Ok. So it seems that I may have used a poor example of exoplanet atmosphere detection using Hubble's Infrared NICMOS. (There aren't that many to choose from at the moment and the technique is evolving …).
It seems that since the announcement of HD 189733b's atmosphere detection in post #15 and referred to in my post below, there has been controversy over the measurement technique.
Swain has produced several papers on it all. The most up to date ones are:
A ground-based near-infrared emission spectrum of the exoplanet HD 189733b (submitted 12 Feb 2010):
Quote:
Detection of molecules via infrared spectroscopy probes the conditions and composition of exoplanet atmospheres. To date, water (H2O), methane (CH4), carbon dioxide (CO2), and carbon monoxide (CO) have been detected in two hot-Jupiter type exoplanets. These previous results relied on space-based telescopes that do not provide spectroscopic capability in the important 2.4–5.2 μm spectral region. Here we report ground-based observations of the dayside emission spectrum for HD 189733b between 2.0–2.4 μm and 3.1–4.1 μm, where we find a bright emission feature. Where overlap with space-based instruments exists, our results are in excellent agreement with previous measurements.
The feature around 3.25 μm is completely unexpected and is difficult to explain with models that assume local thermodynamic equilibrium
(LTE) conditions in the 1 bar to 1×10-6 pressures typically sampled by infrared measurements. The most likely explanation for this emission is non-LTE emission from CH4, similar to what is seen in the atmosphere of planets in our own solar system. These results suggest that non-LTE effects may need to be considered when interpreting measurements of strongly irradiated exoplanets.
…
Detection of molecules via infrared spectroscopy probes the conditions and composition of exoplanet atmospheres. To date, water (H2O), methane (CH4), carbon dioxide (CO2), and carbon monoxide (CO) have been detected in two hot-Jupiter type exoplanets. These previous results relied on space-based telescopes that do not provide spectroscopic capability in the important 2.4–5.2 μm spectral region. Here we report ground-based observations of the dayside emission spectrum for HD 189733b between 2.0–2.4 μm and 3.1–4.1 μm, where we find a bright emission feature. Where overlap with space-based instruments exists, our results are in excellent agreement with previous measurements.
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They went on to say they used the SpeX instrument on the NASA Infrared Telescope Facility (IRTF)..
The SpeX instrument was configured to observe between
1.9– 4.2 μm at an average spectral resolution of 470. (!!!!)
Then someone challenged the measurement technique….
Cheers