Posted on by Fraser Cain

Dust Storm on Mars Visible By Amateurs

Image credit: Hubble

Now that Mars is closer than ever, amateur astronomers with regular backyard telescopes can see incredible details on the planet’s surface. On July 1, astronomers were able to see a dust storm in the Hellas Basin; four days later it was 1,800 kilometres wide, obscuring nearly a quarter of the planet. Two years ago a similar storm grew in the same region and ended up obscuring the entire planet for months. Earth and Mars will reach their closest point in 60,000 years on August 27, 2003, and the Red Planet should offer up some tremendous views.

Something is happening on Mars and it’s so big you can see it through an ordinary backyard telescope.

On July 1st a bright dust cloud spilled out of Hellas Basin, a giant impact crater on Mars’ southern hemisphere. The cloud quickly spread and by the Fourth of July was 1100 miles wide–about one-fourth the diameter of Mars itself.

“The cloud can be seen now through a telescope as small as 6 inches,” says Donald Parker, executive director of the Association of Lunar and Planetary Observers (ALPO). “Its core is quite bright.”

Parker has been tracking the cloud through his own 16-inch telescope. “A red filter helps,” he notes. “Even a piece of red or orange gelatin held between the eye and ocular will improve the visibility of the dust.”

Two years ago, a similar cloud from Hellas Basin grew until it circled the entire planet. Features on Mars long familiar to amateur astronomers–the dark volcanic terrain of Syrtis Major, for example–were hidden for months. “The planet looked like an orange billiard ball,” recalls Parker.

Will it happen again?

“No one knows,” says astronomer James Bell of Cornell University who studied the dust storm of 2001 using the Hubble telescope. “We don’t yet understand the mechanism that causes regional clouds to self-assemble into giant dust storms.”

Mars Global Surveyor and Mars Odyssey, two NASA spacecraft circling Mars, have seen many “regional storms” like the cloud near Hellas Basin now. They persist for a few days or weeks, then dissipate. Rarely do they become a planet-wide event.

“Only 10 global or planet-encircling dust storms have been reported since 1877,” notes Parker.

All dust storms on Mars, no matter what size, are powered by sunshine. Solar heating warms the martian atmosphere and causes the air to move, lifting dust off the ground.

Because the martian atmosphere is thin–about 1% as dense as Earth’s at sea level–only the smallest dust grains hang in the air. “Airborne dust on Mars is about as fine as cigarette smoke,” says Bell. These fine grains reflect 20% to 25% of the sunlight that hits them; that’s why the clouds look bright. (For comparison, the reflectivity of typical martian terrain is 10% to 15%.)

Sunlight on Mars is about to become unusually intense. The planet goes around the sun in a 9%-elliptical orbit with one end 40 million km closer to the sun than the other. Mars reaches perihelion–its closest approach to the sun–on August 30th. During the weeks around perihelion, sunlight striking Mars will be 20% more intense than the annual average.

“This means the season for dust storms is just beginning,” says Bell.

A total of four spacecraft from NASA, the European Space Agency and Japan are en route to Mars now. They include three landers and two orbiters. Will dust storms cause problems for those missions?

Probably not. NASA spacecraft have encountered Mars dust before. The Viking landers of 1976, for instance, weathered two big dust storms without being damaged. As far as researchers were concerned, it was a good opportunity to study such storms from the inside–something Mars colonists may do again one day for themselves. Viking data will give them a head start.

Five years earlier, in 1971, the Mariner 9 spacecraft reached Mars during the biggest dust storm ever recorded. The planet was completely obscured; not even the polar caps were visible. Mission controllers simply waited a few weeks for the storm to subside. Then they carried on with Mariner 9’s mission: to photograph the entire surface of the planet. It was a complete success.

As 2003 unfolds, Earth and Mars are drawing together for their closest approach in some 60,000 years on August 27th. Already in July Mars is a pleasing sight. Step outside before dawn anytime this month. Mars will be there in the southern sky, a remarkably bright red star. (If you live in the southern hemisphere, look northeast instead.)

Right: John Nemy and Carol Legate took this recent picture of bright Mars and a meteor above their campsite on Blackcomb Mountain, Whistler, British Columbia.

Even a small telescope will reveal the planet’s orange disk and its icy south polar cap. And if “seeing is good” you might catch a glimpse of some dust clouds. Swirling, surging, merging with others … building the next global dust storm? “They’re fun to watch,” says Parker. Now is a great time to see for yourself.

Original Source: NASA Science Story

Posted on by Fraser Cain

Age Wasn’t a Cause of the Columbia Disaster

During a press briefing on Friday, investigators ruled out the age of the space shuttle Columbia as a contributing cause to its destruction. With the most recent foam test, which knocked a large hole in sample shuttle wing panel, the force of the impact would have broken through, even if the panel was brand new. Investigators believe the hole in Columbia was smaller than the one in the test panel; otherwise it would have broken up much earlier upon re-entry.

Posted on by Fraser Cain

World’s Astronomers Meet in Sydney

Astronomers from around the world have descended on Sydney, Australia for the 25th general assembly of the International Astronomical Union. Around 2,000 astronomers will be in the city to attend the event which will cover a vast range of topics, such as “Young Neutron Stars and their Environments”.

During this event, astronomers are announcing all kinds of discoveries, so don’t be surprised if Universe Today is a little bigger than normal and astronomy-focused for the next few weeks. I’ll try to stay on top of it as much as possible.

If you’re in Sydney, let me know how it all goes.

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

Opportunity is Working Well

Image credit: NASA/JPL

Opportunity, NASA’s second Mars Exploration rover, has been in space for a few days now and everything seems to be going according to plan. The spacecraft has reduced its spin rate from 12 rotations a minute to just 2; enabling it to switch to celestial navigation using its star scanner. In fact, one of the first reference points Opportunity used was Mars – already one of the brightest objects in view. It’s already over 7 million kilometres away from the Earth and on track to arrive at Mars on January 25.

NASA’s Opportunity spacecraft, the second of twin Mars Exploration Rovers, has successfully reduced its spin rate as planned and switched to celestial navigation using a star scanner.

Prior to today?s maneuver, Opportunity was spinning 12.13 rotations per minute. Onboard thrusters were used to reduce the spin rate to approximately 2 rotations per minute, the designed rate for the cruise to Mars. After the spinning slowed, Opportunity’s star scanner found stars that are being used as reference points for spacecraft attitude. One of the bright points in the star scanner’s first field of view was Mars.

All systems on the spacecraft are in good health. As of 6 a.m. Pacific Daylight Time July 10, Opportunity will have traveled 6.6 million kilometers (4.1 million miles) since its July 7 launch. The Mars Exploration Rover flight team at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., is preparing to command Opportunity’s first trajectory-correction maneuver, scheduled for July 18.

Opportunity will arrive at Mars on Jan. 25, 2004, Universal Time (evening of Jan. 24, 2004, Eastern and Pacific times). The rover will examine its landing area in Mars’ Meridiani Planum area for geological evidence about the history of water on Mars.

Opportunity’s twin, Spirit, also continues in good health on its cruise to Mars. As of 6 a.m. Pacific Daylight Time July 10, it will have traveled 82.6 million kilometers (51.3 million miles) since its June 10 launch.

JPL, a division of the California Institute of Technology, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Additional information about the project is available from JPL at http://mars.jpl.nasa.gov/mer or and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

NASA Has Too Many Astronauts

Image credit: NASA

A new report released Thursday by NASA’s Inspector General says that the agency has too many astronauts for the number of shuttle flights. As of December 2002, 53 of the agency’s 116 astronauts had yet to actually go into space because of fewer shuttle flights than originally planned; what was supposed to be 8 or 9 flights a year ended up being only five times a year. Ironically, this report was prepared before the Columbia disaster, so the loss of another orbiter will make this problem even worse. Astronauts selected for the 2004 class probably won’t make it to space until 2009.

The review “Improving Management of the Astronaut Corps” (G-01-035) has been posted to the NASA Office of Inspector General Web.

The NASA Office of Inspector General (OIG) evaluated the management of the astronaut corps. The OIG considered whether the NASA astronaut corps was being used effectively, was supportive of the Agency’s current and future mission, and was managed in accordance with governing policies and procedures. We conducted this review because the effective management of the astronaut corps is integral to the success of NASA’s mission.

Our report was scheduled to be released in final form in February 2003. However, when the Space Shuttle Columbia and its crew were lost we decided to delay the release of the report until a more appropriate time. Now that NASA is working to recruit an Astronaut Candidate Class of 2004 that includes pilots, mission specialists, and educator astronauts, we believe that our recommendations will aid the decision- making process.

Results of Review
The substance of the report has not been adjusted to reflect the loss of the Columbia or its crew. We found overly optimistic predictions of future flight rates, minimal regulation of astronaut candidate selection, and the need to staff engineering positions at Johnson Space Center to be factors in the Agency’s astronaut hiring process. As a result, costs for the astronaut program were higher than necessary and not all individuals trained to be astronauts were being used in a manner commensurate with their expensive training. We projected that the mission specialists in the class of 2000 would wait an average of 105 months to fly for the first time. Based on our projection, the last mission specialist in that class would not fly until April 2010 (116 months after joining the astronaut corps).

Recommendations
To assist the Agency in assuring that the size of the corps is more closely aligned with mission and program needs, we recommended that the Agency establish formal guidelines for certain aspects of the astronaut candidate selection process, conduct more realistic analyses of astronaut corps size needs, document reasons for deviating from those analyses, and establish formal criteria for astronaut technical assignments.

Management’s Response
NASA management concurred with our recommendations and has planned corrective actions that we consider responsive.

Original Source: NASA News Release

Posted on by Fraser Cain

Hubble Identifies the Oldest Known Planet

Image credit: Hubble

The Hubble Space Telescope was recently used to identify the oldest extrasolar planet ever discovered. The 2.5 Jupiter mass planet was originally discovered around a pulsar in the globular cluster M4 way back in 1988; astronomers detected a regular dimming of the pulsar’s radio wave emissions. By using Hubble, astronomers were better able to explain how the planet ended up around a pulsar. This discovery could reshape the current models of planetary development, which predicted that stars needed to go through at least one complete cycle to create the heavier elements that planets require.

Long before our Sun and Earth ever existed, a Jupiter-sized planet formed around a sun-like star. Now, 13 billion years later, NASA’s Hubble Space Telescope has precisely measured the mass of this farthest and oldest known planet. The ancient planet has had a remarkable history because it has wound up in an unlikely, rough neighborhood. It orbits a peculiar pair of burned-out stars in the crowded core of a globular star cluster.

The new Hubble findings close a decade of speculation and debate as to the true nature of this ancient world, which takes a century to complete each orbit. The planet is 2.5 times the mass of Jupiter. Its very existence provides tantalizing evidence that the first planets were formed rapidly, within a billion years of the Big Bang, leading astronomers to conclude that planets may be very abundant in the universe.

The planet now lies in the core of the ancient globular star cluster M4, located 5,600 light-years away in the summer constellation Scorpius. Globular clusters are deficient in heavier elements because they formed so early in the universe that heavier elements had not been cooked up in abundance in the nuclear furnaces of stars. Some astronomers have therefore argued that globular clusters cannot contain planets. This conclusion was bolstered in 1999 when Hubble failed to find close-orbiting “hot Jupiter”-type planets around the stars of the globular cluster 47 Tucanae. Now, it seems that astronomers were just looking in the wrong place, and that gas-giant worlds orbiting at greater distances from their stars could be common in globular clusters.

“Our Hubble measurement offers tantalizing evidence that planet formation processes are quite robust and efficient at making use of a small amount of heavier elements. This implies that planet formation happened very early in the universe,” says Steinn Sigurdsson of Pennsylvania State University.

“This is tremendously encouraging that planets are probably abundant in globular star clusters,” says Harvey Richer of the University of British Columbia. He bases this conclusion on the fact that a planet was uncovered in such an unlikely place, orbiting two captured stars ? a helium white dwarf and a rapidly spinning neutron star ? near the crowded core of a globular cluster, where fragile planetary systems tend to be ripped apart due to gravitational interactions with neighboring stars.

The story of this planet’s discovery began in 1988, when the pulsar, called PSR B1620-26, was discovered in M4. It is a neutron star spinning just under 100 times per second and emitting regular radio pulses like a lighthouse beam. The white dwarf was quickly found through its effect on the clock-like pulsar, as the two stars orbited each other twice per year. Sometime later, astronomers noticed further irregularities in the pulsar that implied that a third object was orbiting the others. This new object was suspected to be a planet, but it could also be a brown dwarf or a low-mass star. Debate over its true identity continued through the 1990s.

Sigurdsson, Richer, and their co-investigators settled the debate by at last measuring the planet’s actual mass through some ingenious celestial detective work. They had exquisite Hubble data from the mid-1990s, taken to study white dwarfs in M4. Sifting through these observations, they were able to detect the white dwarf orbiting the pulsar and measure its color and temperature. Using evolutionary models computed by Brad Hansen of the University of California, Los Angeles, the astronomers estimated the white dwarf’s mass. This in turn was compared to the amount of wobble in the pulsar’s signal, allowing the astronomers to calculate the tilt of the white dwarf’s orbit as seen from Earth. When combined with the radio studies of the wobbling pulsar, this critical piece of evidence told them the tilt of the planet’s orbit, too, and so the precise mass could at last be known. With a mass of only 2.5 Jupiters, the object is too small to be a star or brown dwarf, and must instead be a planet.

The planet has had a rough road over the last 13 billion years. When it was born, it probably orbited its youthful yellow sun at approximately the same distance Jupiter is from our Sun. The planet survived blistering ultraviolet radiation, supernova radiation, and shockwaves, which must have ravaged the young globular cluster in a furious firestorm of star birth in its early days. Around the time multi-celled life appeared on Earth, the planet and star were plunging into the core of M4. In this densely crowded region, the planet and its sun passed close to an ancient pulsar, formed in a supernova when the cluster was young, that had its own stellar companion. In a slow-motion gravitational dance, the sun and planet were captured by the pulsar, whose original companion was ejected into space and lost. The pulsar, sun, and planet were themselves flung by gravitational recoil into the less-dense outer regions of the cluster. Eventually, as the star aged it ballooned to a red giant and spilled matter onto the pulsar. The momentum carried with this matter caused the neutron star to “spin-up” and re-awaken as a millisecond pulsar. Meanwhile, the planet continued on its leisurely orbit at a distance of about 2 billion miles from the pair (approximately the same distance Uranus is from our Sun).

It is likely that the planet is a gas giant, without a solid surface like the Earth. Because it was formed so early in the life of the universe, it probably doesn’t have abundant quantities of elements such as carbon and oxygen. For these reasons, it is very improbable the planet would host life. Even if life arose on, for example, a solid moon orbiting the planet, it is unlikely to have survived the intense X-ray blast that would have accompanied the spin-up of the pulsar. Regrettably, it is unlikely that any civilization witnessed and recorded the dramatic history of this planet, which began at nearly the beginning of time itself.

Original Source: Hubble News Release

Posted on by Fraser Cain

Rocket Telescope Gets a Look at the Sun

Image credit: NASA

Scientists got the best ever ultraviolet view of the Sun using a telescope and camera launched on board a sounding rocket. The pictures will help researchers understand how the Sun’s outer atmosphere heats up to over one million degrees Celsius. The telescope was able to resolve areas in the ultraviolet spectrum as small as 240 kilometres across; three times better than any space-based observatory. The rocket trajectory only let the telescope take 21 images during its 15 minute flight.

Scientists got their closest-ever ultraviolet look at the Sun from space, thanks to a telescope and camera launched aboard a sounding rocket. The images revealed an unexpectedly high level of activity in a lower layer of the Sun’s atmosphere (chromosphere). The pictures will help researchers answer one of their most burning questions about how the Sun works: how its outer atmosphere (corona) heats up to over one million degrees Celsius (1.8 million Fahrenheit), 100 times hotter than the chromosphere.

A team of Naval Research Laboratory (NRL) scientists used the Very high Angular resolution ULtraviolet Telescope (VAULT) to take pictures of ultraviolet (UV) light (1216 ?) emitted from the upper chromosphere. Resolving areas as small as 240 kilometers (150 miles or 0.3 arcseconds) on each side, the June 14, 2002, flight captured images about three times better than the previous-best pictures from space. A few ground-based telescopes can observe the Sun in 150-kilometer (93-mile) increments, but only at visible wavelengths of light. UV and X-ray wavelength observations most directly matter to solar weather.

Since most solar weather originates as explosions of the electrified gas (plasma) in the corona, understanding the heating and magnetic activity of the coronal plasmas will lead to better predictions of solar weather events. Severe solar weather, like solar flares and coronal mass ejections, can disrupt satellites and power grids, affecting life on Earth.

The VAULT observations reveal a highly structured, dynamic upper chromosphere, with structures visible for the first time thanks to the detailed resolution. A large number of structures in the pictures change rapidly from one image to the next, 17 seconds later. Scientists previously thought these changes occurred over five minutes or more. The transience of the physical processes in this layer has significant theoretical implications, such as the fact that proposed heating mechanisms must now also be effective over relatively short time scales.

Scientists found chromospheric features in the VAULT images that match features, based on shape and spatial correlation, which they see in Transition Region And Coronal Explorer (TRACE) satellite images of the corona taken simultaneously. This comparison shows that these two layers have much higher correlation than previously thought and implies that similar physical processes likely heat each. However, theory predicts the activity in the chromosphere should be lower than what scientists observed in the VAULT emissions. “[There are] more things happening below [in the upper chromosphere] than you see in the corona,” says VAULT project scientist Angelos Vourlidas of the NRL.

VAULT also revealed unexpected structures in quiet areas of the Sun. The plasma and magnetic field bubble up like boiling water on the Sun’s visible surface (photosphere), and, like bubbles gathering and forming a ring at the edge of a pot, the field builds up in rings (network cells) in the quiet areas. VAULT captured images of smaller features and significant activity within the network cells, surprising scientists.

The telescope took 21 images in the Lyman-alpha wavelength of the electromagnetic spectrum during a six-minute-nine-second picture-taking window on its 15-minute flight. Offering the brightest solar emissions, the Lyman-alpha wavelength assured the best likelihood for pictures from the rocket and allowed for shorter exposure times and more pictures. An increase in Lyman-alpha radiation may indicate an increase in solar radiation reaching Earth.

The VAULT payload consists of a 30-centimeter (11.8-inch) Cassegrain telescope with a dedicated Lyman-alpha spectroheliograph focusing images onto a charge-coupled device (CCD) camera. The CCD, also employed in consumer digital cameras, has a photosensitivity 320 times greater than photographic film previously used. The Normal Incidence X-ray Telescope (NIXT) from the Harvard-Smithsonian Center for Astrophysics took the previous best-resolution pictures of the Sun from space in September 1989, also aboard a sounding rocket.

The scientists verified the payload performance with an engineering flight from White Sands Missile Range, N.M., May 7, 1999. The June 14, 2002, flight from White Sands was the first scientific flight of the payload. The NRL team led a campaign combining observations from satellites and ground-based instruments. Scientists plan a third launch in Summer 2004. The mission was conducted through NASA’s Sounding Rocket Program.

Original Source: NASA News Release

Posted on by Fraser Cain

Book Review: Our Final Hour by Sir Martin Rees

It’s strange how many “the world is going to end” books cross my desk here at Universe Today. Our Final Hour: A Scientist’s Warning: How Terror, Error, and Environmental Disaster Threaten Humankind’s Future In This Century–On Earth and Beyond is the latest offering is by Sir Martin Rees, England’s Astronomer Royal, and delves into the possiblility that the fate of humanity, the Earth, and maybe even the entire universe is in the hands of well-intentioned (or malicious) scientists as they push the boundaries of nature.

Scientists will destroy the world! We’ve all heard that before, but found it kind of a strange statement coming from one of the more prominent scientists in the world. In “Our Final Hour”, however, Rees makes some well-reasoned arguments about the dangers of scientific exploration. Not that we shouldn’t explore nature, just that we should be mindful of the risks and take extra precautions.

The book is a quick read, only 228 pages, and takes us through the range of doomsday scenarios that scientists can unleash: environmental disasters that warm/cool the Earth and make it unlivable; bioterrorism that could unleash a plague of germs on the populace; and exotic physics experiments that could convert all matter in the universe into something… unpleasant.

Rees is calm and reasoned in his arguments; at no point does he stray into “science is bad” rants. Instead, he adopts the tone of a scientific professional, concerned about the ethical implications of scientific discovery. But he doesn’t argue that science should be slowed down, in fact, Rees believes that it’s pretty much impossible to stop scientific development. For every country that has a ban on genetic research, there will be one happy to support it. And technology will allow the tools to create viruses and other nastiness by a much larger group of people – some with nasty intentions.

I guess that’s where the book fell down a bit for me. It offers up lots challenges the world could face from science, but it’s short on solutions that could help guide policy. I got the impression that Rees feels largely pessimistic that anything can really be done to slow progress, and the inevitable disasters science could cause. It’s unrealistic to tell scientists what they can and can’t work on; even more difficult to enforce ethical guidelines; and probably impossible to stop technology from falling into the wrong hands. The only hope Rees sees is in human spaceflight – essentially escaping the problem and heading to the stars. That’s all well and good, but the Earth is where I keep all my stuff. There’s got to be more than that. I was hoping for a much longer book that offered up some deeper policy suggestions, but I suspect the implications are just too far reaching to make realistic suggestions.

Still, it’s an interesting read.

Here’s a link to Amazon.com, Amazon UK, and Amazon Canada.

Posted on by Fraser Cain

New Observatories Could Spot Waterworlds

Image credit: ESA

The European Space Agency is planning a series of space-based observatories designed to search space for evidence of Earth-like worlds. But an easier target to spot should be waterworlds; six times the mass of the Earth and covered with an ocean 100km deep. The CNES/ESA mission Corot will launch in 2005, and should just barely be able to spot dimming stars as these “waterworlds” pass in front. Even more powerful Eddington will launch in 2008 and should be able to see planets half the size of Earth. Finally, Darwin will launch in 2014 and search for signs of life on Earthlike planets.

Science fiction writers and movie-makers have imagined a world completely covered by an ocean, but what if one really existed? Would such a world support life, and what would this life be like?

ESA could make science fiction become science fact when it finds such a world, if the predictions of a group of European astronomers are correct. The ESA mission Eddington, which is now in development, could be the key.

At the recent ESA co-sponsored ‘Towards Other Earths’ conference, nearly 250 of the world’s leading experts in planet detection discussed the strategy for finding Earth-like worlds. Alain L?ger and colleagues of the Institut d’Astrophysique Spatiale, France, described a new class of planets that could be awaiting discovery: ‘waterworlds’.

According to L?ger and his colleagues, these waterworlds would contain about six times the mass of Earth, in a sphere twice as wide as our planet. They would possess atmospheres and orbit their parent star at roughly the same distance that the Earth is from the Sun. Most excitingly, an ocean of water entirely covers each world and extends over 25 times deeper than the average depth of the oceans on Earth.

A hundred kilometres deep
According to calculations, the internal structure of a waterworld would consist of a metallic core with a radius of about 4000 kilometres. Then there would be a rocky mantle region extending to a height of 3500 kilometres above the core?s surface, covered by a second mantle made of ice up to 5000 kilometres thick. Finally, an ocean blankets the entire world to a depth of 100 kilometres, with an atmosphere on top of this.

With twice the radius of the Earth, they will be easily spotted by the Eddington spacecraft, which is designed to detect planets down to half the size of the Earth. “A waterworld passing in front of a star, somewhat cooler than the Sun, will cause a dimming in the stellar light by almost one part in a thousand. That’s almost ten times larger than the smallest variation Eddington is designed to detect. So, waterworlds ? if they exist ? will be a very easy catch for Eddington,” says Fabio Favata, ESA?s Eddington Project Scientist.

The CNES/ESA mission Corot, which is a smaller, precursor mission to Eddington due for launch around 2005, may also be just able to glimpse them, if they are close enough to their parent stars.

Origins of life
Scientists are now asking if such worlds could support life, and what would it be like, especially since water is a prime ingredient for life on Earth. While waterworlds seem to have everything to sustain life, there is a big question mark over whether they could actually allow it to start in the first place.

One of the leading theories for life’s origin in deep oceans is that it requires hot springs on the ocean floor, heated by volcanic activity like the ‘black smokers’ found here on Earth. On a waterworld however, 5000 kilometres of ice separate the ocean floor from any possible smokers. On the other hand, a water-surface origin may still be possible.

Perhaps the only way to know if anything lives on a waterworld will be to study them with ESA’s habitable-planet-finding mission, Darwin. When it launches in around 2014, this flotilla of spacecraft will look for tell-tale signs of life in the atmospheres of any planets, including waterworlds.

Original Source: ESA News Release

Posted on by Fraser Cain

How the Owl Nebula Got its Shape

Image credit: Hubble/NOAO

A team of astronomers have created a model to explain how the Owl Nebula (NGC 3587) got its unique shape. They believe that the outer halo was formed when the star first lost mass and blew off its outer layer; the circular middle shell was caused by solar wind from the star blowing additional material; and then an even faster solar wind created the inner layer. Other planetary nebulae show a similar triple-shell appearance, so it’s likely they formed the same way.

Astronomers have assembled the first effective model for both the shape and evolutionary history of the Owl Nebula, the well-known planetary nebula in the constellation Ursa Major.

Named for its ghostly similarity to the face of the carnivorous bird of prey, the Owl Nebula (NGC 3587) has a complex structure consisting of three concentric shells. The aptly named nebula boasts a faint outer halo, a circular middle shell, and a roughly elliptical inner shell. The inner shell houses a bipolar cavity that forms the owl?s ?eyes,? and two areas of enhanced brightness are seen as the owl?s ?forehead? and ?beak.?

In an article published in the June 2003 Astronomical Journal, researchers from the University of Illinois at Urbana-Champaign, the Instituto de Astrofisica de Canarias in Spain, and Williams College in Williamstown, MA, present the first cohesive model for the appearance and evolution of the Owl Nebula.

Using observations made with the William Herschel Telescope in La Palma, Spain, and the 0.6-meter Burrell Schmidt telescope at Kitt Peak National Observatory, the researchers concluded that the halo of the Owl was formed when the parent star first underwent significant mass loss after the cessation of fusion in its core. The resulting instabilities then produced a stellar wind, driven by a combination of stellar pulsations and radiation pressure.

Evolution of the Owl?s parent star caused the stellar wind to intensify to a ?superwind,? driving even more gas and dust outward to form the middle shell. A subsequent faster stellar wind compressed the superwind to form the inner shell and bipolar cavity, but that wind has since ceased. The cavity is currently being back-filled with nebular material in the absence of the fast stellar wind, much as air flows back out of a balloon if you stop blowing into it.

?Different evolutionary models can produce the same structure for the nebula, but until now none has been able to also account for its motion,? says Martin A. Guerrero of the University of Illinois, the lead author of the recent study. ?There are many investigations of physical structures of planetary nebulae, but most studies only look at one piece of data and tend to ignore the bigger picture.?

Other planetary nebulae show triple-shell structure similar to the Owl Nebula and it is likely that they followed this same evolutionary path, according to co-author Karen Kwitter of Williams College. ?These nebulae form an illuminating sample to study, and the Owl Nebula is the nearest one, only about 2,000 light-years from Earth.?

Despite the name, planetary nebulae are not related to planets. Sir William Herschel gave these fascinating objects their misleading name in 1782 because, through his telescope, they resembled the appearance of Uranus and Neptune. In reality, planetary nebulae are shells of gas and dust ejected from aging stars. When the mass loss is finished, the hot core of the star is exposed, causing the ejected gas to glow.

A newly processed image of the Owl Nebula from this study is available above.

The Burrell Schmidt telescope is part of the Warner and Swasey Observatory of Case Western Reserve University, Cleveland, OH. The telescope is located at Kitt Peak National Observatory near Tucson, AZ, which is part of the National Optical Astronomy Observatory (NOAO). NOAO is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a cooperative agreement with the National Science Foundation.

Original Source: NRAO News Release