Magnetic reconnection is a fundamental physical process in plasmas whereby stored 40 magnetic energy is converted into heat and kinetic energy of charged particles. 41Reconnection occurs in many astrophysical plasma environments and in laboratory 42 plasmas. Using very high time resolution measurements, NASA's Magnetospheric 43 2 Multiscale Mission (MMS) has found direct evidence for electron demagnetization and 44 acceleration at sites along the sunward boundary of Earth's magnetosphere where the 45 interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) 46 observed the conversion of magnetic energy to particle energy, (ii) measured the electric 47 field and current, which together cause the dissipation of magnetic energy, and (iii) 48identified the electron population that carries the current as a result of demagnetization 49 and acceleration within the reconnection diffusion/dissipation region. 50 51 Introduction 52

[1] Spacecraft potential measurements by the EFW electric field experiment on the Cluster satellites can be used to obtain plasma density estimates in regions barely accessible to other type of plasma experiments. Direct calibrations of the plasma density as a function of the measured potential difference between the spacecraft and the probes can be carried out in the solar wind, the magnetosheath, and the plasmashere by the use of CIS ion density and WHISPER electron density measurements. The spacecraft photoelectron characteristic (photoelectrons escaping to the plasma in current balance with collected ambient electrons) can be calculated from knowledge of the electron current to the spacecraft based on plasma density and electron temperature data from the above mentioned experiments and can be extended to more positive spacecraft potentials by CIS ion and the PEACE electron experiments in the plasma sheet. This

Norway * These authors contributed equally to this workComets are believed to preserve almost pristine dust particles, thus providing a unique sample of the properties of the early solar nebula. The microscopic properties of this dust play a key role in particle aggregation during Solar System formation 1,2 . Prior to Rosetta cometary dust was considered to comprise irregular, fluffy agglomerates based on interpretation of remote observations in the visible and infrared [3][4][5][6] MIDAS, the Micro-Imaging Dust Analysis System 13,14 , is the first spaceborne atomic force microscope (AFM) and a unique instrument designed to measure the size, shape, texture and microstructure of cometary dust. Flying on the Rosetta spacecraft, it collects dust on sticky targets during passive exposures and images its 3D topography with an unprecedented nanometre to micrometre resolution 13 .Cometary dust was first collected in mid-November 2014. In this work we focus on particles collected from then until the end of February 2015. The collected particles cover a range of sizes from tens of micrometres down to a few 100 nanometres, and have various morphologies, from single grains to aggregate particles with different packing densities. Five examples are presented here. Figure 1 shows topographic images (height fields) of three particles (A, B and C). Particles A and C will be referred to as compact, since their sub-units (hereafter grains) are tightly packed, and B appears to be a homogeneous grain. The next example (D) is also a compact particle scanned with a higher lateral resolution of 80 nm (Fig. 2) -a factor four better than the previous scan. The final particle (E), presented in Fig. 3, is best described as a loosely packed "fluffy" aggregate comprising many grains. Detailed collection times and geometries for all particles can be found in Extended Data Fig. 1-3.Aided by the 3D nature of the data, individual grains can be identified, as shown in Fig. 1b, Fig. 2b and 1.09 −0.25 +0.01 µm in size, again similar to the grains in A-C. However, the higher resolution reveals that this micrometre-sized particle is itself an aggregate of smaller units; seven grains can be resolved, with sizes ranging from 260 −120 +50 nm to 540 −250 +20 nm. The visible part of particle E has a maximum extent of 14 µm in X and 37 µm in the Y direction. Analysis of its component grains (Fig. 3d) shows sizes in the range from 0.58 −0.20 +0.15 to 2.57 −0.51 +004 µm with the grain heights ranging between 0.2 µm and 3 µm with 90% smaller than 1.7 µm. These measurements are the first evidence for a continuation of the aggregate nature of dust particles below the size range observed by COSIMA (10s-100s micrometres) 15 .Particle E also shows a morphology strongly reminiscent of stratospheric chondritic porous (CP) IDPs, long suspected of having a cometary origin. This link is consistent with observations by COSIMA for larger dust particles, which also measured similar compositions for dust at 67P and IDPs 15,16 . One notable difference to IDPs is the extre...