NASA Astrobiology Institute (NAI)

Molecular material that may lead to life on planet surfaces has its origin in interstellar space. Using a combination of laboratory spectroscopic measurements and radio astronomical observations, this module has been tracing the life cycle of carbon and phosphorus containing compounds from their formation in outflows around old stars to their arrival on planet surfaces via exogenous delivery. We have been investigating what carbon and phosphorus compounds are found in matter lost from stars, and how the chemical composition changes as this material flows into the interstellar medium and forms dense clouds
in space. We are following what happens to these compounds as these clouds evolve into solar systems, and how comets, meteorites, and dust particles may have brought interstellar pre-biotic material to Earth and other planets.

We have made substantial progress in our study of phosphorus chemistry in interstellar space. Following our discovery of PO in the circumstellar ejecta of the Supergiant star VY Canis Majoris by Tenenbaum, Woolf, and Ziurys (2007), we have subsequently found four new phosphorus-bearing compounds in the
outflows from carbon-rich evolved stars: PN, HCP, PH₃, and CCP (Tenenbaum and Ziurys 2008: Halfen, Clouthier and Ziurys 2008; Milam et al. 2008). These discoveries were made using the telescopes of the Arizona Radio Observatory: the Submillimeter Telescope (SMT) and the 12 m. In approximately one year’s time, the inventory of known interstellar phosphorus compounds has therefore increased by 300%.
Particularly intriguing is the detection of the CCP radical, which has phosphorus attached to a C-C bond.
Discovery of this molecule was made possible by spectroscopic measurements conducted in the Ziurys laboratory, in collaboration with Dennis Clouthier (University of Kentucky). A new phosphorus source has been developed for one of the spectrometer systems that has not only enabled the measurements for CCP, but several other possible new interstellar phosphorus-bearing compounds, including PCN, HPS,
and CH₃PH₂. A picture of this new source is shown in Figure 1, and the laboratory spectrum of CCP in Figure 2. In Figure 3, the interstellar spectra from the carbon-rich star IRC+10216 are presented. The interstellar detections indicate that at least 20-40% of the available phosphorus is in the gas-phase in circumstellar material. Phosphorus is thus taking on forms other than the mineral schreibersite, [Fe,Ni]3P. Astronomical searches are currently being conducted for possible new gas-phase phosphorus molecules.
We have also been investigating carbon chemistry in oxygen-rich circumstellar gas. We are finding that carbon chemistry is far more active than previously thought, as evidenced by the detection of HCO⁺ in several of these objects by Pulliam and Ziurys.

Fig 1. Gas-phase phosphorus source developed in the Ziurys laboratory to study CCP and other interstellar phosphorus-bearing species.

Fig 2. Spectra of CCP measured in the Ziurys laboratory which enabled its astrophysical detection. Three rotational transitions are shown, each which display a doublet feature, labeled as e and f, due to lambda-doubling interactions.

Fig 3. Spectra of CCP observed in the C-rich circumstellar gas of the evolved star, IRC+10216. Four rotational transitions were observed, indicated by the lines underneath the spectra. Each transition consists of doublets, labeled e and f. One doublet is clearly visible in the data. The e component of the other transitions is obscured by other molecular lines.