Kepler wraps prime mission, begins extension

Nov 15, 2012 by Whitney Clavin, Michele Johnson & J. Harrington
This artist's concept shows the Kepler spacecraft.

(Phys.org)—NASA is marking two milestones in the search for planets like Earth; the successful completion of the Kepler Space Telescope's three-and-a-half-year prime mission and the beginning of an extended mission that could last as long as four years.

Scientists have used Kepler data to identify more than 2,300 and confirm more than 100 planets. Kepler is teaching us that the galaxy is teeming with planetary systems and that planets are prolific, and is giving us hints that nature makes small planets efficiently.

So far, hundreds of Earth-size planet candidates have been found, as well as candidates that orbit in the habitable zone, the region in a where liquid water might exist on the surface of a planet. None of the candidates is exactly like Earth. With the completion of its prime mission, Kepler now has collected enough data to begin finding true sun-Earth analogs—Earth-size planets with a one-year orbit around stars similar to the sun.

"The initial discoveries of the indicate at least a third of the stars have planets and the number of planets in our galaxy must number in the billions," said William Borucki, Kepler principal investigator at NASA's Ames Research Center in Moffett Field, Calif. "The planets of greatest interest are other Earths, and these could already be in the data awaiting analysis. Kepler's most exciting results are yet to come."

NASA's Kepler Space Telescope searches for planet candidates orbiting distant suns, or exoplanets, by continuously measuring the brightness of more than 150,000 stars. When a planet candidate passes, or transits, in front of the star from the spacecraft's vantage point, light from the star is blocked. Different-sized planets block different amounts of starlight. The amount of starlight blocked by a planet reveals its size relative to its star.

Kepler was launched March 6, 2009. Its mission was to survey a portion of the galaxy to determine what fraction of stars might harbor potentially habitable, Earth-sized planets. Planets orbiting in or near habitable zones are of particular interest.

Kepler began the search for small worlds like our own on May 12, 2009, after two months of commissioning. Within months, five exoplanets, known as hot Jupiters because of their enormous size and orbits close to their stars, were confirmed.

Results from Kepler data continue to expand our understanding of planets and planetary systems. Highlights from the prime mission include:

  • In August 2010, scientists confirmed the discovery of the first planetary system with more than one planet transiting the same star. The Kepler-9 system opened the door to measurement of gravitational interactions between planets as observed by the variations in their transit timing. This powerful new technique enables astronomers, in many cases, to calculate the mass of planets directly from Kepler data, without the need for follow-up observations from the ground.
  • In January 2011, the Kepler team announced the discovery of the first unquestionably rocky planet outside the solar system. Kepler-10b, measuring 1.4 times the size of Earth, is the smallest confirmed planet with both a radius and mass measurement. Kepler has continued to uncover smaller and smaller planets, some almost as small as Mars, which tells us small rocky worlds may be common in the galaxy.
  • In February 2011, scientists announced Kepler had found a very crowded and compact planetary system—a star with multiple transiting planets. Kepler-11 has six planets larger than Earth, all orbiting closer to their star than Venus orbits our sun. This and other subsequently identified compact, multi-planet systems have orbital spacing relative to their host sun and neighboring planets unlike anything envisioned prior to the mission.
  • In September 2011, Kepler data confirmed the existence of a world with a double sunset like the one famously portrayed in the film "Star Wars" more than 35 years ago. The discovery of Kepler-16b turned science fiction into science fact. Since then, the discoveries of six additional worlds orbiting double stars further demonstrated planets can form and persist in the environs of a double-star system.
  • In December 2011, NASA announced Kepler's discovery of the mission's first planet in a habitable zone. Kepler-22b, about 2.4 times the size of Earth, is the smallest-radius planet yet found to orbit a sun-like star in the . This discovery confirmed that we are getting continually closer to finding planets like our own.
  • In February 2012, the Kepler team announced more than 1,000 new transiting planet candidates for a cumulative total of 2,321. The data continue the trend toward identifying smaller planets at longer orbital periods, similar to Earth. The results include hundreds of planetary systems.
  • Recently, citizen scientists participating in Planet Hunters, a program led by Yale University, New Haven, Conn., that enlists the public to comb through Kepler data for signs of transiting planets, made their first planet discovery. The joint effort of amateur astronomers and scientists led to the first reported case of a planet orbiting a double star. The three bodies are, in turn, being orbited by a second distant pair of stars.
"Kepler's bounty of new planet discoveries, many quite different from anything found previously, will continue to astound," said Jack Lissauer, planetary scientist at Ames. "But to me, the most wonderful discovery of the mission has not been individual planets, but the systems of two, three, even six planets crowded close to their stars, and, like the planets orbiting about our sun, moving in nearly the same plane. Like people, interact with their neighbors and can be greatly affected by them. What are the neighborhoods of Earth-size like? This is the question I most hope Kepler will answer in the years to come."

In April 2012, NASA awarded Kepler an extended mission through as late as 2016. More time will enable the continued search for worlds like our own—worlds that are not too far and too close to their sun.

"The Earth isn't unique, nor the center of the universe," said Geoff Marcy, professor of astronomy at the University of California at Berkeley. "The diversity of other worlds is greater than depicted in all the science fiction novels and movies. Aristotle would be proud of us for answering some of the most profound philosophical questions about our place in the universe."

Ames manages Kepler's ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed the Kepler mission development. Ball Aerospace & Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. The 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.

Explore further: Video gives astronaut's-eye view inside NASA's Orion spacecraft

More information: For more information about NASA's Kepler mission, visit: www.nasa.gov/kepler .

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User comments : 18

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GSwift7
1 / 5 (2) Nov 15, 2012
I think they are all surprised by the magnitude of this mission's success. To find SO MANY planets in the first phase of the mission is astounding. They are surveying around 150k stars, and they found around 2500 potential planets. That's about 1.5%, and Kepler can only see planets that transit their star. Also, we should continue to detect longer orbit planets amongst these stars, so that percentage will get bigger. The final percentage of stars that actually have planets is looking like it might be over 50%, or perhaps even higher. I personally still have a suspiciion that the Centauri system has planets. The J Webb telescope might be able to see them, if they are there. If there isn't a semi-habitable planet at Centauri, then our hopes for expanding beyond Sol are automatically set back really far.
gopher65
not rated yet Nov 15, 2012
GSwift7: The Centauri system definitely has planets, as one has been detected. Whether or not it has habitable-zone planets of the right size is another matter (likely not based on the distance between the two primary stars, but you never know I guess).
Modernmystic
1 / 5 (1) Nov 15, 2012
1.5%....

I get that it can only see planets that transit the star, but that number seems awfully low to me...
Pkunk_
1 / 5 (1) Nov 15, 2012
1.5%....

I get that it can only see planets that transit the star, but that number seems awfully low to me...

Extrapolate that over the 100 billion stars in the Milky way and you arrive at a figure of 1.5 bn planets in the galaxy. That is in no way an "awfully low" number.
maxb500_live_nl
not rated yet Nov 15, 2012
Gswift: A European ESO team using their 'HARPS' instrument recently found the first planet at Alpha Centauri after 4 years of extensive data collection. NASA called it the greatest astronomical discovery in a decade. The planet is close to the size of earth but it orbits to closely for life to exist. The ESO data also suggest their might be more planets and they have begun follow up observations.
nkalanaga
not rated yet Nov 15, 2012
The Centauri AB system could easily have planets in both habitable zones. Computer simulations consistently show that orbits would be stable out to at least twice the "Earth-like" distance for both stars, so even a Mars-analogue would be stable.

Whether such a world would have received enough water to be habitable is open to debate, as simulations have said both yes and no, depending on beginning assumptions.
Modernmystic
1 / 5 (1) Nov 15, 2012
1.5%....

I get that it can only see planets that transit the star, but that number seems awfully low to me...

Extrapolate that over the 100 billion stars in the Milky way and you arrive at a figure of 1.5 bn planets in the galaxy. That is in no way an "awfully low" number.


It most certainly is in comparison to how many were estimated prior to our getting hard data....
GSwift7
1 / 5 (2) Nov 15, 2012
1.5%....

I get that it can only see planets that transit the star, but that number seems awfully low to me...


1.5% is just what Kepler has been capable of detecting so far. That's 2500/150000=.015

After the extended mission is complete, and we've had time to analyze the existing data completely, the count will probably rise to more like 5000/150000=3%

Then you need to multiply that by a factor to account for systems that are not lined up directly with us, which is probably >95% of them. If you use a factor of 95%, that takes the 3% up to 60%.

Then there's also a factor to account for undetectable planets. Any planet with a long year is undetectable by Kepler, and so are small ones like Mercury. Using our solar system as a template (probably not a good idea, but best we have), Kepler would probably only detect Venus, Earth, Mars, and maybe Jupiter, Saturn and Uranus if you got lucky and caught them at the right time of their year, but you'd only get one transit.
GSwift7
1 / 5 (2) Nov 15, 2012
The Centauri AB system could easily have planets in both habitable zones. Computer simulations consistently show that orbits would be stable out to at least twice the "Earth-like" distance for both stars, so even a Mars-analogue would be stable.


That's correct. Centauri A and B are very far apart. They go from Pluto-Sun distance at the farthest to Saturn-Sun distance at their closest. If you were standing on an exact copy of Earth orbiting in either A or B's habitable zone, the second star would be barely visible in the daytime, and would be dimmer than our moon at night.
gopher65
not rated yet Nov 15, 2012
Using our solar system as a template (probably not a good idea, but best we have), Kepler would probably only detect Venus, Earth, Mars, and maybe Jupiter, Saturn and Uranus if you got lucky and caught them at the right time of their year, but you'd only get one transit.

Actually, Kepler discoveries can only be thought of as reliable(ish) if at least 3 transits have been observed. Due to the observing time, an alien Kepler *might* have confirmed Mars during its extended mission, but it would never confirm Jupiter or anything further out.

Also, due to the fact that the closer a planet is to its star the more likely it is to transit, It's more likely that only Mercury would have been discovered, while the rest of the system would be invisible to observers using this method (if the orbit is slightly out of alignment with Earth's line of sight you can see planets close to their stars, but not planets farther out).

So the transit method really underestimates the number of planets
GSwift7
1 / 5 (1) Nov 15, 2012
an alien Kepler *might* have confirmed Mars during its extended mission, but it would never confirm Jupiter or anything further out


Like I said, it would only get one transit, so the 'planet' would only be classified as a 'planet candidate' awaiting follow-up verification from another source.

It's more likely that only Mercury would have been discovered, while the rest of the system would be invisible to observers using this method


Mercury is too small for Kepler. Read the wiki page.

I was wrong above, the odds of us being lined up with the ecliptic are only 0.5%, so that leaves 99.5% of them undetectable by this method. It had it in the wiki page.

So, if we have detected almost 2500 planets so far, that means the galaxy is LOADED with planets.
GSwift7
1 / 5 (2) Nov 15, 2012
if the orbit is slightly out of alignment with Earth's line of sight you can see planets close to their stars, but not planets farther out


Only if they are jupiter sized or larger, and close to the star. They do that by using the phases of the planet when it's of axis with us. Only the larger planets show a bright enough phase change for this. Once again, it says this on the wiki page.

I didn't realize that Kepler was performing under design specs. We are lucky that it works at all. They apparantly underestimated the variability of the stars themselves. Oh well, that leaves room for improvement if a future mission is done with better technology.

It's also a shame that so much of the actual data is discarded due to limitations on bandwidth.
chromosome2
not rated yet Nov 15, 2012
I'd love to see a dynamic solar system chart where it shows you, at this time, the probability of detecting any given planet in *our* system using tools with equivalent power to our own at any specific distance from us and angle relative to the primary plane of our system, and then projects those percentages with the launch of expected tools and the collection of additional data over the next few decades.
nkalanaga
not rated yet Nov 16, 2012
GSwift7: Even at maximum separation Alpha Centauri A and B would be much brighter than the full Moon, as seen from each others planets. The Sun from Saturn is about 1/100 as bright as it is from Earth, but is still about 10,000 times as bright as the full Moon. A is a little brighter than Sol, and B is a little less than half as bright.

I'll agree that they probably wouldn't be noticeable in the daytime sky, although they would still be visible. Venus is visible in the daytime if one knows exactly where to look.
Osiris1
1 / 5 (1) Nov 16, 2012
We will find that planets are the mundane companions of all stars, living or dead. We will also find that the orbital planes of star systems vary widely in all three angular degrees of freedom about the orbital center. Size and content of these orbital planes will vary also, as well as the stability of those planets in their orbits. Hot jupiters though unstable are the low hanging fruit. Bottom line, we are only glimpsing hints of the immense numbers of planets that actually exist. Think of a dinner plate in Denver, USA with an amoeba at the center representing the orbital centroid of mass of the system..a movable point sports fans, and the 'jupiters' as blood cells and the terrestrial planets as viruses. Now put that flat plate on edge and see how tiny an aperture of visibility you have to see a 'transit' from thousands of miles away-IF u see plate edgewise exactly. Orbital plane not coplanar with ur line of sight..U R out of luck...period. We see less than .000001% of reality.
Torbjorn_Larsson_OM
not rated yet Nov 17, 2012
Nice roundup.

@ GSwift 7: "If there isn't a semi-habitable planet at Centauri, then our hopes for expanding beyond Sol are automatically set back really far."

No, the real large step in colonization, on a logarithmic scale suitable to exponentially expanding resources, will be to reach the Oort cloud. A comet has all the neccessary resources to build biospheres out of.

In comparison, planet are risky and costly (diluted resources, deep gravity wells).

"the odds of us being lined up with the ecliptic are only 0.5%, so that leaves 99.5% of them undetectable by this method."

These objects are extended and doesn't have to line up perfectly. Your initial guess was better, IIRC Kepler catches 2-5 % of planets depending on distance from the star et cetrea.

@ nkalanaga: You mean if there is sufficiently little water, terrestrials are very dry compared to asteroids. Luckily it seems inner planets are naturally non-water worlds.
nkalanaga
not rated yet Nov 18, 2012
True, compared with asteroids and other objects formed beyond the "snow line". However, some simulations indicate that inner planets have even less water without a large outer planet to direct icy bodies into the inner system. Fortunately, not all agree, and a few simulations of binary systems similar to Alf Cen show the second star serving the same function, as long as the separation is in right range. Given all of the simulations, it seems that Alf Cen's habitable zone planets have a reasonable chance of having water amounts similar to Earth.

And then there's the simulation from several years ago of water delivery to Earth, with Jupiter in its current location throughout the period. They ran the early Solar System thousands of times, with the same mass in various regions, but the individual bodies randomly distributed, and came up with Earths with anywhere from 0.01 to 100 oceans of water, all from the same initial conditions.
gopher65
1 / 5 (1) Nov 18, 2012
Yeah, Kepler has had several problems that have really gimped it. I hope they put up new telescopes based on the same idea with better (and more robust) hardware.

Given the issues that Kepler has, it's remarkable they've managed to pull as much useful data out of it as they have:).

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