Kepler Mission Options

[belleraphon1]

Congratulations to the mission launch team on this beautiful launch. Heart was in my mouth waiting for confirmation of Goldstone signal.

In 1991, when the pulsar planets were announced, we started writing the Book of ExoWorlds. How many pages will be added in 4 years time?

KEPLER (and COROT) will answer a question I have been wanting an answer to ever since I was old enough to understand the question. How common are Earth sized planets?

As Alan Boss has noted, we are entering the platinum age of explanetary science.

Craig

[BrianJ]

Yes, the radial velocity method can determine the eccentricity...

Using spectroscopy/doppler shift measurements? That's possible for Earth-sized planets? Even if there's a Jupiter-sized planet in the same system(messing things up)? Wow.

I think I'll have to try to crunch some numbers on that, to get my head around it.

The more I think about it, the more amazing the process of making those measurements, and disentangling them, becomes.

Thanks.

[Del Palmer]

1. Why wasn't an L2 orbit used (similar to the forthcoming Herschel and Planck missions)? Wouldn't an L2 orbit give a longer mission lifetime?

I recall L2 being mentioned early on, but they descoped along the way in order to fit on a Delta II -- it's sobering to think Kepler was rejected four times before being accepted!

[MahFL]

We saw the launch last night in real life from our location in Orange Park, FL. The Delta 2 looked like a large firework rocket at first. Then an orange light which noticeably accelerated. We have seen the Shuttle launch several times and also I think one of the Rovers.

[tasp]

It would not be confirmable by the 3 observation criteria, but it would still be interesting to review Kepler light curve data for brightenings possibly due to equivalents of Kreutz sun grazers. (IIRC, some Kreutz sun grazers have been visually observed in daytime near the sun, implying a summed magnitude increase greater than the expected decrease in magnitude due to a planetary type stellar transit)

[nprev]

Considering that the Kreutz group is thought to have originated from the breakup of a single large object perhaps less than a thousand years ago, and that a comet's peak brightness during periastron lasts only a few days at most, I think detection of such events by Kepler are statistically unlikely in the extreme.

[scalbers]

Using spectroscopy/doppler shift measurements? That's possible for Earth-sized planets? Even if there's a Jupiter-sized planet in the same system(messing things up)? Wow.

I think I'll have to try to crunch some numbers on that, to get my head around it.

The more I think about it, the more amazing the process of making those measurements, and disentangling them, becomes.

Thanks.

Well I should qualify that the radial velocity method generally works for planets larger than the Earth, depending on how close they are to their parent star. I've heard radial velocity limits between .3 and 3 m/s that would depend on the brightnesss of the parent star.

http://kepler.nasa.gov/sci/capabilities.html

It can determine the eccentricity though as well as work with multiple planets to disentangle the individual signals.

[scalbers]

It seems to me that many more opportunities happen than this. We need only look at the light curve of medium to large asteroids as the Earth, or Venus, or Mars, or Jupiter transit the Sun from their locations. There must be dozens of such events per year. More if you want to look at smaller objects.

Perhaps though the light curves of the asteroids would be more influenced by their rotation compared with a star?

[climber]

We saw the launch last night in real life from our location in Orange Park, FL. The Delta 2 looked like a large firework rocket at first. Then an orange light which noticeably accelerated. We have seen the Shuttle launch several times and also I think one of the Rovers.

Opportunity was launched at night.
An watch out next wednesday you'll enjoy Discovery's night launch too.
Lucky man.

[BrianJ]

I recall L2 being mentioned early on, but they descoped along the way in order to fit on a Delta II -- it's sobering to think Kepler was rejected four times before being accepted!

Thanks Del. I'm certainly glad Kepler made the cut in the end!

Some back-of-the-envelope calculations tell me that Kepler has a max. dV of ~23m/s (assuming 12kg propellant, ISP 2000Ns/kg)
From what I can find out on the web, Herschel(direct injection to L2 halo orbit) will need ~200m/s dV (inc. safety margin). So Kepler would require ~90kg of extra propellant on board to match that.

The largest component of the Herschel dV budget seems to be for correction of launcher error. So I guess it's largely down to the accuracy required for a launch to L2 halo orbit (compared to a launch to Earth-trailing heliocentric orbit).

@scalbers: Thanks so much for the link to the Kepler/Planet Detection Methods page. That makes the limitations of the different methods quite clear. I was just wondering if a system similar to the Earth/Sun were detected, could we tell whether it was a "habitable" place (low eccentricity) or being alternately roasted and frozen every orbit (high eccentricity).

Best regards,
Brian

[Mongo]

That makes the limitations of the different methods quite clear. I was just wondering if a system similar to the Earth/Sun were detected, could we tell whether it was a "habitable" place (low eccentricity) or being alternately roasted and frozen every orbit (high eccentricity).

It would be possible to determine that a particular planet had a high-eccentricity orbit using only transit information (under certain viewing circumstances), but many high-eccentricity planets would not be recognized as such.

The time between successive planetary transits (combined with the primary star's estimated mass) determines the semi-major axis, while the total duration of the transit from first to last contact is determined by the "impact factor" (how central the transit is, relative to the stellar disk), the diameter of the stellar primary and the velocity of the planet while transiting in front of the star. So if the stellar parameters are reasonably well-known, a transit duration longer than that expected from a central transit of a low-eccentricity planet says that the planet must be slower (and hence farther from its primary) at that moment than expected at any time in a low-eccentricity orbit, and so its eccentricity must be high.

However, a transit duration less than the expected duration of a central transit and a low-eccentricity orbit means little, since the transit might be off-center or grazing, which would reduce its duration as well.

[Syrinx]

I made it out to the Kepler launch party here at NASA Ames in Mountain View, CA. After the launch, masses of people starting filing out and I was able to grab a few minutes with Dr. Tom Roellig, co-investigator for Kepler. There were a few of us pelting him with questions, some of them interesting.

- "Flea on a headlight" whatever, what's the intensity resolution? Kepler has 16-bit A2Ds.

- Kepler has an 90 megapixel digital camera. Is all that data beamed back to Earth? No, just the pixels that have a star sitting on them, about 5%. Then compression is about 2:1.

- Does a star move from pixel to pixel during measurements? No. A star will sit within one pixel with a LARGE amount of the pixel to spare.

- What if a star just happens to be right on the border of one pixel and another pixel? Kepler blurs adjacent pixels to account for this. (Not clear to me if this is accomplished in software or hardware.)

- Why is Kepler's life span just six years? Not enough fuel. Have to desaturate from time to time, no choice.

- (My question) Can we expect preliminary data to be published in May or June? Yes and no. The Kepler team will have some data and preliminary "subjects of interest" but they won't publish it. Because some media will misrepresent the data and you'll have headlines such as "30 Earths found!!!" and NASA will look bad for no reason when NASA has to clean up the mess.

[scalbers]

It would be possible to determine that a particular planet had a high-eccentricity orbit using only transit information (under certain viewing circumstances), but many high-eccentricity planets would not be recognized as such.

The time between successive planetary transits (combined with the primary star's estimated mass) determines the semi-major axis, while the total duration of the transit from first to last contact is determined by the "impact factor" (how central the transit is, relative to the stellar disk), the diameter of the stellar primary and the velocity of the planet while transiting in front of the star. So if the stellar parameters are reasonably well-known, a transit duration longer than that expected from a central transit of a low-eccentricity planet says that the planet must be slower (and hence farther from its primary) at that moment than expected at any time in a low-eccentricity orbit, and so its eccentricity must be high.

However, a transit duration less than the expected duration of a central transit and a low-eccentricity orbit means little, since the transit might be off-center or grazing, which would reduce its duration as well.

Perhaps in principle a transit can be determined to be off-center if we time the steepness of the light curve's descent/ascent. I'm unsure though that Kepler would have the requisite time resolution.

Brian, it looks like an Earth-Sun analogue would have a few times less radial velocity than would be needed, though one might get close if the star was near and bright with lots of photons.

Syrinx, I was at a similar launch party at CU/LASP where the mission is being controlled from. I gather most of the science activity will be at Ames.

[dilo]

- What if a star just happens to be right on the border of one pixel and another pixel? Kepler blurs adjacent pixels to account for this. (Not clear to me if this is accomplished in software or hardware.)

Syrinx, my understanding is that star images are deliberately unfocused at sensor and their blurred images are about 7 pixel wide. This "hardware blur" offers many advantages in terms of precison and dynamic range because it reduces effect of different pixel responses and avoid fast saturation...
Take in mind that Kepler camera is not used to took real pictures ( ) but only extremely accurate photometry of selected stars in the field.

[robspace54]

I am an engineer for MAG Cincinnati (formerly Cincinnati Machine) and we built a large vertical milling machine which was used as a grinder to grind the 1.4 meter diameter photometer mirror for Kepler. The U5 machine was built for L-3 Communications (Brashear) who performed the work for NASA.

So I say bon voyage to Kepler and use your mirror well! Catch a few Earth-sized objects!!!

Rob

Attached thumbnail(s)