Kepler

[orin stepanek]

Kepler is still finding more candidates. Latest! http://www.kepler.arc.nasa.gov/news/ind ... NewsID=128

Click to view full size image

[orin stepanek]

kepler discovers inviible world! http://www.kepler.arc.nasa.gov/news/nas ... NewsID=148

Click to view full size image

What does Kepler-19c look like? We don't know—we have have very few clues. “Kepler-19c has multiple personalities consistent with our data. For instance, it could be a rocky planet on a circular 5-day orbit, or a gas-giant planet on an oblong 100-day orbit,” said co-author Daniel Fabrycky of the University of California, Santa Cruz (UCSC). This a depiction of the Kepler-19 system by artist David Aguilar..

[bystander]

kepler discovers inviible world!

Invisible World Discovered
Center for Astrophysics | Kepler | 2011 Sept 08

Usually, running five minutes late is a bad thing since you might lose your dinner reservation or miss out on tickets to the latest show. But when a planet runs five minutes late, astronomers get excited because it suggests that another world is nearby.

NASA's Kepler spacecraft has spotted a planet that alternately runs late and early in its orbit because a second, "invisible" world is tugging on it. This is the first definite detection of a previously unknown planet using this method. No other technique could have found the unseen companion.

"This invisible planet makes itself known by its influence on the planet we can see," said astronomer Sarah Ballard of the Harvard-Smithsonian Center for Astrophysics (CfA). Ballard is lead author on the study, which has been accepted for publication in The Astrophysical Journal.

"It's like having someone play a prank on you by ringing your doorbell and running away. You know someone was there, even if you don't see them when you get outside," she added.

Both the seen and unseen worlds orbit the Sun-like star Kepler-19, which is located 650 light-years from Earth in the constellation Lyra. The 12th-magnitude star is well placed for viewing by backyard telescopes on September evenings.

Kepler locates planets by looking for a star that dims slightly as a planet transits the star, passing across the star's face from our point of view. Transits give one crucial piece of information - the planet's physical size. The greater the dip in light, the larger the planet relative to its star. However, the planet and star must line up exactly for us to see a transit.

The first planet, Kepler-19b, transits its star every 9 days and 7 hours. It orbits the star at a distance of 8.4 million miles, where it is heated to a temperature of about 900 degrees Fahrenheit. Kepler-19b has a diameter of 18,000 miles, making it slightly more than twice the size of Earth. It may resemble a "mini-Neptune," however its mass and composition remain unknown.

If Kepler-19b were alone, each transit would follow the next like clockwork. Instead, the transits come up to five minutes early or five minutes late. Such transit timing variations show that another world's gravity is pulling on Kepler-19b, alternately speeding it up or slowing it down.

Historically, the planet Neptune was discovered similarly. Astronomers tracking Uranus noticed that its orbit didn't match predictions. They realized that a more distant planet might be nudging Uranus and calculated the expected location of the unseen world. Telescopes soon observed Neptune near its predicted position.

"This method holds great promise for finding planets that can't be found otherwise," stated Harvard astronomer and co-author David Charbonneau.

So far, astronomers don't know anything about the invisible world Kepler-19c, other than that it exists. It weighs too little to gravitationally tug the star enough for them to measure its mass. And Kepler hasn't detected it transiting the star, suggesting that its orbit is tilted relative to Kepler-19b.

"Kepler-19c has multiple personalities consistent with our data. For instance, it could be a rocky planet on a circular 5-day orbit, or a gas-giant planet on an oblong 100-day orbit," said co-author Daniel Fabrycky of the University of California, Santa Cruz (UCSC).

‘Invisible’ World Discovered Around a Distant Star
Universe Today | Nancy Atkinson | 2011 Sept 08

Stealth Alien Planet Discovered By New Technique
Space.com | Mike Wall | 2011 Sept 08

[orin stepanek]

http://www.kepler.arc.nasa.gov/news/new ... NewsID=149

Click to view full size image

[orin stepanek]

You can be kept abreast on Kepler news for new planets here! http://www.kepler.arc.nasa.gov/news/nasakeplernews/

[bystander]

Kepler announces 11 planetary systems hosting 26 planets
NASA JPL-Caltech | Ames Research Center | Kepler | 2012 Jan 26

Kepler's Planetary Systems: The artist's rendering depicts the multiple planet systems discovered by NASA's Kepler mission. (Credit: NASA Ames/Jason Steffen, Fermilab Center for Particle Astrophysics)

Kepler's Planetary Systems' Orbits: The image shows an overhead view of orbital positions of the planets in systems with multiple transiting planets discovered by NASA's Kepler mission. (Credit: NASA Ames/Dan Fabrycky, University of California, Santa Cruz)

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NASA's Kepler mission has discovered 11 new planetary systems hosting 26 confirmed planets. These discoveries nearly double the number of verified Kepler planets and triple the number of stars known to have more than one planet that transits, or passes in front of, its host star. Such systems will help astronomers better understand how planets form.

The planets orbit close to their host stars and range in size from 1.5 times the radius of Earth to larger than Jupiter. Fifteen of them are between Earth and Neptune in size, and further observations will be required to determine which are rocky like Earth and which have thick gaseous atmospheres like Neptune. The planets orbit their host star once every six to 143 days. All are closer to their host star than Venus is to our sun.

"Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky," said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Now, in just two years staring at a patch of sky not much bigger than your fist, Kepler has discovered more than 60 planets and more than 2,300 planet candidates. This tells us that our galaxy is positively loaded with planets of all sizes and orbits."

Kepler identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars to detect when a planet passes in front of the star. That passage casts a small shadow toward Earth and the Kepler spacecraft.

“Confirming that the small decrease in the star's brightness is due to a planet requires additional observations and time-consuming analysis," said Eric Ford, associate professor of astronomy at the University of Florida and lead author of the paper confirming Kepler-23 and Kepler-24. “We verified these planets using new techniques that dramatically accelerated their discovery.”

Each of the new confirmed planetary systems contains two to five closely spaced transiting planets. In tightly packed planetary systems, the gravitational pull of the planets among themselves causes one planet to accelerate and another planet to decelerate along its orbit. The acceleration causes the orbital period of each planet to change. Kepler detects this effect by measuring the changes, or so-called Transit Timing Variations (TTVs).

Planetary systems with TTVs can be verified without requiring extensive ground-based observations, accelerating confirmation of planet candidates. The TTV detection technique also increases Kepler's ability to confirm planetary systems around fainter and more distant stars.

“By precisely timing when each planet transits its star, Kepler detected the gravitational tug of the planets on each other, clinching the case for ten of the newly announced planetary systems,” said Dan Fabrycky, Hubble Fellow at the University of California, Santa Cruz and lead author for a paper confirming Kepler-29, 30, 31 and 32."

Five of the systems (Kepler-25, Kepler-27, Kepler-30, Kepler-31 and Kepler-33) contain a pair of planets where the inner planet orbits the star twice during each orbit of the outer planet. Four of the systems (Kepler-23, Kepler-24, Kepler-28 and Kepler-32) contain a pairing where the outer planet circles the star twice for every three times the inner planet orbits its star.

“These configurations help to amplify the gravitational interactions between the planets, similar to how my sons kick their legs on a swing at the right time to go higher,” said Jason Steffen, the Brinson postdoctoral fellow at Fermilab Center for Particle Astrophysics in Batavia, Ill., and lead author of a paper confirming Kepler-25, 26, 27 and 28.

The system with the most planets among these discoveries is Kepler-33, a star that is older and more massive than our sun. Kepler-33 hosts five planets, ranging in size from 1.5 to 5 times that of Earth and all located closer to their star than any planet is to the sun.

The properties of a star provide clues for planet detection. The decrease in the star's brightness and duration of a planet transit combined with the properties of its host star present a recognizable signature. When astronomers detect planet candidates that exhibit similar signatures around the same star the likelihood of any of these planet candidates being a false positive is very low.

“The approach that was used to verify the Kepler-33 planets shows that the overall reliability of Kepler's candidate multiple transiting systems is quite high," said Jack Lissauer, planetary scientist at NASA Ames Research Center at Moffett Field, Calif., and lead author of the paper confirming Kepler-33. “This is a validation by multiplicity.”

Almost All of Kepler's Multiple Planet Candidates are Planets - Jack J. Lissauer et al

arXiv.org > astro-ph > arXiv:1201.5424 > 26 Jan 2012

Transit Timing Observations from Kepler: II.
Confirmation of Two Multiplanet Systems via a Non-parametric Correlation Analysis - Eric B. Ford et al

arXiv.org > astro-ph > arXiv:1201.5409 > 25 Jan 2012

Transit Timing Observations from Kepler: III.
Confirmation of 4 Multiple Planet Systems by a Fourier-Domain Study of Anti-correlated Transit Timing Variations - Jason H. Steffen et al

arXiv.org > astro-ph > arXiv:1201.5412 > 25 Jan 2012

Transit Timing Observations from Kepler: IV.
Confirmation of 4 Multiple Planet Systems by Simple Physical Models - Daniel C. Fabrycky et al

arXiv.org > astro-ph > arXiv:1201.5415 > 25 Jan 2012

11 New Planetary Systems… 26 New Planets… Kepler Racks ‘Em Up!
Universe Today | Tammy Plotner | 2012 Jan 26

11 New Alien Solar Systems Crammed with Exoplanets
Discovery News | Ian O'Neill | 2012 Jan 26

New Multiple Planet Systems Verified
Centauri Dreams | Paul Gilster | 2012 Jan 27

[neufer]

Kepler announces 11 planetary systems hosting 26 planets
NASA JPL-Caltech | Ames Research Center | Kepler | 2012 Jan 26

<<Five of the systems (Kepler-25, Kepler-27, Kepler-30, Kepler-31 and Kepler-33) contain a pair of planets where the inner planet orbits the star twice during each orbit of the outer planet. Four of the systems (Kepler-23, Kepler-24, Kepler-28 and Kepler-32) contain a pairing where the outer planet circles the star twice for every three times the inner planet orbits its star.

<<The orbits of Pluto and the plutinos are stable, despite crossing that of much larger Neptune, because they are in a 2:3 resonance with it. The resonance ensures that, when they approach perihelion and Neptune's orbit, Neptune is consistently distant (averaging a quarter of its orbit away). There are also smaller but significant groups of resonant trans-Neptunian objects occupying the 1:1 (Neptune trojans), 3:5, 4:7, 1:2 (twotinos) and 2:5 resonances with respect to Neptune.

In the [outer] asteroid belt beyond 3.5 AU from the Sun, the 3:2, 4:3 and 1:1 resonances with Jupiter are populated by clumps of asteroids (the Hilda family, 279 Thule, and the Trojan asteroids, respectively).

Orbital resonances can also destabilize one of the orbits. For small bodies, destabilization is actually far more likely. For instance:

In the asteroid belt within 3.5 AU from the Sun, the major mean-motion resonances with Jupiter are locations of gaps in the asteroid distribution, the Kirkwood gaps (most notably at the 3:1, 5:2, 7:3 and 2:1 resonances). In the rings of Saturn, the Cassini Division is a gap between the inner B Ring and the outer A Ring that has been cleared by a 2:1 resonance with the moon Mimas.

A Laplace resonance occurs when three or more orbiting bodies have a simple integer ratio between their orbital periods. For example, Jupiter's moons Ganymede, Europa and Io are in a 1:2:4 orbital resonance. The extrasolar planets Gliese 876e, Gliese 876b and Gliese 876c are also in a 1:2:4 orbital resonance (with periods of 124.3, 61.1 and 30.0 days).>>

<<In astronomy, a resonant trans-Neptunian object is a trans-Neptunian object (TNO) in mean motion orbital resonance with Neptune. The orbital periods of the resonant objects are in a simple integer relations with the period of Neptune e.g. 1:2, 2:3 etc. Resonant TNOs can be either part of the main Kuiper belt population, or the more distant scattered disc population.

Distribution of the known trans-Neptunian objects in relation to the orbits of the planets together with centaurs for reference. Resonant objects are plotted in red. Orbital resonances with Neptune are marked with vertical bars; 1:1 marks the position of Neptune’s orbit (and its trojans), 2:3 marks the orbit of Pluto and plutinos, 1:2, 2:5 etc. a number of smaller families).

Detailed analytical and numerical studies of Neptune’s resonances have shown that they are quite "narrow" (i.e. the objects must have a relatively precise range of energy). If the object semi-major axis is outside these narrow ranges, the orbit becomes chaotic, with widely changing orbital elements.

As TNOs were discovered, a substantial (more than 10%) proportion were found to be in 2:3 resonances, far from a random distribution. It is now believed that the objects have been collected from wider distances by sweeping resonances during the migration of Neptune.

Well before the discovery of the first TNO, it was suggested that interaction between giant planets and a massive disk of small particles would, via momentum transfer, make Jupiter migrate inwards while Saturn, Uranus and especially Neptune would migrate outwards. During this relatively short period of time, Neptune’s resonances would be sweeping the space, trapping objects on initially-varying heliocentric orbits into resonance.
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2:3 resonance ("plutinos", period ~250 years)

The 2:3 resonance at 39.4 AU is by far the dominant category among the resonant objects, with 92 confirmed and 104 possible member bodies. The objects following orbits in this resonance are named plutinos after Pluto, the first such body discovered. Large, numbered plutinos include:

90482 Orcus
(84922) 2003 VS2
2003 AZ84
28978 Ixion
38628 Huya
----------------------------------------------------------------------------

1:2 resonance ("twotinos", period ~330 years)

This resonance at 47.8 AU is often considered as the outer "edge" of the Kuiper belt and the objects in this resonance are sometimes referred to as twotinos. Twotinos have inclinations less than 15 degrees and generally moderate eccentricities (0.1 < e < 0.3). An unknown number of the 2:1 resonants likely did not originate in a planetesimal disk that was swept by the resonance during Neptune's migration.

There are far fewer objects in this resonance (a total of 14 as of October, 2008) than plutinos. Long-term orbital integration shows that the 1:2 resonance is less stable than 2:3 resonance; only 15% of the objects in 1:2 resonance were found to survive 4 Gyr as compared with 28% of the plutinos. Consequently it might be that twotinos were originally as numerous as plutinos, but their population has dropped significantly below that of plutinos since.

Objects with well established orbits include (in order of the absolute magnitude):

(119979) 2002 WC19
(26308) 1998 SM165
(137295) 1999 RB216
(20161) 1996 TR66
(130391) 2000 JG81

[orin stepanek]

http://www.kepler.arc.nasa.gov/news/ind ... NewsID=182

[Doum]

Newfound super-Earth might support life, scientists say

http://www.msnbc.msn.com/id/46237284/#.TyqyuvnEdBk

A tree sun system with a planet in the habitable zone of one of the star.? WOW (signal)

[orin stepanek]

All kinds of new planet candidates! http://www.kepler.arc.nasa.gov/news/index.cfm?FuseAction=ShowNews&NewsID=190

[orin stepanek]

Happy B-day Kepler; launched March 6 2009

[bystander]

Four more years of data collecting.

NASA Approves Kepler Mission Extension
NASA Kepler News | 2012 Apr 04

NASA's Kepler Mission Awarded Mission Extension
NASA Ames Research Center | 2012 Apr 04

Kepler mission extended through 2016
University of Colorado, Boulder | 2012 Apr 04

[orin stepanek]

Thanks bystander; that's good news. Kepler already has found oodles of planets in the short time it has been in use.

[Sam]

XKCD 2012-06-20

Planets are turning out to be so common that to show all the planets in our galaxy, this chart would have to be nested in itself--with each planet replaced by a copy of the chart--at least three levels deep

[owlice]

"This is an exciting time."

Indeed!!

[orin stepanek]

more planets than you could shake a stick at!

[bystander]

41 New Transiting Planets in Kepler Field of View
NASA | Ames Research Center | Kepler | 2012 Aug 22

41 New Planets in 20 Star Systems
(Credit: Jason Steffen, Fermilab Center for Particle Astrophysics)

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Two newly submitted studies verify 41 new transiting planets in 20 star systems. These results may increase the number of Kepler’s confirmed planets by more than 50 percent: to 116 planets hosted in 67 systems, over half of which contain more than one planet. The papers are currently under scientific peer-review.

Nineteen of the newly validated planetary systems have two closely spaced transiting planets and one system has three. Five of the systems are common to both of these independent studies.

The planets range from Earth-size to more than seven times the radius of Earth, but generally orbit so close to their parent stars that they are hot, inhospitable worlds.

The planets were confirmed by analyzing Transit Timing Variations (TTVs). In closely packed systems, the gravitational pull of the planets causes the acceleration or deceleration of a planet along its orbit. These "tugs" cause the orbital period of each planet to change from one orbit to the next. TTV demonstrates that two transiting planet candidates are in the same system and that their masses are planetary in nature.

“These systems, with their large gravitational interactions, give us important clues about how planetary systems form and evolve,” said lead researcher Jason Steffen, the Brinson postdoctoral fellow at Fermilab Center for Particle Astrophysics in Batavia, Ill. “This information helps us understand how our own solar system fits into the population of all planetary systems.”

The two research teams used data from NASA's Kepler space telescope, which measures dips in the brightness of more than 150,000 stars, to search for transiting planets.

“The sheer volume of planet candidates being identified by Kepler is inspiring teams to look at the planet confirmation and characterization process differently. This TTV confirmation technique can be applied to large numbers of systems relatively quickly and with little or no follow-up observations from the ground,” said Natalie Batalha, Kepler mission scientist at NASA's Ames Research Center, Moffett Field, Calif. “Perhaps the bottleneck between identifying planet candidates and confirming them just got a little wider.”

The Transit Timing Variation (TTV) Planet-finding Technique Begins to Flower
NASA | Ames Research Center | Kepler | 2012 Aug 23

Transit Timing Observations from Kepler: VII. Confirmation of 27 planets in
13 multiplanet systems via Transit Timing Variations and orbital stability - Jason H. Steffen et al

arXiv.org > astro-ph > arXiv:1208.3499 > 16 Aug 2012

Transit Timing Variation of Near-Resonant KOI Pairs:
Confirmation of 12 Multiple Planet Systems - Ji-Wei Xie

arXiv.org > astro-ph > arXiv:1208.3312 > 16 Aug 2012

[orin stepanek]

Oh my! Two suns being orbited by two planets; one in the habitable zone! Only trouble it is a Neptunium size planet; though there may be moons that have water and lakes!!!

Click to view full size image

September 15, the discovery of Kepler-16b was our first binary star (two stars orbiting each other) with a planet orbiting both stars (circumbinary). Now Kepler mission has discovered Kepler-47b and 47c, the first transiting circumbinary system — multiple planets orbiting two suns. To compound the excitement of the discovery, one of those planets is in the binary system's habitable zone (where liquid water may exist)!


Kepler-47 system diagram


Kepler-47 system diagram. Credit: NASA/JPL-Caltech/T. Pyle


"The presence of a full-fledged circumbinary planetary system orbiting Kepler-47 is an amazing discovery," Greg Laughlin, professor of Astrophysics and Planetary Science, University of California, Santa Cruz, Calif. "These planets are very difficult to form using the currently accepted paradigm, and I believe that theorists, myself included, will be going back to the drawing board to try to improve our understanding of how planets are assembled in dusty circumbinary disks."

"Unlike our Sun, many stars are part of multiple-star systems where two or more stars orbit one another. The question has always been: do they have planets and planetary systems? This Kepler discovery proves that they do," said William Borucki, Kepler mission principal investigator at NASA's Ames Research Center, Moffett Field, Calif. "In our search for habitable planets, we have found more opportunities for life to exist."


Photo of Jerry Orosz


Jerome A. Orosz


Jerome Orosz, associate professor of astronomy at San Diego State University and lead author of the discovery paper published in Science, explained that "In contrast to a single planet orbiting a single star, the planet in a circumbinary system must transit a 'moving target.' As a consequence, time intervals between the transits and their durations can vary substantially, sometimes short, other times long. That was the telltale sign that these planets are in circumbinary orbits."

While the inner planet, Kepler-47b, orbits in less than 50 days and must be a sweltering world, the outer planet, Kepler-47c, orbits every 303 days, putting it in the "habitable zone," where liquid water might exist. But Kepler-47c is slightly larger than Neptune, and hence in the realm of gaseous giant planets, difficult to imagine as suitable for life. That does not preclude the chance that it has large a moon with a solid surface and liquid water lakes or seas. Kepler-16b was likened to Tatooine, Luke Skywalker's home planet in the movie Star Wars—a world with a double sunset. Kepler-47c suggests a different possible scene: our hero standing on a moon, gazing at a double sunset, with a Neptune-class planet rising behind her.

The research team used data from the Kepler space telescope, which measures dips in the brightness of more than 150,000 stars, to search for transiting planets. Using ground-based telescopes at the McDonald Observatory at the University of Texas at Austin, they made crucial spectroscopic observations to determine characteristics of the stars in the binary system which is 4,900 light-years from Earth. They are orbiting each other very fast, eclipsing each other every 7.5 days. One star is similar to the Sun in size, but only 84 percent as bright. The second star is a red dwarf star only one-third the size of the Sun and less than one percent as bright.


photo of William Wlesh


William F. Welsh


According to William Welsh, a co-author of the discovery paper, the number of planets discovered in multiple star systems is growing—about 70 to date. In binary star systems, planets are of two types: P-type: a planet that orbits both stars (circumbinary, like Kepler-47b and c)
S-type: a planet that orbits just one of the stars (referred to as circumstellar)

viewtopic.php?f=31&t=29418

[bystander]

Kepler Completes Prime Mission, Begins Extended Mission
NASA Ames Research Center | Kepler | 2012 Nov 14

NASA is marking two milestones in the search for planets like Earth; the successful completion of the Kepler Space Telescope's 3 1/2- year prime mission and the beginning of an extended mission that could last as long as four years.

[orin stepanek]

I've been hoping for some Kepler news releases; but the site seems to be quiet since the end of November!

[Beyond]

They're probably just busy counting all the new planets they've found.

[bystander]

Billions and Billions of Planets
NASA | JPL-Caltech | 2013 Jan 03

Planets Abound
Caltech | 2013 Jan 03

Look up at the night sky and you'll see stars, sure. But you're also seeing planets—billions and billions of them. At least.

An assortment of planets beyond our solar system is depicted in this artist's concept. (Credit: NASA/Ames/JPL-Caltech)

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That's the conclusion of a new study by astronomers at the California Institute of Technology (Caltech) that provides yet more evidence that planetary systems are the cosmic norm. The team made their estimate while analyzing planets orbiting a star called Kepler-32—planets that are representative, they say, of the vast majority in the galaxy and thus serve as a perfect case study for understanding how most planets form.

"There's at least 100 billion planets in the galaxy—just our galaxy," says John Johnson, assistant professor of planetary astronomy at Caltech and coauthor of the study, which was recently accepted for publication in the Astrophysical Journal. "That's mind-boggling."

"It's a staggering number, if you think about it," adds Jonathan Swift, a postdoc at Caltech and lead author of the paper. "Basically there's one of these planets per star."

The planetary system in question, which was detected by the Kepler space telescope, contains five planets. The existence of two of those planets have already been confirmed by other astronomers. The Caltech team confirmed the remaining three, then analyzed the five-planet system and compared it to other systems found by the Kepler mission.

The planets orbit a star that is an M dwarf—a type that accounts for about three-quarters of all stars in the Milky Way. The five planets, which are similar in size to Earth and orbit close to their star, are also typical of the class of planets that the telescope has discovered orbiting other M dwarfs, Swift says. Therefore, the majority of planets in the galaxy probably have characteristics comparable to those of the five planets.

While this particular system may not be unique, what does set it apart is its coincidental orientation: the orbits of the planets lie in a plane that's positioned such that Kepler views the system edge-on. Due to this rare orientation, each planet blocks Kepler -32's starlight as it passes between the star and the Kepler telescope.

By analyzing changes in the star's brightness, the astronomers were able to determine the planets' characteristics, such as their sizes and orbital periods. This orientation therefore provides an opportunity to study the system in great detail—and because the planets represent the vast majority of planets that are thought to populate the galaxy, the team says, the system also can help astronomers better understand planet formation in general.

"I usually try not to call things 'Rosetta stones,' but this is as close to a Rosetta stone as anything I've seen," Johnson says. "It's like unlocking a language that we're trying to understand—the language of planet formation."

One of the fundamental questions regarding the origin of planets is how many of them there are. Like the Caltech group, other teams of astronomers have estimated that there is roughly one planet per star, but this is the first time researchers have made such an estimate by studying M-dwarf systems, the most numerous population of planets known.

To do that calculation, the Caltech team determined the probability that an M-dwarf system would provide Kepler-32's edge-on orientation. Combining that probability with the number of planetary systems Kepler is able to detect, the astronomers calculated that there is, on average, one planet for every one of the approximately 100 billion stars in the galaxy. But their analysis only considers planets that are in close orbits around M dwarfs—not the outer planets of an M-dwarf system, or those orbiting other kinds of stars. As a result, they say, their estimate is conservative. In fact, says Swift, a more accurate estimate that includes data from other analyses could lead to an average of two planets per star.

M-dwarf systems like Kepler-32's are quite different from our own solar system. For one, M dwarfs are cooler and much smaller than the sun. Kepler-32, for example, has half the mass of the sun and half its radius. The radii of its five planets range from 0.8 to 2.7 times that of Earth, and those planets orbit extremely close to their star. The whole system fits within just over a tenth of an astronomical unit (the average distance between Earth and the sun)—a distance that is about a third of the radius of Mercury's orbit around the sun. The fact that M-dwarf systems vastly outnumber other kinds of systems carries a profound implication, according to Johnson, which is that our solar system is extremely rare. "It's just a weirdo," he says.

The fact that the planets in M-dwarf systems are so close to their stars doesn't necessarily mean that they're fiery, hellish worlds unsuitable for life, the astronomers say. Indeed, because M dwarfs are small and cool, their temperate zone—also known as the "habitable zone," the region where liquid water might exist—is also further inward. Even though only the outermost of Kepler-32's five planets lies in its temperate zone, many other M dwarf systems have more planets that sit right in their temperate zones.

As for how the Kepler-32 system formed, no one knows yet. But the team says its analysis places constraints on possible mechanisms. For example, the results suggest that the planets all formed farther away from the star than they are now, and migrated inward over time.

Like all planets, the ones around Kepler-32 formed from a proto-planetary disk—a disk of dust and gas that clumped up into planets around the star. The astronomers estimated that the mass of the disk within the region of the five planets was about as much as that of three Jupiters. But other studies of proto-planetary disks have shown that three Jupiter masses can't be squeezed into such a tiny area so close to a star, suggesting to the Caltech team that the planets around Kepler-32 initially formed farther out.

Another line of evidence relates to the fact that M dwarfs shine brighter and hotter when they are young, when planets would be forming. Kepler-32 would have been too hot for dust—a key planet-building ingredient—to even exist in such close proximity to the star. Previously, other astronomers had determined that the third and fourth planets from the star are not very dense, meaning that they are likely made of volatile compounds such as carbon dioxide, methane, or other ices and gases, the Caltech team says. However, those volatile compounds could not have existed in the hotter zones close to the star.

Finally, the Caltech astronomers discovered that three of the planets have orbits that are related to one another in a very specific way. One planet's orbital period lasts twice as long as another's, and the third planet's lasts three times as long as the latter's. Planets don't fall into this kind of arrangement immediately upon forming, Johnson says. Instead, the planets must have started their orbits farther away from the star before moving inward over time and settling into their current configuration.

"You look in detail at the architecture of this very special planetary system, and you're forced into saying these planets formed farther out and moved in," Johnson explains.

The implications of a galaxy chock full of planets are far-reaching, the researchers say. "It's really fundamental from an origins standpoint," says Swift, who notes that because M dwarfs shine mainly in infrared light, the stars are invisible to the naked eye. "Kepler has enabled us to look up at the sky and know that there are more planets out there than stars we can see."

Characterizing the Cool KOIs IV: Kepler-32 as a prototype for the formation of
compact planetary systems throughout the Galaxy - Jonathan J. Swift et al

arXiv.org > astro-ph > arXiv:1301.0023 < 31 Dec 2012

[neufer]

Billions and Billions of Planets
NASA | JPL-Caltech | 2013 Jan 03

Planets Abound
Caltech | 2013 Jan 03

"There's at least 100 billion planets in the galaxy—just our galaxy," says John Johnson, assistant professor of planetary astronomy at Caltech and coauthor of the study, which was recently accepted for publication in the Astrophysical Journal. "That's mind-boggling."

"It's a staggering number, if you think about it," adds Jonathan Swift, a postdoc at Caltech and lead author of the paper. "Basically there's one of these planets per star."

The planetary system in question, which was detected by the Kepler space telescope, contains five planets. The existence of two of those planets have already been confirmed by other astronomers. The Caltech team confirmed the remaining three, then analyzed the five-planet system and compared it to other systems found by the Kepler mission.

The planets orbit a star that is an M dwarf—a type that accounts for about three-quarters of all stars in the Milky Way.

Jonathan Swift staggered by the le-M-uel dwarfs.

[Ann]

The fact that M-dwarf systems vastly outnumber other kinds of systems carries a profound implication, according to Johnson, which is that our solar system is extremely rare. "It's just a weirdo," he says.

That's what I've felt for a long time. Isn't it remarkable that we are in orbit around a G-type star, when M dwarfs are vastly more common?

There are five ways of looking at this, I think. One is that our Earth is a very rare kind of planet for a number of reasons, one of which is that it orbits a G-type star. This might also mean that planets similar to the Earth are exceedingly rare in the Milky Way. We are special!

Another way of looking at it is to think that life is the norm in the universe, and if we are here even though we orbit a G-type star, then there must be incredible numbers of other civilizations in our galaxy, most of them orbiting an M-type star.

A third way of looking at it is to say that habitable worlds follow a sort of Bell curve, and the fact that we are in orbit around a G-type star is no more surprising than the fact that a small number of students get academic scores that are quite unlike the scores of most students.

A fourth way of looking at it is to say that life typically thrives underground, and then it doesn't matter what kind of star it orbits, or even if it orbits a star at all. (But that would still set us apart, since there is so much life on the surface of the Earth.)

A fifth way of looking at it is to say that we don't understand very well what life requires and how it evolves, so we should shut our mouths about what kind of stars can be orbited by planets that are suitable hosts for life.

But I still feel pretty special!

Ann

[Chris Peterson]

The fact that M-dwarf systems vastly outnumber other kinds of systems carries a profound implication, according to Johnson, which is that our solar system is extremely rare. "It's just a weirdo," he says.

That's what I've felt for a long time. Isn't it remarkable that we are in orbit around a G-type star, when M dwarfs are vastly more common?

I don't see it as remarkable. That our type of star is statistically rare just means there are millions of them in the galaxy, not billions. That we find ourselves around a "rare" star type is pretty meaningless- like the mind games behind the anthropic principle. We are, after all, where we are.

A fifth way of looking at it is to say that we don't understand very well what life requires and how it evolves, so we should shut our mouths about what kind of stars can be orbited by planets that are suitable hosts for life. :?:

I can't imagine any scientist supporting that!