Did you know that a fly- by took the first photo of another planet? In 1965 Mariner 4, the first spacecraft to fly by Mars, took the first photos of another planet. Mariner 4 returned images and other measurements that helped scientists and engineers learn more about Mars and its environment, so that they could ask more specific questions in the future.

Every 175 years or so, a rare arrangement occurs where the four outer planets- Jupiter, Saturn, Uranus, and Neptune- all align. The Voyager mission intended to take advantage of this rare occurrence in order to benefit from "gravity assist".

What is gravity assist? Gravity is the force of a body with mass to draw objects towards its center. Like the Sun and Earth, other bodies in space have a gravitational pull. Voyager's mission used the gravitational pull of the outer planets to propel it forward towards its next destination. This use of "gravity assist" was previously modeled through the Mariner 10 mission to Venus, a planet similar in size to Earth, and Mercury, the smallest planet in the Solar System, in the early 1970s. Venus and Mercury are the two planets closest to the Sun- Mercury is around 36 million miles away and Venus around 67.3 million miles away.

Voyagers 1 & 2 were not the first probes or fly-bys created. Pioneers 10 & 11, created in the 1960s, were the first tools of exploration sent beyond Mars. Rather than creating just one spacecraft, NASA made two Voyagers in order to simplify and limit mission expenses. The Voyager mission was developed as a more elaborate version of the Pioneer mission, which was the first spacecraft to fly beyond Mars and Jupiter. The goals for the project were to create tools that could do as much science as possible and withstand longer periods of time.

Voyagers 1 & 2 are actually still in interstellar space! Initially, the Voyager mission was to go to Jupiter and Saturn. These two planets are the gas giants- made mostly of hydrogen and helium- and the two largest planets in our Solar System. Jupiter and Saturn are 477.7 million and 930 million miles away from the Sun. After successfully making many discoveries of these planets, the mission was extended for exploring the outer ice giants- Uranus and Neptune- around 1.8 billion and 2.782 billion miles away.

Voyagers 1 & 2 continued their missions past Neptune, becoming the first two man-made tools to reach interstellar space. While their cameras were turned off in 1989 and 1990, they are still collecting data. Voyager 1 is around 13.944 billion miles from Earth while Voyager 2 is around 11.537 billion miles from Earth. They have both been in space for 42 years as of 2020. To learn more about where Voyagers 1 & 2 are today, visit the Voyager page on the NASA website.

Look at the image below. What do you see? This is one of the last images taken by Voyager 1 before its cameras were turned off. The "pale blue dot", in the top right of the picture, is Earth. Carl Sagan, a planetary scientist, coined this term while looking at the photo of Earth. Sagan was an astronomy professor, NASA consultant and project manager, author, and science communicator- his TV series Cosmos was the most popular PBS series until Ken Burns' The Civil War documentary aired in 1990. His papers currently reside at the Library of Congress.

“That’s here. That’s home. That’s us. On it, everyone you love, everyone you know, everyone you have ever heard of, every human being who ever was, lived out their lives...[E]very king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every revered teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species lived there–on a mote of dust suspended in a sunbeam.”