This is Not Your Parents' Universe
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It wasn't so long ago that we thought our entire expanding universe might eventually slow down, maybe even ultimately fall back in on itself in a Big Crunch; now we have evidence that some unknown force is speeding up the expansion! We used to think there were just three dimensions of space in and around us; now it appears there may be more than ten dimensions. We used to think that all there was in the cosmos was matter and energy; now we suspect the presence of an unseen "dark matter" and, more bizarre, a "dark energy."
Closer to home were our old trusty friends that made us feel safe from the fantastic, foreign nature of the cosmos --- the nine planets around the sun, with a belt of asteroids for good measure, and the occasional comet to give us a good fright. But things have changed even here.
Just last week, another discovery was announced by the team of Mike Brown (Caltech), Chad Trujillo (Gemini Observatory), and David Rabinowitz (Yale University). Using the Samuel Oschin Telescope on our very own and beloved Palomar Mountain, a telescope given new life with the innovative QUEST camera, the team has found another strange heavenly object to challenge our view of the local landscape. This one was not too far from home, just out in the suburbs of our solar city.
Appropriately christened Sedna after the Inuit goddess who rules the depths of the cold, dark sea, this very reddish, very cold, very distant mini-planet is getting us thinking again about the contents of our solar system.
The present model of the solar system includes not just the usual gang --- the sun, the planets, some asteroids, and the occasional comet. It also includes a thin donut of icy crud --- leftovers from the creation of the solar system --- that spreads out from Pluto's orbit, at very roughly 30 AU, out to about 50 AU. (An AU is an "astronomical unit," the average distance between the sun and the earth, equal to about 93 million miles.)
This monster warehouse of surplus planet-making debris is called the Kuiper Belt and is the probable source of what are called short-period comets, those with short, quick orbits. There have been many Kuiper Belt Objects seen out there recently, one of which was Quaoar, more than half the size of Pluto, discovered in 2002 by this same team that found Sedna.
But Sedna is very far away presently --- about 90 AU!
And its highly elliptical orbit will bring it no closer than about twice
the distance of Pluto and Neptune. But that is far beyond the Kuiper Belt.
So where is it from?!
Enter Jan Oort.
In 1950, accomplished astronomer Jan Oort put two and two together and solved, we believe, what was then a cosmic comet mystery. Some comets he observed had orbits that, once the comet had passed around the sun, took them far, far, far away --- maybe never to return. Moreover, these "long period comets" came from seemingly random directions in space.
Oort proposed that there must be a giant spherical shell of maybe a trillion icy "proto-comets" very, very far from the sun, way beyond the Kuiper Belt, tens of thousands of AU out, extending nearly halfway to the nearest star. They would be the far-flung flotsam and jetsam from the early violent youth of our solar system.
Occasionally, a passing star might come close enough to perturb the frail orbit of one of these remote icy wannabe comets, and in it would fly, towards the sun. Centuries later it might make it into the inner solar system and in a twinkle of cosmic time light up as our typical textbook comet. It is believed that comets Halley and Hyakutake and Hale-Bopp may all have their origin in the mysterious Oort cloud.
Then is Sedna from the Oort cloud? It is too far for a Kuiper Belt Object but, alas, it is too close to be the hypothetical Oort cloud object. Proclaims Mike Brown, "We believe that the existence of Sedna is evidence that the Oort cloud actually extends much further in towards the sun than previously thought. This ‘inner Oort cloud' was formed in the same manner as the previously known "outer Oort cloud.'"
And so we add "inner Oort cloud" to our growing list of solar system ingredients.
There are still many unanswered question concerning Sedna itself. Why is it so red? Why is its orbit so elliptical? Is there something even bigger than Sedna out there that perturbed its orbit? At about 1000 miles across, how should it be classified: as a planet, a planetoid, an Inner Oort Cloud Object? What is it made of? Does its slow rotation imply it has its own tiny moon? How many more are there?
This is a humbling time for all astronomy. Humbling because we who thought we knew nearly all there was to be known are recently eating a lot of humble pie. Thanks to the hard work of some good astronomers --- like Brown's team --- we realize there is much yet to discover and decipher even here in our own backyard.
But it is also an exciting time. New discoveries can bring out the best in all sciences. New ideas are boldly brought forth, new ways of looking at the universe are examined in the light of new evidence, minds closed shut with decades or centuries of the Old Ways of thinking are forced open and rejuvenated.
What a humbling, exciting ... what a great time for astronomy!
Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.
Posted by Administrator at 2004.03.20 12:41 PM | Comments (0)
