Retro moon: Cassini spacecraft studies moon that orbits Saturn backward

The tiny moon of Hyrrokkin is one of the Norse group of Saturn's 60 or so moons, which orbits the gas giant in a retrograde direction.

|
NASA/JPL-Caltech/Space Science Institute
Tiny Hyrrokkin hides amongst a field of stars in this image taken by NASA's Cassini spacecraft on Aug. 7, 2015.

Sen—When we think of the moons of Saturn, many worlds spring to mind: cloud-shrouded Titan, water-spewing Enceladus, and Death Star-like Mimas merely form the head of the line. But, while impressive, these satellites and others like them form a relatively small fraction of all Saturnian moons. Wandering much farther from Saturn is a group whose population comprises nearly half of the planet’s more than 60 satellites, and this week NASA’s Cassini spacecraft took time to study one of these distant objects.

Twenty-nine moons make up the so-called Norse group of satellites around Saturn. Only large Phoebe has been studied in detail, but this week’s target, Hyrrokkin, is much smaller— only around 8 km in size—and farther away. That means that even in Cassini’s high-powered Narrow-Angle Camera, Hyrrokkin appears as nothing more than a point of light.

What can we learn from that point of light? For one, it will help scientists pin down the moon’s orbital trajectory. Hyrrokkin’s orbit has high eccentricity, meaning it moves dramatically closer and farther from Saturn as it circles the planet. But what sets the Norse group apart is the direction they orbit: retrograde, astronomy jargon for backwards. This means that these objects probably did not form with Saturn. Instead, over the last few billion years, they were probably captured when straying too close to the planet.

By monitoring how the apparent brightness of Hyrrokkin changes over time, astronomers will also be able to deduce better constraints on the shape and rotational characteristics of the moon.

The Cassini-Huygens mission is a collaborative effort between NASA, ESA, and the Italian Space Agency. Launched in 1997, it reached Saturn in 2004 and has since been studying the planet, its moons, and its rings. In 2005, the Huygens probe made the first landing on Titan, Saturn’s largest moon. After completing its second mission extension in 2017, Cassini will make a series of close passes to the planet and then end its time at Saturn by plunging into the planet’s atmosphere.

Related Links:

Saturn's oddball Phoebe was a wannabe planet

Cassini studies tiny, distant moon Kiviuq

More on Cassini

Original story from Sen. © 2015 Sen TV Limited. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. For more space news visit Sen.com and follow @sen on Twitter.

Follow CSMonitor's board Astronomy on Pinterest.
You've read  of  free articles. Subscribe to continue.
Real news can be honest, hopeful, credible, constructive.
What is the Monitor difference? Tackling the tough headlines – with humanity. Listening to sources – with respect. Seeing the story that others are missing by reporting what so often gets overlooked: the values that connect us. That’s Monitor reporting – news that changes how you see the world.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to CSMonitor.com.

QR Code to Retro moon: Cassini spacecraft studies moon that orbits Saturn backward
Read this article in
https://www.csmonitor.com/Science/2015/0817/Retro-moon-Cassini-spacecraft-studies-moon-that-orbits-Saturn-backward
QR Code to Subscription page
Start your subscription today
https://www.csmonitor.com/subscribe