Kepler-9: TTVs with two Saturns and a hot Super Earth

tesh90 wrote:

Also, wrt this being not disappointing, isn't this first case of TTVs?

That's right!

Another thing, note that the equilibrium temperatures for b and c are 750 K and 540 K respectively. These aren't what you think of when the term 'hot Jupiter' gets thrown around.

deep blue clearified jovian?

I think so.

From the impact parameters for b and c, I calculate inclinations of ~88.63° and ~89.07°, respectively. So the two planets have a mutual inclination of > ~0.4°

The EPE has updated its Kepler-9 parameters, and inclues what appears to be a 'best guess' to the mass of Kepler-9 d.
http://exoplanet.eu/star.php?st=Kepler-9#a_publi

Though still unconfirmed. A 7 Me planet with 1.68 Earth radii would result a density of 8.65 g/cc. An Iron planet??

If you use the mass-radius relationships given in this paper (note that the entries in table 4 for Earth-like and Mercury-like compositions are interchanged), the predicted radius for a 7 Earth masses planet with a composition similar to Earth comes out as 1.67 Earth radii.

As for using this to infer the planet's makeup, sorry but no. There is no mass measurement, the estimate is based on what they put into the model. You learn something about the assumptions that were put in to derive the mass estimate, but you don't get any information about the planet.

Lazarus wrote:

As for using this to infer the planet's makeup, sorry but no. There is no mass measurement, the estimate is based on what they put into the model. You learn something about the assumptions that were put in to derive the mass estimate, but you don't get any information about the planet.

I'm not sure I understand. Are you saying the quoted mass for Kepler-9 d is an estimate from its radius?

Sirius_Alpha wrote:

I'm not sure I understand. Are you saying the quoted mass for Kepler-9 d is an estimate from its radius?

Yes, precisely. The system has not been extensively studied via radial velocity measurements, the referenced paper says there are only 6 observations. This is enough to get decent mass estimates for the resonant giant planets, for which TTVs provide additional constraints, but no way are you going to be able to get any handle on KOI-377.03 with that.

Okay, I understand now, thanks
I was under the impression that the mass of KOI-377.03 was guessed at from TTVs.

http://exoplanet.eu/star.php?st=Kepler-9#a_publi
This link shows the measurement error of the outer planets in +/- 3 Earth masses. And this is for a period of 20 and 40 days. Why, then, can not determine the mass of the planet with a period of only 1.5 days? In general, the shorter the period -> the higher ratio signal to noise.

There's only six RV measurements and transit timing variations to go along with that. As far as I know, there's no transit timing variations yet detected that come from d.

And anybody know what error (meters per second) measurements of these six measurements of the radial velocity?

The 2:1 resonance between planets b and c means the system evolves rapidly, so the TTVs are detectable even within the short timespan of the Kepler measurements, so you can get estimates of the masses from modelling the 3-body problem (star+2 planets). The third planet (if it exists) is not resonant, the evolution of its orbit is slower. This means you have to get RVs to measure the planet's orbit, and since there are five RV parameters per planet, plus the RV offset for the system, and you have to fit the two giant planets as well, six RV measurements are clearly inadequate.

Latest update.

Quote :

Science team members are preparing to announce the mission’s latest discovery in early November. Additionally, the science team is expected to validate the Kepler 9d planet in the near future.

From Twitter.
"Lissauer (and previous speakers): Third planet, Kepler 9d, confirmed in system with transit timing variations. Asterisk removed."

Nice. Who needs to discover a double-transit system when you can discover a triple-transit system?

Links to the twitter feed? And is anyone aware of anyone blogging from this conference?

I am not well versed with twitter... this is the means through which I've been getting info.

http://search.twitter.com/search?q=%23dps2010

Interestingly mass determined?

http://www.cfa.harvard.edu/news/2010/su201037.html

Quote :

The quest for other earths is making good progress, however. Writing in the latest issue of the journal Science, a team of twelve CfA astronomers led by Matt Holman, together with a large group of colleagues, report using Kepler to discover an earth-sized extrasolar planet. They carefully analyzed the orbital motions of two Saturn-sized extrasolar planets in the system known as Kepler-9, and found that by meticulously accounting for their motions they could subtract their effects to hunt for even smaller dips, as small as 0.02% in stellar intensity. They report finding a planet whose size is only about 1.5 earth-radii, making it one of the smallest extrasolar planets known. This planet orbits the star (its "year") in only 1.5924 days, however, and so it is very close to its star, hot, and thoroughly unearth-like. Nevertheless it represents a major step forward in the search for small planets. Unlike other recent discoveries (like that of a planet in its habitable, "Goldilocks," zone but considerably larger than the Earth), this new planet is small enough to raise expectations and the excitement for soon discovering extrasolar earths.

I don't see anything in that paragraph relating to the mass of the planet.

Kepler-9 d listed between Confirmed planets (though without any precise mass estimate yet)

http://exoplanet.eu/star.php?st=Kepler-9

Preprint:

http://exoplanet.eu/papers/Kepler-9-d.pdf

A couple new papers on Kepler-9, the latter of the two finding the system is well-aligned with the stellar equator.

Transiting Exoplanet Monitoring Project (TEMP). III. On the Relocation of the Kepler-9~b Transit
https://arxiv.org/abs/1712.06297

Stellar Spin-Orbit Alignment for Kepler-9, a Multi-transiting Planetary system with Two Outer Planets Near 2:1 Resonance
https://arxiv.org/abs/1712.06409

Kepler Object of Interest Network II. Photodynamical modelling of Kepler-9 over 8 years of transit observations
https://arxiv.org/abs/1807.00007

Quote :

The Kepler Object of Interest Network (KOINet) is a multi-site network of telescopes around the globe organised to follow up transiting planet candidate KOIs with large transit timing variations (TTVs). Its main goal is to complete their TTV curves, as the Kepler telescope no longer observes the original Kepler field. Combining Kepler and new ground-based transit data we improve the modelling of these systems. To this end, we have developed a photodynamical model, and we demonstrate its performance using the Kepler-9 system as an example. Our comprehensive analysis combines the numerical integration of the system's dynamics over the time span of the observations along with the transit light curve model. This model is coupled with a Markov chain Monte Carlo algorithm, allowing the exploration of the model parameter space. Applied to the Kepler-9 long cadence data, short cadence data and 13 new transit observations collected by KOINet between the years 2014 to 2017, our modelling provides well constrained predictions for the next transits and the system's parameters. We have determined the densities of the planets Kepler-9b and 9c to the very precise values of rho_b = 0.439 +/-0.023 g/cm3 and rho_c = 0.322 +/- 0.017 g/cm3. Our analysis reveals that Kepler-9c will stop transiting in about 30 years. This results from strong dynamical interactions between Kepler-9b and 9c, near 2:1 resonance, that leads to a periodic change in inclination. Over the next 30 years the inclination of Kepler-9c (-9b) will decrease (increase) slowly. This should be measurable by a substantial decrease (increase) in the transit duration, in as soon as a few years' time. Observations that contradict this prediction might indicate the presence of additional objects. If this prediction proves true, this behaviour opens up a unique chance to scan the different latitudes of a star.

Lower masses for the planets, and reconciling RV + TTV measurements.

HARPS-N radial velocities confirm the low densities of the Kepler-9 planets
https://arxiv.org/abs/1901.05471

Quote :

We investigated the discrepancy between planetary mass determination using the transit timing variations (TTVs) and radial velocities (RVs), by analysing the multi-planet system Kepler-9. Despite being the first system characterised with TTVs, there are several discrepant solutions in the literature, with those reporting lower planetary densities being apparently in disagreement with high-precision RV observations. To resolve this, we gathered HARPS-N RVs at epochs that maximised the difference between the predicted RV curves from discrepant solutions in the literature. We also re-analysed the full Kepler data-set and performed a dynamical fit, within a Bayesian framework, using the newly derived central and duration times of the transits. We compared these results with the RV data and found that our solution better describes the RV observations, despite the masses of the planets being nearly half that presented in the discovery paper. We therefore confirm that the TTV method can provide mass determinations that agree with those determined using high-precision RVs. The low densities of the planets place them in the scarcely populated region of the super-Neptunes / inflated sub-Saturns in the mass-radius diagram.