|
|
|
|
|
Case of Sedna's missing moon reported solved HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS NEWS RELEASE Posted: April 5, 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.
"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. Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe. |
|
|
|
 |
|||||||||||||||||||||
A preview of Discovery's STS-114 flight is presented in this narrated movie about the shuttle return to flight mission. (10min 15sec file)
Play video:
The impact to the International Space Station by this two-year grounding of the space shuttle fleet in the wake of Columbia is examined in this narrated movie. (6min 46sec file)
Take a behind-the-scenes look at the seven astronauts who will fly aboard the space shuttle return-to-flight mission in this movie that profiles the lives of the STS-114 crew. (10min 04sec file)
Walk alongside space shuttle Discovery as the motorized transporter hauls the ship a quarter-mile from the Orbiter Processing Facility to the Vehicle Assembly Building. (3min 21sec QuickTime file)
This time-lapse movie captured from an overhead camera shows space shuttle Discovery's middle-of-the-night departure from its processing hangar at Kennedy Space Center to the roll to the Vehicle Assembly Building. (4min 30sec file)
Discovery arrives in the Vehicle Assembly Building as viewed in this time-lapse movie. The shuttle will be mated to the redesigned external fuel tank and twin solid rocket boosters in the VAB before rolling to the launch pad for the first post-Columbia mission. (5min 00sec file)
A foot-long Russian nanosatellite is flung overboard by the spacewalking International Space Station Expedition 10 crew. Station cameras watched the hand-launched deployment and the nanosat as it floated away. (4min 52sec file)
Highlights of the second spacewalk of the International Space Station's Expedition 10 crew is compiled into this movie. The crew completed external outfitting of gear that will guide European cargo ships to the outpost during dockings starting in 2006. (5min 00sec file)
Mission managers preview the next spacewalk by the Expedition 10 crew aboard the International Space Station, which will install external equipment on the Russian segment and hand-launch a tiny nanosatellite. (37min 00sec file)
This video retrospective remembers the first flight of space shuttle Endeavour. The maiden voyage set sail in May 1992 to rescue the Intelsat 603 communications spacecraft, which had been stranded in a useless orbit. Spacewalkers attached a rocket booster to the satellite for the critical boost to the correct altitude.
This video retrospective remembers the 2002 mission of Columbia that made a long distance service call to the Hubble Space Telescope, giving the observatory a new power system and extending its scientific reach into the Universe. Astronauts performed five highly successful spacewalks during the mission.
This retrospective remembers the third voyage of space shuttle Columbia. The March 1982 mission served as another developmental test flight for the reusable spacecraft, examining performance of its systems while also conducting a limited science agenda. STS-3 is distinguished by making the first landing at Northrup Strip in White Sands, New Mexico.