Mercury Planets: Mercury. Planet.

Surface conditions and Exosphere Of MerCury :

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 (-93 °C) at the poles, Due to the absence of an atmosphere and a steep temperature gradient between the equator and the poles. At perihelion, the equatorial subsolar point is located at longitude 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.182 On the dark side of the planet, temperatures average 110 K, 110 K (-163 °C) The intensity of sunlight on Mercury's surface ranges between 4.59 and 10.61 times the solar constant (1,370 W·m-2),

Mercury Planets

Designations

Pronunciation : /'m3:rkjuri

Alternative names : Hermes Apollo

Adjectives

- Mercurian /merkjuāriən/

- Mercurial /merkjuarial/

- Hermean/h3:r'mi:en

Symbol :

Orbital characteristics Epoch J2000

Aphelion : 0.466697 AU (69.82 million km)

Perihelion : 0.307499 AU (46.00 million km)

Semi-major axis : 0.387098 AU

(57.91 million km)

Eccentricity : 0.205 630

Orbital period (Sidereal) : 87.9691 d

0.240 846 yr

0.5 Mercury synodic days

Orbital period (synodic) : 115.88 d

Average orbital speed : 47.36 km/s

Mean anomaly : 174.796°

Inclination :  7.005° to ecliptic

3.38° to Sun's equator

6.35° to invariable plane

Longitude of ascending node : 48.331°

Argument of perihelion : 29.124°

Satellites : None

Physical characteristics

Mean radius :  2,439.7 ± 1.0 km

0.3829 Earths

Flattening : 0.0009

Surface area : 7.48 x 107 km2 0.147 Earths

Volume : 6.083 x 1010 km3 0.056 Earths

Mass : 3.3011 x 1023 kg 0.055 Earths

Mean density : 5.427 g/cm³

Surface gravity : 3.7 m/s² (0.38 go)

Moment of inertia factor : 0.346 ± 0.014

Escape velocity : 4.25 km/s

Synodic rotation period : 176 d

Sidereal rotation period : 58.646 d

1 407.5 h

Equatorial rotation velocity : 3.026 m/s

Axial tilt : 2.04' ± 0.08' (To orbit) (0.034°)

North pole right ascension : 18h 44m 2s

281.01°

North pole declination : 61.41°

Albedo : 0.088 (Bond) 0.142 (geom.)

Temperature : 437 K (164 °C) (blackbody temperature)

Surface temp : 0°N, 0°W  85°N, 0°W

Min : -173 °C  -193 °C

Mean : 67 °C  -73 °C

Max : 427 °C  106.85 °C

Apparent magnitude : -2.48 to +7.25

Absolute magnitude (H) : -0.4

Angular diameter : 4.5-13

Atmosphere

Surface pressure : Trace (≤ 0.5 nPa)

Composition by volume : atomic oxygen Sodium magnesium

Atomic hydrogen

Potassium

Calcium

Helium

Trace amounts of iron, aluminium, argon, dinitrogen, dioxygen, carbon dioxide, water vapor, xenon, krypton, and neon.

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. IBS 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. 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 1014-1015 kg of Ice, and may be covered by a layer of regolith that inhibits sublimation. By comparison, the Antarctic ice sheet on Earth has a mass of about 4 x 1018 kg, and Mars's south polar cap contains about 1016 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. (RS)

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 at a surface pressure of less than approximately 0.5 hPa (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 hellum 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 sodiurn 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 H₂O" was a surprise. Because of the quantities of these lons 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 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 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 the planet.

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 Earths. The magnetic-field strength at Mercury's equator is about 300 Like that of Earth, Mercury's magnetic field is dipolar1969 and nearly aligned with the planet's spin axis (10' dipolar tilt, compared to 11° for Earth), Measurements from both 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 the planet's high orbital eccentricity would serve to keep part of the core in the liquid state necessary for this dynamo effect, Graph showing relative strength of Mercury's magnetic field

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 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.198

During its second flyby of the planet on October 6, 2008, MESSENGER discovered that Mercury's magnetic field can be extremely "Teaky". 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, 110% 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.