In the zero gravity conditions aboard the International Space Station, scientists get to play around with plant growth in ways not possible on Earth. NASA has strongly supported zero-gravity plant research since the beginning, given its crucial importance to any sustainable long-term space exploration.
Recent research from ‘Hydrotropism and Auxin-Inducible Gene expression in Roots Grown Under Microgravity Conditions’, or the HydroTropi experiment, promises to provide new insights into plant growth on a molecular level in response to water (hydrotropism) and gravity (gravitropism). Scientists are growing cucumber seedlings ‘in microgravity’ conditions, providing controlled levels of water to determine the magnitude of root growth responses. They are specifically looking at auxins, a suite of plant growth hormones that, when induced, stimulate cell division at a growing root tip. Understanding how environmental parameters such as water induce auxins in zero gravity will allow scientists to refine their understanding of plant gene expression and how to optimize plant growth in such an alien environment.
Science this week reports new data from the Cassini probe confirming that Saturn’s moon Rhea has the tenuous beginnings of an atmosphere. A thin veil of O2 and CO2 gas skirts the moon’s icy surface at one in five trillionth the pressure of Earth’s atmosphere.
The Cassini probe captured a sample of the atmosphere and used mass spectroscopy to confirm the presence of CO2 and O2. A model produced from this data indicates that O2 was formed at the ice surface by irradiation from solar ultraviolet light and possibly charged particles from deep space. UV rays cause chemical changes in the ice, leading to the spontaneous ejection of O2 gas.
The origin of CO2 in Rhea’s atmosphere is less clear. It is hypothesized that the CO2 is native to Rhea’s ice, or that it formed by interactions between atmospheric O2 and carbonaceous grains on the surface. The authors suggest that carbonaceous grains may have been depsited by micrometeorites from elsewhere in the solar system, possibly even Earth.
O2 and CO2 are believed to have accumulated on Earth during the evolution of life and metabolic processes such as aerobic respiration and photosynthesis. The presence of these gases is considered a criterion for the possible presence of life on a planet. However, the formation of an O2-rich atmosphere on Rhea of entirely photo-driven origin calls this assumption into question. The study provides novel insight into some of the processes that lead to formation of an atmosphere.
B. D. Teolis et al., Science 330, 1813 (2010); 10.1126/science.1198366.
microbes, carbon, energy, the planet. life is a struggle for order in a disorderly world.