Sunday, November 27, 2011

The Jets of Enceladus

The jets in the southern hemisphere of Enceladus 
taken by the Cassini spacecraft in 2005.

I’ve always been intrigued by the moons in our solar system. Each has a unique personality. Take Enceladus for example. In 2005, while orbiting Saturn, the spacecraft Cassini observed this unique moon up close for the first time. It seems peaceful enough with an icy surface on its south pole. Without warning, geysers of water and ice are ejected, blasting hundreds of kilometers into space at over 2,000 kph, making it the largest snow-making machine in the solar system. The spray of icy particles coat the small moon, giving it a clean, white surface. It is the most-reflective body in our solar system.
   Enceladus has a frigid atmosphere, but it must have a liquid ocean beneath its icy surface. We know this because Cassini was able to capture and analyze the ice particles on several of its flybys, and it discovered that the ice was salty. So the ice must have come from salty ocean water since if it were surface ice there would be very little salt in it. Ocean water is ejected and freezes to form ice particles when it hits the frosty atmosphere. The subsurface water is heated enough to remain liquid through a combination of tidal heating and radioactive decay. Enceladus has a slightly elliptical obit of Saturn which causes gravitational flexing, generating heat. And where there is liquid water, you have environmental conditions favorable to the emergence of life.
   It is also thought that Saturn’s outermost ring, known as its E ring, is supplied by the material from the jets of Enceladus. Enceladus orbits in the densest part of the E ring. In 2009, Cassini found salty ice grains in Saturn’s E ring. About 200 kilograms of water vapor is ejected every second in these plumes. Smaller amounts of ice grains are also ejected. Without the Cassini mission which can sense these compounds in its close flybys, we would never know just how fascinating this moon is.

Thursday, November 17, 2011

A Turkey Tall Tale

Navigating the blood-brain barrier is tricky business.

With Thanksgiving just around the corner, it’s only fitting we examine the age-old belief that eating turkey makes you drowsy.
Turkey contains tryptophan, an amino acid that the human body doesn’t produce naturally. Tryptophan is essential to good health and must be acquired through diet. L-tryptophan is metabolized by the body to create serotonin and melatonin, neurotransmitters that act as calming agents in the brain and regulate sleep. So its easy to see why the turkey gets blamed when you’re snoozing on the couch after dinner, but it’s not so simple.
Metabolism of L-tryptophan into serotonin
and melatonin. Transformed functional
groups after each reaction shown in red.
  First off, turkey contains about the same amount of tryptophan as most other meats, 0.24 grams per 100 grams of food. Our bodies only need about 0.2 grams per day, and we get more than five times that amount in an average meal. So eating turkey is not going to make a huge difference in and of itself. If one were to consume pure tryptophan on an empty stomach, then yes, it would make you drowsy. But you would have to take it as a supplement. In turkey, however, it’s only one of several amino acids and must compete to cross the blood-brain barrier. And because it has a large molecular weight, it’s not easily absorbed.
  So what is making you drowsy after your Thanksgiving dinner? Carbohydrates, mostly. Carbohydrates cause the pancreas to produce insulin. When this occurs, some of the competing amino acids leave the bloodstream and enter muscle tissue. This causes a relative increase in the concentration of tryptophan in the bloodstream. The tryptophan is carried to the blood-brain barrier through glucose transporters (GLUTs). Some of it then crosses the barrier and is metabolized first to serotonin and then melatonin which makes you sleepy.
  There are other factors involved in the conspiracy to make you miss that last quarter of football. Eating two days worth of food in one meal will have an effect. Your body will have to direct more blood flow to aid in digestion at the expense of your other organs, including your nervous system. If you drink alcohol with your meal it will act as a depressant and increase your drowsiness. Fatty foods will also slow down digestion and sap your energy. Maybe the best course of action is to just sit back, relax, and let Mother Nature take its course.

Monday, November 14, 2011

The Science of Sue

Sue the T. rex. Notice the wishbone or furcula (circled),
the first such bone ever found on a T. rex.

Sue, the world’s biggest, most complete, and best preserved T. rex ever found, has been visited by millions at The Field Museum in Chicago. Many of Sue’s bones have rarely or never before been found in a T. rex. Plus, at 90% complete, Sue’s skeleton provides scientists with the unusual opportunity to reconstruct what T. rex may have looked like and how it moved when alive. Finding most of the bones from a single specimen gave scientists excellent detailed information about Sue’s anatomy and biology.
   T. rex is know for its tiny forelimbs, and Sue’s right arm is only the second nearly-complete arm ever found. It will help scientists better understand the strength and motion of this oddly small appendage. Sue’s arms are about the same size as human arms, making them too short to reach her mouth. Yet the bones are quite thick which indicates they would have been very powerful. Current thinking is that the arms were more useful to T. rex in its early life when it would have been proportionately larger.
   If you do visit Sue at the Field Museum, you won’t see all of her bones attached. For example, there are long thin bones that were formed just beneath Sue’s skin on her belly called gastralia. They are different from her ribs and scientists are trying to figure out their positioning and how they should be attached. They might have helped her breathe or perhaps they helped protect her internal organs. Usually, these delicate bones are incomplete or missing, but Sue has about 75% of her gastralia intact.
   Sue’s has a wishbone or furcula in her chest. This bone is the first ever found on a T. rex. Only carnivorous dinosaurs have a furcula and it’s one of the many links between dinosaurs and birds.
   The tail on Sue is the most complete tail ever found on a T. rex. A complete tail allows for an accurate measurement of the animal’s length.
   Perhaps the most significant part of Sue’s skeleton is her skull, and Sue’s is one of the most complete and best preserved T. rex skulls ever found. Its structure and arrangement provides some of the best clues about how Sue lived and related to her environment. Before being put on display, Sue’s skull spent 500 hours inside a powerful CT scanner. As a result, scientists can now learn about the structure of T. rex’s brain. These CT images show Sue’s brain cavity. The brain itself was about the size and shape of a big sweet potato. Sue had large olfactory bulbs and sinus cavities indicating she had a strong sense of smell which would have been important for hunting or scavenging for food.

Sunday, November 6, 2011

A Dinosaur Named Sue

Sue the T. rex, on display at the 
Field Museum in Chicago.

This is a story about a T. rex names Sue. In her 28 years of life she suffered many injuries and illnesses. A careful study of her bones tell us much about the hard life she lived. She suffered nine broken ribs, torn ligaments, infections and arthritis. Yet what probably killed her was a parasite. Holes in her lower jaw indicate she may have suffered from trichomonosis, a killer of modern-day birds of prey. If Sue had this disease, as indicated by the holes, it would have caused a serious infection in the back of the throat, making it very difficult to eat and breathe. So even if she did survive the infection, swallowing would have been so painful that she would have likely died of starvation. A difficult end to a difficult life.
   Fast forward 67 million years to the summer of 1990. Fossil hunter Sue Hendrickson was working near Faith, South Dakota, for the Black Hills Institute, a commercial fossil-collecting team. They were digging at the ranch of Maurice Williams and discovered that one of their trucks had a flat tire. While the team went into town to get it fixed, Sue stayed behind to investigate a weathered bluff she had noticed previously. Quickly she found some bone fragments that had fallen down the hillside. Looking to see where they fell from, she saw several vertebrae exposed in bluff face. Sue immediately knew they were bones from a large carnivorous dinosaur, possibly a T. rex. When her team returned, they verified her findings and named it Sue in her honor.
   After the Black Hills Institute finished excavating Sue, they knew they had an incredible specimen, possibly the best ever found. Sue was unique because she was so large and well preserved. Over 90% of her bones were intact. As word of their discovery spread, a fight erupted over the ownership of Sue. The Black Hills Institute had paid Mr. Williams $5,000 for permission to dig on his land and believed they owned the fossil. But Mr. Williams claimed that the money was only for permission to dig. And because the property fell within the boundaries of a Sioux reservation, the tribe also claimed ownership. Even the federal government became involved to determine if Sue had been found on federal land, launching an investigation against the Black Hills Institute. Meanwhile, Sue was locked away awaiting a decision as to who owned her. In the end, after a five-year legal battle, a judge determined that Sue belonged to Mr. Williams who promptly decided to sell Sue to the highest bidder.
   On October 4, 1997, Sue was put on the auction block at Sotheby’s in New York. In just eight short minutes Sue had a new owner. The Field Museum in Chicago bought Sue for a record $8.36 million. Sue made her public debut on May 17, 2000. The culmination of ten years of effort had finally brought the world’s biggest, most complete, and best preserved T. rex to a public stage and Sue’s fans were elated.
   Next week we’ll finish up our story about Sue and discover what has been learned since she has been in the care of the Field Museum.