By Glynn Wilson –
In just the third time ever that Earth has been photographed from the outer solar system, Nasa has released images of Earth and the moon taken by the Cassini spacecraft orbiting Saturn almost a billion miles away in outer space.
Scientists, wanting to pay homage to the “Pale Blue Dot” image captured by the Voyager 1 probe in 1990, released this photo of Earth and its only moon, which appear as tiny dots in the picture taken July 19. As part of the event launched by NASA, people on Earth were asked to wave in what Carolyn Porco, who leads Cassini’s camera team, described as an “interplanetary cosmic photo session.”
“It thrills me no end that people all over the world took a break from their normal activities to go outside and celebrate the interplanetary salute between robot and maker that these images represent,” said Dr Porco, from the Space Science Institute in Boulder, Colorado.
The wide-angle image is part of a larger mosaic — or multi-image portrait — that imaging scientists are putting together of the entire Saturn system. Pictures of Earth from the outer Solar System are rare since the Earth is so close to the Sun. People can damage their retinas by looking directly at the Sun, and a camera’s sensitive detectors can be damaged by the bright rays too.
The images were taken when the sun had moved behind the planet Saturn from the spacecraft’s point of view, blocking out most of the light. It is only one footprint in a mosaic of 33 footprints covering the entire Saturn ring system, including Saturn itself. At each footprint, images were taken in different spectral filters for a total of 323 images. Some were taken for scientific purposes and some to produce a natural color mosaic. This is the only wide-angle footprint that has the Earth-moon system in it.
The dark side of Saturn, its bright limb, the main rings, the F ring, and the G and E rings are clearly seen. The limb of Saturn and the F ring are overexposed. The “breaks” in the brightness of Saturn’s limb are due to the shadows of the rings on the globe of Saturn, preventing sunlight from shining through the atmosphere in those regions. The E and G rings have been brightened for better visibility.
Earth, which is 898 million miles (1.44 billion kilometers) away in this image, appears as a blue dot at center right. The moon can be seen as a fainter protrusion off its right side. An arrow indicates their location in the annotated version. The two are clearly seen as separate objects in the accompanying narrow angle frame. The other bright dots nearby are stars.
This view looks toward the unilluminated side of the rings from about 20 degrees below the ring plane. Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained with the Cassini spacecraft wide-angle camera on July 19 at a distance of approximately 753,000 miles (1.212 million kilometers) from Saturn, and approximately 898.414 million miles (1.445858 billion kilometers) from Earth. Image scale on Saturn is 43 miles (69 kilometers) per pixel; image scale on the Earth is 53,820 miles (86,620 kilometers) per pixel.
The illuminated areas of neither Earth nor the Moon are resolved here. Consequently, the size of each “dot” is the same size that a point of light of comparable brightness would have in the wide-angle camera.
The Cassini-Huygens mission is a cooperative project of the National Aeronautics and Space Administration, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at the Jet Propulsion Laboratory. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.
For more information about the Cassini-Huygens mission click here.
© 2013 – 2016, Glynn Wilson. All rights reserved.