Sunday, May 26, 2013

Tasty Pesticides

A while back I was musing on the fact that some of the plant-derived substances many people enjoy on a daily basis are basically natural pesticides.

(One term that will come up in the post is “LD50”; this is the median lethal dose, the amount of chemical per unit of body mass at which roughly half of a population will be killed by said chemical. It's a way of comparing toxicities between different substances.)

One such natural pesticide consumed by pretty much everyone in developed countries in one form or another is good ol' caffeine. In the wild, caffeine paralyzes and kills certain insects that feed upon the plants that make it. It can also have toxic effects in mammals (including humans), although the toxicity is fairly low: it's estimated the average adult would need to drink 80 to 100 cups of coffee in a short period of time to receive a lethal dose. (The  LD50 is estimated to be about 150-200 milligrams per kilogram of body weight; the amount in a cup of coffee ranges from 80-125 milligrams [typical soda about half that], while average adult body mass is on the order of 60-100 kilograms.) Obviously drinking that much coffee in a short enough time is impossible, but there have apparently been reported deaths after overdosing on various caffeine pills that give extremely high doses at once.  For the majority of my readers that shouldn't be a concern though I imagine.

Another cocktail blend near and dear to my heart is peppermint oil. Peppermint is my panacea of choice and I love the taste, which comes from a complex blend of various chemicals. These chemicals, again, act as natural pesticides against various browsers. Keeping that mind that everything is poisonous at a high enough dosage, I didn't find anything specifically about peppermint toxicity in mammals, nor an LD50. Probably the fact that it's a mixture of chemicals rather than a single specific one has something to do with that.

Another natural insecticide that many people enjoy is nicotine. It's no secret that nicotine is toxic, and it is definitely quite dangerous to mammals. For comparison, remember that the LD50 of caffeine is estimated to be about 150–200 mg/kg; that of nicotine is a mere 0.5–1 mg/kg, around 75–200 times more toxic. (Or if you want, you can flip it on its head and tell people that caffeine is 75–200 times less toxic than nicotine.) Although it's unlikely anyone could get that amount from most of the various recreational sources of nicotine (though it is possible to overdose), pure nicotinic acid is highly dangerous because of how easily and quickly it get absorbed by the skin, and there are reports of people getting deathly sick simply by spilling a tiny amount of high-concentration nicotine solution on their skin.

Another chemical used by plants for defense against mammals, capsaicin has ironically enough become one of the main reasons peppers are cultivated around the world. Capsaicin is an incredibly nasty chemical. I should know, having had a lot of exposure to it growing up since my father is a pepper breeder. Pure, isolated capsaicin is such a hellish material that it requires proper respiratory apparatus, face protection, and strict adherence to hazardous materials guidelines.  I couldn't find an  LD50 for humans; for mice it's about 47 mg/kg, which puts it somewhere between caffeine and nicotine in toxicity.

Edit: according to my dad, the LD50  of Tabasco Sauce is 24 milliliters per kilogram of body weight. It's not straight capsaicin, but it definitely contains a lot of it. To put it in perspective, a fatal dose for the average person would be about 3 pints (about 1.5 liters), though I'd imagine you'd never want to see the stuff ever again long before you managed to down that much in a single sitting...

Finally, another natural pesticide is allicin, the active ingredient in garlic. Allicin, however, mainly targets bacteria and viruses rather than multi-cellular organisms (although its pungent taste can certainly drive them away). I couldn't find an  LD50 for it for mammals, but it's incredibly effective at killing pretty much any bacteria brought in contact with it, even ones resistant to other antibiotics.

These five chemicals are just the ones I could think of off the top of my head. I'm sure there are plenty more out there if I were to do some digging, but these are common ones that many people will be familiar with (the form they come in, if not the chemical itself). So the next time you consume some “pesticide free!” organic food, just remember, some of the potentest pesticides in nature come from within.

Sunday, May 19, 2013

Birthday Bach

I feel it is a fair assumption that most of my readers know that Johann Sebastian Bach is well-known for his organ compositions (not to mention considerable personal talent in organ-playing).

What is probably not nearly as well known is that Antonio Vivaldi, much better known for his prodigious number of concerti for various strings, wrote a few organ concerti of his own (no more than thirteen are known if you count every work that includes an organ, of which two are incomplete and one is of doubtful authenticity).

That one of doubtful authenticity, labeled RV 542, Organ Concerto in F, I've had in my musical collection for about a year now (along with five other organ works of Vivaldi). In the third movement, an Allegro, it contains a very interesting solo organ passage that lasts for 3 minutes and 36 seconds (half the length of the entire movement), during which the organ is the only instrument playing. This is very unusual for Vivaldi who in my experience never has single instruments playing for more than a few seconds, which may lend some credence to the idea that the piece had a different author. That notwithstanding it's a beautiful organ solo and one of my favorites parts of any of his organ concerti.

Anyway, my dear aunt got me a collection of five of Bach's organ concerti for my birthday on Friday, and while listening to them I made a remarkable discovery: in the third movement (also an Allegro) of Bach's organ concerto BWV 594 in C major, I found the exact same organ solo! It's slightly shorter in this version at 3 minutes 23 seconds (it has a slightly faster tempo), but is unmistakably the same section.

Interestingly, while looking up BWV 594 on Wikipedia, it came with a note saying "after Antonio Vivaldi," but listing another of his concerti: a concerto for violin in Opus 7, RV208. Two of the other Bach organ concerti in the set I got were likewise listed as borrowing from two different Vivaldi concerti from his Opus 3. Since I don't have either his Opuses 3 or 7, this suggests an avenue for continued research in the future.

Monday, May 13, 2013

The Scale of the Universe

Some time ago I stumbled upon a fascinating website that let you change your scale, from the size of the observable universe down to the Planck length, showing objects of each size as you went up or down. It was absolutely amazing, the exact kind of thing I would love to have created myself, and I meant to share it but lost the address. Thankfully, I stumbled upon it again by chance recently, and get to share it with you now.

Here's the link: The Scale of the Universe 2. Go check it out!

Edit (5/14/2013): It might help if I actually had the right link! Fixed now.

Thursday, May 9, 2013

Partial Eclipse, Wholly Cloudy

Some of you may have been aware that there was a partial solar eclipse today (the 9th) that was visible only in a fairly narrow swath almost entirely over the Pacific Ocean. Since the Moon was close to apogee when it happened, and thus at its farthest point from Earth, it would not have been a total eclipse from anywhere on the Earth's surface (the Moon would have been too small); however, Hawai‘i was in the path close enough to the mid-line to have gotten about a 30% coverage of the Sun.

Unfortunately, despite the day beginning in bright sunshine, by noon it had clouded over, and by three o’ clock when the eclipse would have been most deep it had actually begun to rain (down in Hilo, though the web cam up at the Visitor Center showed a fair bit of cloud cover as well). So I wasn't able to see it this time, in case you were wondering (for the record, that makes the second partial solar eclipse I've been clouded out for since coming here).

Sunday, May 5, 2013

Moons and Months

It's probably not a big surprise to most of you to learn that the words for "moon" and "month" are related in English (and some other languages as well). Our Moon's orbital period of 27 days, 7 hours, and 41.1 minutes comes very close to the number of days you get when you divide the Earth's orbital period by twelve, and makes a nice natural division of time.

But have you ever thought about the moons of other planets? For example Mars' two moons, Phobos and Deimos, orbit their parent planet in just 7 hours 40 minutes and 30.3 hours respectively. Many of Jupiter and Saturn's close-in moons likewise orbit in less than an Earth day. In fact, there are dozens of moons with a shorter orbital period than our Moon.

On the flip side of the scale, there are also dozens of moons with longer orbital periods than our Moon. Jupiter and Saturn both also have lots of small, irregular moons that orbit far from their parent body, which can take months or even years to complete one orbit. Saturn's moon Phoebe, for instance, takes 550.3 days to make a complete circuit, nearly two Earth years. Prior to last week, I knew of a few Jovian moons with orbital periods measured in days in the 600's and 700's. Given Jupiter's humongous mass, you'd expect that it would be able to hold onto satellites further out than other planets, which would have correspondingly long orbital periods.

So you can imagine my surprise when I, on a whim, looked up the satellite with the longest orbital period and discovered it belonged to...Neptune?? And not just by a few days or even a few months – we're talking years here.

In fact, it turns out the four longest orbital-period moons all belong to Neptune. The two inner ones, Sao and Laomedia, have orbital periods of 7.97 and 8.68 years respectively. The two outer ones, Psamathe and Neso, take 24.84 and 26.67 years to orbit Neptune once, respectively.

I found this revelation absolutely mind-boggling. Neither of these moons has completed an orbit since I've been born. They have longer orbital periods than the first five inner planets. They orbit Neptune at a mean distance of around 48-49 billion kilometers (about 30 million miles), which is nearly a third of the distance from the Earth to Sun. At its furthest point, Neso can be further from Neptune than Mercury ever gets from the Sun!

If you wondered, like me, how Neptune and not Jupiter can have the furthest-out and longest-orbiting satellites, it has to do with something called the Hill sphere (named after 19th-century American astronomer and mathematician George William Hill). The Hill sphere is basically the region of space in which an object's gravitational pull dominates the attraction from other objects in the region. For a moon to remain in orbit about a planet, it must remain entirely inside the planet's Hill sphere, or it will eventually be pulled loose by the gravitational perturbations of other planets. This limits how long of an orbital period a moon (or other satellite) can have before it is no longer stably bound to its parent planet. For instance, the mathematics suggests that it is impossible for the Earth to have a satellite with an orbital period of longer than about seven months.

To get to the point, a planet's Hill sphere depends both on its mass, and its distance from the Sun (and other massive sources of gravitational perturbation). Jupiter, of course, is many times more massive than Neptune (and all the other planets combined), but Neptune is several times further from the Sun. Add in the inverse-square nature of gravity, and Neptune manages to eke out a victory in the "largest planetary Hill sphere" competition. (Interestingly, of the four outer planets, Jupiter has the smallest Hill sphere; it increases slightly but steadily in size from Jupiter through Saturn and Uranus on to Neptune. Turns out increased distance from the Sun is more important than decreasing mass.) Neso and Psamathe are orbiting nearly at the outer limit of Neptune's Hill sphere, so they are likely to remain the moons with the longest orbital periods for the foreseeable future.

Of course, they were only discovered in 2002 and 2003, respectively, so who knows what else could be out there! It's an exciting time for us lovers of planetary science and Solar System dynamics.

Anyway, I hope you found that as interesting as I did. If you're interested in other comparisons between the moons of the Solar System, this page on Wikipedia has a nice table that you can sort by various categories.