January Science Shorts: Planets and Life

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The Search for ExoEarths with Starshades

By: Aggie Mika

“Are we alone?”

Andrew Harness, a graduate student within the Department of Astrophysical and Planetary Sciences is working with Professor Webster Cash to answer this age-old question. Specifically, Harness is interested in developing new technology to look for life on other planets. He believes that our generation may finally possess the tools to be able to seriously pursue this question.

Exoplanets are planets outside of our solar system that are known to orbit sun-like stars. Within these planetary systems, there are habitable zones, or Goldilocks zones, where exoplanets are neither too far from nor too close to their star and conditions may be just right to support life. These planets are ideal candidates for further exploration. However, how can researchers find and study exoplanets that are located light-years away?

“Locating exoplanets,” Harness says, “is like looking for a firefly next to a lighthouse.” Parent stars are so much brighter than their orbiting planets that the planets tend to be completely obscured by starlight.

When researchers are able to locate an exoplanet within a habitable zone of a planetary system, they can use a technique called spectroscopy to analyze its atmosphere. Spectroscopy looks for “biosignature gases” to determine whether that planet may be suited for life. The composition of Earth’s atmosphere and the characteristics of its gases--oxygen, ozone, methane and water vapor--support life. Scientists use spectroscopy to try to find these gases on other planets. This technique relies on the dissection and analysis of a planet’s light; each gas leaves a particular fingerprint in the spectrum that can be used to learn about the planet’s atmosphere. 

However, a planet located within a star’s habitable zone is so close to the star that it is incredibly difficult to distinguish those spectral fingerprints from those of the overwhelming starlight.

Dr. Cash may have a solution for this problem: a giant flower-shaped screen called a Starshade. This unique screen, about 50 meters in diameter, is flown into space and positioned in front of space telescopes to block out starlight in order to improve our ability to locate exoplanets and measure their biosignature gases. The “petals” are precisely designed so that they block not only the light traveling straight from the star to the telescope – the way you can block the light from a bright bulb with your hand – but also minimize the additional starlight which diffracts, or bends, around the edges of objects.

“If you were to place an arbitrarily shaped screen in from of the star, the starlight would bend around it,” Harness explains. “You need a special way to suppress the starlight.” 
The Starshade can be used to reveal new exoplanets around stars, as well as directly study them. According to Harness, this is the only way scientists have so far to look for exoearths in the near future.

Artist's rendition of a starshade. Source: http://science.gsfc.nasa.gov/

Antibiotic resistance in space: determining microgravity's influence on bacteria

By: Roni Dengler

Ever dream of becoming an astronaut as a kid? The thought of being on the frontiers of space exploration is thrilling. However, it also comes with its share of uncertainties. For example, what do you do if you get sick? Research under the direction of Dr. David Klaus in the Bioastronautics program focuses on questions such as this. Because astronauts are isolated in space and unfathomably far from medical assistance, finding out what might make astronauts more likely to get sick is important not only for astronauts’ health but also for the longevity of space exploration programs.

Given that the universe is often portrayed as consisting of vast emptiness, is it even possible to get sick in space? Unfortunately, the answer is yes. In fact, astronauts are more susceptible to catching a bug up there than when they’re here on Earth.

Are the bacteria “stronger” up there, or are our bodies just not as good at fighting them off? Luiz Zea, a PhD candidate in the Bioastronautics program, says it’s both. As part of his thesis work, he wants to figure out why bacteria in space seem to have super powers. He starts with a fundamental difference between space and Earth: gravity. The force of gravity is not as strong in space as it is on Earth. Through his research, Luis wants to understand the effects of this reduced gravity setting, an environment known as ‘microgravity’, on bacteria. His goal is to identify the readily-observable differences, as well as the genetic changes, occurring in bacteria that enable them to more-readily cause disease in space.

To figure this out, Luis sends E. colibacterial cultures to the International Space Station, where they are subjected to the demands of microgravity over five to eight months.

Compared to bacterial cultures on Earth, bacteria in microgravity grow and divide more quickly, meaning more bacteria are produced in the same amount of time. Amazingly, these rapid reproducers take up about half as much space by clustering together. Both of these factors make the bacteria more resistant to standard treatments. In fact, killing off bacteria in microgravity requires higher concentrations of the common antibiotic gentamicin sulfate. 

Back on Earth, Luis works with Hudson Alpha, a biotechnology institute based in Huntsville, Alabama, to identify changes in genes responsible for the differences he observed­­. These genetic differences could provide further clues as to why bacteria are more resistant to antibiotics in space, why they replicate at a faster rate and ultimately, tune us into why astronauts are more susceptible to catching a bug in microgravity.

What about physiologically relevant combinations of bacteria like, for example, the distinct combinations of microbial species that populate our guts? Is microgravity affecting this bacterial ecosystem to the detriment of the astronauts? Luis hopes to address these kinds of questions in the near future.

To learn more about the Bioastronautics program, click here

Using Sunlight to Synthesize Primitive Membranes

By: Bridget Menasche
When thinking about the emergence of life, we often think about how individual molecules that provide the information and machinery for life might have arisen on the early Earth. But in order for DNA, RNA, and proteins to become the engines of something like life they had to have been concentrated and enclosed. How did the membranes that surround cells first emerge?

Rebecca Rapf, a Chemistry graduate student working in Professor Veronica Vaida’s lab, is on the hunt for the first hint of order that would later become the cell. She focuses on the prebiotic chemistry occurring on Earth 4.2 to 4.0 billion years ago before either the RNA world or life as we know it emerged. Researchers in the Vaida lab focus on the sun as a source of energy for prebiotic reactions, and on air-water interfaces as a reaction environment for the chemistry to occur.

Rapf and colleagues developed this model to explain how the first 
self-assembled vesicles might have formed on the early earth – and how 
they likely form in their experiments. First, single tailed-surfactants start to 
collect near the air-water interface. Next, photochemistry creates double-
tailed surfactants, which interact with each other near the interface. Lastly, 
these interactions lead to the assembly of a bilayer structure that might be 
similar to today’s biological membranes.
Membranes are made of surfactants, which consist of a water-loving, polar head and a hydrophobic, non-polar tail. When thinking about prebiotic chemistry, many researchers focus on proto-cells made of fatty acids, which have a single hydrophobic tail, and which shift between states easily. Modern biological membranes are composed of phospholipids, which make incredibly stable membranes and have two tails. It’s unlikely that phospholipids were available before life emerged because there’s no easy way for them to be made spontaneously in the environment. So what molecules might have served to create stable membranes on the early Earth, if fatty acids were too changeable and phospholipids impossible to make? How did prebiotic chemistry create a double-tailed surfactant from a single-tailed one and yield molecules similar to the components of current biological membranes?

These questions drive Rebecca Rapf’s current research. One starting point that Rapf and other researchers have honed in on is 2-oxooctanoic acid (2-OOA). It’s a surfactant with an 8-carbon hydrophobic tail, making it similar to a fatty acid if you squint. Rapf and her coworkers in Dr. Vaida’s lab found that when multiple 2-OOA molecules are exposed to sunlight, they merge together into a double-tailed molecule, OOA-OOA, like a simpler phospholipid. And when this reaction occurs at an air-water interface, the products can self-assemble into three-dimensional structures. They also found that these structures are about 100nm in diameter, big enough to be vesicles formed from a bilayer of surfactant molecules.

Because the vesicles form during exposure to sunlight, they are likely composed from a mix of double and single-tailed surfactants. Rapf has hypothesized that the ratio between the two types is important for vesicle formation and stability. She found that with longer exposure to sunlight, the vesicles become less stable: suggesting that as the mix of single and double tailed molecules changes over time, so does the process of vesicle formation.

This leaves another open question: what exactly happens during self-assembly? By what mechanism does this mix of surfactants form, interact, and coalesce? The water surface likely plays a key role in how these molecules mingle and merge, but Rapf wants to find out how. Future research in Dr. Vaida’s lab may unravel this process and reveal more about how reactions important to the emergence of life could have occurred on the early earth.

Chemistry and early Earth buffs can find more details in this paper describing these discoveries: “Photoinitiated Synthesis of Self-Assembled Vesicles

And you can learn more about research in the Vaida lab here.

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