Mercury – the densest planet after the earth

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Mercury is the densest planet after the earth. It has 85% of its metallic core while it is the smallest planet in the solar system.

Mercury is the smallest planet in the Solar system and the closest to the Sun. It takes 87.97 Earth days to complete an orbit around the sun. It is the fastest orbiting the sun amongst all planets in the solar system. It is appropriately named for the swiftest of the ancient Roman gods.

Mercury is the smallest planet with no moons but the second densest planet after the sun due to its massive metallic core. It was given separate names for its appearance as both a morning star and an evening star.

The nearest planet to the sun is Mercury but it doesn’t mean that it would be the hottest planet on the solar. It is even colder than venus due to its excellent atmosphere structure and composition. Venus is the hottest planet in the solar system.


Mercury is the second densest planet, after Earth. It has a large metallic core with a radius of about 1,289 miles (2,074 kilometers), about 85 percent of the planet’s radius. Nasa has evidence that it is partly molten or liquid. Mercury’s outer shell, comparable to Earth’s outer shell (called the mantle and crust), is only about 400 kilometers (250 miles) thick.

Mercury’s Surface

The surface of Mercury, at first glimpse, looks very much like that of the Moon, but in fact, it is different in several ways, slashed by many impact craters resulting from collisions with meteoroids and come back ts. Basins and features on Mercury are named after famous perished artists, musicians, or authors, including children’s author Dr. Seuss and dance pioneer Alvin Ailey.

Very large impact craters, including Caloris (960 miles or 1,550 km in diameter) and Rachmaninoff (190 miles, or 306 km in diameter), were created by asteroid impacts on the planet’s surface early in the solar system’s history. While there are large areas of smooth landscape, there are also mountains, some hundreds of miles long and soaring up to a mile high. They rose as the planet’s interior cooled and contracted over the billions of years since Mercury formed.

Most of Mercury’s surface would appear greyish-brown to the human eye. The bright streaks are called “crater rays.” They are formed when an asteroid or comet strikes the surface.

Temperatures on Mercury are extreme. During the day, temperatures on the surface can reach 800 degrees Fahrenheit (430 degrees Celsius). Because the planet has no atmosphere to retain that heat, nighttime climates on the surface can drop to minus 290 degrees Fahrenheit (minus 180 degrees Celsius).

Mercury may have water ice at its north and south poles inside deep craters, but only in regions in permanent shadows. In those shadows, it could be cold enough to preserve water ice despite the high temperatures on sunlit parts of the planet

Some surface Reviews of mercury

Mercury has some unique landforms, more smooth plains, and surface compositions (low in iron and high in sulfur) that are unlike any measured on the Moon.

Impact Basin – Caloris basin

Caloris basin is one of the largest impact basins in the solar system and the largest feature on Mercury. The Caloris Basin is 1300 kilometers (810 miles) in diameter. After the impact, the basin was flooded by lava. Ridges and fractures formed when the volcanic rock contracted and stretched as it settled under its own weight.

Impact basin of mercury known caloris

Rembrandt — Young Impact Basin

Rembrandt — Young Impact Basin of mercury
Rembrandt – Image courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Smithsonian Institution/Carnegie Institution of Washington

The Rembrandt Basin displays a “wheel and spoke” pattern on its central floor that has never been seen on any other planet or moon. The size of the Rembrandt basin is 715 km (444 miles) wide which is large enough to cover the northeastern United States.


Lobate scarps:- The surface of Mercury has landforms that indicate its crust may have contracted. They are long, sinuous cliffs called lobate scarps. These scarps appear to be the surface expression of thrust faults, where the crust is broken along an inclined plane and pushed upward. What caused Mercury’s crust to shrink? As the interior of the planet cooled it contracted. Gravity then forced the crust to adjust to a smaller interior.

Lobate Scarps surface structure of mercury
Lobate Scarps – Image courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution

Discovery Rupes:- Another expansive lobate scarp on Mercury is Disclosure Rupes. (Rupes is Latin for a cliff.) Disclosure is approximately 550 kilometers (350 miles) long and up to 1.5 kilometers (1 mile) tall. Take note that the dividers and floors of two affected holes have been distorted by the pushed blame that shaped the scarp.

Rules the surface structure of mercury
Rupes – Image courtesy of T.R. Watters, M.S. Robinson, and A.C. Cook


Mercury’s exosphere is composed generally of oxygen, sodium, hydrogen, helium, and potassium. Mercury claims a lean exosphere made up of particles impacted off the surface by the sun-based wind and striking meteoroids. It includes an exceptionally dubious and exceedingly variable atmosphere containing hydrogen, helium, oxygen, sodium, calcium, potassium, and water vapor, with a combined weight level of approximately 10−14 bar (1 NPA).

The Mercurian exosphere comprises an assortment of species starting either from the Sun-powered wind or from the planetary outside. The primary constituents found were nuclear hydrogen (H), helium (He), and nuclear oxygen (O), which were watched by the bright radiation photometer of the Sailor 10 space test in 1974.

The temperature of Mercury’s exosphere depends on species as well as topographical area. For exospheric nuclear hydrogen, the temperature shows up to be around 420 K,  esteem gotten by both Mariner 10 and MESSENGER. The temperature for sodium is much higher, coming to 750–1,500 K on the equator and 1,500–3,500 K at the poles. Some perceptions appear that Mercury is encompassed by a hot crown of calcium iotas with temperatures between 12,000 and 20,000 K.

Magnetosphere of mercury

The magnetic field of mercury is balanced relative to the planet’s equator. Be that as it may Mercury’s attractive field at the surface has fair 1% the quality of Earth’s, it interatomic with the attractive field of the sun based wind to now and then make seriously attractive tornadoes that pipe the quick, hot sun oriented wind plasma down to the surface of the planet. When the particles strike the surface, they thump off impartially charged molecules and send them on a circle tall into the sky.

Orbit and Rotation

The orbit and rotation of mercury:-

  • It takes 59 earth days to complete a rotation but it is still the fastest orbiting planet in the solar system.
  • Mercury takes 87.97 Earth days to complete an orbit around the sun.
  • The average speed of mercury in orbiting the sun is 46.7 kilometers per second.

Mercury’s exceedingly offbeat, egg-shaped circle takes the planet as near as 29 million miles (47 million kilometers) and as distant as 43 million miles (70 million kilometers) from the Sun. It speeds around the Sun every 88 days, traveling through space at about 29 miles (47 kilometers) per second, quicker than any other planet.

Mercury turns gradually on its axis and completes one rotation each 59 Earth days. But when Mercury is moving speediest in its circular orbit around the Sun, each revolution isn’t gon by dawn and dusk like it is on most other planets. The morning sun shows up to rise briefly, set, and rise once more from a few parts of the planet’s surface. One Mercury sun-oriented day (one full day-night cycle) breaks even with 176 Earth days – fair over two years on Mercury.

Size and volume

  • The radius of mercury is 2438 km which is 0.384 times the Earth’s radius.
  • The volume of mercury is 6.083 x 1010 cubic km.
  • The surface area of mercury is 74.8 million km².
  • The mass of mercury is 3.3×1023kg. It is equivalent to 318 times earth masses even 2.5 times of all planets in the solar system.

The radius of mercury is 1,516 miles (2,440 kilometers), and it may be a small more than 1/3 the width of the earth. From a normal separation of 36 million miles (58 million kilometers), Mercury is 0.4 galactic units absent from the Sun. One galactic unit (truncated as AU), is the distance from the Sun to Earth. From this distance, it takes daylight 3.2 minutes to travel from the Sun to Mercury.

FAQ of mercury

Why Mercury is the second densest planet in the solar system after the earth?

Mercury is a metallic planet. It has a massive metallic which is an 85% ratio of this planet. The large proportion of metallic composition makes it denser.

why does mercury spin slowly on its axis?

The rotation of mercury may be affected by the sun’s gravitational force. A unique Oscillation of mercury with a high speed around the sun may slower the rotational speed.

  1. Author/Curator: Dr. David R. Williams Nasa Mercury fact sheet
  2. Overview of mercury by Nasa – Solar system exploration
  3. Surface Review of Mercury by Smithsonian National Air and Space Museum – A surface feature of Mercury

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