AstroWright

"This is Golden Age of Astronomy"

By Jason T Wright on May 13, 2012 4:46 PM | 0 Comments | 0 TrackBacks

The title is the editor's [sic] but the original article text is mine (slightly edited). The Centre Daily Times is running a series of weekly columns on research at Penn State, and I was asked to write this week's entry.

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I wanted to give readers a sense of both the perspective I have of how much we've learned within the lifetime of practicing astronomers, as well as a future perspective of how much we stand to learn in the near- and medium-term, along with some of the jargon they'll see in the media.

I've been thinking a lot lately about the search for life in the Universe, and the distinctions between the hunt for planets capable of hosting life, for life itself, and for intelligent life (more on this later). This entry reflects a draft of this thinking -- how we, on one hand, look for the places life-as-we-know-it could flourish, and on the other we seek to know how we would know life-as-we-know-it if we found it. (I like to point out that we don't really know how to search for life-as-we-don't-know-it: that's a big search space, with the exception of one dimension in that space, and how would you know life-as-we-don't-know-it if you found it? More about the exception next month.)

I can't find a good link to all entries in the series (this is the second). Here is the first, by Prof. Andrew Read regarding drug resistance.

"Dispositive Null"

By Jason T Wright on April 23, 2012 8:25 AM | 0 Comments | 0 TrackBacks

I've been getting some good feedback through the FaceBook regarding the idea of "dispositive null" as good new jargon; so let's consolidate the discussion and near consensus here (see that post for a synopsis of the contributions from others to this idea).

A "null detection" or "non detection" is the absence of a detection; it often means that you have shown that there is no signal down to some upper limit. In a statistical sense, we often write that we have ruled out signals of strength K or stronger within certain parameters with some confidence (X% or n-sigma).

This is a logical prerequisite to ruling out a specific model, but not its rhetorical equivalent. In the title of a paper, or its abstract, or in a press release, we want to write that we have disproved someone's claim, or some conventional wisdom, or some popular model of some effect. Saying that we have "failed to detect" it makes it sound like the experiment was a failure, when in fact the experiment may be definitive.

A great example is the Michelson-Morley experiment which disproved the existence of "ether", the medium in which light travels. If the ether existed, as most physicists assumed, then the motion of the Earth through the ether (as it rotates and revolves around the Sun) would cause light to travel at different speeds depending on its direction: in the direction of Earth's motion it would seem to be going more slowly, the same way that a car moving down the highway in the lane next to you seems to me moving more slowly than 55 mph. Light traveling opposite Earth's motion would seem to be going quite quickly, the way that cars moving in the other direction seem to go past you very fast.

Michelson and Morley showed that the speed of light was independent of direction to a precision far beyond the signal expected from the motion of the Earth. Their purpose was not to determine if the speed of light was direction dependent, but to determine if that directional dependence had a particular value. They showed that if it did have a nonzero value, it was much smaller than the ether hypothesis predicted, so there was no ether. Their null detection of the ether was dispositive.

Now, in principle they actually had an upper limit and only ruled out the ether to some very high confidence, but the term "dispositive null" is a qualitative conclusion, not a strictly quantitative assessment of their confidence. The term "statistical significance" plays a similar role in statistics: it has no universally-agreed-upon quantitative meaning, but indicates that the authors are claiming a result is real, and not the result of a statistical fluke.

We had a similar experience with HD 149382 b; we were ruling out a specific claim, and we did so beyond any "reasonable doubt". We also put strong upper limits on the existence of any planet in that system, but only subject to a complex set of parameter space (short period orbits except those commensurate with one sidereal day... etc. etc.) So we had an "n-sigma upper limit" for many kinds of planet, but a dispositive null for Geier et al.'s claim.

I also linked to two other cases of similar results: HD 97657, whose transit was erroneously reported, and Fomalhaut b, whose thermal emission remains undetected. In the former case, the transits were claimed, but this paper shows that if they exist are not at the claimed depth. In principle, this is a strong upper limit, but with respect to the earlier claim this is a dispositive null.

With respect to Fomalhaut b, things are a bit more subtle. The detection of that object in optical emission implied that it was a planet of a certain mass and age. Models say that if that is true, then there should be a certain level of thermal emission, which Janson et al. would see, but do not. This is thus a dispositive null with respect to a certain class of model explaining the HST detection of Fomalhaut b: that it is a young-Jovian mass planet. Something is there with a lot of optical emission, but it's not what Kalas et al. postulated (this is mildly unfair to Kalas et al., though: they knew that the infrared emission was below the expected value, and suggested reasons that might be so. The new Spitzer observations are an order of magnitude more sensitive than Kalas et al.'s upper limit, ruling out most of those reasons.)

Evidence of Absence

By Jason T Wright on April 17, 2012 8:24 AM | 1 Comment | 0 TrackBacks

Science is filled with jargon: words that have very specific meaning in the context of science, that might otherwise be ambiguous or have very different meanings. When an economist says that an effect is "marginal" she doesn't mean it's small, or not important, or relegated to the margins: she means that it is measured differentially with respect to the current value. For instance, suppose your overall income tax rate (taxes divided by income) is 25%, but because of your tax bracket if you make one more dollar your tax will go up by 33 cents. Your marginal tax rate is then 33%.

Astronomy is filled with jargon. We say that light is "extinguished" (some astronomers say "extincted", making the more pedantic astronomers flinch), but we don't mean it "went out", we mean that it has been absorbed or scattered out of the line of sight to its source by intervening material. We might write that a star has an "infrared color excess of 0.5 magnitude"; in this case the jargon serves as useful shorthand for what would take many paragraphs and equations to explain to someone not trained in the field.

Jargon is good: it saves time, and it allows people to be precise and concise at the same time.

One bit of jargon that I think needs a consensus regards the common practice of finding out that a purported effect or object doesn't exist. There is a big difference between looking for something and not finding it, and finding that something isn't there. If you go needle hunting in a haystack and don't find one, it's possible that you just missed it. If you burn down the haystack and then methodically sieve and magnetically search every bit of the ashes and still don't find it, you can say rather definitively that there is no needle.

Carl Sagan like to express a similar idea with the phrase "absence of evidence is not evidence of absence" -- not having much information about something (whether the needle is in the haystack) is a lot different from knowing that something is not true.

But we don't really have any jargon that distinguishes inconclusive searches from searches that conclusively show there is nothing to be found. We ran into this issue with HD 149382 b when trying to show that it does not exist -- we wanted to be clear that it's not that we didn't find the planet there, it's that we found that the planet wasn't there! It came up again here and here.

The terms I see used are "no detection", "non detection", and "null detection". A quick search on astro-ph shows that "no detection" yields 338 results, "null detection" yields only 46, and "non detection" yield 667 (Google gets confused by papers detecting the molecule NO). Spot checking reveals that all three terms are used in both senses, and interchangeably.

One solution would be to propose that we reserve the term "null detection" for the rejection of a specific hypothesis: one would have detected a certain object or effect, if it existed, but you did not, so it does not. This makes sense to me because you have made a positive development: the detection of nothing.

In this scheme "non detection" is then the simple lack of a detection. I would keep the phrase "no detection," which is not a noun, with its ordinary English meaning (that is, not jargon at all; its meaning should be clear from context).

Unfortunately, "null detection" echoes the common statistical jargon "null hypothesis" for which one finds "null evidence". This sense is similar, but perhaps confusingly so, since it is formally impossible to prove most versions of the null hypothesis (at least in the standard statistical formulation of the term).

Also, according to Wikipedia the jargon "null result" constitutes evidence of absences, but not proof of it, so corresponds to the "non detection" in the scheme above.

I just chatted with astrostatistician Farhan Feroz, who pointed this out, and suggested that saying something is a "non detection to X% significance" resolves the ambiguity. I agree, but I don't always know "X"; just that it is close to 100. Also, that makes for more unwieldy paper titles.

So instead, let's try something else: a "dispositive null detection" or "dispositive non detection". This makes it clear that not only have you not detected anything, but that your lack of detection is so strong that it settles the issue (the term is common in law).

I might start using this terms this way, and footnote it to explain its precise meaning. If other researchers find it useful (or presume that I am repeating a definition, rather than coining jargon), then maybe they'll teach it to their students, and we'll have more (useful!) jargon.

Update: It looks like this entry has gotten picked up in the corner of the social-media-verse nearest me (thanks John Johnson). To address a common discussion point there: a "dispositive null result" refutes a specific hypothesis of a specific magnitude. If you are trying to rule out a whole class of models down to the limits of your experiment, it's just an "n-sigma upper limit" (thanks Peter Plavchan). If your upper limit is far below a purported signal, it's a dispositive null. Scott Dolim points out the classic example: the Michelson-Morley experiment that disproved the ether to high significance (further experimentation was unnecessary because the putative signal had a known magnitude). Adam Kraus approves of the modifier "dispositive" and points to a useful definition. Charley Noecker pointed out the misspelling of "Michelson-Morley" and echoed Fomaulhaut b as a nuanced example.

Interferometers and spectrographs

By Jason T Wright on March 27, 2012 3:10 PM | 0 Comments | 0 TrackBacks

One of the primary difficulties in determining the radial velocities of stars so that we can detect planets around them is measuring exactly what wavelength (or color) a particular spectral feature is at.

When we put starlight from a telescope through a spectrograph (basically a fancy prism) the light is dispersed into all of the colors of the rainbow with very high resolution. This means that we can distinguish between incredibly subtle shades of color, which is necessary because as stars wobble from the presence of planets their color varies by incredibly small amounts (less than one part in 1 hundred million!)

The problem is that when we go back to the telescope to see if these wavelengths (colors) have shifted, we have to make sure that the spectrograph is still calibrated properly -- we don't want to mistake a shift in the instrument for a shift in the star's light. The two ways to do this are by keeping your spectrograph ultra-stable (as the European HARPS instrument does) or by having a calibration filter or cell in place that remove very specific colors from your spectrum, allowing you to calibrate any instrumental shifts (like the iodine cell technique I use).

I have now worked with two different teams that have tried to use an interferometer to solve the problem. The idea is to create a physical device that removes very specific wavelengths of light through interference fringes. The first project, called TEDI, did this in a very clever way that created spectral beat patterns of starlight against the interferometer light. This allowed us to turn a low-resolution spectrograph into a high precision velocimeter (I know that's a highly technical description -- but it's a very technical and fancy project, so I don't know how else to describe it!)

The other team is led by our own Suvrath Mahadevan at the Center for Exoplanets and Habitable Worlds here at Penn State. Dr. Mahadevan's team, and especially his student Sam Halverson (who, totally coincidentally, also worked on TEDI as a Berkeley undergrad) have used a Fabry-Pérot interferometer to create interference fringes with the prototype for the Habitable Zone Planet Finder. These fringes can be used to calibrate a spectrograph similar to the way that HARPS operates. This is technique very similar to one that uses the new, Nobel Prize winning technology called frequency laser combs, except that these Fabry-Pérot devices are an order of magnitude cheaper and easier to build.

The first results are shown above. The image is a close-up of several sections of the spectrum. The color is green, but in reality these wavelengths are in the infrared portion of the spectrum. Each dot is a bright interference peak from the interferometer, and each column contains dots of light of slowly but steadily increasing wavelength. Think of this as a portion of a page that reads top to bottom, like a Chinese text: you "read" the dots from top to bottom (I'm not showing the whole column) and then when you get to the bottom start over at the top of the next column and continue. There are thousands of these dots over hundreds of columns spanning almost a factor of 2 in wavelength.

It's a beautiful and exciting result, and I hope that it turns into more reliable exoplanet detection everywhere.

Dr. Mahadevan describes the work he has done here.

Hot Exoplanets from Palomar

By Jason T Wright on March 5, 2012 1:05 PM | 0 Comments | 0 TrackBacks

When close-in planets have their orbits oriented just right, they can appear to pass behind their parent star once every orbit. Since these planets are very hot, it is possible to detect the disappearance and reappearance of their thermal emission (they glow like coals) during this "secondary eclipse" (the "primary eclipse" is also called a "transit", when the planet passes in front of the star). The Spitzer Space Telescope was the first to detect this phenomenon, but it is a very small effect and so remains very difficult to detect from the ground.

My postdoc Ming Zhao, in his capacity as a researcher with the Center for Exoplanets and Habitable Worlds, has recently worked with folks at Palomar and Caltech to get the famed 200-inch Hale telescope's WIRC instrument up to the task of making these measurements from the ground. This is a big deal because Spitzer won't be with us much longer, and there are few other options for measuring these important properties of transiting planets. Now, we can hopefully expect a lot more of these measurements from the "Big Eye" at Palomar, and to learn a lot about how these planet's atmospheres work!

Ming Zhao writes about his efforts here.

Hubble Time

By Jason T Wright on February 24, 2012 4:48 PM | 0 Comments | 0 TrackBacks

Seminars are empty, meetings are postponed, doors are closed, coffee pots are quickly drained and refilled. The Hubble Space Telescope Cycle 20 deadline is upon us (5pm PT, today).

All around the world collaborators are sending drafts around, sentences are being carefully built, figures are being tweaked and packed with simulated data to demonstrate plausibility, scientific promises are being made. People read their colleagues' words with a critical eye -- what sounds weak about this proposal that can be fixed? What might a reviewer grab on as a problem or concern?

Hubble time is so oversubscribed (by a factor of 7), that only the best, most carefully crafted proposals have a chance. But a successful proposal means the data you need for your science, and the funding you need to make it happen.

We're lucky HST is still around, but it will not be serviced again, so these we are approaching its last days. There will probably be another couple of cycles, but until JWST is operational this is still the premier optical telescope in (or above) the world. Gotta make the most of it!

TAC's Time

By Jason T Wright on February 4, 2012 3:44 PM | 0 Comments | 0 TrackBacks

One of the rituals of observational astronomy is the application for telescope time. Once, twice, or three times per year, observatories around (and even above!) the world solicit proposals for the best use of their telescopes. Each observatory has its own rules on who can apply for time. Private observatories, like Keck, Palomar, Lowell, and McDonald, restrict access to partner institutions and staff (though some reserve a small amount of time for "public" access). National facilities, like those at Kitt Peak National Observatories, are open to all astronomers (though there may be some restrictions on foreign proposals), and in particular anyone in the world may apply to time on the Hubble Space Telescope. National facilities and institutions also purchase or trade for small amounts of time on private telescopes; for instance, I apply to time on the Keck telescopes (which are private to the Universities of California and Caltech) through a small amount of time that NASA purchases to pursue narrow science goals in support of its space missions.

Different telescopes offer different instruments with different capabilities, and so astronomers seeking to answer a particular astronomical question need to determine which facilities can meet their needs. Here at Penn State, we have access to about 25% of the time on the Hobby-Eberly Telescope, which I regularly apply for time on. We also have a small share of the South Africa Large Telescope (SALT), and have "preferred" access to the public time offered at McDonald Observatory. We also manage the Swift spacecraft, which many Penn State astronomers have programs on.

With HET I use the iodine cell in the high resolution spectrograph to collect radial velocity measurements of bright, nearby stars. I propose for time through Penn State's Time Allocation Committee, or TAC (which I have sat on, though naturally I must recuse myself from discussions of my own proposals!). Penn State's TAC decides which proposals from Penn State faculty and staff are good uses of this limited resources by reading all of the proposals, judging the likelihood of success, the scientific merit of the observations, the track record of the proposer, and the amount and quality of the time requested. The proposals are then awarded time in ranked order until Penn State's entire share for the trimester is exhausted.

This year, my student and postdoc also applied for some of the public time at McDonald Observatory to use their 2.7-m telescope's coudé spectrograph to get high resolution spectra. Dr. Ming Zhao would like to observe the bright star sigma Draconis, a common precise velocity standard target, at very high resolution to determine its spectrum to exquisite accuracy. This will help us diagnose systematic errors in our velocity reduction pipeline. My student Jason Curtis wants to observe some stars in the cluster Ruprecht 147 that are too far south for HET to observe.

This April I will head back down to Tucson to judge proposals sent to the National Optical Astronomical Observatory (NOAO) for use of the national facilities, including the Kitt Peak telescopes, the Gemini telescopes, telescopes at Cerro Telolo Inter-American Observatory in Chile, and a few other facilities that NOAO has purchased or traded for small amounts of time on. I sit on the Solar System TAC, meaning that we read the proposals for observations of objects in the Solar System. This is a bit outside my field, but this is also the TAC that judges proposals to look for or characterize exoplanets, so they need expertise on this subject, too. I have learned a lot about comets, asteroids, Kuiper Belt objects, and planetary atmospheres, in the last few years!

Serving on TAC's is a lot of work, but it is important service and has to be done well. It is important that good science and ideas be rewarded and that facilities are used to maximize their scientific potential. Perhaps the hardest part is explaining to those who did not get time what concerns or problems put their proposal below the successful ones; this can be very difficult when there are many more excellent proposals than time to be handed out, because there may be no strong reason to pick one over another! In those cases you have to admit to having made a hard choice based on some small, almost inconsequential demerit.

Everyone who applies regularly for time has stories of their brilliant ideas that were unjustly under-appreciated, misunderstood, or even unread by the TAC members, and of the ludicrous TAC reports they have received, which reveal the TAC members to be lazy, unread ignoramuses. I have several. The only antidote I can offer: fix the problem by agreeing to serve on a TAC and do it very well! It will make astronomy better.

The "Super Bowl" of Astronomy

By Jason T Wright on January 19, 2012 10:36 AM | 0 Comments | 0 TrackBacks

I got back from the Austin Meeting of the American Astronomical Society late Friday night. The AAS likes to call it the winter meetings the "Super Bowl of Astronomy."

These winter meetings typically have around 3,000 participants, most of whom are professional astronomers (there are also smaller, summer meetings, often in smaller cities. This summer's meeting is in Anchorage!)

Many astronomers "save up" their big announcements for these meetings so that the AAS press office can help with the big announcement. I happened to chair the scientific session where the latest big Kepler news was announced: two new transiting circumbinary planets, Kepler-34 b and Kepler-35 b. These planets, like Kepler-16 b, each orbit a pair of stars, like Tatooine from Star Wars. These systems offer extraordinary opportunities to learn about planet formation and stellar astrophysics.

Even more exciting, Phil Muirhead, whom I informally supervised as a graduate student at Cornell when I was a postdoc there, and John Asher Johnson, a close friend and former officemate at Berkeley, announced the smallest planets yet from Kepler! They are around a very small star (an M dwarf) and very hot (way inside the Habitable Zone), but they are really small -- one is around the size of Mars!

Lots of important business gets conducted at these meetings, including plenary awards lectures, "town halls" for astronomers to discuss NSF and NASA policies and priorities, and for many astronomers it is the one time that all of their collaborators are in one place, so lots of working lunches and dinners are arranged all week long. In a surprise talk, Congressman Lamar Smith, a member of the House Science, Space, and Technology Committee, addressed the meeting on the last day and described the attempted de-funding of the James Webb Space Telescope, explaining that Congress supports JWST and was just trying to get NASA and the White House to be honest about its budgeting.

In the morning Tuesday session I had the honor of seeing two people I had nominated for prizes win awards. My collaborator John Asher Johnson of Caltech won the Newton Lacy Pierce Prize, which is awarded annually to a young observational astronomer for outstanding achievement. The list of prior winners is impressive; the award is clearly a good indicator of future success! Also the AAS posthumously recognized former astronomy Frank Kameny for his service to the field and the country. Dr. Kameny, a Harvard PhD under the legendary Cecelia Payne-Gaposchkin was fired from his government astronomy position in 1957 because he was gay. He spent the next 63 years fighting that decision, and eventually received a formal apology from the federal government and broad recognition for arguably being the founder of the gay rights movement in America, and the world. You can read more about Dr. Kameny's efforts and their relation to the AAS here.

Earth Sized Planets!

By Jason T Wright on December 20, 2011 2:28 PM | 0 Comments | 0 TrackBacks

Kepler just won't quit! Just after discovering a slightly-larger-than-Earth planet in the Habitable Zone, Kepler now announces a pair of actually-Earth-sized planets. These planets are in very, very short period orbits (6 and 20 days), and so sit very, very close to their parent star (Mercury orbits the Sun every 88 days). They're super hot!

This bodes very well for Kepler's ultimate goal -- combining the features of the Kepler-20 and Kepler-22 systems: Earth sized planets in the Habitable Zone, maybe even with giant planets further out (or closer in?). It will take a while - these planets were discovered despite their very small size because they orbit so frequently that Kepler could see them transit their parent star many, many times, and so the signal built up over time. A planet in the Habitable Zone will only transit 3-7 times over the course of the mission, and so the analysis is much, much harder, especially for such small planets.

Unfortunately, we're in the middle of a big upgrade to exoplanets.org and our undergraduate maintainers Katherina and Eunkyu are away for the holidays, so Kepler-20 may have to wait a little while before it appears in the Exoplanet Orbit Database. Soon though!

Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star

By Jason T Wright on December 6, 2011 8:39 AM | 0 Comments | 0 TrackBacks

Pop the champagne!

The Kepler mission has bagged its first big game -- or small game, rather.

The Kepler mission always promised to find rocky planets in the Habitable Zones of Sun-like stars with the transit method.

This means that it watches around 100,000 stars very carefully from space, waiting to see if any of them get briefly dimmer due to the passage of a planet in front of it. If the star has a close-in giant planet, the dimming is more likely (the alignment has to be just right for this to work), frequent (the planet will go around quickly), and more easily detected (the planet blocks a lot of light from the star). If the planet is small and far away from its central star then the dimming is less likely, infrequent, and very hard to detect. Kepler can barely detect a planet like Earth going around a star like the Sun -- but it can do it!

Kepler-22 b is bigger than Earth -- it has around 2.3 times the Earth's radius. We don't know what it is made of or what its composition is, but at that size there is nothing like it in the Solar System. It could be a big ball of rock, a huge "water world" with oceans hundreds or thousands of miles deep, or maybe even a smaller rocky planet with an enormous atmosphere of hydrogen, water and other gasses. We don't know because it is too small for us to detect with radial velocities, so we cannot measure its mass. The Kepler team has done an enormous amount of work to "validate" this planet, which is their jargon for proving that the signal is really coming from a planet, and not from any of hundreds of possible other sources (the most common such "false positive" is a grazing eclipsing binary pair of stars that happen to appear right next to a brighter star, which "dilutes" the eclipse signature into what looks like a planetary transit).

Kepler-22 b sits in the "Habitable Zone" of its host star, which is a G star like the Sun. This means that it probably has a surface temperature compatible with liquid water, if it has a solid surface at all. This doesn't mean we know we could live there, but it is the first planet we've found that we might be able to live on. This concept of the Habitable Zone was first rigorously developed by Penn State University professor James Kasting.

Bill Boruki, the Kepler Principle Investigator, pointed out how lucky we are to have this system now. The planet takes almost a year to orbit its star (it's a lot like Earth that way, and it takes so long because it is in the Habitable Zone -- if it were closer to the star it would orbit more quickly). In general Kepler needs to see a planet transit twice to measure the orbital period (the period between transits) and then a third time to confirm that the signal is real (it has to happen again at precisely the first period or it's not actually a planet).

But the Kepler mission has only been up for around 2 or 3 years, which means that the first transit happened almost right away -- in fact just 3 days into the mission! This made the 3rd transit occur with as soon as possible, given the period, which is why this is the first discovery announced. There will be more.

A few months back co-I Dimitar Sasselov gave a TED talk that caused quite a stir. He implied that Kepler had already discovered 140 "Earth like" planets and that they were in the process of finding which ones were Habitable. Dr. Sasselov was careful to point out that this was a statistical result -- he couldn't point to any particular planet as being "Earth like", but the fact that there were so many detections and Kepler was so good was a sign that eventually there would be a lot of discoveries. He was saying that the writing was on the wall, and it was good news.

The reaction was confusing and mixed. One website declared "Kepler Co-Investigator Spills The Beans: Lots of Earth-like Planets." Since the Kepler team had not validated any of these planets, they had not made a big announcement about them, but some venues took this TED talk in the UK to be NASA's big "announcement" about Kepler. NASAwatch.com asked "Is the Kepler team hiding something? Why is Sasselov talking about data that the Kepler team said that they did not want to discuss yet?" Dr. Sasselov and Kepler issued a clarifying statements, which only seemed to make some venues strangely irate.

With that backdrop, think about Kepler-22 b. Kepler saw this planet only 3 days after it began its mission. It would have been immediately flagged as a planet candidate by the team. It may even have been among the 140 candidates in Dr. Sasselov's talk. In some sense, this planet was "discovered" almost 3 years ago, but it has taken that long to find this needle in a haystack among many, many other, similar signals. Of course, NASA hasn't been hiding anything -- nature has! Data analysis is hard.

The discovery and rapid announcement of Kepler-22 is a tribute to the hard work of the Kepler team. With a few more years of data, the Kepler team should be able to validate a planet that is no larger than earth in its Habitable Zone -- a virtual Earth twin (that will be around 6 times harder than this one!). Astronomers worldwide will have to do a huge amount of work to learn what that planet is made of, whether it has water on its surface, and what it might be like there, but at least we'll know where to look!

Disclaimer: I have no affiliation with Kepler or any pertinent nonpublic knowledge about its misison.