Growth, Viability, and Death of Planktonic and Biofilm Sphingomonas desiccabilis in Simulated Martian Brines

This research was supported by the UK Science Technology and Facilities Council under Grant ST/M001261/1.Aqueous solutions on Mars are theorized to contain very different ion compositions than those on Earth. To determine the effect of such solutions on typical environmental micro-organisms, which could be released from robotic spacecraft or human exploration activity, we investigated the resistance of Sphingomonas desiccabilis to brines that simulate the composition of martian aqueous environments. S. desiccabilis is a desiccation-resistant, biofilm-forming microbe found in desert crusts. The viability of cells in both planktonic and biofilm forms was measured after exposure to simulated martian brines. Planktonic cells showed a loss of viability over the course of several hours in almost all of the seven brines tested. Biofilms conferred greater resistance to all the brines, including those with low water activity and pH, but even cells in biofilms showed a complete loss of viability in <6 h in the harsher brines and in <2 days in the less harsh brines. One brine, however, allowed the microbes to maintain viability over several days, despite having a water activity and pH lower and ionic strength higher than brines that reduced viability over the same timescales, suggesting important ion-specific effects. These data show that biofilm-forming cells have a greater capacity to resist martian aqueous extremes, but that evaporative or deliquescent brines are likely to be destructive to many organisms over relatively short timescales, with implications for the habitability of Mars and for micro-organisms dispersed by robotic or human explorers.Publisher PDFPeer reviewe

An optical fiber double scrambler and mechanical agitator system for the Keck planet finder spectrograph

We present the design and test results of a double-scrambler and fiber agitator system for the Keck Planet Finder (KPF) spectrograph. The mechanical agitator for modal noise suppression is constructed from two linear stages with the fibers mounted in a “W” curve. When driven back-and-forth at different rates, the stages change the position of the fiber curves, and hence vary the modes propagating through the fiber. Near-field temporal centroid shifts caused by modal-noise are reduced by a factor of 100 by the agitator, while mid-range spatial frequencies have reduced power by a factor of ∼300 in the near-field, and ∼1000 in the far-field. The scrambling system incorporates two octagonal fibers, and a scrambler consisting of two identical cemented lenses ∼20 cm apart, which exchanges the optical near- and far-fields of the fibers. The scrambler shows scrambling gains >16,000 in the near-field, and >40,000 in the far-field. The measured throughput efficiency of 99.3% of the expected maximum demonstrates that scrambler-induced focal ratio degradation (FRD) is minimal. The scrambler also serves as the feed-through into the vacuum chamber where the spectrograph is housed, thereby removing concerns about stressing the fibers, and introducing FRD, at this interface. Our illumination stabilization system, consisting of two octagonal fibers, a two lens scrambler, and a mechanical agitator, produces very homogeneous fiber output in both the near and far-fields. When coupled to the Keck Planet Finder spectrograph, this system provides illumination stability corresponding to a velocity of 0.30 m s^(−1)

An optical fiber double scrambler and mechanical agitator system for the Keck planet finder spectrograph

We present the design and test results of a double-scrambler and fiber agitator system for the Keck Planet Finder (KPF) spectrograph. The mechanical agitator for modal noise suppression is constructed from two linear stages with the fibers mounted in a “W” curve. When driven back-and-forth at different rates, the stages change the position of the fiber curves, and hence vary the modes propagating through the fiber. Near-field temporal centroid shifts caused by modal-noise are reduced by a factor of 100 by the agitator, while mid-range spatial frequencies have reduced power by a factor of ∼300 in the near-field, and ∼1000 in the far-field. The scrambling system incorporates two octagonal fibers, and a scrambler consisting of two identical cemented lenses ∼20 cm apart, which exchanges the optical near- and far-fields of the fibers. The scrambler shows scrambling gains >16,000 in the near-field, and >40,000 in the far-field. The measured throughput efficiency of 99.3% of the expected maximum demonstrates that scrambler-induced focal ratio degradation (FRD) is minimal. The scrambler also serves as the feed-through into the vacuum chamber where the spectrograph is housed, thereby removing concerns about stressing the fibers, and introducing FRD, at this interface. Our illumination stabilization system, consisting of two octagonal fibers, a two lens scrambler, and a mechanical agitator, produces very homogeneous fiber output in both the near and far-fields. When coupled to the Keck Planet Finder spectrograph, this system provides illumination stability corresponding to a velocity of 0.30 m s^(−1)