55 Cancri e -- Transits detected!!

Well a highly-reflective molten surface with a thin atmosphere ("lava ocean world") seems to be excluded but only at 1-sigma. I guess it doesn't help distinguishing between the various other possibilities (supercritical water world, carbon planet, etc.)

IIRC there is no sign yet of disintegrated carbon planets from observations of white dwarfs though...

Apparently you shouldn't neglect tidal heating when trying to estimate the albedo, especially if there are additional perturbing planets around.

Tidal dissipation and eccentricity pumping: Implications for the depth of the secondary eclipse of 55 Cnc e
http://arxiv.org/abs/1304.0459

Can tidal heating explain the radius of the planet without carbon composition?

Detecting the spin-orbit misalignment of the super-Earth 55 Cnc e
http://arxiv.org/abs/1406.6813

Quote :

We present time-resolved spectroscopy of transits of the super-Earth 55 Cnc e using HARPS-N observations. We devised an empirical correction for the "color effect" affecting the radial velocity residuals from the Keplerian fit, which significantly improves their dispersion with respect to the HARPS-N pipeline standard data-reduction. Using our correction, we were able to detect the smallest Rossiter-McLaughlin anomaly amplitude of an exoplanet so far (~60 cm/s). The super-Earth 55 Cnc e is also the smallest exoplanet with a Rossiter-McLaughlin anomaly detection. We measured the sky-projected obliquity lambda = 72.4 (+12.7 -11.5 deg), indicating that the planet orbit is prograde, highly misaligned and nearly polar compared to the stellar equator. The entire 55 Cancri system may have been highly tilted by the presence of a stellar companion.

So we now have a second example of a coplanar, misaligned planetary system. I vaguely recall this setup being proposed for the system in the past. Neat to see it confirmed.

If 55 Cnc B is responsible, then it likely has a very eccentric orbit, with a periastron of only ~35 AU or so. So the misalignment might also suggest that 55 Cnc Ad is the outermost planet in the system.

Boué & Fabrycky "Compact planetary systems perturbed by an inclined companion: II. Stellar spin-orbit evolution"
http://arxiv.org/abs/1405.7636

However, another group fails to detect the R-M effect...

Rossiter-McLaughlin Observations of 55 Cnc e
http://arxiv.org/abs/1408.2007

Quote :

We present Rossiter-McLaughlin observations of the transiting super-Earth 55 Cnc e collected during six transit events between January 2012 and November 2013 with HARPS and HARPS-N. We detect no radial-velocity signal above 35 cm/s (3-sigma) and confine the stellar v sin i to 0.2 +/- 0.5 km/s. The star appears to be a very slow rotator, producing a very low amplitude Rossiter-McLaughlin effect. Given such a low amplitude, the Rossiter-McLaughlin effect of 55 Cnc e is undetected in our data, and any spin-orbit angle of the system remains possible. We also performed Doppler tomography and reach a similar conclusion. Our results offer a glimpse of the capacity of future instrumentation to study low amplitude Rossiter-McLaughlin effects produced by super-Earths.

They argue that the R-M effect amplitude reported by Bourrier & Hérard imply a v sin i of 3.3 km/s -- incompatible with their measurements of the v sin i, P_rot, age, R'_HK.

Yeah, I'm inclined to agree. The stellar radius of 0.943 ± 0.010 R_⊙ observed by von Braun et al. and the rotational period of ~39.8 days observed in the activity indicators (data from Wright et al. and Isaacson et al.) necessitate a v sin i of ~<1.2 km/s. Trying to get an R-M effect measurement from such an old star is going to be very difficult.

Now the transits have been detected from the ground, too.

de Mooij et al. "Ground-Based Transit Observations of the Super-Earth 55 Cnc e"
http://arxiv.org/abs/1411.7660

Neat. It's good to see that relatively good precision is obtainable for a bright star with a fairly moderate-sized telescope, as this will be of considerable value in the TESS era.

Demory et al. (2015) "Variability in the super-Earth 55 Cnc e"
http://arxiv.org/abs/1505.00269

4-sigma variation in the dayside thermal emission. Cause is uncertain, but they also find a smaller radius (and thus higher density) planet, which has implications for the composition:

Quote :

Using internal structure models of super-Earths (Madhusudhan et al. 2012), we find that the mass and bulk radius of the planet, given by the minimum radius observed, are consistent with an Earth-like interior composition of the planet, i.e. composed of an Iron core (30% by mass) overlaid by a silicate mantle and crust. Previous studies which used a larger radius of the planet required a thick water envelope (Demory et al. 2011; Gillon et al. 2012; Winn et al. 2011) or a carbon-rich interior (Madhusudhan et al. 2012), neither of which are now required but cannot be ruled out either.

If the planet has Earth-like composition, the variability might be due to large-scale volcanic activity. Alternatively, circumplanetary/circumstellar material may be the explanation.

Further observations needed, but certainly 55 Cnc e seems to be quite a puzzling world!

That's amazing! Very interesting read.

Detection of an atmosphere around the super-Earth 55 Cancri e
http://arxiv.org/abs/1511.08901

Quote :

Before the discovery of extrasolar planets, super-Earths belonged in the realm of science fiction. However, they appear to constitute the most common planetary type in our galaxy. We know very little about these planets beyond very basic planetary and orbital parameters. The WFC3 camera onboard the HST has enabled the spectroscopic observations of the atmospheres of two super-Earths, GJ1214b and HD97658b, with unprecedented precision; but the published spectra of these two objects are featureless, suggesting an atmosphere covered by thick clouds or made of molecular species much heavier than hydrogen. We report here the analysis of the observations performed with the WFC3 of a third, very hot, super-Earth, 55 Cancri e. Given the brightness of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length and a very high scanning speed. These observational parameters are coupled with the geometrical distortions of the instrument, so we have developed a specialized pipeline to de-correlate the signal from the systematics. We measure the transit depth per wavelength channel with an average relative uncertainty of 21 ppm and find a spectral modulation of about 100 ppm. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is hydrogen-rich. Our fully Bayesian spectral retrieval code, TauREx, has identified HCN to be one of the possible trace gases in the atmosphere. While additional observations in a broader wavelength range will be needed to confirm the HCN detection, we discuss here the implications of such result. We adopt a chemical scheme developed with combustion specialists and validated by a wide range of experiments. Our chemical model indicates that a relatively high mixing ratio of HCN would reveal a high C/O ratio, suggesting the atmosphere of 55 Cancri e is a carbon-rich environment.

I guess planet e could retain very thin atmosphere but hydrogen rich means it only started as gas giant if we assess old age of host star 55 Cancri

http://spaceref.com/extrasolar-planets/first-detection-of-super-earth-atmosphere.html

Using observations made with the Wide Field Camera 3 (WFC3) on board the NASA/ESA Hubble Space Telescope, the scientists were able to analyse the atmosphere of this exoplanet. This makes it the first detection of gases in the atmosphere of a super-Earth. The results allowed the team to examine the atmosphere of 55 Cancri e in detail and revealed the presence of hydrogen and helium, but no water vapour. These results were only made possible by exploiting a newly-developed processing technique
(…)
Intriguingly, the data also contain hints of the presence of hydrogen cyanide, a marker for carbon-rich atmospheres

Wow it is surprising for me so small planet and so close to the host still has little bit of H,He it proves this planet started as gas giant

Press release from the University of Cambridge: Map of rocky exoplanet reveals a lava world

Paper in Nature: Demory et al. (2016) "A map of the large day–night temperature gradient of a super-Earth exoplanet"

There appears to be a hotspot about 41 degrees eastwards of the substellar point. Heat transfer to the nightside is inefficient, leading to a large temperature contrast but the night side is still 1380K. The planet seems to be hotter than can be explained by heating from the star, not yet clear what the heat source is (tidal?).

Despite NameExoWorlds, the press materials still use "55 Cancri e" rather than "Janssen". Good.

Article in Scientific American - seems there may be reasons to be cautious about this result, as this is pushing the limits of what you can do with Spitzer.

arXiv paper for the above result: http://arxiv.org/abs/1604.05725

Ridden-Harper et al. "Search for an exosphere in sodium and calcium in the transmission spectrum of exoplanet 55 Cancri e"
http://arxiv.org/abs/1606.08447

Some suggestions that there may be a time-variable signal due to Ca⁺ but not at a significant enough level to claim a detection.

An attempt to detect water on 55 Cnc e, finding that if the atmosphere is optically-thin then it is water depleted, although indirect evidence suggests the atmosphere is optically-thick. There's a decent summary of the results so far in section 1.1.

Esteves et al. "Search for water in a super-Earth atmosphere: High-resolution optical spectroscopy of 55 Cancri e"
https://arxiv.org/abs/1705.03022

Angelo & Hu "A Case for an Atmosphere on Super-Earth 55 Cancri e"
https://arxiv.org/abs/1710.03342

Hammond & Pierrehumbert "Linking the Climate and Thermal Phase Curve of 55 Cancri e"
https://arxiv.org/abs/1710.03556

Thick atmosphere seems to fit the observations best, as heat transport by a lava ocean wouldn't be able to shift the hotspot sufficiently. The nightside may have clouds of material evaporated from a lava ocean, while main atmospheric constituent may be nitrogen or carbon monoxide.

Confirmation of variability.

Confirming Variability in the Secondary Eclipse Depth of the Super-Earth 55 Cancri e
https://arxiv.org/abs/1804.03735

Crida et al. "Mass, radius, and composition of the transiting planet 55 Cnc e : using interferometry and correlations"
https://arxiv.org/abs/1804.07537

Estimates the gaseous envelope is approximately 8% of the planet's radius.

The 55 Cnc system reassessed
https://arxiv.org/abs/1807.04301

There's a full five-planet (+magnetic cycle) fit to the RV data.

Quick update.

Mass, radius, and composition of the transiting planet 55 Cnc e : using interferometry and correlations --- A quick update
https://arxiv.org/abs/1809.08008

Quote :

In a recent paper (Crida et al. 2018, accepted on April 19), we presented a method to derive the mass and radius of a transiting exoplanet and their intrinsic correlation, that we applied to 55 Cnc e. We wrote: "More precise observations of the transit would be very useful in this particular case and would allow to increase significantly the gain on the planetary density precision." Three months later, Bourrier et al. (2018) published new observations of the system. Additionally, Gaia's DR2 was released on April 25, 2018. The purpose of this research note is solely to implement these precise new data in our pipeline to provide an up-to-date result of our model. We find Rp=1.947±0.038R⊕ and Mp=8.59±0.43M⊕. We also double the precision on the planetary density (ρp=1.164±0.062ρ⊕), which allows us to refine the estimates for all interior parameters of interest. In particular, we now find that the radius of the gaseous envelope is 0.03±0.02Rp.