It could be Mars or jupiter also? https://www.space.com/pale-blue-dot-earth-space-photo-remastered.html
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$\begingroup$ I consider your question to be on-topic on Space Exploration StackExchange. However, they could have known the planetary configurations before hand. They know the relative position of Earth with respect to the star background. Further, they know from where radio signals reach the spacecraft. $\endgroup$– VishnuFeb 13, 2020 at 10:32
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1$\begingroup$ Also, "pale blue dot" is Earth and it could be Mars if it were "pale red dot". $\endgroup$– VishnuFeb 13, 2020 at 10:33
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$\begingroup$ But Uranus and Neptune are also blue in color $\endgroup$– user-2147482075Feb 13, 2020 at 10:45
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2$\begingroup$ They need the Voyager to be pointed at Earth for telecommunications. I assume it's not difficult to make the camera face the same direction. $\endgroup$– John DvorakFeb 13, 2020 at 11:03
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$\begingroup$ @Mohit Sinha No, i believe the lack of stars is due to the exposure of the camera and not any sort of editing. $\endgroup$– ThatpotatoisaspyFeb 13, 2020 at 11:12
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1 Answer
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There is no way it could be Mars or Jupiter. Keep in mind that Voyager was designed to be a moving astronomical image platform. It knows exactly where it is pointed at all times, using the Attitude and Articulation Control Subsystem (AACS) to maintain the craft's orientation. The AACS uses a sun sensor for yaw and pitch reference, and a star tracker trained continuously on a bright star at right angles to the sun point for a roll reference. Since it knows its own orientation and the orientation of the camera, it knows exactly which direction the camera is pointed. Pointing at Earth is a different direction than pointing at Jupiter, even at the distance of Voyager 2 in 1990 when this image was taken.
Consider this diagram of all the images taken to make the "Family Portrait of the Solar System" mosaic. Note how far Jupiter is from the Earth in this perspective-- around three entire images. There is no way it could be mistaken for Earth. And that is just considering how many image widths separate them.
But Voyager astrometry is far better than that. AACS allows the spacecraft to know its orientation to better than one second of arc, and the separation of the planets is far greater than that even within a single image. It has to be, in order for Voyager images to make any useful sense at all.
