Ocorreu um erro neste gadget

sábado, dezembro 05, 2009

Astronomia Computacional

Iniciado o Laboratório de Física Estatística e Biologia Computacional no DFM-FFCLRP-USP. Profs. responsáveis são Ubiraci P. C. Neves e Osame Kinouchi. Para ilustras que, hoje, a ciência não é apenas teoria e experimentos, mas envolve também a parte computacional como o terceiro pé de um tripé científico, reproduzo a notícia do ótimo blog Physics ArXiv Blog:

Collision-free theory explains why Uranus is lying on its side

Posted: 02 Dec 2009 09:10 PM PST

Astronomers have always assumed that Uranus must have been knocked onto its side by a collision. Now a new idea suggests that the planet's remarkable tilt could have another explanation

One of the great mysteries of our Solar System is why Uranus is tilted on its side. Surely, if the solar system formed from the same rotating cloud of dust and gas, then all the bodies within it should rotate in the same way. And yet Uranus' axis of rotation lies at 97 degrees to the plane of the solar system.


The standard explanation is that Uranus must have been involved in some kind of interplanetary collision with and earth-sized protoplanet in the early days of the solar system. That's a tempting idea but it has some shortcomings. For example, it doesn't explain why the orbits of the moons of Uranus are similarly tilted, not that of its rings.


Today, Gwenael Boue and Jacques Laskar at the Observatoire de Paris in France put forward another idea. They say that Uranus may have become tilted during the period soon after formation when the planets were migrating to the orbits we see now. They point out that the presence of satellites around a planet can increase its rate of precession, if it has a high initial inclination of more than say 17 degrees. This increase can be by as much as a factor of 1000 if the mass of the moon and the radius of its orbit have certain values. For Uranus, this is for a moon of 0.01 Uranian mass and at 50 Uranian radii.


The problem, of course, is that Uranus does not have such a moon. Its most distant companion is Oberon with a mass of just 10^-5 Uranian masses and an orbit of 23 Uranian radii.

Boue and Laskar's idea is that Uranus once had a moon of the required size and orbit, which caused the planet to tilt during the planetary migration, but that this moon was ejected during a close encounter towards the end of the migration.

To study whether this idea is feasible, they simulated the process of giant planet migration in the early solar system some 10,000 times. They then discarded all scenarios in which the planets collided or did not end up in the correct final order. They then selected only those outcomes in which Uranus had an inclination of more than 17 degrees and also rejected any simulation in which Uranus came within 50 Uranian radii of another planet, since that would be likely to eject Oberon as well as the additional hypothesised moon. That left 17 simulations.


Boue and Laskar then added the additional moon to see how it would effect the tilt of Uranus and repeated each of these 17 scenarios a further 100 times. In 37 cases, the new moon helped Uranus onto its side and then ended up being ejected after a close encounter with another gas giant.


That's an interesting result and not just because of the tilt: some models of planet formation predict that Uranus ought to have had another moon (albeit somewhat smaller than the one Boue and Laskar introduce). Consequently, this idea has the elegant property of explaining two mysteries for the price of one, never a bad thing in science.


Ref: http://arxiv.org/abs/0912.0181: A Collissionless Scenario For Uranus Tilting

2 comentários:

盧廣仲Alex disse...

cool!i love it!AV,無碼,a片免費看,自拍貼圖,伊莉,微風論壇,成人聊天室,成人電影,成人文學,成人貼圖區,成人網站,一葉情貼圖片區,色情漫畫,言情小說,情色論壇,臺灣情色網,色情影片,色情,成人影城,080視訊聊天室,a片,A漫,h漫,麗的色遊戲,同志色教館,AV女優,SEX,咆哮小老鼠,85cc免費影片,正妹牆,ut聊天室,豆豆聊天室,聊天室,情色小說,aio,成人,微風成人,做愛,成人貼圖,18成人,嘟嘟成人網,aio交友愛情館,情色文學,色情小說,色情網站,情色,A片下載,嘟嘟情人色網,成人影片,成人圖片,成人文章,成人小說,成人漫畫,視訊聊天室,性愛,情色,日本a片,美女,成人圖片區

I LOVE YOU disse...

性愛自拍,美女寫真,亂倫,戀愛ING,免費視訊聊天,視訊聊天,成人短片,美女交友,美女遊戲,18禁,三級片,自拍,後宮電影院,85cc,免費影片,線上遊戲,色情遊戲,日本a片,美女,成人圖片區,avdvd,色情遊戲,情色貼圖,女優,偷拍,情色視訊,愛情小說,85cc成人片,成人貼圖站,成人論壇,080聊天室,080苗栗人聊天室,免費a片,視訊美女,視訊做愛,免費視訊,伊莉討論區,sogo論壇,台灣論壇,plus論壇,維克斯論壇,情色論壇,性感影片,走光,色遊戲,情色自拍,kk俱樂部,好玩遊戲,免費遊戲,貼圖區,好玩遊戲區,中部人聊天室,情色視訊聊天室,聊天室ut,成人遊戲,免費成人影片,成人光碟,ut聊天室