Planetary geophysics

Planetary geophysics

Contact: Tomas Kohout, +358 2941 51008, firstname.lastname (at) helsinki.fi


Recent publications (Tuhat database)

Planetary geophysics research at University of Helsinki is focused on following topics:

Search and study of new meteorite falls

University of Helsinki researches were recently involved in search and study of Annama (2014), Chelyabinsk (2013), and Almahatta Sitta (2008) meteorites. The Annama meteorite is a first meteorite recovered with aid of Finnish Ursa Fireball Network. More information can be found on Ursa (Finnish, English) or Tähdet ja avaruus (Finnish) pages.

Fig. 120 g Annama meteorite.

Fig. 120 g Annama meteorite.

Meteorite petrophysics

Meteorites and cosmic dust are fragments of extraterrestrial bodies (mostly asteroids) impacting Earth. Meteorite physical properties as bulk and grain density, porosity, magnetic susceptibility and hysteresis parameters are being investigated in our laboratory using non-destructive methods. Mobile laboratory facility is used for meteorite measurements in remote meteorite collections. Our meteorite petrophysics database contains measurements of more than 1000 individual meteorite samples.

Fig. Magnetic susceptibility was used to test compositional
homogeneity of Almahata Sitta meteorites and revealed that their
parent asteroid 2008 TC3 was composed of various chondrites mixed
within achondritic ureilites.

Fig. Magnetic susceptibility was used to test compositional homogeneity of Almahata Sitta meteorites and revealed that their parent asteroid 2008 TC3 was composed of various chondrites mixed within achondritic ureilites.

Fig.

Fig. 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.

Rock magnetism of meteorites and minerals common in extraterrestrial materials

Magnetic properties of meteorites and minerals are measured in order to predict magnetic properties of Solar System bodies.

Fig. A new magnetic transition was discovered in common
meteorite iron monosulfide troilite. Below 70 K magnetic response of
troilite is significantly enhanced.

Fig. A new magnetic transition was discovered in common meteorite iron monosulfide troilite. Below 70 K magnetic response of troilite is significantly enhanced.

Modeling of asteroid physical properties

Meteorite petrophysical measurements and database can be used to model density, porosity and internal structure of their parent asteroid bodies.

Fig. The meteorite properties can be used to model internal
structure and mass of their parent asteroids as shown here for
Almahata Sitta meteorites and their 2008 TC3 parent asteroid. The gray
area indicates most probable range of 2008 TC3 asteroid mass as a
function of its albedo and macroporosity based on the properties of
Almahata Sitta meteorites.

Fig. The meteorite properties can be used to model internal structure and mass of their parent asteroids as shown here for Almahata Sitta meteorites and their 2008 TC3 parent asteroid. The gray area indicates most probable range of 2008 TC3 asteroid mass as a function of its albedo and macroporosity based on the properties of Almahata Sitta meteorites.

Physical properties of fine cosmic dust

Bulk and grain density, porosity and internal structure studies of submillimeter micrometeorites is studied using x-ray microtomography.

Fig. This 200 µm micrometeorite recovered in Novaya
Zemlya, Russia, survived its atmospheric entry intact and preserves
its original internal structure. The sample is unique by its
significant internal porosity visible as dark voids. Using the x-ray
microtomography, bulk density (2.13 g/cm³), grain density (3.17
g/cm³) and porosity (33%) of the particle can be derived.

Fig. This 200 µm micrometeorite recovered in Novaya Zemlya, Russia, survived its atmospheric entry intact and preserves its original internal structure. The sample is unique by its significant internal porosity visible as dark voids. Using the x-ray microtomography, bulk density (2.13 g/cm³), grain density (3.17 g/cm³) and porosity (33%) of the particle can be derived.

Instrumentation development for planetary exploration

A magnetic susceptibility meter (MSM) is being developed for asteroid exploration and sample return missions.

Fig. Magnetic susceptibility can be used as nondestructive
tool to distinguish various meteorite types and study composition of
planetary and asteroid surfaces.

Fig. Magnetic susceptibility can be used as nondestructive tool to distinguish various meteorite types and study composition of planetary and asteroid surfaces.