Kepler-186 : 5 planet system with Earth-sized planet in the HZ

NASA Hosts Media Teleconference to Announce Latest Kepler Discovery
April 15, 2014

http://www.nasa.gov/ames/kepler/nasa-hosts-media-teleconference-to-announce-latest-kepler-discovery/#.U01aa6hdUxg

It's about Kepler-186f :
http://spaceref.com/extrasolar-planets/earth-size-planet-found-that-might-hold-liquid-water.html

NASA's Kepler Discovers First Earth-Size Planet In The 'Habitable Zone' of Another Star
http://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star#.U1AYPPldUrU

Finally, a candidate habitable exoplanet that is probably not a mini-Neptune.

Ranks a glorious 17th in the Habitable Exoplanets Catalog, beaten by a bunch of mini-Neptunes that are considered more similar to Earth by its metric. Hmmmm.

Very strange is space between e and f planet,besides it is nearly certain planet is not tidally locked

I do not find the gap strange. There is a big gap in Kepler 62 for example.

What I find interesting is the mixture of super earths and earth like planets planets in this system.

http://www.cieletespace.fr/node/11676

The end :

« …The ideal would be for us to see slight changes in time in the specific time at which occur transits, said Franck Selsis. This way, we could measure the interactions between each of the planets and infer their masses. We also already have good reason to think that there is probably a sixth planet, between the fourth and the fifth. "But this must be observed with the Hubble space telescope. This instrument would even observe a simultaneous transit of several planets in the star, or even a mutual transit, a planet passing in front of another at the same time to the star! «A time request was made for the month of June....»

What's the orbital eccentricity?

Paper on arXiv

http://arxiv.org/abs/1404.4368

FORMATION, TIDAL EVOLUTION AND HABITABILITY OF THE KEPLER-186 SYSTEM

Maybe I'm just dumb...but I was under the impression that a habitable planet around red dwarfs would be so close, they would have to be tidally locked.

-M-

This planet is just outside the region where a planet would be tidally locked if I understand.

From the above-linked paper:

Given that the system is probably older than a few Gyr, simulations of tidal evolution show that the four inner planets of the system are in pseudo-synchronous rotation (respectively, Prot = ~4, ~7, ~13, ~22 and ~130 days) with very low obliquities (< 1 degree). However, in a few simulations the obliquity of Kepler-186d was excited to more than 10 degrees due to a brief but deep crossing of the 5:3 mean motion resonance between Kepler-186c and Kepler-186d. The competition between the excitation due to planet-planet gravitational interactions and tidal damping has the effect of stabilizing this relatively high obliquity on ~10 Myr timescales.

We also showed that given the uncertainties on the age of the star as well as the uncertainties on the composition and tidal dissipation, the rotation state of Kepler-186f is unconstrained. If the system is somewhat younger (1 Gyr old) or if the tidal dissipation of Kepler-186f is lower than that of Earth's, Kepler-186f could still be in the process of pseudo-synchronization and its obliquity could be high. However, if the system is about 4 Gyr old or the tidal dissipation of Kepler-186f is Earth-like, Kepler-186f would be pseudo-synchronized with a long rotation period (~130 days). The variety of spin states of Kepler-186f should then be investigated by exoplanet-climate modelers.

Bolmond & all, page 10 :

"...The age of Kepler-
186 is thought to be higher than a few Gyr, so assum-
ing an Earth dissipation, it would mean that Kepler-
186f should be in a pseudo-synchronous rotation state
with a small obliquity. However, the age of the system
is unconstrained. So if Kepler-186 is somewhat younger
(say 1 Gyr) or if the dissipation within planet f is in-
ecient4, then Kepler-186f should not have reached a
pseudo-synchronous state. In that case, although Kepler-
186f's spin rate would probably have slowed to within a
factor of a few of the pseudo-synchronous rate, its obliq-
uity would be unconstrained and could assume very high
values.."

edit : sorry Mongo !

Lazarus wrote:

Finally, a candidate habitable exoplanet that is probably not a mini-Neptune.

Ranks a glorious 17th in the Habitable Exoplanets Catalog, beaten by a bunch of mini-Neptunes that are considered more similar to Earth by its metric. Hmmmm.

Although to be fair, the radius/density diagram in Occurrence and core-envelope structure of 1--4x Earth-size planets around Sun-like stars indicates that the dividing line between "Super-Earths" and "Mini-Neptunes" appears to be at about 1.8 Earth radii -- below that radius, they all appear to be Earth-like in composition, while above that radius, they all appear to have massive atmospheric envelopes reducing their densities. Setting the upper radius limit at 1.8 times that of Earth, Kepler-186f currently sits at #9 on that list. If the upper limit is reduced to 1.6 times that of Earth for a margin of safety, it moves to #6 on the list.

Including the listed Kepler planet candidates drops Kepler-186f to #38 (no more than 1.8 Earth Radii) and #19 (no more than 1.6 Earth radii) on the respective lists.

The dividing line seems to be at 1.5 not at 1.8...

Stalker wrote:

The dividing line seems to be at 1.5 not at 1.8...

I was going by this diagram:



Which shows the transition happening somewhere between 1.7 and 1.8 Earth radii for confirmed transiting exoplanets.

Like the habitable zone, the rocky/gassy transition point is split into conservative and optimistic values. Dr. Marcy published that graph and he tends to favor more optimistic values for the transition point while more conservative studies have suggested 1.5 earth radii. In reality, the dividing line is the average found with confirmed planets. Kepler has found planets with large radii with high density (Kepler-20b), and with small radii but low density.

I would think it is safe to say that all the planets around Kepler 186 are rocky though.

what is the dark grey area?

I believe it represents a volatile rich planet (H2O, CO2, etc.) without a hydrogen/helium envelope.

It seems to start right at the 1.5 Earth radius point, so I assume that it marks the upper radius limit of the "definitely rocky with no massive atmosphere" planets. Although going by that diagram, the actual upper limit is somewhat greater. The lowest radius associated with a definite "mini-Neptune" by density appears to be 1.8 Earth radii, and the largest radius associated with a definite "Super-Earth" by density appears to be 1.7 Earth radii.

Of course this does not preclude a Venus-type atmosphere, which makes the surface of the planet quite uninhabitable by humans, but which is far from a Neptune-type atmosphere. But I suspect that Venus-type atmospheres owe more to that planet's insolation levels than to the planetary radius.

Lazarus wrote:

Finally, a candidate habitable exoplanet that is probably not a mini-Neptune.

Ranks a glorious 17th in the Habitable Exoplanets Catalog, beaten by a bunch of mini-Neptunes that are considered more similar to Earth by its metric. Hmmmm.

there one observation to be point out here: Planets found Radial velocity method we know the minimun Mass and not size,the real mass value in multiplanetary system probably is near of the minimum mass value for question of orbital stability,But Still we don't the size so the could be well mini-neptunes or Super-earth as we don't the size so we don't the density

Planets found by Kepler is most of them validate,so we know only size but not the mass,I think planets below the 1.5 size of earth are very likely to be rock worlds,we don't know the mass but we know by theoretical stability small planets in size like Kepler-186f can't hold a substantial atmosphere,because to be gas ball this planet need to be very low density and consequently very low mass and with a low mass naturally it have a low gravity and with low gravity it can't retain a dense atmosphere like a mini-neptune  

Example: the case of Kepler-138d  it's a planet with substantial mass 1 earth mass but with Big size 1,6 earth-size,and consequently low density it's is stable,it can hold a atmosphere  
but for Kepler-186f to be the same it's need to be very low mass,and with very low mass consequently it's low density,then it's is unstable can't hold a voluminous atmosphere  

And Here is where I think PHL made a mistake mix planet size and planet mass find by 2 different methods of planet detection transit and radial velocity

So I think Kepler-186f are in well better position that many of that other planets in the catalog

Daniel wrote:

And Here is where I think PHL made a mistake mix planet size and planet mass find by 2 different methods of planet detection transit and radial velocity

I don't understand your point. The only way to obtain planetary radius is via transits, and the only way to obtain planetary mass is by RV (or transit timing for some multi-planet systems). Both methods should be accurate, assuming that the mass  and radius of the host star are known to sufficient accuracy. If both methods are reasonably accurate, then the derived densities should be fairly accurate as well. The chart I posted earlier has error bars for each of the included exoplanets, which in each planet makes it clear whether or not a given plant has, or has not, a massive Neptune-style atmosphere. Every planet with a radius up to 1.7 Earth radii does not have a massive atmosphere, whereas every planet with a radius of at least 1.8 Earth radii does have a massive atmosphere.

the Point is you can't compare planet found by Radial velocity that we have only minimum mass, with planet validate by transit that we have just the planet size.

like PHL do,compare planets find by 2 distinct methods

I don't talk about planet fully constrain where you have the mass and size and then the density