Why are the Voyager spacecraft getting closer to Earth?
For a few months each year, the distances between the Voyager spacecraft and Earth actually decrease. You might know that both Voyager spacecraft were launched into space in the 1970s and visited the outer planets through the 1980s. They’ve been heading out of our solar system ever since. In 2012, Voyager 1 entered interstellar space. Then, in 2018, NASA announced that Voyager 2 had entered interstellar space, too. They are both headed outward, never to return to Earth. So, can they get closer?
The answer is that for a few months each year, Earth in its orbit moves toward the spacecraft faster than they’re moving away. Earth’s motion around the sun is faster than the motion of the Voyager spacecraft. Earth moves through space at a speed of 67,000 miles per hour (30 km/s). Voyager 1 moves at a speed of 38,210 miles per hour (17 km/s). Voyager 2 moves at a speed of 35,000 miles per hour (15 km/s). So, for a portion of the year, Earth comes around the side of the sun and is speeding toward the spacecraft faster than they’re moving away. Therefore their distances to Earth are getting closer, if only temporarily. They never change their outward motion. It is we who change.
From this video, you can see the trajectory of the Voyager spacecraft as they leave Earth, encounter the outer planets (changing their trajectories), and then head in a straight line outward, out of the solar system.
A closer look at Voyager 2 in relation to Earth
Let’s look specifically at Voyager 2 as an example. Every year from late February to the beginning of June, Voyager 2 actually gets closer to Earth. We measure the distance between objects in space in astronomical units, or AU. This measurement is based on the distance between Earth and the sun, which is one AU.
On February 20, 2023, Voyager 2 was 133.22335 AU from Earth. Then, Earth’s orbit began bringing us closer to Voyager 2 once again. The distance between us and Voyager 2 will continue to shrinking until early June. On June 3, 2023, Voyager 2 and Earth will be 132.89427 AU apart. After that, we will begin to separate in distance again, until next February.
Did you know: Every day, sister Voyager 1 travels 1,474,000 km farther from the Sun, & I travel 1,338,000 km. Earth travels ~2,573,000 km in that same day, so Earth is orbiting faster than we are leaving! That is why the distance to both of us is decreasing right now!
— NSFVoyager2 (@NSFVoyager2) March 19, 2022
Bottom line: The Voyager spacecraft are on a never ending journey away from Earth. So, why do the distances between the spacecraft and Earth decrease for a few months every year? It’s because for a few months, Earth moves toward the spacecraft faster in its orbit around the sun than the spacecraft move away from us.