Reviewed by Carl Zimmer
Mars Curiosity, with its sky crane and all, is certainly impressive. But I'm a Cassini fan myself. It left Earth in 1997 and arrived at Saturn in 2004. It has winged around the ringed planet ever since, hurtling by Saturn's many, many moons along the way. Every year it has delivered images back to Earth that are not simply gorgeous but deeply informative about the outer zone of our Solar System. Its success and its stamina have gotten its mission extended twice. It will keep snapping pictures of Saturn and its moons until 2017, when it crashes into the planet.
I've tried to keep up with the flow of images at the Cassini web site, but after eight years of daily footage, there is just too much to handle. To appreciate everything it has found, we need curation.
One form of curation can be found at sites like Bad Astronomy, where Phil Plait regularly posts Cassini images that he finds particularly worthy. Thinx Media now provides curation of a different sort, by loading some 840 images into an app they call Cassini HD.
The images are organized into categories--starting with the planet itself, followed by images of its moons, and then its rings, and finally by false-color pictures. You can plow through the photos one at a time, swipe after swipe, or jump to two navigation systems: either a drop-down menu, or a gallery linked to a diagram of Saturn and its moons.
I preferred jumping around the Saturnian system. At the moment, my favorite moon of Saturn is Daphnis, a five-mile-wide rock that draws a thin path of ice and dust out of the planet's rings. If you like what you see, you can use Cassini HD's nicely integrated functions to email or tweet a photo, save it to the iPad's photo app, or send it to Tumblr or Facebook.
There are two big shortcomings of Cassini HD. For one thing, it's not particularly HD. You can't zoom in on details of the photos on the app. For a closer look at Titan or Enceladus, you will need to look at NASA's biggest versions of their images on their web site.
The other shortcoming is the text--the reason that I'm reviewing this app at Download the Universe. Each section of Cassini HD kicks off with a paragraph, or a few. Each photo comes with a one sentence caption, which you can expand into a longer version. But, as far as I can tell, all the text comes verbatim from NASA's web sites. I won't call this plagiarism, but I will call it disappointing. Every caption comes with an identical paragraph about the Cassini mission. One caption I came across informs you what Cassini will be doing in 2005--because it was written by someone at NASA in 2004. The captions point you to other pictures for further information, but they include the original links, so that you end up on NASA's web site instead of jumping to other images in the app. There's useful information to be gathered the text, but you will get little pleasure along the way. In this respect, Cassini HD is a far cry from The Solar System, which featured original text by the science writer Marcus Chown.
On balance, however, Cassini HD is a good value. The Solar System will set you back $13.99. Cassini HD will cost you just $1.99--and it's free tomorrow, when the app goes live. I like to know that even if I'm out of Wi-Fi range, I can always take a trip through Saturn's rings. The text may not sing, but the pictures are still transporting.
Carl Zimmer writes frequently about science for the New York Times and is the author of 13 books, including Evolution: Making Sense of Life.