Tag: asteroids

OSIRIS-REx’s landing spot on the asteroid Bennu

10:24 am

Bennu, annotated
Click for full resolution unlabeled image.

The OSIRIS-REx science team today released another image of the asteroid Bennu, this time showing the planned Nightingale touch-and-go sample grab landing site.

The image to the right, reduced, cropped, and annotated by me, is that image. From the caption:

The crater where sample site Nightingale is located can be seen near the top, center of the image – it is a small region containing dark, fine-grained material. Bennu’s prime meridian boulder, Simurgh Saxum , is also visible in the lower left of the image, near the asteroid’s limb. Directly east of Simurgh is Roc Saxum . The field of view is 0.3 miles (0.5 km). For reference, Simurgh is 125 ft (38 m) across, which is about the size of a commercial airliner.

Nightingale is only about 50 feet across, which is about a third the size of the kind of smooth areas they had designed their grab-and-go equipment around. This global image illustrates the difficulties they face with that sample grab. Though there appear to be larger areas in this photo that seem smooth, they really are not. The asteroid has no dust, and the sample grab equipment is designed to suck up particles smaller than 0.8 inches in diameter. Most of the surface is covered with pebbles and gravel larger than this.

Thus they needed to find a spot where the bulk of the material is “fine-grained.” Nightingale fits that bill, though it has a small footprint and also has larger particles that pose a risk to the sample grab because they could damage the spacecraft, or clog the sample grab equipment.

Either way, for the spacecraft to autonomously guide itself accurately down to this small spot, surrounded as it is by much larger boulders, will be challenging, and is why they have done one dress rehearsal already, getting as close as 213 feet, and will do a second in June, getting down to 82 feet.

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Bennu’s equatorial craters

10:05 am

Bennu's craters
Click for full image.

The OSIRIS-REx science team today released a neat image of Bennu, highlighting the string of impact craters along the rubble-pile asteroid’s equatorial ridge. The image to the right, cropped and reduced to post here, shows that image. From the release:

Bennu’s darkest boulder, Gargoyle Saxum , is visible on the equator, near the left limb. On the asteroid’s southern hemisphere, Bennu’s largest boulder, Benben Saxum , casts a long shadow over the surface. The field of view is 0.4 miles (0.7 km). For reference, the largest crater in the center of the image is 257 ft (78 m) wide, which is almost the size of a football field.

The photo was taken from a distance of six miles on April 28. The craters illustrate well the rubble pile/sandbox nature of this asteroid. They all look like what you’d expect if the impact was able to easily drive itself deep into the a pile of sand and loose rocks. The resulting crater thus has a very indistinct rim and a sloping floor down to a central point.

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Evidence suggests Ryugu was once closer to Sun

11:38 am

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.

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Movie of OSIRIS-REx’s 1st landing rehearsal

12:55 pm

Closest NavCam-2 image during rehearsal
Click for full movie.

The OSIRIS-REx science team has released a short movie taken by one of the spacecraft’s navigation camera (NavCam-2) during its first landing rehearsal on April 14. The image to the right, cropped to post here, is the closest image in the sequence, and shows the relatively smooth Nightingale target landing site near the bottom of the image, approximately 50 feet in diameter.

According to the release,

NavCam 2 captures images for the spacecraft’s Natural Feature Tracking (NFT) navigation system. The NFT system allows the spacecraft to autonomously guide itself to Bennu’s surface by comparing real-time images with an onboard image catalog. As the spacecraft descends to the surface, the NFT system updates the spacecraft’s predicted point of contact depending on OSIRIS-REx’s position in relation to Bennu’s landmarks. During the sample collection event, scheduled for August, the NavCam 2 camera will continuously image Bennu’s surface so that the NFT system can update the spacecraft’s position and velocity relative to Bennu as it descends towards the targeted touchdown point.

When the image above was taken the spacecraft was at its closest point, about 213 feet above the surface. Based on this movie, it looks like the system was working, and the spacecraft was refining its aim to head towards Nightingale.

Still, the landing site is not in the center of the image, which I would think is a concern, especially because Nightingale is only one-third the size of the kind of smooth target areas they had designed the system for. (When launched they expected to see smooth areas at least 160 feet across, and designed the system for this.)

The second rehearsal is presently scheduled for June 23, and will drop OSIRIS-REx to within 82 feet of the surface.

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First exoplanet imaged was nothing more than a debris cloud

2:41 pm

The uncertainty of science: What had originally been thought to be the first image ever taken of an exoplanet has now turned out to be only the fading and expanding cloud of debris, left over from a collusion.

The object, called Fomalhaut b, was first announced in 2008, based on data taken in 2004 and 2006. It was clearly visible in several years of Hubble observations that revealed it was a moving dot. Until then, evidence for exoplanets had mostly been inferred through indirect detection methods, such as subtle back-and-forth stellar wobbles, and shadows from planets passing in front of their stars.

Unlike other directly imaged exoplanets, however, nagging puzzles arose with Fomalhaut b early on. The object was unusually bright in visible light, but did not have any detectable infrared heat signature. Astronomers conjectured that the added brightness came from a huge shell or ring of dust encircling the planet that may possibly have been collision-related. The orbit of Fomalhaut b also appeared unusual, possibly very eccentric. “Our study, which analyzed all available archival Hubble data on Fomalhaut revealed several characteristics that together paint a picture that the planet-sized object may never have existed in the first place,” said Gáspár.

The team emphasizes that the final nail in the coffin came when their data analysis of Hubble images taken in 2014 showed the object had vanished, to their disbelief. Adding to the mystery, earlier images showed the object to continuously fade over time, they say. “Clearly, Fomalhaut b was doing things a bona fide planet should not be doing,” said Gáspár.

The interpretation is that Fomalhaut b is slowly expanding from the smashup that blasted a dissipating dust cloud into space. Taking into account all available data, Gáspár and Rieke think the collision occurred not too long prior to the first observations taken in 2004. By now the debris cloud, consisting of dust particles around 1 micron (1/50th the diameter of a human hair), is below Hubble’s detection limit. The dust cloud is estimated to have expanded by now to a size larger than the orbit of Earth around our Sun.

This is not the first exoplanet that astronauts thought they had imaged, only to find out later that it was no such thing.

Remember this when next you hear or read some scientist telling you they are certain about their results, or that the science is “settled.” Unless you can get close enough to get a real picture in high resolution, or have tons of data from many different sources over a considerable period of time, and conclusions must always be subject to skepticism

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Movie of OSIRIS-REx touch-and-go rehearsal

10:47 am

Checkpoint rehearsal: last image
Click for movie.

The OSIRIS-REx science team yesterday released a short movie, compiled from thirty images taken during the April 14, 2020 rehearsal of the spacecraft’s planned August touch-and-go sample grab from the asteroid Bennu.

The rehearsal brought the spacecraft through the first two maneuvers of the sampling event to a point approximately 213 feet (65 meters) above the surface, before backing the spacecraft away. These images were recorded over a ten-minute span between the execution of the rehearsal’s “Checkpoint” burn, approximately 394 feet (120 meters) above the surface, and the completion of the back-away burn, which occurred approximately 213 feet (65 meters) above the surface. The spacecraft’s sampling arm – called the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) – is visible in the central part of the frame, and the relatively clear, dark patch of Bennu’s sample site Nightingale is visible in the later images, at the top. The large, dark boulder that the spacecraft approaches during the sequence is 43 feet (13 meters) on its longest axis.

The image to the right is the last frame of the movie, as the spacecraft has begun its retreat. The smoother area of Nightingale is at the top.

Based on the video, it appears as if the spacecraft would have missed the Nightingale target site had the rehearsal continued to touchdown. This might not be so, however. And even if it is, the reason for the rehearsal is to allow engineers to refine the process to make it more accurate. We shall see what changes in the second rehearsal in about a month or so.

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OSIRIS-REx successfully completes touch-and-go rehearsal

8:44 am

OSIRIS-REx yesterday successfully completed its first dress rehearsal of the maneuver that will allow it in August to touch the surface of the asteroid Bennu and grab a sample.

Four hours after departing its 0.6-mile (1-km) safe-home orbit, the spacecraft performed the Checkpoint maneuver at an approximate altitude of 410 feet (125 meters) above Bennu’s surface. From there, the spacecraft continued to descend for another nine minutes on a trajectory toward – but not reaching – the location of the sampling event’s third maneuver, the “Matchpoint” burn. Upon reaching an altitude of approximately 246 ft (75 m) – the closest the spacecraft has ever been to Bennu – OSIRIS-REx performed a back-away burn to complete the rehearsal.

During the rehearsal, the spacecraft successfully deployed its sampling arm, the Touch-And-Go Sample Acquisition Mechanism (TAGSAM), from its folded, parked position out to the sample collection configuration. Additionally, some of the spacecraft’s instruments collected science and navigation images and made spectrometry observations of the sample site, as will occur during the sample collection event.

They plan one more rehearsal, getting even closer to the asteroid, before the August 25 sample grab.

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OSIRIS-REx’s sample grab location on Bennu

12:55 pm

Nightingale site on Bennu
Click for full image.

On April 14th engineers for the probe OSIRIS-REx will do the first of two dress rehearsals of their planned touch-and-go sample grab from the asteroid Bennu, presently planned for August 25.

The image to the right was taken on March 3, 2020 from about 1,000 feet away during the spacecraft’s third reconnaissance phase, and is centered on that touch-and-go site, dubbed Nightingale by the science team. It illustrates why that sample grab carries risks that were unexpected. As they point out on the image’s release page, “the rock in the [upper right] of the image is 2 ft (70 cm) long, which is about the length of a small ice chest.” Moreover, across the entire touchdown site are numerous other rocks ranging in size from fists to laptops.

When they designed the mission, they had assumed there would be places on Bennu’s surface made up mostly of dust. areas where such dust would have gathered into ponds, as seen in other asteroids. The expectation also assumed these areas would be larger than any of the smooth areas found on Bennu. As they have noted:
» Read more

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OSIRIS-REx to do sample-grab rehearsal at Bennu

9:11 am

The OSIRIS-REx science team today released a step-by-step description of the first touch-and-go sample grab rehearsal, planned for April 14, 2020.

During the rehearsal, dubbed “Checkpoint,” they expect the spacecraft to get less than 250 feet from the surface of the asteroid Bennu before pulling away.

Checkpoint rehearsal, a four-hour event, begins with the spacecraft leaving its safe-home orbit, 0.6 miles (1 km) above the asteroid. The spacecraft then extends its robotic sampling arm – the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) – from its folded, parked position out to the sample collection configuration. Immediately following, the spacecraft slews, or rotates, into position to begin collecting navigation images for NFT guidance. NFT allows the spacecraft to autonomously guide itself to Bennu’s surface by comparing an onboard image catalog with the real-time navigation images taken during descent. As the spacecraft descends to the surface, the NFT system updates the spacecraft’s predicted point of contact depending on OSIRIS-REx’s position in relation to Bennu’s landmarks.

Before reaching the 410-ft (125-m) Checkpoint altitude, the spacecraft’s solar arrays move into a “Y-wing” configuration that safely positions them away from the asteroid’s surface. This configuration also places the spacecraft’s center of gravity directly over the TAGSAM collector head, which is the only part of the spacecraft that will contact Bennu’s surface during the sample collection event.

In the midst of these activities, the spacecraft continues capturing images of Bennu’s surface for the NFT navigation system. The spacecraft will then perform the Checkpoint burn and descend toward Bennu’s surface for another nine minutes, placing the spacecraft around 243 ft (75 m) from the asteroid – the closest it has ever been.

They will do a second rehearsal on June 23, getting within 100 feet of the surface. The actual touch-and-go sample grab is now scheduled for August 25.

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Big sections break off of interstellar Comet 2I/Borisov

9:23 am

The uncertainty of science: New observations of the interstellar Comet 2I/Borisov as it exits our solar system indicate that large fragments have recently broken from it, and that the comet might possibly be on the verge of breaking up.

Astronomers have seen evidence of two fragments, but the data suggests these are relatively small compared to the entire comet. On the other hand,

Before perihelion, Jewitt’s analysis of Hubble images showed that Comet Borisov is much smaller than had been thought. The comet’s nucleus is not directly visible, but in the January 10th Astrophysical Journal Letters, Jewitt put its diameter between 0.4 and 1 kilometer. That’s small enough that solar vaporization of surface ices on the side facing the Sun could spin up its rotation beyond gravity’s ability to hold it together.

However, the comet’s size is tricky to estimate, as its surface appears to be emitting so much gas and dust that it obscures the nucleus. The fragment that Jewitt observed is about as bright as the comet itself, but because its surface is so icy and active, he thinks the fragment’s mass is less than 1% of the whole comet. That would make the split more like a side mirror dropping off a car than a car falling apart. Why the fragment split from the comet is unclear, but possibilities include thermal vaporization after new material was exposed, as well as the force from the comet’s spin if it’s spinning as fast as Jewitt suggests.

Whether the comet is about to break up remains unknown. Wouldn’t it be nice if someone was racing to put a mission together to visit it?

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Triple impact on Moon

11:27 am

Impact craters Messier and Messier A on the Moon

Cool image time! A new image release from Lunar Reconnaissance Orbiter (LRO) takes a look at the impact process that created the crater Messier and its neighbor crater Messier A. The photo to the right, cropped to post here, shows both craters.

Take a close look at Messier A. It is actually a double crater itself. From the release:

Messier A crater, located in Mare Fecunditatis, presents an interesting puzzle. The main crater is beautifully preserved, with a solidified pond of impact melt resting in its floor. But there is another impact crater beneath and just to the west of Messier A. This more subdued and degraded impact crater clearly formed first.

Did these three craters happen as separate events. According to the data, it appears no. Instead, they might have all been part of a single rain of asteroids, all occurring in seconds.
» Read more

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OSIRIS-REx makes closest reconnaissance of Bennu yet

9:07 am

The spacecraft OSIRIS-REx yesterday made its closest reconnaissance yet of the asteroid Bennu, sweeping past its primary touch-and-go landing site Nightingale by a distance of only 820 feet.

The main goal of yesterday’s low flyover was to collect high-resolution imagery of the site’s surface material. The spacecraft’s sample collection mechanism is designed to pick up small rocks less than 0.8 inches (2 cm) in size, and the PolyCam images from this low pass are very detailed, allowing the team to identify and locate rocks of this size. Several of the spacecraft’s other instruments also took observations of the Nightingale site during the flyover event, including the OSIRIS-REx Thermal Emissions Spectrometer (OTES), the OSIRIS-REx Visual and InfraRed Spectrometer (OVIRS), the OSIRIS-REx Laser Altimeter (OLA), and the MapCam color imager.

After completing the flyover, the spacecraft returned to orbit – but for the first time, OSIRIS-REx reversed the direction of its safe-home orbit and is now circling Bennu clockwise (as viewed from the Sun). This shift in orbital direction positioned the spacecraft for its next close encounter with the asteroid – its first rehearsal for the sample collection event.

The touch-and-go sample grab is targeted to take place in August.

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Protein molecules found in meteorite

9:00 am

Scientists have discovered bits of a protein molecule inside a meteorite that fell in Algeria in 1990 and was quickly recovered.

The protein is called hemolithin.

For hemolithin to have formed naturally in the configuration found would require glycine to form first, perhaps on the surface of grains of space dust. After that, heat by way of molecular clouds might have induced units of glycine to begin linking into polymer chains, which at some point, could evolve into fully formed proteins. The researchers note that the atom groupings on the tips of the protein form an iron oxide that has been seen in prior research to absorb photons—a means of splitting water into oxygen and hydrogen, thereby producing an energy source that would also be necessary for the development of life.

The real significance of this find is what it reveals we do not know. Most asteroid material from the very beginnings of the solar system (the type of material that would contain such a protein) is very fragile, and does not survive the journey though the Earth’s atmosphere. Thus, our meteorite sample obtained here on Earth, which is our entire sample, is very biased.

When we start getting samples back from asteroids (as both Hayabusa-2 and OSIRIS-REx are about to do), our understanding of the early solar system, as well as that of asteroids, will change radically. This story only gives us a hint of that fact.

Hat tip reader and fellow caver John Harman.

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OSIRIS-REx bypasses laser altimeter issue

1:40 pm

The science team for OSIRIS-REx has figured out a bypass for the failure of one of the spacecraft’s laser altimeters, originally used during close flyovers of the surface of the rubble-pile asteroid Bennu.

The mission has made the decision to use OLA’s High Energy Laser Transmitter (HELT) to provide the ranging data to focus PolyCam during the Mar. 3 flyover of site Nightingale. OLA consists of two laser subsystems, the HELT and the Low-Energy Laser Transmitter (LELT). OLA’s LELT was originally scheduled to provide these data, however, as a result of the anomaly that occurred during the Recon B site Osprey flyover, the team has determined that the LELT system is no longer operable. Despite the LELT’s condition, the HELT system has continued to operate as expected, and will be used to focus PolyCam for the remaining reconnaissance passes.

According to Erin Morton, head of communications for OSIRIS-REx in the Principal Investigator’s Office, the failure of LELT will not impact the touch-and-go sample grab, presently scheduled for sometime in August.

We don’t need OLA [either the low or high energy transmitters] for the sample collection event. OLA’s main purpose was to collect the altimetry data needed to make topographical maps for the sample site decision. It successfully accomplished that last year – which means that the instrument has completed all of its primary mission requirements. OLA isn’t used for navigation.

Instead, they are using an autonomous system that compares previous high resolution images with images taken during descent. In addition, they have a lidar system available as well.

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Falcon Heavy wins launch contract for NASA’s Psyche asteroid mission

11:57 pm

Capitalism in space: NASA today awarded the launch contract for its Psyche asteroid mission, set to launch in July 2022, to SpaceX’s Falcon Heavy rocket.

The total bid price was $117 million, which according to the release includes “the launch service and other mission related costs.” Though this is higher than the normal price SpaceX charges for a Falcon Heavy launch ($100 million), it is far lower than the typical price of a ULA launch. Furthermore, Falcon Heavy has more power, so it can get the spacecraft to the asteroid faster.

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First image of possible asteroid in orbit around the Earth

3:37 pm

asteroid orbiting the Earth?
Click for full image.

The Gemini telescope in Hawaii has produced the first image of what might be only the second asteroid ever discovered in orbit around the Earth.

The newly discovered orbiting object has been assigned the provisional designation 2020 CD3 by the International Astronomical Union’s Minor Planet Center. If it is natural in origin, such as an asteroid, then it is only the second known rocky satellite of the Earth ever discovered in space other than the Moon. The other body, discovered in 2006, has since been ejected out of Earth orbit. 2020 CD3 was discovered on the night of 15 February 2020 by Kacper Wierzchos and Teddy Pruyne at the Catalina Sky Survey operating out of the University of Arizona’s Lunar and Planetary Laboratory in Tucson, Arizona.

The photo to the right has been cropped to post here. The streaks are stars, since the telescope was tracking the asteroid in an attempt to cull the most resolution of it from the image.

This object is only a few yards across, and could very well be a piece of space junk from a mission launched many decades ago. It is also not in a stable orbit around the Earth, and is expected to be ejected from that orbit in April.

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New OSIRIS-REx close-up image of secondary asteroid landing site

9:40 am

Osprey landing site on Bennu
Click for full image.

The OSIRIS-REx science team today released one of the images taken during the spacecraft’s recent close reconnaissance of its secondary touch-and-go landing site on the asteroid Bennu.

I have cropped their oblique image to focus, in full resolution, on that landing site, dubbed Osprey, which is the crater on the left side of the photo. The boulder in that crater “is 17 ft (5.2 m) long, which is about the length of a box truck.”

After the fly-by, the science team had announced that the spacecraft’s laser altimeter had failed to operate, and the images taken by its highest resolution camera (not the camera that took today’s image) “are likely out of focus.”

Based on this image, what look like tiny pebbles inside the crater are actually boulders ranging in size from mere inches to as much as five feet across. If their high resolution images are soft, it will thus be hard to map out the terrain sufficiently to safely make a touch-and-go landing here.

More important, there is still no word on whether they have fixed the laser altimeter. Without it I suspect a landing will be very difficult, if not impossible.

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Anomaly during OSIRIS-REx flyover of secondary landing site

9:14 am

During its close fly-over of its secondary candidate touch-and-go landing site on the asteroid Bennu, OSIRIS-REx’s laser altimeter failed to work as planned.

On Feb. 11, NASA’s OSIRIS-REx spacecraft safely executed a 0.4-mile (620-m) flyover of the backup sample collection site Osprey as part of the mission’s Reconnaissance B phase activities. Preliminary telemetry, however, indicates that the OSIRIS-REx Laser Altimeter (OLA) did not operate as expected during the 11-hour event. The OLA instrument was scheduled to provide ranging data to the spacecraft’s PolyCam imager, which would allow the camera to focus while imaging the area around the sample collection site. Consequently, the PolyCam images from the flyover are likely out of focus.

They are analyzing their data to figure out what went wrong and whether it can be fixed. The press release implies that this loss will not impact the touch-and-go at the primary landing site, but does not say so directly. Without the laser altimeter I wonder, how they will know their exact distance as they approach?

Then again, they have not yet downloaded the full dataset from the fly-over, so they might be able to get the instrument working again.

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An update on Comet 2I/Borisov

8:23 am

Link here.

Overall, this second known interstellar object to pass through the solar system appears to be a very typical comet. They have found however that its nucleus is much smaller than at first thought, only 200 to 500 meters across, which means that radiation pressure from the Sun could cause its rotation to spin up, with the possibility that this spin could get fast enough to cause the comet to break up.

The comet made its closest approach to the Sun in December, and will spend the next year-plus flying outward to beyond Saturn.

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OSIRIS-REx completes close fly-over of Bennu touchdown site

9:38 am

OSIRIS-REx has successfully completed the first of a series of increasingly closer fly-overs of its primary sample grab sites on the asteroid Bennu.

The spacecraft got as close as about 2,000 feet in order to take more high resolution images of the Nightingale landing site where they hope in August to do a touch-and-go sample grab.

A similar flyover of the backup sample collection site, Osprey, is scheduled for Feb. 11. Even lower flybys will be performed later this spring – Mar. 3 for Nightingale and May 26 for Osprey – as part of the mission’s Reconnaissance C phase activities. The spacecraft will perform these two flyovers at an altitude of 820 feet (250 m), which will be the closest it has ever flown over asteroid Bennu’s surface.

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The oldest known meteorite strike?

9:09 pm

The uncertainty of science: Scientists think they have identified the oldest meteorite strike known on Earth, dated at 2.33 billion years ago, located in a known impact site in Yarrabubba, Western Australia.

Lead author Dr Timmons Erickson, from Curtin’s School of Earth and Planetary Sciences and NASA’s Johnson Space Center, together with a team including Professor Chris Kirkland, Associate Professor Nicholas Timms and Senior Research Fellow Dr Aaron Cavosie, all from Curtin’s School of Earth and Planetary Sciences, analysed the minerals zircon and monazite that were ‘shock recrystallized’ by the asteroid strike, at the base of the eroded crater to determine the exact age of Yarrabubba.

The team inferred that the impact may have occurred into an ice-covered landscape, vaporised a large volume of ice into the atmosphere, and produced a 70km diameter crater in the rocks beneath.

Professor Kirkland said the timing raised the possibility that the Earth’s oldest asteroid impact may have helped lift the planet out of a deep freeze. “Yarrabubba, which sits between Sandstone and Meekatharra in central WA, had been recognised as an impact structure for many years, but its age wasn’t well determined,” Professor Kirkland said. “Now we know the Yarrabubba crater was made right at the end of what’s commonly referred to as the early Snowball Earth – a time when the atmosphere and oceans were evolving and becoming more oxygenated and when rocks deposited on many continents recorded glacial conditions”.

Associate Professor Nicholas Timms noted the precise coincidence between the Yarrabubba impact and the disappearance of glacial deposits. “The age of the Yarrabubba impact matches the demise of a series of ancient glaciations. After the impact, glacial deposits are absent in the rock record for 400 million years. This twist of fate suggests that the large meteorite impact may have influenced global climate,” Associate Professor Timms said. [emphasis mine]

I truly believe they have determined the approximate age of this impact, making it one of the oldest known impacts. Implying however a “precise” linkage to other only vaguely known climate events, and inferring that the former was the cause of the latter seems to me to be a very large overstatement. Their data might suggest this conclusion, but the uncertainties here demand a bit less certitude..

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First asteroid discovered that circles Sun closer than Venus

9:33 am

Astronomers have detected the first asteroid circling the Sun in an orbit that lies entirely inside Venus’s orbit.

In addition to being the first known asteroid with this orbit, the space rock, called 2020 AV2, has the smallest aphelion, or distance from the sun, of any known natural object in the solar system, excluding Mercury. Moreover, by traveling around the sun in a mere 151 days, 2020 AV2 has the shortest orbital period of any known asteroid, according to The Virtual Telescope Project, an online observatory based in Italy.

The reason this is a first is because it is very hard to find such small objects orbiting closer to the Sun than Earth. The glare of the Sun limits what can be spotted. This fact is also why the scientists are unsure of the size of 2020 AV2.

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Stardust found in meteorite older than Earth

9:12 am

Scientists studying what they think is grains of stardust in a meteorite the hit the Earth in 1969 have discovered the oldest material ever found on Earth, material that is actually older than the Earth itself.

The meteorite, dubbed the Murchison meteorite after the nearest city in Australia where it landed, has been a treasure trove of information for planetary scientists because so much of it was recovered right after impact.

About 30 years ago it was found that the rocks housed “presolar grains” – tiny grains of silicon carbide older than the Sun. But their exact age hadn’t been determined until now.

To figure that out, the researchers on the new study measured how long these presolar grains had been exposed to cosmic rays. These high-energy particles flit around space and can pass through solid matter, creating new elements inside the existing minerals as they interact with them. That means the scientists can measure the amount of these new elements in the grains to determine how long they were floating around in space – and, ultimately, how old they are.

In doing so, the team found that most of the grains were between 4.6 and 4.9 billion years old. The Sun itself is at the younger end of that range, at 4.6 billion years old, while the Earth didn’t form until 4.5 billion years ago.

But the oldest of the grains were dated to more than 5.5 billion years, making them the oldest known material on Earth. The team says that the history of these grains could be traced back even further, to the stars that birthed them some 7 billion years ago. According to the researchers, this finding suggests that our galaxy went through a period of intense star formation around that time.

Obviously there are uncertainties with this result, though their age estimates are quite reasonable and largely robust.

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Probe to visit 8 asteroids, not 7

12:11 am

Scientists developing the Lucy mission to visit seven Trojan asteroids that share an orbit with Jupiter have found an eighth satellite they will also be able to visit.

This first-ever mission to the Trojans was already going to break records by visiting seven asteroids during a single mission. Now, using data from the Hubble Space Telescope (HST), the Lucy team discovered that the first Trojan target, Eurybates, has a satellite. This discovery provides an additional object for Lucy to study.

“If I had to bet that one of our destinations had a satellite, it would have been this one,” said SwRI’s Hal Levison, principal investigator of the mission. “Eurybates is considered the largest remnant of a giant collision that occurred billions of years ago. Simulations show that asteroid collisions like the one that made Eurybates and its family often produce small satellites.”

The mission is targeting a 2021 launch date.

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The importance of small telescopes to science and civilization

10:58 am

The main cluster of telescopes, on Mount Lemmon
Largest cluster of telescopes on Mount Lemmon, six visible with three just out of view.

On December 11, 2019 I was kindly given a personal tour by Alan Strauss, director of the Mount Lemmon Sky Center, of the telescopes located on the mountaintops of the Santa Catalina Mountains overlooking Tucson. Strauss runs the educational outreach program for the University of Arizona astronomy department and the Steward Observatory, both of which operate the mountaintop facility.

The telescopes, numbering almost a dozen, are in two groups, two telescopes on the peak of Mount Bigelow and the rest clustered on the higher peak of Mount Lemmon. None are very gigantic by today’s standards, with their primary mirrors ranging in size from 20- to 61-inches. For comparison, the largest operating telescope in the world on the Canary Islands is 409 inches across. Hubble has a 94-inch mirror. And the new giant telescopes under design or being built have mirrors ranging from 842 inches (Giant Magellan) to 1,654 inches (European Extremely Large Telescope).

Thus, the small telescopes in the Santa Catalinas generally don’t make the news. They are considered passe and out-of-date, not capable of doing the kind of cutting edge astronomy that all the coolest astronomers hunger for.

Yet, without them, we likely would not have future astronomers. » Read more

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OSIRIS-REx team picks primary sample site

12:03 pm

Four candidate landing sites
Click for full image.

The OSIRIS-REx science team has picked the site they have dubbed Nightingale as the primary landing site where they will attempt to obtain a sample from the asteroid Bennu in the summer of 2020. The back-up site is Osprey at the equator.

I have embedded the replay of the NASA live stream of the press event below the fold. The first 21 minutes of the video are an overview of the mission, leading up to the announcement by Dante Lauretta, OSIRIS-REx’s principal investigator. He notes then that the site “does have some hazards” but they chose it for its “scientific value.” While its higher latitude location has some advantages, it also makes it more difficult for landing. The one large boulder there, which Lauretta calls “Mt Doom,” also carries risk for the touch-and-go operations.

The back-up site, Osprey, is on the equator with less hazards, but will present more problems obtaining the tiny-sized particles the sample grab equipment was designed to get.

Not that this matters, but if I have been in a betting pool I would have won, since Nightingale has been my guess for which site they’d pick since early November.
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OSIRIS-REx completes reconnaissance of four candidate sample sites

10:04 am

Four candidate landing sites
Click for full image.

OSIRIS-REx has completed its high resolution reconnaissance of the four candidate sites on the asteroid Bennu, chosen for possible sample capture during touch-and-go operations planned for the summer of 2020.

In the next few days the science team will decide which of these four sites, shown above, will be the primary and back-up landing locations. The decision however appears challenging, based on the information gathered.

Bennu has also made it a challenge for the mission to identify a site that won’t trigger the spacecraft’s safety mechanisms. During Recon A, the team began cataloguing Bennu’s surface features to create maps for the Natural Feature Tracking (NFT) autonomous navigation system. During the sample collection event, the spacecraft will use NFT to navigate to the asteroid’s surface by comparing the onboard image catalog to the navigation images it will take during descent. In response to Bennu’s extremely rocky surface, the NFT system has been augmented with a new safety feature, which instructs it to wave-off the sampling attempt and back away if it determines the point of contact is near a potentially hazardous surface feature. With Bennu’s building-sized boulders and small target sites, the team realizes that there is a possibility that the spacecraft will wave-off the first time it descends to collect a sample.

Based on the information at the link, plus the presentation by Dante Lauretta, OSIRIS-REx’s principal investigator, given at the asteroid conference I attended in November, I suspect that Nightingale will be primary landing site.

Regardless, it appears the science team has recognized that the landing will difficult, and will likely require multiple attempts before the spacecraft’s navigation system lets it happen.

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Hayabusa-2 fires main ion engines for return to Earth

8:20 am

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.

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Hayabusa-2 begins journey back to Earth

9:32 am

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.

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