¿ Astronomy Picture of the Day [1]Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2020 September 16 [2]See Explanation. Clicking on the picture will download the highest resolution version available. Gravel Ejected from Asteroid Bennu Image Credit: [3]NASA's [4]GSFC, [5]U. Arizona, [6]OSIRIS-REx [7]Lockheed Martin Explanation: [8]Why does asteroid Bennu eject gravel into space? No one is sure. [9]The discovery, occurring during several episodes by [10]NASA's visiting [11]ORISIS-REx spacecraft, was unexpected. Leading ejection hypotheses include impacts by Sun-orbiting [12]meteoroids, [13]sudden thermal fractures of internal structures, and the [14]sudden release of a water vapor jet. The [15]featured two-image composite shows an ejection event that occurred in early 2019, with sun-reflecting ejecta seen on the right. Data and [16]simulations show that large gravel typically falls right back to the rotating 500-meter asteroid, while smaller rocks skip around the surface, and the smallest rocks completely escape the low gravity of the Earth approaching, diamond-shaped asteroid. [17]Jets and surface ejection events were thought to be predominantly the domain of comets, responsible for their [18]tails, [19]comas, and later [20]meteor showers on Earth. Robotic OSIRIS-REx arrived at [21]101955 Bennu in late 2018, and is [22]planned to touchdown to collect a surface sample in October 2020. If all goes well, this sample will then be returned to Earth for a [23]detailed analysis during 2023. Bennu was chosen as the destination for OSIRIS-REx in part because its surface shows potential to reveal [24]organic compounds from the [25]early days of [26]our Solar System, compounds that could have been the building blocks for [27]life on Earth. Experts Debate: [28]How will humanity first discover extraterrestrial life? Tomorrow's picture: cycle 25 __________________________________________________________________ [29]< | [30]Archive | [31]Submissions | [32]Index | [33]Search | [34]Calendar | [35]RSS | [36]Education | [37]About APOD | [38]Discuss | [39]> __________________________________________________________________ Authors & editors: [40]Robert Nemiroff ([41]MTU) & [42]Jerry Bonnell ([43]UMCP) NASA Official: Phillip Newman [44]Specific rights apply. [45]NASA Web Privacy Policy and Important Notices A service of: [46]ASD at [47]NASA / [48]GSFC & [49]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2009/BennuEjecting_OsirisRex_1169.jpg 3. https://www.nasa.gov/ 4. https://www.nasa.gov/goddard 5. https://www.lpl.arizona.edu/missions/osiris-rex 6. https://solarsystem.nasa.gov/missions/osiris-rex/in-depth/ 7. https://www.lockheedmartin.com/en-us/products/osiris-rex.html 8. https://www.jpl.nasa.gov/news/news.php?release=2020-174 9. https://www.jpl.nasa.gov/news/news.php?feature=7553 10. https://nasa.gov/ 11. https://www.nasa.gov/osiris-rex 12. https://en.wikipedia.org/wiki/Meteoroid 13. https://youtu.be/-v-II1FPFSU 14. https://apod.nasa.gov/apod/ap151118.html 15. https://www.asteroidmission.org/?attachment_id=15595 16. https://youtu.be/G526VAj0X2c 17. https://apod.nasa.gov/apod/ap171106.html 18. https://apod.nasa.gov/apod/ap200722.html 19. https://spaceplace.nasa.gov/comet-nucleus/en/cometwest_labels.en.jpg 20. https://apod.nasa.gov/apod/ap180808.html 21. https://en.wikipedia.org/wiki/101955_Bennu 22. https://apod.nasa.gov/apod/ap191223.html 23. https://i.kym-cdn.com/photos/images/facebook/001/705/995/a66.png 24. https://en.wikipedia.org/wiki/Organic_compound 25. https://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System 26. https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth/ 27. https://science.nasa.gov/solar-system/big-questions/how-did-life-begin-and-evolve-earth-and-has-it-evolved-elsewhere-solar-system 28. https://apod.nasa.gov/debate/debate100th.html 29. https://apod.nasa.gov/apod/ap200915.html 30. https://apod.nasa.gov/apod/archivepix.html 31. https://apod.nasa.gov/apod/lib/apsubmit2015.html 32. https://apod.nasa.gov/apod/lib/aptree.html 33. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 34. https://apod.nasa.gov/apod/calendar/allyears.html 35. https://apod.nasa.gov/apod.rss 36. https://apod.nasa.gov/apod/lib/edlinks.html 37. https://apod.nasa.gov/apod/lib/about_apod.html 38. http://asterisk.apod.com/discuss_apod.php?date=200916 39. https://apod.nasa.gov/apod/ap200917.html 40. http://www.phy.mtu.edu/faculty/Nemiroff.html 41. http://www.phy.mtu.edu/ 42. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 43. http://www.astro.umd.edu/ 44. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 45. https://www.nasa.gov/about/highlights/HP_Privacy.html 46. https://astrophysics.gsfc.nasa.gov/ 47. https://www.nasa.gov/ 48. https://www.nasa.gov/centers/goddard/ 49. http://www.mtu.edu/