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Geophysics and Astronomy

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Our scientists study the interstellar medium and star formation, stellar astrophysics, galaxy formation, planetary system, space physics, solid earth and the hydrosphere. In August 2012 Alexis Finoguenov started as a professor in observational astronomy. The research topics of his group lie in the area of extragalactic astronomy, with a particular emphasis on cosmology and galaxy formation. At the end of September 2012 the professor in solid earth geophysics Lauri Pesonen retired. He was succeeded by Ilmo Kukkonen who started in January 2013.

Astronomy and space physics

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. Our goal of integrating astronomy and space physics more tightly together was praised in the evaluation of research and doctoral training of the University of Helsinki.

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). At the end of 2012 four of our astronomers were FINCA employees.

We study the interstellar medium within the Milky Way, with a special emphasis on the early stages of the star formation process. A wide range of observations were carried out at optical, infrared, and radio wavelengths. The ESO telescopes and the data from Planck and Herschel satellites were central in the observational work and, as an example, we completed in 2012 the observations of the Herschel key programme “Galactic Cold Cores” that we are coordinating. The studies were complemented with strong theoretical and numerical work. Several papers were published on the chemical and physical evolution of pre-stellar cores

The extensive observational and modeling efforts to understand activity in the Sun and more active late-type rapid rotators has been continued by the magnetohydrodynamics group. As a major breakthrough, direct numerical simulations of magnetized convection in spherical wedge geometry have for the very first time reproduced equatorward propagation of activity belts. The cycle period (33 years) is comparable with that in the Sun (22 years). See the figure below in the “Highlights” section.

In the theoretical extragalactic group our focus is on studies of the formation and evolution of galaxies using numerical simulations run on high-performance computing facilities (e.g. CSC - IT Center for Science). We simulate both isolated galaxy mergers and the formation of galaxies in a full cosmological framework. Highlights for 2012 include simulating the cosmological formation of massive early-type galaxies. Observations have shown that massive elliptical galaxies were much smaller and more concentrated in the early Universe. Our simulations confirm this picture and demonstrate that the subsequent growth of massive elliptical galaxies until the present-day took place predominantly through minor merging of gas-poor lower mass galaxies. In addition, detailed investigations were undertaken on the structure of massive gas-rich disk galaxies in the early Universe, with our simulations confirming the observed picture that these galaxies consist of multiple short-lived star-forming gaseous clumps. In 2012 we also started preparations for the upcoming ESA mission Euclid, whose goal is study the nature of dark energy, dark matter and the evolution of galaxies up to a redshift of z~2. In this mission the Department of Physics is carrying the main responsibility for the Finnish participation in the Science Ground Segment.

In planetary system research our focus is on asteroids and comets as well as on small particles in regoliths and atmospheres, including the atmosphere of the Earth. In 2012, asteroid astrometric and photometric studies resulted in a Ph.D. thesis highlighting Markov-chain Monte Carlo methods. Studies on electromagnetic scattering by small particles and random media composed of such particles have continued, culminating in the acceptance of the ERC Advanced Grant proposal entitled "Scattering and absorption of electromagnetic waves in particulate media" with substantial promise for future activities. 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 continued and our future spacecraft involvement includes ESA’s astrometry mission Gaia 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. 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. We study how terrestrial dust and ice particles scatter solar radiation and quantify their direct radiative impacts.

In space physics we study the dynamics of Solar System plasmas in close co-operation with space physics research at the Finnish Meteorological Institute. Our key research questions are lift-off, propagation and geoefficiency of coronal mass ejections (CMEs), solar-wind interaction with the magnetosphere, physics of shock waves and solar energetic particle acceleration. We develop numerical simulations and use them to analyse observations from several ESA and NASA spacecraft. Highlights of 2012 were successful numerical simulation of the CME lift-off from the Sun and the first combined observation-simulation study of the approach of an interplanetary shock to the Earth’s bow shock and demonstration of Fermi acceleration of ions in the process. See figure and video below in the “Highlights” section. These studies resulted in two excellent PhD theses in 2012.

We are currently involved in three projects within EU’s 7th Framework Programme, of which two are coordinated by our scientists: In the E-SQUID project an improved SQUID-based readout suitable for large X-ray to infrared detector arrays in space research is being developed. In the SEPServer project an integrated web-based interface to a comprehensive set of solar energetic particle data, related data on electromagnetic solar emissions and tools on analysing these data will be established. Furthermore, we participate within a consortium led by the British Antarctic Survey in the SPACECAST project to produce improved forecasting methods for space weather.

As a leading Finnish scientific satellite instrument provider we worked intensively with the production of the flight model of a solar X-ray and particle instrument onboard ESA’s Mercury mission BepiColombo to be launched in 2015. In addition to its main task to provide background information to a UK-led X-ray instrument to determine the elemental composition of the surface of Mercury, the instrument can be used independently in studies of solar eruptions. Furthermore, we provide instrumentation for the student satellite project Aalto-1 of the Aalto University.

Geophysics

Participants of the Supercontinent Symposium investigating the opholite outcrop in Jormua, Kainuu. (Photo: Toni Veikkolainen)

The research of the Solid Earth Geophysics laboratory is concentrated on reconstructions of supercontinents, testing the Geocentric Axial Dipole (GAD) hypothesis of the Earth’s magnetic field using Precambrian data, research of physical properties of meteorite impact structures and meteorites, determination of seismic velocities of rocks using ultrasonic methods, petrophysical properties of the Kevitsa intrusion, and applying magnetic, geochemical and micromorphological methods in studies of urban pollution generated by road traffic. The main conclusions drawn from our research include (1) three methods (inclination frequency, paleosecular variation and asymmetry analysis) that show the GAD hypothesis to be a credible approximation of the geomagnetic field, (2) the supercontinent Rodinia did not amalgamate until the end of Neoproterozoic, (3) petrophysical models of the Kevitsa area are compatible with the observed magnetic minimum, (4) ICDP (International Continental Scientific Drilling Program) borehole measurements of the Russian El´gygytgyn structure clearly show the presence of impactites, (5) roadside snow gives a better insight into the spatiotemporal distribution of traffic-generated magnetic particles than barren soil.

A highlight of the year was the very successful international Supercontinent Symposium in September 2012. It was arranged at the Kumpula Campus after an excursion to eight geological landmark sites in Finland.

Our planetary geophysics research focused on laboratory X-ray micro tomography investigations of cosmic dust grains. The method allows nondestructive investigation of physical properties and internal structure of cosmic dust with submicron resolution. The planetary research group started a study of Magnetic Susceptibility Meter for Asteroid Regolith Composition Studies instrument. The instrument was proposed to the ESA MarcoPolo-R sample return mission to an asteroid and was under review at the end of 2012.

Hydrospheric research goes into cryosphere science, hydrology and oceanography. In sea ice dynamics basic research is performed and field data are analysed from Arctic and subarctic seas. The coastal zone of freezing seas is examined with applications to ecology and engineering. Ice-covered lakes are examined in northern Eurasia, with emphasis on the role of the ice season in the annual cycle of lake ecology. Epiglacial lakes are studied in Dronning Maud Land, resulting in analysis of their life history and biological productivity. 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 Glaciological Society’s symposium on Seasonal Snow and Ice in Lahti in May 27 – June 1, 2012.

The oceanographic research focuses on circulation and water mass transformations in the North Atlantic and the Arctic Ocean and their relations to climate and climate change. The relative importance of two inflows of Atlantic water to the Arctic Ocean, through Fram Strait and over the Barents Sea, has been studied, and the spatial and temporal variations of heat and freshwater content in different water masses have been examined, as well as the seasonal freshwater input due to ice melt to the surface layer of the Arctic Ocean. The primary observational sources have been different icebreaker cruises conducted in the Arctic Ocean in the last 20 years. The changes in the water column in the Greenland Sea over one year, caused by winter convection summer heating, have been examined using observations from ARGO floats as well as from numerical one-dimensional models. The evolution in the intermediate and deep waters in Fram Strait and in the Greenland Sea during the last decade have been described using observations taken by research vessel Polarstern the from Alfred Wegener Institute in Bremerhaven, showing the effects of the weakening of the dense water formation in the Greenland Sea in recent years. The overflow of dense water from the Arctic Mediterranean across the Greenland-Scotland Ridge has been studied within the EU THOR (ThermoHaline Overturning – at Risk?) project with special emphasis on mixing and entrainment into the overflow plume.

Highlights of research

The butterfly diagram of the migration of stellar activity belts toward the equator based on numerical simulations of magnetized convection. Time runs on the horizontal axis and the latitude is on the vertical axis. (Käpylä et al., Astrophys. J. Lett., 755:L22).

An interplanetary shock approaching the Earth’s bow shock (left) from the Sun (right). The black lines indicate the direction of the interplanetary magnetic field. The colours show the heating of solar wind ions through Fermi acceleration during the process (Hietala et al., Astrophys. J. Lett., 751:L14, 2012).

A clearer version of the figure can be seen from:

 http://www.physics.helsinki.fi/vuosikertomukset/2012/images/fig3S_snaps.eps.  

A video of the approaching shock can be seen from:

 http://www.physics.helsinki.fi/vuosikertomukset/2012/images/fig3S.mpeg.