A Transiting Hot Neptune

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Swiss astronomers have discovered that the Neptune mass planet orbiting GJ 436 transits its host star. The planet was discovered back in 2005, but was just found to be transiting. This is arguably the most exciting exo-planet news this year since it opens the window to studying the structure of smaller planets - and indeed, the thing has a radius that's comparable to Neptune. That tells us that the planet is largely composed of water (ices) rather than rock or pure hydrogen, formed beyond the snow line, and has migrated in. The planet has a fairly high eccentricity, so there may very well be more planets in the system, which may also be transiting. If you can do better than 1% photometry (many amateurs can, the transit was first detected with an amateur class telescope), I highly recommend that you follow the thing up!<br /><br />More info here:<br />http://oklo.org/?p=213<br /><br />and here:<br />http://www.swissinfo.org/eng/front/detail/Small_Swiss_observatory_finds_ice_planet.html?siteSect=105&sid=7826748&cKey=1179329826000<br /><br />The discovery paper here:<br />http://xxx.lanl.gov/abs/0705.2219<br /><br />In terms of scientific impact, I'd say this is significantly more exciting than the discovery of the potentially habitable planet a few weeks ago. <div class="Discussion_UserSignature"> </div>

 

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I should mention that there is some uncertainty whether the planet has a 10% by mass atmosphere of hydrogen or water steam (which would then be above a high-pressure/temperature water phase, making the thing an ocean planet). A better radius determination from more precise photometry should answer that question. Also, the star is only 10.2 pc away, and fairly bright (V = 10.67), and it's a M2.5 dwarf. So there's actually a very good chance that the temperature/infra-red spectrum of this planet can be obtained with Spitzer, which should really tell us whether or not this thing has a water atmosphere. <div class="Discussion_UserSignature"> </div>

 

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Hopefully COROT will reveal more.<br /><br />Sounds fascinating.<br /><br />Interesting link here GJ 436.<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>

 

[robnissen]

<font color="yellow">That tells us that the planet is largely composed of water (ices)</font><br /><br />With a minimum estimated temperature of over 600 F, it seems unlikely, to put it mildly, that this planet would contain any ice, or even liquid water. I think I will stick with Gliese C as the most interesting planetary discovery this year.

 

[MeteorWayne]

From the article<br />"Hot ice is a situation in which under very great pressure water stays like ice. It cannot be found naturally on Earth but has been made in laboratories, he added."<br /><br /> <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>

 

[robnissen]

As Emily Litella would say, "Never mind then."<br /><br />My bad.

 

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I think it's ice XII that would be the primary state for the planet's mantle. <br /><br />The key point though is that we actually know that the planet is probably ~90% ices (if it were terrestrial it'd have to be denser, if it were gas it would have to be less dense), and we have the potential to figure out a lot more about the planet in fairly short order. That's quite a bit more than can be said for the potentially habitable planet for which all we know is its mass and semi-major axis (and which probably won't be habitable if it has an atmosphere). <div class="Discussion_UserSignature"> </div>

 

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<blockquote><font class="small">In reply to:</font><hr /><p>"Hot ice is a situation in which under very great pressure water stays like ice. It cannot be found naturally on Earth but has been made in laboratories, he added."<p><hr /></p></p></blockquote><br /><br />Here is some more info here: http://www.smh.com.au/news/science/under-pressure-liquid-becomes-solid/2007/05/17/1178995324172.html<br />