Right now, somewhere in the world, children stand at the edge of a lake counting the hops of stones skidding across the surface of the water. It’s hard to explain the tranquil pleasure of watching the ripples emanate farther and farther till nearly out of sight, but it’s even more of a challenge to fathom the distances to which we’ve launched objects into the dark ocean of space. As of February 2018, the Voyager 1 drifts 13 billion miles away from the surface of the earth, 42 years since its launch. It is one of five manmade objects that has ever left our solar system.

Pioneer 10

Credit: NASA.gov

Five years before the launch of the Voyager probes, on March 2, 1972, NASA launched the Pioneer 10 to investigate the surface of Jupiter. Weighing 569 pounds, the Pioneer 10 was the first spacecraft to cross the asteroid belt between Mars and Jupiter and, eventually, escape our solar system by nature of its velocity. It was also the first spacecraft to launch from the three-stage Atlas-Centaur launch vehicle to achieve its launch speed of 32,400 mph. It took the Pioneer 10 twelve weeks to cross the orbit of Mars. On December 3, 1973, the Pioneer 10 passed by the cloud tops of Jupiter to obtain the first close-up images of the planet.

Following its flyby of Jupiter, Pioneer 10 continued to gather data for NASA of the outer solar system until the end of its mission in March 31, 1977. The last faint signal from Pioneer 10 was received on January 23, 2003, as its radioisotope power source had decayed to the point of being unable to send further signals.

Pioneer 11

Credit: NASA.gov

The launch of Pioneer 10 was succeeded just a year later on April 5, 1973. The launch this time was accelerated by an additional 210 ft/sec and aimed to pass Jupiter at a point closer to its surface. The closer proximity to Jupiter caused the spacecraft to accelerate by gravitational pull to the muzzle velocity of a rifle (110,000 mph), allowing it to obtain the velocity and direction necessary to approach Saturn.

On September 1, 1979, Pioneer 11 flew to within 13,000 miles of Saturn to obtain the first close-up images of the planet and discover two previously-unobserved moons. By September of 1995, the spacecraft could no longer make observations and by November, the last communication with the spacecraft was made.

Voyager 1 & 2

Credit: NASA.gov

The Voyager spacecrafts were initially tasked with observing the properties and magnetospheres of our neighboring planets using their onboard instrumentation. Target planets included Jupiter, Saturn, and Saturn’s moon Titan. Data from the Pioneer 10 mission was used to create more robust spacecraft to tolerate the intense radiation around Jupiter. Voyager 1 started its observation of Saturn, the final phase of its initial mission, on August 22, 1980, whereas the Voyager 2 was sent on a longer trajectory to observe Uranus and Neptune, reaching Neptune on August 25, 1989.

In addition to their planetary observations, both Voyager spacecrafts were also tasked with interstellar missions. They were designed to continue scientific observations and signal transmission after escaping the heliosphere and exiting our solar system. They are both still active, with a projected lifetime of about five more years.

New Horizons

Credit: NASA.gov

In 2006, NASA launched the New Horizons spacecraft with a primary mission of observing the dwarf planet Pluto. New Horizons was launched as the fastest man-made object ever launched from Earth with a speed of 36,400 mph. New Horizons started its flyby of Pluto on July 14, 2015. Three years later, in August of 2018, it confirmed the existence of a hydrogen wall previously observed by the Voyager launch.