Gas giants and brown dwarfs

[bearack]

<p><span style="font-size:10pt;font-family:Verdana">I remember reading in one thread if Jupiter could be considered a sun or not.&nbsp; This has spurred a question in my little brain that hopefully can be properly explained by there experts here.</span></p><p><span style="font-size:10pt;font-family:Verdana">&nbsp;I understand that brown dwarfs emit heat and pretty sure I understand that gas giants even emit heat to some extent.&nbsp; In the case of Titan, or a similar type moon, could such a gas giant or brown dwarf emit enough heat to heat the surface of a moon such as Titan, even though its distance is very far from the sun?</span></p><p><span style="font-size:10pt;font-family:Verdana">If Saturn was 50 times larger than it currently is, could Titan be warm enough to sustain life?</span><span style="font-size:10pt;font-family:Verdana">Appreciate all corrections of my speculation.</span><font face="Times New Roman" size="3">&nbsp;</font></p><p><font face="Times New Roman" size="3">And by life, I mean organic vegatation.</font></p> <div class="Discussion_UserSignature"> <p><br /><img id="06322a8d-f18d-4ab1-8ea7-150275a4cb53" src="http://sitelife.space.com/ver1.0/Content/images/store/6/14/06322a8d-f18d-4ab1-8ea7-150275a4cb53.Large.jpg" alt="blog post photo" /></p> </div>

 

[titanium22]

<p>Its not the heat emitted from Jupiter & Saturn (if there is any to speak of) some of the moons like Io have there own internal heat source also&nbsp;the gravitational tug exerted by these massive planets on there moons can help move and crack the crust of the moons. Make no mistake tho, it's darn cold on titan the hydrocarbon gases you find here on earth are in liquid form on titans surface, that is what rains there.&nbsp;I believe it is around -280 F on titan. But to answer your question I don't Believe either of those gas giants emits heat, at least noting that would warm any of there satellites, how much bigger would they need to be? I don't know, but I would guess&nbsp;it would need enoug mass&nbsp;to ignite it's nuclear fusion core.</p><p>&nbsp;That in it's self dose not mean life of some sort&nbsp;cant exist there, maybe not life as we know it, but cant rule out life as a whole.</p> <div class="Discussion_UserSignature"> <p> </p><p><font size="1" color="#333399"><em>...and the search for life and earth like planets continues.</em></font></p> </div>

 

[doubletruncation]

<p>The gas giants do radiate energy (in fact they actually emit more than they receive from the Sun), this is their initial heat from formation which they slowly lose over time - so that they cool off over the eons. When they were younger they emitted quite a bit more heat than they do now. As titanium mentioned, gas giants can be very effective at heating their close in moons via tides. It's true that if Saturn were 50 times larger, it would emit quite a bit more heat than it does now. You can use the calculator at http://zenith.as.arizona.edu/~burrows/evolution3.html to estimate how much energy it would emit - I get 1.85*10^-7 that of the Sun (taking the age to be 4.5 Gyr, which is the age of the solar system), note that this calculator predicts 2*10^-12 for Saturn at its actual mass/age, so if it were 50 times larger it would emit almost 100 thousand times more energy. Would that be enough to make Titan habitable?&nbsp; You can do a very gross approximation of the equilibrium surface temperature using the formula:</p><p>&nbsp;T_titan = 0.71 * sqrt(R_S / d) * T_S </p><p>&nbsp;where T_titan would be the surface temperature of titan, R_S is the radius of saturn, d is the distance between saturn and titan, and T_S is the surface temperature of Saturn. Note that this formula assumes a few things that are blantantly false (it assumes that titan absorbs all the heat it receives from Saturn without any reflection, that the energy is instantly transported evenly over the entire moon, and that titan doesn't have an atmosphere - the last assumption is -very- erroneous), nonetheless it provides a decent first rough estimate. If you increase the mass of Saturn by a factor of 50 and keep Titan at the same distance from Saturn, the above formula gives an equilibrium temperature of ~60 K for Titan - way too cold to be habitable. Even if you were to boost Saturn up to 73 jupiter masses (a huge brown dwarf that is just shy of being a star), Titan would have an equilbrium temperature of 190 K, which is quite a bit warmer, but still too cold for it to be habitable (though that depends on how much extra warming its atmosphere provides to the surface). Of course, if you're willing to play with parameters, you could bring Titan in a little closer to Saturn to make it warmer, or you could look at the System when it was younger. If you take a 73 jupiter mass brown dwarf at 1.0 Gyr, a moon at the distance of titan would have an equilibrium temperature of ~308 K - quite balmy (and probably quite a bit hotter below the atmosphere)! </p> <div class="Discussion_UserSignature"> </div>

 

[bearack]

<font color="#ff0000"><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The gas giants do radiate energy (in fact they actually emit more than they receive from the Sun), this is their initial heat from formation which they slowly lose over time - so that they cool off over the eons. When they were younger they emitted quite a bit more heat than they do now. As titanium mentioned, gas giants can be very effective at heating their close in moons via tides. It's true that if Saturn were 50 times larger, it would emit quite a bit more heat than it does now. You can use the calculator at http://zenith.as.arizona.edu/~burrows/evolution3.html to estimate how much energy it would emit - I get 1.85*10^-7 that of the Sun (taking the age to be 4.5 Gyr, which is the age of the solar system), note that this calculator predicts 2*10^-12 for Saturn at its actual mass/age, so if it were 50 times larger it would emit almost 100 thousand times more energy. Would that be enough to make Titan habitable?&nbsp; You can do a very gross approximation of the equilibrium surface temperature using the formula:&nbsp;T_titan = 0.71 * sqrt(R_S / d) * T_S &nbsp;where T_titan would be the surface temperature of titan, R_S is the radius of saturn, d is the distance between saturn and titan, and T_S is the surface temperature of Saturn. Note that this formula assumes a few things that are blantantly false (it assumes that titan absorbs all the heat it receives from Saturn without any reflection, that the energy is instantly transported evenly over the entire moon, and that titan doesn't have an atmosphere - the last assumption is -very- erroneous), nonetheless it provides a decent first rough estimate. If you increase the mass of Saturn by a factor of 50 and keep Titan at the same distance from Saturn, the above formula gives an equilibrium temperature of ~60 K for Titan - way too cold to be habitable. Even if you were to boost Saturn up to 73 jupiter masses (a huge brown dwarf that is just shy of being a star), Titan would have an equilbrium temperature of 190 K, which is quite a bit warmer, but still too cold for it to be habitable (though that depends on how much extra warming its atmosphere provides to the surface). Of course, if you're willing to play with parameters, you could bring Titan in a little closer to Saturn to make it warmer, or you could look at the System when it was younger. If you take a 73 jupiter mass brown dwarf at 1.0 Gyr, a moon at the distance of titan would have an equilibrium temperature of ~308 K - quite balmy (and probably quite a bit hotter below the atmosphere)! <br />Posted by doubletruncation</DIV></font><br /><br /><font size="3">Thanks to both of you for detailed response.&nbsp; This got me thinking because of how the odds of finding a habitable planet might change if a dwarf planet or moon had the right atmosphere and elements and was heated with help from a much larger gas giant or brown dwarf.</font>&nbsp; <div class="Discussion_UserSignature"> <p><br /><img id="06322a8d-f18d-4ab1-8ea7-150275a4cb53" src="http://sitelife.space.com/ver1.0/Content/images/store/6/14/06322a8d-f18d-4ab1-8ea7-150275a4cb53.Large.jpg" alt="blog post photo" /></p> </div>

 

[mako71]

<p>Now correct me if I'm wrong, but I think I read some speculations about having habitable planets around red and/or brown dwarfs. Since dwarf stars are the most common in galaxy, it is no wonder that these speculations have had some intrest.</p><p>The problem is that the habitable zone is close to the star. Thus, the rotation of the planet will be (relatively) quickly locked by tidal forces and the planet turns always the same side to the central star. This will make the other side very hot, and the other side extremely cold. Some speculations have been made that if the planet has a thick atmosphere, that could balance the temperatures at the surface of the planet. </p><p>___________</p><p>Well, I found a Wikipedia article discussing this:</p><p>Habitability of a red dwarf system&nbsp;</p> <div class="Discussion_UserSignature"> <p> </p><p>________________ </p><p>reaaliaika.net </p> </div>

 

[PistolPete]

<p>Everybody here has done a good job of explaining the situation, but I wan't to chime in with a few more details about Brown Dwarves.</p><p>Brown Dwarves are stars below 8% of the mass of the Sun (~80 x mass of Jupiter) and can be as small as 13 x the mass of Jupiter.&nbsp; The criteria that most astronomers can agree on for brown dwarves is that they lack the mass to start hydrogen fusion, but have enough mass to fuse deuterium (or lithium if the brown dwarf is massive enough).&nbsp; Because deuterium is a rare element, it is not found in large abundances and is eventually consumed after a few million years.&nbsp; Brown dwarves above about 65 x the mass of Jupiter can fuse lithium as well but will also run out of this after roughly 500 million years.&nbsp; This is barely enough time for planets to evolve, let alone for life to evolve on those planets, and as Doubletruncation showed us, the heat produced by this fusion would be negligible anyway.</p><p>There is one possibility that I can think of for life to evolve around a brown dwarf.&nbsp; If the planet's core is kneaded by tidal forces like Europa's is, then life may be able to evolve without the need for thermal energy from the brown dwarf.&nbsp; The thermal energy will instead come from the planet's core. </p><p>Incidentally, Saturn is 30% of the mass of Jupiter and after doing some back-of-the-envelope calculations, if Saturn were 50 times larger, then it would be 15 times the mass of Jupiter (0.30x50=15).&nbsp; This would put it just inside the limit as a brown dwarf.&nbsp;</p> <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[mako71]

Yes, PistolPete, you're right; red dwarfes are (AFAIK) the longest lasting stars (yet not possible stable during their lifetime), and brown dwarfs consume their energy source quite quickly. Gaseous planets, which are smaller than the size of a brown dwarf never use fusion as an energy source - the only source of energy is the gravitational "shrinking", and, like said above, that gets smaller and smaller after formation. So, as you point out, for small gaseous planets (lets say 10-60 times Jupiter or less, depending on the construction), the main source of energy for a moon would be tidal forces, creating vulcanic activity. <div class="Discussion_UserSignature"> <p> </p><p>________________ </p><p>reaaliaika.net </p> </div>

 

[bearack]

<font color="#ff0000"><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Yes, PistolPete, you're right; red dwarfes are (AFAIK) the longest lasting stars (yet not possible stable during their lifetime), and brown dwarfs consume their energy source quite quickly. Gaseous planets, which are smaller than the size of a brown dwarf never use fusion as an energy source - the only source of energy is the gravitational "shrinking", and, like said above, that gets smaller and smaller after formation. So, as you point out, for small gaseous planets (lets say 10-60 times Jupiter or less, depending on the construction), the main source of energy for a moon would be tidal forces, creating vulcanic activity. <br />Posted by mako71</DIV></font><br /><br />Excellent synopsis from everyone.&nbsp; Well explained and easy for a simpleton, like myself to understand.&nbsp; Thanks a mint to everyone. <div class="Discussion_UserSignature"> <p><br /><img id="06322a8d-f18d-4ab1-8ea7-150275a4cb53" src="http://sitelife.space.com/ver1.0/Content/images/store/6/14/06322a8d-f18d-4ab1-8ea7-150275a4cb53.Large.jpg" alt="blog post photo" /></p> </div>