Posted on by Nancy Atkinson

JAXA: Hayabusa Capsule Contains Particles, Maybe of Asteroid

Artist concept of the Hayabusa spacecraft, which visited asteroid Itokawa in 2005 and returned samples to Earth in 2010. Credit: JAXA
Artist concept of the Hayabusa spacecraft, which visited asteroid Itokawa in 2005 and returned samples to Earth in 2010. Credit: JAXA

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At a press conference yesterday, officials from the Japan Aerospace Exploration Agency (JAXA) announced that they had “scraped up” a hundred or so particles of dust, perhaps grains of dust from the asteroid, Itokawa, inside the sample return capsule of the Hayabusa spacecraft. This is great news, as previous reports from JAXA indicated they weren’t sure if there were any particles at all inside the container. Originally, the mission had hoped to bring back “peanut-sized” asteroid samples, but the device that was supposed to fire pellets at the asteroid may not have worked, and for a time, scientists were even unsure if the spacecraft had even touched down on the asteroid.

During the seven-year round trip journey, Hayabusa arrived at Itokawa in November, 2005. After a circuitous and troubled-filled return trip home, the sample return capsule was ejected and landed in Australia in June of this year.

The 100 or so grains reported yesterday are extremely tiny, and the micron-sized particles were scraped off the sides of container and are now being examined with an electron microscope. They don’t appear to be metallic, so are not fragments from the container, but they don’t have absolute proof yet that the particles are from the asteroid.

Soon, the grains will be examined using particle accelerator/synchrotron. Additionally, some reports indicated there is another yet unopened compartment that will be examined soon.

A little surfing of the net (in all languages) reveals there are tons of news articles out there reporting this. The only problem is that some of these news reports called the potential asteroid particles “extraterrestrial,” which then became translated as “extraterrestrial life” in the next article in another language. Ah, the wonders of the internet!

We’ll keep you posted!

Posted on by Jon Voisey

Trojans May Yet Rain Down

It would be an interesting survey to catalog the initial reactions readers have to “Trojans”. Do you think first of wooden horses, or do asteroids spring to mind? Given the context of this website, I’d hope it’s the latter. If so, you’re thinking along the right lines. But how much do you really know about astronomical Trojans?

While most frequently used to discuss the set of objects in Jupiter’s orbital path that lie 60º ahead and behind the planet, orbiting the L4 and L5 Lagrange points, the term can be expanded to include any family of objects orbiting these points of relative stability around any other object. While Jupiter’s Trojan family is known to include over 3,000 objects, other solar system objects have been discovered with families of their own. Even one of Saturn’s moons, Tethys, has objects in its Lagrange points (although in this case, the objects are full moons in their own right: Calypso and Telesto).

In the past decade Neptunian Trojans have been discovered. By the end of this summer, six have been confirmed. Yet despite this small sample, these objects have some unexpected properties and may outnumber the number of asteroids in the main belt by an order of magnitude. However, they aren’t permanent and a paper published in the July issue of the International Journal of Astrobiology suggests that these reservoirs may produce many of the short period comets we see and “contribute a significant fraction of the impact hazard to the Earth.”

The origin of short period comets is an unusual one. While the sources of near Earth asteroids and long period comets have been well established, short period comets parent locations have been harder to pin down. Many have orbits with aphelions in the outer solar system, well past Neptune. This led to the independent prediction of a source of bodies in the far reaches by Edgeworth (1943) and Kuiper (1951). Yet others have aphelions well within the solar system. While some of this could be attributed to loss of energy from close passes to planets, it did not sufficiently account for the full number and astronomers began searching for other sources.

In 2006, J. Horner and N. Evans demonstrated the potential for objects from the outer solar system to be captured by the Jovian planets. In that paper, Horner and Evans considered the longevity of the stability of such captures for Jupiter Trojans. The two found that these objects were stable for billions of years but could eventually leak out. This would provide a storing of potential comets to help account for some of the oddities.

However, the Jupiter population is dynamically “cold” and does not contain a large distribution of velocities that would lead to more rapid shedding. Similarly, Saturn’s Trojan family was not found to be excited and was estimated to have a half life of ~2.5 billion years. One of the oddities of the Neptunian Trojans is that those few discovered thus far have tended to have high inclinations. This indicates that this family may be more dynamically excited, or “hotter” than that of other families, leading to a faster rate of shedding. Even with this realization, the full picture may not yet be clear given that searches for Trojans concentrate on the ecliptic and would likely miss additional members at higher inclinations, thus biasing surveys towards lower inclinations.

To assess the dangers of this excited population, Horner teamed with Patryk Lykawka to simulate the Neptunian Trojan system. From it, they estimated the family had a half life of ~550 million years. Objects leaving this population would then undergo several possible fates. In many cases, they resembled the Centaur class of objects with low eccentricities and with perihelion near Jupiter and aphelion near Neptune. Others picked up energy from other gas giants and were ejected from the solar system, and yet others became short period comets with aphelions near Jupiter.

Given the ability for this the Neptunian Trojans to eject members frequently, the two examined how many of the of short period comets we see may be from these reservoirs. Given the unknown nature of how large these stores are, the authors estimated that they could contribute as little as 3%. But if the populations are as large as some estimates have indicated, they would be sufficient to supply the entire collection of short period comets. Undoubtedly, the truth lies somewhere in between, but should it lie towards the upper end, the Neptunian Trojans could supply us with a new comet every 100 years on average.

Posted on by Nicholos Wethington

Rosetta Uncovers a Thick, Dusty Blanket on Lutetia

An image taken by the Rosetta spacecraft on its closest approach to 21-Lutetia in July. Recent analysis of the data shows a thick, dusty blanket coating the asteroid. Image Credit:ESA 2010 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

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If you think that asteroids are boring, unchanging rocks floating in space waiting only to crop up in bad science fiction films, think again. Images and data that are being returned from various asteroid flybys – such as those by the Rosetta spacecraft and Hayabusa sample return mission – show that asteroids are dynamic, changing miniature worlds unto themselves.

During the recent flyby of the asteroid 21-Lutetia in July, the ESA’s Rosetta spacecraft took an amazing amount of data. After combing through all of this data over the past few months, astronomers have calculated that the asteroid is covered in a 2000-foot (600 meter)-thick blanket of rocks and dust called regolith. This dust is not unlike the outer layer of the Earth’s Moon, consisting of pulverized material that has accumulated over billions of years.

Rosetta is on a course to meet up with the comet 67P/Churyumov-Gerasimenko in 2014, but the spacecraft is no stranger to asteroid visits – on September 6th, 2008, Rosetta made its closest approach of the asteroid 2867-Steins. During this brief visit, Rosetta came within 500 miles (800km) of the small, diamond-shaped asteroid. Among the discoveries made were a chain of impact craters that were likely caused by the collision with a meteoroid stream, or the impact with another small body.

It then approached 21-Lutetia on July 10th of 2010, monitoring the asteroid with 17 instruments on board the spacecraft.

Rosetta took a number of images of the flyby, as well as examining the asteroid with electromagnetic detectors that covered the gamut from the UV to radio waves. Here’s a short animation showing the flyby:

Dr. Rita Schulz from the ESA Research and Scientific Support Department in the Netherlands presented this new information about 21-Lutetia’s regolith today at the Division for Planetary Sciences meeting in Pasadena, CA. She said that the regolith on the asteroid has been determined to be about 2000 feet (600 meters) thick, and that it resembles the regolith on the Moon. Images from the flyby reveal landslides, boulders, ridges, and other kinds of different geologic (or asterologic?) features.

21-Lutetia was determined by the July flyby to have a large, bowl-shaped impact crater on its surface, as well as an abundance of smaller craters. The thick covering of dust “softens” the sharper edges of impact craters in many of the images taken. Whether or not most asteroids of this size are covered in a similar blanket of material remains to be seen.

Boulders can be seen in this close-up image of 21-Lutetia, as taken by Rosetta during the July flyby. Image Credit: mage credit: ESA 2010 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

In understanding more about asteroids and comets, astronomers are better able to hone their model of how our Solar System formed. By studying the composition and frequency of impacts of various asteroids, they can improve their data of just how things have changed since the primordial Solar System.

You can bet your boulders that Rosetta isn’t the only spacecraft to be making multiple rendezvous missions with the smaller denizens of our Solar System. Close flybys, impacts and landings on asteroids and comets are becoming almost commonplace for spacecraft.

There’s the Deep Impact mission, which slammed a huge copper weight into the comet Tempel 1, and has since been renamed EPOXI and is set to approach the comet Hartley 2. The upcoming approach of Vesta and Ceres by the Dawn mission is very much anticipated, and of course the recent success of the Hayabusa asteroid explorer has been a terrific tale of just how much we stand to learn from the trail of small celestial cairns that lead into our past.

Source: ESA, DPS Press Release

Posted on by Jon Voisey

Does a “Rock Comet” Generate the Geminids?

Meteor
Geminid meteor shower

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Many annual meteor showers have parent bodies identified. For example, the Perseids are ejecta from the comet, Swift-Tuttle and the Leonids from Tempel-Tuttle. Most known parent bodies are active comets, but one exception is the Geminid meteor shower that peaks in mid December. The parent for this shower is 3200 Phaethon. Observations of this object have shown it to be largely inactive pegging it as either a dead comet or an asteroid. But on June 20, 2009, shortly after perihelion, 3200 Phaethon brightened by over two magnitudes indicating this object may not be as dead as previously considered. A new paper considers the causes of the brightening and concludes that it could be a new mechanism leading to what the authors deem a “rock comet”.

David Jewett and Jing Li of UCLA, the authors of this new paper, consider several potential causes. Due to the size of 3200 Phaethon, they suggest that a collision is unlikely. One clue to the reason for the sudden change in brightness was a close link of a half of a day to a brightening in the solar corona. Given a typical solar wind speed and the distance of 3200 Phaethon at the time, this would put the Geminid parent just at the right range to be feeling the effects of the increase. However, the authors conclude that this cannot be directly responsible by imparting sufficient energy on the surface of the object to cause it to fluoresce due to an insufficient solar wind flux at that distance.

Instead, Jewett and Li consider more indirect explanations. Due to the temperature at 3200 Phaethon’s perihelion (0.14 AU) the presence of ices and other volatile gasses frozen solid and then blasting away as often happens in comets was ruled out as they would have been depleted on earlier orbits. However, the blow from the increased solar wind may have been sufficient to blow off loosely bound dust particles. While this is plausible, the authors note that the amount of mass lost if this were the case would be a paltry 2.5 x 108 kg. While it’s possible that this may have been the cause of this single brightening, this amount of mass loss to the overall stream of particles responsible for the Geminid shower would be insufficient to sustain the stream and similar losses would have to occur ~10 times per orbit of the body. Since this has not been observed, it is unlikely that this event was tied to the production of the meteors. Additionally, it is somewhat unlikely that it could even be the event for this sole case since repeated perihelions would slowly deplete the reservoir of available dust until the body was left with only a bare surface. Unlike active comets which continually free dust to be ejected through sublimation of ice, 3200 Phaethon has no such process. Or does it?

The novel proposition is that this object may have an unusual mechanism by which to continually generate and liberate dust particles of the size of the Geminids. The authors propose that the heating at perihelion causes portions of the rock to decompose. This process is greatly enhanced if the rock has water molecules bonded to it and lab experiments have shown that this can lead to violent fracturing. Such processes, if present, could easily lead to the production of new dust particles that would be liberated during close approach to the sun. This would make this object a “rock comet” in which the properties of a comet’s dust ejection via gasses would be carried out by rocks.

To confirm this hypothesis, future observations would be needed to search for subsequent brightening at perihelion. Similarly, it should be expected that such a process may make a faint cometary tail with only a dust component that may be visible as well, although the lack of any such detection so far, despite studies looking for cometary tails, casts some doubt on this process.

Posted on by Jon Voisey

Follow-up Studies on June 3rd Jupiter Impact

Color image of impact on Jupiter on June 3, 2010. Credit: Anthony Wesley

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Poor Jupiter just can’t seem to catch a break. Ever since 1994, when our largest planet was hit by Comet Shoemaker-Levy, detections of impacts on Jupiter have occurred with increasing regularity. Most recently, an impact was witnessed on August 20. On June 3rd of 2010, (coincidentally the same day pictures from Hubble were released from a 2009 impact) Jupiter was hit yet again. Shortly after the June 3rd impact, several other telescopes joined the observing.

A paper to appear in the October issue of The Astrophysical Journal Letters discusses the science that has been gained from these observations.

The June 3rd impact was novel in several respects. It was the first unexpected impact that was reported from two independent locations simultaneously. Both discoverers were observing Jupiter with aims of engaging in a bit of astrophotography. Their cameras were both set to take a series of quick images, each lasting a fifth to a tenth of a second. This short time duration is the first time astronomers have had the ability to recreate the light curve for the meteor. Additionally, both observers were using different filters (one red and one blue) allowing for exploration of the color distribution.

Analysis of the light curve revealed that the flash lasted nearly two seconds and was not symmetric; The decay in brightness occurred faster than the increase at onset. Additionally, the curve showed several distinct “bumps” which indicated a flickering that is commonly seen on meteors on Earth.

The light released in the burning up of the object was used to estimate the total energy-released and in turn the mass of the object.  The total energy released was estimated to be between roughly (1.0–4.0) × 1015 Joules (or 250–1000 kilotons).

Follow-up observations from Hubble three days later revealed no scars from the impact. In the July 2009 impact, a hole punched in the clouds remained for several days. This indicated the object in the June 3 impact was considerably smaller and burned up before it was able to reach the visible cloud decks.

Observations intended to find debris came up empty. Infrared observations showed that no thermal signature was left even as little as 18 hours following the discovery.

Assuming that the object was an asteroid with a relative speed of ~60 km/sec and a density of ~2 g/cm3, the team estimated the size of the object to be between 8 and 13 meters, similar to the size of the two asteroids that recently passed Earth. This represents the smallest meteor yet observed on Jupiter. An object of similar size was estimated to be responsible for the impact on Earth in 1994 near the Marshall Islands. Estimates “predict objects of this size to collide with our planet every 6–15 years” with significantly higher rates on Jupiter ranging from one to one hundred such events annually.

Clearly, amateur observations led to some fantastic science. Modest telescopes, “in the range 15–20 cm in diameter equipped with webcams and video recorders” can easily allow for excellent coverage of Jupiter and continued observation could help in determining the impact rate and lead to a better understanding of the population of such small bodies in the outer solar system.

Posted on by Jon Voisey

Two New Asteroids to Pass Earth This Week

Orbits of 2010 RF12 and 2010 RX30

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Two newly discovered asteroids will pass the Earth this week. The asteroids were discovered on September 5th of this year by Andrea Boattini using the 1.5 metre reflector at Mount Lemmon in Arizona as part of the Mount Lemmon Survey.

These two new asteroids have been given the designations of 2010 RF12 and 2010 RX30. Both are small bodies, which is why they were not discovered until mere days before they would pass the Earth. Estimates put the size of RF12 at 5 – 15 meters with a best estimate being around 8 meters (26 ft). The larger, RX30 is estimated to be 12 meters (39 ft), but the range of estimates go from 7 – 25.

Due to the large range of estimates on sizes, as well as poorly constrained relative velocities and an unknown composition, it would be difficult to predict the damage an impact from these bodies could cause. The majority of the mass for such small objects would burn up in the atmosphere with only small fragments surviving to the ground. For comparison, the estimated size of the object that caused the Tunguska event was estimated to be at least a few tens of meters in diameter at the point it exploded in the atmosphere some few miles up. Since the diameter helps to determine the volume, and thus the mass and kinetic energy, this factor increases the potential damage rapidly. However, although the bodies were just discovered this week, their orbits have already been well established for the near future and neither will collide with Earth. Both are rated at a 0 on the Torino scale (data from NASA’s NEO Program for RF12 and RX30 can be seen here and here respectively).

Although both objects will pass closer to the Earth than the moon, due to their small size, neither will be visible to the naked eye. 2010 RF12 is expected to pass the Earth at 21% of the Earth-moon distance and at maximum brightness, reach only 14th magnitude, which is just over 600 times too faint to see with the unaided eye. RX30 will approach at 66% of the Earth-moon distance and is expected to reach a similar peak magnitude. For those interested in tracking or photographing these objects, the Fawkes Telescope Project has created a page dedicated to these two objects, including best exposure times and filters for cameras that can be found here. Ephemeris for RF12 and RX30 can be found here and here respectively.

Although both of these asteroids were discovered on the same day and will be approaching near the same time, their orbits do not appear to be related. RF12’s orbit extends from 0.82 to 1.17 AU and it orbits the Sun once every year. Predictions have shown it only passes near the Earth once every one hundred years. Initially, RX30 was thought to be rotate extremely fast, but revised observations have shown that it takes at least 6 hours to rotate about its axis.

Posted on by Nancy Atkinson

Near Earth Asteroids Vary Widely in Composition, Origin

Eros Asteroid
The asteroid Eros, as seen by the NEAR mission. Credit: NASA

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From the Spitzer website:

New research from NASA’s Spitzer Space Telescope reveals that asteroids somewhat near Earth, termed near-Earth objects, are a mixed bunch, with a surprisingly wide array of compositions. Like a piñata filled with everything from chocolates to fruity candies, these asteroids come in assorted colors and compositions. Some are dark and dull; others are shiny and bright. The Spitzer observations of 100 known near-Earth asteroids demonstrate that the objects’ diversity is greater than previously thought.

The findings are helping astronomers better understand near-Earth objects as a whole — a population whose physical properties are not well known.

“These rocks are teaching us about the places they come from,” said David Trilling of Northern Arizona University, Flagstaff, lead author of a new paper on the research appearing in the September issue of Astronomical Journal. “It’s like studying pebbles in a streambed to learn about the mountains they tumbled down.”

After nearly six years of operation, in May 2009, Spitzer used up the liquid coolant needed to chill its infrared detectors. It is now operating in a so-called “warm” mode (the actual temperature is still quite cold at 30 Kelvin, or minus 406 degrees Fahrenheit). Two of Spitzer’s infrared channels, the shortest-wavelength detectors on the observatory, are working perfectly.

One of the mission’s new “warm” programs is to survey about 700 near-Earth objects, cataloging their individual traits. By observing in infrared, Spitzer is helping to gather more accurate estimates of asteroids’ compositions and sizes than what is possible with visible light alone. Visible-light observations of an asteroid won’t differentiate between an asteroid that is big and dark, or small and light. Both rocks would reflect the same amount of visible sunlight. Infrared data provide a read on the object’s temperature, which then tells an astronomer more about the actual size and composition. A big, dark rock has a higher temperature than a small, light one because it absorbs more sunlight.

Trilling and his team have analyzed preliminary data on 100 near-Earth asteroids so far. They plan to observe 600 more over the next year. There are roughly 7,000 known near-Earth objects out of a population expected to number in the tens to hundreds of thousands.

“Very little is known about the physical characteristics of the near-Earth population,” said Trilling. “Our data will tell us more about the population, and how it changes from one object to the next. This information could be used to help plan possible future space missions to study a near-Earth object.”

The data show that some of the smaller objects have surprisingly high albedos (an albedo is a measurement of how much sunlight an object reflects). Since asteroid surfaces become darker with time due to exposure to solar radiation, the presence of lighter, brighter surfaces for some asteroids may indicate that they are relatively young. This is evidence for the continuing evolution of the near-Earth object population.

In addition, the fact that the asteroids observed so far have a greater degree of diversity than expected indicates that they might have different origins. Some might come from the main belt between Mars and Jupiter, and others could come from farther out in the solar system. This diversity also suggests that the materials that went into making the asteroids — the same materials that make up our planets — were probably mixed together like a big solar-system soup very early in its history.

The research complements that of NASA’s Wide-field Infrared Survey Explorer, or WISE, an all-sky infrared survey mission also up in space now. WISE has already observed more than 430 near-Earth objects — of these, more than 110 are newly discovered.

In the future, both Spitzer and WISE will tell us even more about the “flavors” of near-Earth objects. This could reveal new clues about how the cosmic objects might have dotted our young planet with water and organics — ingredients needed to kick-start life.

Posted on by Nancy Atkinson

Astounding Video Shows 30 Years of Asteroid Discoveries

This incredible video by Scott Manley/Armagh Observatory (and recommended by Neil deGrasse Tyson on Twitter) shows the locations of all the known asteroids starting in 1980, adding more as they are discovered (highlighted in white so you can pick out the new ones.) But the final color of the asteroids tells you more about them: Earth crossing asteroids are red, Earth Approachers (with a perihelion less than 1.3AU) are yellow, while all others are Green.

In the video you can see the pattern of discovery follows the Earth around its orbit and most discoveries are made in the region directly opposite the Sun.
Continue reading “Astounding Video Shows 30 Years of Asteroid Discoveries”

Posted on by Nancy Atkinson

JAXA Delays Releasing Details of Hayabusa Sample Return

Hayabusa's shadow beside a circled reflective target it dropped as a guide for its sample recovery approach. Credit: JAXA

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No news yet if there are specks of asteroid dust in the Haybusa sample return container. JAXA has decided to postpone releasing any information, including publishing a detailed analysis of the particles that may have been collected. According to The Japan Times, JAXA said it is taking more time than originally expected to collect the particles because they are smaller than it was assumed they’d be. This provides some hope, however, that there is actually something of interest in the container.

Originally, JAXA had hoped to publish a report by September, but now it’s looking like December or later.

JAXA said it is going to take several hours to collect just one particle, which likely measures just a few thousandths of a millimeter in diameter. Munetaka Ueno, a senior JAXA official, said the agency wants to analyze the particles with extreme care because repeating the process will be difficult.

The original plan was for JAXA to remove the particles and then let researchers across the country for a more detailed analysis.

We waited seven years for Haybusa to fly to and then return home from asteroid Itokawa, so we should be able to wait a couple more months. Here’s hoping the particle extraction doesn’t encounter as many problems as the spacecraft had.

Source: The Japan Times

Posted on by Nancy Atkinson

Asteroids Can Create Their Own Mini Planetary Systems

Illustration of a binary asteroid. Credit: Courtesy ESO/L. Calcada

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From a University of Colorado-Boulder press release:

While the common perception of asteroids is that they are giant rocks lumbering about in orbit, a new study shows they actually are constantly changing “little worlds” that can give birth to smaller asteroids that split off to start their own lives as they circle around the sun.

Astronomers have known that small asteroids get “spun up” to fast rotation rates by sunlight falling on them, much like propellers in the wind. The new results show when asteroids spin fast enough, they can undergo “rotational fission,” splitting into two pieces which then begin orbiting each other. Such “binary asteroids” are fairly common in the solar system.

An international team of astronomers led by Petr Pravec of the Astronomical Institute in the Czech Republic found that many of these binary asteroids do not remain bound to each other but escape, forming two asteroids in orbit around the sun when there previously was just one. The study appears in the Aug. 26 issue of Nature.

The researchers studied 35 so-called “asteroid pairs,” separate asteroids in orbit around the sun that have come close to each other at some point in the past million years — usually within a few miles, or kilometers — at very low relative speeds. They measured the relative brightness of each asteroid pair, which correlates to its size, and determined the spin rates of the asteroid pairs using a technique known as photometry.

“It was clear to us then that just computing orbits of the paired asteroids was not sufficient to understand their origin,” said Pravec. “We had to study the properties of the bodies. We used photometric techniques that allowed us to determine their rotation rates and study their relative sizes.”

The research team showed that all of the asteroid pairs in the study had a specific relationship between the larger and smaller members, with the smallest one always less than 60 percent of the size of its companion asteroid.

The conclusion fits a theory of binary asteroid formation originated by co-author Daniel Scheeres, from the University of Colorado, Boulder. His theory predicts that if a binary asteroid forms by rotational fission, the two can only escape from each other if the smaller one is less than 60 percent the size of the larger asteroid. Of all the asteroid pairs in the study, the smallest of each pair was always less than 60 percent of the mass of its companion asteroid.

Scheeres’ theory predicts that if a binary asteroid forms by rotational fission, the two can only escape from each other if the smaller one is less than 60 percent of the size of the larger asteroid. When one of the asteroids in the pair is small enough, it can “make a break for it” and escape the orbital dance, essentially moving away to start its own “asteroid family,” he said. During rotational fission, the asteroids separate gently from each other at relatively low velocities.

“This is perhaps the clearest observational evidence that asteroids aren’t just large rocks in orbit about the sun that keep the same shape over time,” said Scheeres. “Instead, they are little worlds that may be constantly changing as they grow older, sometimes giving birth to smaller asteroids that then start their own life in orbit around the sun.”

Read more at the University of Colorado-Boulder.