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The Oort Cloud
 
The Oort Cloud and its implications A vast cloud of comets far beyond our solar system. The semimajor axis of the outermost planet (Pluto) is about 40 AU, and the predicted semimajor axis of the cloud is about 50,000 to 100,000 AU. The distance from Sun to the cloud is about .8 light years. It may extend to 2 light years.
A little history about discovering comets.... From Aristotle in the 4th century B.C., to Tycho Brahe in the 15th century, and to Edmond Halley in 1705. Halley looked at a parabolic orbit of comets and thought that comets may travel in a great distance around the sun. By the early 20th century, enough long-period cometary orbits were studied, and categorized into period: short, intermediate, and long or to origin such as Jupiter family comets. There were questions such as: what are comets? Where do they come form? From antiquity. Dutch astronomer Jan Oort suggested that there is a vast spherical cloud surrounding the planetary system and extending halfway to the nearest stars.
 
The long period comets seemed to have an hyperbolic orbit and their averaged semimajor axis is about 50,000 to 100,000 AU. Some hyperbolic orbits would originate in and return to interstellar space. Periodic comets lose a little material each time they pass the sun and eventually comets are completely outgassed. Then, how can we explain their abundance?
* There must be an reservoir for comets that nurtures and replenishes comets.
Where these comets come from?
* Most of the long period comets are from the Oort cloud and others are from the Kuiper Belt.
What's kicking out (perturbing) the comets from the Oort cloud?
* A dozen stars pass within one parsec (206,000 Au/3.26 light year) of the sun every one million years.
* There maybe a 10th planet.
* Galactic tidal force.
* Encountering Giant Molecular Cloud.
Our Solar system is not completely isolated.

Studying the Oort cloud, comets and asteroids give us important clues about "origin of life" as well as the formation of the solar system. Giant Molecular Cloud/interstellar medium may contain the same hydrocarbon compounds. HAC (hydrogenated amorphous carbon), PAH (polycyclic aromatic hydrocarbon) and POM (polymer polyoxymethylene) are found in comet's coma, and interstellar mediums.
 

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INTRODUCTION
 
INTEREST ME
EVIDENCE
JAN OORT
TIDAL FORCE
IMPORTANCE
References
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Astronomy Presentation, Oort Cloud
2/2/2000

INTRODUCTION

A.  WHAT IS THE OORT CLOUD?

A Oort Cloud is a vast cloud of comets far beyond our solar system. The semimajor axis of the outermost planet Pluto is about 40 AU, and the predicted semimajor axis of the cloud is about 50,000 AU. While Earth-Sun distance in light speed is about 500 seconds or 8 minutes, the distance from Sun to the cloud is .8 light years.  It*s like a Galactic halo, and it is surrounding our solar system.

In the article in the Scientific American, an research scientist, Paul Weissman stated:

"The Oort cloud is the Siberia of the solar system, a vast, cold frontier filled with exiles of the sun's inner empire and only barely under the way of the central authority."
I don't think what he's saying is totally correct, I will argue that the cloud is more like a nursery.
 

B.  WHY IT INTEREST ME.

Implication about the Oort cloud is fascinating for in terms of Astrobiology as well as in physics.  The Oort cloud is a reservoir that contains samples of material and history of our solar system.  I am enthusiastic about *origin of life* as well as *formation* of our solar system. Realizing that we may need a major shift or leap in the current concept of *life* while the Webster*s dictionary defines life as "the general condition that distinguishes organisms from inorganic objects and dead organisms, being manifested by growth through metabolism, a means of reproduction, and internal regulation in response to the environment."  If you please pay a decent attention to this definition, am I the only one to realize it sound just like *particle physics*?.

 Allow me to quote from the paper "Structure Formation with Generalized Dark Matter" by Wayne Hu, 1998.

"Upcoming cosmic microwave background missions, galaxy redshift surveys, and high-redshift observations will produce such a wealth of high-quality data that even the extended cold dark matter model with 11 free parameters may fail to fit them.  One must face the very real possibility that none of our current ab initio models will survive the upcoming confrontation with the data."
The paper discusses constructing a model for a generalized dark matter with stress tensor.  I am interested in one sentence in the paper:  "If none of these candidates (CDM, HDM, WIMPs, etc.,) survive the confrontation with high-precision cosmological measurements, we will be forced to solve the inverse problem."
This sentence encouraged me to do this research. I have been thinking about nanobacteria since it attracted me two years ago.  Since Folk published his paper about nanobacteria in 1997, the word has spread, and now we can easily find various information about from carbon tubes to infectious bacteria entitled *nanobacteria* through Internet (including rubbish).  Nanobacteria has been found in various places such as; in blood, in kidney stones, and in basaltic rock since it originally was found in hot springs.  I thought nanobacteria could be one of candidate for dark matter.  The Oort cloud was a good place to start because it is the situ/nursery for comets and asteroids which contains some evidence of organic compounds as well as some materials from earlier stage of solar nebula.  The readings lead me to some interesting information about findings of organic compounds in interstellar mediums.  I believe it is important to learn about formation of our solar system to investigate formation of life.

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WHAT EVIDENCE SUGGESTS OORT CLOUD (CELESTIAL MECHANICS)

 There is a history of discovering comets from Aristotle in the 4th century B.C., to Tycho Brahe in the 15th century, and to Edmond Halley in 1705.  Halley looked at a parabolic orbit of comets and predicted that comets may travel in a great distance around the sun. By the early 20th century, comets were categorized into short, intermediate, and long period, or Jupiter family comets that are considered to originate in the Kuiper belt. The Kuiper belt is a region in the ecliptic beyond the orbit of Neptune.  The intermediate and long period comets appear to come from the Oort cloud. Some of the intermediate and long period comets were found to have hyperbolic orbit.  Hyperbolic orbits would originate in and return to interstellar space. Also, periodic comets lose a little material each time they pass the Sun and eventually comets are completely outgassed.  How, then can we explain their abundance?
 

A.  DUTCH ASTRONOMER JAN OORT'S PROPOSITION (1950)

In 1950, Dutch astronomer Jan Oort recognized that long-period comets might have a source in a great distance. He suggested a vast spherical cloud surrounding the planetary system and extending halfway to the nearest stars. Comets are gravitationally attached to the sun, but the most long period orbital seemed to have an orbit not around the sun but the center of mass of the planetary system.  From the observed orbits, we find that the average value of their semimajor axes is about 50,000 to 100,000 AU, and the corresponding orbital period is about one million years.  The orbits are highly elliptical; in accord with Kepler*s second law, the comets travel very slowly at aphelion, only a few kilometers per day, and so such comets spend most of their time coasting far from the Sun where Oort suggest there would be a cloud. His model explains that there must be an reservoir for comets that nurtures and replenishes comets.  This reservoir is called Oort*s cloud.  The supply of Sun-approaching comets must be replenished with new comets from the cloud.

Long-period comets entering the planetary region for the first time come from an average distance of 44,000 AU, and such orbit have periods of 3.3 million years.
 He also suggested that about a dozen stars pass within one parsec (206,000 AU/3.26 light year) of the sun every one million years. Stars passing by or through the cloud purterb orbits of comets, and some comets get kinetic energy fly into inner solar system.  This stellar perturbations are not alway gentle.  Occasionally a star comes so close to the sun that it passes right through the Oort cloud, violently disrupting the cometary orbits.  Statistically a star is expected to pass within 10,000 AU of the sun every 36 million years, and 3000 AU every 400 million years.  Our solar system is not completely isolated from other stars.  Our solar system is interacting with other stars or maybe systems (if there are such) through comets.  Comets are cultured and nurtured in the Oort cloud.
 
Processing of comets:  The typical spacing between comets is 15 AU in the outer cloud and ~a AU in the inner cloud.  The typical temperature is that of interstellar space, ~10K.  It si now recognized, variety of processes act on the cometary nuclei over the history of the Solar system
1.  Irradiation, sputtering and polymerization by galactic cosmic rays
2.  Heating by passing stars and nearby supernovae
3.  Gardening by cometary debris impacts
4.  the accretion of interstellar dust and gas and accompanying erosion by hypervelocity dust impacts  (Weissman, Nature, 1990)
 The cloud might have encountered interstellar molecular cloud.  Comets from Oort cloud also might be originated in a various source such as Jupiter-Saturn and Uranus-Neptune.(R.C., Science News, Vol.151-23,1997) Therefor the comets may have a wide range of formation temperatures.  This fact could be explained by the compositional diversity.  The Oort cloud may contain asteroids from the inner planets, and may constitute 2 to 3 percent of the total Oort cloud population.

l How may comets inhabit the Oort cloud?:  Astronomers estimate the cloud has six trillion comets.  The total mass of comets in the Oort cloud at present is about 40 times that of Earth.  (2.4 x 10^26 kg)

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B. GALACTIC TIDAL FORCE

"In Astrophysical Journal Letters for Novermber 20, 1996, John Matese and Daniel Whitmire provide evidence for a theory proposed more than a decade ago: that galactic matter can perturb comets from their stable orbits in the Oort cloud.  Every 30 to 35 million years as suggested by crater ages a periodicity in the pull of the galaxy*s tide.  The timing of this oscillating tidal force suggest that we are now entering a time of increasing activity. This idea seems dismissal that there is not much evidence and data about the galaxy*s gravitational influence to comet orbits.  A lot more research needs to be done for this theory.
 

WHY THE STUDY OF THE OORT CLOUD IS IMPORTANT

A.  GIVES US CLUES TO FORMATION OF OUR SOLAR SYSTEM
B.  GIVES US INFORMATION ABOUT ORIGIN OF LIFE/EXTRATERRESTRIAL LIFE
CONCLUSION


Through this research, I am convinced myself again that we need to think carefully about our concept of life.  Discovering new life forms does not necessary mean that they are newly formed.  They may have been existed for billion years.  Automatically replicating particles that produce something
A Finnish scientist has asked the University of Kuipio to investigate the work of one of its senior researchers, who he syas, is making misleading but widely publicized claims to have discovered a new form of life, know as nanobacteria.  He seemed to fail to produce the neccessay biochemical evidence to prove that the particles he claims to nanobacteria are in fact alive.  AS I STATED EARLIER IN MY INTRODUCTION, MY MAIN INTEREST IS EXTRATERRESTRIAL AND ORIGIN OF LIFE.  WHY IT INTEREST ME.
 

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References & bibliography:

Comets, the Oort Cloud and the Kuiper Belt http://cat.apg.ph.ucl.ac.uk/3c37/3c37-12.html

Chemical Evolution of Carbonaceous Material in Interstellar Clouds, W.W. Duley, School of Physics

Structure Formation with Generalized Dark Matter, 1998
by Wayne Hu, Institute for Advanced study, Princeton, NJ 08540

Marching to the beat of the Milky Way*s drum?
Edited by Joshua Roth, Sky & Telescope, Apr 97, Vol. 93 Issue 4, p14

Hidden Worlds: Hunting for distant comets and rogue planets
by Freeman J. Dyson, Sky & Telescope, Jan 94, Vol. 87 Issue 1, p26

Is there life elsewhere in the universe?
By Tarter, Chyba, Scientific American, Dec 99, Vol 281 Issue 6, p118

Odd Visitor from the Oort Cloud
by Constance Holden, Science, 10/10/97, Vol. 278 Issue 5336, p229

Comet Reservoir Gets More Real
by R. Cowen, Science News, 06/07/97, Vol. 151 Issue 23, p352

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Updated:  2/2002