually up to 8 km (5.0 mi) in diameter. It is thus a "compound volcano".[76] The vent floors are at least 1 km (0.62 mi) below their brinks and they bear a closer resemblance to volcanic craters sculpted by explosive eruptions or modified by collapse into void spaces created by magma withdrawal back down into a conduit.[76] Scientists could not quantify the age of the volcanic complex system but reported that it could be on the order of a billion years.[76]
Surface conditions and exosphere
The surface temperature of Mercury ranges from 100 to 700 K (−173 to 427 °C; −280 to 800 °F).
Although daylight temperatures at the surface of Mercury are generally extremely high, observations strongly suggest that ice (frozen water) exists on Mercury. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below 102 K, far lower than the global average.[82] This creates a cold trap where ice can accumulate. Water ice strongly reflects radar, and observations by the 70-meter Goldstone Solar System Radar and the VLA in the early 1990s revealed that there are patches of high radar reflection near the poles.[83] Although ice was not the only possible cause of these reflective regions, astronomers thought it to be the most likely explanation.[84] The presence of water ice was confirmed using MESSENGER images of craters at the north pole.[77]
The icy crater regions are estimated to contain about 1014–1015 kg of ice,[85] and may be covered by a layer of regolith that inhibits sublimation.[86] By comparison, the Antarctic ice sheet on Earth has a mass of about 4×1018 kg, and Mars's south polar cap contains about 1016 kg of water.[85] The origin of the ice on Mercury is not yet known, but the two most likely sources are from outgassing of water from the planet's interior and deposition by impacts of comets.[85]
Mercury is too small and hot for its gravity to retain any significant atmosphere over long periods of time; it does have a tenuous surface-bounded exosphere[87] at a surface pressure of less than approximately 0.5 nPa (0.005 picobars).[4] It includes hydrogen, helium, oxygen, sodium, calcium, potassium, magnesium, silicon, and hydroxide, among others.[17][18] This exosphere is not stable—atoms are continuously lost and replenished from a variety of sources. Hydrogen atoms and helium atoms probably come from the solar wind, diffusing into Mercury's magnetosphere before later escaping back into space. The radioactive decay of elements within Mercury's crust is another source of helium, as well as sodium and potassium. Water vapor is present, released by a combination of processes such as comets striking its surface, sputtering creating water out of hydrogen from the solar wind and oxygen from rock, and sublimation from reservoirs of water ice in the permanently shadowed polar craters. The detection of high amounts of water-related ions like O+, OH−, and H3O+ was a surprise.[88][89] Because of the quantities of these ions that were detected in Mercury's space environment, scientists surmise that these molecules were blasted from the surface or exosphere by the solar wind.[90][91]
Sodium, potassium, and calcium were discovered in the atmosphere during the 1980s–1990s, and are thought to result primarily from the vaporization of surface rock struck by micrometeorite impacts[92] including presently from Comet Encke.[93] In 2008, magnesium was discovered by MESSENGER.[94] Studies indicate that, at times, sodium emissions are localized at points that correspond to the planet's magnetic poles. This would indicate an interaction between the magnetosphere and the planet's surface.[95]
According to NASA, Mercury is not a suitable planet for Earth-like life. It has a
Magnetic field and magnetosphere
Despite its small size and slow 59-day-long rotation, Mercury has a significant, and apparently global, magnetic field. According to measurements taken by Mariner 10, it is about 1.1% the strength of Earth's. The magnetic-field strength at Mercury's equator is about 300 nT.[100][101] Like that of Earth, Mercury's magnetic field is dipolar[95] and nearly aligned with the planet's spin axis (10° dipolar tilt, compared to 11° for Earth).[102] Measurements from both the Mariner 10 and MESSENGER space probes have indicated that the strength and shape of the magnetic field are stable.[102]
It is likely that this magnetic field is generated by a dynamo effect, in a manner similar to the magnetic field of Earth.[103][104] This dynamo effect would result from the circulation of the planet's iron-rich liquid core. Particularly strong tidal heating effects caused by the planet's high orbital eccentricity would serve to keep part of the core in the liquid state necessary for this dynamo effect.[105][106]
Mercury's magnetic field is strong enough to deflect the solar wind around the planet, creating a magnetosphere. The planet's magnetosphere, though small enough to fit within Earth,[95] is strong enough to trap solar wind plasma. This contributes to the space weathering of the planet's surface.[102] Observations taken by the Mariner 10 spacecraft detected this low energy plasma in the magnetosphere of the planet's nightside. Bursts of energetic particles in the planet's magnetotail indicate a dynamic quality to the planet's magnetosphere.[95]
During its second flyby of the planet on October 6, 2008, MESSENGER discovered that Mercury's magnetic field can be extremely "leaky". The spacecraft encountered magnetic "tornadoes" – twisted bundles of magnetic fields connecting the planetary magnetic field to interplanetary space – that were up to 800 km wide or a third of the radius of the planet. These twisted magnetic flux tubes, technically known as flux transfer events, form open windows in the planet's magnetic shield through which the solar wind may enter and directly impact Mercury's surface via magnetic reconnection.[107] This also occurs in Earth's magnetic field. The MESSENGER observations showed the reconnection rate was ten times higher at Mercury, but its proximity to the Sun only accounts for about a third of the reconnection rate observed by MESSENGER.[107]
Orbit, rotation, and longitude
Mercury has the most
Mercury's orbit is inclined by 7 degrees to the plane of Earth's orbit (the ecliptic), the largest of all eight known solar planets.[110] As a result, transits of Mercury across the face of the Sun can only occur when the planet is crossing the plane of the ecliptic at the time it lies between Earth and the Sun, which is in May or November. This occurs about every seven years on average.[111]
Mercury's
At certain points on Mercury's surface, an observer would be able to see the Sun peek up a little more than two-thirds of the way over the horizon, then reverse and set before rising again, all within the same
For the same reason, there are two points on Mercury's equator, 180 degrees apart in
Mercury attains an inferior conjunction (nearest approach to Earth) every 116 Earth days on average,[4] but this interval can range from 105 days to 129 days due to the planet's eccentric orbit. Mercury can come as near as 82,200,000 km (0.549 astronomical units; 51.1 million miles) to Earth, and that is slowly declining: The next approach to within 82,100,000 km (51 million mi) is in 2679, and to within 82,000,000 km (51 million mi) in 4487, but it will not be closer to Earth than 80,000,000 km (50 million mi) until 28,622.[118] Its period of retrograde motion as seen from Earth can vary from 8 to 15 days on either side of an inferior conjunction. This large range arises from the planet's high orbital eccentricity.[25] Essentially, because Mercury is closest to the Sun, when taking an average over time, Mercury is most often the closest planet to the Earth,[119][120] and—in that measure—it is the closest planet to each of the other planets in the Solar System.[121][122][123][b]
Longitude convention
The longitude convention for Mercury puts the zero of longitude at one of the two hottest points on the surface, as described above. However, when this area was first visited, by Mariner 10, this zero meridian was in darkness, so it was impossible to select a feature on the surface to define the exact position of the meridian. Therefore, a small crater further west was chosen, called Hun Kal, which provides the exact reference point for measuring longitude.[124][125] The center of Hun Kal defines the 20° west meridian. A 1970 International Astronomical Union resolution suggests that longitudes be measured positively in the westerly direction on Mercury.[126] The two hottest places on the equator are therefore at longitudes 0° W and 180° W, and the coolest points on the equator are at longitudes 90° W and 270° W. However, the MESSENGER project uses an east-positive convention.[127]
Spin-orbit resonance
For many years it was thought that Mercury was synchronously tidally locked with the Sun, rotating once for each orbit and always keeping the same face directed towards the Sun, in the same way that the same side of the Moon always faces Earth. Radar observations in 1965 proved that the planet has a 3:2 spin-orbit resonance, rotating three times for every two revolutions around the Sun. The eccentricity of Mercury's orbit makes this resonance stable—at perihelion, when the solar tide is strongest, the Sun is nearly stationary in Mercury's sky.[128]
The 3:2 resonant tidal locking is stabilized by the variance of the tidal force along Mercury's eccentric orbit, acting on a permanent dipole component of Mercury's mass distribution.[129] In a circular orbit there is no such variance, so the only resonance stabilized in such an orbit is at 1:1 (e.g., Earth–Moon), when the tidal force, stretching a body along the "center-body" line, exerts a torque that aligns the body's axis of least inertia (the "longest" axis, and the axis of the aforementioned dipole) to always point at the center. However, with noticeable eccentricity, like that of Mercury's orbit, the tidal force has a maximum at perihelion and therefore stabilizes resonances, like 3:2, ensuring that the planet points its axis of least inertia roughly at the Sun when passing through perihelion.[129]
The original reason astronomers thought it was synchronously locked was that, whenever Mercury was best placed for observation, it was always nearly at the same point in its 3:2 resonance, hence showing the same face. This is because, coincidentally, Mercury's rotation period is almost exactly half of its synodic period with respect to Earth. Due to Mercury's 3:2 spin-orbit resonance, a solar day lasts about 176 Earth days.
Simulations indicate that the orbital eccentricity of Mercury varies chaotically from nearly zero (circular) to more than 0.45 over millions of years due to perturbations from the other planets.[25][130] This was thought to explain Mercury's 3:2 spin-orbit resonance (rather than the more usual 1:1), because this state is more likely to arise during a period of high eccentricity.[131] However, accurate modeling based on a realistic model of tidal response has demonstrated that Mercury was captured into the 3:2 spin-orbit state at a very early stage of its history, within 20 (more likely, 10) million years after its formation.[132]
Numerical simulations show that a future secular orbital resonant interaction with the perihelion of Jupiter may cause the eccentricity of Mercury's orbit to increase to the point where there is a 1% chance that the orbit will be destabilized in the next five billion years. If this happens, Mercury may fall into the Sun, collide with Venus, be ejected from the Solar System, or even disrupt the rest of the inner Solar System.[133][134]
Advance of perihelion
In 1859, the French mathematician and astronomer
The observed
Observation
Mercury's
Ground-based telescope observations of Mercury reveal only an illuminated partial disk with limited detail. The Hubble Space Telescope cannot observe Mercury at all, due to safety procedures that prevent its pointing too close to the Sun.[141] Because the shift of 0.15 revolutions of Earth in a Mercurian year makes up a seven-Mercurian-year cycle (0.15 × 7 ≈ 1.0), in the seventh Mercurian year, Mercury follows almost exactly (earlier by 7 days) the sequence of phenomena it showed seven Mercurian years before.[142]
Like the Moon and Venus, Mercury exhibits
Mercury is best observed at the first and last quarter, although they are phases of lesser brightness. The first and last quarter phases occur at greatest elongation east and west of the Sun, respectively. At both of these times, Mercury's separation from the Sun ranges anywhere from 17.9° at perihelion to 27.8° at aphelion.[142][145] At greatest western elongation, Mercury rises at its earliest before sunrise, and at greatest eastern elongation, it sets at its latest after sunset.[146]
Mercury is more often and easily visible from the Southern Hemisphere than from the Northern. This is because Mercury's maximum western elongation occurs only during early autumn in the Southern Hemisphere, whereas its greatest eastern elongation happens only during late winter in the Southern Hemisphere.[146] In both of these cases, the angle at which the planet's orbit intersects the horizon is maximized, allowing it to rise several hours before sunrise in the former instance and not set until several hours after sundown in the latter from southern mid-latitudes, such as Argentina and South Africa.[146]
An alternate method for viewing Mercury involves observing the planet with a telescope during daylight hours when conditions are clear, ideally when it is at its greatest elongation. This allows the planet to be found easily, even when using telescopes with 8 cm (3.1 in) apertures. However, great care must be taken to obstruct the Sun from sight because of the extreme risk for eye damage.[147] This method bypasses the limitation of twilight observing when the ecliptic is located at a low elevation (e.g. on autumn evenings). The planet is higher in the sky and less atmospheric effects affect the view of the planet. Mercury can be viewed as close as 4° to the Sun near superior conjunction when it is almost at its brightest.
Mercury can, like several other planets and the brightest stars, be seen during a total solar eclipse.[148]
Observation history
Ancient astronomers
The earliest known recorded observations of Mercury are from the
The
In
In
In India, the Kerala school astronomer Nilakantha Somayaji in the 15th century developed a partially heliocentric planetary model in which Mercury orbits the Sun, which in turn orbits Earth, similar to the Tychonic system later proposed by Tycho Brahe in the late 16th century.[165]
Ground-based telescopic research
The first telescopic observations of Mercury were made by
A rare event in astronomy is the passage of one planet in front of another (
The difficulties inherent in observing Mercury meant that it was far less studied than the other planets. In 1800,
In June 1962, Soviet scientists at the
In 1965, Italian astronomer Giuseppe Colombo noted that the rotation value was about two-thirds of Mercury's orbital period, and proposed that the planet's orbital and rotational periods were locked into a 3:2 rather than a 1:1 resonance.[178] Data from Mariner 10 subsequently confirmed this view.[179] This means that Schiaparelli's and Antoniadi's maps were not "wrong". Instead, the astronomers saw the same features during every second orbit and recorded them, but disregarded those seen in the meantime, when Mercury's other face was toward the Sun, because the orbital geometry meant that these observations were made under poor viewing conditions.[169]
Ground-based optical observations did not shed much further light on Mercury, but radio astronomers using interferometry at microwave wavelengths, a technique that enables removal of the solar radiation, were able to discern physical and chemical characteristics of the subsurface layers to a depth of several meters.[180][181] Not until the first space probe flew past Mercury did many of its most fundamental morphological properties become known. Moreover, technological advances have led to improved ground-based observations. In 2000, high-resolution lucky imaging observations were conducted by the Mount Wilson Observatory 1.5-metre (4.9 ft) Hale telescope. They provided the first views that resolved surface features on the parts of Mercury that were not imaged in the Mariner 10 mission.[182] Most of the planet has been mapped by the Arecibo radar telescope, with 5 km (3.1 mi) resolution, including polar deposits in shadowed craters of what may be water ice.[183]
Research with space probes
Reaching Mercury from Earth poses significant technical challenges, because it orbits so much closer to the Sun than Earth. A Mercury-bound spacecraft launched from Earth must travel over 91 million kilometres (57 million miles) into the Sun's gravitational potential well. Mercury has an orbital speed of 47.4 km/s (29.5 mi/s), whereas Earth's orbital speed is 29.8 km/s (18.5 mi/s).[110] Therefore, the spacecraft must make a larger change in velocity (delta-v) to get to Mercury and then enter orbit,[185] as compared to the delta-v required for, say, Mars planetary missions.
The potential energy liberated by moving down the Sun's potential well becomes kinetic energy, requiring a delta-v change to do anything other than pass by Mercury. Some portion of this delta-v budget can be provided from a gravity assist during one or more fly-bys of Venus.[186] To land safely or enter a stable orbit the spacecraft would rely entirely on rocket motors. Aerobraking is ruled out because Mercury has a negligible atmosphere. A trip to Mercury requires more rocket fuel than that required to escape the Solar System completely. As a result, only three space probes have visited it so far.[187] A proposed alternative approach would use a solar sail to attain a Mercury-synchronous orbit around the Sun.[188]
Mariner 10
The first spacecraft to visit Mercury was NASA's Mariner 10 (1974–1975).[19] The spacecraft used the gravity of Venus to adjust its orbital velocity so that it could approach Mercury, making it both the first spacecraft to use this gravitational "slingshot" effect and the first NASA mission to visit multiple planets.[189] Mariner 10 provided the first close-up images of Mercury's surface, which immediately showed its heavily cratered nature, and revealed many other types of geological features, such as the giant scarps that were later ascribed to the effect of the planet shrinking slightly as its iron core cools.[190] Unfortunately, the same face of the planet was lit at each of Mariner 10's close approaches. This made close observation of both sides of the planet impossible,[191] and resulted in the mapping of less than 45% of the planet's surface.[192]
The spacecraft made three close approaches to Mercury, the closest of which took it to within 327 km (203 mi) of the surface.[193] At the first close approach, instruments detected a magnetic field, to the great surprise of planetary geologists—Mercury's rotation was expected to be much too slow to generate a significant dynamo effect. The second close approach was primarily used for imaging, but at the third approach, extensive magnetic data were obtained. The data revealed that the planet's magnetic field is much like Earth's, which deflects the solar wind around the planet. For many years after the Mariner 10 encounters, the origin of Mercury's magnetic field remained the subject of several competing theories.[194][195]
On March 24, 1975, just eight days after its final close approach, Mariner 10 ran out of fuel. Because its orbit could no longer be accurately controlled, mission controllers instructed the probe to shut down.[196] Mariner 10 is thought to be still orbiting the Sun, passing close to Mercury every few months.[197]
MESSENGER
A second NASA mission to Mercury, named MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging), was launched on August 3, 2004. It made a fly-by of Earth in August 2005, and of Venus in October 2006 and June 2007 to place it onto the correct trajectory to reach an orbit around Mercury.[198] A first fly-by of Mercury occurred on January 14, 2008, a second on October 6, 2008,[199] and a third on September 29, 2009.[200] Most of the hemisphere not imaged by Mariner 10 was mapped during these fly-bys. The probe successfully entered an elliptical orbit around the planet on March 18, 2011. The first orbital image of Mercury was obtained on March 29, 2011. The probe finished a one-year mapping mission,[199] and then entered a one-year extended mission into 2013. In addition to continued observations and mapping of Mercury, MESSENGER observed the 2012 solar maximum.[201]
The mission was designed to clear up six key issues: Mercury's high density, its geological history, the nature of its magnetic field, the structure of its core, whether it has ice at its poles, and where its tenuous atmosphere comes from. To this end, the probe carried imaging devices that gathered much-higher-resolution images of much more of Mercury than Mariner 10, assorted spectrometers to determine the abundances of elements in the crust, and magnetometers and devices to measure velocities of charged particles. Measurements of changes in the probe's orbital velocity were expected to be used to infer details of the planet's interior structure.[202] MESSENGER's final maneuver was on April 24, 2015, and it crashed into Mercury's surface on April 30, 2015.[203][204][205] The spacecraft's impact with Mercury occurred at 3:26:01 p.m. EDT on April 30, 2015, leaving a crater estimated to be 16 m (52 ft) in diameter.[206]
BepiColombo
The European Space Agency and the Japanese Space Agency developed and launched a joint mission called BepiColombo, which will orbit Mercury with two probes: one to map the planet and the other to study its magnetosphere.[207] Launched on October 20, 2018, BepiColombo is expected to reach Mercury in 2025.[208] It will release a magnetometer probe into an elliptical orbit, then chemical rockets will fire to deposit the mapper probe into a circular orbit. Both probes will operate for one terrestrial year.[207] The mapper probe carries an array of spectrometers similar to those on MESSENGER, and will study the planet at many different wavelengths including infrared, ultraviolet, X-ray and gamma ray.[209] BepiColombo conducted three of its six planned Mercury flybys from October 1, 2021[210] to June 19, 2023.[211][212]
Perseverance rover
On March 5, 2024, NASA released images of transits of the moon Deimos, the moon Phobos and the planet Mercury as viewed by the Perseverance rover on the planet Mars.
See also
- Astronomy on Mercury
- Colonization of Mercury
- Mercury in astrology
- Mercury in fiction
- Outline of Mercury (planet)
Notes
- ^ The Sun's total angular displacement during its apparent retrograde motion as seen from the surface of Mercury is ~1.23°, while the Sun's angular diameter when the apparent retrograde motion begins and ends is ~1.71°, increasing to ~1.73° at perihelion (midway through the retrograde motion).
- ^ It is important to be clear about the meaning of "closeness". In the astronomical literature, the term "closest planets" often means "the two planets that approach each other most closely". In other words, the orbits of the two planets approach each other most closely. However, this does not mean that the two planets are closest over time. For example, essentially because Mercury is closer to the Sun than Venus, Mercury spends more time in proximity to Earth; it could, therefore, be said that Mercury is the planet that is "closest to Earth when averaged over time". However, using this time-average definition of 'closeness'—as noted above—it turns out that Mercury is the closest planet to all other planets in the solar system. For that reason, arguably, the proximity-definition is not particularly helpful. An episode of the BBC Radio 4 programme "More or Less" explains the different notions of proximity well.[120]
- ^ Some sources precede the cuneiform transcription with "MUL". "MUL" is a cuneiform sign that was used in the Sumerian language to designate a star or planet, but it is not considered part of the actual name. The "4" is a reference number in the Sumero–Akkadian transliteration system to designate which of several syllables a certain cuneiform sign is most likely designating.
References
- ^ "Mercurian". Lexico UK English Dictionary. Oxford University Press. Archived from the original on March 27, 2020.
- ^ "Mercurial". Lexico UK English Dictionary UK English Dictionary. Oxford University Press. Archived from the original on December 22, 2019.
- J2000epoch.
- ^ a b c d e f g h i j k l m Williams, David R. (November 25, 2020). "Mercury Fact Sheet". NASA. Archived from the original on April 3, 2019. Retrieved April 19, 2021.
- . A133.
- ^ a b c d e f g Davis, Phillips; Barnett, Amanda (February 15, 2021). "Mercury". Solar System Exploration. NASA Jet Propulsion Laboratory. Archived from the original on April 18, 2021. Retrieved April 21, 2021.
- S2CID 122772353.
- (PDF) from the original on September 29, 2021. Retrieved August 25, 2019.
- ^ S2CID 22408219.
- ^ "ESO". ESO. Archived from the original on December 4, 2008. Retrieved June 3, 2021.
- arXiv:1703.02670 [astro-ph.EP].
- .
- ^ "Atmospheres and Planetary Temperatures". American Chemical Society. July 18, 2013. Archived from the original on January 27, 2023. Retrieved January 3, 2023.
- ^ doi:10.1006/icar.1999.6175. Figure 3 with the "TWO model"; Figure 5 for pole. Archived(PDF) from the original on November 13, 2012. Retrieved February 18, 2012.
- ^ S2CID 69912809.
- ^ "Encyclopedia - the brightest bodies". IMCCE. Archived from the original on July 24, 2023. Retrieved May 29, 2023.
- ^ S2CID 122285073.
- ^ .
- ^ a b c Dunne, James A.; Burgess, Eric (1978). "Chapter One". The Voyage of Mariner 10 – Mission to Venus and Mercury. NASA History Office. Archived from the original on November 17, 2017. Retrieved July 12, 2017.
- Perseus Project.
- ^ "Greek Names of the Planets". April 25, 2010. Archived from the original on May 9, 2010. Retrieved July 14, 2012.
Ermis is the Greek name of the planet Mercury, which is the closest planet to the Sun. It is named after the Greek God of commerce, Ermis or Hermes, who was also the messenger of the Ancient Greek gods.
See also the Greek article about the planet. - ISBN 978-0-904094-02-2.
- ^ Duncan, John Charles (1946). Astronomy: A Textbook. Harper & Brothers. p. 125.
The symbol for Mercury represents the Caduceus, a wand with two serpents twined around it, which was carried by the messenger of the gods.
- ISBN 9780871692337. Archived from the original on April 11, 2023. Retrieved March 19, 2023.] 4272, 4274, 4275 [...]). Mercury's is a stylized caduceus.
It is now possible to trace the medieval symbols for at least four of the five planets to forms that occur in some of the latest papyrus horoscopes ([ P.Oxy.
- ^ ISBN 978-1-85233-731-5.
- ^ Talbert, Tricia, ed. (March 21, 2012). "MESSENGER Provides New Look at Mercury's Surprising Core and Landscape Curiosities". NASA. Archived from the original on January 12, 2019. Retrieved April 20, 2018.
- ^ Genova, Antonio; et al. (April 17, 2023). "Scientists find evidence Mercury has a solid inner core" (Press release). AGU Newsroom. Archived from the original on April 17, 2019. Retrieved April 17, 2019.
- S2CID 119021137.
- ^ "Mercury". US Geological Survey. May 8, 2003. Archived from the original on September 29, 2006. Retrieved November 26, 2006.
- S2CID 122572625.
- S2CID 17668886.
- ^ Gold, Lauren (May 3, 2007). "Mercury has molten core, Cornell researcher shows". Chronicle. Cornell University. Archived from the original on June 17, 2012. Retrieved May 12, 2008.
- ^ Finley, Dave (May 3, 2007). "Mercury's Core Molten, Radar Study Shows". National Radio Astronomy Observatory. Archived from the original on May 3, 2012. Retrieved May 12, 2008.
- from the original on June 5, 2023. Retrieved June 5, 2023.
- from the original on February 12, 2019. Retrieved December 15, 2018.
- ISBN 978-1-107-15445-2. Archivedfrom the original on March 1, 2024. Retrieved November 19, 2022.
- .
- Bibcode:1994LPI....25.1203S.
- Bibcode:2004LPI....35.1886W.
- .
- ^ from the original on September 5, 2019. Retrieved August 25, 2019.
- ^ .
- .
- ^ Sappenfield, Mark (September 29, 2011). "Messenger's message from Mercury: Time to rewrite the textbooks". The Christian Science Monitor. Archived from the original on August 21, 2017. Retrieved August 21, 2017.
- ^ "BepiColombo". Science & Technology. European Space Agency. Archived from the original on March 6, 2018. Retrieved April 7, 2008.
- ^ Cartwright, Jon (September 30, 2011). "Messenger sheds light on Mercury's formation". Chemistry World. Archived from the original on August 6, 2017. Retrieved August 21, 2017.
- ^ Morris, Jefferson (November 10, 2008). "Laser Altimetry". Aviation Week & Space Technology. 169 (18): 18.
Mercury's crust is more analogous to a marbled cake than a layered cake.
- Bibcode:2012LPI....43.2151H. 2151.
- ^ Blue, Jennifer (April 11, 2008). "Gazetteer of Planetary Nomenclature". US Geological Survey. Archived from the original on April 12, 2012. Retrieved April 11, 2008.
- ^ a b Dunne, James A.; Burgess, Eric (1978). "Chapter Seven". The Voyage of Mariner 10 – Mission to Venus and Mercury. NASA History Office. Archived from the original on November 17, 2017. Retrieved May 28, 2008.
- S2CID 135051680.
- S2CID 135268415.
- ^ "Categories for Naming Features on Planets and Satellites". US Geological Survey. Archived from the original on July 8, 2014. Retrieved August 20, 2011.
- S2CID 122563809.
- S2CID 7790470.
- doi:10.3133/i2596.
- PMID 17741171. Archived from the original(PDF) on July 21, 2018. Retrieved October 25, 2017.
- ^ "Scientists see Mercury in a new light". Science Daily. February 28, 2008. Archived from the original on December 5, 2020. Retrieved April 7, 2008.
- ^ Bibcode:2001mses.conf..100S.
- ^ Ritzel, Rebecca (December 20, 2012). "Ballet isn't rocket science, but the two aren't mutually exclusive, either". The Washington Post. Washington, D.C., United States. Archived from the original on December 23, 2012. Retrieved December 22, 2012.
- ^ Shiga, David (January 30, 2008). "Bizarre spider scar found on Mercury's surface". NewScientist.com news service. Archived from the original on December 10, 2014. Retrieved September 4, 2017.
- S2CID 121225801.
- from the original on May 12, 2011. Retrieved May 12, 2008.
- . E00L08.
- Bibcode:2008LPI....39.1750D.
- ^ Bibcode:2001mses.conf..106W.
- S2CID 150072193.
- ^ a b Choi, Charles Q. (September 26, 2016). "Mercuryquakes May Currently Shake Up the Tiny Planet". Space.com. Archived from the original on September 28, 2016. Retrieved September 28, 2016.
- .
- ^ doi:10.1038/ngeo2814.
- S2CID 210298205.
- .
- (PDF) from the original on July 19, 2018. Retrieved August 20, 2019.
- from the original on August 22, 2017. Retrieved July 19, 2017.
- ^ S2CID 14393394. Archived from the original(PDF) on July 18, 2019. Retrieved August 25, 2019.
- ^ (PDF) from the original on March 6, 2020. Retrieved August 20, 2019.
- ^ a b Chang, Kenneth (November 29, 2012). "On Closest Planet to the Sun, NASA Finds Lots of Ice". The New York Times. p. A3. Archived from the original on November 29, 2012.
Sean C. Solomon, the principal investigator for MESSENGER, said there was enough ice there to encase Washington, D.C., in a frozen block two and a half miles deep.
- ^ Prockter, Louise (2005). Ice in the Solar System (PDF). Vol. 26. Johns Hopkins APL Technical Digest. Archived (PDF) from the original on September 24, 2021. Retrieved July 27, 2009.
- ISBN 978-0-12-446744-6.
- S2CID 38824994.
- ISBN 978-0-12-446744-6. Archivedfrom the original on March 1, 2024. Retrieved June 3, 2008.
- .
- S2CID 34009087.
- ^ Williams, David R. (June 2, 2005). "Ice on Mercury". NASA Goddard Space Flight Center. Archived from the original on January 31, 2011. Retrieved May 23, 2008.
- ^ Bibcode:1995DPS....27.2112R.
- .
- S2CID 121301247.
- ISBN 978-0-8165-1085-6. Archivedfrom the original on February 19, 2020. Retrieved February 19, 2020.
- ^ Lakdawalla, Emily (July 3, 2008). "MESSENGER Scientists "Astonished" to Find Water in Mercury's Thin Atmosphere". The Planetary Society. Archived from the original on April 4, 2017. Retrieved May 18, 2009.
- S2CID 206513512.
- ^ "Instrument Shows What Planet Mercury Is Made Of". University of Michigan. June 30, 2008. Archived from the original on March 22, 2012. Retrieved May 18, 2009.
- from the original on October 9, 2022. Retrieved October 16, 2022.
- hdl:2060/20150010116.
- S2CID 5578520.
- ^ ISBN 978-0-521-64587-4.
- ^ "Mercury". NASA. October 19, 2021. Archived from the original on July 5, 2022. Retrieved July 4, 2022.
- ^ Hall, Shannon (March 24, 2020). "Life on the Planet Mercury? 'It's Not Completely Nuts' – A new explanation for the rocky world's jumbled landscape opens a possibility that it could have had ingredients for habitability". The New York Times. Archived from the original on March 24, 2020. Retrieved March 26, 2020.
- PMID 32179758.
- ^ "Vast Collapsed Terrains on Mercury Might be Windows Into Ancient – Possibly Habitable – Volatile-Rich Materials". Planetary Science Institute. March 16, 2020. Archived from the original on August 28, 2022. Retrieved August 27, 2022.
- ISBN 978-0-534-42111-3.
- ^ Williams, David R. (January 6, 2005). "Planetary Fact Sheets". NASA National Space Science Data Center. Archived from the original on September 25, 2008. Retrieved August 10, 2006.
- ^ a b c "Mercury's Internal Magnetic Field". NASA. January 30, 2008. Archived from the original on April 21, 2021. Retrieved April 21, 2021.
- ^ Gold, Lauren (May 3, 2007). "Mercury has molten core, Cornell researcher shows". Cornell University. Archived from the original on June 17, 2012. Retrieved April 7, 2008.
- from the original on March 1, 2024. Retrieved October 29, 2023.
- .
- S2CID 56282397.
- ^ a b Steigerwald, Bill (June 2, 2009). "Magnetic Tornadoes Could Liberate Mercury's Tenuous Atmosphere". NASA Goddard Space Flight Center. Archived from the original on May 18, 2012. Retrieved July 18, 2009.
- .
- ^ "Space Topics: Compare the Planets: Mercury, Venus, Earth, The Moon, and Mars". Planetary Society. Archived from the original on July 28, 2011. Retrieved April 12, 2007.
- ^ a b Williams, David R. (October 21, 2019). "Planetary Fact Sheet – Metric". NASA. Archived from the original on July 19, 2012. Retrieved April 20, 2021.
- ^ Espenak, Fred (April 21, 2005). "Transits of Mercury". NASA/Goddard Space Flight Center. Archived from the original on August 29, 2015. Retrieved May 20, 2008.
- ISBN 978-0-7923-5813-8.
- ^ S2CID 8863681.
- ISBN 9789813143265. Archivedfrom the original on October 31, 2023. Retrieved October 25, 2023.
- ^ Popular Astronomy: A Review of Astronomy and Allied Sciences. Goodsell Observatory of Carleton College. 1896. Archived from the original on March 1, 2024. Retrieved December 24, 2016.
although in the case of Venus the libration in longitude due to the eccentricity of the orbit amounts to only 47' on either side of the mean position, in the case of Mercury it amounts to 23° 39'
- ^ Seligman, C. "The Rotation of Mercury". cseligman.com. NASA Flash animation. Archived from the original on August 6, 2019. Retrieved July 31, 2019.
- S2CID 122761699.
- original researchconcerns and to support general long-term trends)
Marius noted in the dedication from June 30, 1612, in the Prognosticon auf 1613 "that Mercury is illuminated by the Sun in the same way as the Venus and the Moon" and reports his observations of the brightness.
External links
- Atlas of Mercury. NASA. 1978. SP-423.
- Mercury nomenclature and map with feature names from the USGS/IAU Gazetteer of Planetary Nomenclature
- Equirectangular map of Mercury Archived May 20, 2016, at the Wayback Machine by Applied Coherent Technology Corp
- 3D globe of Mercury by Google
- Mercury at Solarviews.com
- Mercury by Astronomy Cast
- MESSENGER mission web site
- BepiColombo mission web site