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Ad Astra
Volume 15, Number 2 March/April/May 2003

Mission Control
Spacebeat

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Dodging Those Great Balls of Fire
Getting slammed by a kilometer-wide space rock—the kind that doomed the dinosaurs—is a little less dicey than once thought according to new research from asteroid hunters. However, they warned that close encounters of the worst kind with smaller meteors could still leave a deadly trail of destruction. “Most of our attention has focused on the bigger guys which can cause global damage, but the mean time of them occurring is about 700,000 years,” said Peter Brown, an astronomer and author of a study published in Nature. “However, the smaller guys can cause significant regional damage and do it much more often,” he cautioned.
Scientists using previously secret U.S. military satellite data estimated that a destructive impact causing a “Tunguska-like event” would occur an average of once every 1,000 years. That event cut a swath of destruction across Siberia when a meteor estimated to be 50 to 70 meters wide exploded in mid-air in 1908. Releasing the energy equivalent to a conventional hydrogen bomb, the explosion flattened trees and created a scar in the czar’s backyard hundreds of kilometers across near the Tunguska River. Because the area was uninhabited, there were no deaths. However, “if a similar event took place over a densely populated area in the world today, the death toll could easily be many millions of people,” predicted Robert Jedicke, an astronomer who wrote a companion article.

Present efforts have focused on detecting and possibly diverting asteroids much larger—a kilometer or more wide—that are known to cross the Earth’s orbit. Objects of this size are thought to have caused global damage on a catastrophic scale, such as the death of the dinosaurs, when they collided with the Earth in the past. Nearly 500 such large bodies—astronomers believe the total number is twice that—have been identified. Various proposals, such as changing an asteroid’s orbit by setting off atomic bombs on its surface, have been proposed to protect the Earth from cataclysmic collisions.
However, Tunguska-sized bodies would likely escape detection. “The most likely warning we would get about them would be no warning whatsoever,” Brown said. “We’d only know about them after the satellites or some other device said they have hit.” The chance of detecting smaller, but still nettlesome space rocks, may improve in the future if a recent U.S. proposal to build a series of three-meter telescopes with automatic monitoring equipment is adopted. These telescopes could scan the entire sky every few weeks looking for Tunguska-sized objects.

In Touch with the Universe
A new book of majestic images taken by NASA’s Hubble Space Telescope puts the wonders of the universe at the fingertips of visually impaired space buffs. The 64-page book called Touch the Universe: A NASA Braille Book of Astronomy presents color images of planets, nebulae, stars, and galaxies embossed with lines, bumps, and other textures. The raised patterns translate colors, shapes, and other intricate details of the cosmic objects to allow visually impaired people to get in touch with the universe they cannot see. The raised images not only represent the outlines of stars, planets, and galaxies, but consistent patterns denote color and matter. Raised lines, for example, represent blue. Rings are illustrated with dotted lines, whereas wavy ones signify gas currents. Braille and large-print descriptions accompany each of the book’s 14 photographs, making the design of this book accessible to readers of all visual abilities.

“I think this book will help the blind community to better understand the variety of objects in space,” explains the book’s author, Noreen Grice. “This book brings amazing celestial objects, seen with the Hubble Space Telescope, to the fingertips of the visually impaired, where they can better understand the universe and their place within it.”
Touch the Universe takes the reader on a cosmic journey, beginning with an image of the Hubble Space Telescope orbiting Earth and then traveling outward, showing objects such as Jupiter and the Ring Nebula. The journey ends with the Hubble Deep Field, an image revealing thousands of galaxies billions of light-years away. NASA, which helped fund the book, and the book’s publisher, the Joseph Henry Press, trade imprint of the National Academies Press (publisher for the National Academy of Sciences), released Touch the Universe in November 2002.
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Giants Get Gas Fast
New research suggests that protoplanets circling young stars can become bloated gasbags in a few hundred—not millions—of years. Getting gas fast is necessary, scientists say, because aspiring gas giants must survive the effects of nearby stars dispersing the gases. If the process takes too long, the gases will be dissipated by the radiation from those stars. “If a gas giant planet can’t form quickly, it probably won’t form at all,” said astrophysicist Thomas Quinn.

The standard model of planet formation holds that the spinning disk of matter, called a protoplanetary disk, that surrounds a young star gradually congeals into masses that form the cores of planets. That process was thought to take a million years or so, and then the giants gradually accumulate their gaseous envelopes over perhaps another 1 million to 10 million years. But the new research, culled from a much-refined mathematical model, suggests that the protoplanetary disk begins to fragment after just a few spins around its star. As the disk breaks up, clusters of matter begin to form quickly and immediately attract the gases that form vapor shrouds around gas giants. “If these planets can’t form quickly, then they should be a relatively rare phenomenon, whereas if they form according to this mechanism they should be a relatively common phenomenon,” said Quinn.

The new model also explains why two other giant planets in our system, Uranus and Neptune, don’t have gas envelopes like Jupiter and Saturn. At the time those planets were being formed, the solar system was part of a star cluster, and Uranus and Neptune were too close to a nearby star—one that has since migrated away—and therefore lost whatever gas envelopes they might have accumulated.

Hubble ‘Weighs’ Distant Planet
Astronomers using the Hubble Space Telescope have used a new measurement technique to make a precise estimate of the mass of a planet in another star system. The Hubble results show that the planet—dubbed Gliese 876b—is 1.89 to 2.4 times as massive as Jupiter, our solar system’s heavyweight champion. Previous estimates indicated that the mass of the planet, which is about 15 light-years away, was between 1.9 and 100 times that of Jupiter’s.

Gliese 876b is only the second extrasolar planet for which a precise mass has been calculated and the first whose mass has been verified using a technique called “astrometry.” Dozens of planets have been discovered indirectly using the Doppler technique, but measuring a planet’s spectral “wobble” can’t reveal the angle of a planet’s orbit. Therefore, estimating the maximum mass is difficult. The astrometry technique, on the other hand, measures the miniscule “wiggle” in the motion of a star caused by a companion object. From this celestial jiggle, researchers can estimate the shape of the orbit and pin down the mass of an extrasolar planet.” There are a few more stars where we can do this kind of research with Hubble,” said George Benedict, co-author of a report in Astrophysical Journal Letters.

Determining the mass of more extrasolar planets could help astron-omers answer many questions about how planets form. “When we get hundreds of these mass determinations for planets around all types of stars, we’re going to see what types of stars form certain types of planets. Do big stars form big planets and small stars form small planets?” asked Benedict, a researcher at the University of Texas.

Orbital Space Plane Gets the Nod
The loss of the space shuttle Columbia has focused even greater attention on proposals to develop a new space plane capable of ferrying astronauts to and from the International Space Station. The space plane, which could be launched from Cape Canaveral aboard an emerging breed of rockets, was part of the space agency’s Integrated Space Transportation Plan presented last year. Originally, the Plan called for deploying the space plane as a space station crew rescue vehicle around the end of the decade, and making it available to transport crews by 2012. NASA envisioned phasing out the space shuttle around 2020. However, the loss of Columbia has raised questions about how much longer NASA should rely on an aging shuttle fleet. Several observers believe Washington has no option but to accelerate the space plane program. “The real question is should you accelerate the [space plane] program and the related funding for a shuttle follow-on,” said Gil Rye, a former director of space and intelligence programs at the National Security Council.

Release of technical requirements for the space plane were delayed temporarily following the shuttle accident, but were later issued virtually unchanged. At least some of the infrastructure to field a space plane is already in development. To get a boost to orbit, the craft could use launchers already being developed by Boeing and Lockheed Martin. That would save money by avoiding the cost of creating an entirely new launch system, as was done for the shuttle fleet. The two companies have new launch complexes on NASA and Air Force property at Cape Canaveral.

Boeing and Lockheed executives have been working with NASA to figure out what it would take to prove the rockets are safe to launch humans. “We have been working with them to try to look at different alternatives, but we’ve not been given anything officially as far as funding or a final decision,” said Adrian Laffitte, director of launch operations for Lockheed’s Atlas 5. “We’re interested in exploring all different market possibilities.”

Developing a space plane ensures that the road to orbit (and back) remains open in the event the shuttle fleet is grounded. Such a system would also allow the United States to end its reliance on Russian Soyuz spacecraft used for emergency escape by the three-person station crew. Versions of the venerable Russian three-seater have flown in space since the 1960s. However, the ships can stay on the station for only six months because their batteries and other systems degrade while docked to the station. The Russians are obligated to provide fresh escape pods through the spring of 2006, however, the Russians’ largest space contractor, Energia, has said money problems could force it to stop building Soyuz.
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China On “Long March” Toward Human Spaceflight
China recently parted its “Bamboo Curtain” and gave the rest of the world a peak into the communist giant’s plans in space. According to state-run media, China is planning its first manned space launch later this year. If successful, China will join the United States and Russia as the only nations capable of sending humans into orbit. Such an expedition would represent both a scientific watershed and a public relations victory for China’s military-linked space program. The Chinese government has long been enthusiastic about its space program, which it casts as a symbol of technological progress in a nation ascendant.
The announcements came as the latest unmanned Chinese craft, Shenzhou IV, orbited the Earth as a direct precursor to a manned flight. Shenzhou IV has all the facilities necessary for manned flight, and the Xinhua news agency reported that “taikonauts,” the Chinese version of an astronaut, have been training. The next mission, Shenzhou V, will contain at least one “taikonaut” according to a report from China News Service. Shenzhou, which means “divine vessel,” is modeled on Russian space technology, and can accommodate a three-person crew.

Taikonaut wannabes picked from the ranks of fighter pilots in China’s air force have been training for several years. Any such pioneers would immediately become legendary figures in China, whose propaganda machine is always on the lookout for new demonstrations of patriotism. “The short-term goal is to send Chinese into space. The grand vision for the future is to explore space. Both are inspiring to the Chinese people,” said Huang Chunping, chief commander of rocketry for the Shenzhou project.

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