International audienceThe MAVEN spacecraft launched in November 2013, arrived at Mars in September 2014, and completed commissioning and began its one-Earth-year primary science mission in November 2014. The orbiter’s science objectives are to explore the interactions of the Sun and the solar wind with the Mars magnetosphere and upper atmosphere, to determine the structure of the upper atmosphere and ionosphere and the processes controlling it, to determine the escape rates from the upper atmosphere to space at the present epoch, and to measure properties that allow us to extrapolate these escape rates into the past to determine the total loss of atmospheric gas to space through time. These results will allow us to determine the importance of loss to space in changing the Mars climate and atmosphere through time, thereby providing important boundary conditions on the history of the habitability of Mars. The MAVEN spacecraft contains eight science instruments (with nine sensors) that measure the energy and particle input from the Sun into the Mars upper atmosphere, the response of the upper atmosphere to that input, and the resulting escape of gas to space. In addition, it contains an Electra relay that will allow it to relay commands and data between spacecraft on the surface and Earth

Abstract. Recent high-sensitivity imaging of the Sun's white-light corona from space has revealed a variety of unexpected small-scale phenomena, including plasma blobs that are ejected continually from the cusplike bases of streamers, fine raylike structures pervading the outer streamer belt, and inflows that occur mainly during times of high solar activity. These phenomena can be interpreted as different manifestations of magnetic field line reconnection, in which plasma and magnetic flux are exchanged between closed and open field regions of the corona. The observations provide new insights into a number of longstanding questions, including the origin of the streamer material in the outer corona, the sources of the slow solar wind, and the mechanisms that regulate the interplanetary magnetic field strength. The Streamer Belt as a Warped Plasma SheetAs has long been known from eclipse observations, the large-scale structure of the corona changes systematically over the l 1-year sunspot cycle. This effect is illustrated in Figure 1, which shows a pair of polarized-brightness images recorded with the LASCO C2 coronagraph in May 1997 and September 1999, respectively. In the earlier image, representative of the white-light corona near sunspot minimum, the streamers lie close to the heliographic equator, the higher latitudes being dominated by dark polar coronal holes traversed by faint polar plumes. In the later image, representative of the corona near sunspot maximum, the bright streamers are distributed more or less symmetrically about the solar disk, and the large polar holes are no longer present.The visual impression obtained from images like those in Figure 1 is that of a disjunct collection of cylindrical stalks.However, as we now demonstrate, the observed streamer structure beyond r • 2.5 Rs can be described by a model in which the scattering electrons are confined to a narrow, warped sheet located where the magnetic field reverses its polarity.We employ Sun-centered spherical coordinates (r, X, •b), with ;t denoting heliographic latitude and •b denoting Car-25,133

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A coronal mass ejection (CME) observed by LASCO exhibits evidence that its magnetic field geometry is that of a flux rope. The dynamical properties throughout the fields of view of C2 and C3 telescopes are examined. The results are compared with theoretical predictions based on a model of solar flux ropes. It is shown that the LASCO observations are consistent with a two-dimensional projection of a three-dimensional magnetic flux rope with legs that remain connected to the Sun.