The International Rosetta Mission is set for a rendezvous with Comet 67 P/Churyumov-Gerasimenko in 2014. On its 10 year journey to the comet, the spacecraft will also perform a fly-by of the two asteroids Stein and Lutetia in 2008 and 2010, respectively. The mission goal is to study the origin of comets, the relationship between cometary and interstellar material and its implications with regard to the origin of the Solar System. Measurements will be performed that shed light into the development of cometary activity and the processes in the surface layer of the nucleus and the inner coma. The Micro-Imaging Dust Analysis System (MIDAS) instrument is an essential element of Rosetta's scientific payload. It will provide 3D images and statistical parameters of pristine cometary particles in the nm-μm range from Comet 67P/Churyumov-Gerasimenko. According to cometary dust models and experience gained from the Giotto and Vega missions to 1P/Halley, there appears to be an abundance of particles in this size range, which also covers the building blocks of pristine interplanetary dust particles. The dust collector of MIDAS will point at the comet and collect particles drifting outwards from the nucleus surface. MIDAS is based on an Atomic Force Microscope (AFM), a type of scanning microprobe able to image small structures in 3D. AFM images provide morphological and statistical information on the dust population, including texture, shape, size and flux. Although the AFM uses proven laboratory technology, MIDAS is its first such application in space. This paper describes the scientific objectives and background, the technical implementation and the capabilities of MIDAS as they stand after the commissioning of the flight instrument, and the implications for cometary measurements
The Micro-Imaging Dust Analysis System (MIDAS) atomic force microscope (AFM) onboard the Rosetta orbiter was the first such instrument launched into space in 2004. Designed only a few years after the technique was invented, MIDAS is currently orbiting comet 67P Churyumov-Gerasimenko and producing the highest resolution 3D images of cometary dust ever made in situ. After more than a year of continuous operation much experience has been gained with this novel instrument. Coupled with operations of the Flight Spare and advances in terrestrial AFM a set of "lessons learned" has been produced, cumulating in recommendations for future spaceborne atomic force microscopes. The majority of the design could be reused as-is, or with incremental upgrades to include more modern components (e.g. the processor). Key additional recommendations are to incorporate an optical microscope to aid the search for particles and image registration, to include a variety of cantilevers (with different spring constants) and a variety of tip geometries.
Clustered regularly interspaced short palindromic repeats (CRISPR)-associated Cas9protein is an effector that plays a major role in a prokaryotic adaptive immune system, by which invading DNA can be targeted and cut for inactivation. The Cas9 endonuclease is directed to target sites by a guide RNA (gRNA) where Cas9 can recognize specific sequences (PAMs) in foreign DNA, which then serve as an anchoring point for cleavage of the adjacent RNA-matching DNA region. Although the CRISPR-Cas9 system has been widely studied and repurposed for diverse applications (notably, genome editing), its origin and evolution remain to be elucidated. Here, we investigate the evolution of Cas9 from resurrected ancient nucleases (anCas) in extinct firmicutes species as old as 2600 myr to the current day. Surprisingly, we demonstrate that these ancient forms were much more flexible in their PAM and gRNA scaffold requirements compared to modern day Cas9 enzymes. In addition, anCas portrays a gradual paleoenzymatic adaptation from nickase to double-strand break activity, suggesting a mechanism by which ancient CRISPR systems could propagate when harboring Cas enzymes with minimal PAMs. The oldest anCas also exhibit high levels of activity with ssDNA and ssRNA targets, resembling Cas nucleases in related system types. Finally, we illustrate editing activity of the anCas enzymes in human cells. The prediction and characterization of anCas proteins uncovers an unexpected evolutionary trajectory leading to ancient enzymes with extraordinary properties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.