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Return To The Pale Blue Dot


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The original pale blue dot - Earth from 3.7 billion miles away (NASA/JPL/Voyager)

One of the most enduring and captivating images from our exploration of space in the late 20th century was Voyager 1′s mosaic of our own solar system – a family portrait from 3.7 billion miles away. Captured in these shots was a faint speck of bluish light, in one single pixel of Voyager’s digital camera, the result of polarization and scattering of sunlight from a small and otherwise insignificant inner planet. This speck was us, and Carl Sagan’s wickedly beautiful prose immortalized this hint of light as ‘the pale blue dot’ – encapsulating all that we had ever been to that moment.

Human imagination is a powerful thing, and we’ve drawn enormous inspiration from this rather innocuous looking image, we’ve been able to see ourselves in its smattering of photons – diminished but unbowed. So it’s rather wonderful that we’re about to do this again, to make another portrait of our homeworld, another deliberate reach for a sense of cosmic perspective.

On July 19th 2013, between 5.27pm EDT and about 5.42 pm EDT the Cassini mission, currently in orbit around Saturn, will use this giant planet as a sunshade to capture a series of images that will include the glow of reflected light from the Earth peering through some of the rings.

The plan for the portrait - Earth is down on the lower right (NASA/Cassini)

An earlier Earth portrait by Cassini, circa 2006 (NASA/JPL)

Although it’s not the first time Earth has been imaged by Cassini, it is the first time using the high resolution camera, and it will be the first time that the color information of visible light will be captured. This will indeed be another version of the pale blue dot – reflected light from the America’s and the Pacific ocean.

The view of Earth from Saturn on July 19th, 5.27pm EDT (NASA/Cassini)

At the time of the portrait we’ll be some 898 million miles away from Cassini, reduced again to a single pixel, but that doesn’t mean you shouldn’t mark your calendars. It’s not inconceivable that if you are on the right part of the Earth, and you stand outside and wave, that one or two of the photons of sunlight that reflect from you are going to make it out to Saturn and into Cassini’s telescope. (Of course they’ll take some 80 minutes to get there, but the Cassini team have accounted for that – I presume – the time of the portrait is given appropriately).

NASA is promoting a ‘Wave at Saturn’ campaign, you can check it out here.

The primary science goal of this Cassini mosaic is to study the detailed structure of Saturn’s rings, but I suspect it’s the opportunity to pause and consider our rather shockingly diminutive place in the cosmos that most of us will remember.

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His latest book is 'Gravity's Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos', and he is working on 'The Copernicus Complex' (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Bill_Crofut 7:09 pm 06/20/2013

    Re: “…Carl Sagan’s wickedly beautiful prose…”

    Wickedly beautiful would seem to be a contradiction in terms:

    “Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves. It is up to us. It’s been said that astronomy is a humbling, and, I might add, a character-building experience. To my mind, there is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world.”

    [http://refspace.com/quotes/Carl_Sagan/s:15]

    Perhaps Prof. Sagan was unaware(?!) of certain facts:

    “…[I]t takes a lot of factors to have a habitable planet in a planetary system….The number of factors that have been postulated has grown. Currently the typical number you’ll see in a typical list would have something like 20…[I]f every element has to be there at the same time. You have to multiply the probabilities … And that’s what makes the probability at the end so small. You’ve got 10% of this and 10% of that. And these things rapidly multiply to exceedingly small numbers…numbers on the order of 10^-15, which is one one-thousandth of one, one trillionth…and it’s a number like that, that you have to compare to the 100 billion stars that are in the galaxy. 100 billion is a very large number, but a thousandth of a trillionth is much, much smaller. On their face value, these probabilities are speaking. What they are telling us that is ‘this can’t happen, or this is very unlikely to happen in the galaxy.’ And that’s where the evidence is pushing us.”

    [Guillermo Gonzalez and Bijan Nemati. 2005 Interviews.
    THE PRIVILEGED PLANET DVD (Transcript). Sections 49, 82, 86]

    Link to this
  2. 2. SciLover 8:09 pm 06/20/2013

    Well, it looks like the Americas can do the wave at Cassini, but pretty much no one else — yet another gripe the Russians, Chinese and other competitors on the world stage can lodge. But Cassini an’t theirs it it? If my astronomy software is correct, they can wave at Uranus instead. Of course how many of us know just where to wave in broad daylight? “Up” won’t cut it from the USA, as Saturn is well south of “up”. My guess is the Brazilians will look good on the Cassini photo, as it will be dark there, and Saturn from that venue is indeed “up”. Say ‘queijo’ Brazil!

    Link to this
  3. 3. SachiNewDelhi 1:36 am 06/29/2013

    YESS! I am ‘excited’ about this project which is being promoted by Carolyn Porco and her collaborators as #DayEarthSmiled.

    I created the Wikipedia page as well as and hope to see this become as historic as the Pale Blue Dot and on July 19, I hope the news media gives it as much prominence as they did to Curiosity’s landing.

    http://en.wikipedia.org/wiki/The_Day_The_Earth_Smiled

    Link to this

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