Meanwhile, from the primary mission, another unexpected discovery.
Shades of Clement's 'Mission of Gravity', but truth is yet again stranger than fiction...

Since people always want to know, and I didn't find the numbers anywhere else, I calculated the surface gravity to be 3.0 +/- 0.4 -times the surface gravity of Earth (using 2.35 Earth radii, and density 7.1 +/- 1.0 g/cm³).

Edit: More technical details.

Surface gravity is linearly proportional to density and radius - I think your result is too high.

Edit - Apologies! No it isn't. My error!

Andy

space dot com article on binary exo-earths - http://www.space.com/27832-binary-earth-si...en-planets.html

A pair of smaller planets would possibly give a signal that looks like one bigger planet in the Kepler survey, perhaps?

Yes, I guess, in that they would block more light from the star than either one individually. Presumably as they orbited each other, each eclipse ingress would look different (stepwise eclipse versus simultaneous), and if they occulted each other the depth of the eclipse would sometimes vary during the eclipse or between eclipses... I think the details of the binary could be worked out in ideal circumstances.

Phil

http://spaceref.com/exoplanets/reborn-kepl...ew-mission.html

NASA's planet-hunting Kepler spacecraft makes a comeback with the discovery of the first exoplanet found using its new mission -- K2.
(…)
The newly confirmed planet, HIP 116454b, is 2.5 times the diameter of Earth and follows a close, nine-day orbit around a star that is smaller and cooler than our sun, making the planet too hot for life as we know it. HIP 116454b and its star are 180 light-years from Earth, toward the constellation Pisces.

I'm delighted and surprised that Kepler has been brought back online!

In every way but one, the new discovery is just one more planet on a huge list. But there's one remarkable thing: Its distance from Earth. 180 light years is very close for a Kepler discovery. Most Kepler discoveries are in the range of 1000-6000 light years, because of its "deep stare" strategy. The ones that are just a couple of hundred light years away or less are much more accessible for follow-up study.

http://www.nasa.gov/press/2015/january/nas...mall-worlds-in/

NASA’s Kepler Marks 1,000th Exoplanet Discovery, Uncovers More Small Worlds in Habitable Zones

Two of the newly validated planets, Kepler-438b and Kepler-442b, are less than 1.5 times the diameter of Earth. Kepler-438b, 475 light-years away, is 12 percent bigger than Earth and orbits its star once every 35.2 days. Kepler-442b, 1,100 light-years away, is 33 percent bigger than Earth and orbits its star once every 112 days.
Both Kepler-438b and Kepler-442b orbit stars smaller and cooler than our sun, making the habitable zone closer to their parent star, in the direction of the constellation Lyra. The research paper reporting this finding has been accepted for publication in The Astrophysical Journal.

With the detection of 554 more planet candidates from Kepler observations conducted May 2009 to April 2013, the Kepler team has raised the candidate count to 4,175. Eight of these new candidates are between one to two times the size of Earth, and orbit in their sun's habitable zone. Of these eight, six orbit stars that are similar to our sun in size and temperature. All candidates require follow-up observations and analysis to verify they are actual planets

Our galaxy may host billions of planets where liquid water can exist - http://www.spacedaily.com/reports/Milky_Wa..._study_999.html



->edited to remove content heading into Rule 1.3 territory

Telecon tomorrow morning:

http://www.jpl.nasa.gov/news/news.php?feature=4660

Interesting list of speakers...

There's speculation that today's announcement might indicate something like "the most earthlike" planets found so far. Determining the properties of Kepler discoveries always leaves significant uncertainty regarding size and temperature, so any announcement could only go so far and be probabilistic in its conclusions regarding any single planet. So I might guess that they've found a few candidates, leaving a high probability that one of them really is in some interesting range of size-temperature even if we don't know which of the candidates that is.

Another possibility is that a new type of analysis of existing data has been utilized. The existing pipeline was finding a couple of (possibly, loosely speaking) "earthlike" planets and might find a couple more. Jeff Coughlin's research might be doing something new. He's looked at:

Secondary eclipses to try to find the properties of larger planets (which might work on some rare smaller ones?).
Absorption during primary eclipses to try to find the properties of planets' atmospheres.
And, searching for smaller planets in general.

It seems like one of these methods has turned up something new. We'll find out soon.

Starting in a few minutes: almost 50,000 viewing now....
Graphics here: http://www.nasa.gov/keplerbriefing0723

The real significance here is not the particular discovery itself – a Super Earth in the habitable zone of a sunlike star – but the fact that we're getting a data point that extends the already very-very-near-certain likelihood that planets of earthlike size exist in these situations.

The previous discovery, of Kepler 186-f, indicated that "earthlike" planets exist around smaller, cooler stars. The only way in which this new discovery is "more earthlike" is in the nature of its star.

Well -- the other big thing about this new discovery is that it's a planet orbiting in the habitable zone of a sunlike star, and thus, unlike those orbiting smaller stars, is far enough away from its star to avoid tidal lock. I has a 385-day year.

Even if it's five Earth masses, it's roughly 6 billion years old, and has spent almost all of that time in the habitable zone of its star. And hasn't been tidally locked to its primary. I have to think that life is more possible in such a situation than on a smaller planet orbiting a cooler star in less than 100 days that always shows the same face to its star.

-the other Doug

Generally speaking, most Kepler discoveries are going to be difficult targets for follow-up study, and I would anticipate that in almost every case of a small planet discovery, we'll be able to perform follow-up science on closer planets that are yet to be discovered before we can do it with the particular Kepler discoveries. So my mantra is that the real significance of Kepler work will be to provide a partial statistical survey of planet type frequencies. Systems within 50-250 light years will be where the details will eventually come from.

But, definitely, the main excitement around "sunlike stars" is that they are unlikely to put "earthlike planets" into tidal lock, whereas dwarf stars may do that quite often. On the other hand, dwarf stars outnumber sunlike stars, so there may be more un-locked earthlike planets around the former than the latter.

I dunno. 1.6 Earth radii is marginal for Earth-like habitability at best. I've read several papers that indicate that the transition between terrestrial and Neptune-like planets covers a range of radii, not a single value, but that anything over 1.6 Earth radii must definitely be Neptune-like.

If this would be a 1.2 Earth-radii planet, then yes it is probably Earth-like (which includes Venus as an Earth-like planet, of course), but 1.6 Earth radii is probably not.

I wouldn't expect 1.6 to be "earthlike" at all. More, that since we've seen a healthy ratio of earth-sized planets to Super Earths elsewhere, finding Super Earths here indicates that similar stars almost certainly have earth-sized planets, since there's no magic cutoff that we know of that would allow one and not the other. But this one itself is getting overhyped ("Earth 2.0" is trending on Twitter now).

This discovery is really just whittling away at a doubt that nobody really had in the first place.

Yeah, this release really has a "Water detected on Mars!" feel to it. Maybe Emily or another science media member can fill us in with details on why this was significant.

I'm surprised to find that this announcement is something to complain about!
How many other exoplanets of this size with a near earth-year orbit around a sun-like star have been found?
Maybe the only complaint is with the use of the term "earth-like". Getting too hung up on that is starting to look like the forbidden Pluto debate. Is Venus earth-like?

I think this was a case in the familiar category of "Significant but overhyped." It's good to get popular attention, but it's better to get popular attention that isn't misleading. This churned up a lot of references to "Earth 2.0" which is certainly overstating the case. Maybe all PR is good PR, but that's a difficult claim to make objective.

At present, the only three attributes we can ascertain of a terrestrial world are radius, mass, level of illumination/heating, and orbital parameters (which may give us a hint about tidal lock). We haven't yet found a close match to Earth, although nobody has reason to doubt that close matches to Earth must certainly exist in vast numbers (i.e., a percentage of all stars, and therefore a vast number per galaxy).

Because of observational biases, it's easier to find worlds on the "Hot Jupiter" side of parameter space, and not coincidentally, all of the best earthlike candidates remain significantly more "Hot Jupiter"-like than Earth itself in one or more ways: Bigger, hotter, and/or shorter orbital period.

Individual discoveries aren't likely going to change what we already know so long as only those few properties are detectible. It's great to get the public thinking about this stuff as long as we don't produce a "discovery fatigue" by re-announcing the same basic idea over and over, when the discoveries haven't actually changed what we know.

When we are able to perform spectroscopy on any of these vaguely (or highly) earthlike planets, or when we find one that's significantly closer than the ones we've found so far, that'll be the next real news in this area. Kepler probably won't contribute directly to either of those investigations.

just for your viewing pleasure
( if one thinks it is "Earth like" )
youtube 1080 video - K452/b
https://youtu.be/-jiipfZDv0I

now it might be a BIG Venus or small Neptune'ish thing ????? so......

Very pleasant John.

Your video did pop a question into my head. How would cloud and weather dynamics be affected with increased gravity on a super Earth analog planet? Could we expect a more rapid weathering process with 'heavier' rain drop and such?

Looks like Kepler is going to have its own Pluto observation campaign:
http://www.jpl.nasa.gov/news/news.php?feature=4656

Judging by the number of other observations being undertaken by other craft, Pluto would certainly seem to be the 'Prom Queen' at this time. Just goes to show the importance placed on the NH mission, for what is almost definitely a once in our lifetime encounter.

Note that when a planet is discovered by the transit method, we get a measure of its optical radius, but that may or may not correspond to its solid surface.

In the solar system, Titan has an optical radius significantly greater than its solid surface, and Venus somewhat less so, but worlds in the "Super Earth" size range may blur the boundary between terrestrial planets and gas giants. So, for two worlds with a radius of, say, 1.4 R[earth], that may be a solid surface in one case, and a high, opaque haze layer in the other case, with significant differences in the size of their respective solid bodies and, conversely, the quantity of bulk (or merely opacity!) in their atmospheres.

This could, in principle, be entirely ambiguous from the transit data. It could even remain ambiguous after the mass is known, as the density of terrestrial bodies may also vary by a factor of 3 or so.

One of the great advances to hope for is to get a survey of small and mid-sized exoplanets where we start to understand what the ground truth is like given the scant parameters – radius, mass, and insolation – that we have (in short supply) today. TESS and JWST might advance that a great deal.

Exoplanets ....... a few data points will be very nice

even a spectral analysis of the atmosphere would help

when ever WEBB gets going , maybe we will start getting a few

right now for 99% it is mass or radii only but not both

The prospects of measuring the mass of "earthlike" planets using current methods is strained: An earth-mass planet orbiting a sunlike star at ~1 AU doesn't impart much of an acceleration on its star, and is seemingly destined to be lost in the noise. It would be easier with red dwarfs.

If the planet had a detectible satellite, or changed other transiting planets in its own system, that might offer a value. The latter could work with the methods we use now, but requires a lot of luck.

In re the question as to whether a 1.6x Earth mass planet could be a rocky planet, vs. if such a planet would become Neptune-like -- wouldn't that depend a lot on the nature of the planetary disk from which the planets formed, where in the system it formed (i.e., inside or outside of the frost line), the dynamics of the other planets in the system, etc.?

I've heard speculation that the migration of Jupiter in and out "stole" some of the material that would otherwise have been available for Mars' accretion, gathering some of that material into itself and scattering the rest into our asteroid belt. So, depending on the dynamics of other planets in the 452b system, as well as the original composition of the planetary disk and the timing of the star's T-Tauri phase (which would have blown gasses out of the inner system) and, of course, the impact of being inside the frost line when you develop enough mass to begin to accrete a large gaseous shell, perhaps it is quite easy to develop a fully rocky planet of the size of 452b without passing over into becoming a Neptune-like object?

I think it's a little simplistic to state that all objects above a certain size will become Neptune-like, when Neptune itself is defined by a lot of factors that would not apply if such a body formed far closer to its star than Neptune itself did...

-the other Doug

it is rather unlikely it is a water and plant world
at the time of the announcement i was working on a EARTH mark 2 type procedure

hay art is FUN

i would really guess it is more of a rocky BIG Venus type planet
something more along these lines
-- 100% artistic ( 1920 x 1080 px) --


until there is a good MASS guesstimate this or a small WATER cloud gas giant is up in the air



i would NEED a geologist to run through the numbers but...
there are a lot of unknown variables

the greater the gravity the more force is applied to the fault zones and the more pressure is applied .So more force will be needed for them to slip
-- less quakes but they will be BIG 8 .?+'s
so less plate movement ?? maybe ??

bigger mass bigger core , more heat and more turbulence in the core and mantle
this might speed up plate movement

The greater volume the faster the crust will cool
so less plate movement

now if there is liquid water the rain WILL hit the ground harder but smaller drops ?? maybe ??
if the atmosphere is rather thick the drops will be bigger because the atmosphere is more buoyant

see the problems
everything has a yes AND no

but it would be nice to see some of the NOAA climate models ran with other world settings

and some of the CSDMS Models ran with non earth settings
( h t t p : / / csdms.colorado.edu/wiki/Model_download_portal )

.

Other Doug, it certainly seems possible for a rocky-only world, with about 1.6 RE and no thick atmosphere to exist very close to the star. In fact, it's possible for a gas dwarf consisting of metals and silicates (molten or gaseous) to exist very close to the primary.

The size distribution data from Kepler and other sources suggest that there is no gap in the size distribution, which is interesting given that a catastrophic size increase will occur in situations where a world becomes large enough to retain helium while the nebula still has a lot of hydrogen and helium. That suggests a binary outcome where you get either an Earth or a Neptune, depending upon whether or not the threshold is reached. And perhaps there is such a binary outcome in terms of what kind of world you end up with, but there is no gap in the size distribution, so there must be large rocky worlds with more or less the same size as small mini-giants.

When we have more Super Earths where the radius and mass are both known, we can start to understand that. However, finding the mass of Super Earths that are not close to their star will be challenging, so any such understanding may be confined to planets in short orbital periods for quite some time to come.

Very, very good points, JRehling. You're absolutely right. And I think JohnVV has a good point, too -- and one that the team who announced this discovery mentioned -- that 452b may very well be a giant Venus at this point, what with the extra insolation it's getting now due to its star's advancing age.

The rate at which water would be driven off by the solar wind, as seems to have happened on Venus, would also depend on whether or not 452b has a magnetic field, would it not?

-the other Doug

A paper with interesting implications is out on arXiv:

High Order Harmonics in Light Curves of Kepler Planets





To me, the most obvious source of "Non-sinusoidal periodic light curve variations" would be permanent or quasi-permanent static features on the visible surface of the planet -- either geological features or (for completely cloud-enshrouded planets) long-lived weather features like Jupiter's Great Red Spot. A first step towards exo-planetary cartography?

The light being detected here is (almost) 100% from the star, not the planet, so features on the planet are completely out of the question as a cause. The Great Red Spot changes Jupiter's light curve (although very slightly), but it doesn't change the Sun's light curve.

My first grasp at an explanation would be that in systems with an observable transiting planet, there may be a large, close-in planet that is not being observed because of orbital inclination, and it is that planet which both locked the observable planet in its orbital period and creates tidal effects that alter the star's light curve.

From the paper:

Non-sinusoidal light curves might for example be caused by non-isotropic reflection or thermal emission from the planet’s surface.

Is Kepler 452b a Rocky Planet or Not?

A couple of weeks ago, the media was filled with reports about the discovery of Kepler 452b. While NASA’s Kepler mission had found a number of potentially habitable planets earlier, all of these previous discoveries orbited dim K and M-dwarf stars which are very different than our Sun and present a number of still unresolved issues affecting habitability (see A Review of the Best Habitable Planet Candidates in Centauri Dreams for a full review of earlier finds). What made this new Kepler find unique was that Kepler 452b was a nearly-Earth-sized planet orbiting inside the HZ of a Sun-like star – the first of potentially many more such exoplanets to come from the continuing analysis of Kepler’s data set. But being a bit of a skeptic when it comes to often overhyped media reports about the potential habitability of any newly discovered exoplanet, I wanted to dig deeper into this claim.

Is It in the Habitable Zone?

According to the discovery paper submitted for publication in The Astronomical Journal with Jon Jenkins (NASA Ames Research Center) as the lead author, Kepler 452 is a G2 type star like the Sun with a surface temperature of 5757±85 K, a mass of 1.04±0.05 times that of the Sun and a radius of 1.11 +0.15/-0.09 times the Sun’s. Based on these data, it can be calculated that Kepler 452 has a luminosity about 20% greater than that of the Sun making this it a slightly heavier and brighter version of the Sun. Comparison of the known properties of this star with standard models of stellar evolution yields an age of 6±2 billion years or about 1½ billion years older than the Sun and its system of planets. Compared to the stars earlier announced with potentially habitable exoplanets, Kepler 452 was certainly quite Sun-like.

While a full assessment of the habitability of any exoplanet would require very detailed information about all of its properties, obtaining such information is simply beyond the reach of our current technology. At this early stage in our search for other Earth-like worlds, the best we can do is compare what properties we can derive to our current expectations of the range of properties for habitable worlds to determine if a new find is potentially habitable. One of those important set of properties is the orbit of an exoplanet. According to Jenkins et al., Kepler 452b is in a 384.84-day orbit with an average orbital radius of Kepler 452b is 1.046 +0.019/-0.015 AU. This orbital radius is far outside that where a planet would become tidally locked and be affected by severe stellar flare activity – two unresolved issues that call into question the potential habitability of worlds tightly orbiting much dimmer stars like those found to date.

This orbital radius combined with the stellar properties yields an effective stellar flux for Kepler 452b that is 1.10 +0.29/-0.22 times that the Earth receives from the Sun. This effective stellar flux places Kepler 452b just inside the conservative HZ of a Sun-like star as defined by the runaway greenhouse limit. Given the current uncertainties in the properties of Kepler 452b and the star it orbits, Jenkins et al. calculate that there is only a 28.0% probability that Kepler 452b actually orbits inside of the conservatively defined HZ but there is a 96.8% chance that it orbits inside a more optimistic definition of the HZ corresponding to early conditions on Venus. However, it appears that Jenkins et al. used a definition of the HZ limits for an Earth mass planet. If Kepler 452b has a mass closer to five times that of the Earth (or 5 ME), which is likely to be the case, the effective stellar flux for the inner edge of the HZ increases from 1.10 to 1.18 times that of the Earth raising the chances that Kepler 452b orbits inside of the HZ to probably better than even odds. And since Kepler 452, like all stars, would have been dimmer in its youth, Kepler 452b would have been even more comfortably inside the HZ for billions of years. Considering all these facts combined with the limitations of current models in defining the true inner boundary of the HZ, this is close enough even for this skeptic to consider Kepler 452b as potentially habitable at least in terms of its orbit and effective stellar flux.

Is It a Rocky Planet?

The other important planetary property we can measure using current detection techniques is the size of a planet. Unfortunately, it is here where many past discoveries have run into trouble. It has been suspected for some time now that somewhere between the size of the Earth (or 1 RE) and Neptune with a radius of 4 RE, planets transition from being predominantly rocky with some chance of being habitable like the Earth to being rich in volatiles such as water, hydrogen and helium becoming mini-Neptunes with little chance of being habitable in the conventional sense. Based on recent analyses of Kepler data on the radius of exoplanets smaller than Neptune combined with independently derived masses from radial velocity measurements and other techniques, we now know that this transition from predominantly rocky worlds to predominantly volatile-rich worlds occurs somewhere around 1½ to 2 RE although the precise value and nature of this transition is uncertain due to the small number of planets with measured radii and precisely determined masses in this size range as well as the measurement uncertainties of those values (see The Transition from Rocky to Non-Rocky Planets in Centauri Dreams).

While many earlier claims of finding potentially habitable planets have run afoul of this transition and turned out to be much more likely to be mini-Neptunes than rocky terrestrial planets, in recent months astronomers have started making some effort to address this issue in discovery papers of potentially habitable planets including Jenkins et al.. Based on the analysis of the Kepler photometric data and the properties of the star, Jenkins et al. report that Kepler 452b has a radius of 1.63 +0.23/-0.20 RE which is close to the transition value. Based on their calculations, Jenkins et al. claimed that there was a better than 50% chance that Kepler 452b is a rocky planet. But how did they arrive at this figure?

Jenkins et al. used two different distributions of probable radius values for Kepler 452b and compared them to two different published mass-radius relationships for sub-Neptune sized planets to calculate the odds that their find has a density consistent with a predominantly rocky composition. The radius value distributions were derived from the measured 1.63 +0.23/-0.20 RE radius of Kepler 452 combined with two different models used to determine the host star’s properties. The first model, SPC (Spectral Parameter Classification), determines the star’s parameters by comparing its spectrum to a collection of synthetically generated stellar spectra to find the best fit. The second model, called SpecMath, is considered more conservative and compares the star’s spectrum to a collection of 800 well-studied stellar spectra to derive the star’s properties.

To calculate the probability that Kepler 452b is a rocky planet based on those radius distributions, Jenkins et al. used two different mass-radius relationships. The first was formulated by graduate student Lauren Weiss and famed exoplanet hunter Geoff Marcy (University of California – Berkeley) which was published in March 2014. Weiss and Marcy fitted radius and mass data for 65 exoplanets to come up with a deterministic mass-radius function where a particular radius value corresponds to a single mass value. While simple, this model admittedly does not reflect the fact that exoplanets with a particular radius value can actually have a range of possible mass values reflecting a variety of bulk compositions.

The second mass-radius relationship used by Jenkins et al. was derived by Angie Wolfgang (University of California – Santa Cruz), Leslie A. Rogers (California Institute of Technology), and Eric B. Ford (Pennsylvania State University) and was submitted for publication in April of 2015. They evaluated data for 90 exoplanets using a hierarchal Bayesian technique which allowed them not only to derive the parameters for a best fit of the available data, but also to quantify the uncertainty in those parameters as well as the distribution of actual planetary mass values. Using their approach, they derived a probabilistic mass-radius relationship where the most likely mass and the distribution of likely values are determined that better reflects the uncertainties in the data and the fact that exoplanets with a particular radius value can have a range of actual masses (for a detailed discussion of this work, see A Mass-Radius Relationship for ‘Sub-Neptunes’ in Centauri Dreams).

Using the radius distributions for Kepler 452b derived from SPC and SpecMath, Jenkins et al. found that the mass-radius relationship created by Weiss and Marcy yielded 64% and 40% probabilities, respectively, that their new find has a bulk density consistent with models of rocky planets. When employing the mass-radius relationship of Wolfgang et al., they found a 49% and 62% probability, respectively, that Kepler 452b is a rocky planet. The average of these results is the origin of the quoted greater than 50% odds that the new find is a rocky planet.

Is It Really a Rocky Planet?

While this is a clever solution to a difficult problem, there are problems with this approach. First of all, while the work of Weiss and Marcy was an excellent first attempt to derive the mass-radius relationship using the newly available Kepler data set, the relationship derived by Wolfgang et al. is superior since it uses more data of higher quality that is analyzed in a mathematically more rigorous way. While Jenkins et al. recognize this and prefer the higher probabilities calculated using Wolfgang et al., they used the parameters of the mass-radius relationship derived using all 90 planets with radii up to 4 RE in the original analysis. Based on earlier work by Leslie Rogers, it was recognized that the transition from being predominantly rocky to predominantly volatile-rich takes place at radius values no greater than 1.6 RE (for a full discussion of this work, see Habitable Planet Reality Check: Terrestrial Planet Size Limit on my web site, Drew Ex Machina).

When Wolfgang et al. analyzed just the subset of exoplanets with radii less than 1.6 RE, they derived different parameters for the mass-radius relationship for these smaller planets. For a planet with a radius of 1.6 RE, for example, the most probable mass when using parameters derived from fitting all planets with radii less than 4 RE, as used by Jenkins et al., comes out to about 5 ME. If the parameters derived from just smaller planets with radii less than or equal to 1.6 RE are used, a smaller probable mass value of 4 ME is found. As a result, the probabilities derived by Jenkins et al. are biased towards higher mass outcomes with corresponding higher probabilities of finding Kepler 452b to be a rocky planet.

A better approach for determining the probability that Kepler 452b is a rocky planet would be to compare its properties directly to the population of exoplanets with known radii and accurately determined masses. Unfortunately, Rogers’ paper does not include a simple function that others can use to calculate such a probability since this was outside the scope of her work. Despite this shortcoming, the title of her paper published in March 2015 in The Astrophysical Journal really says it all: “Most 1.6 Earth-Radius Planets are not Rocky”. In other words, Kepler 452b with a radius of 1.63 RE is most likely not a rocky planet but is a mini-Neptune instead, contrary to the claims by Jenkins et al..

Other astronomers trying to calculate the odds that their finds are rocky planets or not have derived probabilities in different ways. Guillermo Torres (Harvard-Smithsonian Center for Astrophysics) on January 6, 2015 announced the discovery of eight habitable zone planets using Kepler data where they quantified the probabilities that their finds were rocky (see Habitable Planet Reality Check: 8 New Habitable Zone Planets on my web site, Drew Ex Machina). Although somewhat different from the method used by Rogers, the approach used by Torres et al. to calculate the probability that a planet with a particular radius is rocky gives qualitatively similar results. Using their model, the chances that Kepler 452b is rocky is about 45%. This is closer to the low-end 40% figure derived by Jenkins et al. than the often quoted “greater than 50%” figure.

Unfortunately, the chance that Kepler 452b is a terrestrial planet might not be as good as even 40%. Recent work by Rebekah I. Dawson, Eugene Chiang and Eve J. Lee (University of California – Berkeley) recently submitted for publication in Monthly Notices of the Royal Astronomical Society strongly suggests that planets with masses greater than about 2 ME (which would have a radius of about 1.2 RE, assuming an Earth-like bulk composition) which orbit stars with a high metallicity are more likely to be mini-Neptunes. This is because stars with higher metallicities tend to have more solid material available to form planetary embryos more quickly making it more likely for them to acquire some gas directly from the protoplanetary disk before it dissipates. Only 1% or 2% of a planet’s total mass in hydrogen and helium is sufficient to puff up its observed radius and make it a mini-Neptune. Stars with lower metallicity values tend to form planetary embryos more slowly and they might not reach the required 2 ME mass threshold fast enough to begin to acquire any more than trace amounts of gas before it has already dissipated from the protoplanetary disk. With a iron-to-hydrogen ratio about 60% higher than the Sun, Kepler 452 has a slightly higher metallicity than the Sun increasing the odds somewhat that Kepler 452b is a mini-Neptune. Taken together with Rogers work, this strongly suggests that the odds that Kepler 452b is a rocky planet are less than 50% not greater as is being claimed.

Conclusion

To be perfectly honest, quibbling over a couple of tens of percent probability one way or the other about the nature of Kepler 452b is most likely not all that important considering the uncertainties in its properties as well as the still substantial uncertainties in the mass-radius relationships available at this time. In the end, we will have to wait for a more definitive derivation of the mass-radius relationship and a more quantitative description of the nature of the transition from rocky planet to mini-Neptune to settle this question more accurately. Despite the outstanding issue of the nature of Kepler 452b, it still has very real prospects of being potentially habitable. But even if it proves not to be, future studies of its properties will provide scientists with vital information on the limits of planetary habitability.

While some might be disappointed by this less rosy assessment, it should be remembered that scientists are still actively analyzing the Kepler data set and performing follow up observations. There are already several potentially habitable Earth-size planet candidates found orbiting Sun-like stars that are being actively studied by members of the Kepler science team and their colleagues. It is only a matter of time before the discovery of true “Earth twins” is announced.

The preprint of the Kepler 452b discovery paper by Jenkins et al., “Discovery and Validation of Kepler-452b: A 1.6-RE Super Earth Exoplanet in the Habitable Zone of a G2 Star”, can be found here.

I stand corrected, Mongo! Although, like work on the Pioneer acceleration anomaly, I think some of what they're including is to be logically inclusive and at the far ranges of plausibility.

Thats a lot of great information mongo. Depending on the trajectory change(s), perhaps New Horizons could get an extended mission to view transits of the local planets to further the understanding of mass and radius, though I think its probably too far out of the ecliptic.

Do you mean local extrasolar planets? New Horizon's location would have almost zero effect on whether or not it would witness transits of any given extrasolar planet. The distance it has traveled from Earth is negligible compared to interstellar distances.

Also, it is not designed to perform precision photometry. And even if it were, that wouldn't provide any information about mass.

I'm not sure what you're proposing here. I may have misunderstood.

I remember Deep Impact had an extended mission that did this sort of thing, but the HRI on that was quite different from LORRI, right?

Perhaps ZLD is referring to having NH look back at our own solar system to view transits?

brellis had the right idea. Its a pretty slim shot that there would be any transits between NH and the sun that would be measurable. All of the planets would miss the plane of view I think but I was thinking large asteroids, comets or KBOs that might transit after the current proposed extended mission. Was only considering that NH has a unique view of the Solar System where the Sun isn't anything but another star and this effect is just going to grow 5 years from now. May not be precise enough, as mentioned though.

NH looking back at the Sun could "see" in the form of transits any object that happened to pass through the tiny fraction of its FOV that wandered into the way of the Sun, and an unknown asteroid (25 km) would block such a tiny fraction of the Sun's light that the signal would be impossible to pull out of the noise.

Meanwhile, a telescope on Earth looking back at the same object would be able to detect any such object against the black background, regardless of its position, and the signal to noise would be much greater.

Basically, any amateur with a 3" scope is better suited to find asteroids than NH looking for them to transit the Sun.

The point wouldn't be to find new objects. The point was to look at known objects so that we could get a better understanding of the mass-radius of <1.6RE bodies. If we could view distant transits of objects that otherwise have a pretty good estimated mass already, it would give a little in the way of a control for the mass-radius relationship that is being disputed among scientists.

There are no distant objects with a good estimated mass, besides the few with an orbiting companion or that a spacecraft has flown by closely. Small objects have very little gravity and don't influence other objects unless they are exceedingly close.

Even if an object transited the Sun as seen from NH, the signal-to-noise would be much worse than observing the same object from Earth against a black background. It is nearly impossible to notice the signal even of Mercury transiting the Sun vs. the noise, and every object larger than Mercury has already been measured very well.

For measuring transiting exoplanets, having a defocused image is actually better than an in-focus image - spreading out the signal helps prevent saturation of the star's light on the imager. Deep Impact's EPOCh (part of the EPOXI extended misision) used the HRIs aberration in a similar way.

Assume the PSF for LORRI is 1 pixel - then the minimum signal detection is the change of that pixel by 1 unit. At far distances, the change in signal due to an eclipse is going to be the ratio of the effective sky area of the two objects, or Re^2/Rs^2. So the effect of the Earth on the Sun's brightness would be 3.2e-5, or assuming 12 bit pixels, about .13 units. So a perfect LORRI with no noise could not detect the Earth pass in front of a perfect Sun with no noise. Now, if the PSF spread out over 100 pixels, then you can detect a change of 1/sqrt(100) or .1 units across all the pixels (I think it's sqrt because that's normally how signal adds on more samples), so just barely detectable assuming perfect conditions.

Hmm, I had not thought about it too much before, but... Isn't this 2d data? As in a bright disk and a dark disk, not necessarily 3d spheres?

So, can we resolve the differences in the light curves of a luminous sphere being transited by a circle, a triangle, a square, a hexagon?
If the light curve data turns out to be a match for a 1 x 4 x 9 monolith, this gets really, really interesting.

MOD: And really, REALLY close to breaking Forum rules. This discussion is slipping beyond acceptable Forum subject matter--only warning.

Possible Trojan planet found?

Characterization of Kepler-91b and the Investigation of a Potential Trojan Companion Using EXONEST

That possible Trojan, associated with Kepler-91b, is a very weird case. The star is a red giant, but the planet is orbiting very close to it (6 day period). The quirk: The orbit is inclined 68° to the line of sight, but we still observe transits because the star is so large and the planet is so close. So, the usual paradigm of the planet's image slicing through the star's image in a straight-line chord is not a good approximation here, and the image it presents to us (though it cannot be resolved as such) is more like the ground track of a satellite orbiting the Earth in Low Earth Orbit, taking a curved path across the star's disc. This creates deviations from the usual case as the planet's entire transit may occur near the star's limb, where limb darkening is significant, so the whole light curve is apt to be unusual.

All told, if we see something strange in this case, it's a good puzzle to work out, and I'm not sure the correct interpretation will easily be had, as this paper indicates. I imagine we have a lot to learn about red giants and exoplanet research can actually further that.

Kepler has also provided some badly needed, new data on a poorly known (and for some reason, one of my favorite) solar system body:
Nereid from space: Rotation, size and shape analysis from Kepler/K2, Herschel and Spitzer observations

MOD NOTE: Moved posts about KIC 8462852 to a dedicated topic to free up the Kepler thread for other mission findings.