Free Astronomy Magazine July-August 2025 ARABIC VERSION

piecesfromthatbreakupclumpto- gethertoformnew,looselyheld-to- gether bodies. On the surfaces of theserubble-pileasteroids,weoften seelargeboulders—someaslargeas ~60meters.At50-60metersinsize, YR4 falls into this size range, sug- gestingitcouldhavebeenaboulder thatoncesatonthesurfaceofa largerrubble-pileasteroid.Scientists rely on the Yarkovsky Effect to ex- plainandpredicttheorbitsofaster- oids. There is a subtle force that happens when an asteroid absorbs sunlight and then re-emits that energy as heat. That heat, in the form of infrared light, pushes back slightlyontheasteroid,slowly changing its orbit. How strongly an asteroidrespondstothiseffectde- pends on its thermal inertia – how quicklyitheatsupandcoolsdown. Small, 50-meter-sized asteroids, like YR 4 ,mayhavelowthermalinertia, whichsuggeststhey’remadeof solidrock.Thisdiffersfromlarger, rubble-pileasteroids,whichtendto ﻣﺠﻠﺔ FreeAstronomy ﺎﻟﻌﺮ ﺔ 27 ﺗﺘﺠﻤﻊ اﻟﻘﻄـﻊ اﻟ ﻨﺎﺗﺠـﺔ ﻋـﻦ ﻫـﺬا اﻟﺘﻔﻜـﻚ ﻟﺘﺸﻜﻞ أﺟﺴﺎﻣ ﺎً ﺟﺪﻳـﺪة ﻣﺘﻤﺎﺳـﻜﺔ ﺑﺸـﻜﻞ ﻓﻀـﻔﺎض ﻋـ . ﲆ أﺳـﻄﺢ ﻫـﺬه اﻟﻜﻮﻳﻜﺒـﺎت ا ﺤﻄﻤﺔ ﺎً ﺒﻏﺎﻟ ﻣﺎ ﻧﺮى ﺻﺨﻮر اً ﻛﺒ ة ﺑﻌﻀﻬﺎ ﻳﺼﻞ ﺣﺠﻤﻪ إﱃ ﺣﻮاﱄ 60 . اً ﻣـﱰ ﻋﻨـﺪ ﺣﺠـﻢ ﻳﱰاوح ﺑ 50 و 60 اً ﻣﱰ ﻳﻘـﻊ YR4 ﺿـﻤﻦ ﻫﺬا اﻟﻨﻄﺎق اﻟﺤﺠﻤﻲ ﻣﻤﺎ ﻳﺸ إﱃ أﻧﻪ رﺑﻤـﺎ ﻛﺎن ﺻﺨﺮة اﺳﺘﻘﺮت ﰲ وﻗـﺖ ﺳـﺎﺑﻖ ﻓـﻮق ﺳﻄﺢ ﻛﻮﻳﻜﺐ ﺣُﻄﺎم أﻛﱪ . ﻳﻌﺘﻤـﺪ اﻟﻌﻠﻤـﺎء ﻛﺒ ﻛﻮﻳﻜﺐ ﻣﻦ اﻟﺤﻄﺎم . ﻳﻌﺘﻤﺪ اﻟﻌﻠﻤﺎء ﻋﲆ ﺗــﺄﺛ ﻳﺎرﻛﻮﻓﺴــﻜﻲ ﻟﺘﻔﺴـــ ﻣــﺪارات اﻟﻜﻮﻳﻜﺒﺎت اﻷﴎع واﻟﺘﻨﺒﺆ ﺑﻬﺎ . ﻫﻨـﺎك ﻗـﻮة ﺧﻔﻴﺔ ﺗﺤﺪث ﻋﻨ ﺪﻣﺎ ﻳﻤﺘﺺ اﻟﻜﻮﻳﻜـﺐ ﺿـﻮء اﻟﺸﻤﺲ ﺛﻢ ﻳ ﻌﻴﺪ إﺻﺪار ﺗﻠﻚ اﻟ ﻄﺎﻗﺔ ﻋﲆ ﺷﻜﻞ . ﺣﺮارة ﻫﺬه اﻟﺤﺮارة ﻋﲆ ﺷﻜﻞ ﺿـﻮء ﺗﺤـﺖ أﺣﻤﺮ ﺗﺪﻓﻊ اﻟﻜﻮﻳﻜﺐ ﻟﻠﺨﻠـﻒ ﻗﻠـﻴﻼً ﻣ ﻐـ ةً ﻣﺪاره ﺑﺒﻂء . ﺗﻌﺘﻤﺪ ﻗﻮة اﺳﺘﺠﺎﺑﺔ اﻟﻜﻮﻳﻜـﺐ ﻟﻬﺬا اﻟﺘﺄﺛ ﻋﲆ ﻗﺼﻮره اﻟﺬاﺗﻲ اﻟﺤﺮاري أي - ﻟﻬﺬا اﻟ ﺘﺄﺛ ﻋﲆ ﻗﺼﻮره اﻟﺬاﺗﻲ اﻟﺤـﺮاري أي ﴎﻋــﺔ ﺗﺴــﺨﻴﻨﻪ وﺑﺮودﺗــﻪ . ﻗــﺪ ﻳﻜــﻮن ﻟﻠﻜﻮﻳﻜﺒﺎت اﻟﺼﻐ ة اﻟﺘﻲ ﻳﺒﻠـﻎ ﺣﺠﻤﻬـﺎ 50 ﻣﱰاً ﻣﺜﻞ YR4 اﻧﺼﻬﺎ ر ﺣﺮاري ﻣﻨﺨﻔﺾ ﻣﻤﺎ ﻳﺸ إﱃ أﻧﻬﺎ ﻣﻜﻮﻧﺔ ﻣﻦ ﺻﺨﻮر ﺻﻠﺒﺔ وﻫـﺬا ﻳﺨﺘﻠﻒ ﻋﻦ اﻟﻜﻮﻳﻜﺒﺎت اﻷﻛﱪ ﺣﺠﻤـﺎً واﻟﺘـﻲ ﺗﻤﻴﻞ إﱃ أن ﺗﻜﻮن أﺳـﻄﺤﻬﺎ ﻣﻐﻄـﺎة ﺑﻤـﻮاد ﻓﻀﻔﺎﺿﺔ واﻧﺼﻬﺎر ﺣﺮاري أﻋﲆ . رﺳـــــﻢ ﺗﺨ ﻠـــــﻲ ﻟﻠ ﻮ ﻜـــــﺐ 2024 YR4 اﻟــــــﺬ ﻌ ﻣﺪار اﻷرضواﺗﺠﺎﻫﮫ ﻣﺪروس ﺪﻗﺔ . [W.M.KeckObs./AdamMakarenko] ﻳﻮﻟﻴﻮ - ﺃﻏﺴﻄﺲ 2 0 2 5