Pick a Crater, Any Crater!

Space.com; Feb. 12, 2001, News: "NASA Wants You ... To Identify Martian Craters" 

Mars Clickworker logo -- NASA

As a "clickworker" George Jetson of 1960's cartoon fame complained about his "button clicking finger" at work.  With the introduction of the personal computer and the Internet that cartoon jab at the future is now a reality.  But instead of killing time in chat-rooms or surfing the 'net why not be a clickworker that contributes to planetary science?

Since mid-November a test project has allowed anyone with an Internet connection to do Mars crater science.  The interactive online Clickworkers project allows volunteers to identify and classify craters imaged by the Mars Viking orbiter [News Flash! High-resolution Mars Global Surveyor images are now part of the project!].  The test is "to see if public volunteers, each working for a few minutes here and there, can do some routine science analysis."  And it doesn't hurt that the project saves taxpayer's money and relieves scientists to work on other projects.

According to Bob Kanefsky, who designed and oversees the project, no scientific training is required: "The whole idea is to see if non-scientists can help with the 95 percent of the task that requires only basic human abilities like recognizing pictures. If you know a mountain from a hole in the ground, you can be a crater-marking clickworker."

ID'd craters -- NASA

On a daily basis 8,000 to 12,000 craters are analyzed.  About 37% percent of the work is done by one-time visitors and the rest by returning volunteers.  The volume of work can be credited to the ease of participation: no software downloading is required, once you see a crater you can identify it by making four mouse-clicks around the rim.  A red outline of the crater appears to confirm your clicks match your intentions.  There is an on-line tutorial for those that want to try their hand at crater classification.  The classification system works by showing volunteers a crater and letting them decide if it is a fresh, degraded, or ghost crater based on visual examples of these classes .

So far the low-budget $40,000 project has generated 300,000 crater-marking entries and over 80,000 crater-classification entries.  If the project works, permanent funding may be allocated to allow it to continue on a regular basis using images from recent and future Mars missions. 

Milky Way's Uranium Clock is Ticking

European Southern Observatory; Feb. 7, 2001; Press Release: "How Old is the Universe?"

The Big Bang at the instant of cosmological creation was responsible for creating the hydrogen, helium and lithium elements in the Universe.  These elements formed the first generation of stars.  Stellar fusion reactions and nova explosions from that first generation produced and spread heavier elements throughout space.  As detected in their spectral lines, stars formed in succeeding generations start life with traces of these heavier elements.  

The age of a star can be determined by searching these spectral lines for the presence of radioactive isotopes and their stable offspring.  Comparing the relative strengths of these lines indicates how much of the isotope has decayed since it was incorporated in the star.  Because decay-rate ("half-life") is an immutable property of an isotope -- not affected by stellar evolution -- the relative quantities of these elements can be converted into the length of time that has passed since the star formed from nova explosion debris of a prior generation.

Finding the suitable radioactive "chronometer" isotope in a star's spectrum is a problem.  Chronometer isotopes must have a long half-life to allow measurable amounts of the original isotope to exist over the possible time-span of the star.  This can be the age of the Universe -- perhaps 15-billion years.  On the other hand the half-life must not be so long as to make decay detection impossible.  Uranium-238, with a half-life of 4.47- billion years, it a good chronometer for determining a star's age.  Unfortunately a typical star's uranium spectral line is very weak for this rare element and normally blotted-out by the spectral lines of more common elements. 

A large spectral survey over the previous several decades has uncovered hundreds of stars in our galaxy with very low metal content.  These "metal-poor" stars must have been formed in more "pristine" conditions early in the history of our Milky Way galaxy.  Containing a 1000 times less of the common elements than our Sun, the spectra of rare uranium lines is much easily discerned in these stars.  A team using the European Southern Observatory's Very Large Telescope (Chile) with a highly efficient spectrograph is studying these stars to determine their composition and age. 

CS 31082-001 -- ESO

The first star in this observation program yielded an abundance of faint lines from rare heavy elements.  The spectrum was unusually free of interfering lines from the more common elements.  The 12th-magnitude target star -- designated CS 31082-001 -- contained the spectral line of singly ionized uranium in the near-ultraviolet region of the spectrum.  Analysis indicates that the uranium has decayed by a factor of eight since this star was born, indicating an age of about 12.5 billion years.  Hence our galaxy must be at least that old.

More stars are being examined for their uranium spectral lines.  It is thought they will also show similar ages and help pin down the age of our galaxy and set a lower limit for the age of the Universe. 

This research was published in the February 8 issue of the journal Nature.

Skeletons in Milky Way's Closet

John Hopkins University; Jan. 8, 2001; Press Release: "Survey's early results hint at galactic fossils"

Milky Way -- NASA

A current movie depicts a man who's name rhymes with his obsession: Hannibal the cannibal.  While Hannibal is widely known to have many skeletons in his closet, who would have thought that the wholesome sounding "Milky Way" galaxy had the same compulsion in its past?  Just as Hannibal may hide the evidence of his deed behind a full belly, some astronomers now think a puffed-up feature in our Milky Way is the remains of a cannibalistic galaxy meal.  Astronomers conducting the "2dF Old Stellar Population Survey" at the Anglo-Australian Observatory in Australia revealed this evidence at the recent American Astronomical Society meeting in San Diego. 

According to co-investigator Rosemary Wyse of Johns Hopkins University, "The Milky Way is a fairly large galaxy, and we believe it was formed by the merging of a number of smaller galaxies."  Galaxy formation theory is dominated by non-stellar matter that can't be directly detected by astronomers.  This cold, dark matter theory "predicts that big galaxies started off as small ones which merged together.  But it also predicts that lots of the small galaxies survived this process. And we do not see nearly as many small ones left as are predicted to survive," says Wyse.  For instance the Milky Way has approximately 10 satellite galaxies, but cold, dark matter theory says that 30 to 100 satellite galaxies should be present.

While most of the stars in the Milky Way follow circular orbits in the plane of the galaxy, there exists a "thick disk" of stars that orbit above the disk.  This could be the historical legacy of a massive satellite galaxy that pumped orbital energy into the Milky Way as it was being consumed 10-billion years ago.  This initial result is based on 1,500 sun-like stars studied by the survey.  In total the study will determine the composition, distance, and movement of 10,000 Sun-like stars in an attempt to map out structural details in parts of the galaxy.  The bulk of these stars are away from the disk of the Milky Way. 

Surveying these stars may reveal telltale clues of the Milky Way's cannibalistic past.  "Just as the tidal interactions between the moon and the Earth cause distortions, there's going to be tidal interactions as a satellite galaxy comes into the Milky Way, and those can be severe enough to actually tear mass off the outer parts of the satellite galaxy," according to Wyse. "Those stars should be left behind on an orbit that is similar to the orbit of the satellite galaxy at that time."  The stars from the devoured galaxies may also reveal themselves by unusual composition compared to Milky Way stars. 

That  the last significant galactic merger for the Milky Way happened when the Universe was maybe a third of its present age is an important result for theories of galaxy formation and cosmology.

Squaring Circle May Reveal Earth-size Planets

New Scientists; Feb. 7, 2001; Press Release: "Squares could make planets more visible"

From the public's point of view the "planet hunters" must have the coolest job in astronomy.  Media sources happily tout the news of Jupiter-size planets orbiting other stars.  Multi-planet discoveries -- no independent verification needed -- are "in" with the news media.  But faddish media is cooling to the discoveries of new Jupiter-size planets: they are becoming too common now.  The next "big thing" to catch the media's attention may be the discovery of Earth-like planets outside the solar system.     

Unfortunately small planets won't cause the positional or spectrographic wobble in a star that is used to detect the gas giants.  Spotting them directly using current imaging systems is out of the question.  These planets are estimated to be a billion times dimmer than their sun and telescope optics diffraction creates a blur around star images that mask these planets out of the picture.  Research shows that infrared imaging could help overcome this light deficit: in that part of the spectrum a planet appears only a million times less bright than a star.  But now a better idea has been proposed, one that will make terrestrial planet hunters "cool" with the media -- but they'd have to be a bit of square to employ it. 

"This could be a big breakthrough."
 -- astronomer Frank Shu at UCal, Berkeley