Planetary Potential from Protoplanetary Disks
Written by Nancy Atkinson
How planets form is one of the major questions in astronomy. Only recently have we been able to study the disks of dust and gas surrounding other stars in an effort to understand the process of how planets coalesce and form from these "protoplanetary" materials. But this is a difficult task at best, given the observational distances. "This is a vast topic with many challenges," said David Wilner from the Harvard-Smithsonian Center for Astronomy at his talk at the American Astronomical Society meeting this week. "But over the course of the past few decades with observations of nearby star systems, we've come to a basic outline of the process of solar system formation."
There are a couple of hurdles to overcome in studying protoplanetary disks. First, the bulk of the disk mass is cold and dark, as the molecular hydrogen doesn’t radiate. These areas are probed only through a couple of minor constituents: thermal emission from dust and scattered light from the star.
Second, the amount of "stuff" astronomers are looking at is actually fairly small. Usually, the amount of protoplanetary material is about 1/100th the mass of the star, and about 1/4000th of a degree in the sky.
Through observations of many systems with several telescopes, we can see these disk systems in a variety of wavelengths in an effort to see both the star and the disk components. Wilner said there are two properties that are particularly important to know: Disk masses in general, as the luminosity is directly proportional to the mass, and second is the disk lifetime. From current knowledge, the dust disk disperses by 50% in 3 million years, and 90% by 5 million years.
As an example, Milner discussed the Rho Ophiuchi nebula, (image above), located near the constellations Scorpius and Ophiuchus, about 407 light years away from Earth.
"The Rho Oph cloud is spectacular, with beautiful dark regions that are columns of gas and dust extinguishing the background star field. This is the material that is forming stars and planets."
Wilner said the steps in solar system formation are as follows: first the formation of a primordial proto-star disk, then the protoplanetary disk, and then debris disk within a planetary system.
But the main problems in our understanding lies in that astronomers haven't yet actually seen all the steps in this process, and can't prove directly that these early disks go on to form the planets. There are several clues, such as that gaps form in the dust around clumps of materials, similar to the gaps in the rings of Saturn around moons.
For the past 15 years protoplanetary disks have been studied with various interferometers at the Keck Observatory on Mauna Kea at various wavelengths from .87 microns to 7 mm. And the past five years the Spitzer Space Telescope has lent its infrared capabilities to further our knowledge to our current understanding. But soon, a new telescope in the high Chilean desert might provide the resolution needed to offer a glimpse at not only the gaps in the disks, but a new window on how materials around emerging planets may form moons. The Atacama Large Millimeter/submillimeter Array (ALMA), will operate at wavelengths of 0.3 to 9.6 millimeters.
Wilner obviously looks forward to putting observational capabilities of this array to work. Scheduled to be completed in 2012, ALMA will help fill in the "gaps" of our knowledge about planetary formation.
Source: AAS Meeting presentation, with clarification from Chris Lintott
Filed under: Observatories, Planetary Formation
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June 6th, 2008 at 11:24 am
planets are not made in "discs" i cannot believe what im reading. God made the earth and the rest of the planets
June 6th, 2008 at 11:44 am
Lol, yet another awesome post by MegaChrist.
I have a question though:
Don't planets form relatively around the same time that a star does?? How do we know where to point the detector if the light emitted (in all wavelengths) would be faint? I'd imagine that most or all of the disc would be used up by the time it would be detectable…
June 6th, 2008 at 12:13 pm
It looks like its kind of a chain reaction a dying star creates other stars which in turn create planets. and all this kept in place by a massive black hole….am I right?
June 7th, 2008 at 2:41 am
Thankyou LLDIAZ. I'm no scientist and haven't even had a look through a good telescope, but [Planets can't form in rough neighborhoods] is what I've been saying for nearly 40 years. A collapsing nebula, its contraction into a disc, it's destiny clearly is to plunge into the growing star. – Unless it's all in orbital angular momentum. It isn't. And as the star grows, so does the cumulative gravity shift to the center of the action. By virtue of that continuity, it is hardly likely that planetoids could form and remain in orbit whilst everything else rushes past them. Imagine if earth slammed into even a small cloud of dust at 1000 kms a second. We are talking about a nebula disc circling an almost created new star likely to be 100 times the size of the sun.
Look at the solar system; imagine our 4 inner planets and moons being where they are now in the final throws of gas and dust gathering by a flaming object 100 times larger than the sun. [Science has said that a new star has to be that size or larger at birth].
Planets and moons, in my view, have to born after the sun has solar wind capability, so that they have a clean neighborhood to live in. My website reveals the rest of the drama. But think about this first. Mercury would appear to be less developed than Venus – Venus less developed than earth, and earth less developed than Mars. Could this mean that there is an age progression here where Mars may be say 3 billion years older than earth?
June 7th, 2008 at 6:46 am
To Megachrist: Aren't you curious how God did it? Why on earth do U even read this stuff? Obviously you're not interested in any real answers.
Sorry 'bout another "God reply", but sometimes peoples ignorance really bothers me.
June 8th, 2008 at 3:31 am
Neoguru says- 'Aren't you curious how God did it'? Well, convince me. Yes I'd like to know. But think about this first if you are going to take the first pages of Genesis as your authority. Creation of the sun, planets, the stars. – Creation out of what? What material did he use?
Creation of man. What material did he use?
The big question then is this:- Why did he need a handful of earth to make a human but give the impression that He made everything else from nothing – It says that there was a void. So, what's a void?
I guess that's why the Bible is different things to different people.
Another thing. If, as you say, God made it all, what's wrong with folk trying to find out how? Did He say, 'it is a sin to investigate My work'?
My interest in this subject is that whilst there is ignorance in the world, and we all live in dogmatic realms of diversity, there will never be peace and unity. Open your mind and seek the truth with respect and love for all those who see the universe as incredibly wonderful and beautiful. Guard your planet and it's wonderful diversity of life and turn the book of Revelations into a load of ru – compost.
June 9th, 2008 at 4:53 am
MegaChrist,
Seems Christians believe there had to be some spiritual being with universal power to create something like 'man'.
If there is no way man could evolve; then how could a 'being' or diety come to be? Especially one which could create the universe and everything else?
I find it hard to believe a diety with all power of all the universe could just appear from nowhere and exist, yet man could not evolve.
Doesn't make sense, does it?
June 9th, 2008 at 12:49 pm
Gentleman please when speaking of the Lord ( I dont mean just our Christain Lord I mean whoever that may be to you) do not disrespect. In a way if you look at it science is just another opinion another point of view. None of us were there so how could you say with certainty that things were not as the bible says(not that I beleive that some of those things actually took place) but it would be foolish of you not to be open minded about such things..
P.S. Its funny for me to hear people say that they believe in dark matter but not GOD….
June 9th, 2008 at 4:12 pm
If you love and respect your planet and everything you may have an impact on, then surely God would not be offended.
June 13th, 2008 at 4:33 pm
My apologies to Neoguru. All this God involvement should have been addressed to Megachrist.
If the people who spend time praying would use that time to plant a tree and look after it, wouldn't that be doing 'God's work'? If He made everything as claimed, surely that was a practical effort on his part, and not something magical. I can't see how wasting time thanking and bowing to Him helps our planet. Don't give thanks for a threatened planet with the hope that he will fix it. All the prayer in the world won't cut carbon emissions or plant a tree, and in fact, getting the car out and driving to and from church simply adds more carbon.
If God is real, He must be weeping.
April 15th, 2009 at 9:11 am
This is very hot info. I think I'll share it on Facebook.