Show Date: August 16, 2006 
Pam Eastlick for THE DEEP on line

THE DEATH STAR MOON

Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond. Join us each week on Newstalk K57 on Wednesday night from 7 to 8 p.m. for exciting live science expeditions or listen live on our web site www.thedeepradioshow.com

Ever since we discovered that Mars is a cold dry desert with no liquid water and that the surface of Venus very closely approximates most religious concepts of hell, many science fiction writers have moved their aliens and alien ecosystems to planets that circle other stars. Perhaps they’ve abandoned the solar system too soon. Our wandering robot spacecraft have discovered some bizarre and wonderful worlds right here in our very own backyard; the moons of the outer planets.
Some of these moons apparently harbor world-sized oceans. We’ve long speculated that Jupiter’s Europa, Ganymede and Callisto each harbor more liquid water than the seas of Earth hidden beneath their solidly frozen ice crusts. They all wobble as they orbit Jupiter, implying that some of their insides are liquid. These are NOT small worlds; Ganymede, the solar system’s largest Moon is bigger than Mercury!

We currently have a very sophisticated robot in orbit around Saturn and the Cassini spacecraft has taken pictures of a fountain of water erupting from the surface of Saturn’s Moon Enceladus. We don’t have to speculate about Enceladus; we know it contains liquid water and as one of the scientists who studies Europa said “Do you really think you can have a liquid water ocean for 5 billion years and NOT have life in it?”

But in my opinion, these world oceans can’t hold a candle to the most bizarre moon in the solar system. For me, that honor belongs to one of Saturn’s medium-sized moons, Iapetus. Iapetus is little over 500 miles across, making it about one quarter the size of our own Moon. Iapetus also has a very low density implying that the entire moon is made of water ice. We’ve known for years that there was something a little odd about Iapetus; because one half of it is blacker than charcoal and the other half is blindingly white. The dark half is the moon’s leading edge, which implies that it’s running over dark material although it could have come from the interior of Iapetus.
Iapetus:
Half black: Half white

The robot Cassini has discovered that the dark material is very thin, implying that it came from outside Iapetus, but that’s not all Cassini discovered. At the equator, on the dark side, there is a 12-mile tall seam. It extends over 800 miles and in some places, it’s almost as tall as Olympus Mons on Mars (the highest mountain in the solar system). Furthermore, Iapetus is neither a sphere nor an ellipse—unusual for a large moon; parts of its globe appears to be squashed flat, and the equatorial ridge is so high it visibly distorts the moon's shape even when viewed from a distance. Virtually all Saturn’s moons orbit in the same plane as the rings, but not Iapetus, its orbit is tilted almost 15 degrees (compare to Pluto’s inclination of 17 degrees).

The dark side of Iapetus

So what’s up with Iapetus? Scientists quite frankly don’t know and we’ll have to wait a year for more information. The Cassini spacecraft will make a very close approach to this mystery moon in September 2007. Of course, there’s other speculation as well. The very light density of Iapetus could be explained if it were....hollow. That density and the odd color patterns have occasionally led to speculation that Iapetus might be an artificial construction made by aliens. The discoveries of the ‘seam’ and the moon’s strange shape (not considered likely to have happened because of the pressures generated by its own gravity) have only added fuel to these speculations. Join us this week on The Deep as we talk about some of the solar system’s odder moons. The Deep is broadcast on Newstalk K57 every Wednesday night at 7:00 p.m. You can also listen live from our web site www.thedeepradioshow.com. Join Jim Sullivan, Pam Eastlick, and Peter Melyan on the deepest radio show on Earth.
	The equatorial seam