The surface of Mercury, in short, resembles the Moon. Vast plains and many craters indicate that geological activity on the planet ceased billions of years ago.
Surface pattern
The surface of Mercury (photo is given later in the article), taken by the probes "Mariner-10" and "Messenger", outwardly looked like the moon. The planet is largely dotted with craters of various sizes. The smallest visible in the most detailed photographs of the Mariner are several hundred meters in diameter. The space between large craters is relatively flat and consists of plains. It is similar to the surface of the moon, but takes up much more space. Similar regions surround Mercury's most prominent impact structure, formed as a result of a collision, the Zhara Plain Basin (Caloris Planitia). When meeting with Mariner 10, only half of it was illuminated, and it was completely opened by Messenger during its first flyby of the planet in January 2008.
Craters
The most common landforms on the planet are craters. They cover a lot of the surface. Mercury. The planet (pictured below) looks like the Moon at first glance, but upon closer examination, they reveal interesting differences.
Mercury's gravity is more than twice that of the moon, partly due to the high density of its huge core of iron and sulfur. The strong gravity tends to keep the material ejected from the crater close to the impact site. Compared to the Moon, it fell at only 65% of the lunar distance. This may be one of the factors that contributed to the formation of secondary craters on the planet, formed under the influence of ejected material, in contrast to the primary ones that arose directly from a collision with an asteroid or comet. The higher gravity means that the complex shapes and structures characteristic of large craters - central peaks, steep slopes and a flat base - are observed on Mercury at smaller craters (minimum diameter about 10 km) than on the Moon (about 19 km). Structures smaller than these dimensions have simple cup-like outlines. Mercury's craters are different from those on Mars, although the two planets have comparable gravity. Fresh craters on the first are usually deeper than comparable formations on the second. This may be due to the low volatile matter content of Mercury's crust or higher impact velocities (because the speed of an object in solar orbit increases as it approaches the Sun).
Craters larger than 100 km in diameter begin to approach the oval shape characteristic of suchlarge formations. These structures - polycyclic basins - are 300 km or more in size and are the result of the most powerful collisions. Several dozen of them were found on the photographed part of the planet. Messenger images and laser altimetry have contributed greatly to understanding these residual scars from the early asteroid bombardments of Mercury.
Zhara Plain
This impact structure extends for 1550 km. When it was first discovered by Mariner 10, it was believed that its size was much smaller. The interior of the object is smooth plains covered with folded and broken concentric circles. The largest ranges stretch for several hundred kilometers in length, about 3 km in width and less than 300 meters in height. More than 200 breaks, comparable in size to the edges, emanate from the center of the plain; many of them are depressions bounded by furrows (grabens). Where grabens intersect with ridges, they tend to pass through them, indicating their later formation.
Surface types
Zhara Plain is surrounded by two types of terrain - its edge and relief formed by discarded rock. The edge is a ring of irregular mountain blocks reaching 3 km in height, which are the highest mountains found on the planet, with relatively steep slopes towards the center. The second much smaller ring is 100-150 km away from the first one. Behind the outer slopes there is a zone of linearradial ridges and valleys, partially filled with plains, some of which are dotted with numerous hillocks and hills several hundred meters high. The origin of the formations that make up the wide rings around the Zhara basin is controversial. Some of the plains on the Moon were formed mainly as a result of the interaction of ejecta with pre-existing surface topography, and this may also be true for Mercury. But the results of Messenger suggest that volcanic activity played a significant role in their formation. Not only are there few craters compared to the Zhara Basin, indicating a long period of plains formation, but they have other features more clearly associated with volcanism than could be seen in the Mariner 10 images. Critical evidence of volcanism has come from Messenger images showing volcanic vents, many along the outer edge of the Zhara Plain.
Radithlady Crater
Caloris is one of the youngest large polycyclic plains, at least in the explored part of Mercury. It probably formed at the same time as the last giant structure on the Moon, about 3.9 billion years ago. The Messenger images revealed another much smaller impact crater with a visible inner ring that may have formed much later, called the Raditlady Basin.
Strange antipode
On the other side of the planet, exactly 180° opposite the Zhara Plain, is locateda patch of oddly distorted terrain. Scientists interpret this fact by speaking of their simultaneous formation by focusing seismic waves from events that affected the antipodal surface of Mercury. The hilly and lined terrain is a vast zone of uplands, which are hilly polygons 5-10 km wide and up to 1.5 km high. The craters that existed before were turned into hills and cracks by seismic processes, as a result of which this relief was formed. Some of them had a flat bottom, but then its shape changed, which indicates their later filling.
Plains
The Plain is the relatively flat or gently undulating surface of Mercury, Venus, Earth and Mars, which is found everywhere on these planets. It is a "canvas" on which the landscape developed. The plains are evidence of the process of breaking down the rough terrain and creating a flattened space.
There are at least three ways of "polishing" that probably flattened the surface of Mercury.
One of the ways - increasing the temperature - reduces the strength of the bark and its ability to hold high relief. Over millions of years, the mountains "sink", the bottom of the craters will rise and the surface of Mercury will level out.
The second method involves the movement of rocks towards lower areas of the terrain under the influence of gravity. Over time, the rock accumulates in the lowlands and fills the higher levelsas its volume increases. this is how lava flows from the bowels of the planet behave.
The third way is to hit fragments of rocks on the surface of Mercury from above, which ultimately leads to the alignment of the rough terrain. Crater ejections and volcanic ash are examples of this mechanism.
Volcanic activity
Some evidence in favor of the hypothesis of the influence of volcanic activity on the formation of many of the plains surrounding the Zhara basin has already been presented. Other relatively young plains on Mercury, particularly visible in regions lit at low angle during the first flyby of the Messenger, show characteristic features of volcanism. For example, several old craters were filled to the brim with lava flows, similar to the same formations on the Moon and Mars. However, the widespread plains on Mercury are more difficult to assess. Since they are older, it is clear that volcanoes and other volcanic formations may have eroded or otherwise collapsed, making them difficult to explain. Understanding these old plains is important as they are likely responsible for the disappearance of more of the 10–30 km diameter craters compared to the Moon.
Escarps
Hundreds of jagged ledges are the most important landforms of Mercury, which allow us to get an idea of the internal structure of the planet. The length of these rocks varies from tens to more than thousands of kilometers, and the height varies from 100 m to 3 km. If aviewed from above, their edges appear rounded or jagged. It is clear that this is the result of crack formation, when part of the soil rose and lay on the surrounding area. On the Earth, such structures are limited in volume and arise under local horizontal compression in the Earth's crust. But the entire investigated surface of Mercury is covered with scarps, which means that the planet's crust has decreased in the past. From the number and geometry of scarps, it follows that the planet has decreased in diameter by 3 km.
Furthermore, shrinkage must have continued until relatively recently in geologic history, as some scarps have altered the shape of well-preserved (and therefore relatively young) impact craters. The slowdown of the initially high speed of the planet's rotation by tidal forces produced a compression in the equatorial latitudes of Mercury. The globally distributed scarps, however, suggest a different explanation: late mantle cooling, possibly combined with the solidification of part of the once completely molten core, led to core compression and deformation of the cold crust. The shrinking of Mercury's size as its mantle cooled should have resulted in more longitudinal structures than can be seen, suggesting that the contraction process is incomplete.
Mercury's surface: what is it made of?
Scientists tried to figure out the composition of the planet by studying sunlight reflected from different parts of it. One of the differences between Mercury and the Moon, besides the former being slightly darker, is that the spectrumits surface brightness is less. For example, the seas of the Earth's satellite - smooth spaces visible to the naked eye as large dark spots - are much darker than the highlands dotted with craters, and the plains of Mercury are only slightly darker. The color differences on the planet are less pronounced, although the Messenger images taken with a set of color filters showed small very colorful areas associated with the vents of volcanoes. These features, plus the relatively inconspicuous visible and near-infrared spectrum of reflected sunlight, suggest that Mercury's surface is composed of iron- and titanium-poor, darker-colored silicate minerals than the lunar seas. In particular, the planet's rocks may be low in iron oxides (FeO), leading to the assumption that it was formed under much more reducing conditions (i.e. lack of oxygen) than other terrestrial members.
Problems of distance research
It is very difficult to determine the composition of the planet by remote sensing of sunlight and the spectrum of thermal radiation that reflects the surface of Mercury. The planet heats up strongly, which changes the optical properties of mineral particles and complicates direct interpretation. However, the Messenger was equipped with several instruments that were not on board the Mariner 10, which measured the chemical and mineral composition directly. These instruments required a long period of observation while the ship remained close to Mercury, so concrete results after the first threeThere were no short flights. Only during the orbital mission of the Messenger did enough new information about the composition of the planet's surface appear.
