With the new Kepler telescope findings having hit the news-feeds this month, I thought I would post an update to my original data. The tally of Kepler planetary candidates now stands at 2,326, with one particularly noteworthy find: Kepler-22b. Also known as Kepler Object of Interest (KOI) 87.01, or Kepler Input Catalog ID 10593626, this planet deserves special attention, as it is one of the first confirmed planets that resides within the habitable zone of its star. At only 2.4 times Earth’s diameter, and with an orbital period of around 290 days, it seems to be a pretty close match to the Earth.

The Kepler web-site has a nice article describing the planet, with the image below showing how it stacks up against the inner planets in our own solar system.

NASA Mission Page – Kepler (image credit: NASA/Ames/JPL-Caltech)

After reading about the new planet, and trying to find the raw data for the most recent 1,000+ planetary candidates to no avail, I got to thinking about the process that is used to detect transits like those for Kepler-22b. I know it’s pretty tricky, not just because of the miniscule amount of dimming due to the planet passing in front of the star, but also because the stars themselves have turned out to be more variable than anyone suspected. In addition, there are changes in the array of detectors on the spacecraft that must be nulled out, and a host of other considerations.

Given all that, I pulled the corrected light curves from Kepler-22b from the NASA site where the data is stored. The plot below shows the results. Looking at this data, which has already gone through a significant transformation process, should give you some idea of the difficulty in finding small planets.

Raw, Corrected Light Curves – NASA MAST web-site

Finally, if we normalize each successive observation to the median for that run, this allows us to plot all the data on one scale in order to compare each and look for the tell-tale dips that signal a planetary transit. It’s surely not intuitively obvious when the transits occurred, so I’ve pointed them out with arrows. The smaller, embedded plot is a zoom in on each of the transits, showing how similar they appear. This fact, coupled with the a common interval of 289.9 days between them, gives scientists high confidence they’ve found their target.

Normalized Light Curves – Data processed with Matlab R2011b

There are many articles on the web that describe Kepler-22b and the remaining planetary candidates. One of my favorites is from the Sky & Telescope web-site. And all the data that’s available on the web makes it easy to forget that there’s an actual star out there that is being measured. The scientific journal article had a nice picture of the star, Kepler-22, reproduced below.

“Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star”; Borucki, et al; eprint arXiv:1112.1640

Earth as an Asteroid Target

Good news regarding the likelihood of getting hit by an asteroid: the estimated count of those bodies that cross Earth’s orbit has gone down. Although the probability that any one rock might hit us has always been very low, the calculation shrunk even further after data from the WISE spacecraft (Wide-field Infrared Survey Explorer) was analyzed. The number shrunk by almost half (35,000 to 19,500).

Finding small objects (less than about a mile across) is challenging because they’re not very bright to begin with, and past surveys have relied on visible light to see them. WISE uses heat (infrared radiation) emitted from the object, which doesn’t depend on how reflective the surface is. Since asteroid surface brightness varies across a wide range, it was difficult to determine how big each of them was (observations could be bright because the asteroid was large, or because it had a very high surface brightness). WISE took care of that problem, and found that there were not as many large asteroids as had been predicted.

Plot of known and estimated Earth-crossing asteroids, showing the inner planet orbits.

WISE New vs. Old
The new count of near-Earth asteroids vs. the old count.
(both images courtesy NASA/JPL-Caltech)

   The screenshots I’ve included here are captures from an animation that shows how all these things move around the sun. It’s interesting to watch the swirling progression of the swarm; some of them move against the crowd (retrograde), and many have orbits that are not even close to circular, taking them from far out in the solar system to close encounters with the sun. Fascinating stuff.

As an aside, the Dawn spacecraft is in orbit around Vesta right now (the second largest asteroid in the main belt). It’s in a low orbit and taking spectacular photos.

South pole of Vesta

SOFIA and Pluto occultation

NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) just completed a very cool assignment: watch how the light from a distant star is blocked by Pluto. As you might imagine, getting directly into Pluto’s star-shadow here on Earth is a pretty tricky task, especially since the Earth is moving pretty rapidly with respect to Pluto, and spinning on its axis to boot. But SOFIA is mounted in a 747, and can move to whatever location is necessary to do the job.

SOFIA in flight. The opening in the back of the 747 is where the telescope is located.

Because SOFIA can measure light very accurately, seeing how the star dims and brightens as it disappears and reappears behind Pluto tells scientists about its atmosphere. These results will provide data that supplements our scant knowledge of Pluto, the only solar system planet not yet visited by any of our robots (well, I guess Pluto is no longer officially a full-fledged planet, but it’s still commonly thought of that way…it’s hard to change a lifetime of being taught there are 9 planets overnight).

Another NASA mission will expand our knowledge of Pluto in July, 2015: New Horizons is on its way there now, and will fly by the little planet, much like the Pioneer and Voyager missions did with the gas giants.

To find out more about SOFIA, click here, or about New Horizons, click here.