Misplaced Pages

#647352

101-496: Kepler-11 , also designated as 2MASS J19482762+4154328 , is a Sun-like star slightly larger than the Sun in the constellation Cygnus , located some 2,110 light years from Earth . It is located within the field of vision of the Kepler space telescope , the satellite that NASA 's Kepler Mission uses to detect planets that may be transiting their stars. Announced on February 2, 2011,

202-406: A 3:2 ratio. This relationship is called spin–orbit resonance , and sidereal here means "relative to the stars". Consequently, one solar day (sunrise to sunrise) on Mercury lasts for around 176 Earth days: twice the planet's sidereal year. This means that one side of Mercury will remain in sunlight for one Mercurian year of 88 Earth days; while during the next orbit, that side will be in darkness all

303-424: A conduit. Scientists could not quantify the age of the volcanic complex system but reported that it could be on the order of a billion years. The surface temperature of Mercury ranges from 100 to 700 K (−173 to 427 °C; −280 to 800 °F). It never rises above 180 K at the poles, due to the absence of an atmosphere and a steep temperature gradient between the equator and the poles. At perihelion ,

404-451: A diameter of 1,550 km (960 mi), which is about 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 sidereal year (88.0 Earth days) and sidereal day (58.65 Earth days) are in

505-474: A general paucity of smaller craters below about 30 km (19 mi) in diameter. 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 localization and rounded, lobate shape of these plains strongly support volcanic origins. All

606-566: A layer of regolith that inhibits sublimation . By comparison, the Antarctic ice sheet on Earth has a mass of about 4 × 10  kg, and Mars's south polar cap contains about 10  kg of water. 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. Mercury is too small and hot for its gravity to retain any significant atmosphere over long periods of time; it does have

707-528: A layered, chemically heterogeneous crust with large-scale variations in chemical composition observed on the surface. The crust is low in iron but high in sulfur, resulting from the stronger early chemically reducing conditions than is found on other terrestrial planets. The surface is dominated by iron-poor pyroxene and olivine , as represented by enstatite and forsterite , respectively, along with sodium-rich plagioclase and minerals of mixed magnesium, calcium, and iron-sulfide. The less reflective regions of

808-450: A list of solar-type stars would be quite extensive. Solar-type stars show highly correlated behavior between their rotation rates and their chromospheric activity (e.g. Calcium H & K line emission) and coronal activity (e.g. X-ray emission) Because solar-type stars spin down during their main-sequence lifetimes due to magnetic braking , these correlations allow rough ages to be derived. Mamajek & Hillenbrand (2008) have estimated

909-487: A possibly separate subsequent episode called the Late Heavy Bombardment that ended 3.8 billion years ago. Mercury received impacts over its entire surface during this period of intense crater formation, facilitated by the lack of any atmosphere to slow impactors down. During this time Mercury was volcanically active; basins were filled by magma , producing smooth plains similar to the maria found on

1010-551: A prolonged interval. 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 ". 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

1111-462: A revolution would have caused a libration of 23.65° in longitude. For the same reason, there are two points on Mercury's equator, 180 degrees apart in longitude , at either of which, around perihelion in alternate Mercurian years (once a Mercurian day), the Sun passes overhead, then reverses its apparent motion and passes overhead again, then reverses a second time and passes overhead a third time, taking

SECTION 10

#1732791362648

1212-429: A series of smaller "corpuscules") might exist in an orbit even closer to the Sun than that of Mercury, to account for this perturbation. Other explanations considered included a slight oblateness of the Sun. The success of the search for Neptune based on its perturbations of the orbit of Uranus led astronomers to place faith in this possible explanation, and the hypothetical planet was named Vulcan , but no such planet

1313-469: A significant hydrogen / helium atmosphere is predicted for planets c , d , e , f , and g , while planet b may be surrounded by a steam atmosphere or perhaps by a hydrogen atmosphere. The low densities likely result from high-volume extended atmospheres that surround cores of iron, rock, and possibly H 2 O. The inner constituents of the Kepler-11 system were, at the time of their discoveries,

1414-465: A solid, metallic outer core layer, a deeper liquid core layer, and a solid inner core. 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. The planet's density is the second highest in the Solar System at 5.427 g/cm , only slightly less than Earth's density of 5.515 g/cm . If

1515-409: A tenuous surface-bounded exosphere at a surface pressure of less than approximately 0.5 nPa (0.005 picobars). It includes hydrogen , helium , oxygen , sodium , calcium , potassium , magnesium , silicon , and hydroxide , among others. This exosphere is not stable—atoms are continuously lost and replenished from a variety of sources. Hydrogen atoms and helium atoms probably come from

1616-409: A total of about 16 Earth-days for this entire process. In the other alternate Mercurian years, the same thing happens at the other of these two points. The amplitude of the retrograde motion is small, so the overall effect is that, for two or three weeks, the Sun is almost stationary overhead, and is at its most brilliant because Mercury is at perihelion, its closest to the Sun. This prolonged exposure to

1717-524: Is 17%. Research published in 2007 suggests that Mercury has a molten core. The mantle-crust layer is in total 420 km (260 mi) thick. Projections differ as to the size of the crust specifically; data from the Mariner 10 and MESSENGER probes suggests a thickness of 35 km (22 mi), whereas an Airy isostacy model suggests a thickness of 26 ± 11 km (16.2 ± 6.8 mi). One distinctive feature of Mercury's surface

1818-411: Is a G-type star that is approximately 104% the mass of and 102% the radius of the Sun . It has a surface temperature of about 5836 K and is estimated to have an age of around 3.2 billion years. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K. With an apparent magnitude of 14.2, it is too faint to be seen with the naked eye. All known planets transit

1919-424: Is a rocky body like Earth. It is the smallest planet in the Solar System, with an equatorial radius of 2,439.7 kilometres (1,516.0 mi). Mercury is also smaller —albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan . Mercury consists of approximately 70% metallic and 30% silicate material. Mercury appears to have a solid silicate crust and mantle overlying

2020-560: 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. Historically, humans knew Mercury by different names depending on whether it

2121-490: Is ideally defined as variability of less than 1%, but 3% is the practical limit due to limits in available data. Variation in irradiance in a star's habitable zone due to a companion star with an eccentric orbit is also a concern. Terrestrial planets in multiple star systems, those containing three or more stars, are not likely to have stable orbits in the long term. Stable orbits in binary systems take one of two forms: S-Type (satellite or circumstellar) orbits around one of

SECTION 20

#1732791362648

2222-461: Is in May or November. This occurs about every seven years on average. Mercury's axial tilt is almost zero, with the best measured value as low as 0.027 degrees. This is significantly smaller than that of Jupiter , which has the second smallest axial tilt of all planets at 3.1 degrees. This means that to an observer at Mercury's poles, the center of the Sun never rises more than 2.1 arcminutes above

2323-504: Is sometimes noted as twin, but is part of a triple star system and is very old for a solar twin at 6.8 Ga. Two solar sibling candidates (similar age, metallicity (−0.113), and kinematics) are Gaia DR2 1927143514955658880 and 1966383465746413568. Another way of defining solar twin is as a "habstar"—a star with qualities believed to be particularly hospitable to a life-hosting planet. Qualities considered include variability, mass, age, metallicity, and close companions. The requirement that

2424-436: 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. 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

2525-427: Is that Mercury originally had a metal–silicate ratio similar to common chondrite meteorites, thought to be typical of the Solar System's rocky matter, and a mass approximately 2.25 times its current mass. Early in the Solar System's history, Mercury may have been struck by a planetesimal of approximately 1 ⁄ 6 Mercury's mass and several thousand kilometers across. The impact would have stripped away much of

2626-419: Is the presence of numerous narrow ridges, extending up to several hundred kilometers in length. It is thought that these were formed as Mercury's core and mantle cooled and contracted at a time when the crust had already solidified. 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

2727-400: The Mariner 10 and MESSENGER space probes have indicated that the strength and shape of the magnetic field are stable. It is likely that this magnetic field is generated by a dynamo effect, in a manner similar to the magnetic field of Earth. This dynamo effect would result from the circulation of the planet's iron-rich liquid core. Particularly strong tidal heating effects caused by

2828-486: The VLA in the early 1990s revealed that there are patches of high radar reflection near the poles. Although ice was not the only possible cause of these reflective regions, astronomers thought it to be the most likely explanation. The presence of water ice was confirmed using MESSENGER images of craters at the north pole. The icy crater regions are estimated to contain about 10 –10  kg of ice, and may be covered by

2929-459: 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. Alternatively, it has been suggested that this terrain formed as a result of

3030-472: 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. 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 moment of inertia factor of 0.346 ± 0.014 . Hence, Mercury's core occupies about 57% of its volume; for Earth this proportion

3131-488: The solar wind . A third hypothesis proposes that the solar nebula caused drag on the particles from which Mercury was accreting , which meant that lighter particles were lost from the accreting material and not gathered by Mercury. 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

Kepler-11 - Misplaced Pages Continue

3232-403: The 1980s–1990s, and are thought to result primarily from the vaporization of surface rock struck by micrometeorite impacts including presently from Comet Encke . In 2008, magnesium was discovered by MESSENGER . 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

3333-428: 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. At

3434-582: The Greek Hermes, because it moves across the sky faster than any other planet, though some associated the planet with Apollo instead, as detailed by Pliny the Elder . The astronomical symbol for Mercury is a stylized version of Hermes' caduceus ; a Christian cross was added in the 16th century: [REDACTED] . Mercury is one of four terrestrial planets in the Solar System , which means it

3535-414: The Kepler-11 planetary system have likely to undergone a substantial inward migration in the past, producing an observed pattern of lower-mass planets on tightest orbits. Additional yet unobserved gas giant planets on wider orbit are likely necessary for migration of smaller planets to proceed that far inward. The system is among the most compact known; the orbits of planets b - f would easily fit inside

3636-442: The Moon, the surface of Mercury has likely incurred the effects of space weathering processes, including solar wind and micrometeorite impacts. There are two geologically distinct plains regions on Mercury. Gently rolling, hilly plains in the regions between craters are Mercury's oldest visible surfaces, predating the heavily cratered terrain. These inter-crater plains appear to have obliterated many earlier craters, and show

3737-524: The Moon. One of the most unusual craters is Apollodorus , or "the Spider", which hosts a series of radiating troughs extending outwards from its impact site. Craters on Mercury range in diameter from small bowl-shaped cavities to multi-ringed impact basins hundreds of kilometers across. They appear in all states of degradation, from relatively fresh rayed craters to highly degraded crater remnants. Mercurian craters differ subtly from lunar craters in that

3838-400: The Solar System. To strengthen the similarities, the star is class G5V, has a temperature of 5750 K, has a Sun-like mass and radius, and is only 500 million years younger than the Sun. As such, the habitable zone would extend in the same area as the zone in the Solar System, around 1 AU. This would allow an Earth-like planet to exist around 1 AU. Mercury (planet) Mercury is

3939-523: The Sun and having the following qualities: Other Sun parameters: The following are the known stars that come closest to satisfying the criteria for a solar twin. The Sun is listed for comparison. Highlighted boxes are out of range for a solar twin. The star may have been noted as solar twin in the past, but are more of a solar analog. Some other stars are sometimes mentioned as solar-twin candidates such as: Beta Canum Venaticorum ; however it has too low metallicities (−0.21) for solar twin. 16 Cygni B

4040-400: The Sun at its brightest makes these two points the hottest places on Mercury. Maximum temperature occurs when the Sun is at an angle of about 25 degrees past noon due to diurnal temperature lag , at 0.4 Mercury days and 0.8 Mercury years past sunrise. Conversely, there are two other points on the equator, 90 degrees of longitude apart from the first ones, where the Sun passes overhead only when

4141-442: The Sun's apparent motion ceases; closer to perihelion, Mercury's angular orbital velocity then exceeds the angular rotational velocity. Thus, to a hypothetical observer on Mercury, the Sun appears to move in a retrograde direction. Four Earth days after perihelion, the Sun's normal apparent motion resumes. A similar effect would have occurred if Mercury had been in synchronous rotation: the alternating gain and loss of rotation over

Kepler-11 - Misplaced Pages Continue

4242-448: The Sun) on Mercury last exactly two Mercury years, or about 176 Earth days. 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. 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

4343-551: The Sun, collide with Venus, be ejected from the Solar System, or even disrupt the rest of the inner Solar System. In 1859, the French mathematician and astronomer Urbain Le Verrier reported that the slow precession of Mercury's orbit around the Sun could not be completely explained by Newtonian mechanics and perturbations by the known planets. He suggested, among possible explanations, that another planet (or perhaps instead

4444-411: The Sun, having the following qualities: Solar analogs not meeting the stricter solar twin criteria include, within 50 light years and in order of increasing distance (The Sun is listed for comparison.): To date no solar twin that exactly matches the Sun has been found. However, there are some stars that come very close to being identical to the Sun, and are such considered solar twins by members of

4545-401: The Sun, this cross-checking cannot be done. These stars are broadly similar to the Sun. They are main-sequence stars with a B−V color between 0.48 and 0.80, the Sun having a B−V color of 0.65. Alternatively, a definition based on spectral type can be used, such as F8V through K2V , which would correspond to B−V color of 0.50 to 1.00. This definition fits approximately 10% of stars, so

4646-422: The Sun. This varying distance to the Sun leads to Mercury's surface being flexed by tidal bulges raised by the Sun that are about 17 times stronger than the Moon's on Earth. Combined with a 3:2 spin–orbit resonance of the planet's rotation around its axis, it also results in complex variations of the surface temperature. The resonance makes a single solar day (the length between two meridian transits of

4747-469: The ages for the 108 solar-type (F8V–K2V) main-sequence stars within 52 light-years (16 parsecs) of the Sun based on their chromospheric activity (as measured via Ca, H, and K emission lines). The following table shows a sample of solar-type stars within 50 light years that nearly satisfy the criteria for solar analogs (B−V color between 0.48 and 0.80), based on current measurements (the Sun is listed for comparison): These stars are photometrically similar to

4848-463: The area blanketed by their ejecta is much smaller, a consequence of Mercury's stronger surface gravity. According to International Astronomical Union rules, each new crater must be named after an artist who was famous for more than fifty years, and dead for more than three years, before the date the crater is named. The largest known crater is Caloris Planitia , or Caloris Basin, with a diameter of 1,550 km (960 mi). The impact that created

4949-461: The astronomical community. An exact solar twin would be a G2V star with a 5,778 K surface temperature, be 4.6 billion years old, with the correct metallicity and a 0.1% solar luminosity variation. Stars with an age of 4.6 billion years are at the most stable state. Proper metallicity, radius , chemical composition, rotation , magnetic activity, and size are also very important to low luminosity variation. The stars below are more similar to

5050-410: 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. The original reason astronomers thought it was synchronously locked

5151-433: The convergence of ejecta at this basin's antipode. Overall, 46 impact basins have been identified. A notable basin is the 400 km (250 mi)-wide, multi-ring Tolstoj Basin that has an ejecta blanket extending up to 500 km (310 mi) from its rim and a floor that has been filled by smooth plains materials. Beethoven Basin has a similar-sized ejecta blanket and a 625 km (388 mi)-diameter rim. Like

SECTION 50

#1732791362648

5252-438: 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

5353-445: The creation of a solar analog category for stars that were particularly similar to the Sun. Later still, continued improvements in precision allowed for the creation of a solar-twin category for near-perfect matches. Similarity to the Sun allows for checking derived quantities—such as temperature, which is derived from the color index—against the Sun, the only star whose temperature is confidently known. For stars that are not similar to

5454-503: The crust are high in carbon, most likely in the form of graphite. Names for features on Mercury come from a variety of sources and are set according to the IAU planetary nomenclature system. Names coming from people are limited to the deceased. Craters are named for artists, musicians, painters, and authors who have made outstanding or fundamental contributions to their field. Ridges, or dorsa, are named for scientists who have contributed to

5555-473: The data is needed. Mercury's surface is similar in appearance to that of the Moon, showing extensive mare -like plains and heavy cratering, indicating that it has been geologically inactive for billions of years. It is more heterogeneous than the surface of Mars or the Moon, both of which contain significant stretches of similar geology, such as maria and plateaus. Albedo features are areas of markedly different reflectivity, which include impact craters,

5656-438: The early 20th century, Albert Einstein 's general theory of relativity provided the explanation for the observed precession, by formalizing gravitation as being mediated by the curvature of spacetime. The effect is small: just 42.980 ± 0.001 arcseconds per century (or 0.43 arcsecond per year, or 0.1035 arcsecond per orbital period) for Mercury; it therefore requires a little over 12.5 million orbits, or 3 million years, for

5757-408: 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/cm versus Earth's 4.4 g/cm . 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

5858-404: The effects of the eccentricity, showing Mercury's orbit overlaid with a circular orbit having the same semi-major axis . Mercury's higher velocity when it is near perihelion is clear from the greater distance it covers in each 5-day interval. In the diagram, the varying distance of Mercury to the Sun is represented by the size of the planet, which is inversely proportional to Mercury's distance from

5959-427: The equatorial subsolar point is located at latitude 0°W or 180°W, and it climbs to a temperature of about 700 K . During aphelion , this occurs at 90° or 270°W and reaches only 550 K . On the dark side of the planet, temperatures average 110 K . The intensity of sunlight on Mercury's surface ranges between 4.59 and 10.61 times the solar constant (1,370 W·m ). Although daylight temperatures at

6060-420: The features has suggested a total shrinkage of Mercury's radius in the range of ~1–7 km (0.62–4.35 mi). Most activity along the major thrust systems probably ended about 3.6–3.7 billion years ago. Small-scale thrust fault scarps have been found, tens of meters in height and with lengths in the range of a few kilometers, that appear to be less than 50 million years old, indicating that compression of

6161-498: The first planet from the Sun and the smallest in the Solar System . In English, it is named after the ancient 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

SECTION 60

#1732791362648

6262-400: The habitable zone themselves, and could potentially host Earth-like moons. One example of such a star is HD 70642   , a G5V, at temperature of 5533 K, but is much younger than the Sun, at 1.9 billion years old. Another such example would be HIP 11915 , which has a planetary system containing a Jupiter-like planet orbiting at a similar distance that the planet Jupiter does in

6363-516: The horizon. By comparison, the angular size of the Sun as seen from Mercury ranges from 1 + 1 ⁄ 4 to 2 degrees across. 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 Mercurian day . This is because approximately four Earth days before perihelion, Mercury's angular orbital velocity equals its angular rotational velocity so that

6464-429: The interior and consequent surface geological activity continue to the present. There is evidence for pyroclastic flows on Mercury from low-profile shield volcanoes . Fifty-one pyroclastic deposits have been identified, where 90% of them are found within impact craters. A study of the degradation state of the impact craters that host pyroclastic deposits suggests that pyroclastic activity occurred on Mercury over

6565-468: The most comprehensively understood extrasolar planets smaller than Neptune. Currently, observations do not place a firm constraint on the mass of planet g (<25 M E ). However, formation and evolution studies indicate that the mass of planet g is not much greater than about 7 M E . Kepler-11 planets may have formed in situ (i.e., at their observed orbital locations) or ex situ , that is, they may have started their formation farther away from

6666-416: The orbit of Mercury , with g only slightly outside it. Despite this close packing of the orbits, dynamical integrations indicate the Kepler-11 system has the potential to be stable on a time scale of billions of years. However, it may be approaching instability due to a secular resonance involving b and c . If this happens, b will most likely become eccentric enough that it collides with c . None of

6767-510: 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. 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. However, accurate modeling based on a realistic model of tidal response has demonstrated that Mercury

6868-678: The original crust and mantle, leaving the core behind as a relatively major component. A similar process, known as the giant impact hypothesis , has been proposed to explain the formation of Earth's Moon. Alternatively, Mercury may have formed from the solar nebula before the Sun's energy output had stabilized. It would initially have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2,500 and 3,500 K and possibly even as high as 10,000 K. Much of Mercury's surface rock could have been vaporized at such temperatures, forming an atmosphere of "rock vapor" that could have been carried away by

6969-407: The permanently shadowed polar craters. The detection of high amounts of water-related ions like O , OH , and H 3 O was a surprise. 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. Sodium, potassium, and calcium were discovered in the atmosphere during

7070-545: The perspective of Earth . Kepler-11 is the first discovered exoplanetary system with more than three transiting planets. Kepler-11 is named for the Kepler Mission: it is the 11th star with confirmed planets discovered in the Kepler field of view. The planets are named alphabetically, starting with the innermost: b , c , d , e , f , and g , distinguishers that are tagged onto the name of their home star. Kepler-11

7171-528: The planet is at aphelion in alternate years, when the apparent motion of the Sun in Mercury's sky is relatively rapid. These points, which are the ones on the equator where the apparent retrograde motion of the Sun happens when it is crossing the horizon as described in the preceding paragraph, receive much less solar heat than the first ones described above. Mercury attains an inferior conjunction (nearest approach to Earth) every 116 Earth days on average, but this interval can range from 105 days to 129 days due to

7272-571: 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. 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

7373-458: The planet's high orbital eccentricity would serve to keep part of the core in the liquid state necessary for this dynamo effect. 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, is strong enough to trap solar wind plasma . This contributes to the space weathering of

7474-441: The planet's high orbital eccentricity. Essentially, because Mercury is closest to the Sun, when taking an average over time, Mercury is most often the closest planet to the Earth, and—in that measure—it is the closest planet to each of the other planets in the Solar System. 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

7575-442: The planet's surface. According to NASA, Mercury is not a suitable planet for Earth-like life. It has a surface boundary exosphere instead of a layered atmosphere, extreme temperatures, and high solar radiation. It is unlikely that any living beings can withstand those conditions. Some parts of the subsurface of Mercury may have been habitable , and perhaps life forms , albeit likely primitive microorganisms , may have existed on

7676-504: The planet's surface. 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. 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

7777-482: The planet. 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 . Like that of Earth, Mercury's magnetic field is dipolar and nearly aligned with the planet's spin axis (10° dipolar tilt, compared to 11° for Earth). Measurements from both

7878-439: 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 . This also occurs in Earth's magnetic field. The MESSENGER observations showed

7979-406: The planets are in low-ratio orbital resonances , in which multiple planets gravitationally tug on and stabilize each other's orbits, resulting in simple ratios of their orbital periods. However, b and c are close to a 5:4 ratio. There could conceivably be other planets in the system that do not transit the star, but they would only be detectable by the effects of their gravity on the motion of

8080-458: 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 . Mercury has the most eccentric orbit of all the planets in the Solar System; its eccentricity is 0.21 with its distance from the Sun ranging from 46,000,000 to 70,000,000 km (29,000,000 to 43,000,000 mi). It takes 87.969 Earth days to complete an orbit. The diagram illustrates

8181-450: The resulting ejecta, and ray systems . Larger albedo features correspond to higher reflectivity plains. Mercury has " wrinkle-ridges " (dorsa), Moon-like highlands , mountains (montes), plains (planitiae), escarpments (rupes), and valleys ( valles ). The planet's mantle is chemically heterogeneous, suggesting the planet went through a magma ocean phase early in its history. Crystallization of minerals and convective overturn resulted in

8282-445: 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. The 3:2 resonant tidal locking

8383-756: 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. An unusual feature of Mercury's surface is the numerous compression folds, or rupes , that crisscross the plains. These exist on the Moon, but are much more prominent on Mercury. As Mercury's interior cooled, it contracted and its surface began to deform, creating wrinkle ridges and lobate scarps associated with thrust faults . The scarps can reach lengths of 1,000 km (620 mi) and heights of 3 km (1.9 mi). These compressional features can be seen on top of other features, such as craters and smooth plains, indicating they are more recent. Mapping of

8484-452: 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

8585-508: The star remain on the main sequence for at least 0.5–1 Ga sets an upper limit of approximately 2.2–3.4 solar masses, corresponding to a hottest spectral type of A0 - B7V . Such stars can be 100x as bright as the Sun. Tardigrade -like life (due to the UV flux) could potentially survive on planets orbiting stars as hot as B1V, with a mass of 10 M☉, and a temperature of 25,000 K, a main-sequence lifetime of about 20 million years. Non-variability

8686-590: The star system is among the most compact and flattest systems yet discovered . It is the first discovered case of a star system with six transiting planets. All discovered planets are larger than Earth, with the larger ones being about Neptune 's size. Kepler-11 and its planets were discovered by NASA 's Kepler Mission , a mission tasked with discovering planets in transit around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits move in front of their stars from

8787-406: The star while migrating inward through gravitational interactions with a gaseous protoplanetary disk . This second scenario predicts that a substantial fraction of the planets' mass is in H 2 O. Regardless of the formation scenario, the gaseous component of the planets accounts for less than about 20% of their masses but for ≈40 to ≈60% of their radii. In 2014, the dynamical simulation shown what

8888-438: The star. Simulations suggest that the mean mutual inclinations of the planetary orbits are about 1°, meaning the system is probably more coplanar (flatter) than the Solar System , where the corresponding figure is 2.3°. The estimated masses of planets b - f fall in the range between those of Earth and Neptune . Their estimated densities, all lower than that of Earth, imply that none of them have an Earth-like composition;

8989-422: The star; this means that all six planets' orbits appear to cross in front of their star as viewed from the Earth's perspective. Their inclinations relative to Earth's line of sight, or how far above or below the plane of sight they are, vary by a little more than a degree. This allows direct measurements of the planets' periods and relative diameters (compared to the host star) by monitoring each planet's transit of

9090-445: The stars, and P-Type (planetary or circumbinary) orbits around the entire binary pair. Eccentric Jupiters may also disrupt the orbits of planets in habitable zones. Metallicity of at least 40% solar ([Fe/H] = −0.4) is required for the formation of an Earth-like terrestrial planet. High metallicity strongly correlates to the formation of hot Jupiters , but these are not absolute bars to life, as some gas giants end up orbiting within

9191-514: The study of Mercury. Depressions or fossae are named for works of architecture. Montes are named for the word "hot" in a variety of languages. Plains or planitiae are named for Mercury in various languages. Escarpments or rupēs are named for ships of scientific expeditions. Valleys or valles are named for abandoned cities, towns, or settlements of antiquity. Mercury was heavily bombarded by comets and asteroids during and shortly following its formation 4.6 billion years ago, as well as during

9292-445: 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. 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

9393-406: 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. BepiColombo , which will arrive at Mercury in 2025, will make observations to test these hypotheses. The findings so far would seem to favor the third hypothesis; however, further analysis of

9494-456: The time until the next sunrise after another 88 Earth days. 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

9595-541: The visible planets (much as how Neptune was discovered). The presence of additional gas giant planets is currently excluded up to orbital radius of 30 AU . Solar analog Defining the three categories by their similarity to the Sun reflects the evolution of astronomical observational techniques. Originally, solar-type was the closest that similarity to the Sun could be defined. Later, more precise measurement techniques and improved observatories allowed for greater precision of key details like temperature, enabling

9696-480: The westerly direction on Mercury. 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. For many years it was thought that Mercury was synchronously tidally locked with the Sun, rotating once for each orbit and always keeping

9797-487: Was an evening star or a morning star. By about 350 BC, the ancient Greeks had realized the two stars were one. They knew the planet as Στίλβων Stilbōn , meaning "twinkling", and Ἑρμής Hermēs , for its fleeting motion, a name that is retained in modern Greek ( Ερμής Ermis ). The Romans named the planet after the swift-footed Roman messenger god, Mercury (Latin Mercurius ), whom they equated with

9898-464: 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. 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

9999-520: Was ever found. The observed perihelion precession of Mercury is 5,600 arcseconds (1.5556°) per century relative to Earth, or 574.10 ± 0.65 arcseconds per century relative to the inertial ICRF . Newtonian mechanics, taking into account all the effects from the other planets and including 0.0254 arcseconds per century due to the oblateness of the Sun, predicts a precession of 5,557 arcseconds (1.5436°) per century relative to Earth, or 531.63 ± 0.69 arcseconds per century relative to ICRF. In

10100-472: 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. The center of Hun Kal defines the 20° west meridian. A 1970 International Astronomical Union resolution suggests that longitudes be measured positively in

10201-460: 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. A sidereal day (the period of rotation) lasts about 58.7 Earth days. Simulations indicate that

#647352