What is the surface of Mercury? Features of Mercury

The surface of Mercury, briefly speaking, resembles the Moon. Extensive plains and many craters indicate that geological activity on the planet has ceased billions of years ago.

The nature of the surface

The surface of Mercury (photo is given further in the article), taken with the probes "Mariner 10" and "Messenger", looked like the moon. The planet is largely littered with craters of various sizes. The smallest of the "Mariner" visible in the most detailed photographs are measured several hundred meters in diameter. The space between the large craters is relatively flat and is a plain. It looks like the surface of the moon, but takes up much more space. Similar areas surround the most notable strike structure of Mercury formed as a result of a collision - the basin of the Plain of the Heat (Caloris Planitia). At the meeting with "Mariner 10" only half of it was highlighted, and it was completely opened by the "Messenger" during its first flight past the planet in January 2008.

Craters

The most common structures of the relief of the planet are craters. They largely cover the surface of Mercury. The planet (pictured below) looks like the Moon at first glance, but with closer study, interesting differences are revealed.

Gravity on Mercury is more than twice the lunar one, in part because of the high density of its huge core, consisting of iron and sulfur. A large force of gravity tends to hold the substance thrown from the crater near the place of collision. Compared to the Moon, it fell at a distance of only 65% of the lunar one. This may be one of the factors that contributed to the emergence on the planet of secondary craters formed under the impact of ejected material, in contrast to the primary ones that appeared directly in a collision with an asteroid or comet. Higher gravity means that the complex shapes and structures characteristic of large craters - the central peaks, steep slopes and even ground - on Mercury are observed in smaller craters (the minimum diameter is about 10 km) than on the Moon (about 19 km). Structures smaller than these sizes have simple cup-like outlines. Mercury's craters are different from Martian, although these two planets have comparable gravity. Fresh craters on the first, as a rule, are deeper than the commensurate formations on the second. This may be the result of a low content of volatile substances in the Mercury crust or higher impact velocities (since the object's velocity in the solar orbit increases when approaching the Sun).

Craters more than 100 km in diameter begin to approach the oval form, characteristic for such large formations. These structures - polycyclic basins - have dimensions of 300 km and more and are the result of the most powerful collisions. A few dozen of them were found on the photographed part of the planet. Images of the "Messenger" and laser altimetry made a great contribution to understanding these residual scars from the early asteroid bombardment of Mercury.

Plain of Heat

This shock structure extends for 1550 km. At its initial detection, the Mariner 10 was considered to be much smaller. The inner space of the object is a smooth plain, covered by folded and broken concentric circles. The largest ranges extend a few hundred kilometers in length, about 3 km wide and less than 300 meters in height. More than 200 kinks, comparable in size to the edges, come 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, which indicates their later formation.

Surface types

The Plain of the Heat is surrounded by two types of terrain - its edge and relief formed by the 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 from the first. Behind the outer slopes is a zone of linear radial 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 contradictory. Some of the plains on the Moon were formed mainly as a result of the interaction of the outbursts with the already existing surface relief, and this is probably also true for Mercury. But the results of the "Messenger" give grounds to assume that a significant role in their formation was played by volcanic activity. There are not only few craters there, compared to the pool of Zhara, which indicates a long period of the formation of the plains, but they have other features more clearly associated with volcanism than could be seen in the images obtained by Mariner 10. The decisive evidence of volcanism was obtained with the help of pictures of the "Messenger", showing the vents of volcanoes, many of which are located along the outer edge of the Zhara Plain.

Raditlater Crater

Caloris is one of the youngest large polycyclic plains, at least on 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. Images of the "Messenger" revealed yet another, much smaller impact crater with a visible inner ring, which could have formed much later, called Raditladi's basin.

Strange antipode

On the other side of the planet, exactly 180 ° opposite the Zhara plain, there is a site of a strange distorted terrain. Scientists interpret this fact, referring to their simultaneous formation by focusing seismic waves from events that affected the antipodal surface of Mercury. The hilly and patchy terrain is an extensive zone of hills, which are hilly polygons 5-10 km wide and 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, indicating a later filling.

Plains

The plain is a relatively flat or smoothly wavy surface of Mercury, Venus, Earth and Mars, which is found everywhere on these planets. It is a "canvas" on which the landscape developed. Plains are evidence of the process of breaking rough terrain and creating a smoothed space.

There are at least three methods of "grinding", due to which, probably, the surface of Mercury was leveled.

One way - raising the temperature - reduces the strength of the bark and its ability to maintain high relief. For millions of years the mountains "drown", the bottom of the craters will rise and the surface of Mercury is leveled.

The second method involves moving the rocks towards the lower parts of the terrain under the influence of gravity. Over time, the rock accumulates in the lowlands and fills the higher levels as its volume increases. Thus, lava flows from the interior of the planet.

The third way is to hit fragments of rocks on the surface of Mercury from above, which ultimately leads to a leveling of the rough terrain. An example of this mechanism can be rock outbursts during the formation of craters and volcanic ash.

Volcanic activity

Some evidence that tends to the hypothesis of the effect of volcanic activity on the formation of many plains surrounding the Jara basin has already been cited. Other relatively young plains on Mercury, especially noticeable in regions illuminated at a small angle during the first flyby of the Messenger, show the 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 estimate. Because they are older, it is obvious that volcanoes and other volcanic formations could be eroded or destroyed otherwise, making their explanation difficult. Understanding these old plains is important, as they are probably implicated in the disappearance of most of the craters 10-30 km in diameter, compared to the Moon.

Scammers

The most important forms of the relief of Mercury, which allow one to get an idea of the inner structure of the planet, are hundreds of crenellations. The length of these rocks varies from tens to more than thousands of kilometers, and the height ranges from 100 m to 3 km. If you look from above, then their edges appear round or jagged. It is clear that this is the result of a cracking, when a part of the soil has risen and laid on the adjacent terrain. On Earth, such structures are limited in volume and arise with local horizontal compression in the earth's crust. But the whole investigated surface of Mercury is covered with escarpments, from which it follows that the crust of the planet in the past has decreased. From the number and geometry of the escarp follows that the planet has decreased in diameter by 3 km.

In addition, the shrinkage must have lasted until a relatively recent time in geological history, as some of the escarpas changed the shape of the well-preserved (and therefore relatively young) impact craters. The slowing of the initially high speed of the planet's rotation by tidal forces produced compression in the equatorial latitudes of Mercury. Globally distributed escarpas, however, suggest another explanation: the later cooling of the mantle, possibly in combination with the solidification of part of the once completely molten core, led to compression of the core and deformation of the cold crust. Reducing the size of Mercury while cooling its mantle should lead to more longitudinal structures than can be seen, which indicates the incompleteness of the compression process.

The surface of Mercury: what does it consist of?

Scientists have tried to find out the composition of the planet, exploring the sunlight reflected from its different sites. One of the differences between Mercury and the Moon, in addition to the fact that the first is slightly darker, is that its surface brightness spectrum is smaller. For example, the seas of the Earth's satellite - the smooth spaces visible to the naked eye as large dark spots - are much darker than the crested highlands, and the plains of Mercury are just a little darker. Color differences on the planet are less pronounced, although the images of the "Messenger", made with a set of color filters, showed small very colorful areas associated with the vents of volcanoes. These features, as well as the relatively inexpressive visible and near infrared spectrum of reflected sunlight, suggest that the surface of Mercury consists of less rich in iron and titanium silicate minerals of a darker color, compared to the lunar seas. In particular, in the rocks of the planet there may be a low content of iron oxides (FeO), and this leads to the assumption that it was formed under much more reducing conditions (i.e., with a lack of oxygen) than other representatives of the terrestrial group.

Problems of remote research

It is very difficult to determine the composition of the planet by remote sensing of sunlight and a spectrum of thermal radiation that reflects the surface of Mercury. The planet is highly heated, which changes the optical properties of the mineral particles and complicates direct interpretation. However, the Messenger was equipped with several instruments that were absent on board the Mariner 10, which measured the chemical and mineral composition directly. These devices required a long period of observation, while the ship remained near Mercury, so there were no concrete results after the first three brief spans. Only during the orbital mission of "Messenger" appeared quite new information about the composition of the surface of the planet.