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Earth viewed from a billion miles away

Space shot: This image taken on July 19, 2013, the wide-angle camera on NASA's Cassini spacecraft has captured Saturn's rings and our planet Earth and its moon in the same frame.

Space shot: This image taken on July 19, 2013, the wide-angle camera on NASA's Cassini spacecraft has captured Saturn's rings and our planet Earth and its moon in the same frame.

 

From the remote vantage point of Saturn, planet Earth seems mighty small and insignificant. Yet the first interplanetary portrait to be taken in natural colour is a stark reminder of how alone and potentially vulnerable we are in the vastness of space.

The series of snaps was taken early last Saturday by NASA's Saturn-orbiting space probe, Cassini, from a distance of 1.44 billion kilometres.

The images – facilitated by a unique version of an outer solar system eclipse in which the sun's glowing dial hid safely behind Saturn – are short on detail. Earth, after all, shows up as a trifling 1.5 pixels wide, with the illuminated part less than a pixel across.

The Earth images, perhaps more art than science, will eventually form part of a mosaic, or multi-image gallery, of the Saturnian system being composed by Cassini, named after the Italian astronomer who made discoveries about the ringed planet and its multiple moons.

"A small version of the mosaic will take about three weeks," says the initiator of the Earth-image project and leader of Cassini's imaging team, Carolyn Porco of the Space Science Institute in Boulder, Colorado. "The big, full mosaic of the all the rings, with Earth, will be ready in roughly two months."

She is pleased with the results so far. "What made this special was that we let everyone know ahead of time," Dr Porco explains. "This was the first time people of the world knew in advance that their picture was being taken from a billion miles away."

Dr Porco adds: "I wanted this to happen so it would serve as a day to celebrate life on planet Earth and our accomplishments in exploring the solar system."

Meaning

Like the old Apollo-era shots of Earth rising, the pictures show our home orb as little more than a pale blue speck perched precariously in deep space somewhere beneath Saturn's delicate rings.

"And yet here, in our solar system's habitable zone, our planet can sustain life," says Swinburne University astrophysicist Sarah Maddison.

"The day the Earth smiled", as Saturday's event was dubbed, offered a sense of the amazing scope and achievements of space science, Associate Professor Maddison points out. "To be able to send a human-built spacecraft nearly 1.5 billion kilometres away, have it orbit another planet and do amazing science – for 15 years in the case of Cassini – was a remarkable feat."

Ring research

Although the Earth pictures themselves are of little scientific significance, the spacecraft's position, lurking in Saturn's shadow, provided backlit views of the rings – enabling researchers to scrutinise variations in their shape, colour and brightness. This shed light on the ring composition.

Cassini has a range of instruments for investigating the origin, evolution, dynamics and composition of Saturn's atmosphere, rings and moons. As the sun was blocked out by Saturn, more light-sensitive equipment could be used, CSIRO astrophysicist Kurt Liffman explains: "In 2006, a new ring was discovered under similar circumstances and more detailed images were obtained of Saturn's E-ring."

Throughout much of human history, the planets have been regarded as tiny, bright, wandering points of light in the sky, says Swinburne University astronomer Chris Fluke. "This was the Earth's turn."

Few opportunities have arisen for photographing Earth from the solar system's outer suburbs, he notes: "So, it's great that the spacecraft could take time out from its scientific schedule to take a rare portrait of our home planet."

From a scientific standpoint, the pictures demonstrate the progress made by space science, says another Swinburne astrophysicist, Francesco Pignatale:

"As well as sending humans into space and robotic probes to the outer solar system, we could now take a 'self-portrait' of ourselves from afar."

Rationale

The new images are not the most distant snaps taken of Earth. That was achieved on 14 February 1990 when NASA's Voyager 1 probe, now leaving the solar system, imaged our planet from beyond the orbit of Neptune, roughly 6 billion kilometres away.

Scientists also observed Earth among Saturn's rings in September 2006, in a mosaic that has become one of Cassini's most popular images. "Since then, I wanted to do it all over again – only better," beams Dr Porco, Cassini's imaging team leader. "And we did it!"

Further reading

Try your hand at this contest: diamondskyproductions.com/recent/

Take part in a Flash-based game that lets you play golf on Saturn's moons at www.ciclops.org/sector6/index.php

Discover more about the Earth snap at: saturn.jpl.nasa.gov/waveatsaturn

Use the hashtag #DayEarthSmiled to follow the story on Twitter, Facebook and Google Plus.

Please send bright ideas for new topics to pspinks@fairfaxmedia.com.au

8 comments

  • Puts things into perspective...

    Commenter
    The pale blue dot
    Date and time
    July 26, 2013, 4:22PM
    • And yet, it's all about us.

      Commenter
      Hugo Thundercrotch
      Date and time
      July 26, 2013, 4:25PM
      • Awe-inspiring and completely humbling. Beautiful, too.

        Commenter
        Sarah
        Date and time
        July 26, 2013, 6:15PM
        • Marvellous now to give everybody a feed for tea, a bed, clean water to drink, and no threats to life, way ahead and way behind, ah a thrill to be human.

          Commenter
          Rabbitflat
          Location
          Ballarat
          Date and time
          July 26, 2013, 6:38PM
          • I feel even more insignificant than usual. What a magnificent photo.

            Commenter
            mutt
            Date and time
            July 26, 2013, 6:49PM
            • Beautiful.

              It's just a shame that we don't look after our only home a bit better. The air we breath comes to us for free courtesy of places like the Tarkine. Mining asteroids makes demolishing ancient forests and turning the earth into slurry pointless, but the human race doesn't look like it's capable of taking a very long term view so far. We could stop CO2 emissions tomorrow if we had the will, but we choose to dice with the future of the entire human race instead.

              I think manned missions to mars and beyond will show very clearly that trying to set up earth-like habitats on any of our solar system's planets or moons is going to be fraught with hazards, and we really don't know how good we've got it on earth, how kind mother nature is to us.

              Commenter
              yoghurt
              Location
              Sydney
              Date and time
              July 26, 2013, 8:42PM
              • I remember the day Cassini was launched like it was yesterday. I was at a mate's house in the Inner West, and we were talking about the risks of the plutonium battery if the rocket exploded in earth's atmosphere. But the mission has been a huge success, with a Titan landing by the Huygens probe and amazing photos from Cassini.

                Commenter
                yoghurt
                Location
                Sydney
                Date and time
                July 26, 2013, 8:45PM
                • Just stunning. I'm looking for a high res version for my desktop wallpaper. Even though we were facing the other way, I did get up early on Saturday and looked up :)

                  On a semi-related note, it makes me sad that articles like this don't get the attention they deserve. Instead, this and other papers publish stories on the xenophobia by our political leaders, stories of royals having babies, and advice on how to get noticed in an office.

                  Articles like this should inspire awe that we as a species are capable of wonderful feats such as this, yet this always gets overshadowed by the mundane.

                  If I ever develop god like powers for a day, I'm teleporting everyone in the world who isn't interested in the pursuit of knowledge to another planet to start a new offshoot of humanity elsewhere. Those of us interested in science can stay here!

                  There'd be no more Big Brother, The Block, or Master Chef!! HEAVEN

                  Commenter
                  TechHead
                  Location
                  in your base
                  Date and time
                  July 26, 2013, 9:59PM
                  Comments are now closed
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