Universe Today

December 6, 2004June 3, 2013 by Fraser Cain

Astronauts Running Low on Food

The International Space Station?s Expedition 10 crewmembers completed the first 50 days of their six-month mission this week, highlighted by a short flight in their Soyuz spacecraft.

To put the Station in the preferred configuration for two spacewalks out of the Russian Pirs Docking Compartment next year, Commander Leroy Chiao and Flight Engineer Salizhan Sharipov moved their ISS Soyuz 9 spacecraft Monday from Pirs to the Earth-facing docking port on the Zarya module during a 21-minute flight. The work to prepare the Station for possible autonomous operations, and then to reconfigure it for normal operations, stretched from Sunday afternoon until early Monday afternoon.

After getting off duty time Tuesday and Wednesday to rest, Chiao and Sharipov spent the rest of the week on routine maintenance tasks, such as the regeneration of filter cartridges in the Elektron oxygen generation system. They also completed audits of on board computer hardware and food as mission managers finalize the appropriate manifest for the next Russian cargo craft. The ISS Progress 16 spacecraft will ferry food, fuel, clothing and other supplies to the Station. The audit of food supplies aboard the Station confirmed that sufficient food remains for the crew until arrival of the next supply craft. Managers have adjusted the amount of food to be carried on the Progress, however, to ensure onboard stores are fully replenished.

Included in the cargo are three laptop computers that will return the Station Support Computer network to full functionality. This week, one of the computers that crewmembers use to access messages while working at the Zvezda module?s command post, failed. Another computer is being temporarily moved from Sharipov?s sleep station to the command post until the new laptops are delivered.

The new Progress cargo ship is targeted for launch from the Baikonur Cosmodrome in Kazakhstan at 4:19 p.m. CST on Dec. 23 (2219 GMT), and is due to arrive at the Station just after 6 p.m. CST on Christmas night (0005 GMT on Dec. 26).

Chiao and Sharipov will spend time over the next three weeks loading unneeded materials from throughout the Station into the Progress currently mated to the Zvezda module. It will be undocked and deorbited on Dec. 22.

On Tuesday, Sharipov located a missing component of an American spacesuit?s cooling pump. The shim, a washer-shaped piece of metal that is custom fit for each spacesuit, was missing last month at a time when Chiao was repairing the spacesuit?s pump assembly. The shim was planned to be installed in a portion of the spacesuit in a pure oxygen environment to ensure it is in pristine condition and free of contamination. Spacewalk specialists at the Johnson Space Center decided further spacesuit repair attempts will utilize a new shim to be delivered on the upcoming Progress to avoid any potential contamination from the shim that was temporarily lost.

Information on the crew’s activities aboard the Space Station, future launch dates, as well as Station sighting opportunities from anywhere on the Earth, is available on the Internet at:

http://spaceflight.nasa.gov/

Details on Station science operations can be found on an Internet site administered by the Payload Operations Center at NASA’s Marshall Space Flight Center in Huntsville, Ala., at:

http://scipoc.msfc.nasa.gov/

Original Source: NASA Status Report

December 6, 2004 by Fraser Cain

Sweeping View of Saturn’s Rings

Any doubts about the grandeur of Saturn’s rings will be dissolved by sweeping portraits like this one from Cassini. There is a magnificent level of detail visible in this view, which captures almost the entire ring system — from the thin, outer F ring to faint narrow features in the D ring, interior to the C ring. Along the ringplane, differences in brightness reveal the varying concentrations of the particles that comprise the rings.

Cassini is viewing the rings from below. The portion of the rings near the top of the image is closer to the spacecraft, and the portion near the bottom is farther away.

The image was taken with the Cassini spacecraft wide angle camera on Oct. 29, 2004, at a distance of about 836,000 (519,000 miles) from Saturn through a filter sensitive to wavelengths of infrared light centered at 742 nanometers. The image scale is 46 kilometers (29 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

December 3, 2004March 24, 2012 by Fraser Cain

Prometheus Disrupting Saturn’s Rings

As it completed its first orbit of Saturn, Cassini zoomed in on the rings to catch this wondrous view of the shepherd moon Prometheus (102 kilometers, or 63 miles across) working its influence on the multi-stranded and kinked F ring.

The F ring resolves into five separate strands in this closeup view. Potato-shaped Prometheus is seen here, connected to the ringlets by a faint strand of material. Imaging scientists are not sure exactly how Prometheus is interacting with the F ring here, but they have speculated that the moon might be gravitationally pulling material away from the ring. The ringlets are disturbed in several other places. In some, discontinuities or “kinks” in the ringlets are seen; in others, gaps in the diffuse inner strands are seen. All these features appear to be due to the influence of Prometheus.

The image was taken in visible light with the narrow angle camera on Oct. 29, 2004, at a distance of about 782,000 kilometers (486,000 miles) from Prometheus and at a Sun-Prometheus-spacecraft, or phase, angle of 147 degrees. The image scale is 4.7 kilometers (2.9 miles) per pixel. The image has been magnified by a factor of two, and contrast was enhanced, to aid visibility.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

December 3, 2004December 21, 2015 by Fraser Cain

Mars Was Once Suitable For Life

Image credit: NASA
Scientists have long been tantalized by the question of whether life once existed on Mars. Although present conditions on the planet would seem to be inhospitable to life, the data sent back over the past 10 months by NASA’s two exploration rovers, Spirit and Opportunity, showed a world that might once have been warmer and wetter — perhaps friendly enough to support microbial organisms.

Now a Cornell University-led Mars rover science team reports on the historic journey by the rover Opportunity, which is exploring a vast plain, Meridiani Planum, and concludes with this observation: “Liquid water was once present intermittently at the martian surface at Meridiani, and at times it saturated the subsurface. Because liquid water is a key prerequisite for life, we infer that conditions at Meridiani may have been habitable for some period of time in martian history.”

The article is one of 11 published this week (Dec. 3, 2004) in a special issue of the journal Science, authored by scientists connected with the Mars rover mission, several from Cornell and from the Jet Propulsion Laboratory in Pasadena, Calif., the mission’s manager. The issue covers Opportunity through its first 90 days of exploring its landing site of Eagle crater in Meridiani Planum. This was before the rover drove to and entered the large crater dubbed Endurance, from which it is now about to emerge.

Steve Squyres, Cornell professor of astronomy and leader of the rovers’ Athena science team, is the lead author of the main paper, “The Opportunity Rover’s Athena Science Investigation at Meridiani Planum, Mars.” In another paper, on which he is also the lead author, Squyres again refers to the geological record at Meridiani Planum as suggesting that conditions were suitable for “biological activity” for a period of time in the history of mars. In the article, “In Situ Evidence for an Ancient Aqueous Environment at Meridiani Planum, Mars,” he writes: “We cannot determine whether life was present or even possible in the waters at Meridiani, but it is clear that by the time the sedimentary rocks in Eagle crater were deposited, Mars and Earth had already gone down different environmental paths. Sample return of Meridiani rocks might well provide more certainty regarding whether life developed on Mars.”

The Mars rover mission is not designed to look for microbial life but to look for evidence of whether conditions were once right for life. As Squyres recently stated, “What we were seeking was rocks that were actually formed in liquid water so that we could read the record in those rocks, not just to say liquid water was on Mars but to learn something about what the environmental conditions were like, would they have been suitable for life and, importantly, do the minerals that were formed have the capability to preserve for long periods of time evidence of former life? That’s probably the single most important thing we have found: evidence for minerals at Meridiani that are the kinds of things that are very good at preserving evidence of ancient life for very long periods of time.”

Opportunity bounced down on Jan. 25, 22 days after its twin, the rover Spirit, landed on the opposite side of Mars in Gusev crater. Last August Science published a special issue on Spirit.

“This is the first peer-reviewed presentation of the data from Opportunity,” notes Jim Bell, Cornell associate professor of astronomy and the lead scientist for the rovers’ Pancam color imaging system.

Bell also is prominent in the special issue of Science , including his lead authorship of a paper, “Pancam Multispectral Imaging Results from the Opportunity Rover at Meridiani Planum.”

When Opportunity landed on the red planet last January, the robot geologist sent back images of its landing site that were unlike any of the other places where earlier lander probes and rovers had gone. Instead of rusty deserts of dusty soil and boulders strewn to the horizon, Opportunity had landed in a relatively small crater in a vast sea of sand nearly devoid of rocks. Fortunately, an intriguing outcrop of bedrock presented itself nearby, which scientists hoped would be a sample of the original crust underneath the layers of dust.

The scientists were not disappointed. Scattered among the outcrop rocks were large numbers of small, round mineral deposits that the Athena science team named “blueberries.” On Earth, such formations appear when large amounts of water course through rock layers, leaching out the iron-bearing minerals into small spherical rocks and granules. The rovers also detected large amounts of sulfate salt deposits. Enough evidence was collected by Opportunity in the two months it spent examining Eagle crater that the science team felt confident enough to announce in early March that liquid water had flowed over the crater’s rocks long ago, possibly for a long time. Following on this, the latest Science articles largely focus on Opportunity’s most important scientific and geological accomplishment: the discovery of evidence that liquid water once flowed through the region.

Like the coverage given to Spirit in the August issue of Science , the latest edition contains several foldouts with big color panoramas and images from Opportunity’s region of exploration.

Original Source: Cornell News Release

December 3, 2004 by Fraser Cain

Greenland Glacier Speeds Up

When people talk about something moving at a glacial pace, they are referring to speeds that make a tortoise look like a hare. While it is all relative, glaciers actually flow at speeds that require time lapses to recognize. Still, researchers who study Earth’s ice and the flow of glaciers have been surprised to find the world’s fastest glacier in Greenland doubled its speed between 1997 and 2003.

The finding is important for many reasons. For starters, as more ice moves from glaciers on land into the ocean, it raises sea levels. Jakobshavn Isbrae is Greenland’s largest outlet glacier, draining 6.5 percent of Greenland’s ice sheet area. The ice stream’s speed-up and near-doubling of ice flow from land into the ocean has increased the rate of sea level rise by about .06 millimeters (about .002 inches) per year, or roughly 4 percent of the 20th century rate of sea level increase.

Also, the rapid movement of ice from land into the sea provides key evidence of newly discovered relationships between ice sheets, sea level rise and climate warming.

The researchers found the glacier’s sudden speed-up also coincides with very rapid thinning, indicating loss of ice of up to 15 meters (49 feet) in thickness per year after 1997. Along with increased rates of ice flow and thinning, the thick ice that extends from the mouth of the glacier into the ocean, called the ice tongue, began retreating in 2000, breaking up almost completely by May 2003.

The NASA-funded study relies on data from satellites and airborne lasers to derive ice movements. The paper appears in this week’s issue of the journal Nature.

“In many climate models glaciers are treated as responding slowly to climate change,” said Ian Joughin, the study’s lead author. “In this study we are seeing a doubling of output beyond what most models would predict. The ice sheets can respond rather dramatically and quickly to climate changes.” Joughin conducted much of this research while working at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. Joughin is currently a glaciologist at the Applied Physics Laboratory at the University of Washington, Seattle.

The researchers used satellite and other data to observe large changes in both speeds and thickness between 1985 and 2003. The data showed that the glacier slowed down from a velocity of 6700 meters (4.16 miles) per year in 1985 to 5700 meters (3.54 miles) per year in 1992. This latter speed remained somewhat constant until 1997. By 2000, the glacier had sped up to 9400 meters (5.84 miles) per year, topping out with the last measurement in spring 2003 at 12,600 meters (7.83 miles) per year.

“This finding suggests the potential for more substantial thinning in other glaciers in Greenland,” added Waleed Abdalati, a coauthor and a senior scientist at NASA’s Goddard Space Flight Center, Greenbelt, Md. “Other glaciers have thinned by over a meter a year, which we believe is too much to be attributed to melting alone. We think there is a dynamic effect in which the glaciers are accelerating due to warming.”

Airborne laser altimetry measurements of Jakobshavn’s surface elevation, made previously by researchers at NASA’s Wallops Flight Facility, showed a thickening, or building up of the glacier from 1991 to 1997, coinciding closely with the glacier’s slow-down. Similarly, the glacier began thinning by as much as 15 meters (49 feet) a year just as its velocity began to increase between 1997 and 2003.

The acceleration comes at a time when the floating ice near the glacier’s calving front has shown some unusual behavior. Despite its relative stability from the 1950’s through the 1990s, the glacier’s ice tongue began to break apart in 2000, leading to almost complete disintegration in 2003. The tongue’s thinning and breaking up likely reduced any restraining effects it had on the ice behind it, as several speed increases coincided with losses of sections of the ice-tongue as it broke up. Recent NASA-funded research in the Antarctic Peninsula showed similar increases in glacier flow following the Larson B ice shelf break-up.

Mark Fahnestock, a researcher at the University of New Hampshire, Durham, N.H., was also a co-author of this study.

Original Source: NASA News Release

December 3, 2004 by Fraser Cain

Wallpaper: Saturn’s Rings in Black and White

This close-up of the lit side of Saturn’s outer B ring and the Cassini Division looks something like a phonograph record. There are subtle, wavelike patterns, hundreds of narrow features resembling a record’s ‘grooves’ and a noticeable abrupt change in overall brightness beyond the dark gap near the right. To the left of the gap is the outer B ring with its sharp edge maintained by a strong gravitational resonance with the moon Mimas. To the right of the Huygens Gap are the plateau-like bands of the Cassini Division. The narrow ringlet within the gap is called the Huygens ringlet.

The image was taken in visible light with the Cassini spacecraft narrow angle camera on Oct. 29, 2004, at a distance of about 819,000 (509,000 miles) from Saturn. The image scale is 4.5 kilometers (2.8 miles) per pixel.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

December 2, 2004September 13, 2007 by Mark Mortimer

Book Review: Centauri Dreams

First a bit of a background. We’ve a long way to go. Alpha Centauri is 4.3 light years away (about 13 zeros after the one when considering kilometres). Voyager 1, the fastest man made object, is speeding at 3.6 AU’s per year (about 8 zeros after the one in kilometres per year). Were a person to be on it, some 100,000 years would pass before entering Alpha Centauri’s solar system. This won’t happen as Voyager 1 travels another path, but this is the problem in a nutshell, it’s too far for today’s chemically driven rockets. With most people expecting a return on investment well within ten years then there would be little support in waiting thousands of generations for payback. Given this impracticality Gilster presents options and methods that might reduce the travel time to within one generation.

The first chapter sets the background of who’s doing what, where they are keeping themselves busy and, sometimes, when their activities first appear upon the scene. Scores of researchers’ names arise, especially physicists, mathematicians and astronomers, but a sprinkling of other esoteric specialists such as Internet designers, clearly demonstrates the broad response to this challenge. NASA’s programs and facilities predominate. CERN appears as does the Brookhaven National Laboratory. Early visionaries from the 1800’s and even earlier make a brief appearance. Applicable science fiction stories from the early 1900’s get noted, while the predominance of technically valid work dates from about 1960 on. This shows that on the whole, considerable thought and work has gone into advancing concepts for high speed interstellar travel.

Five chapters follow and represent the real meat of this book. These look at different methods of getting a useful payload to our neighbouring stars and they focus on well known and lesser known means of propulsion. Antimatter, sails, ramjets and fusion runways get their dues. Field-drives, providing force from the interaction of matter and fields get an honourable mention. Each chapter clearly and simply describes the methods of the chosen propulsion and the state (or technical level) of the research. Interviews with today’s investigators provide a superb insider’s view of activities. If you’re looking to identify locations for grad studies, there is a bonus as key investigating sites get identified alongside. Exciting sections detail the latest in experiments and technical investigations. The Planetary Society’s solar sail lifts off soon, antimatter is getting expansive new containers, lasers push model crafts up against Earth’s gravitational pull and a mini-magentospheric plasma propulsion prototype undergoes testing. Each of these might answer the riddle about how we propel ourselves at near light speed but as pointed out, the breakthrough technology may yet be around the corner.

One chapter seems a little bit like a lost child. This deals with communication and guidance. Of course these issues will need to be addressed, but it seems a bit early to be worrying about setting up extra-planetary webs or designing their communication protocol for that real long distance feeling. The guidance/navigation portion seems equally out of place. As the propulsion method so drastically constrains the mission, this discussion is preemptive. Still, as the title states, this book plans for interstellar exploration, hence communication and guidance are relevant and their consideration is warranted.

And yes, the title says it all. Alpha Centauri is a dreamers destination but dreams are only the beginning. Imagination gets us out of the constraints of everyday thinking and planning will see that effort gets well applied. As depicted within the book, many people share this dream. Some are incredibly lucky and can make it their life’s work. Others contribute directly in their part time or indirectly whether through related research, writing fiction or, as Gilster is undertaking, performing outreach activities. The link from imagination, to serious consideration and eventual trials constantly arises as either a sign of humanity’s adaptability or perhaps a sign of genetic coding. Nevertheless, time and again, imaginations are shown to conceive of the knowledge that thrusts plans out of the realm of fiction and into the laboratory where researchers make it reality.

Stars twinkle all about us at night. Perhaps maliciously inviting or teasing like a temptress, either way they remain today too far to fathom visiting today. Science fiction had imaginaries who gave detailed if somewhat fanciful means of propulsion between the stars. Paul Gilster in Centauri Dreams: Imagining and Planning Interstellar Exploration shows that real science is advancing technologies that could make this trip practical. The plans of the scientists and other technical may soon bear fruit and future generations of humans would have a much better and more exciting life amongst the stars.

Read more reviews online or order your own copy from Amazon.com.

Review by Mark Mortimer

December 2, 2004June 3, 2013 by Fraser Cain

Would We Mistake Signals from ET?

Researchers from the University of Michigan think that the current programs to search for extraterrestrial intelligence (SETI) might not be able to distinguish signals from the noise of nearby stars. They showed how an efficient message sent through radio waves is nearly indistinguishable from the ordinary thermal radiation coming from stars. If extraterrestrial civilizations have been transmitting for a long time, they’ll probably have optimized their communications to save power, and so we won’t recognize it when we hear it.

If ET ever phones home, chances are Earthlings wouldn’t recognize the call as anything other than random noise or a star.

New research shows that highly efficient electromagnetic transmissions from our neighbors in space would resemble the thermal radiation emitted by stars.

University of Michigan physicist Mark Newman, along with biologist Michael Lachmann and computer scientist Cristopher Moore, have extended the pioneering 1940s research of Claude Shannon to electromagnetic transmissions in a paper published last month in the American Journal of Physics called, “The Physical Limits of Communication, or Why any sufficiently advanced technology is indistinguishable from noise.” Lachmann is at the Max Planck Institute in Leipzig, Germany; Moore is at the University of New Mexico in Albuquerque.

Shannon showed that a message transmitted with optimal efficiency is indistinguishable from random noise to a receiver unfamiliar with the language in the message. For example, an e-mail message whose first few letters are AAAAA contains little information because the reader can easily guess what probably comes next?another A. The message is totally non-random. On the other hand, a message beginning with a sequence of letters like RPLUOFQX contains a lot of information because you cannot easily guess the next letter.

Paradoxically, however, the same message could just be a random jumble of letters containing no information at all; if you don’t know the code used for the message you can’t tell the difference between an information-rich message and a random jumble of letters.

Newman and his collaborators have shown that a similar result holds true for radio waves.

When electromagnetic waves are used as the transmission medium, the most information efficient format for a message is indistinguishable from ordinary thermal radiation?the same kind of radio waves that are emitted by hot bodies like stars. In other words, an efficiently coded radio message coming from outer space would look no different from a normal star in the sky.

So, suppose an alien in space decided to pick up signs of Earth life. It would have a pretty easy time of it, since our radio and television signals are zigzagging all over the place and are inefficiently coded and easily distinguishable from stars.

But say a human tries to tune into extraterrestrial life.

“People do this, and when they do, they are looking for non-random stuff,” Newman said. “But what if (the aliens) have gotten it down? With a few hundred years practice at doing this, you’d have discovered the most efficient way to encode your radio messages. So to us, their communication would look just like another star, a hot object.”

After all, Newman said, in the universe’s 12 billion-year history, it’s likely that extraterrestrials?if they exist?have communicated with each other longer than our paltry 80-year history of radio broadcasting. “In which case, they’ve probably gotten very good at this by now.”

Said Newman: “Our message is that, even for the people who do believe this, they’re probably wasting their time. If they did pick up a signal from little green men, it would probably look like a star to them and they would just pass over it and move on to the next thing.”

Original Source: UMich News Release

December 2, 2004March 24, 2012 by Fraser Cain

Dusty Universe is a Mystery

Image credit: NASA/JPL/UA
Astronomers who think they know how the very early universe came to have so much interstellar dust need to think again, according to new results from the Spitzer Space Telescope.

In the last few years, observers have discovered huge quantities of interstellar dust near the most distant quasars in the very young universe, only 700 million years after the cosmos was born in the Big Bang.

“And that becomes a big question,” said Oliver Krause of the University of Arizona Steward Observatory in Tucson and the Max Planck Institute for Astronomy in Heidelberg. “How could all of this dust have formed so quickly?”

Astronomers know two processes that form the dust, Krause said. One, old sun-like stars near death generate dust. Two, infrared space missions have revealed the dust is produced in supernovae explosions.

“The first process takes several billion years,” Krause noted. “Supernovae explosions, by contrast, produce dust in much less time, only about 10 million years.”

So when astronomers reported detecting submillimeter emission from massive amounts of cold interstellar dust in the supernova remnant Cassiopeia A last year, some considered the mystery solved. Type II supernovae like ‘Cas A’ likely produced the interstellar dust in the very early universe, they concluded. (Type II supernovae come from massive stars that blow apart in huge explosions after their cores collapse.)

Krause and colleagues from UA’s Steward Observatory and the Max Planck institute in Heidelberg have now discovered that the detected submillimeter emission comes not from the Cas A remnant itself but from the molecular cloud complex known to exist along the line of sight between Earth and Cas A. They report the work in the Dec. 2 issue of Nature.

Cas A is the youngest known supernova remnant in our Milky Way. It is about 11,000 light years away, behind the Perseus spiral arm clouds that are roughly 9,800 light years away. Krause suspects that the Perseus clouds explain why late 17th century astronomers didn’t report observing the brilliant Cas A outburst around A.D. 1680. Cas A is so close to Earth that the supernova should have been the brightest stellar object in the sky, but dust in the Perseus clouds eclipsed the view.

The Arizona and German team mapped Cas A at 160-micron wavelengths using the ultra-heat-sensitive Multiband Imaging Photometer (MIPS) aboard the Spitzer Space Telescope. These long wavelengths are the most sensitive to cold interstellar dust emission. They then compared the results with maps of interstellar gas previously made with radio telescopes. They found that the dust in these interstellar clouds account for virtually all the emission at 160 microns from the direction of Cas A.

Minus the emission from this dust, there is no evidence for large amounts of cold dust in Cas A, the team concludes.

“Astronomers will have to go on searching for the source of the dust in the early universe,” UA Steward Observatory astronomer and Regents’ Professor George Rieke said. Rieke is principal investigator for the Spitzer Space Telescope’s MIPS instrument and a co-author of the Nature paper.

“Solving this riddle will show astronomers where and how the first stars formed, or perhaps indicate there is some non-stellar process that can produce large amounts of dust,” Rieke said. “Either way, (finding the source of the dust) will reveal what went on at the formative stage for stars and galaxies, an epoch that is nearly unobserved in any other way.”

Authors of the Nature article, “No cold dust within the supernova remnant Cassiopeia A,” are Oliver Krause, Stephan M. Birkmann, George H. Rieke, Dietrich Lemke, Ulrich Klaas, Dean C. Hines and Karl D. Gordon.

Birkmann, Lemke and Klaas are with the Max Planck Institute for Astronomy in Heidelberg. Krause, Rieke, and Gordon are with the University of Arizona Steward Observatory. Hines is with the Space Science Institute in Boulder, Colo.

Original Source: UA News Release

December 2, 2004March 24, 2012 by Fraser Cain

Sun Could Have Traded With Another Star

A hit TV program like “Antiques Roadshow” lures viewers with its universal appeal. Who wouldn’t want to find secret riches in their attic or basement? But rare paintings and heirloom jewelry aren’t the only valuable items waiting to be discovered. Cosmic treasures also lay hidden in the vast realm of outer space. Among the most highly prized of those treasures are planets that formed around other stars.

Astronomers have just gained an important clue to guide their hunt for extrasolar worlds. And that clue points to the unlikeliest of places – our own backyard.

“It’s possible that some of the objects in our solar system actually formed around another star,” says astronomer Scott Kenyon (Smithsonian Astrophysical Observatory).

How did these adopted worlds join our solar family? They arrived through an interstellar trade that took place more than 4 billion years ago when a wayward star brushed past our solar system. According to calculations made by Kenyon and astronomer Benjamin Bromley (University of Utah) and published in the Dec. 2, 2004, Nature, the Sun’s gravity plucked asteroid-sized objects from the visiting star. At the same time, the star pulled material from the outer reaches of our solar system into its grasp.

“There may not have been an equal exchange, but there was certainly an exchange,” says Bromley.

A Close Brush
Kenyon and Bromley reached this surprising conclusion while working to explain the mystery object Sedna, a world almost as large as Pluto but located much farther from the Sun. Sedna’s discovery in 2003 puzzled astronomers because of its unusual orbit – a 10,000-year-long oval whose closest approach to the Sun, 70 astronomical units, is well beyond the orbit of Neptune. (One astronomical unit, abbreviated A.U., is the average distance between the Earth and the Sun, or about 93 million miles.)

Understanding Sedna is a challenge because its orbit is far away from the gravitational influence of other planets in our solar system. However, the gravity of a passing star can pull objects beyond the orbit of Neptune, in the Kuiper Belt, into orbits like Sedna’s. Kenyon and Bromley have performed detailed computer simulations to show how this stellar fly-by likely took place.

The fly-by must have met two key requirements. First, the star must have stayed far enough away that it did not disrupt Neptune’s nearly circular orbit. Second, the encounter must have happened late enough in our solar system’s history that Sedna-like objects had time to form within the Kuiper Belt.

Kenyon and Bromley suggest that the near-collision occurred when our Sun was at least 30 million years old, and probably no more than 200 million years old. A fly-by distance of 150-200 A.U. would be close enough to disrupt the outer Kuiper Belt without affecting the inner planets.

According to the simulations, the passing star’s gravity would sweep clear the outer solar system beyond about 50 A.U., even as our Sun’s gravity pulled some of the alien planetoids into its grasp. The model explains both the orbit of Sedna and the observed sharp outer edge of our Kuiper Belt, where few objects reside beyond 50 A.U.

“A close fly-by from another star solves two mysteries at once. It explains both the orbit of Sedna and the outer edge of the Kuiper Belt,” says Bromley.

A Crowded Birthplace
But where did such a star come from, and where did it go? Since the fly-by happened more than 4 billion years ago, any suspects have long since escaped the Sun’s neighborhood. There is no practical way to find the culprit today.

The visitor’s origin may seem equally mystifying because the Sun currently lives in a sparse region of the Milky Way. Our closest neighbor is a distant 4 light-years away, and stellar close encounters are correspondingly rare. However, a near-collision would be much more likely for a young Sun if it were born in a dense star cluster, as recent evidence suggests.

“We believe that 90 percent of all stars form in clusters with a few hundred to a few thousand members,” says astronomer Charles Lada (Harvard-Smithsonian Center for Astrophysics). “The denser the cluster, the more likely the chance for an encounter between member stars.”

“This work is an important piece of evidence that the Sun formed in near proximity to other stars,” he adds.

Searching for Adopted Worlds
Kenyon and Bromley’s simulations indicate that thousands or possibly millions of alien Kuiper Belt Objects were stripped from the passing star. However, none have yet been positively identified. Sedna is probably homegrown, not captured. Among the known Kuiper Belt Objects, an icy rock dubbed 2000 CR105 is the best candidate for capture given its unusually elliptical and highly inclined orbit. But only the detection of objects with orbits inclined more than 40 degrees from the plane of the solar system will clinch the case for the presence of extrasolar planets in our backyard.

Kenyon and Bromley’s next goal is to estimate the sky density of captured objects so that they can make a survey to find such adopted worlds.

“In principle, large telescopes like the MMT Telescope [a joint Smithsonian/University of Arizona observatory] can find them if they’re numerous enough,” says Kenyon.

The calculations reported here were made using about 3,000 cpu-days of computer time at the supercomputing center at the Jet Propulsion Laboratory, Pasadena, Calif.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release