Feeds

Boffins crack walnut-shaped Iapetus moon mystery

Moon-moon became ring, prominent bulge followed

Top 5 reasons to deploy VMware with Tegile

Space boffins studying the puzzling mystery of Iapetus, the walnut-shaped moon of Saturn, believe they may have discovered how the strange body's unique equatorial ridge was formed. The mighty ridge at some places stands 12 miles above the surface average – more than twice as high as Mount Everest's summit is above sea level.

Iapetus, walnut-shaped moon of Saturn. Credit: NASA/JPL/SSI

Saturnian moon, ideal with port

According to William McKinnon and Andrew Dombard, space-sciences profs in America, the curious ridge results from the long-ago breakup of a satellite body in orbit about Iapetus – a moon of a moon.

"Some people have proposed that the ridge might have been caused by a string of volcanic eruptions, or maybe it's a set of faults," says McKinnon. "But to align it all perfectly like that – there is just no similar example in the solar system to point to such a thing."

Dombard adds: "There are three critical observations that any model for the formation of the ridge has to satisfy. They are: Why the feature is sitting on the equator; why only on the equator, and why only on Iapetus. I think we have something here that explains all those observations."

According to the calculations of the two profs and their colleagues, the ancient satellite-satellite would have gradually descended towards the surface of Iapetus as its orbit decayed. At a given point, tidal stress would finally have torn it apart, generating a ring of debris whose pieces would continue to descend until they crashed into the moon's equator, eventually creating the ridge we see today and so giving Iapetus its curious festive-nut-esque shape.

"When you have a debris ring around a body, the collisional interactions steal energy out of the orbit," explains Dombard. "And the lowest energy state that a body can be in is right over the rotational bulge of a planetary body – the equator. That's why the rings of Jupiter, Saturn, Uranus and Neptune are over the equator."

The equatorial ridge of Iapetus, imaged by the Cassini probe. Credit: NASA/JPL/SSI

More than twice as tall as Mount Everest

"Imagine all of these particles coming down horizontally across the equatorial surface at about 400 meters per second, the speed of a rifle bullet, one after the other, like frozen baseballs," chips in McKinnon. "Particles would impact one by one, over and over again on the equatorial line. At first the debris would have made holes to form a groove that eventually filled up."

The scientists believe that the ripped-up-moon theory also neatly explains why it is only Iapetus that has such a ridge.

"Only Iapetus could have had the orbital space for the sub-satellite to then evolve and come down toward its surface and break up and supply the ridge," contends Dombard.

It seems that with moons – or moons of moons – in general they will recede from their parent body if they are further out than geosynchronous orbit, as in the case of our own Moon. But if they are inside this limit, as the ancient satellite of Iapetus was, they will gradually spiral inward, break up, and then scatter themselves on the surface.

Dombard will make a presentation on the team's preliminary findings on Wednesday at a convention in San Francisco. ®

Choosing a cloud hosting partner with confidence

More from The Register

next story
Rosetta probot drilling DENIED: Philae has its 'LEG in the AIR'
NOT best position for scientific fulfillment
'Yes, yes... YES!' Philae lands on COMET 67P
Plucky probot aces landing on high-speed space rock - emotional scenes in Darmstadt
THERE it is! Philae comet lander FOUND in EXISTING Rosetta PICS
Crumb? Pixel? ALIEN? Better, it's a comet-catcher!
SEX BEAST SEALS may be egging each other on to ATTACK PENGUINS
Boffin: 'I think the behaviour is increasing in frequency'
HUMAN DNA 'will be FOUND ON MOON' – rocking boffin Brian Cox
Crowdfund plan to stimulate Blighty's space programme
Post-pub nosh neckfiller: The MIGHTY Scotch egg
Off to the boozer? This delicacy might help mitigate the effects
I'M SO SORRY, sobs Rosetta Brit boffin in 'sexist' sexy shirt storm
'He is just being himself' says proud mum of larger-than-life physicist
NASA launches new climate model at SC14
75 days of supercomputing later ...
prev story

Whitepapers

Why and how to choose the right cloud vendor
The benefits of cloud-based storage in your processes. Eliminate onsite, disk-based backup and archiving in favor of cloud-based data protection.
A strategic approach to identity relationship management
ForgeRock commissioned Forrester to evaluate companies’ IAM practices and requirements when it comes to customer-facing scenarios versus employee-facing ones.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Beginner's guide to SSL certificates
De-mystify the technology involved and give you the information you need to make the best decision when considering your online security options.
Top 5 reasons to deploy VMware with Tegile
Data demand and the rise of virtualization is challenging IT teams to deliver storage performance, scalability and capacity that can keep up, while maximizing efficiency.