Kepler Mission Options

[scalbers]

"706 targets from this first data set have viable exoplanet candidates with sizes as small as that of the Earth..." Hot earths, to be sure, but this is a stunning validation of the mission already!

It seems the size distribution they show has a cutoff around twice the Earth radius (in figure 2). Does this imply that the 400 stars/planets to be released later will be mostly around the size of the Earth?

[Hungry4info]

Well those 400 candidates orbit brighter stars, too. So we can expect that the 400 may be on average smaller than the ones we were just given. I expect some of the undisclosed candidates to be larger planets.

They seem to have just given out all the hard ones to confirm to the public, while keeping the easier ones to confirm, or really interesting ones, to themself.

[scalbers]

True, thought the cutoff in figure 2 is very sharp. There is a maximum of planets between 2-3, and 3-4 Earth radii, then virtually none from 1-2. This seems maybe more than a simple observational bias.

[nprev]

...virtually none from 1-2. This seems maybe more than a simple observational bias.

...uh-huh.

[Drkskywxlt]

True, thought the cutoff in figure 2 is very sharp. There is a maximum of planets between 2-3, and 3-4 Earth radii, then virtually none from 1-2. This seems maybe more than a simple observational bias.

The article says that they didn't release stars with any possible planet smaller than 1.5 Earth-radii. However, the frequency of possible planets continues to increase right up until that cutoff.

[Syrinx]

Previously I had thought the data released last week contained candidates which had been "confirmed" with a minimum of three transits. Thus, I was expecting more long-period candidates to be announced as the years roll by.

But I read this in the "Characteristics..." paper (linked earlier) when describing the candidate vetting process:

At least three transits must be observed. This test confirms the orbital period and avoids
confusion for the circumstance when two planets of similar size are detected. (For
completeness of the released candidate list we included candidates with a single transit
event.)

So it seems like the 706 number might be close to final.

[Habitable Zoner]

Previously I had thought the data released last week contained candidates which had been "confirmed" with a minimum of three transits. Thus, I was expecting more long-period candidates to be announced as the years roll by.

But I read this in the "Characteristics..." paper (linked earlier) when describing the candidate vetting process:

So it seems like the 706 number might be close to final.

Well, those were single transits observed during a six-week period, right? Only something like one-eighth of all planets in earth-like orbits would have been observed even once during that period.

Also, let's not forget the missing 400. I doubt if they're reserving a bunch of boring candidates...

[Syrinx]

I think you're correct. The paper does say:

[...] only 33.5 days of data are available for most candidates discussed herein.

- The appendix shows most candidates with periods of 53 days and lower. I'm guessing these went through the ordinary vetting process, but aren't all that interesting (hah!) and so were released.
- There are a few with periods up to 200 days. It would be difficult to verify a period of 200 days with barely 400 days of observations. These might have been fast-tracked through the vetting process and perhaps the FOP as well, but for whatever reason fell out of favor and were released.
- One has a period of 10389 days, which must be a typo. Probably 10.389.
- What's interesting is the appendix contains period data for 311 candidates. Forgetting for a moment that 400 + 311 > 706, how can they have period data with just a single transit?

At any rate, it seems that the data from days 33.5 to 365+ have yet to be vetted or followed up. They were not part of the paper to any significant degree.

Hopefully we should expect future announcements with ever-increasing-period candidates. The Kepler team must hate us. We beg and beg for data, they give us data for 156000 stars and 306 candidate planets, and we're already asking when the next data will arrive.

[Byran]

- One has a period of 10389 days, which must be a typo. Probably 10.389.

Not a misprint.

http://archive.stsci.edu/kepler/data_search/search.php
Kepler ID 11465813

Available photometry for 7 months. Single transit (circle) is observed in July 2009.

[Byran]

Transit close. Its duration is greater than 2 days.

In addition, is visible the asymmetry transit. This is probably evidence of orbits with large eccentricity of the orbit.

[Mongo]

My guess is that the 10389 day period was made under the assumption that the transiting planet was in a circular orbit, which would result in an orbital motion slow enough to explain the lengthy transit time.

But I think it is considerably more likely that we are instead looking at a highly eccentric body like HD 80606 b (e = 0.921, p = 111.436 days) seen transiting its primary near apoapsis, and hence moving so slowly that its transit signal resembles that of a much more distant low eccentricity planet.

[Hungry4info]

That transit is highly symmetric. Fold it over itself and you will see this.

Attached thumbnail(s)

 

[djellison]

Neptune's orbit is 60,190 days. Uranus, 30,800. That Kepler would find an object >10,000 days is neither surprising nor unusual.

[Hungry4info]

It isn't surprising that such a planet exists, I'll agree with that.

But it it actually a nice surprise for Kepler to find one as fast as it did. Recall that Kepler detects planets by observing them transit across the stellar disk. For this to happen, their orbits have to be orientated in a certain way for such transits to occur.

For your typical hot Jupiter, there's a ~10% chance of it transiting, assuming a randomly oriented orbit. That number drops steeply with increasing semi-major axis.
If we assume a circular orbit, then the probability of a planet transiting is given by (R_p + R_star) / a, where a is the semi-major axis of the planet.

For a 1 solar-mass star, ~10,000 days corresponds to a transit probability of 0.000541351523
Out of 150,000 stars, if we assume every one has a planet like this, 81 should transit.

But Kepler has been observing for 43 days, that's 0.43% of the orbital period. So out of these 81 planets, Kepler should have observed 0.3483

So the odds of such a planet having been found in the first 43 days of data were around 34% (again, under the assumption that all of them have a planet at 10,000 d).

Sure, the candidate is a G-type giant, but considering the overwhelming prevalance of non-giant stars, I don't belive this significantly affects the probability of detecting such a planet.

[tasp]

Another way to get a 10,000+ day object so quickly in the search is that there are many more such objects than we suppose.

There are, after all, far more 'hot Jupiters' than might have been expected 20 yeas ago, maybe 'cold Neptunes' are a dime a dozen.



{wink}