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domingo, 7 de julio de 2013

NASA - NASA'S Kepler Discovers its Smallest 'Habitable Zone' Planets to Date




Kepler-62f with 62e as Morning Star
The artist's concept depicts NASA's Kepler misssion's smallest habitable zone planet. Seen in the foreground is Kepler-62f, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra.

Kepler-62f orbits it's host star every 267 days and is roughly 40 percent larger than Earth in size. The size of Kepler-62f is known, but its mass and composition are not. However, based on previous exoplanet discoveries of similar size that are rocky, scientists are able to determine its mass by association.

Much like our solar system, Kepler-62 is home to two habitable zone worlds. The small shining object seen to the right of Kepler-62f is Kepler-62e. Orbiting on the inner edge of the habitable zone, Kepler-62e is roughly 60 percent larger than Earth.

Image credit: NASA Ames/JPL-Caltech

New NASA Kepler Mission Data

 
This diagram illustrates the flow of Kepler data through the stages of becoming a planet candidate. 
This diagram illustrates the flow of Kepler data through the stages of becoming a planet candidate.
Image credit: NASA Ames/W. Stenzel

On May 28, 2013, NASA's Kepler mission delivered new data to the NASA Exoplanet Archive. I sat down with Michael Haas, Kepler science office director at NASA Ames Research Center, to find out more.

MJ: Mike, what information has the Kepler mission recently delivered to the NASA Exoplanet Archive?

MH: The Kepler mission has just opened the Q1-Q12 activity table at the NASA Exoplanet Archive and delivered a majority of the Kepler Objects of Interest (KOIs) found by searching the data from Quarters 1 to 12 (May 2009 – March 2012) for transit-like signatures. In addition to finding many KOIs that were known from earlier searches of smaller data sets, the current delivery also includes 1,924 new KOIs.

MJ: That's exciting! Does this mean that the Kepler mission has added 1,924 new planet candidates to the count?

MH: No. The 1,924 new KOIs have not been completely analyzed yet. The term KOI means exactly what the name implies – Kepler has declared these to be "objects of interest," not planetary candidates. By promoting these transit-like signatures to KOI status, all we are saying is that their light curves contain interesting patterns of repetitive dips that might indicate the presence of a transiting planet.

However, there are several other ways to produce similar looking transit-like patterns. For example, the dips could be due to stellar variability, excess detector noise, other transient events associated with the spacecraft, or a background star occulting a second background star (i.e., a background eclipsing binary). We use the term "false positive" to describe those KOIs that are explainable by means other than the planetary hypothesis. We know that with further analysis, many of these new KOIs will become false positives.

MJ: If you haven't finished the analysis, why are you releasing this information now? It seems rather preliminary.

MH: You are right, it is preliminary, but it also represents a significant body of work and contains valuable information for the scientific community.

Remember how this process works. We started with the light curves of 192,313 stars that were observed for some or all of Quarters 1-12. That's a lot of data to plow through. When we began searching the Q1-Q12 data last fall, we identified 18,406 threshold-crossing events (TCEs). These TCEs had to pass a series of tests, each with a threshold, that were designed to identify the events that look transit-like. This list of TCEs and their accompanying diagnostic reports (i.e., data validation reports and one-page summaries) were released to the public through the NASA Exoplanet Archive in December 2012.

The criteria required to pass this first set of tests are intentionally lenient. We prefer to include many non-transit-like events at this early stage of analysis, rather than to miss some really good events (i.e., small, Earth-size candidates in the habitable zone – the hardest candidates to find).

MJ: So, what happens next? Have you been analyzing the Q1-Q12 TCEs to figure out which are the most interesting?

MH: That is exactly right. We evaluated each TCE using objective criteria that are difficult to program into a computer. This exercise is called "triage" because it is a relatively quick assessment that eliminates the obvious false positives, while retaining anything that looks even remotely transit-like for further assessment. During this exercise, most of the events produced by spacecraft transients and stellar variability were discarded. This is process step 1 in the figure 'The Making of Kepler Planet Candidates.'

MJ: Is every TCE that passes triage automatically promoted to KOI status?

MH: No. If at least two scientists determine that a TCE looks transit-like, then the light curve is fit with a computer model of a transiting planet. If the model fit looks reasonable, then the TCE is promoted to KOI status. If the model fit is poor, then the TCE is ignored and receives no further analysis. As shown in the figure, slightly more than half of the TCEs that passed triage were promoted to KOI status.

Moreover, many of the KOIs found amongst the Q1-Q12 TCEs are old ones that were discovered and cataloged during previous transit searches – we have set these old KOIs aside for now. The remaining 1,924 KOIs are brand new. In the coming months, we will focus our attention on this set of new KOIs. We know that many of them will eventually become false positives, but we can now afford the additional analysis because we have reduced the number of light curves that require in-depth assessment by a factor of 100 (from 192,313 to 1,924).

MJ: Does that mean you don't have to reanalyze the old KOIs?

MH: No, not at all. With more quarters of data and major improvements in our diagnostic tools, some of these old KOIs will change status when we disposition them again. (See process step 3 in the figure.) Some planet candidates will become false positives and some false positives will become planet candidates. It will be fun and extremely interesting to see how this all shakes out.

MJ: So, does this mean you will redisposition all the old KOIs as well as disposition the new KOIs?

MH: That is the long-term plan. However, it is not possible to complete all this work before the Q1-Q16 search results become available later this summer. Hence, we plan to disposition all of the new Q1-Q12 KOIs over the next few months, and then plan to redisposition the old KOIs using all 16 quarters of data and even better diagnostic tools that are currently under development.

MJ: With previous Kepler data releases, the term 'KOI' was synonymous with planet candidate. Can you explain what has changed?

MH: This is a common misperception. Actually, the definition of KOI has not changed; but our reporting philosophy has. In the past, the Kepler mission published lists of KOIs that were deemed to be planet candidates; and separately posted the KOIs that were declared false positives at MAST (Mikulski Archive for Space Telescopes). This may have given some the mistaken impression that all KOIs are planet candidates, but this has never been the case. For example, four of the first ten KOIs identified using the first month of data are currently marked as false positives in the cumulative activity table at the NASA Exoplanet Archive.

The reporting philosophy has been modified so that all KOIs can be archived in one place. This makes it much easier to change the status of a KOI from 'planet candidate' to 'false positive,' and vice versa. In addition, the new format enables more rapid release of incremental information as progress is made.

MJ: In the Q1-Q12 data set there are a surprising number of KOIs with orbital periods near one Earth-year. Do Earth-size planets tend to prefer Earth-like periods?

MH: Excellent question. Remember that the Kepler spacecraft orbits the sun every 371 days. Given its extremely stable environment, some noise sources associated with the local detector electronics exhibit repetitive behavior with this periodicity. Since these electronics read-out the charge-coupled devices (CCDs), this noise is intertwined with the astronomical signals in such a way that the two are almost impossible to disentangle. Hence, this repetitive noise can mimic the signature of a transiting planet.

Fortunately, we can identify these noise-produced TCEs and distinguish them from true planet candidates in one Earth-year orbits, but it requires a lot of effort. Although most of these bogus TCEs were ignored at the triage or model fitting stage, a small fraction of them have crept into the KOI population and still need to be identified and declared false positives. That work will occur over the next few months. Meanwhile, don't get too hyped up by the pile-up of KOIs with one Earth-year periods, or the smaller, associated pile-up at 180 days. Most of these are probably not real planet candidates; then again, there may be some real gems there – that's what makes this work so exciting.

This explanation is well documented in the Q1-Q12 TCE Release Notes [PDF] at the archive.

MJ: If that is the case, then why weren't these bogus one Earth-year TCEs and KOIs seen in earlier releases?

MH: Remember that the Kepler spacecraft is in a 371-day orbit (i.e., just over one Earth-year) and that three transits are required to define a TCE (and therefore a KOI). Hence, we have just begun to see these bogus events now because we have searched three years (i.e., 12 quarters) of data for the first time.

MJ: Are there other reasons for an increased number of false positives in the Q1-Q12 delivery?

MH: Yes. In the past we have tossed out the eclipsing binaries (EBs) as soon as they were identified, so many of them have never been made into KOIs. This means that every time we search a dataset for transits, we end up finding and re-evaluating the EBs again. Once we realized this, we decided to retain all those found in the Q1-Q12 search, pass them through triage, fit models to them, and turn them into KOIs. Now they can be documented as false positives, giving us a lasting record of past decisions that help to minimize the amount of work going forward.

So yes, there are likely to be a higher percentage of EBs in this set of 1,924 KOIs than have been seen in past releases.

MJ: You mentioned earlier that this represents the "majority of the KOIs" found in Q1-Q12. Are you holding some back?

MH: We have finished triage and have identified KOIs up to 4914. That is the final KOI number for the Q1-Q12 search, but there are gaps (i.e., some KOIs are missing) in this first delivery because they are troublesome cases that require manual processing. For example, some KOIs were found in the initial computer search of the Q1-Q12 data, but their properties were incorrectly calculated. For these KOIs, we need to recompute their properties before they can be delivered.

By staging the deliveries as we have done, the best information is delivered to the community in a timely fashion rather than waiting for a complete analysis of all KOIs.

MJ: To summarize, the new 1,924 KOIs are not fully analyzed and not all the Q1-Q12 KOIs have been delivered yet. What guidance do you have for the scientific community about using the Q1-Q12 data now?

MH: The value of this delivery greatly depends on your scientific objectives. If you are looking for interesting KOIs to study or observe, then we have narrowed the search down from 192,313 light curves to 1,924. That's a big help. If you are trying to understand the statistical population of small planets in the galaxy, this delivery isn't going to hand you what you need right now. Stay tuned; good planets are hard to find. A team member once said that searching for planets is not like "looking for a needle in a haystack," but more like looking for an aluminum needle made out of one aluminum alloy in a pile of needles made out of a different alloy. This delivery is an important step in that type of process.

The NASA Exoplanet Archive is funded by NASA's Exoplanet Exploration Program to collect and make data public to support the search for and characterization of exoplanets and their host stars. The archive is hosted at the Infrared Processing and Analysis Center at the California Institute of Technology.

For information about the NASA Exoplanet Archive, click here.

For information about the Kepler Mission, click here.

WASHINGTON - NASA's Kepler mission has discovered two new planetary systems that include three super-Earth-size planets in the "habitable zone," the range of distance from a star where the surface temperature of an orbiting planet might be suitable for liquid water.
The Kepler-62 system has five planets; 62b, 62c, 62d, 62e and 62f. The Kepler-69 system has two planets; 69b and 69c. Kepler-62e, 62f and 69c are the super-Earth-sized planets.

Two of the newly discovered planets orbit a star smaller and cooler than the sun. Kepler-62f is only 40 percent larger than Earth, making it the exoplanet closest to the size of our planet known in the habitable zone of another star. Kepler-62f is likely to have a rocky composition. Kepler-62e, orbits on the inner edge of the habitable zone and is roughly 60 percent larger than Earth.

The third planet, Kepler-69c, is 70 percent larger than the size of Earth, and orbits in the habitable zone of a star similar to our sun. Astronomers are uncertain about the composition of Kepler-69c, but its orbit of 242 days around a sun-like star resembles that of our neighboring planet Venus.

Scientists do not know whether life could exist on the newfound planets, but their discovery signals we are another step closer to finding a world similar to Earth around a star like our sun.

"The Kepler spacecraft has certainly turned out to be a rock star of science," said John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington. "The discovery of these rocky planets in the habitable zone brings us a bit closer to finding a place like home. It is only a matter of time before we know if the galaxy is home to a multitude of planets like Earth, or if we are a rarity."

The Kepler space telescope, which simultaneously and continuously measures the brightness of more than 150,000 stars, is NASA's first mission capable of detecting Earth-size planets around stars like our sun.

Orbiting its star every 122 days, Kepler-62e was the first of these habitable zone planets identified. Kepler-62f, with an orbital period of 267 days, was later found by Eric Agol, associate professor of astronomy at the University of Washington and co-author of a paper on the discoveries published in the journal Science.

The size of Kepler-62f is now measured, but its mass and composition are not. However, based on previous studies of rocky exoplanets similar in size, scientists are able to estimate its mass by association.

"The detection and confirmation of planets is an enormously collaborative effort of talent and resources, and requires expertise from across the scientific community to produce these tremendous results," said William Borucki, Kepler science principal investigator at NASA's Ames Research Center at Moffett Field, Calif., and lead author of the Kepler-62 system paper in Science. "Kepler has brought a resurgence of astronomical discoveries and we are making excellent progress toward determining if planets like ours are the exception or the rule."

The two habitable zone worlds orbiting Kepler-62 have three companions in orbits closer to their star, two larger than the size of Earth and one about the size of Mars. Kepler-62b, Kepler-62c and Kepler-62d, orbit every five, 12, and 18 days, respectively, making them very hot and inhospitable for life as we know it.

The five planets of the Kepler-62 system orbit a star classified as a K2 dwarf, measuring just two-thirds the size of the sun and only one-fifth as bright. At seven billion years old, the star is somewhat older than the sun. It is about 1,200 light-years from Earth in the constellation Lyra.

A companion to Kepler 69c, known as Kepler 69b, is more than twice the size of Earth and whizzes around its star every 13 days. The Kepler-69 planets' host star belongs to the same class as our sun, called G-type. It is 93 percent the size of the sun and 80 percent as luminous and is located approximately 2,700 light-years from Earth in the constellation Cygnus.

"We only know of one star that hosts a planet with life, the sun. Finding a planet in the habitable zone around a star like our sun is a significant milestone toward finding truly Earth-like planets," said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, Calif., and lead author of the Kepler-69 system discovery published in the Astrophysical Journal.

When a planet candidate transits, or passes in front of the star from the spacecraft's vantage point, a percentage of light from the star is blocked. The resulting dip in the brightness of the starlight reveals the transiting planet's size relative to its star. Using the transit method, Kepler has detected 2,740 candidates. Using various analysis techniques, ground telescopes and other space assets, 122 planets have been confirmed.

Early in the mission, the Kepler telescope primarily found large, gaseous giants in very close orbits of their stars. Known as "hot Jupiters," these are easier to detect due to their size and very short orbital periods. Earth would take three years to accomplish the three transits required to be accepted as a planet candidate. As Kepler continues to observe, transit signals of habitable zone planets the size of Earth orbiting stars like the sun will begin to emerge.

Ames is responsible for Kepler's ground system development, mission operations, and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed Kepler mission development.

Ball Aerospace & Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

The Space Telescope Science Institute in Baltimore archives, hosts and distributes Kepler science data. Kepler is NASA's 10th Discovery Mission and was funded by the agency's Science Mission Directorate.

For more information about the Kepler mission, visit:



Kepler Mission Manager Update: Preparing for Recovery

Operations in Point Rest State (PRS) have continued for the spacecraft. The spacecraft was placed in PRS on May 15, 2013, after the failure of reaction wheel 4. It has been 53 days since the spacecraft collected new science data.
As noted in the last update, the team has made adjustments to onboard fault parameters for the star trackers to lessen the possibility of entry into safe mode. We have also made additional adjustments to the Thruster-Control Safe Mode to improve its fuel efficiency. This provides yet more protection for spacecraft fuel reserves while the team continues to work on reaction wheel performance assessment and recovery plans.
The engineering team has devised initial tests for the recovery attempt and is checking them on the spacecraft test bed at the Ball Aerospace facility in Boulder, Colo. The team anticipates that exploratory commanding of Kepler’s reaction wheels will commence mid-to-late July. The Kepler spacecraft will remain in PRS until and during the tests.
Later this month, an update to the data processing pipeline software will be deployed. Called SOC 9.1, this enhancement has been underway for several months and is in the final stages of verification and validation. This software release provides additional refinements to better tease out small planet signatures from the four years of Kepler data. It will also decrease the frequency of false positives.
The team continues to disposition Kepler Objects of Interest (KOIs) found by searching the observational data from Quarters 1 to Quarter 12. With 63 more planet candidates added since the last report, the count now stands at 3,277.
While Kepler data analysis continues, we were pleased to note the discoveries recently announced by European Southern Observatory (ESO).  A team of astronomers has combined new observations of Gliese 667C with existing data from HARPS at ESO’s 3.6-metre telescope in Chile, revealing a system with at least six planets. A record-breaking three of these planets are super-Earths lying in the zone around the star where liquid water might exist, making them possible candidates for the presence of life. This is the first system found with a fully packed habitable zone.
Also this month, a research team from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., used Kepler data to find two planets smaller than three times the size of Earth orbiting sun-like stars in a one billion year old star cluster named NGC 6811. The result demonstrates that small planets can form and persist in an open cluster, and casts the net wider in the search for planets the size and temperature of Earth. With this discovery, 134 planets have been confirmed using Kepler data.
And, finally we note the announcement from France's space agency, Centre National d’Etudes Spatiales (CNES), on the retirement of the Convection, Rotation, and planetary Transits (CoRoT) mission. The CoRoT spacecraft was launched Dec. 26, 2006, and paved the way for Kepler in terms of space-based identification of transiting exoplanets and also the detection of acoustic oscillations in sun-like stars. We congratulate CNES on a great run with the CoRoT spacecraft!

Regards,
Roger
 
NASA
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com
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