Log in

No account? Create an account
03 October 2008 @ 09:06 pm
Exoplanet HD 189733b  
Picture this:

A planet, tidally locked to its star (this means only one side of the planet faces its star).
On the star-side, the surface temperature is 1,700°F.
On the dark-side, the surface temperature is 1,200°F.

Welcome to exoplanet HD 189733b, 63 light years away in the Vulpecula (Fox) constellation.

I expected the temperature disparity from star-side to dark-side to be much more pronounced. Apparently, so do the astrophysicists.

Now, my poetic-souled, sharp-minded friends, without researching it, tell me why it's so warm on the dark side, or, if you'd like to go a more philosophical route, tell me how our light-is-warmth dark-is-cold mentality might blind us from understanding our Foxy celestial neighbors.

My intuitive explanation differed from the one offered by the article "Forbidden Planets: A Whirlwind Tour of the Oddest Exoplanets" by Julie Thole in the Discovery Presents the Whole Universe magazine I've been raving about, though I suspect both are relevant factors.

The light from the star HD 189733 hitting Earth right now was produced two years before my dad was born. The distance is beyond my ken.
Current Mood: hunh
Current Music: "I'm Gonna Be an Engineer" - Peggy Seeger
Kburgunder on October 4th, 2008 04:33 am (UTC)
Article suggests: 6,000mph winds pushing hot air from star-side

My first thought: the planet itself is of a material composition that is conducting the temperature star-side to dark-side through the core

The wiki article indicates that high sodium signals have been detected, but my material science and thermodynamics is crap so I can't say whether or not that says anything about the planet's internal thermal conductivity. :/ Would love your comments if you can speak to this.
Zen Anarchymetalmensch on October 4th, 2008 05:40 am (UTC)
Nevermind...I guess it does! :) That would explain the small differential. Our water content and spin is the supposed reason ours is such a small difference.

And now...I really want to watch Chronicles of Riddick.
Zen Anarchymetalmensch on October 4th, 2008 06:04 am (UTC)
You need atmo for wind, which is a surprisingly good conductor. Imagine that...the wind being literally hotter than a blowtorch.
Zen Anarchymetalmensch on October 4th, 2008 05:38 am (UTC)
Does it have an atmosphere?
Douglaschiaspod on October 4th, 2008 05:47 am (UTC)
I'm thinking convection, not conduction.
Kburgunder on October 4th, 2008 06:26 am (UTC)
The astrophysicists agree with you :)

As I'm typing this, I have another thought...

The Earth's molten iron core is way hotter than its crust. What if this planet is still pre-cooled-crust? Hunh. (Fuck, do I even remember my rogue geology properly? Planet formation - everything's hot for a long time, cools outside to inside...?)
Chriscryophile on October 4th, 2008 05:27 pm (UTC)
There's not going to be any visible crust on this planet. From radial velocity measurements, we know that it's mass is slightly greater than Jupiter's. This means that it is certainly a gas giant planet like Jupiter and Saturn, with no surface to speak of. The HD189733 system is one of those lucky cases where the planet's orbit is aligned so that we can observer it transit the disk of its sun--an eclipse nearly 70 light years distant. The radius of a transiting planet can be inferred from the degree that the star dims when the planet passes in front of it. HD189733 has been measured by this technique to be slightly larger than Jupiter. So, similar mass and radius as Jupiter -> similar density -> HD189733 is gas giant.

The dense atmosphere of a gas giant is very effective at transporting heat around, which is why there's temperature difference between day and night hemispheres isn't as great as you might expect. Models of Earth-sized planets that are tidally locked to their stars suggest that even a much thinner Earth-like atmosphere is effective enough at heat transport to prevent the permanently dark side from freezing out. In contrast a planet like Mercury has no atmosphere, and the temperature on its night side drops below 100K while the day side cooks at 500K or more.
interit: blueberrya_muse_d on October 4th, 2008 06:36 am (UTC)
the planet's distance from its star would make a difference. plus the heat has gone through the planet. i wouldn't be surprised if Mercury has a similar heat ratio.