Kepler Mission Options

[Greg Hullender]

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

[Tom Womack]

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

[NGC3314]

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).

[Syrinx]

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.

[Mongo]

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.

[algorimancer]

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.

[NGC3314]

One thing I wonder is why not go with a scanning camera for a subsequent mission.

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).

[algorimancer]

That puts the mission in a different part of parameter space...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.

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.

[MahFL]

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.

[Hungry4info]

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

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.

[Explorer1]

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

[NGC3314]

The point he was making is that the area Kepler is looking might not be representative of the rest of the Universe.

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).

[MahFL]

Look under your keyboard, measure how much water is there....

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

[djellison]

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

[Gsnorgathon]

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

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...