Mercury (planet) Mercury is gravitationally locked and rotates in a way that is unique in the Solar System. As seen relative to the fixed stars, it rotates exactly three times for every two revolutions[b] it makes around its orbit.[13] As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two years. Because Mercury's orbit lies within Earth's orbit (as does Venus's), it can appear in Earth's sky in the morning or the evening, but not in the middle of the night.
Also, like Venus and the Moon, it displays a complete range of phases as it moves around its orbit relative to Earth. Although Mercury can appear as a very bright object when viewed from Earth, its proximity to the Sun makes it more difficult to see than Venus. Two spacecraft have visited Mercury: Mariner 10 flew by in the 1970s and MESSENGER, launched in 2004, remains in orbit. Internal structure. Mercury. Mercury as Never Seen Before. Mercury as Never Seen Before Date: 6 Oct 2008 The spectacular image shown here is one of the first to be returned from MESSENGER's second flyby of Mercury. The image shows the departing planet taken about 90 minutes after the spacecraft's closest approach. The bright crater just south of the center of the image is Kuiper, identified on images from the Mariner 10 mission in the 1970s.
For most of the terrain east of Kuiper, toward the limb (edge) of the planet, the departing images are the first spacecraft views of that portion of Mercury's surface. A striking characteristic of this newly imaged area is the large pattern of rays that extend from the northern region of Mercury to regions south of Kuiper. This extensive ray system appears to emanate from a relatively young crater newly imaged by MESSENGER, providing a view of the planet distinctly unique from that obtained during MESSENGER's first flyby.
Catalog of Transits of Mercury. A transit is the passage of a planet across the Sun's bright disk. At this time, the planet can be seen as a small black disk slowly moving in front of the Sun. The orbits of Mercury and Venus lie inside Earth's orbit, so they are the only planets which can pass between Earth and Sun to produce a transit. Transits are very rare astronomical events. In the case of Mercury, there are on average thirteen transits each century. A transit of Mercury occurs only if the planet is in inferior conjunction with the Sun (between Earth and Sun) and is also crossing the through Earth's orbital plane (the Ecliptic). During the present period in Earth's history, Mercury's orbit crosses Earth's orbital plane in early May and early November each year.
During the seven century period 1601 CE to 2300 CE1, Earth experiences 94 transits of Mercury across the Sun. All Transits = 94 = 100.0% May (Descending Node2) = 31 = 33.0 % November (Ascending Node3) = 63 = 67.0 % Footnotes Key to Catalog of Transits. Mercury's magnetic field. Strength[edit] Whether the magnetic field changed to any significant degree between the Mariner 10 mission and the MESSENGER mission remains an open question. A 1988 J.E.P. Connerney and N.F. Ness review of the Mariner magnetic data noted eight different papers in which were offered no less than fifteen different mathematical models of the magnetic field derived from spherical harmonic analysis of the two close Mariner 10 flybys, with reported centered magnetic dipole moments ranging from 136 to 350 nT-RM3 (nT is nanoteslas, RM is a Mercury radius of 2436 km).
In addition they pointed out "[e]stimates of the dipole obtained from bow shock and/or magnetopause positions (only) range from approximately 200 nT-RM3 (Russell 1977) to approximately 400 nT-RM3 (Slavin and Holzer 1979b). " Origins[edit] This dynamo is probably weaker than Earth's because it is driven by thermo-compositional convection associated with inner core solidification. Magnetic poles and magnetic measurement[edit] Mercury & Venus The Inner Planets (The Universe 1) part 27 of 60.