Measurements of Physical and Optical Properties of Individual  Cosmic and Lunar Dust Grains

Investigators:

Principal Investigator (NASA/MSFC):
Dr. Mian Abbas
Co-investigator (USRA/NASA/MSFC):
Dragana Tankosic
Collaborators (NASA/MSFC):
Dr. Jim Spann,
Dr. Paul Craven,
Edward West,
Richard Hoover

INTRODUCTION:

Dust grains constitute a major component of matter in the universe. About half of all elements in the interstellar medium (ISM) heavier than helium are in the form of dust.  Micron/sub-micron size cosmic dust grains play an important role in physical and dynamical processes in the galaxy, the ISM, and the interplanetary and planetary environments. Knowledge of the physical, optical, and charging properties of the cosmic dust provides valuable information about many issues dealing with the role of dust in astrophysical environments.

Dust in the Interstellar Medium/ Cosmic Dust Cycle:

Dust particles are formed in astrophysical environments by processes such as stellar outflows and supernovae.  Ejected into the ISM, they lead to the formation of diffuse and dense molecular clouds of gas and dust.  The gas and dust in the interstellar clouds undergo a variety of complex physical and chemical evolutionary processes leading to the formation of stars and planetary systems, forming a cosmic dust cycle.

Dust in the Interplanetary Medium:

The interplanetary dust cloud (IDC) constitutes the dust in the interplanetary medium extending from the inner solar system to the asteroid belt.  Zodiacal light is the visible light scattered by dust particles in the IDC. Particles in the IDC spiral towards the Sun (Poynting-Robertson effect) with lifetimes of ~10⁴to 10⁵ years and are evaporated or driven out of the solar system. The sunlight absorbed and re-radiated in the infrared by the dust dominates the sky in the 3-70 mm spectral region.

Dust in the Lunar Environment:

The Apollo astronauts found lunar dust to be unexpectedly high in its adhesive characteristics, sticking to the suits, instruments, and the lunar rover. The Lunar Surveyor spacecraft and the Lunar Ejecta and Meteorite Experiment on Apollo 17 indicated the presence of transient dust clouds. A horizon glow over the lunar terminator and high altitude streamers were observed by the astronauts on the Apollo 17 spacecraft.

Neil Armstrong on the Moon

The lunar dust phenomena are attributed to the electrostatic charging of the dust grains by UV photoelectric emissions on the dayside leading to positively charged grains. On the night side, the electron or ion collisions generally lead to negatively charged grains, with electrons dominating the charging process. Secondary electron emission induced by solar wind electrons with sufficiently high energy may produce positively charged grains. Measurements of the optical and physical properties of individual lunar dust grains are required to understand and mitigate the hazardous effects of the lunar dust phenomena.

SEM images of Apollo 17 dust grains

Measurements on Individual Micron Size Dust Grains in the Dusty Plasma Laboratory at Marshall:

The Lab Setup and the EDB

The above photo shows an experimental facility developed at MSFC that is based on an electrodynamic balance (EDB) for investigation of the properties of individual micron/submicron size dust grains in simulated space environments. A number of unique experiments have been conducted at this facility to investigate several different properties and processes of astrophysical interest.  These studies employed dust grains comprising the analogs of cosmic dust as well as dust grains selected from the sample returns of the Apollo-17 and Luna 24 missions.

Recent Investigations:

1. First Laboratory measurements of radiation pressure on individual micron-sized dust grains (pdf 200K)
2. First Measurements of rotation and alignment of micron-sized dust grains (pdf 424K) simulating the rotation and alignment of interstellar grains. Theories of rotation and alignment of dust grains are expected to provide possible means for evaluation of the galactic magnetic fields, and for investigation of the phenomena of rotational bursting in the interstellar medium.
3. Measurements of the photoelectric efficiencies for charging of
   1. the analogs of individual cosmic (pdf 311K) dust grains and
   2. Apollo lunar dust grains (pdf 229K) by UV radiation. The results are found to be substantially different from the only available measurements made on bulk materials reported in the literature.
4. Measurements of the charging of Apollo lunar dust grains by electron impact (pdf 229K), simulating the charging of lunar dust by the solar wind plasma.

Future Work:

1. Comparison of charging by photoelectric emissions and by electron impact of Apollo 11, 12, 14, 15, 16, and 17 dust grains collected from different lunar sites. 
2. Experimental evaluation of the effect of the lunar temperature cycle (~100 to 400 K) on the dust charging rates and the equilibrium potentials. 
3. Experiments on condensation of volatile gases on interstellar type cryogenically cooled dust grains for investigations of the formation and growth of icy mantles.
4. Measurements of the infrared optical properties in the middle- and far-infrared spectral regions (10 to 2500 cm^-1) with the growth of icy mantles. 
5. Laboratory investigation of the alignment mechanisms of rotation of dust grains

Selected Publications:

• Abbas, M. M., D. Tankosic, Spann, J.F., Dube, M.J., and Gaskin, J.A., Measurements of Charging of Apollo 17 Lunar Dust Grains by Electron Impact, STAIF Conference Proceeding, 942-948, 2008.
• Abbas, M. M., D. Tankosic, P. D. Craven, J. F. Spann, A. LeClair, and E. A. West, Lunar dust charging by photoelectric emissions, Planet. Space Sci. 55, 953-965, 2007.
• Abbas, M. M., D. Tankosic, P. D. Craven, J. F. Spann, A. LeClair, E. A. West, J. C. Weingartner, A. G. G. M. Tielens, J.A. Nuth, R. P. Camata and P. A. Gerakines, Photoelectric emission measurements on the analogs of individual cosmic dust grains, Astrophysical Journal, Vol. 645. No.1, July 1, 2006.
• Abbas, M. M., Craven, P. D., Spann, J. F., Tankosic, D., LeClair, A., Gallagher, D. L., West, E.A., Weingartner, J. C., Witherow, J. C. and Tielens, A. G. G. M., Laboratory Experiments on Rotation and Alignment of the Analogs of Interstellar Dust Grains by Radiation, Astrophysical Journal, Vol. 614, 781-795, 2004.
• Abbas, M. M., P. D. Craven, J. F. Spann, W. K. Witherow, E. A. West, D. L. Gallagher, M. L. Adrian, G. J. Fishman, D. Tankosic, A. LeClair, R. Sheldon, and E. Thomas Jr., Radiation pressure measurements on micron-size individual dust grains, J. Geophys. Res. 108, 1229, 2003.
• Spann, J. F.,  M. M. Abbas, C. C. Venturini, and R. H. Comfort, Electrodynamic balance for studies of cosmic dust particles, Physica Scripta. Vol. T89, 147-153, 2001.