17:15 〜 18:30
[MIS02-P04] Evaluation of cosmic ray from nearby supernova
キーワード：宇宙線、大気イオン化、宇宙線の拡散近似
It is suggested that strong cosmic ray from nearby supernova had influenced the past Earth environment including biota significantly. We used diffusion approximation model which was proposed by Mellot et al.(2017) and evaluated cosmic-ray flux spectrum from nearby supernova and atmospheric ionization rates which is number of ions produced at each altitude. It was confirmed that the similar results to the original paper ones were obtained. Additionally, we changed the distance between Earth and nearby supernova, which is a parameter r in the equation of cosmic-ray density at earth, and calculated the time that is neceaary for cosmic ray intensity at earth to return to the present one.
As the latest case of nearby supernova which influenced earth environment, Maiz-Apellaniz of Johns Hopkins University discovered that the supernovae belonging to Scorpius-Centaurus OB association in Gould's Belt approached solar system about 2.6Ma and suggested that it is thought to be a cause of mysterious die of marine creatures between Pliocene and pleistocene. Actually, decrease of number of whales, decrease of diversity of penguins, extinction of large sharkes(megalodon), etc. are reported as moderate extinction of marine megafaunas all over the world. In some study, it is suggested that there is a possibility that strong cosmic ray from nearby supenova caused strong irradiation of muon at Earth ground and many marine megafaunas died due to cancer.
We used the diffusion approximation model which was proposed by Mellot et al.(2017) to discuss the influence of nearby supernova. In the model, it is assumed that Earth and the nearby supernova existed in local bubble which is high temperature and low density interstellar area produced by past supernova explosion. In the local bubble, it can be thought that Galactic magnetic field(GMF) is expelled and cosmic ray diffuses isotropically from the supernova. We postulated that the distance between Earth and nearby supernova was 50pc following the past study. Matlab R2019b was used to run simulations on note PC easily.
In order to calculate the atmospheric ionization rates induced by cosmic-ray flux, we utilized the table data of atmospheric ionization values which is public on internet(http://kusmos:phsx:ku:edu/melott/Astrobiology:htm). We convolved the calculated cosmic-ray flux spectrum with the table of atmospheric ionization values and obtained atmospheric ionization rates. Atmospheric ionization rates are important to discuss the atmospheric chemical influence of cosmic ray because ion pairs in air produce NO and NO2 which cause the destruction of ozone layer by catalytic reaction. It was confirmed that the similar results to the original paper ones were obtained.
Then we changed the distance between Earth and nearby supernova, which is a parameter r in the equation of cosmic-ray density at earth, and calculated the time that is necessary for cosmic-ray flux to return to the present one. The present cosmic-ray flux is assumed to be equal to the one that r is 50pc and time measued from the release of cosmic ray is 10ky. We confirmed the change of time associated with the change of distance for the isotropic diffusion model. If another approximation model is applied, the different results will be obtained.
In the future, we are going to discuss influences of cosmic ray including atmospheric chemical reactions which induce the destruction of ozone layer based on these results.
Reference: A.L.Mellot, B.C.Thomas, M.Kachelries, D.V.Semikoz and A.C.Overholt, "A Supernova at 50pc: Effects on the Earth's Atmosphere and Biota", The Astrophysical Journal,840:105,2017 May 10
As the latest case of nearby supernova which influenced earth environment, Maiz-Apellaniz of Johns Hopkins University discovered that the supernovae belonging to Scorpius-Centaurus OB association in Gould's Belt approached solar system about 2.6Ma and suggested that it is thought to be a cause of mysterious die of marine creatures between Pliocene and pleistocene. Actually, decrease of number of whales, decrease of diversity of penguins, extinction of large sharkes(megalodon), etc. are reported as moderate extinction of marine megafaunas all over the world. In some study, it is suggested that there is a possibility that strong cosmic ray from nearby supenova caused strong irradiation of muon at Earth ground and many marine megafaunas died due to cancer.
We used the diffusion approximation model which was proposed by Mellot et al.(2017) to discuss the influence of nearby supernova. In the model, it is assumed that Earth and the nearby supernova existed in local bubble which is high temperature and low density interstellar area produced by past supernova explosion. In the local bubble, it can be thought that Galactic magnetic field(GMF) is expelled and cosmic ray diffuses isotropically from the supernova. We postulated that the distance between Earth and nearby supernova was 50pc following the past study. Matlab R2019b was used to run simulations on note PC easily.
In order to calculate the atmospheric ionization rates induced by cosmic-ray flux, we utilized the table data of atmospheric ionization values which is public on internet(http://kusmos:phsx:ku:edu/melott/Astrobiology:htm). We convolved the calculated cosmic-ray flux spectrum with the table of atmospheric ionization values and obtained atmospheric ionization rates. Atmospheric ionization rates are important to discuss the atmospheric chemical influence of cosmic ray because ion pairs in air produce NO and NO2 which cause the destruction of ozone layer by catalytic reaction. It was confirmed that the similar results to the original paper ones were obtained.
Then we changed the distance between Earth and nearby supernova, which is a parameter r in the equation of cosmic-ray density at earth, and calculated the time that is necessary for cosmic-ray flux to return to the present one. The present cosmic-ray flux is assumed to be equal to the one that r is 50pc and time measued from the release of cosmic ray is 10ky. We confirmed the change of time associated with the change of distance for the isotropic diffusion model. If another approximation model is applied, the different results will be obtained.
In the future, we are going to discuss influences of cosmic ray including atmospheric chemical reactions which induce the destruction of ozone layer based on these results.
Reference: A.L.Mellot, B.C.Thomas, M.Kachelries, D.V.Semikoz and A.C.Overholt, "A Supernova at 50pc: Effects on the Earth's Atmosphere and Biota", The Astrophysical Journal,840:105,2017 May 10