smooth plains: Apparently young plains on Mercury formed by lava flows at or soon after the formation of the Caloris Basin.
Smooth Plains - Widespread sparsely cratered regions of the surface of Mercury possibly having a volcanic origin ...
Craters and smooth plains
Enceladus has the highest albedo (>0.9) of any body in the solar system. Its surface is dominated by fresh, clean ice.
Two units of smooth plains were also observed by Voyager 2. These plains generally have low relief and have far fewer craters than in the cratered terrains and plains, indicating a relatively young surface age.
In the lunar geologic mapping program, before we had Lunar Orbiter or anything like that, the USGS geologists had identified these smooth plains - light-colored in the highlands - that seemed relatively young.
The surface of Ariel is a mixture of heavily-cratered terrain, smooth plains, and systems of interconnected valleys, called chasmata, which are hundreds of kilometers long and more than 10 km deep.
The smooth plains continued to form, as did craters and smaller impact basins. During this time period, the planet also started to contract, and initial thrust faulting occurred.
Mercury is similar in appearance to the Moon: it is heavily cratered with regions of smooth plains, has no natural satellites and no substantial atmosphere.
Despite the predominance of cratered areas called "uplands," there are also regions of relatively smooth plains. Some may be the result of ancient volcanic activity but others may be made of debris from meteoric impacts.
Smooth plains dominate the foreground and the rim of a newly discovered impact basin can be seen at lower left. At the centre of the bright halo is an irregular depression, which may have formed through volcanic processes.
What process produced Mercury's smooth plains?
No iron has been seen in spectroscopic studies of the planet's surface. That's odd given its presumed large iron core.
Starting about 3.8 billion years ago, the smooth plains were created, possibly from volcanic activity triggered by the earlier meteor impacts and erupting from the large impact basins.
Objects such as volcanoes, lava flows, impact craters, sand dunes, ice caps, faults and large, smooth plains are seen not only on the Earth but other planets as well, as we shall see.
The other terrain consists of smooth plains marked by ridges that are hundreds of miles long. The ridges may form as Jupiter's gravity rips apart the thin ice sheet.
MESSENGER's first flyby has given important information about morphologies and size-frequency distributions of impact craters. The size distribution of craters on smooth plains matches that of lunar craters postdating the Late Heavy Bombardment, ...
Volcanoes appear as bright spots on the smooth plains. Notice the large volcano in the upper right. At the center of this 35 km (22 mi) volcano is a caldera; its western edge appears to be either a debris flow or a lava flow.
Its surface, believed to be dominated by fresh, clean ice, is marked by few craters, smooth plains, and extensive fissures and ridges. Observations indicate that Enceladus has had five distinct geologic periods.
During this time the planet was volcanically active; basins such as the Caloris Basin were filled by magma from within the planet, which produced smooth plains similar to the maria found on the Moon.
 See also: Smooth plain, Orbit, Diameter, Solar, Crater
  
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