Earth based Spectroscopy of Exoplanetary Atmospheres
a talk by Dr. Matteo Brogi at UW, Dec. 4th, 2014.
Last Thursday’s Astronomy colloquium was delivered by Matteo Brogi,
Hubble Fellow at the University of Colorado. He described very recent
use of Doppler shifted, earth based absorption spectroscopy to detect
carbon monoxide [CO] in the atmosphere an M-Dwarf ‘Goldilocks’
satellite [G-1214b]. That is, one where temperature permits liquid
water.
Note that CO, CO2, and H20 have earlier been detected on this planet
by the Kepler mission. What is novel, and remarkable, in Brogi’s talk
is that earth based spectroscopy has been made possible by the very
large aperture telescopes at Cerro Paranal over the Altacama desert,
Chile, 2635 meters [~8000 ft] above sea level. That ‘instrument’
consists of four mirrors of 8.2 meters diameter at a central site,
surrounded by four others of 1.8 meters diameter each located ~100
meters apart from the central stack. All of them may be ganged
together to form a single spectral interferometer of truly
extraordinary resolution, which permits use of Doppler shifts to
resolve and separate the spectra of a parent star from that of
orbiting satellites around it.
Also novel, and equally remarkable, is that some information about
the vertical distribution of CO was also recovered, with a hint
of a stratosphere. That is, an upper-atmosphere layer where the
temperature is increasing with altitude, as it does on the Earth.
This last [probably] results ultra-violet photochemistry of CO2
dissociation, analogous to the process that forms our ozone layer.
Signal to noise ratios for these detections were ‘only’ order of
unity, but still .. as I keep saying .. remarkable. [How quickly we
become blase over truly spectacular results.]
Several other investigators have attempted to discover methane [CH4]
in the atmospheres of M-Dwarf exoplanets, but none has been reported,
so far, with significant signal-to-noise. [One group has controvers-
ially reported CH4 at S/N something less than unity.] The importance
of this search is that CO [or CO2] and CH4 are not thermodynamically
stable in the presence of each other. If both are found together,
then some non-equilibrium process must be operating. Such as Life.
’nuff
hh
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