Reviewing some basic concepts...

[MaxCathedral]

This is to be a true and false exam.

 

The Moon... a mars like object crashed into us...and finally became the moon.

 

Not only does the moon orbit us...be WE orbit it?

 

The Moon, Jupiter, and Saturn may have all been instrumental in allowing complex life to exist, by warding off astroieds, meteorites?

 

 

Passing Comets may have created our oceans?

 

The Rare Earth theory is viable...cause we haven't found any complex life anywhere...yet? Are we the first?

 

 

There is the Oort Cloud and Kuiper Belt..are they the same thing..and where are they located?

 

While the might Zep has lots of passion, they aint got nothing on the Lad from Liverpool...the Beatles, because....oh, wrong board?

 

 

The student patiently awaits corrections.

[[Tycho?]]

Huh.

 

The mars like thing hitting us and creating the moon remains theorectical. Dont know how well accepted it is, but I havn't heard any other explanations.

 

The moon and the earth orbit around their mutual center of gravity. It would be closer to or maybe inside earth, because earth is a lot more massive.

 

Again, theoretical. Jupiter in particular has a large gravitational field and sucks in a lot of comets. It follows that had jupiter not existed some of these comets may have hit earth. Or not. So yes it probably helped, wasn't necessarly a requirement.

 

Comets thing I dont know, they do contain water, but that would have to be a ton of comets to form out oceans.

 

We have found very few planets the size of earth, I dont know if any of them are in a position around their sun similar to ours. We need to discover a lot more planets before this theory can be discussed in more detail.

 

Kuiper Belt is the collection of stuff past the orbit or Uranus I believe, or around there. Oort cloud I'm not sure.

 

 

Uh, this is all just fact stuff, no physics. If you want real answers, look them up.

 

http://www.google.com

[Thales]

The Moon... a mars like object crashed into us...and finally became the moon.

 

True. The 'Mars' like object was a proto-planet similar in mass to mars but different in material. It is thought to have formed at one of the Lagrange points (most likely L4) in the proto-earth - Sun system.

 

Not only does the moon orbit us...be WE orbit it?

False. The Earth-Moon system rotates around its shared centre of mass or barycenter. The Earth is much larger than the Moon so the barycenter is in the Earths interior. There is a 'wobble' caused by the Moon (when viewing the earths orbit around the Sun. However it is the Moon that orbits Earth.

 

The Moon' date=' Jupiter, and Saturn may have all been instrumental in allowing complex life to exist, by warding off astroieds, meteorites?

[/quote']

 

True. The amount of material with the potential to destroy life on Earth flying around the Solar System is quite large. The gravitational influence of ALL other planets reduce the likelyhood of a large asteroid hitting the Earth. There is a theory however that asteroid impacts have been instrumental in forwarding evolution (to an extent).

 

Passing Comets may have created our oceans?

Partially True. Some water would have been deposited via comets. Much of it however is also thought to have come from the rocks in the earth.

 

The Rare Earth theory is viable...cause we haven't found any complex life anywhere...yet? Are we the first?

False. If there is the potential for life to exist elsewhere then it would be highly highly highly improbable that we are the first. The Earth however is not only rare but unique' date=' but seeing as the organic material needed for life exists in comets one would assume that other Earth-like planets may exists and even if they don't it would be naive to assume life cannot exist in different forms/environments to ours.

 

There is the Oort Cloud and Kuiper Belt..are they the same thing..and where are they located?

False. The Kuipier Belt is located just beyond Pluto (at about 10^6 km). The Oort cloud is much futher away, a large fraction of the distance to the nearest star (around one light year). They are not the same but are thought to consist of similar objects, ie cold, small, icey/rocky, objects.

 

While the might Zep has lots of passion' date=' they aint got nothing on the Lad from Liverpool...the Beatles, because....oh, wrong board?

[/quote']

Not my area of expertise...

 

Gimme more, please

[MaxCathedral]

Thales, Thank you...concise and wonderful answers...

[Sayonara]

'']We have found very few planets the size of earth, I dont know if any of them are in a position around their sun similar to ours. We need to discover a lot more planets before this theory can be discussed in more detail.

I think it needs to be made more clear that this is because of the limitations of our detection technology, and not necessarily because no such planets are there.

[[Tycho?]]

I think it needs to be made more clear that this is because of the limitations of our detection technology, and not necessarily because no such planets are there.

 

Yeah I guess I should have specified that. The galaxy could be ripe with earth sized planets, but at the moment we can generally only see very large planets that create a detectable wobble in the star they orbit.

[[Tycho?]]

False. The Kuipier Belt is located just beyond Pluto (at about 10^6 km)[/b']. The Oort cloud is much futher away, a large fraction of the distance to the nearest star (around one light year). They are not the same but are thought to consist of similar objects, ie cold, small, icey/rocky, objects.

 

 

Umm... 10^6km? Something wrong there I think.

 

Also, the kiuper belt stats beyond Neptunes orbit, Pluto is sometimes considered a kuiper belt object instead of a proper planet.

 

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

[swansont]

The Earth-Moon system rotates around its shared centre of mass or barycenter[/i'].

 

Revolves.

[Wolverine]

']Umm... 10^6km? Something wrong there I think.

 

Also' date=' the kiuper belt stats beyond Neptunes orbit, Pluto is sometimes considered a kuiper belt object instead of a proper planet.

 

http://en.wikipedia.org/wiki/Kuiper_belt[/quote']

 

yea isn't that why there's still some debate as to the validity of Pluto as a planet? With it's eccentric orbital plane as well. Wouldn't several other objects within the Kuiper Belt theoretically qualify as planets if Pluto is to be considered as a true planet?

 

The Wolverine

[[Tycho?]]

yea isn't that why there's still some debate as to the validity of Pluto as a planet? With it's eccentric orbital plane as well. Wouldn't several other objects within the Kuiper Belt theoretically qualify as planets if Pluto is to be considered as a true planet?

 

The Wolverine

 

Thats about the gist of it yeah. Pluto and its moon are way bigger than any other kuiper belt objects, but then they are really far our, wierd orbit, very small etc. There are some other moderately sized kuiper belt objects, and the question is where does one draw the line between planet and.... not planet. I guess.

[john5746]

The new planets found recently approx. 14 times the size of earth. Do planets need to be close to the size of earth to have life? Do we assume all very large planets must have choking gas?

[Thales]

The figure I posted was of the radial distance to the kupier belt not to pluto itself. i should have specified that one.

 

John, we shouldn't assume anything about life beyond or Solar System because we have no evidence for it taking one form or another. In terms of the composition/mass of most planets, you will hear about being detected over the next few years, almost all of them will be Jovian (gas giants) in nature. This is because the current method of detecting extra-solar planets is studying the 'wobble' these planets cause by pulling on the parent star.

 

The definition of a planet usually dictates that it is massive enough for its gravity to pull it into a spherical form. It is a shady definition at best though, many smaller objects that revolve around the sun can indeed be considered to be planetoids(as in planet-like).

 

Earlier this year astronomers discovered a planetoid called and named it Sebna. It was located much futher away and it thought to originated from the Oort Cloud.

 

Another interesting fact I came to bear upon recently was that the Sun is in transit between spiral arms as its orbital speed around the center of the Galaxy is in fact faster than the rotation rate of the galaxy as a whole. What i found most interesting about this fact is that the times in which we penetrate the arms, coincide with the times of the major extinctions on earth. It is theorised that on the journey through the spiral arms some of the Oort cloud's objects are dislodged from their gravitationally stable points by passing stars, sending them towards the sun. So perhaps a 'wandering' star killed the Dinosaurs(in a roundabout way).

[john5746]

Yes, I heard about this theory on a NOVA special I think. Mass extinction of species does seem to have a cycle and it is a large one.

 

The reason I ask about planet size is the articles suggest scientists want to find a planet near Earth - size. Why can't a planet 14 times the size of the earth have life? In fact, could it be Earth Like? Well, 14G's would be different.

[Thales]

There are many theories pertaining to the limitations on environments which can/do support life. The main problem with all of them is that we don't have any example of life other than our own immediate experience and based on that, we make assumptions about the ease in which complex life can evolve in varying environments.

 

I think the main arguement for a small rocky body vs a jovioan giant in terms of their ability/limitations for supprting complex sentient beings is one of scale. To have a large biological entity, say one which could hypothetically exist on Jupiter, would require for one a much more stable environment. Gas giants are notorious for their turbulant atmosphere's, which would hinder the stablity and indeed limit the opportunities for molecules to 'dwell' long enough adjacent to each other in order to 'try' the various combinations and indeed 'figure out' which ones are stable.

 

Another arguement against the existance of life on large gaseous worlds is the amount of energy needed to evolve life in such atmosphere vs the amount of energy recieved from the host star. Because it is thought that gaseous giants tend to grow in the outer regions of solar systems(with a few exceptions) they recieve much less sunlight per square cm and therefore have less energy available to them to actuate the required reactions.

 

Finally there is the question of scale. One can assume that sentient beings on these larger worlds would be larger themselves. To evolve to this much larger size and maintain the complexities required for conscious thought would require enormous amounts of energy, energy that without some as yet unknown orgainc reaction, is simply not available in the cold desolate atmosphere of the Jovian world.

 

Its based primarily on conjecture because at the start I pointed out we have no other examples of life, to study its robustness, in what to us seems like extreme conditions. Small rocky bodies the size of earth have alot of things balanced perfectly to create the stable, but not too stable, enviroments to harbour the complexities of biological evolution as we know it.