8 ms·

Rosetta finds comet's water vapour to be significantly different from Earth's

234 points by twowo 12y ago

smeyer 12y ago
(For future readers, see dang's comment on how he changed the title from "Rosetta first results: ocean water not from comets")[1]) I don't know why you changed the title to something claiming a stronger result than their title: "ROSETTA FUELS DEBATE ON ORIGIN OF EARTH’S OCEANS". I'm not a planetary guy, but I think while the evidence is moving that way, the claim in your title is definitely premature. Here's a distillation of their results (from their post) that seems far more in line with their claims than your title: >“Our finding also rules out the idea that Jupiter-family comets contain solely Earth ocean-like water, and adds weight to models that place more emphasis on asteroids as the main delivery mechanism for Earth’s oceans.” [1] https://news.ycombinator.com/item?id=8731304 https://news.ycombinator.com/item?id=8731304
- contingencies 12y ago
  Here's a distillation of their results I see what you did there. :)
- aruggirello 12y ago
  I'm eager to see New Horizons arriving at Pluto, to see whatever water it finds.
dang 12y ago
The submitted title was "Rosetta first results: ocean water not from comets". Since the article's own title is not very informative, we changed it to the first sentence, which is. We also changed the url from http://blogs.esa.int/rosetta/2014/12/10/rosetta-fuels-debate-on-origin-of-earths-oceans/ http://blogs.esa.int/rosetta/2014/12/10/rosetta-fuels-debate..., which points to this.
- Florin_Andrei 12y ago
  Right. We don't have a very large sample size currently, so it's a bit premature for definitive statements such as "earthly water not from comets". All we know is that this comet shows a different fraction of deuterium, compared to Earth, and some other comets we've checked are all different. So the jury is still out. We need more data, lots more.
- bmm6o 12y ago
  It would be great if edits like this could be displayed at the top of the thread rather than as the bottom-most comment.
  - dang 12y ago
    I understand why you'd say that, but the cure would be much worse than the disease—the top subthreads would all be about the edits and editing practices.
    - bmm6o 12y ago
      It wouldn't have to be a replyable subthread, just a note somewhere are the top of the page.
tokenadult 12y ago
The two comments submitted previously as I type this explain why the article title on HN is as it is. I was puzzled by what the title MEANT, so I looked into the article, and what the article says farther down is "Previous measurements of the deuterium/hydrogen (D/H) ratio in other comets have shown a wide range of values. Of the 11 comets for which measurements have been made, it is only the Jupiter-family Comet 103P/Hartley 2 that was found to match the composition of Earth’s water, in observations made by ESA’s Herschel mission in 2011." When I first read the headline, I wasn't sure if the claim was that the water vapor had mixtures of other chemical molecules in it, or what. Okay, a different isotope ratio in water from a comet as contrasted with water generally found on earth would indeed be a clue to how water might have traveled from one orbiting body to another early in the development of the solar system. This kind of isotype checking (for isotopes of other elements) is one of the things done to confirm that rocks found on earth are presumptively from other parts of the solar system.
- emcrazyone 12y ago
  I'm surprised that scientists believe water was delivered. Why wouldn't water be one of the by products of the big-bang and during Earth's creation?
  - deleted 12y ago
    [deleted]
  - Bjoern 12y ago
    http://en.wikipedia.org/wiki/Panspermia http://en.wikipedia.org/wiki/Panspermia
    - AnimalMuppet 12y ago
      Panspermia has nothing to with where the water came from.
      - Balgair 12y ago
        http://www.nature.com/news/dna-has-a-521-year-half-life-1.11555 http://www.nature.com/news/dna-has-a-521-year-half-life-1.11... DNA has a 'half-life' of ~500 years. Panspermania may still be a viable theory, but it is very restricted in terms of stellar distance/time in transit.
grecy 12y ago
I didn't realize the standing theory is that Earth's water was delivered by lots of meteor strikes. Has there ever been an estimate made of the number of strikes needed to deliver the volume of water currently on Earth? I have to think it's enormous.
- Retric 12y ago
  Current theory is that much/most of the early water ended up excaping back into space. Further, there is an extremely large range of meteor sizes making such estimates almost meaningless. https://what-if.xkcd.com/83/ https://what-if.xkcd.com/83/
- pcrh 12y ago
  The amount of (surface) water on earth may not be as much as you would intuitively think, given that it covers 70% of the surface area. have a look at the image in this link: http://water.usgs.gov/edu/earthhowmuch.html http://water.usgs.gov/edu/earthhowmuch.html
  - dangayle 12y ago
    What about the water in the earth's core? >>A reservoir of water three times the volume of all the oceans has been discovered deep beneath the Earth's surface. The finding could help explain where Earth's seas came from. http://www.newscientist.com/article/dn25723-massive-ocean-discovered-towards-earths-core.html#.VIjQPWbvgSo http://www.newscientist.com/article/dn25723-massive-ocean-di...
    - Balgair 12y ago
      My wife looks at carbon in the deep earth, but water is a very related chemical in these cases. She says that the amount of water in the core is indeterminable at this time, but it is likely a lot more than a mere 3x the ocean volume (also, volume depends on pressure and temp, which are extreme in the core) Note: at extreme temps and pressures in the core, water as we know it is not a good guidepost. It may be crystallized or associating strongly with other exotic crystals and 'plastic'-y compounds at the Moho layer and other transition zones deep down. Also, just counting O and H elements is likely to not get you far there either. The story of how we got our oceans is FAR from complete. I'd wager we are in the 2nd page of the prologue though, which, for 60 years of real work, is pretty good compared to most fields.
acqq 12y ago
It doesn't appear to be a result for which the landing was necessary? Also it seems it was something already achieved before ("measuring D/H"). The text mentions that the D/H ratio was already measured in 11 comets, I believe by just flying through their "tail" (1)? 1) http://adsabs.harvard.edu/full/1987A%26A...187..435E http://adsabs.harvard.edu/full/1987A%26A...187..435E How was it done this time?
AYBABTME 12y ago
They mention that water already on earth would have boiled off in its youth. I don't understand this, wouldn't the vapor stay around the planet, then return to liquid when the planet cooled? Or else, what would have attracted the water away from the earth's atmosphere? And if so, why wouldn't it have attracted away the azote and oxygen and all of the atmosphere at the same time? Or was there not yet an atmosphere?
- mixmastamyk 12y ago
  Yeah, that doesn't make sense. Venus is a good deal smaller and was able to hold a dense atmosphere, so Earth should be even more able to hold water vapor. Probably lost most bare hydrogen though.
- has2k1 12y ago
  Simulations do not like this scenario. The gravity is not enough to counter the expansion due to the heat, so the water (vapour) leaks off far and wide with little chance of coalescing in the inner solar system.
wavesum 12y ago
This one puzzles me: "One of the leading hypotheses on Earth’s formation is that it was so hot when it formed 4.6 billion years ago that any original water content should have boiled off. " So where would it actually have boil to? I thought gravity affected water also in gas state. Just like the atmosphere doesn't "boil off", why would the water?
- dataduck 12y ago
  Actually, some fractions of the atmosphere do "boil off": https://en.wikipedia.org/wiki/Atmospheric_escape https://en.wikipedia.org/wiki/Atmospheric_escape Essentially, because the distribution of thermal energy has a fairly long tail, it is possible for some lighter particles to reach escape velocity. The hotter the atmosphere, the more (and heavier) particles escape.
wavesum 12y ago
This one puzzles me: "One of the leading hypotheses on Earth’s formation is that it was so hot when it formed 4.6 billion years ago that any original water content should have boiled off. " So where would it actually have boil to? I thought gravity affected water also in gas state. Just like the atmosphere doesn't "boil off", why would the water?
lnanek2 12y ago
I think it is pretty obvious D/H would be higher for a comet that has been out a long time and that doesn't really tell us much about if Earth's water came from comets a long time ago since those crashed early. H is a lot lighter than D, so it is a lot easier for a body to lose it, especially if the body has no magnetic field like a comet or Venus (D/H is also very high on Venus). Thinking the ratios would be the same seems like a mistake. Their graph should really compare the values normalized for loss rates and time since solar system formation.

234 points by twowo 12y ago

(For future readers, see dang's comment on how he changed the title from "Rosetta first results: ocean water not from comets")[1]) I don't know why you changed the title to something claiming a stronger result than their title: "ROSETTA FUELS DEBATE ON ORIGIN OF EARTH’S OCEANS". I'm not a planetary guy, but I think while the evidence is moving that way, the claim in your title is definitely premature. Here's a distillation of their results (from their post) that seems far more in line with their claims than your title: >“Our finding also rules out the idea that Jupiter-family comets contain solely Earth ocean-like water, and adds weight to models that place more emphasis on asteroids as the main delivery mechanism for Earth’s oceans.” [1] https://news.ycombinator.com/item?id=8731304 https://news.ycombinator.com/item?id=8731304

contingencies 12y ago
Here's a distillation of their results I see what you did there. :)
aruggirello 12y ago
I'm eager to see New Horizons arriving at Pluto, to see whatever water it finds.

dang 12y ago

The submitted title was "Rosetta first results: ocean water not from comets". Since the article's own title is not very informative, we changed it to the first sentence, which is. We also changed the url from http://blogs.esa.int/rosetta/2014/12/10/rosetta-fuels-debate-on-origin-of-earths-oceans/ http://blogs.esa.int/rosetta/2014/12/10/rosetta-fuels-debate..., which points to this.

Florin_Andrei 12y ago
Right. We don't have a very large sample size currently, so it's a bit premature for definitive statements such as "earthly water not from comets". All we know is that this comet shows a different fraction of deuterium, compared to Earth, and some other comets we've checked are all different. So the jury is still out. We need more data, lots more.
bmm6o 12y ago
It would be great if edits like this could be displayed at the top of the thread rather than as the bottom-most comment.
- dang 12y ago
  I understand why you'd say that, but the cure would be much worse than the disease—the top subthreads would all be about the edits and editing practices.
  - bmm6o 12y ago
    It wouldn't have to be a replyable subthread, just a note somewhere are the top of the page.

tokenadult 12y ago

The two comments submitted previously as I type this explain why the article title on HN is as it is. I was puzzled by what the title MEANT, so I looked into the article, and what the article says farther down is "Previous measurements of the deuterium/hydrogen (D/H) ratio in other comets have shown a wide range of values. Of the 11 comets for which measurements have been made, it is only the Jupiter-family Comet 103P/Hartley 2 that was found to match the composition of Earth’s water, in observations made by ESA’s Herschel mission in 2011." When I first read the headline, I wasn't sure if the claim was that the water vapor had mixtures of other chemical molecules in it, or what. Okay, a different isotope ratio in water from a comet as contrasted with water generally found on earth would indeed be a clue to how water might have traveled from one orbiting body to another early in the development of the solar system. This kind of isotype checking (for isotopes of other elements) is one of the things done to confirm that rocks found on earth are presumptively from other parts of the solar system.

emcrazyone 12y ago
I'm surprised that scientists believe water was delivered. Why wouldn't water be one of the by products of the big-bang and during Earth's creation?
- deleted 12y ago
  [deleted]
- Bjoern 12y ago
  http://en.wikipedia.org/wiki/Panspermia http://en.wikipedia.org/wiki/Panspermia
  - AnimalMuppet 12y ago
    Panspermia has nothing to with where the water came from.
    - Balgair 12y ago
      http://www.nature.com/news/dna-has-a-521-year-half-life-1.11555 http://www.nature.com/news/dna-has-a-521-year-half-life-1.11... DNA has a 'half-life' of ~500 years. Panspermania may still be a viable theory, but it is very restricted in terms of stellar distance/time in transit.

grecy 12y ago

I didn't realize the standing theory is that Earth's water was delivered by lots of meteor strikes. Has there ever been an estimate made of the number of strikes needed to deliver the volume of water currently on Earth? I have to think it's enormous.

Retric 12y ago
Current theory is that much/most of the early water ended up excaping back into space. Further, there is an extremely large range of meteor sizes making such estimates almost meaningless. https://what-if.xkcd.com/83/ https://what-if.xkcd.com/83/
pcrh 12y ago
The amount of (surface) water on earth may not be as much as you would intuitively think, given that it covers 70% of the surface area. have a look at the image in this link: http://water.usgs.gov/edu/earthhowmuch.html http://water.usgs.gov/edu/earthhowmuch.html
- dangayle 12y ago
  What about the water in the earth's core? >>A reservoir of water three times the volume of all the oceans has been discovered deep beneath the Earth's surface. The finding could help explain where Earth's seas came from. http://www.newscientist.com/article/dn25723-massive-ocean-discovered-towards-earths-core.html#.VIjQPWbvgSo http://www.newscientist.com/article/dn25723-massive-ocean-di...
  - Balgair 12y ago
    My wife looks at carbon in the deep earth, but water is a very related chemical in these cases. She says that the amount of water in the core is indeterminable at this time, but it is likely a lot more than a mere 3x the ocean volume (also, volume depends on pressure and temp, which are extreme in the core) Note: at extreme temps and pressures in the core, water as we know it is not a good guidepost. It may be crystallized or associating strongly with other exotic crystals and 'plastic'-y compounds at the Moho layer and other transition zones deep down. Also, just counting O and H elements is likely to not get you far there either. The story of how we got our oceans is FAR from complete. I'd wager we are in the 2nd page of the prologue though, which, for 60 years of real work, is pretty good compared to most fields.

acqq 12y ago

It doesn't appear to be a result for which the landing was necessary? Also it seems it was something already achieved before ("measuring D/H"). The text mentions that the D/H ratio was already measured in 11 comets, I believe by just flying through their "tail" (1)? 1) http://adsabs.harvard.edu/full/1987A%26A...187..435E http://adsabs.harvard.edu/full/1987A%26A...187..435E How was it done this time?

AYBABTME 12y ago

They mention that water already on earth would have boiled off in its youth. I don't understand this, wouldn't the vapor stay around the planet, then return to liquid when the planet cooled? Or else, what would have attracted the water away from the earth's atmosphere? And if so, why wouldn't it have attracted away the azote and oxygen and all of the atmosphere at the same time? Or was there not yet an atmosphere?

mixmastamyk 12y ago
Yeah, that doesn't make sense. Venus is a good deal smaller and was able to hold a dense atmosphere, so Earth should be even more able to hold water vapor. Probably lost most bare hydrogen though.
has2k1 12y ago
Simulations do not like this scenario. The gravity is not enough to counter the expansion due to the heat, so the water (vapour) leaks off far and wide with little chance of coalescing in the inner solar system.

wavesum 12y ago

This one puzzles me: "One of the leading hypotheses on Earth’s formation is that it was so hot when it formed 4.6 billion years ago that any original water content should have boiled off. " So where would it actually have boil to? I thought gravity affected water also in gas state. Just like the atmosphere doesn't "boil off", why would the water?

dataduck 12y ago
Actually, some fractions of the atmosphere do "boil off": https://en.wikipedia.org/wiki/Atmospheric_escape https://en.wikipedia.org/wiki/Atmospheric_escape Essentially, because the distribution of thermal energy has a fairly long tail, it is possible for some lighter particles to reach escape velocity. The hotter the atmosphere, the more (and heavier) particles escape.

wavesum 12y ago

lnanek2 12y ago

I think it is pretty obvious D/H would be higher for a comet that has been out a long time and that doesn't really tell us much about if Earth's water came from comets a long time ago since those crashed early. H is a lot lighter than D, so it is a lot easier for a body to lose it, especially if the body has no magnetic field like a comet or Venus (D/H is also very high on Venus). Thinking the ratios would be the same seems like a mistake. Their graph should really compare the values normalized for loss rates and time since solar system formation.