Hello, everyone! It’s the second Saturday of the month, which means I am here with a science post. I’ve been taking a class about biotechnology (which actually ended this past week), so I’ve been finding various biotech things to give presentations about and so forth. Today’s topic, bacteria-produced bioplastics, was one of those biotech things.
What is bioplastic? I’m glad you asked! Bioplastics are biodegradable plastics which are being investigated to replace petroleum-based plastics, since they could reduce costs and environmental impacts of plastic use. A major type of bioplastic, which I’m going to focus on today, is the polyhydroxyalkoanates (PHAs for short). These are polyesters (a type of organic molecule) naturally produced in bacteria as reserves of carbon and energy. They can then be broken down when the bacterium needs the carbon or energy, which makes them truly biodegradable. (Fun fact: I read about a PhD student who got a certain bacterium to produce 80% of its weight in PHAs by using ice cream as a nutrient medium.)
PHAs have many and varied potential applications. They have been proposed as a packaging for foods like cheese, as biodegradable containers for things like drugs and fertilizers, as a material for disposable items like razors, cups, and shampoo bottles, and in the medical field, to be used as a material for things like sutures and bone replacements. Their properties are similar to those of currently used plastics like polypropylene, which could make the transition smoother if they were to go into use.
The difficulty, up until recently, has not been getting the bacteria to make PHAs, but getting the PHAs out of the bacteria. Last month, however, it was reported that a Spanish research team has developed and patented a method for genetically engineering a predatory bacterium, Bdellovibrio bacteriovorus, to break down the PHA producers, but not the PHAs. A number of companies are already interested in using this method commercially; it could be used for extracting valuable enzymes and other proteins as well as for bioplastic production. This method is much safer and less expensive than previous methods that used things like chemical detergents to extract PHAs. I think it’s a big step forward in making PHAs practical.
This is what I got when I searched Google. Simple, right? A planet is anything orbiting a star, like our sun. That includes all of these:
But wait just a minute. Wasn’t there a big deal a few years back about Pluto not being a planet anymore? What was all that about? And if a planet is anything orbiting the sun, what about that asteroid belt between Mars and Jupiter? Instead of eight planets (or nine, depending on whether you include Pluto or not), are there really a thousand or a million? And are there any more “real” planets out there?
Great questions! I’m glad you asked. Let’s get started, shall we?
Pluto was discovered in 1930, and for the next seventy-six years, it enjoyed the distinction of being the ninth planet in our solar system. In 2006, though, it was stripped of its status as “planet” and reassigned to the new category “dwarf planet,” which, believe it or not, is not the same thing. So why did poor Pluto suddenly become a dwarf planet?
The answer to that question, my friends, lies in the Kuiper Belt, a band of “objects” (including comets and dwarf planets like Pluto) out past Neptune, in Pluto’s vicinity. In fact, Pluto is listed on the NASA website as “King of the Kuiper Belt.”
Scientists have discovered many other small “planets” similar to (some maybe bigger than) Pluto in the Kuiper Belt, as well as in the asteroid belt, and the International Astronomical Union decided it needed a new classification for these worlds. Hence, the dwarf planet was born.
The IAU, you see, has three criteria that a space object must meet before it can be called a planet. First, it must be round (which Pluto is). Secondly, it has to orbit the sun (which Pluto does). And third, it must be massive enough to dominate its orbit, that is, clear it of space debris. This is where Pluto fails. It doesn’t even quite dominate its primary moon, Charon; NASA considers them a binary system. Hence, Pluto is a dwarf planet, no longer the smallest of the planets. Various other Kuiper Belt objects, as well as Ceres in the asteroid belt, join Pluto in this designation.
So there are only eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. But might there be another real planet out there? The answer is, well, maybe. Scientists have never actually seen it, but they have noticed that six Kuiper Belt objects are all orbiting along the same path, suggesting that a planet five to twenty times Earth’s size is out there dominating its orbit. Several research teams are busy investigating to find out whether Planet Nine, as it’s called, actually exists. Some are trying to zero in on its location, based on the aligned orbits of Kuiper Belt objects. Others are trying to catch a glimpse of Planet Nine itself, based on the conjecture that its atmosphere might contain highly reflective gases.
So there you have it! Everyone has a different definition of the word “planet.” The International Astronomical Union says Pluto is not a planet, since it doesn’t dominate its orbit quite right. There just might, though, be another proper planet out beyond Pluto. We shall see as the research goes on.
If you’re interested in reading more about Pluto and Planet Nine, here are my sources!
As some of you may know, I am currently taking a class called “Myths and Misconceptions about Nuclear Science.” It’s a great class. I’ve been learning a lot: about nuclear physics and radiation and nuclear power and how stupid people can really be.
So today, on that last point, I am going to talk a bit about Chernobyl.
Chernobyl was the worst nuclear power disaster in history. You can kind of get a feel for that from the above photo. It involved a nuclear fission reactor in the Soviet Ukraine, one of four reactors on the site. (The other three kept working just fine for years after the accident.) The accident spread radiation all over Europe, killed 31 people either directly in the accident or from acute radiation sickness after it, and to this day, no one can live in a 1,000-square mile “exclusion zone” around the reactor.
So what happened? What was wrong with the reactor that caused this horrible accident?
Obviously, all kinds of things were wrong with it later on, or we wouldn’t have photographs like the one above to show you all the devastation. But initially, the reactor was working just fine, like it was supposed to.
So, we have the same question again. What happened?
Well, on April 25th, 1986, the operators of the reactor started a test to see if they could make the reactor safer.
They wanted to find out if they could keep the electricity-generating turbines (in the upper right of the diagram above) going during shutdown, so they could keep the reactor core cool without having to use a generator or the like. (It’s very important to keep the core cool, even when the reactor isn’t running. You’ve heard of nuclear meltdowns? If the fuel gets too hot, it will melt through the floor of the reactor vessel, and sometimes through the building.) At Chernobyl, as in most reactors, the coolant was water, composed of hydrogen and oxygen.
Let me take a moment to explain some other components of a nuclear reactor. The most obvious necessity is fuel; usually, as at Chernobyl, this is uranium, a mixture of two different types, one of which splits more readily when slow neutrons are shot at it. In order to slow the neutrons down so you can keep a chain reaction going, you need a “moderator,” in this case, graphite. As we’ve already discussed, you need coolant to keep the core from overheating. Last but not least, you need a control system, usually rods made of neutron-absorbing material that can be pulled in and out of the core (see diagram). This helps keep the reaction in check.
Back at Chernobyl, the first thing the operators did for the test was to turn off the emergency core-cooling system, a violation of reactor operation guidelines. They then lowered the power of the reactor, but instead of holding it at the recommended level, they let it drop too much and started pulling out control rods to try to get the power back up. They turned on two extra water pumps for the test, then realized there was too much water in the reactor and reduced the flow, causing the reaction to increase. And when, ignoring safety system warnings, they pulled out too many control rods, the reaction rate skyrocketed (by a factor of 10,000 in 5 seconds), the water in the reactor flashed to steam, the reactor exploded twice, and the graphite lit on fire for a couple weeks, ultimately spreading radiation across Europe.
Clearly, this accident was caused largely by human stupidity (don’t turn off the safety systems in a nuclear reactor!), but the reactor’s design played a role as well. The RBMK was a cheaper style of reactor, so the containment building (which in U.S. reactors is often feet-thick concrete that can withstand missile blasts) was not adequate to contain the initial boiler explosion and the hydrogen explosion that followed. Because of the design of the reactor with graphite as the moderator and water as the coolant, instead of water being both moderator and coolant as in other reactors, removing water increased the reaction rate rather than decreasing it. In addition, without graphite, there would have been less chance of a fire and thus less radiation spread.
In sum, Chernobyl, the worst nuclear power accident ever, was caused by a combination of human error and design flaws, but mostly by human error, since humans made the faulty containment and graphite-moderated design that contributed to the severity of the accident. Further, the reactor was working fine before the operators turned off and ignored various safety systems. Does this make nuclear power unsafe? The answer is complicated. Nothing is perfectly safe; humans can make grave errors with any power system. And in fact, chemical accidents have caused more deaths even than this worst nuclear accident. I think what we can learn from Chernobyl is that we need to be smart about safety: use the best designs, don’t skimp on safety systems, and never, ever turn them off.
If you’re interested in learning more about nuclear science and technology, you can check out Nuclear Choices: A Citizen’s Guide to Nuclear Technology by Richard Wolfson. Although it’s a bit dated (it was published when the USSR was still a country), it is easily readable for non-physicists and deals with many aspects of nuclear technology in an unbiased way. It is my textbook for my nuclear science class and my main source for this blog post.
What do you think of Chernobyl? Have you heard much about it before? Are you surprised at how much of a role human error played? How about design flaws? Do you have any questions? What do you think of nuclear power? Tell me in the comments!