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Kepler Mission
ugordan
post Nov 3 2009, 03:01 PM
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http://blogs.discovery.com/space_disco/200...until-2011.html

QUOTE
"There is a mistake in the Nature article. The Kepler Mission is actually doing very well and is producing planet discoveries that will be announced early next year. Data from 3 of the 84 channels that have more noise than the others will be corrected or the data flagged to avoid being mixed in with the low noise data prior to the time an Earth twin could be discovered." --William Borucki, Kepler Science Principal Investigator


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Greg Hullender
post Nov 3 2009, 04:36 PM
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It would help a lot if we knew what they mean by 84 "channels". Are the data transmitted back at 84 different frequencies? If so, how are the results divided among them? Obviously not by position on the CCD.

This is probably written up somewhere, but my first shot at finding it came up dry.

--Greg
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Hungry4info
post Nov 3 2009, 04:52 PM
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This article describes the channels in detail (in Russian)
http://infox.ru/science/universe/2009/11/0...netsearch.phtml

TheoA on the exoplanet forum said that that
QUOTE
The present algorithm adjusts the photon count received by comparing the light from one star to all the others.
The essential concept behind differential photometry.

So its the light from all 100% of the data that is being compromised 3.84% before being sent to Earth.


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-- Hungry4info (Sirius_Alpha)
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djellison
post Nov 3 2009, 04:52 PM
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There are 24 CCD's - each with two 'havles. Each half with two channels

http://kepler.nasa.gov/gif_files/Channel_numbers.jpg

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Greg Hullender
post Nov 3 2009, 07:05 PM
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Kepler does have a page on "differential photometry" but that doesn't really address the problem:

http://kepler.nasa.gov/sci/basis/diffphot.html

If anything, it implies problems with a channel should be limited to the stars on that channel. It definitely doesn't say "all the stars" -- it just says "nearby stars". Of course, it doesn't actually talk about "channels" at all . . .

--Greg
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tacitus
post Nov 3 2009, 11:23 PM
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One thing that exacerbates the problem is that the field rotates 90 degrees every three months, so even if the problem is contained within a small number of sensors (3 max) then that still means that up to 12 out of the 42 segments within the field will be affected. There does seem to be some confusion over how the software processing on board Kepler works -- some say that the processing integrates all the data across all sensors and amplifiers, and others are not so sure. I think we're going to have to wait for a detailed explanation from the Kepler team themselves, who are still claiming that it's not that bad a problem.
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Syrinx
post Nov 4 2009, 12:06 AM
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If you look at this picture:

http://en.wikipedia.org/wiki/File:329161ma...llFFIHot300.png

you can clearly see 42 segments in the FOV. I would imagine there are two "channels" per segment, for a total of 84 channels.

If I'm reading Borucki's update correctly, the data from the 3 noisy channels won't be mixed together with the other 81 channels until after extrasolar Earths have been searched for within the 81 channels. Only after that will the 3 noisy channels be mixed in.

I'm not sure what exactly entails "mixing" nor do I know why it's beneficial. Any of us could make some guesses I suppose.
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tacitus
post Nov 4 2009, 06:36 PM
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Good news:

QUOTE
Three of these channels are plagued by electronic noise that makes stars in their field of view appear to flicker – "like it's changing its brightness at a rapid rate", says Kepler chief scientist William Borucki of NASA's Ames Research Center in Moffett Field, California.

The tiny brightness dips from a transiting Earth-size planet could be lost amid these fluctuations. But since the problem affects only a few of the 84 channels, it is not expected to hide all Earth-size planets, Borucki says.

"People have found a pimple here and they are trying to make it into a mountain," he told New Scientist. "A lot of the planets will show up regardless."

...

The team is developing software to automatically remove the noise from data after it is sent down to Earth, but rigorous testing means it will not be ready until 2011.


http://www.newscientist.com/article/dn1809...ien-earths.html

It's worth reading the whole article (I would quote more but that would be against the rules).
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MahFL
post Nov 4 2009, 06:52 PM
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I think there is a mistake in the article, it says Earth's twin would have a one year orbit, but from what I see it could be longer or shorter depending on the heat of the star and/or distance.
Is my thinking correct ?

Also I find it interesting that they say the stars are not as variable as they orginally thought.
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Syrinx
post Nov 4 2009, 07:20 PM
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QUOTE (MahFL @ Nov 4 2009, 10:52 AM) *
it says Earth's twin would have a one year orbit, but from what I see it could be longer or shorter depending on the heat of the star and/or distance.


It depends on how "Earth's twin" is defined. You could be correct or the article could be correct.

As an aside, most scientists, IMHO, would have the definition include liquid water in addition to temperature, size, and mass.

I've never seen an official definition. Anybody know if there is one?
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tacitus
post Nov 4 2009, 07:27 PM
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I believe they deem an Earth-twin to be an Earth-like planet orbiting a Sun-like star in the habitable zone -- which necessarily means that the planet's orbit will take about a year, give or take a month or two.

They are hoping to find Earth-like planets around other stars -- notably cooler stars than our Sun, like red dwarfs, where the habitable zone is closer in. It is the detection of these planets, with orbits of perhaps only 3 to 6 months that will be most affected by the delay in data processing, since if there were no glitchy amplifiers, they should be detectable before the software fix is available in 2011.

But if all the transits of such planets are caught by the detectors with clean amplifiers, then there is still a chance that they will be able to announce some discoveries of this type next year, but remember that the spacecraft is rotated 90 degrees every three months, increasing the chances that at least one of the three required transits will by masked by a glitchy amplifier, and thus detection will be delayed until the fix is available.
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tacitus
post Nov 4 2009, 07:47 PM
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The Kepler press kit doesn't mention the word "twin" but it's clear that they are distinguishing between Earth-like (or Earth-sized) planets orbiting M class stars (red dwarfs) and those orbiting Sun-like stars:

QUOTE
Approximately in December 2010, scientists expect to announce any discoveries they have made in the
first year. This will be the first possible announcement of Earth-size planets in the habitable zones of
M-type stars
, which are stars smaller and cooler than the sun.

Discovery of Earth-size planets in Earth-like orbits requires nearly the full lifetime of the 3.5 year mission,
although in some cases three transits are seen in just a little more than two years. Other results that
require the full 3.5 years of data are: Planets as small as Mars in short period orbits, which utilizes the
addition of dozens or more transits to be detectable; and the detection of giant-inner planets that do not
transit the star, but do periodically modulate the apparent brightness due to reflected light from the planet.

Approximately in December 2011, scientists are expected to announce any discoveries made during the
first two years of the mission. The announcement will be made at NASA Headquarters and later at the
January 2012 American Astronomical Society (AAS) meeting held in Seattle, Wa., as well as at NASA’s
Ames Research Center. This will be the first possible announcement of Earth-size planets in the habitable
zones of K-type stars.

Around December 2012, scientists are expected to announce any discoveries made during the first
three years of the mission. The announcement will be made at NASA Headquarters and later at the AAS
meeting held in Austin, Texas, as well as at NASA’s Ames Research Center. This is the first possible
announcement of Earth-size planets in the habitable zones of solar-like or G stars.


It's the December 2010 announcements that will be impacted most by the faulty amplifiers, but assuming they can successfully filter out the signal noise introduced by those amps, detection of the affected transits will only be delayed, not lost.

Hey, I just realized that if all goes well they could be announcing the first "Earth-twin" in my home town in Dec 2012. I wonder if they would notice a non-astronomer sneaking in at the back?
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Syrinx
post Nov 4 2009, 09:27 PM
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QUOTE (tacitus @ Nov 4 2009, 11:47 AM) *
Hey, I just realized that if all goes well they could be announcing the first "Earth-twin" in my home town in Dec 2012.

Nice!

Austin is my home city and Mountain View (Ames Research Center) is my city of residence. smile.gif
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tacitus
post Nov 5 2009, 03:27 AM
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I think your avatar kind of gave that away smile.gif
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Byran
post Nov 5 2009, 07:58 AM
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http://archive.stsci.edu/mast_news.php?out...sc=t&id=342

QUOTE
Kepler Dropped Targets now Public
11/04/09
Roughly 7,500 Kepler Light curve files are now available to the public for download. To see the available files, go to the Kepler Data Search form , enter " < 2010" in the box labelled "Release Date", and click the "Search" button.
Please note the Data Use Policy comments regarding the use and interpretation of the current Kepler data.


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