• Damming the rivers of the Amazon basin

      Latrubesse, Edgardo M.; Arima, Eugenio Y.; Dunne, Thomas; Park, Edward; Baker, Victor R.; d’Horta, Fernando M.; Wight, Charles; Wittmann, Florian; Zuanon, Jansen; Baker, Paul A.; et al. (NATURE PUBLISHING GROUP, 2017-06-14)
      More than a hundred hydropower dams have already been built in the Amazon basin and numerous proposals for further dam constructions are under consideration. The accumulated negative environmental effects of existing dams and proposed dams, if constructed, will trigger massive hydrophysical and biotic disturbances that will affect the Amazon basin's floodplains, estuary and sediment plume. We introduce a Dam Environmental Vulnerability Index to quantify the current and potential impacts of dams in the basin. The scale of foreseeable environmental degradation indicates the need for collective action among nations and states to avoid cumulative, far-reaching impacts. We suggest institutional innovations to assess and avoid the likely impoverishment of Amazon rivers.
    • A triple protostar system formed via fragmentation of a gravitationally unstable disk

      Tobin, John; Kratter, Kaitlin M.; Persson, Magnus V.; Looney, Leslie W.; Dunham, Michael M.; Segura-Cox, Dominique; Li, Zhi-Yun; Chandler, Claire J.; Sadavoy, Sarah I.; Harris, Robert J.; et al. (NATURE PUBLISHING GROUP, 2016-10-26)
      Binary and multiple star systems are a frequent outcome of the star formation process1;2, and as a result, almost half of all sun-like stars have at least one companion star3. Theoretical studies indicate that there are two main pathways that can operate concurrently to form binary/multiple star systems: large scale fragmentation of turbulent gas cores and filaments4;5 or smaller scale fragmen- tation of a massive protostellar disk due to gravitational instability6;7. Observa- tional evidence for turbulent fragmentation on scales of >1000 AU has recently emerged8;9. Previous evidence for disk fragmentation was limited to inferences based on the separations of more-evolved pre-main sequence and protostellar multiple systems10;11;12;13. The triple protostar system L1448 IRS3B is an ideal candidate to search for evidence of disk fragmentation. L1448 IRS3B is in an early phase of the star formation process, likely less than 150,000 years in age14, and all protostars in the system are separated by <200 AU. Here we report observations of dust and molecular gas emission that reveal a disk with spiral structure surrounding the three protostars. Two protostars near the center of the disk are separated by 61 AU, and a tertiary protostar is coincident with a spiral arm in the outer disk at a 183 AU separation13. The inferred mass of the central pair of protostellar objects is ∼1 M⊙, while the disk surrounding the three protostars has a total mass of ∼0.30 M⊙. The tertiary protostar itself has a minimum mass of ∼0.085 M⊙. We demonstrate that the disk around L1448 ppears susceptible to disk fragmentation at radii between 150 AU and 320 AU, overlapping with the location of the tertiary protostar. This is consis- tent with models for a protostellar disk that has recently undergone gravitational instability, spawning one or two companion stars.