"This means we have now made the final deal with NASA in terms of the mission objective, the cost cap and the schedule all the way from development and launch through Earth return," said Dante Lauretta, UA planetary science professor and the mission's principal investigator.

"We have presented our plan, including all aspects of the mission, from the engineering to the science to the schedule, and NASA has accepted that plan and committed to fully fund the mission."

The UA is leading the mission. For the first time in space-exploration history, the mission will travel to and return pristine samples of a carbonaceous asteroid with known geologic context. Such samples are critical to understanding the origin of the solar system, Earth and life, Lauretta explained.

"Successfully passing KDP-C is a major milestone for the project," said Mike Donnelly, OSIRIS-REx project manager for NASA's Goddard Space Flight Center in Greenbelt, Md. "This means that the agency believes we have an executable plan to return a sample from the asteroid, Bennu. It now falls upon the project and its development team members to execute that plan."

The OSIRIS-REx mission will travel to near-Earth asteroid Bennu (named via a recent student competition), study it for a year with a variety of instruments, collect a sample and return it to Earth in 2023.

Measuring more than 1,600 feet in diameter, the OSIRIS-REx target asteroid is uniquely interesting scientifically, while at the same time one of the most potentially hazardous objects known, with a one-in-2,000 chance of colliding with Earth in the late 22nd century. The asteroid could hold clues to the origin of the solar system.

So-called primitive carbonaceous chondrites are very special to scientists studying the origins of our solar system because they represent time capsules from the very beginning of the solar system 4.5 billion years ago. They are believed to hold primordial building blocks of organic material that potentially could have provided the very basic ingredients for life on Earth.

OSIRIS-REx will map the asteroid's global properties, measure non-gravitational forces and provide observations that can be compared with data obtained by telescope observations from Earth. OSIRIS-REx will collect at least 60 grams (about 2 ounces) of surface material. The spacecraft will return samples to Earth for scientists to study for decades.

The return to Earth of pristine samples with known geologic context will enable precise analyzes that cannot be duplicated by spacecraft-based instruments. Pristine carbonaceous materials obtained directly from an asteroid surface have never before been analyzed in laboratories on Earth.

The mission's cost breaks down roughly into $800 million for the flight system and science operations and $240 million for the launch rocket. Science operations will be performed on the UA campus; University scientists and engineers will build the camera suite for the spacecraft.

On OSIRIS-REx, the UA is partnering with the NASA Goddard Space Flight Center, which will manage the mission, and Lockheed Martin Space Systems in Littleton, Colo., which will build and operate the spacecraft.

Through extensive study of meteorites, which are essentially fragments of asteroids that fell to the Earth's surface, UA scientists have been able to formulate leading theories of asteroid formation, composition and their role in answering the important questions of the source of water and organics that may have seeded life on Earth.

"The entire OSIRIS-REx team has worked very hard to get to this point. We have a long way to go before we arrive at Bennu in 2018, but I have every confidence that when we do, we will have built a supremely capable system to return a sample of this primitive asteroid," Lauretta said.

Lauretta said obtaining NASA's final approval was a great achievement in continuing the vision and legacy of Michael Drake, former director of the UA's Lunar and Planetary Lab who died in September 2011.

"He would be very proud and happy about this milestone," Lauretta said. "He was my friend and mentor and worked tirelessly until the very last day on seeing this mission become a reality."

All mission science operations will be performed on the UA campus. OSIRIS-REx will provide a significant boost to the Arizona economy; approximately $200 million will be spent in Tucson and across Arizona.

]]> Thu, 23 MAY 2013 22:52:29 AEST Greenbelt MD (SPX) May 17, 2013 - NASA's first mission to sample an asteroid is moving ahead into development and testing in preparation for its launch in 2016.

The Origins-Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-REx) passed a confirmation review Wednesday called Key Decision Point (KDP)-C. NASA officials reviewed a series of detailed project assessments and authorized the spacecraft's continuation into the development phase.

OSIRIS-REx will rendezvous with the asteroid Bennu in 2018 and return a sample of it to Earth in 2023.

"Successfully passing KDP-C is a major milestone for the project," said Mike Donnelly, OSIRIS-REx project manager at NASA's Goddard Space Flight Center in Greenbelt, Md.

"This means NASA believes we have an executable plan to return a sample from Bennu. It now falls on the project and its development team members to execute that plan."

Bennu could hold clues to the origin of the solar system. OSIRIS-REx will map the asteroid's global properties, measure non-gravitational forces and provide observations that can be compared with data obtained by telescope observations from Earth. OSIRIS-REx will collect a minimum of 2 ounces (60 grams) of surface material.

"The entire OSIRIS-REx team has worked very hard to get to this point," said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona in Tucson.

"We have a long way to go before we arrive at Bennu, but I have every confidence when we do, we will have built a supremely capable system to return a sample of this primitive asteroid."

The mission will be a vital part of NASA's plans to find, study, capture and relocate an asteroid for exploration by astronauts. NASA recently announced an asteroid initiative proposing a strategy to leverage human and robotic activities for the first human mission to an asteroid while also accelerating efforts to improve detection and characterization of asteroids.

NASA's Goddard Space Flight Center in Greenbelt, Md., will provide overall mission management, systems engineering and safety and mission assurance. The University of Arizona in Tucson is the principal investigator institution.

Lockheed Martin Space Systems of Denver will build the spacecraft. OSIRIS-REx is the third mission in NASA's New Frontiers Program. NASA's Marshall Space Flight Center in Huntsville, Ala., manages New Frontiers for NASA's Science Mission Directorate in Washington.

]]> Thu, 23 MAY 2013 22:52:29 AEST Pasadena CA (JPL) May 16, 2013 - On May 31, 2013, asteroid 1998 QE2 will sail serenely past Earth, getting no closer than about 3.6 million miles (5.8 million kilometers), or about 15 times the distance between Earth and the moon. And while QE2 is not of much interest to those astronomers and scientists on the lookout for hazardous asteroids, it is of interest to those who dabble in radar astronomy and have a 230-foot (70-meter) - or larger - radar telescope at their disposal.

"Asteroid 1998 QE2 will be an outstanding radar imaging target at Goldstone and Arecibo and we expect to obtain a series of high-resolution images that could reveal a wealth of surface features," said radar astronomer Lance Benner, the principal investigator for the Goldstone radar observations from NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"Whenever an asteroid approaches this closely, it provides an important scientific opportunity to study it in detail to understand its size, shape, rotation, surface features, and what they can tell us about its origin. We will also use new radar measurements of the asteroid's distance and velocity to improve our calculation of its orbit and compute its motion farther into the future than we could otherwise."

The closest approach of the asteroid occurs on May 31 at 1:59 p.m. Pacific (4:59 p.m. Eastern / 20:59 UTC). This is the closest approach the asteroid will make to Earth for at least the next two centuries. Asteroid 1998 QE2 was discovered on Aug. 19, 1998, by the Massachusetts Institute of Technology Lincoln Near Earth Asteroid Research (LINEAR) program near Socorro, New Mexico.

The asteroid, which is believed to be about 1.7 miles (2.7 kilometers) or nine Queen Elizabeth 2 ship-lengths in size, is not named after that 12-decked, transatlantic-crossing flagship for the Cunard Line.

Instead, the name is assigned by the NASA-supported Minor Planet Center in Cambridge, Mass., which gives each newly discovered asteroid a provisional designation starting with the year of first detection, along with an alphanumeric code indicating the half-month it was discovered, and the sequence within that half-month.

Radar images from the Goldstone antenna could resolve features on the asteroid as small as 12 feet (3.75 meters) across, even from 4 million miles away.

"It is tremendously exciting to see detailed images of this asteroid for the first time," said Benner. "With radar we can transform an object from a point of light into a small world with its own unique set of characteristics. In a real sense, radar imaging of near-Earth asteroids is a fundamental form of exploring a whole class of solar system objects."

Asteroids, which are always exposed to the Sun, can be shaped like almost anything under it. Those previously imaged by radar and spacecraft have looked like dog bones, bowling pins, spheroids, diamonds, muffins, and potatoes.

To find out what 1998 QE2 looks like, stay tuned. Between May 30 and June 9, radar astronomers using NASA's 230-foot-wide (70 meter) Deep Space Network antenna at Goldstone, Calif., and the Arecibo Observatory in Puerto Rico, are planning an extensive campaign of observations.

The two telescopes have complementary imaging capabilities that will enable astronomers to learn as much as possible about the asteroid during its brief visit near Earth.

NASA places a high priority on tracking asteroids and protecting our home planet from them. In fact, the U.S. has the most robust and productive survey and detection program for discovering near-Earth objects. To date, U.S. assets have discovered over 98 percent of the known NEOs.

In 2012, the NEO budget was increased from $6 million to $20 million. Literally dozens of people are involved with some aspect of near-Earth object (NEO) research across NASA and its centers.

Moreover, there are many more people involved in researching and understanding the nature of asteroids and comets, including those that come close to the Earth, plus those who are trying to find and track them in the first place.

In addition to the resources NASA puts into understanding asteroids, it also partners with other U.S. government agencies, university-based astronomers, and space science institutes across the country that are working to track and better understand these objects, often with grants, interagency transfers and other contracts from NASA.

In 2016, NASA will launch a robotic probe to one of the most potentially hazardous of the known NEOs. The OSIRIS-REx mission to asteroid (101955) Bennu will be a pathfinder for future spacecraft designed to perform reconnaissance on any newly-discovered threatening objects.

Aside from monitoring potential threats, the study of asteroids and comets enables a valuable opportunity to learn more about the origins of our solar system, the source of water on Earth, and even the origin of organic molecules that lead to the development of life.

NASA recently announced developing a first-ever mission to identify, capture and relocate an asteroid for human exploration. Using game-changing technologies advanced by the Administration, this mission would mark an unprecedented technological achievement that raises the bar of what humans can do in space.

Capturing and redirecting an asteroid will integrate the best of NASA's science, technology and human exploration capabilities and draw on the innovation of America's brightest scientists and engineers.

]]> Thu, 23 MAY 2013 22:52:29 AEST Pasadena CA (JPL) May 06, 2013 - Nearly three times as far from Earth as the sun is, the Dawn spacecraft is making very good progress on its ambitious trek from Vesta to Ceres. After a spectacular adventure at the second most massive resident of the main asteroid belt between Mars and Jupiter, Dawn used its extraordinary ion propulsion system to leave it behind and undertake the long journey to a dwarf planet.

Ceres orbits the sun outside Vesta's orbit, yet Dawn is now closer to the sun than both of these alien worlds. How can it be that as the probe climbs from one to the other, it seems to be falling inward? Perhaps the answer lies in the text below; let's venture on and find out!

On Halloween we discussed why Dawn is heading in toward the sun, but this question is different. Vesta also is getting closer to the sun, but what's of interest now is that Dawn, despite its more remote destination, has been approaching the sun more quickly. That earlier log stands out as the best one ever written on this exciting mission in the entire history of October 2012, but if you prefer not to visit it now, we can summarize here the explanation for the spacecraft moving toward the sun.

Like all members of the sun's entourage, Vesta and Ceres follow elliptical orbits, their distances from the master of the solar system growing and shrinking as they loop around it. Even Earth's orbit, although nearly round, certainly is not perfectly circular. Our planet is a little closer to the sun in the northern hemisphere winter (southern hemisphere summer) than it is in the summer (southern hemisphere winter).

Dawn's orbit is elliptical as well, so it naturally moves nearer to the sun sometimes, and now is such a time. But that does not address why it is currently closer to the sun than Vesta, even though it is seeking out the more distant Ceres.

Because it will orbit Ceres, and not simply fly past it (which would be significantly easier but less valuable), Dawn must make its own orbit around the sun be identical to its target's. But that is not the entire story. After spending 14 months orbiting Vesta, Dawn's challenge is more than to change the shape of its orbit to match Ceres's. The spacecraft also must be at the same place in Ceres's heliocentric orbit that Ceres itself is.

It would not be very rewarding to follow the same looping path around the sun but always be somewhere else on that path. You can visualize this if you have one of the many defective - er, exotic clocks from the Dawn gift shop on your planet that have two minute hands.

If the clock starts with one hand pointed at 12 and another pointed at 1, they will take the same repetitive route, but neither hand will ever catch up with the other. For Dawn's goal of exploring Ceres, this would not prove satisfying. Therefore, part of the objective of the ion thrusting is to ensure the spacecraft arrives not only on the same heliocentric course as Ceres but is there when Ceres is also.

This is a problem familiar to all readers who have maneuvered in orbit, where the principles of orbital mechanics are the rules of the road. To solve it, we rely on one of the laws that we have addressed many times in these logs: objects in a lower orbit travel faster. We described this in more detail in February, and we can recall the essential idea here.

The gravitational attraction of any body, whether it is the sun, Earth, a black hole, or anything else, is greater at shorter ranges. So to balance that strong inward pull, an orbiter is compelled to race around quickly. At higher orbits, where gravity is weaker, a more leisurely orbital pace suffices.

We can take advantage of this characteristic of orbits. If we drop to a slightly lower orbit, we travel along more swiftly. That is precisely what Dawn needs to do in order to ensure that when it finishes expanding and tilting its orbit in 2015 so that it is the same as Ceres's, it winds up at the same location as its target. This would be like speeding up the minute hand that had begun at the 12, allowing it to catch up with the hand that would otherwise always be leading it.

Dawn's orbital maneuvering is a little bit more complicated than that of clock hands, but thanks to the ingenuity and creativity of the operations team and the unique capability of its ion propulsion system, the interplanetary ship is sailing on a carefully plotted course to its next celestial port. As soon as it departed from Vesta's gravitational embrace in September, it slipped in closer to the sun.

Today, Vesta is 2.53 AU from the sun, and Dawn is 2.51 AU, so the spacecraft is three million kilometers (1.9 million miles) nearer to the sun. (Dawn is farther from Vesta than that, because they are not aligned with the sun. The spacecraft has also moved ahead of the rocky behemoth.)

Of course, eventually Dawn will climb to higher altitudes from the sun than Vesta, because its destination lies beyond. As they progress on their own independent orbits, with Dawn constantly reshaping its, they will be at the same solar distance on July 31, 2013.

After that, the robotic explorer will never again be as close to the sun as Vesta. By then, they will be 18 million kilometers (11 million miles) apart. But they will always be connected. Dawn was Earth's first probe to take up residence in the main asteroid belt, and Vesta was its first target.

The exotic world had beckoned to humankind for over two centuries before the spacecraft obtained its richly detailed view. Now what was little more than an indistinct point of light is known as a complex and fascinating place with a unique character.

And as it follows its repetitive orbit around the sun, its erstwhile companion seeks to reveal the secrets of another extraterrestrial enigma, Ceres. Great treasures await Dawn as it patiently continues its extraordinary deep-space expedition.

Dawn is 10 million kilometers (6.3 million miles) from Vesta and 56 million kilometers (35 million miles) from Ceres. It is also 2.99 AU (448 million kilometers or 278 million miles) from Earth, or 1,215 times as far as the moon and 2.97 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 50 minutes to make the round trip.

]]> Thu, 23 MAY 2013 22:52:29 AEST Washington DC (SPX) May 03, 2013 - The target of NASA's OSIRIS-REx spacecraft is an asteroid that has had the provisional name (101955) 1999 RQ36. Believing the asteroid deserved a more memorable name, the OSIRIS-REx team, led by the University of Arizona, partnered with The Planetary Society and MIT's Lincoln Laboratory, which discovered the asteroid, to sponsor a contest to rename the asteroid.

More than 8,000 students from more than 25 countries entered the Name that Asteroid! contest. The International Astronomical Union approved the name, Bennu, in late April.

Judges enjoyed reading through the imaginative and informative entries. Dante Lauretta, principal investigator of the OSIRIS-REx mission and one of the judges, said, "There were many excellent entries that would be a fitting name and would provide us an opportunity to educate the world about the exciting nature of our mission."

The judges had to make a choice, however, and now the asteroid formerly known as (101955) 1999 RQ36 has a new name - (101955) Bennu.

The OSIRIS-REx spacecraft will launch in 2016, rendezvous with Bennu in 2018 and take a sample in 2019. The spacecraft will return a small sample of the asteroid to Earth in 2023.

Bennu was an important avian deity in ancient Egypt and one of the symbols of Osiris. Egyptians usually depicted Bennu as a gray heron. The dual nature of asteroids, bringers of life's molecules and sometime bringers of destruction, inspired the name.

The contest winner, 9-year-old Michael Toler Puzio from North Carolina, suggested that the large heron-like Touch-and-Go Sample Mechanism (TAGSAM) arm and winged OSIRIS-REx spacecraft made him think of Bennu. Puzio stated, "The winged OSIRIS-REx and its heron-like TAGSAM also evoke attributes of Bennu, as does the egg shape of the asteroid itself."

Bruce Betts, director of projects for the Planetary Society and another judge in the contest, said: "Bennu stuck a chord with many of us right away. While there were many great entries, the similarity between the image of the heron and the TAGSAM arm of OSIRIS-REx was a clever choice.

"The parallel with asteroids as both bringers of life and as destructive forces in the solar system also created a great opportunity to teach."

The heron-TAGSAM and egg-asteroid parallels weren't the only similarities that struck the judges. The god Bennu was commonly associated with the gods Atum, the primeval deity, and Re, the Sun god.

Astronomers think that the OSIRIS-REx target asteroid is a primitive object that dates back to the creation of the solar system because earthly analogues for the asteroid Bennu are carbonaceous chondrite meteorites, which have compositions very similar to that of the Sun.

Indeed, our own long-lived solar system was "reborn" from the remnants of stellar explosions more than 4.5 billion years ago. Therefore, origins, rebirth and duality are all part of the story of this asteroid.

The naming contest was a partnership among the UA, The Planetary Society and MIT's Lincoln Near-Earth Asteroid Research (LINEAR) asteroid survey. Contestants submitted one name along with a short explanation for their choice.

The partners assembled a panel to review the submissions and to submit a top choice to the International Astronomical Union (IAU) Committee for Small Body Nomenclature, which approved the name. Names were required to comply with naming guidelines from the IAU.

"We are so impressed with the quality of the contest entries that we have decided to recommend four runner-up submissions as names for other minor planets discovered by the LINEAR program," said judge Grant Stokes, head of the Aerospace Division at MIT Lincoln Laboratory and principal investigator for the LINEAR program.

"The names Muninn, Nabu, Polymatheia and Ragnarok will be submitted to the IAU as recommended names."

Students living in the United States and Brazil provided these four names.

The OSIRIS-REx mission has also invited the contest winner and runners-up to provide messages on the microchip that will travel to Bennu and return.

The microchip will contain names of thousands of people from around the world. Watch for more information about this activity in summer 2013.

]]> Thu, 23 MAY 2013 22:52:29 AEST Moscow (RIA Novosti) Apr 30, 2013 - A celestial body 20 meters in diameter will pass dangerously close to Earth's surface in 13 years, according to new data published on Thursday.

The flyby of 2013 GM3 on April 14, 2026, may bring it within 15,000 kilometers of Earth's center, or 8,620 kilometers from the planet's surface, said Italian astronomer Francesco Manca of the Sormano Astronomical Observatory near Milan.

The latter figure is slightly more than one radius of the planet, and within the geostationary orbit of 35,700 kilometers.

The 2013 GM3 was discovered in mid-April by Mount Lemmon Observatory in Arizona, but earlier calculations by NASA showed it would pass 39,000 kilometers from Earth's surface.

The asteroid may pass as far as 74,000 kilometers from Earth, Manca said in a message to the Minor Planet Mailing List.

More observations are needed to better determine the asteroid's trajectory, the astronomer added.

NASA estimates the probability of 2013 GM3's collision with Earth between 2028 and 2113 at 0.018%, or 1 in 5,560.

2013 GM3's size is comparable to that of the meteorite that exploded in the air over the city of Chelyabinsk in the Urals in mid-February, injuring about 1,500 people, most of whom were injured by glass shattering as a result of the shockwave from the meteorite's passing.

Source: RIA Novosti

]]> Thu, 23 MAY 2013 22:52:29 AEST Milan, Italy (UPI) Apr 25, 2013 - An Italian astronomer says new data suggest an asteroid 65 feet in diameter could pass dangerously close to Earth's surface in 13 years.

Francesco Manca of the Sormano Astronomical Observatory near Milan, Italy, said the April 14, 2026, flyby of the asteroid 2013 GM3 could bring it within 5,300 miles of Earth, RIA Novosti reported Thursday.

The asteroid was discovered in mid-April by researchers an observatory in Arizona, but preliminary calculation by NASA suggested it would pass 24,000 miles from Earth.

More observations are needed to better determine the asteroid's trajectory, Manca said.

The asteroid is comparable in size to the meteorite that exploded in the air over the city of Chelyabinsk in the Urals in mid-February, injuring about 1,500 people when windows shattered in the shockwave from the meteorite's passing.

]]> Thu, 23 MAY 2013 22:52:29 AEST Tucson AZ (SPX) Apr 26, 2013 - Scientists eagerly await the arrival of a recently discovered, highly active comet that will skim 730,000 miles above the Sun's surface on Nov. 28 and has the potential to be readily visible from Earth.

The comet, C/2012 S1 (ISON), is highly unusual in that it comes to the inner solar system for the first time and will skirt around the Sun within less than two solar radii from the Sun's surface on Nov. 28. Comet C/ISON was discovered in September 2012 when it was farther away from the Sun than Jupiter, and was already active at such a great distance.

This is distinct from most other sungrazers - comets that pass extremely close to the sun - that are only discovered and remain visible for several hours nearest the Sun. At such a close perihelion distance from the Sun, sungrazers are expected to be intensely heated by the Sun, and sublimate not only ice but also silicates and even metals, releasing a tremendous amount of dust. The expectation is high that Comet C/ISON will be much brighter and more spectacular than most other sungrazers when it puts on a show late this year.

"As a first-time visitor to the inner solar system, Comet C/ISON provides astronomers a rare opportunity to study a fresh comet preserved since the formation of the solar system," said Planetary Science Institute Research Scientist Jian-Yang Li, who led a team that imaged the comet.

"The expected high brightness of the comet as it nears the Sun allows for many important measurements that are impossible for most other fresh comets."

Comet C/ISON was imaged with the Hubble Space Telescope on April 10 using the Wide Field Camera 3, when the comet was slightly closer than Jupiter: 386 million miles (621 million kilometers) from the Sun and 394 million miles (634 million kilometers) from the Earth.

The team is using these images to measure the activity level of this comet and determine the size of the nucleus, in order to predict the comet's activity when it passes perihelion, or closest to the Sun, later this year.

Preliminary measurements from the Hubble images suggest that the nucleus, the solid, icy body at the center of the comet, is no larger than three or four miles across. This is remarkably small considering the high level of activity observed in the comet so far. This small size also means that the outcome from its close perihelion passage near the Sun is extremely hard to foresee.

The comet is active as sunlight warms the surface and causes frozen volatiles to sublimate. The comet's dusty coma, or head of the comet, is currently approximately 3,100 miles (5,000 kilometers) across, or 1.2 times the width of Australia. A dust tail extends more than 57,000 miles (92,000 kilometers), far beyond Hubble's field of view.

A detailed analysis of the dust coma surrounding the nucleus reveals a strong jet blasting dust particles off the sunward-facing side of the comet's nucleus. This jet, as projected on the sky, extends at least 2,300 miles (3,700 kilometers).

More careful analysis is currently under way to improve these measurements and to predict the possible outcome of the sungrazing perihelion passage of this comet.

Whether Comet C/ISON will become a "Comet of the Century" and outshine all other bright comets in the past still remains to be seen. But the new Hubble images of Comet C/ISON have revealed much valuable information about this highly unusual comet.

]]> Thu, 23 MAY 2013 22:52:29 AEST Los Angeles CA (SPX) Apr 26, 2013 - Many collisions occur between asteroids and other objects in our solar system, but scientists are not always able to detect or track these impacts from Earth. The "rogue debris" created by such collisions can sometimes catch us by surprise.

UCLA space scientists have now devised a way to monitor these types of collisions in interplanetary space by using a new method to determine the mass of magnetic clouds that result from the impacts.

Their findings, published online this month in the journal Meteoritics and Planetary Science, are the result of nearly 30 years of observations of collisions and could help scientists better understand where to look first to find new meteroid debris that could become dangerous.

"The passage by the Earth earlier this year of the small asteroid 2012 DA14 and the explosion the same week of an even smaller asteroid in the atmosphere above central Russia remind us that while space is mostly empty, the objects that are orbiting the sun do occasionally collide with other orbiting bodies, and the energy released in such collisions can be catastrophic to the bodies involved," said Christopher T. Russell, a professor in UCLA's Department of Earth and Space Sciences and a co-author of the research.

"We have found a way by which we can monitor such collisions in space by identifying the magnetic signature produced in these collisions," he said. "While the colliding objects may be only tens to hundreds of feet across, the resulting magnetic signature can be hundreds of thousands of miles in width and be carried outward from the sun by the solar wind for millions of miles."

Hairong Lai, a graduate student in Russell's laboratory, devised the method for finding the mass of collision-produced magnetic clouds, which contain fine, electrically charged dust.

"We have used multiple spacecraft encounters with these magnetized clouds to determine their dimensions," said Lai, the lead author of the research.

"Then we calculate the magnetic force applied to the dust, which balances the sun's gravitational force, allowing us to weigh the fine component of the debris created by the collision. These dust clouds weigh from about 10,000 to 1 million tons - very similar in mass to the asteroids the Earth recently encountered over Russia and over Australia."

The technique of monitoring the debris cloud of collisions magnetically was applied to material that co-orbits with the asteroid known as 2201 Oljato. This asteroid was first associated with collisions near Venus in the early 1980s; Oljato made successive passes by Venus in 1980, 1983 and 1986, when NASA's Pioneer Venus spacecraft was in orbit around the planet.

In 2006, the European Space Agency's Venus Express mission entered orbit and resumed monitoring the collisions. Now, some 30 years later, the collision rates have dropped dramatically in the sector in which impacts with material in Oljato's orbit could be detected, but the rates are unchanged elsewhere.

"The collisions have destroyed both the impactors and their targets in this longitude sector, demonstrating that meteor streams can be quite dynamic," said Hairong, who presented research last week at the third Planetary Defense Conference of the International Academy of Astronautics, in Flagstaff, Ariz. "They can be created by collisions and also destroyed by collisions."

Asteroids whose positions are known by scientists are all potential producers of smaller meteroids that can change orbits more rapidly, making it difficult to keep track of them, Russell said. This new method, he said, makes such tracking much easier.

The research was made possible by the acquisition of data by Pioneer Venus and by Venus Express missions.

]]> Thu, 23 MAY 2013 22:52:29 AEST Paris (ESA) Apr 25, 2013 - Astronomers have finally found direct proof that almost all water present in Jupiter's stratosphere was delivered by comet Shoemaker-Levy 9, which struck the planet in 1994. The result is based on new data from Herschel that revealed more water in Jupiter's southern hemisphere, where the impacts occurred, than in the north as well as probing the vertical distribution of water in the planet's stratosphere.

The origin of water in the upper atmospheres of the Solar System's giant planets has been debated for almost two decades. Astronomers were quite surprised at the discovery of water in the stratosphere - an intermediate atmospheric layer - of Jupiter, Saturn, Uranus and Neptune, which dates to observations performed with ESA's Infrared Space Observatory (ISO) in 1997.

While the source of water in the lower layers of their atmospheres can be explained as internal, the presence of this molecule in their upper atmospheric layers is puzzling due to the scarcity of oxygen there - its supply must have an external origin. Since then, astronomers have investigated several possible candidates that may have delivered water to these planets, from icy rings and satellites to interplanetary dust particles and cometary impacts.

Answers are now starting to flow in from studies using ESA's Herschel space observatory. Herschel boasts unprecedented sensitivity as well as high spatial and spectral resolution at the far-infrared wavelengths, where many water emission lines can be observed.

In 2011, a study based on Herschel data indicated that water in the stratosphere of Saturn is provided by its icy moon Enceladus; in 2012, the same origin was suggested for water in the atmosphere of Titan, another of Saturn's moons. Now it's the turn of Jupiter.

Soon after ISO's results, astronomers suspected that stratospheric water on Jupiter may have been, at least in part, supplied by comet Shoemaker-Levy 9, whose fragments famously hit the planet in July 1994.

Until now, the claims were based on indirect evidence, such as the observations of carbon dioxide (CO2), which can be produced from the photo-chemistry of water; but the new Herschel data have yielded the long-sought direct proof.

"We have been eagerly looking forward to observing Jupiter with Herschel," comments Thibault Cavalie from the Laboratoire d'Astrophysique de Bordeaux, France, who led the study.

"Herschel has a unique combination of instruments that allowed us to perform a three-dimensional reconstruction of water in Jupiter's stratosphere: using PACS, we could map the distribution of water across the entire disc of the planet, and we probed the vertical profile of water in the stratosphere using HIFI. The combination of both data sets was crucial to linking the source of water to the famous cometary impact of almost 19 years ago," he adds.

Cavalie and his colleagues collected their first observations of Jupiter with PACS during Herschel's Science Demonstration Phase in late 2009, obtaining a set of spectra that coarsely spanned the planet's disc.

"The first observations were not yet optimised for the purpose of our study, but they already showed an asymmetric distribution of stratospheric water across Jupiter's disc. This first hint that water is overly abundant in the southern hemisphere motivated the rest of our observations," explains co-author Paul Hartogh of the Max-Planck-Institut fur Sonnensystemforschung (MPS) in Katlenburg-Lindau, Germany. Hartogh is the Principal Investigator of the Herschel Key Programme 'Water and Related Chemistry in the Solar System' within which the observations were performed. "After all, Shoemaker-Levy 9 hit Jupiter at intermediate southern latitudes."

In 2010, the astronomers observed Jupiter again with PACS, this time gathering spectra at a much larger number of points across the planet's disc. This enabled them to obtain an accurate map of Jupiter's emission at 66.4 microns, a wavelength that corresponds to one of water's many spectral signatures.

A comparison of this map with mid-infrared data from NASA's Infrared Telescope Facility (IRTF) that probe the atmospheric temperature indicated that the asymmetry in the water emission detected with Herschel is not linked to temperature fluctuations and must be due to an uneven distribution of water around the planet.

"The asymmetry between the two hemispheres suggests that water was delivered during a single event and rules out icy rings or moons as candidate sources," says Cavalie. "Local sources would provide a steady supply of water, which over time would lead to a hemispherically symmetric distribution in the stratosphere. Depending on whether the chemical species are transported in neutral or ionised form, local sources of water would result in higher concentrations either at the poles or along the equator, but not in a north-south asymmetry," he adds.

The PACS data, which enabled the astronomers to collect spectra across Jupiter's disc at great spatial resolution, were complemented with a set of high spectral resolution measurements from HIFI. Taken at 25 points across the planet's disc, these spectra were centred at 179.5 microns, another wavelength corresponding to an emission line of the water molecule.

"Exploiting the high spectral resolution of HIFI data, we could probe the vertical distribution of water across Jupiter's stratosphere," explains Hartogh, "This was our 'smoking-gun' proof to exclude other possible sources and confirm that at least 95 per cent of the water currently present in Jupiter's stratosphere was brought there by comet Shoemaker-Levy 9."

The HIFI spectra indicate that the bulk of water is confined to pressures lower than 2 millibars, corresponding to high stratospheric altitudes - well above the uppermost part of the troposphere. The troposphere lies below the stratosphere, in Jupiter's lower atmosphere, and its uppermost layer can be regarded as the visible planetary 'surface'.

This part of the troposphere is also referred to as the 'cold trap' because it prevents water vapour from below to rise into the stratosphere, where it would condense into ice due to the low temperatures. For this reason, any trace of water in the stratosphere must have been delivered from an external source.

Furthermore, the absence of water in the lower stratosphere pinpoints the origin of this water to a sporadic event: had it been brought by interplanetary dust particles, it would have had more time to be redistributed throughout the stratosphere and its vertical distribution would have extended to much lower altitudes.

The results do not exclude that interplanetary dust particles, icy rings and satellites or other cometary impacts may have brought water to Jupiter's stratosphere, but only in marginal amounts compared to that supplied by the 1994 impact.

"As the bulk of water we see in Jupiter's stratosphere was delivered at a single time in the past, we expect its content to slowly decline over the years, and we plan to keep monitoring Jupiter with the Swedish-led Odin spacecraft to study this decrement," says Cavalie.

Significant amounts of water will still be present in the planet's stratosphere by the 2030s, when ESA's Jupiter Icy moons Explorer (JUICE) mission will reach the Jovian system. Among other goals, the mission's Sub-millimetre Wave Instrument (SWI) will target a variety of molecules - including water - as tracers to study the circulation, winds and other phenomena in Jupiter's atmosphere.

"We are now certain that most water currently present in Jupiter's stratosphere is a remnant of the spectacular 1994 break-up and subsequent impact of comet Shoemaker-Levy 9," comments Goran Pilbratt, Herschel Project Scientist at ESA.

"After showing that the water in Saturn's stratosphere, and possibly also in the atmosphere of Titan, is being provided by the moon Enceladus, Herschel has now clarified its origin in the largest of the giant planets, painting a diverse picture of the history of water in the Solar System."

T. Cavalie, et al., "Spatial distribution of water in the stratosphere of Jupiter from Herschel-HIFI and PACS observations", 2013, Astronomy and Astrophysics, 553, A21; doi: 10.1051/0004-6361/201220797.

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