Free Astronomy Magazine July-August 2025 ARABIC VERSION

that an abiotic origin cannot be ruledout.DMSwasproducedinthe laboratorybysimulatingtheatmos- phereoftheprimordialEarthwith- out the need for living organisms being present (N.W. Reed et al., 2024), and it has also been discov- ered in an interstellar molecular cloudthankstotworadiotelescopes (M.Sanz-Novoetal.,2025),anenvi- ronmentnotreallysuitableforlife, however one wants to imagine it. These recent works cast doubt on thereliabilityofDMS(andDMDS)as astrongbiosignature.K2-18bisnot well enough known to establish whethertheDMSperhapsdetected in its atmosphere was produced by life forms. It is also not known whether in an atmosphere of that type, rich in hydrogen and meth- ane, the lifetime of that molecule is comparable to that recorded in the Earth’s atmosphere. Ultimately, what is a valid biosignature on Earth may not be so elsewhere. As if the above were not enough, weaddthatiftheoriginoftheDMS onK2-18bwasbiotic,weshouldsi- multaneously have detected other compoundsandby-productsderiv- ing from the decomposition of the raw materials used to produce it, such as H 2 S (hydrogen sulfide), but there is no trace of that chemical corollary. Ifitweretrue,itwould be incredible There are many good reasons not to believe in the biotic origin of the DMS on K2-18 b, but however small the chances that microalgae or sim- ilar organisms actually exist on that planet, those chances are not zero percent. We can, as one possibility, consider this chance of life in the context of the “mediocrity prin- ciple,” which proposes that the properties of a randomly-selected sample are likely to represent prop- erties of the larger set of samples. Having “neighbors” just 124 light yearsawaymightreasonablylead totheconclusionthattheMilky Way is overflowing with life. Withina radius of 124 years around the Earth, there are about 10,000 stars (some say half, some say double). Since wedo notlivein aparticularly privileged region, we can assume thatifthereareatleasttwoplanets forevery10,000starsonwhichlife thrives,thenintheentireMilkyWay, which includes about 200 billion stars(somesayhalf,somesaydou- ble), life should exist on about 40 millionplanets,oronabout10mil- lion if we adopt the most unfavor- ableparametersfortheprojection. This would not be an overly opti- mistic scenario because we know thatthevastmajorityofstarshave a planetary system, and we also know that sub-Neptunes like K2-18 barethemostnumerousexoplanets discovered so far in the galaxy. So the Milky Way is teeming with life? Sixty-five years of SETI research tellsusthatrealitycanhardlybethis in terms of intelligent life. The ob- servationswiththeJWSTonlyletus nowbegintodevelopmodelstoex- plaintherealityofexoplanetaryat- mospheres and conditions. Confi- dentassessmentofmerelythe plau- sible existence of life on an exo- planet based on these observations will only come with many years of hypotheses, model development, andcriticalscientificreview.     JULY-AUGUST2025 أُﻧ ـﺘﺞ ﺛﻨ ـﺎﺋﻲ ﻣﻴﺜﻴــﻞ اﻟﻜﱪﻳﺘﻴ ـﺪ ﰲ ا ﺨﺘ ـﱪ ﺑﻤﺤﺎﻛﺎة اﻟﻐﻼف اﻟﺠﻮي ﻟﻸرض اﻟﺒﺪاﺋﻴﺔ دون اﻟﺤﺎﺟﺔ إﱃ وﺟﻮد ﻛﺎﺋﻨﺎت ﺣﻴﺔ ﻛﻤﺎ اﻛﺘُﺸ ﻒ ﰲ ﺳﺤﺎﺑﺔ ﺟﺰﻳﺌﻴﺔ ﺑ ﻧﺠﻤﻴﺔ ﺑﻔﻀﻞ ﺗﻠﺴﻜﻮﺑ رادﻳﻮﻳ وﻫﻲ ﺑﻴﺌﺔ ﻏ ﻣﻨﺎﺳﺒﺔ ﻟﻠﺤﻴﺎة ﻣﻬﻤﺎ ﻛﺎن ﺗﺼﻮرﻫﺎ . ﺗُﻠﻘﻲ ﻫﺬه اﻷﻋﻤﺎل اﻟﺤﺪﻳﺜﺔ ﺑﻈﻼل ﻣﻦ اﻟﺸﻚ ﻋﲆ ﻣﻮﺛﻮﻗﻴﺔ ﺛﻨﺎﺋﻲ ﻣﻴﺜﻴﻞ اﻟﻜﱪﻳﺘﻴﺪ ﺛﻨـﺎﺋﻲ و ﻣﻴﺜﻴﻞ ﺛﻨﺎﺋﻲ اﻟﻜﱪﻳﺘﻴﺪ ﻛﻌﻼﻣﺔ ﺣﻴﻮﻳﺔ ﻗﻮﻳﺔ . ﻻ ﻳﻌﺮف اﻟﻜﻮﻛﺐ K2-18bi اً ﺟﻴﺪ ﺑﻤﺎ ﻳﻜﻔـﻲ ﻟﺘﺤﺪﻳﺪ ﻣﺎ إذا ﻛﺎن ﺛﻨـﺎﺋﻲ ﻣﻴﺜﻴـﻞ اﻟﻜﱪﻳﺘﻴـﺪ اﻟﺬي رﺑﻤﺎ اﻛﺘُﺸﻒ ﰲ ﻏﻼﻓﻪ اﻟﺠﻮي ﻗﺪ أﻧﺘﺠﺘﻪ أﺷﻜﺎل اﻟﺤﻴﺎة . ﻛﻤﺎ أﻧﻪ ﻣﻦ ﻏ ا ﻌـﺮوف ﻣـﺎ إذا ﻛﺎن ﻋﻤﺮ ﻫﺬا اﻟﺠﺰيء ﰲ ﻏﻼف ﺟﻮي ﻣـﻦ ﻫـﺬا اﻟﻨـ ﻮع اﻟﻐﻨـﻲ ﺑﺎﻟﻬﻴـﺪروﺟ وا ﻴﺜـﺎن ﻳ ﻀﺎﻫﻲ اﻟﻌﻤـﺮ ا ﺴـﺠﻞ ﰲ اﻟﻐـﻼف اﻟﺠـﻮي ﻟﻠﻜﺮة اﻻرﺿﻴﺔ . ﰲ اﻟﻨﻬ ﺎﻳﺔ، ﻣﺎ ﻳﻌﺘﱪ ﻋﻼﻣﺔ ﺣﻴﻮﻳﺔ ﺻـﺤﻴﺤﺔ ﻋﲆ اﻷرض ﻗﺪ ﻻ ﻳﻜﻮن ﻛﺬﻟﻚ ﰲ ﻣﻜﺎن آﺧـﺮ . وﻛﺄن ﻣﺎ ﺳﺒﻖ ﻟﻢ ﻳﻜﻦ ﻛﺎﻓﻴﺎً ﻧﻀـﻴﻒ أﻧـﻪ إذا ﻛﺎن أﺻﻞ ﺛﻨﺎﺋﻲ ﻣﻴﺜﻴﻞ اﻟﻜﱪﻳﺘﻴﺪ ﻋﲆ اﻟﻜﻮﻛﺐ K2-18b ﺎً ﺣﻴﻮﻳ ﻛـﺎن ﻳﻨﺒﻐـﻲ ﻟﻨـﺎ ﰲ اﻟﻮﻗـﺖ ﻧﻔﺴﻪ اﻛﺘﺸﺎف ﻣﺮﻛﺒـﺎت أﺧـﺮى وﻣﻨﺘﺠـﺎت ﺛﺎﻧﻮﻳـﺔ ﻣﺸـﺘﻘﺔ ﻣـﻦ ﺗﺤﻠـﻞ ا ـﻮاد اﻟﺨـﺎم ا ﺴــﺘﺨﺪﻣﺔ ﰲ إﻧﺘﺎﺟـــﻪ ﻣﺜ ــﻞ ﻛﱪﻳﺘﻴ ــﺪ اﻟﻬﻴـﺪروﺟ وﻟﻜــﻦ ﻻ ﻳﻮﺟـﺪ أي أﺛــﺮ ﻟﻬـﺬه ـــــــــــــــــــــــــــــــــــــ ا ﺮﻛﺒﺎت ا ﺼﺎﺣﺒﺔ . ﻫﺬا اﻟﻐﻴﺎب ﻳﺜ ﺷـﻜﻮﻛﺎً ﺟﺪﻳﺔ ﺣﻮل اﻟﻔﺮﺿﻴﺔ اﻟﺤﻴﻮﻳـﺔ ﻣﻤـﺎ ﻳـﺪﻓﻌﻨﺎ ﻟﻠﺒﺤﺚ ﻋﻦ ﺗﻔﺴ ات ﻏ ﻋﻀـﻮﻳﺔ ﻣﺤﺘﻤﻠـﺔ ﻟﻮﺟـﻮد ﺛﻨـﺎﺋﻲ ﻣﻴﺜﻴـﻞ اﻟﻜﱪﻳﺘﻴ ـﺪ ﰲ ﻏــﻼف اﻟﻜﻮﻛﺐ K2-18b اﻟﺠﻮي . ﻟﻮ ﺎن اﻹﻛﺘﺸﻒﺻﺤﻴﺤﺎً ﻟ ﺎن اً أﻣﺮ اﺳﺘﺜﻨﺎﺋ ﺎً ﻫﻨﺎك اﻟﻌﺪﻳﺪ ﻣـﻦ اﻷﺳـﺒﺎب اﻟﻮﺟﻴﻬـﺔ ﻟﻌـﺪم اﻻﻋﺘﻘـﺎد ﺑﺎﻷﺻـﻞ اﻟﺤﻴــﻮي ﻟ ﺜﻨـﺎﺋﻲ ﻣﻴﺜﻴـﻞ اﻟﻜﱪﻳﺘﻴ اﻟ ﻋﲆ ﺪ ﻜﻮﻛﺐ K2-18 b وﻟﻜﻦ ﻣﻬﻤﺎ ﻛﺎﻧﺖ اﺣﺘﻤﺎﻻت وﺟﻮد اﻟﻄﺤﺎﻟﺐ اﻟﺪﻗﻴﻘـﺔ أو اﻟﻜﺎﺋﻨﺎت اﻟﺤﻴ ﺔ ا ﻤﺎﺛﻠﺔ ﻋـﲆ ذﻟـﻚ اﻟﻜﻮﻛـﺐ ﺿﺌﻴﻠﺔ ﻓﺈن ﻫﺬه اﻻﺣﺘﻤﺎﻻت ﻟﻴﺴـﺖ ﺻـﻔﺮ . اً ﻳﻤﻜﻨﻨﺎ ﻛﺄﺣﺪ اﻻﺣﺘﻤﺎﻻت اﻟﻨﻈﺮ ﰲ اﺣﺘﻤﺎﻟﻴـﺔ وﺟﻮد اﻟ ﺤﻴﺎة ﻫﺬه ﰲ ﺳﻴﺎق " ﻣﺒﺪأ ا ﺘﻮﺳـﻂ " اﻟـﺬي ﻳﻘـ ﱰح أن ﺧﺼـﺎﺋﺺﻋﻴﻨـﺔ ﻣﺨﺘـﺎرة ﻋﺸـﻮاﺋﻴﺎ ﻣـﻦ ا ـﺮﺟﺢ أن ﺗ ﻤﺜـﻞ ﺧﺼـﺎﺋﺺ ﻣﺠﻤﻮﻋﺔ اﻟﻌﻴﻨﺎت اﻷﻛﱪ . إن ﻋـﲆ " ﺟ ان " وﺟﻮد ﻣﺴـﺎﻓﺔ 124 ﺳـﻨﺔ ﺿﻮﺋﻴﺔ ﻓﻘﻂ ﻗـﺪ ﻳـﺆدي ﺑﺸـﻜﻞ ﻣﻌﻘـﻮل إﱃ اﺳﺘﻨﺘﺎج أن ﻣﺠﺮة درب اﻟﺘﺒﺎﻧﺔ ﺗﺰﺧﺮ ﺑﺎﻟﺤﻴﺎة . ﰲ داﺋﺮة ﻧﺼﻒ ﻗﻄﺮﻫـﺎ 124 ﺳـﻨﺔ ﺿـﻮﺋﻴﺔ ﺣ ـﻮل اﻷرض ﻳﻮﺟ ـﺪ ﺣ ـﻮاﱄ 10,000 ﻧﺠــﻢ ـــــــــــــــــــــــــــــــــــــ ﻳﻘﻮل اﻟﺒﻌﺾ اﻟﻨﺼﻒ واﻟﺒﻌﺾ اﻵﺧﺮ ﺿﻌﻔﻬﺎ . ﺑﻤﺎ أﻧﻨﺎ ﻻ ﻧﻌﻴﺶ ﰲ ﻣﻨﻄﻘﺔ ذات اﻣﺘﻴﺎز ﺧﺎص ﻳﻤﻜﻨﻨﺎ اﻓﱰاض أﻧـﻪ إذ ا و ﺟـﺪ ﻛﻮﻛﺒـﺎن ﻋـﲆ اﻷﻗﻞ ﻟﻜﻞ 10,000 ﻧﺠﻢ ﺗﺰدﻫﺮ ﻋﻠﻴﻬﺎ اﻟﺤﻴـﺎة ﻓﻔﻲ ﻣﺠﺮة درب اﻟﺘﺒﺎﻧﺔ ﺑﺄﻛﻤﻠﻬﺎ واﻟﺘﻲ ﺗﻀﻢ ﺣﻮاﱄ 200 ﻣﻠﻴﺎر ﻧﺠﻢ ﻳﻘﻮل ) اﻟﺒﻌﺾ ﻧﺼﻔﻬﺎ وﻳﻘـﻮل اﻟـﺒﻌﺾﺿـ ( ﻌﻔﻬﺎ ﻳﺠـﺐ أن ﺗﻮﺟـﺪ اﻟﺤﻴﺎة ﻋﲆ ﺣﻮاﱄ 40 ﻣﻠﻴﻮن ﻛﻮﻛـﺐ أو ﻋـﲆ ﺣﻮاﱄ 10 ﻣﻼﻳـ إذا اﻋﺘﻤـﺪﻧﺎ أﻗـﻞ ا ﻌـﺎﻳ ﻤﺔ ﻣﻼﺋ ﻟﻠﺘﻘﺪﻳﺮ . ﻟﻦ ﻳﻜﻮن ﻫﺬا ﺳﻴﻨﺎرﻳﻮ ﻣﺘﻔﺎﺋﻼً ﺑﺸﻜﻞ ﻣﻔﺮط ﻷﻧﻨﺎ ﻧﻌﻠﻢ أن اﻟﻐﺎﻟﺒﻴﺔ اﻟﻌﻈﻤﻰ ﻣﻦ اﻟﻨﺠﻮم ﻟﻬﺎ ﻧﻈـﺎم ﻛـﻮﻛﺒﻲ وﻧﻌﻠ ـﻢ أﻳﻀـ ﺎً أن اﻟﻜﻮاﻛ ـﺐ اﻟﻔﺮﻋﻴﺔ ﻟﻨﺒﺘﻮن ﻣﺜﻞ اﻟﻜﻮﻛﺐ K2-18b ﻫـﻲ أﻛﱪ ﻋﺪد ﻣﻦ اﻟﻜﻮاﻛـﺐ اﻟﻨﺠﻤﻴـﺔ ا ﻜﺘﺸـﻔﺔ ﺣﺘﻰ اﻵن ﰲ ا ﺠﺮة . اً إذ ﻣﺠﺮة ﻫﻞ درب اﻟﺘﺒﺎ ﻧـﺔ ﺗﺰﺧـﺮ ﺑﺎﻟﺤﻴـﺎة؟ ﺧﻤﺴﺔ وﺳﺘﻮن ﻋﺎﻣ ﺎً ﻣﻦ أﺑﺤـﺎث ﻣــﴩوع اﻟﺒﺤـﺚ ﻋـﻦ ذﻛـﺎء ﺧـﺎرج اﻷرض ( ﺳـﻴﺘﻲ ) ﺗﺨﱪﻧﺎ أن اﻟﻮاﻗﻊ ﻗﺪ ﻻ ﻳﻜﻮن ﻛﺬﻟﻚ ﻣﻦ ﺣﻴﺚ اﻟﺤﻴﺎة اﻟﺬﻛﻴﺔ . دﻋﻮﻧ ﺎ اﻵن ﻧﺒﺪأ ﺑﺘﻄﻮﻳﺮ ﻧﻤﺎذج ﻟﺘﻔ ﺴ ﺣﻘﻴﻘـﺔ أﺟـﻮاء اﻟﻜﻮاﻛـﺐ اﻟ ﻨﺠﻤﻴـﺔ وﻇﺮوﻓﻬﺎ وﻟﻦ ﻳﺘﺄﺗﻰ اﻟﺘﻘﻴﻴﻢ اﻟﻮاﺛﻖ ﻻ ﺣﺘﻤﺎﻟﻴﺔ وﺟﻮد ﺣﻴﺎة ﻋﲆ ﻛﻮﻛﺐ ﻧﺠﻤﻲ ﺑﻨﺎءً ﻋﲆ ﻫـﺬه ا ﻷرﺻﺎد إﻻ ﺑﻌﺪ ﺳﻨﻮات ﻃﻮﻳﻠﺔ ﻣـﻦ ﺗﻄـﻮﻳﺮ اﻟﻨﻤﺎذج وا ﺮاﺟﻌﺔ اﻟﻌﻠﻤﻴﺔ اﻟﻨﻘﺪﻳﺔ . ﻳﻮﻟﻴﻮ - ﺃﻏﺴﻄﺲ 2 0 2 5