Posted on by Fraser Cain

Solar Flares Altered Mars’ Atmosphere

Solar flare. Image credit: ESA Click to enlarge
Boston University astronomers announced today the first clear evidence that solar flares change the upper atmosphere of Mars. In an article published in the February 24th issue of the journal Science, the researchers describe how X-ray bursts from the Sun in April 2001 recorded by satellites near Earth reached Mars and caused dramatic enhancements to the planet’s ionosphere ??bf? the region of a planet’s atmosphere where the Sun’s ultraviolet and X-rays are absorbed by atoms and molecules. The measurements were made by the Mars Global Surveyor (MGS) spacecraft at the Red Planet as it transmitted signals to NASA’s antenna sites back on Earth.

“On April 15th and 26th of 2001, radio signals from MGS showed that the Martian ionosphere was unusually dense, and this was the clue that some extra production of ions and electrons had occurred,” explained Michael Mendillo, professor of astronomy, who led the BU research team in its Center for Space Physics.

“At Earth, the GOES satellites measure the Sun’s X-rays almost continuously,” said Dr. Paul Withers of BU. “Our search of their large database discovered several cases of flares occurring just minutes before MGS detected enhancements in Mars’ ionosphere.”

The extra electrons produced by the Sun’s X-rays cause subtle changes in how the MGS radio waves travel toward Earth. Therefore, the team wanted to find several unambiguous case study events before announcing their findings.

The Radio Science Experiment on MGS has made observations of Mars’ ionosphere since its arrival there in late 1999. Its radio transmissions are received by NASA and then cast into scientifically meaningful data by Dr. David Hinson at Stanford University who provides open access to researchers worldwide via a Web site. “We needed Dr. Hinson’s expert advice to make sure that some odd changes in the MGS radio signal had not occurred just by chance,” Dr. Withers added.

To confirm that the photons from these flares had sufficient fluxes to actually modify an ionosphere, additional evidence was sought using measurements on Earth. “During this period, the Sun, Earth and Mars were nearly in a straight line and thus the X-rays measured at Earth should have caused enhancements here as well as at Mars,” Mendillo added.

Using several ionospheric radars spread over the globe, operated by scientists at the University of Massachusetts/Lowell, Professor Bodo Reinisch confirmed that the Sun’s X-rays caused equally impressive modifications to Earth’s ionosphere at the precise times required on those days.

“The science yield from this work will be in the new field of Comparative Atmospheres,” Mendillo pointed out. “By that I mean studies of the same process in nature, in this case making an ionosphere on two planets simultaneously, offer insights and constraints to models not always possible when studying that process on a single planet. The fifth member of our team, Professor Henry Rishbeth of the University of Southampton in England, provides the expertise in theory and modeling that will be the focus of our follow-up studies.”

Founded in 1839, Boston University is an internationally recognized institution of higher education and research. With more than 30,000 students, it is the fourth largest independent university in the United States. BU contains 17 colleges and schools along with a number of multi-disciplinary centers and institutes which are central to the school’s research and teaching mission.

Original Source: Boston University

Posted on by Fraser Cain

Van Allen Safe Zone Migrates

The Van Allen Belts pulsing from solar particles. Image credit: NASA/Tom Bridgman. Click to enlarge
A “safe zone” in the radiation belts surrounding Earth moves higher in altitude and latitude during peaks in solar activity, according to new research by a NASA-led team. The safe zone offers reduced radiation intensities to any potential spacecraft that must fly in the radiation belt region.

“This new research brings us closer to understanding how a section of the radiation belt disappears,” said Dr. Shing Fung of NASA’s Goddard Space Flight Center, Greenbelt, Md. Fung is lead author of a paper on this research appearing in the on-line version of Geophysical Research Letters February 22.

The team based its results on measurements of high-speed particles (electrons), which comprise the “Van Allen radiation belt”, from the National Oceanic and Atmospheric Administration’s series of polar-orbiting meteorological spacecraft during 1978 to 1999. As the spacecraft flew in their polar orbits, they detected fewer radiation belt particles at a certain latitude range, indicating safe zone passages by the spacecraft. The researchers compared the data taken during relatively low solar activity periods, called solar minimum, to data from peak solar activity periods, called solar maximum. They noticed a shift in the safe-zone location towards higher latitudes, and therefore altitudes, during solar maximum.

If the radiation belts were visible, they would resemble a pair of donuts around the Earth, one inside the other with the Earth in the “hole” of the innermost donut. The safe zone, called the “slot region”, would appear as a gap between the inner and outer donut. The belts are actually comprised of high-speed electrically charged particles (electrons and atomic nuclei) that are trapped in the Earth’s magnetic field.

The Earth’s magnetic field can be represented by lines of magnetic force emerging from the South Polar region, out into space and back into the North Polar region. Because radiation-belt particles are charged, their motions are guided by the magnetic lines of force. Trapped particles would bounce between the poles while spiraling around the field lines.

Very Low Frequency (VLF) radio waves and background gas (plasma) are also trapped in this region. Just like a prism that can bend a light beam, the plasma can bend the VLF wave propagation paths, causing the waves to flow along the Earth’s magnetic field. VLF waves clear the safe zone by interacting with the radiation belt particles, removing a little of their energy and changing their direction. This lowers the place above the polar regions where the particles bounce (called the mirror point). Eventually, the mirror point becomes so low that it is in the Earth’s atmosphere. When this happens, the trapped particles collide with atmospheric particles and are lost.

According to the team, the safe zone is created in a region where conditions are favorable for the VLF waves to kick the particles. Their research is the first indication that the location of this region can change with the solar activity cycle. The Sun goes through an 11-year cycle of activity, from maximum to minimum, and back again. During solar maximum, increased solar ultraviolet (UV) radiation heats the Earth’s upper atmosphere, the ionosphere, causing it to expand. This increases the density of the plasma trapped in Earth’s magnetic field.

Favorable conditions for the VLF wave-particle interaction depend on the specific combination of plasma density and magnetic field strength. Although plasma density generally decreases with altitude, expansion of the ionosphere during solar maximum makes the plasma denser at the safe zone’s solar-minimum altitude, and forces the favorable plasma density for the safe zone to migrate to a higher altitude. In addition, magnetic field strength also decreases with altitude. To find the favorable magnetic field strength for the safe zone at higher altitudes, one would have to migrate toward the poles (higher latitudes), where the magnetic field lines are more concentrated and thus stronger.

“This discovery helps narrow down the search for the primary wave-particle interaction region that creates the safe zone,” said Fung. “Although no known spacecraft uses the safe zone extensively now, our knowledge could help planning and operations of future missions that want to take advantage of the zone.”

According to the researchers, their discovery was enabled by a new data selection and retrieval tool developed by the team, called the Magnetospheric State Query System. The research was funded by NASA and the National Research Council. The team includes Fung, Dr. Xi Shao (National Research Council, Washington), and Dr. Lun C. Tan (QSS Group, Inc., Lanham, Md.).

Original Source: NASA News Release

Posted on by Fraser Cain

The High Cost of Boots on the Moon

Artist impression of astronauts returning to the Moon. Image credit: NASA. Click to enlarge.
President Bush suggested that this approach would be both ambitious and reasonable:

Achieving these goals requires a long-term commitment. NASA’s current five-year budget is $86 billion. Most of the funding we need for the new endeavors will come from reallocating $11 billion within that budget. We need some new resources, however. I will call upon Congress to increase NASA’s budget by roughly a billion dollars, spread out over the next five years. This increase, along with refocusing of our space agency, is a solid beginning to meet the challenges and the goals we set today. It’s only a beginning. Future funding decisions will be guided by the progress we make in achieving our goals.

NASA’s new administrator, Michael Griffin further noted in a speech in September 2005 that “not one thin dime” would be directed away from NASA science programs.

As reasonable and optimistic as this statement was, reality has caught up with NASA. And science was the victim.

The White House released President Bush’s new NASA budget proposal for 2007 on February 6. Overall, the budget allocates $16.8 billion for NASA; a 3.2% rise over 2006’s budget.

Specifically, the budget proposes:

  • $6.2 billion for the shuttle and space station
  • $5.3 billion for science
  • $4.0 billion for the new exploration systems

While NASA’s overall budget increases 3.2%, science will only go up by 1.5%, and future budget increases are expected to go up just 1.0% a year through 2011. Factored against inflation, this is essentially a budget decrease. New Scientist gives a good breakdown.

NASA Administrator Michael Griffin dropped the hammer on February 8, explaining what impact this new budget would have on the agency, specifically for its various science programs.

  • Funding for Astrobiology will be cut to 50% of its 2005 levels.
  • Europa mission that would search for life under the moon’s icy surface… cancelled.
  • The Terrestrial Planet Finder – an observatory capable of seeing Earth-sized planets around other stars, and even signs of life… cancelled.
  • The Space Interferometry Mission… delayed.
  • Two scout missions to Mars… cancelled.
  • Dawn mission to explore two asteroids… cancelled.

Ouch. The Terrestrial Planet Finder could make one of the most important discoveries in all of human history; that there’s life on other planets. Please, Mike, anything but that.

The response in the space community was immediate, and ferocious. With good reason. So much good science is being chopped away from NASA.

What’s insane about this whole situation is that NASA should even be forced to choose. If I were in Mike Griffin’s shoes, I’d probably make many of the same decisions. What other decision can he make? The President and Congress have essentially said, “keep flying the shuttle to build the International Space Station, put humans back on the Moon, and figure out how to pay for it.” Science is all that’s left to cut from. If the new exploration vehicle goes over budget, science will have to pay for that too.

Flying the shuttle isn’t about rocket fuel, it’s about the standing army of thousands of employees who work across the United States. These people do important, complicated and specialized work on the shuttle, and you can’t just wish them away with a magic wand. NASA exists in the real world, with all the political considerations that go along with it. People work for NASA, and they’re voters, and they can apply pressure back on Congress, who ultimately approves the budget. The shuttle program has momentum, and nobody can make this process turn on a dime.

The human exploration of space is one of the greatest endeavours we can embark on. The whole point of space exploration is to learn how to get humans into space. At some point that requires putting human beings into rocket ships, blasting them into space, and figuring out what it takes to survive outside of the Earth. You have to keep doing that until humans don’t need to come back, and humanity becomes a true spacefaring civilization.

NASA shouldn’t be forced to choose between science and exploration. Why not pick up all of NASA’s science related activities and put them under the umbrella of the National Science Foundation? They’re slated to receive $5.8 billion for FY2007.

I would still be uncomfortable to have to choose between particle accelerators, genetic research and Martian rovers, but it’s probably a much more appropriate choice to have to make.

Written by Fraser Cain

Posted on by Fraser Cain

Redesigning Universe Today… Again

In case you haven’t noticed yet, I’ve redesigned Universe Today… again. I know I do this almost every year, but I just get itchy feet. Anyway, I’m taking an HTML/CSS design course as part of my computer science degree, so I figured I’d put it to good use. Right now on the homepage and the article pages have been redesigned, but I thought I’d get your feedback. Here are some of the changes I made:
– pushed stuff to the sides so you don’t have go so far down before reading articles
– spaced out the text on articles a little bit to make them easier to read
– implemented printer templates for everything. Now every page is “printable”. Check it out, just click “Print Preview” in your brower and you’ll see what it’ll look like.

I’m still fine tuning stuff, so please feel free to give me any feedback, suggestions, or complaints. Email me at [email protected]. Once the website’s done, I’ll update the newsletter, etc.

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

Pluto Was Born With Its Moons

Artist’s illustration showing a giant collision similar to Pluto’s newly discovered moons scenario. Image credit: Don Davis Click to enlarge
In a paper published today in Nature, a team of U.S. scientists led by Dr. S. Alan Stern of Southwest Research Institute (SwRI), concludes that two newly discovered small moons of Pluto were very likely born in the same giant impact that gave birth to Pluto’s much larger moon, Charon. The team also argues that other, large binary Kuiper Belt Objects (KBOs) may also frequently harbor small moons, and that the small moons orbiting Pluto may generate debris rings around Pluto.

The team making these findings included Drs. Bill Merline, John Spencer, Andrew Steffl, Eliot Young and Leslie Young of SwRI; Dr. Hal Weaver of the Johns Hopkins University Applied Physics Laboratory; Max Mutchler of the Space Telescope Science Institute; and Dr. Marc Buie of the Lowell Observatory. This team discovered Pluto’s two small moons in 2005 using sensitive images obtained by the Hubble Space Telescope, as reported by Weaver et al. in an accompanying paper in the February 23 issue of Nature.

“The evidence for the small satellites being born in the Charon-forming collision is strong; it is based around the facts that the small moons are in circular orbits in the same orbital plane as Charon, and that they are also in, or very near, orbital resonance with Charon,” says lead author Stern, executive director of the SwRI Space Science and Engineering Division.

“Tests of this scenario will come from refined orbital data, from measuring the rotational periods of these moons, and from determinations of their densities and surface compositions,” says co-author Weaver.

Collisions, both large and small, are major processes that shaped many aspects of our solar system. Scientists use computer simulations to study the origin of planetary systems formed by impact events of a scale much larger than could be simulated in a laboratory. Another large collision, like the one thought to have created Charon and Pluto’s small moons, is believed responsible for the formation of the Earth-moon pair.

“The idea that Pluto’s small moons and Charon resulted from a giant impact now seems compelling. Future simulations to determine the characteristics of the impact required to produce all three satellites should provide improved constraints on the early dynamical history of the Kuiper Belt,” adds Dr. Robin Canup, director of SwRI’s Space Studies Department, who in 2005 produced the most comprehensive models to date of the Charon-forming impact.

Based on the growing realization that binary “ice dwarf” pairs like Pluto-Charon are common in the Kuiper Belt, the Pluto satellite discovery team concludes that numerous triple, quadruple and even higher-order systems may be discovered across the Kuiper Belt in years to come.

“Finding small satellites around KBOs is difficult because their large distance from the Sun makes them appear very faint. As a result, we don’t really know how common it is for KBOs to have multiple satellites,” adds co-author Steffl. “One good way to test this is to search around objects that have been ejected from the Kuiper Belt into orbits that bring them much closer to the Sun. So far, about 160 of these objects, called Centaurs, have been discovered. We hope to use Hubble to search for faint moons around some of them.”

Co-author Merline adds, “If Pluto’s small moons generate debris rings from impacts on their surfaces, as we predict, it would open up a whole new class of study because it would constitute the first ring system seen around a solid body rather than a gas giant planet.”

“The Pluto system never fails to reward us when we look at it in new ways,” concludes Stern. “What a bonanza and an illustration of the richness of nature Pluto has consistently proved to be. Our discovery of its two new moons reinforces that lesson yet again.”

The paper, “A Giant Impact Origin for Pluto’s Small Moons and Satellite Multiplicity in the Kuiper Belt,” by Stern et al. is available in the February 23 issue of Nature. NASA funded this work.

Original Source: SwRI News Release

Update: Pluto is no longer a planet.

Posted on by Fraser Cain

Dark Lava Floor of Crater Billy

Lunar crater Billy as seen by SMART-1. Ima ge credit: ESA/SPACE-X Click to enlarge
This composite image, taken by the Advanced Moon Imaging Experiment (AMIE) on board ESA’s SMART-1 spacecraft, shows crater Billy at the edge of a large lava plain on the Moon.

The AMIE camera obtained two images in consecutive orbits, from a distance of about 1260 kilometres with a ground resolution of approximately 114 metres per pixel. Each image has a field of view of 56 kilometres.

Crater Billy is located on the southern fringes of the Oceanus Procellarum, on the western half of the Moon’s Earth-facing side (50??bf? West, 13.5??bf? South). It lies to the south-east of the similar-sized crater Hansteen and west-south-west of the lava-flooded crater Letronne.

The Oceanus Procellarum’s southern area is low on spectacle but high in terms of geological interest. An irregular bay, the Mare Humorum on the edge of the ‘ocean’ can be seen below and to the east of the craters Billy and Hansteen.

Billy is an old impact crater, 46 kilometres in diameter, with a rim rising to 1300 metres above its flat floor. The floor of Billy has been flooded by basaltic lava with a low albedo, meaning it leaves a dark surface.

Billy’s floor is one of the darkest spots on the Moon’s face, and can easily be seen any time when it is illuminated, even at full Moon. Billy contrasts with Hansteen, which is light-coloured with a hummocky floor.

Billy is named after the French Jesuit astronomer Jacques de Billy (1602-79), who was one of the first to reject the role of astrology in science, along with superstitious notions about the malevolent influence of comets.

Original Source: ESA Portal

Posted on by Fraser Cain

Nearby Exoplanet is Scorching Hot

Artist’s concept of planet orbiting a star. Image credit: NASA Click to enlarge
A NASA-led team of astronomers have used NASA’s Spitzer Space Telescope to detect a strong flow of heat radiation from a toasty planet orbiting a nearby star. The findings allowed the team to “take the temperature” of the planet.

“This is the closest extrasolar planet to Earth that has ever been detected directly, and it presents the strongest heat emission ever seen from an exoplanet,” said Drake Deming of NASA’s Goddard Space Flight Center, Greenbelt, Md. Deming is the lead author of a paper on this observation to be published in the Astrophysical Journal on June 10. An advance copy of the paper will be posted on the astro-ph website on Feb. 22.

The planet “HD 189733b” orbits a star that is a near cosmic neighbor to our sun, at a distance of 63 light years in the direction of the Dumbbell Nebula. It orbits the star very closely, just slightly more than three percent of the distance between Earth and the sun. Such close proximity keeps the planet roasting at about 844 Celsius (about 1,551 Fahrenheit), according to the team’s measurement.

The planet was discovered last year by Francois Bouchy of the Marseille Astrophysics Laboratory, France, and his team. The discovery observations allowed Bouchy’s team to determine the planet’s size (about 1.26 times Jupiter’s diameter), mass (1.15 times Jupiter), and density (about 0.75 grams per cubic centimeter). The low density indicates the planet is a gas giant like Jupiter.

The observations also revealed the orbital period (2.219 days) and the distance from the parent star. From this distance and the temperature of the parent star, Bouchy’s team estimated the planet’s temperature was at least several hundred degrees Celsius, but they were not able to measure heat or light emitted directly from the planet.

“Our direct measurement confirms this estimate,” said Deming. This temperature is too high for liquid water to exist on the planet or any moons it might have. Since known forms of life require liquid water, it is unlikely to have emerged there.

Last year, Deming’s team and another group based at the Harvard-Smithsonian Center for Astrophysics used Spitzer to make the first direct detection of light from alien worlds, by observing the warm infrared glows of two other previously detected “Hot Jupiter” planets, designated HD 209458b and TrES-1.

Infrared light is invisible to the human eye, but detectable by special instruments. Some infrared light is perceived as heat. Hot Jupiter planets are alien gas giants that zip closely around their parent stars, like HD 189733b. From their close orbits, they soak up ample starlight and shine brightly in infrared wavelengths.

Deming’s team used the same method to observe HD 189733b. To distinguish the planet’s glow from its hot parent star, the astronomers used an elegant method. First, they used Spitzer to collect the total infrared light from both the star and its planet. Then, when the planet dipped behind the star as part of its regular orbit, the astronomers measured the infrared light coming from just the star. This pinpointed exactly how much infrared light belonged to the planet. Under optimal circumstances this same method can be used to make a crude temperature map of the planet itself.

“The heat signal from this planet is so strong that Spitzer was able to resolve its disk, in the sense that our team could tell we were seeing a round object in the data, not a mere point of light,” said Deming. “The current Spitzer observations cannot yet make a temperature map of this world, but more observations by Spitzer or future infrared telescopes in space may be able to do that.”

Deming’s team includes Joseph Harrington, Cornell University, Ithaca, N.Y.; Sara Seager, Carnegie Institution of Washington; and Jeremy Richardson, NASA Postdoctoral Fellow at Goddard, in the Exoplanets and Stellar Astrophysics Laboratory.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for the agency’s Science Mission Directorate. Science operations are conducted at the Spitzer Science Center at Caltech. JPL is a division of Caltech.

Original Source: NASA News Release

Posted on by Fraser Cain

New Type of Star Discovered

An artist’s impression of a neutron star with its magnetic field lines showing. Image credit: Russell Kightly Media. Click to enlarge
Astronomers of the University of Manchester’s Jodrell Bank Observatory (UK) have led an international team which used the Parkes radio telescope in Australia to find a new kind of cosmic object which sends out radio flashes. These flashes are very short and very rare: one hundredth of a second long, the total time the objects are visible amounts to only about one tenth of a second per day.

The discovery will be published in this week’s issue of the journal Nature.

Eleven sources of flashes have been found in different parts of the plane of the Milky Way in a survey for radio pulsars, which are small, compressed, highly-magnetised, neutron stars that produce regular pulses as they rotate, like cosmic light-houses. While that survey found over 800 pulsars and is the most successful in history, it also uncovered this new type of star. Rather than searching only for the periodic trains of pulses, the astronomers developed new techniques for detecting single short bursts of radiation.

Dr Maura McLaughlin explained: “It was difficult to believe that the flashes we saw came from outer space, because they looked very much like man-made interference”. The isolated flashes last for between 2 and 30 milliseconds. In between, for times ranging from 4 minutes to 3 hours, the new stars are silent.

After confirmation of their celestial nature, studies over the next 3 years revealed that 10 of the 11 sources have underlying periods of between 0.4 seconds and seven seconds.

“The periodicities found suggest that these new sources are also rotating neutron stars, but different from radio pulsars”, says Professor Andrew Lyne. “It is for this reason that we call them Rotating Radio Transients or RRATs. It’s as if, following a flash, a RRAT has to gather its strength during perhaps a thousand rotations before it can do it again !”.

RRATs are a new flavour of neutron stars in addition to the conventional radio pulsars and to the magnetars, which are also believed to be rotating neutron stars and are known to give off powerful X-ray and gamma-ray bursts. It is possible that RRATs represent a different evolutionary phase of neutron stars to or from magnetars.

The new objects probably far outnumber both their cousins. “Because of their ephemeral nature, RRATs are extremely difficult to find and so we believe that there are about 4 RRATs for every pulsar” says Dr Richard Manchester of the Australia Telescope National Facility. He is part of the team which also includes astronomers from the US, Canada and Italy.

Original Source: Jodrell Bank Observatory

Posted on by Fraser Cain

Southern Enceladus Covered in Fresh Snow

Saturn’s moon Enceladus. Image credit: NASA/JPL/SSI Click to enlarge
A false color look reveals subtle details on Enceladus that are not visible in natural color views.

The now-familiar bluish appearance (in false color views) of the southern “tiger stripe” features and other relatively youthful fractures is almost certainly attributable to larger grain sizes of relatively pure ice, compared to most surface materials.

On the “tiger stripes,” this coarse-grained ice is seen in the colored deposits flanking the fractures as well as inside the fractures. On older fractures on other areas of Enceladus, the blue ice mostly occurs on the exposed wall scarps.

The color difference across the moon’s surface (a subtle gradation from upper left to lower right) could indicate broad-scale compositional differences across the moon’s surface. It is also possible that the gradation in color is due to differences in the way the brightness of Enceladus changes toward the limb, a characteristic which is highly dependent on wavelength and viewing geometry.

See PIA07709 for a monochrome version of this view.

Terrain on the trailing hemisphere of Enceladus (505 kilometers, or 314 miles across) is seen here. North is up.

The view was created by combining images taken using ultraviolet, green and infrared spectral filters, and then was processed to accentuate subtle color differences. The images were taken with the Cassini spacecraft narrow-angle camera on Jan. 17, 2006 at a distance of approximately 153,000 kilometers (95,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 29 degrees. Image scale is 912 meters (2,994 feet) 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 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 operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Gemini Counts Up the Dark Matter in NGC 3379

NGC 3379. Image credit: NASA/University of Michigan. Click to enlarge
Using Gemini observations of globular clusters in NGC 3379 (M105), a team led by PhD student Michael Pierce and Prof. Duncan Forbes of Swinburne University in Australia, have found evidence for normal quantities of dark matter in the galaxy??bf?s dark halo. This is contrary to previous observations of planetary nebulae that indicated a paucity of dark matter in the galaxy.

The observations of 22 globular clusters in the Leo Group elliptical galaxy were made using the Gemini Multi-Object Spectrograph (GMOS) on Gemini North in early 2003. The data were obtained in the GMOS multi-slit mode with exposures of 10 hours on-source at a spectral resolution of FWHM ~4Aa over an effective wavelength range of 3800A-6660A. The final spectra have a signal-to-noise ratio of 18-58/A at 5000 A. The spectroscopic data allowed the team to derive ages, metallicities and α-element abundance ratios for the sample of globular clusters. All of the globular clusters were found to be >~ 10 Gyr, with a wide range of metallicities. A trend of decreasing α-element abundance ratio with increasing metallicity is also identified.

Most significantly, including 14 extra globular clusters from Puzia, et al. (2004), the projected velocity dispersion of the globular cluster system was found to be constant with radius from the galaxy center, indicating significant dark matter at large radii in its halo. This result is in stark contrast to the ??bf?No/Low Dark Matter??bf? interpretation by Romanowsky, et al. (2003) in the journal Science using observations of planetary nebula that indicated a decrease in the velocity dispersion profile with radius.

Reconciling the two velocity dispersion profiles is possible. Dekel, et al. (2005) recently showed that stellar orbits in the outer regions of merger-remnant elliptical galaxies are elongated and that declining planetary nebula velocity dispersions do not necessarily imply a dearth of dark matter.

Another possibility the authors suggest is that NGC 3379 could be a face-on S0 galaxy (as originally suggested by Capaccioli, et al. 1991). If a significant fraction of the planetary nebulae belong to the disk, this could suppress the line-of-sight velocity dispersion of the planetary nebulae relative to that of the globular clusters that lie in a more spherical halo.

Original Source: Gemini Observatory