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Cassini snaps picture of Pluto on day of New Horizons flyby

Morgan Rehnberg, Correspondent
Jul 18, 2015, 0:04 UTC

Sen—NASA’s Cassini spacecraft was far from the center of attention this week, but it did provide a helping hand. Just as the New Horizons spacecraft zipped past the dwarf planet Pluto in its historic first visit to a Kuiper belt object, Cassini turned its powerful narrow-angle camera towards this icy world and snapped a picture.

The image looks nothing like the stunning views of Pluto’s seemingly-young and active surface that have been revealed this week. In fact, Cassini’s image is nothing more than a dot—Pluto, Charon, its smaller moons, and New Horizons all fit within a single pixel. That’s because, due to their current orbital configurations, Saturn is only about 20 per cent closer to Pluto than the Earth is.

So why even take this image now that we have spent hundreds of millions of dollars to actually go there? It's a matter of perspective. While New Horizons flew through the Pluto system, it was lost in the trees; with Cassini, we could simultaneously see the forest. Assigning such a task to a ground-based observatory would run the risk of being clouded out. Cassini offered a guaranteed view with an impeccably calibrated instrument.

In a broader view, Cassini also offers New Horizons something else—experience. Several members of the latter’s science team have spent decades working on the former, including leader of the New Horizons Student Dust Collector Mihaly Horanyi and Cassini imaging chief Carolyn Porco.

And, more symbolically, Cassini also serves as a reminder of how far we’ve come technologically. New Horizons carried seven instruments past Pluto. In total, they weigh less than a single camera onboard the Saturn orbiter. What a difference nine years can make!

Cassini's image was captured just two days after Europe's Rosetta spacecraft took its own photo of Pluto, but this time through a veil of comet dust! Twenty 10-minute exposures made with the spacecraft's powerful OSIRIS camera were combined, then carefully processed to remove the haze and reveal the distant world as a tiny dot of light.

The Cassini-Huygens mission is a collaborative effort between NASA, ESA, and the Italian Space Agency. Launched in 1997, it reached Saturn in 2004 and has since been studying the planet, its moons, and its rings. In 2005, the Huygens probe made the first landing on Titan, Saturn’s largest moon. After completing its second mission extension in 2017, Cassini will make a series of close passes to the planet and then end its time at Saturn by plunging into the planet’s atmosphere.


Annotated version of the main image. Pluto as seen from Cassini is a far cry of the images of New Horizons, but it will still provide scientists with valuable information. Image credit: NASA/JPL-Caltech/Space Science Institute