Date: May 4, 2010
Title: Iapetus and the Cassini Regio
Podcaster: Alice Enevoldsen
Organization: Pacific Science Center, Seattle, WA and Alice’s AstroInfo: pacificsciencecenter.org and alicesastroinfo.com
Description: In today’s podcast Alice answers a phone call from a friend, and tells her a story about Cassini’s mysterious moon, Iapetus.
Bio: Alice Enevoldsen is currently the planetarium specialist at Pacific Science Center in Seattle, Washington, a part-time evening Astronomy instructor at South Seattle Community College, and volunteers as one of NASA’s Solar System Ambassadors. She has been working in planetariums since 1996, has a B.A. in Astronomy-Geology from Whitman College, and a Masters in Teaching from Seattle University. Her fascination with the stars led her to try her hand at astronomy research, where she realized that her calling in life was actually to share her love of the stars and excitement about astronomy with as many people as possible.
Today’s sponsor: This episode of “365 Days of Astronomy” is brought to you by Bob Moler, an amateur astronomer in northern lower Michigan, and volunteer broadcaster of the week-daily astronomy program, Ephemeris, on Interlochen Public for what will be 35 years this June 1st.
Additional sponsorship for this episode of 365 Days of Astronomy has been provided by Kylie Sturgess and the Token Skeptic podcast, a weekly show about superstition, science and why we believe – at www.tokenskeptic.org.
Transcript:
Hello this is Alice? … Oh hello! I’m so glad you called, I’ve got a great story to tell you:
Iapetus and the Cassini Regio by Alice Enevoldsen
Once upon a time there was a moon named Iapetus. She orbited Saturn at a distance of over 3 and a half million kilometers, and there were only two larger moons of Saturn, but still all the other moons made fun of her.
They made fun of her because her front hemisphere was a lot darker than her back hemisphere. This darker area was called the Cassini Regio, but the other moons laughed at her and said she looked like a spherical Oreo. Iapetus thought this wasn’t really fair, since she wasn’t even spherical herself, more lumpy in places.
One July, the Cassini Spacecraft showed up. He noticed how the other moons wouldn’t let Iapetus play with them, and how they always made fun of her. “Come over here, Iapetus,” he said, “I have a story to tell you.”
“Me?” asked Iapetus, “You have a story to tell me?”
“Yes, but only for you, your other friends don’t get to listen to this story.”
Suddenly the play-space became silent. The other moons stopped their games, their hula-hoops fell off, the ones running on the track slowed down, and they all turned around to look at Cassini and Iapetus talking quietly as they orbited around Saturn.
“Once upon a time there was a moon named Iapetus,” started Cassini.
“No, no! We already did that part, Cassini!” protested Iapetus, “get to the good part!”
“Well,” said Cassini, “the first time anyone from Earth saw Iapetus was in 1671, and that man’s name was Cassini.”
“Hey, that’s your name too! Wait, which one is Earth, is that the third or the fourth one out from the Sun?” asked Iapetus.
“Fourth, silly!” said Titan, one of the other moons, stepping closer to Cassini. “Don’t you know anything?”
“I’m not silly!” yelled Iapetus.
“Titan, Earth is the third one. Now if you’re going to listen you both need to sit down and be quiet like Phoebe,” said Cassini gently. “Back then no one knew what mysteries awaited them on the surface of Iapetus.”
“See? I’m not silly, I’m mysterious!” said Iapetus, sticking out her tongue at Titan.
“Shh! No more interruptions.” Cassini frowned at the two of them.
“Since Voyagers 1 and 2 first glimpsed Iapetus’s interesting surface there has been much speculation by scientists all over Earth about how Iapetus came to be this way. I will tell you a few of these ideas, and then Iapetus can tell us what really happened.
“The first idea involves Phoebe. Where is Phoebe? Ah, there she is. A scientist named Hamilton proposed that micrometeors could have knocked some dark dust off Phoebe, then Iapetus could have swept up this material such that it all collected on the front hemisphere.”
“But Cassini, I’m a different color than either Iapetus’s dark side or Iapetus’s light side. I don’t think we’re related!” protested Phoebe.
“Yes, that’s a problem with this idea, as the Earth scientists found out in 1998,” said Cassini.
“What about me?” asked Hyperion, “I’m close to Iapetus too, maybe I’m part of this.”
“That was the very next idea I was going to mention, Hyperion, thank you for bringing it up. There are two different theories relating to you. The first thing though is to find out if the dust can actually get from Hyperion to Iapetus. The scientist Marchi and his colleagues think that’s pretty easy, but how do you get the dust off Hyperion in the first place?”
“Hit it with something!” chorused all the moons of Saturn, making a terrible racket and almost waking the Sun up from her mid-afternoon nap.
“I see you know the secret,” agreed Cassini. “If you need to get something from one place to another in the Solar System, you usually need to slam two things together.”
“And look,” said Hyperion, holding his arm up next to Iapetus’s dark side, “we’re basically the same color on this side of Iapetus.”
“So you are,” observed Cassini. “That makes this idea seem plausible. One last puzzling idea is that perhaps this dark material is from somewhere else, and was collected on both of you.
“One of my jobs in coming here is to take a better look at you Iapetus, and see if I can provide any useful data for the scientists to use in figuring out where your Cassini Regio came from. Do you know the answer?”
“Wow, everyone’s looking at me?” asked Iapetus, “I dunno, I can’t remember when it happened. I am pretty sure that the light side of me is ice, because my backside is always a little chilly. Anyway, if I did know where the dark stuff came from, shouldn’t I leave it as a puzzle for you to find out?” With that she ran off to play hula-hoop by herself, but Hyperion and some of the smaller moons followed her and they all started a game of Occultation.
The End
This story is an example of what my friend Michael likes to call a fact-tale. It’s like a fairy tale, except it’s true. Now obviously not all of it is true: Iapetus doesn’t play hula hoop, Cassini doesn’t talk and tell a story to the moons, and I don’t think the Sun takes a mid-afternoon nap. But I hope that you’re able to tease apart the parts of the story that are true (the mysteries of Iapetus) and the parts of the story that are made up. I hope you had fun listening to it, I certainly had fun writing it.
More is being learned about Iapetus every year, and this story was originally written in 2003. If you’d like to learn more about Iapetus stop by my website (Alice’s AstroInfo.com), Emily Lakdawalla’s blog at the Planetary Society, or NASA’s Cassini mission homepage. All these links will be up on the 365 Days of Astronomy Website.
Stay tuned for further mysteries of the Solar System: Iapetus and the Equatorial Ridge, Mars and the Missing Water, and more!
I’ll talk to you later… bye!
http://www.alicesastroinfo.com – Alice’s AstroInfo
http://redrover.planetary.org/blog/article/00001202/ – Emily Lakdawalla about Iapetus
http://saturn.jpl.nasa.gov/ – NASA’s Cassini Homepage
End of podcast:
365 Days of Astronomy
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