Free Astronomy Magazine January-February 2024 ARABIC VERSION

on a paper published in the Astro- physical Journal Letters . “We knew from Hubble observations that there must be aerosols – tiny particles mak- ing up clouds or haze – in WASP-17 b’s atmosphere, but we didn’t expect them to be made of quartz.” Silicates (minerals rich in silicon and oxygen) make up the bulk of Earth and the Moon as well as other rocky objects in our solar system, and are extremely common across the gal- axy. But the silicate grains previously detected in the atmospheres of ex- oplanets and brown dwarfs appear to be made of magnesium-rich sili- cates like olivine and pyroxene, not quartz alone – which is pure SiO 2 . The result from this team, which also includes researchers from NASA’s Ames Research Center and NASA’s Goddard Space Flight Center, puts a new spin on our understanding of how exoplanet clouds form and evolve. “We fully expected to see magnesium silicates,” said co-au- thor Hannah Wakeford, also from the University of Bristol. “But what we’re seeing instead are likely the building blocks of those, the tiny ‘seed’ particles needed to form the larger silicate grains we detect in cooler exoplanets and brown dwarfs.” With a volume more than seven times that of Jupiter and a mass less than one-half of Jupiter, WASP-17 b is one of the largest and puffiest known exoplanets. This, along with its short orbital period of just 3.7 Earth-days, makes the planet ideal for transmission spectroscopy: a technique that involves measuring the filtering and scattering effects of a planet’s atmosphere on starlight. JANUARY-FEBRUARY 2024 ﻣﺠﻠﺔ FreeAstronomy ﺎﻟﻌﺮ ﺔ 23 ُﻈﻬــﺮ ﻫــﺬا اﻟﺮﺳــﻢ اﻟﺘﺨ ﻠــﻲ اﻟﺸــ ﻞ اﻟــﺬ ــــــﮫ اﻟ ﻮﻛــــــﺐ ــــــﺪو ﻋﻠ ﻤﻜــــــﻦ أن ﻳ اﻟﻨ ﻤــــــﻲ WASP-17 b ﺑﺮﻳﺴﺘﻮل ﰲ ا ﻤﻠﻜﺔ ا ﺘﺤ ﺪة وا ﺆﻟـﻒ اﻷول ﰲ ورﻗـــﺔ ﺑﺤﺜﻴـــﺔ ﻣﻨﺸـــﻮرة ﰲ ﻣﺠﻠـــﺔ Astrophysical Journal Letters " . ﻟﻘــﺪ ﺷﻌﺮﻧﺎ ﺑﺴﻌﺎدة ﻏـﺎﻣﺮة ﻓـﻨﺤﻦ ﻋﻠﻤﻨـﺎ ﻣـﻦ ارﺻﺎد ﺗﻠﺴﻜﻮب ﻫﺎﺑﻞ أﻧﻪ ﻻ ﺑـﺪ ﻣـﻦ وﺟـﻮد ﻫﺒﺎء ﺟﻮي - وﻫﻲ ﺟﺰﻳﺌﺎت ﺻـﻐ ة ﺗﺸـﻜﻞ اﻟﺴﺤﺐ أو اﻟﻀﺒﺎب - ﰲ اﻟﻐﻼف اﻟﺠـﻮي ﻟــ اﻟﺴـﺤﺐ أو اﻟﻀـﺒﺎب - ﰲ اﻟﻐـﻼف اﻟﺠــﻮي ﻟﻠﻜﻮﻛﺐ WASP-17 b ﻟﻜﻨﻨـﺎ ﻟـﻢ ﻧﺘﻮﻗـﻊ أن ﺗﻜﻮن ﻣﺼﻨﻮﻋﺔ ﻣﻦ اﻟﻜﻮارﺗﺰ ." ﺗﺸــﻜﻞ اﻟﺴــﻴﻠﻴﻜﺎت ) ا ﻌ ــﺎدن اﻟﻐﻨﻴـــﺔ ﺑﺎﻟﺴﻴﻠﻴﻜﻮن واﻷﻛﺴﺠ ( اﻟﺠﺰء اﻷﻛـﱪ ﻣـﻦ اﻷرض واﻟﻘﻤــﺮ ﺑﺎﻹﺿــﺎﻓﺔ إﱃ اﻷﺟﺴــﺎم اﻟﺼﺨﺮﻳﺔ اﻷﺧﺮى ﰲ ﻧﻈﺎﻣﻨﺎ اﻟﺸ ﻤﴘـ وﻫﻲ ﺷﺎﺋﻌﺔ ﻟﻠﻐﺎﻳﺔ ﰲ ﺟﻤﻴﻊ أﻧﺤﺎء ا ﺠـﺮة وﻟﻜـﻦ ﻳﺒ ـﺪو أن ﺣﺒﻴﺒــﺎت اﻟﺴــﻴﻠﻴﻜﺎت اﻟﺘــﻲ ﺗــﻢ اﻛﺘﺸﺎﻓﻬﺎ ﺳﺎﺑﻘ ﺎً ﰲ أﺟﻮاء اﻟﻜﻮاﻛﺐ اﻟﻨﺠﻤﻴﺔ واﻷﻗﺰام اﻟﺒﻨﻴﺔ ﻣﺼﻨﻮﻋﺔ ﻣﻦ ﺳﻴﻠﻴﻜﺎت ﻏﻨﻴﺔ ﺑﺎ ﻐﻨ ﻴﺴﻴﻮم ﻣﺜـﻞ اﻷوﻟﻴﻔـ واﻟﺒ وﻛﺴـ وﻟﻴﺲ اﻟﻜﻮارﺗﺰ وﺣﺪه - وﻫﻮ SiO2 اﻟﻨﻘﻲ . إن اﻟﻨﺘﻴﺠ ﺔ اﻟﺘﻲ ﺗﻮﺻﻞ إﻟﻴﻬـﺎ ﻫـﺬا اﻟﻔﺮﻳـﻖ واﻟﺬي ﻳﻀﻢ أﻳﻀ ﺎً ﺑﺎﺣﺜ ﻣﻦ ﻣﺮﻛـﺰ أﺑﺤـﺎث أﻣـﻴﺲ وﻣﺮﻛـﺰ ﺟـﻮ دارد ﻟـﺮﺣﻼت اﻟﻔﻀـﺎء اﻟﺘﺎﺑﻌ ﻟﻨﺎﺳﺎ ﺗﻀﻊ ﻓﻜﺮة ﺟﺪﻳﺪة ﻋﲆ ﻓﻬﻤﻨﺎ ﻟﻜﻴﻔﻴـﺔ ﺗﺸـﻜﻞ وﺗﻄـﻮر ﻏﻴ ـﻮم اﻟﻜﻮاﻛ ـﺐ اﻟﻨﺠﻤﻴـﺔ . ﻗﺎﻟـ ﺖ ا ﺆﻟﻔـﺔ ا ﺸـﺎرﻛﺔ ﻫﺎﻧـﺎ وﻳﻜﻔﻮرد ﻣﻦ ﺟﺎﻣﻌﺔ ﺑﺮﻳﺴﺘﻮل أﻳﻀًﺎ " : ﻛﻨـﺎ ﻧﺘﻮﻗﻊ ﺗﻤﺎﻣ ر ﺎً ؤﻳﺔ ﺳﻴﻠﻴﻜﺎت ا ﻐﻨﻴﺴﻴﻮم ﻟﻜﻦ ﻣﺎ ﻧﺮاه ﻫﻮ ﻋﲆ اﻷرﺟﺢ اﻟﻠﺒﻨـﺎت اﻷﺳﺎﺳـﻴﺔ ﻟﺘﻠﻚ اﻟﺠﺴﻴﻤﺎت وﻫـﻲ ﺟﺰﻳﺌـﺎت اﻟﺒـﺬور " " اﻟﻼزﻣﺔ ﻟﺘﺸ ﻜﻴﻞ ﺣﺒﻴﺒﺎت اﻟﺴﻴﻠﻴﻜﺎت اﻷﻛـﱪ ﺎً ﺣﺠﻤ اﻟﺘﻲ ﻧﻜﺘﺸﻔﻬﺎ ﰲ اﻟﻜﻮاﻛـﺐ اﻟﻨﺠﻤﻴـﺔ اﻟﺒﺎردة واﻷﻗﺰام اﻟﺒﻨﻴﺔ ." ﺑ ﺤﺠﻢ ﻳﺰﻳﺪ ﻋﻦ ﺳﺒﻌﺔ أﺿﻌﺎف ﺣﺠﻢ ﻛﻮﻛﺐ ا ﺸﱰي وﻛﺘﻠﺘﻪ أﻗﻞ ﻣﻦ ﻧﺼﻒ ﻛﺘﻠﺔ ا ﺸﱰي ﻳﻌﺪ WASP-17 b اً واﺣﺪ ﻣﻦ أﻛـﱪ اﻟﻜﻮاﻛـﺐ اﻟﻨﺠﻤﻴﺔ ا ﻌﺮوﻓﺔ وأﻛﺜﺮﻫﺎ اﻧﺘﻔﺎﺧـﺎً إﺿـﺎﻓﺔ ا ﺗﻪ ﻟﻔﱰ ﺪارﻳﺔ اﻟﻘﺼ ة اﻟﺒﺎﻟﻐـﺔ 3.7 ﺎً ﻳﻮﻣـ أرﺿﻴ ﺎً ﺗ ﻓﻘﻂ ﺠﻌﻞ اﻟﻜﻮﻛﺐ ﻣﺜﺎﻟﻴـ ﺎ ﻟﻠﺘﺤﻠﻴـﻞ اﻟﻄﻴﻔﻲ ﻟﻺرﺳﺎل : وﻫﻲ ﺗﻘﻨﻴﺔ ﺗﺘﻀﻤﻦ ﻗﻴﺎس ﺗﺄﺛ ات اﻟﱰﺷﻴﺢ واﻟﺘﺸﺘﺖ ﻟﻠﻐـﻼف اﻟﺠـﻮي ﻟﻠﻜﻮﻛ ﺐ ﻋﲆ ﺿﻮء اﻟﻨﺠﻮم . ﻳﻨﺎﻳﺮ ﻓﺒﺮﺍﻳﺮ 2 0 2 4