[FPSPACE] What a strange little world it is

[David M Harland]

>All the planets in the solar system orbit the sun in a circle. Not 
>Sedna. All the planets orbit in the same plane. Sedna's orbit is 
>canted 12 degrees.

Hmm, now there was me thinking that Pluto's inclination was 17 
degrees, which sort of puts this 12 degrees into context.

dmh



At 9:45 pm -0500 14/2/05, DwayneDay wrote:
>[note: he's wrong about the orbital inclination--not all of the 
>planets are in the same plane]
>
>http://www.washingtonpost.com/wp-dyn/articles/A21549-2005Feb13.html
>
>Distant Object Could Hold Secrets to Earth's Past
>By Guy Gugliotta
>Washington Post Staff Writer
>Monday, February 14, 2005; Page A06
>
>When the icy red world called Sedna edged into the solar system from 
>the shadows of deep space, astronomers marveled at its unexpected 
>arrival even as they wondered at its origins. Where did it come 
>from? And why was it there?
>
>A year after its public debut, Sedna remains an enigma in search of 
>an explanation.
>
>It is the most distant object in the solar system ever identified -- 
>traveling around the sun every 10,500 years in a highly elliptical 
>orbit that keeps it 7 billion to 93 billion miles from Earth. 
>Nothing else that far out has ever been seen.
>
>All the planets in the solar system orbit the sun in a circle. Not 
>Sedna. All the planets orbit in the same plane. Sedna's orbit is 
>canted 12 degrees. All the planetoids and comets that orbit in deep 
>space just beyond Pluto were probably hurled there by Neptune's 
>gravity. Sedna is too far away for that.
>
>Unlocking Sedna's secrets has important implications for scientists' 
>understanding of Earth's origins, for whatever happened to Sedna 
>must have happened 4.5 billion years ago as the infant sun's "dust 
>disk" created the solar system. Sedna is a visitor from the 
>beginning of time.
>
>Last month, Alan Stern, based in Boulder, Colo., for the Southwest 
>Research Institute, reported in the Astronomical Journal that 
>computer models showed Sedna could have formed from the dust disk 
>much like the planets -- as a circular-orbiting body.
>
>He said in a telephone interview, however, that for Sedna to be at 
>its current distance, the disk had to have extended at least 7 
>billion miles into deep space, with particles traveling at slow 
>enough relative speeds to "accrete" -- gathering together to form 
>planets, rather than bouncing off one another like balls on a 
>billiard table.
>
>"These are considerable ifs," he said, because no evidence exists of 
>anything substantial besides Sedna beyond 4.7 billion miles from the 
>sun, even though other stars have dust disks that extend for 100 
>billion miles or farther.
>There are other, more exotic, possibilities. One team has suggested 
>that Sedna formed inside the planetary system, traveled in a 
>scattered disk kicked outward by Neptune's gravity, then somehow 
>flew even farther into space before the gravity of a passing star 
>stretched its orbit into an ellipse and yanked it out of the solar 
>plane.
>Others have suggested there is a 10 percent chance that the passing 
>star may have resulted in an exchange of material between the two 
>solar systems. The sun may have lost a big piece of its dust disk to 
>this interloper and picked up Sedna in exchange. Sedna, literally, 
>may be an arrival from outer space.
>
>Astronomers led by Michael Brown of the California Institute of 
>Technology announced the discovery of Sedna last March. It is a 
>small, spherical, body 800 to 1,100 miles in diameter, about 
>one-seventh the size of Earth, and colored bright red -- redder than 
>anything in the solar system except Mars. The team named the 
>discovery Sedna,
>after the Inuit goddess of the sea.
>
>The first question about Sedna was whether it is a planet or a 
>smaller orbiting body known as a planetoid. This is also quite 
>likely to be the last question as astronomers cannot agree on what a 
>planet is. Exhibit one is Pluto, which after 75 years of debate 
>remains in semantic limbo.
>
>Far more provocative are efforts to fit Sedna into what astronomers 
>know about the origins of the solar system, when the sun and its 
>spinning disk of dust and gas emerged from a star cluster to spiral 
>into space like a gigantic pinwheel.
>
>Over time, masses of material accreted to form the sun and the 
>planets, including Earth. Beyond Neptune this fan created an icy 
>girdle of asteroids known as the Kuiper Belt. Pluto is a Kuiper Belt 
>object, as are many comets that migrate to the inner solar system.
>
>The Kuiper Belt, however, ends abruptly 4.7 billion miles from 
>Earth. Sedna, whose closest point of approach to Earth is 7 billion 
>miles, cannot be a Kuiper Belt object and has no obvious 
>relationship to anything else ever seen.
>"Sedna is awesome," said planetary scientist Harold F. Levison of 
>the Southwest Research Institute, expressing the view of many 
>astronomers. "I started working in the Kuiper Belt before it was 
>discovered, and every time I turn around, something sensational 
>happens."
>
>Brown suggested that Sedna might be a migrant from the Oort cloud, a 
>spherical shell of icy bodies surrounding the solar system and 
>extending out toward the nearest star. The Oort cloud, however, is 
>supposed to begin beyond Sedna -- about five-sixths of a light year 
>from the sun. Sedna, Brown said, could be the first sighting of 
>something from a possible "inner" Oort cloud.
>
>Such an explanation would account for Sedna's inclined orbit because 
>Oort cloud comets, the principal evidence that the Oort cloud 
>exists, come into the solar system from all angles, probably after 
>passing stars jog them from their icy habitat.
>
>"There's no disagreement that Sedna's orbit had to be disturbed," 
>Stern said, and gravitational pull from a passing star is a likely 
>way this could have happened. There is, however, much disagreement 
>on where Sedna was in the first place and how it got there.
>
>Last year Levison and Alessandro Morbidelli of France's Cote d'Azur 
>Observatory examined various theories for Sedna's formation and 
>concluded that it most likely came from part of the sun's dust disk 
>that was "scattered" and flung outward in different directions by 
>repeated gravity boosts from the giant outer planets. This view in 
>part echoes Brown's inner Oort cloud hypothesis.
>
>In a separately researched paper, Scott J. Kenyon of the 
>Harvard-Smithsonian Center for Astrophysics and Benjamin C. Bromley 
>of the University of Utah suggested that Sedna could have formed 
>near Neptune in the scattered disk or beyond the Kuiper Belt, as 
>Stern suggests, then had its orbit radically altered by a close 
>brush with a passing star.
>
>"It rips out the outer part of the solar disk, making the edge" of 
>the Kuiper Belt, Kenyon said in a telephone interview. "We would 
>like a messiness to the encounter to explain these messy orbits." A 
>sufficiently messy encounter, he said, could cause the two passing 
>solar systems to exchange material -- including Sedna.
>
>Some theories require evidence for something that has not yet been 
>seen in the vastness beyond the Kuiper Belt, either Brown's inner 
>Oort cloud or Stern's extended disk, and there is only one way to 
>determine whether these things exist: "We must find more objects," 
>Levison said.
>
>
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