SUMMARY: Most research seems to indicate that planets form around stars in only the first few million years. Many stars have protoplanetary disks at one million years, but they're all gone by 10 million years. The trick for astronomers is to find stars in that in-between age, and catch planets in the act of forming around the parent stars. One star, Trumpler 37, seems to be at that middle age and is actively accreting material at the equivalent of 10 Jupiter masses in a million years.

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Oh now I learn one thing. most of the planets in our solar system form within the age in between 1 million - 10 million years... hmm I wonder why is for most of the young stars, planet form within the protoplanetary disk so massive than Jupiter, can someone explain why?

Littlemews,

We have very, very limited data on Jupiter. However, the Galileo probe found evidence of "strange Xenon" there, like that found in diamond inclusions of carbonaceous chondrites.

http://www.umr.edu/~om/abstracts2001/windl...leranalysis.pdf

Parent/daughter ratios of short-lived radioactive isotopes in meteorites and the inner planets show that:

1. Some material condensed into solids about 1 Million years (My) after a supernova explosion.

2. Those first condensates were highly radioactive.

3. Isotopes made in different regions of the supernova were still not mixed.

4. Later, probably when H-fusion ignited in the Sun, flash heating partially melted most grains, but not the most refractory grains (like diamond and silicon carbide).

5. This flash heating produced the aerodynamically shaped droplets in meteorites, called "chondrules".

6. When iron meteorites formed, Pd-107 (half-life = 6.5 My) was still alive.

7. Careful analyese at the University of Tokyo and Harvard University showed that Molybdenum isotopes made in different regions of the supernova were not quite completely mixed. Abundances of the seven Mo isotopes in iron meteorites still show tiny variations from synthesis by different nuclear reactions in the parent star (r-process, s-process and p-process).

8. The Earth formed and produced its crust and atmosphere while radioactive I-129 (half-life = 6.5 My) and Pu-244 (half-life = 82 My) were still alive. We observe their decay products trapped in the Earth's mantle today.

With kind regards,

Oliver
http://www.umr.edu/~om

Littlemews,

Oliver believes in a theory that the core of the sun is a neutron star and is otherwise mostly made of iron. This is not widely accepted and the good Doctor is trying to compile evidence to convince the skeptics, but there are still several.

I'm afraid I don't understand your question about Jupiter, however...

__________________
...and we'll be saying a big hello to all intelligent life forms everywhere; and to everyone else out there, the secret is to bang the rocks together, guys...

Sorry if I confuse you I was trying to ask, how could big planets that form so near their stars? In my notes, the teacher had only talk about like cuz they form within a very dense disk of matter and therefore they are massive...

The current theory is that big Jupiter like planets don't form close to their parent stars. They actually form further out, where Jupiter is in our solar system, but instabilities in the disk of material cause the Jupiter sized planets to slowly spiral inwards toward the star. As it does this it would kick any Earth-like planets out of the solar system, too. It is one theory to explain the close Jupiters, but I'm sure there are others that are just as plausible.

__________________
...and we'll be saying a big hello to all intelligent life forms everywhere; and to everyone else out there, the secret is to bang the rocks together, guys...

I think I get it now, Planets that form in an especially dense disk of matter could spiral inward and which makes it very massive, something like that. Oh one more thing, what is short-period plantes and what is long period planet?

It takes Mercury 88 Earth days to orbit the sun. We have found giant Jupiter-like planets that orbit their star in as little as 3 days, meaning they are extremely close to the star. These planets that orbit the star in only a few days (their year) are the short period planets. Jupiter takes nearly 12 Earth years to orbit the sun (its year) and is therefore considered a long period planet.

Remember that almost all of the extrasolar planets that have been discovered were found by observing the wobble they cause in their parent star (the Radial Velocity method). A big planet like Jupiter is easy to see this way because it make the star it orbits noticably wobble. Earth, tiny in comparison, barely budges the Sun at all. Now, in order to find these planets they have to watch the star for more than the orbiting planets year, and then graph the wobble of the star. If it is a nice smooth up and down wave, then there is probably a planet tugging it back and forth as it orbits the star. Based on the wobble they can figure out how big the planet probably is - how big a planet it would take to make the star wobble that much.

To see a short period planet using this method, you would need to watch the star for more than one of that planet's years. If the year is only 3 days long, then you could watch the star for a week and get two full orbits of the planet in your data. It would be easy to show the wobble and say there is a planet of this many Jupiter masses orbiting this star.

To see a long period planet like Jupiter you would need to watch the star for at least one full of the planet's years. If it is in an orbit like Jupiter's you would have to watch the star for 12 years just to see one orbit's effect on the star's wobble! To be sure you would want to watch for a longer period of time.

That is why most of the planets we've found are in short period orbits. They don't take very long to find. In the coming years more planets like Jupiter will be found as we've now been looking for several years. The longer we look, the more we'll find in larger and larger orbits until we'll be able to see Saturn-like orbits and beyond. It just takes a lot of time...

__________________
...and we'll be saying a big hello to all intelligent life forms everywhere; and to everyone else out there, the secret is to bang the rocks together, guys...