Scroll down to read this post.


My July fund-raising campaign, celebrating the 13th anniversary of the start of this website, has now ended. This was the second most successful monthly fund-raising campaign ever. Thank you again to everyone who has who donated or subscribed. It is difficult to explain what your support means to me.


You can still donate or subscribe to support my work if you wish, either by giving a one-time contribution or a regular subscription. There are four ways of doing so:


1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.


2. Patreon: Go to my website there and pick one of five monthly subscription amounts, or by making a one-time donation.

3. A Paypal Donation:

4. A Paypal subscription:

5. Donate by check, payable to Robert Zimmerman and mailed to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652

The rings of Saturn

The rings of Saturn up close

Cool image time! The image to the right, cropped to post here, is part of one of the closest and highest resolution images that Cassini has yet taken of Saturn’s rings. The image was taken in January during one of the spacecraft’s ring grazing orbits, and has a resolution of 2,300 feet per pixel. And yet, as noted by the Cassini science team, “Even at this level of detail, it is still not fine enough to resolve the individual particles that make up the ring.”

In prepping the image, all I did was crop it to show the closest rings. I purposely did not reduce its resolution, so that you can see that no individual particles are visible. The rings of Saturn are truly made up of billions of small objects, behaving in many ways like liquid floating in the gravity well of Saturn. If you don’t believe me, download the full image and zoom in on it as much as you like. All you will see are pixels.

The fundamental science question therefore is not how Saturn’s rings behave (though this is certainly important and quite fascinating) but why did those rings end up the way they are. No other planet has rings anything like Saturn’s in their density and make-up. Why? Are Saturn’s rings a normal process that only occurs for short times around planets, which is why only Saturn has these types of rings at present? Or is it a rare event, so rare that we happen to be very lucky to see such a thing at all?

Even more important, Saturn’s rings and their behavior are likely linked closely to the same phenomenon that describe the formation of planets around a star. The more we can learn about why these rings exist, the more we will learn about why planets exist, both here circling the Sun as well as around stars everywhere else.

Genesis cover

On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.

The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.

The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.

"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News


  • BSJ

    I wonder if Cassini’s cameras are ‘fast’ enough to capture fine detail as it zip past on the closer approaches.

  • Diane Wilson

    If camera “speed” (really sensor speed) is the only issue, the result might be streaks in place of particles. We can still learn a lot from streaks. If the issue is resolution, well, we still don’t know the particle size, so I don’t think we can do more than guess. Yet.

    I’d love to know how much real control the Cassini team has over its orbit. If Cassini could come close to matching velocity with the rings, then we would get some truly astonishing images.

    This does promise to be an interesting year, with Cassini’s mission end, Juno, Curiosity finally across the dunes, and SpaceX’s several possibilities (Falcon Heavy, reusing both Falcon and Dragon, Dragon 2 first flight). Let’s hope that all the surprises this year are good ones.

  • LocalFluff

    If ringed planets were common, I would think that many confirmed transiting exoplanets would have had them. I don’t think more than a handful out of 4000 exoplanets have been detected to have rings. There was an online talk on how to discover exoplanetary rings on the SETI institute just the other week, I haven’t seen, but Cassini makes this topic hot this year:

    Since the particles are so small and bafflingly well organized, just intuitively to me it looks as if the ring system is VERY long lived. What force is there around to disrupt this? Still I heard only months ago that they could be as young as 0.2 billion years, based on how three or so of the moons near the rings should’ve changed orbital resonances with each other. That was probably also a SETI talk.

  • BSJ

    All of our gas giants have rings.

  • BSJ: Of course they all do. But when you can take a picture of Jupiter, Neptune, Uranus and show a ring as striking as Saturn’s, talk to me then. The differences here are quite profound. Don’t be silly and make believe they don’t exist.

  • LocalFluff

    Even Mars will have rings in only 10-30 million or so years (at 99% of Mars’ existence, active old warrior!) when its moon Phobos disintegrates from tidal forces. It is supposed to transform from a discernible moon to a ring within a matter of weeks when it happens. Phobos is a more than half-vacuous “ring in a box” to be delivered. Rings could be common also at terrestrial planets.

    Earth cannot have any small rubble pile moonlet because our Big Sister Luna wouldn’t accept it with her eccentric orbit. Luna has cleared away anything during her billions of years long spiraling outwards.

    Venus could’ve had moonlets like Phobos. Maybe that was what destroyed her life? After having been endowed with a ring of marriage for a while before it came crashing down and melted her surface maybe about 0.3 billion years ago.

    Mercury is way too eccentric, the Sun would’ve rubbed him of any moonlets right from the nursery home.

    The (new) planet definition is based on roundness. If a collection of mass is great enough to have its own gravity push it to became round(ish), then it will also stick together. Anything less than roundish is at great risk of being tidally disrupted by anything major in its vicinity. The Moon will never get tidally disrupted (because it is round). Phobos will (because it isn’t round). That is probably not an explicit part of the new planet definition (because there are likely some exceptions), but it is an argument for it.

  • BSJ

    My response was to The Local Fluffer’s “If ringed planets were common,” comment.

    100% in our system makes ’em pretty common in my book.

Readers: the rules for commenting!


No registration is required. I welcome all opinions, even those that strongly criticize my commentary.


However, name-calling and obscenities will not be tolerated. First time offenders who are new to the site will be warned. Second time offenders or first time offenders who have been here awhile will be suspended for a week. After that, I will ban you. Period.


Note also that first time commenters as well as any comment with more than one link will be placed in moderation for my approval. Be patient, I will get to it.

Leave a Reply

Your email address will not be published. Required fields are marked *