New planets around GJ 436

http://www.sciencedaily.com/releases/2012/07/120718114944.htm Revolve around gj 436 so c and maybe d.These objects are candidates only

Detected by Spitzer, UCF-1.01 could be as small as 2/3 of Earth's diameter. The orbital period is 1.4 days. No further information on UCF-1.02.

A sub-Earth planet at 1.4-days? Especially given the eccentricity of the orbit of GJ 436b (itself in a 2.6-day orbit) that's quite a surprise. Wonder whether transit timing variations will be useful in determining the mass.

Any info on UCF-1.02, beyond its existence (e.g. orbital period)?

(Incidentally I do like the numeric system for the unconfirmed candidates, would have saved quite a bit of a mess with certain systems, e.g. Mu Arae)

Could be merged with gj 435.I wondered about it is well lazarus but big difference in mass could be problem for ttv.Third planet candidate seems to have longer period than gj 436 b

I found both candidates are 2/3 earth radii.First is 0.0185 AU from host

The Spitzer press release is painfully lacking in exact numbers.

Thanks for the link. The preprint will be available in arXiv.org, good.

I guess neither of these are good candidates for maintaining the eccentricity of Gliese 436b. Hmmmm.

Here's the preprint.
http://arxiv.org/abs/1207.4245

If you can rule out a false positive as the source of transits, you can probably constrain the mass to the planetary regime through dynamical arguments alone. It must be less than some value to avoid imprinting significant TTVs onto the b planet.

This is not the first time a possible sub-Earth-sized planet has reported around GJ 436.

Edit: Changed the title of the thread to list the star name instead of the planet name.

Ah, so there are only two transits observed for candidate 02. Interval is about 151.5 days, so presumably the orbital period is going to be around 151.5/N, where N is the number of orbits that took place. (Obviously if the planet is undergoing TTV then things may change a bit).

Great find. Is there any chance that, despite its small aperture, a long continuous stare by MOST could provide an indipendent confirmation at least of candidate 01? GJ 436 is not as bright as 55 Cancri, but the SNR should quickly rise up as transits pile up.

I don't think the planet (or the star) are bright enough for MOST. The task is much easier for Spitzer since the contrast between the star and the planet is much smaller in infrared.

Talk about nearby Red Dwarf transit small that earth size planets

In my opinion I think that ELEKTRA mission would be Ideal to Detect Rock Planets around our nearby cool Red dwarf stars (and many Brown Dwarfs) in the Habitable Zone

http://nexsci.caltech.edu/conferences/Flagstaff/posters/missions.05_beichman.pdf

http://nexsci.caltech.edu/conferences/Flagstaff/posters.shtml

I don't know Why this so interesting mission has been forgotten... I can't find anything more about this interesting project.

With news candidates and Red Dwarf HZ small Planets seens common ( http://www.eso.org/public/news/eso1214/ ) will be a good time to fund the ELEKTRA mission

The planet candidate ucf 1.02 can not be too far from host star because of short transit duration.I counted considering the duration of transit this candidate that ucf 1.02 is between 0.035-0.038 AU.Possible 4:5 resonance with gliese 436b

Did you consider that the short transit duration could be a result of a high impact parameter?

Ups I did mistake ,forgot. Planet can cross close to edge of star disc(the farthest from central point of star disc hardly transiting) with long ingress and egress times .There is no data about impact parameter in released paper you are right

I wonder what kind of constraints can be obtained from the shape of the transit and considering the limb darkening of the star.

Ingress /egress of ucf 1.01 is 0.025 and ucf 1.02 is 0.06 any sugestion?

Their fit had an ingress/egress duration of "< 0.1" hr, with the actual transit duration being 1.04^+0.26_-0.15 hr. I think the data is clearly too noisy to take a shot at estimating the impact parameter. The best you can do is set some constraints where you assume the highest and lowest reasonable impact parameters and transit duration. e.g. calculate the orbital period for a planet with a 1.3 hr transit and an ingress of 0.09 hr for the slowest orbital velocity (and thus longest period), and the minimum value for the period would be derived from the case of a 0.78 hr transit with an impact parameter of b = 0 for the fastest orbital velocity and shortest period.

jyril wrote:

I don't think the planet (or the star) are bright enough for MOST. The task is much easier for Spitzer since the contrast between the star and the planet is much smaller in infrared.

On the other hand, MOST was used to rule out transits of Gliese 581 c. Gliese 436 is at V=10.59, as compared to V=10.61 for Gliese 581, so maybe there is a chance that MOST can be useful though the transit depth might be pushing things a bit.

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Today's arXiv brings us this paper looking to explain Gliese 436b's eccentricity using Kozai migration - I guess the existence of UCF-1.01 would be problematic for this scenario. Looks like this was written before the UCF-1.01 paper was made public as there is no reference to it.

A global analysis of Spitzer and new HARPS data confirms the loneliness and metal-richness of GJ 436 b
http://arxiv.org/abs/1409.4038

Quote :

Context. GJ 436b is one of the few transiting warm Neptunes for which a detailed characterisation of the atmosphere is possible, whereas its non-negligible orbital eccentricity calls for further investigation. Independent analyses of several individual datasets obtained with Spitzer have led to contradicting results attributed to the different techniques used to treat the instrumental effects. Aims. We aim at investigating these previous controversial results and developing our knowledge of the system based on the full Spitzer photometry dataset combined with new Doppler measurements obtained with the HARPS spectrograph. We also want to search for additional planets. Methods. We optimise aperture photometry techniques and the photometric deconvolution algorithm DECPHOT to improve the data reduction of the Spitzer photometry spanning wavelengths from 3-24 {\mu}m. Adding the high precision HARPS radial velocity data, we undertake a Bayesian global analysis of the system considering both instrumental and stellar effects on the flux variation. Results. We present a refined radius estimate of RP=4.10 +/- 0.16 R_Earth, mass MP=25.4 +/- 2.1 M_Earth and eccentricity e= 0.162 +/- 0.004 for GJ 436b. Our measured transit depths remain constant in time and wavelength, in disagreement with the results of previous studies. In addition, we find that the post-occultation flare-like structure at 3.6 {\mu}m that led to divergent results on the occultation depth measurement is spurious. We obtain occultation depths at 3.6, 5.8, and 8.0 {\mu}m that are shallower than in previous works, in particular at 3.6 {\mu}m. However, these depths still appear consistent with a metal-rich atmosphere depleted in methane and enhanced in CO/CO2, although perhaps less than previously thought. We find no evidence for a potential planetary companion, stellar activity, nor for a stellar spin-orbit misalignment. [ABRIDGED]

They see no evidence of transits of additional sub-Earth-sized planets that have been reported earlier.

They have too low masses for RV and period is not determined due not enough transits events

Another transit-based non-detection, this time with HST.

A Hubble Space Telescope Search for a Sub-Earth-Sized Exoplanet in the GJ 436 System
http://arxiv.org/abs/1410.0002

Both papers are rather damning. I think it's reasonable to chalk up both candidates as noise, though rather convincing noise.