Free Astronomy Magazine January-February 2024 ARABIC VERSION

small portion of the parent star’s disk. This would yield an inaccurate lower limit of the planet’s diameter. “There was a chance that this system has an unlucky geometry and if that’s the case, we wouldn’t meas- ure the right size. But with Hubble’s capabilities we nailed its diameter,” said Emily Pass of the Harvard-Smith- sonian Center for Astrophysics in Cambridge, Massachusetts. Hubble observations show that the planet makes a normal transit fully across the star’s disk, yielding a true size of only 1.07 times Earth’s diameter. This means the planet is a rocky world, like Earth, with approximately the same surface gravity. But at a sur- face temperature of roughly 260 de- grees Celsius, it is too hot for life as we know it. The planet orbits the star LTT 1445A, which is part of a triple system of three red dwarf stars that is 22 light-years away in the constellation Eridanus. The star has two other re- ported planets that are larger than LTT 1445Ac. A tight pair of two other dwarf stars, LTT 1445B and C, lies about 4.7 billion kilometres away from LTT 1445A, also resolved by Hubble. The alignment of the three stars and the edge-on orbit of the BC pair suggests that everything in the system is coplanar, including the known planets. “Transiting planets are exciting since we can characterise their atmos- pheres with spectroscopy, not only with Hubble but also with the James Webb Space Telescope. Our meas- urement is important because it tells us that this is likely a very nearby ter- restrial planet. We are looking for- ward to follow-on observations that will allow us to better understand the diversity of planets around other stars,” said Pass. “Hubble remains a key player in our characterisation of exoplanets” , added Professor Laura Kreidberg of the Max Planck Institute for Astron- omy in Heidelberg (who was not part of this study). “There are pre- cious few terrestrial planets that are close enough for us to learn about their atmospheres — at just 22 light years away, LTT 1445Ac is right next door in galactic terms, so it’s one of the best planets in the sky to follow up and learn about its atmospheric properties.”    JANUARY-FEBRUARY 2024 ﻘﺎرن ﻟﻜ ﻔ ﺔ ﻣـﺮور ﻮﻛـﺐ ﻫﺬا اﻟﺮﺳﻢ اﻟﺒ ﺎﻧﻲﺳ ﻨﺎر ﻮﻫ ﻧ ﻤـﻲ ـﻢ اﻷرض أﻣـﺎم ﻧ ﻤـﮫ ﺑﺤ . ُﻈﻬـﺮ اﻟﻤﺴﺎر اﻟﺴﻔﻠﻲ اﻟ ﻮﻛـﺐ وﻫـﻮ " ﻣﻤـﺎس " اﻟـﻨ ﻢ . دراﺳـﺔ اﻟﻀـﻮء اﻟﻨـﺎﺗﺞ ﻋـﻦ ﻣﺜـﻞ ﻫـﺬا اﻟﻌﺒـﻮر ﻗـﺪ ﺗـﺆد إﻟــﻰ ﺗﻘــﺪﻳﺮ ﻏــ دﻗﻴــﻖ ﻟــ ـ ﺤ ﻢ اﻟ ﻮﻛـــﺐ ــﮫ ــﺪو أﺻــﻐﺮ ﻣﻤـــﺎ ﻫــﻮ ﻋﻠ ﻣﻤــﺎ ﻳﺠﻌﻠــﮫ ﻳ ﺎﻟﻔﻌــﻞ . ُﻈﻬــﺮ اﻟﻤﺴـــﺎر ــﺔ اﻟﻌﻠــﻮي اﻟﻬﻨﺪﺳـــﺔ اﻟﻤﺜﺎﻟ ـــﺚ ﻌـــ اﻟ ﻮﻛــﺐ اﻟﻘـــ ﺣ ﺮص اﻟ ﺎﻣــﻞ ﻟﻠـــﻨ ﻢ و ﻤﻜـــﻦ ﻟﺪﻗــﺔ ﺗﻠﺴـــ ﻮبﻫﺎﺑـــﻞ اﻟﻔﻀﺎﺋ ﻫﺬﻳﻦ اﻟﺴ ﻨﺎر ﻮﻫ ﻲ اﻟﺘﻤﻴ ﺑ إﻟﻰﻗ ﺎسدﻗﻴﻖ ﻟﻘﻄﺮاﻟ ﻮﻛﺐ ﻣﻤﺎ ﻳﺆد . إن ﻫﺬا اﻷﻣﺮ ﻗﺪ ﻳﺆدي إﱃ ﺗﺤﺪﻳﺪ ﻏـ دﻗﻴـﻖ ﻟﻘﻄﺮ اﻟﻜﻮﻛﺐ . ﻫﻨﺎك اﺣﺘﻤﺎل أن ﻳﻜﻮن ﻟﻬـﺬا ا ﻟﻨﻈﺎم ﻫﻨﺪﺳﺔ ﻏﺮﻳﺒﺔ وإذا ﻛﺎن اﻷﻣﺮ ﻛـﺬﻟﻚ ﻓﻠﻦ ﻧﺘﻤﻜﻦ ﻣﻦ ﻣﻌﺮﻓـﺔ اﻟﺤﺠـﻢ اﻟﺼـﺤﻴﺢ . ــــ ﻗﺎﻟـﺖ إﻳﻤـﻴﲇ ﺑـﺎس ﻣـﻦ ﻣﺮﻛـﺰ ﻫﺎرﻓـﺎرد ﺳﻤﻴﺜﺴﻮﻧﻴ ﺎن ﻟﻠﻔﻴﺰﻳﺎء اﻟﻔﻠﻜﻴﺔ ﰲ ﻛﺎﻣﱪﻳﺪج ﻣﺎﺳﺎ ﺗﺸﻮﺳﺘﺲ " : ﻟﻘﺪ ﺗﻤﻜﻨﺎ ﻣﻦ ﺗﺤﺪﻳﺪ ﻗﻄﺮ ﻫﺬا اﻟﻜﻮﻛﺐ ﺑﻔﻀﻞ ﻗﺪرات ﺗﻠﺴﻜﻮب ." ﻫﺎﺑﻞ ﺗﻈﻬﺮ أرﺻﺎد ﺗﻠﺴـﻜﻮب ﻫﺎﺑـﻞ أن اﻟﻜﻮﻛـﺐ ﻳﻘﻮم ﺑﻌﺒﻮر ﻋﺎدي ﺑﺸﻜﻞ ﻛﺎﻣﻞ ﻋـﱪ ﻗـﺮص اﻟﻨ ﺠﻢ ﻣﻤﺎ ﻳﺆدي إﱃ ﻣﻌﺮﻓﺔ اﻟ اﻟ ﺤﺠﻢ ﺤﻘﻴﻘﻲ اﻟﺬي ﻳﺒﻠﻎ 1.07 ﻣﺮة ﻓﻘﻂ ﻗﻄﺮ اﻷرض وﻫﺬا ﻳﻌﻨﻲ أن اﻟﻜﻮﻛﺐ ﻋﺎﻟﻢ ﺻﺨﺮي ﻣﺜـﻞ اﻷرض ﻟﻪ ﻧﻔﺲ اﻟﺠﺎذﺑﻴﺔ اﻟﺴﻄﺤﻴﺔ ﺗﻘﺮﻳﺒـﺎً وﻟﻜـﻦ ﻋﻨﺪ درﺟﺔ ﺣﺮارة ﺳﻄﺤﻴﺔ ﺗﺒﻠﻎ ﺣـﻮاﱄ 260 درﺟﺔ ﻣﺌﻮﻳﺔ ﻳﻜﻮن اﻟﺠﻮ ﺣﺎر اً ﺟﺪ اً ﻟﺪرﺟﺔ ﻻ ﺗﺴﻤﺢ ﻟ ﻮﺟﻮد ا ﻟﺤﻴﺎة ﻛﻤﺎ ﻧﻌﺮﻓﻬﺎ . ﻳﺪور اﻟﻜﻮﻛﺐ ﺣﻮل اﻟﻨﺠﻢ LTT 1445A وﻫﻮ ﺟﺰء ﻣﻦ ﻧﻈﺎم ﺛﻼﺛﻲ ﻣﻜﻮن ﻣﻦ ﺛﻼ ﺛﺔ ﻧﺠـﻮم ﻗﺰﻣﺔ ﺣﻤﺮاء ﻳﻘﻊ ﻋﲆ ﺑﻌﺪ 22 ﺳﻨﺔ ﺿـﻮﺋﻴﺔ ﰲ ﻛﻮﻛﺒﺔ اﻟﻨﻬﺮ وﻟﻠﻨﺠﻢ ﻛﻮﻛﺒـﺎن آﺧـﺮان ﺗـﻢ اﻹﻋﻼن ﻋﻨﻬﻤﺎ أﻛﱪ ﻣﻦ LTT 1445Ac . ﻳﺒﻌﺪ اﻟﺜﻨـﺎﺋﻲ ﻣـﻦ ﻧﺠﻤـ ﻗـﺰﻣ آﺧـﺮﻳﻦ LTT 1445B و C ﻋﲆ ﻣﺴـﺎﻓﺔ ﺣـﻮاﱄ 4.7 ﻣﻠﻴـﺎر ﻛﻴﻠﻮﻣﱰ ﻣﻦ LTT 1445A واﻟﺬي ﺗﻢ ﺗﺤﺪﻳﺪه أﻳﻀ ﺎً ﺑﻮاﺳﻄﺔ ﺗﻠﺴﻜﻮب . ﻫﺎﺑﻞ ﺗﺸ ﻣﺤﺎذاة اﻟﻨﺠﻮم اﻟﺜﻼﺛﺔ وا ﺪار اﻟﺠﺎﻧﺒﻲ ﻟﻠﺜﻨﺎﺋﻲ BC إﱃ أ ن ﻛﻞ ﳾء ﰲ اﻟﻨﻈﺎم ﻣﺘﺤﺪ ا ﺴﺘﻮى ﺑﻤـﺎ ﰲ ذﻟﻚ اﻟﻜﻮاﻛﺐ ا ﻌﺮوﻓﺔ . " إن اﻟﻜﻮاﻛﺐ اﻟﻌﺎﺑﺮة ﻣﺜ ة ﻟﻼﻫﺘﻤـﺎم ﻷﻧﻨـﺎ ﻧﺴﺘﻄﻴﻊ وﺻﻒ أﻏﻠﻔﺘﻬﺎ اﻟﺠﻮﻳﺔ ﺑﺎﺳـﺘﺨﺪام اﻟﺘﺤﻠﻴﻞ اﻟﻄﻴﻔـﻲ، ﻟـﻴﺲ ﻓﻘـ ﻂ ﺑﺎﺳـﺘﺨﺪام ﺗﻠﺴـﻜﻮب ﻫﺎﺑ ـﻞ وﻟﻜـﻦ أﻳﻀـ ﺎً ﺑﺎﺳـﺘﺨﺪام ﺗﻠﺴﻜﻮب ﺟﻴﻤﺲ وﻳﺐ اﻟﻔﻀﺎﺋﻲ . إن ﻗﻴﺎﺳﻨﺎ ﻣﻬﻢ ﻷﻧﻪ ﻳﺨﱪﻧﺎ أن ﻣـﻦ ا ﺤﺘﻤـﻞ أن ﻳﻜـﻮن ﺎً ﻫﺬا ﻛﻮﻛﺒ ﺻﺨﺮﻳﺎً . اً ﺟﺪ ﺎً ﻗﺮﻳﺒ : " ﺑﺎس ﺖﻗﺎﻟ إﻧﻨﺎ ﻧﺘ ﻄﻠﻊ إﱃ ﻣﺘﺎﺑﻌﺔ اﻷ رﺻـﺎد اﻟﺘـﻲ ﺳﺘﺴـﻤﺢ ﻟﻨـﺎ ﺑﻔﻬـﻢ أﻓﻀـﻞ ﻟﺘﻨـﻮع اﻟﻜﻮاﻛﺐ ﺣﻮل اﻟﻨﺠﻮم اﻷﺧﺮى ." أﺿﺎﻓﺖ اﻟﱪوﻓﻴﺴﻮر ﻟﻮرا ﻛﺮﻳﺪﺑﺮج ﻣﻦ ﻣﻌﻬﺪ ﻣﺎﻛﺲ ﺑﻼﻧﻚ ﻟﻌﻠﻢ اﻟﻔﻠ ﻚ ﰲ ﻫﺎﻳﺪﻟﱪج واﻟﺘﻲ ) ﻟﻢ ﺗﻜﻦ ﺟﺰء اً ﻣـﻦ ﻫـﺬه اﻟﺪراﺳـﺔ ﻳﻈـﻞ »(: ﺗﻠﺴﻜﻮب ﺎً ﻫﺎﺑﻞ ﻻﻋﺒـ ﺎً رﺋﻴﺴـﻴ ﰲ ﺗﻮﺻـﻴﻔﻨﺎ ﻟﻠﻜﻮاﻛﺐ اﻟﻨﺠﻤﻴﺔ « . ﻫﻨﺎك ﻋـﺪد ﻗﻠﻴـﻞ ﻣـﻦ اﻟﻜﻮاﻛـﺐ اﻟﺼـﺨﺮﻳﺔ اﻟﻘﺮﻳﺒﺔ ﺑﻤﺎ ﻓﻴﻪ اﻟﻜﻔﺎﻳﺔ ﺑﺎﻟﻨﺴﺒﺔ ﻟﻨﺎ ﻟﻠﺘﻌﺮف ﻋﲆ أﻏﻠﻔﺘﻬﺎ اﻟ ﺠﻮﻳﺔ ﻋﲆ ﻣﺴـﺎﻓﺔ 22 ﺳـﻨﺔ . ﺿﻮﺋﻴﺔ ﻓﻘﻂ ﻳﻮﺟــﺪ اﻟﻜﻮ ﻛــﺐ LTT 1445Ac ﺑﺠﻮارﻧــﺎ ﻣﺒﺎﴍة ﻣﻦ ا ﺠﺮة، ﻟﺬﻟﻚ ﻓﻬـﻮ أﺣـﺪ أﻓﻀـﻞ اﻟﻜﻮاﻛﺐ اﻟﺘﻲ ﻳﻤﻜـﻦ ﻣﺘﺎﺑﻌﺘﻬـﺎ ﰲ اﻟﺴـﻤﺎء واﻟﺘﻌﺮف ﻋﲆ ﺧﺼﺎﺋﺼﻪ اﻟﺠﻮﻳﺔ . ﻣﺠﻠﺔ FreeAstronomy ﺎﻟﻌﺮ ﺔ 37 - ﻳﻨﺎﻳﺮ ﻓﺒﺮﺍﻳﺮ 2 0 2 4