Mariner 10 facts for kids

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*Mariner 10*
Spacecraft properties
Mariner 10 flight spare

Mission type	Planetary exploration
Operator	NASA / JPL
Mission duration	1 year, 4 months and 21 days


Spacecraft	Mariner-J
Manufacturer	Jet Propulsion Laboratory
Launch mass	502.9 kilograms (1,109 lb)
Power	820 watts (at Venus encounter)


Start of mission
Launch date	3 November 1973, 05:45:00 (1973-11-03UTC05:45Z) UTC
Rocket	Atlas SLV-3D Centaur-D1A
Launch site	Cape Canaveral, LC-36B


End of mission
Disposal	Decommissioned
Deactivated	24 March 1975 (1975-03-25) 12:21 UTC


Flyby of Venus
Closest approach	5 February 1974
Distance	5,768 kilometers (3,584 mi)
Flyby of Mercury
Closest approach	29 March 1974
Distance	704 kilometers (437 mi)
Flyby of Mercury
Closest approach	21 September 1974
Distance	48,069 kilometers (29,869 mi)
Flyby of Mercury
Closest approach	16 March 1975
Distance	327 kilometers (203 mi)

Mariner program ← Mariner 9

Reprocessed Mariner 10 data was used to create this image of Mercury. The smooth band shows an area that was not photographed.

Imagine a robot explorer zooming through space! That's what Mariner 10 was. This amazing robot was sent by NASA on November 3, 1973. Its main job was to fly past two planets: Mercury and Venus. It made history as the very first spacecraft to visit Mercury. It was also the first to visit more than one planet on a single trip!

Mariner 10 was the last mission in the Mariner program. Its main goals were to study Mercury's surroundings, air, surface, and how it's built. It also did similar studies for Venus. A cool extra goal was to learn about space between planets. It also tested a special trick called a gravity assist. This trick uses a planet's gravity to help a spacecraft change direction and speed.

Exploring Space with Mariner 10

An artist's drawing of the Mariner 10 mission. It used Venus's gravity to change its path. This helped the spacecraft visit Mercury three times.

Mariner 10 was a very clever spacecraft. It was the first mission to use a special trick called a gravity assist. This means it used the gravity of one planet, Venus, to help it reach another planet, Mercury. Venus's gravity bent Mariner 10's path. This made it possible for the spacecraft to repeatedly fly close to Mercury.

The idea for this amazing maneuver came from an Italian scientist named Giuseppe Colombo. He figured out how to use Venus's gravity to set Mariner 10 on a path that would bring it back to Mercury again and again.

Mariner 10 also used sunlight to help steer itself! It used the gentle push of solar radiation on its solar panels and antenna. This helped it stay pointed in the right direction during its long journey. It was the first spacecraft to use this active solar pressure control.

How Mariner 10 Was Built and Traveled

The Mariner 10 spacecraft was built by Boeing. It had a central body shaped like an eight-sided box. This box held all the important electronics. Attached to this central hub were the solar panels, instruments, and antennas.

NASA had a strict budget for Mariner 10, about $98 million. This was the first time a mission had such a firm spending limit. To save money, engineers worked quickly. They designed the spacecraft's parts to be efficient. In the end, the mission even came in slightly under budget!

Keeping the Spacecraft Running

To work properly, Mariner 10 needed to stay pointed correctly. This is called attitude control. It used special sensors to find the Sun and a bright star called Canopus. Three gyroscopes also helped it know its direction. Small nitrogen gas thrusters gently pushed the spacecraft to adjust its aim.

The spacecraft's computer could store some commands, but most instructions came from Mission Control on Earth. Solar panels collected sunlight to make electricity. This power was then changed to the right voltage for all the spacecraft's parts. A nickel–cadmium battery stored extra power, like a backup battery.

Protecting Against the Sun's Heat

Flying close to Mercury was a big challenge. Mercury is very near the Sun. This meant Mariner 10 would face 4.5 times more solar radiation than it did near Earth. The spacecraft needed special protection from the intense heat.

Engineers added thermal blankets and a sunshade to the main body. They used a special material called beta cloth, which is like a super-strong, heat-resistant fabric. But the solar panels, which make electricity, couldn't be covered.

To keep the solar panels cool, they were designed to tilt. This allowed them to change the angle at which they faced the Sun. This clever design helped keep the panels from overheating while still making power.

Fueling Up for the Journey

Performing the gravity assist at Venus perfectly was very important. If Mariner 10's path was off by more than 200 kilometers (about 124 miles) near Venus, it wouldn't reach Mercury correctly. To make sure it could make all the necessary adjustments, Mariner 10 carried extra hydrazine fuel. It also had more nitrogen gas for its thrusters than previous missions. These extra supplies were key to making the second and third Mercury flybys possible.

NASA usually launched two identical probes for important missions, just in case one failed. But because of the strict budget, Mariner 10 flew alone. A backup spacecraft was built, but it was never launched. It is now on display at the Smithsonian museum.

What Mariner 10 Carried to Space

An illustration showing the instruments of Mariner 10

Mariner 10 carried seven special tools, called instruments, to study Venus and Mercury. These tools were chosen to gather as much information as possible without going over budget. Together, these instruments cost about $12.6 million.

Taking Pictures of Planets

A close-up view of one of Mariner 10's television cameras.

The main camera system was called the Television Photography Experiment. It had two telescopes that took pictures. It could take a picture every 42 seconds. Each picture was very detailed, with 832 by 700 pixels. The cameras took about 7,000 photos of Venus and Mercury.

Early in the mission, the camera heaters didn't work. This was a problem because the cameras were placed on the cold, shaded side of the spacecraft. Engineers found a way to keep them warm by running them continuously. Luckily, the heaters started working later in the mission.

Measuring Temperatures

The infrared radiometer was like a super-thermometer. It measured the infrared radiation coming from Venus's atmosphere and Mercury's surface. This helped scientists figure out how hot or cold these places were. It could measure temperatures from a very cold -193°C (-315°F) to a very hot 427°C (800°F).

Looking for Atmospheres

Two ultraviolet spectrometers helped search for atmospheres. One looked for ultraviolet light being absorbed by gases around Mercury. This would show if the planet had an atmosphere. The other looked for UV light given off by atoms like hydrogen and helium. This helped study the air around Earth, Venus, and Mercury.

Studying Space Particles

The Mariner 10 flight spare, a backup spacecraft.

The plasma detectors studied the plasma (ionized gases) in the solar wind. This helped scientists understand how the planets affected these fast-moving particles. One part of the detector didn't open properly after launch, but the other part still collected important data. Mariner 10 was the first mission to study the solar wind from inside Venus's orbit.

The charged particle telescopes looked for high-energy electrons and atomic particles. This helped scientists understand how cosmic radiation interacts with the space around planets. It also helped confirm if Mercury had a magnetic field.

Understanding Planet Gravity

Two fluxgate magnetometers were on a long boom. They were designed to find out if Mercury had its own magnetic field. They also studied the magnetic field in space between the planets.

The Celestial Mechanics and Radio Science experiment studied Mercury's mass and how its gravity worked. This was important because Mercury is so close to the Sun and has a unique orbit. By sending radio signals through Mercury's atmosphere, scientists could also measure its size and density.

Mariner 10's Amazing Journey

Launching into Space

Boeing finished building Mariner 10 in June 1973. After many tests, it was taken to Florida for launch. Engineers filled it with 29 kilograms (64 pounds) of hydrazine fuel for steering.

On November 3, 1973, at 5:45 AM UTC, the Atlas-Centaur rocket launched Mariner 10 from Cape Canaveral. The rocket had two stages. The first stage burned for four minutes, then fell away. The second stage, Centaur, pushed Mariner 10 into a temporary orbit around Earth. Then, a second burn by Centaur sent Mariner 10 on its way to Venus. This was the first time a planetary mission used two separate rocket burns during launch.

Journey to Venus

The three-month trip to Venus was not easy! Mariner 10 had many technical problems. Mission control teams worked hard to fix them. For example, a sensor that tracked a guide star sometimes got confused by flakes of paint from the spacecraft. The onboard computer also reset itself sometimes.

In January 1974, Mariner 10 observed Comet Kohoutek using its ultraviolet instruments.

Visiting Venus

Mariner 10 flew past Venus on February 5, 1974. It came closest at 5,768 kilometers (3,584 miles) away. It was the twelfth spacecraft to reach Venus and the first to send back pictures of the planet.

As Mariner 10 swung around Venus, it took amazing photos. These showed an arc of clouds over Venus's north pole. The cameras revealed many details in Venus's clouds that couldn't be seen with regular telescopes. The spacecraft continued taking pictures until February 13, 1974. It captured 4,165 photos during this time.

The mission showed that Venus's thick atmosphere has distinct cloud patterns. It also revealed that the atmosphere is layered. The gravity assist at Venus was a huge success. It changed Mariner 10's speed and path perfectly, setting it up for its encounters with Mercury.

Venus encounter
Venus in UV light. This image is a mosaic of two frames.
Venus cloud patterns
Venus in real colors, processed from clear and blue filtered images
Color composite using orange and ultraviolet filters with modern image processing software

First Stop at Mercury

Mariner 10 flew past Mercury three times. The first time was on March 29, 1974, at 8:47 PM UTC. It passed only 703 kilometers (437 miles) from the planet, flying over its dark side.

First Mercury encounter
Mariner 10's first image of Mercury, taken on March 24, 1974.
This mosaic shows Mercury as seen by Mariner 10 as it flew away on March 29, 1974.
One of the most famous cliffs, called Discovery Scarp, photographed by Mariner 10.

Second Visit to Mercury

After orbiting the Sun once (while Mercury orbited twice), Mariner 10 flew by Mercury again. This happened on September 21, 1974. This time, it was further away, about 48,069 kilometers (29,869 miles) below Mercury's southern half.

Hero Rupes is a long, curved cliff seen in this image. Mariner 10 image 0166842.
Cervantes basin (left), Bernini (right), and Van Gogh (bottom center). South is towards the upper right.
Mercury's south pole was photographed during the second flyby on September 21.
A mosaic of images from the second encounter, showing the area from the equator to the south pole.

Final Flyby of Mercury

The third and final encounter with Mercury was the closest. It happened on March 16, 1975, at a distance of only 327 kilometers (203 miles). Mariner 10 passed almost directly over Mercury's north pole.

Third Mercury encounter
Mercury in color
Mercury in false-color
The Australia region
The Aurora region
The Caduceata region
The Schubert basin, 190 kilometers (118 miles) wide, filled with smooth plains.
A computer mosaic of the Caloris Basin.

The End of a Great Mission

By March 1975, Mariner 10's maneuvering gas was almost gone. It began another orbit around the Sun. Engineers continued tests until March 24, 1975. At that point, the nitrogen fuel ran out completely. Commands were immediately sent to turn off its radio transmitter. The signals to Earth stopped.

Mariner 10 is likely still orbiting the Sun today. Its electronics have probably been damaged by the Sun's radiation over the years. No one has seen or tracked Mariner 10 since it stopped sending signals.

What Mariner 10 Discovered

During its flyby of Venus, Mariner 10 found signs of rotating clouds. It also detected a very weak magnetic field around the planet. Using a special ultraviolet filter, it photographed Venus's unique chevron-shaped clouds. These studies greatly improved our understanding of Venus's atmosphere.

The spacecraft flew past Mercury three times. Because of its orbit, the same side of Mercury was lit by the Sun each time. This meant it could only map about 40–45% of Mercury's surface. It took over 2,800 photos. These pictures showed a surface that looked a lot like Earth's Moon.

Mariner 10 helped us understand Mercury much better. Before this mission, telescopes couldn't see Mercury's surface clearly. The mapped areas included many important regions of the planet.

Mariner 10 also discovered that Mercury has a very thin atmosphere. This atmosphere is mostly made of helium. It also found that Mercury has a magnetic field and a large, iron-rich core. Its temperature readings showed that Mercury's night side can get as cold as -183°C (-297°F). The daytime side can reach a scorching 187°C (369°F).

The information gathered by Mariner 10 was very important. It helped scientists plan for future missions, like MESSENGER. MESSENGER surveyed Mercury until 2015, building on what Mariner 10 taught us.

Remembering Mariner 10

A U.S. postage stamp from 1975 featuring the Mariner 10 space probe.

In 1975, the U.S. Post Office released a special commemorative stamp to honor the Mariner 10 space probe. The 10-cent stamp was issued on April 4, 1975, in Pasadena, California.