Kepler

Kickstarting WTF star monitoring

catdynamics — Fri, 10 Jun 2016 21:53:13 +0000

Kickstarting WTF star monitoring

Tabby's Star - KIC 8462852 - remains one of the more interesting and mysterious objects in the sky.

There is a good update at "Updates on Boyajian’s Star" - Astrowright's blog and "Bradley Schaefer: Further Thoughts on the Dimming of KIC 8462852" at Centauri Dreams has the latest on the controversy over whether the star has undergone long term fading.

Update: "The Most Mysterious Star in the Galaxy" - another guest blog by Schaefer providing a good overview of the issues.

Ultimately to resolve this more data is needed.
There is a Kickstarter Project - "The most mysterious star in the Galaxy" - to get serious time on Las Cumbres Observatory, the request is almost 2/3 of the way there with a few days to go.

Kick in if you can!

"Planet Hunters X. KIC 8462852 - Where's the Flux?" - Boyajian et al.

catdynamics Fri, 06/10/2016 - 17:53

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astro

Kepler

KIC8462852

SETI

WTF

A New Kepler Orrery

catdynamics — Mon, 30 Nov 2015 21:10:24 +0000

A New Kepler Orrery

Ethan Kruse has update the Kepler Orrery, just in time for Extreme Solar Systems III now under way.

Enjoy

catdynamics Mon, 11/30/2015 - 16:10

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astro

Kepler

The Dance of Neptune

catdynamics — Tue, 10 Nov 2015 14:26:38 +0000

The Dance of Neptune

The Kepler 2 mission serendipitously observed Neptune about a year ago.

The images were posted on the K2 website, but according to the website stat like nobody shared them, which sucks.

The animation was just shown at the Division for Planetary Sciences meeting, #DPS15, in DC so it is time to show it again.

Enjoy.

Kepler Observes Neptune Dance with Its Moons

Check Emily Lakdwalla's planetary blog for #DPS15 news

catdynamics Tue, 11/10/2015 - 09:26

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KIC 8462852: Whence The Fading Star

catdynamics — Mon, 19 Oct 2015 09:04:15 +0000

KIC 8462852: Whence The Fading Star

As of this morning we have discovered over 1,500 exoplanets, planets orbiting stars other than the Sun.
In addition to the confirmed discoveries, we have over 3,000 candidate exoplanets, most discovered by the NASA Kepler Mission through transits, where we see the shadow of a planet as it crosses in front of its parent star.
We know, statistically, that most of the candidate planets are real, but a few % are weird misalignments of something else that makes us think there might be a planet there. Filtering those out is hard.

We also see other things, weird and wonderful things...

Little over year ago, I got an email telling me to check out KIC 8462852 - the Kepler Input Catalog entry star number 8426852 - the Planet Hunters, the crowd sourced amateurs who eyeball all the Kepler data, had tagged this star as interesting, and Dr Tabetha Boyajian at Yale and her colleagues were quietly floating what they'd seen to various people because it was really interesting.

Light Curve for KIC8462852 from Boyajian et al 2015 (click to embiggen)

Interesting it was. The star, an F3 main sequence star, apparently a quiet middle aged normal star, somewhat more luminous than the Sun, is dimmed, but a large amount, 10-20%, for many days, in irregular patterns and in asymmetric ways.

For comparison, the shadows of planets dim stars typically by somewhere between 1% and 0.0001%, or less, and for hours or a day or two, not weeks.

Now, we do see things somewhat like this around very young stars, from huge dusty debris disks from which planets are being made, but those often completely obscure the star, and we see their signature in infrared observations as a huge heat glow, as the disk radiates absorbed star light.
The WISE satellite had observed this star somewhat earlier, and it had no measurable infrared glow.
So no big obscuring disk. It is also not young by any age indicator we know of. (Or is it?)

This is a puzzle, because whatever is obscuring the star has to be local to the star; it is moving slow, but not very slow (probably orbiting between 1 and 10 AU from the star); and it has to be BIG - to obscure the star to that extent we are either talking about opaque objects that are several hundred thousand kilometers across - several times bigger than Jupiter - or we are talking translucent clouds that are bigger than the Star itself, more than a million km across.
Really nothing else will work.
Planets don't come that big.
A star that big would be very easily visible.

Most anything else is ruled out by various other observational constraints.

This is fun, it is what most scientists live for - the unexpected mystery, the open puzzle, something new!

What made this particularly interesting is that Jason Wright and collaborators were at the same time working on the Ĝ - G-hat project exploring astronomical signatures of alien civilizations, and were working on a paper on transit signatures of alien megastructures.
Section 4 of the paper discusses KIC8426852 as an example of the sort of thing you might see if there were alien megastructures orbiting stars out in the galaxy, and suggests that currently KIC8426852 is the best known candidate. Which it is.
Which does not mean that the dimming of the star is caused by alien megastructures.

The first transit, looks like a backward comet transit - a comet leading with its tail - a very very big comet; but maybe that is a hint, and we can play with some numbers and try to find testable observables to check.

If the transits are cometary, then they are not actual comets, they have to be disrupted debris clouds from multiple cometary bodies.

The optimal scenario has the comets shattered into perfect 0.1-1 μm dust grains, doesn't matter much whether it is ice, carbon or silicates.
Opacity of such grains is maximal and robust for optical, and fairly flat - though there is still a prediction if the dimming is from optically thin (translucent) dust, then the amount of dimming is different depending on the colour of the light, Kepler only looked in white light so we haven't seen that yet.

So how much dust do we need?
The opacity is ~ 10^-21 /N_H cm² - for standard solar dust/H ratio.
There is no H here, but that is ok, we can ignore that.

1) If the cloud is opaque, it is few 100,000 km across and some 'rithmetic suggest a total absolute minimum dust mass of ~ 10¹⁶ gm.
This corresponds to about 2 km radius rocky/icy body totally shattered into micron dust grains.

2) If the cloud is translucent and ~ 1,000,000 km across, then you need more dust, but can still do with ~ 3 km radius rock. As an absolute minimum, if ground up perfectly into micron dust. Which it won't be.

Ok that is surprisingly doable.
NB: for realistic dust from comets you need a much bigger comet, since actual comets rarely get ground up evenly into perfectly distributed 1 micron dust grains - which is a problem.

But, these dust clouds are not bound.
They ought to be spreading apart with speeds ~ 0.1 km/sec or so.
So they only last ~ few days-to-months!
This is not much longer than their transit time.

And they had to cross right in front of our line of sight at just the right time. Odds of them doing that were about 1/1,000.

But, Kepler did look at over 100,000 stars!

But, most of them were boring stars unlike this one...

There is one thing about this star - it has a probable close companion.

KIC8462852 candidate companion

There is an apparent M star projected about 1,000 AU from the primary star. In just the right place to be in an orbit that would send it careening through the Kuiper belt of the primary star every million years or so, triggering a comet shower onto the star!

We know that the distribution of comet close approaches ~ 1/a where a is the distance of closest approach. So roughly one comet in 100 comes within 1 AU of star if they start at 100 AU.

We have to keep up the comet showers every million years for a billion years without running out of comets.
So, how many comets do we need?

The answer is well over a billion.

That, is not impossible.

So is that the answer?
Well, maybe - if it is, then we won't see those transits again, because the comets will be on near hyperbolic orbits that won't come around and we saw many different objects on adjacent orbit.
We'd also expect the dust clouds to dissipate.

The infrared glow from such clouds is ~ 10^-6 the luminosity of the star, maybe 0.1% or less of the infrared glow of the star (depending on their exact distance and temperature), which is very hard to pick out.

However, the real question would then be, what broke the comets? It could be a fast very close passage to the star, or a very close passage to a planet, or a very unlikely comet-comet collision, but none of those seem likely to produce the sort of dust clouds required to explain the dimming we see.

There is an alternative, non-alien scenario, for the next post...

In the mean time, contemplate this: we just learned that normal middle aged stars can naturally have stuff come and dim them by 10-20% for multiple days.

Imagine that happening to the Sun.

catdynamics Mon, 10/19/2015 - 05:04

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Brrrrrrrrrrr

Is it at all plausible that the star could be an intrinsic variable? Say, with the internal dynamo doing strange things like this?

The lack of an infrared signature is a dealbreaker for quite a few otherwise plausible models. Including one in which putative aliens are using a piece of megastructure like a partial Dyson sphere--they have to dissipate heat somehow, and for surfaces with temperatures of a few hundred kelvin (as anything involving alien engineering would have to be), it would be dissipated in infrared. Suppressing that would involve such tremendous amounts of liquid helium that they'd have to devote some large fraction of the collected energy to re-liquefying the helium, so I'm not sure that would be worthwhile.

No, there is no way the star can dim like that on these time scales intrinsically.

The problem with many natural phenomena is you'd expect the structure to be circumstellar or radially extended, which is precluded by the absence of mid-IR emission in the WISE data.

So, any IR has to be either transient, having appeared post-WISE observations; or, be low enough to be below WISE upper limits, which requires fairly small large patches of obscuration; or, all the re-emission is in far-IR outside WISE's sensitivity range.
The latter two are broadly consistent with alien megastructure conjectures.

The real tests will be whether the transits (if they repeat) are achromatic; whether the shapes are time variable; if there is any mid/far IR (now); whether the star is really young (GAIA will nail that down); and what the transits look like in detail over time. if they repeat - there is some high S/N data possible on this.

It is really hard to fit anything plausible to these things. Lots of clever people have been trying for over a year. Requires either lots of arbitary free parameters, or amazingly freakish luck to have caught a rare phenomenon in the act; or we are very wrong about something.

If the objects are orbiting, wouldn't there be positions from which starlight would be reflected rather than occulted ? The graphs only appear to show dips.

In general, yes, you can get forward scattering and reflections possible. We see them in some cases for transiting planets.
They depend on the albedo of the object transiting.

If you look carefully at the lights curve, there are in fact a few places where the light curve seem to be above the baseline at bit less than 1% level - that is a huge signal for Kepler, and may be real.

Suddenly a weird newspaper headline became way more interesting.

Distant Cousins: Kepler-186f

catdynamics — Thu, 17 Apr 2014 12:48:58 +0000

Distant Cousins: Kepler-186f

Big Eyed Beans from Venus - Captain Beefheart and his Magic Band!

Cool. Literally

Comparable to Mars in effective temperature, bit larger than Earth, probably slightly more massive than Earth (mean density could be lower), atmosphere unknown.
Might well have extensive surface regions with persistent liquid water.

Kepler-186f comparison

catdynamics Thu, 04/17/2014 - 08:48

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Most of Earth's twins aren't identical, or even close!

esiegel — Wed, 05 Jun 2013 15:11:14 +0000

Most of Earth's twins aren't identical, or even close!

"You can spend too much time wondering which of identical twins is the more alike." -Robert Brault

You've of course heard by now the news that Kepler, the most successful and prolific planet-finding mission of all time, has probably reached the end of its useful lifespan.

Image credit: NASA / Kepler Mission / Wendy Stenzel.

With nearly 3,000 planet candidates under its belt, including many approximately Earth-sized (and some even smaller), and many within their parent star's habitable zone, we now know that, at least planet-wise, we're not alone in our galaxy.

Image credit: NASA Ames / JPL-Caltech.

In fact, there are at minimum some 17 billion Earth-sized planets just in the disk of the Milky Way. But it takes a lot more than that to make a genuine twin of the Earth! Yes, we've taken some amazing steps forward in the past few years, but let's not lose sight of the ultimate goal here: to find another planet that harbors some type of advanced life.

Image credit: Museum Mensch und Natur in München / Wikimedia Commons user Ghedoghedo.

That is, chemical-based life akin to what we know on Earth. Even if it were akin to life on Earth as it was 500 million years ago, that'd be incredibly interesting! There are plenty of other possibilities than the chemical-based kind we've developed and grown accustomed to here on Earth, and in fact that may actually be more common in the Universe than the life we know.

There are some good reasons to believe this.

Image credit: the Morgan-Keenan spectral classification / Wikimedia Commons user LucasVB.

Our Sun is a 4.6 billion year-old G-class star. While you might look at the diagram above and think this makes us an "ordinary" star, the fact of the matter is our star is more massive than 95% of all stars out there! M-dwarfs, the little red guys all the way on the end, are by far the most common star type in the Universe, with three-out-of-every four stars being M-stars. In addition, our oceans will boil after another billion years or so, but M-stars burn at a stable temperature for up to tens of trillions of years!

Image credit: Expedition 13 / ISS / NASA / United States Government Works.

But that's a digression that could lead us far off course; if we're looking for Earth's twin, or a planet that's an awful lot like our own around a star that's a lot like our own, let's think about what we'll need.

First off, we'll need a star like the Sun. That means a star of both the same temperature and spectral class, but also of roughly the same age.

Image credit: Retrieved from Margaret Murray Hanson at University of Cincinnati.

It takes time for life to develop and evolve into something interesting, and that means we need a star system that's at least many billions of years old. But we also can't wait too long, because as stars age, the region of the core that fuses hydrogen into helium grows, meaning that power output (and brightness, and hence temperature) increases. Eventually, the planets (like Earth) that were once habitable will get too hot, permanently boiling the surface water and ending life-as-we-know-it.

Image credit: artist Ron Miller of http://www.black-cat-studios.com/.

So let's say we've got about a billion-year-window, or about 10% of the life of the star. There are some 200-400 billion stars in our galaxy, and about 7.6% of them are G-class stars, or the same type as our Sun. Even though our Sun is more accurately classified as a G2V star, that still means that around 10% of all G-class stars are the same type as our Sun.

Image credit: NASA's Solar Dynamics Observatory.

Estimating on the high end, that should tell you that there are 400 billion stars, 7.6% of which are G-class, about 10% of those are the same sub-class as our Sun, and about 10% of those are the right age to have interesting life, or some 300 million candidate stars.

Well, maybe. You see, we need something more than that.

Image credit: Nigel Sharp, NOAO / National Solar Observatory at Kitt Peak / AURA / NSF.

This is the spectrum of the Sun. Or, in other words, these lines you see are representative of all the different atoms -- and their ratios -- that come from the period table of elements. They're abundant in our Sun, and they come in very specific ratios.

The amount of everything that isn't hydrogen or helium to all the fuse-able material in the Sun is what astronomers call metallicity. If we want an Earth-like world, we need a star with a Sun-like metallicity.

Image credit: Wikimedia Commons user Rursus, based on Gunnar Larsson-Leander's work.

This isn't so bad; as many as 25% of the stars that were formed around the same time as our Sun were Intermediate Population I stars (like we are), and a great many of them (perhaps around 15% of those) have the same metallicity as our Sun, shown in green, below.

Image credit: Zeljko Ivezic/University of Washington/SDSS-II Collaboration.

That means there are some 11 million stars in our galaxy that have the same type of home star we do, with the same abundance of heavy elements, that formed at the right time that they could have complex life on their worlds the same way Earth does. (And this doesn't even take into account that many of the worlds with more or fewer metals could be more likely than Earth to have life. Like I said, just because it happened under our conditions does not mean our conditions are the most favorable for complex life to have happened!)

So out of these 11 million solar "twins," how many of them have Earth-twins in their habitable zones?

Well...

Image credit: NASA / JPL-Caltech / T. Pyle.

We need to form a rocky planet of the right size with the right elemental abundances, the right amount of water, and in the right location to be considered a twin of the Earth.

These problems are all inter-related. The first one is easy: if the central star has the right elemental abundances, then the planets it formed should have the same density-radius relationship as our Solar System does.

Image credit: Dimitar D. Sasselov, Nature 451, 29-31 (2008).

It's difficult to say how abundant this is, because Kepler wasn't really sensitive to that sort of information. If we make our best "guesstimate" using what we know, about 4% of Sun-like stars will have Earth-sized planets in the inner Solar System, and using what we know from simulations of orbital mechanics, maybe 10% of those systems will have an Earth-sized planet in a similar location to Earth around our Sun.

Illustration credit: NASA.

All of which is to say, based on the best that we know right now, there ought to be some 45,000 Earth-twins out there with the same age and the same elemental abundances as ours, and in orbit around a star virtually indistinguishable from our Sun.

To find out how many are more like identical twins than fraternal twins, we need to know a few more things we have no data about yet.

Image credit: (c) Lynette Cook. (Yes, this is artwork!)

How many of those have both significant oceans and continents like we do?

How many of those have rapid rotations between night-and-day like Earth and Mars do, but like Venus and Mercury don't?

And then, we can get to the real questions, like how many of them had life develop on them? Complex life? How many of them have oxygen-rich atmospheres? How many have magnetically active dynamos in their core?

Image credit: Joe Tucciarone.

And maybe the most restrictive in the search for an Earth-twin: How many have a substantial Moon like we do?

Regardless, what I wanted to impress upon you are the following three things, even if you take nothing else away:

Most of the planets we're finding, that we call "Earth-like" (or even Earth-twins if we're feeling poetic) are more like distant cousins, with more differences than similarities.
True "twins" of the Earth, where a planet has the same size, elemental abundances, rotation period, a similar Moon, the same age, and orbiting a virtually identical star are really, really rare; there may only be a handful in the entire galaxy when all is said-and-done.
But if we're looking for complex life, there's no reason to restrict ourselves to Earth-twins; much of what we adore about our planet might not even be the optimal conditions for complex life to have developed!

But -- even with Kepler in the rear-view mirror -- what we know now is incredible.

Image credit: NASA / Ames / JPL-Caltech.

Unless we're grossly wrong about a whole bunch of things, the conditions for complex life are everywhere in our galaxy, and they're there right now. An Earth-twin might be romantic, but it's a horribly restrictive way to seek out the most distant of our cosmic cousins. Our search continues.

esiegel Wed, 06/05/2013 - 11:11

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Ethan, you just blew my fucking mind. I've been reading you for years and enjoying every word. Thanks much for what you do as an educator.

Really great piece, with excellent informative graphics too, thanks!

This is a great story, and please forgive my nitpicking about two details that I have issues with:

- The billion-year-window for advanced life. Eukaryotes have been around for 2 billion years, bacteria for twice as long. They should definitely count as advanced life: a yeast cell is in fact more complex than a human cell, since it has to account for *all* functions, whereas a human cell can specialize.
- The oxygen atmosphere. The Earth acquired one only recently, and as a *consequence* of advanced life, not as a required condition. Oxygen was in fact very toxic for the organisms a few billion years ago, and may have caused the largest mass extinction in history.

Ethan,

Is there still a significant selection bias in the planets that Kepler finds? In the earliest days of exoplanet detection, there were many more Jupiter-type planets found than there were Earth-type ones. This was because it was much easier to detect Jupiter-type planets, not because they were actually more common. Is there still a significant selection bias?

I felt from a young age that there must be some similar planets to the earth. This argument shows that not only are there many possibilities for life but there are likely some very similar planets. It is nice to have a thoughtful confirmation of my gut feel.

It is astounding how many planets there probably are out there. It has also been nice for Kepler to confirm that feeling too.

It's interesting to think that it *could* be that Earth is actually an outlier - we have about the most energetic star possible for life to actually evolve on a planet around. Any bigger and it would have either blown up by now or the higher UV flux would have stripped the atmosphere (at least of water)

BUT..

This effect - specifically photodissociation of water - may be important in driving the overall oxidation of the planet - hydrosphere plus upper mantle - which in turn allows sharp redox gradients and hence 'interesting' life. Bear in mind that the process of 'oxidising' earth took perhaps 2-3 billion years, and it was only after that happened

So a hypothesis from this is that there may be many, many habitable planets around less energetic stars that are still undergoing this process, and won't be suitable for advanced life for a *long* time.

Counter-problem: These planets will become geologically inactive over this time scale, which then leads to problems maintaining the atmosphere..

But it could be that the Earth is in fact one of the first planets on which complex life emerged, and from the perspective of 10 billion years hence there could be a stream of civilizations emerging..

Did you just update the Drake equation as the Siegel equation?

Sean @3: The factors that bias in favor of detecting hot Jupiters are still present in the Kepler data. Most of the methods we have for detecting exoplanets involve effects that are larger for large and close-in planets than for smaller, further out planets. I know of one case where a candidate exoplanet has been imaged directly; that method favors cold Jupiters (you still need a big planet to see it, but you want it to be far enough from the star that the direct light from the star doesn't overwhelm the reflected light from the planet). It's an old problem in astronomy, known as the Malmquist bias. There are ways to deal with it, but they involve assuming a function for how mass is distributed with respect to some intrinsic parameter (brightness, in the case of stars).

Andrew @4: As I've always understood it, the key change in Earth's atmospheric chemistry came about with the evolution of photosynthesis. The Earth originally had a reducing atmosphere (CH4 and CO2), but photosynthesis released large quantities of O2, which is the prototypical oxidant. In addition, while it took between 3.5 and 4 billion years on Earth for multicellular life to arise, we don't know if that could happen faster on other planets. We can have the parent star be a bit brighter than the Sun before the window drops to zero--I don't have a good feel for exactly how spectral class maps to stellar mass, but there could be enough time to get multicellular life around an F8 or F9 star (F5 or brighter would probably not live long enough). On the flip side, the habitable zone moves closer with smaller stars, partially compensating for their lower UV flux. You could probably get life around any G class star, and probably the brighter K class stars. With M class stars, you run into a different problem: you have to get so close that you risk being wiped out by a coronal mass ejection.

And it's that imbalance in O2 that will be used to determine if there's life on other planets: look at the atmosphere of the planet and check the relative abundance of O2.

If it's as high as ours, then there's life there.

And of course there is the likely importance of the asteroid belt, and thus a giant planet like Jupiter beyond, for seeding the maturing Earth with water and organic materials and periodically clearing a bunch of species off the table.

I don't think destroying 99% of life on the planet and putting them back to the bacterial age counts as helping life survive.

It helped US turn up, but it is entirely unsupported to say that it was needed for life to thrive here.

And AFAIK it's still an open question whether Jupiter is a net benefit or detriment -- if the objects it captures or tosses out of the solar system outweigh the outer solar system objects it disturbs and puts on a path through the inner solar system.

@ Sean T, Eric Lund

Another important factor in the Kepler data is that it needs to see multiple transitions in order to distinguish a planet candidate from a transient event. So the amount of time the mission has run dictates what planets it's even conceivably possible Kepler could have detected -- thus another reason why the mission was front-loaded with hot planets in small orbits.

The original metric was three transitions -- so Kepler's Prime Mission timeline of 3.5 years was to give us a good chance of seeing the required 3 transitions of a planet at 1 AU from its star.

This criterion was designed based on the assumption that our sun was a fairly typical star in terms of sunspot activity. It was discovered early on in the mission (and is thus yet another science achievement for Kepler) that our sun is actually relatively quiet and stable in comparison to most of the stars out there. This extra source of noise meant that now they would need FIVE transitions to be able to clearly distinguish an exoplanet candidate.

Unfortunately, this means the Kepler mission ended before it could have possibly seen five transitions of an earth-like planet around an earth-like star. While I would never call Kepler a failure, it is true that this was one of the goals, and it did not accomplish it.

Maybe someone will figure out a clever way to tease extra signal from the noise and we can find some extra candidates from just 3 or 4 transitions... or maybe we'll just need a new exoplanet surveying tool with updated assumptions!

Its an interesting exercise, but I didn't think any serious SETI types were really looking for Earth's twin, were they? This might be the sort of search we might be interested in if we were looking to colonize another star, but it seems somewhat overspecified as search criteria for life-bearing worlds.

Spin off blog posts from this would be numerous. One would be the importance of our moon to this question of advanced life.

On a different note, if the moon was the result of a massive collision, it would seem that the original orbits of the earth-moon system would be very eccentric. How long would it take to "settle down"?

Or, as is often the case, am I missing something?

This is vary interesting post i really like it.

We need to hurry up and create a vehicle of some sort that can sustain light speed already ! I want to meet the people that live on a twin of our planet before I pass away!

To date no identical solar twin (thus no advanced life) has been found, an identical solar twin would be a G2V star with a 5,778k temperature, be 4.6 billion years old, with the correct metallicity and a 0.1 % solar luminosity variation. While some G type stars are close, none have the identical proprieties of the sun that would give a star low luminosity variation. Middle age stars at 4.6 billion years old are at the most stable state. Proper metallicity and size are also very important to low luminosity variation. We have 2.5 million star logged and not one identical solar twin, thus no advanced life. Each day it looks more like we are alone.

Kepler: the little spacecraft that could

catdynamics — Wed, 15 May 2013 14:07:08 +0000

Kepler: the little spacecraft that could

I come to praise Kepler, not to bury it...

Kepler!

The Kepler Mission is one of the little NASA spacecraft that so frequently comes along, exceeds all expectations and changes our perspective of the universe.

There is a good Quick History of the transit method and Kepler Mission concept on the website.

Otto Struve noted in his seminal 1952 note that planetary "eclipses" of their parent stars ought to be detectable by photoelectric methods, a proposal that some two decades later was quantified by Rosenblatt, and then explored in detail (including development research) by Borucki and collaborators at NASA Ames.

A space based transit mission was first proposed more than 20 years ago, and was highly rated, IF the detector technology could get to the point where very low transit amplitudes could be measured and small radii planets detected. The review also noted that there would be significant secondary astrophysical science accomplished by any such mission.

A decade later, Kepler was finally selected, the fourth time it was proposed to the Discover class medium size NASA mission. By that point the detector technology was mature, a testbed demonstrator had been built, and the concept of transit observations of exoplanets had been demonstrated both from the ground, and from space, using the Hubble Space Telescope. The latter demonstrated that very high precision relative photometry was in fact achievable from space.

Kepler launched in March 2009, just over 4 years ago.
It had a nominal mission life of three years, and a main mission goal to find earth size planets in the habitable zone of solar like stars.

After the nominal mission, Kepler was given a three year mission extension to 2016, to continue the continuous monitoring of the 150,000 or so stars in the Kepler field.

Kepler Field

Kepler has discovered almost 3,000 planetary candidates, of which about 100 have been confirmed through a variety of techniques, and, statistically, most of the rest are likely to be real planets.

Kepler has not quite found earth like planets in the habitable zone, yet.
It is heartbreakingly close to doing so.
More time for observations is needed, primarily because the stars being observed are a little bit noisier than expected. The periodic signal from the planetary transits can be dug out of the noise, but more observations of repeated transits are needed to get the signals out as you approach the limit of detectability.
Six years of observations ought to get Kepler to its goal of detecting earth size planets orbiting stars similar to the Sun at a distance where liquid water can persist on the planet's surface.

To operate, Kepler's orientation has to be held very stably to view the stars it is looking at. To do that it uses reaction wheels:

Kepler Reaction Wheel

Kepler needs three reaction wheels to stay on target.
Any less and the spacecraft drifts, losing lock on the stars.
It has thrusters but cannot use those to stay on target for any length of time before they run out fuel.
Kepler carries 4 reaction wheels. They are heavy and expensive.
That is one spare.

One reaction wheel, wheel #2, failed in 2012.
A second reaction wheel started to show symptoms of degradation a few months ago. Twice in the last few weeks the spacecraft has safed, gone to a rest pointing, while the reaction wheels were despun with the thrusters, and diagnosis tests runs.
Reaction wheels are moving parts, they wear and tear, and have finite life expectancies.
Since the reaction wheels are all the same, they are vulnerable to common mode failure.

Then, last night Kepler went into a safe mode, again.
Switching back to reaction wheel mode the diagnosis showed reaction wheel #4 had seized.

That is the end of Kepler's primary science mission.
The data is in the archives available for analysis. There will be no more.
It is just short of finding the other Earth.
So very very close..

Kepler can do some stuff with only three reaction wheels, basically driftscan observing. It is a wide band wide field optical telescope with a 1 m mirror.
Whether it is worth doing so to keep the spacecraft going will be an interesting decision.

catdynamics Wed, 05/15/2013 - 10:07

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Thanks for the nice piece on very short notice. A few points...

The original spacecraft design was for 4 years. The primary mission was shortened to 3.5 years due to budget pressures. I think that the spacecraft probably reached the four year design requirement for science operations on May 12, 2013.

It is not entirely clear that data collection can not be resumed. During the press briefing, they mentioned that they will consider various options for how to resume data collection. Yes, there's a chance it won't reach the same quality as before, but there's also a chance it could resume planet hunting at a similar precision (e.g., if the reaction wheel that failed previously were to be operable again now that it's been rested). We need to wait for the engineering work to evaluate the situation, so they can devise the best strategy and order for trying things out and determining the spacecraft's current capabilities before writing it off.

Even if no further data collection were possible, there is additional data on the ground that will take time to be reduced before it becomes available to the science team and the public via the MAST archive. There is also additional data still on the spacecraft. I have no reason to believe that data won't be downloaded to Earth, reduced, placed in the archive and lead to good science.

Finally, I'll add my own speculation. I'm not an engineer, so I don't know what is really possible (or perhaps more relevantly, what is financially feasible).
Yes, drift scanning isn't ideal for searching for Earth-size planets, but could Kepler have enough precision with two reaction wheels to conduct a survey of more stars for Neptune or Jupiter-size planets?
I would guess that even with only two reaction wheels the spacecraft could still obtain photometry of eclipsing binaires with precision good enough to search for circumbinary planets (and brown dwarfs, triple stars, etc.) via Ecipse Timing Variations. Whether it will may come down to how much it would cost to modify the software and someone at NASA weighing that against other mission operations.

Of course, it's possible that someone could propose a new and creative use. Eclipsing binary survey? Supernovae search? Near-Earth asteroids? I suspect that the project team at Ames would be interested in hearing from people who have interesting and practical ideas that could become part of a proposal for a modified extended mission for the upcoming Senior Review cycle. It will be interesting to think about these things once the engineers have assessed the remaining technical capabilities.

Quick comment: Kepler has peculiar constraints because the solar cells are on the side of the telescope - it can't point anti-solar, has to point at some oblique angle to Sun.
It also has to maintain Earth communications.
So it has a very hard time pointing now - I think it will be stuck doing a conical drift off the ecliptic.

Secondly, it can't download the whole field - with a fixed field choosing the stamps to diff and send down is easy, with a drifting field data sampling and sending will be hard.

Thirdly, the PSF is huge - about ten times the diffraction limit. This is great for relative photometry of bright stars but degrades almost all other astrophysical applications.

Then the question becomes is the residual science worth $20 million in ops? I fear the answer will be No. After a politely short interval.

Then the question is how much will go to archival research - funding for that ought to be sharply increased, but still less than the mission ops cost, to dig as deep as possible into the data and do associated modeling.

Not that I'm biased or anything...

Kepler already downloads full frame images periodically. I think it is roughly once a month.

If instead of slewing back and forth to point at the Kepler field, Kepler could point in a direction relative to Earth and Sun that allowed quickly alternating between data collection and downlinking without significant slewing, then one could get a lot of new data for new targets without having to define apertures.
In theory, one could pick just the best CCD modules to store/downlink to further cut down on data volume and increase the duty cycle. I can imagine that might be great practice for astronomers who specialize in data mining and help astronomers prepare for LSST. Would that be worth $20M/yr? Would it cost more to rewrite the software? Could it be done for less because NASA would be willing to accept a lot more risk? I don't know.

I definitely agree that NASA should maintain and even increase the funding for archival research. This is a beautiful data set, but it will be a challenge to pull out the smallest and longest-period planets. If there were only 4 years of Kepler data, then it would be even more important to develop out new statistical methods to maximize the planet detection capabilities. Once you start digging into the noise, then it becomes even more important for multiple research groups to perform independent analyses of the data to make sure that results are robust.

exoplanetology sundries

catdynamics — Mon, 11 Mar 2013 22:54:13 +0000

exoplanetology sundries

There were a number of interesting results reported today, the start of what promises to be an interesting week:

IR spectra of HR 8799 planets - Scharf at SciAm blogs reports on the Oppenheimer et al paper using the P1640 at the Palomar telescope.

Their interpretation of the rather low signal-to-noise low resolution spectra is that the outer two planets have little methane in their upper atmosphere and the inner planets do seem to have methane and that there is evidence for ammonia in the outer planets.

I suspect more data is needed.

HR8799 is an interesting system, I'm still not convinced by the standard model, but my alternative conjecture may be too alternative....
Maybe I ought to just write it up.

Charles Cockerell goes all negative on alien life - I'm getting a strange negative vibe from the SETI community, not sure what is driving it, my personal sense is the opposite that prospects for life are massively improving as we learn more.

Kepler Mission Manager Update: urgh.
After the deliberate entry into safe mode of the spacecraft earlier this year, the preliminary read is that reaction wheel #4 is still acting up - exhibiting symptoms consistent with the failure mode of the previous reaction wheel.
Kepler only has 4 reaction wheels.
One is broken.
It needs 3 to operate.

The housekeeping data was downloaded last week, and ought to give a more robust diagnosis of what is going on once it has been analysed.

We really need Kepler to survive the extended mission and not flake out just as things are about to get really interesting.

New blog - High Metallicity

catdynamics Mon, 03/11/2013 - 18:54

Tags

Just a note. blog URL/name have changed.

Thanks for the free publicity :P

Free?!
"There ain't no such thing as Free Publicity!"

Exoplanets in Multi-body Systems in the Kepler Era

catdynamics — Wed, 13 Feb 2013 12:49:26 +0000

Exoplanets in Multi-body Systems in the Kepler Era

The shadow of a shadow of a planet... and other fun Kepler discoveries

Exoplanets in Multi-body Systems in the Kepler Era is a conference currently under way at the Aspen Center for Physics

Physicists hard at work

The meeting is very vibrant, with a mostly very young crowd of active researchers.

There have been a number of very interesting talks reporting some very interesting discoveries, many of which are embargoed...

One, still unpublished discovery, from Josh Carter et al, for a KOI-not-to-be-named, used transit geometry from two planets and measurements of the stellar spin from astroseismology to show that the stellar spin was misaligned to the plane of the transiting planets, but that the two planets were very close to coplanar.
This is somewhat puzzling, because the disk the planets form from carries a lot of angular momentum and should also accrete onto the star and align its spin, but there is a hint of a third planet in the system, which may be misaligned with the other two. If it is aligned with the stellar spin axis, things will get very interesting.

A very cute discovery was presented by Hirano et al: Planet-Planet Eclipse and the Rossiter-McLaughlin Effect of a Multiple Transiting System: Joint Analysis of the Subaru Spectroscopy and the Kepler Photometry

What they found is a two planet transiting system - two separate planets cross in front of the star. The planets are in 10 and 22 day orbits,
but, the planets are closely aligned, and they have caught one planet shadowing the other during transit!

Double shadow transit of KOI-94 - from Hirano et al 2012

ie there are times when both planets are crossing the star, and their tracks are so closely aligned that some of the time one planet shadows the other while they are crossing in front of the star!
This shows up as a very slight re-brightening of the star.
That is the little bump in the middle of the transit dip.
The bump fits the predictions of Ragozzine and Holman (2010).
This is a very cute result.

I'll add more interesting results as they come and as I have time to do so, except of course those embargoed, we'll hear about them soon enough... and they're Soooo COOL! ZOMG!

I did a poster - done enough talking for now:

Kepler-16

This is from The SDSS-HET Survey of Kepler Eclipsing Binaries: Spectroscopic Dynamical Masses of the Kepler-16 Circumbinary Planet Hosts - Bender et al, ApJL 2012. Ours is the poster on the right, the one on the left is from John John.

We, by which I mean "they", since I am but a Pet Theorer, got spectra of the rather faint secondary of Kepler-16 - the first Kepler circumbinary planet - which allowed an independent test of the transit timing variation model to confirm the discovery.
Tricky bit of observation, if I say so meself, using the HRS spectrograph on HET...

More later, hopefully, it is a busy week.

catdynamics Wed, 02/13/2013 - 07:49

Tags

Sounds like some new and exciting things are on the horizon. I will be checking in here often to see when the embargo is lifted. Maybe we can somehow get Julian Asange involved so we dont have to wait for the actual release!

Julian Assange may yet beat the DoJ but I wouldn't fancy his chances against Leslie Sage.
Wait.

Kepler

Kickstarting WTF star monitoring

A New Kepler Orrery

The Dance of Neptune

KIC 8462852: Whence The Fading Star

More Than One Right Answer

Distant Cousins: Kepler-186f

Most of Earth's twins aren't identical, or even close!

Kepler: the little spacecraft that could

exoplanetology sundries

Exoplanets in Multi-body Systems in the Kepler Era