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SharkByte
2007-Apr-11, 05:45 PM
So in the last few years astronomers have located a couple hundred planets around other stars. The majority of them have been what I'll call gas Super-giants orbiting in close to thier stars with an orbital period of a few days and some as fast as a few hours.

As I look at our solar system we have Mercury, a tiny little hunk of rock orbiting in close to our star followed by the other three rocky planets, then our gas giants. But this leads me to wonder, what if Mercury actually formed as a gas supergiant and what we see now as the planet Mercury is actually just whats left of the core of the planet after the sun stole its atmosphere? Is it possible that a planet in a close orbit to its star could have its atmosphere leached away by its parent star like that?

unknownspiritx
2007-Apr-11, 09:37 PM
don't take my word for it, but it seems possible? I mean, the star probably has more mass, thus more gravity which could pull away the atmosphere of the planet thats orbiting it.

As for mercury and our sun, I'm not too sure, but that may also be possible (that it used to have an atmosphere before)--i'm just guessing from what i've learned so far.

Amber Robot
2007-Apr-11, 09:56 PM
The majority of them have been what I'll call gas Super-giants orbiting in close to thier stars with an orbital period of a few days and some as fast as a few hours.

There is currently a strong bias towards observing these types of systems, so there's no way to know if these are the norms or the exceptions.

SharkByte
2007-Apr-11, 10:26 PM
There is currently a strong bias towards observing these types of systems, so there's no way to know if these are the norms or the exceptions.

I think thats just because they are the easiest systems to find planets in. Most of the extra-solar planets that have been discovered were found by measuring the wobble they induce in thier parent star as the orbit it. If the planet takes 237 years to orbit the wobble isn't going to be all that noticable:)

I guess what I'm really wondering is if it is possible that Mercury formed as a gas giant in the outer solar system then migrated to its current orbit where the sun leached its atmosphere away. If this could be proven we could learn quite a bit about the inner workings of the gas giant planets by studying Mercury.

I know most people say that jupiter, saturn, Uranus and Neptune have no solid surface but in all honesty, if a single commet or asteroid has ever hit the planet that didn't completely vaporize then there has to be something of that rock left somewhere in the atmosphere. It may be a pile of rock being crushed under the un-imaginable weight of Jupiters atmosphere but there has got to be a rock in there somewhere:)

Glutomoto
2007-Apr-12, 01:42 AM
I guess what I'm really wondering is if it is possible that Mercury formed as a gas giant in the outer solar system then migrated to its current orbit where the sun leached its atmosphere away. If this could be proven we could learn quite a bit about the inner workings of the gas giant planets by studying Mercury.


One can guess almost anything is possible if you like. But considering the extreme complications of celestial mechanics, and the time scales involved, a guess is all that can be done.

Therefore using any of the newly discovered systems to extrapolate what the SOL system was like billions of years ago would be nothing more than wild guessing.

Maybe it is just me but I can't imagine any impactor on a gas giant world could survive in any kind of solid form. The internal dynamics of something the size of Jupiter would simply obliterate any thing that was unfortunate enough to crash into it.

well anyway that is my guess.


p.s.
how many bits are in a shark byte ?

:)

Romanus
2007-Apr-12, 02:56 AM
At Mercury's distance from the Sun, definitely not--perhaps at super-hot Jupiter distances (less than 3-day periods), and even then it may be a stretch. In any event, Mercury's composition and surface features would have features very different from the actual case if it were a naked core.

For instance, take a hypothetical super-hot Jupiter with a mass identical to Jupiter itself, which is getting ablated away at 10 million tons a second. At that rate, it would take about 6 billion years to be totally "erased", much older than the Solar System itself (though I guess realistically, the rate would increase with decreasing mass). In any event, for planets like HD209458, mass-loss rates are probably orders of magnitude less than this.

Amber Robot
2007-Apr-12, 03:03 AM
I think thats just because they are the easiest systems to find planets in. Most of the extra-solar planets that have been discovered were found by measuring the wobble they induce in thier parent star as the orbit it. If the planet takes 237 years to orbit the wobble isn't going to be all that noticable:)

Yes, I know. That's why I said there's a bias towards observing those systems.


I guess what I'm really wondering is if it is possible that Mercury formed as a gas giant in the outer solar system then migrated to its current orbit where the sun leached its atmosphere away. If this could be proven we could learn quite a bit about the inner workings of the gas giant planets by studying Mercury.

My guess is that you'd never be able to "prove" that. One problem I see in particular with the scenario is that I believe that most theories of planet migration would clear out most of the material that they migrate through, so you'd have to come up with a way to create Venus, Earth, and Mars after the gas-giant Mercury migrated through.

tusenfem
2007-Apr-12, 06:51 AM
There is a lot of simulation going on on Jupiters wandering in a solar system, getting closer to the sun and losing their outer shells etc.

At my institute(Space Research Institute (http://iwf.oeaw.ac.at) of the Austrian Academy of Sciences (http://www.oeaw.ac.at)) there are several people working on it (not me) because we were involved in building part of CoRoT. Here (http://esoads.eso.org/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&db_key=PRE&qform=PHY&aut_logic=OR&author=Lammer%2C+H.&ned_query=YES&sim_query=YES&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=&txt_logic=OR&text=&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1) you can find a list of papers involving Helmut Lammer, who does such calculations. Note that I have done only a rough search, so not all papers are appropriate (apparently).

jamesabrown
2007-Apr-12, 01:31 PM
Don't forget that Mercury is covered with craters, which suggests it formed as is during the solar system's early heavy bombardment phase.

Your theory is interesting, but it requires several steps:

A) A star collapses and pushes out the lighter gases to the outer disk.
B) The gas coallesces into a gas giant.
C) The gas giant wanders into the inner solar system.
D) The gas giant doesn't scoop up the asteroid belt, Mars, Earth, and Venus.
E) The gas giant stops at Mercury's orbit and doesn't migrate any further.
F) All the gas is blown off of the gas giant.
G) Mercury is then bombarded by countless asteroids and comets.
H) Mercury remains essentially untouched for another few billion years.

Another element to consider is that Mercury is small and rocky like Venus, Earth, and Mars. I think it's less of a stretch to say that Mercury formed as is, rather than that all four rocky planets were once gas giants. The evidence doesn't support Mercury being that much of an odd-ball.

Still, it's a nifty idea.

Ronald Brak
2007-Apr-12, 01:54 PM
Jupiter's escape velocity is about 60 km/s. If it were in the position that Mercury is it should be able to hold onto it's atmosphere with loss insignificant in relation to the mass of the planet and it should stay Jupiter sized until the sun expands and gobbles it up.

Of course mercury and the other terrestrial planets did start with hydrogen and helium atmospheres but lost them due to their lower escape velocities.

SharkByte
2007-Apr-12, 04:19 PM
p.s.
how many bits are in a shark byte ?

:)

Shark's Teeth Facts:

*Within its lifetime a shark can have thousands of teeth.
*Most sharks have one row of teeth exposed at a time, but they have up to 7 sets of fully-grown teeth waiting in their jaw.
*A young shark may lose a set of teeth in a week.

But SharkByte is actually a name I've been using since 1999 when I bought my C3 Corvette. The body style is commonly called the Shark and my Air Force Career field is Computer, Cryptographic, Network and Switching Systems Maintenance. I deal mostly in data delivery systems so Byte kind of fit:)


At Mercury's distance from the Sun, definitely not--perhaps at super-hot Jupiter distances (less than 3-day periods), and even then it may be a stretch. In any event, Mercury's composition and surface features would have features very different from the actual case if it were a naked core.

For instance, take a hypothetical super-hot Jupiter with a mass identical to Jupiter itself, which is getting ablated away at 10 million tons a second. At that rate, it would take about 6 billion years to be totally "erased", much older than the Solar System itself (though I guess realistically, the rate would increase with decreasing mass). In any event, for planets like HD209458, mass-loss rates are probably orders of magnitude less than this.


So its not very likely that this is what happened in the case of our solar system although it is theoretically possible.

This brings up a slightly different, although maybe related question though... Lets pretend Gas-Supergiant Mercury formed where the asteroid belt is today then somehow managed to migrate to the inner solar system and placed itself into a close enough orbit around the sun where the sun was able to start leaching away its atmosphere. Would its orbit migrate further out from the sun as its mass was leached away? The loss of mass would speed up the process of blowing away its atmosphere by lowering the planets escape velocity but would the migration out from the star be enough to compensate for this and keep the actual rate of loss relatively constant?

01101001
2007-Apr-12, 04:33 PM
Would its orbit migrate further out from the sun as its mass was leached away?

Does a pendulum's rate depend on its mass? What about the legendary balls of different mass that Galileo dropped from that tower in Pisa?

Through what mechanism would the lost mass alter a planet's orbit? More massive planets would orbit faster or slower? Or doesn't it matter?

Delvo
2007-Apr-12, 05:01 PM
Why are we talking about gases being sucked up by the sun? Last I'd heard, the idea that the inner planets once had bigger atmospheres than they do now had them being removed by T-Tauri wind from the sun (a brief period early in the star's history with much more intense solar wind than now), with Mercury's inability to partially replace it being explained by its lack of volcanism and the sun's tendency to drive off any gases that close to it with the much more intense radiation and wind. And since the planets are in orbit, not falling in to the sun, drifting in freefall without experiencing a net inward pull, why would this be true of the solids but not the gases?

Ilya
2007-Apr-15, 05:36 PM
I know most people say that jupiter, saturn, Uranus and Neptune have no solid surface but in all honesty, if a single commet or asteroid has ever hit the planet that didn't completely vaporize then there has to be something of that rock left somewhere in the atmosphere. It may be a pile of rock being crushed under the un-imaginable weight of Jupiters atmosphere but there has got to be a rock in there somewhere:)
These four giant planets certainly have rocky cores, estimated to mass around 10 Earths in all four cases. It's just a bit silly to call the surface of that core "Jupiter's surface", when almost all of its mass is above it.

Notice that in Uranus and Neptune the core is more than half the planet's mass, and the pressure at the boundary is not high enough to form metallic hydrogen. So in these cases talking about "solid surface" is more meaningful.