Mariner 10
Mariner 10 was an American robotic
Robotic spacecraft
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...

 space probe
Space probe
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...

 launched by NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 on November 3, 1973, to fly by the planets Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

 and Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

. It was launched approximately two years after Mariner 9
Mariner 9
Mariner 9 was a NASA space orbiter that helped in the exploration of Mars and was part of the Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 from Cape Canaveral Air Force Station and reached the planet on November 13 of the same year, becoming the first spacecraft to orbit...

 and was the last spacecraft in the Mariner program
Mariner program
The Mariner program was a program conducted by the American space agency NASA that launched a series of robotic interplanetary probes designed to investigate Mars, Venus and Mercury from 1963 to 1973...

 (Mariner 11 and 12 were allocated to the Voyager program
Voyager program
The Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...

 and redesignated Voyager 1
Voyager 1
The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...

 and Voyager 2
Voyager 2
The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...

). The mission objectives were to measure Mercury's environment, atmosphere, surface, and body characteristics and to make similar investigations of Venus. Secondary objectives were to perform experiments in the interplanetary medium
Interplanetary medium
The interplanetary medium is the material which fills the solar system and through which all the larger solar system bodies such as planets, asteroids and comets move.-Composition and physical characteristics:...

 and to obtain experience with a dual-planet gravity assist mission.

Design and trajectory

Mariner 10 was the first spacecraft to make use of an interplanetary gravitational slingshot
Gravitational slingshot
In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense...

 maneuver, using Venus to bend its flight path and bring its perihelion down to the level of Mercury's orbit. This maneuver, inspired by the orbital mechanics calculations of the Italian scientist Giuseppe Colombo
Giuseppe Colombo
Giuseppe Colombo , better known by his nickname Bepi Colombo, was an Italian scientist, mathematician and engineer at the University of Padua, Italy Giuseppe Colombo (Padua, October 2, 1920 – Padua, February 20, 1984), better known by his nickname Bepi Colombo, was an Italian scientist,...

, put the spacecraft into an orbit that repeatedly brought it back to Mercury. Mariner 10 used the solar radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...

 on its solar panel
Photovoltaic module
A solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...

s and its high-gain antenna as a means of attitude control during flight, the first spacecraft to use active solar pressure control.


Mariner 10 instruments included:
  1. Twin telescope/cameras with digital tape recorder
  2. Ultraviolet spectrometer
    A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...

  3. Infrared radiometer
    A radiometer is a device for measuring the radiant flux of electromagnetic radiation. Generally, the term radiometer denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength....

  4. Solar plasma
    Plasma (physics)
    In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

  5. Charged particles
  6. Magnetic fields
  7. Radio occultation
    Radio occultation
    Radio occultation is a remote sensing technique used for measuring the physical properties of a planetary atmosphere. It relies on the detection of a change in a radio signal as it passes through the planet's atmosphere i.e. as it is occulted by the atmosphere. When electromagnetic radiation...

  8. Celestial mechanics
    Celestial mechanics
    Celestial mechanics is the branch of astronomy that deals with the motions of celestial objects. The field applies principles of physics, historically classical mechanics, to astronomical objects such as stars and planets to produce ephemeris data. Orbital mechanics is a subfield which focuses on...

The imaging system, the Television Photography Experiment, consisted of two 15 cm (5.9″) Cassegrain
Cassegrain reflector
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas....

 telescopes feeding vidicon tubes. The main telescope could be bypassed to a smaller wide angle optic, but using the same tube. It had a 8-position filter wheel, with one position occupied by a mirror for the wide-angle bypass. They system returned about 7000 photographs of Mercury and Venus during Mariner 10's flybys.

Departing the Earth–Moon system

During its first week of flight, Mariner 10 tested its camera system by returning five photographic mosaics
Panoramic photography
Panoramic photography is a technique of photography, using specialized equipment or software, that captures images with elongated fields of view. It is sometimes known as wide format photography. The term has also been applied to a photograph that is cropped to a relatively wide aspect ratio...

 of Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 and six of the Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

. It also obtained photographs of the north polar region of the moon where prior coverage was poor. These provided a basis for cartographers to update lunar maps and improve the lunar control net
Selenographic coordinates
Selenographic coordinates are used to refer to locations on the surface of Earth's moon. Any position on the lunar surface can be referenced by specifying two numerical values, which are comparable to the latitude and longitude of Earth...


Cruise to Venus

A trajectory correction maneuver was made on November 13, 1973. Immediately afterwards, the star-tracker locked onto a bright flake of paint which had come off the spacecraft and lost tracking on the guide star Canopus
Canopus |Alpha]] Carinae) is the brightest star in the southern constellation of Carina and Argo Navis, and the second brightest star in the night-time sky, after Sirius. Canopus's visual magnitude is −0.72, and it has an absolute magnitude of −5.53.Canopus is a supergiant of spectral...

. An automated safety protocol recovered Canopus, but the problem of flaking paint recurred throughout the mission. The on-board computer also experienced unscheduled resets occasionally, which necessitated reconfiguring the clock sequence and subsystems. Periodic problems with the high-gain antenna also occurred during the cruise. In January 1974, Mariner 10 made ultraviolet observations of Comet Kohoutek
Comet Kohoutek
Comet Kohoutek, formally designated C/1973 E1, 1973 XII, and 1973f, was first sighted on 7 March 1973 by Czech astronomer Luboš Kohoutek. It attained perihelion on 28 December that same year....

. Another mid-course correction was made on January 21, 1974.

Venus flyby

The spacecraft passed Venus on February 5, 1974, the closest approach being 5,768 km at 17:01 UT. Using a near-ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 filter, it photographed the Cytherean
Cytherean is an adjective meaning pertaining to Cythera , a small island now part of Greece, southeast of the Peloponnesus. It is also an adjective meaning pertaining to the planet Venus.When planetary scientists began to have a need to discuss Venus in detail, an adjective was needed...

 chevron clouds
Cirrus uncinus cloud
Cirrus uncinus is a type of cirrus cloud. The name cirrus uncinus is derived from Latin, meaning "curly hooks". Also known as mares' tails, these clouds are generally sparse in the sky, and very thin....

 and performed other atmospheric studies. It was discovered that extensive cloud detail could be seen through Mariner's ultraviolet camera filters. Venus's cloud cover is nearly featureless in visible light. Earth-based ultra-violet observation did reveal some indistinct blotching even before Mariner 10, but the detail seen by Mariner was a surprise to most researchers.

First Mercury flyby

The first Mercury encounter took place at 20:47 UT
Universal Time
Universal Time is a time scale based on the rotation of the Earth. It is a modern continuation of Greenwich Mean Time , i.e., the mean solar time on the Prime Meridian at Greenwich, and GMT is sometimes used loosely as a synonym for UTC...

 on March 29, 1974, at a range of 703 kilometres (436.8 mi), passing on the shadow side.

Second Mercury flyby

After looping once around the Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 while Mercury completed two orbits, Mariner 10 flew by Mercury again on September 21, 1974, at a more distant range of 48069 km (29,868.8 mi) below the southern hemisphere.

Third Mercury flyby

After losing roll control in October 1974, a third and final encounter, the closest to Mercury, took place on March 16, 1975, at a range of 327 km (203.2 mi), passing almost over the north pole.

End of mission

With its maneuvering gas just about exhausted, Mariner 10 started another orbit of the Sun. Engineering tests were continued until March 24, 1975, when final depletion of the nitrogen supply was signaled by the onset of an un-programmed pitch turn. Commands were sent immediately to the spacecraft to turn off its transmitter, and radio signals to Earth ceased.

Mariner 10 is still orbiting the Sun, although its electronics have probably been damaged by the Sun's radiation. Dave Williams of NASA's National Space Science Data Center said in 2005: "[Mariner 10] has not been tracked or spotted from Earth since it stopped transmitting. We can only assume it's still orbiting [The Sun], but the only way it would not be orbiting would be if it had been hit by an asteroid or gravitationally perturbed by a close encounter with a large body, the odds of that happening are extremely small so it is assumed to still be in orbit."


During its flyby of Venus, Mariner 10 discovered evidence of rotating clouds and a very weak magnetic field.

The spacecraft flew past Mercury three times. Owing to the geometry of its orbit – its orbital period was almost exactly twice Mercury's – the same side of Mercury was sunlit each time, so it was only able to map
A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes....

 40–45% of Mercury’s surface, taking over 2,800 photos. It revealed a more or less moon-like surface. It thus contributed enormously to our understanding of the planet, whose surface had not been successfully resolved through telescopic observation. The regions mapped included most or all of the Shakespeare, Beethoven, Kuiper, Michelangelo, Tolstoj, and Discovery quadrangles, half of Bach and Victoria, and small portions of Solitudo Persephones, Liguria, and Borealis.

Mariner 10 also discovered that Mercury has a tenuous atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 consisting primarily of helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

, as well as a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

 and a large iron-rich core
Planetary core
The planetary core consists of the innermost layer of a planet.The core may be composed of solid and liquid layers, while the cores of Mars and Venus are thought to be completely solid as they lack an internally generated magnetic field. In our solar system, core size can range from about 20% to...

Its radiometer readings suggested that Mercury has a night time temperature of −183 °C (−297 °F
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...

) and maximum daytime temperatures of 187 °C (369 °F).

Mariner 10 Commemoration

On February 10, 1975, the US Post Office issued a commemorative stamp
U.S. space exploration history on U.S. stamps
With the advent of unmanned and manned space flight a whole new era of American history had presented itself. Keeping with the tradition of honoring the country's history on the face of U.S. postage stamps, the U.S. Post Office began honoring the various events with its commemorative postage stamp...

 featuring the Mariner 10 space probe. The 10-cent Mariner 10 commemorative stamp was issued on April 4, 1975, at Pasadena, California.

External links

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