24 [125] 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.[125]. [88] 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. [123][124] At greatest western elongation, Mercury rises at its earliest before sunrise, and at greatest eastern elongation, it sets at its latest after sunset.[125]. Mercury is the closest planet to the Sun and due to its proximity it is not easily seen except during twilight. [95] 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 the planet is at aphelion in alternate years, when the apparent motion of the Sun in Mercury's sky is relatively rapid. Venus – Venus’ thick atmosphere makes it the hottest planet in our solar system. [24] A sidereal day (the period of rotation) lasts about 58.7 Earth days. This allows the planet to be found easily, even when using telescopes with 8 cm (3.1 in) apertures. The MESSENGER observations showed the reconnection rate is ten times higher at Mercury, but its proximity to the Sun only accounts for about a third of the reconnection rate observed by MESSENGER. The first part, as the [105] 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 point always at the center. Mercury Closest Approaches to Earth generated with: Davies, M. E., "Surface Coordinates and Cartography of Mercury," Journal of Geophysical Research, Vol. Lack of Doppler measurements at low altitude over the southern hemisphere limited the Planetary Manifestation Activator™- Mercury. [105], 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. Mercury’s temperature range is the most extreme of the solar system’s four inner, terrestrial planets, but the planet’s nightside would be even colder if Mercury kept one face perpetually toward the Sun and the other in perpetual darkness. A data set is a collection of related data products, usually products acquired by a particular instrument and processed in a certain way. It takes 87.969 Earth days to complete an orbit. Atoms that are blasted off the surface by the solar wind and micrometeoroid impacts create Mercury's exosphere. Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune; diameter (Earth=1) 0.382 0.949 1 0.532 11.209 9.44 4.007 3.883; diameter (km) 4,878 12,104 12,756 6,787 142,800 120,000 51,118 49,528; mass (Earth=1) 0.055 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, with noticeable eccentricity, like that of Mercury's orbit, the tidal force has a maximum at perihelion and therefore stabilizes resonances, like 3:2, enforcing that the planet points its axis of least inertia roughly at the Sun when passing through perihelion. 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. From the perspective of the warm poles, the Sun is already low on the horizon and about to set when it grows the brightest and performs its brief course reversal. - planetarypy/planetary_test_data [98][99][d], The longitude convention for Mercury puts the zero of longitude at one of the two hottest points on the surface, as described above. [29], Mercury's magnetic field is strong enough to deflect the solar wind around the planet, creating a magnetosphere. [159][160] The theory that Mercury's rotation was synchronous had become widely held, and it was a surprise to astronomers when these radio observations were announced. The Planetary Data System is pleased to announce Release 12 of data collected by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, including raw and calibrated products acquired High-quality gravity field data are significant to refine the physical characterization of Mercury in planetary exploration missions. [79] In 2008, magnesium was discovered by MESSENGER. [127], The Hubble Space Telescope cannot observe Mercury at all, due to safety procedures that prevent its pointing too close to the Sun. [103], 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. ESA’s Mercury Planetary Orbiter (MPO) carries 11 instruments dedicated to the study of Mercury’s surface, interior structure, composition, exosphere, and magnetic field. [138], In ancient China, Mercury was known as "the Hour Star" (Chen-xing 辰星). [70], The icy regions are estimated to contain about 1014–1015 kg of ice,[71] and may be covered by a layer of regolith that inhibits sublimation. An alternate method for viewing Mercury involves observing the planet during daylight hours when conditions are clear, ideally when it is at its greatest elongation. References: MESSENGER Mercury Dual Imaging System (MDIS) Experiment Data Record (EDR) Software Interface Specification (SIS) document, The Johns Hopkins University, APL, V2T, Jun. [153], 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. If Mercury were tidally locked, its dark face would be extremely cold, but measurements of radio emission revealed that it was much hotter than expected. "Rotation" is the turning of a body about an axis that passes through the body, as in "Earth rotates once a day." Planetary data for Mercury *Time required for the planet to return to the same position in the sky relative to the Sun as seen from Earth. "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. [169] A proposed alternative approach would use a solar sail to attain a Mercury-synchronous orbit around the Sun. Therefore, a small crater further west was chosen, called Hun Kal, which provides the exact reference point for measuring longitude. [188], 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. = [24] BERLIN (AP) — A spacecraft bound for Mercury swung by Venus on Thursday, using Earth’s neighbor to adjust its course on the way to the solar system’s smallest and innermost planet. Its average distance from the sun is about 36 million miles (58 million kilometers). planets (planetary systems for planets with natural satellites) were taken from published val-ues derived from spacecraft tracking data. 2 While the suite of sensors are designed to study the rocky, atmosphere-free environment at Mercury, the flyby offered a unique opportunity to collect valuable science data at Venus. [96] Its period of retrograde motion as seen from Earth can vary from 8 to 15 days on either side of inferior conjunction. The planet’s rocky outer shell—its surface crust and underlying mantle—is only some 300 km (200 miles) thick. Mercury is the second densest planet after Earth, with a huge metallic core roughly 2,200 to 2,400 miles (3,600 to 3,800 km) wide, or about 75 percent of the planet's diameter. [129] The cuneiform name used to designate Mercury on the Mul.Apin tablets is transcribed as Udu.Idim.Gu\u4.Ud ("the jumping planet"). Especially, one of the major differences between plasma physics of Mercury and Earth is the non-adiabatic motion of charged particles. Data from the October 2008 flyby of MESSENGER gave researchers a greater appreciation for the jumbled nature of Mercury's surface. Each planet (Mercury, Venus and Mars) has a different orbital period around the sun than Earth does and as a result, interesting patterns emerges. Average distance from the Sun: 0.39 x Earth distance; Orbital period: 87.9 days; Diameter: 0.38 x Earth diameter ; Mass: 0.055 x Earth mass; Rotation period: 58.6 days; Average density: 5.43 g/cm 3; Composition: rocky (including both rock and metal) Average surface temperature: 425°C (day), –175°C (night) Moons: 0 [166] 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.[167]. They provided the first views that resolved surface features on the parts of Mercury that were not imaged in the Mariner 10 mission. Surface temperatures drop to about 90 K (−300 °F, −180 °C) during Mercury’s long nights before sunrise. Hydrogen atoms and helium atoms probably come from the solar wind, diffusing into Mercury's magnetosphere before later escaping back into space. It’s a little bigger than Earth’s Moon. It travels around the sun at a faster speed than any other planet. 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.Because knowledge of Mercury's geology had been based only on the 1975 Mariner 10 flyby and terrestrial observations, it is the least understood of the terrestrial planets. Similar, but much smaller, effects exist for other Solar System bodies: 8.62 arcseconds per century for Venus, 3.84 for Earth, 1.35 for Mars, and 10.05 for 1566 Icarus. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft regularly observed the magnetospheric flanks of Mercury during its orbital phase. The largest of any planet after the Mariner 10, it zips around the Sun because the! Other explanations considered included a slight oblateness of the planet 's surface precession of Mercury’s orbit around the.! 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