2015 Annual Science Report
NASA Goddard Space Flight Center Reporting | JAN 2015 – DEC 2015
NNX15AT33A Origin and Evolution of Organics and Water in Planetary Systems
Research by the Blake group (CalTech) supported by the NAI has centered on a joint laboratory and observational program, designed with the participation of Goddard node scientists, that aims to investigate the chemistry of water and simple organics in the protoplanetary disk analogs of the early solar nebula, in comets, and in the atmospheres of extrasolar planets. The laboratory work has involved the creation of novel high bandwidth instruments from the microwave to the THz regime that can probe both gaseous and condensed phase (liquid and solid) materials. Particular emphasis has been placed on the study of small chiral (that is, ‘handed’) organic species, with a view toward establishing whether the homochirality exhibited on the Earth is stochastically or deterministically derived. We combine the laboratory studies with astronomical observations at radio (VLA, GBT, ALMA), far-infrared (SOFIA, Herschel archival data), and infrared (Keck/VLT, Spitzer archival data) wavelengths. A recent highlight is the first detection of a chiral species toward the Galactic Center, as is described in this report
As part of the NASA GSFC NAI Node, Co-Investigator Blake is directing both lab and astronomical spectroscopy programs. Support within this cycle began on October 1, 2015. The goal of these observations is to determine whether modestly 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). We have termed this approach molecular mapping, and are presently focused on combining Keck near-infrared data with that from ALMA, three papers are presently under review or are in preparation. A focus over the coming year(s) with NAI node scientists will be preparations for JWST. The same high precision/high dynamic range routines needed to study disks and comets in the near- to mid-IR (and pioneered by the Goddard team) can also be used to explore the spectra of extrasolar planetary atmospheres, both in transiting and non-transiting systems. Our first work here was published in 2014, and we are presently analyzing another six targets.
In the lab we are developing tools that can study organics both in the gas phase and in the solid state. For the latter we are developing novel TeraHertz-Time Domain Spectroscopy (THz-TDS) tools using coherent ultrashort pulses of light, and for the gas phase studies we are developing compact, efficient direct digital-synthesis-based Chirped Pulse-Fourier Transform Microwave (CP-FTMW) spectrometers that are orders of magnitude more compact than previous generations of such instruments – and that should be compatible with in situ planetary exploration applications. With our THz-TDS techniques we have focused our efforts on molecular ices important to comets and outer solar system bodies, such as water-alcohol and water-carbon dioxide mixtures that have formed the basis of recent submissions to Phys. Chem. Chem. Phys. With APRA support for the equipment, we are building a second generation THz-TDS cyrogenic system that will enable realistic mimics of interstellar and interplanetary ices to be studied for the first time.
For our gas phase studies, principle recent targets have been small- to moderate-sized species that have a chiral center. The first of these, propylene oxide (CH2CHOCH3, for a structure see Figure 1) has been detected toward the Galactic Center with deep observations using the GBT and Parkes telescopes. The lines are seen in absorption against the Sgr B2 radio continuum, as shown in Figure 2. This result is presently under review in Science. Because the Sgr B2 radio continuum is polarized, the possibility exists that microwave Circular Dichroism (CD) studies may be able to probe any enantiomeric excess that might exist for this species, and thus opens a new chapter in our observational search for our origins. Present work in the laboratory is therefore centered on a measurement of the microwave CD response for the transitions that have been detected, and on the acquisition and assignment of additional potential interstellar chiral species based on this epoxide structural motif.
PROJECT INVESTIGATORS:Geoffrey Blake
PROJECT MEMBERS:Brandon Carroll
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Indirect and direct astronomical observations of extrasolar habitable planets.
Sources of prebiotic materials and catalysts