Spitzer Sees Light From Faraway Planets

[yevaud]

<i>NASA's Spitzer Space Telescope has captured for the first time enough light from planets outside our solar system, known as exoplanets, to identify signatures of molecules in their atmospheres. The landmark achievement is a significant step toward being able to detect possible life on rocky exoplanets and comes years before astronomers had anticipated.<br /><br />"This is an amazing surprise," said Spitzer project scientist Dr. Michael Werner of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We had no idea when we designed Spitzer that it would make such a dramatic step in characterizing exoplanets."<br /><br />Spitzer, a space-based infrared telescope, obtained the detailed data, called spectra, for two different gas exoplanets. Called HD 209458b and HD 189733b, these so-called "hot Jupiters" are, like Jupiter, made of gas, but orbit much closer to their suns.<br /><br />The data indicate the two planets are drier and cloudier than predicted. Theorists thought hot Jupiters would have lots of water in their atmospheres, but surprisingly none was found around HD 209458b and HD 189733b. According to astronomers, the water might be present but buried under a thick blanket of high, waterless clouds.<br /><br />Those clouds might be filled with dust. One of the planets, HD 209458b, showed hints of tiny sand grains, called silicates, in its atmosphere. This could mean the planet's skies are filled with high, dusty clouds unlike anything seen around planets in our own solar system.<br /><br />"The theorists' heads were spinning when they saw the data," said Dr. Jeremy Richardson of NASA's Goddard Space Flight Center, Greenbelt, Md.<br /><br />"It is virtually impossible for water, in the form of vapor, to be absent from the planet, so it must be hidden, probably by the dusty cloud layer we detected in our spectrum," he said. Richardson is lead author of a Nature paper appearing Feb. 22 that describes a spectrum for HD 209458b.<br /><br />In addition to Richardson's team, two oth</i> <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>

 

[rybanis]

Holy crap, a DUSTY atmosphere? Thats strange.<br /><br />Well, congrats to the Spitzer team! <div class="Discussion_UserSignature"> </div>

 

[summoner]

Just got done reading that and you beat me to the post. <img src="/images/icons/wink.gif" /> This is truly remarkable. It's amazing the advances that have been made in the last 15 years of exoplanet study. I can't even image what will happen in the next 15, hopefully TPF will still happen. <div class="Discussion_UserSignature"> <p> </p><p> </p><p> </p><p> <br /><table cellpadding="0" cellspacing="0" style="width:271px;background-color:#FFF;border:1pxsolid#999"><tr><td colspan="2"><div style="height:35px"><img src="http://banners.wunderground.com/weathersticker/htmlSticker1/language/www/US/MT/Three_Forks.gif" alt="" height="35" width="271" style="border:0px" /></div>

 

[yevaud]

<i>Just got done reading that and you beat me to the post.</i><br /><br />Timing is everything. <img src="/images/icons/wink.gif" /> Any designer of thermonuclear weaponry can tell you that. <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>

 

[voyagerwsh]

<i>The planet seems to contain silicate dust at high altitudes, according to one broad emission peak, a mineral common on Earth and in our Solar System. There is also an unidentified feature in the spectrum, a much sharper peak at a wavelength of around 7.78 micrometres, which is hard to identify but may correspond to polycyclic aromatic hyrocarbons, or PAHs, ("a more exotic possibility"), and what the team says are "several other suggestive features."</i>-- http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2007/02/22/nalien22.xml<br /><br />That's interesting as well, PAHs may be very common through out the deep space.<br /><br />

 

[mithridates]

I noticed that article earlier today and it was a nice surprise for me too. Why did it catch them by surprise though? How did they design a telescope that had capabilities that they didn't know about before launch? Any idea on how many more planets it should be able to analyze during its time in use? <div class="Discussion_UserSignature"> <p>----- </p><p>http://mithridates.blogspot.com</p> </div>

 

[silylene old]

<font color="yellow">The planet seems to contain silicate dust at high altitudes, according to one broad emission peak, a mineral common on Earth and in our Solar System.</font><br /><br />I wonder how that occurs too.<br /><br />Atmospheric silicates could easily form from reaction of gaseous SiH4 or halosilanes such as SiCl4 with O2 or H20, or (much less likely) from condensation of silyl ethers such as Si(OR)4, or by oxidation of polysilicon dusts.<br /><br />Which then drives the next questions: was any silane, or halosilane seen in the atmosphere? No water was seen, but how about oxygen? I am not sure whether silanes react with CO2 or CO at high temperature. I am sure that may be possible.<br /><br />Silicates shouldn't have a geologically long residence time in gaseous suspension, due to the fact that they tend to agglomerate when they collide, to form larger particles, which then should settle out. This means that the silicate source is either renewing itself, or just happens to be coincidentally high just when we observed the planet.<br /><br />Finally, there are the other two rather exciting explanations:<br />1) that there are huge very active volcanoes on the surface of the planet which can spew silicate ashes high into the planetary stratosphere. I assume the high heat of being close to the star, plus gravitational contraction, plus the tidal stresses must drive a lot of geothermal heating in the planet.<br />2) that a large silicate-rich asteroid or moonlet recently struck with the planet, and its disruption released a lot of silicate dust into the atmosphere. <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>

 

[voyagerwsh]

(1). http://www.spitzer.caltech.edu/Media/releases/ssc2007-04/ssc2007-04a.shtml<br /> <br />(2). <br />http://www.arxiv.org/PS_cache/astro-ph/pdf/0702/0702507.pdf<br /><br />The authors observed the silicates spectrum which should contain rich oxygen, water molecules may hide in lower altitude.<br /><br />This exoplanet might be a Jupiter-sized terrestrial one.

 

[MeteorWayne]

I read the article in Nature or Science, and it was very difficult to tease the planet's spectra out of the noise and that of the star. I'm not sure anyone thought it could be done when Spitzer was designed.<br /><br />A lot has changed in a few decades. <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>

 

[silylene old]

<font color="yellow">The authors observed the silicates spectrum which should contain rich oxygen, water molecules may hide in lower altitude. <br /></font><br /><br />I know that, I am not doubting that there is silicates in the atmosphere, and I am well aware that silicates have an average composition of (SiO2)n, which includes oxygen atoms.<br /><br />My previous post was speculating <i>why</i> silicates might be in the atmosphere. To me, that is a very interesting question. Especially that in reading the paper which you kindly linked, the authors did not mention observing the presence of potential oxidizing gases such as O2, CO, CO2, H2O, NO, NO2 or SO2. <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>

 

[doubletruncation]

<font color="yellow">Silicates shouldn't have a geologically long residence time in gaseous suspension, due to the fact that they tend to agglomerate when they collide, to form larger particles, which then should settle out.</font><br /><br />It's a good point. The evidence for silicates from these papers is fairly tentative, however more compelling evidence has been found for silicates in brown dwarf atmospheres. A hypothesis that I've seen for how these silicates keep from settling out is that they are constantly replenished by convection in the atmosphere of the brown dwarf. The particles in a given dust cloud will tend to settle out, however they'll be vaporized and mixed with the gas as they fall into the high temperature interior of the brown dwarf. This gas containing silicates is carried back up to the cooler surface by convection at which point the silicates condense again into a cloud and settle out (see for example, a fairly interesting paper on the subject at http://xxx.lanl.gov/abs/astro-ph/0405438 ). <br /><br />For the hot giant planets this might be more difficult to understand since their upper atmospheres are thought to be radiative to a fairly deep level (the reason is that the nearby star heats up the outer atmosphere of the planet which leads to a fairly flat temperature profile. Convection will only occur for fairly steep temperature gradients). Of course, if the planet is tidally locked to the star (as expected) this could vary between the day and night side. Also, the clouds themselves could shield the lower atmosphere from the star's radiation and thus allow for convection below the cloud decks. <div class="Discussion_UserSignature"> </div>

 

[silylene old]

I am happy someone read my prior post, and wanted to discuss what I think is a key subject to the model of why a hot Jupiter may have clouds of silicates in the upper atmosphere.<br /><br />And, thank you for bringing this article to my attention. I don't have access to much of the original astronomy literature, as my library at work carries only primary journals and chemistry journals.<br /><br />If the silicate particles sublime as they decend, I would assume that the it would form SiO2(g), or perhaps SiO(g) and O2(g). If these silicon-containing gases were present within the hot atmosphere, they should have very distinctive, bright IR signatures (NOT observed!). Of course SiO2(g) and SiO(g) are extremely reactive, and would not be seen in a cooler zone.<br /><br />Therefore, one would have to assume that:<br />1) The model of suspended silicates is wrong, and they are not present.<br />2) Other explanations exists for the suspended silicate particles (see my previous post)<br />3) The gaseous SiO2 and SiO species are invisble to infrared because these layers are shielded by clouds in upper cooler layers.<br /><br />It is a very interesting situation.<br /><br />I thought this paragraph from the article you cited was interesting:<br /><blockquote><font class="small">In reply to:</font><hr /><p>. In fact, in a static equilibrium model there is no solution that allows<br />dust to remain suspended in the photosphere at all, as the grains will eventu-<br />ally sink to lower layers, and take all condensible elements with them until their<br />abundance has decreased below the saturation pressure. Radiation pressure is<br />negligible at such low luminosities and certainly cannot provide the force re-<br />quired to keep grains lifted up. Because of the relatively inefficient transport of<br />energy by radiation and the large molecular opacities, these cool atmospheres<br />are all convective. Convection can thus provide the essential replenishment of<br />condensible material in the cl</p></blockquote> <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>