A single year lasts only 88 days on Mercury, but thanks again to its slow rotation, a day lasts twice as long! That means that if you could stand on the surface of Mercury, it would take a staggering Earth days for the Sun to rise, set and rise again to the same place in the sky just once!
Mercury is the closest planet to our Sun, but it also has the most eccentric orbit 0. This means that while its average distance semi-major axis from the Sun is 57,, km 35,, mi or 0. Because of this proximity, Mercury has a rapid orbital period, which varies depending on where it is in its orbit.
Naturally, it moves fastest when it is at its closest to the Sun, and slowest when it is farthest. On average, its orbital velocity is Astronomers used to suspect that Mercury was tidally locked to the Sun, meaning that it always showed the same face to the Sun — similar to how the Moon is tidally locked to the Earth. A very nearly uniform rotational motion of This rotational motion could have the axis of minimum moments of inertia nearly aligned with the Sun—Mercury radius vector at every perihelion passage.
The axial asymmetry of Mercury's inertia ellipsoid may result in a torque that counterbalances the tidal torque, giving a stable motion with this orientation and with a period two-thirds of the orbital period.
It would therefore be possible for Mercury to have a higher permanent rigidity than that permitted by Peale and Gold. Peale, S. Article Google Scholar. Pettingill, G. Download references. Smithsonian Astrophysical Observatory, Cambridge, Massachusetts.
You can also search for this author in PubMed Google Scholar. Reprints and Permissions. Rotational Period of the Planet Mercury. Nature , Download citation. If Earth were the size of a nickel, Mercury would be about as big as a blueberry. From an average distance of 36 million miles 58 million kilometers , Mercury is 0.
One astronomical unit abbreviated as AU , is the distance from the Sun to Earth. From this distance, it takes sunlight 3. Mercury's highly eccentric, egg-shaped orbit takes the planet as close as 29 million miles 47 million kilometers and as far as 43 million miles 70 million kilometers from the Sun.
It speeds around the Sun every 88 days, traveling through space at nearly 29 miles 47 kilometers per second, faster than any other planet. Mercury spins slowly on its axis and completes one rotation every 59 Earth days. But when Mercury is moving fastest in its elliptical orbit around the Sun and it is closest to the Sun , each rotation is not accompanied by sunrise and sunset like it is on most other planets.
The morning Sun appears to rise briefly, set, and rise again from some parts of the planet's surface. The same thing happens in reverse at sunset for other parts of the surface. One Mercury solar day one full day-night cycle equals Earth days — just over two years on Mercury.
Mercury's axis of rotation is tilted just 2 degrees with respect to the plane of its orbit around the Sun. That means it spins nearly perfectly upright and so does not experience seasons as many other planets do. Mercury formed about 4. Like its fellow terrestrial planets, Mercury has a central core, a rocky mantle, and a solid crust.
Mercury is the second densest planet, after Earth. It has a large metallic core with a radius of about 1, miles 2, kilometers , about 85 percent of the planet's radius. There is 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 kilometers miles thick.
Mercury's surface resembles that of Earth's Moon, scarred by many impact craters resulting from collisions with meteoroids and comets. Craters and features on Mercury are named after famous deceased artists, musicians, or authors, including children's author Dr. Seuss and dance pioneer Alvin Ailey. Very large impact basins, including Caloris miles or 1, kilometers in diameter and Rachmaninoff miles, or kilometers 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 terrain, there are also cliffs, 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.
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