Space physics

  • Article |

    Operating in space, NASA’s Deep Space Atomic Clock, a trapped-ion clock, is shown to have long-term stability and drift that are an order of magnitude better than current space clocks.

    • E. A. Burt
    • , J. D. Prestage
    •  & T. A. Ely
  • Article |

    Observations from the eROSITA telescope reveal soft-X-ray-emitting bubbles extending above and below the Galactic plane, which arose from energy injected into the Galactic halo from past activity in the Galactic centre.

    • P. Predehl
    • , R. A. Sunyaev
    •  & J. Wilms
  • Review Article
    | Open Access

    NumPy is the primary array programming library for Python; here its fundamental concepts are reviewed and its evolution into a flexible interoperability layer between increasingly specialized computational libraries is discussed.

    • Charles R. Harris
    • , K. Jarrod Millman
    •  & Travis E. Oliphant
  • Article |

    The Parker Solar Probe mission has reached the inner heliosphere of the Sun and made measurements of energetic particle events in the near-Sun radiation environment.

    • D. J. McComas
    • , E. R. Christian
    •  & A. P. Rouillard
  • Letter |

    The merger of two white dwarfs created a massive, hot, luminous, rotating and magnetized star with a lifetime of several thousand years, which will collapse into a type Ic supernova.

    • Vasilii V. Gvaramadze
    • , Götz Gräfener
    •  & Olga I. Spiridonova
  • Letter |

    High-angular-resolution measurements allow the direct observation of the scattering of energetic electrons by chorus waves in the magnetosphere, which causes quasiperiodic electron precipitation that gives rise to pulsating aurorae.

    • S. Kasahara
    • , Y. Miyoshi
    •  & I. Shinohara
  • Letter |

    Measurements and modelling of a large confined eruption on the Sun show that its evolution is controlled by a multilayer magnetic cage containing a twisted flux rope, which can sometimes be ejective.

    • Tahar Amari
    • , Aurélien Canou
    •  & Fréderic Alauzet
  • Letter |

    Simulations of a solar coronal jet driven by filament ejection demonstrate that magnetic reconnection underlies the energy release, implying that a universal ‘breakout’ model explains both tiny jets and huge mass ejections from the Sun.

    • Peter F. Wyper
    • , Spiro K. Antiochos
    •  & C. Richard DeVore
  • Letter |

    One-arcsecond-resolution millimetre-wave images enable the surface of the Orion Bar molecular cloud to be resolved, revealing a fragmented ridge of high-density substructures, photoablative gas flows and instabilities that suggest that the cloud edge has been compressed by a high-pressure wave expanding into the molecular cloud, in contrast to predictions from static equilibrium models.

    • Javier R. Goicoechea
    • , Jérôme Pety
    •  & Paolo Pilleri
  • Letter |

    The relationship between the X-ray activity and rotation of a star is a well-established proxy for the behaviour of the stellar dynamo; observations of four fully convective stars for which this relationship is similar to that of solar-type stars imply that the same dynamo mechanism is at work despite their structural differences to the Sun.

    • Nicholas J. Wright
    •  & Jeremy J. Drake
  • Letter |

    Coronal mass ejections are driven by a sudden release of magnetic energy stored in flux ropes in the Sun’s corona, but when the ambient magnetic field that runs toroidally along an unstable flux rope is strong enough to prevent the flux rope from kinking, a dynamic magnetic tension force halts the eruption.

    • Clayton E. Myers
    • , Masaaki Yamada
    •  & Edward E. DeLuca
  • Letter |

    A study of the formation of X-ray jets in solar coronal holes suggests that this process does not follow the popular ‘emerging-flux’ model, but instead results from a minifilament eruption akin to the larger-scale filament eruptions that drive larger solar flares and mass ejections.

    • Alphonse C. Sterling
    • , Ronald L. Moore
    •  & Mitzi Adams
  • Letter |

    A model of the heating of the quiet Sun, in which magnetic fields are generated by a subphotospheric fluid dynamo intrinsically connected to granulation, shows fields expanding into the chromosphere, where plasma is heated at the rate required to match observations by small-scale eruptions that release magnetic energy and drive sonic motions, while the corona is heated by the dissipation of Alfvén waves.

    • Tahar Amari
    • , Jean-François Luciani
    •  & Jean-Jacques Aly
  • Letter |

    Analysis of data obtained by probe spacecraft shows that ultrarelativistic electrons in the Van Allen radiation belts are prevented from entering a sharply defined region around the Earth, possibly owing to a combination of slow natural inward diffusion and pitch angle scattering.

    • D. N. Baker
    • , A. N. Jaynes
    •  & L. J. Lanzerotti
  • Letter |

    Modelling the solar magnetic field using observations of the photospheric field in the four-day period preceding a coronal mass ejection shows that the formation and later ejection of a twisted rope of magnetic flux provides the physical mechanism responsible for the ejection.

    • Tahar Amari
    • , Aurélien Canou
    •  & Jean-Jacques Aly
  • Letter |

    The contribution of solar-wind ions exchanging electrons with helium and hydrogen near the Sun is shown to be only about 40 per cent of the 1/4-keV X-ray flux observed in the Galactic plane; this supports the existence of a local ‘hot bubble’ filled with X-ray-emitting gas, accounting for the rest of the flux.

    • M. Galeazzi
    • , M. Chiao
    •  & B. M. Walsh
  • Letter |

    The distributions of energetic electrons across the entire spatial extent of Earth’s inner radiation belt are found to be organized in regular, highly structured and unexpected ‘zebra stripes’, produced by Earth’s rotation.

    • A. Y. Ukhorskiy
    • , M. I. Sitnov
    •  & B. H. Mauk
  • Letter |

    High-resolution measurements of electrons obtained by satellite during the geomagnetic storm of 9 October 2012 together with a data-driven global wave model are analysed to show that scattering by a magnetospheric electromagnetic emission, known as ‘chorus’, can explain the temporal evolution of the observed increase in relativistic electron flux.

    • R. M. Thorne
    • , W. Li
    •  & S. G. Kanekal
  • Letter |

    A pattern of features is detected, superposed on Saturn’s low-latitude infrared glow, that implies the transfer of charged species derived from water (ring ‘rain’) from the ring plane to the ionosphere, ultimately leading to the global modulation of upper atmospheric chemistry.

    • J. O’Donoghue
    • , T. S. Stallard
    •  & J. S. D. Blake
  • Letter |

    Solar observations at a resolution of 0.2 arc seconds show the reconnection and relaxation of magnetic braids in a coronal active region, leading to the dissipation of sufficient energy to heat the structures to about 4,000,000 K.

    • J. W. Cirtain
    • , L. Golub
    •  & C. E. DeForest
  • Letter |

    The radially outward flow of plasma from the Sun is expected to be deflected when it meets the flow of interstellar plasma through which the Solar System moves, but the spacecraft Voyager 1 unexpectedly finds that the deflected, meridional, flow is consistent with zero within the transition region.

    • Robert B. Decker
    • , Stamatios M. Krimigis
    •  & Matthew E. Hill
  • Letter |

    Rotating magnetic structures in the Sun can channel energy outwards from the convection zone and may explain how the energy required to heat the outer layers of the Sun reaches its upper atmosphere.

    • Sven Wedemeyer-Böhm
    • , Eamon Scullion
    •  & Robert Erdélyi
  • Letter |

    Experimental study of the interactions between intense X-rays and solid matter illustrate the generation of a solid-density plasma governed by electron–ion collisions; these results should inform future high-intensity X-ray experiments involving dense samples, such as X-ray diffractive imaging of biological samples, material science investigations, and the study of matter in extreme conditions.

    • S. M. Vinko
    • , O. Ciricosta
    •  & J. S. Wark
  • Letter |

    Direct observations over the past four centuries show that the number of sunspots observed on the Sun's surface varies periodically. After sunspot cycle 23, the Sun went into a prolonged minimum characterized by a very weak polar magnetic field and an unusually large number of days without sunspots. This study reports kinematic dynamo simulations which demonstrate that a fast meridional flow in the early half of a cycle, followed by a slower flow in the latter half, reproduces both characteristics of the minimum of sunspot cycle 23.

    • Dibyendu Nandy
    • , Andrés Muñoz-Jaramillo
    •  & Petrus C. H. Martens
  • Letter |

    Earth's diffuse aurora occurs over a broad latitude range, and is mainly caused by the precipitation of low-energy electrons originating in the central plasma sheet. Theory suggests that two classes of magnetospheric plasma waves — electrostatic electron cyclotron harmonic waves and whistler-mode chorus waves — could be responsible for the electron scattering that leads to diffuse auroral precipitation. Here it is found that scattering by chorus is the dominant cause of the most intense diffuse precipitation.

    • Richard M. Thorne
    • , Binbin Ni
    •  & Nigel P. Meredith
  • Letter |

    Asteroidal disruption, through high-velocity collisions or rotational spin-up, is believed to be the primary mechanism for the production and destruction of small asteroids. These authors report observations of P/2010 A2 — a previously unknown inner-belt asteroid with a peculiar, comet-like morphology — that reveal an approximately 120-metre-diameter nucleus with an associated tail of millimetre-sized dust particles. They conclude that it is most probably the evolving remnant of a recent asteroidal disruption in February/March 2009.

    • David Jewitt
    • , Harold Weaver
    •  & Michal Drahus
  • Letter |

    Radiative forcing over an '11-year' solar cycle is thought to be in phase with related influences on climate, but recent satellite data reveal a surprising spectral component in solar variability. These authors show that these spectral variations lead to decreases in ozone below 45 km and increases above. As a consequence, radiative forcing of surface climate is out of phase with solar activity, suggesting that a major revision of our current understanding of solar forcing of climate may be required.

    • Joanna D. Haigh
    • , Ann R. Winning
    •  & Jerald W. Harder
  • Letter |

    It has long been suspected that the development of hydrodynamical instabilities can compress or fragment a molecular cloud (in which stars are born). One key signature of an instability would be a wave-like structure in the gas, although this has not yet been seen. Now, the presence of 'waves' is reported at the surface of the Orion cloud, near where massive stars are forming. The waves probably arise as gas that is heated and ionized by massive stars is blown over pre-existing molecular gas.

    • Olivier Berné
    • , Núria Marcelino
    •  & José Cernicharo