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WASP-104b is Darker than Charcoal
By analysing the K2 short-cadence data from Campaign 14 we detect phase-curve modulation in the light curve of the hot-Jupiter host star WASP-104. The ellipsoidal modulation is detected with high significance and in agreement with theoretical expectations, while Doppler beaming and reflection modulations are detected tentatively. We show that the visual geometric albedo is lower than 0.03 at 95% confidence, making it one of the least-reflective planets found to date. The light curve also exhibits a rotational modulation, implying a stellar rotational period likely to be near 23 or 46 days. In addition, we refine the system parameters and place tight upper limits for transit timing and duration variations, starspot occultation events, and additional transiting planets.
WASP-104b's albedo was previously thought to be 0.4 (absorbing 60% of incoming light).
Also at ScienceAlert.
Related: NASA Finds a Pitch-Black Hot Jupiter Exoplanet (WASP-12b)
(Score: 2) by takyon on Wednesday April 25 2018, @07:40PM (3 children)
The Moon's [wikipedia.org] albedo is 0.136. This object appears to be 0.03, and it's a "hot Jupiter".
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(Score: 2) by Megahard on Wednesday April 25 2018, @08:51PM (2 children)
The planet in our system with the lowest albedo is Mercury, at 0.06. Gas giants are much higher, and Venus is highest at 0.75. Maybe it's a hot rocky Jupiter?
(Score: 3, Informative) by takyon on Wednesday April 25 2018, @10:28PM (1 child)
Rocky probably isn't the right way to think of it. It is probably a lot like Jupiter or other gas giants, in which there is a rocky core and metallic hydrogen which can be many Earth masses, but the key point seems to be composition + high temperature allowing certain metals to exist in a gas state, and apparently doing a great job at absorbing light from the star.
There may be a different class of planet that has a "mini-Neptune" or much larger mass, but doesn't have a thick atmosphere.
https://en.wikipedia.org/wiki/Giant_planet#Massive_solid_planets [wikipedia.org]
https://en.wikipedia.org/wiki/Chthonian_planet [wikipedia.org]
This is not the case here as they measured the volume, mass, and density of WASP-104b, and it's very Jupiter-like:
Planet mass = 1.311 ± 0.053 MJup
Planet radius = 1.106 ± 0.019 RJup
Planet density = 0.969 ± 0.028 ρJup
Planet equilibrium temperature = 1507 ± 39 Kelvins
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(Score: 2) by Immerman on Thursday April 26 2018, @03:47AM
Hmm, at roughly the same density as Jupiter I would assume it would have to be mostly hydrogen as well. Presumably "hot" is one of the defining features, so that a much wider range of materials can remain gaseous, even in the visible upper atmosphere.
Or, just to make things more fun, maybe the planet simply hosts a thriving population of high-efficiency atmospheric photovores. Or it may not even be a gas giant, but rather a civilization that has built a dense array of efficient orbital solar collectors, leaving a much smaller, denser planet completely hidden within it. Perhaps even a previously super-Jupiter Chthionian world, rich in "exotic" minerals formed under the intense heat and pressures the atmosphere once provided.