The Japanese asteroid probe Hayabusa-2 has successfully completed the course corrections necessary prior to the release of its sample return capsule on December 5th, with the capsule landing in the Australian outback the next day.
To put it mildly, the scientific community is waiting eagerly to get their hands on the probe’s samples from the asteroid Ryugu.
When Hayabusa-2 fired an impactor into the asteroid Ryugu in order to access subsurface material in a sample grab, it apparently shook the asteroid, shifting boulders and rocks as far as 130 feet away.
The artificial impactor disturbed boulders within a 30m radius from the center of the impact crater- providing important insight into asteroids’ resurfacing processes.
Professor ARAKAWA Masahiko (Graduate School of Science, Kobe University, Japan) and members of the Hayabusa2 mission discovered more than 200 boulders ranging from 30cm to 6m in size, which either newly appeared or moved as a result of the artificial impact crater created by Japanese spacecraft Hayabusa2’s Small Carry-on Impactor (SCI) on April 5th, 2019. Some boulders were disturbed even in areas as far as 40m from the crater center. The researchers also discovered that the seismic shaking area, in which the surface boulders were shaken and moved an order of cm by the impact, extended about 30m from the crater center. Hayabusa2 recovered a surface sample at the north point of the SCI crater (TD2), and the thickness of ejecta deposits at this site were estimated to be between 1.0mm to 1.8cm using a Digital Elevation Map (DEM).
This data makes all the more important for OSIRIS-REx to get post-sample-grab images of its Nightingale site, if at all possible.
Japanese scientists today announced that 21 rocks identified by Hayabusa-2 on the asteroid Ryugu have a composition that suggests they were formed on another asteroid.
Although Ryugu’s surface is uniformly dark [because it is a C-type asteroid], the scientists behind the new research found numerous boulders scattered across the asteroid that were 1.5 or more times brighter than their surroundings — that is, they reflected at least 50% more light than most of the rest of Ryugu. This contrast made the researchers suspect these boulders may have come from outside the asteroid.
By analyzing the spectrum of light reflected off 21 of these boulders, the scientists deduced they were made of minerals known as anhydrous silicates. Prior studies have suggested that such water-poor, silicon-rich rocks make up silicaceous or S-type asteroids, the most common kind of asteroid found in the inner main asteroid belt. The brightness of these boulders also matches the brightness of S-type asteroids.
This result compliments the result yesterday from scientists studying Bennu with OSIRIS-REx, and was in fact released at the same time. Both asteroids apparently contain material from other asteroids, suggesting that asteroids in their initial formation (as rubble piles) are routinely a mixture of material from many asteroids, thrown out during impacts and then recaptured.
The new colonial movement: It appears that Japan has chosen the next asteroid that its probe Hayabusa-2 will visit in 2031, after it releases its samples to Earth in December from Ryugu.
Japan’s Hayabusa2 space explorer will aim to probe the asteroid “1998KY26” located between the orbits of Earth and Mars in 2031 after completing its current mission of collecting samples from another asteroid, the country’s science minister said Tuesday.
It is hoped Hayabusa2 will approach the ball-shaped asteroid, which has a diameter of around 30 meters and rotates about every 10 minutes, in July 2031, Education, Culture, Sports, Science and Technology Minister Koichi Hagiuda said.
It will not obtain samples from this second asteroid, only observe it close up by camera.
Though it really has been a foregone conclusion for more than a year, the Australian government this week gave its stamp of approval allowing the return capsule of Hayabusa-2 to land in Australia on December 6, 2020, bringing with it samples from the asteroid Ryugu.
What would we do without government bureaucrats!?
Link here. There are two prime candidate asteroid targets, both near Earth astroids.
The possible secondary targets include the oblong asteroid 2001 AV43 or the asteroid 1998 KY 26. They’re each about the size of a large house and both orbit the Sun in roughly 500 days. The proposed plan would see Hayabusa 2 arriving at 2001 AV43 in the late 2029 time frame, or reaching 1998 KY 26 in July 2031. Both asteroids have a low enough relative speed relative to the spacecraft to put them within (eventual) reach after Hayabusa 2’s December flyby.
Interestingly, 2001 AV43 will fly 313,000 km from Earth (0.8 times the Earth-Moon distance) on November 11, 2029.
The two asteroids were selected from an initial field of 354 candidates, which was winnowed down based on accessibility and scientific interest. Both are fast rotators, as evidenced by their light curves, each spinning on its respective axis once every 10 minutes. This represents the shortest “day” of any known object in the solar system, suggesting that these asteroids are in fact solid objects and not simply loosely aggregated “rubble piles.” A visit to one of these asteroids would mark the first time a space mission has seen such an enigmatic fast rotator up close.
The asteroid 1998 KY26 is also a possible carbonaceous (C-type) asteroid, and Hayabusa 2’s exploration of such a space rock would be another first.
Going to 1998 KY26 would also require a distant pass of another asteroid. Going to 2001 AV43 would require a fly-by of Venus, which could provide more data on that planet. Based on this information, my guess is that they will opt for 1998 KY26.
The decision must likely be made before Hayabusa-2 drops off its Ryugu samples to Earth on December 6, 2020.
Japan’s space agency JAXA has revealed that it is looking at two fast-spinning asteroids as possible destinations for its Hayabusa-2 spacecraft after it has dropped off its samples from the asteroid Ryugu on December 6.
The candidate asteroids on the agency’s list are asteroid 2001AV43 which Hayabusa2 would reach in November 2029 after flying by Venus, and asteroid 1998KY26 which the probe would reach in July 2031 after passing by another asteroid.
JAXA says both asteroids are rotating on their axis once every 10 minutes. The high-speed spinning indicates that the asteroids’ inner structures are likely different from that of asteroid Ryugu on the first mission, which consists of pieces of rocks.
The spacecraft will no longer have the equipment for returning additional samples, but everything else is functioning and it has the fuel.
The uncertainty of science: Spectral data collected of the surface of Ryugu by Japan’s Hayabusa-2 probe suggests that the asteroid once spent a period of time much closer to the Sun.
The combined data show an oddly striated world. Ryugu’s equator and poles are tinged blue and are brighter compared with its darker, reddish mid-latitudes. These color differences wouldn’t be obvious to the human eye, although the brightness changes might be.
…As Tomokatsu Morota (University of Tokyo) and colleagues write in the May 8th Science, Ryugu’s boulders likely start bluish. Then a combination of solar wind exposure, meteoroid impacts, and solar heating reddens them. This redder stuff migrates to the asteroid’s mid-latitudes over time, because topographically those are the lowest on Ryugu’s surface. That movement leaves the higher equator and polar regions relatively bluer and brighter.
Based on this data, the scientists posit that Ryugu was closer to the Sun from 800,000 to 8 million years ago, and that the evidence also suggests that the asteroid is only at most 17 million years old.
To put it mildly, there are great uncertainties to these conclusions.
After spending two weeks testing its main ion engines just beyond the gravitational sphere of influence of the asteroid Ryugu, Japanese engineers today initiated full engine operation, beginning the spacecraft’s journey back to Earth.
Hayabusa-2 is expected to return to Earth space in December 2020, where it will release a small capsule containing the two samples it obtained of Ryugu will be released to land on Earth and be recovered. At that point, if Hayabusa-2 is still in good condition it will be available to send to other locations in the solar system.
The Hayabusa-2 science team has fired up the spacecraft’s ion engine to leave the asteroid Ryugu and began its begins journey back to Earth.
It will take about six days to exit the gravitational sphere of influence of Ryugu. During that time period they will be continually releasing real time images of the asteroid from the spacecraft’s navigation camera, as it slowly gets farther away.
In mid-December they will fire the spacecraft’s main engines for an arrival near Earth in late 2020. At that point the small return capsule holding the samples from Ryugu will separate and land in the Australian desert. Hayabusa-2, still operational, might then be given a new subsequent mission.
In a press conference today the science team for the asteroid probe Hayabusa-2 announced that the spacecraft will begin the first stage of its journey back to Earth tomorrow, using its ion engine to slowly pull away from Ryugu.
That first stage will take a little less than a week. Once the spacecraft gets about 25 miles from Ryugu it will leave its sphere of gravitational influence, when it will then begin its cruise phase back to Earth.
Bennu’s equatorial ridge. Click for full image.
This week the science team operating the OSIRIS-REx spacecraft at the asteroid Bennu hosted a joint conference in Tucson, Arizona, with the scientists operating the Hayabusa-2 spacecraft at the asteroid Ryugu. Both gave up-to-date reports on the science so far obtained, as well as outlined upcoming events. I was fortunate enough to attend.
First an overview. Both Bennu and Ryugu are near earth asteroids, with Bennu having an orbit that might even have it hit the Earth in the last quarter of 2100s. Both are very dark, and are rubble piles. Both were thought to be of the carbonaceous chondrite family of asteroids, sometimes referred to as C-type asteroids. This family, making up about 75% of all asteroids, includes a bewildering collection of subtypes (B-types, F-types, G-types, CI, CM, CV, CH, CB, etc), all of which were initially thought to hold a lot of carbon. We now know that only a few of these categories, the CI and CM for example, are carbon rich.
Even so, we actually know very little about these types of asteroids. They are very fragile, so that any that reach the Earth’s surface are not a good selection of what exists. About 90% of the material gets destroyed in the atmosphere, with the remnant generally coming from the innermost core or more robust nodules. We therefore have a biased and limited sample.
It is therefore not surprising that the scientists are finding that neither Bennu nor Ryugu resembles anything else they have ever seen. Both have aspects that resemble certain types of carbonaceous chondrite asteroids, but neither provides a very good fit for anything.
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The Hayabusa-2 science team today released their last mini-lander, dubbed MINERVA-II2, toward Ryugu, with an expected landing expected no later than October 8.
After MINERVA-II2 lands, it will do the same as the first, operate for about two days on the surface, moving by a series of bounces/rolls and taking close-up pictures of the surface as it does so.
Hayabusa-2 has successfully completed its rehearsal for its planned drop of its last MINERVA-II bouncer/rover, releasing two reflective targets in order to track how they spiral down to the surface of Ryugu.
Hayabusa 2’s cameras will track the movement of the two navigation aids as they fly in space around Ryugu over the next several days. Scientists expect Ryugu’s tenuous gravity will pull the target markers to the asteroid’s surface within a week.
The release of that last bouncer is now expected in about a month. After spending time obtaining the data from that drop, Hayabusa-2 will then head back to Earth by the end of the year.
In preparation for the release and landing of Hayabusa-2’s second MINERVA-II2 tiny rover/bouncer, the spacecraft today began a close-approach to the asteroid Ryugu, where it will release two target markers.
Once released, Hayabusa-2 will back off to observe these markers as they spiral down into Ryugu, landing sometime around September 23.
This operation is a rehearsal for the release and landing of MINERVA-II2, which like the first two bouncers back in September 2018 will bounce along the asteroid’s surface, taking pictures and gathering data.
Japan’s Hayabusa-2 space probe automatically entered safe mode for one day on August 29, causing engineers to postpone a planned operation set for Sept 5.
Hayabusa2 is equipped with four reaction wheels that are used to control the posture of the spacecraft, and posture control is usually performed using three of these reaction wheels. On August 29, the back-up reaction wheel that has not been used since October last year was tested, and an abnormal value (an increased torque) as detected. The spacecraft therefore autonomously moved into the Safe-Hold state. Details of the cause of the abnormal torque value are currently under investigation. On August 30, restoration steps were taken and the spacecraft returned to normal. However, as the spacecraft moved away from the home position due to entering Safe-Hold, we are currently having to return to the home position. We will return to the home position this weekend.
The attitude of the spacecraft is controlled by three reaction wheels as before. Entering the Safe-Hold state is one of the functions employed to keep the spacecraft safe, which means that procedures have worked normally.
In this case it is very clear that this event actually demonstrated that the spacecraft’s systems are operating properly to prevent it from becoming lost. However, the event also underlined the urgency of getting its samples from the asteroid Ryugu back to Earth.
The scientists in charge of the tiny MASCOT lander dropped from Japan’s Hayabusa-2 spacecraft today released the results from the lander’s short seventeen hour observations of the surface of Ryugu.
They found that the asteroid has two different types of rocks (why is a mystery) and practically no dust.
Ralf Jaumann and his team were particularly surprised by the lack of dust: “Ryugu’s entire surface is littered with boulders, but we have not discovered dust anywhere. It should be present, due to the bombardment of the asteroid by micrometeorites over billions of years, and their weathering effect. However, as the asteroid has very low gravity – only one-sixtieth of that experienced on Earth’s surface – the dust has either disappeared into cavities on the asteroid or has escaped into space. This gives an indication of the complex geophysical processes occurring on the surface of this small asteroid.”
They also confirmed that the asteroid is a very fragile rubble pile.
“If Ryugu or another similar asteroid were ever to come dangerously close to Earth and an attempt had to be made to divert it, this would need to be done with great care. In the event that it was impacted with great force, the entire asteroid, weighing approximately half-a-billion tonnes, would break up into numerous fragments. Then, many individual parts weighing several tonnes would impact Earth,” says Jaumann, who is supervising the MASCam experiment, interpreting the observations. The asteroid is very similar to carbonaceous meteorites found on Earth, which date back 4.5 billion years. With an average density of just 1.2 grams per cubic centimetre, Ryugu is only a little ‘heavier’ than water ice. But as the asteroid is made up of numerous pieces of rock of different sizes, this means that much of its volume must be traversed by cavities, which probably makes this diamond-shaped body extremely fragile.
MASCOT was another example of a cubesat demonstrating that these tiny spacecraft can do very sophisticated science.
Japan’s today provided an update on what it has done to prepare the location where Hayabusa-2’s samples from the asteroid Ryugu will land on Earth.
The landing site is in the Woomera Prohibited Area (WPA) in the outback of southern Australia. Japan has already signed an agreement with that country for the recovery, as well as done preliminary surface work
The recovery site is an Australian Government prohibited area and is not accessible to the public. As part of the preparatory work, a field survey of the proposed recovery site in the WPA was conducted with permission from the Australian Government. This preparatory work confirmed the suitability of both the proposed recovery site and the candidate site for the antenna station that will search for the capsule.
The landing of the recovery capsule is now scheduled for late in 2020.
The Hayabusa-2 science team has released a short movie showing the spacecraft’s second touch-and-go sample grab on the surface of Ryugu.
The movie is available at the link above, or here.
From the burst of material that flies off the surface at touchdown, it is very clear why the science team was so worried about damaging Hayabusa-2 during this event.
New data from Hayabusa-2 has confirmed the long-held suspicions of astronomers that the reason they find so few fragments of C-class asteroids, such as Ryugu, on Earth is because they are too delicate to reach the Earth’s surface.
Ryugu and other asteroids of the common ‘C-class’ [chondritic] consist of more porous material than was previously thought. Small fragments of their material are therefore too fragile to survive entry into the atmosphere in the event of a collision with Earth.
…Until now, only a few chondritic meteorites found on Earth have been identified as fragments of C-type asteroids, which are very common in the Solar System (‘C’ is the chemical symbol for the element carbon). …”We can now confirm that fragments of these asteroids are very likely to break up further when they enter Earth’s atmosphere, and then usually burn up completely. This means that only the largest fragments reach the Earth’s surface,” explains Grott. “That is why meteorites from this type of asteroid are so rarely found on Earth.”
The good news is that, because of this, Earth’s atmosphere offers increased protection from C-type asteroids, which account for 75 percent of all asteroids. …However, further research is necessary to determine the maximum asteroid size for which this atmospheric protection is effective.
It is likely that even the largest rubble-pile C-asteroids will not pose much risk. Even if some pieces reach the Earth’s surface they are probably going to be small and unable to do much harm.
