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NASA's Kepler Spacecraft

As I write this, astronomers know of about 700 planets which lie beyond the solar system. Yet in just 16 months, NASA’s Kepler mission has discovered an additional 2,326 potential new planets. This figure is hitting the mainstream news today thanks to NASA’s announcement that the Kepler space observatory has confirmed the existence of Kepler-22b, a planet which exists within the so-called habitable zone of a yellow G-class star about 600 light years from here.  Kepler-22b orbits its star every 290 Earth days and is reckoned to have an average temperature of about 22 degrees Celsius (approximately 72 degrees Fahrenheit).  Although closer in size to Earth than most exoplanets, the new world still has a radius which is more than twice that of our planet(which means that Kepler-22b’s mass is immensely greater).  Scientists have no idea what Kepler-22b is made of, but because of its high gravity, its atmosphere is likely to be a heavier, sludgier affair than that of Earth.

A Diagram Contrasting the Solar System with Kepler 22-b's Star System (Image credit: NASA/Ames/JPL-Caltech)

The discovery of new worlds is becoming progressively more common–which means that new planets are more difficult to write about (I can testify to this because I have been trying to think of novel and exciting things to say about this new exoplanet). The top google search result for Kepler-22b is currently a smug caricature of the foibles of earthlings.  Within a few days the sparse prose of Wikipedia’s equally scanty entry will probably be the top search result—and that is likely the way that things will remain for a long time (or forever). We are beginning to compile a massive database of different worlds.  As the numbers add up, the true stories will be within the statistical understanding of new planets–unless of course a habitable zone planet leaps out of the news with electromagnetic signatures characteristic of life and intelligence.  That result becomes progressively likely as we begin to learn where to point our telescopes.  Out of the thousands of planets the Kepler mission is finding, Kepler-22b is the first habitable zone world of dozens–or of hundreds.

Someday

[Alien clipart by Elizabeth Aragon at www.sweetclipart.com]

An artist's conception of the earthlike world, HD 85512 b (CREDIT: ESO/M. Kornmesser)

Today it was reported that HARPS, (High Accuracy Radial velocity Planet Searcher) a device operated from the European Southern Observatory’s station atop Mount la Silla in the Andes, has discovered 50 new exoplanets (planets which orbit stars other than the sun).  Sixteen of these new planets are “super-earths” rocky planets with a mass from 1 to 10 times that of our planet. One of these newly-discovered planets, HD 85512 b, is estimated to be only three-and-a-half times the mass of the Earth and it seems like it is located at the edge of the habitable zone, the orbital belt around a star where water can exist in liquid form.  This is only the second exoplanet discovered within the habitable zone, the first being Gliese 581 d.  Interestingly HARPS has disproved the existence of Gliese 581 g (which I wrote about last year) as a mathematical phantasm–so um, you might want to take that post with a grain of salt. The planet HD 85512 b orbits a star which is is approximately 35 light years from Earth.

In the eight years since the program has started, HARPS has discovered more than 150 exoplanets. HARPS discovers new planets by means of a mind-boggling technology: a spectrograph of stupendous precision is mounted on a 3.6 meter telescope in order to take painstaking observations of numerous nearby stars over a prolonged period of time.  A computer program then compares the tiny variances in the light emitted by these stars.  Stars with planets orbiting them undergo slight changes of radial velocity as the planets’ gravity tugs lightly at the stellar bodies. These shifts can be measured via Doppler shift and compared against the expected spectrographic signature caused by the stars relative drift toward or away from the observatory. Over many years the computer can thereby model the mass and approximate orbit of planets around stars (considering the math and the precise observations required for such calculations makes my hair stand on end).

Kepler, the NASA exoplanet discovery project uses an entirely different technology which involves measuring changes in brightness caused by the transit of a planet across a star’s glowing face.

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