. 24/7 Space News .
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



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


Pluto's Horizon Gets Page One Treatment At NASA.gov
Washington DC (SPX) Mar 11, 2005
In March 1930 the Lowell Observatory in Arizona announced the discovery of a small, odd world, roaming beyond the known planets in a region barely visible through the most powerful telescopes.







  • Northrop Grumman, Boeing Announce Companies Supporting CEV Team
  • Wyle Joins "All-Star" Team To Propose New Crew Exploration Vehicle
  • Industry Panel Urges Space Shuttle Fly-Out Plan, Space Station Integration
  • Space Watch: A Cultural Change At NASA?

  • Durable Mars Rovers Sent Into Third Overtime Period
  • The Martian Mortal Coil
  • Spirit Slipping On New Terrain
  • Opportunity Takes Soil Survey As Rover Drives Over 200 Meters A Day

  • Sounding Rocket MASER 10 In Final Tests
  • LockMart Delivers Atlas V For Nasa's Mars Reconnaissance Orbiter Mission
  • Kazakhs, Russians Create Space Venture
  • Russian Space Launch Prices Scrutinized

  • Remote Sensing Helps New Caledonia Monitor Sediment Erosion
  • Climatologists Discover Deep-Sea Secret
  • Rate Of Atmospheric Co2 Increase Returns To Average, NOAA Reports
  • Indian Ocean Climate Watch Network Grows

  • Case Of Sedna's Missing Moon Solved
  • Pluto's Horizon Gets Page One Treatment At NASA.gov
  • NASA Awards Contract For Kepler Mission Photometer
  • Pluto At 75: A Uniquely American Anniversary

  • Swift Mission Nabs Its First Distance Measurement To Star Explosion
  • Moon Fountains
  • Temperature Inside Collapsing Bubble Four Times That Of Sun
  • In The Stars: Starmaking's Helping Hand

  • Chandrayaan-I: ISRO Selects American Geologist To Map Moon
  • First "Private" Lunar Mission Succeeded Despite NASA Roadblocks
  • Feature: 'Apollo' Program Lives On
  • ESA Gives Go-Ahead To Cooperation With Indian Lunar Mission

  • KVH Fiber Optic Gyros Make Automated Inventory Tracking Easy, Affordable
  • Satamatics Launches Ocean Alert Map Viewer Product
  • GPS Production Value Globally Expected To Grow To $21.5 Billion In 2008
  • Russia To Enlarge Satellite Array

  • The content herein, unless otherwise known to be public domain, are Copyright 1995-2006 - SpaceDaily.AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA PortalReports are copyright European Space Agency. All NASA sourced material is public domain. Additionalcopyrights 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 SpaceDaily on any Web page published or hosted by SpaceDaily. Privacy Statement