Opportunity's Mad Dash

Someone once said, "Opportunity knocks only once, but temptation bangs on your door for years." And ever since NASA plopped twin rovers onto the ruddy surface of Mars in early 2004, mission scientists have exploited the longevity of their mechanical marvels to explore ever-wider swaths of Martian real estate.

An orbital view of Victoria crater, which Opportunity explored for more than a year, and much larger Endeavour crater, where the rover is now headed. Endeavour is about 14 miles (22 km) across and 1,000 feet (300 m) deep. This scene is a mosaic of about 50 images captured by the THEMIS instrument aboard Mars Odyssey.

NASA / JPL / Arizona State Univ.

The rover Opportunity, in particular, recently wrapped up an entire year of scientific prospecting along the rocky inner slopes of Victoria crater — after rolling 4 miles (6 km) to get there. Measuring 2,400 feet across and about a tenth as deep, Victoria provided a ready-made "road cut" in the upper crust that allowed geologists to peer back into recent Martian history.

Now rover-meister Steven Squyres wants to dispatch Opportunity on an even more audacious undertaking: a 7-mile (12-km) trek to an even larger crater named Endeavour. It's about as far away as the entire distance that the rover has traveled to date, and the craft is already well past its 90-day warranty.

But reaching (or even nearing) 14-mile-wide Endeavour would provide a scientific boon, since the impact that created it undoubtedly unearthed countless rocks from deep crustal layers and lobbed them onto the surrounding terrain. Squyres also points out that heading south, toward that big pit, is where Opportunity would be heading next anyway.

The craft is in excellent shape, though there's a balky motor in the shoulder joint of its instrument-tipped robotic arm. And it'll have two advantages that should make the going easier. One is the eagle-eyed Mars Reconnaissance Orbiter, whose High Resolution Imaging Science Experiment (HiRISE) camera can record surface details smaller than the rover itself. The other is new onboard programming that helps the both rovers optimize their routes to avoid hazards such as sand dunes.

Still, Opportunity will have to hustle to reach Endeavour. Even clipping along at 110 yards per day, engineers estimate that the journey could take two years.

By the way, NASA's exploration of Mars was featured last week on National Public Radio's "Talk of the Nation: Science Friday." If you missed the broadcast, you can listen to streamed audio here.

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Lucimary Vargas

Observatório Astronômico Monoceros

Além Paraíba-MG-Brasil

observatorio.monoceros@gmail.com

Ulysses reveals Sun is blowing a weaker solar wind

 

SOUTHWEST RESEARCH INSTITUTE NEWS RELEASE
Posted: September 23, 2008

SAN ANTONIO -- Surprising data from NASA's Ulysses spacecraft show that the solar wind -- the continuous outflow of plasma and magnetic fields from the Sun's atmosphere (corona) into interplanetary space -- is only about three fourths as strong as it was a decade ago, during the last interval of low solar activity.

Artist concept of heliosphere. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab

Since its launch in 1990, Ulysses has completed nearly three polar orbits around the Sun, enabling researchers to observe the three-dimensional structure of the solar wind and heliosphere, or region of space dominated by our Sun, for the first time.

"This pioneering spacecraft has allowed us to discover new and fascinating things about the Sun's million-mile-per-hour solar wind and how it changes over time," says Dr. David J. McComas, principal investigator of the Solar Wind Observations Over the Poles of the Sun (SWOOPS) experiment onboard Ulysses and senior executive director of the Space Science and Engineering Division at Southwest Research Institute. "To see such a significant and consistent long-term reduction in the solar wind output is really remarkable."

Over its 18 years in orbit about the Sun, Ulysses has observed the solar wind at both the minimum and maximum phases of the solar activity (or sunspot) cycle. During solar minimum, the wind is well ordered, with a fast, steady wind over the poles and a slow variable wind at lower latitudes; at solar maximum, the solar wind is highly chaotic, with fast and slow wind streams and more frequent coronal mass ejections at all solar latitudes.

Now, three-quarters of the way through its third orbit, Ulysses is again observing a solar wind structure characteristic of low levels of solar activity. "During the third orbit, we weren't surprised to see a return to a solar minimum configuration," says McComas, "but we were surprised to find that the solar wind is much less powerful than it had been in the previous solar minimum. The wind speed is almost the same, but the density and pressure are significantly lower, and the wind is blowing out about a quarter less hard."

The strength of the solar wind appears to be determined to a significant degree by where in the solar corona the energy that drives the solar wind is inserted. Energy inserted at low altitudes results in lower pressures and densities, without affecting solar wind speed. Energy inserted at higher coronal altitudes is expected to produce a change in the solar wind speed, which was not observed.

To determine whether the weaker solar wind is a whole-sun phenomenon, the team compared Ulysses' high-latitude observations with measurements made by the Advanced Composition Explorer spacecraft at low solar latitudes. The data show a close correlation in the dynamic pressure of the wind measured at all latitudes, confirming that the unusually weak outflow is a global phenomenon.

The effects of the weaker wind will be felt several billion miles beyond the orbit of Pluto, at the farthest limits of the Sun's influence. "The heliosphere is a big bubble that's inflated from the inside by the million-mile-per-hour solar wind blowing out in all directions," says McComas. "The size of the bubble is determined by the balance of pressure of the solar wind pushing from the inside out and the pressure of interstellar space pushing from the outside in. If the solar wind is blowing out a quarter less hard, that means the outer boundaries of the heliosphere must be shrinking. The entire heliosphere must be getting smaller."

Some variations in the strength of the solar wind aren't unusual. In the early 1990s, the solar wind weakened for some time and regained strength over the following two years. Further observations will determine whether the solar wind continues to lose strength as the Sun moves from the solar minimum back toward maximum. If the strength of the solar wind stays weak, Voyager 1, which is headed outside of our solar system, should reach the edge of the solar system, called the heliopause, earlier than expected and will become the first spacecraft to enter interstellar space.

Future NASA missions will help resolve some of the intriguing questions brought forth by Ulysses. NASA is scheduled to launch the Interstellar Boundary Explorer (IBEX) spacecraft in October to make the first global images of the outer boundaries of the solar system. IBEX will be able to image interactions in that region caused by a weaker solar wind. In addition, NASA is about to begin development of the Solar Probe mission to fly in close to the Sun and determine what heats its corona and accelerates the solar wind.

The article "Weaker Solar Wind from the Polar Coronal Holes and the Whole Sun," by McComas, R.W. Ebert, H.A. Elliott, B.E. Goldstein, J.T. Gosling, N.A. Schwadron and R.M. Skoug, was published in Geophysical Research Letters, 35, L18103, doi:10.1029/2008GL034896.

SwRI is an independent, nonprofit, applied research and development organization based in San Antonio, Texas, with more than 3,300 employees and an annual research volume of more than $501 million.

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Lucimary Vargas

Observatório Astronômico Monoceros

Além Paraíba-MG-Brasil

observatorio.monoceros@gmail.com

 

The Solar Wind Takes a Breather

 

I've always had a soft spot for an interplanetary pioneer called Ulysses. Built by the European Space Agency, it was launched in 1990 toward Jupiter, where the planet's powerful gravity yanked the craft out of the ecliptic plane and onto a looping path that carries it over and under the Sun every six years.

The Ulysses spacecraft, launched in 1990, recently completed its third and final pass over the Sun's polar regions.

European Space Agency

The initial mission concept, known as the International Solar Polar Mission, called for two identical craft — one European and one American — to study high-latitude regions of the Sun that can't be studied from Earth. But NASA reneged on its end of the deal, so Ulysses has soldiered on alone.

Recently it completed its third and final pass over the Sun's poles. That kind of longevity, far exceeding the planned 5-year-long mission, has really paid off. Ulysses's observations show that the solar wind is particularly feeble right now, with just 75% the strength it had a decade ago. In fact it's never been this weak since monitoring began a half century ago.

Space physicists had expected the flow to tail off, because the Sun's 11-year activity cycle is now at a minimum. But it's got far less punch than that seen during the last minimum. "The wind speed is almost the same, but the density and pressure are significantly lower," notes investigator David McComas (Southwest Research Institute), whose SWOOPS instrument aboard Ulysses has been key to the new finding.

The solar wind consists of plasma (ionized matter) and entrained solar magnetic field lines that pushed outward from the Sun's atmosphere into interplanetary space. Ulysses had previously shown that the wind comes off the Sun's poles faster and with less turbulence than it does from its midsection. But both the polar and equatorial flows have throttled back to historic lows.

There'd been earlier hints, in deep-space observations from IMP 8 and Voyager 2, that the solar wind variously ebbed and flowed during a solar cycle. Still, McComas and his colleagues, who detail their results in the September 18th issue of Geophysical Research Letters, don't know why the solar wind is taking a breather. One suspicion: perhaps the outflow is somehow being energized higher up in the Sun's corona, where there's less mass available to push outward into space.

Earth's magnetosphere (blue lines) protects our planet from space radiation and from the electromagnetic "wind" (at left) that continually flows from the Sun. During episodes of intense solar activity, as depicted here, the solar wind strengthens and can penetrate the magnetosphere more readily, triggering intense auroral displays.

NASA / Goddard Space Flight Center

In any case, the low flow means that the gigantic electromagnetic bubble that surrounds the Sun and planets must be shrinking inward and, with it, the solar system's boundary with interstellar space (called the heliopause). Both Voyager spacecraft are nearing this threshhold; they've aleady encountered a shock front inside the heliopause, and if this weak solar wind keeps up, Voyager 1 may find itself popping outside the heliosphere years sooner than expected.

Meanwhile, Ulysses itself is nearing the end of its historic mission. FLight controllers have been keeping a death watch all year, because the craft's source of heat and power (radioactive plutonium) has dwindled so much that the fuel lines are in imminent danger of freezing.

I contacted ESA project manager Richard Marsden for an update on the craft's health. "True to its name, Ulysses refuses to give up without a fight," he replied. "We're still getting science data, albeit only a few hours per day." The team has kept the fuel from freezing by firing thrusters every two hours. But the fuel is running low, and the team expects Ulysses to run dry sometime between the end of September and December. "With a bit of luck," Marsden adds, "we'll encounter the slow solar wind once again before then."

Hang in there, Ulysses!

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Lucimary Vargas
Presidente
Observatório Astronômico Monoceros
Além Paraíba-MG-Brasil
observatorio.monoceros@gmail.com

Haumea: Dwarf-Planet Name Game

On September 17th, the International Astronomical Union announced that an object in the Kuiper Belt — the fifth solar-system body large enough to qualify as a "dwarf planet" — had been named. It'll be called Haumea (pronounced how-MAY-uh), after the goddess of childbirth and fertility in Hawaiian mythology.

But there's far more to the story. When it comes to naming Kuiper Belt objects, the IAU typically accommodates whatever's suggested by the discoverer(s). In the case of Haumea, formerly designated 2003 EL₆₁ and now formally numbered minor planet 136108, there's debate — controversy, actually — over who discovered it.

The shape of Haumea (formerly 2003 EL₆₁) is roughly 1,960 by 1,000 km — making it a fast-rotating squashed football. Its two satellites are Hi'iaka and Namaka.

NASA, ESA, and A. Feild (STScI)

Haumea is the name suggested by Michael Brown (Caltech), who together with Chad Trujillo and David Rabinowitz spotted it on December 28, 2004. But Brown didn't report his team's observations right away to the IAU's clearinghouse for such discoveries, the Minor Planet Center in Cambridge, Massachusetts, as he explains on his website. Instead, he and others continued to scrutinize this relatively bright and thus sizable body — learning a month later, for example, that it had a moon. (They eventually found a second moon as well.)

In July 2005, just as Brown was preparing to announce all this, Spanish astronomers Pablo Santos-Sanz and José Luis Ortiz Moreno sent the MPC some observations of the same object taken two years earlier at little-known Sierra Nevada Observatory. What's become clear since then is that the Spaniards accessed the American team's publicly accessible observing records 39 hours before submitting their discovery claim to the MPC but, they insist, after deducing the existence of 2003 EL₆₁ themselves.

To recap: Brown's team chanced upon the object first, but the Spanish observers reported its discovery first. There's still bad blood over this, and it's not likely to be resolved soon. For now, the MPC's record for asteroid 136108 lists "Sierra Nevada" as both the discoverer(s) and the discovery site, though those details are omitted from Haumea's official naming citation. But you won't find the discoverers' names listed next to Sierra Nevada (which is apparently how the Spaniards wanted it).

So why didn't 2003 EL₆₁ get christened Ataecina, the name suggested by Ortiz and his colleagues? Ataecina was a goddess worshiped by ancient inhabitants of the Iberian peninsula, and she was usually associated to Proserpina, Roman goddess of the underworld. Therein lies the problem: by IAU convention, deities of the underworld are reserved for objects in Pluto-like orbits (in resonance with Neptune), which 2003 EL₆₁ is not.

Brown's team proposed not only Haumea but also Hi'iaka and Namaka (two of Haumea's many children) for the two moons. It all fits together nicely.

But there's been plenty of behind-the-scenes rancor about how these names gained approval. Two groups, the Working Group for Planetary System Nomenclature and the Committee for Small-Body Nomenclature, were under pressure from IAU general secretary General Secretary Karel van der Hucht to resolve the 2003 EL₆₁ naming issue quickly. However, the CSBN's vote on Haumea ended in a tie or at best a slim majority, depending on who's doing the tallying (some of its members sit on the WGPSN as well).

Since the IAU wasn't bound to accept the name proposed by either team, one wonders why the WGPSN and CSBN didn't work harder to come up with something more politically neutral.

Oh, by the way, here's a question for any CSBN or WGPSN members who happen to read this: Is Ceres a dwarf planet? I know that was the IAU's intention when the controversial Pluto votes were cast back in 2006 — but unless I'm missing something, the approved resolutions never mention Ceres.

 

A 'wild cousin' emerges from family tree of exploding stars

UNIVERSITY OF CHICAGO NEWS RELEASE
Posted: October 1, 2008

Astronomers may have discovered the relative of a freakishly behaving exploding star once thought to be the only one of its kind.

For more than two decades, astronomers have intensively studied supernova 1987A, an exploding star that had behaved like no other. Instead of growing dimmer with time, 1987A has grown brighter at X-ray and radio wavelengths.

This composite image shows the central regions of the nearby Circinus galaxy, located about 12 million light years away. Data from NASA's Chandra X-ray Observatory is shown in blue and data from the Hubble Space telescope is shown in yellow, red, cyan and light blue. The blue source near the lower right hand corner of the image is the supernova SN 1996cr, that has finally beenidentified over a decade after it exploded. Credit: X-ray (NASA/CXC/Columbia/F.Bauer et al); Optical (NASA/STScI/UMD/A.Wilson et al.)

A team of astronomers that includes the University of Chicago's Vikram Dwarkadas is asking if supernova 1996cr, discovered by Columbia University's Franz Bauer, is actually the "wild cousin" of supernova 1987A.

"This may be the second case, after '87a, where we see emission that's increasing dramatically," said Dwarkadas, Senior Research Associate in Astronomy & Astrophysics at Chicago. "Normally, you would expect the emission to decrease over time."

In a new paper that will appear in the Astrophysical Journal, Bauer, Dwarkadas and five co-authors call 1996cr a potential "wild cousin" of the earlier supernova. "These two look alike in many ways, except this newer supernova is intrinsically 1,000 times brighter," Bauer said.

Supernova 1996cr is located 12 million light years from Earth in the spiral galaxy Circinus, making it one of the nearest-known exploding stars of the last quarter-century.

When 1996cr exploded in the mid-1990s, no one noticed. Bauer first detected the object in 2001 using NASA's Chandra X-ray Observatory. Although intrigued by its exceptional qualities, Bauer, then at Pennsylvania State University, and his associates were unable to verify it as a supernova.

But recently acquired data from the European Southern Observatory's Very Large Telescope in Chile prompted further investigation. After searching archival images from Australia's Anglo-Australian Telescope, Bauer determined that the explosion occurred between Feb. 28, 1995, and March 15, 1996.

All told, Bauer's team examined data from 18 different telescopes, both orbiting and ground-based, nearly all of it coming from the observatories' Internet archives.

Most supernovas grow dimmer with the passage of time as they release their energy. But the X-ray and radio emissions from 1987A grew brighter because its shock wave had crashed into a dense cloud of gas and dust. Supernova shock waves initially move at speeds of 10,000 miles or more each second.

According to the calculations of Dwarkadas and other theoreticians, these interstellar gas clouds form a bubble around stars at least eight times more massive than the sun, possibly the product of smaller upheaval or a lifetime of mass-loss from solar wind emissions that took place before the supernova.

These wind-blown bubbles, as astronomers call them, are like a balloon: empty in the middle with a shell around the outside. The explosion moves rapidly through the cavity for several years because there's almost nothing to stop it. "Then it hits this dense shell. It slows down and begins to give off a lot of emission," Dwarkadas said.

Supernovas close enough to be studied in such detail come by only once a decade, Bauer said. "It's a bit of a coup to find SN1996cr in the manner we did, and we could never have nailed it without the serendipitous data taken by all of these telescopes. We've truly entered a new era of 'Internet astronomy,'" he said.

Co-authors of the paper included Niel Brandt, Penn State; Stefan Immler, NASA Goddard Space Flight Center; Norbert Bartel, York University, Canada; and Michael Bietenholz, York University and Hartebeesthoek Radio Observatory, South Africa. The National Science Foundation, the National Aeronautic and Space Administration, and the European Science Foundation provided funding.

Sharpening up Jupiter

EUROPEAN SOUTHERN OBSERVATORY NEWS RELEASE
Posted: October 2, 2008

A record two-hour observation of Jupiter using a superior technique to remove atmospheric blur has produced the sharpest whole-planet picture ever taken from the ground. The series of 265 snapshots obtained with the Multi-Conjugate Adaptive Optics Demonstrator (MAD) prototype instrument mounted on ESO's Very Large Telescope (VLT) reveal changes in Jupiter's smog-like haze, probably in response to a planet-wide upheaval more than a year ago.

Credit: ESO/F. Marchis, M. Wong, E. Marchetti, P. Amico, S. Tordo See a larger image here

Being able to correct wide field images for atmospheric distortions has been the dream of scientists and engineers for decades. The new images of Jupiter prove the value of the advanced technology used by MAD, which uses two or more guide stars instead of one as references to remove the blur caused by atmospheric turbulence over a field of view thirty times larger than existing techniques.

"This type of adaptive optics has a big advantage for looking at large objects, such as planets, star clusters or nebulae," says lead researcher Franck Marchis, from UC Berkeley and the SETI Institute in Mountain View, California, USA. "While regular adaptive optics provides excellent correction in a small field of view, MAD provides good correction over a larger area of sky. And in fact, were it not for MAD, we would not have been able to perform these amazing observations."

MAD allowed the researchers to observe Jupiter for almost two hours on 16 and 17 August 2008, a record duration, according to the observing team. Conventional adaptive optics systems using a single Jupiter moon as reference cannot monitor Jupiter for so long because the moon moves too far from the planet. The Hubble Space Telescope cannot observe Jupiter continuously for more than about 50 minutes, because its view is regularly blocked by the Earth during Hubble's 96-minute orbit.

Using MAD, ESO astronomer Paola Amico, MAD project manager Enrico Marchetti and Sébastien Tordo from the MAD team tracked two of Jupiter's largest moons, Europa and Io ­ one on each side of the planet ­ to provide a good correction across the full disc of the planet. "It was the most challenging observation we performed with MAD, because we had to track with high accuracy two moons moving at different speeds, while simultaneously chasing Jupiter," says Marchetti.

With this unique series of images, the team found a major alteration in the brightness of the equatorial haze, which lies in a 16 000-kilometre wide belt over Jupiter's equator. More sunlight reflecting off upper atmospheric haze means that the amount of haze has increased, or that it has moved up to higher altitudes. "The brightest portion had shifted south by more than 6000 kilometres," explains team member Mike Wong.

This conclusion came after comparison with images taken in 2005 by Wong and colleague Imke de Pater using the Hubble Space Telescope. The Hubble images, taken at infrared wavelengths very close to those used for the VLT study, show more haze in the northern half of the bright Equatorial Zone, while the 2008 VLT images show a clear shift to the south.

"The change we see in the haze could be related to big changes in cloud patterns associated with last year's planet-wide upheaval, but we need to look at more data to narrow down precisely when the changes occurred," declares Wong.

Worlds in collision

UNIVERSITY OF CALIFORNIA-LOS ANGELES NEWS RELEASE
Posted: October 2, 2008
Two terrestrial planets orbiting a mature sun-like star some 300 light-years from Earth recently suffered a violent collision, astronomers at UCLA, Tennessee State University and the California Institute of Technology will report in a December issue of the Astrophysical Journal, the premier journal of astronomy and astrophysics.

An artist's conception of the planetary collision in the BD +20 307 binary system. Credit: Lynette Cook

"It's as if Earth and Venus collided with each other," said Benjamin Zuckerman, UCLA professor of physics and astronomy and a co-author on the paper. "Astronomers have never seen anything like this before. Apparently, major catastrophic collisions can take place in a fully mature planetary system."

"If any life was present on either planet, the massive collision would have wiped out everything in a matter of minutes ‹ the ultimate extinction event," said co-author Gregory Henry, an astronomer at Tennessee State University (TSU). "A massive disk of infrared-emitting dust circling the star provides silent testimony to this sad fate."

Zuckerman, Henry and Michael Muno, an astronomer at Caltech at the time of the research, were studying a star known as BD+20 307, which is surrounded by a shocking 1 million times more dust than is orbiting our sun. The star is located in the constellation Aries. The astronomers gathered X-ray data using the orbiting Chandra X-ray Observatory and brightness data from one of TSU's automated telescopes in southern Arizona, hoping to measure the age of the star.

"We expected to find that BD+20 307 was relatively young, a few hundred million years old at most, with the massive dust ring signaling the final stages in the formation of the star's planetary system," Muno said.

Those expectations were shown to be premature, however, when Carnegie Institution of Washington astronomer Alycia Weinberger announced in the May 20, 2008, issue of the Astrophysical Journal that BD+20 307 is actually a close binary star ‹ two stars orbiting around their common center of mass.

"That discovery radically revised the interpretation of the data and transformed the star into a unique and intriguing system," said TSU astronomer Francis Fekel who, along with TSU's Michael Williamson, was asked to provide additional spectroscopic data from another TSU automated telescope in Arizona to assist in comprehending this exceptional binary system.

The new spectroscopic data confirmed that BD+20 307 is composed of two stars, both very similar in mass, temperature and size to our own sun. They orbit about their common center of mass every 3.42 days.

"The patterns of element abundances in the stars show that they are much older than a few hundred million years, as originally thought," Fekel said. "Instead, the binary system appears to have an age of several billion years, comparable to our solar system."

"The planetary collision in BD+20 307 was not observed directly but rather was inferred from the extraordinary quantity of dust particles that orbit the binary pair at about the same distance as Earth and Venus are from our sun," Henry said. "If this dust does indeed point to the presence of terrestrial planets, then this represents the first known example of planets of any mass in orbit around a close binary star."

Zuckerman and colleagues first reported in the journal Nature in July 2005 that BD+20 307, then still thought to be a single star, was surrounded by more warm orbiting dust than any other sun-like star known to astronomers. The dust is orbiting the binary system very closely, where Earth-like planets are most likely to be and where dust typically cannot survive long. Small dust particles get pushed away by stellar radiation, while larger pieces get reduced to dust in collisions within the disk and are then whisked away. Thus, the dust-forming collision near BD+20 307 must have taken place rather recently, probably within the past few hundred thousand years and perhaps much more recently, the astronomers said.

"This poses two very interesting questions," Fekel said. "How do planetary orbits become destabilized in such an old, mature system, and could such a collision happen in our own solar system?"

"The stability of planetary orbits in our own solar system has been considered for nearly two decades by astronomer Jacques Laskar in France and, more recently, by Konstantin Batygin and Greg Laughlin in the U.S.A.," Henry noted. "Their computer models predict planetary motions into the distant future and they find a small probability for collisions of Mercury with Earth or Venus sometime in the next billion years or more. The small probability of this happening may be related to the rarity of very dusty planetary systems like BD+20 307."

"There is no question, however," Zuckerman said, "that major collisions have occurred in our solar system's past. Many astronomers believe our moon was formed from the grazing collision of two planetary embryos ‹ the young Earth and a body about the size of Mars ‹ a crash that created tremendous debris, some of which condensed to form the moon and some of which went into orbit around the young sun. By contrast with the massive crash in the BD+20 307 system, the collision of an asteroid with Earth 65 million years ago, the most favored explanation for the final demise of the dinosaurs, was a mere pipsqueak."

In their 1932 novel "When Worlds Collide," science fiction writers Philip Wylie and Edwin Balmer envisioned the destruction of Earth by a collision with a planet of a passing star. The 1951 classic movie based on the novel began a long line of adventure stories of space rocks apocalyptically plowing into Earth.

"But," Zuckerman noted, "there is no evidence near BD+20 307 of any such passing star."

When it comes to galaxies, diversity is everywhere

There's an old saying in astronomy: "Galaxies are like people. They're only normal until you get to know them." That view is supported by a group of astronomers after using NASA's Hubble Space Telescope to study a large number of galaxies in our cosmic backyard.

See larger image here

The detailed survey, called the ACS Nearby Galaxy Survey Treasury (ANGST) program, observed roughly 14 million stars in 69 galaxies. The survey explored a region called the "Local Volume," and the galaxy distances ranged from 6.5 million light-years to 13 million light-years from Earth. The Local Volume resides beyond the Local Group of galaxies, an even nearer collection of a few dozen galaxies within about 3 million light-years of our Milky Way Galaxy.

A typical galaxy contains billions of stars but looks "smooth" when viewed through a telescope, because the stars are blurred together. In contrast, the galaxies in the new survey are close enough to Earth that the sharp "eyes" of Hubble's Advanced Camera for Surveys and Wide Field Planetary Camera 2 can resolve their brightest individual stars. By measuring the brightness and colors of these stars, scientists can derive the local history of star formation within a galaxy and can tease out subtle features in a galaxy's shape.

"Past Hubble observations of the local neighborhood have provided dramatic insights into the star-formation histories of individual galaxies, but the number of galaxies studied in detail has been rather small," said Julianne Dalcanton of the University of Washington in Seattle and leader of the ANGST survey. The survey's results were submitted to The Astrophysical Journal Supplement Series. Another paper that details the star-formation history in galaxy M81 has been submitted to The Astronomical Journal.

"Instead of picking and choosing particular galaxies to study, our survey will be complete by virtue of looking at 'all' the galaxies in the region. This gives us a multi-color picture of when and where all the stars in the local universe formed."

Many stars in nearby galaxies are the fossil equivalents of the active star formation seen in galaxies in the distant universe. "When we look back in time at distant, young galaxies, we see lots of vigorous star formation. However, we can only guess as to what those galaxies might eventually turn into," Dalcanton explained. "Using the galaxies in the nearby universe as a 'fossil record,' we can compare them with young galaxies far away. This comparison gives us a history of star formation and provides a better understanding of the masses, structures, and environments of the galaxies."

Early results of the ANGST survey show the rich diversity of galaxies. Some galaxies are made up entirely of ancient stars, while others have been forming stars nearly continuously during their whole lives. There are even a few examples of galaxies that have only started forming stars in the recent past.

"With these images, we can see what makes each galaxy unique," said team member Benjamin Williams of the University of Washington. "When we look at the distribution and development of stars in each survey galaxy, we can learn how differences in the galaxies' histories have produced the diversity of galaxy shapes and colors."

The ANGST survey also includes maps of many large galaxies, including M81. "With these maps, we can track when the different parts of the galaxy formed," explained Evan Skillman of the University of Minnesota, describing work by students Dan Weisz of the University of Minnesota and Stephanie Gogarten of the University of Washington.

In a separate paper describing the star-formation history in M81, astronomers confirmed that massive spiral galaxies formed most of their stars in the early universe. Analyzing M81's outer disk, the astronomers found that most of the stars formed more than 7 billion years ago, when the universe was half its present age. M81 and other mammoth galaxies also experienced rapid enrichment of heavy elements, such as carbon, through the deaths of massive stars in supernova explosions. "We were surprised by how quickly the elements formed and how the subsequent star-formation rate for the bulk of the stars in M81 changed after that," said Williams, the paper's lead author.

"This rich survey will add to Hubble's legacy, providing a foundation for future studies," Dalcanton said. "The ANGST sample offers superb targets for future multi-wavelength surveys, which will allow us to combine the star-formation maps with the properties of gas and dust in the galaxies. With this information, we will be able to trace the complete cycle of star formation in detail."

Sonda Phoenix vê neve cair em Marte

A sonda Phoenix, que explora o solo de Marte, detectou a formação de neve vinda das nuvens do planeta. Os experimentos também mostraram uma interação no passado entre minerais e água em estado líquido, um processo que ocorre na Terra.
A neve foi detectada por instrumentos que usam laser em nuvens localizadas a cerca de 4 km acima de onde a sonda está instalada. Entretanto, os flocos evaporam antes de chegar ao solo.

Solo de Marte, explorado pela Phoenix desde maio; sonda vê neve caindo e presença de carbonato de cálcio no planeta

"Nada como isso havia sido visto em Marte", afirma Jim Whiteway, da York University, em Toronto, um dos líderes de pesquisa da missão. "Nós agora vamos procurar sinais de que a neve chegue até o solo."
Em 18 de setembro, a Folha Online adiantou a descoberta de água líquida em Marte, feita pelo brasileiro Nilton Rennó, também líder de pesquisa da missão da sonda. Para o grupo de Rennó não resta dúvida de que a substância possa ser encontrada no Planeta Vermelho, embora haja outros cientistas que dizem ver apenas "indícios".
Os experimentos realizados na Phoenix também indicam a presença de carbonato de cálcio, elemento presente em esqueletos dos corais e no giz da Terra. Também há indicações de partículas que podem ser argila. "A maioria dos carbonatos na Terra se formam apenas na presença de água líquida", afirma a direção da missão, em nota.
"Nós ainda estamos coletando dados e temos muitas análises pela frente, mas estamos progredindo nas grandes questões que fizemos para nós mesmos", afirma Peter Smith, chefe de pesquisa da Phoenix, no comunicado.
A missão da Phoenix, que começou em 25 de maio e originalmente estava planejada para durar três meses, entrou no quinto mês. Agora, a nave sofre com a queda na energia solar --esse deve ser o motivo para o encerramento dos trabalhos, até o fim do ano.
Até o fim de outubro, não deve haver energia suficiente para o funcionamento do braço robótico da sonda, que faz escavações no planeta. Depois, a Phoenix deve virar "ferro velho" marciano.

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A prima desconhecida de SN1987A

 

 
 
A explosão da supernova de SN1987A foi um marco na astronomia moderna. Esse foi o evento de morte de uma estrela de muita massa mais próximo de nós ocorrido na era dos telescópios modernos.  Ela explodiu na Pequena Nuvem de Magalhães, a meros 160 mil anos-luz de distância. A uma distância tão pequena (comparada, claro, com a de outras galáxias a milhões de anos-luz), a supernova SN1987A tem sido estudada praticamente mês a mês e, desse monitoramento quase contínuo, muitos pontos da teoria das fases finais de vida de estrelas de alta massa puderam ser aprimorados.
Agora, uma outra supernova com características similares foi identificada em arquivos públicos de imagens. A supernova explodiu entre 28 de fevereiro de 1995 e 15 de março de 1996 na galáxia de Circinus, a 13 milhões de anos luz. Essa foi a única supernova entre as cinco mais próximas (dos últimos 25 anos) que não foi detectada tão logo explodiu. A galáxia de Circinus é uma bastante estudada por ser uma das mais próximas e por mostrar gás ejetado em forma de anéis.
SN1996cr, como foi batizada, foi observada pela primeira vez apenas em 2001, por
Franz Bauer, dos EUA, analisando uma imagem de raios-X obtida pelo Telescópio Espacial Chandra. Na hora ele confessou que não entendeu muito bem o que tinha descoberto, e só depois de vasculhar os bancos de imagens públicos de observatórios do mundo inteiro é que ele se deu conta de estar diante de uma supernova. Essa explosão
passou despercebida porque, na faixa da luz visível, ela foi fraca e numa região da galáxia com muita poeira e gás. Como a galáxia de Circinus é bem observada, Bauer encontrou várias imagens, antes e depois da explosão, e percebeu que as similaridades com SN1987A eram imensas. Na verdade, a única diferença apreciável é a intensidade de brilho em rádio e raios-X. Comparada à SN1987A, essa prima distante é muito mais intensa. Ela aparece na imagem composta do Chandra (em azul) e do Hubble neste post como a bolota azul no canto inferior direito.
As semelhanças são principalmente no que se refere aos momentos antes da explosão. As duas supernovas mostram uma grande quantidade de material ejetado. Esse material se move com uma velocidade muito grande e forma uma onda de choque que limpa o meio onde a estrela moribunda está. No caso da supernova de Circinus, a onda foi tão violenta que quase não restou material em volta, e por isso ela brilha mais em raios-X do que a supernova na Grande Nuvem de Magalhães.
Agora veja só o que Nathan Smith achou de Eta Carina a singelos 7.500 anos luz de distância: material ejetado a altas velocidades, no caso em 1843. Em duas supernovas relativamente próximas, isso aconteceu logo antes da explosão. Isso significa que esse deve ser mesmo o sinal de que a hora final de uma estrela com muita massa é precedida por eventos violentos desse tipo. Então, como eu disse no post abaixo, é só esperar que a Eta Carina logo, logo vai virar uma bela atração nos céus.

Empresa privada coloca foguete em órbita

O foguete Falcon 1, da empresa norte-americana SpaceX, se tornou no domingo (28) o primeiro foguete movido a propulsão líquida inteiramente desenvolvido por uma empresa privada a alcançar a órbita terrestre, segundo um comunicado divulgado nesta segunda-feira (29).
"A Space Exploration Technologies Corp. (SpaceX) anuncia que o vôo 4 do foguete Falcon 1 foi lançado com sucesso e alcançou a órbita terrestre", indicou a nota. "Ao atingir essa etapa, o Falcon 1 se torna o primeiro foguete a propulsão líquida desenvolvido pelo setor privado a ser colocado em órbita em torno da Terra".
O Falcon 1, inteiramente concebido pela SpaceX, decolou às 20h15 de Brasília, da base militar norte-americana de Kwajalein, nas Ilhas Marshall (Oceano Pacífico).
O Falcon 1 é um pequeno lançador de 21 metros de altura criado pela SpaceX, sociedade fundada em 2002 por Elon Musk, magnata da internet.

Aquecimento global ou era do gelo?

 

 
Na segunda feira passada, dia 22, começou a primavera, e coincidentemente surgiu uma pequena mancha solar. Tão pequena que já no dia 24 ela tinha desaparecido, durando dois dias ou menos. Manchas solares vêm e vão e possuem um ciclo de 11 anos, alternando períodos de alta intensidade, caracterizado por um grande número delas, e períodos de baixa atividade solar, quando poucas manchas aparecem no Sol. Estamos justamente em um período de mínimo solar, com poucas manchas visíveis.
E qual a novidade nisso?
Bem, o evento em si é bem trivial, manchas vêm e vão, como eu já disse, mas essa foi especial em dois sentidos. O primeiro: ela apareceu depois de um longo período de baixíssima atividade solar, e suas características indicam que se trata uma mancha do ciclo 24. Esse ciclo iniciou-se em janeiro, marcando a saída do mínimo solar. Em outras palavras, de janeiro em diante o número de manchas só deve aumentar, até atingir o máximo entre outubro de 2011 e agosto de 2012. Ao menos em tese. A baixa atividade solar tinha posto em dúvida o momento em que o ciclo 23 tinha acabado, muita gente acreditava que ele ainda estivesse em curso, pois o número de manchas não aumentou como esperado. E isso levanta a segunda questão.
A atividade solar tem perdido força ao longo dos anos. Desde que a intensidade do vento solar começou a ser monitorada, há uns 50 anos, ela nunca esteve tão baixa. O vento solar é responsável por criar uma bolha chamada de helioesfera, que envolve e protege o Sistema Solar dos raios cósmicos de alta energia provenientes do resto do Universo. Com o vento solar menos intenso, a bolha se encolhe e fica mais fina, facilitando a passagem dos raios cósmicos. Em princípio, estamos a salvo na Terra, pois nosso campo magnético e nossa atmosfera nos protegem, mas satélites, astronautas e qualquer equipamento fora dessa proteção estará sujeito a esse bombardeio. Na prática, a vida útil de sondas espaciais será encurtada.
Além disto, existe um estudo controverso que liga a quantidade de raios cósmicos à quantidade de nuvens na Terra. Essa hipótese diz que o bombardeio de raios cósmicos na nossa atmosfera favorece a criação de nuvens. Se a helioesfera se enfraquecer, é justamente isso que vai acontecer, aumento de raios cósmicos e aumento de nuvens.
Aumentar a capa de nuvens significa bloquear a quantidade de raios solares que penetram a atmosfera. O topo das nuvens acaba refletindo a luz do Sol de volta ao espaço e, como conseqüência, a Terra esfriaria. É claro que isso não explica a atual onda de frio em plena primavera.
A hipótese é um tanto controversa, mas entre 1645 e 1715, aproximadamente, o número de manchas solares registrado foi muito pequeno, e o período ficou conhecido como "Mínimo de Mauner". Nesse mesmo período a Europa sofreu com temperaturas muito baixas, com rios que normalmente são fluidos o ano inteiro ficando congelados durante um ano inteiro! Esse período é conhecido em geologia ou meteorologia como "Pequena Idade do Gelo". Apesar dos registros do número de manchas da época não serem tão bons quanto atualmente, parece que o número atual de manchas é menor que o verificado no Mínimo de Mauner.
No final das contas, pode ser que o Sol nos dê uma força para impedir que as temperaturas se elevem com o aquecimento global.