The Astronomy Discussion Thread

[Jinto]

Originally Posted by C.A.

Yea, that's why some scientists think that instead of being blasted apart, it could be a planet that failed during formation, billions of years ago, during the formation of the solar system.

It didn't have enough mass to have a gravity strong enough to compact itself into a 'ball'. So it formed numerous lumps instead and got dispersed by the gravitational forces of Mars and Jupiter.

One thing that supports the theory of not having enough mass, is that the combined mass of all the asteriods would make up only 4% of the Earth's moon, with Ceres itself making 1/4 of the total mass.(Mass info taken from Wikipedia)

With such a small amount of mass, it can't form anything, or couldn't have existed as a single object of such size. The gravitational forces between Mars and Jupiter simply wouldn't allow it to form anything.

Hm thats possible too, but if you consider time in this example 4% might just be the leftovers. I could imagine this object was once between mercury's and earth moon's size.
Scientist claim planets where formed when the sun began to form. Now one should not forget that was after a supernovae explosion in this system. The remaining plasma contained relatively equal amounts of dense and not so dense matter (in ionized gas form). (Thats contrary to the believe of some scientist who belief it was born out of cooled down supernovae leftovers). When sun formed in the centre of this system, the gas began to rotate like the many stars do around the black hole in our milky way's centre. A possible explanation is gravitational inconsistencies in the centre of the forming sun, that forced gas particles (ionized gas) to flow to the local gravitational hotspots. The way those hotspots where located, resulted in conflicting ranges/zones of attracting matter. The consequence are directed impact areas per localized gravitational hotspot. Leading to a favored direction of impacting in localized hotspots. This leads to something like blowing wind in a windmill... it will start to rotate. And while the centre started to rotate the ionized gas surrounding became forced to rotate with the centre in a swirl like way.
That swirl had its outer limits in the region of today's cuiper belt to orth cloud.

(One additional note, thats important for further explanation. Gas ions with light atomic cores will cool down faster then those with heavy cores)

Now there are several forces that will start to impact the spherical matter cloud. First and most important is the gravitation in the centre of the system, it reaches out to the helio pause. Next is the rotational forces of the rotating centre, reaching to the orth cloud but with decreasing influnce in the cuiper belt region. These rotational forces did 2 major things, first it forced particles to rotate around the centre's main rotation axis and thereby flattened it (like in our milkyway, that looks like a thin disc), second by forcing the matter of spheresized space into the space of a disc with the same diameter, the matter became more dense (but still very hot... ionized gases cannot cool down that fast in the second beginning of our solar system, because outer gasclouds kept the termal energy inside - at least to a large enough extend).

By the time the gas became cool enough, so the first types of matter with very high boiling temperatures began to condense, and forming to something like raindrops in the atmosphere (just the atmosphere was a disclike object and not a spherical one like on earth). When such a matterdrop collides with usual ionized gas, not much happens... the ionized gas will rebounce and fly away (it just has too much termal energy to stick with the matterdrop). But if a matterdrop collides slowly with another matterdrop, they likely form a larger matterdrop. Thats how local gravitational hotspots start to form in the gas disc around the sun.

The cuiper belt is not so much affected by the rotational forces thatswhy it remains more like a cloud of matter, but since it is in the outer regions and not so dense, it cools down much faster. There are the same localised gravitational hotspots, but they are rather evenly spread over large ring like cloud, so these gravitational centres do atract evenly much matter each of them. Thats not enough to form outstanding localised gravitational forces, before matter becomes too cold to agglutinate. Such objects where tracked into each other, but since they were cooling down too fast, they busted each other into smaller pieces again, and formed what the cuiper belt is today.

Back to the matter disc and their local gravitational hotspots. With increasing size of these hotspots, a third main force did appear (or lets say several third type main forces, because there were several such local grav. hotspots).
So, basically ionized gas and most smaller particles where still mainly attracted by the two former afore mentioned forces, but the condensating, denser objects started were very much impacted by the local gravitational forces in the matter disc. And as much as such objects began to grow, there gravitational influence began to grow. So between 2 such local grav. hotspots, matter would proportionately arrange (or stick to) to the local grav. hotspots according to its strength of grav. forces. That means there is a minimum distance between two such local hotspots, otherwise they would attract each other too much and collide some day. Thats how planets began to form orbits around sun. But why weren't they just sucked into sun? Like the masses of ionized gas have been?
I could imagine some of them were actually sucked into sun, outer objects started the rotation process in an outer diameter. That means these objects could gain higher velocities of circulation before coming close to the sun. And because they were more dense and had more mass (or were gaining density and mass and stability due to their own grav. forces), such objects gained in inertia too. A small ionised gas particle will slow down much faster in velocity of circulation when coming near the early sun as i.e. a "rich of mass" planet sized object. Why?
If gas collides with gas the kinetic energy is spread rather random, and thatswhy gas particles with their low inertia will much easier be slowed down by the main feeding streams for the early sun. Dense "rich of mass" objects with much inertia, won't be affected as much by this process.

By the time all gas-type particles, especially those with light atomic core weight cooled down. But most of the particles with light atomic core weight remain gas after cooling down to lets say 800K. The denser and condensated particles do not cool down that fast for three reasons... a) their cores are heavier and need more time to cool down. b) they form big spherelike objects, with a shrinking surface to volume/mass ratio, that means radiation of thermal enregy is dramatically slowed down and c) Heavier unstable cores tend to break to stable lighter cores by setting free additional thermal energy (nuclear energy). These compound objects (depending on their size) remain hot much longer then the gases.

With the ever growing size of local grav. hotspots in the matter disc, elements became attracted differently dependend on their distance to the centre of the solar system. If you see the history of the planetry system 4-dimensional (including dimension of time), objects in the far outer regions could gain more mass while drawing nearer to the sun. And they reached higher velocities of circulation. But I mentioned it before, the closer to the sun objects are, the more differently they behaved in circulation speed according to their density/mass/inertia. So in the outer regions such grav. hotspots could attract even some of the cooled down gases, because their rotational velocity was rather equal to the gas.

Thatswhy these objects tend to grow even faster (in terms of mass/gravitation). And that would also explain why there were 5 inner planets that could just catch the dense material, and outer gas planets (but we are however not at the end of the process yet). The outer planets with their big gas masses (considered in contrast to their small sized cores of heavier elements), formed little systems themselves (their gravitation was high enough to do so). (regarding the distance vs. attraction aspect) That leads to a good explanation why the huge gas planets have so many moons. The core with the highest mass in such a system would slowly attract the gas of other cores in the local system. Thereby growing faster, and attracting even more gas from its neighbouring core in the local system. By gaining all the gas mass of the other cores, it becomes the center of the system. The remaining cores, would now be its moons.
For the inner planets its not exactly the same, because of the missing gas. Another important aspect is, that inner planets where closer to the sun to begin with, and disc volume per disc diameter wise there was less material to form planets from (and distances between objects in the same orbit where much closer). So these objects had a) no gas, and b) had not that much large sized objects in a near orbit (when I say large sized I mean it in a certain relation... like the moon). So if system became formed, it usually consisted of few participating objects (like earth and moon).

By the time, all the free gases where either absorbed by sun or blown away by solar winds. The only remaing objects where the still very hot planets (inner ones no amtosphere, outer ones with giant gas atmosphere... well basically they existed of atmosphere) and their moons... and many medium sized objects flying around.
Objects cooled down according to their size (the bigger, the slower) and distance to the sun, little and medium sized objects became the first solid ones. Moonsized objects followed and so on... I believe the 5th inner planet was somewhat the size between Moon and Mercury and very far away from sun (compared to Mercury), so it cooled down really fast and became a victim of such a medium sized object. Since the 5th planet wasn't molten anymore it did bust when such an object impacted. The other inner planets rather absorb such objects, thereby gaining size.

I could imagine huge breaking of parts of the 5th planet were tracked closer to the sun or to the jupiter by the impact. Either way it would be consumed by either one of the inner planets or outer planets.
The remaining debris of the 5th planet were disposed in the belt, because without a local centre of gravitation these parts no longer stick together (if they were molten, that'ld be different maybe).

Later when the surface of the planets cooled down, further impacts of space objects lead to thin atmospheres and water on the inner planets (rule of thumb... the more gravity, the more atmosphere... the colder the surface, the more water -but still in relation to the planets gravity).

Well thats basically what I believe that went on when sun was born.

[Muir Woods]

Originally Posted by Loniat

I don't think our sun was formed after a supernova.

I think he meant our Sun was born from supernova remnants. It has to. The composition of the inner terrestrial planets contains heavy elements: Carbon, Lead, Uranium, Copper, Silver, Gold...etc. From The Big Bang, after initial expansion and cooling, the universe started with only elements of hydrogen and helium and perhaps trace amounts of lithium. So where did all the metals come from? Just a note of nomenclature, we astronomers pretty much call any elements heavier than helium "metals", because the total mass of all elements above metals in the universe is tiny compared to the mass portions made up by hydrogen and helium, so we conveniently call the rest "metals". Anyways, supernovas are the only natural process that can input enough energy to create heavy elements above iron and spread them into the interstellar medium. The planets and our Sun are formed from the same blob of space gas and dust with heavy metals, and those heavy metals were expelled from supernovas, however many generations it may be before the whims of gravity destined the creation of our Solar System. Imagine, all the carbon atom in your body were once made in the burning furnace of stars some billions of years ago. You can wondrously and accurately say, "we are all made of stardust".

Originally Posted by C.A.

It didn't have enough mass to have a gravity strong enough to compact itself into a 'ball'. So it formed numerous lumps instead and got dispersed by the gravitational forces of Mars and Jupiter.

One thing that supports the theory of not having enough mass, is that the combined mass of all the asteriods would make up only 4% of the Earth's moon, with Ceres itself making 1/4 of the total mass.(Mass info taken from Wikipedia)

With such a small amount of mass, it can't form anything, or couldn't have existed as a single object of such size. The gravitational forces between Mars and Jupiter simply wouldn't allow it to form anything.

Allow me to delve deeper and correct a few misconceptions. *Digging up old astronomy lecture notes, again* First, if all the asteriods in the asteriod belt were compressed, it would form an object about or less than 2000 kilometers in diameter. There are moons that have a smaller diameter than this. The moon of Mimas is about the mininum mass limit in which its gravity is sufficient to compress itself into a spherical shape. So if the asteriods altogether can form an object 2000 kilometers in diameter, considering its density, it should have more than enough mass to "compact itself into a ball". For concrete numbers, the mass of Mimas is 3.70x10^19 kilograms. The mass of the Moon is 7.349x10^22 kg. And the asteriod's mass, 4% of that, as you said, is 2.938x10^21 kg, which is far larger than Mimas. So what prevented them from forming anything? Answer and part two: orbital resonances.

Orbital resonances occur whenever two objects line up together periodically. When the objects are in alignment with each other at such times, gravity tugs at the objects in the same way. The effect can build up over time, and this tends to move/clear objects at such resonances. Objects that will line up, and hence have an orbital resonance, whenever an object's period is a simple ratio of another, such as 1/2, 1/3, 2/5...etc. Think about it as an analogy to music. If a tuning fork rings at a set frequency next to a piano, the strings that ring in full, half, or even quarter ratio of the tuning fork's frequency will also begin to vibrate. The formation of the asteroid belt is due to the orbital resonances that occur between Jupiter and left over planetesimals from the beginning of the formation of the Solar System. At distances in which the asteriod periods are simple ratios of Jupiter's, there are clear gaps in number distribution. For example, any asteriod at a distance (about 3.3 AU, or 4.937x10^8 km) that has an orbital period of 6 years, half of Jupiter's 12, would recieve the same gravitational nudge every 12 years from Jupiter and this nudge would eventually push the asteriods out of this orbit. It is because of these orbital resonance disturbances that prevented the asteriods from clumping together and forming a spherical object. And Mars is a nonplayer regarding this. Jupiter's mass dominates the rest of the planets, and thus its gravity also dominates the rest of the Solar System other than the Sun. The gravitational contributions from the other planets are negligable compared to Jupiter's. Here is a diagram of the asteriod belt distribution that I scanned, courtesy of The Cosmic Perspective (pg. 371).

Spoiler for Diagram:

[Jinto]

Originally Posted by Muir Woods

...

Spoiler for Diagram:

According to this graph I would suggest there were possibly even more former inner planets maybe.

[Loniat]

Originally Posted by Muir Woods

I think he meant our Sun was born from supernova remnants

Yes, that is safe to assume until a certain degree. This is what is called metalicity in stars, which can more or less indicate their age, isn't it? But that is not only the only wayof formation of elements heavier than Hydrogen and helium. Planetary nebulas also have the same "effect" so to speak, and there isn't any way to tell, as far as I know, how much of metals were formed due to one or the other(actually, it is much more feasible that most of the stars will end up as a planetary nebula than a supernova) . So, saying that the our sun was formed by supernovae is not totally true, and indeed a bit misleading since just a part of the elements presented in it come from these sources.

[Aoie_Emesai]

If I remember correctly; Gravity exist everywhere, but it dissipate over long spans of space (from like point A to point B, ex. Earth to Alpha Centauri). Would the gravity of the Sun (which probably the only unnegligible mass body inside the inner solar system) play any role in keeping the astroides within their orbits along side with all the gas giants excluding pluto because of its distance and relatively meger size. Would this also be included within it's explaination of orbital resonance? Or does orbital resonance dominate the one I gave earlier?

[Muir Woods]

Originally Posted by Loniat

Yes, that is safe to assume until a certain degree. This is what is called metalicity in stars, which can more or less indicate their age, isn't it? But that is not only the only wayof formation of elements heavier than Hydrogen and helium. Planetary nebulas also have the same "effect" so to speak, and there isn't any way to tell, as far as I know, how much of metals were formed due to one or the other(actually, it is much more feasible that most of the stars will end up as a planetary nebula than a supernova) . So, saying that the our sun was formed by supernovae is not totally true, and indeed a bit misleading since just a part of the elements presented in it come from these sources.

I never said the Sun was totally made from supernovas, but you are right. The death of 8 solar mass or less stars, planetary nebulas, also enrich the interstellar medium, but elements above iron has to have come from supernovas. That was the point I was trying to make. As for the age-metallicity relation, that depends if the stars are Population I or Population II stars, and then there are arguments that puts the age to [Fe/H] correlation into question. But then that's another complicated subject that I think is beyond the average interest of the people here.

Originally Posted by Aoie_Emesai

If I remember correctly; Gravity exist everywhere, but it dissipate over long spans of space (from like point A to point B, ex. Earth to Alpha Centauri). Would the gravity of the Sun (which probably the only unnegligible mass body inside the inner solar system) play any role in keeping the astroides within their orbits along side with all the gas giants excluding pluto because of its distance and relatively meger size. Would this also be included within it's explaination of orbital resonance? Or does orbital resonance dominate the one I gave earlier?

By "asteroids within their orbits along side with all the gas giants", do you mean rocks and particles that form rings around the gas giants, or sparse asteroids that happen to be orbiting at the gas giants' orbits?

[Jinto]

Originally Posted by Aoie_Emesai

If I remember correctly; Gravity exist everywhere, but it dissipate over long spans of space (from like point A to point B, ex. Earth to Alpha Centauri). Would the gravity of the Sun (which probably the only unnegligible mass body inside the inner solar system) play any role in keeping the astroides within their orbits along side with all the gas giants excluding pluto because of its distance and relatively meger size. Would this also be included within it's explaination of orbital resonance? Or does orbital resonance dominate the one I gave earlier?

Gravity reaches everywhere but its force is decreasing by the square of the distance between 2 objects. Sun's gravity basically keeps the Asteroids in their orbit. Influences from planets like Jupiter are rather negligible. But if there is enough time, negligbile forces will become observable. In space there is basically just a game of inertia vs. forces of all kinds (there is no air resistance or something like that).

The orbit of a space object is basically dependend on 2 main attributes, its absolute velocity (absolute as in tangential velocity to sun) and its elliptic barycenter. The higher the velocity, the higher is the orbit. If the elliptic barycenter is very off centric, the objects distance to the sun will increase and decrease very much within one orbit-cycle. The same goes for the relative velocity of the object (if it draws closer to the sun it accelerates, and decelerates when moving away from sun).

Objects with a very centric elliptic barycenter are considered to be more stable, because tiny changes regarding their velocity vectors do not alter much the orbit. Objects with a very off centric elliptic barycenter have much less stable orbits, their orbits can be heavily influenced, when such objects are in their "far away from sun" part of their orbit.
The stabilty of an objects orbit is basically dependend on its inertia, its gravity, and its distance to other sources of inertia, gravity.
For example objects with much inertia, will influence the orbit of objects with less inertia more, than it is the other way around. The more gravity a object has, the stronger it will interact with other sources of gravity.

Why do the debris in the asteriod belt do not agglutinate? The debris are solid, and of different size, very little changes in gravitational forces, can alter their orbit enough to collide with other debris. Since they are solid objects, they rather bust and bounce. If it was gooey substance both objects would intermix more and go through each other, thereby absorbing each others energy (resulting from the kinetic energy based on their different velocity vectors and mass). A gooey substance is able to rearrange on melocule level, so there will always be a spherelike shape after enough time of reballancing the local gravitational barycenter (molecules have rather high friction).
If solid objects were able to stick to each other (without busting or bouncing off), they'ld still have no chance to reballance their local gravitational barycenter. That leads to further erosion of the two objects until they are even smaller debris.
So over a longer period of time, big solid debris become small debris, and they will spread out. Because all the tiny gravitational outside influences will make them rebounce more and more chaotically (since they cannot absorb impact energy in small amounts over time (like the gooey objects), they rather reflect it by busting and rebouncing).
Thatswhy even negligible forces have so much influence (espacially on solid debris) over time.

[Aoie_Emesai]

Originally Posted by Muir Woods

By "asteroids within their orbits along side with all the gas giants", do you mean rocks and particles that form rings around the gas giants, or sparse asteroids that happen to be orbiting at the gas giants' orbits?

Yes, the asteroids as their orbit around the sun.

Originally Posted by Jinto Lin

Gravity reaches everywhere but its force is decreasing by the square of the distance between 2 objects. Sun's gravity basically keeps the Asteroids in their orbit. Influences from planets like Jupiter are rather negligible. But if there is enough time, negligbile forces will become observable. In space there is basically just a game of inertia vs. forces of all kinds (there is no air resistance or something like that).

The orbit of a space object is basically dependend on 2 main attributes, its absolute velocity (absolute as in tangential velocity to sun) and its elliptic barycenter. The higher the velocity, the higher is the orbit. If the elliptic barycenter is very off centric, the objects distance to the sun will increase and decrease very much within one orbit-cycle. The same goes for the relative velocity of the object (if it draws closer to the sun it accelerates, and decelerates when moving away from sun).

Objects with a very centric elliptic barycenter are considered to be more stable, because tiny changes regarding their velocity vectors do not alter much the orbit. Objects with a very off centric elliptic barycenter have much less stable orbits, their orbits can be heavily influenced, when such objects are in their "far away from sun" part of their orbit.
The stabilty of an objects orbit is basically dependend on its inertia, its gravity, and its distance to other sources of inertia, gravity.
For example objects with much inertia, will influence the orbit of objects with less inertia more, than it is the other way around. The more gravity a object has, the stronger it will interact with other sources of gravity.

Why do the debris in the asteriod belt do not agglutinate? The debris are solid, and of different size, very little changes in gravitational forces, can alter their orbit enough to collide with other debris. Since they are solid objects, they rather bust and bounce. If it was gooey substance both objects would intermix more and go through each other, thereby absorbing each others energy (resulting from the kinetic energy based on their different velocity vectors and mass). A gooey substance is able to rearrange on melocule level, so there will always be a spherelike shape after enough time of reballancing the local gravitational barycenter (molecules have rather high friction).
If solid objects were able to stick to each other (without busting or bouncing off), they'ld still have no chance to reballance their local gravitational barycenter. That leads to further erosion of the two objects until they are even smaller debris.
So over a longer period of time, big solid debris become small debris, and they will spread out. Because all the tiny gravitational outside influences will make them rebounce more and more chaotically (since they cannot absorb impact energy in small amounts over time (like the gooey objects), they rather reflect it by busting and rebouncing).
Thatswhy even negligible forces have so much influence (espacially on solid debris) over time.

.......(my mouth has slammed shut) (i'm not astronomy genius like you and muir). Still trying to grasp the knowledge that ya have filled me with.

[C.A.]

Plutons and asteroids aside, here's the latest astronomical news:

Team finds 'proof' of dark matter

[Jinto]

@Aoie_Emesai,

There is just one thing I wasn't very exact about.

To gain a higher orbit you need to speed up to advance from the current orbit. But to hold the new orbit, speed is slower then in the lower orbit.

So higher orbit = lower velocity and lower orbit = higher velocity. (if seen as speed tangential to the orbit)

The potential energy however is higher in higher orbits.
Thats rather hard to explain...



In the example graphic there is given an orbit with the radius r. The object in the orbit has a certain velocity v (that is tangential to the orbit). The attraction/gravitational acceleration is g in this example, and a is the centripetal acceleration. v needs to be high enough to result in an a that is equal to g. This is one way to explain the orbit.

There is another method to explain the orbit. Imagine the object to be constantly in freefall to the center object. Or to phrase it differently:
In the same time the object falls down h (because of g) it moves forward the length of v. Now falling down h and moving forward the length of v is a smooth transition that describes the orbit.

Now I want to explain the thing with the different velocities in different orbits.

First of all the easy part. Since gravity's force decreases by the square of r. One can say, that g decreases when r increases. With decreasing g the object needs less a and therefore less v. So staying in a higher orbit needs less velocity then staying in a lower orbit.

a = v²/r
g=G*m/r² (m is the mass of the centre object)
since g should be equal to a...

v²/r = G*m/r²
v² = G*m/r
v = sqrt(G*m)/sqrt(r) (sqrt(G*m) is const.)
v = const./sqrt(r)

=> higher orbit = less velocity needed to stay in orbit.

To leave an orbit for a higher orbit, an object needs to accelerate however. It needs to accelerate about as much as:

acceleration when falling from higher orbit to lower orbit - acceleration for increasing tangential velocity from higher orbit to lower orbit.



For example if an object is in a very high orbit around earth:

r1 = 384,400,000 m (moon orbit)
m = 5.97*10^24kg (mass of earth)
G = 6.67259 *10^-11 m³/(kg*s²)

v=sqrt(G*m/r1)= 1017.98 m/s approx. 1km/s

in a lower orbit (lets say 7500km above earth's centre):

r2 = 7,500,000 m
v=7287.92 m/s approx. 7.3 km/s

difference r1,r2 = 376900000 m

acceleration from point r1 to r2 will result in a speed of approximately 9 km/s (if the object was not moving in an orbit, but directly falling to earth... this is not easy to calculate because g is increasing while the object falls down to earth (or lets say in the lower orbit))

edit: (there has been still a logical error, now it should be right)

Ekin = 1/2 m1*v² (m1 = mass of object)
WG = G*m1*m2*(1/r2-1/r1) (m2 = mass of earth)
The gravitational energy build up while moving from r1 to r2 is equal to the final kinetic energy of the object (when it reaches r2).

Ekin = WG
1/2*m1*v² = G*m1*m2*(1/r2-1/r1)
v² = 2*G*m2*(1/r2-1/r1)
v = sqrt(2*G*m2*(1/r2-1/r1))
v = 10205 m/s approx. 10.2km/s

WG + Ekin_high - Ekin_low = dEkin

dEkin = 1/2*m1*vG² + 1/2*m1*vhigh² - 1/2*m1*vlow²

vdelta² = vG² + vhigh² - vlow²

vdelta = sqrt(10205² + 1018² - 7287²) m/s
vdelta = 7216 m/s
7.2 km/s + 7.3 km/s = 14.5 km/s

The kinetic energy needed to go from the low to the high orbit is very high. A sudden speed up of 7.2 km/s in the lower orbit would catapult the object into the higher orbit (the object would slow down from 14.5 km/s to 1km/s in the process of reaching the higher orbit).

[Kensuke]

Pluto loses status as a planet

The decision was made at a meeting of the International Astronomical Union (IAU) in the Czech capital Prague.

"The eight planets are Mercury, Earth, Venus, Mars, Jupiter, Saturn, Uranus and Neptune," said the IAU resolution, which was passed following a week of stormy debate.

New term for Pluto and large Kuiper Belt objects, like those which were considered to be planets, is Dwarf planet Wikipedia has also been updated, no more Pluto in planet list, it takes a while until all school and other books are updated.

Also, final definition for planet (from wikipedia):

A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
Pluto is a dwarf planet by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

All other objects orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

[Kinny Riddle]

Originally Posted by Kensuke

Pluto loses status as a planet



New term for Pluto and large Kuiper Belt objects, like those which were considered to be planets, is Dwarf planet Wikipedia has also been updated, no more Pluto in planet list, it takes a while until all school and other books are updated.

Also, final definition for planet (from wikipedia):

This would mean major re-writes for all school textbooks and updates for all science musuems around the world. The new school term is going to start in a few weeks, looks like teachers worldwide will have to settle with their "outdated" textbooks for this year.

For over 70 years, a lot of people has been taught that the Solar System has 9 planets, so this is going to take some time to settle in. But from a scientific point of view, this decision makes sense, as Pluto is simply too small in size, not to mention even larger trans-Neptunian objects out there. Just my opinion based on my meagre knowledge of astronomy.

[i0td]

Originally Posted by Kensuke

Pluto loses status as a planet

lol MVEMJSUN, My Very Educated Mother Just Showed Us Nine.... ?!? All those children who have learned that there are nine planets.

But I have to agree though. Ever since all these new objects have hit the news and the debate floor, the idea of categorizing Pluto a planet becomes iffy.

[Aoie_Emesai]

Jinto_Lin - So this basically works for the asteroids from mars to jupiter, no? I mean the formulas for caculating relative speed to stay in high orbit.

[Jinto]

Originally Posted by Aoie_Emesai

Jinto_Lin - So this basically works for the asteroids from mars to jupiter, no? I mean the formulas for caculating relative speed to stay in high orbit.

Basically yes. The centre object would be the sun in this case. But there are several forces that influence the asteroids in their orbit (all the spaceobjects in this universe influence each other, except those that drift away from each other with the speed of light. But most of these objects, only have infinitesmal influence on a certain other object). So if you want to calculate the orbit of an space object vaguely right, you need to include all the objects that have a relevant force on the target object).

For asteroids in the asteroid belt, the most important grav. source is the sun. Than there is minimal influence of other objects, like planetoids (Ceres), planets (Jupiter) and so on.
But there is a problem, said formula (WG) doesn't work with more than two sources of gravity (because with more than 2 grav. sources, one need to somehow implement the position of the objects and their direction vectors). That may be calculated by using approximation algorithms, but I don't know how it is done.


On another note ... Pluto is not considered a planet anymore (now the solar system makes sense )

[USB500]

Originally Posted by Kensuke

Pluto loses status as a planet



New term for Pluto and large Kuiper Belt objects, like those which were considered to be planets, is Dwarf planet Wikipedia has also been updated, no more Pluto in planet list, it takes a while until all school and other books are updated.

Also, final definition for planet (from wikipedia):

oh my, looks like my knowledge on the solar system will have to be corrected, too

[Kensuke]

Lockheed to build spacecraft for NASA's moon missions

Nasa has awarded a multi-billion-dollar contract to the group to develop the Orion vehicle, which will replace the space shuttle when it retires in 2010.

The agency is dropping the shuttle's winged, reusable design and is going back to the capsule-style ships that first carried Americans into orbit.

The first Orion vehicles should fly in 2014 or soon after.

Long time to wait and I really hope that this will be successful. I almost wish that there will be a new space race, like during 50's and 60's between Soviet Union and USA but more friendlier without the threat of nuclear war, as Russians, Europeans and Chinese are also in the game.

Abandoning the current shuttle desings and going back to capsules is like jumping back in time for 40 or so years, but I guess capsule desing is best for space traver, wings are just deadweight in space.

Wikipedia: Orion spacecraft

[NoSanninWa]

The only way we'll have a new space race, like during the 50s and 60s, is if someone creates weapons that can kill from orbit.

Or governments otherwise become convinced that space is a tactical asset.

[Catgirls]

Wow...the Mars rover (Opportunity) is STILL going!

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Mars rover reaches its biggest target yet
After 20-month trek, Opportunity sends photos from Victoria Crater’s rim

NASA's Opportunity rover has returned its first photos of Victoria Crater at Meridiani Planum on Mars.

The robot has started to relay tantalizing glimpses of the huge impact crater after a lengthy day-by-day grind across the Martian landscape that ended up being a 20-month journey to reach the destination.

The initial images, stitched into a black-and-white panorama, show rugged walls with layers of exposed rock. The floor is shown to be blanketed with dunes, as researchers already knew. The far wall is about a half-mile (1 kilometer) away.

(more...)

[USB500]

Originally Posted by NoSanninWa

The only way we'll have a new space race, like during the 50s and 60s, is if someone creates weapons that can kill from orbit.

Or governments otherwise become convinced that space is a tactical asset.

This post reminds me of Strangereal (Ace Combat), where Arkbird is a multi-billion-dollar spaceship designed as a super weapon, but in the end gets destroyed by the demons of Razgriz.

I don't think the world really needs a space-born weapons of mass destruction unless if its purpose is to defend Earth from asteroids. But even if we do, will it worth it?