55 Cancri e -- Transits detected!!

Galzi wrote:

Well, if someone were to plot the function of Neptune-like in that graphic, it would be out of view.

Actually, it would be about a third of the way from the '10' marker to the right edge of the graphic, and somewhere near the blue line.

I've marked Neptune's position on this graphic.


Ask yourself, is 55 Cnc e closer to the blue line (the Neptune-like composition) or the red line? (the Earth-like composition?)

Sirius_Alpha wrote:

Galzi wrote:

Well, if someone were to plot the function of Neptune-like in that graphic, it would be out of view.

Actually, it would be about a third of the way from the '10' marker to the right edge of the graphic, and somewhere near the blue line.

I've marked Neptune's position on this graphic.


Ask yourself, is 55 Cnc e closer to the blue line (the Neptune-like composition) or the red line? (the Earth-like composition?)

To my knowledge Neptune radius is over 24000 km, out of the ordinate axis range of the graphic. You marked a roughly 17-18000 km radius in your graphic; by losing the equivalent of an Earth radii, while keeping equal mass, it's no wonder that this shrinked denser Neptune is nearer to 55 Cancri e.

Not to count that if we were to put a Neptune in the orbit of 55 Cancri e, the radius will probably increase and the average density shrink, further increasing the difference between the two planets.

A Neptune-like structure is inadequate to explain the nature of 55 Cancri e. A very solid rocky composition, superimposed by a huge atmosphere due to the very hot temperatures, is needed to explain the high mean density of the planet.

Comparing 55Cnc e to neptune should have place where both planets had similar radii and density now e has lost most volatiles due to stellar irradiation so is simply remnants of gas or ice giant.Probability that e has 45% water is rather unlikely and much higher compression rather exagerrated

Galzi wrote:

To my knowledge Neptune radius is over 24000 km, out of the ordinate axis range of the graphic. You marked a roughly 17-18000 km radius in your graphic; by losing the equivalent of an Earth radii, while keeping equal mass, it's no wonder that this shrinked denser Neptune is nearer to 55 Cancri e.

You're right. "brain-fart" on my part. I retract my statement.

Sirius_Alpha wrote:

300 additional RV measurements provide no evidence for a sixth planet, but there is a weak signal at 131 days (low power, not statistically significant).

Interesting, that's half the period of 55 Cnc f. Maybe the high eccentricity of planet f (which is substantially higher than the eccentricities of the other planets in the system) is a result of confusion between an eccentric orbit and a 2:1 resonance?

I noticed this also(131 days) Problem with eccentricity hiding 2-1 resonance is very similar to the situation with gj 581 system planet d,g

We have to wait preprint from arXiv or something similar to know more, but sounds really interesting.

This could also mean there are more stringent limits about orbital inclination and true mass of 55 Cnc Ab as for Tau Boo Ab.

Very interesting hmm if is partly transiting with mass of star, period of planet and known impact parameter radius is possible to be determined

It's on arXiv now.
http://arxiv.org/abs/1210.0531

That's pretty neat, though as they say the observations need confirmation by observations at other epochs due to the X-ray variability of 55 Cnc A. Also the implications of the non-detection of 55 Cnc e at Lyα are interesting.

A Possible Carbon-rich Interior in Super-Earth 55 Cancri e
http://arxiv.org/abs/1210.2720

Apparently you can explain the radius of the transiting super-Earth without a volatile envelope if you assume some carbon-rich compositions.

Nice, looks like my armchair speculations aren't too far-fetched...

Sirius_Alpha wrote:

A Possible Carbon-rich Interior in Super-Earth 55 Cancri e
http://arxiv.org/abs/1210.2720

Apparently you can explain the radius of the transiting super-Earth without a volatile envelope if you assume some carbon-rich compositions.

If they got it right, instead of a hot "waterworld" we have a carbon planet with possibly a few Earth masses of diamonds.

Maybe our terms for these class of planets - "Super-Earths" or "Mini-Neptune" - unconsciously mislead us in a Solar System based view. We have to be open - within the laws of physics - to every type of exotic possibility regard their compositions.

I'm not sure I see where all this diamond stuff is supposed to come from. The density of the planet is still equal to that of Earth, which, given its mass, requires it to be made out of materials that have a lower uncompressed density. If I'm not mistaken, diamond is significantly more dense than Earth.

No sirius density graphite 2,2 g/cm3 diamond 3.52

Anyway I am not sure is it clear carbon planet

tommi59 wrote:

No sirius density graphite 2,2 g/cm3 diamond 3.52

Ah yes. Thanks.

And according to Wikipedia, silicon carbide is 3.21 g/cc.

Down to 3.5 g/cm3 still can be solid surface if carbon rich

Sirius_Alpha wrote:

I'm not sure I see where all this diamond stuff is supposed to come from. The density of the planet is still equal to that of Earth, which, given its mass, requires it to be made out of materials that have a lower uncompressed density. If I'm not mistaken, diamond is significantly more dense than Earth.

Theoretical research pointed out the possibility of "terrestrial" planets being rich in diamonds, if enough carbon is provided

http://www.scientificamerican.com/podcast/episode.cfm?id=some-terrestrial-exoplanets-may-be-11-12-14

Quote :

The researchers were fixing to study how diamonds form here on Earth, under the conditions found in the planet’s lower mantle. So they took a tiny sample of iron, carbon, and oxygen, elements abundant in Earth’s interior, and cooked it up at about 3,800 degrees Fahrenheit and 9.5 million pounds of pressure per square inch. What they saw was that iron hooks up with oxygen to produce rust, and leaves behind pockets of carbon, which become diamond.

Now, what happens if they look not at Earth but at a planet in a solar system where there’s even more carbon? According to the model, the carbon merges with iron to form a core made of steel, leaving a carbon mantle rich with diamond.

The authors of the paper fully endorse the massive presence of diamonds if the planet is carbon rich:

http://www.theglobeandmail.com/technology/astronomers-discover-55-cancri-e-a-diamond-planet-40-light-years-from-earth/article4605246/

Quote :

“We’re talking about a rocky planet. Not much gas, almost entirely solid. The outermost layer is at an extremely high temperature ... There could also be a lot of diamonds on the surface because of the geophysical movements in the interior. The diamonds could come to the surface very easily,” Dr. Madhusudhan said in an interview.

“But just below the surface there is a very thick layer, about a third of the whole radius [of the planet], just in diamonds.”

http://www.newscientist.com/blogs/shortsharpscience/2012/10/watery-planet-diamond.html

Quote :

Based on estimates of the temperature and pressure throughout the planet, this carbon could be in the form of diamond, which requires extreme conditions to form. One of five known planets in its solar system, 55 Cancri e, sits very close to its host star. "When you form diamond, it's only a matter of temperature and pressure, and the temperature is very high on the surface," says Mousis.

A planet with a steel core and immense reservoirs of diamonds.. If the model is confirmed by future followup observations we're dealing with a kind of beast never seen in the Solar System.

Certainly a carbon-planet would be extremely refractory in nature and also neatly explain the lack of Lyα detection of the planet (though this is still not conclusive).

It would certainly be interesting if the 55 Cnc b atmospheric transit is confirmed, perhaps it may offer some clues as to whether it is carbon-enriched. However it is significantly cooler than the hot Jupiters for which carbon-enriched atmospheres have been inferred.

New MOST Photometry of the 55 Cancri System
http://arxiv.org/abs/1302.3321

Quote :

Since the discovery of its transiting nature, the super-Earth 55 Cnc e has become one of the most enthusiastically studied exoplanets, having been observed spectroscopically and photometrically, in the ultraviolet, optical and infrared regimes. To this rapidly growing data set, we contribute 42 days of new, nearly continuous MOST photometry of the 55 Cnc system. Our analysis of these observations together with the discovery photometry obtained in 2011 allows us to determine the planetary radius (1.990$^{+0.084}_{-0.080}$ R_Earth) and orbital period (0.7365417$^{+0.0000025}_{-0.0000028}$ days) of 55 Cnc e with unprecedented precision. We also followed up on the out-of-transit phase variation first observed in the 2011 photometry, and set an upper limit on the depth of the planet's secondary eclipse, leading to an upper limit on its geometric albedo of 0.6.

New data rather rule out other surface than solid for e ,no confirmation of transiting b atmosphere