A few days ago, NASA announced that on July 19 the Cassini spacecraft was taking a picture of the Earth and the Moon from Saturn’s orbit. On that occasion the agency also launched an initiative inviting people to wave at Cassini and it’s estimated that more than 20,000 people participated. Obviously, from a distance of nearly a 1,5 billion kilometers (about 900 million miles) the Earth is just a dot but it was a symbolic gesture. Almost simultaneously, the MESSENGER spacecraft took a similar picture but from Mercury’s orbit.
It’s not easy to take pictures of the Earth from Saturn’s orbit not only because of the distance but also because there’s often the Sun to disturb it with its proximity. The risk is that the excessive light might damage the Cassini space probe’s detectors so it needed to wait for the right time to do it without danger.
On July 19, the Cassini spacecraft was able to take this photograph of the Earth and the Moon due to the fact that the Sun was covered by Saturn so most of its light was blocked. Earth and Moon are so small that they can only be distinguished in an enlarged view of the surrounding area but in the photograph that includes part of Saturn and its rings form a single dot.
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The MESSENGER spacecraft is closest to Earth in comparison with Cassini, “only” 98 million kilometers (about 60 million miles). Among its tasks is to look for possible satellites of Mercury too small and dark to be seen from Earth. For this reason, MESSENGER also takes photos of the surrounding space and this has also allowed to take a picture of the Earth and Moon.
In this case, Earth and Moon are easily distinguished but they’re relatively large because the picture is overexposed. It’s not a mistake, on the contrary long exposures are normal, necessary to try to capture as much light as possible to detect a possible very small satellite of Mercury.
The astronauts who have the opportunity to see the Earth from space come back to the planet with a new perspective because they saw it without all the artificial divisions created by humans. Let’s hope that seeing the Earth from other planets, even if only in a photograph, can help to overcome certain pettyness by giving people a broader perspective.
