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Project Progress

As part of the NASA GSFC NAI Node, Co-I Blake is directing both lab & astronomical spectroscopy programs, the goal of which is to determine whether complex organics are detectable in the circumstellar accretion disks that encircle young stars and in the comae of comets. In particular, with NAI support we have used the high angular and spectral resolution data to study circumstellar disks, cometary comae, and extrasolar planetary atmospheres. For disks, we have begun to investigate whether the smoothly varying conditions in disks enable abundance profiles to be retrieved from even spatially and spectrally unresolved data (provided the lines span a significant range in excitation Zhang et al. 2013), and have recently used ALMA to detect the CO frost line via chemical contrast imaging (Qi et al. 2013) and to image the gaps and vortices induced by Jovian planet formation (Zhang et al. 2014).

Because the organics in the inner regions of disks are so closely tied to water, we also used the HIFI instrument on Herschel to search for gas phase water signatures in the outer regions of disks and in comets, to great effect. We have made the first measurements of the D/H ratio in water from a Jupiter family comet, specifically Comet 103P Hartley 2 that was the subject of the EPOXI flyby, and have worked with the Mumma group on infrared observations using Keck in support of the EPOXI and Herschel campaigns. Such Herschel observations are no longer possible, and so we have concentrated our efforts this past year on Keck NIRSPEC observations in collaboration with the GSFC team (see publications), especially the Comet ISON campaign in Oct-Nov 2013. The same high precision/high dynamic range routines needed to study disks and comets can also be used, with sufficiently bright targets, to explore the spectra of extrasolar planetary atmospheres, both in transiting and non-transiting systems (such as tau Boo, Lockwood et al. 2014). As part of this research, we have worked with the NIRSPEC instrument design team and the Keck Observatory to submit proposals for the detector and electronics upgrades needed to meet the future challenges of such spectroscopic campaigns in (exo)planetary science.
The broad wavelength coverage of the Herschel archive should also permit a much improved understanding of ices in disks, and thus the origin of icy bodies such as comets – but only if the necessary lab data are obtained. We have recently constructed two TeraHertz Time Domain Spectrometers, or THz TDSs. With these instruments we now have complete coverage of the spectral ranges accessible to Herschel/SOFIA at a dynamic range of >106 and without any need for cryogens, at a spectroscopic resolution much better than the Doppler limit using novel frequency comb approaches (Finneran et al. 2015). We have concentrated our measurements on the principal icy grain mantle components, on a suite of amino acids, and on >100 naturally occurring silicate and carbonate compounds. The structure of the THz signatures are sensitive to temperature; and so if eventually detected can provide not only species identification but a characterization of the physical state of the molecular ices on interstellar or protostellar grains as well.

The other area we are exploiting involves the rapid development of Direct Digital Synthesis (DDS) capabilities at microwave through mm-wave frequencies that we tie to astronomical surveys for complex organics. In particular, we have found that inexpensive DDS evaluation boards can replace (>$70k) arbitrary waveform generators in so-called chirped-pulse Fourier Transform Microwave (CP-FTMW) instruments. We have used these capabilities to search for and detect new organic species using the publically available PRIMOS survey. Longer term, the great sensitivity of the CP-FTMW approach enables the non-destructive detection of stable isotopologues in natural abundance, and in a site-specific manner that can leverage a great deal of information about the formation pathways of organics in carbonaceous chondrites. Our first replicate tests indicate a shot-noise limited sensitivity floor, as expected, and we will thus be working with Node scientists to carry out initial lab spectroscopy on moderately volatile prebiotic species.