Our long history of taking beautiful images of Earth actually predates the space age, thanks to high-flying missiles fitted with cameras. But the latest image of Earth from space, captured on NASA’s Cassini mission to Saturn, blows them all out of the water. It’s a portrait of Earth behind a backlit Saturn, with a handful of Saturnian moons, Venus, and Mars all in one breathtaking shot.
An image like this doesn’t come in a single shot like some of the amazing Apollo-era pictures astronauts took with a hand held Hasselblad camera. A shot like this took some planning and, because Cassini’s instruments are designed for science and not beauty, a fair bit of work after the fact to create the full image.
The Cassini Orbiter's suite of instruments have immense capabilities. Some gather optical data, some are designed to measure fields, particles, and waves in space, and some measure microwaves. The optical remote sensing payload that takes the stunning images we’ve seen consists of a series of instruments: a composite infrared spectrometer designed to look for heat signatures and return data on an object’s composition, an ultraviolet imaging spectrograph that consists of four telescopes honed to see ultraviolet light, and a visible and infrared mapping system comprised of two cameras that can see these two wavelengths of light and gather information on surfaces, atmospheres, and compositions.
The fourth instrument in the optical payload is the Imaging Science Subsystem. This is the orbiter’s eyes, the system that turns light wave data into fantastic images. This instrument consists of two cameras, a wide-angle camera to capture larger areas at a lower resolution and a narrow-angle camera to capture high-resolution images of more specific targets.
Knowing images of the Earth from space are immensely powerful, the Cassini team took advantage of a celestial photo op. On July 19th of this year, Cassini passed into Saturn’s shadow. This allowed it to see the inner planets that are normally overpowered by sunlight. While in the ringed planet’s shadow, Cassini used its wide and narrow angle cameras to capture 323 images using red, green, and blue spectral filters in a little over four hours.
Cassini’s imaging team has since processed 141 of these images, increasing the contrast, brightness, and color balance to create a natural-coloor mosaic that shows a backlit Saturn in stunning detail as it would appear to the human eye. And yes, hiding there as a simple, insignificant dot, is Earth.
This single image covers a span of 404,880 miles, enough to include all of Saturn's rings going out to the second-outermost E ring. To put this into some kind of perspective: the roughly quarter of a million mile distance between the Earth and the Moon would fit comfortably within the E ring. The fully annotated version of the image gives the best look into the details captured in the shot, spokes and clumps in the rings and distant planets.
But the best details might be Saturn’s moons Tethys and Enceladus. They’re both big enough to be clearly round in the image, not just points of light like the Earth and Mars. The image even resolves icy spray erupting from Enceladus, which you can see as a slight glow around the moon if you stick your face right up to your monitor.
Carolyn Porco, the leader of Cassini's imaging team based at the Space Science Institute in Boulder, Colorado, brings humanity to Cassini’s images. "What our cameras do is miraculous really. They convert the fleeting and indifferent fluctuations of electric and magnetic fields into powerful emotion,” Porco said previously about the Imaging Science Subsystem. "Who can fail to be moved when seeing some of our beautiful images? Certainly not I.” Of all the images taken in space—distant young galaxies and the surfaces of nearby planests—some of the most meaningful, spectacular, and frequently reprinted are the images that show our home planet.