...is a big topic. Posing here just two questions: What are the most dense and least dense objects in solar system?
I suspect it is going to hang on what you define as an object. Osmium - Wikipedia Interplanetary medium - Wikipedia
Object large enough to be bound by gravity. I think we are pretty sure there are no black holes in solar system. Really sure there are no neutron stars. No shame if one needs to look it up - I had to
Without looking it up, I'd go for Mercury as most dense, Sun as least. --------------------- Dang, missed on both. Very close on the former, factor of 2 on the later. But the Sun will very easily win as least when it hits Red Giant phase, then claim the most when it goes for White Dwarf.
Least dense grav-bound body is SATURN. It is half as dense as the Sun. The other gas giant planets bracket Sun's density, Uranus and Jupiter are under and Neptune is over. Saturn at 0.687 grams/cm3 closely matches some hardwoods, in case you want to make a ball and hold in your God-like hand. No idea why Saturn is such an underperformer here. But all eyes are on Cassini space probe now doing 22 loop de loops that will end with 'entry'. Most dense is EARTH! Tahdah! we win. Mercury finishes second, then Venus, with Mars coming in distant 4th. My only guess as to why Earth is this way, is that collision with another Mars-size body that made the Moon. On what would have been a contender for The Worst Day Ever. Double up on iron (etc.) and maybe irretrievably blow off some light stuff. Anyway, Earth has the density thing nailed. Perhaps related to being the only one (around here) that has sustained tectonics and a good 'nuff magnetic field. Possibly of interest in hunting for biological exoplanets. If you want to make an Earth Ball of correct density to hold, start with zinc (because its cheap) and drill out about 23%. Then you have 5.514 gram/cm3 Make a Sun Ball from aluminum foil wad it up and squish down to about 48% 'air'. Saturn ball gets half as squished. As iron meteors are...iron... they have density of 7.85. Thus they'd be winners here if gravitationally bound. But not. Just nice crystals, which we hope mange to miss Target Earth for as long as possible.
I would say the center of the sun is the most dense. The least dense gravitationally bound object would be the Oort Cloud.
Any red giant star will have very low density as fuzzy1 pointed out. But still a hot dense fusion core. That photon energy goes though so many handoffs that, by the time it gets out, they are...well...red. +++ Saturn (maybe all gas giants?) emit more energy than solar input. Seems a bit mysterious. Likely they are all slowly shrinking and it's basically friction.
drysider, my arbitrary game rules do not allow you to 'part out' the sun. Disregarding that, Jupiter's metallic hydrogen core is very much more dense*. I think ya got me with the Oort Cloud though. It is arguably grav-bound, whacking big, and perhaps only 2 Earth masses in total. But it subsumes the entire solar system so I wiggle ut by way of no parting out rule. Two Earth masses of water, carbon monoxide, and whatever else Oort is, is a lot though. Stay far away please. *This incorrect assertion corrected below
Ah Pluto, we still love you. Density 1.86 means mostly ice and not much 'rock' there. Absolutely the last object found by photo flickering. Eyeball astronomy has since been supplanted. Among minor planets (planetoids), Pluto will always be the best.
By different estimates, Jupiter would need to be 10 to 100 times more massive to conduct fusion. Other gas giants haven't nearly enough to give. Can't happen. Metallic hydrogen core of this non-star is the strangest place aside from fusion places. Best not to visit either. Studies of exoplanets reveal many super-jupiters (that did not 'light' either). Only a small subset of the Galactic Zoo is represented in our local system. We happen to be living in a most congenial corner.
My "Jupiter's metallic hydrogen core"@11 is incorrect. Near as I can work it out, Jupiter's weird place has density about 2.6. Solar core is about 150.
At PriusChat one can only give one 'like'. drysider told us that Sun fusion core far exceeds Jupiter and I am happy to be corrected on that. May just go to show that Fusion is a Hard Road, and all other means of earthly energy production ought to be fully explored first. But dang, those laser/inertial confinement and magnetic confinement gadgets are fun to look at, yes?
Checking a bit deeper since my previous reply, I found than comets average 0.6, and at least one named comet is down at 0.3. I believe we can count these as gravitationally bound, so they would rank as even less dense than Saturn. But if one wants gravitationally rounded, or hydrostatic equilibrium, then the known comets may get excluded. ... and an extremely close second too, within 2%. I.e. mechanically bound. I'm not aware of any minor planets / asteroids having enough iron (versus standard rock) to win this contest. I don't think this Cloud can qualify under the 'gravitationally bound' rule. While it is bound to the sun, if the sun is removed, this Cloud would mostly drift away into interstellar space. With any orbital speed at all, to keep from falling into the Sun, it has too much energy (or not enough mass) to be self-bound.
Either way, 'Nine Planets' is not currently tenable. Either shrink it to 8, or open it up for a major increase in count.
Oh Man! Fuzzy1 killed my Saturn-win on the low density side. I really wanted Saturn to win this as an odd fellow. But OK, a grav-bound snowball comet of 0.3 is The Least Dense. Hope you're happy. Meanwhile Saturn is a fabulous planet. All that ring-sheperding moon stuff? C'mon
Depending on how you define 'gravitationally bound', you may still pull out a win for Saturn. That low density comet (I checked only a small sample, so there could be better winners) is 19P/Borrelly - Wikipedia and the pictures clearly show that it is not pulled into any spheroidal shape by gravity. It only has enough gravity to keep its gravel pile together, not to overcome mechanical shaping forces.
