- 3623 - ASTEROIDS - saga of Bennu and Ryugu? December 3, 2018, was NASA’s first mission to return a sample from an ancient asteroid arrived at its target, the asteroid Bennu. This mission, the Origins is a seven-year long voyage set to conclude upon the delivery to Earth of at least 2.1 ounces (60 grams) and possibly up to almost four and a half pounds of sample. It promises to be the largest amount of extraterrestrial material brought back from space since the Apollo.
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Asteroid Ryugu
--------------------- 3623 - ASTEROIDS - saga of Bennu and Ryugu?
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- The 20-year anniversary of the asteroid’s discovery was in September 2019 and scientists have been collecting data ever since. Here’s what we know about this pristine remnant from the early days of our solar system
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--------------------------- 1. It’s Very, Very Dark…
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- Bennu is classified as a “B-type asteroid“, which means it contains a lot of carbon in and along with its various minerals. Bennu’s carbon content creates a surface on the asteroid that reflects about four percent of the light that hits it. 4%.
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- For contrast, the solar system’s brightest planet, Venus, reflects around 65 percent of incoming sunlight, and Earth reflects about 30 percent. Bennu is a carbonaceous asteroid that hasn’t undergone drastic, composition-altering change, meaning that on and below its deeper-than-pitch-black surface are chemicals and rocks from the birth of the solar system.
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--------------------------- 2. … It’s Very, Very Old.
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- Bennu has been undisturbed for billions of years. Not only is it conveniently close and carbonaceous, it is also so primitive that scientists calculated it formed in the first 10 million years of our solar system’s history, over 4.5 billion years ago.
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- Thanks to the “Yarkovsky effect” which is the slight push created when the asteroid absorbs sunlight and re-emits that energy as heat, and gravitational tugs from other celestial bodies, it has drifted closer and closer to Earth from its likely birthplace, which is the Main Asteroid Belt between Mars and Jupiter.
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--------------------------- 3. Bennu Is a “Rubble-Pile” Asteroid.
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- While “rubble pile” sounds like an insult, it’s actually a real astronomy classification. Rubble-pile asteroids like Bennu are celestial bodies made from lots of pieces of rocky debris that gravity compressed together. This kind of detritus is produced when an impact shatters a much larger body. Bennu was a parent asteroid around 60 miles wide.
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- Bennu is about as tall as the Empire State Building. It likely took just a few weeks for shards of space wreckage to coalesce into the rubble-pile that is Bennu.
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- Bennu is full of holes inside, with 20 to 40 percent of its volume being empty space. The asteroid is actually in danger of flying apart, if it starts to rotate much faster or interacts too closely with a planetary body.
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-------------------- 4. Asteroids May Harbor Hints About the Origin of All Life on Earth…
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- Bennu is a primordial artifact preserved in the vacuum of space, orbiting among planets and moons and asteroids and comets. Because it is so old, Bennu could be made of material containing molecules that were present when life first formed on Earth.
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- All Earth life forms are based on chains of carbon atoms bonded with oxygen, hydrogen, nitrogen and other elements. However, organic material like the kind scientists hope to find in a sample from Bennu doesn’t necessarily always come from biology. It would further scientists’ search to uncover the role asteroids rich in organics played in catalyzing life on Earth.
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------------------------------ 5. …But Also Platinum and Gold!
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- Extraterrestrial jewelry sounds great, and Bennu is likely to be rich in platinum and gold compared to the average crust on Earth. Although most aren’t made almost entirely of solid metal. But asteroid “16 Psyche” may be! Many asteroids do contain elements that could be used industrially in lieu of Earth’s finite resources.
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- Closely studying this asteroid will give answers to questions about whether asteroid mining during deep-space exploration and travel is feasible. Although rare metals attract the most attention, water is likely to be the most important resource in Bennu.
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- Water is two hydrogen atoms bound to an oxygen atom. It can be used for drinking or separated into its components to get breathable air and rocket fuel. Given the high cost of transporting material into space, if astronauts can extract water from an asteroid for life support and fuel, the cosmic beyond is closer than ever to being human-accessible.
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------------------------------ 6. Sunlight Can Change the Asteroid’s Entire Trajectory.
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- Gravity isn’t the only factor involved with Bennu’s destiny. The side of Bennu facing the Sun gets warmed by sunlight, but a day on Bennu lasts just 4 hours and 17.8 minutes, so the part of the surface that faces the Sun shifts constantly. As Bennu continues to rotate, it expels this heat, which gives the asteroid a tiny push towards the Sun by about 0.18 miles per year, changing its orbit.
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------------------------ 7. There Is a Small Chance That Bennu Will Impact Earth?
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- The NASA Lincoln Near-Earth Asteroid Research team discovered Bennu in 1999. NASA’s Planetary Defense Coordination Office continues to track near-Earth objects (NEOs), especially those like Bennu that will come within about 4.6 million miles of Earth’s orbit and are classified as potentially hazardous objects.
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- Between the years 2175 and 2199, the chance that Bennu will impact Earth is only 1-in-2,700, but scientists still don’t want to turn their backs on the asteroid. Bennu swoops through the solar system on a path that scientists have confidently predicted, but they will refine their predictions with the measurement of the Yarkovsky Effect by “OSIRIS-Rex” and with future observations by astronomers.
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- Captured on August 11, 2020 during the second rehearsal of the OSIRIS-REx mission’s sample collection event, the SamCam imager’s field of view as the NASA spacecraft approached asteroid Bennu’s surface. The rehearsal brought the spacecraft through the first three maneuvers of the sampling sequence to a point approximately 131 feet above the surface, after which the spacecraft performed a back-away burn.
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---------------- 8. Sampling Bennu will be hard.
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- Early Earth-based observations of the asteroid suggested it had a smooth surface with a regolith, the top layer of loose, unconsolidated material, composed of particles less than an inch large.
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- As the OSIRIS-REx spacecraft was able to take pictures with higher resolution, it became evident that sampling Bennu would be far more hazardous than what was previously believed. New imagery of Bennu’s surface show that it’s mostly covered in massive boulders, not small rocks.
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- OSIRIS-REx was designed to be navigated within an area on Bennu of nearly 2,000 square yards, roughly the size of a parking lot with 100 spaces. Now, it must maneuver to a safe spot on Bennu’s rocky surface within a constraint of less than 100 square yards, an area of about five parking spaces.
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----------------------- 9. Bennu was named after an ancient Egyptian Deity
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- In 2013 by a nine-year-old boy from North Carolina who won the ‘Name that Asteroid! Michael Puzio won the contest by suggesting that the spacecraft’s Touch-and-Go Sample Mechanism (TAGSAM) arm and solar panels resemble the neck and wings in illustrations of Bennu, whom ancient Egyptians usually depicted as a gray heron.
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- Bennu is the ancient Egyptian deity linked with the Sun, creation and rebirth. Puzio also noted that Bennu is the living symbol of Osiris. The myth of Bennu suits the asteroid itself, given that it is a primitive object that dates back to the creation of the Solar System.
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----------------------- 10. Bennu Is Still Surprising Us!
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- The spacecraft’s navigation camera observed that Bennu was spewing out streams of particles a couple of times each week. Bennu apparently is not only a rare active asteroid, but possibly with Ceres explored by NASA’s Dawn mission, among the first of its kind that humanity has observed from a spacecraft.
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- The mission team discovered that sunlight can crack rocks on Bennu, and that it has pieces of another asteroid scattered across its surface. More pieces will be added to Bennu’s cosmic puzzle as the mission progresses, and each brings the solar system’s evolutionary history into sharper and sharper focus.
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- In 2020 scientists got their hands on some very rare space rocks, specifically, 5.4 grams of material from the near-Earth asteroid “162173 Ryugu“, which was returned to Earth via the Japanese space agency’s craft, Hayabusa 2, on December 6, 2020.
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- The discoveries alter our understanding of what Ryugu looks like. The diamond-shaped space rock is both darker and more porous than expected. This fragility is important in terms of assessing whether it or similar asteroids could one day threaten Earth.
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- The rocks also contain volatile compounds, suggesting Ryugu preserves material from the outer Solar System. This means scientists now have in their labs some of the most pristine stuff from the Solar System’s infancy, a time capsule from before the beginning of our world.
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- The Ryugu sample reflects just 2 percent of the light it receives. It is also exceptionally fragile. It is about 50 percent more porous than carbonaceous chondrite meteorites that have fallen to Earth. Such high-microporosity materials have not been discovered in any meteorites found on Earth probably due to break-up owing to their fragile nature during entry into the Earth’s atmosphere.
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- The rock contains a wide variety of volatile organic compounds, including non-water molecules made of oxygen and hydrogen atoms known as hydroxyls. These volatiles likely originated in the outer Solar System.
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- The Hayabusa 2 craft launched on a nearly four-year mission to Ryugu in December 2014, arriving at the asteroid in June 2018.
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- Ryugu is a C-type, or “carbonaceous” asteroid, asteroids that contain large portions of carbon and are the most common asteroid type in the Solar System. It’s also a member of the Apollo group, near-Earth asteroids with orbits ranging from just outside Earth’s to inside our planet’s orbit, crossing Earth’s orbit during their trip around the Sun.
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- Hayabusa 2 collected surface and subsurface material from the asteroid in late 2019. It dropped the samples to Earth on December 3, 2020. Hayabusa 2 continued on for an extended mission to another near-Earth Apollo asteroid, 1998 KY26.
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- Japan, researchers began the first wave of nondestructive analysis of the Ryugu samples, using spectrographs and optical microscopes to probe the dust for clues to some of the biggest questions we have about our Solar System.
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- Asteroids like Ryugu represent unique archives from the early days of the Solar System, material kept in a deep freeze, and therefore unchanged, from the time before planets formed. The Ryugu sample is the second of its kind ever returned to Earth.
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- The first arrived in 2005 when the Japan Aerospace Exploration Agency mission Hayabusa managed to return a few micrograms of dust from the near-Earth asteroid “25143 Itokawa“. Until NASA’s ORISIS-Rex returns with its samples of the near-Earth asteroid 101955 Bennu in 2023, these are the only samples we have.
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- Reflectance spectra and colors of surface rocks on Bennu look different from those of Ryugu.
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- It’s comforting to learn that at least some near-Earth asteroids that cross our path around the Sun may be too spongy and fragile to survive entering Earth’s dense atmosphere and remain intact enough to cause tremendous damage on impact.
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- The return of samples of the asteroid Bennu in 2023 is the next really big step. A member of the Apollo group like Ryugu, Bennu is a B-type asteroid, with a more blue spectrum and likely a very different composition than Ryugu. It also has a one in 1,800 chance of hitting Earth sometime in the 2100s.
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- “C-type asteroids1” are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing and on-asteroid measurements with Hayabusa2.
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- The average of the estimated bulk densities of Ryugu sample particles is 1,282 ± 231 kg m^3, which is lower than that of meteorites, suggesting a high microporosity down to the millimeter scale.
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July 10, 2022 ASTEROIDS - saga of Bennu and Ryugu? 3623
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