Comets are overrated

[jimcolyer]

Comets were peripheral objects until 25 years ago. Since then, we hear that they wiped out the dinosaurs and will wipe out mankind. We are told they may have brought the seeds of life to earth. I just read that all the water on earth came from comets. It is out of control. I believe earth's water formed from the atmosphere which came from volcanos. Let's give Pluto the respect it deserves and stop exaggerating the importance of comets.<br /><br />Astronomy http://jimcolyer.com/papers/entry?id=2

 

[MeteorWayne]

Now lets not get crazy here.<br /><br />Point 1: comets have never been peripheral objects.<br />In the past they were highly weighted omens. History was altered by their appearence. I hardly consider that peripheral. They shaped history!!<br /><br />Point 2: AFAIK, no definitive classification has been made of the Chixalub impactor, but so far an asteroid is more likely.<br /><br />Yes comets have some potential to wipe out life on earth. Beacuse the energy is squared for the impact velocity, and most asteroid impacts are near 25 km/s, while comets can reach 73 km/sec, a smaller comet can wreak the same damage as a much less massive asteroid.<br />That's all a crapshoot. And because an Oort cloud comet comes sceaming in,<br />we may only have months to react, rather than the decades fo a known asteroid.<br /><br />Earth's water may have had multiple souces, i.e. volcanism, comets, and even an unknown source. All the evidence is not in yet.<br /><br />What the heck does Pluto have to do with this????????<br />You must explain that! <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[3488]

Hi MeteorWayne,<br /><br />I agree, comets are not over rated.<br /><br />Hi jimcolyer,<br /><br />In fact as MeteorWayne said Earth's water likely came from Comets AND, the solar nebula AND<br />type C asteroids.<br /><br />I think that because Pluto is a KBO, that's where you are coming from.<br /><br />So are Eris, Quaoar, Ixion, Varuna, Orcus, etc. huge stores of frozen water.<br /><br />Many of Saturn's, Uranus's & Neptune's moons are predominately water ice.<br /><br />There too is a lot of H2O ice in the Jupiter moons Europa, Ganymede & Callisto, <br />some of it deep under the surface may even be liquid.<br /><br />Taking all of this evidence, terrestrial water, has had more than one source.<br /><br />Also comets in their natural habitat far from the Sun, are time capsules, with the original chemistry,<br />frozen solid at cryogenically cold temperatures.<br /><br />So comets hold the history of the earliest times of our solar system.<br /><br />So I disagree strongly.<br /><br />Comets are not over rated.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[weeman]

<font color="yellow"> What the heck does Pluto have to do with this???????? <br />You must explain that! </font><br /><br />This person might be very Pro-Pluto. People are angry that Pluto is not a planet anymore. So, when people become angry their thoughts and/or judgments may become foggy and tangled. This leads to very scattered thoughts, often not making any sense!<br /><br /><img src="/images/icons/laugh.gif" /> <img src="/images/icons/laugh.gif" /> <img src="/images/icons/laugh.gif" /> <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>

 

[vandivx]

it is not vise to make sweeping comments on any subject that one has only just read about<br /><br />it may seem like comets did this, comets did that and it was good and than it was bad <br /><br />in the past before life developped here, comets hitting Earth were all good while now with life flourishing they are all bad, naturaly we don't want them anymore (those that could hit us anyway, astonomers like to study them and they make for nice sights for the rest of us) but they keep coming albeit in lesser numbers since the space got fairly cleaned out over the eons, still too many comets are left for us to feel comfortable<br /><br />since Earth was never big enough to ignite nuclear processes it couldn't make most if any of the elements it now has, likely they all came from comets during the early days when Earth got built up by them and seeded with most of the elements<br /><br />now we don't need anymore buildup material and elements since the cost would be too high for the minuscule amount any one comet could bring<br /><br />by cosmic measures comets are extremely plentifull even now since one can easily see several of them during one's lifetime which is extremely short time on cosmic scale, fortunately most fly by at safe distances but sooner or later one will hit or maybe just disturb our atmosphere and almost certainly some extinctions will again happen<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[silylene old]

<font color="yellow">Comets are overrated</font><br /><br />Why do we have to treat comets like overpaid sports teams? <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[lukman]

<blockquote><font class="small">In reply to:</font><hr /><p> Yes comets have some potential to wipe out life on earth. Beacuse the energy is squared for the impact velocity, and most asteroid impacts are near 25 km/s, while comets can reach 73 km/sec, a smaller comet can wreak the same damage as a much less massive asteroid. <p><hr /></p></p></blockquote><br /><br />faster but less densed comet will burn faster when entering atmosphere than slower and denser asteroid, is that correct? then the outcome will be pretty much the same. Or maybe atmosphere factor wil not be significant? <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

It all comes down to the energy at this scale. What it's made of makes no difference, only mass and velocity relative to the earth.It doesn't really "burn". At these energy levels, it's just a pulse delivered to the atmosphere and surface.<br />Exactly where in that 100 km the energy dump happens, doesn't make much difference.<br />There may be some subtle differences, but to the creatures below, it will be a rather moot point.<br /><br />Energy= 1/2*mass*velocity squared. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[dragon04]

<font color="yellow">I believe earth's water formed from the atmosphere which came from volcanos.</font><br /><br />That's really not a hypothesis we can prove to a satisfactory certainty.<br /><br />But think about the composition of comets, and the chaotic nature of the early Solar System.<br /><br />The inner solar system must have been a shooting gallery. Without the stability that has come over epochal time, it's not real hard to believe that a bunch of water-laden comets smacked into the proto-Earth to provide such a HUGE amount of water.<br /><br />In fact, we're discovering that there's more water the farther out we go. SO where did all our water come from?<br /><br />Did we have SO much Hydrogen and Oxygen laying around early on, or did we benefit from picking it up from comets? <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[3488]

The real question is, did water form this close to the Proto Sun?<br /><br />If anyone can find out how powerful the protosun was, or what the temperature of <br />the protoplanetary disk was at the Earth's orbit, we will have a much clearer understanding<br />of whether or not the Earth had formed with its own water.<br /><br />Also AFAIK, the general concensus is that the Earth was a ball of molten rock & metal during the formative<br />period. Could water have<br />survived that stage before the crust formed?<br /><br />Not to mention when the iron sank to form the core, the silicate rich mantle in places likely<br />erupted onto the surface of early Earth.<br /><br />Too many unknows, but I think that comets played a key role in hydrating the Earth.<br /><br />Volcanoes certainly gave the Earth an atmosphere, no doubting that fact, but was it dry or humid?<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[docm]

Where do you see 99.9% of non-solar H and the ice in todays solar system? The outer reaches like the outer planets, Oort cloud etc. Save for what has come into the inner solar system due to gravitational perturbation by the outer planets & passing stars IMO it stayed where it formed.<br /><br />I see the early solar system being bombarded for a billion years by objects from the outer reaches, most heavy in water like comets or icy planetoids displaced by Jupiter's gravity into the inner solar system. <br /><br />Early ones impacting a searing hot earth most likely had their water disassociated into H and O, the result being oxides & other compounds with a lot of hydrogen escaping. <br /><br />It's the later ones impacting a much cooler Earth that would have contributed their moisture content intact, forming the oceans. <div class="Discussion_UserSignature"> </div>

 

[3488]

Thanks docm.<br /><br />Your post only confirms what I had already thought.<br /><br />The precrustal earth would have been searing hot, perhaps 1,500 C. A huge magma ocean.<br /><br />It is understood though, that near enough, as soon as the crust formed, liquid water was present.<br /><br />I can only assume this was from still impacting comets, but the Earth's surface was now cool<br />enough to prevent disaccociation into Hydrogen & Oxygen.<br /><br />Yes , I beleive you are correct. 99.9% of all frozen primordial ice is still where <br />it formed.<br /><br />Thank you very much. <br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[emperor_of_localgroup]

Here is my dumb question to all. Can ice be formed directly from chemicals without going through the middleman 'water'? If not, I dont think the comets or asteroids, moving at high speed, have enough gravity to keep water on their surfaces.<br /><br />Here are other humorless overrated things(IMHO):<br />black holes<br />big bang, may be, time will tell.<br /> <div class="Discussion_UserSignature"> <font size="2" color="#ff0000"><strong>Earth is Boring</strong></font> </div>

 

[Smersh]

<font color="yellow">I just read that all the water on earth came from comets. </font><br /><br />I've heard this theory too but I wouldn't have thought there would have been enough comet strikes on the Earth in its entire history for the amount of water we have. <br /><br />Therefore, as most of you guys are suggesting, there HAS to be other sources, such as volcanism etc surely? <br /><br />(And I'm a comet so I should know.)<br /><br />Dragon04<br /><font color="yellow">The inner solar system must have been a shooting gallery. Without the stability that has come over epochal time, it's not real hard to believe that a bunch of water-laden comets smacked into the proto-Earth to provide such a HUGE amount of water. </font><br /><br />Thanks, Dragon, just noticed you wrote that. I'm still not convinced though. <div class="Discussion_UserSignature"> <h1 style="margin:0pt;font-size:12px">----------------------------------------------------- </h1><p><font color="#800000"><em>Lady Nancy Astor: "Winston, if you were my husband, I'd poison your tea."<br />Churchill: "Nancy, if you were my wife, I'd drink it."</em></font></p><p><font color="#0000ff"><strong>Website / forums </strong></font></p> </div>

 

[docm]

You think Earth has too much water to be from thousands or millions of impactors? If so then consider this; the minor planet Ceres has ~200 million cu/km water, so even just a few bodies like that would have given Earth a huge head start. <div class="Discussion_UserSignature"> </div>

 

[dragon04]

<font color="yellow">Also AFAIK, the general concensus is that the Earth was a ball of molten rock & metal during the formative<br />period. Could water have survived that stage before the crust formed?</font><br /><br />I'm afraid I know very little about planetary genesis, but what would make me lean towards cometary (and protoplanetary) impacts imparting the copious amounts of water we have on our planet would be the lack of an explanation (to my knowledge) of the required oxygen generation to provide so much water <i>in situ</i> reacting with what ambient H2 there was in and around the proto-Earth.<br /><br />Not being a Chemist, I can't guess at what reactions would have liberated such amounts of Oxygen as a result of the formation process of Earth in and of itself.<br /><br /><br /><br /><br /><br /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[Smersh]

<font color="yellow">You think Earth has too much water to be from thousands or millions of impactors? If so then consider this; the minor planet Ceres has ~200 million cu/km water, so even just a few bodies like that would have given Earth a huge head start.</font><br /><br />Yes, I'm sure that number of Ceres size/mass objects would be enough, but has it ever been proven that there were "thousands or millions?" (Well, millions anyway.)<br /><br />That's what I'm not sure about.<br /><br /> <div class="Discussion_UserSignature"> <h1 style="margin:0pt;font-size:12px">----------------------------------------------------- </h1><p><font color="#800000"><em>Lady Nancy Astor: "Winston, if you were my husband, I'd poison your tea."<br />Churchill: "Nancy, if you were my wife, I'd drink it."</em></font></p><p><font color="#0000ff"><strong>Website / forums </strong></font></p> </div>

 

[yevaud]

We know there were for several reasons, notably close examinations of T. Tauri stars and their accretion disc of material as it evolves, and the clear example of the massive cratering on the Moon from the Terminal Bombardment Phase. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[MeteorWayne]

Maybe not Ceres size, Yevaud, at least not millions it that range.<br />Millions of "average asteroid size", yeah that makes sense.<br /><br />Hundreds perhaps in Ceres size range.<br /><br />Remember, Ceres is pretty darn big. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[yevaud]

Yeah. Wasn't implying a large series of Ceres sized impactors; more like hundreds of thousands of smaller, ice-bearing bodies. Quantity, not quality, so to speak. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[MeteorWayne]

I agree, just trying to clear that up.<br />Wayne <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[lampblack]

Plenty of quantity -- but no doubt a bit of quality along the way, too. After all, <i>something</i> was big enough and hit hard enough to rip the moon away from the earth and eject it into its present-day orbit. Who's to say that this object -- whatever it was -- wasn't laden with water? <div class="Discussion_UserSignature"> <font color="#0000ff"><strong>Just tell the truth and let the chips fall...</strong></font> </div>

 

[yevaud]

Might well have been. Of course, at those impact energies, it was disassociated via extreme temperatures, so the net gain was probably negligible. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[MeteorWayne]

Correct. The moon is VERY dry!!<br /><br />Whatever smaller objects impacted the earth later, we had enough gravity and a magnetosphere to keep some of it hanging around...which has proved very useful for the last 4 billion years or so <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[dragon04]

How does Hydrogen and Oxygen combine to make water?<br /><br />Do they have a natural affinity for one another? It seems to me that one of two cases had to apply. Either there was a lot of Oxygen in the primordial atmosphere, or it got delivered in the form of water ice by comets or a large impactor that was laden with water.<br /><br /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>