Mercury

(TFS) - Mercury is a telluric planet. The closest planet to the sun and its observation is very difficult because of this situation. We know it a little more thanks to the probe Mariner 10, sent by the Americans and which flew over it in 1974. Its surface is rich in craters. Scientists have given artists names to all these craters, like Beethoven, Rabelais, Matisse, Renoir, Hugo, etc.

Planet Profile

orbit: 57,910,000 km from Sun

diameter: 4,880 km

mass: 3.30e23 kg

Since it is closer to the Sun than the Earth, the illumination of Mercury's disk varies when viewed with a telescope from our perspective. Galileo's telescope was too small to see Mercury's phases but he did see the phases of Venus.

Mercury has been now been visited by two spacecraft, Mariner 10 and MESSENGER. Marriner 10 flew by three times in 1974 and 1975. Only 45% of the surface was mapped (and, unfortunately, it is too close to the Sun to be safely imaged by HST). MESSENGER was launched by NASA in 2004 and has been in orbit Mercury since 2011. Its first flyby in Jan 2008 provided new high quality images of some of the terrain not seen by Mariner 10. Since then Messenger has taken over 250,000 photographs coving the entire planet. Global Mosaics.

The mission has provided support for the hypothesis that water ice and other volatiles do exist in the polar regions in permanent shadow.

Nasa's Discovery of ice on Mercury

Until 1962 it was thought that Mercury's "day" was the same length as its "year" so as to keep that same face to the Sun much as the Moon does to the Earth. However, this was shown to be false in 1965 by doppler radar observations. It is now known that Mercury rotates three times in two of its years. Mercury is the only body in the solar system known to have an orbital/rotational resonance with a ratio other than 1:1 (though many have no resonances at all).

Temperature variations on Mercury are the most extreme in the solar system ranging from 90 K to 700 K. The temperature on Venus is slightly hotter but very stable.

Composition & Atmosphere

Mercury Close up

Mercury’s craters are in many ways similar to the Moon: its surface is heavily cratered and very old; it has no plate tectonics.

 On the other hand, Mercury is much denser than the Moon (5.43 gm/cm3 vs 3.34). Mercury is the second densest major body in the solar system, after Earth. Actually Earth's density is due in part to gravitational compression; if not for this, Mercury would be denser than Earth. This indicates that Mercury's dense iron core is relatively larger than Earth's, probably comprising the majority of the planet. Mercury therefore has only a relatively thin silicate mantle and crust.

Mercury's interior is dominated by a large iron core whose radius is 1800 to 1900 km.. Measurements from the Messenger spacecraft show Mercury’s magnetic field is approximately three times stronger in the northern hemisphere than the southern hemisphere and has led to breakthrough research.

Mercury actually has a very thin atmosphere consisting of atoms blasted off its surface by the solar wind. Because Mercury is so hot, these atoms quickly escape into space. Thus in contrast to the Earth and Venus whose atmospheres are stable, Mercury's atmosphere is constantly being replenished.

This planet is located 58 million kilometers from the sun and, as it slowly turns on itself, there are large temperature variations between illuminated and shaded areas (430 ° C to -180 ° C). Mercury has no atmosphere to protect itself; As a result, it is covered with a thick layer of small debris that Venus has crashed into it for billions of years.

Southwest Mercury ; The surface of Mercury exhibits enormous cliffs, some up to hundreds of kilometers in length and as much as three kilometers high. 

Some cut through the rings of craters (huge volcanic holes) and other features in such a way as to indicate that they were formed by compression. It is estimated that the surface area of Mercury shrank by about 0.1%

In addition to the heavily cratered terrain, Mercury also has regions of relatively smooth plains. Some may be the result of ancient volcanic activity.

A re-analysis of the Mariner data provides some preliminary evidence of recent volcanism on Mercury. But more data will be needed for confirmation.

Amazingly, radar observations of Mercury's north pole (a region not mapped by Mariner 10) show evidence of water ice in the protected shadows of some craters.

Water ice on Mercur's craters

Mercury has a small magnetic field whose strength is about 1% of Earth's.
Mercury has no known satellites.

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source: http://nineplanets.org/mercury.html