Something else besides a toastier Earth to look forward to in 2007 comes in September when the NASA peeper Cassini has another skid past Iapetus, #17 in Saturn’s seemingly endless brood of moons (33 and counting), and at 900 miles wide its third largest.

The spacecraft was last there on New Year’s Eve 2004 and got some drunken-college-girls snapshots that whetted appetites for more among the men of science and the men of pseudo-science, because either way you look at it, there are some remarkable features on this frosty globe named after the son of Uranus and father of the fathers of mankind, Prometheus and Atlas. Iapetus is Granddad to everyone on Earth.

This story is appealing to amateur geologists like me who got their start by breaking fingernails trying to pry apart factory-built earth globes along that equatorial ridge to see what was inside. Iapetus has one of those ridges, on the equator no less, and we’ve got a guy here named Richard Hoagland who’s sure it’s as hollow as those tin classroom globes.

One busy photographer everywhere in Saturn’s neighbourhood, Cassini is on a another sentimental journey as it returns to this specific moon: Iapetus was first spotted in 1671 by Jean-Dominique Cassini, France’s chief astronomer, after whom the shutterbug was named.

The 2004 pictures were tantalising but still too remote. Next autumn’s visit will produce images 100 times better.

For NASA, it looks like a lot of unusual volcanic activity was once going on there. For Richard Hoagland, who noisily continues to insist that the infamous “Face on Mars” is man-made, it looks like a lot of construction activity took place on Iapetus. His claims are amusing almost to the point of hilarity, but it’s wonderful to see how his mind works. Only the commercial aspect of his website stops me from saying, “Okay, Rich, let’s see more.”

Where NASA admits to “anomalies” on what is already a strange astral body (the hemispheres are in different shades), Hoagland charges in with many, many exclamation marks and “proof” that the ridge he calls “the Great Wall of Iapetus” is an artificial wall 60,000 feet high, 60,000 feet wide, and four million feet long (everything sounds better in feet), right on its equator.

Hoagland: “Clearly these are NOT random, ’square craters’ — but remarkable, highly ordered evidence of sophisticated, aligned, repeating architectural relief!” He says many of the craters “clearly” lined up along north-south, east-west lines are collapsed hexagons, the foundations of bygone geodesic domes, and he poses this question: “What if Iapetus is not a natural satellite at all … but a 900-mile-wide spacecraft — an artificial ‘moon’?!”

Naturally, he’s not going to let anyone else answer the question, jumping in to head off our resonse: “Iapetus is not one of the normal ‘moons’ of Saturn — but is actually a 900-mile-wide, manufactured, ancient world-sized spaceship!”

Much of the intrigue in his theory comes from colourfully citing Arthur C Clarke and Jules Verne, as well as Bucky Fuller. And, since one guy can’t be a conspiracy, Hoagland has Tobias Owen (who first noticed the face on Mars) and Donald Goldsmith writing in “The Search for Life in the Universe” that Iapetus is “the only object in the Solar System which we might seriously regard as an alien signpost — a natural object deliberately modified by an advanced civilisation to attract our attention”.

The Cassini mission to Saturn was a great success, even landing its Huygens probe on the moon Titan, but Voyager 1 had sent us postcards from “two-toned” Iapetus (”the yin-yang moon”) in 1980 and Voyager 2 a year later. Photo credits for the long shots of Iapetus goes to the Voyager twins.