Dr. Lynn Rothschild

Co-Investigator, NASA Ames


Ultra Violet Radiation: The Key to Understanding Evolution and Survival of Life on Earth and Beyond


The overall objective of our research is to understand ultraviolet radiation (UVR) as a limiting environmental factor for life on earth and beyond. UVR is unique in that it places limits on the range of life through the destruction of biopolymers as well as acting directly on the genetic material through DNA damage and mutation. Extraterrestrial life would likely be based on organic biopolymers, and thus subject to UVR effects. Terrestrial life arose under a higher UVR flux and different spectrum than modern life endures, thus the replication of early earth UVR conditions is imperative for astrobiological applications.

In the proposed work we focus on four objectives:
1. To determine the upper limits of UVR on the earth today.  Specifically, areas will be targeted that are likely to have the highest levels of UVB radiation and potentially UVC. We will do broad-band measurements and complete solar spectra (200-1100 nm) in locations and during times when, based on NASA’s TOMS data, the highest UVB fluxes should occur.  In several of these locations, continuous monitoring stations will be deployed to measure broad-band changes during the course of the day and over the year.
2. To determine the relative contribution of UVB and possibly UVC to DNA damage as a proxy for the hazards of these forms of radiation to living organisms. DNA dosimeters will be subjected to unfiltered and filtered solar radiation using a solar simulator, and during radiation measurements in the field, to assess several common forms of DNA damage as a proxy for severity of exposure and likely lethality and mutagenesis.
3. To assess the microbial ecosystem composition of locations with the highest levels of UV radiation. In the sites identified as being subjected to the highest levels of UVR, community composition will be assessed from morphological and sequence-based identification techniques.
4. To screen microbes collected from the ecosystems studied in objective 3 for radiation resistance for  their potential to survive exposure to the space environment.

Significance. The major significance to astrobiology will be to obtain data showing high levels of UVR with broad-band and spectral resolution, and to understand the limits of ecosystems in nature in a high UVB radiation environment. This will have implications for a diversity of fields from medicine to human evolution.

Planetary Biology, Evolution and Intelligence


The survival of microorganisms in very high UV environments can also be tested empirically through the exploration of Earth's highest altitude lakes and ponds, in Bolivia and Chile. We propose (Drs. Nathalie Cabrol and Edmond Grin) a series of investigations of these lakes to examine the strategies employed by these microorganisms.

Just as global-scale changes in oxygen (or iron) were critical for the early biosphere, so too would have been global processes involving other key "biogenic" elements such as carbon (Dr. Bakes) or nitrogen (Drs. Rocco Mancinelli, Amos Banin, David Summers, and Bishun Khare).

We propose coupled laboratory and field research to understand the partitioning of nitrogen on early Earth-and on Mars-between different possible reservoirs, and the abiotic to biotic transition in this cycling.

The work described so far examines the evolution of planetary surface habitability. With the recognition that a subsurface ocean likely exists on Jupiter's moon Europa, we know that habitability in possibly entirely subsurface environments must also be explored. We propose spacecraft data analysis and modeling to examine the geology of Europa and its implications for the free energy sources that would be needed to power a europan biosphere (Dr. Cynthia Phillips). We will then couple these results with terrestrial analog work and direct low-temperature laboratory experiments (Dr. Max Bernstein) to make predictions about the possible abundance and survivability of any oceanic biomarkers that might reach Europa's surface through active geology. These results will have implications for astrobiological exploration of Europa from either an orbiter or a surface lander.
Finally, we suggest research (Drs. Peter Backus and Jill Tarter) to examine the prospects of planets orbiting dwarf M stars being habitable for either microscopic or complex life.

The results of this work will directly influence the strategy employed in the next generation SETI search program.

Peter Backus
Amos Banin
Max Bernstein
Janice Bishop
Nathalie Cabrol
Christopher Chyba
Friedemann Freund
Edmond Grin
Bishun Khare
Cynthia Phillips
Lynn Rothschild
Seth Shostak
David Summers
Jill Tarter

SETI Institute NAI

NASA Astrobiology Institute (NAI)