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2014 Annual Science Report

NASA Goddard Space Flight Center Reporting  |  SEP 2013 – DEC 2014

NNX09AH63A Origin and Evolution of Organics in Planetary Systems

Project Summary

The Blake group has been carrying out joint observational and laboratory programs with NAI node scientists on the water and simple organic chemistry in the protoplanetary disk analogs of the solar nebula and in comets. Observationally, we continue to build on our extensive (>100 disks) Spitzer IRS survey of the infrared molecular emission from the terrestrial planet forming region of disks with follow-up work using the high spectral resolution ground-based observations of such emission (via the Keck and the Very Large Telescopes, the Herschel Space Observatory, SOFIA, and ALMA) along with that from comets. This year, we emphasized disk studies with the rapidly maturing capabilities of the ALMA observatory, that promises to revolutionize our understanding of the formation and migration of protoplanets, and with infrared studies of the molecular volatiles detectable in both comets and exoplanetary atmospheres. In the lab, we have continued to exploit our novel approach to broad-band chirped pulse microwave spectroscopy that promises to drop the size, mass and cost of such instruments by one to two orders of magnitude, and have developed a decade-spanning THz frequency comb with unprecedented precision. We are using these new instruments to measure the rotational spectra of prebiotic compounds, along with a detailed characterization of their large amplitude vibrations. Looking forward, these techniques have the potential to make site-specific stable isotope measurements, a capability we will continue to explore with GSFC Node scientists.

4 Institutions
3 Teams
10 Publications
3 Field Sites
Field Sites

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.

ALMA Cycle 0 Observations
Figure 1.– ALMA Cycle 0 observations of the dust and gas from the transitional disk J1604-2130, adapted from Zhang et al. 2014). The truncation radii of the mm-sized dust grains and molecular gas differ by nearly a factor of two, a situation that arises naturally by the pressure traps induced by Jovian planet formation in the disk.

Overview of the THz Time Domain Spectrometer
Figure 2.– An overview of the THz Time Domain Spectrometer, or TDS. Here, intense THz pulses are generated by plasma filamentation in air. They are directed through a He compressor-driven cry-ostat to enable combined THz/FT-IR measurements of ices and other samples over the 10-300 K temperature range. Coverage is complete from 10 cm-1 up into the near-infrared.

THz Time Domain Spectra
Figure 3. – THz time domain spectra of various crystalline (left) and amorphous molecular ices, measured in the frequency range from 0.3 to 7.5 THz (adapted from Ioppolo et al. 2014).

    Geoffrey Blake
    Project Investigator

    Brandon Carroll

    Daniel Holland

    Alexandra Lockwood

    Objective 1.1
    Formation and evolution of habitable planets.

    Objective 1.2
    Indirect and direct astronomical observations of extrasolar habitable planets.

    Objective 3.1
    Sources of prebiotic materials and catalysts