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Kepler’s first crop

January 4th, 2010


The long-awaited initial discoveries from the 600M Kepler mission are in!

At a scientific talk at the AAS Meeting in Washington DC this morning, and in an afternoon press briefing packed with journalists, bright lights and television cameras, the Kepler Team announced the discovery of five new transiting planets. Four are inflated hot Jupiters, and one is a hot Neptune reminiscent of Gliese 436b and HAT-P-11b. Most importantly, the Kepler satellite appears by all accounts to be performing beautifully as it continuously monitors over 150,000 stars for planetary transits.

Here’s a to-scale line-up of the Kepler starting five. Kepler-4b is so small that it’s just barely resolved at a scale where its orbit spans 480 pixels.

The Kepler planets are primarily orbiting high-metallicity, slightly inflated, slightly evolved stars. These particular parent stars were likely selected for high-priority confirmation observations because their abundant, narrow spectral lines should permit maximally efficient, cost-effective Doppler-velocity follow-up.

Among the planets, Kepler-4b, with its composition that’s likely largely water-based, provides further evidence that the majority of short-period planets formed far from their parent stars, beyond the iceline in the protostellar disk, and subsequently migrated inward. Kepler-7b is approximately the density of styrofoam. In a conversation with a reporter, I scrambled for an analogy:

It’s like looking at a football team. You might guess from the team photo that they’re all 250 to 300 pounds. But then you find out that some of them are 25 pounds; that would come as a surprise…

Everyone is looking forward to the big-picture results that will be coming from Kepler a few years hence, as it probes into the habitable zones of Solar-type stars. In the interim, though, the veritable flood of ultra-high precision photometric data arriving via the the Deep Space Network will keep Doppler velocity follow-up observers working the late-night shifts. The parent stars of the new planets are in the V=12.6 to V=13.9 range, roughly 100 times fainter than the prime transit-bearing stars such as HD 209458 and HD 189733.

According to a S&T editor Bob Naeye, who reported on Bill Borucki’s scientific talk this morning, the first 43 days of photometric observations from the satellite generated 175 transit candidates, of which 50 were followed up in detail to extract the 5 announced planets. The Keck I telescope has been the major workhorse for the high-precision RV follow-up efforts that are required to get accurate masses. According to the Keck I Telescope Schedule, 17 nights were allocated to the Kepler team from July through December of last year. Within this time alotment, roughly 50 RV measurements for the 5 new planets were obtained. The velocity precision for Kepler-4b looks to be of order 2-3 m/s, which is excellent. Here are two thumbnails from Borucki’s talk (look carefully to read the y-axis scale):

With a slew of nights and good weather during 2010, it should be possible to get a significant number of additional planets confirmed…

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  1. January 4th, 2010 at 16:54 | #1

    Based on the 4b RV data, can they exclude a larger, non-transiting gas giant out to a certain semimajor axis for a given mass?

  2. greg
    January 4th, 2010 at 21:06 | #2

    That’s certainly possible, but the constraints are likely not yet that strong. Nevertheless, assuming a 2-3 month time baseline, if there was something like HAT-P-13c in the Kepler-4 system, then it’d likely show up as an RV trend. The constraints on an exterior non-transiting companion will get much better as more RV data is accumulated.

  3. Allan Schmitt
    January 5th, 2010 at 11:28 | #3

    Greg,

    As we all know, the major bottleneck for exoplanet discoveries is the RV confirmation process. According to “http://kepler.nasa.gov/Science/KeplerScience/expectedResults/”, the
    Kepler project is expected to find literally hundreds of exoplanets. Based on the current detection rate of 5 exoplanets in 6 months (10 exoplanets/yr projected), do you believe
    that the Kepler project can meet all of its scientific objectives in a reasonable time
    frame?

    From my perspective, I don’t see how Kepler can meet all of its scientific objectives unless it can boost the detection rate from 10 to 50 exoplanets/yr minumum. Either the confirmation process has to become significantly more efficient or access to additional telescopes is required. Do you concur?

    Thanks!

  4. January 5th, 2010 at 12:08 | #4

    Are you excited that ESA’s Herschel infrared space scope is resuming “HiFi” heterodyne observations on the 11th of January? I am. Do you know whether we have three ( http://en.wikipedia.org/wiki/Closure_phase ) or more infrared telescopes in space with enough clocks on them to measure phase changes at water and ozone spectroscopy frequencies from spacecraft pitch and yaw? I have been trying to ask @NASAJPL on Twitter without much success so far. I hope you will try to find out, too, please. Cheers!

  5. horatius
    January 5th, 2010 at 12:12 | #5

    regarding “generated 175 transit candidates, of which 50 were followed up in detail to extract the 5 announced planets.” fragment of Your post. I have 3 questions:

    1) does it mean that only 10percent of candidates passed through the ground based confirmation test? Or maybe there were not enough time to confirm the remaining 45?

    2) what about 125 of the rest (and future cadidates as well) – are they also going to be confirmed by Keck observations? Or maybe if Kepler proves to make no mistakes no ground telescopes will be involved?

    3) where is a precision limit for such confirmation procedure (in terms of planet size/orbit)?

    Can you help me with that?

  6. greg
    January 5th, 2010 at 12:19 | #6

    @Allan — I do concur…

  7. greg
    January 5th, 2010 at 12:21 | #7

    @James Salsman
    Have to confess that I wasn’t aware of Hershel’s resumption of heterodyne observations, and I have to plead ignorance with ozone spectroscopy. Any readers with 411 on this one?

  8. greg
    January 5th, 2010 at 12:47 | #8

    @horatius
    1) It’s not clear what fraction of the 50 candidates received significant Keck attention. 17 nights, however, is a monster time allocation for Keck I, and works out to 2.94 velocities per night to get the 50 observations that are in the plots in the Borucki talk. Even at magnitude 13.9, it’s unlikely that they’re spending significantly more than 0.5 hours per RV measurement, so my guess is that there are a fair number of stars with RVs that either are still awaiting a secure mass determination or which have been dropped from planet-consideration.

    2) There’s a difficulty associated with the fact that transit light curves are of little scientific utility unless there are accompanying RV mass measurments. So I think a significant ongoing Keck expenditure is going to be required to justify the 600M investment in high-cadence ultra-high precision space-based photometry.

    3) CoRoT-7 (see Queloz et al. 2009) provides a good practical example of going to the limit in terms of RV confirmation on a V=11.7 star. In that case, they got to K=3.3 m/s with a _massive_ HARPS effort, presumably expedited so as to ensure a scoop of Kepler on a transiting super-Earth. But they suffered from the fact that the star was intrinsically noisy. With a really cooperative star — e.g. a HD 40307 clone, Keck could probably confirm K=2 m/s around a 13th magnitude star, but it’d require a heroic effort at the telescope. Given that 600M has been spent, though, and given that Keck time is only 100K per night, I think you’ll see this sort of effort occur on one or two of Kepler’s very best candidates.

  9. January 5th, 2010 at 12:48 | #9

    The detection of the tidal bulge induced by HAT-P-7b (a.k.a. Kepler 2b) on its star is pretty impressive, no? I wonder how useful that kind of effect will be in confirming planets without having to involve RV measurements.

  10. January 5th, 2010 at 19:09 | #10

    Doesn’t the Kelper price tag include a huge slab of pre-paid ground-based telescope time? Although I was wondering- can candidates be excluded using a smaller telescope, or dies the dimness of the candidates mean that they still need lots of glass?

  11. January 6th, 2010 at 03:45 | #11

    Andy,
    How can you model the size of the tidal bulge without knowing the mass of the planet?

  12. January 6th, 2010 at 10:41 | #12

    cwmagee: I’m wondering whether it would be possible to model the size of the bulges from the photometry and work back from that to the planetary mass. In fact having read the paper in more detail, the idea of using the ellipsoidal variation to constrain the system mass ratio is mentioned at the start of section 4.

  13. Alex
    January 6th, 2010 at 11:04 | #13

    @cwmagee
    @cwmagee
    Quote from Kepler-2b’s Wikipedia page:

    “Mass (m) 1.776+0.077?0.049 MJ”

    If the Planet Transits, does it not mean the mass can be found?
    (I’m not totally sure, but it’s what I’ve picked up over all the Transit discoveries I’ve seen)

  14. Alex
    January 6th, 2010 at 11:05 | #14

    I waited patiently since last year for first results. I’m overjoyed now =D

  15. coolstar
    January 7th, 2010 at 22:59 | #15

    Several talks by various Kepler team members at the meeting made it quite clear that they were NOT expecting to get RV confirmation on many of their discoveries. In fact, since the primary mission goal is to obtain transits of earth sized planets in the habitable zones of their stars, this was obviously known going in. Thus I don’t understand the phrase about transits being of little scientific value unless masses can be confirmed thru RV measurements. Of course, everyone, most of all the Kepler team, would like to know the masses and densities of earth-sized transiting planets, but that’s not going to be possible on stars this faint until the next generation of ground based telescopes come on line. $600 M is actually cheap, IMNSHO , relative to the science Kepler is returning.
    I’d be interested in knowing Greg’s opinion on Scott Gaudi’s estimate of the fraction of solar system like exo-systems based on microlensing data (I certainly learned something: that with the right data masses CAN be obtained thru microlensing events).

  16. coolstar
    January 7th, 2010 at 23:05 | #16

    @Andy What Welsh and collaborators didn’t mention is that there should be at least dozens of NON-transiting hot planets for which phase + ellipsoidal variations should be observable. In fact, they may prove easier to model than the transiting cases.

  17. January 16th, 2010 at 00:18 | #17

    @Greg, it looks like the algorithm for space VLBI at 9-10 microns (ozone) is pretty much exactly the same as the algorithm for synthetic aperture radar. If we admitted we knew how to to the former, then we would have to admit we have sub-millimeter accuracy for map making. Is that likely a military secret? Check out Fig. 19 on page 1351, “2 cm” scale detail: http://dsp.rice.edu/~wailam/research/ImagingTHzRadiation2007.pdf

  18. January 26th, 2010 at 18:08 | #18

    @ James:
    You can’t map Earth at sub-millimeter accuracy, because plate tectonics drags continents around at tens of mm/yr.

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