Subscribe to our free daily newsletters
. 24/7 Space News .




Subscribe to our free daily newsletters



Case Of Sedna's Missing Moon Solved

Artist's rendering of Sedna.
Cambridge MA (SPX) Apr 06, 2005
When the distant planetoid Sedna was discovered on the outer edges of our solar system, it posed a puzzle to scientists. Sedna appeared to be spinning very slowly compared to most solar system objects, completing one rotation every 20 days.

Astronomers hypothesized that this world possessed an unseen moon whose gravity was slowing Sedna's spin. Yet Hubble Space Telescope images showed no sign of a moon large enough to affect Sedna.

New measurements by Scott Gaudi, Krzysztof (Kris) Stanek and colleagues at the Harvard-Smithsonian Center for Astrophysics (CfA) have cleared up this mystery by showing that a moon wasn't needed after all.

Sedna is rotating much more rapidly than originally believed, spinning once on its axis every 10 hours. This shorter rotation period is typical of planetoids in our solar system, requiring no external influences to explain.

"We've solved the case of Sedna's missing moon. The moon didn't vanish because it was never there to begin with," said Gaudi.

Sedna is an odd world whose extreme orbit takes it more than 45 billion miles from the Sun, or more than 500 astronomical units (where one astronomical unit is the average Earth-Sun distance of 93 million miles).

Sedna never approaches the Sun any closer than 80 astronomical units, and takes 10,000 years to complete one orbit.

In comparison, Pluto's 248-year-long oval orbit takes it between 30 and 50 astronomical units from the Sun.

"Up until now, Sedna appeared strange in every way it had been studied. Every property of Sedna that we'd been able to measure was atypical," said Gaudi.

"We've shown that Sedna's rotation period, at least, is entirely normal."

Sedna appears unusual in other ways besides its orbit. First and foremost, it is one of the largest known "minor planets," with an estimated size of 1,000 miles compared to Pluto's 1,400 miles. Sedna also displays an unusually red color that is still unexplained.

Initial measurements indicated that Sedna's rotation period was also extreme - extremely long compared to other solar system residents.

By measuring small brightness fluctuations, scientists estimated that Sedna rotated once every 20-40 days. Such slow rotation likely would require the presence of a nearby large moon whose gravity could apply the brakes and slow Sedna's spin.

As a result of this interpretation, artist's concepts released when Sedna's discovery was announced showed a companion moon. One month later, images taken by NASA's Hubble Space Telescope demonstrated that no large moon existed.

In true detective fashion, Gaudi and his colleagues re-investigated the matter by observing Sedna using the new MegaCam instrument on the

6. 5-meter-diameter MMT Telescope at Mount Hopkins, Ariz.

They measured Sedna's brightness looking for telltale, periodic brightening and dimming that would show how fast Sedna rotates.

As noted by Matthew Holman, one of the members of the CfA team, "The variation in Sedna's brightness is quite small and could have been easily overlooked."

Their data fits a computer model in which Sedna rotates once every 10 hours or so. The team's measurements definitively rule out a rotation period shorter than 5 hours or longer than 10 days.

While these data solve one mystery of Sedna, other mysteries remain. Chief among them is the question of how Sedna arrived in its highly elliptical, eons-long orbit.

"Theorists are working hard to try to figure out where Sedna came from," said Gaudi.

Astronomers will continue to study this strange world for some time to come.

"This is a completely unique object in our solar system, so anything we can learn about it will be helpful in understanding its origin," said Stanek.

This research has been submitted to The Astrophysical Journal Letters for publication and is posted online at http://arxiv.org/abs/astro-ph/0503673

Related Links
SpaceDaily
Search SpaceDaily
Subscribe To SpaceDaily Express

SwRI Researchers Show Planetoid Sedna May Have Formed Far Beyond Pluto
Boulder CO (SPX) Jan 12, 2005
Recently, astronomers reported the surprising discovery of a very large diameter Kuiper Belt planetoid - (90377) Sedna - on a distant, 12,500-year-long, eccentric orbit centered approximately 500 astronomical units from the Sun.



Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only






Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News








The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.