 Discovery Raises Hope Of Life Out Here |
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 Mar 21 2008, 07:10 AM
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  Group: Supporters Posts: 1,704 Joined: 17-July 07 From: Perpignan, Toulouse Member No.: 6,074 |
Water of life is found on distant gas planet too hot for survival
Nature 452, 329-331 (20 March 2008) - Excerpts: To date, molecular signatures have not been resolved in the emission spectra of hot-Jupiter extrasolar planets (exoplanets). Transmission spectroscopy during the primary eclipse (when the planet occults a portion of the stellar disk, and a fraction of light from the star is seen after traversal through the atmosphere around the planet's limb) has the advantage of being insensitive to temperature structure in the exoplanet's atmosphere. Owing to the presence of strong molecular absorption bands, near-infrared spectroscopy from 1 to 2.5 μm is well suited for detection of the signatures of H2O, CO and CH4. For a hot-Jupiter atmosphere in purely thermochemical equilibrium, the dominant carbon-bearing molecule is expected to be CO at higher temperatures (temperature T > 1,200 K) and CH4 at lower temperatures (T < 800 K). On the daysides of the short-period, tidally locked hot-Jupiters, the local carbon chemistry should be dominated by CO; disequilibrium effects may result in CO as the dominant carbon-carrying molecule, even on the terminators and nightsides of such planets. Our detection of the onset of the CH4 bandhead at 2.2 μm is the first clear spectral signature of a carbon-based molecule in an exoplanet atmosphere. … We show the corrected spectrum as relative absorption depth in Fig. 2. The signature of the H2O absorption band centred around 1.9 μm is immediately obvious. The steep increase in absorption at the short-wavelength edge is also most probably due to an adjacent water band centred at a wavelength less than 1.5 μm. Thus, the new spectrum allows an unambiguous identification of water vapour in the atmosphere of HD 189733b, confirming its earlier inference from broadband photometry. As a steep change in absorption occurs at 2.2 μm, the observations decisively show that methane is present in addition to water. To explore the abundance of H2O and CH4 and possible contributions of CO and NH3, simulated transmission spectra were generated using a recent version of a planetary spectral model. The model covers a range of pressure from 10 to 10^-10 bar and includes transitions for H2–H2 (the most common molecular species). The temperature and density at each atmospheric level are determined by the pressure–temperature profile, and the absorption contribution from each molecule is computed on the basis of its mixing ratio. The H2O absorption coefficients incorporate a new, high-accuracy line list, and the CO absorption coefficients were estimated with the HITEMP data base. The CH4 absorption coefficients were evaluated using a combination of line lists. For all the molecules, the opacities are calculated for the selected spectral band at the different temperatures of the atmospheric layers (from 500 K to 2,000 K) and in some cases interpolated for intermediate values of the available temperatures. We used the 'evening terminator' pressure–temperature profile; significantly different temperature profiles produce results that do not match the observed water vapour absorption features. The theoretical spectra were binned to the same spectral resolution as the measurements, and the results of different compositions were compared with the observations using the reduced χ^2 value. Combinations of H2O and CO, as well as H2O and NH3, failed to match the observed spectrum. The model best fitting the observations has a mixing ratio of 5 10^-4 for H2O, and 5 10^-5 for CH4 (see Fig. 2); the addition of NH3 with a mixing ratio of 1 10^-5 improves the fit slightly. The agreement between our H2O mixing ratio value and previous results is significant because a wide range of wavelengths, covering three major H2O absorption bands, can be modelled self-consistently; this implies that the estimated H2O mixing ratio is robust. The pressure at which the atmosphere becomes optically thick ranges from a few millibars, when the absorption is strong, to 0.2 bar, when the absorption is weaker (for example, 1.7 μm). We have modelled the effect of aerosols and determined that our spectrum is haze-free, as their contribution would depress the spectral signature of both H2O and CH4 relative to the measured absorption depth. If aerosols are present, as is suggested by recent measurements, they must be in the form of small particles and their effects confined to wavelengths shorter than 1.5 μm.  FIGURE 2. A comparison of observations with simulated water and methane absorption. The measured spectrum (black triangles), and two theoretical spectra of the predominantly H2 atmosphere, showing the effects of small amounts of water (blue) and methane in combination with water (orange). The measured spectrum contains significant differences at 1.7–1.8 μm and at 2.15–2.4 μm from what is expected due to water vapour alone. We interpret these departures as additional absorption features due to the presence of one or more other species in addition to water. When considering only water and methane, the theoretical spectrum best fitting the data was determined by binning the model (shown as white crosses) to the spectral resolution of the observations. Different model predictions based on changing abundances and molecules were compared to the observations using the reduced χ^2; the best fitting model has a water abundance of 5 10^-4 and a methane abundance of 5 10^-5. The model spectrum can be improved slightly with the addition of small ( 1 10^-5) amounts of either ammonia or carbon monoxide (shown in green and purple crosses, respectively). Error bars show 1 ; the error includes the uncertainty in the correction of systematic effects. Note that determining the zero point for the spectrum depends on the diameter assumed for the planet and assumptions in the starspot correction. Thus, the shape of the spectrum is robust; there is an uncertainty of 2 10^-4 in the absolute level. ...Although we can unambiguously determine that CH4 is present, the CH4 abundance estimate is dependent on uncertainties in the high-temperature transitions. Additionally, the presence of CH4 masks the effect of CO in the absorption spectrum. Although the best fit is obtained using only H2O and CH4, CO can be included up to the abundance of H2O with a modest increase in χ^2. Thus, we cannot strongly constrain abundance of CO or the elemental C/O ratio. The relatively high concentration of CH4 could be due in part to photochemistry. Photolysis of CO and CH4 is probably not significant in the upper atmosphere (pressure P < 10^-4 bar) of HD 189733b because of the strength of C–O and C–H bonds and the deficit of ultraviolet flux from its cool parent star (spectral type K2V). However, the photolysis of the weaker bonds of sulphur-, nitrogen- and oxygen-bearing compounds and the accompanying availability of fast-reacting free radicals could have a significant effect on the relative abundance of CH4 compared to CO. -------------------- Ille potens sui, laetusque deget cui licet in diem dixisse: 'Vixi': cras uel atra nube polum Pater occupato uel sole puro. - Q. Horatius Flaccus
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Mar 21 2008, 07:10 AM
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Mar 21 2008, 07:36 AM
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  Group: Members Posts: 1,322 Joined: 24-April 06 From: Here Member No.: 4,083 |
Umm I think we need a translator
 i think what that boils down to is that we have found a planet with water on it but it is not in the Goldilocks zone so its too hot? Is that correct?
This post has been edited by Dundee: Mar 21 2008, 07:37 AM |
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Mar 21 2008, 08:59 AM
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#3
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 Group: Members Posts: 1,332 Joined: 1-November 05 From: U.K. Member No.: 3,115 |
i like that term the goldilocks zone
-------------------- '' Open the pod bay doors HAL ''
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Mar 21 2008, 10:22 AM
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#4
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 Group: Members Posts: 4,149 Joined: 18-June 06 From: Cambridgeshire England Member No.: 4,543 |
QUOTE (Dundee @ Mar 21 2008, 01:26 PM)  Umm I think we need a translator i think what that boils down to is that we have found a planet with water on it but it is not in the Goldilocks zone so its too hot? Is that correct? Maybe to hot for us Dundee, but life in the ocean on this planet flourishes next to and on hydrothermal vents at stupid temperatures, so if there is liquid water then life is possible... QUOTE Hydrothermal vents
How do hydrothermal vents form? In some areas along the Mid-Ocean Ridge, the gigantic plates that form the Earth’s crust are moving apart, creating cracks and crevices in the ocean floor. Seawater seeps into these openings and is heated by the molten rock, or magma, that lies beneath the Earth’s crust. As the water is heated, it rises and seeks a path back out into the ocean through an opening in the seafloor. As the vent water bursts out into the ocean, its temperature may be as high as 400°C (750°F). Yet this water does not boil because it is under so much pressure from the tremendous weight of the ocean above. When the pressure on a liquid is increased, its boiling point goes up. Chimneys top some hydrothermal vents. These smokestacks are formed from dissolved metals that precipitate out (form into particles) when the super-hot vent water meets the surrounding deep ocean water, which is only a few degrees above freezing. So-called “black smokers” are the hottest of the vents. They spew mostly iron and sulfide, which combine to form iron monosulfide. This compound gives the smoker its black color. “White smokers” release water that is cooler than their cousins’ and often contains compounds of barium, calcium, and silicon, which are white. Geologists are intrigued by how rapidly vent chimneys grow — up to 9 meters (30 ft) in 18 months. A scientist at the University of Washington has been monitoring the growth of “Godzilla,” a vent chimney in the Pacific Ocean off the coast of Oregon. It reached the height of a 15-story building before it toppled. It is now actively rebuilding. There are many other reasons why scientists want to learn more about hydrothermal vents. These underwater geysers are believed to play an important role in the ocean’s temperature, chemistry, and circulation patterns...Source -------------------- Nathanial "a_skeptic" Meade 1979-2007 RIP |
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Mar 21 2008, 12:52 PM
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#5
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Group: Members Posts: 3,135 Joined: 26-August 06 Member No.: 4,857 |
QUOTE (Fen Star @ Mar 21 2008, 04:12 PM) Maybe to hot for us Dundee, but life in the ocean on this planet flourishes next to and on hydrothermal vents at stupid temperatures, so if there is liquid water then life is possible... Fen....I agree.....and other lifeforms may also have higher tolerances of heat, cold and preasure than earthbound life.....so its really hard to say life can't exist.....unless we go there to find out. Sounds like a road trip to me..... 
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Mar 21 2008, 02:14 PM
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#6
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  Group: Super Moderators Posts: 4,124 Joined: 10-July 06 From: Wild Rose, Wisconsin Member No.: 4,643 |
Agreed.
And like is always brought up, we must consider the possibilities of life-as-we-don't-know-it as well. |
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Mar 27 2008, 01:42 PM
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#7
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 Group: Members Posts: 16,772 Joined: 10-April 04 From: USA Member No.: 524 |
QUOTE (Castle-Bravo354 @ Mar 21 2008, 06:42 PM) Fen....I agree.....and other lifeforms may also have higher tolerances of heat, cold and preasure than earthbound life.....so its really hard to say life can't exist.....unless we go there to find out. Sounds like a road trip to me..... I'd say its more than possible...I'd say its likely. This post has been edited by iwant2believe2: Mar 27 2008, 01:42 PM |
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Mar 27 2008, 07:59 PM
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#8
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Group: Members Posts: 3,135 Joined: 26-August 06 Member No.: 4,857 |
QUOTE (iwant2believe2 @ Mar 27 2008, 07:32 PM) I'd say its more than possible...I'd say its likely. IW2....I bet we'll find some amazing life forms in the future.....unless they come here first....
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Mar 30 2008, 12:58 AM
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#9
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 Group: Members Posts: 1,720 Joined: 17-May 05 Member No.: 2,325 |
QUOTE (Castle-Bravo354 @ Mar 21 2008, 06:42 PM) Fen....I agree.....and other lifeforms may also have higher tolerances of heat, cold and preasure than earthbound life.....so its really hard to say life can't exist.....unless we go there to find out. Sounds like a road trip to me..... Actually, there are some life forms on earth that show amazing resiliency. Like the extremophiles that live near underwater volcanic vents. |
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Mar 30 2008, 09:10 AM
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#10
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Group: Members Posts: 3,135 Joined: 26-August 06 Member No.: 4,857 |
QUOTE (ThePredator @ Mar 30 2008, 06:48 AM) Actually, there are some life forms on earth that show amazing resiliency. Like the extremophiles that live near underwater volcanic vents. TP....thanks, but I am aware of the deep benthic rift communities and other extreme life forms on earth. I meant life forms that were based on different elements and/or could exist in environments beyond what would exist on earth. |
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