Milestone Missions

Forty years ago, theVoyager 1and2missions began their journey from Earth to become the farthest-reaching missions in history. In the course of their missions, the two probes spent the next two decades sailing past the gas giants ofJupiterandSaturn. And whileVoyager 1then ventured into the outer Solar System,Voyager 2swung byUranusandNeptune, becoming the first and only probe in history to explore these worlds.

This summer, the probes will be marking thefortieth anniversaryof their launch on September 5th and August 20th, respectively. Despite having traveled for so long and reaching such considerable distances from Earth, the probes are still in contact with NASA and sending back valuable data. So in addition to being the most distant missions from Earth, they are the longest-running mission in history.

In addition to their distance and longevity, theVoyagerspacecraft have also set numerous other records for robotic space missions. For example,in 2012, theVoyager 1probe became the first and only spacecraft to have entered interstellar space.Voyage 2, meanwhile, is the only probe that has explored all four of the Solar Systems gas/ice giants Jupiter, Saturn, Uranus and Neptune.

Their discoveries also include the first active volcanoes beyond Earth on Jupiters moonIo the first evidence of a possible subsurface ocean onEuropa, the dense atmosphere aroundTitan(the only body beyond Earth with a dense, nitrogen-rich atmosphere), the craggy surface of Uranus Frankenstein Moon Miranda, and the ice plume geysers of Neptunes largest moon,Triton.

These accomplishments have had immeasurable benefits for planetary science, astronomy and space exploration. Theyve also paved the way for future missions, such as theGalileoandJunoprobes, theCassini-Huygensmission, and theNew Horizonsspacecraft. As Thomas Zurbuchen, the associate administrator for NASAs Science Mission Directorate (SMD), said in a recent press statement:

I believe that few missions can ever match the achievements of the Voyager spacecraft during their four decades of exploration. They have educated us to the unknown wonders of the universe and truly inspired humanity to continue to explore our solar system and beyond.

But what is perhaps most memorable about the Voyager missions is the special cargo they carry. Each spacecraft carries what is known as theGolden Record, a collection of sounds, pictures and messages that tell of Earth, human history and culture. These records were intended to serve as a sort of time capsule and/or message to any civilizations that retrieved them, should they ever be recovered.

As noted, both ships are still in contact with NASA and sending back mission data. TheVoyager 1probe, as of the writing of this article, is about 20.9 billion km (13 billion mi; 140 AU) from Earth. As it travels northward out of the plane of the planets and into interstellar space, the probe continues to send back information about cosmic rays which are about four times as abundant in interstellar space than around Earth.

From this, researchers have learned that the heliosphere the region that contains the Solar Systems planets and solar wind acts as a sort of radiation shield. Much in the say that Earths magnetic field protects us from solar wind (which would otherwise strip away our atmosphere), the heliopause protects the Solar planets from atomic nuclei that travel at close to the speed of light.

Voyager 2, meanwhile, is currently about 17.7 billion km (11 billion mi; 114.3 AU) from Earth. It is traveling south out of the plane of the planets, and is expected to enter interstellar space in a few years. And much likeVoyager 1, it is also studying how the heliosphere interacts with the surroundings interstellar medium, using a suite of instruments that measure charged particles, magnetic fields, radio waves and solar wind plasma.

OnceVoyager 2crosses into interstellar space, both probes will be able to sample the medium from two different locations simultaneously. This is expected to tell us much about the magnetic environment that encapsulates our system, and will perhaps teach us more about the history and formation of the Solar System. On top of that, it will let us know what kinds of hazards a possible interstellar mission will have to contend with.

The fact that the two probes are still active after all this time is nothing short of amazing. As Edward Stone the David Morrisroe Professor of Physics at Caltech, the former VP and Director of NASAs Jet Propulsion Laboratory, and the Voyager project scientist said:

None of us knew, when we launched 40 years ago, that anything would still be working, and continuing on this pioneering journey. The most exciting thing they find in the next five years is likely to be something that we didnt know was out there to be discovered.

Keeping the probes going has also been a challenge since the amount of power they generate decreases at a rate of about four watts per year. This has required that engineers learn how to operate the twin spacecraft with ever-decreasing amounts of power, which has forced them to consult documents that are decades old in order to understand the probes software and command functions.

Luckily, it has also given former NASA engineers who worked on theVoyagerprobes the opportunity to offer their experience and expertise. At present, the team that is operating the spacecraft estimate that the probes will run out of power by 2030. However, they will continue to drift along their trajectories long after they do so, traveling at a distance of 48,280 km per hour (30,000 mph), covering a single AU every 126 days.

At this rate, they will be within spitting distance of the nearest star in about 40,000 years, and will have completed an orbit of the Milky Way within 225 million years. So its entirely possible that someday, the Golden Records will find their way to a species capable of understanding what they represent. Then again, they might find their way back to Earth someday, informing our distant, distant relatives about life in the 20th century.

And if the craft avoid any catastrophic collisions and can survive in the interstellar medium of space, it is likely that they will continue to be emissaries for humanity long after humanity is dead. Its good to leave something behind!

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NASA Voyager Probes Still Going Strong After 40 Years - Futurism