Kepler and Exoplanet Detection

[the asinine cretin]

I don't know that much about it, but I was just imaging what might happen if Kepler were many light years away with Sol in its field of view. I imagine:

 

1. A very small probability that Venus and/or Earth could be detected via transit (considering their diameters and orbits and the chances of favorable orientation with far away Kepler spacecraft).

2. I may be wrong, but I suspect that Mercury and Mars may not be detectable by Kepler.

3. The planets in the outer solar system seem to be too distant from the sun to be detected by Kepler (guess based on what I know of the transmit method).

4. The many fascinating moons in the solar system would obviously go undetected (Galilean satellites, Titan, etc).

 

Again, I don't know the details on this and am only speculating. I wouldn't mind learning the details. If the above is true then the exoplanets Kepler has been able to detect may be a mere tip of the iceberg, no?

 

ETA: I mean, we might say "Kepler discovers Jupiter-sized world in orbit of such and such star," but the reality could be a solar system containing many other worlds and perhaps an array of super fascinating moons in orbit of that lone detected planet. My hunch: Detection of one planet does not rule out many more; failure to detect rules out nothing. Again, if Kepler were to include Sol in its field of view from some remote vantage point, what might it find?

Edited September 8, 2011 by Ceti Alpha V

[the asinine cretin]

THE EXOPLANET CENSUS: A GENERAL METHOD, APPLIED TO KEPLER

 

ABSTRACT

 

We develop a general method to fit the planetary distribution function (PLDF) to exoplanet survey data. This maximum likelihood method accommodates more than one planet per star and any number of planet or target star properties. Application to Kepler data relies on estimates of the efficiency of discovering transits around Solar type stars by Howard et al. (2011). These estimates are shown to agree with theoretical predictions for an ideal transit survey. Using announced Kepler planet candidates, we fit the PLDF as a joint powerlaw in planet radius, down to 0.5R⊕, and orbital period, up to 50 days. The estimated number of planets per star in this sample is ∼ 0.7 —1.4, where the broad range covers systematic uncertainties in the detection efficiency. To analyze trends in the PLDF we consider four planet samples, divided between shorter and longer periods at 7 days and between large and small radii at 3 R⊕. At longer periods, the size distribution of the small planets, with index α ≃ −1.2 ± 0.2 steepens to α ≃ −2.0 ± 0.2 for the larger planet sample. For shorter periods, the opposite is seen: smaller planets follow a steep powerlaw, α ≃ −1.9 ± 0.2 that is much shallower, α ≃ −0.7 ± 0.2 at large radii. The observed deficit of intermediate-sized planets at the shortest periods may arise from the evaporation and sublimation of Neptune and Saturn-like planets. If the trend and explanation hold, it would be spectacular observational confirmation of the core accretion and migration hypotheses, and allow refinement of these theories.

 

Here's a brief summary of the paper.

 

Astrobites: The Kepler Exoplanet Consensus

 

"Extrapolating the occurrence rate of small planets out to one year orbital periods, Youdin finds that the average solar-like star hosts ~3 Earth-like planets with orbital periods less than one year."

 

Damn.

[Airbrush]

Last gem I heard about Kepler was that it appears that small planets, such as Earth, are even more common than the gas giants.

 

"Again, I don't know the details on this and am only speculating. I wouldn't mind learning the details. If the above is true then the exoplanets Kepler has been able to detect may be a mere tip of the iceberg, no?"

 

You can extrapolate Kepler's findings by multiplying the numbers it detects by approx 200.

 

Kepler has a steady focus on an area of our galaxy thousands of light years away. No it does not watch anything inside our solar system.

Edited September 14, 2011 by Airbrush

[the asinine cretin]

Last gem I heard about Kepler was that it appears that small planets, such as Earth, are even more common than the gas giants.

Kepler has found very few gas giants compared to the number of Neptune-size and smaller worlds, but, my entire curiosity hear is with the parameters in which Kepler can detect. Can we really say that gas giants are less common? Maybe they tend to be outside of Kepler's range. For example, would our outer planets be detectable?

 

You can extrapolate Kepler's findings by multiplying the numbers it detects by approx 200.

How have you determined this? Do you have a source and or reasoning?

 

Kepler has a steady focus on an area of our galaxy thousands of light years away. No it does not watch anything inside our solar system.

I am familiar with the gist of the Kepler mission (including its field of view), and I wasn't asserting that Kepler watches our solar system, it was a hypothetical question. But thank you.

[insane_alien]

Kepler has found very few gas giants compared to the number of Neptune-size and smaller worlds, but, my entire curiosity hear is with the parameters in which Kepler can detect. Can we really say that gas giants are less common? Maybe they tend to be outside of Kepler's range. For example, would our outer planets be detectable?

 

kepler can indeed detect gas giants. and has.

 

only, its not really looking for gas giants and it has an easier time of detecting smaller plants if it looks at relatively close stars. in this region, the majority of the gas giants in existance have already been discovered so the chances of detecting a NEW gas giant are slim(not to say it won't happen however).

 

So there will be some bias in the results because of the simple fact that it isn't looking for them.

 

think of the first people looking for viruses, they probably detected a crap load of bacteria too but those bacteria were already known, it was only the viruses they cared about.

[the asinine cretin]

kepler can indeed detect gas giants. and has.

Has anyone suggested that they can't, and have not? Look at the text you're quoting from me. I don't say that Kepler hasn't detected gas giants, only that it has detected far more Neptune-sized and smaller worlds. This fact can be confirmed by going to the Kepler mission site or just glancing at the Kepler wikipedia article.

 

only, its not really looking for gas giants and it has an easier time of detecting smaller plants if it looks at relatively close stars. in this region, the majority of the gas giants in existance have already been discovered so the chances of detecting a NEW gas giant are slim(not to say it won't happen however). So there will be some bias in the results because of the simple fact that it isn't looking for them.

What makes you say that Kepler isn't looking for gas giants? The majority of gas giants in existence have already been discovered? When did this happen? My understanding of the transit method and the design of the Kepler spacecraft suggests that it is perfectly equipped to detect gas giants so long as their orbital period is favorable.

[Realitycheck]

Notably, only 5 of the 54 detected by Kepler (in the Goldilocks zone) appear to be in the size range for rocky planets ...

 

 

http://planetary.org/news/2011/0203_Kepler_Discoveries_Suggest_a_Galaxy.html

Edited September 15, 2011 by Realitycheck

[the asinine cretin]

This came out yesterday.

 

Of particular interest to planethunters.org, the Kepler team announced an astounding number of new planet candidates, and more than doubled the number of candidates in the habitable zone. The list of 1235 planet candidates announced in February has grown to 1781 with 121 now in the habitable zone. The number of earth-sized planet candidates increased by 95%!

News from Exteme Solar Systems II.

[Realitycheck]

And here is an easy to use catalog:

 

http://www.planetary.org/exoplanets/list.php

Edited September 15, 2011 by Realitycheck

[Airbrush]

How have you determined this [that you can extrapolate by multiplying by about 200]? Do you have a source and or reasoning?

 

"...The probability of a random planetary orbit being along the line-of-sight to a star is the diameter of the star divided by the diameter of the orbit. For an Earth-like planet at 1 AU transiting a Sol-like star the probability is 0.465%, or about 1 in 215."

 

In Wikipedia look under "Objectives and Methods" at about the middle paragraph.

 

http://en.wikipedia.org/wiki/Kepler_mission

 

So if we see an Earth-like planet at 1 AU transiting a Sol-like star, that means there are probably about 215 of those. For every transit we can see means the orbital plane of that solar system is aligned, by chance, with us, and probably 214 others are not aligned with us.

Edited September 15, 2011 by Airbrush

[the asinine cretin]

"...The probability of a random planetary orbit being along the line-of-sight to a star is the diameter of the star divided by the diameter of the orbit. For an Earth-like planet at 1 AU transiting a Sol-like star the probability is 0.465%, or about 1 in 215."

 

In Wikipedia look under "Objectives and Methods" at about the middle paragraph.

 

http://en.wikipedia..../Kepler_mission

 

So if we see an Earth-like planet at 1 AU transiting a Sol-like star, that means there are probably about 215 of those. For every transit we can see means the orbital plane of that solar system is aligned, by chance, with us, and probably 214 others are not aligned with us.

I'm familiar with the wiki article and I don't agree that it supports your earlier statement.

 

"You can extrapolate Kepler's findings by multiplying the numbers it detects by approx 200."

 

The orientation of the planetary orbit is just one criterion of detectability. I was hoping someone on this forum knew more about Kepler than I do. Oh well.

Edited September 16, 2011 by Ceti Alpha V

[Airbrush]

I'm familiar with the wiki article and I don't agree that it supports your earlier statement.

 

You can extrapolate Kepler's findings by multiplying the numbers it detects by approx 200

 

Why don't you agree? The Wiki article said to the effect that for every transit detected, probably there are approximately 215 similar solar systems among that population of stars, but they are aligned so we cannot see transits. There may be more or less, and I would like to hear a plus or minus number, but that is besides the point. I stated "approx 200" because I didn't know exactly. Is approx 200 so far off from 215? Do you disagree with the Wiki article?

Edited September 18, 2011 by Airbrush

[the asinine cretin]

Why don't you agree? The Wiki article said to the effect that for every transit detected, probably there are approximately 215 similar solar systems among that population of stars, but they are aligned so we cannot see transits. There may be more or less, and I would like to hear a plus or minus number, but that is besides the point. I stated "approx 200" because I didn't know exactly. Is approx 200 so far off from 215? Do you disagree with the Wiki article?

Very briefly,

 

1. If you look at my original post you will see that I alluded to solar system orientation (it's my first numbered item). The entire purpose of this thread was to consider ALL of the major factors related to detectability, orientation probabilities alone are not enough.

2. I don't agree with your interpretation of the wiki article. It describes the orientation factor as a simple geometry problem, but that doesn't lead one to make the kind of extrapolation you're suggesting.

3. Again, I'm familiar with the wikipedia article and the gist of Kepler and I made this thread hoping to interact with experts or pseudo-experts (I know, a tall order).

4. The following video is a decent (though introductory) talk followed by an absolutely phenomenal Q&A which has addressed most of my questions so this thread is now obsolete from my standpoint. I highly recommend this video.

 

 

 

Regards.

Edited September 20, 2011 by Ceti Alpha V

[Airbrush]

"2. I don't agree with your interpretation of the wiki article. It describes the orientation factor as a simple geometry problem, but that doesn't lead one to make the kind of extrapolation you're suggesting."

 

Thanks for the Youtube about Kepler. I hope to watch that when I have time. Then maybe I can ask you an intelligent question and find out exactly what I'm missing. If anyone else knows what Ceti Alpha V means by his point #2 above please help. There is a misunderstanding here.

 

"3. The planets in the outer solar system seem to be too distant from the sun to be detected by Kepler (guess based on what I know of the transmit method)."

 

Yes, the outer gas giants have long orbits, so it would take decades to see an outer gas giant make a single transit. Terrestrial planets, especially around smaller stars, will be easier to find because they have more frequent transits. And scientists are more interested in the smaller Earth-sized planets in the Goldilocks Zone.

Edited September 22, 2011 by Airbrush

[the asinine cretin]

Thanks for the Youtube about Kepler. I hope to watch that when I have time. Then maybe I can ask you an intelligent question and find out exactly what I'm missing. If anyone else knows what Ceti Alpha V means by his point #2 above please help. There is a misunderstanding here.

I'll try to explain, I think there is a misunderstanding too. I'm referring to this:

 

"You can extrapolate Kepler's findings by multiplying the numbers it detects by approx 200."

In my understanding there are many more factors to take into account and it is too preliminary to make such a general extrapolation at all. Further, the wiki article isn't saying, "For an Earth-like planet at 1 AU transiting a Sol-like star the probability is 0.465%," therefore, it is appropriate use this figure to make a general extrapolation about all stars and possible planets.

[Airbrush]

After seeing the wonderful 1.5 hour Kepler talk (see above) by Geoffe Marci, I want to thank Ceti Alpha V for posting it. Very good talk. The first 10 minutes you can skip, but after that the talk and fabulous question and answer following should not be missed.

 

Regarding the question of transits we can see because by chance the star system is aligned with Keplers view, he said they can extrapolate to about 30% of all the 150,000 stars in Kepler's view are now known to probably have planets. They have already detected about 1,250 planetary systems, out of 150,000 stars, and that is a little less than 1% of the total number of stars in Kepler's field of vision. Although Kepler has been watching for about 2 years, the data so far analyzed is from about the first 6 months of watching since there is so much data to analyze which takes time. In several more years they will probably detect far more of the longer period Earth-sized planets in habbitable zones of larger and larger stars. Since most stars are smaller than our Sun, the habbitable zone of most stars will be closer to the star, and therefore we would see their shorter periods within the next year or two.

Edited September 30, 2011 by Airbrush

[the asinine cretin]

Awesome! I'm glad you liked it. I was pretty stoked to find that. Actually, if you dig space I recommend subscribing to that SETI channel; their talks are great.