Monday, March 28, 2011

Mysteries of Mercury

Artist’s rendering of the MESSENGER spacecraft 
orbiting Mercury.

NASA’s MESSENGER probe successfully began orbiting Mercury earlier this month, and as a result some of the enduring mysteries associated with this planet may be solved in the near future. Insights gained by this mission could shed light on how planets were formed in our solar system. MESSENGER stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging, which is NASA’s clever way to tie the mission to Mercury with the Roman messenger of the gods. Launched over six years ago, MESSENGER’s trip has included 15 orbits around the sun and flybys of Earth, Venus and Mercury in order to slingshot into position where, after a 15 minute burn of its main thruster to slow down, it finally settled into orbit on March 18, 2011. 
   Mariner 10, the first and only other probe to approach Mercury, made three flybys from 1974 to 1975. Mariner was able to image 45% of the planet. It also unexpectedly discover that Mercury has a magnetic field. It is thought that planets generate magnetic fields because they have molten iron cores that spin quickly, but Mercury only rotates once every 59 day. Plus it’s so small that its core should have cooled off long ago. MESSENGER will analyze Mercury’s magnetic field which should yield insights about Mercury’s core. One thought is that Mercury’s core is shrinking as it slowly freezes. The planet’s surface is marked with mile-high cliffs that stretch for hundreds of miles and suggest that the planet is indeed shrinking. MESSENGER will look for more such evidence.
   Another mystery regarding Mercury’s core: why is it so large for such a small planet? Scientists believe that its iron core takes up about three fourths of the planets diameter, which is roughly twice that of Earth. Perhaps impacts over billions of years have stripped away Mercury’s surface, leaving only the inner mantle and core untouched. MESSENGER will analyze the planet’s geology which should shed some light on how it evolved. 
   Temperatures on Mercury reach a blistering 425° C, yet at the poles there are deep craters that are permanently shielded from sunlight, and there might be ice deposits hidden away. If so, MESSENGER will be able to detect such an unlikely source of water, not unlike finding an ice cube in an oven. The probe will collect data for one year, and I will be publishing updates as this data gets interpreted and shared with the public.

1) True or false: Mercury has been thoroughly explored.

2) It is thought that planets need _______ to have a magnetic field.
a) a solid iron core  b) a liquid iron core  c) a rapidly rotating iron core  d) both b) and c)

3) True or false: MESSENGER has detected ice at Mercury’s poles

4) Mile-high cliffs on Mercury are thought to be evidence that the planet is ______________.
a) shrinking  b) very hot  c) small  d) both b) and c)

5) The first probe to visit Mercury was ________________.

Saturday, March 19, 2011

Nature’s Ultimate Commuter

The Arctic tern is an elegant flyer performing an annual 
long-distance migration between the Arctic and the 
Antarctica. Photo: Carsten Egevang/

The Arctic tern is a medium-sized seabird, white with a black head and a bright orange beak. It has long, slender wings, and is an elegant flyer, but its legs are short which makes it clumsy on the ground. Its diet consists of small fish, insects and invertebrates. Arctic terns have been known to live 30 years or longer and their current population is estimated at about one million.
   The Arctic tern is nature’s ultimate commuter. This seabird migrates from its northern breeding grounds in Iceland and Greenland to the Southern Ocean around Antarctica and back, seeing two summers each year. This circumpolar trip of about 70,000 km is the longest yearly migration in the animal kingdom. Over the course of its lifetime, the Arctic tern flies a distance six times greater than the distance from the Earth to the Moon. Starting its trip in August, it pauses for a month in the mid-Atlantic Ocean where it fuels up on a rich supply of fish before continuing on to its winter habitat in Antarctica, arriving in December. In spring it returns north to Iceland and Greenland to nest. Once it has nested it starts out on another long southern migration.
   While flying long distance, the Arctic tern is able to put half of its brain to sleep while the other half remains alert and functioning. This is call unihemispheric sleep—the bird will actually sleep with one eye open and half of its brain awake, and it is able to use this ability at will.
   Arctic terns live together in colonies of about 50 birds. The male tern will court a female by taking a small fish in its bill and making a low pass over the female on the ground. If successful in attracting her attention, she will join him in this “fish flight” and they will soon mate. Both parents help incubate the eggs which hatch about 23 days after being laid. Chicks will leave the nest and hide from predators in nearby vegetation. The parents catch small fish for the hatchlings until they can feed themselves, but in recent years up to 90 percent of the tern chicks have died from hunger when food sources are not plentiful.
   Arctic terns are not fond of swimming and will do everything possible to stay out of the water. They hardly ever land. Most of the time they eat while flying, either swooping down to catch their fish, or catching insects on the wing.

The Arctic tern’s migration patterns, from the breeding sites in Greenland 
and Iceland to the winter grounds at Antarctica. The southbound migration 
is indicated by yellow lines with a month-long pause in the North Atlantic 
(small circle) before continuing to Antarctica (large circle). In spring, the 
northbound migration indicated by the white line is more than twice as fast.

1) True or false: The Arctic tern sees more sunlight in a year than any other creature on Earth.

2) A migration that includes both the Arctic and Antarctic regions is known as __________.

3) True or false: Arctic terns, while clumsy on land are excellent swimmers.

4) “Fish flight” refers to the Arctic terns’ _____________.

a) ability to catch fish during flight  b) mating ritual  c) migration  d) both a) and c).

5) The ability of terns to sleep with one eye open and half of their brain awake is called ______________________  sleep.

Thursday, March 10, 2011

Why Dark Matter Matters

Surprisingly, only about one sixth of all the matter in the universe can be accounted for through observation. For example, when astronomers measure the hot gas clouds in the outer portion of galaxies they can calculate how much gravity that galaxy must have in order to keep the gas from escaping. Comparing that with how much matter is actually observed in the galaxy they come up short by a factor of five or six. This undetectable mass is called dark matter. Some of this dark matter is in the form of very dim dwarf stars, cold gas clouds, unlit planets or even black holes. These are called MACHOs (MAssive Compact Halo Objects). The halo refers to the outer part of a galaxy that extends beyond what is visible. Think of a large planet like Jupiter, for example. It can only be seen because it reflects the light of the Sun. If Jupiter was set adrift through interstellar space it would only be indirectly observable by its gravitational effect. When a MACHO passes in front of a background star, its gravity bends the starlight around it which causes the star to briefly shine much brighter. This focusing of the star’s light is called gravitational lensing. Astronomers have searched the skies for evidence of MACHOs by gravitational lensing, and it does not account sufficiently for the missing mass.
   Another type of dark matter consists of theoretical particles which are yet to be detected. They are called WIMPs (Weakly Interacting Massive Particles), and astrophysicists are hoping to bridge the missing matter gap by finding evidence of their existence. Because WIMPs only interact through gravitational and weak forces, they are quite difficult to detect. Billions of them could pass through the Earth every second without leaving a trace. There are many experiments currently underway to detect WIMPs either directly or indirectly.
According to the Big Crunch theory, the universe 
will end in an infinitely dense singularity.
   There is much we don’t know about dark matter, yet the eventual fate of the universe depends on how much of it there is. We know that the universe has been expanding since the Big Bang, but will it continue to do so forever? That depends on its total mass which counteracts the expansion through gravity. With enough dark matter it will eventually collapse back in a Big Crunch. Otherwise, our universe will keep expanding forever and likely end in a Big Freeze. But don’t worry too much—either fate is at least 15 billion years away.

1) True or false: Most of the matter in the universe is dark matter.

2) MACHOs can be detected by their _________________.
a) reflection  b) magnetic field  c) spectral signature  d) gravitational effects

3) True or false: MACHOs are theoretical particles.

4) WIMP stands for __________.
a) Weakly Involved Massive Planets  b) Wandering Interactive Micro Particles c) Weakly Interacting Massive Particles  d) Wandering Irradiated Micro Planets

5) Two eventual fates of the universe are ________________.

Wednesday, March 2, 2011

The Melting Spoon

Scientists can have a rather odd sense of humor. Take, for example, the chemistry professor demonstrating to his class how strong a beaker full of acid is by using it to dissolve a spoon. Then, a minute later, he absentmindedly grabs the very same beaker which he left sitting next to his glass of water and starts drinking from it—much to the horror of his students. Miraculously, though, he is unharmed. What just happened? Well, the acid was really just a cup of hot water. And the spoon didn’t really dissolve, it just melted and formed a metallic puddle at the bottom of the beaker. You see, the spoon was made of gallium instead of steel. And gallium (atomic number 31) has a melting point of only about 30 °C (85 °F)!
Crystals of 99.999% pure gallium.
  Gallium is primarily refined for the electronics industry, and 98% if the gallium consumption in the U.S. is for the production of semiconductor materials for electronic components such as integrated circuits. Gallium’s boiling point is very high, approximately 2,400 °C, which makes it the ideal substitute for mercury (which boils at 357 °C) in high-temperature thermometers capable of monitoring the core of a nuclear reactor.
  The largest amount of gallium ever collected was for the neutrino detector at the Baksan Neutrino Observatory in Russia. This detector contains over 50 metric tons of pure liquid gallium and is located 3,500 meters underground to shield the experiment from cosmic rays. It is used jointly by Russian and American physicists to detect Solar neutrinos—ghostly particles that rarely ever react with matter, and pass through the entire earth without leaving a trace, But at this detector they will occasionally cause a few atoms of gallium to change to germanium which can then be extracted and measured. These low-energy particles, made by the main fusion reaction that provides the Sun’s energy, have not been observed in any other way. Many measurements of solar neutrinos were made this way, and from this data scientists have discovered a large deficit of neutrinos from what is mathematically predicted by the Standard Solar Model. Looks like the joke is on them.

1) True or false: Gallium is solid at room temperature.

2) Gallium is often used in the production of ______________.
a) jewelry  b) integrated circuits  c) telescopes  d) neutrinos

3) True of false: The gallium neutrino detector at Baksan confirms the Standard Solar Model prediction on neutrinos.

4) If a neutrino reacts with an atom of gallium, it cause it to change to ______________.

5) The main reaction that provide’s the Sun’s energy is called ______________.