Here’s a 1024×768 resolution wallpaper of the amazing first photograph of Mars taken by the European Space Agency’s Mars Express spacecraft. The stereoscopic image was taken on January 14, 2004 by Mars Express when it was 275 kilometres above the Valles Marineris – a 1700 km long by 65 km wide canyon that runs across the surface of Mars.
Spirit Investigates a Nearby Rock
Image credit: NASA/JPL
NASA’s Mars Exploration Rover Spirit drove a few metres yesterday to get nice and close to a large rock nearby the landing site which scientists have dubbed “Adirondack”. Spirit will examine the rock with its microscope and two instruments that will reveal its composition. To make the drive to this rock, Spirit turned 40-degrees and then rolled 1.9 metres. Engineers are still taking “baby steps” with Spirit, since this first target took the rover 30 minutes to travel.
NASA’s Spirit rover has successfully driven to its first target on Mars, a football-sized rock that scientists have dubbed Adirondack.
The Mars Exploration Rover flight team at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., plans to send commands to Spirit early Tuesday to examine Adirondack with a microscope and two instruments that reveal the composition of rocks, said JPL’s Dr. Mark Adler, Spirit mission manager. The instruments are the M?ssbauer spectrometer and the alpha particle X-ray spectrometer.
Spirit successfully rolled off the lander and onto the martian surface last Thursday. To make the drive to Adirondack, the rover turned 40 degrees in short arcs totaling 95 centimeters (3.1 feet). It then turned in place to face the target rock and drove four short moves straightforward totaling 1.9 meters (6.2 feet). The moves covered a span of 30 minutes on Sunday, though most of that was sitting still and taking pictures between moves. The total amount of time when Spirit was actually moving was about two minutes.
“These are the sorts of baby steps we’re taking,” said JPL’s Dr. Eddie Tunstel, rover mobility engineer.
“The drive was designed for two purposes, one of which was to get to the rock,” Tunstel said. “From the mobility engineers’ standpoint, this drive was geared to testing out how we do drives on this new surface.” Gathering new information such as how much the wheels slip in the martian soil will give the team confidence for more ambitious drives in future weeks and months.
“Adirondack is now about one foot (30 centimeters) in front of the front wheels,” he said.
Scientists chose Adirondack to be Spirit’s first target rock rather than another rock, called Sashimi, that would have been a shorter, straight-ahead drive. Rocks are time capsules containing evidence of the environmental conditions of the past, said Dr. Dave Des Marais, a rover science-team member from NASA Ames Research Center, Moffett Field, Calif. “We needed to decide which of these time capsules to open.”
Sashimi appears dustier than Adirondack. The dust layer could obscure good observations of the rock’s surface, which may give information about chemical changes and other weathering from environmental conditions affecting the rock since its surface was fresh. Also, Sashimi is more pitted than Adirondack. That makes it a poorer candidate for the rover’s rock abrasion tool, which scrapes away a rock’s surface for a view of the interior evidence about environmental conditions when the rock first formed. Adirondack has a “nice, flat surface” well suited to trying out the rover’s tools on their first martian rock, Des Marais said.
“The hypothesis is that this is a volcanic rock, but we’ll test that hypothesis,” he said. Spirit arrived at Mars Jan. 3 (EST and PST; Jan. 4 Universal Time) after a seven-month journey. In coming weeks and months, according to plans, it will be exploring for clues in rocks and soil to decipher whether the past environment in Gusev Crater was ever watery and possibly suitable to sustain life.
Spirit’s twin Mars Exploration Rover, Opportunity, will reach Mars on Jan. 25 (EST and Universal Time; 9:05 p.m., Jan. 24, PST) to begin a similar examination of a site on the opposite side of the planet from Gusev Crater.
JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Images and additional information about the project are available from JPL at http://marsrovers.jpl.nasa.gov and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu.
Original Source: NASA/JPL News Release
Stardust Surprised Scientists
Image credit: NASA/JPL
When NASA’s Stardust spacecraft swept past Comet Wild-2, it captured material from the comet’s tail and revealed incredible details about the surface of the fast moving object. The few images that Stardust was able to take also provided some surprises. Scientists anticipated that that comet would be a dusty snowball, with very few surface features, but Stardust found impact craters, barn-sized boulders, and tall cliffs. This indicates that the comet isn’t the loose collection of material that scientists theorized, since it’s obviously withstood quite a beating.
On Jan. 2nd, 2004, NASA’s Stardust spacecraft approached Comet Wild 2 and flew into a storm. Flurries of comet dust pelted the craft. At least half a dozen grains moving faster than bullets penetrated Stardust’s outermost defenses. The craft’s 16 rocket engines struggled to maintain course while a collector, about the size of a tennis racquet, caught some of the dust for return to Earth two years hence.
All that was expected.
Then came the surprise. It happened when Stardust passed by the core of the comet, only 236 km distant, and photographed it using a navigation camera. The images were intended primarily to keep the spacecraft on course. They also revealed a worldlet of startling beauty.
Right: The nucleus of Comet Wild 2 photographed by Stardust with approximately 20 meter resolution. Click on the image to see a much larger version.
At the heart of every comet lies a “dirty snowball,” a compact nucleus of dust and ice that the sun vaporizes, little by little, to form the comet’s spectacular tail. These nuclei are hard to see. For one thing, most are blacker than charcoal; they reflect precious little sunlight for cameras. Plus they’re hidden deep inside a cloud of vaporizing gas and dust, called “the coma.” Stardust’s plunge into Wild 2’s coma allowed it to view the nucleus at close range.
Previous flybys of Comet Halley by the European Giotto probe and Comet Borrelly by NASA?s Deep Space 1 revealed lumpy cores without much interesting terrain–as expected. These comets have been sun-warmed for many thousands of years. Solar heating has melted away their sharpest features.
Comet Wild 2, however, looks different. “We were amazed by the feature-rich surface of the comet,” says Donald Brownlee of the University of Washington, the mission’s principal investigator. “It is highly complex. There are barn-sized boulders, 100-meter high cliffs, and some weird terrain unlike anything we’ve ever seen before. There are also some circular features,” he adds, “that look like impact craters as large as 1 km across.”
“The high cliffs tell us that the crust of the comet is reasonably strong,” notes Brownlee. It’s probably a mixture of fine-grained rocky material held together by frozen water, carbon monoxide and methanol. Certainly a lander could touch down there, or an astronaut could walk across the surface without worrying too much about the ground collapsing.
An astronaut standing on Comet Wild 2 would see a truly fantastic landscape, speculates Brownlee. ?I imagine them inside one of the craters, surrounded by deep cliffs.” Icy spires, as tall as a person, might rise out of the crater floor. “These would be be the comet-equivalent of ‘snow spikes’ on Earth–those little jagged ridges that form when snow is exposed to sunlight and melts.”
Getting out of the crater would be easy. “Just jump,” says Brownlee, “but not too hard.” The comet?s gravity is only 0.0001-g, so “you could easily leap into orbit.”
Some of the photos from Stardust reveal gaseous jets. “The jets come from active regions on the comet’s surface, fissures or vents probably, where the ice is vaporizing and rushing into space,” Brownlee says. This is how mass is transferred from the comet’s nucleus to its tail.
Viewed from the surface, the jets would be nearly transparent. But an astronaut could spot them by looking for “dust entrained with the gas. Dust grains glinting in the sunlight would look like tracer bullets shooting out of the ground.”
A careful explorer could survey the entire 5-km nucleus in only a few hours, leaping high above the surface, dodging the occasional jet. “What an experience that would be,” he says.
There are billions of comets in the solar system. “We’ve gotten a close-up look at only three,” says Brownlee. And one of the three, Comet Halley, presented its night side to the cameras. So it’s too soon to say whether Comet Wild 2, among comets, is truly unusual.
Unlike comets Halley and Borrelly, notes Brownlee, “Wild 2 is a very recent arrival to the inner solar system.” For billions of years it orbited in the cold deep space beyond Jupiter, until 1974 when it was nudged by Jupiter’s gravity into a sun-approaching orbit. Since then the comet has passed by the Sun only five times; solar heating is only beginning to mold its surface.
And, according to Brownlee, that might be the key to the comet’s appearance. “Wild 2’s surface is a mixture of young and old that we haven’t see before,” he explains. Young features include possible sinkholes collapsing as the terrain is warmed. Impact craters and their ejecta, on the other hand, are old scars from time spent in the outer solar system.
The old parts of Wild 2 are what make the comet an attractive target for the Stardust probe, which captured a thousand or more grains of comet dust during the flyby. Such material, little altered since the formation of the solar system, could tell us a great deal about our origins.
The craft’s payload will return to Earth in 2006 for analysis by scientists. If a single picture from the navigation camera can surprise researchers, just imagine what’s in store when they get their hands on a thousand pieces of the comet itself.
Original Source: Science@NASA
Planetary Nebula in Glowing Detail
Image credit: UA
Astronomers with the University of Arizona tested a new infrared camera on the 6.5-metre MMTO telescope, and produced an extremely detailed image of planetary nebula IC 2149. The object, located 3,600 light-years away, consists of a cloud of dust and gas shed from a dying star. The image is so clear because of the telescope’s adaptive optics system, which removes distortion caused by the Earth’s atmosphere – the telescope’s secondary mirror changes shape thousands of times a second to compensate for fluctuations in the light.
Astronomers testing a new near-infrared camera on southern Arizona’s 6.5-meter (21-foot) MMTO telescope have produced a sharp, detailed image of an aged planetary nebula basking in the light of its several-thousand-times brighter dying central star.
It is the most detailed wide-angle picture yet taken using the large telescope’s unique adaptive optics system, a technique that removes atmospheric blurring.
Astronomers from the University of Arizona’s Steward Observatory and Center for Astronomical Adaptive Optics made this picture of Planetary Nebula IC 2149 from exposures taken at the UA/Smithsonian MMT Observatory on 8,550-foot Mount Hopkins, Ariz. The planetary nebula, a cloud of gas and dust shed from a dying star, is 3,600 light-years away and 1.5 trillion miles (2.5 trillion kilometers) across.
The observers used UA astronomer Donald W. McCarthy’s near-infrared camera ARIES to search for specific gases in the star’s debris. They took images in three infrared colors of light, then combined them into a single false-color image.
While astronomers took the images, the large telescope’s secondary mirror changed its shape thousands of times each second to compensate in real-time for atmospheric turbulence that distorts starlight. The MMTO’s ultra-thin, 2-foot-diameter secondary mirror focuses light as steadily as if Earth had no atmosphere. For more about the MMTO’s superb adaptive optics, click here.
The resulting images demonstrate two benefits of the MMTO’s adaptive optics system, McCarthy and UA astronomy graduate student Patrick A. Young said.
First, the images are about three times sharper than images obtained with UA’s NICMOS cameras on the Hubble Space Telescope, and they are as sharp as Hubble images at shorter visible wavelengths.
Second, the sharper images show faint structure close to bright objects like stars in much greater detail. The image of IC2149 shows a contorted mixture of gas and dust several thousand times dimmer than the star itself. The halo around the star is the size of solar systems.
The team selected Planetary Nebula IC 2149 for the engineering tests of ARIES from 10 candidate targets during their telescope time last October, Young said.
“What you are seeing here is a star, a little less massive than the sun, that has used up all the fuel at its nuclear-burning core,” Young said. “Unable to produce energy, the core starts to contract, and turns into a ball of carbon and oxygen the size of the Earth. This gravitational contraction releases a lot of energy, and that causes the star to shed its outer atmosphere. The material we are actually seeing in the picture is the gas and dust being lit up by the light from the central star.”
Their observations suggest that all of the molecular hydrogen in the nebula has been destroyed by radiation from the central star, leaving only ionized hydrogen. Added to other evidence, this indicates that the nebula is several thousands of years old, Young said. Most planetary nebulae disperse and vanish in less than 10,000 years. The gas and dust ejected by the dying star contain heavy elements from which future planets may form.
Original Source: University of Arizona News Release
First Image from Mars Express
Image credit: ESA
Even though it hasn’t reached its final operating orbit, the European Space Agency’s Mars Express has delivered some amazing images of the surface of Mars. This featured image shows a portion of the Martian Grand Canyon, called Valles Marineris, from two perspectives. It’s the first image to show the surface of Mars with such high resolution, in colour, and in 3D. Although it has so far failed to make contact with Beagle 2, the spacecraft will have several more opportunities when the lander goes into a special communications mode where it attempts to communicate constantly throughout the Martian day.
ESA’s Mars Express, successfully inserted into orbit around Mars on 25 December 2003, is about to reach its final operating orbit above the poles of the Red Planet. The scientific investigation has just started and the first results already look very promising, as this first close-up image shows.
Although the seven scientific instruments on board Mars Express are still undergoing a thorough calibration phase, they have already started collecting amazing results. The first high-resolution images and spectra of Mars have already been acquired.
This first spectacular stereoscopic colour picture was taken on 14 January 2004 by ESA?s Mars Express satellite from 275 km above the surface of Mars by the High Resolution Stereo Camera (HRSC). This image is available on the ESA Portal at: http://mars.esa.int
The picture shows a portion of a 1700 km long and 65 km wide swath which was taken in south-north direction across the Grand Canyon of Mars (Valles Marineris). It is the first image of this size that shows the surface of Mars in high resolution (12 metres per pixel), in colour, and in 3D. The total area of the image on the Martian surface (top left corner) corresponds to 120 000 km?. The lower part of the picture shows the same region in perspective view as if seen from a low-flying aircraft. This perspective view was generated on a computer from the original image data. One looks at a landscape which has been predominantly shaped by the erosional action of water. Millions of cubic kilometres of rock have been removed, and the surface features seen now such as mountain ranges, valleys, and mesas, have been formed.
The HRSC is just one of the instruments to have collected exciting data. To learn more about the very promising beginning to ESA’s scientific exploration of Mars, media representatives are invited to attend a press conference on Friday, 23 January 2004, at 11:00 CET at ESA?s Space Operations Centre in Darmstadt, Germany, and in video-conference with the other ESA centres.
There, under the auspices of ESA Council Chair, Germany’s Minister for Education and Research, Mrs Edelgard Bulmahn, ESA’s Director of the Scientific Programme, Prof. David Southwood and the Principal Investigators of all instruments on board Mars Express will present the first data and preliminary results.
Also a spectacular, three-dimensional video sequence, featuring famous landmarks on the surface of Mars ‘as seen through European eyes’ will be unveiled for the first time on Friday 23 January .
Original Source: ESA News Release
Spirit Examines the Martian Soil
Image credit: NASA/JPL
NASA’s Spirit rover reached out and examined the Martian soil with its microscope instrument at the end of its robotic arm; this is the first microscopic image ever taken of another planet. The microscope can reveal objects as small as the width of a human hair, and will help scientists look at the fine details of rock to learn if they were formed by standing water. The rover will examine the same area with two other instruments: the M?ssbauer Spectrometer to find iron-bearing minerals, and the Alpha Particle X-ray Spectrometer which identifies the elements in rocks and soils.
NASA’s Spirit rover reached out with its versatile robotic arm early today and examined a patch of fine-grained martian soil with a microscope at the end of the arm.
“We made our first use of the arm and took the first microscopic image of the surface of another planet,” said Dr. Mark Adler, Spirit mission manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.
The rover’s microscopic imager, one of four tools on a turret at the end of the arm, serves as the functional equivalent of a field geologist’s hand lens for examining structural details of rocks and soils.
“I’m elated and relieved at how well things are going. We got some great images in our first day of using the microscopic imager on Mars,” said Dr. Ken Herkenhoff of the U.S. Geological Survey Astrogeology Team, Flagstaff, Ariz. Herkenhoff is the lead scientist for the microscopic imagers on Spirit and on Spirit’s twin Mars Exploration Rover, Opportunity.
The microscope can show features as small as the width of a human hair. While analysis of today’s images from the instrument has barely begun, Herkenhoff said his first impression is that some of the tiny particles appear to be stuck together.
Before driving to a selected rock early next week, Spirit will rotate the turret of tools to use two spectrometer instruments this weekend on the same patch of soil examined by the microsope, said Jessica Collisson, mission flight director. The M?ssbauer Spectrometer identifies types of iron-bearing minerals. The Alpha Particle X-ray Spectrometer identifies the elements in rocks and soils.
The rover’s arm is about the same size as a human arm, with comparable shoulder, elbow and wrist joints. It is “one of the most dextrous and capable robotic devices ever flown in space,” said JPL’s Dr. Eric Baumgartner, lead engineer for the robotic arm, which also goes by the name “instrument deployment device.”
“Best of all,” Baumgartner said, “this robotic arm sits on a rover, and a rover is meant to rove. Spirit will take this arm and the tremendous science package along with it, and reach out to investigate the surface.”
The wheels Spirit travels on provide other ways to examine Mars’ soil. Details visible in images of the wheel tracks from the rover’s first drive onto the soil give information about the soil’s physical properties.
“Rover tracks are great,” said Dr. Rob Sullivan of Cornell University, Ithaca, N.Y., a member of the science team for Spirit and Opportunity. “For one thing, they mean we’re on the surface of Mars! We look at them for engineering reasons and for science reasons.” The first tracks show that the wheels did not sink too deep for driving and that the soil has very small particles that provide a finely detailed imprint of the wheels, he said.
Opportunity, equipped identically to Spirit, will arrive at Mars Jan. 25 (Universal Time and EST; 9:05 p.m. Jan. 24, PST). The amount of dust in the atmosphere over Opportunity’s planned landing site has been declining in recent days, said JPL’s Dr. Joy Crisp, project scientist for the Mars Exploration Rover Project.
Today, Spirit completes its 13th martian day, or “sol”, at its landing site in Gusev Crater. Each sol lasts 39 minutes and 35 seconds longer than an Earth day. The rover project’s goal is for Spirit and Opportunity to explore the areas around their landing sites for clues in the rocks and the soil about whether the past environments there were ever watery and possibly suitable for sustaining life.
JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for NASA’s Office of Space Science, Washington, D.C. Pictures and additional information about the project are available from JPL at http://marsrovers.jpl.nasa.gov and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu.
Original Source: NASA/JPL News Release
Hubble Servicing Mission Canceled
NASA has canceled all space shuttle flights to service the Hubble Space Telescope, which has provided revolutionary astronomy data and photographs. The decision was influenced by President Bush’s new space initiative, which called for the space shuttle to be retired by 2010. Without a servicing mission, Hubble will continue to degrade over time, lasting at least until 2007 or 2008. When it finally does stop functioning, NASA will launch a robot thruster to de-orbit the school bus-sized observatory safely.
Space Advocates Feel the Bush Plan Needs Work
Image credit: NASA
Although they appreciated President Bush’s new space initiative, many space advocacy groups were a little disappointed that this return to the Moon will probably be fashioned in the same mold as previous NASA projects, such as the space shuttle and the International Space Station. The groups, such as the Space Frontier Foundation, believe that NASA should be restructured to involve the private sector at all levels, to “let NASA do the exploring, but leave the operations to those who do such things best ? American industry”.
The Space Frontier Foundation today applauded President George W. Bush’s unveiling of a plan to get NASA out of Earth orbit and on a path to the Moon and Mars, but the group said that unless there are major changes at the agency and in U.S. space policy ? including the private sector in a leadership role for example ? the plan will fail.
?It was an excellent speech, very inspiring, and if we can do the things the president listed, then we will be on a path to the stars,? said Rick Tumlinson of the Foundation, who was invited by the White House to attend the speech. ?Unfortunately the NASA of today can’t do what the president has asked of it within a reasonable budget, in a reasonable time and in a way that leads to permanent human expansion beyond the Earth.?
The Foundation believes that NASA must be radically re-structured and it must learn new ways of doing business if it is to succeed in accomplishing the President’s vision. The group is calling on the government to include the private sector in all levels of the program’s planning and development as a way to dramatically lower costs, and assure permanence once the Moon base is established. Examples include: buying payload services from new U.S. space transportation firms; the establishment of prizes to be awarded for certain activities and technological milestones; and for private companies to build and operate the long term habitats that will be needed after the initial base camps are established by government astronauts.
?If America is going to reach for the Moon and Mars, we should do it in an American way, by creating a true partnership between the public and private sectors,? said Tumlinson. ?Let NASA do the exploring, but leave the operations to those who do such things best ? American industry. Federal Express, Hilton, Southwest Airlines and their competitors have driven costs down while improving services on Earth, so let’s let them or their space equivalents do the same in space. It isn’t all rocket science.?
The Foundation is glad to see that NASA will be ?leaving Earth orbit? as the President declared, and is hopeful that this means the government will support the development of space businesses such as commercial space flight, space hotels and industrial research in the Near Frontier around the Earth by clearing away regulatory barriers and creating tax incentives and space enterprise zones to encourage investment. The organization believes that if this initiative is to really be the first step to the human settlement of space, it has to eventually pay for itself. Thus, the government should build towards that goal from the beginning.
?I was glad to hear the President say that ?human beings are headed into the cosmos,? but so far that has meant mainly government employees traveling on government vehicles to government buildings. If this is to succeed, we need to begin blazing a trail that can be eventually be taken by anyone who wants to go,? said Tumlinson. ?The government should handle exploration and science ?out there? and the private sector should handle business and entertainment in space. Together we really can open the ?Space Frontier? of which the President spoke.?
To help build this new alliance for the frontier, the Foundation will be holding its 5th Return to the Moon Conference in Las Vegas in July. The conference will be held July 16-18 and will include attendees from government and the private sector. Registration for the conference is at: https://www.space-frontier.org/Events/RTM5/.
Original Source: Space Frontier Foundation News Release
Getting Closer to Saturn
Image credit: ESA
NASA’s Cassini spacecraft is on track to reach Saturn in summer 2004. Before it reaches Saturn, however, the spacecraft will release a tiny probe called Huygens that will parachute into Titan, Saturn’s largest moon, to give scientists an idea of what’s underneath those thick clouds. Astronomers think that the environment on Titan is very similar to primordial conditions here on planet Earth billions of years ago. Huygens will take more than a thousand pictures and countless samples as it travels down to the surface in January 2005.
This time next year, ESA?s Huygens spaceprobe will be descending through the atmosphere of Saturn?s largest moon, becoming the first spacecraft to land on a body in the outer Solar System.
Earlier this month, the giant ringed planet Saturn was closer to Earth than it will be for the next thirty years. All the planets orbit the Sun as if on a giant racetrack, travelling in the same direction but in different lanes.
Those in the outer lanes have further to travel than those on the inside lanes. So, Earth regularly ?laps? the further planets. On New Year?s Eve 2003, Earth overtook Saturn, drawing closer than at any time in the next three decades.
Through a small telescope, Saturn is normally visible as a creamy yellow ?star?. You may be able to see the ring system that the planet is famous for, and its largest moon Titan will show up as a tiny dot of light.
That tiny dot is the destination for ESA?s Huygens probe and may hold vital clues about how life began on Earth. Titan is the only moon with a thick atmosphere in the Solar System.
Astronomers think this atmosphere might closely match the one Earth possessed millions of years ago, before life began. Certainly Titan?s atmosphere is rich in carbon, the chemical necessary for life on Earth. What is more, this is all stored in ?deep freeze?, ten times further from the Sun than the Earth.
The big mystery is Titan?s surface, which is hidden by a cloud layer. This is why ESA built Huygens, to probe through this layer which is impenetrable by Earth-based observations.
In January 2005, Huygens will parachute below the clouds to see what is really going on. Its battery of instruments will return over 1000 images as it floats down and samples the chemistry of this exotic place.
The Titan probe was named Huygens in honour of the Dutch astronomer who discovered Titan in 1655. Launched in October 1997, Huygens is currently in space, hitching a ride on NASA?s Cassini spacecraft.
So look forward to seeing more of Saturn and a tiny European spacecraft called Huygens, that in one year?s time will make an historic landing in the quest to uncover the origins of life.
Original Source: ESA News Release
Evidence that Brown Dwarfs are Failed Stars
Image credit: UofM
Researchers from the University of Michigan have gathered evidence that brown dwarf stars have a very similar life to the early stages our own Sun went through when it first formed. The astronomers searched for dusty disks around young brown dwarfs by observing their infrared emissions. They found that most brown dwarfs did have disks at a million years old, which is very similar to young stars at the same age. Other observations showed that they accrete material from the disk in the same way stars do as well.
In cosmic circles, brown dwarfs are something of a flop. Too big to be considered true planets, yet not massive enough to be stars, these free-floating celestial bodies are, in fact, sometimes referred to as failed stars. But do they really form as stars do?from collapsing clouds of gas?or are their origins completely different? A series of publications by University of Michigan astronomer Ray Jayawardhana and collaborators, including a paper in the January 16 issue of Science, offers evidence that brown dwarfs and Sun-like stars are born in much the same way. “They at least have very similar infancies, which may mean that they also have very similar origins,” said Jayawardhana, an assistant professor of astronomy.
Stars form in cold clouds of gas and dust in interstellar space. Dense clumps within these clouds contract under their own gravity, spinning up in the process and gathering material from the surroundings into a disk. Eventually, if a growing protostar accumulates enough mass, its core becomes hot and dense enough for nuclear fusion to occur, and the new star begins to shine. Some scientists have suggested that brown dwarfs form the same way but simply don’t accumulate enough mass to ignite hydrogen fusion, and calculations show that it’s at least theoretically possible for objects with masses as low as those of brown dwarfs to be born this way.
But other scientists have proposed that brown dwarfs are runts kicked out of stellar litters. In this scenario, brown dwarfs are born in multiple star systems and compete with their siblings for matter from the natal cloud. In such systems, the slowest-growing object may be ejected before it gathers enough material to become a star, computer simulations suggest.
One way to distinguish between the two possibilities is by studying disks of dust and gas around young brown dwarfs. If brown dwarfs form as stars do, they should have large, long-lived accretion disks like those found around young stars. But if they have been ejected from multiple star systems, their disks should be shaved down by the gravitational interactions that lead to ejection.
Jayawardhana and colleagues searched for dusty disks around young brown dwarfs by observing their infrared emission with the 8-meter Very Large Telescope (VLT) of the European Southern Observatory in Chile and the 10-meter Keck I telescope in Hawaii. Because dust particles in a disk absorb light and re-radiate the energy at infrared wavelengths, a brown dwarf with a disk will emit more infrared light than one without a disk.
“We found that the majority of brown dwarfs are surrounded by dusty disks at an age of a million years or so,” said Jayawardhana. “That’s similar to young stars at the same age.” Although it’s not possible to directly determine the disks’ sizes, their presence around some brown dwarfs as old as 10 million years suggests that they aren’t pared away in early life.
Other spectroscopic observations, using the twin 6.5-meter Magellan telescopes in Chile (in which the University of Michigan is a partner institution) and the Keck I telescope, showed that brown dwarfs also accrete material from surrounding disks the same way as stars do?although at a slower pace. “We detect telltale signs of gas flowing from the inner edge of the disk onto the brown dwarf at velocities of over a hundred kilometers per second,” said Jayawardhana. In one intriguing case, astronomers have alsofound evidence of material spewing out from the poles of a brown dwarf. Such jets have been seen in young stars of the same age, but not until now in brown dwarfs. “If confirmed, the presence of jets would further strengthen the case for remarkably similar infancies for brown dwarfs and Sun-like stars,” said Jayawardhana, whose collaborators include Subhanjoy Mohanty (Harvard-Smithsonian Center for Astrophysics), Gibor Basri (University of California, Berkeley), David Barrado y Navascues (Laboratory of Space Astrophysics and Fundamental Physics in Madrid, Spain), David Ardila (Johns Hopkins University), Beate Stelzer (Astronomical Observatory of Palermo in Italy), and Karl Haisch, Jr. and Diane Paulson (both at the University of Michigan).
“I wouldn’t say that the story is signed, sealed and delivered,” Jayawardhana said, “but the preponderance of evidence is very much leaning in the direction of these things forming the same way as stars.” And the evidence uncovered so far leads to even more tantalizing prospects. “Now that we know many young brown dwarfs are surrounded by disks,” he said, “I can’t help but wonder if comets and asteroids?if not small planets?could form in these disks.”
This research was supported primarily by a grant from the National Science Foundation.
Original Source: University of Michigan News Release