Tag: asteroids

Bennu from two miles

9:02 am

Bennu from two miles
Click for full image.

In late March OSIRIS-REx completed its fourth fly-by of the asteroid Bennu. The image on the right, cropped and reduced to post here, was taken when the spacecraft was only 2.1 miles above the surface. If you were standing among these large boulders, we could easily see you.

The image itself shows the asteroid’s southern limb, and thus the shadows are accentuated. This makes it easier to see surface details. Though it is clear once again that Bennu is a pile of boulders and rocks cemented together and floating in space, the photograph also shows that it also has areas where the material is either much larger or fused together more solidly, as shown by the more massive sections in the left center of this picture. We might be looking a very large boulders peeking up from below the surface, or possibly this is the hint of some real bedrock.

The OSIRIS-REx team is continuing the spacecraft’s survey phase, gathering high resolution images in order to compile a detailed map of the surface, prior to planning the touch-and-go sample grab.

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Lunar eclipse meteorite hit the Moon at almost 38,000 mph

10:33 am

By analyzing the data obtained of the meteorite impact that hit the Moon during the January 21 lunar eclipse, astronomers now estimate it crashed into the surface at almost 38,000 miles per hour and would have produced a crater about 50 feet across.

They also estimate that the meteorite itself had a mass of about 100 pounds with a diameter of between one to two feet.

The new crater itself has not yet been spotted, and probably can only be photographed with the high resolution camera on Lunar Reconnaissance Orbiter (LRO). I expect the LRO science team has already scheduled observations for this location. It will be interesting to see if the actual crater corresponds to the estimates of these astronomers.

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The new man-made crater on Ryugu

8:24 am

Man-made crater on Ryugu

The Hayabusa-2 science team has released before and after images of the spot on Ryugu where the spacecraft’s explosive projectile caused the creation of a small crater.

On the left above is the before, with the new crater indicated by the circle on the right. Note the rocks in both pictures, some now partly covered with debris. They did not give a scale, but this is a very small area, probably less than a few feet across.

They now need to analyze whether they can safely touchdown at this spot and grab a sample.

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Hayabusa-2 confirms man-made crater on Ryugu

8:53 am

In a planned fly-over of Ryugu yesterday Hayabusa-2 took its first direct images of the location where it had fired an explosive projectile and thus confirmed the creation of a man-made crater by that projectile.

“The asteroid’s terrain has clearly been altered,” said Yuichi Tsuda, an associate professor at the Japan Aerospace Exploration Agency.

Hayabusa2, which began its descent toward the asteroid Wednesday afternoon, captured images of its surface to determine the existence of the crater after it successfully shot a metal projectile at Ryugu on April 5 in an experiment deemed the first of its kind.

According to the JAXA, the probe photographed the area hit by the projectile from a distance of 1.7 km. The agency compared images of the asteroid’s surface before and after the shooting of the projectile to determine the presence of a man-made crater.

They have not yet released any of these images. They will use them however for planning a touchdown and sample grab within this crater in next few months.

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Did an interstellar meteor hit the Earth in 2014?

5:55 am

By analyzing the speed in which it traveled through the atmosphere, astronomers propose that a meteor that hit the ground in 2014 was probably an interstellar object.

The scientists analyzed the Center for Near-Earth Object Studies’ catalog of meteor events detected by U.S. government sensors. They focused on the fastest meteors, because a high speed suggests a meteor is potentially not gravitationally bound to the sun and thus may originate from outside the solar system.

The researchers identified a meteor about 3 feet (0.9 meters) wide that was detected on Jan. 8, 2014, at an altitude of 11.6 miles (18.7 kilometers) over a point near Papua New Guinea’s Manus Island in the South Pacific. Its high speed of about 134,200 mph (216,000 km/h) and its trajectory suggested it came from outside the solar system, the scientists said. “We can use the atmosphere of the Earth as the detector for these meteors, which are too small to otherwise see,” Loeb told Space.com.

The meteor’s velocity suggested it received a gravitational boost during its journey, perhaps from the deep interior of a planetary system, or a star in the thick disk of the Milky Way.

To put it mildly, there are a lot of uncertainties about this conclusion. Nonetheless, their approach and hypothesis is very intriguing, and seems logical.

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April 25 set for Hayabusa-2’s first observations of artificial crater

9:12 am

The Hayabusa-2’s science team has scheduled their first observations of the artificial crater the spacecraft made on the surface of the asteroid Ryugu for April 25.

The probe will observe the crater, which was generated during an impact experiment on April 5, from a height of 1.7 kilometers. JAXA will collate the data with photographs of the surface taken near the impact point to measure the size and location of the crater. It will also examine the dispersion of rocks and judge whether Hayabusa2 can land to take samples.

This is only their first assessment. Once they feel comfortable about getting closer, they will then plan the spacecraft’s second touchdown and sample collection, this time hopefully from within that crater.

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Bennu’s cobbled equatorial ridge

10:38 am

Bennu as seen by OSIRIS-REx
Click for full image.

The OSIRIS-REx science team has released a new close-up image of Bennu, this time showing the asteroid’s equatorial ridge. The image on the right is that photograph, reduced to post here.

When the image was taken, the spacecraft was positioned over Bennu’s northern hemisphere, looking southward over the asteroid’s equatorial bulge. The field of view shown is 168 ft (51.2 m) wide. For scale, the bright, rectangular rock above the dark region is 8 ft (2.4 m) wide, about the size of a long bed on a pickup truck

Like Ryugu, the scientists for OSIRIS-REx are going to be challenged in finding a location smooth enough for their touchdown sample grab. That surface reminds me of some avalanche scree slopes I’ve hike across, where you’ve got nothing but rough rocks to walk on.

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OSIRIS-REx maps Bennu by laser

8:32 am

The OSIRIS-REx science team today released a short animation showing a topographical global map of the asteroid Bennu, created by the spacecraft’s laser altimeter, dubbed OLA.

From Feb. 12 through 17, OLA made more than 11 million measurements of the distance between OSIRIS-REx and Bennu’s surface as the spacecraft flew less than 1.2 miles (2 km) above the surface – the closest orbit ever achieved by spacecraft. OLA obtained these measurements by firing laser pulses at Bennu and measuring the amount of time it takes for the light to bounce off the asteroid’s surface and return to the instrument. That time measurement is then translated into altitude data. Using this data, the OLA team created the 3-D model of Bennu’s surface.

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Hayabusa-2’s successfully bombs Ryugu

7:51 am

impact on Ryugu

Japan’s Hayabusa-2 probe yesterday successfully impacted an explosive charge on the surface of the asteroid Ryugu, creating a crater for observing the interior geology.

The image to the right was taken by a camera that has separated from Hayabusa-2 and stayed closer to the impact. It shows material flying off the asteroid’s surface, at the horizon line.

Hayabusa-2 — which moved to the other side of the asteroid to stay clear of any ejecta — will next arc around and get close to this impact site to study it. They first need to make sure the ejecta has cleared.

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Global map of Bennu

9:26 am

Global map of Bennu

The OSIRIS-REx science team today released a global map of Bennu, compiled from images taken in December.

The map is above. It was released with no commentary. In comparing it with this global map of Ryugu, created by the Japanese probe Hayabusa-2, I am struck by how much both asteroids resemble each other.

This fact is in many ways a first. Since the first planetary probes left Earth in the 1960s the one reliable expectation that has consistently proven true is that no planetary object, be it planet, dwarf planet, moon, asteroid, or comet, was going to resemble any other planetary object. Each has been entirely unique, and unique in very startling and obvious ways.

Ryugu and Bennu represent the first planetary objects that actually look pretty much the same. Scientist will of course be able to note differences, but overall these objects clearly belong to a specific class of asteroids, which in this case is the rubble pile.

In a sense, this similarity marks a significant advancement in our knowledge. Up until now, we had observed so few objects that our knowledge base wasn’t large enough to start seeing patterns within our general classifications of planet, asteroid, or comets. That is now finally changing.

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Hayabusa-2 to take close look at planned explosive impact point on Ryugu

10:14 am

Flight plan for Hayabusa-2's rehearsal

Beginning today Hayabusa-2 will do a two-day close approach of Ryugu in order to get good baseline images of the point on the surface where they will fire an explosive projectile in the first week in April. As they note:

Currently, we have scheduled the small carry-on impactor operation (SCI operation) for the first week in April. The purpose of the SCI operation is to create a crater on the surface of Ryugu, and it is important to be able to compare the asteroid surface before and after the SCI operation.

The graph on the right shows the flight plan. I expect they will do the same for this maneuver as they have done with previous close approaches, and provide real-time images as they happen.

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Confirmed: Ryugu is a rubble pile

2:48 pm

Close-up of Ryugu's surface
Click for source paper [pdf].

At a special session today dedicated to results from the Hayabusa-2 probe to the asteroid Ryugu at the 50th Lunar and Planetary Science Conference in Texas, scientists confirmed from numerous data and images that the asteroid has a low density, is covered with boulders and pebbles, is very porous, and is thus a rubble pile that is held together by gravity, barely.

From their lead presentation [pdf]:

The estimated total porosity is even higher than that of rubble-pile asteroid Itokawa (44 ± 4%), indicating that asteroid Ryugu is also a rubble pile. This is consistent with a theory arguing that all Solar System bodies with diameter of ~1 km should be rubble piles and might have formed from reaccumulation of fragments generated by catastrophic disruption events of ~100-km sized parent bodies.

They also posit that the asteroid’s diamond shape is caused by the asteroid’s 3.5 hour rotation, which causes its weak rubble pile structure to be easily pulled to the equator, and then outward.

Another paper [pdf] did crater counts, and found that there are fewer large craters than one would expect.

The density of large craters (D>100 m) on Ryugu is lower than the empirical saturation level and its slope is steeper than that of the saturated distribution, suggesting that craters larger than 100 m are not saturated and the size distribution reflects the crater production function. However, craters smaller than 100 m are significantly under-saturated, suggesting that some crater erasure processes such as seismic shaking and armoring effect are active on the Ryugu surface. Based on cratering chronology model for the main belt, the surface age of Ryugu is estimated to be 5–200 [million years] from the size–frequency distribution of craters larger than 100 m.

In other words, this rubble pile is constantly being shaken by its rotation and time and later impacts, which steadily rewrites the surface.

If this asteroid was headed to Earth, I imagine the only safe solution to prevent disaster would be to slowly and gently deflect it so it only flies past. To do this will require an arrival far in advance of the schedule impact, to give time for the deflection process to work.

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A rock on Bennu

9:58 am

A rock on Bennu
Click for full image (which is rotated 180 degrees).

Cool image time! The OSIRIS-REx science team today released a close-up image of the surface of the asteroid Bennu. The image on the right is a cropped and rotated section of that image, focusing on the image’s star, its largest rock.

The boulders on Bennu’s surface sport a variety of surface textures, from smooth, to hummocky, striated, and crumbly “cauliflower” in nature. The large boulder in the image center is ~92 ft (~28 m) across and has a somewhat round shape, though many smaller boulders surrounding it are very angular. Some of these appear to be fragments that may have disaggregated from the central boulder and display layering effects that may reflect some of the properties of their mineral composition. Other boulders show signs of surface exfoliation and fractures that may have been caused by impacts, mechanical weathering, and other forms of rock breakdown active on Bennu’s surface.

The image was taken from less than a mile away, and shows a spot near the asteroid’s south pole.

Why the larger boulder has a rounded look, but the pebbles around it are jagged, is a puzzle.

The science team also revealed today that they have detected plumes of particles being released from the asteroid’s surface. They have also found Bennu to present them with the same problem faced by the Hayabusa-2 team at Ryugu: The asteroid is far rougher than expected.

The higher-than-expected density of boulders means that the mission’s plans for sample collection, also known as Touch-and-Go (TAG), need to be adjusted. The original mission design was based on a sample site that is hazard-free, with an 82-foot (25-meter) radius. However, because of the unexpectedly rugged terrain, the team hasn’t been able to identify a site of that size on Bennu. Instead, it has begun to identify candidate sites that are much smaller in radius.

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Hayabusa-2 schedules explosion on Ryugu

9:49 am

The Hayabusa-2 science team has scheduled April 5 for when it will use the spacecraft to fire an explosive device into Ryugu to create a crater and debris cloud.

The probe is scheduled to detach a device loaded with explosives some 500 meters away from Ryugu. The device will set off the explosives using a timer some 40 minutes later and launch a copper “impactor” weighing about 2 kilograms into the asteroid’s surface.

The target point is several hundreds of meters away from where the space probe first touched down. The mission will require the spacecraft to move quickly to the other side of the asteroid so it won’t get hit by flying shards from the blast. A detached camera will shoot the moment of impact.

JAXA will analyze the size and shape of the crater, and how rocks fly off in a bid to collect underground samples for possible clues to the origin of the solar system.

This is different than the touchdown last month, as the spacecraft itself will not get close to the asteroid.

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A pond on Bennu

9:42 am

Pond on Bennu
Click for full resolution.

The OSIRIS-REx science team has released new high resolution images of one particular area on Bennu’s northern hemisphere. The image on the right, cropped and reduced to post here, shows what they label a “pond of regolith,” seen as the relatively smooth area in the upper left.

This is not literally a pond, but instead is a low-lying spot where smaller particles have settled over time, producing a flattish area that looks, and in some ways, resembles a pond or puddle, only in this case the material isn’t water but fine-grained dust or pebbles.

On March 19 the science team will be presenting their initial results at a special session at the 50th Lunar and Planetary Science Conference in Texas. That same day they will hold a press conference summarizing the most interesting aspects of those results. Stay tuned.

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New research detects increase in Bennu’s rotation

10:32 am

New research using ground-based observations has detected a slight increase over time in the daily rotation of the asteroid Bennu.

The new research finds the asteroid’s rotation is speeding up by about 1 second per century. In other words, Bennu’s rotation period is getting shorter by about 1 second every 100 years.

While the increase in rotation might not seem like much, over a long period of time it can translate into dramatic changes in the space rock. As the asteroid spins faster and faster over millions of years, it could lose pieces of itself or blow itself apart, according to the study’s authors.

…The change in Bennu’s rotation could be due to a change in its shape. Similar to how ice skaters speed up as they pull in their arms, an asteroid could speed up as it loses material.

Nolan and his co-authors suggest the reason for the increase in Bennu’s rotation is more likely due to a phenomenon known the YORP effect. Sunlight hitting the asteroid is reflected back into space. The change in the direction of the light coming in and going out pushes on the asteroid and can cause it to spin faster or slower, depending on its shape and rotation.

Truth is, this is not a very significant finding. Asteroids don’t weight much, and thus have very weak gravitational fields. It is therefore very easy to change their orbit and rotation, as well as add or subject material from them.

In this sense, the conclusion above is likely incorrect. What they have found is that the asteroid’s rotation increased at a pace of about 1 second per century, during their study period. Their data only covers the period from 1999 to 2005. Bennu could easily slowed its rotation, or increased it even more, during other times.

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Hayabusa-2 to get close to Ryugu again to observe next touchdown point

9:16 am

Hayabusa-2’s engineering team has decided it will on March 8 do a close approach to within 75 feet of its next planned touchdown target site in order to inspect it.

The DO-S01 operation schedule is shown in Figure 2. The spacecraft will begin descending on March 7 at 13:27 (JST, onboard time: times below are stated similarly) at a speed of 0.4m/s. The speed will then be reduced to 0.1 m/s around 23:47 on the same day. Continuing descent at this rate, we will reach our lowest altitude at around 12:22 on March 8 and then immediately begin to rise. The altitude of this lowest point will be about 23m. Please note that the times stated here are the planned values but the actual operation times may differ.

As before, they will upload navigation images as this approach is happening.

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Video from Hayabusa-2’s touchdown

7:51 am

The Hayabusa-2 science team has released a video taken of the spacecraft’s quick touchdown and sample grab on the asteroid Ryugu.

I have embedded the video below the fold. It not only shows the incredible rockiness of Ryugu’s surface, with the spacecraft barely missing a large rock as it came down, it also clearly shows the resulting debris cloud and surface changes after touchdown and the firing of Hayabusa-2’s projectile into the surface to throw up material that the spacecdraft could catch. You can actually see pebbles flying about below and around the spacecraft as it quickly retreats.

The Hayabusa-2 science team plans another touchdown in the next few months, this time using a different technique to disturb the surface and grab the resulting ejecta.
» Read more

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