Category: Asteroids

In addition to the Moon, the Earth also has a collection of co-orbital satellites. These are really nothing more than asteroids briefly captured by the Earth’s gravity. Instead of orbiting the Earth, they take corkscrew paths around our planet, eventually escaping back into the Solar System. One asteroid, 2003 YN107, has been traveling with us since 1999, and now it’s about to depart, building up enough speed to escape the Earth’s gravity.
Continue reading “Earth’s Second Moon is About to Leave Us”

Asteroid Itokawa. Image credit: JAXA. Click to enlarge
Itokawa, a spud-shaped, near-Earth asteroid, consists mainly of the minerals olivine and pyroxene, a mineral composition similar to a class of stony meteorites that have pelted Earth in the past.

This asteroid ingredient list, published in Science, comes courtesy of Hayabusa, the spacecraft launched in 2003 by the Japanese Aerospace Exploration Agency (JAXA). The mission of Hayabusa is to bring back first-ever samples from an asteroid to better understand their role as building blocks of the solar system.

Itokawa, an elongated rocky object nearly as long as five football fields, circles the sun more than 321 million miles away from Earth. Along with a few hundred known asteroids, Itokawa’s orbit is close to Earth’s orbit and was discovered by the Lincoln Near-Earth Asteroid (LINEAR) program, which detects near-Earth asteroids and provides advance warning if any are bound for Earth. Itokawa doesn’t currently pose such a threat, but its close proximity made it a tempting scientific target.

A near-infrared spectrometer aboard Hayabusa helped identify Itokawa’s mineralogy, mostly a mixture of the rock-forming minerals olivine and pryroxene, and possibly some plagioclase and metallic iron. But to truly understand what they had, the team turned to Takahiro Hiroi, a Brown University researcher who is expert in determining the composition of asteroids and meteorites, bits of asteroids that have fallen to Earth.

Hiroi is a senior research associate in the Department of Geological Sciences at Brown and the operations manager of the University’s NASA-funded Reflectance Experiment Laboratory (RELAB). For the Hayabusa project, Hiroi obtained samples of meteorites from museums, measured them at RELAB, and compared these results with spectral data from Itokawa.

Hiroi was able to determine that the mineral composition of the surface of Itokawa was similar to that of LL chondrites, a common class of stony meteorites relatively low in metallic iron. This link helped the team place a probable source of origin for Itokawa: the inner portion of the main asteroid belt, a ring of tens of thousands of rocks orbiting the sun between Mars and Jupiter.

Using Hayabusa data, the team was also able to better describe the surface of Itokawa. Much of it is studded with boulders, although the asteroid contains a smoother area known as Muses Sea. This diversity of terrain, the team concludes, may be the result of past meteoroid impacts and space weathering, a rock-altering process due to bombardments by dust particles and solar wind.

“We’ve never had a close-up look at such a small asteroid until now,” Hiroi said. “Large asteroids such as Eros are completely covered with a thick regolith, a blanket of looser material created by space weathering. With Itokawa, we believe we have witnessed a developing stage of the formation of this regolith. And these boulders sitting on Itokawa are no different from the meteorites that have fallen on Earth. So we may be seeing an earlier stage of asteroid evolution, of a type that has touched this planet.”

NASA and JAXA funded the work.

Original Source: Brown University

Aorounga impact crater. Image credit: NASA/JPL. Click to enlarge
Comet 73P/Schwassmann Wachmann 3 is a beautiful sight in the night sky, especially now that it’s fractured into many pieces. There’s evidence for these kinds of impacts on several planets and moons in the Solar System, and astronomers watched 23 fragments of Comet Shoemaker-Levy 9 smash into Jupiter in 1993. What if a string of comet fragments like this hit the Earth? There are only a few examples of these kinds of impacts on the Earth; unfortunately, wind, rain and tectonic forces work to hide the evidence.

As the fragments of shattered comet 73P/Schwassmann Wachmann 3 glide harmlessly past Earth this month in full view of backyard telescopes, onlookers can’t help but wonder, what if a comet like that didn’t miss, but actually hit our planet?

For the answer to that question, we look to the Sahara desert.

In a remote windswept area named Aorounga, in Chad, there are three craters in a row, each about 10 km in diameter. “We believe this is a ‘crater chain’ formed by the impact of a fragmented comet or asteroid about 400 million years ago in the Late Devonian period,” explains Adriana Ocampo of NASA headquarters.

Ocampo and colleagues discovered the chain in 1996. The main crater “Aorounga South” had been known for many years?it sticks out of the sand and can be seen from airplanes and satellites. But a second and possibly third crater were buried. They lay hidden until radar onboard the space shuttle (SIR-C) penetrated the sandy ground, revealing their ragged outlines.

“Here on Earth, crater chains are rare,” says Ocampo, but they are common in other parts of the solar system.

The first crater chains were discovered by NASA’s Voyager 1 spacecraft. In 1979 when the probe flew past Jupiter’s moon Callisto, cameras recorded a line of craters, at least fifteen long, evenly spaced as if someone had strafed the moon with a Gatling gun. Eventually, eight chains were found on Callisto and three more on Ganymede.

At first the chains were a puzzle. Were they volcanic? Had an asteroid skipped along the surface of Callisto like a stone skipping across a pond?

The mystery was solved in 1993 with the discovery of Comet Shoemaker-Levy 9. SL-9 was not a single comet, but a “string of pearls,” a chain of 21 comet fragments created a year earlier when Jupiter’s gravity ripped the original comet apart. SL-9 struck back in 1994, crashing into Jupiter. Onlookers watched titanic explosions in the giant planet’s atmosphere, and it only took a little imagination to visualize the result if Jupiter had had a solid surface: a chain of craters.

Astronomers have since realized that fragmented comets and rubble-pile asteroids are commonplace. Comets fall apart rather easily; sunlight alone can shatter their fragile nuclei. Furthermore, there is mounting evidence that many seemingly solid asteroids are assemblages of boulders, dust and rock held together by feeble gravity. When these things hit, they make chains.

In 1994, researchers Jay Melosh and Ewen Whitaker announced their finding of two crater chains on the Moon. One, on the floor of the crater Davy, is spectacular–an almost perfect line of 23 pockmarks each a few miles in diameter. This proved that crater chains exist in the Earth-Moon system.

But where on Earth are they?

Earth tends to hide its craters. “Wind and rain erode them, sediments fill them in, and the tectonic recycling of Earth’s crust completely obliterates them,” says Ocampo. On the Moon, there are millions of well-preserved craters. On Earth, “so far we’ve managed to find only about 174.”

Sounds like a job for Google. Seriously. Amateur astronomer Emilio Gonzalez pioneered the technique in March 2006. “I use Google Earth,” he explains. Google Earth is a digital map of our planet made of stitched-together satellite images. You can zoom in and out, fly around and inspect the landscape in impressive detail. It’s a bit like a video game-except it is real.

Gonzalez began by calling up Kebira impact crater in Libya?the Sahara’s largest. It was so easy to see, he recalls, “I decided to look around for more.” Minutes later he was “flying” over the Libya-Chad border when another crater appeared. And then another. They both had multiple rings and a central peak, the telltale splash of a high-energy impact. “It couldn’t be this easy!” he marveled.

But it was. At least one of the craters had never been catalogued before, and both, almost incredibly, lined up with the Aorounga crater 200 km away: map. In less than 30 minutes, Gonzalez had found two good impact candidates and possibly multiplied the length of the Aorounga chain. Hours of additional searching produced no new results. “Beginner’s luck,” he laughs. (If you would like to hunt for your own craters online, Gonzalez offers these tips.)

Ocampo doubts that these new craters are related to Aorounga. “They don’t appear to be the same age.” But she can’t rule it out either.

“We need to do some fieldwork,” she says. To prove a crater is a crater-and not, say, a volcano-researchers must visit the site to look for signs of extraterrestrial impact such as “shatter cones” and other minerals forged by intense heat and pressure. This kind of geological study can also reveal the age of an impact site, marking it as part of a chain or an independent event.

Answers may have to wait. Civil war in Chad and the possibility of war between Chad and Sudan prevent scientists from mounting an expedition. Meanwhile, researchers are scrutinizing candidate chains in Missouri and Spain. Although those sites are more accessible than Chad, researchers still can’t decide if they are chains or not. It’s difficult work.

Ocampo believes it’s worth the effort. “The history of Earth is shaped by impacts,” she says. “Crater chains can tell us important things about our planet.”

And so the search goes on.

Original Source: NASA News Release

Impacts with very large asteroids are uncommon. Image credit: ESA Click to enlarge
Asteroids don’t hit the Earth often, but when they do, the results can be catastrophic. The European Space Agency is working on several approaches to minimize the chances we’ll make a close encounter with an asteroid. A new mission, called Don Quijote, will launch in 2011 and slam an impactor probe into an asteroid to see what happens. An orbiter spacecraft will remain in orbit around the asteroid and continue to study the aftereffects of the impact. There are now three European teams working on preliminary studies for the potential mission.

If a large asteroid such as the recently identified 2004 VD17 – about 500 m in diameter with a mass of nearly 1000 million tonnes – collides with the Earth it could spell disaster for much of our planet. As part of ESA’s Near-Earth Object deflecting mission Don Quijote, three teams of European industries are now carrying out studies on how to prevent this.

ESA has been addressing the problem of how to prevent large Near-Earth Objects (NEOs) from colliding with the Earth for some time. In 1996 the Council of Europe called for the Agency to take action as part of a “long-term global strategy for remedies against possible impacts”. Recommendations from other international organisations, including the UN and the Organisation for Economic Cooperation and Development (OECD), soon followed.

In response to these and other calls, ESA commissioned a number of threat evaluation and mission studies through its General Studies Programme (GSP). In July 2004 the preliminary phase was completed when a panel of experts appointed by ESA recommended giving the Don Quijote asteroid-deflecting mission concept maximum priority for implementation.

Now it is time for industry to put forward their best design solutions for the mission. Following an invitation to tender and the subsequent evaluation process, three industrial teams have been awarded a contract to carry out the mission phase-A studies. :

– a team with Alcatel Alenia Space as prime contractor includes subcontractors and consultants from across Europe and Canada; Alcatel Alenia Space developed the Huygens Titan probe and is currently working on the ExoMars mission

– a consortium led by EADS Astrium, which includes Deimos Space from Spain and consultants from several European countries, brings their experience of working on the design of many successful ESA interplanetary missions such as Rosetta, Mars and Venus Express

– a team led by QinetiQ (UK), which includes companies and partners in Sweden and Belgium, draws on their expertise in mini and micro satellites including ESA’s SMART-1 and Proba projects

This month the three teams began work and a critical milestone will take place in October when the studies will be reviewed by ESA with the support of an international panel of experts. The results of this phase will be available next year.

The risk is still small however, and may decrease even further when new observations are carried out. Still, if this or any other similar-sized object, such as 99942 Apophis, an asteroid that will come close enough to the Earth in 2029 to be visible to the naked eye, collided with our planet the energy released could be equivalent to a significant fraction of the world’s nuclear arsenal, resulting in devastation across national borders.

Luckily, impacts with very large asteroids are uncommon, although impacts with smaller asteroids are less unlikely and remote in time. In 1908 an asteroid that exploded over Siberia devastated an unpopulated forest area of more than 2000 km2; had it arrived just a few hours later, Saint Petersburg or London could have been hit instead.

Asteroids are a part of our planet’s history. As anyone visiting the Barringer Meteor Crater in Arizona, USA or aiming a small telescope at the Moon can tell, there is plenty of evidence that the Earth and its cosmic neighbourhood passed through a period of heavy asteroid bombardment. On the Earth alone the remains of more than 160 impacts have been identified, some as notorious as the Chicxulub crater located in Mexico?s Yucatan peninsula, believed to be a trace of the asteroid that caused the extinction of the dinosaurs 65 million years ago.

Collisions have shaped the history of our Solar System. Because asteroids and comets are remnants of the turbulent period in which the planets were formed, they are in fact similar to ‘time capsules’ and carry a pristine record of those early days. By studying these objects it is possible to learn more about the evolution of our Solar System as well as ‘hints’ about the origins of life on Earth.

Comet 67P/Churyumov-Gerasimenko is one of these primitive building blocks and will be visited by ESA’s Rosetta spacecraft in 2014, as a part of a very ambitious mission – the first ever to land on a comet. Rosetta will also visit two main belt asteroids (Steins and Lutetia) on its way to comet 67P/Churyumov-Gerasimenko. The mission will help us to understand if life on Earth began with the help of materials such as water and organisms brought to our planet by ‘comet seeding’.

ESA’s Science programme is already looking at future challenges, and its Cosmic Vision 2015-2025 plan has identified an asteroid surface sample return as one of the key developments needed to further our understanding of the history and composition of our Solar System.

Asteroids and comets are fascinating objects that can give or take life on a planetary scale. Experts around the world are putting all their energy and enthusiasm into deciphering the mysteries they carry within them.

With an early launch provisionally scheduled for 2011, Don Quijote will serve as a ‘technological scout’ not only to mitigate the chance of the Earth being hit by a large NEO but also for the ambitious journeys to explore our solar system that ESA will continue to embark upon. The studies now being carried out by European industry will bring the Don Quijote test mission one step nearer.

Original Source: ESA Portal

An artist’s illustration of the binary asteroids Patroclus (center) and Menoetius. Image credit: W.M. Keck Observatory. Click to enlarge
A bound pair of icy comets similar to the dirty snowballs circling outside the orbit of Neptune has been found lurking in the shadow of Jupiter.

Astronomers at the University of California, Berkeley, working with colleagues in France and at the Keck Telescope in Hawaii, have calculated the density of a known binary asteroid system that shares Jupiter’s orbit, and concluded that Patroclus and its companion probably are composed mostly of water ice covered by a patina of dirt.

Because dirty snowballs are thought to have formed in the outer reaches of the solar system, from which they are occasionally dislodged and end up looping closer to the sun as comets, the team suggests that the asteroid probably formed far from the sun. It most likely was captured in one of Jupiter’s Trojan points – two eddies where debris collects in Jupiter’s orbit – during a period when the inner solar system was intensely bombarded by comets, around 650 million years after the formation of the solar system.

If confirmed, this could mean that many or most of the probably thousands of Jupiter’s Trojan asteroids are dirty snowballs that originated much farther from the sun and at the same time as the objects now occupying the Kuiper Belt.

“It’s our suspicion that the Trojans are small Kuiper Belt objects,” said study leader Franck Marchis, a research astronomer at UC Berkeley.

Marchis and colleagues from the Institut de M??bf?canique C??bf?leste et Calculs d’??bf?ph??bf?m??bf?rides (IMCCE) at the Observatoire de Paris and from the W. M. Keck Observatory report their findings in the Feb. 2 issue of Nature.

The team’s conclusion adds support to a recent hypothesis about the evolution of the orbits of our solar system’s largest planets, Jupiter, Saturn, Uranus and Neptune, put forth by a group of researchers headed by Alessandro Morbidelli, a theoretical astronomer with the Conseil National de la Recherche Scientifique laboratory of the Observatoire de la Cote d’Azur, Nice, France.
Diagram of the asteroid 617 Patroclus and its companion in the solar system

In a Nature paper last year, Morbidelli and colleagues proposed that icy comets would have been captured in Jupiter’s Trojan points during the early history of the solar system. According to their scenario, during the first few hundred million years after the birth of the solar system, the large gas planets orbited closer to the sun, enveloped in a cloud of billions of large asteroids called planetesimals, perhaps 100 kilometers (62 miles) in diameter or less. Interactions with these planetesimals caused the large gaseous planets to migrate outward until about 3.9 billion years ago, when Jupiter and Saturn entered resonant orbits and began tossing the planetesimals around like confetti, some of them leaving the solar system for good.

The bulk of the remaining planetesimals settled into orbits beyond Neptune – today’s Kuiper Belt and the source of short-period comets – but a small number were captured in the Trojan eddies of the giant planets, in particular Jupiter.

“This is the first time anyone has determined directly the density of a Trojan asteroid, and it supports the new scenario proposed by Morbidelli,” said coauthor Daniel Hestroffer, an astronomer at the IMCEE. “These asteroids would have been captured in the Trojan points at a time when the rocky planets were still forming, and this perturbation of the planetesimals about 650 million years after the birth of the solar system could have created the late bombardment of the moon and Mars.”

Though Marchis refers to the scenario as “a nice story,” he admits that more work needs to be done to provide support for it.

“We need to discover more binary Trojans and observe them to see if low density is a characteristic of all Trojans,” he said.

Trojan asteroids are those caught in the so-called Lagrange points of Jupiter’s orbit, located the same distance from Jupiter as Jupiter is from the sun – 5 astronomical units, or 465 million miles. These points, one leading and the other trailing Jupiter, are places were the gravitational attraction of the sun and Jupiter are balanced, allowing debris to collect like dust bunnies in the corner of a room. Hundreds of asteroids have been discovered in the leading (L4) and trailing (L5) points, each orbiting around that point as if in an eddy.

The asteroid 617 Patroclus, originally discovered at L5 and named in 1906, was found to have a companion in 2001, and so far is the only known Trojan binary. The discoverers were not able to estimate the orbit of the components because they had too few observations.

As experienced asteroid hunters, Marchis and his colleagues in August this year discovered the first triple asteroid system, 87 Sylvia, much closer to the sun in the main asteroid belt between Mars and Jupiter, and used a powerful 8-meter telescope of the European Southern Observatory’s Very Large Telescope in Chile to study the three objects. They were able to chart the orbits of the asteroids to estimate the density of Sylvia, from which they concluded it is a rubble-pile of loosely, packed rock.

The French and American team tried the same technique with the much more distant Patroclus, employing imaging data from the Keck II Laser Guide Star System at the W. M. Keck Observatory on Mauna Kea, which yields a sharp resolution impossible with any other ground-based telescope.

“Before, we could only look at objects near a bright reference star, limiting the use of adaptive optics to a small percentage of the heavens,” Marchis said. “Now, we can use adaptive optics to view almost any point on the sky.”

The laser guide star system uses a laser beam to excite sodium atoms within a small spot in the upper atmosphere. This artificial “star” is used to measure atmospheric turbulence, which is then removed by the movable mirrors of the Keck adaptive optics system.

With the system providing an unparalleled 58 milliarcsecond resolution, the Keck team made five observations in the infrared between November 2004 and July 2005. Marchis and his colleagues determined that the density of Patroclus and its companion, which are about the same size and circle around their center of mass every 4.3 days at a distance of 680 kilometers (423 miles), was very low: 0.8 grams per cubic centimeter, about one third that of rock and light enough to float in water. Assuming a rocky composition similar to that of Jupiter’s moons Callisto and Ganymede, the components of the system would have to be very loosely packed – about half empty space, an internal characteristic which is not expected for a same-size binary system, the researchers concluded.

The team suggests a more reasonable composition of water ice with only 15 percent open space, which makes these objects similar to comets and small Kuiper Belt objects, which have been determined to have densities less than water.

Marchis suspects that the binary system formed when a single large asteroid was torn asunder by the gravitational tug of Jupiter.

“The Patroclus system displays similar characteristics to the binary Near Earth Asteroids, which are believed to have formed during an encounter with a terrestrial planet by tidal splitting,” he said. “In the case of a Trojan asteroid, it is only when the work of our collaborators was published recently that we could suggest that this encounter was with Jupiter.”

Because in Homer’s Iliad, Patroclus was Achilles’ companion and a hero of the Trojan War, Achilles would have been an appropriate name for one of the two asteroids, which are about the same size. However, another asteroid already has the name Achilles, so Marchis and his collaborators proposed naming the smallest member of the binary system Menoetius, after the father of Patroclus. The Committee on Small Body Names of the International Astronomical Union has tentatively accepted the name. The asteroid designated Menoetius is about 112 kilometers (70 miles) in diameter, while Patroclus is about 122 kilometers (76 miles) wide.

In addition to Marchis, the team included astronomy professor Imke de Pater and postdoctoral fellow Michael H. Wong of UC Berkeley; Daniel Hestroffer, Pascal Descamps, J??bf?r??bf?me Berthier and Fr??bf?d??bf?ric Vachier of the Institut de M??bf?canique C??bf?leste et de Calculs des ??bf?ph??bf?m??bf?rides (IMCCE); and Antonin Bouchez, Randall Campbell, Jason Chin, Marcos van Dam, Scott Hartman, Erik Johansson, Robert Lafon, David Le Mignant, Paul Stomski, Doug Summers and Peter Wizinovich of the W. M. Keck Observatory.

The project was supported by grants from the National Science Foundation through the Science and Technology Center for Adaptive Optics and by the National Aeronautics and Space Administration. Most of the data were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership between the California Institute of Technology, the University of California and NASA, with additional observations obtained at the Gemini Observatory operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership.

Original Source: UC Berkeley News Release

The Earth. Image credit: NASA Click to enlarge
In a new study that provides a novel way of looking at our solar system’s past, a group of planetary scientists and geochemists announce that they have found evidence on Earth of an asteroid breakup or collision that occurred 8.2 million years ago.

Reporting in the January 19 issue of the journal Nature, scientists from the California Institute of Technology, the Southwest Research Institute (SwRI), and Charles University in the Czech Republic show that core samples from oceanic sediment are consistent with computer simulations of the breakup of a 100-mile-wide body in the asteroid belt between Mars and Jupiter. The larger fragments of this asteroid are still orbiting the asteroid belt, and their hypothetical source has been known for years as the asteroid “Veritas.”

Ken Farley of Caltech discovered a spike in a rare isotope known as helium 3 that began 8.2 million years ago and gradually decreased over the next 1.5 million years. This information suggests that Earth must have been dusted with an extraterrestrial source.

“The helium 3 spike found in these sediments is the smoking gun that something quite dramatic happened to the interplanetary dust population 8.2 million years ago,” says Farley, the Keck Foundation Professor of Geochemistry at Caltech and chair of the Division of Geological and Planetary Sciences. “It’s one of the biggest dust events of the last 80 million years.”

Interplanetary dust is composed of bits of rock from a few to several hundred microns in diameter produced by asteroid collisions or ejected from comets. Interplanetary dust migrates toward the sun, and en route some of this dust is captured by the Earth’s gravitational field and deposited on its surface.

Presently, more than 20,000 tons of this material accumulates on Earth each year, but the accretion rate should fluctuate with the level of asteroid collisions and changes in the number of active comets. By looking at ancient sediments that include both interplanetary dust and ordinary terrestrial sediment, the researchers for the first time have been able to detect major dust-producing solar system events of the past.

Because interplanetary dust particles are so small and rare in sediment-significantly less than a part per million-they are difficult to detect using direct measurements. However, these particles are extremely rich in helium 3, in comparison with terrestrial materials. Over the last decade, Ken Farley has measured helium 3 concentrations in sediments formed over the last 80 million years to create a record of the interplanetary dust flux.

To assure that the peak was not a fluke present at only one site on the seafloor, Farley studied two different localities: one in the Indian Ocean and one in the Atlantic. The event is recorded clearly at both sites.

To find the source of these particles, William F. Bottke and David Nesvorny of the SwRI Space Studies Department in Boulder, Colorado, along with David Vokrouhlicky of Charles University, studied clusters of asteroid orbits that are likely the consequence of ancient asteroidal collisions.

“While asteroids are constantly crashing into one another in the main asteroid belt,” says Bottke, “only once in a great while does an extremely large one shatter.”

The scientists identified one cluster of asteroid fragments whose size, age, and remarkably similar orbits made it a likely candidate for the Earth-dusting event. Tracking the orbits of the cluster backwards in time using computer models, they found that, 8.2 million years ago, all of its fragments shared the same orbital orientation in space. This event defines when the 100-mile-wide asteroid called Veritas was blown apart by impact and coincides with the spike in the interplanetary seafloor sediments Farley had found.

“The Veritas disruption was extraordinary,” says Nesvorny. “It was the largest asteroid collision to take place in the last 100 million years.”

As a final check, the SwRI-Czech team used computer simulations to follow the evolution of dust particles produced by the 100-mile-wide Veritas breakup event. Their work shows that the Veritas event could produce the spike in extraterrestrial dust raining on the Earth 8.2 million years ago as well as a gradual decline in the dust flux.

“The match between our model results and the helium 3 deposits is very compelling,” Vokrouhlicky says. “It makes us wonder whether other helium 3 peaks in oceanic cores can also be traced back to asteroid breakups.”

This research was funded by NASA’s Planetary Geology and Geophysics program and received additional financial support from Czech Republic grant agency and the National Science Foundation’s COBASE program. The Nature paper is titled “A late Miocene dust shower from the breakup of an asteroid in the main belt.”

Original Source: caltech News Release

Artist’s concept of Xena the Sun, appearing from a distance. Image credit: NASA/JPL-Caltech. Click to enlarge
In the not-too-distant past, the planet Pluto was thought to be an odd bird in the outer reaches of the solar system because it has a moon, Charon, that was formed much like Earth’s own moon was formed. But Pluto is getting a lot of company these days. Of the four largest objects in the Kuiper belt, three have one or more moons.

“We’re now beginning to realize that Pluto is one of a small family of similar objects, nearly all of which have moons in orbit around them,” says Antonin Bouchez, a California Institute of Technology astronomer.

Bouchez discussed his work on the Kuiper belt at the winter meeting of the American Astronomical Society (AAS).

Bouchez says that the puzzle for planetary scientists is that, as a whole, the hundreds of objects now known to inhabit the Kuiper belt beyond the orbit of Neptune have only about an 11 percent chance of possessing their own satellites. But three of the four largest objects now known in the region have satellites, which means that different processes are at work for the large and small bodies.

Experts have been fairly confident for a decade or more that Pluto’s moon Charon was formed as the result of an impact, but that the planet seemed unique in this. According to computer models, Pluto was hit by an object roughly one-half its own size, vaporizing some of the planet’s material. A large piece, however, was cleaved off nearly intact, forming Pluto’s moon Charon.

Earth’s moon is thought to have been formed in a similar way, though our moon most likely formed out of a hot disk of material left in orbit after such a violent impact.

Just in the last year, astronomers have discovered two additional moons for Pluto, but the consensus is still that the huge Charon was formed by a glancing blow with another body, and that all three known satellites-as well as anything else not yet spotted from Earth-were built up from the debris.

As for the other Kuiper belt objects, experts at first thought that the bodies acquired their moons only occasionally by snagging them through gravitational capture. For the smaller bodies, the 11 percent figure would be about right.

But the bigger bodies are another story. The biggest of all – and still awaiting designation as the tenth planet – is currently nicknamed “Xena.” Discovered by Caltech’s Professor of Planetary Science Mike Brown and his associates, Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale University, Xena is 25 percent larger than Pluto and is known to have at least one moon.

The second-largest Kuiper belt object is Pluto, which has three moons and counting. The third-largest is nicknamed “Santa” because of the time of its discovery by the Mike Brown team, and is known to have two moons.

“Santa is an odd one,” says Bouchez. “You normally would expect moons to form in the same plane because they would have accreted from a disk of material in orbit around the main body.

“But Santa’s moons are 40 degrees apart. We can’t explain it yet.”

The fourth-largest Kuiper belt object is nicknamed “Easterbunny” – again, because of the time the Brown team discovered it – and is not yet known to have a moon. But in April, Bouchez and Brown will again be looking at Easterbunny with the adaptive-optics rig on one of the 10-meter Keck telescopes, and a moon might very well turn up.

Original Source: NASA Astrobiology

An Orbit Synthesis Example for Hayabusa Return starting in 2007. Image credit: JAXA Click to enlarge
Hayabusa spacecraft currently undergoes the recovery operation to resume the communication with the ground stations. It was hit by an abrupt disturbing torque owing to the fuel leak that occurred before, and has been out of the ground contact since December 9th. The project team has a good expect to have the spacecraft resume the communication soon. However, the project is now not so sure to make the spacecraft return to earth in June of 2007 and has decided to lengthen the flight period for three years more to have it return to the Earth in June of 2010.

On December 8th, Usuda station observed the sudden shifts of the range-rate measurements at 4:13 UTC with the corresponding gradual decrease of signal intensity AGC (Automated Gain Controller) read. The measurement and the intensity change slowly and are currently estimated due to the out-gassing effect that derived from the fuel leak-out at the end of last month. The leak occurred on November 26th and 27th. Since the beacon signal communication resumed on 29th, the project has made an effort to exclude the vapor gas of the fuel from the spacecraft. The project has by now identified the out-gassing has successfully been performed, as its exponential acceleration decay has shown so far.

On December 8th, the spacecraft was under the resume operation phase for the chemical propulsion, and was given a slow spin whose period is about six minutes. From the beginning of December, the project has introduced the Xenon gas thruster control strategy for emergency, replacing the chemical propulsion system. But the control capability of it was not enough strong for the spacecraft to withstand the disturbance on December 8th. Current estimation says the spacecraft may be in a large coning motion and that is why the spacecraft has not responded to the commands sent from the ground station.

The spacecraft has been out of communication since December 9th. Analysis predicting the attitude property relating to both the Sun and Earth shows that there will be high possibility counted on for the resumption of the communication from the ground for several months or more ahead. However, the spacecraft may have to undergo another long term baking cycle before it starts the return cruise operation using ion engines aboard. And it is concluded that the commencement of the return cruise during December is found difficult. The project has determined that the return cruise should start from 2007 so that the spacecraft can return to the Earth in June of 2010, three years later than the original plan, as long as no immediate resumption tales place very soon.

The spacecraft operation will shift from the normal mode to the rescue mode for several months to one year long. Long term predict indicates high probability of having the spacecraft communicated with the ground station again, with the spacecraft captured well in the beam width of the Usuda deep space antenna.

The spacecraft will take the advantage of Xenon gas attitude control again after enough length of baking operation. The Xenon gas that remains is adequate for the return cruise devised by the ion engines carried by Hayabusa.

The Hayabusa web page will report anything updated, as soon as it becomes available.

(Supplement) Hayabusa Rescue Operation

Hayabusa spacecraft is designed to allow the spin-stabilization and the attitude will converge to a certain pure spin around its high gain antenna axis ultimately. About the current state affected by the disturbance on December 8th, the attitude is conceived not to meet either of the Sun and Earth geometry requirement in terms of power and communication.

Once the coning motion damps, there will be some high probability that the spacecraft spin attitude satisfies both the power and communication conditions in several months.

There will be little possibility that the spacecraft position is out of the deep space antenna beam width for at least several months.

The Hayabusa system is designed to be initialized even once the whole power is down. Actually, on November 29th, the Hayabusa system restarted as these procedures functioned as prescribed.

There has been come up with a new trajectory synthesis that makes the spacecraft return to the earth in June of 2010. Without immediate communication resumption, the project thinks it should take this new schedule soon.

Original Source: JAXA News Release

Artist’s impression of Hayabusa spacecraft. Image credit: JAXA Click to enlarge
As has been reported, it is estimated that part of a series of attitude and orbit control commands to restore the Hayabusa from its safe-hold mode have not gone well, and the functions of its major systems, including its attitude and communication network, have significantly deteriorated. However, on Nov. 29, a beacon line through a low gain antenna was restored.

On Nov. 30, we started a restoration operation by turning on and off the radio frequency modulation through the autonomous diagnostic function. Subsequently, on Dec. 1, telemetry data were acquired at 8 bits per second through the low gain antenna, although the line was weak and often disconnected. According to the data transmitted so far, the attitude and orbit control commands sent on Nov. 27 did not work well due to an unknown reason, and either major attitude control trouble or a large electric power loss seems to have occurred. It is estimated that the overall power switching systems for many pieces of onboard equipment were reset as their temperature dropped substantially due to the evaporation of leaked propellant, and also because of a serious discharge of electricity from the batteries of many sets of onboard equipment and systems due to declining power generation. Details are still under analysis.

On Dec. 2, we tried to restart the chemical engine, but, even though a small thrust was confirmed, we were not able to restore full-scale operations. Consequently, the cause of the anomaly on Nov 27 is still under investigation, and we suspect that one of the causes could be the malfunction of the chemical engine.

On Dec. 3, we found that the angles between the axis of the onboard high gain antenna (+Z angle) and the Sun, and also that with the earth, had increased to 20 to 30 degrees. As an emergency attitude control method, we decided to adopt a method of jetting out xenon for the ion engine operation. Accordingly, we immediately started to create the necessary operation software. As we completed the software on Dec. 4, we changed the spin speed by xenon jet, and its function was confirmed. Without delay, we sent an attitude change command through this function.

As a result, on Dec. 5, the angle between the +Z axis and the sun, and the earth, recovered to 10 to 20 degrees, and the telemetry data reception and acquisition speed was restored to the maximum 256 bits per second through the mid gain antenna.

After that, we found that there was a high possibility that the projectile (bullet) for sampling had not been discharged on Nov. 26, as we finally acquired a record of the pyrotechnics control device for projectile discharging from which we were not able to confirm data showing a successful discharge. However, it may be because of the impact of the system power reset; therefore, we are now analyzing the details including the confirmation of the sequence before and after the landing on Nov. 26.

As of Dec. 6, the distance between the Hayabusa and the Itokawa is about 550 kilometers, and that from the earth is about 290 million kilometers. The explorer is relatively moving from the Itokawa toward the earth at about 5 kilometers per hour.

We are now engaging in turning on, testing, and verifying onboard equipment of the Hayabusa one by one to start the ion engine. We currently plan to shift the attitude control to one using the Z-axis reaction wheel, and restart the ion engine. The restart is expected to happen no earlier than the 14th. We are currently rescheduling the plan for the return trip to earth. We need to study how to relax the engine operation efficiency. We will do our utmost to solve the problem with the attitude control (such as the restoration of the chemical engine), then find a solution for the return trip.

Original Source: JAXA News Release