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From Proplyds to Solar Systems...


Okay. So the Universe was formed some 13.7 billion years ago. Fast forward the DVD several billion years to a time when the Local Group (the neighborhood of galaxies in which we reside) and the Milky Way were formed (the neighborhood of solar systems in which we reside). Press stop. Let’s take a brief look at how solar systems form because it might gives us an idea as to where water came from on our planet.



Just before 4.6 billion years ago, our Sun and all of the matter that makes up our solar system began to condense into what is known as a protoplanetary disc. Scientists speculate that solar systems formed from the gravitational “condensation” of interstellar dust and gas. Nicknamed proplyds (short for protoplanetary disks), these structore, which have been observed using the Hubble Space Telescope, are thought to represent nascent solar systems (nascent meaning coming or having recently come into existence).

Proplyds are believed to represent the latter stage in the formation of a solar nebula, a model introduced by Laplace (and since modified) to describe how solar systems are formed. As interstellar materials are thrown off by planetary nebulas (the product of large star collapse and explosion) they experience a kind of shock wave that causes these materials to condense and spin (called angular momentum in the business). The rotation of these materials results in a “rotating disc” (see Figure above) that flattens and, through a series of physical and chemical processes, evolves into a star (or more commonly, two stars) with planets.

Observations of proplyds reported at the 202nd meeting of the American Astronomical Society in May 2003 have ignited a veritable Wrestlemania among planetary scientists concerning the origins of large planets like Jupiter. At the heart of the debate is whether large planets form by a core-gravity process (the traditional model) where planets aggregate slowly over periods up to 10 million years or a gas-instability scenario (the “radical” model) where large planets form rapidly within 3 million years.

Two key findings reported at the meeting have caused astronomers to rethink these models:

  1. cosmic dust vanishes from proplyds some 3 to 5 million years after their formation;
  2. cosmic gases do not appear to be present near stars from 1 to 10 million years old

The bottom line: planets appear to form quickly, in ~3 million years.

Proponents of the gas-instability model cite these observations as supporting their mechanism of planetary formation. On the other hand, traditionalists state that the core-gravity model can be revised to shorten the time scale over which planetary formation occurs, without the need for a new model.

This particular debate helps shape our understanding of how water might have originated on our planet because cosmic gases contain water. When and where they appear becomes paramount to accepting or rejecting them as a source of water for our ocean. If cosmic gases were trapped within Earth as it formed, then they represent a possible significant source of water for Earth. However, if a supernova or solar flare blasted these gases away before Earth formed, then cosmic gases would be an unlikely source of water.

New observations from the Chandra X-Ray Observatory indicate that intense radiation from solar flares may be common during planetary formation and may have played a role in the chemical makeup of our early solar system. This observation would appear to lessen the likelihood of cosmic gases as a source of Earth’s water. However, to my knowledge, these new data have not yet been evaluated in this light. We’ll just have to keep our eyes and ears posted for the latest on this topic.

In any case, these observations from deep space offer great insights into the processes that may have formed Earth. In particular, they help us understand:

  1. the conditions under which stars and planets form
  2. the timescales of their formation (important for modeling the physics and geochemical evolution of planets
  3. the observed chemical makeup of Earth and other planets in our solar system
  4. the influence of solar flares on the chemical composition of materials from which planets form
  5. the likelihood that water was trapped or not trapped under such conditions

s remote and irrelevant space science may seem to the general public, you now know better. Space science provides a wealth of fascinating clues to better understand our planet and how it works.

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