|An artist imagining Kepler-62f, a potentially |
habitable exoplanet discovered using
data from the Kepler Spacecraft
The first step in finding extraterrestrial life is to find extra-solar planets, or, exoplanets. The first technique used to detect extra-solar planets was through the measurement of the shift in the radial velocity of a host star. A planet or planets orbiting a star will produce shifts in the spectral lines of the star as they tug on it, making the star appear to wiggle back and forth, as it moved through space. In 1952, Otto Struve suggested that extra-solar planets might be detected by dips in a host star's light during a planet's transit. Even then, techniques were available to detect such a drop in light but it was forgotten about for decades. In 1999, two professional astronomers using a 10-centimeter telescope discovered the first telltale signs of such a transiting extra-solar planet. Amateur and professional astronomers have since detected countless candidates.
NASA's Ames Research Center lists a table of 70-plus confirmed exoplanets discovered by Kepler as of May 2012 and designated by the name 'Kepler' followed by a letter. Planetary characteristics in the table for each planet include the following headings: Jupiter Masses, Earth Masses, Jupiter Radii, Earth Radii, Density, Temperature, Transition Duration, Period, Semi-Major Axis (UA), Eccentricity, Inclination (in degrees) and Distance (in parsecs). The table also lists characteristics of the host star. It should be noted here that Kepler-23b – Kepler-30b are planets that are within just a few Earth radii, though they are several hundred times more massive and their orbital periods seem much too short (just a few days) to be within the habitable zone. Nevertheless, it tells us that exoplanets, roughly the size of Earth, are detectable and are indeed out there.
Earth like Exoplanets Discovered by the Kepler
Spacecraft Chart Courtesy of NASA
|Open Cluster NGC 6819 in Cygnus - Image by Al Kelly|
Ultimately, we should not limit our search to Earth-like planets exclusively, but it's a good place to start. Life, as we know it - or not - may be a far more interesting story than we think, and one thing is becoming clearer; the "Habitable Zone" around a given star may be less distinct than many of us imagine!