Presenting: The Milky Way

It was only a lifetime ago, in the 1920s, that Edwin Hubble and others discovered galaxies as we know them today. Prior to that time, it was assumed that all stars in the Universe were part of our "Milky Way" galaxy. Hubble's red shift measurements and new methods of distance measurement proved that many of the nebulous objects known to astronomers were really huge galaxies in their own right. (A third of the over-100 objects on Charles Messier's famous 18th-century list turned out to be galaxies.) Taking advantage of new photographic emulsions, large telescopes at Mount Wilson, Lick Observatory, and Mount Palomar were pioneers in imaging galaxies near and far. They shaped the image of what a typical "spiral galaxy" looked like, so no explanation is needed when such an object appears in science or science fiction media. New telescopes and CCD technology do an even better job of imaging galaxies -- with Edwin Hubble's orbiting namesake the most well-known to the public. But there is one important, nearby galaxy that is difficult to image: the Milky Way itself.

The Milky Way: dust and stars.  Credit: John Carpenter and Robert Hurt of the 2MASS Project

It is the classic case of not being able to "see the forest" because of all the trees. From our Solar System's (disad)vantage point in the galaxy's plane, it is hard to discern details of stellar distribution -- the galaxy's shape. A large part of the problem is due to clouds of dust and gas obscuring the view. Years of effort has concluded that the Milky Way is similar to other spirals in the Universe. But a description is not the same as having a picture to point to.

Now we have a picture to point to. Telescopes on Mount Hopkins in Arizona and Cerro Tololo in Chile have been imaging the sky as part of the Two Micron All Sky Survey (2MASS). This is a survey of the celestial sphere in the longer-than-visual wavelength of infrared light. "Two Micron" in the name of the project is a wavelength of light in the infrared. This wavelength bypasses dust particles instead of being absorbed by them. This is what allows infrared technology to detect people and hot spots through dense smoke. Warm objects, including the 2MASS detectors, emit infrared light.  So the 2MASS detectors are chilled to super-cold temperatures to prevent interference.

But displaying an infrared view of the Milky Way is not as simple as pasting together images of all 500-million stars detected by the survey. The computer-generated map, shown above, is based on the three-dimensional placement of 30,000 "carbon stars", as they would appear from a viewpoint above the galaxy's central disk. Carbon stars have long ago fused away their original hydrogen allotment and continue to fuse heavier elements. They are left with carbon "ash" in their cores; that causes a distinct carbon signature in their spectrum. The key value of carbon stars is that all have about the same intrinsic brightness -- so distance to a carbon star is determined on a simple brightness scale. Hence the carbon stars tell us the distribution of stars behind the visually obscuring dust and gas in the galaxy.

More information:
University of Virginia; Jan. 9, 2002; Press Release: "Infrared Sky Survey Yields A Bird's-Eye View Of Our Home Galaxy"

Administration's NASA Budget Nixes Pluto and Europa

The good news: President Bush's proposed 2003 NASA budget adds a half-billion dollars to what the agency got in 2002. The bad news begins for fans of the Outer Planets program: probes to Pluto and Jupiter's moon Europa would be scrapped. The budget axe even swung into Earth orbit with a huge $230-million cut in the International Space Station budget, funded at $1.7-billion last year. This was not unexpected, due to criticisms of cost overruns in the program. The Space Shuttle Transportation System was not immune, suffering a small $65-million cut from last year's $3.3 billion budget.

Nuclear Generators and Ion Drives To date, all outer planet missions have relied on chemical rockets to give probes a single massive push away from the Earth. The probes then spend years gliding through space, making small correction maneuvers with onboard systems. Often the probes will use "gravity assist" techniques -- through encounters with other planets -- to obtain the necessary energy to make it out to the objective. This constrains a mission's launch date to certain "windows" of planetary alignments. For example: the Cassini probe spent almost two years dashing between Earth and Venus to built-up speed for a gravity encounter with Jupiter, with its objective being the more distant planet Saturn. These Earth/Venus gravity assists gave the mission a boost that was equivalent of expending 75-tons of rocket fuel -- but it still took over three years to reach Jupiter.  RTGs on Pioneer 10 have been operational since 1972.  NASA Cassini, like all the major planetary missions past the orbit of Mars (including Pioneer, Voyager, and Galileo missions), relies on radioisotope thermoelectric generators (RTGs) to provided electricity for operations. They generate electricity from the heat of radioactive decay. RTGs have a great cost and weight advantage over photovoltaic cells widely used in the vicinity of Earth and the near planets: solar energy drops off with the square of the distance from the Sun. For example, a parking-space sized solar panel in Earth orbit would have to be the size of a 1,600 car parking lot to provide the same amount of power in the region of Pluto and the Kuiper Belt -- 40 times further from the Sun than Earth.  Deep Space 1 - NASA NASA and the space industry have decades of experience with ion drives in the lab and for satellite station-keeping. Ion drives are an order of magnitude more efficient than chemical rockets: they deliver a higher thrust per fuel mass expenditure. Unlike the large, short-duration "burns" made by chemical rockets, current ion drives expend fuel slowly -- over the course of months and years -- building up speed gradually. Theoretically, if they operate long enough, they'll reach speeds greater than provided by chemical rockets. The recent success of the Deep Space 1 probe proved the viability of the technology for main propulsion in long-duration missions.  NASA appears to be ready to take the "next step" and combine RTG-like power systems with the ion drive to form radioisotope electric propulsion (REP) systems. The dependable electric power from radioisotope decay will deliver the steady thrust it takes to reach the outer planets.

If the cuts to Pluto and Europa stand, it means the entire Outer Planets program will be wiped out. Then again, the probes might not be completely axed in the end: proponents of the Outer Planets program have the ear of Congressional appropriations committees. This allowed NASA enough funds to continue proposal work on a Pluto probe last year, even after the administration cut it out of the budget. Since it was part of the budget last year, the decision to can the Europa probe is a surprise.

The administration plans to replace the Outer Planets program with a "New Frontiers" program. NASA will set the science goals and a budget cap of $650-million for each mission; missions will be flown every three years. Interested organizations will submit mission designs that meet these requirements; winning designs will receive further funding before a final selection is made. For Summer 2003, there will be $15-million available in "seed money" for proposal-winning research. Unfortunately, full funding does not begin until 2005 or 2006, so the current Outer Planets missions cannot be reconfigured and funded as New Frontier programs.

"We want to develop steam engines to get the locomotives out there to explore the solar system."
 -- Ed Weiler, NASA Office of Space Science Associate Administrator 

Pluto did get a mention at the budget's press conference. NASA Administrator Sean O'Keefe said: "the objectives of space exploration are limited by our capacity to overcome distances -- to go to the far reaches of our Solar System to observe Pluto for example." As part of the O'Keefe's "back to basics" policy, he wants NASA to develop new propulsion technologies to cut the travel time to Solar System bodies. Office of Space Science Associate Administrator Ed Weiler concurred that our current means of reaching into space is akin to "covered wagons" in terms of speed. "We want to develop steam engines to get the locomotives out there to explore the solar system," says Weiler. NASA's new propulsion push will be to combine two proven technologies: nuclear thermal generators to provide electricity for ion drives.

The final say on outer planet exploration and the propulsion initiatives will be determined in the yearly tug-of-war, known as the "budget process", between Congress and the President.

More information:
SpaceDaily.com; Feb. 11, 2002; Outer Rim: "A Plutonic Commitment To Space" 
SpaceRef.com; Feb. 5, 2002; News: "NASA's Budget: Back to the Future - and to Basics" 
CNN.com; Feb. 5, 2002; Space: "NASA Budget Cuts Human Flight, Pushes Nukes"

Gold Star

The Sun imaged by the SOHO spacecraft's Extreme Ultraviolet Imaging Telescope. ESA/NASA

While every cloud may have a "silver lining", the stars may be filled with gold. That's right, the element gold was discovered in an ancient star -- "BD+17 3248" -- on the outskirts of our galaxy. And it's not alone in bearing that element. Though gold has been detected in our own Sun, BD+17 3248 formed when the galaxy was only a half-million years old. The presence of gold -- in a 15-billion year-old star and our 5-billion year-old Sun -- indicates the element has been present since our galaxy's infancy.

Under current models, neither the star nor our Sun could have produced the gold detected in their atmospheres: only the supernova explosion of massive stars produces gold in great abundance. This gold debris infuses into hydrogen clouds that form new stars. So the amount of gold detected in a star tells us something about the history of the generations of stars that came before it. Other elements detected in BD+17 3248 include silver, platinum, radioactive thorium, and perhaps uranium -- each gives clues to the age of the star and the composition of the stellar cloud it emerged from.

Even if every star contains some gold, detection is not easy. Detection of gold in a star other than our Sun is the result of over two-decades of research. Researchers believe it was worth the effort for the information it will bear on the evolution of stars and the galaxy. Timothy Beers of Michigan State University is one of the astronomers that conducted the research. "The discovery of gold and other interesting elements in this star reaffirms our picture that the story of the creation of the elements is written in the atmospheres of these ancient stars," he says. "The most exciting thing is that we are finally in a position to begin reading, and understanding, this intriguing history."

How much gold does BD+17 3248 contain? The estimated value is 7-billion trillion dollars -- at the current rate.

More information:
Michigan State University; Jan. 10, 2002; Press Release: "Astronomers Discover Gold in Ancient Star"