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  • richardmitnick 8:09 am on August 12, 2021 Permalink | Reply
    Tags: "New odds on asteroid Bennu. Will it strike Earth?", , OSIRIS-REx Sheds Light on Hazardous Asteroid Bennu., Yarkovsky effect: the tiny push resulting from solar heating can cause asteroids to drift across vast distances over millions of years.   

    From EarthSky : “New odds on asteroid Bennu. Will it strike Earth?” 


    From EarthSky

    August 12, 2021
    Deborah Byrd

    OSIRIS-REx Sheds Light on Hazardous Asteroid Bennu.
    NASA Goddard Space Flight Center (US)

    At a news conference on August 11, 2021, NASA scientists said there is a 1-in-1,750 chance that asteroid Bennu could collide with Earth between now and the year 2300. The greatest chance in the next 300 years will come on September 24, 2182. The estimates suggest a slightly greater chance than previously, but scientists say they are not worried. Planetary scientist Lindley Johnson of NASA’s Planetary Defense Coordination Office said at Wednesday’s press briefing:

    “I don’t think we need to do anything about Bennu.”

    Still, Bennu and another asteroid known as (29075) 1950 DA remain the two most hazardous asteroids to Earth, as far as scientists know at this time. NASA was concerned enough about Bennu that it sent a spacecraft to the asteroid. The OSIRIS-REx spacecraft rendezvoused with Bennu in late 2018 and touched down on the asteroid’s surface in late 2020, successfully collecting a sample.

    The spacecraft learned, among other things, that Bennu is a very dark, and very ancient. It’s a bit wider than the Empire State Building in New York City is tall. A NASA statement said that, along with collecting a sample from the Bennu’s surface, the spacecraft provided precision data to better predict the near-Earth object’s orbit around the sun. Those predictions were published in a study, also released on August 11. The journal Icarus published the new study, which is titled Ephemeris and hazard assessment for near-Earth asteroid (101955) Bennu based on OSIRIS-REx data. The NASA statement said:

    “In 2135, asteroid Bennu will make a close approach with Earth. Although the near-Earth object will not pose a danger to our planet at that time, scientists must understand Bennu’s exact trajectory during that encounter in order to predict how Earth’s gravity will alter the asteroid’s path around the sun – and affect the hazard of [future] Earth impact.

    Using NASA’s Deep Space Network and state-of-the-art computer models, scientists were able to significantly shrink uncertainties in Bennu’s orbit, determining its total impact probability through the year 2300 is about 1 in 1,750 (or 0.057%).

    NASA Deep Space Network. Credit: National Aeronautics Space Agency (US).

    The researchers were also able to identify Sept. 24, 2182, as the most significant single date in terms of a potential impact, with an impact probability of 1 in 2,700 (or about 0.037%).”

    Davide Farnocchia, a scientist at JPL-Caltech (US) in California and lead author of the paper, told The New York Times:

    “It’s not a significant change. I’m not any more concerned about Bennu than I was before. The impact probability remains really small.”

    OSIRIS-REx left Bennu on May 10, 2021. It gathered information about the asteroid’s size (it is about one-third of a mile, or 500 meters, wide), shape, mass, and composition, and its spin and orbital trajectory. The spacecraft will deliver its precious sample of rock and dust from the asteroid’s surface to Earth on September 24, 2023. Farnocchia commented:

    “The OSIRIS-REx data give us so much more precise information, we can test the limits of our models and calculate the future trajectory of Bennu to a very high degree of certainty through 2135. We’ve never modeled an asteroid’s trajectory to this precision before.”

    This mosaic image of asteroid Bennu is composed of 12 PolyCam images collected on Dec. 2, 2018 by the OSIRIS-REx spacecraft from a range of 15 miles (24 km). Image via NASA/ University of Arizona (US).

    Gravitational keyholes

    In recent year, scientists have sometimes spoken about close-passing asteroids in terms of a “gravitational keyhole”. Bennu will pass through a gravitational keyhole during its 2135 close approach. NASA said:

    “These keyholes are areas in space that would set Bennu on a path toward a future impact with Earth if the asteroid were to pass through them at certain times, due to the effect of Earth’s gravitational pull.

    To calculate exactly where the asteroid will be during its 2135 close approach – and whether it might pass through a gravitational keyhole – Farnocchia and his team evaluated various types of small forces that may affect the asteroid as it orbits the Sun. Even the smallest force can significantly deflect its orbital path over time, causing it to pass through or completely miss a keyhole.

    Among those forces, the sun’s heat plays a crucial role. As an asteroid travels around the sun, sunlight heats up its dayside. Because the asteroid spins, the heated surface will rotate away and cool down when it enters the nightside. As it cools, the surface releases infrared energy, which generates a small amount of thrust on the asteroid – a phenomenon called the Yarkovsky effect. Over short timeframes, this thrust is minuscule, but over long periods, the effect on the asteroid’s position builds up and can play a significant role in changing an asteroid’s path.”

    Steve Chesley, senior research scientist at JPL and study co-investigator, commented:

    “The Yarkovsky effect will act on all asteroids of all sizes, and while it has been measured for a small fraction of the asteroid population from afar, OSIRIS-REx gave us the first opportunity to measure it in detail as Bennu traveled around the sun. The effect on Bennu is equivalent to the weight of three grapes constantly acting on the asteroid – tiny, yes, but significant when determining Bennu’s future impact chances over the decades and centuries to come.”

    NASA said the team considered many other perturbing forces as well, including the gravity of the sun, the planets, their moons, and more than 300 other asteroids, the drag caused by interplanetary dust, the pressure of the solar wind, and Bennu’s particle-ejection events. NASA said:

    “The researchers even evaluated the force OSIRIS-REx exerted when performing its Touch-And-Go (TAG) sample collection event October 20, 2020, to see if it might have slightly altered Bennu’s orbit, ultimately confirming previous estimates that the TAG event had a negligible effect.”

    Rich Burns, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, explained:

    “The force exerted on Bennu’s surface during the TAG event were tiny even in comparison to the effects of other small forces considered. TAG did not alter Bennu’s likelihood of impacting Earth.”

    Tiny risk, huge gain

    Although a 0.057% impact probability through the year 2300 and an impact probability of 0.037% on September 24, 2182, are low, this study highlights the crucial role that OSIRIS-REx operations played in precisely characterizing Bennu’s orbit, NASA said. Dante Lauretta, OSIRIS-REx principal investigator and professor at the University of Arizona, commented:

    “The orbital data from this mission helped us better appreciate Bennu’s impact chances over the next couple of centuries and our overall understanding of potentially hazardous asteroids – an incredible result. The spacecraft is now returning home, carrying a precious sample from this fascinating ancient object that will help us better understand not only the history of the solar system but also the role of sunlight in altering Bennu’s orbit since we will measure the asteroid’s thermal properties at unprecedented scales in laboratories on Earth.”

    Illustration of the orbits of asteroid Bennu, OSIRIS-Rex and Earth, via NASA.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.orgin 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.

  • richardmitnick 4:41 pm on March 19, 2021 Permalink | Reply
    Tags: "Karma Asteroid Family Might Be Sending Members Near Earth", , , , , Eventually the lost Karma members cross Mars’s orbit to become near-Earth asteroids., Kirkwood gap: an unstable region of the main belt around 2½ times farther out from the Sun than Earth's orbit., , The Karma family is named after its largest member asteroid 3811 Karma discovered in 1953., University of Belgrade [Универзитет у Београду](RS)(CZ), Yarkovsky effect: the tiny push resulting from solar heating can cause asteroids to drift across vast distances over millions of years.   

    From University of Belgrade [Универзитет у Београду](RS)(CZ) via Sky & Telescope: “Karma Asteroid Family Might Be Sending Members Near Earth” 

    From University of Belgrade [Универзитет у Београду](RS)(CZ)


    Sky & Telescope

    March 15, 2021
    Theo Nicitopoulos

    This artist’s illustration shows a near-Earth asteroid passing by Earth.
    Credit: NASA / JPL-Caltech

    In a study published in MNRAS, researchers simulated the orbital evolution of asteroids in the Karma family, starting with the initial family-creating impact. The results suggest that over the family’s lifetime, 350 members have transferred close to Earth’s orbit — and around 10 might currently be in near-Earth space right now.

    The Karma Family

    The Karma family is named after its largest member asteroid 3811 Karma discovered in 1953. The researchers estimate that approximately 137 million years ago, another object hit a body between 34 and 41 kilometers wide (21 to 25 miles), splintering off unknown numbers of family members. They’re carbonaceous chondrites, so they reflect little light and are therefore difficult to find.

    “However, new sky surveys within the last couple of years have been able to observe the tiny specks of light of these fainter asteroids, and these observations allowed us to identify 317 Karma family members,” says undergraduate student and lead author Debora Pavela (University of Belgrade).

    The researchers simulated the evolution of the members’ orbits beginning with the family-making collision. In addition to the gravitational pull of the planets, the researchers also included the Yarkovsky effect, in which the tiny push resulting from solar heating can cause asteroids to drift across vast distances over millions of years.

    A spinning body radiates the most heat from its afternoon side, creating a slight thermal imbalance called the Yarkovsky effect. Over time an asteroid rotating in the same sense as its motion around the Sun is gradually accelerated and pushed into a wider orbit. Conversely, a retrograde spinner will spiral inward. Credit: Sky & Telescope.

    Near-Earth Asteroids

    The simulations show that over the family’s lifetime, the Yarkovsky effect caused 350 large asteroids (more than 1 kilometer in diameter) to migrate to the so-called Kirkwood gap: an unstable region of the main belt around 2½ times farther out from the Sun than Earth’s orbit. Here, the asteroids experience a 3:1 mean-motion resonance with Jupiter, completing three orbits for every one orbit of Jupiter. As Jupiter repeatedly tugs more strongly at certain relative positions, the asteroids’ orbits gradually elongate. Eventually the lost Karma members cross Mars’s orbit to become near-Earth asteroids, Pavela says.

    According to the simulations, the first asteroid entered the 3:1 resonance approximately 70 million years ago, and roughly 5 additional family members come in every million years or so.

    Based on past studies that show most asteroids entering this resonance end up as near-Earth asteroids, remaining in near-Earth space for about 2 million years, coauthor Bojan Novakovic (University of Belgrade) estimates there are currently 10 asteroids from the Karma family in the near-Earth region.

    “The Yarkovsky effect together with the resonance is interesting, because you can potentially get a meteorite from any part of the asteroid belt,” says Thomas Burbine (Mount Holyoke College), who was not involved in the study. “This potentially provides an opportunity to study samples from different parts of the belt to learn about the early solar system.”

    Future Studies

    Identifying asteroid families that are supplying asteroids to near-Earth space is the first step in linking meteorites found on Earth to asteroids in the main belt. Ultimately, studies like this one contribute to a better understanding of the early solar system.

    “We could have near-Earth asteroids and maybe even meteorite samples here on Earth that are from the Karma family,” says Burbine, “This family identification invites people to study these members and perhaps even collect spectral data in the future to try to match a meteorite sample.”

    While linking the composition of meteorites to asteroid families is difficult, future space missions could target families believed to supply near-Earth asteroids and even bring back samples.

    “Our study is a small piece of the big puzzle of understanding the early solar system that researchers are eager to solve,” says Novakovic.

    See the full article here.


    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of Belgrade [Универзитет у Београду](RS)(CZ) is a public university in Serbia. It is the oldest and largest university in Serbia.
    The university was founded by Dositej Obradović, Serbian key figure in the Age of Enlightenment.

    Founded in 1808 as the Belgrade Higher School in revolutionary Serbia, by 1838 it merged with the Kragujevac-based departments into a single university. The University has around 97,700 enrolled students and over 4,800 members of academic staff. Since its founding, the University has educated more than 378,000 bachelors; around 25,100 magisters; 29,000 specialists; and 14,670 doctors. The University comprises 31 faculties; 12 research institutes, the university library, and 9 university centres. The faculties are organized into 4 groups: social sciences and humanities; medical sciences; natural sciences and mathematics; and technological sciences.

    19th century

    It was the highest ranking educational institution in Serbia between 1808 and 1905 as the first Higher School (1808–1813)- the Belgrade Lyceum, and the second Higher School (1863–1905). It was initially located at the Princess Ljubica’s Residence building and then moved to another significant site in Belgrade- the Captain Miša’s Mansion, today’s seat of the university.
    Dositej Obradović, founder of the university

    The second Higher School (also known as the Great School or Great Academy of Belgrade) was established as the successor of the Lyceum and was a combination of a classical gymnasium and a college, and as such developed into the University of Belgrade. Under the law, it was defined as a “scientific institute for higher and professional education”. The Minister of Education had control over this institution and it was managed by the Rector (elected by the monarch) and Academic Council.

    During its early history it had three departments: Philosophy, Engineering and Law. The Higher School formally became the University of Belgrade through the Law on the University from February 27, 1905. In addition to the Philosophy, Law and Electrical Engineering departments, this law introduced the Orthodox Theology and Medical schools.

    In the early 19th century, the studies of law lasted three years and the curriculum included comparative and state (constitutional) law; international law; criminal law and judicial procedure; as well as general subjects. This is how the modern legal education in Serbia emerged in the year 1808. Before enrolling the legal department, it was compulsory to graduate at the philosophy department where the studies lasted two years. So the legal studies lasted a total of five years. Since 1853, the legal education became independent from the studies of philosophy and from 1863 the legal education in Serbia lasted four years.

    The lectures were held by well-known professors who had earned their diplomas in Austria, Germany and France (Jovan Sterija Popović, Josif Pančić, Đura Daničić, and others).

    During the 1850s, the Philosophy (General) Department developed into a particular college. The University of Belgrade’s Faculty of Philosophy is today’s continuation of this department.

    The first academic lecture on electrical engineering in Serbia was held in 1894. Professor Stevan Marković was the first lecturer and founder of the Engineering Department at the Higher School. Only four years later, Professor Marković also established the first Serbian electrical engineering laboratory. Since then, this academic discipline has been studied at the Higher School and the University of Belgrade. The first diplomas in this field were given in 1922.

    20th century

    The University of Belgrade witnessed a massive growth and expansion in the years before the Second World War and especially after the founding of the second Yugoslavia. The first woman graduated from the University of Belgrade’s Law School in 1914.

    In the 1960s and 70s, the University developed into a remarkable regional and international educational institution. Many students from other countries were trained there. In the socialist Yugoslavia, the University was expanded, but it was also exposed to state and ideological influence. It has also been the driving force for the establishment of almost all other universities in today’s Serbia, Montenegro, North Macedonia and several universities in Bosnia and Herzegovina.

    In 1968, its students organized the first mass protest in post-World War II Yugoslavia.

    In the early 1990s the quality of university programs deteriorated as a consequence of the political instability in the country and the subsequent wars of Yugoslavia. There was a lack of financial resources and the quality dropped significantly. During the Milošević government in Serbia, the University had to face external political pressure and the lack of academic and administrative autonomy.

    In the mid-1990s, the University of Belgrade became an internationally recognized center of the political opposition in Serbia. Massive anti-government protests were staged by the Belgrade students and professors. The University’s student organizations (especially “Otpor!”) significantly contributed to overthrowing the government.

    21st century

    Since 2000, the University of Belgrade has taken important steps and has revitalized and improved the facilities and its teaching quality. There have been many reforms in higher education of the country. The University has made great efforts since then to improve the internal structure and has become a signatory of the Bologna declaration. Being one of Europe’s largest universities with an enrollment of nearly 90,000 students, the University broadly cooperates with international academic institutions and is involved in countless bilateral and multilateral academic projects.

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