Tectonic and Volcanic evidences on Mercury

Formation

Mercury was created around 4.5 billion years ago when gravity drew whirling gas and dust together to form the tiny planet closest to the Sun. Mercury, like its other terrestrial planets, has a solid crust, a rocky mantle, and a central core.

Internal Structure

Mercury, after Earth, is the second most dense planet. The metal core of the planet has a huge metallic radius of around 2.074 km, almost 85% of the radius of the planet. It has been shown to be somewhat molten or fluid. The external shell of Mercury is only approximately 400 kilometers thick (250 miles) and is similar to Earth's external shell (named mantle and crust).

Mercury's comparatively massive nickel-iron core and thin crustal mantle imply a catastrophic collision occurred during the planet's final phases of creation. Most of the planet's original mantle may have been blasted into space by a glancing hit from a massive planetesimal, leaving behind a planet with a comparatively big core.

Surface Features

Mercury's surface appears to be very similar to that of the Moon at first glance, but it differs in several ways. Mercury has some unique landforms, more smooth plains, and surface compositions (low in iron and high in sulphur) that are unlike anything measured on the Moon, according to the MESSENGER spacecraft.

Impact Basins – Caloris Basin

This is the biggest feature on Mercury and one of the largest impact basins in the solar system. Caloris Basin has a diameter of 1300 kilometers (810 miles). In the 1970s, Mariner 10 only photographed half of the basin; however, the MESSENGER mission completed the picture. The basin was inundated by lava after the collision. The volcanic rock constricted and stretched as it settled under its own weight, resulting in ridges and cracks.

Figure 1 Mariner 10 image courtesy of M.S. Robinson. Applied Physics Laboratory / Carnegie Institution in Washington MESSENGER picture via NASA/Johns Hopkins University.

Rembrandt – Young Impact Basin

The center floor of the Rembrandt Basin contains a "wheel and spoke" design that has never been observed on any other planet or moon.

Figure 2 Image courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/ Smithsonian Institution/Carnegie Institution of Washington.

The Rembrandt basin, which is 715 km (444 miles) wide, is huge enough to engulf the whole of the northeastern United States.

Figure 3 Illustration of Rembrandt basin size comparisons to NE United States.

SCARPS

Is mercury a shrinking planet?

Mercury's surface includes formations that suggest the planet's crust has shrunk. Long, sinuous cliffs are known as lobate scarps. These scarps appear to be the surface manifestation of thrust faults, in which the crust is fractured and forced upward along an inclined plane. What caused the shrinkage of Mercury's crust? The planet's interior chilled, and it shrank. The crust was then forced to adapt to a smaller interior by gravity.

Figure 4 Lobate scarps on mercury.

Discovery Rupes

Discovery Rupes is another huge lobate scarp on Mercury. (The Latin word for cliff is rubes.) Discovery stretches over roughly 550 kilometers (350 miles) and rises to a height of 1.5 kilometers (1 mile). Two impact craters' walls and floors have been distorted by the thrust fault that created the scarp.

Figure 5 Discovery Rupes, T.R. Watters, M.S. Robinson, and A.C. Cook contributed to this image.

Digital Elevation Model

How high is discovery Rupes? One method is to combine two pictures to create a stereo (3-D) representation of the feature. The heights (elevations) of all the locations covered by a stereo pair may be computed using a computer, and a digital elevation model can be created. The stereo pair's coverage area is shown in this Mariner 10 pictures, with the digital elevation model color-coded to indicate the highest altitudes in white and the lowest elevations in black. Parts of Discovery Rupes are shown by white arrows in the picture.

Figure 6 Digital elevation model of Discovery Rupes.

Volcanism on Mercury

Three flybys were conducted in 2008–2009 in order to bring the MESSENGER spacecraft into orbit around Mercury. The first MESSENGER flyby of Mercury captured photos of 21% of the surface that Mariner 10 missed, including the Caloris basin's center and western half, as well as sections around the terminator that reveal the nature of smooth and intercrater plains. These new findings aided in the rapid resolution of a number of long-standing issues about the occurrence and type of volcanism on Mercury, as well as the dispersion of volcanic debris. The following observations were interpreted as suggesting the presence of volcanism based on data from the MDIS aboard the MESSENGER mission.

Flowing Lava

Many characteristics discovered by the MESSENGER mission point to the occurrence of volcanism on Mercury in the past. A small river runs into a vast basin in the northern plains in this picture. Hot lava, according to scientists, may have poured down this channel, sculpting the ground as it went. Nearby, there are odd-shaped pits that might have been lava vents.

Figure 7 Mercury lava flows, image courtesy by NASA.

Presence of Volcanic Vents

As seen in figure 8, high-resolution photos indicated the presence of many volcanic vents in the form of irregularly shaped rimless depressions. These were found to be abundant towards the Caloris impact basin's interior margin.

Figure 8 Along the southwest border of the Caloris basin, a central kidney-shaped depression with an annulus of brilliant material regarded as pyroclastic in origin (A) and a sketch map supporting interpretation (B). Adapted from Head et al (2008). Image of the MESSENGER MDIS.

Pyroclastic Eruptions

Bright haloes surrounding several of these vents, which were interpreted as pyroclastic deposits from explosive eruptions.

Flow Margins

Plains unit lobate borders, previously identified in Mariner 10 data, we're better recorded in MESSENGER pictures and were demonstrated to be often unique in shape and color characteristics, confirming the hypothesis that these features represent lava flow unit edges.

Spectral Individuality

The interior of the Caloris basin was found to be filled with plains units that were spectrally distinct from the rim deposits, and a comparison with the lunar Imbrium basin and superposed impact crater stratigraphy revealed that these units are volcanic in origin; however, the detailed differences in the lava flow unit mineralogy that was visible in the Imbrium basin interior was not seen in the Caloris basin interior.

Figure 9 The Imbrium basin on the moon and the Caloris basin on Mercury are compared.

(A) Earth-based telescopic image of the Moon's Imbrium basin from the Consolidated Lunar Atlas. (B) Imbrium basin color-composite Clementine picture (red: 750 nm/415 nm; green: 750 nm/950 nm; blue: 415 nm/750 nm). The arrow points to the crater Archimedes, which erupted after the basin but was later outwardly embayed and internally filled by lava. (C) Caloris basin MESSENGER and MDIS mosaic. (D) False-color MESSENGER MDIS picture of the Caloris basin. Large impact craters in the Caloris inner plains deposits contain blue rims similar to ejecta deposits, whereas smaller craters excavate orange material similar to the smooth plains and irregular rimless depressions along the edges interpreted as pyroclastic vents. These connections support the idea that the plains are volcanic in origin and superposed crater diameters may be utilized to determine the thickness of volcanic plains.

Distant Plains Units

At long distances, some of the smooth plains around the outside of the Caloris basin revealed notable color and morphological variations from the surrounding basin textured ejecta. This significant divergence suggested a volcanic origin rather than the ponded ejecta origin supposed to have produced the lunar Cayley plains at the Apollo 16 landing site.

Stratigraphic Relationships

New high-resolution imaging data of huge new impact craters, as well as their older, more degraded counterparts, revealed a sequence of an embayment of the inner floor and outer ejecta deposits, indicating that the embayment and filling processes were caused by volcanic activity.

Figure 10 On Mercury, new craters and stratigraphic connections reveal the interior and exterior floods caused by volcanic plains. (9.6° N, 125.8° E) Fresh impact crater with main characteristics identified. (B) A degraded 240-km-diameter crater (2° N, 113° E) that has been modified and flooded as a result of subsequent impacts. (C) A rough map depicting the main characteristics. Smooth volcanic plains have resurfaced the crater floor and the outside of the superimposed inner crater. MDIS and MESSENGER images From (Head et al., 2008).

The thickness of Volcanic Deposits

 High-resolution photos showed crater embayment and flooding relationships that suggested normal thicknesses of volcanic plains of several hundreds of meters, and local thicknesses inside impact craters of up to several kilometers.

Evidence of Ice

The presence of water ice in permanently shadowed craters at Mercury's poles has been firmly substantiated by MESSENGER data. This image of Mercury's north pole has Earth-based radar data placed on it. The radar signal is heavily reflected in the yellow spots, which are assumed to be places where ice is trapped in cold dark shadows.

Figure 11 A mosaic of photos from NASA's MESSENGER mission, which orbited Mercury from 2011 to 2015. Inside the craters around Mercury's the North Pole, the image appears to show layers of water ice.

Ridges and Troughs

In MESSENGER images, distinctive ridge and trough systems have been discovered on Mercury. These structures appear in relation to "ghost craters," impact craters that have been filled and covered by volcanic deposits but have their contour visible by ridges that grow above the crater rim. The ridges and troughs are generated by the expansion and contraction of extraordinarily thick lava flows and the planet's interior as they cool.

Mercury is Tectonically Active

Mercury appears to be tectonically active right now. It is the only rocky planet in our solar system, aside from Earth, that is still gently pushing up sections of its crust and changing its surface over time. This implies we can finally compare Earth's active geology to something else.

“It paints a whole new picture of what Mercury's history must have been like, when combined with the tectonic history,” says Thomas Watters, senior scientist at the Smithsonian's Center for Earth and Planetary Studies at the National Air and Space Museum and lead author of a new paper on Mercury's geology. “It brings Mercury extremely near to Earth in terms of sluggish cooling, allowing the outside to stay cool while the inside gets hot.”

Figure 12 The MESSENGER mission returned high-resolution photographs of Mercury's surface, confirming not only tectonic activity (arrows highlight faults and other surface structures), but also that the planet is still geologically active. (NASA/Applied Physics Laboratory at Johns Hopkins).