Geophysics and Astronomy

Our scientists study the interstellar medium and star formation, stellar astrophysics, galaxy formation, planetary system, space physics, solid earth and the hydrosphere. At the beginning of 2013 Ilmo Kukkonen started as a new professor in solid earth physics replacing Lauri Pesonen. A particular highlight of 2013 was start of the European Research Council's Advanced Grant project "Scattering and absorption of electromagnetic waves in particulate media" led by Prof. Karri Muinonen.

Astronomy and space physics research is conducted within the joint Kumpula Space Centre with the Finnish Meteorological Institute and the School of Electrical Engineering of Aalto University. For our astronomers the telescopes of the European Southern Observatory (ESO) in Chile, the space-borne observing facilities of the European Space Agency (ESA), and the Nordic Optical Telescope (NOT) in La Palma are the key sources of data. The ESO-related research is conducted in close co-operation with the Finnish Centre for Astronomy with ESO (FINCA). In 2013 four of our astronomers were FINCA employees.

Astronomy

In the theoretical extragalactic group our focus is on studying the formation and evolution of galaxies using numerical simulations run on high-performance computing facilities. Highlights for 2013 include new adaptive-mesh-refinement simulations that model the formation of the very first supermassive black holes in the Universe. Observations have revealed that black holes with masses up to a billion solar masses existed when the Universe was less than a billion years old. Currently it is a theoretical challenge to reproduce this rapid growth of supermassive black holes and our simulations have explored a scenario in which massive gas clouds directly collapse to seed black holes with resulting masses of the order of 100 000 solar masses. In addition, we carried out detailed investigations of the origin of elliptical galaxies and the details of their dark matter haloes using numerical galaxy merging simulations. Finally, we developed new physical models for better describing the astrophysical processes of gas cooling, star formation, chemical enrichment and black hole formation in numerical galaxy simulations. In 2013 we also continued the preparations for the upcoming ESA Euclid mission, which will study the nature of dark energy, dark matter and the evolution of galaxies. In this mission the Department of Physics is carrying the main responsibility for the Finnish participation in the Science Ground Segment.

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Adaptive-mesh-refinement simulation of a forming supermassive black hole at a redshift of z~18, i.e., 200 million years after the Big Bang. (Regan, Johansson, Haehnelt, 2013, Submitted to Monthly Notices of the Royal Astronomical Society.

Studies were continued into star formation inside the Milky Way galaxy. The investigations concentrated on the properties of pre-stellar cores in interstellar clouds. Several studies were published on the chemistry and dust properties of these objects. "Galactic Cold Cores", a key programme of the ESA Herschel satellite coordinated by us is nearing completion. The user-reduced data have been submitted to the Herschel archive and statistical studies of the full source sample will be completed in the near future. Corresponding studies with the Planck satellite of ESA are in progress and we are preparing for the publication of the final catalog of Planck-detected cold interstellar clouds.

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A star-forming cloud observed with the Herschel satellite. In this composite image a cold cloud filament is seen as blue against the warmer background. Herschel has revealed cloud filaments as an important step in the star formation process. Also this filament is undergoing gravitational fragmentation, with a number of protostellar cores being visible in the image.

The "Active Suns" project aims at modelling and understanding the magnetic activity of the Sun and other late-type stars; work towards this goal was continued. As a scientific highlight, the group members' direct numerical simulation efforts resulted in the detection of dynamo waves propagating in the azimuthal direction. This remarkable result indicates that stars with higher rotation rate than the Sun (e.g. Sun itself at a younger age) exhibit a totally different dynamo mode than the mostly axisymmetric present-day solar magnetic field with latitudinal migration of the dynamo wave. We also continued our long-term spectropolarimetric (with ESO and NOT facilities) and photometric observations of late-type stars and evidence of azimuthal dynamo waves were also seen in these observations. Another highlight of the year was Academy of Finland's decision to fund the Centre of Excellence ReSoLVE (Research on Solar Long-term Variability and Effects), coordinated from the University of Oulu, with participating teams from Aalto University and Finnish Meteorological Institute (FMI), for the years 2014-2019. The group members are core collaborators of the ReSoLVE research teams.

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Simulated azimuthal magnetic field close to the surface of a star (Cole et al., Azimuthal dynamo wave in spherical shell convection, submitted to ApJ Letters, 2013, arXiv:1309.6802)

In planetary system and planetary geophysics research, our focus is on asteroids and comets as well as on cosmic dust and small particles in regoliths and atmospheres, including the atmosphere of the Earth. In 2013, studies on scattering of solar radiation by dust and ice particles in the Earth's atmosphere and on the related direct radiative impact have resulted in a Ph.D. thesis. Studies on electromagnetic scattering by small particles and random media composed of such particles have continued, culminating in the kick-off of the ERC Advanced Grant project entitled "Scattering and absorption of electromagnetic waves in particulate media" (SAEMPL). The primary goal of the SAEMPL project is theoretical, that is, the development of an unprecedented numerical method for multiple scattering by close-packed media of small particles. In the method, the ladder and maximally crossed cyclical diagrams of the multiple electromagnetic interactions are to be rigorously computed. For the validation of the method, the SAEMPL project includes a unique experimental part including the development of a nano-mechanical device for scattering measurements for single particles and media of such particles. The samples are to be characterized by an Atomic Force Microscope.

Astronomical observations are carried out using modern ground-based telescopes (e.g., VLT of ESO and NOT) and satellite instruments. Analysis of observations with ESA's Moon mission SMART-1 has matured for publication. Furthermore, light scattering methods are used in preparations for the Global Precipitation Measurement mission of NASA by modelling radar backscattering from winter-type precipitating particles. Our future spacecraft involvement includes ESA's astrometry mission Gaia (launch in December 20, 2013) and the Mercury mission BepiColombo. We also assess the risk of near-Earth asteroid collisions and participate in the upcoming Canadian NEOSSat mission as well as in the proposed ESA near-Earth asteroid sample return mission MarcoPolo-R. In the StreakDet project funded by ESA, we develop automated pattern recognition methods and software for the analysis of space debris streaks in both ground-based and space-based imaging data. As for the uncontrolled decay of the ESA GOCE satellite, together with colleagues at the Finnish Geodetic Institute and Finnish Meteorological Institute, we have provided impact hazard advice for the government of Finland.

In February 15, 2013, a 20-m sized small asteroid exploded in the atmosphere over the Chelyabinsk region, Russia, resulting in a meteorite shower and environmental damage associated with a shock wave. Reflectance spectra in visual and near-infrared range, physical properties and mineralogy studies of the recovered meteorites were performed in several laboratories, including our solid earth geophysics laboratory. The spectral measurements took advantage of our new integrating-sphere spectrometer at the astrophysics laboratory. The unique combination of the measurements resulted in a novel interpretation of asteroid spectra and effect of shock on asteroid taxonomy. A press release was sent out at the DPS/AAS meeting (Division for Planetary Sciences, American Astronomical Society) in Denver, Colorado. For the extensive study of the Chelyabinsk meteor published in Science (November 7, 2013), we have contributed with an assessment on the origin and evolution of the Chelyabinsk meteoroid.

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Reflectance spectra of Chelyabinsk meteorites show that shock related to ancient space collisions turns asteroid spectra to appear dark with invisible silicate absorption bands. Light-colored lithology are moderately shocked meteorites. Dark-colored and impact-melt lithology are heavily shocked meteorites.

Space Physics

Our space physics research is strongly focused on physical mechanisms driving perturbations in the Earth's magnetosphere and ionosphere, i.e., space weather. Our key research areas are the studies of how coronal mass ejections (CME) evolve from the Sun to the orbit of the Earth and how the solar wind interacts with the outer boundary of magnetosphere. We have developed a scheme to estimate CME rotation and deflection using widely separated observations from the STEREO spacecraft and their heliospheric imagers. CMEs are treated as 3-dimensional objects, which allows connecting their geometrical properties close to the Sun and further out in the heliosphere. We also compare CME morphologies in-situ and in remote white-light observations with the goal to improve the understanding on CME eruption and space weather forecasting. In Autumn 2013 two PhD theses, one in numerical simulations and the second in data-analysis of solar wind – magnetosphere interactions supervised jointly with the Finnish Meteorological Institute were successfully defended.

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Composition of our studies tracking coronal mass ejections from the solar disk to the vicinity of the Earth

We have also been involved in two space weather-related projects in the 7th Framework Programme of EU. In the SEPServer project, led by us, an integrated web-based interface to a comprehensive set of solar energetic particle (SEP) data, related data on electromagnetic solar emissions and tools on analysing these data has been established in 2013. The server is available to the science community at http://server.sepserver.eu. In addition to the data itself, the server provides preliminary analysis results for hundreds of SEP events in form of catalogues offering the analysis results in an electronic format for further analysis by the community. In the SPACECAST project, coming to conclusion in early 2014, our role was to produce a semi-empirical model to explain acceleration of solar protons up to energies that are harmful for satellites and astronauts.

As the leading scientific satellite instrument provider in Finland we worked intensively on the design, manufacturing, and scientific planning of the Solar Intensity X-ray and particle Spectrometer SIXS onboard ESA's Mercury cornerstone mission BepiColombo which will be launched in 2016. In addition to its main task to provide the reference solar X-ray spectrum information to the UK X-ray instrument MIXS to determine the elemental composition of the surface of Mercury, the instrument will produce independent data of X-ray and particle spectra of solar eruptions, which will be used for the modelling of solar X-ray flares, SEP events and the magnetosphere of planet Mercury. As a major highlight and milestone for this activity, the Flight Model of SIXS was delivered to ESA in 2013. Furthermore, our radiation monitor instrument to the student satellite Aalto-1 of the Aalto University reached the Critical Design Review in November 2013.

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Visual inspection of the SIXS instrument Flight Model by representatives of ESA, Astrium and University of Helsinki at Oxford Instruments Analytical Oy's clean room facility.

Geophysics

Year 2013 was very productive in terms of doctoral theses in geophysics. Four theses were defended on a great variety of topics: meteorite impacts, use of seismic reflectance in ore exploration, properties of Baltic Sea ice, and snow and ice in Antarctica.

In solid earth physics the activities in analysing various samples, including meteorites discussed above in the context of astronomy, were continued. A big effort was invested in preparing a special issue of the Precambrian Research (vol. 244, 2014) based on the very successful Symposium "Precambrian Supercontinents" held in Helsinki, September, 2012. In addition to the editorial work Department's geophysicists authored 7 articles in the issue.

Hydrospheric research goes into cryosphere science, hydrology and oceanography. In sea ice dynamics basic research is performed and field data are analysed from subarctic and Antarctic seas. The coastal zone of freezing seas is examined with applications to ecology and engineering, but otherwise there was only limited activity in oceanographic research due to retirement of professor Bert Rudels. Snow research includes seasonal snow in Finland in the Climate Change programme FICCA of the Academy of Finland and the snow surface layer (10 m) in the Dronning Maud Land. The cryosphere team organized the International Annual Meeting of the Nordic Branch of the Glaciological Society's in Lammi Biological Station, October 31 – November 2, 2013.

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Supraglacial lake Suvivesi at the Finnish station Aboa in the Dronning Maud Land has been a major research object. The margins of the lake are bog-like porous ice, and its hydraulic properties have been examined by pump tests.

Ice-covered lakes have been in the focus of cryosphere science in 2013. They are examined globally, with emphasis on the role of the ice season in the annual cycle of lake ecology. The climatology work is done in the GLEON (Global Lake Ecological Observatory Network) ice modelling team. In Finland the main sites are the boreal lakes in Häme Region and tundra lakes in Northwest Lapland. Epiglacial lakes are studied for their life physics and biological productivity. The structure, life history and biota of supraglacial lakes in the Dronning Maud Land was clarified based on field data and mathematical modelling.