The Solar system’s planetary layout does not fit with predictions of how such systems would form but many exo-planetary systems do.
You would expect in a rotating disc of material where accretion is taking place, for the larger planets to form closer to the central body (ie the star) and the smaller planets to occupy the outer orbits. This is because the amount of available material decreases as you move put from the star. In our system, we have the small rocky planets close to the star, and 4 gas giants way out.
One theory for our situation is that the rocky inner planets formed after the gas giants. Once a rocky core gets beyond a certain size, it quickly sucks up surrounding gas and this is most likely how the gas giants formed (Saturn is a bit different since it is the least dense planet in our system).
Re the terraforming Galu - yes s I-Fi writer stuff, but I do think we will have to do this kind of stuff in the far future.
You would expect in a rotating disc of material where accretion is taking place, for the larger planets to form closer to the central body (ie the star) and the smaller planets to occupy the outer orbits. This is because the amount of available material decreases as you move put from the star. In our system, we have the small rocky planets close to the star, and 4 gas giants way out.
One theory for our situation is that the rocky inner planets formed after the gas giants. Once a rocky core gets beyond a certain size, it quickly sucks up surrounding gas and this is most likely how the gas giants formed (Saturn is a bit different since it is the least dense planet in our system).
Re the terraforming Galu - yes s I-Fi writer stuff, but I do think we will have to do this kind of stuff in the far future.
Last edited:
There is (still?) this NASA "ask a cosmology expert" to which I for along time ago sent the question: "The universe seem very non-symmetric but if the BB happened as we think, wouldn't all the stars and galaxies be nicely evenly distributed and the universe highly symmetric?"
The answer was: But they are / it is.
//
Typically what happens is you have a cloud of gas and dust - a nebula. Due to gravity between the material (or a gravitational nudge from a passing star which will also do it), or due to shockwave from say a supernova, accretion starts. As material falls into the increasing gravity well, it beings to rotate about the centre of mass and it flattens out (conservation of energy and conservation of angular momentum). There is usually more stuff toward the centre of the disc because this is where gravity is stronger. The same accretion process also takes place on a smaller scale around the main centre of mass (which usually end up being a star) and this is how the planets are formed. The denser material ends up in the core and the lighter stuff (gas etc) in the outer shell of the planets.
As mentioned in the earlier post, our Solar system does not seem to follow the norm - the bigger planets are towards the outer edges of the system and the small rocky planets near the Sun - lucky for us.
Certainly, on the small scale of our Milky Way galaxy, we see non-symmetry.
However, if we look at the distant galaxies, there seems to be more or less the same number in every direction, so there is symmetry on the large scale
The usual analogy is that of a forest. The nearest trees may be at different distances and even grow in clumps, but on the large scale these kinds of differences average out and the forest looks symmetric.
Bit of a cross thread here but it still is pertinent I think. I've read somewhere that Australia's strange marsupial/egg laying mammalian and unique birds may have come to be via some sort of ancient cataclysmic event which caused massive genetic mutation there. If so, does it stand to reason that this is how viruses came into existence also? A blob of DNA bombarded by a surge of radioactivity from an incoming asteroid?
I used to speculate about the size of the Universe, an' all that... 😱
AFAIK, if our own Milky Way Galaxy was a yard or metre across and residing in our beloved town of Portsmouth, then the end of the Universe is about as far away as Bristol at 150 miles.
Which is about 200 Km away for those Europeans not versed in our ancient units of measurement.
Interestingly, we are on a shock direct collision course with the Andromeda Galaxy. On this scale it's about 20 metres away currently. Andromeda looks about the width of the full moon right now and just like a bit of the Milky Way, but getting bigger. It ain't gonna happen for about 2 Billion Years though. So don't lose too much sleep over it. 😀
That, TBH, is in a Classical Universe. Since then we have had the Quantum Theory.
IMO, the greatest demonstration of Wonder in our own puny Solar System is the Nightly Surprise of the innermost Moons of Jupiter, Io, Europa and Ganymede: Orbital Resonance.
Honestly, it's like watching microscopic Quantum Theory in a macroscopic sense! A neat 1:2:4 ratio.
Intellectually though, I can commend a mathematician known as Ramanujan. He is famous for finding the number 1729 interesting when Hardy couldn't see it at all.
IMO, a man 100 years ahead of his time: Why the Sum of Three Cubes Is a Hard Math Problem
Absolutely staggeringly brilliant. Elliptical curves invented, Fermat's Last Theorem (almost) proved. I am in awe. 😎
AFAIK, if our own Milky Way Galaxy was a yard or metre across and residing in our beloved town of Portsmouth, then the end of the Universe is about as far away as Bristol at 150 miles.
Which is about 200 Km away for those Europeans not versed in our ancient units of measurement.
Interestingly, we are on a shock direct collision course with the Andromeda Galaxy. On this scale it's about 20 metres away currently. Andromeda looks about the width of the full moon right now and just like a bit of the Milky Way, but getting bigger. It ain't gonna happen for about 2 Billion Years though. So don't lose too much sleep over it. 😀
That, TBH, is in a Classical Universe. Since then we have had the Quantum Theory.
IMO, the greatest demonstration of Wonder in our own puny Solar System is the Nightly Surprise of the innermost Moons of Jupiter, Io, Europa and Ganymede: Orbital Resonance.
Honestly, it's like watching microscopic Quantum Theory in a macroscopic sense! A neat 1:2:4 ratio.
Intellectually though, I can commend a mathematician known as Ramanujan. He is famous for finding the number 1729 interesting when Hardy couldn't see it at all.
IMO, a man 100 years ahead of his time: Why the Sum of Three Cubes Is a Hard Math Problem
Absolutely staggeringly brilliant. Elliptical curves invented, Fermat's Last Theorem (almost) proved. I am in awe. 😎
Last edited:
Our Milky Way galaxy and its nearest galactic neighbour, the Andromeda galaxy, are actually hurtling towards each other at a speed of 402,000 kilometres per hour.
YouTube
The two galaxies are destined to 'collide' in 4 billion years time. I put the word collide in inverted commas because, although the two galaxies each contain hundreds of billions of stars, there is so much empty space between the stars that the two galaxies will simply pass through each other and no actual collisions will take place.
After the two galaxies pass through each other, their mutual gravitational attraction will pull them back together. After oscillating back and forth for a billion or so years they will eventually coalesce into one giant galaxy.
The distance between neighboring stars in the Milky Way galaxy is approximately equal to 10 million times the diameter of a star.
Stars collide with each other very rarely. By comparison, galaxies collide quite frequently as the distances between galaxies is only approximately equal to 20 times the diameter of a galaxy.
To illustrate the vastness of interstellar space, let's imagine a model in which the diameters of the Sun and its nearest stellar neighbour, Proxima Centauri, are represented by table tennis balls. On this scale the distance between the two stars would be 1100 kilometres.
In comparison, intergalactic space is much more crowded. Imagine a model in which the diameters of the Milky Way galaxy and the Andromeda galaxy are represented by table tennis balls. On this scale the galaxies would only be 1 metre apart.
That's most interesting Steve!
Given a clear and dark sky, the Andromeda galaxy is visible to the naked eye as a faint, fuzzy patch which, as you say, stretches as long as the full width of the Moon. With powerful magnification, we can actually see that it stretches six times that length!
The attachment shows how the Andromeda galaxy would appear in the sky if the light from it was not so dim, and it reinforces its close proximity to us.
Attachments
Yes, that is how it would appear to the naked eye if it were brighter, no binoculars involved!
More information here: Moon and Andromeda: Relative size in the sky.
More information here: Moon and Andromeda: Relative size in the sky.
Yes - Andromeda is spectacular. I've got a very nice app on the iPad that allows me to identify thousands of stars etc
Interesting to note that both the Milky Way and Andromeda are considered 'big' galaxies. There are some monsters out there, but our and the neighbour are considered to be on the big side.
I never got why the Sun is always referred to as an 'ordinary star'. If you pareto'd all the stars in the Milky Way, the Sun would lie in the 80th percentile - ie in the top 20%. Most of the stars in galaxies appear to be red dwarfs with a mass of 4-8 times that of Jupiiter.
Of course, star size balloons in the top 10 % so you end up with monsters like Betelgeuse and U Y Scuti (which I think is the biggest we know of).
Let your mind boggle at this UY Scuti Facts | Constellation, Information, History & Definition
I never got why the Sun is always referred to as an 'ordinary star'. If you pareto'd all the stars in the Milky Way, the Sun would lie in the 80th percentile - ie in the top 20%. Most of the stars in galaxies appear to be red dwarfs with a mass of 4-8 times that of Jupiiter.
Of course, star size balloons in the top 10 % so you end up with monsters like Betelgeuse and U Y Scuti (which I think is the biggest we know of).
Let your mind boggle at this UY Scuti Facts | Constellation, Information, History & Definition
10 largest Galaxies
10 Largest Galaxies in the Known Universe | Largest.org
(Andromeda is #10 - IIRC the Milky Way is in the top 20)
10 Largest Galaxies in the Known Universe | Largest.org
(Andromeda is #10 - IIRC the Milky Way is in the top 20)
- Status
- Not open for further replies.