I think one of the best reasons for a long extended mission is that they seem to be able to detect planets that do not transit simply by looking for variations in the timings of the transits they do observe. In particular, that might give us a lot more info about large outer planets on long-period orbits.

I wonder if anyone is talking about a followup mission? Maybe something big enough to cover a large fraction of the sky. Or at least the Milky Way.

--Greg

The ESA has plans for a followup mission 'PLATO' which is roughly SuperWASP-in-space: twenty-eight 100mm rich-field telescopes, each with a (2x3854x18µm)^2 focal-plane array, mounted on a single very stable platform located at L2. It will cover a 550-square-degree field (a bit over 1% of the sky, five times Kepler); the idea is to look for planets around rather brighter stars than Kepler (because follow-up for Kepler apparently proved harder than anticipated), and with a bit more of a focus on asteroseismology (in particular, with the aim of characterising the planet-hosting stars by seismology rather than by ground-based observation).

http://www.lesia.obspm.fr/perso/claude-catala/plato_web.html

This could get uncomfortable - based on the last few years of NASA funding, a Kepler extended mission will be competing directly with continued operation of Hubble, Chandra, Swift, Fermi... (all astrophysics missions which have gone past their nominal mission durations). Hubble had a sort of separate status for a while, but that may no longer be the case. At the least, they'd be likely to need a minimal-cost operation (which would make lots of sense, of course, since it would be a mature mission whose upkeep is presumably well-understood).

Last I heard Borucki speak, he said there were no plans for a "Kepler 2" mission. He had plans for a spectroscopy mission (rather, plans to present plans to the powers that be).

A Kepler 2 wouldn't do much more than confirm the results of Kepler, and even if Kepler's results are off by 50% we still have more exoplanets than we know what to do with in every direction we might choose to look.

I have no idea what plans ESA may have.

I think the way to go would be a TESS-like mission, focusing on the brightest solar-type stars over the entire sky. Any planets found by transits would be far more amenable to spectroscopic follow-up observations, due to their primary's much greater apparent brightness.

One thing I wonder is why not go with a scanning camera for a subsequent mission, rather than staring at a single location for years at a time? Simplest case, put a spin on the spacecraft and image a 360 degree by whatever the #degrees spanned by the imager every cycle. Set the cycle to whatever minimum is needed to capture these transits -- perhaps .01-1 Hz wouldn't be unreasonable.

That puts the mission in a different part of parameter space, since the number of photons per unit time for a given star goes down by the fraction of a scanning circle spanned by the instantaneous field. Kepler doesn't only get nearly complete time coverage, but maximizes the count rate for each star by staring. Fainter than a certain limit (where systematics take over), scanning reduces the S/N per orbit or transit. Since the number of stars is a very steep function of flux, changing the brightness threshold changes the whole balance between number of targets and precision.

(Edit to add: this presumes that we don't already know all timescales of interest and thus don't already know that we will not have to coadd multiple observations to detect transits, for example).

Agreed -- and it is definitely good to take the Kepler approach to get a sense of the needed sampling resolution. My concern with Kepler's data (speaking as a statistician) is that it is not necessarily taking a representative sample of stars. Kepler is focusing on a tiny piece of the local galactic arm, which may or may not be representative of the galaxy as a whole. This could be addressed by either repeating the Kepler approach in one or two other directions (like towards the galactic core), or taking the lower precision, but better sampling, panning approach.

I don't think it really matters where Kepler looks, if it finds possible Earth like conditions then multily that by the barely unimaginable size of the Universe, and the chances of other life existing goes up.

Look under your keyboard, measure how much water is there, and multiply by the surface area of Earth -- a rough estimate of how much surface water Earth has.

The point he was making is that the area Kepler is looking might not be representative of the rest of the Universe. Kepler's looking slightly 'above' the Galactic disk for example. If there's a metallicity gradient in the disk, then the census Kepler finds may not represent what we find in the solar neighborhood, and might not represent the galaxy as a whole, and there's especially no reason to assume it applies to the Universe as a whole.

A microlensing mission might give us a fairly good stab at the galaxy-scale statistics of planets. It would definitely not be as confined to short periods as Kepler.

Isn't Kepler deliberately targeting a more crowded portion of the sky, for best efficiency?

Although at this point, for many purposes we are not so much interested in the rest of the Universe or the overall picture for the Milky Way, as in the solar neighborhood and what Kepler statistics suggest about the likely distance to the nearest (non-transiting) Earth-analog. Since the Kepler field isn't a place but a direction, the results are inevitably smeared along a line at roughly the same galactic radius. Its penetration for sunlike stars is shallow by Milky Way standards, so even looking in versus out in the disk would sample only a small part of the typical abundance gradient. There have been shorter transit surveys in the inner disk and at least one globular cluster with HST, mostly telling us that hot Jupiters must be quite rare in globulars (OK, this is astronomy, the actual statement would be "in 47 Tucanae").

I fully take the point that (at least scientifically) the rest of the planet types are just as interesting and that we may be unduly missing things by a premature focus on potential habitats (something I've argued about Mars exploration in the past, but that would be a different thread).

Well if its one of those days when you spill something on your keyboard, your going to need to evolve gills pretty quickly !

Rule 1.3 people - you're tip-toeing along the edge of it perilously.

No. The most crowded portion of the sky would be toward the galactic center, but there would be zillions* of transits caused by stars rather than planets; and therefore a whole lot more work to figure out just which transits really were planets.

* Within a few orders of magnitude or so...

I'm not sure why the fraction of false positives should be higher toward the galactic centre.

I'm pretty sure the Kepler field was chosen due to constraints with needing to look perpendicular to the plane of the ecliptic, so the solar arrays could get sufficient power. That narrows it to two areas of the sky -- Cygnus and whatever is opposite from that. IIRC, Cygnus was chosen as it had more stars.

Ah yes, now I remember, thanks.
Let's hope Kepler sticks around for a nice long time...

One issue would be eclipsing binaries blended with the star in question, which would be more numerous in directions with more stars. Toward the galactic center, there is that whole deep disk and bulge contributing blends. No idea wether that was a consideration for Kepler - being at right angles to the ecliptic and wanting a northern field for convenient radial-velocity followup could have been quite enough to narrow the field down a lot.

Interesting article in Sky & Telescope: http://www.skyandtelescope.com/news/home/126242378.html

It seems that Kepler has some difficulties detecting earth-size planets because of more than expected stellar variability (noisy stars!) and it probably needs a longer run for detection.

http://www.nasa.gov/mission_pages/kepler/n...m-20110811.html

There is a nice news article in the latest issue of Nature describing the Kepler Mission's need for a mission extension to achieve its primary goals. For those who have access, the article is available here. for those who don't, the salient points are these:

• Due to the extra signal noise in a large proportion of the Kepler sample of stars, smaller planets are more difficult to detect. See R. L. Gilliland et al. preprint at http://arxiv.org/abs/1107.5207; 2011.
  
• It is likely that the stellar noise is due to the equivalent of sun spots, and the higher activity would suggest that half of the Kepler stars are younger than the sun, an unexpected result if it proves true.
  
• A full eight years would be required to definitively pin down the frequency of earth-like planets in the sample. Because of budget shortfalls, an extension is by no means certain; a decision is expected next spring.
  
• If Kepler does not get the hoped for extension, the team may need to restrict their search to planets at least 1.2 x the size of earth.
  
• "More exoplanet discoveries are expected to be announced next week in Moran, Wyoming, at a conference on extreme solar systems."
  
• The next data release will come in two weeks. It is based on 674 million observations recorded from September to December 2009.

Four planets at KOI-730.
http://exoplanet.eu/star.php?st=KOI-730

They are in a 3:4:6:8 resonance.

Thanks for the salience, HZ :-)

Amazing that they can discern between things like noise from distant sunspots and planet transits in these observations; it's a great benefit from not blinking for several years.

Let's hope K can keep staring at this delicious slice of galactic stellar pie for many more years to come without blinking!

Kepler's really pulling in the nice ones:
Kepler-19 b and c, the latter of which is the first non-transiting planet discovered through transit-timing variations.
http://kepler.nasa.gov/news/nasakeplernews...&NewsID=148

Kepler-12b, an extremely inflated planet (M = 0.431 M_J, R = 1.695 R_J)

Europeans stealing the show again?

http://www.space.com/12908-alien-planet-an...bservatory.html

About this? http://adsabs.harvard.edu/abs/2011arXiv1108.3561K ?
It's on a Monday, so probably no Nature/Science results...

ah! http://www.eso.org/public/news/eso1134/

Oh, definitely. The timing is not coincidental. The HARPS team spoke this morning at the "Extreme Solar System II" conference in Wyoming from 9:00 - 9:15, then scheduled the press conference for 10:00. Kepler results will be featured in several talks later on. Here's a sample:

Monday, September 12

"Kepler Results," Eric Ford, 2:00 - 2:15
"New Kepler Results," Jason Rowe, 2:15 - 2:30
"The Validation of a 2 R_Earth Planet Showing Transit Timing Variations with Kepler and Warm Spitzer," Sarah Ballard, 2:30 - 2:45
"Update to Intrinsic Planetary Frequencies Based on Kepler Observations," William J. Borucki," 4:15 - 4:30
"Spitzer Observations Suggest a Low Kepler False Postive Rate," Jean-Michel Desert, 4:30 -4:45

And too many more to list, all week. So there are plenty of exoplanets to discover and there is plenty of limelight to share. I am intensely looking forward to learning more soon!

The HARPS search for southern extra-solar planets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass planets

We report on the results of an 8-year survey carried out at the La Silla Observatory with the HARPS spectrograph to detect and characterize planets in the super-Earth and Neptune mass regime. The size of our star sample and the precision achieved with HARPS have allowed the detection of a sufficiently large number of low-mass planets to study the statistical properties of their orbital elements, the correlation of the host-star metallicity with the planet masses, as well as the occurrence rate of planetary systems around solar-type stars. A robust estimate of the frequency of systems shows that more than 50% of solar-type stars harbor at least one planet of any mass and with period up to 100 days. Different properties are observed for the population of planets less massive than about 30M-Earth compared to the population of gaseous giant planets. The mass distribution of Super-Earths and Neptune-mass planets (SEN) is strongly increasing between 30 and 15M-Earth. The SEN occurence rate does not exhibit a preference for metal rich stars. Most of the SEN planets belong to multi-planetary systems. The orbital eccentricities of the SEN planets seems limited to 0.45. At the opposite, the occurence rate of gaseous giant planets is growing with the logarithm of the period, and is strongly increasing with the host-star metallicity. About 14% of solar-type stars have a planetary companion more massive than 50M-Earth? on an orbit with a period shorter than 10 years. Orbital eccentricities of giant planets are observed up to 0.9 and beyond. The precision of HARPS-type spectrographs opens the possibility to detect planets in the habitable zone of solar-type stars. Identification of a significant number of super-Earths orbiting solar-type of the Sun vicinity is achieved by Doppler spectroscopy. 37 newly discovered planets are announced in the Appendix of this paper, among which 15 Super-Earths.

Fascinating news, and a great achievement to be sure, but dear god I wish they'd stop using the term "Super Earth", or tagging the word "Earth" onto *any* of these exoplanets. I'd ban its use if I could. And labelling a planet a "Super Earth" plants in the minds of non-scientists an image of a planet that is basically just Earth 'scaled up', a planet just like Earth that's essentially just a lot larger. It's so misleading.

Almost every talk I do I get someone asking me about "the Earth like planets" that have been found, and I have to tell them that as exciting as the news is of *every* exoplanet discovery, no truly "Earth-like planets" have been found.

The use of the word "Earth" should be restricted to planets that are actually, you know, *like* Earth, with *confirmed* breathable atmospheres, fluffy white clouds and water oceans. And kittens.

Although it's extrapolating beyond the data, I think it's a pretty safe one to say that if so many stars host super-Earths/sub-Neptunes, an even larger fraction will support smaller terrestrial planets. Fun times ahead.

Absolutely!

Hey Stu, I also heard they've found water on Mars. What about that?

Congratulations. Good to know you're paying attention.

Yeah, finding a potential "Venus-like" or "Super-Venus" planet doesn't seem to pull in the media interest.

(Once again, Venus gets dissed.)

Earth is an anthropocentric word, too. Properly speaking, they should be called Super Crusty-Magma Blobs.

Can we save the meaningless semantic argument for another forum please.

Predictably, the Kepler team has scheduled a press conference of its own on Thursday at 2 pm EDT. Interestingly, they have invited a visual effects specialist from Industrial Light and Magic to the event. Stay tuned. A paper in this week's Science will follow. See: http://www.space.com/12938-nasa-kepler-pla...m-thursday.html. (Could they have found a binary star system with a planet? That would explain the ILM connection...)

More news from the conference:
http://www.astronomynow.com/news/n1109/13browndwarf/

Brown Dwarf weather... 30% brightness change in a few hours.

A reminder about rule 1.3 - a rule this thread is rapidly approaching and likely to start leaping towards in the near future. (which is why it's been a pending admin nightmare for years)

Conf. starting soon...

Circumbinary planet! Kepler 16B

for those having access to Science, Kepler-16: A Transiting Circumbinary Planet

The abstract alone makes extraordinary and surprising reading, to me at least. The planet must orbit at a distance only about 3 times the binary separation. Does the full paper discuss the stability of this arrangement? Is it a very young system?

the paper say they investigated the stability of the system by integrating it over 2 million years. there are short-term variations of the parameters, but none that would lead to instability

I noticed at the press conference they flashed a graphic of a representation of the Alpha Centauri system. I suppose the implication is that this discovery increases the plausibility that the Alpha Centauri binary may have planets.

If it does, their orbital plane (and presumably that of the binary) must be nearly perpendicular to the line of sight; otherwise, we would have seen something in radial velocity measurements by now. Even so, shouldn't we have noticed timing variations in the orbit of the binaries caused by the tug of planets?

There's been several studies that have shown that planets in sufficiently close orbits would be stable around Alpha Centauri A or B. Their average separation distance is something like 20 AU. I think orbits within a couple AU of each star are gravitationally stable. So I don't think Alpha Centauri is a true analog of this system.

For those without, a preprint can be found at http://exoplanet.eu/star.php?st=Kepler-16%20%28Ab%29 edit: Also on arxiv now http://arxiv.org/abs/1109.3432

Related paper on arxiv http://arxiv.org/abs/1109.3198 "Spin-Orbit Alignment for the Circumbinary Planet Host Kepler-16A." which has some discussion of the age (the Science paper basically says "we don't know".)

This one almost slipped past me, but if their adjustments are confirmed, this is HUGE.

Near-Infrared Spectroscopy of Low-Mass Kepler Planet-Candidate Host Stars: Effective Temperatures, Metallicities, Masses and Radii

Abstract: We report stellar parameters for low-mass planet-candidate host stars recently announced by the Kepler Mission. We obtained medium-resolution, K-band spectra of 84 low-mass Kepler Objects of Interest (KOIs). We identified one KOI as a giant; for the remaining dwarfs, we estimated effective temperatures by comparing measurements of K-band regions dominated by H2O opacity with predictions of synthetic spectra for low-mass stars. We measured overall metallicities ([M/H]) using the equivalent widths of Na I and Ca I absorption features and an empirical metallicity relation calibrated with nearby stars. With effective temperatures and metallicities, we estimate the masses and radii of the low-mass KOIs by interpolation onto evolutionary isochrones. The resultant stellar radii are roughly half of the values reported in the Kepler Input Catalogue and, by construction, correlate better with effective temperature. Our results significantly reduce the sizes of the corresponding planet-candidates, with many less than 1 Earth radius. Recalculating the equilibrium temperatures of the planet-candidates from the implied stellar luminosities and masses, and assuming Earth's albedo and re-radiation fraction, we find that six of the planet-candidates are terrestrial-sized with orbital semi-major axes that lie within the habitable zones of their low-mass host stars. The stellar parameters presented in this letter serve as a resource for further characterization of the planet-candidates.

******

Scaling the Earth’s equilibrium temperature of 255 K by the orbital semi-major axis, stellar Teff and stellar radius of the KOIs in this letter, we find that KOIs 463.01, 1422.02, 947.01, 812.03, 448.02 and 1361.01 all have equilibrium temperatures between 217 K and 261 K: the limits of the habitable zone as described in Kasting et al. (1993).

******

The six habitable zone candidates. Assuming that the planet densities are equal to that of the Earth, the surface gravity varies directly with the radius (Mass varies with radius cubed, but gravitational force varies with mass over distance (radius) squared, leaving the surface gravity directly proportional to the radius)

KOI 448.02 (M0-V Primary) -- Radius 1.85 Earth -- 240 K -- Year 43.62 days
KOI 463.01 (M3-V Primary) -- Radius 0.93 Earth -- 232 K -- Year 18.48 days
KOI 812.03 (M0-V Primary) -- Radius 1.16 Earth -- 228 K -- Year 46.19 days
KOI 947.01 (M1-V Primary) -- Radius 1.24 Earth -- 254 K -- Year 28.60 days
KOI 1361.01 (M0-V Primary) -- Radius 1.58 Earth -- 232 K -- Year 59.88 days
KOI 1422.02 (M2-V Primary) -- Radius 0.85 Earth -- 249 K -- Year 19.85 days

There is another candidate (with a calculated radius that is a close match to that of Earth) that has a calculated equilibrium temperature just above the upper limit given above, which I think should be considered as well:

KOI 494.01 (M1-V Primary) -- Radius 1.05 Earth -- 268 K -- Year 25.70 days

Thanks Reed for those links. I don't fully trust the integration of the orbital motion over 2 million years, and in any case that's a very short time in cosmic terms.

Mongo - thanks also for your reporting.