Winter 2008 - Volume 37, Number 1
Table of Contents
[14] The Mystery of Dark Energy, Robert Naeye
Contrary to expectations, the expansion of the universe is accelerating. The force behind this acceleration has a name -- dark energy -- but to date, little else is known about it.
[20] Melted Crumbs from Asteroid Vesta, Linda M.V. Martel
Micrometeorites found at the bottom of a South Pole water well are giving researchers clues as to the chemical composition of a distant asteroid.
[24] Astronomy in the News
From a new age for Saturn’s rings to colliding white-dwarf stars and a new appreciation for the evolution of galaxies, here are some of the latest discoveries that have recently made news in the astronomical community.
Departments
[4] Editorial, Paul Deans
Turning Points
[5] First Word, Jim Manning
Shadow Play
[7] Astronomer's Notebook, Jennifer Birriel
Type Ia Supernovae Progenitors
[8] Planetary Perspectives, Daniel D. Durda
HDTV Earthrise
[9] Armchair Astrophysics, Christopher Wanjek
UHECR . . .
[10] Echoes of the Past, Katherine Bracher
Comet Holmes
[11] Annals of Astronomy, Clifford J. Cunningham
John Dee at 400
[12] Education Matters, David Bruning
What Do We Keep?
[13] Societal Impact , Vivian White and Tierney O’Dea
Slooh for Schools
[28] Book Corner
Disney Learning: Wonderful World of Space by Andrew Fraknoi
[30] Reflections
Pickering's Triangle
[32] ASP 2008 Meeting, Andrew Fraknoi
Preparing for the International Year of Astronomy
[35] Society Scope/ASP Supporters
[40] Sky Events, Richard Talcott
The Mystery of Dark Energy
by Robert Naeye
Ten years ago a startling discovery stunned the astronomical community. Contrary to expectations, the expansion of the universe is accelerating, and remote galaxies are speeding away from us so rapidly that they will someday disappear from view. This finding was so profound that it has revolutionized our understanding of the universe's past, present and future.
To picture the effect of a runaway universe, imagine an inflating balloon that can grow for eons without bursting. At first, an operator pumps air into the balloon at a constant rate, causing it to inflate in a smooth and steady fashion. As the operator ages, the pumping slows and the balloon's rate of expansion also starts to slow. But after a few billion years, the operator's teenage son takes over and cranks up the pressure. Suddenly, the balloon begins expanding faster and faster. This scenario is somewhat analogous to what's happening today.
Michael Turner of the University of Chicago coined the term "dark energy" to describe the unknown force that is hastening cosmic expansion. Whatever it is, dark energy makes up the bulk of the universe's mass-energy budget — about 74%. Of the rest, 22% consists of dark matter and a mere 4% of the cosmos contains the type of matter we can actually see. To put it another way, scientists are in the same position with respect to dark energy as someone who has no idea what water is despite the fact it covers more than 70% of Earth's surface. Explaining dark energy's nature is one of the greatest challenges in modern physics.
Melted Crumbs from Asteroid Vesta
by Linda M.V Martel
Micrometeorite bombardment accounts for almost 30,000 tons of material entering Earth's atmosphere each year. Though most of the material evaporates during entry or is lost at sea or falls on the land unnoticed, thousands of micrometeorites have been collected successfully from deep-sea sediments, from the snow and ice of the polar caps, and now from a water well at the South Pole.
If you think it's cold where you live, consider this cool little story about ice...Antarctic ice...studded with minuscule grains from the cosmos. Researchers are studying extraterrestrial materials that are particles and spherules less than a millimeter in size but whose combined mass accounts for about 1,000 tons of new stuff added to Earth yearly. A micrometeorite is generally defined as a tiny meteorite larger than 50 micrometers but smaller than a millimeter. Micrometeorites that have either partially or completely melted when plunging through Earth's atmosphere are called cosmic spherules.
Just as the Antarctic blue ice serves as an ideal collector of meteorites, it also preserves micrometeorites and cosmic spherules that land on the surface and are subsequently incorporated into ice layers.
Astronomy in the News
MESSENGER's First Look at Mercury's Previously Unseen Side
NASA / JHUAPL
When Mariner 10 flew past Mercury three times in 1974 and 1975, the same hemisphere was in sunlight during each encounter. As a consequence, Mariner 10 was able to image less than half the planet.
On January 14, 2008, the MESSENGER spacecraft observed about half of the hemisphere missed by Mariner 10. Other images obtained during the flyby will reveal surface features in color and in much more detail. Collectively, these images and measurements made by other MESSENGER instruments will soon provide a detailed global view of the surface of Mercury, yielding key information for understanding the formation and geologic history of the innermost planet.
