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Kullat Nunu
2006-May-17, 06:17 PM
* Space.com article (http://www.space.com/scienceastronomy/060517_netpune_planets.html)
* The Extrasolar Planets Encyclopaedia data (http://exoplanet.eu/star.php?st=HD+69830)
* Nature news article (http://www.nature.com/nature/journal/v441/n7091/full/441292a.html) and discovery article (http://www.nature.com/nature/journal/v441/n7091/abs/nature04828.html), available only to subscribers

sol_g2v
2006-May-17, 06:44 PM
That third Neptune planet in the HZ zone may be the first waterworld.

Kullat Nunu
2006-May-17, 06:46 PM
* ESO press release (http://www.eso.org/outreach/press-rel/pr-2006/pr-18-06.html)

The star was already known to be special, since it harbors an asteroid belt. Now the belt is believed to be located between the planets c and d, although it's still possible that it may actually be beyond the orbit of the furthest planet.

Blob
2006-May-17, 06:54 PM
http://static.flickr.com/49/148288772_797ce8b533_m.jpg
Expand (http://static.flickr.com/49/148288772_797ce8b533_o.gif) (10kb, 792 x 497)

Position(2000): RA 08:18:23.9 Dec: -12:37:55.8

Blob
2006-May-17, 06:56 PM
In 2005, the Spitzer Space Telescope detected dust in the HD 69830 system consistent with the existence of an asteroid belt twenty times more massive than that in our own system lying inside an orbit equivalent to that of Venus in our own solar system.

http://en.wikipedia.org/wiki/HD_69830

mikeh9741
2006-May-18, 02:11 PM
Very exciting! Note that the size of the third planet is estimated at 18 Earth masses.

FTL_Diesel
2006-May-18, 04:28 PM
Also exciting because it means they were able to goose HARPS (the spectrometer they used) down to a precision of 60 cm/s, and keep it stable there for over a year.

Means that stellar variablity might not be such a show-stopper as everyone thought to sub-1m/s spectroscopy.

Kullat Nunu
2006-May-18, 05:14 PM
Related news: A new transiting planet discovered. (http://exoplanet.eu/star.php?st=XO-1)

The star, designated GSC 02041-01657, or XO-1 by the discoverers, is located about 200 pc (650 ly) from the Sun and is remarkably similar to it. The planet itself seems to be a very typical hot Jupiter, which on the other hand is not very typical to transiting planets as they tend to orbit extremely close to their stars.

mikeh9741
2006-May-19, 03:23 AM
Related news: A new transiting planet discovered. (http://exoplanet.eu/star.php?st=XO-1)

The star, designated GSC 02041-01657, or XO-1 by the discoverers, is located about 200 pc (650 ly) from the Sun and is remarkably similar to it. The planet itself seems to be a very typical hot Jupiter, which on the other hand is not very typical to transiting planets as they tend to orbit extremely close to their stars.

I think you might be misunderstanding. It looks like the planet's orbital period is about 4 days, from which I would deduce an orbit that I would consider extremely close to the star.

01101001
2006-May-19, 04:35 AM
Ahem, now if Denis12 (http://www.bautforum.com/member.php?u=11620) were still active, we could be asked something like: "What is the possibility of manned (or unmanned) spaceflight to HD 69830 d, so we could plant a flag there or drive around? How long would it take and what would it be like there to explore and live, and what would the possible extraterrestrial life there be like? How about HD 69830 c? Comments please."

Kullat Nunu
2006-May-19, 05:25 AM
I think you might be misunderstanding. It looks like the planet's orbital period is about 4 days, from which I would deduce an orbit that I would consider extremely close to the star.

No, that's "only" very close to star. ;) Many transiting planets discovered so far are "very hot Jupiters", with orbital periods around 2 days or less. Planets found by radial velocity surveys, however, have usually orbital periods of 3-4 days. Of the 10 hot Jupiters that have orbital periods less than 3 days half are transiting planets.

davidhw
2006-May-19, 10:16 AM
Reading this article, I was thinking: if one or more of these worlds are "terrestrial", is there an upper limit to the mass of a terrestrial planet? That is, could you have a "rocky" planet with Jupiter's mass (318x Earth) or larger?

markg85
2006-May-19, 10:42 AM
Reading this article, I was thinking: if one or more of these worlds are "terrestrial", is there an upper limit to the mass of a terrestrial planet? That is, could you have a "rocky" planet with Jupiter's mass (318x Earth) or larger?


i think it can be possible.. just think of how giant the universe is!! and than think of how manny different sized stars there are.. in my opoinion it`s possible that giant stars can have giant planets (maybe even giant creatures on it) nothing can be ruled out or tought as "impossible" because the human race just isn that advanced to say something.. wa aren`t even out the solar system yet (with humans..) there is a probe that left our solar system but that isn`t really a advanced thing.. it`s just sending beeps ;)

so at this moment your question can`t be anwsered. any anwsers are just the opinions of people but not based on facts simply because we know to little to say something and besides that we keep discovering bigger things and more extraordinary things.

Eckelston
2006-May-19, 12:54 PM
The problem I see with this that any rocky planet that huge would be able to accrete and keep a huge hydrogen atmosphere. After all hydrogen is the most abundant element in the circumstellar disc, right? That being said there could be planets or brown dwarfs with a pretty large rocky or metallic core out there and it might just be possible to lose the atmosphere if the planet is very close to an unusually active star. Or maybe through some other cataclysmic event like a supernove explosion.

mikeh9741
2006-May-19, 01:09 PM
Kullat:
Ok, now I see what you meant. Thanks.

The subject of maximum Earth-like planet size came up in September 2004, just after a 14 Earth mass planet was found. See this page: http://www.bautforum.com/showthread.php?p=275784#post275784

There is a link there to an article with an estimate of about 15 Earth masses as the max.

publiusr
2006-May-19, 09:03 PM
You might only have large creature on a waterworld type planet.. You would have a lot of gravity--but could stay bouyant...I wonder how that would work.

eburacum45
2006-May-20, 04:07 PM
A large waterworld like this would also have a considerable atmosphere; it would resemble Neptune in many ways, except that it would have liquid water under the atmophere instead of ice. There would probably be high pressure, high temperature ice under the water layer (this would be a type of ice denser than water, perhaps ice-VIII or ice-X).
(phase diagram of water (//www.lsbu.ac.uk/water/phase.html))
I doubt if life could emerge on such a water-giant, however; there would be no easy way for the components of life to become concentrated together to form complex organic compounds.

Joe87
2006-May-20, 05:53 PM
You might only have large creature on a waterworld type planet.. You would have a lot of gravity--but could stay bouyant...I wonder how that would work.
It wouldn't necessarily have a high surface gravity. I calculate that the HZ planet with 18 times the earth's mass would have a surface gravity of only 84% of the earth's surface gravity if its density is 1, i.e., it is made of water or ice only. If it is made of rock with a density of 3.3, then surface gravity would be 1.86 times the earth's gravity. If it has the earth's density of 5.5, (i.e., an iron core overlaid by rock) then surface gravity would be 2.62 times that of the earth.

Those surface gravity values would not necessarily result in a massive atmosphere, although it could happen, look at Venus with a surface gravity of 0.91 g's. Is Venus within the sun's HZ?

Bynaus
2006-May-22, 09:17 AM
Surface gravity could even be larger. I once saw a paper where they showed that terrestrial planets of "earth" composition scale with M^0.27. This would give this world a surface gravity of a crushing 4.8 g's.

Kullat Nunu
2006-May-22, 09:53 AM
If the planet is a so-called "ocean planet", it might have an ice mantle thousands of kms thick making it much larger than a terrestrial planet. Therefore its gravity wouldn't be so crushing. From the point of life, the ice may be problematic because the ocean (tens to a hundred km thick!) might not have necessary elements as they are trapped in the silicate core under the ice.

Mungascr
2006-May-24, 09:11 AM
It wouldn't necessarily have a high surface gravity. I calculate that the HZ planet with 18 times the earth's mass would have a surface gravity of only 84% of the earth's surface gravity if its density is 1, i.e., it is made of water or ice only. If it is made of rock with a density of 3.3, then surface gravity would be 1.86 times the earth's gravity. If it has the earth's density of 5.5, (i.e., an iron core overlaid by rock) then surface gravity would be 2.62 times that of the earth.

Those surface gravity values would not necessarily result in a massive atmosphere, although it could happen, look at Venus with a surface gravity of 0.91 g's. Is Venus within the sun's HZ?

My understanding was that the surface of Venus was at a pressure (if not gravity) many times the crushing seafloor depths on Earth. That, as well as being corroded, burned and suffocated there, you'd also get squashed flat.

My guess is any planet with more mass would have proportionately higher surface gravity although I see where people are going (I hope) with composition & density.

I also think a more massive planet implies a more massive atmosphere - deeper, more likely to trap heat and to result in a Venus-type runaway Greenhouse FXT with higher pressures at the surface. NOT good unless the planet is at the far end of what's possibly habitable & the greenhouse FXT traps heat enough to keep a world warm that by rights should freeze ...

As far as Venus goes it is NOT in the Sun's Habitable Zone - as I understand -because liquid water can't stay liquid there. Venus once was in the HZ when the Sun was younger but then as the Sun grew brighter any Venusian oceans boiled, turned to steam, trapped heat and broke down.

Mars, OTOH, is, I gather, in the HZ but lacks enough size and gravity to maintain an atmosphere thick enough for liquid H2O.

Now, if Venus were where Mars is instead - & vice-versa - perhaps, just perhaps, we'd have three habitable planets in our solar system today : Mars would get enough heat without having too much through its smaller gravity & atmosphere trapping less heat. Earth being just right as it is now. Plus Venus being further away from the Sun but with its compensatingly larger atmosphere trapping more heat & keeping it warmer than Mars and thus able to support life ..

BTW. Made another quite different post on this same '3 Neptunes round a Puppis star' topic but another thread, here~ish. Universe today / Bad astronomy - different forum /same forum? I'm confused, more than usual that is... Is this meant to happen? Should we link to or combine the two threads .. Or .. what?

NB. That other thread that I just visited (w. sim. title) was started by 'Fraser', an administrator, & linked to the BAUT-F. My response there was dealing with the difference betwixt Jove & brown dwarfs plus a (probl'y bad) joke involving exoplanet 70-Virginis-b & Islam followed by an addendum on its implications & preceeded by a joke warning.

Sorry if this breeches netiquette. Moderators feel free to edit.

Bynaus
2006-May-30, 09:23 AM
That, as well as being corroded, burned and suffocated there, you'd also get squashed flat.

This is a common mistake: High atmospheric pressure doesn't get you squashed flat. You don't feel atmospheric pressure the way you would feed direct pressure from, say a airplane falling on your head - atmospheric pressure comes from all sides: If you are in a high pressure lab (say, 3 atmospheres), you dont feel "pressed" to the ground: the experience isn't quite diffrent from beeing in a room with 1 atmosphere. You may well be cooked (not burned, since there's no oxygen, and not corroded, since the corrosives are only in the higher atmosphere and never reach the ground) and suffocated, but not squashed flat.

If Mars and Venus were to switch places, I agree that Venus could very well be a habitable planet. But Mars would loose its thin atmosphere so close to the sun: The amount of atmosphere a planet can hold does not only depend on gravity, but also on the temperature of the atmosphere.