Mercury is the smallest of the 8 planets in the solar system. Its orbit has the highest eccentricity, meaning that its orbit is more elliptical than circular. Its farthest point from the sun aphelion is about 1. Mercury also lacks an atmosphere, and, as evidenced by the abundant craters covering its surface, appears to have been geologically inactive for billions of years. Another strange trait of Mercury is that it has a surprisingly high density given its tiny size.
The white arrows in the image indicate the location of part of Discovery Rupes. Between the heavily cratered regions of Mercury's surface lie large expanses of smooth plains. Much of the north polar region of the planet is covered by these plains outlined in yellow which may be volcanic basalt deposits several kilometers thick.
In this image a narrow channel leads into a large basin near the northern plains. Scientists propose that hot lava flowed through this channel, perhaps carving the terrain as it went. Nearby are odd-shaped pits that may be vents through which the lava flowed. The mysterious features named hollows appear on the floor of the crater Tyagaraja. A pit in the center of the crater may be a volcanic vent.
The origin of the hollows is under study, but may relate to the release of gases or to sublimation of material exposed by the crater impact. The crater Tyagaraja is named after a 19th Century composer from India. Craters on Mercury are named after famous artists, authors, and musicians. Earth-based radar data is superimposed on this image of Mercury's north pole.
The yellow areas, where the radar signal is reflected strongly, are thought to be sites where ice is trapped in frigid dark shadows. These features form in relation to "ghost craters," impact craters that are filled and buried by volcanic deposits, but whose outline is revealed by ridges that form over the crater rim. The patterns of the ridges and troughs are caused by extension and contraction due to cooling of very thick lava flows and the planet's interior.
Surface Features of Mercury The surface of Mercury, at first glance, looks very much like that of the Moon, but in fact it is different in several ways. Impact Basins Caloris Basin — Impact Site This is one of the largest impact basins in the solar system and the largest feature on Mercury. Rembrandt — Young Impact Basin The Rembrandt Basin displays a "wheel and spoke" pattern on its central floor that has never been seen on any other planet or moon.
Craters on Mercury range in diameter from small bowl-shaped cavities to multi-ringed impact basins hundreds of kilometers across. The largest known crater is Caloris Basin , which measures 1, km mi in diameter. The impact that created it was so powerful that it caused lava eruptions on the other side of the planet and left a concentric ring over 2 km 1. Overall, about 15 impact basins have been identified on those parts of Mercury that have been surveyed.
Both above and below sea level, there are mountainous features, volcanoes, scarps trenches , canyons, plateaus, and abyssal plains. The remaining portions of the surface are covered by mountains, deserts, plains, plateaus, and other landforms.
However, geological activity ceased billions of years ago and its crust has been solid ever since. Meanwhile, Earth is still geologically active, owning to convection of the mantle.
The lithosphere the crust and upper layer of the mantle is broken into pieces called tectonic plates. When it comes to their atmospheres, Earth and Mercury could not be more different.
Earth has a dense atmosphere composed of five main layers — the Troposphere, the Stratosphere, the Mesosphere, the Thermosphere, and the Exosphere. The hottest temperature ever recorded on Earth was It is believed this exosphere was formed from particles captured from the Sun, volcanic outgassing and debris kicked into orbit by micrometeorite impacts.
Because it lacks a viable atmosphere, Mercury has no way to retain the heat from the Sun. As a result of this and its high eccentricity, the planet experiences far more extreme variations in temperature than Earth does. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below the planetary average.
In this respect, Mercury and Earth have something else in common, which is the presence of water ice in its polar regions. Much like Earth, Mercury has a significant, and apparently global, magnetic field, one which is about 1.
It is likely that this magnetic field is generated by a dynamo effect, in a manner similar to the magnetic field of Earth.
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