Saturday, February 4, 2012

Sedna: Goddess Of The Arctic Sea

The myth of the Inuit goddess, Sedna, has been told for generations throughout the Arctic. According to this myth, Sedna was a beautiful, young Inuit bride, who drowned in the frigid Arctic Sea following a harsh betrayal by her new husband--who is not really a human being, but an evil, gigantic raven disguised as a man. This evil bird reveals the monster that he really is to Sedna after he has contrived to seclude her as a captive in his nest on a remote cliff. Sedna's father attempts to rescue her from this evil avian creature, but the attempt fails, resulting in Sedna's death. After her death, she undergoes a metamorphosis and becomes an immortal ocean goddess. This once beautiful mortal woman undergoes a sea-change to become the sinister goddess of the Inuit underworld, "Adlivun", which she now rules as a darkly witchy immortal; a hideous, one-eyed giantess.

The Inuits are naturally familiar with darkness and bitterly cold temperatures. So, too, are remote objects dwelling in the outermost fringes of our Solar System.

The very remote dwarf planet Sedna was named for the Inuit goddess. This small, ice-world was discovered on November 13, 2003 by Drs. Michael Brown (Caltech), Chad Trujillo (Gemini Observatory), and David Rabinowitz (Yale University). The discovery was made on the Samuel Oschin Telescope at the Palomar Observatory located east of San Diego. In the discovery images, Sedna appears as only a pin-point of light. Astronomers now think that Sedna's diameter is between 1,200 and 1,600 kilometers. It is also one of the reddest objects in the Solar System--almost as red as Mars. Dr. Trujillo and his colleagues suggest that Sedna's dark red color is the result of a surface coating of hydrocarbon goo, or "tholin", formed when simpler organic compounds undergo a metamorphosis resulting from long exposure to ultraviolet radiation. Its surface is homogeneous in color and spectrum. This is probably because Sedna is rarely hit by other bodies--unlike objects nearer the Sun. Such impacts would expose areas of bright, fresh ice. Sedna's surface is thought to be composed of 24% tholins, 26% methanol, 33% methane, 10% nitrogen, and 7% amorphous carbon. When Sedna was first discovered, astronomers erroneously believed it to possess a weirdly long rotational period of 20 to 50 days. It was then speculated that Sedna's long rotational period was caused by the gravitational influence of a large moon. However, a search for this moon by the venerable Hubble Space Telescope came up empty-handed, and later measurements suggested that Sedna actually has a much shorter rotation period of 10 hours. This is typical for an object of its size.

The remote and frigid body was first observed at a distance more than 90 times greater than that from the Earth to the Sun--about three times further out than the very remote dwarf planet Pluto--once considered the ninth major planet from the Sun. Dr. Brown explained on his website that "Our newly discovered object is the coldest most distant place known in the Solar System, so we feel it is appropriate to name it in honor of Sedna, the Inuit goddess of the sea, who is thought to live at the bottom of the frigid Arctic Ocean." Dr. Brown further asked the International Astronomical Union's (IAU) Minor Planet Center to name any future similar small worlds discovered in Sedna's remote, dark and frigid orbital vicinity after entities in Arctic mythologies. The IAU's Committee on Small Planet Nomenclature formally accepted the name Sedna in September 2004.

When Sedna was first spotted by Drs. Brown, Trujillo, and Rabinowitz, it was seen to travel by about 4.6 arcseconds over 3.1 hours relative to stars. This suggested to the astronomers that its distance is about 100 Astronomical Units (one Astronomical Unit, or AU, is the mean distance of the Earth to the Sun--150 million kilometers or 93 million miles). Subsequent observations conducted using the SMARTS Telescope at Cerro Tololo Inter-American Observatory in Chile as well as with the Tenegra IV Telescope and the W.M. Keck Observatory in Hawaii showed that the tiny, remote world is skittering along in a distant, highly eccentric (out-of-round) orbit. Furthermore, the icy object was later spotted on older pre-discovery images that allowed for a more exact calculation of its elliptical orbit.

With the exception of some comets and a smattering of tiny Solar System objects, Sedna sports the longest orbital period of any known object in our Solar System--calculated to be roughly 11,400 years. Its orbit is extremely eccentric, with an aphelion (the location in its orbit most distant from the Sun) of 937 AU and a perihelion (the location in its orbit closest to the Sun) of about 76 AU.

Sedna is a fascinating and mysterious world for a number of reasons. For one thing, it is thought to dwell in a still-hypothetical region of our Solar System called the Oort Cloud, a place astronomers think hosts a multitude of comets and other icy, bizarre objects. The Oort Cloud is thought to be a shell of icy proto-comets somersaulting in very loose orbits around the Sun, reaching almost halfway to the nearest star. Every so often, passing stars alter the orbit of one of the proto-comets, sending it thrashing into the region of the inner Solar System, where it streaks across the sky, a bright object sporting an enormous incandescent tail. These comets, mysterious visitors from the outer Solar System, have fascinated humanity since time immenorial. The ancients viewed comets as magical omens of great import, and sometimes harbingers of doom. The Oort Cloud is thought to be much further out than the orbit of Sedna. So why do astronomers think that Sedna is a member of the Oort Cloud population? Astronomers now think that the existence of Sedna indicates that the Oort Cloud actually extends much further inwards towards the Sun than once thought.

In fact, Sedna has the distinction of being, perhaps, the very first object in the Oort Cloud to be discovered by astronomers. It is classified as a "dwarf planet", rather than a major planet, because it shares its orbital region with numerous and diverse other objects (not including moons) that are large, small, and mid-sized. For example, the planet Earth has one Moon, and a smattering of very tiny objects sharing its orbital vicinity. In contrast, the asteroid Ceres, the largest asteroid in the Main Asteroid Belt, which is located between the major planets Mars and Jupiter, is classified as a "dwarf planet". This is because Ceres shares its orbital vicinity with a number of other large asteroids, medium-sized asteroids, and small asteroids. Ceres was the first member of the Main Asteroid Belt to be discovered. When astronomers first discovered Ceres, it was classified as a major planet. But when other members of the Main Asteroid Belt were discovered, Ceres was re-classified as an asteroid.

A major planet must also be spherical in shape due to the effects of its own gravity. Ceres is round, but it is surrounded by a multitude of sister objects in the Main Asteroid Belt. A major planet, by definition, must be almost a "loner" in its orbital space.

Dr. Brown noted in the May 2006 issue of Discover Magazine that "Sedna shouldn't be there. There's no way to put Sedna where it is. It never comes close enough to be affected by the Sun, but it never goes far enough away from the Sun to be affected by other stars... Sedna is stuck, frozen in place; there's no way to move it, basically there's no way to put it there--unless it formed there. But it's in a very elliptical orbit like that. It simply can't be there. There's no possible way--except it is. So, how then?"

Dr. Brown continued to explain that "I'm thinking it was placed there in the earliest history of the Solar System. I'm thinking it could have gotten there if there used to be stars a lot closer than they are now and those stars affected Sedna on the outer part of its orbit and then later on moved away. So I call Sedna a fossil record of the earliest Solar System. Eventually, when other fossil records are found, Sedna will help tell us how the Sun formed and the number of stars that were close to the Sun when it formed."

Today our Sun, and its enchanting retinue of planets and other smaller objects, seems to be isolated in space. Our closest stellar neighbors are so distant that they appear to us as tiny sprinkles of light; glitter thrown by a mischievous child into the darkness of a wild cosmic party. The more remote stars do not even appear to us as a shower of glitter--all that we can see of them is a blurred, weak glow that is the relic of their combined light. Space secludes us like an icy sea, far from the madding crowd of the multitude of stars that bedeck our cosmic home. But 4.5 billion years ago, when our Solar System was young, the night sky would have appeared to be ablaze with light. The night sky at the dawn of our Solar System would have been brilliant enough to read by. This is because a thousand or so stars formed within a few light-years of our Sun from the same cold and dark molecular cloud.

About one in 10 stars belong to a cluster, a shower of hundreds to tens of thousands of glittering stars. The cluster usually has a diameter of only a few light years. Scraps of evidence collected from meteorites, as well as from the arrangement of comets, whisper out a haunting secret from the remote past, telling us that our Sun was no exception. Our own Sun's birth cluster could well have contained as many as 1,500 to 3,500 sister stars within a diameter of only 10 light-years. This very large family of sister-stars would have been completely dysfunctional; a violent place where the larger sister stars bullied their smaller siblings, and which naturally broke up--shortly after our Solar System was born--largely due to this familial abuse.

One such explanation for Sedna's bizarre orbit has been provided by Dr. Scott Kenyon of the Harvard-Smithsonian Astrophysical Observatory (SAO) and Dr. Benjamin Bromley of the University of Utah. According to their calculations, published in the December 2, 2004 issue of the journal Nature, the Sun's gravity may have actually stolen asteroid-sized worldlets away from the family of a passing long-lost stellar sister of the Sun.

"It's possible that some of the objects in our Solar System actually formed around another star," commented Dr. Kenyon in a December 1, 2004 Harvard Smithsonian Center for Astrophysics (CfA) Press Release.

Drs. Kenyon and Bromley came to this fascinating conclusion while studying the enigma that is Sedna. Understanding this weird icy worldlet presents quite a challenge to astronomers because its orbit is so vastly distant from the gravitational grasp of the planets dwelling in our own Solar System. However, the gravity of a passing star would be able to ensnare such a little world, as it floated around the Sun, in a remote region beyond Neptune called the Kuiper Belt. The Kuiper Belt is a ring of icy small worlds of which the former planet Pluto and its large moon Charon are members. This passing sister star could have pulled Sedna into its present weird orbit. Drs. Kenyon and Bromley performed detailed computer simulations showing how this might have occurred long ago when our Solar System was young, and the Sun's long-lost-sisters were still close enough to wreak havoc with one another.

This close encounter of the stellar kind must have occurred late enough in the history of our Solar System to permit Sedna-type wandering worldlets to have sufficient time to take shape within the remote Kuiper Belt. In addition, the encroaching sister star would have had to stay far enough away so that it did not disturb Neptune's nearly circular orbit. This near-collision had to occur, according to Drs. Kenyon and Bromley's calculations, when our Sun was at least 30 million years old--and probably no more than 200 million years old. A near-collision at a distance of 150-200 AU would be near enough to disturb the outer Kuiper Belt without wreaking havoc with the inner planets: Mercury, Venus, our Earth and Mars.

Where did this encroaching star come from? Since the close encounter occurred more than 4 billion years ago, the stellar wanderer probably was a refugee from the Sun's original birth cluster. The culprit star has long since flown off from the Sun's neighborhood, and there is little hope of finding it today.

Drs. Kenyon and Bromley's simulations suggest that perhaps millions of alien Kuiper Belt Objects were torn from the family of that disruptive sister star, and are now adopted members of the Sun's own family. None of these objects, however, have been positively identified, and it is thought by most astronomers that Sedna is most likely a true daughter of our Sun--and not the alien offspring of a disruptive sister-star.

Nevertheless, the possibility that Sedna is really an adopted alien object, the child of another wandering star, cannot be completely ruled out. Drs. Kenyon and Bromley's simulations indicate that there is a 1 percent chance that Sedna is a body that was captured during an ancient stellar close encounter.

Dr. Bromley told the press that "There may be thousands of objects like Sedna near the edge of our Solar System. So there is an even greater chance that some may be alien worlds captured from another solar system."

The Kuiper Belt cuts off suddenly at 50 AU from the Sun and "there is no evidence that the hard edge of the Kuiper Belt is in any sense natural," Dr. Bromley added.

If the edge of our Solar System had not been disturbed by an ancient stellar close encounter, scientists would predict a gradual diminishing of relic debris at increasing distances from the Sun. Drs. Kenyon and Bromely's computer simulations suggest that a close brush by another sister solar system could well explain why icy, rocky Kuiper Belt Objects suddenly disappear at 50 AU.

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