Can Astrobiologically Important Organics Survive and Evolve in the Near-surface Ices Under an Extreme Radiation Environment?
- To quantitatively determine penetration depths for electrons that cause radiation damage to organics in icy surfaces.
- To understand the phenomenon of ice-surface charging due to magnetospheric electron and ion bombardment of Jovian and Saturnian icy moons.
- Develop and assess spectroscopic identification methods for remote sensing organics on icy moons of giant planets.
Research by Murthy S. Gudipati (3227), Irene Li (3227/IGPP, UCLA), Antti Lignell (3227), Krishan Khurana (IGPP, UCLA)
Potential future outer planet missions need a comprehensive understanding of radiation processing of icy surfaces in order to define instrument needs.
In order to better understand surface properties of icy bodies including Europa, Enceladus and Ganymede among others, scientists at JPL demonstrated the use of polycyclic aromatic hydrocarbons (PAHs) to study quantitative electron penetration into ice.
Studies presented here were conducted at JPL's "Ice Spectroscopy Lab (ISL)" of Dr. Murthy Gudipati, on ices kept at 30 K (on a 4 K cryogenic system). The electron gun is mounted on a translation stage (left), sample entry is towards the viewer, and on the right are the fiber optics for UV transmission (absorption) spectroscopy.
Demonstration of a New Idea to quantify penetration depths of electrons into ices
- PAHs imbedded in thin ice layer are used as detectors, as they degrade upon electron irradiation.
- UV-VIS spectroscopy is used to monitor remaining PAH concentration.
- First Demonstration using low-energy (5 eV - 2 keV) electron into planetary ice analogs.
Single Layered Ices
- Pyrene (PAH) depletion is linear with respect to electron energy
- Threshold electron energy to observe measurable degradation of PAH molecules in ice is ~100 eV
- No temperature dependence (5 K or 100 K)
Double Layered Ices
- Two distinct linear segments in electron penetration
- At higher energies, the linear curve compares well with the slope of the 'pure' pyrene/ice film (dashed orange line)
- As water layer increases, this correlation shifts to higher energies
So far there have not been direct quantitative electron penetration measurements (energy vs. depth) on ices. All the models use data derived from other targets such as silicon. Our experiments show that electrons penetrate deeper than predicted by existing models. The scientists plan to extend these experiments to higher electron energy region and compare with the existing models. Organics in ices are easily destroyed even with low-energy electrons, implying that it may be difficult to detect organics on highly irradiated surfaces and subsurface probing may be inevitable.
Significance to Solar System Exploration
The proposed Europa Jupiter System Mission (EJSM), with its focus on Europa and Ganymede, need the understanding of radiation processing of icy surfaces in order to define instrument needs. This research not only strongly helps these goals, but also in the data analysis of present and future flagship missions to icy bodies.
Last Updated: 24 January 2011