Humanity's furthest traveler

Asking a spacecraft “How are you?” Asking and waiting for an answer for two days sounds like science fiction.

For Voyager 1, however, this will soon be the physical limit of communication. The spacecraft that NASA sent into space in 1977 will be approximately "25.9 billion kilometers" from Earth on November 18, 2026, that is, the distance that light travels in 24 hours.

A light day is actually a measure of distance, not time. It will take approximately 24 hours for a radio signal sent to Voyager to reach the Earth, and approximately 24 hours for the response sent by Voyager to return to Earth. As NASA Voyager project manager Suzanne Dodd describes it, it will be necessary to wait two days for a response after saying "hello."

A JOURNEY STARTED IN 1977

Voyager 1 and Voyager 2 were sent into space in 1977. Their initial goal was not to reach interstellar space, but to closely examine giant planets outside the Solar System.

The two spacecraft were taking advantage of a planetary alignment that occurs approximately every 175 years. Thanks to the favorable positions of Jupiter, Saturn, Uranus and Neptune, it could accelerate towards the next target by using the gravity of a planet. Thus, humanity had the opportunity to see the outer planets and their moons closer than ever before.

After visiting Jupiter and Saturn, Voyager 1 set out on a different path. Voyager 2 visited Uranus and Neptune. The first and still the only human-made vehicle to examine these two planets closely is Voyager 2.

Afterwards, both vehicles went out of the heliosphere, where the Sun's influence dominates. Voyager 1 did this in 2012, and Voyager 2 in 2018. Today, both are the only spacecraft operating in interstellar space.

HE IS GETTING OLD.

What makes Voyager 1's story special is not just its age. It is the farthest human-made object humanity has ever made and sent farthest from Earth.

The spacecraft's electricity comes from systems that convert the heat generated by the decay of radioactive plutonium into electricity. However, this resource is constantly decreasing. Voyager's usable electrical power is decreasing by about 4 watts per year. Therefore, NASA engineers have to decide, one by one, which devices will continue to work.

Some scientific instruments and heaters had previously been turned off to save energy. This year, the low-energy charged particle device was shut down. NASA expects this will give the spacecraft about a year of additional operating time.

The vehicle, once sent to explore the outer planets of the Solar System, is today an old machine trying to preserve its energy.

WHAT WILL HAPPEN WHEN THE ENERGY RUNS OUT?

Running out of Voyager's energy will not mean the end of its journey.

Because what keeps Voyager moving forward is not a constantly running engine. The spacecraft is traveling with the same motion it has had for years. Their engines are used to change direction and maneuver. Once the energy is completely depleted, these will not be able to work, but Voyager will continue to move in space.

In other words, Voyager's mission will one day end, but its journey will not.

According to NASA's calculations, Voyager 1 will pass approximately 1.7 light-years from the star Gliese 445 in approximately 40 thousand years. By then, the spacecraft will no longer be able to collect data and communicate with Earth. However, it will continue to move on its route away from the Solar System.

I think this is the saddest part of Voyager's story: One day, all its systems will shut down, but it will continue on its way alone in the void of space.

THE TWIN'S DIVERTING PATHS

Voyager 1 and Voyager 2 launched at the same time but did not follow the same route. Voyager 1 followed a faster orbit, becoming humanity's most distant object. Voyager 2 followed a longer route and spotted Uranus and Neptune. Today, Voyager 2 is also moving through interstellar space. It is expected to reach one light-day distance around 2035, about nine years after Voyager 1.

The two spacecraft are now moving away from the Solar System in different directions. These vehicles, once two products of the same laboratory, are now two silent travelers moving away from each other within the galaxy.

A MACHINE LOOKING AT US

It is enough to look at the Golden Record Voyager carries to understand that it is not just a vehicle we send into space. Humanity left sounds, images and music from Earth on Voyager, thinking about the possibility of it being found by another civilization one day.

On the other hand, one of the most powerful images he left us actually came from the camera he turned towards the Earth.

Voyager's camera was pointed at Earth for the last time in 1990 before it was turned off because it was no longer scientifically necessary. In the photograph, the Earth was an almost negligible dot. This photo was called “pale blue dot”.

Now Voyager 1 is traveling one light-day away from Earth. For us, this is a 24-hour drive. For him, it is just another stop on a journey that has been going on for 49 years. And one day, when the last signal from Earth stops, Voyager will be moving forward again. As an object that does not work, does not speak, but carries the traces of humanity on it.

WHAT DOES ONE LIGHT DAY'S DISTANCE MEAN?

Voyager actually shows us the past. Once it reaches a distance of one light day, the signal from it will reach us with a delay of about 24 hours. In other words, we learn not what Voyager is doing "right now", but what it did about a day ago.

Because light also has a speed. Light travels approximately 300 thousand kilometers per second. As the distance increases, the information reaching us becomes older.

Moon: We see it as it was about 1.3 seconds ago.

Sun: We see it as it was approximately 8 minutes and 20 seconds ago.

Mars: Depending on its position, we see it as it was 3-22 minutes ago.

Neptune: We see it as it was about 4 hours ago.

Voyager 1: When it is one light-day away, we hear what it was like 24 hours ago.

Proxima Centauri: 4.24 light-years away. So we see it as it was approximately 4.24 years ago.

Andromeda: Approximately 2.5 million light-years away. The Andromeda we see is the Andromeda of about 2.5 million years ago.

VOYAGER'S COSMIC USER MANUAL

On the cover of Voyager's Golden Record, there is symbolic information explaining how a civilization that finds the record can read it. In other words, humanity left a "user manual" along with the message.

TIME - HYDROGEN

The transition between the two fundamental energy states of the hydrogen atom is used as a universal measure of time. Thus, there is no need for an Earth-specific unit such as the second.

ADDRESS - PULSARS

The map, showing the locations of 14 pulsars, describes the location of the Solar System in the galaxy. The precise rotation periods of pulsars are also indicated on the map.

AGE - URANIUM-238

The radioactive decay of Uranium-238 placed on the plate serves as a kind of cosmic clock. Its half-life is approximately 4.5 billion years. Someone who finds a record can calculate the time that has passed by examining its degradation products.

CONTENT - WORLD

The record contains 115 images, natural and human-made sounds from the Earth, music from different cultures and greetings in 55 languages.

22.5 SAT WAITING

One of the most striking examples of Voyager 1's aging occurred in 2023. Due to a memory problem in the spacecraft's computer, it was unable to send meaningful data to Earth for months. NASA engineers could not replace the faulty part. The solution was to remotely refactor a portion of the 46-year-old software.

Voyager 1 was more than 24 billion kilometers away from Earth at the time. Engineers had to wait approximately 45 hours to see the results of each change.

The critical command was sent on April 18, 2024. The team waited for almost two days. When data started coming in from Voyager on April 20, everyone responded with applause. The spacecraft, which had been silenced for five months, was again explaining its situation to the Earth.