Channel: ADVEXON TV

Category: Science & Technology

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Description: It is a distracting, inconvenient coincidence that we are living in times of paradigm-shifting astronomical discoveries overshadowed by the deepest financial crisis since the Great Depression. Amid a battery of budget cuts, the astronomical community has discovered more planets outside of our Solar System—called extrasolar planets or simply exoplanets—in the past decade than in previous millennia. In the last couple of years alone, the Kepler Space Telescope has located more than 2,000 exoplanet candidates, including Earth-sized ones potentially capable of sustaining liquid water, demonstrating the ease at which nature seems to form them and hinting that we may be uncovering the tip of an iceberg. Discovering and characterizing distant, alien worlds is an endeavor no longer confined to the realm of science fiction. In tandem with numerous surveys of the night sky performed from the ground, the Hubble, Kepler, and Spitzer Space Telescopes observe the universe from outside of Earth’s atmosphere. These devices detect an exoplanet by recording the diminution of light as the body, residing in an edge-on orbit, passes in front of its host star. In the past few years, astronomers also have achieved the remarkable feat of measuring the diminution of light as the exoplanet passes behind its star, known as the secondary eclipse. In other words, astronomical techniques have advanced to the point where we can detect a star masking the light from its exoplanet, which is a demonstrably small effect—at most a few parts in a thousand in the infrared and much smaller in the optical range of wavelengths. During a secondary eclipse, the light from an exoplanetary system originates only from the star, and these data can be used to subtract out the starlight when the exoplanet is not eclipsed. All that remains is the light of the exoplanet and its atmosphere (if it exists). Such a technique has enabled astronomers to make the first detections of the light directly emitted by an exoplanet, which typically appears at its brightest in the infrared. Measuring transits and eclipses at several different wavelengths allows one to construct a spectrum of the exoplanetary atmosphere, of which a spectral analysis yields its composition and elemental abundances. (A spectrum describes the range of colors of the photons emanating from the exoplanet, but it generally extends beyond what our eyes can see toward both shorter and longer wavelengths.) In some cases, astronomers were able to record the ebb and rise of the brightness of the exoplanet as it orbits its parent star, otherwise known as the phase curve. An inversion technique, developed by Nick Cowan of Northwestern University and Eric Agol of the University of Washington, allows one to convert the phase curve into a “brightness map,” which is the latitudinally averaged brightness of the exoplanet across longitude. Recent work by the same researchers has yielded two-dimensional information on the brightness of the exoplanet HD 189733b as a function of both latitude and longitude. In other words, we have started to do cartography on exoplanets! Tidal Locks The first studies of exoplanetary atmospheres were performed on a class of objects known as hot Jupiters. A combination of the transit technique with a measurement of the radial velocity (which is the gravitational wobble of a star as its exoplanet orbits around their common center of mass) yields the radius and mass of a hot Jupiter, respectively, and reveals that they are similar in these aspects to our own Jupiter. The startling difference is that hot Jupiters are found about a hundred times closer to their parent stars than Jupiter, which raises their surface temperatures to between 1,000 and 3,000 degrees Kelvin. With spatial separations of a hundredth to a tenth of an astronomical unit (the average distance from the Earth to the Sun) from their stars, the discovery of hot Jupiters caught the astronomical community by surprise, because their existence was neither predicted by astrophysical theory nor subsequently explained by it. Their large sizes render hot Jupiters easier to observe and thus the most obvious laboratories for extrasolar atmospheric studies. Furthermore, the belief that their atmospheres are dominated by molecular hydrogen—which is consistent with the densities of the exoplanets, inferred from the astronomical observations to be about 1 gram per cubic centimeter—offers some hope that the atmospheres are primary, reflecting the composition of the primordial nebulae from which they formed, rather than secondary and reprocessed by geological mechanisms (such as on Earth). Thanks for watching Make sure to subscribe and leave a comment below.