Mostrando entradas con la etiqueta NASA's Kepler mission. Mostrar todas las entradas
Mostrando entradas con la etiqueta NASA's Kepler mission. Mostrar todas las entradas

domingo, 18 de agosto de 2013

NASA - NASA Hosts Kepler Spacecraft Status Teleconference




The spacecraft provides the power, pointing and telemetry for the photometer. Other than the four reaction wheels used to maintain the precision pointing and an ejectable cover, there are no other moving or deployable parts on the spacecraft.
Image Credit: NASA Ames/Ball Aerospac

Kepler Mission Manager Update: Pointing Test
Aug. 2, 2013
The team has continued exploratory recovery testing of Reaction Wheel 4 (RW4). On Thursday, July 25, 2013, the wheel spun in both directions in response to commands.
While both RW4 and RW2 have spun bi-directionally, friction levels remain higher than would be considered good for an operational wheel. However, it will be important to characterize the stability of the friction over time. A constant friction level may be correctable in the spacecraft’s attitude control system, whereas a variable friction level will likely render the wheels unusable.
Reaction wheel
High-precision pointing of the Kepler spacecraft is controlled by reaction wheels, which are small electric motors mounted on the spacecraft that control the three axes of motion: up/down, forward/back and left/right.
Image Credit:  Ball Aerospace
 
With the demonstration that both wheels will still move, and the measurement of their friction levels, the functional testing of the reaction wheels is now complete.  The next step will be a system-level performance test to see if the wheels can adequately control spacecraft pointing.
The team is preparing for the next test using RW2. Friction levels on RW4, the wheel that failed in May, are higher and no additional testing is planned at this time. The pointing test involves determining the performance of the wheel as part of the spacecraft system. The test will be conducted in three stages.
The first stage of the pointing test will determine if the spacecraft can sustain coarse-point mode using RW1, 2 and 3. Coarse-point mode is regularly used during normal operations, but has insufficient pointing accuracy to deliver the high-precision photometry necessary for exoplanet detection. During coarse-point the star trackers measure the pointing accuracy of the spacecraft. When using wheels to control the spacecraft, pointing is typically controlled to within an arcsecond, with a fault declared if the pointing error exceeds a quarter of a degree. This degree of pointing accuracy would be equivalent to keeping an imaginary Kepler telescope pointed at a theatre-size movie screen in New York City's Central Park from San Francisco.
The Kepler spacecraft
The spacecraft provides the power, pointing and telemetry for the photometer. Other than the four reaction wheels used to maintain the precision pointing and an ejectable cover, there are no other moving or deployable parts on the spacecraft.
Image Credit:  NASA Ames/Ball Aerospace
 
In the first stage, testing will demonstrate whether or not operation with RW2 can keep the spacecraft from entering safe mode. A safe mode is a self-protective measure that the spacecraft takes when an unexpected event occurs, such as elevated friction levels in the wheels.
In the second stage, testing will investigate RW2's ability to help control the spacecraft pointing with enough accuracy to transmit science data to the ground using NASA's Deep Space Network. If RW2 can sustain coarse-point in stage 1, the second stage of the test will be to point the high-gain antenna to Earth and downlink the data currently stored aboard. This requires that the pointing be controlled more tightly than simply avoiding safe mode, yet does not require the very fine control needed to return to science data collection.
The final stage of the test will determine if RW2 can achieve and maintain fine-point, the operating mode for collecting science data. During fine-point the fine-guidance sensors measure the spacecraft pointing. When using wheels to control the spacecraft, pointing is controlled to within a few milliarcseconds. Using our imaginary Kepler telescope example, this degree of pointing accuracy would be equivalent to pointing at a soccer ball in New York City's Central Park from San Francisco.
The team anticipates beginning the pointing performance testing on Thursday, August 8, 2013 and will continue into the following week if all goes well. A determination of whether Kepler can return to exoplanet data collection is expected a couple weeks after these pointing tests are complete.
As engineers explore recovery of the spacecraft, scientists continue to analyze the existing data. Earlier this week the team delivered their findings for 1,236 new Kepler Objects of Interest (KOIs) to the NASA Exoplanet Archive. The new KOIs were found by searching the observational data from Quarters 1 to Quarter 12. Of the 1,236 new KOIs, 274 were judged to be planet candidates, while many others were determined to be false positives. These newly announced Kepler planet candidates bring the current count to 3,548. Some of these new planet candidates are small and some reside in the habitable zone of their stars, but much work remains to be done to verify these results.
Also announced this week is the Kepler Science Conference II Nov. 4-8, 2013 at NASA Ames Research Center at Moffett Field, Calif. Registration is now open.
Regards,
Roger
NASA
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com
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sábado, 6 de julio de 2013

NASA - NASA Hosts Kepler Spacecraft Status Teleconference Today


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 Hosts Kepler Spacecraft Status Teleconference Today
 
 WASHINGTON - NASA will host a news teleconference at 4 p.m. EDT, today, May 15, to discuss the status of the agency's Kepler Space Telescope

Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zone, which is the range of distance from a star where the surface temperature of an orbiting planet might be suitable for liquid water. Launched in 2009, Kepler has been detecting planets and planet candidates with a wide range of sizes and orbital distances to help scientists better understand our place in the galaxy.

The briefing participants are:
- John Grunsfeld, associate administrator, Science Mission Directorate, NASA Headquarters, Washington
- Paul Hertz, astrophysics director, NASA Headquarters, Washington
- William Borucki, Kepler science principal investigator, Ames Research Center, Calif.
- Charles Sobeck, deputy project manager, Ames Research Center, Calif.

For dial-in information, journalists should e-mail their name, affiliation and telephone number to J.D. Harrington at j.d.harrington@nasa.gov. Media representatives and the public also can questions via Twitter to #AskNASA.

Audio of the teleconference will be streamed live on NASA's website at:  

For more information about the Kepler mission, visit:
 http://www.nasa.gov/kepler
NASA
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com
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domingo, 2 de junio de 2013

NASA - New NASA Kepler Mission Data Q&A


New NASA Kepler Mission Data
05.31.2013
 
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.
Michele Johnson
Ames Research Center, Moffett Field, Calif.
NASA
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com
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jueves, 15 de marzo de 2012

Astronomy: Compact Planetary System

Hi My Friends: AL VUELO DE UN QUINDE EL BLOG., This artist's concept depicts a planetary system so compact that it's more like Jupiter and its moons than a star and its planets. Astronomers using data from NASA's Kepler mission and ground-based telescopes recently confirmed that the system, called KOI-961, hosts the three smallest exoplanets currently known to orbit a star other than our sun. An exoplanet is a planet that resides outside of our solar system.Compact Planetary System
This artist's concept depicts a planetary system so compact that it's more like Jupiter and its moons than a star and its planets. Astronomers using data from NASA's Kepler mission and ground-based telescopes recently confirmed that the system, called KOI-961, hosts the three smallest exoplanets currently known to orbit a star other than our sun. An exoplanet is a planet that resides outside of our solar system.

The star, which is located about 130 light-years away in the Cygnus constellation, is a red dwarf that is one-sixth the size of the sun, or just 70 percent bigger than Jupiter. The star is also cooler than our sun, and gives off more red light than yellow.

The smallest of the three planets, called KOI-961.03, is actually located the farthest from the star, and is pictured in the foreground. This planet is about the size of Mars, with a radius of 0.57 times that of Earth. The next planet to the upper right is KOI-961.01, which is 0.78 times the radius of Earth. The planet closest to the star is KOI-961.02, with a radius 0.73 times the Earth's.

All three planets whip around the star in less than two days, with the closest planet taking less than half a day. Their close proximity to the star also means they are scorching hot, with temperatures ranging from 350 to 836 degrees Fahrenheit (176 to 447 degrees Celsius). The star's habitable zone, or the region where liquid water could exist, is located far beyond the planets.

The ground-based observations contributing to these discoveries were made with the Palomar Observatory, near San Diego, Calif., and the W.M. Keck Observatory atop Mauna Kea in Hawaii.

Image Credit: NASA/JPL-Caltech
NASA.

Guillermo Gonzalo Sánchez Achutegui



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domingo, 4 de marzo de 2012

Astronomy: NASA's Kepler Releases New Catalog- 2,321 Planet Candidates

Hi My Friends: AL VUELO DE UN QUINDE EL BLOG., The histogram summarizes the findings in the Feb. 27, 2012 Kepler Planet Candidate catalog release. The catalog contains 2,321 planet candidates identified during the first 16 months of observation conducted May 2009 to September 2010. Of the 46 planet candidates found in the habitable zone, the region in the planetary system where liquid water could exist, ten of these candidates are near-Earth-size. Kepler Planet Candidates by Size, Feb. 27, 2012
The histogram summarizes the findings in the Feb. 27, 2012 Kepler Planet Candidate catalog release. The catalog contains 2,321 planet candidates identified during the first 16 months of observation conducted May 2009 to September 2010. Of the 46 planet candidates found in the habitable zone, the region in the planetary system where liquid water could exist, ten of these candidates are near-Earth-size.

Credit: NASA Ames/Wendy Stenzel.


Since science operations began in May 2009, the Kepler team has released two catalogs of transiting planet candidates. The first catalog (Borucki et al, 2010), released in June 2010, contains 312 candidates identified in the first 43 days of Kepler data. The second catalog (Borucki et al, 2011), released in February 2011, is a cumulative catalog containing 1,235 candidates identified in the first 13 months of data.

Today the team presents the third catalog containing 1,091 new planet candidates identified in the first 16 months of observation conducted May 2009 to September 2010. These are the same candidates that the team discussed at the Kepler Science Conference held at NASA Ames Research Center in December 2011.

Here are the highlights of the new catalog:
A.- Planet candidates smaller than twice the size of Earth increased by 197 percent, compared to 52 percent for candidates larger than twice the size of Earth.
B.- Planet candidates with orbital periods longer than 50 days increased by 123 percent, compared to 85 percent for candidates with orbital periods shorter than 50 days. Since the last catalog was released in February 2011, the number of planet candidates identified by Kepler has increased by 88 percent and now totals 2,321 transiting 1,790 stars.

The cumulative catalog now contains well over 200 Earth-size planet candidates and more than 900 that are smaller than twice Earth-size. Of the 46 planet candidates found in the habitable zone, the region in the planetary system where liquid water could exist, ten of these candidates are near-Earth-size.

The number of planetary systems found with more than one planet candidate also has increased. Last year, 17 percent, or 170 stars, had more than one transiting planet candidate. Today, 20 percent, or 365, stars have more than one.

"With each new catalog release a clear progression toward smaller planets at longer orbital periods is emerging, " said Natalie Batalha, Kepler deputy science team lead at San Jose State University in California. "This suggests that Earth-size planets in the habitable zone are forthcoming if, indeed, such planets are abundant.

"Nearly 5,000 periodic transit-like signals were analyzed with known spacecraft instrumentation and astrophysical phenomena that could masquerade as transits, which can produce false positives. The most common false positive signatures are associated with eclipsing binary stars- a pair of orbiting stars that eclipse each other from the vantage point of the spacecraft.

The Kepler space telescope identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars in search of planets that pass in front, or "transit," their host star. Kepler must record at least three transits to verify a signal as a planet.


The catalog is available at the Kepler data archive at the Space Telescope Science Institute and can be downloaded from the NASA Exoplanet Archive.

NASA's Ames Research Center in Moffett Field, Calif., manages Kepler's ground system development, mission operations and science data analysis. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., managed the Kepler mission's development.

Ball Aerospace and 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 is funded by NASA's Science Mission Directorate at the agency's headquarters in Washington.

For information about the Kepler Mission,

visit: http://www.nasa.gov/kepler
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com


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miércoles, 11 de enero de 2012

Astronomy: NASA's Kepler Mission Finds Three Smallest Exoplanets

Hi My Friends: AL VUELO DE UN QUINDE EL BLOG., Astronomers using data from NASA's Kepler mission have discovered the three smallest planets yet detected orbiting a star beyond our sun. The planets orbit a single star, called KOI-961, and are 0.78, 0.73 and 0.57 times the radius of Earth. The smallest is about the size of Mars.

Mini Planetary System
This artist's concept depicts an itsy bitsy planetary system -- so compact, in fact, that it's more like Jupiter and its moons than a star and its planets. Astronomers using data from NASA's Kepler mission and ground-based telescopes recently confirmed that the system, called KOI-961, hosts the three smallest exoplanets known so far to orbit a star other than our sun. An exoplanet is a planet that resides outside of our solar system.

The star, which is located about 130 light-years away in the Cygnus constellation, is what's called a red dwarf. It's one-sixth the size of the sun, or just 70 percent bigger than Jupiter. The star is also cooler than our sun, and gives off more red light than yellow.

The smallest of the three planets, called KOI-961.03, is actually located the farthest from the star, and is pictured in the foreground. This planet is about the same size as Mars, with a radius only 0.57 times that of Earth. The next planet to the upper right is KOI-961.01, which is 0.78 times the radius of Earth. The planet closest to the star is KOI-961.02, with a radius 0.73 times the Earth's.

All three planets whip around the star in less than two days, with the closest planet taking less than half a day. Their close proximity to the star also means they are scorching hot, with temperatures ranging from 350 to 836 degrees Fahrenheit (176 to 447 degrees Celsius). The star's habitable zone, or the region where liquid water could exist, is located far beyond the planets.

The ground-based observations contributing to these discoveries were made with the Palomar Observatory, near San Diego, Calif., and the W.M. Keck Observatory atop Mauna Kea in Hawaii.

Image credit: NASA/JPL-Caltech


Sizing Up Exoplanets
This chart compares the smallest known exoplanets, or planets orbiting outside the solar system, to our own planets Mars and Earth. Astronomers using data from NASA's Kepler mission and ground-based telescopes recently discovered the three smallest exoplanets known to circle another star, called KOI-961.01, KOI-961.02 and KOI-961.03.

The smallest of these, KOI-961.03, is about the size of Mars with a radius of only 0.57 times that of Earth. Not long ago, in Dec. of 2011, the Kepler team announced the discovery of Kepler-20e and Kepler-20f -- the first Earth-size planets ever found outside the solar system.

All five of these small exoplanets have toasty orbits close to their stars, and do not lie in the more temperate habitable zone.The ground-based observations contributing to the KOI-961 discoveries were made with the Palomar Observatory, near San Diego, Calif., and the W.M. Keck Observatory atop Mauna Kea in Hawaii.

Image credit: NASA/JPL-Caltech

'Honey I Shrunk the Planetary System'
This artist's conception compares the KOI-961 planetary system to Jupiter and the largest four of its many moons. The KOI-961 planetary system hosts the three smallest planets known to orbit a star beyond our sun (called KOI-961.01, KOI-961.02 and KOI-961.03).

The smallest of these planets, KOI-961.03, is about the same size as Mars. All three planets take less than two days to whip around their star.

The planets were discovered using data from NASA's Kepler mission and ground-based telescopes. The KOI-961 star is a tiny "red dwarf," just one-sixth the size of our sun. This planetary system is the most compact detected to date, with a scale closer to Jupiter and its moons than another star system.

The planet and moon orbits are drawn to the same scale. The relative sizes of the stars, planets and moons have been increased for visibility.
Image credit: Caltech
Astronomers using data from NASA's Kepler mission have discovered the three smallest planets yet detected orbiting a star beyond our sun. The planets orbit a single star, called KOI-961, and are 0.78, 0.73 and 0.57 times the radius of Earth. The smallest is about the size of Mars.

All three planets are thought to be rocky like Earth, but orbit close to their star. That makes them too hot to be in the habitable zone, which is the region where liquid water could exist. Of the more than 700 planets confirmed to orbit other stars -- called exoplanets -- only a handful are known to be rocky.

"Astronomers are just beginning to confirm thousands of planet candidates uncovered by Kepler so far," said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington." Finding one as small as Mars is amazing, and hints that there may be a bounty of rocky planets all around us."

Kepler searches for planets by continuously monitoring more than 150,000 stars, looking for telltale dips in their brightness caused by crossing, or transiting, planets. At least three transits are required to verify a signal as a planet. Follow-up observations from ground-based telescopes also are needed to confirm the discoveries.

The latest discovery comes from a team led by astronomers at the California Institute of Technology in Pasadena. The team used data publicly released by the Kepler mission, along with follow-up observations from the Palomar Observatory, near San Diego, and the W.M. Keck Observatory atop Mauna Kea in Hawaii. Their measurements dramatically revised the sizes of the planets from what originally was estimated.

The three planets are very close to their star, taking less than two days to orbit around it. The KOI-961 star is a red dwarf with a diameter one-sixth that of our sun, making it just 70 percent bigger than Jupiter.

"This is the tiniest solar system found so far," said John Johnson, the principal investigator of the research from NASA's Exoplanet Science Institute at the California Institute of Technology in Pasadena. "It's actually more similar to Jupiter and its moons in scale than any other planetary system. The discovery is further proof of the diversity of planetary systems in our galaxy."

Red dwarfs are the most common kind of star in our Milky Way galaxy. The discovery of three rocky planets around one red dwarf suggests that the galaxy could be teeming with similar rocky planets.

"These types of systems could be ubiquitous in the universe," said Phil Muirhead, lead author of the new study from Caltech. "This is a really exciting time for planet hunters.

"The discovery follows a string of recent milestones for the Kepler mission. In December 2011, scientists announced the mission's first confirmed planet in the habitable zone of a sun-like star: a planet 2.4 times the size of Earth called Kepler-22b. Later in the month, the team announced the discovery of the first Earth-size planets orbiting a sun-like star outside our solar system, called Kepler-20e and Kepler-20f.

For the latest discovery, the team obtained the sizes of the three planets called KOI-961.01, KOI-961.02 and KOI-961.03 with the help of a well-studied twin star to KOI-961, or Barnard's Star. By better understanding the KOI-961 star, they then could determine how big the planets must be to have caused the observed dips in starlight. In addition to the Kepler observations and ground-based telescope measurements, the team used modeling techniques to confirm the planet discoveries.

Prior to these confirmed planets, only six other planets had been confirmed using the Kepler public data.

NASA's Ames Research Center in Moffett Field, Calif., manages Kepler's ground system development, mission operations and science data analysis. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., managed the Kepler mission's development.For information about the Kepler Mission, visit:
http://www.nasa.gov/kepler
http://www.nasa.gov/mission_pages/kepler/main/index.html
NASA
Guillermo Gonzalo Sánchez Achutegui

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