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NASA's Kepler planet-hunting probe has spotted a system where two giant planets are locked in constantly changing orbits — with a super-Earth potentially pinned down in the crossfire.
Astronomers like to think of planets as a kind of celestial clockwork, keeping regular time. For example, the time it takes for the planets in our own solar system to complete their orbits can be calculated to within fractions of a second, and unless something huge happens, they'll stick to that timetable for billions of years.
In contrast, the two Saturn-size planets circling a sunlike star now known as Kepler-9, more than 2,000 light-years from Earth, shift their timetable with every go-round. Kepler-9b has an orbit lasting approximately 19.24 Earth days, while Kepler-9c has an orbit lasting a little more than twice as long, 38.91 days. But on average, Kepler-9b's orbit got about 4 minutes longer every time the Kepler astronomers checked, while Kepler-9c's averaged about 39 minutes shorter.
That suggests the planets are in the midst of a gravitational push-pull that keeps the orbits close to a 2-to-1 ratio, in what's known as a planetary resonance. In our own solar system, Pluto and Neptune are in a similar resonance (2-to-3), which is why little Pluto can't be kicked out of its orbit. The same thing applies to the Kepler-9 system.
"The system is stable in the sense that no planet will be ejected," said Matthew Holman, an astronomer at the Harvard Smithsonian Center for Astrophysics who is the principal author of a Kepler paper being published today on the journal Science's website.
"The orbits of the planets are changing, but these variations are oscillatory," Holman told me in an e-mail. "On average, the period ratio will be very close to 2-to-1. However, at any given instant that ratio may be bigger than 2-to-1 or smaller than 2-to-1."
Orbital variations has long been known to be theoretically possible, but Kepler-9 is the first confirmed planetary system where astronomers have been able to register this type of off-schedule behavior. It's actually quite a lucky break for the Kepler team. "The variations in what we call the transit times are large enough that we can use those transit timing variations to estimate the masses of thes bodies," Holman said in a Science podcast.
A question of timing
The $600 million Kepler mission looks for planets beyond Earth by having an orbiting telescope stare at a section of sky between the constellations of Cygnus and Lyra. That 15-foot-long, one-ton spacecraft looks for telltale dips in starlight that might be caused by planets crossing the disks of alien suns. By analyzing how long those dips last, and how frequently the dips occur, astronomers can figure out how large the planet could be. But they can't directly calculate how massive it is, and there's a chance that what they're seeing is not a planet at all.
The Kepler team is using other methods to make sure which among the hundreds of candidates they've found so far are truly planets — rather than, say, eclipsing binary stars or the glare of variable stars in the background. Usually, that requires follow-up observations by telescopes that look for the subtle shifts in starlight wavelengths caused by planet-induced gravitational wobbles. This interactive graphic explains how the various planet-hunting methods work.
The fact that Kepler-9's transit times were shifting immediately caught the Kepler team's attention, because that suggested a different method for confirming exactly what Kepler-9b and Kepler-9c were. Astronomers could plug those transit times into a computer model and run the numbers to see what types of objects could cause those weird orbits.
Objects the size of stars could be ruled out, because the transit timing variations would have been even larger in that case. Moreover, objects as massive as stars or brown dwarfs would be kicked out of the system relatively quickly. When the Kepler team ran a double-check with data from the Keck I telescope in Hawaii, the detection of a gravitational wobble confirmed that Kepler-9b and Kepler-9c were really, truly planets, Holman said.
"Now we have another tool to measure masses," Holman told me. "The combination of these methods is particularly powerful."
The researchers say this marks not only the first time that the transit timing method has been used to confirm a planetary detection, but also the first time that the transit method has been used to detect multiple planets in an alien solar system. That angle was touted in the NASA news release announcing the discovery.
"NASA's Kepler spacecraft has discovered the first confirmed planetary system with more than one planet crossing in front of, or transiting, the same star," the space agency declared in the news release. Of course, multiple-planet systems have been detected using methods other than pure transit observations. And with regard to the other "first," a different team of researchers previously reported using transit timing variations to study extrasolar planets, but they said the "final interpretation" of their results was still pending.
The Science research was held under embargo until 2 p.m. ET today, but the discovery came to light an hour early when NASA made its news release and other information about the observations publicly available.
Sub-Saturns ... and a super-Earth?
Holman and his colleagues estimate that Kepler-9b and Kepler-9c are both slightly smaller and less massive than Saturn. Theoretical models suggest that they're composed primarily of hydrogen and helium, like your typical gas giants. They appear to orbit in nearly the same plane, like the gas giants in our solar system. But the Kepler-9 planets have orbits that are significantly closer to their parent star than Mercury is to our own sun.
Astronomers assume that the planets formed farther out, in a colder region where ice and gas could collect, and then they circled inward in a complex orbital dance.
There might be another planet even closer in: When the researchers ran the numbers, they saw evidence that a world about one and a half times as wide as Earth was spinning around the Kepler-9 sun every 1.6 Earth days. If the evidence pans out, this planet could be about as massive as Earth, but hotter and more hellish than any world in our own solar system — sort of like the CoRoT-7b super-Earth that was identified a couple of years ago.
However, the Kepler team says it's too early to confirm that the Earth-scale candidate, currently known as KOI-377.03, is indeed a planet, let alone a super-hot super-Earth.
"The approach to confirming this as a planet will first be to exhaustively rule out all other possibilities for what could be causing the signal we see," Holman told me. "However, this will not establish the mass of this body. That will be left to future work."
NASA
Astronomers had to unravel the patterns that Kepler saw in the dimming of starlight from Kepler-9, as shown in this graphic.
Today's Kepler findings have been the subject of intense speculation for the past few days, even before NASA announced that an announcement was on the way. Now that the news is out, the results may not be as world-shattering as some people expected.
To my mind, the announcement earlier this week that five to seven planets had been detected in a far-off solar system seems at least as significant as today's report from Kepler. But there's been an aura of mystery surrounding the hundreds of detections made by the Kepler team because those findings have been so closely held. The fact that today's news broke on Twitter and on the Web just adds to the Kepler aura.
Kepler's principal scientific investigator, Bill Borucki of NASA's Ames Research Center, surmised that the public is so interested in the mission because it could answer some of the biggest questions in astronomy: How common are Earthlike planets? How many possible homes for life exist? "We're not surprised at all about the attention that it's been getting," he told me during today's NASA teleconference.
As more of Kepler's discoveries come out, scientists — and science fans — will develop a better understanding of the wide and weird diversity of planetary systems. Let's hope this stuff never gets old.
More on planetary diversity:
- Smashing news about planets
- Superstorm on an alien world
- An avalanche of alien planets
- Planets go wild around far-off stars
- Looking for alien Earths? Here they come
Join the Cosmic Log corps by signing up as my Facebook friend or hooking up on Twitter. And if you really want to be friendly, ask me about "The Case for Pluto."
Leave a Comment:
Why was the region of the sky between the constellations of Cygnus and Lyra chosen for Kepler to stare at?
Thanks
Ya gotta start somewhere looked a good a place as any...
AS GOOD AS ANY?? really?
that answer doesn't do the question justice. It's a good question, and i'm sure there is actually a reason they chose this region of space.
I've been saying for a while that our math is off...that we don't have all the "puzzle pieces" yet to accurately determine planet distances form their stars in other solar systems. Many seem way to close to their stars and circle them in days, weeks or months....some much larger than Jupiter and closer to their star than Mercury is to our Sun. For me, this seems wrong. I'm not saying it is wrong...just seems wrong.
In any case, has a test ever been conducted to see if a star, even ours, dims as a planet is on the opposite side of our view of the sun? Maybe, the gravity of a planet influences the star enough to cause a dip in its brightness as seen by us here on Earth. If this is or turns out to be the case, then maybe we are counting twice as many planets as are possibly there.
@Bloggerrich: There are an innumerable number of binary (double-star) systems in our galaxy, where the stellar components are actually in contact with each other (or nearly so), and orbiting around a mutual center of gravity in mere minutes. Mass equations do not prohibit these systems from forming very tight and fast orbits -- locked in a dizzying perpetual twirl. In many cases, one, but not both components possesses the mass necessary to kick-start the fusion reaction at its core. Here, we have a failed stellar object (a Jupiter-like planet, but almost always more massive than Jupiter) orbiting a full-fledged star. The orbital radius is relatively small, and the orbital period is relatively short. It happens. A lot.
Gravity alone is not enough for today's instruments to pick up on any brightness variations, although it's most definitely contributory to the astrometric "wobble" we can see in stars as their more massive planets orbit around them. Transits, where the planet's orbital path periodically places it between us and the host star, according to our line of sight, is what is needed to detect the minute brightness variations and, over time, develop a light curve that exhibits that. And those light curves have to be studied and evaluated very carefully, because they can show some pretty odd variations related to how, and what angles, the planetary transit occurs in relation to the host star.
@Rakesh: Because is a rich stellar field, full of a higher concentration of likely candidate systems, and that's due to the fact that the area is near the galactic equator. Looking through The Cygnus/Aquila complex, you're basically looking outward from the Milky Way galaxy, through the Orion and Sagittarius arms, and into intergalactic space. In the opposite direction is the constellation Sagittarius and the center of our galaxy.
Well said, Tiz! I love it when we're able to answer each other's questions (this one would have taken me a while).
Glad to be of assistance, Mr. Boyle. :) I love this stuff, and have been studying it for decades.
Yes Indeed! Thank you Tiz.
What is the significance of being near the galactic equator? (is that a dumb quesiton?)
More stars there. 30,000 LY from the center, the galaxy is only about 2,000 LY thick. The farther off of the equator you look, the fewer stars you find (local variations notwithstanding).
Jim got it essentially right. You're never going to be able determine all the species of trees in a forest by looking straight up from where you stand. You've got to look through the bulk of the forest. If the plan is to bag as many interesting extra-solar planetary systems as possible within a fixed field, you'd better pick a sight line where there's more to look at. If your gaze is along the galactic equator (through the "meat" of the disk of the galaxy), the stellar population in the field is much greater (deeper and varied) than that which can be had by looking out through the "top" or "bottom" of the galaxy. And that's just a general rule. As Jim said, local variations notwithstanding. The reason they chose to look OUTWARD toward the edge of the galaxy, instead of INWARD toward the galactic hub -- something you might think they'd want to do to further maximize the potential of finding good stuff -- is mostly about opportunity as it relates to the position of the instrument. But, also, looking INWARD on the galaxy would be overload. The fields there can get so crowded, it can often become extremely difficult to resolve optical sources. They chose the perfect place to look.
This is why I look forward to each issue of Astronomy. This is what I call News!
Wouldn't Kepler 9-b and Kepler 9-c still be considered "hot Jupiters" since they are gas giants in very close orbits around their parent star? Also, is it correct that if they are in a 2 to 1 resonance, that they cross one another's orbit? If the answer is yes, it means neither of these giants "clear their orbits" and according to the controversial IAU planet definition, would not be considered planets at all.
Laurel, I reckon these could be called hot Jupiters, since they have migrated close in. The researchers compared them more to Saturn, however, maybe because of their density (more Saturnish than Jupiterish). You had to know that I would ask Holman about that orbit-crossing issue. Here's what he said in his e-mail (which I didn't include in the story): "Regarding the orbital configuration, the orbits do not cross. Although the orbits are slightly elliptical, they are well-separated." There are examples of orbit-crossing giant planets, but these are not among them.
Hot Jupiter's have a mass similar to or greater than Jupiter (1.9 × 1027 kg). They are generally closer than 1/2 an AU from their parent star. Some folks use names like "hot-saturn" or "hot-neptune" depending on the mass of the planet in question.
regarding the IAU planet definition and these new kepler discoveries... How does a moon on a gas giant affect the wobble of it's parent star? can kepler discover moon's around Kepler 9's gas giants?
This telescope is telling us that there might be objects circling distant stars at different intervals, but even those observations must be confirmed by the star's gravitational wobble and other methods. Everything else about the possible objects is educated guessing and speculation by Harvard, which answers the question of why. They are observing a tiny fraction [1500?] of the estimated 200 Billion stars in the Milky Way galaxy and we ain't close to discovering Trekie warp speed to get to even the nearest. Knowing the forces that shape our solar system, physicists and astronomers should be able to extrapolate the possible variations of theoretical ones, if they have any imagination. That money could have been better spent reaching out to Islam. If you could somehow take Europe's Very Large Telescope, combine it with the Hubble Space Telescope, and then double that magnification, you still would not be able to detect caring in me. Fun for the kids, yes, useful science, no.
Why just for kids? People of all ages are interested in these discoveries. For centuries, our ancestors have wondered if we are alone in the universe and even if other stars had planets. Obtaining this knowledge is only the tip of the iceberg. Eventually, we will be able to compare the origins and formations of different solar systems with our own. It's fun and meaningful for me too and for many people of all ages.
I truly love our technology. Let's hope this is just a glimpse of what Kepler discovers.
Maybe it`s inhabited by amazon women! Now wouldn`t that be cool?
gitner,
then why bother commenting?
Wondered the same thing myself. Good comment.
Within my lifetime we've learned to use the atom peacefully (and not so peacefully), walked on the moon and confirmed the existence of planetary systems other than our own solar system.
Discovering how these new systems work is a step toward reaching out to them, if only robotically.
So yes, Gittnerdunn, it is useful science. As for reaching out to Islam, I'd suspect we would do well to identify another planet for use by those of us who are sane...
My guess, if there is an interstellar community, they have posted signs around our system saying, "Danger! Contaminated by religion! Do not approach or communicate with the natives!
Fascinating! The grumpy people need to stop fussin' this stuff is cooler than the other side of the pillow!
The dip in light is when the object crosses BETWEEN Earth and the star, not when the object crosses behind the star. Think of a bug crossing in front of a light bulb - with the proper instruments, that transit of the bug can be seen.
In a binary star system we see a change in light level as the stars pass behind each other because the front star blocks the light from the back star.
In a planetary system a planet about to pass behind the star would be in opposition and would be full. So why would we not see a dip in brightness as the planet passes behind the star. While the reflected light would be less than that of the star we seem to be seeing some pretty small objects out there and it seems to me the Saturn sized planets would be relecting a significant percentage of their light.
Just curiosity
Don't the shepard moons of saturn have a similar dance and effect the rings somehow?
By expelling Pluto from our solar system earth bound astronomers have put themselves in danger of being called upon to do the same with Neptune unless the 2 to 3 resonance with now banished Pluto is broken soon or so proved somehow !
I read most of what is posted in here before scrolling down to post anything so forgive me if someone has already mentioned it , but , isnt it a factthat humans on earth have been tracking that area of space for thousands of years? the pyramids at giza line up with stars in orions belt? maya/incan pyramids also? also many native american tribes monitoring the same area of space? possibly even stonehenge? also there are stone formations found to be much older than the egyptian pyramids in the desert somewhere geographically near the giza structures that seem to track stars in the same area of space isnt there? im going to take a stab at this one and toss a theoretical answer out there as to why they chose that area of space...maybe its pure coincidence...maybe not...but I think they just might be going under the assumption that our ancient ancestors knew something that mankind has forgotten and that there may be a good reason that they tracked that area of space for thousands of years. its just a thought but it seems perfectly logical to me :-D
At least others have a chance at discovering some exoplanets whilst kepler is focused thataway....personally, a more practical field of view may well have been immediatly ahead or behind us, as these areas are more likley for us to explore with manned or robotics in the near term, I would think forward most of all. As though we were in a stream and paddled aways forward, stop paddling and drift back to SOL3...a very crude example but the picture is easy to grasp. My personal thoughts are that solar systems closer to the center of the galaxy are older for the most part, and spinning in to feed the beast at he center...here on the outer fringes we tend to be a bit younger, older civs would most likely be closer in though...In later years we will discover that the galactic gravity affects solar system development and species like ours tend to be in the outer realm and species that are more radiation tolerant develop withing the inner realm...just some thoughts to keep ya all on your toes...at least the bad astonomy site wished me a happy day!!..
i understand your argument to be made there, but at the same time you could be wrong. it might be that only panets that are out of the galactic center have a chance at life. It also might be that we evolved late in comparison to how many species there have been at our planet. We dont really know the answers and really can only guess at this point unfortunately.
I have been reading the posts above. It seems that we are looking at the stars and haven't yet solved from where our ancestors came. We haven't at yet solved the mysteries of all the old temples in our world.I am a Maltese citizen( for those who do not know Malta is a very small island in the centre of the Meditterean) and I can boost like all the Maltese that we have the oldest temples built around 3600/3200years before Christ. These are older than the pyramids of Egypt. The people who built them used a special technic which is a yearly calendar using the equinox of june and december. Where these poeple scientist at that time or what. If any of you enter on HERITAGE MALTA WEBSITE you can see for yourself what I mean. Besides I think that scientist should start studying more deeply our ancestors , for maybe there is a link with another world.
Personally I don't believe man Originated on this planet, Possible but not likely, Look at the time line of when were supposed to have evolved and where were at today. The most advanced period has only developed in the past 3000 years or so. Why ? If we did originate here what took so long for us to get to where were at today from the discovery of fire.
To Robert Peery
I think it has taken this long because so many fear the light; developing their mind to go beyond just what they see. For all our dreamers they were mocked and frowned upon but it seems they were in better gracious arms then those that constantly would feud with one another over the most trivial things rather then plainly examine the situation and solve it with some degree of intelligence. Then again even having brains does not ensure success if someone has a bigger club then you. It is a pity that so many fine minds of the past never had offspring to pass on such innate attributes of the mind. The venomous brood fear to think and see their actions, just utter chaos. I would doubt this in what I say but I seem to be just speculating on our developmental hindrances or dear comrade.
....
It begs the question, for if we too look upon the heavens to the other celestial beings for habitable life. Is it in part that one looks also so far away, at us? If that be true then with intelligence and reason one would think that another sentient being would have found this planet and be nearby if they have the same tenacity for exploration. It would make no sense to travel without a plan.
84 years ago this month, The Scopes monkey trial ended; finding Scopes not guilyt on a legal technicality. Since then, the divided opinion creation / evolution has fluctuated hot and cold, and neither side has been able to imperially prove themselves correct; nor the opposition incorrect; how ever it proves to me that the scriptures are correct. the wisdom of this world is foolishness [II Corinthians]
Why? 1. Since the trial; the computer age began. Apparently science did not notice: decimal math lacks the accuracy required for accurate computing. computer buffs struggled through the new math to wind up with basic binary 01, and digital replaced decimal throughout civilization in all fields except Astronomy. 2. as one looks at a clock face it is obvious; there is no midnight hour, nor Noon hour. There are only 120 minutes between 11 PM and 1 Am and the same at 11 AM to 1 PM.. There are only 11 AM & 11 PM hours, which makes it a 22 hour day. This alignes it with the 11th our, as mentioned in the scriptures. 3. Quantum theory tells us their experiments are proving all previous theories are grose human errors; and the earth is a hologram projected by the human mind. [listen to the video]
http://www.youtube.com/watch?v=mcT8YLE-zM4
I for one have lost all confidence in the technological wisdom of civilization which is polluting Planet Earth; encroaching everywhere like melanoma (skin cancer)