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Kepler Mission
nprev
post Jul 25 2010, 06:19 AM
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I think that the real danger here is the potential negative impact on public perception of Kepler & by extension extrasolar planet research as a whole. Interested amateurs like ourselves know the score, of course, but we've very much in the minority. The general public's been bombarded by SF visions for decades, and dashing incorrectly elevated hopes just doesn't ever end well.


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Byran
post Jul 25 2010, 07:26 AM
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QUOTE
Isn't an earth-sized blink of a transiting planet much smaller than an eclipsing binary? If the dip in light is that small, are the other reasons for it?


White dwarfs is the size of the Earth.

QUOTE (brellis @ Jul 25 2010, 10:16 AM) *
Oh, "background eclipsing binaries"... how does that create a dip that resembles an earth-sized planet? Another mystery to plague my tiny, earth-sized, amateur brain! huh.gif


http://arxiv.org/abs/1006.5030
The difference can reach up to 10 magnitudes. Ie if a candidate in the Earth-like planet brightness of 12 magnitude, then the background eclipsing 22 magnitude. But in the near infrared band difference fortunately falls to 6 magnitudes.



So Spitzer Space Telescope will observe the transit in the near infrared.

http://nexsci.caltech.edu/workshop/2009/Fo...warmspitzer.pdf

QUOTE
Goal 2:
Transit photometry of candidate terrestrial planets to reject blends of eclipsing binaries.
– Confirm planetary nature of candidate by color‐invariance of transit depth.
Study 40 candidates at 4.5 μm (one 10 hour transit) for a total of 400 hours


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remcook
post Jul 25 2010, 10:11 AM
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I'm confused by that last slide+quote. An atmosphere will give you a transit depth that is dependent on colour. Why should the transit depth be colour-invariant??

edit- I guess the differences aren't as big as in the above example....
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Hungry4info
post Jul 25 2010, 01:10 PM
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QUOTE (brellis @ Jul 24 2010, 10:46 PM) *
Oh, "background eclipsing binaries"... how does that create a dip that resembles an earth-sized planet? Another mystery to plague my tiny, earth-sized, amateur brain! huh.gif


Imagine a star with a background eclipsing binary. You can't resolve any components, but you have a light curve that is comprised of the total luminosity of the three stars. The eclipsing binary will make regular transit-like signals in your data. Alone these transits would be to deep to resemble a planet (unless it was a grazing transit), but with the third, unrelated foreground star, the transit signals get washed out. The result is that the transits have a depth that resembles a planet transit.


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Syrinx
post Jul 25 2010, 06:32 PM
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QUOTE (nprev @ Jul 24 2010, 08:32 PM) *
Woof. They need to get rid of the term 'Earth-like' immediately & replace it with 'small & rocky', or at the very least 'Earth-sized'.

This could spin right into an unprecedented PR fiasco all too quickly.

Agreed. I will note that in the lectures I've attended, the team has been very careful to not use "Earth-like."

With much help from others on this forum, I wrote this post last year:

http://www.unmannedspaceflight.com/index.p...st&p=149307

in hopes we could avoid the ambiguity.
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brellis
post Jul 25 2010, 06:55 PM
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Thanks, Byran and H4i.

Regarding an eclipsing white dwarf, it would have significantly more mass than a small rocky Earth-sized planet, so it would create a substantially greater wobble. The perturbations caused by background binaries seem more likely to be the culprits in a false-positive planet signature. It's gonna be fun finding out!
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Hungry4info
post Jul 25 2010, 09:30 PM
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Indeed. And, for the case of an transiting white dwarf, the deep secondary tarnsit (where the white dwarf passes behind the star) should be a dead giveaway about a non-planetary nature.

Kepler examples include KOI-74 and KOI-81.


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PDP8E
post Jul 25 2010, 11:49 PM
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Spaceref has a good article on the Kepler data being over reported by news orgs....
http://www.spaceref.com/news/viewnews.html?id=1415


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Greg Hullender
post Jul 26 2010, 04:33 PM
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With regard to the frequency of Earth-diameter objects vs. Neptune or Jupiter-diameter ones, I think we need to keep in mind that this mostly applies to inner orbits. I'm happy to learn (if I'm interpreting this correctly) that "hot Jupiters" are relatively rare. I'd like to believe that most solar systems are more or less like ours, with warm terrestial planets near the star and cold jovian planets further out.

Kepler won't see many of the planets further out. Its methodology is unavoidably doubly biased towards inner planets: from geometry, inner planets are more likely to have transiting orbits in the first place, and from time limits, inner planets are more likely to transit during the lifetime of the mission. (Although big planets only have to transit once, while smaller ones need to do it three times, the example of our own solar system suggests that this doesn't help a whole lot.) So the evidence doesn't really show that small rocky planets are more common than gas/ice giants. It only suggests that this is true in the regions close to stars.

Still, this is exciting new info. Not as exciting as what the Mail claims, but still pretty cool. It makes me think that, with luck, by the end of the summer, Kepler will announce the first "Hot Earths."

--Greg
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Stu
post Jul 26 2010, 05:01 PM
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Oh please, PLEASE don't encourage them to use the term "Hot Earth"; such a planet would be nothing remotely like Earth in anything other than size. People reading or hearing the term "Hot Earth" will just think of a cuddly, Earth-sized jungle planet, or a rainforest planet inhabited by Ewoks. Seriously, I shudder at the very thought of that. sad.gif


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Hungry4info
post Jul 26 2010, 05:19 PM
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Jupiter is the prototypical gas giant. A Jupiter-like planet is one where the majority of the mass is gaseous.
Neptune is the prototypical ice giant. A Neptune-like planet is one where the majority of mass is in ices.
Earth is the prototypical terrestrial planet. An Earth-like planet is one where the majority of mass is in solids.

There's a significant difference between habitable and Earth-like. Venus is an Earth-like planet, but it is not habitable. The atmosphere of a terrestrial planet comprises such a tiny, insignificant fraction of the planet that I don't think it reasonable to distinguish them based on it.

QUOTE ("Greg Hullender")
I'm happy to learn (if I'm interpreting this correctly) that "hot Jupiters" are relatively rare.

You're correct. And, this isn't a new development. Radial velocity surveys find that 0.8% of sun-like stars host hot Jupiters. Thus, the idea that hot Jupiters were rare pre-dates the Kepler mission.


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Stu
post Jul 26 2010, 05:29 PM
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I too worry that the Kepler team's task of Outreaching and press-communicating the whole "Earth-like" tag is going to be walking across a minefield covered in eggshells. Most members here read "Earth-like" and think in terms of mass, orbit, etc. Your average person "out there" will reada press story announcing the discovery of an "Earth like" world and will think of a planet with crystal blue skies, roaring oceans and fluffy kittens stretching in their sleep in butterfly-filled meadows...


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Hungry4info
post Jul 26 2010, 05:36 PM
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QUOTE (Stu @ Jul 26 2010, 11:29 AM) *
...and will think of a planet with crystal blue skies, roaring oceans and fluffy kittens stretching in their sleep in butterfly-filled meadows...


Haha that is true. Maybe some education should go along with the outreach.

"Kepler has found [x] Earth-like planets, that is, planets with radii similar to Earth, ..."

I'm sure when the average person thinks "Jupiter-like," they understand the planet doesn't necessarily have a GRS. Education + outreach could perhaps extend this understanding to Earth-like planets.


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Stu
post Jul 26 2010, 05:39 PM
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I'd drop "Earth-like" and go straight for the does-what-it-says-on-the-tin "Earth-sized". Saying anything is "like" something else instantly suggests to people the two are EXACTLY alike. I hope the Kepler team avoid using "Earth-like" full-stop. That term should be kept until we find a world that truly is "Earth-like", i.e. in terms of size, orbit, and habitability.


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hendric
post Jul 26 2010, 06:24 PM
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QUOTE (Stu @ Jul 26 2010, 11:01 AM) *
Oh please, PLEASE don't encourage them to use the term "Hot Earth"...


I hereby trademark "Lava Earth"! Any and all usage will cost $.01 payable to UMSF as a donation. smile.gif


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