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Mar 28, 2014 · Once you spot Mercury, you may wonder why it has a reputation for being elusive. It is, after all, one of the brightest objects in the sky. Unfortunately, this bright light never climbs high.
Apr 16, 2024 · The planet’s extreme density comes from the fact that it has a large iron core that makes up about 60 percent of the planet’s volume. In contrast, Earth’s core by volume is only...
- Overview
- Mercurial origins
- Missions to Mercury
- Related: Vintage NASA Photos
Learn more about the innermost planet in our solar system.
Named for the fleet-footed Roman messenger god, Mercury is the closest planet to the sun, zipping around our parent star at an average of 36 million miles away. However, Mercury’s orbit is not a perfect circle. The planet can pass as close as 29 million miles and as far away as 43 million miles.
Living up to its name, Mercury is the fastest planet in the solar system, speeding along at about 29 miles per second and completing each orbit around the sun in just 88 Earth days. Mercury is also the smallest planet in the solar system, measuring just 3,032 miles wide at its equator. That makes it only slightly larger than Earth’s moon.
Because Mercury is so small and so close to the sun, it is the most elusive of the five planets that are visible to the naked eye. You can only catch Mercury at dawn and dusk, and it usually does not rise far above the horizon. But that’s not the only time the tiny planet makes an appearance. Because of its position in the solar system, Mercury passes between Earth and the sun 13 times each century in an event known as a transit. During a transit of Mercury, observers on Earth can see the planet in silhouette as it seems to sweep across the sun’s disk.
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Since ancient times, people observing the heavens have noticed that the naked-eye planets sometimes appear to move backward, briefly shifting from their usual eastward motion to a westward path across the sky. This retrograde motion is an illusion created when one planet moves faster in its orbit than another, so that it catches up to and passes the slower world. For observers on Earth, Mercury is in retrograde about three to four times a year.
Like the other planets in the solar system, Mercury was born about 4.5 billion years ago, condensing from the swirling ring of dust and gas left over from the sun’s formation. Mercury became what’s known as a terrestrial planet, with a dense metallic core, a rocky mantle, and a solid crust. However, the small planet cooled very quickly, contracting enough within the first billion or so years to prevent magma from escaping through the outer crust and ending geologic activity such as volcanism on the surface.
Despite its proximity to our star, Mercury is not the hottest planet in the solar system. With no atmosphere to trap heat, surface temperatures on Mercury can swing from 800 degrees Fahrenheit during the day to -290 degrees Fahrenheit at night. Mercury may even have reservoirs of ice sitting deep inside permanently shadowed craters at its poles. By contrast, the surface of hazy Venus sits at a sweltering 880 degrees Fahrenheit year-round, making it the hottest planet in our solar system.
Lack of an atmosphere also means Mercury’s surface is pockmarked by numerous impact craters, since incoming meteors don’t encounter any friction that would cause them to burn up. Seen via telescopes and spacecraft, Mercury looks like a battered world covered in overlapping basins, soaring cliffs, and occasional smooth plains.
Bright lines called crater rays also crisscross the surface where impacts crushed the rock and kicked up reflective debris. One of the most notable features on Mercury is Caloris Basin, an impact crater about 960 miles wide that formed early in the planet’s history. Mercury has no rings, no moons, and a relatively weak magnetic field.
NASA’s Mariner 10 was the first spacecraft to visit Mercury, conducting a series of three flybys in 1974 and 1975. During this mission, Mariner 10 photographed about 45 percent of the planet’s surface.
A NASA mission called MErcury Surface, Space ENvironment, Geochemistry, and Ranging (MESSENGER) became the first probe to orbit Mercury in March 2011. It investigated the planet's composition, the structure of its core, and its magnetic field, in addition to capturing global images of the surface in multiple wavelengths. The mission ended with a planned impact on Mercury's surface in April 2015.
In 2018, the European Space Agency is set to launch the BepiColombo mission, which will use two orbiters to further study the innermost planet inside and out.
SOURCES
· NASA Science: Mercury
· NASA Messenger Mission to Mercury
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This 1946 image of Earth was the first photograph taken in space.
This 1946 image of Earth was the first photograph taken in space.
Photograph by Clyde Holliday, courtesy Bloomsbury Auctions
This article was updated on October 19, 2018.
- Victoria Jaggard
- 3 min
May 19, 2024 · Its closeness to the Sun and its smallness make it the most elusive of the planets visible to the unaided eye. Because its rising or setting is always within about two hours of the Sun’s, it is never observable when the sky is fully dark. Mercury is designated by the symbol ☿.
- Clark R. Chapman
- Mercury has a radius of about 2,440 km, and its surface area is 74,797,000 km2. Its mass is 3.30 × 1023 kg. Mercury is the smallest major planet in...
- Mercury is the smallest planet in the solar system, and it is also the planet closest to the Sun, making it the most difficult of the planets to se...
- Mercury's average orbital distance from the Sun is 58 million km (36 million miles) and it has the shortest year (a revolution period of 88 days)....
- Two locations on Mercury’s equator are called hot poles, and surface temperatures there can exceed 700 kelvins (K; 800 °F, 430 °C). Surface tempera...
- Ganymede, a moon of Jupiter, and Titan, a moon of Saturn, are both larger than Mercury, the smallest major planet.
Mercury Facts. The smallest planet in our solar system and nearest to the Sun, Mercury is only slightly larger than Earth's Moon. From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as seven times brighter.
Mercury: Exploration. Because Mercury is so close to the Sun, it is hard to directly observe from Earth except during dawn or twilight when the Sun's brightness doesn't outshine little Mercury. The first spacecraft to visit Mercury was NASA's Mariner 10, which imaged about 45% of the surface. NASA's MESSENGER spacecraft flew by Mercury three ...
May 15, 2022 · Mercury's searing and freezing temperatures, as well as its abundance of solar radiation, are likely too extreme for any living organisms to handle, according to NASA.
