A Moon, A Mystery (Iapetus) PDF Print E-mail

Originally Posted on "Phenomena Magazine" Website

Andrew Johnson ( This e-mail address is being protected from spam bots, you need JavaScript enabled to view it ), Sept 2005

To Coldly Go…

For some people, the unmanned Space Exploration Programme has been far more interesting and exciting than the manned space programme. In the last 35 years, those who have taken an interest in the Solar System have witnessed the discovery of new Planetary Ring Systems, many new moons orbiting Saturn and Jupiter, active volcanoes on Jupiter’s moon Io, Neptune’s dark spot, Aurorae in the polar regions of Jupiter and Saturn and hundreds of bewilderingly beautiful images from the Hubble Space Telescope. One of the objects in the Solar System that the Hubble Space telescope does not appear to have photographed in any detail, however, is Iapetus – the third-largest moon of Saturn.  In Greek mythology, Iapetus was a Titan – a God - the son of Uranus and Gaia and the ancestor of mankind.

Moon - Light / Shadow

From the time it was discovered in 1671 by Giovanni Domenico Cassini, Iapetus has always been something of a mystery. One of the amazing things to consider is that Cassini observed Iapetus, over 740 million miles distant, using a 17th century refracting telescope whose main lens was only two inches in diameter! (A refracting telescope is one in which only lenses are used, rather than a combination of lenses and mirrors.) When Cassini observed Iapetus over a period of time, he was puzzled – every 40 days or so, it seemed to disappear from view, then re-appear 40 days later. He suggested that Iapetus had a light side and a dark side, and that it always kept the same face turned to Saturn (in the same way that our moon always keeps the same face turned to the Earth).

The orbit of Iapetus around Saturn is somewhat unusual – all but one of Saturn’s other moons orbit “at the same level” as the Ring System (i.e. “in the same plane”) – Iapetus orbits at an angle inclined to the ring system of about 15º. (Phoebe’s orbit is inclined at about 5º in the opposite direction).

The reason for such an orbital inclination is generally assumed to be because the object has been “captured” by the gravitational attraction of the body that it orbits. In other words, it is thought that the object (Iapetus in this case) did not form out of the same cloud of material as the rest of the system. (Similar theories are used to explain the orbit of Pluto, which is also inclined to the plane of all the other planetary orbits). 

“Fly Me to That Moon”

Just over 300 years after the discovery of Iapetus - on August 20th, 1977, Voyager 2 blasted off from the Kennedy Space Centre at Cape Canaveral, Florida. A 4-year journey of fabulous discoveries took the probe to the Saturnian System. In August 1981, we got our first close-up view of this orbiting oddity. Not surprisingly, little fanfare was made of this event, because Iapetus is a relatively obscure object.

As Cassini had predicted, Iapetus’s surface was half dark and half light – the dark half was about 10 times darker than the light half. No explanation was found or given for this.

Voyager pictures seemed to show that the other features of the moon, however, were “run of the mill” – just consisting of cratered rocky features.

The Voyager Spacecraft was used to make more accurate measurements of this unusual moon – to calculate its mass and density. Certain optical measurements were also made and these seemed to indicate that there was another potential mystery – the moon was not a perfect sphere – or at least, it was less spherical than it should be, when compared to other large Saturnian moons such as Titan and Enceladus.

The relative density of Iapetus was also calculated – and found to be about 1.1 or 1.2 (This means it is about 20 or 30% heavier than a similar sized body made of ice). The consensus of opinion is that Iapetus, and many of the moons of similar density, is/are made mainly from water ice.

After taking about 18,000 pictures in the Saturnian system, Voyager was bound for Uranus, and it would be over 20 years before we got our next “eyeball on Iapetus”.

Moon Safari

Following the priceless data gathered by the Voyager probes, more spacecraft were designed, built and launched to both Saturn and Jupiter to get higher resolution pictures and better data. The Galileo Mission launched to Jupiter in 1989, was a huge success and featured a pod which was ejected into the Jovian Atmosphere. In the latter days of this mission, the probe flew through sulphurous clouds only about 200 miles above the surface of the volcanically active moon, Io.

In 1997, an advanced new probe, Cassini (named after the person who discovered Iapetus) was launched. By July 2004, Cassini had reached Iapetus in the Saturnian system. The picture it sent back showed the same elliptically-shaped dark region on the surface of Iapetus

(, but later, on December 31st 2004, Cassini had a much closer encounter – passing at a distance of 40,000 miles.

Dark Side of the Moon

The high resolution pictures returned were posted on the JPL Cassini Mission Website on 7th Jan 2005 ( and they included an astounding discovery:

The most unique, and perhaps most remarkable feature discovered on Iapetus in Cassini images is a topographic ridge that coincides almost exactly with the geographic equator. The ridge is conspicuous in the picture as an approximately 20-kilometer wide (12 miles) band that extends from the western (left) side of the disc almost to the day/night boundary on the right. On the left horizon, the peak of the ridge reaches at least 13 kilometers (8 miles) above the surrounding terrain. Along the roughly 1,300 kilometer (800 mile) length over which it can be traced in this picture, it remains almost exactly parallel to the equator within a couple of degrees. The physical origin of the ridge has yet to be explained.

Only the following explanations of this extraordinary feature were suggested:

It is not yet clear whether the ridge is a mountain belt that has folded upward, or an extensional crack in the surface through which material from inside Iapetus erupted onto the surface and accumulated locally, forming the ridge.

So they are suggesting that it is either an extensive mountain range or a long crack, from which material has been ejected. At first glance, these ideas seem acceptable. However, a small amount of further consideration seems to show they are very unlikely as suitable explanations.

The first “problem” is that the ridge is linear – it runs in a straight line for 800 miles. I can think of no other natural geological features either on Earth or elsewhere in the Solar System which are on this scale, and have such a regular structure. As with anomalies on Mars, it seems difficult to accept that features which exhibit some kind of regular geometry are wholly natural. Indeed, some scientists would agree that evidence of civilisation on a planet can be found in the geometry of surface features.

Natural processes of planet formation are generally chaotic. Clearly, they do not always result in complete irregularity – planets are spherical, for example, and seem to have a layered structure of an atmosphere, a crust, a mantle and so on. But lifeless processes such as vulcanism and tectonic activity create, without exception, features which are irregular and random (on a scale of miles, at least).

The other two oddities with this 12-mile-high ridge are that it runs round the equator and that it divides the darker region on Iapetus’s surface neatly into 2 halves. The equatorial positioning of the ridge could possibly be explained by some effect of centripetal (“spinning”) force as the moon was forming, but if this was true, why don’t we see a remotely similar feature on any other rocky moon of Saturn or Jupiter? Why don’t we see a light/dark colouration for that matter?

According to

The pronounced ridge around its equator has no place in the theory of gravitationally collapsing clouds.

In other words, assuming the accepted models of how planets and satellites form, there is no part of any theory (that I am aware of) that accounts for the existence of the ridge. So, the questions remain - how can a ridge form which is 800 miles long and 8-12 miles high and which runs almost precisely along the equator of this moon? What natural processes could cause this? Isn’t this a fabulous discovery? Why have NASA shown no public interest in it and decided not to try and photograph it again until 2007? It seems like there is a similar attitude to the data about Mars anomalies – NASA will not publicly acknowledge the extent of its strangeness and neither have they attempted to produce coherent models to explain how such features could form naturally.

The discovery of the ridge seems to me to be one which demands a vigorous application of Science rather than a casual discardment of the data. There is still the 300-year-old mystery of the dark colouration of approximately half of Iapetus’s surface. What answers have NASA given for this? From

“The origin of Cassini Regio is a long-standing debate among scientists. One theory proposes that its dark material may have erupted onto Iapetus's icy surface from the interior. Another theory holds that the dark material represented accumulated debris ejected by impact events on dark, outer satellites of Saturn. Details of this Cassini image mosaic do not definitively rule out either of the theories.”

These statements do not mention the curious fact that the ridge bisects the dark region (called Cassini Regio) on Iapetus – this would seem an important observation if anyone wanted to explain one feature or the other.

“Radar, Love”

Another of the instruments which the Cassini probe is equipped with is a sophisticated radar system, capable of several modes of operation. This instrument was used to good effect to map the surface of Titan (which has a thick orange coloured atmosphere mainly of Nitrogen and Methane, which hides the surface) and in view of the discovery of the ridge could have been used to obtain more data about its structure.

Iapetus had already been “radar scanned” from Earth in 2002 using the newly-upgraded Arecibo Radio Telescope and the results obtained were described by Gregory Black, of the University of Virginia:

It is known that the bright [trailing] side is mostly water ice, but we find it does not reflect the radar like other icy satellites that we've studied with the radar before.  The ice on Iapetus appears much less reflective.

In June 2004, preliminary radar scan data for another Saturnian Moon, Phoebe, was discussed and a detailed Scientific Paper about it was released about 5 months later, for discussion at a Planetary Science Conference that November 2005. In this paper, reference was specifically made to intended future radar measurements of Iapetus during the December encounter. So where is this radar data? Doing a Google search of “radar Iapetus” reveals very little in the way of detailed information. Similar exercise for “Phoebe Radar” did produce a more meaningful set of information. Did some malfunction of the Cassini probe prevent successful operation of the radar equipment at the appropriate time when scanning Iapetus?

 A Rock and a Hard Place

Whilst it would be quite difficult for ordinary people to interpret radar data and come up with any sensible questions, there are other glaring oddities in the Iapetus photos that are on the NASA/JPL Websites. A closer look at the Iapetus images reveals some highly unusual craters. 2 Craters in particular are clearly not round. At least one crater is hexagonal in shape, with a raised mound in the centre. Another has an irregular shape (arguably more angular rather than circular) but it too, has an extraordinary linear ridge, roughly in the centre of the crater. Whether this crater formed as a result of an impact or through volcanic action, how can a linear ridge form approximately 24 miles (by my calculation) in length? Again, these extremely odd features are not addressed in NASA’s main description of the photograph.


Another question we can ponder is that if the density of Iapetus indicates it is mainly composed of water ice, wouldn’t this mean that the craters are more likely to be round, or at least, not hexagonal?

Marquee Moon?

Having looked objectively at the data presented here, it seems, from a certain point of view, rather difficult to understand why NASA, and many scientists who work on the data that NASA gather on their behalf, are not more willing to answer questions about Iapetus in a more rigorous fashion. Simple questions such as “Why the linear ridge? Why so long? Why so high?” In everyday life, “political correctness” is something most of us experience or encounter at one level or another. With the failure to engage with the anomalous data from Iapetus (and Mars), it seems all too clear to me now that mainstream science is strongly influenced by a form of “Intellectual Correctness”. This seems to stifle honest debate and discourage curious people (like me) from asking serious questions.

Richard Hoagland looks more deeply at the Iapetus mystery in a series of detailed articles, starting at He is often lambasted for his conclusions – more so than other commentators, perhaps, because he straddles the fields of what might be called “Alternative Astronomy” and its mainstream counterpart. Some criticise his conclusions, his style, or both. However, there seems to be no denying the anomalous nature of the data he presents. One has to consider carefully whether the data shows for sure that Iapetus is a wholly natural body, with features formed entirely by natural geological processes. The choice is a simple one. I believe that the data, even when taken in isolation, supports the idea that Iapetus is wholly or partly artificial in nature – is it this conclusion which gives NASA such cold shivers that they simply ignore the most interesting data and hope that no one will notice? It is my view that when the data from Iapetus is considered in a wider context, it is even less safe to assume that it was formed entirely by natural processes. As ever, you the reader, are left to decide this for yourself.

In the article linked above, it is suggested that, if Iapetus was once populated, it may have been some kind of "retreat" where people went "to enjoy the view". This video was made using Redshift 4 and shows a comparison of a view from Iapetus, looking towards Saturn with a similar view from Titan. As mentioned above, the orbit of Iapetus is inclined to the orbit of  the rings at an angle of about 15 degrees. Titan orbits in the plane of the orbit of the rings, which are then always seen "edge on". So compare how much more varied a view (over time) we see from Iapetus than from Titan.

Also see: Iapetus - A Moon, A Mystery


In a similar vein, what is going on on Mars?


On 10th September 2007, Cassini had a very close flyby of Iapetus. This image

(reproduced below)
Is one of only 5 new ones released posted in the NY TImes. Only 4 of these appear on the main Casini Iapetus page.
There should be some VERY interesting images. What's on the images NASA haven't posted yet? How many new images will we see? And the people watch and wait....

Last week, on Sept. 10, the Cassini probe swept by for a really close look at Iapetus, passing within 1,020 miles of its surface. The moon's odd topological features include a mountain ridge that runs around the moon's equator and reaches six miles high. The Cassini spacecraft first spotted the ridge in 2004. Considering Iapetus is only about 892 miles wide, those are huge mountains for a fairly small moon. How the ridge formed is not known.

Photo: NASA/JPL/Space Science Institute

*** PLEASE *** SHARE ON FACEBOOK ETC!Facebook!StumbleUpon!Free social bookmarking plugins and extensions for Joomla! websites! title=
< Prev   Next >