Planet Search | Kepler 2 Continues

Update 2 :

As of June 2014, the Kepler spacecraft has been given the go ahead for at least a two year extension to the planet search mission. As noted near the bottom of this post, Kepler was broken. Two of the four guidance gyroscopes quit working in March 2013. Scientists have figured out a way to use the remaining two to allow the spacecraft to renew the search.

Previously, Kepler stared at the same location in the night sky for more than three years. Numerous planet candidates were seen among the 100,000 or so stars examined. Astronomers figure one in five stars has Earth-sized planets in a warm enough zone to be habitable. That is not to say they do host life. You can examine the thousands of candidates and confirmed planets at this NASA Exoplanet Archive or at this Kepler page.

With this new Kepler 2 mission, nine different star fields will be observed, each for about 80 days, during the next two years. Each field is in a different part of the night sky. Some will include rich parts of the Milky Way galaxy. Others will be in less populated regions. These new fields actually enhance the data gathering for K2 allowing it to sample planets in a wider variety of star conditions. More proposals are being examined for possible extension to the new mission. Additional details can be found here.

NASA K2 Mission

Update 1 :

The sizes of more than 3/4 of the 3,500 candidate planets found by NASA’s Kepler spacecraft are between that of Earth and Neptune, 4x the size of Earth. Circled in this image are the many planet candidates found by Kepler as of January 2014. It is not known how they form or if they are made of rock, water or gas. Ground based telescopes are used to follow-up on the Kepler candidates and confirm their existence along with other important details about them. The Kepler team reported on these follow-up planets this week at the American Astronomical Society meeting in Washington.

Follow-up observations use Doppler measurements of the planets’ host stars as they wobble. The wobble is caused by the gravitational pull on the star by the orbiting planet. The wobble tells the mass of the planet. More wobble means a more massive planet. Imagine swinging a bucket around you as you spin in a circle. More water in the bucket would make you wobble more. Scientists at W. M. Keck Observatory in Hawaii confirmed 41 of the exoplanets discovered by Kepler and were able to calculate the masses of 16. Knowing mass and diameter, density could be calculated. They could then characterizing the planets as rocky or gaseous, or mixtures of the two.


Most of the planets in our solar system do not fit into this range of sizes. Astronomers wonder why. What evolution of our solar system caused a different outcome than the large population seen elsewhere in the galaxy?

“Kepler’s primary objective is to determine the prevalence of planets of varying sizes and orbits. Of particular interest to the search for life is the prevalence of Earth-sized planets in the habitable zone,” said Natalie Batalha, Kepler mission scientist at NASA’s Ames Research Center in Moffett Field, Calif. “But the question in the back of our minds is: are all planets the size of Earth rocky? Might some be scaled-down versions of icy Neptunes or steamy water worlds? What fraction are recognizable as kin of our rocky, terrestrial globe?”

As Previously Posted:

Our Sun has a multitude of objects in orbit around it. There are comets, asteroids, spacecraft, and planets. Do other stars also have planets? NASA’s Kepler spacecraft launched March 6, 2009 from Cape Canaveral Air Force Station in Florida. The first planet-hunting spacecraft set out on a mission to look for other planets around stars. Astronomers hoped to answer two questions.

  1. What fraction of the stars have planets in orbit around them?
  2. What fraction of those are in the habitable, or Goldilocks, zone where conditions are just right to possibly allow life to exist?

Based on ground telescopic views, large hot Jupiter-sized and large cold icy planets have already been observed around stars. Kepler is looking for those planets known as terrestrial, like Earth, that orbit at a distance that isn’t too hot or too cold. They tend to be smaller and more difficult to detect. A satellite spacecraft above our atmosphere is needed.

What Has Kepler Seen?

Kepler has stared at the same patch of sky for 3.5 yrs. The patch is small. Hold your hand out with your extended arm. That is how big the patch is. It contains 100,000 stars which were monitored continuously. If a planet in orbit around that star passed between the star and us, the level of brightness seen would decrease slightly. That is called a transit.

As of November 2013, Kepler found more than 3,500 potential planet candidates. About 200 have been confirmed. Click on a star named in the confirmation table at that link to see the details of the orbit and transit data. Interesting stuff. The candidates come in a variety of sizes around stars of different sizes. There are quite a few Earth sized candidates. But, fewer than 10 of those have had their data confirmed.


Based upon statistical analysis, most stars in the sky have planets. Furthermore, one in five stars like the Sun is home to a planet up to twice the size of Earth, orbiting in a temperate environment. Those are very encouraging numbers.

Kepler is Broken

The spacecraft launched with 4 small spinning gyroscope-like wheels attached to it. Changing the spin rate of these wheels allowed astronomers to keep the spacecraft pointed accurately at the field of 100,000 stars. Two of those reaction wheels have stopped working. The remaining two cannot keep the spacecraft pointed well enough. The mission is in danger of ending.

Recently, the astronomy team devised a work-around solution that should allow Kepler to resume studying stars. The reaction wheels were needed to counter-balance the effect of solar pressure on the spacecraft which tended to make it roll and point off target. The plan it to orient the spacecraft so the solar pressure is balanced on the ridge of the solar panel, seen in blue here and in the image at the top of this post. It is hoped the two remaining reaction wheels can maintain this alignment for 83 day stretches. Then, the spacecraft has to be repointed to prevent sunlight from entering the sensitive detector.

The plan has one serious tradeoff. It would no longer study the patch of stars it has been viewing for 3.5 yrs. A new patch would be in view each 83 days. But, it would be able to continue gathering data. The final funding decision is expected by the summer of 2014.

At this point in time, there remains over a year of original Kepler data that still needs to be reviewed and analyzed. With that, and the prospect of this new Kepler 2 mission, the spacecraft might still function well into the future. The list of Goldilocks planets will continue to grow.


20 thoughts on “Planet Search | Kepler 2 Continues

  1. I’m reminded of that well known Monty Python ‘not quite dead yet’ scene. 🙂

    To me, one of the most fantastic things about science and exploration is its ability to not only adapt to things not going as expected, but to excel and advance in these moments. I’m amazed by all of the discoveries made primarily because scientists had to find work-arounds to unexpected setbacks. I remember Neil deGrasse Tyson once saying he disliked the phrase ‘going back to the drawing board’. With science, he explained, we never leave the drawing board.


  2. “Two of the four guidance gyroscopes quit working in March 2013. Scientists have figured out a way to use the remaining two to allow the spacecraft to renew the search.”

    That reminds me of a story I once heard. A man is driving and gets a flat tire, so he pulls off to the side of the road to change the tire. He jacks up the car, removes the lug nuts from the flat tire and puts them in the hubcap that he’s placed nearby so he can find them easily when he’s ready to put them back on. As he’s lifting up the spare tire to put it on, he accidentally kicks the hubcap, and all the lug nuts spill out, roll into a drain near the curb, and are lost. What to do? The driver then notices that a man behind a nearby fence has been watching all this. It turns out that the fence encloses the grounds of an insane asylum, and the man who’s been watching is one of the inmates. The resident sees that the driver is baffled and calls out to him: “Here’s what you should do. Take one lug nut off each of the other tires and use it to mount your spare time. You can drive safely for a while with one or even two nuts missing from each wheel.” The motorist sees that that’s the right solution, so he follows the suggestion. When he’s ready to drive off, he turns to the asylum inmate and says: “How did you think of that?” The inmate replies: “I may be crazy but I’m not stupid.”


  3. Kepler would have appreciated the technology and scope of this project named for him. Wonder what he would have made of the potential for ET. Good to hear a work-around has been devised.


  4. I’m intrigued and delighted by the concept of “Goldilocks planets.” Anyone who knows the fairy tale can grasp the importance of “not too close, not too far” immediately. Apparently the term’s been in use for a while, but I’ve never come across it.

    Here’s something else I’ve never thought about. The tale of Goldilocks has been used for generations as a simple illustration of the Golden Mean. I can’t find any evidence that, in later versions of the story, Goldilocks got her name as a nod to Aristotle, but the connection still makes me smile. Besides,”The Philosopher and the Three Bears” just wouldn’t have the same ring to it.

    I’d forgotten that I had a toy gyroscope when I was a kid. It was just like this. I watched the toy gyro video, and now the problem with the two gyroscope-like wheels is understandable. But here’s a question. In a plane, the Mars Rover, the space station or Kepler, what keeps the gyroscopes spinning along? I’m sure they’re not using a length of string!


    • Gyros today are of two main types. One is mechanical with spinning rotors aligned to the x-y-z axes. They are designed to be electrically driven as a motor is driven. Each rotor spins and maintains orientation on its axis. No galaxy long strings are needed. 🙂

      Another more modern version has no moving parts. A laser sends light around a circuit both clockwise and counterclockwise. The circuit can be made with a few mirrors. Or, it can be a fiber optic cable. The two beams rejoin after their circuit. If the gyro is turned, the waves produce some interference. The amount of interference is translated into degrees of turn. A gyro is needed for each axis. These are being used in more applications replacing the traditional mechanical ones.

      I hope that helps. 🙂


      • It does help. I’ve not spent the time with the explanation I need to, but I anticipate being able to carve out a little time for Science Lab this week. If I’ve got any questions, you can be sure I’ll be in touch. Thanks!


      • Relative to gyros on spacecraft, I think you will find that the mechanical version is indispensable. The electronic version can not be used for physical alignment of the craft or its antennas because mass is not involved in their operation.


  5. Relative to the statistical analysis of planets detected, it would not surprise me if updates find even more earth-sized ones. Earth-sized planets are by far the smallest and therefore least detectable. Also, the star-wobble would be less detectable the closer the planetary system is to a polar view, so it would seem planets might be hiding in that data clutter. However, I assume the statistical analysis took that into consideration. The possibility occurs also that habitable zones could be unlike earth’s, as in planets closer to smaller suns or farther from larger ones. They probably thought of that too.


    • Someone asked about the polar view aspect several months back. I wrote to one of the researchers. They confirmed that yes, it has been taken into consideration.

      I tried to find that comment thread but was not successful.


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