Category: Asteroids

Hayabusa Muses-C. Image credit: ISAS Click to enlarge
With a maneuver that scientists compared to landing a jumbo jet in a moving Grand Canyon, Japan’s asteroid explorer, Hayabusa, touched down on the surface of the asteroid Itokawa Saturday for the second time in a week and this time it successfully collected a sample of the surface soils, the Japan Aerospace Exploration Agency (JAXA) announced several hours after its bird had flown.

The world’s first mission to attempt to land on an asteroid, collect samples, and return them to Earth has completed what is, arguably, the most difficult challenge on its agenda, and will begin the long journey back to Earth in early December. If all goes as planned, the sample will be returned in a capsule slated to land in the Australian outback in June 2007.

Every command necessary for the sampling was carried out, JAXA announced Saturday evening Japan Standard Time (JST) on its website, and agency officials firmly believe that the mission succeeded in the world’s first collection of samples of surface materials from an asteroid. It is highly probable, according to the agency, that the asteroid explorer has snatched several grams of surface samples from the near Earth asteroid named after the “father” of Japan’s space program, Hideo Itokawa, but the exact volume will not be known until the spacecraft returns safely to Earth.

The spacecraft was on its own once it began to carry out the series of commands for Saturday’s touch-down, because signals take around 17 minutes to get from Earth to Hayabusa. The spacecraft’s autonomous navigation relies on the Optical Navigation Camera and Light Detection and Ranging (ONC/LD&R) instrument that measures the distance to and the shapes of the asteroid surface. Once the data from those and other instruments are fully analyzed, more specific details will be forthcoming.

Hayabusa which means “falcon” in Japanese — flew up and away from the asteroid after snatching its prey, and was subsequently “restored” by its ground team and instructed to return to its home orbit around 7 kilometers away from the asteroid. Japan, meanwhile, is soaring into space exploration history with a flight that has provided a stellar boost for the Japanese space program, and cause for major celebration in the homeland.

“This is a superb achievement, a great moment is space exploration,” said Planetary Society Executive Director Louis D. Friedman. “Automated surface sample return from another world has been done only from the Moon, and only by the Russians. This venture by the Japanese space agency is bold, and Hayabusa has been brilliantly executed mission.”

Hayabusa which was developed at the Institute of Space and Astronautical Science (ISAS), a space science research division of JAXA — launched from Japan’s Kagoshima Space Center on May 9, 2003 and arrived in September of this year despite being rocked on the way by several solar flares, and losing one of its three reaction wheels used to control the spacecraft’s orientation, point instruments, antennas, or subsystems at chosen targets.

Since then it has met with other misfortunes, including the loss of another reaction wheel and the loss of its tiny robot lander, Minerva, which it released at the wrong time. Still, from every mishap, Hayabusa has rebounded. “It’s the little spacecraft that could,” marveled Donald K. Yeomans, senior research scientist at the Jet Propulsion Laboratory (JPL) and the U.S. project scientist for the mission during an interview with The Planetary Society. “And the operations guys are working their tails off around the clock.”

The touch-down landing Saturday was Hayabusa’s second and final attempt to collect a sample from the small asteroid, which, according to the latest Japanese measurements is only 540 meters by 310 meters by 250 meters (about 1800 feet by 1000 feet by 820 feet), and is some 180 million miles from Earth. Although the spacecraft did bounce down twice and even settled on Itokawa’s surface for 30 minutes last weekend — marking a milestone as the first Japanese spacecraft to land on an extraterrestrial body — the sample collection device did not deploy, so that attempt to get a sample failed.

This time around, Hayabusa began its descent around 10:00 p.m., JST, Friday, November 25. By 7:15 a.m., the following morning, it was just 14 meters above Itokawa. At around 8:45 a.m., at least one tantulum pellet was fired through the cylinder in the sample collection device and into the surface at 300 meters per second and the ejecta from that cratering effect was captured and secured in the sample chamber.

The handful of dirt and dust that Hayabusa snatched Saturday may seem a small prize for all the effort, but the knowledge these samples hold about our solar system is by all accounts great. Asteroids preserve in their make-up the pristine materials that went into formation of the solar system, unlike the Moon or other larger planetary bodies that have undergone thermal alterations over the eons.

Hayabusa is “the next giant step forward” in understanding the role of near-Earth asteroids in the origin of the solar system, their potential threat to Earth, and the future use of their raw materials to expand human presence beyond Earth, according to Yeomans. “Near Earth asteroids are easier to land on than the Moon itself, some of them, and they’re far more rich in minerals,” he pointed out. “If you’re going to build structures in space, you’re not going to build them on the ground and launch them, you’re going to look for raw materials up there and asteroids provide some ready supplies of minerals, metals, and possibly water.”

Perhaps even more remarkable than Hayabusa’s achievements is the fact that the Japanese have pulled this mission off for a price tag of about $170-million-dollars [about one-third the cost of a NASA Discovery mission], and with a small mission operations team at the helm. “That is extraordinary,” said Yeomans.

Before the mission launched, Yeomans and others at JPL and NASA provided JAXA and ISAS division, with the ephemeris, a table that shows the coordinates of a celestial body at a number of specific times during a given period — essentially “directions” on how to get to the asteroid. NASA is tracking the spacecraft with the Deep Space Network (DSN) and the Americans there are providing some back-up navigation assistance. However, Hayabusa is not relying on NASA for navigation. In Yeomans’ words: “Since the spacecraft arrived at the asteroid it, has been Japan’s show.”

And what a show it’s been.

Original Source: NASA Astrobiology

Artist’s impression of ESA’s Hildalgo spacecraft. Image credit: ESA.Click to enlarge
Telescope facilities across the world are watching the skies for rocky remnants from outer space on a collision course with planet Earth. Currently one or two of these so called ‘Near Earth Objects’ [NEOs] are being recorded each day but fortunately for humankind the vast majority are the size of a human fist and pose no threat. Nevertheless, the presence of large impact craters on Earth provides dramatic evidence of past collisions, some of which have been catastrophic for the planet’s species, as was the case with the dinosaurs. This week, experts from across Europe and the US met in London to consider current and future efforts to monitor NEOs in order to better predict those with Earth impacting trajectories, since it is inevitable that a catastrophic collision will happen again in the future.

Professor Monica Grady, a leading expert on meteorites from the Open University explains, “It’s simply a question of when, not if, a NEO collides with the Earth. Many of the smaller objects break up when they reach Earth’s atmosphere and have no impact. However, a NEO larger than 1 km will collide with Earth every few hundred thousand years and an NEO larger than 6 km, which could cause a mass extinction, will collide with Earth every hundred million years. And we are overdue for a big one!”

NEO’s, remnants from the formation of the inner planets, range in size from 10 metre objects to those in excess of 1 km. It is estimated that 100 fist sized meteorites, fragments of NEO’s, fall to Earth on a daily basis but larger objects impact with Earth on a much less regular basis.

Professor Alan Fitzsimmons from Queens University Belfast is a UK astronomer (supported by the Particle Physics and Astronomy Research Council) involved in the study of NEO’s, using telescope facilities such as the European Southern Observatory’s Very Large telescope in Chile, the Isaac Newton Telescope in La Palma and the Faulkes Telescope in Hawaii. He said, “By the end of the decade as new dedicated facilities, such as the Pan-STARR project in Hawaii, come on line there will be a quantum leap in the discovery of NEO’s – with rates anticipated to increase to hundreds per day. This will provide us with a greater ability to determine which ones are on a potential Earth colliding trajectory.”

Studies of one such asteroid (Apophis), which was discovered in June2004, have shown that there is a low probability that this object will impact the Earth in 2036. This has raised a whole series of issues about the prospect of deflecting the asteroid before a very close approach in 2029. Government’s across the world are looking at the issue and in particular at the technologies and methods required to carry out an asteroid deflection manoeuvre in space.

The European Space Agency’s NEO Mission Advisory Panel (NEOMAP), of which Professor Fitzsimmons is a member, has selected “Don Quixote” as their preferred option for an asteroid deflecting test mission. Don Quixote would comprise two spacecraft – one of them (Hildalgo) would impact the asteroid at a very high relative speed while the second spacecraft (Sancho) would arrive earlier to monitor the effect of the impact to measure the variation of the asteroid’s orbital parameters. This attempt to deflect an incoming NEO would act as a precursor mission with the primary objective of modifying the trajectory of a “non-threatening” asteroid.

Richard Tremayne-Smith, from the British National Space Centre, heads up the coordination of UK NEO activity and helps provide an international lead on NEO efforts on the issue. He said, “NEO collisions are the only known natural disaster that can be avoided by applying appropriate technology – and so it is the interest of Governments across the World to take interest in this global issue. Here in the UK we take the matter very seriously and progress is being made in taking forward the recommendations of the UK NEO Task Force Report in an international arena.”

The current method of studying NEOs is achieved through a combination of 3 different methods:- the study of meteorites to understand their structure and composition; earth based astronomical observations of asteroids; and space based observations and encounters with asteroids.

Much can be understood about the nature of asteroids from the study of meteorites which are fragments of asteroids that have broken up and fallen to Earth. Professor Grady explains how the ground based study of meteorites is crucial to future plans for dealing with asteroids.

“In order to define successful strategies for deflecting asteroids that might collide with Earth, it is essential to understand the material properties such as the composition, strength and porosity of asteroids. By putting together such information with data from both ground based and space based studies we can begin to build an accurate picture of these diverse phenomena.”

UK scientists are involved in a number of other missions which will also be investigating the properties of asteroids and comets. This includes NASA’s Stardust mission which collected samples from Comet Wild 2 in January 2004. These samples are set to return to Earth in January 2006 and scientists from the Open University will be involved in their analysis. The European Space Agency’s Rosetta mission which is currently on route to Comet Churyumov-Gerasimenko will pass by two asteroids, Steins and Lutetia, before reaching its target in 2014, gathering data about their properties as it flies past.

Original Source: PPARC News Release

Hayabusa descending on Itokawa before landing. Image credit: JAXA Click to enlarge
Hayabusa attempted its first soft-landing on Itokawa for the purpose of touch down and sample collection on November 20-21, 2005. Below is the data information with the related advance report on its status.

Hayabusa started descending at 9:00pm on Nov. 19th, 2005 (JST) from 1km in altitude. The guidance and navigation during the process of approach was operated normally, and at 4:33am on Nov. 20th, the last approach of vertical descent was commanded from ground, of which soft-landing was successfully achieved almost on the designated landing site of the surface. Deviation from the target point is now under investigation but presumed within a margin of 30cm.

The velocity at the time of starting descent was 12cm/sec. At the altitude 54m at 5:28am, wire-cutting of target marker was commanded, after which, at 5:30am at altitude 40m, the spacecraft autonomously reduced its own speed by 9cm/sec to have substantially separated the target marker. It means that Hayabusa’s speed became 3 cm/sec. Separation and freefall of the marker was confirmed from the image as well as from descending velocity of the spacecraft at the time of reducing the speed. The marker is presumed to have landed on southwest of MUSES Sea.

Hayabusa then switched its range measurement from Laser Altimeter (LIDAR) to Laser Range Finder (LRF) at the altitude 35m and moved to hovering by reducing descending speed to zero at 25m above the surface, below where Hayabusa, at 5:40am at altitude 17m, let itself to freefall, functioning itself to the attitude control mode adjustable to the shapes of the asteroid surface. At this point, the spacecraft autonomously stopped telemetry transmission to the earth (as scheduled) to have changed to transmission with beacon mode more efficient for Doppler measurement by switching to low gain antenna (LGA) coverable larger area.

Since then, checking of the onboard instruments was not possible on a real time basis (as scheduled), but as a result of analyzing the data recorded onboard and sent back to the earth in the past two days, Hayabusa seemed to have autonomously judged to abort descending and attempted emergency ascent because its Fan Beam sensors for obstacle checking detected some kind of catch-light. Allowable margin is set for Hayabusa for its attitude control, in the case the spacecraft takes off the ground by accelerating the velocity on its own. Under such circumstances, the then spacecraft’s attitude was out of the margin, because of which continuing of safe descent was consequently chosen. As a result, Hayabusa did not activate its Touch Down Sensor function.

At the timepoint of Nov. 21, Hayabusa was judged not to have landed on the surface. According to the replayed data, however, it was confirmed that Hayabusa stayed on Itokawa by keeping contact with the surface for about 30 minutes after having softly bounced twice before settling. This can be verified by the data history of LRF and also by attitude control record.

This phenomenon took place during switching interval from Deep Space Network (DSN) of NASA to Usuda Deep Space Center, because of which the incident was not detected by ground Doppler measurement. The descending speed at the time of bouncing twice was 10cm/sec. respectively. Serious damage to the spacecraft has not been found yet except heating sensor that may need checking in some part of its instrument.

Hayabusa kept steady contacting with the surface until signaled from ground to make emergency takeoff at 6:58am (JST). The Touch Down Sensor supposed to function for sampling did not work because of the reason above stated, for which reason firing of projector was not implemented in spite of the fact that the spacecraft actually made landing. The attitude at landing is so presumed that the both bottom ends of +X axis of sampler horn and either the spacecraft or tip end of the solar panels was in contact with the surface. Hayabusa became the world-first spacecraft that took off from the asteroid. Really speaking, it is the world-first departure from an celestial body except the moon.

After departure from the asteroid by ground command, Hayabusa moved into safe mode due to the unsteady communication line and the conflict with onboard controlling and computing priority. The comeback from safety mode to normal 3-axis control mode needed full two days of Nov. 21 and 22. Owing to this reason, replaying of the data recorded on 20th is still midway, which means the possibility to reveal much more new information through further analysis of the data. As of now, the detailed image of the landing site to know its exact location has not been processed yet. Hayabusa is now on the way to fly over to the position to enable landing and sampling sequence again. It’s not certain yet if or not descent operation will be able to carry out from the night of Nov. 25 (JST). We will announce our schedule in the evening of Nov. 24.

Descending and landing operation will all depend upon availability of DSN of NASA. We would like to express our sincere gratitude for cooperation of NASA for tracking networks including backup stations.

Original Source: JAXA News Release

It appears that the Japanese Space Agency (JAXA) has lost contact with a small probe released from its mothership Hayabusa on Saturday. After its release, the Minerva probe failed to make contact with the asteroid Itokawa’s surface, and controllers have no idea where it went. Hayabusa has been having problems with its positioning control system, so it’s possible that it put Minerva on an incorrect vector to reach the asteroid’s surface. Hayabusa is still scheduled to dip down and scoop some material off Hayabusa’s surface to return to Earth for analysis.

Computer animation of Don Quijote and its asteroid target. Image credit: ESA. Click to enlarge.
Based on the recommendations of asteroid experts, ESA has selected two target asteroids for its Near-Earth Object deflecting mission, Don Quijote.

Don Quijote is an asteroid-deflecting mission currently under study by ESA?s Advanced Concepts Team (ACT). Earlier this year the NEO Mission Advisory Panel (NEOMAP), consisting of well-known experts in the field, delivered to ESA a target selection report for Europe?s future asteroid mitigation missions, identifying the relevant criteria for selecting a target and picking up two objects that meet most of those criteria. The asteroids? temporary designations are 2002 AT4 and 1989 ML.

With this input and the support of ESA?s Concurrent Design Facility (CDF) experts, the Advanced Concepts Team has now completed an extensive assessment of suitable mission architectures, launch strategies, propulsion system options and experiments.

The current scenario envisages two spacecraft in separate interplanetary trajectories. One spacecraft (Hidalgo) will impact an asteroid, the other (Sancho) will arrive earlier at the target asteroid, rendezvous and orbit the asteroid for several months, observing it before and after the impact to detect any changes in its orbit.

Industrial studies are now about to start; it will be down to European experts to propose alternative solutions for the design of the low-cost NEO precursor mission. This will be the first step towards the development of a means to tackle asteroid impacts ? one of the few natural disasters that our technology can prevent.

A near miss?
While the eyes of the world were on the Asian tsunami last Christmas, one group of scientists were watching uneasily for another potential natural disaster ? the threat of an asteroid impact.

On 19 December 2004 MN4, an asteroid of about 400 m, lost since its discovery six months earlier, was observed again and its orbit was computed. It immediately became clear that the chances that it could hit the Earth during a close encounter in 2029 were unusually high. As the days passed the probability did not decrease and the asteroid became notorious for surpassing all previous records in the Torino and Palermo impact risk scales – scales that measure the risk of an asteroid impact just as the Richter scale quantifies the size of an earthquake.

Only after earlier observations of the object were found and a more accurate trajectory was computed did it become clear that it would not impact the Earth ? at least not in 2029. Impacts on later dates, though unlikely, have not been totally ruled out. It is extremely difficult to tell what will happen unless we come up with a better way to track this or other NEOs and if necessary take steps to tackle them.

Most world experts agree that this capability is now within our reach. A mission like ESA?s Don Quijote could provide a means to assess a threatening NEO and take concrete steps to deflect it away from the Earth.

But every good performance needs rehearsing and in order to be ready for such a threat, we should try our hardware on a harmless asteroid first. Don Quijote would be the first mission to make such an attempt. The big question was: which asteroid and what should it be like?

Looking for the perfect target
The NEO population contains a confusing variety of objects, and deciding which physical parameters are most relevant for mitigation considerations is no trivial task. But the NEOMAP experts took on the challenge and in February 2005 provided ESA with their recommendations on the asteroid selection criteria for ESA?s deflection rehearsal.

People might wonder whether performing a deflection test, such as that planned for Don Quijote, represents any risk to our planet. What if things go wrong? Could we create a problem, rather than learn how to avoid one?

Experts world-wide say the answer is no. Even a very dramatic impact of a heavy spacecraft on a small asteroid would only result in a minuscule modification of the object?s orbit. In fact the change would be so small that the Don Quijote mission requires two spacecraft ? one to monitor the impact of the other. The second spacecraft measures the subtle variation of the object?s orbital parameters that would not be noticeable from Earth.

Target objects can also be selected so that all possible concerns are avoided altogether, by looking into the way the distance between the asteroid?s and the Earth?s orbits changes with time. If the target asteroid is not an ?Earth crosser?, as is the case with NEOs in the ?Amor? class (which have orbits with perihelion distance well in excess of 1 AU), testing a deflection manoeuvre represents no risk to the Earth.

Other considerations related to the orbit of the target asteroid are also important, especially the change of orbital velocity that is required by the spacecraft to ?catch up? with the target asteroid ? the so-called ?delta V?. This should be sufficiently small to minimise the required amount of spacecraft propellant and enable the use of cheaper launchers, but high enough to allow the same spacecraft to be used with a number of possible targets.

Navigation and deflection measurements requirements set some heavy constraints on the target selection. The shape, density, and size are all important factors, but are often poorly known. A spacecraft orbiting an asteroid needs to know about the object?s gravitational field in order to navigate. The ?impactor spacecraft? must know the position of the centre of mass to define the point it is aiming for.

Asteroids come in all sort of flavours, but as far as composition is concerned two main types dominate. Our still rudimentary knowledge of the abundance of asteroids of different types in the near-Earth asteroid population indicates that the next hazardous asteroid is more likely to be a ?C-type?, than an ?S-type?. C-types have dark surfaces with a carbonaceous spectral signature, while S-types have brighter surfaces, their spectra matching closely that of silicates. The surface properties of the target asteroid -and in particular the percentage of light that it reflects – are a critical factor in the final phase of the impactor spacecraft navigation. The brighter it looks the easier it is to aim at. However for a rehearsal the target should not be too easy.

ESA has selected asteroids 2002 AT4 and (10302) 1989 ML as mission targets because they represent best compromise among all the (sometimes conflicting) selection criteria. A decision on which of the two will become the final destination of both Sancho and Hidalgo spacecraft will be made in 2007.

Don Quijote ? the knight errant rides again
The phase of internal studies on the Don Quijote mission is now over, and it is time for the space industry to suggest suitable design solutions. ESA has made an open invitation to European space companies to submit proposals on possible designs. The selection of the most promising ones will take place towards the end of the year. In early 2006, two teams should start working on their interpretations of this technology demonstration mission. A year later, once the results are available, ESA will select the final design to be implemented, and then Don Quijote will be ready to take on an asteroid!

Additional Notes
Don Quijote is a NEO deflection test mission based entirely on conventional spacecraft technologies. It would comprise two spacecraft – one of them (Hidalgo) impacting an asteroid at a very high relative speed while a second one (Sancho) would arrive earlier at the same asteroid and remain in its vicinity before and after the impact to measure the variation on the asteroid?s orbital parameters, as well as to study the object.

Asteroid 2004 MN has now been given an official designation, (99942) Apophis. Recent observations using Doppler radar using Arecibo radio telescope in Puerto Rico have reduced the impact probability during future encounters to very small levels, though they have not totally ruled out an Earth impact. In 2029, the asteroid will have the closest approach ever witnessed for an object of this size, swinging by the Earth at a distance of around 32,000 kilometres. Its trajectory will be well within the geosynchronous orbit used by most telecommunications and weather satellites, and the object will be visible to the naked eye. Further radar measurements are expected in 2013.

Original Source: ESA News Release

Lunar surface. Image credit: LPI Click to enlarge
University of Arizona and Japanese scientists are convinced that evidence at last settles decades-long arguments about what objects bombarded the early inner solar system in a cataclysm 3.9 billion years ago.

Ancient main belt asteroids identical in size to present-day asteroids in the Mars-Jupiter belt — not comets — hammered the inner rocky planets in a unique catastrophe that lasted for a blink of geologic time, anywhere from 20 million to 150 million years, they report in the Sept. 16 issue of Science.

However, the objects that have been battering our inner solar system after the so-called Late Heavy Bombardment ended are a distinctly different population, UA Professor Emeritus Robert Strom and colleagues report in the article, “The Origin of Planetary Impactors in the Inner Solar System.”

After the Late Heavy Bombardment or Lunar Cataclysm period ended, mostly near-Earth asteroids (NEAs) have peppered the terrestrial region.

Strom has been studying the size and distribution of craters across solar system surfaces for the past 35 years. He has long suspected that two different projectile populations have been responsible for cratering inner solar system surfaces. But there’s been too little data to prove it.

Now asteroid surveys conducted by UA’s Spacewatch, the Sloan Digital Sky Survey, Japan’s Subaru telescope and the like have amassed fairly complete data on asteroids down to those with diameters of less than a kilometer. Suddenly it has become possible to compare the sizes of asteroids with the sizes of projectiles that blasted craters into surfaces from Mars inward to Mercury.

“When we derived the projectile sizes from the cratering record using scaling laws, the ancient and more recent projectile sizes matched the ancient and younger asteroid populations smack on,” Strom said. “It’s an astonishing fit.”

“One thing this says is that the present-day size-distribution of asteroids in the asteroid belt was established at least as far back as 4 billion years ago,” UA planetary scientist Renu Malhotra, a co-author of the Science paper, said. “Another thing it says is that the mechanism that caused the Late Heavy Bombardment was a gravitational event that swept objects out of the asteroid belt regardless of size.”

Malhotra discovered in previous research what this mechanism must have been. Near the end of their formation, Jupiter and the other outer gas giant planets swept up planetary debris farther out in the solar system, the Kuiper Belt region. In clearing up dust and pieces leftover from outer solar system planet formation, Jupiter, especially, lost orbital energy and moved inward, closer to the sun. That migration greatly enhanced Jupiter’s gravitational influence on the asteroid belt, flinging asteroids irrespective of size toward the inner solar system.

Evidence that main belt asteroids pummeled the early inner solar system confirms a previously published cosmochemical analysis by UA planetary scientist David A. Kring and colleagues.

“The size distribution of impact craters in the ancient highlands of the moon and Mars is a completely independent test of the inner solar system cataclysm and confirms our cosmochemical evidence of an asteroid source,” Kring, a co-author of the Science paper, said.

Kring was part of a team that earlier used an argon-argon dating technique in analyzing impact melt ages of lunar meteorites — rocks ejected at random from the moon’s surface and that landed on Earth after a million or so years in space. They found from the ages of the “clasts,” or melted rock fragments, in the breccia meteorites that all of the moon was bombarded 3.9 billion years ago, a true global lunar cataclysm. The Apollo lunar sample analysis said that asteroids account for at least 80 percent of lunar impacts.

Comets have played a relatively minor role in inner solar system impacts, Strom, Malhotra and Kring also conclude from their work. Contrary to popular belief, probably no more than 10 percent of Earth’s water has come from comets, Strom said.

After the Late Heavy Bombardment, terrestrial surfaces were so completely altered that no surface older than 3.9 billion years can be dated using the cratering record. Older rocks and minerals are found on the moon and Earth, but they are fragments of older surfaces that were broken up by impacts, the researchers said.

Strom said that if Earth had oceans between 4.4 billion and 4 billion years ago, as other geological evidence suggests, those oceans must have been vaporized by the asteroid impacts during the cataclysm.

Kring also has developed a hypothesis that suggests that the impact events during Late Heavy Bombardment generated vast subsurface hydrothermal systems that were critical to the early development of life. He estimated that the inner solar system cataclysm produced more than 20,000 craters between 10 kilometers to 1,000 kilometers in diameter on Earth.

Inner solar system cratering dynamics changed dramatically after the Late Heavy Bombardment. From then on, the impact cratering record reflects that most objects hitting inner solar system surfaces have been near-Earth asteroids, smaller asteroids from the main belt that are nudged into terrestrial-crossing orbits by a size-selective phenomenon called the Yarkovsky Effect.

The effect has to do with the way asteroids unevenly absorb and re-radiate the sun’s energy. Over tens of millions of years, the effect is large enough to push asteroids smaller than 20 kilometers across into the jovian resonances, or gaps, that deliver them to terrestrial-crossing orbits. The smaller the asteroid, the more it is influenced by the Yarkovsky Effect.

Planetary geologists have tried counting craters and their size distribution to get absolute ages for surfaces on the planets and moons.

“But until we knew the origin of the projectiles, there has been so much uncertainty that I thought it could lead to enormous error,” Strom said. “And now I know I’m right. For example, people have based the geologic history of Mars on the heavy bombardment cratering record, and it’s wrong because they’re using only one cratering curve, not two.”

Attempts to date outer solar system bodies using the inner solar system cratering record is completely wrong, Strom said. But it should be possible to more accurately date inner solar system surfaces once researchers determine the cratering rate from the near-Earth asteroid bombardment, he added.

The authors of the Science paper are Strom, Malhotra and Kring from the University of Arizona Lunar and Planetary Laboratory, and Takashi Ito and Fumi Yoshida of National Astronomical Observatory, Tokyo, Japan.

Original Source: UA News Release

Mid-infrared image of comet 9P/Tempel 1 after the Deep Impact collision. Image credit: NAOJ Click to enlarge
When NASA’s Deep Impact mission ploughed into comet 9P/Tempel 1 on July 4th of this year, the giant telescopes on Mauna Kea had a unique view of the massive cloud of dust, gas and ice expelled during the collision.

A series of coordinated observations, made under ideal conditions by the world’s largest collection of big telescopes, delivered surprising new insights into the ancestry and l7ife cycles of comets. Specifically, materials beneath the comet’s dusty skin reveal striking similarities between two families of comets where no relationship had been suspected.

The observations also allowed scientists to determine the mass of material blasted out by the collision, which is estimated to be as much as 25 fully-loaded tractor trailer-trucks.

The findings are based on the composition of rocky dust detected by both the Subaru and Gemini 8-meter telescopes and ethane, water and carbon-based organic compounds revealed by the 10-meter W.M. Keck Observatory. The results from these Mauna Kea observations were made available today in a special segment in the journal Science highlighting results from the Deep Impact experiment.

Comet Tempel 1 was selected for the Deep Impact experiment because it orbits the Sun in a stable orbit that allows its surface to be gently baked with solar radiation. As a result, the comet has an old weathered,protective layer of dust that covers the icy material beneath, much like a snowbank builds up dirt on its surface as it melts in the springtime sunlight. The Deep Impact mission was designed to dig deep beneath this crusty exterior to learn more about the true nature of the comet’s dust and ice components. “This comet definitely had something to hide under its veneer of rock and ice and we were ready with the world’s biggest telescopes to find out what it was,” said Chick Woodward of the University of Minneapolis and part of the Gemini observing team.

The combined observations show a complex mix of silicates, water and organic compounds beneath the surface of the comet. These materials are similar to what is seen in another class of comets thought to reside in a distant swarm of pristine bodies called the Oort Cloud. Oort Cloud comets are well preserved fossils in the frozen suburbs of the solar system that have changed little over the billions of years since their formation. When they are occasionally nudged gravitationally toward the Sun they warm up and release a profuse amount of gas and dust on a one-time visit to the inner solar system..

Returning comets like Tempel 1 (known as periodic comets) were believed to have formed in a colder nursery distinctly different from the birthplaces of their cousins, the Oort Cloud comets. The evidence for two distinct “family trees” lies in their vastly different orbits and apparent composition. “Now we see that the difference may really be just superficial: only skin deep.” said Woodward. “Under the surface, these comets may not be so different after all.

This similarity indicates that both types of comets might have shared a birthplace in a region of the forming solar system where temperatures were warm enough to produce the materials observed. “It is now likely that these bodies formed between the orbits of Jupiter and Neptune in a common nursery,” said Seiji Sugita of the University of Tokyo and Subaru team member.

“Another question that the Mauna Kea telescopes were able to address is the amount of mass ejected when the comet was impacted by the chunk of copper about the size of a grand piano from the Deep Impact spacecraft,” Sugita commented. At the time of impact the spacecraft was traveling at about 23,000 miles per hour or nearly 37,000 kilometers per hour.

Because the spacecraft was unable to study the size of the crater created after it was formed, the high-resolution Mauna Kea observations provided the necessary data to get a firm estimate of the mass ejection, which was about 1000 tons. “To release this amount of material, the comet must have a fairly soft consistency,” Sugita said.

“The splash from NASA’s impact probe freed these materials and we were in the right place to capture them with the biggest telescopes on Earth,” said W.M. Keck Director Fred Chaffee. “The close collaboration among Keck, Gemini and Subaru assured that the very best science was done by the best telescopes in the world, demonstrating that the whole is often greater than the sum of its parts.”

All three of Mauna Kea’s largest telescopes observed the comet in the infrared part of the spectrum which is light that can be described as “redder than red.” The Deep Impact spacecraft was not designed to observe the comet in the mid-infrared (or thermal infrared) part of the spectrum, which is what Subaru and Gemini were able to do. The Keck observations used a near-infrared, high-resolution spectrograph. Large instruments of this sort would have been impossible to fit on the Deep Impact spacecraft.

“These observations give us the best glimpse yet at what’s under the dusty skin of a comet,” said David Harker who led the Gemini team. “Within an hour of impact, the comet’s glow was transformed and we were able to detect a whole host of fine dusty silicates propelled by a sustained gas geyser from under the comet’s protective crust. These included a large amount of olivine, similar in composition to what you would find at the beaches below Mauna Kea. This incredible data was really a gift from Mauna Kea!”

Instruments that made these observations were:

* MICHELLE (Mid-Infrared Echelle Spectrograph/Imager) on the 8-meter Fredrick C. Gillett (Gemini North) Telescope
* NIRSPEC (Near-Infrared Spectrograph) on the 10-meter on the Keck II 10-meter telescope
* COMICS (COoled Mid-Infrared Camera and Spectrograph) on the 8-meter Subaru telescope

Original Source: NAOJ News Release

What is the biggest telescope?

Itokawa. Image credit: JAXA Click to enlarge
Hayabusa arrived at Itokawa on September 12. The distance between the spacecraft and Itokawa is approximately 20 kilometers. This is the composite color image of Itokawa taken at September 12, 2005. This image composed of three images with different filters as red, green and blue. The irregular shape is clearly seen.
Hayabusa science observations started.

Original Source: JAXA News Release

Hubble tracks Ceres. Image credit: NASA/ESA Click to enlarge
Observations of 1 Ceres, the largest known asteroid, have revealed that the object may be a “mini planet,” and may contain large amounts of pure water ice beneath its surface.

The observations by NASA’s Hubble Space Telescope also show that Ceres shares characteristics of the rocky, terrestrial planets like Earth. Ceres’ shape is almost round like Earth’s, suggesting that the asteroid may have a “differentiated interior,” with a rocky inner core and a thin, dusty outer crust.

“Ceres is an embryonic planet,” said Lucy A. McFadden of the Department of Astronomy at the University of Maryland, College Park and a member of the team that made the observations. “Gravitational perturbations from Jupiter billions of years ago prevented Ceres from accreting more material to become a full-fledged planet.”

The finding will appear Sept. 8 in a letter to the journal Nature. The paper is led by Peter C. Thomas of the Center for Radiophysics and Space Research at Cornell University in Ithaca, N.Y., and also includes project leader Joel William Parker of the Department of Space Studies at Southwest Research Institute in Boulder, Colo.

Asteroid Ceres is approximately 580 miles (930 kilometers) across, about the size of Texas. It resides with tens of thousands of other asteroids in the main asteroid belt. Located between Mars and Jupiter, the asteroid belt probably represents primitive pieces of the solar system that never managed to accumulate into a genuine planet. Ceres comprises 25 percent of the asteroid belt’s total mass. However, Pluto, our solar system’s smallest planet, is 14 times more massive than Ceres.

The astronomers used Hubble’s Advanced Camera for Surveys to study Ceres for nine hours, the time it takes the asteroid to complete a rotation. Hubble snapped 267 images of Ceres. From those snapshots, the astronomers determined that the asteroid has a nearly round body. The diameter at its equator is wider than at its poles. Computer models show that a nearly round object like Ceres has a differentiated interior, with denser material at the core and lighter minerals near the surface. All terrestrial planets have differentiated interiors. Asteroids much smaller than Ceres have not been found to have such interiors.

The astronomers suspect that water ice may be buried under the asteroid’s crust because the density of Ceres is less than that of the Earth’s crust, and because the surface bears spectral evidence of water-bearing minerals. They estimate that if Ceres were composed of 25 percent water, it may have more water than all the fresh water on Earth. Ceres’ water, unlike Earth’s, would be in the form of water ice and located in the mantle, which wraps around the asteroid’s solid core.

Besides being the largest asteroid, Ceres also was the first asteroid to be discovered. Sicilian astronomer Father Giuseppe Piazzi spotted the object in 1801. Piazzi was looking for suspected planets in a large gap between the orbits of Mars and Jupiter. As more such objects were found in the same region, they became known as “asteroids” or “minor planets”.

Original source: Hubble News Release

The asteroid’s dust trail. Image credit: Sandia National Laboratories. Click to enlarge
Dust from asteroids entering the atmosphere may influence Earth?s weather more than previously believed, researchers have found.

In a study to be published this week in the journal Nature, scientists from the Australian Antarctic Division, the University of Western Ontario, the Aerospace Corporation, and Sandia and Los Alamos national laboratories found evidence that dust from an asteroid burning up as it descended through Earth?s atmosphere formed a cloud of micron-sized particles significant enough to influence local weather in Antarctica.

Micron-sized particles are big enough to reflect sunlight, cause local cooling, and play a major role in cloud formation, the Nature brief observes. Longer research papers being prepared from the same data for other journals are expected to discuss possible negative effects on the planet?s ozone layer.

?Our observations suggest that [meteors exploding] in Earth?s atmosphere could play a more important role in climate than previously recognized,? the researchers write.

Scientists had formerly paid little attention to asteroid dust, assuming that the burnt matter disintegrated into nanometer-sized particles that did not affect Earth?s environment. Some researchers (and science fiction writers) were more interested in the damage that could be caused by the intact portion of a large asteroid striking Earth.

But the size of an asteroid entering Earth?s atmosphere is significantly reduced by the fireball caused by the friction of its passage. The mass turned to dust may be as much as 90 to 99 percent of the original asteroid. Where does this dust go?

The uniquely well-observed descent of a particular asteroid and its resultant dust cloud gave an unexpected answer.

On Sept. 3, 2004, the space-based infrared sensors of the U.S. Department of Defense detected an asteroid a little less than 10 meters across, at an altitude of 75 kilometers, descending off the coast of Antarctica. U.S. Department of Energy visible-light sensors built by Sandia National Laboratories, a National Nuclear Security Administration lab, also detected the intruder when it became a fireball at approximately 56 kilometers above Earth. Five infrasound stations, built to detect nuclear explosions anywhere in the world, registered acoustic waves from the speeding asteroid that were analyzed by LANL researcher Doug ReVelle. NASA?s multispectral polar orbiting sensor then picked up the debris cloud formed by the disintegrating space rock.

Some 7.5 hours after the initial observation, a cloud of anomalous material was detected in the upper stratosphere over Davis Station in Antarctica by ground-based lidar.

?We noticed something unusual in the data,? says Andrew Klekociuk, a research scientist at the Australian Antarctic division. ?We?d never seen anything like this before ? [a cloud that] sits vertically and things blow through it. It had a wispy nature, with thin layers separated by a few kilometers. Clouds are more consistent and last longer. This one blew through in about an hour.?

The cloud was too high for ordinary water-bearing clouds (32 kilometers instead of 20 km) and too warm to consist of known manmade pollutants (55 degrees warmer than the highest expected frost point of human-released solid cloud constituents). It could have been dust from a solid rocket launch, but the asteroid?s descent and the progress of its resultant cloud had been too well observed and charted; the pedigree, so to speak, of the cloud was clear.

Computer simulations agreed with sensor data that the particles? mass, shape, and behavior identified them as meteorite constituents roughly 10 to 20 microns in size.

Says Dee Pack of Aerospace Corporation, ?This asteroid deposited 1,000 metric tons in the stratosphere in a few seconds, a sizable perturbation.? Every year, he says, 50 to 60 meter-sized asteroids hit Earth.

Peter Brown at the University of Western Ontario, who was initially contacted by Klekociuk, helped analyze data and did theoretical modeling. He points out that climate modelers might have to extrapolate from this one event to its larger implications. ?[Asteroid dust could be modeled as] the equivalent of volcanic eruptions of dust, with atmospheric deposition from above rather than below.? The new information on micron-sized particles ?have much greater implications for [extraterrestrial visitors] like Tunguska,? a reference to an asteroid or comet that exploded 8 km above the Stony Tunguska river in Siberia in 1908. About 2150 square kilometers were devastated, but little formal analysis was done on the atmospheric effect of the dust that must have been deposited in the atmosphere.

The Sandia sensors? primary function is to observe nuclear explosions anywhere on Earth. Their evolution to include meteor fireball observations came when Sandia researcher Dick Spalding recognized that ground-based processing of data might be modified to record the relatively slower flashes due to asteroids and meteoroids. Sandia computer programmer Joe Chavez wrote the program that filtered out signal noise caused by variations in sunlight, satellite rotation, and changes in cloud cover to realize the additional capability. The Sandia data constituted a basis for the energy and mass estimate of the asteroid, says Spalding.

The capabilities of defense-related sensors to distinguish between the explosion of a nuclear bomb and the entry into the atmosphere of an asteroid that releases similar amounts of energy ? in this case, about 13 kilotons ? could provide an additional margin of world safety. Without that information, a country that experienced a high-energy asteroid burst that penetrated the atmosphere might provoke a military response by leaders who are under the false impression that a nuclear attack is underway, or lead other countries to assume a nuclear test has occurred.

Original Source: Sandia National Labs