天仓五的两个潜在的适居带行星
本帖最后由 sonic5188 于 2012-12-21 23:18 编辑Two Nearby Habitable Worlds?posted Dec 19, 2012 2:07 AM by Abel Mendez Torres [ updated Dec 20, 2012 5:34 AM ]
Toumi et al. 2012 announced the potential discovery of five super-earth exoplanets around Tau Ceti with one potentially habitable. However, their data suggest that not only one but two are candidates for habitable planets.
http://www.hpcf.upr.edu/~abel/phl/Banner_HD10700ef.jpg
An international group of scientist led by Mikko Toumi, from the University of Hertfordshire, announced the potential discovery of five planets around the nearby star Tau Ceti (aka HD 10700 or Gliese 71). This is the 19th closest stellar system to Earth at 12 light years away. After Alpha Centauri A and B it is the next closest Sun-like star and historically of astrobiological interest, including SETI. Out of the five possible planets, the two farthest away, Tau Ceti e and f, are potentially habitable.
Tau Ceti e and f have minimum masses of 4.3 and 6.6 Earth masses, respectively. They are both superterrans (aka super-Earths) orbiting within the habitable zone of their parent star. There is no information about their size so it is not possible to tell if they are rocky, water, or even gas worlds. However, if we assume that they are composed of a water-rock mix, their radius might be closer to 1.8 and 2.3 Earth radii, respectively.
Habitability of Tau Ceti e
The planet Tau Ceti e orbits close to the inner edge of the habitable zone. It receives about 60% more light than Earth from the Sun making it a hot planet probably only habitable to simple thermophilic (heat-loving) life. Its mean global surface temperature should be near 70°C assuming a similar terrestrial atmosphere. However, it is likely that superterran planets have much denser and heat trapping atmospheres and Tau Ceti e might be instead dominated by a strong greenhouse effect making it more likely a super-Venus than a super-Earth. Without any knowledge of its atmosphere we are not able to tell if it is a mildly hot planet tolerable for simply life forms or a very hot non habitable Venus-like world. Tau Ceti e has an Earth Similarity Index of 0.77 assuming a more terrestrial-like atmosphere.
Habitability of Tau Ceti f
The planet Tau Ceti f orbits close to the outer edge of the habitable zone. It only receives about 27% the light of Earth from the Sun making it a cold planet probably only habitable to simple psychrophilic (cold-loving) life. Its mean global surface temperature should be near -40°C assuming a similar terrestrial atmosphere. However, it is likely that as Tau Ceti e, it is also dominated by a strong greenhouse effect making it even acceptable for complex life, which requires temperatures from 0°C to 50°C. Without any knowledge of its atmosphere we are not able to tell if it is a frozen Mars-like planet tolerable for simply life forms or even an Earth-like world. Tau Ceti e has an Earth Similarity Index of 0.71 assuming a more terrestrial-like atmosphere.
Both Tau Ceti e and f are very interesting planet candidates for astrobiology that need to be confirmed by more observations. Neither fit yet the Earth-like distinction based on the little information we have from them. It is hard to tell which is better for life at this point without more information about their bulk composition and atmospheric structure. There is one thing we can be certain now. Tau Ceti is now the closest and most similar stellar system to our Solar System with potential habitable exoplanet candidates, displacing the notorious Gliese 581 stellar system.
Resources
[*]Science Now Article: Another Earth Just 12 Light-Years Away?
[*]Research ArXiv Paper: Signals embedded in the radial velocity noise. Periodic variations in the tau Ceti velocities
[*]Data for All Potentially Habitable Exoplanets
[*]Graphical Data for All Potentially Habitable Exoplanets
Imageshttp://www.hpcf.upr.edu/~abel/phl/HEC_HD10700ef_Comparison.jpg
Figure 1. Relative size of the two potential habitable exoplanet candidates around Tau Ceti (HD 10700) compared to Earth. Planet sizes were estimated with a mass-radius relationship.
http://www.hpcf.upr.edu/~abel/phl/HEC_HD10700_Orbits.png
Figure 2. Relative size of exoplanets and orbits for the planetary system Tau Ceti (HD 10700). Orbits and planets are not to scale between them. Planet sizes were estimated with a mass-radius relationship.
http://www.hpcf.upr.edu/~abel/phl/HEC_HD10700e.jpg
Figure 3. Artistic representation of Tau Ceti e.
http://www.hpcf.upr.edu/~abel/phl/HEC_HD10700f.jpg
Figure 4. Artistic representation of Tau Ceti f.
http://www.hpcf.upr.edu/~abel/phl/HEC_All_Confirmed_HD10700.jpg
Figure 5. Summary of all the potential habitable exoplanets in the Habitable Exoplanets Catalog.
本帖最后由 sonic5188 于 2012-12-21 22:54 编辑
英国赫特福德大学天文学家米克·托米(Mikko Tuomi)和他的同事们分析了鲸鱼座τ星6000多条观测数据，这些数据来自智利，澳大利亚和夏威夷境内的望远镜。
根据研究组即将递交给《天文学和天体物理学》杂志的论文，
科学家们认为鲸鱼座τ星所显示出的空间晃动可能是由于其周围存在5颗行星，
这些行星的引力扰动导致了这颗恒星的运动发生轻微变化。
这个米克·托米是系外行星领域崛起的闪耀新星，
通过贝叶斯概率分析从原本杂乱无章的径向速度数据中分析出存在系外行星的蛛丝马迹，
看来系外行星猎人的角色已经从纯观测天文学家团队转移到了数据分析的天文学家团队。
http://arxiv.org/abs/1212.4277
唉，可惜还是看不见摸不着
科技发展得再快些吧 这帮子老外，一点奉献精神都没有，过什么节呢 sonic5188 发表于 2012-12-22 10:32 static/image/common/back.gif
天仓五的岩屑盘尘埃的密度是太阳系的10倍，而且分布杂乱
可见木星这类巨行星对清除小行星和彗星的贡献是很 ...
低级生命还是有可能存在的。我认为，如果一个星球的生物圈环境非常好的话，比如，合适的温度，浓厚的大气，稳定的气候，充沛的降水，二氧化碳和氧气含量都足够高，那么这个星球是生命的乐园，但是一定不是智慧生命的乐园，在这个星球上，谁更强壮，恢复能力更好，谁就能活下去。比如远古时代的地球。
潇洒泪 发表于 2012-12-22 11:30 static/image/common/back.gif
低级生命还是有可能存在的。我认为，如果一个星球的生物圈环境非常好的话，比如，合适的温度，浓厚的大气 ...
我自己模拟了一下，觉得d星也可能是部分适居的，辐射温度在320K左右。
d星被潮汐锁定，会出现一个正中心的热极，也是超级台风的中心，这里无法居住。
如果没有强烈的温室气体，d星的晨昏圈附近是适居的地带，缺点就是风速大。
本帖最后由 sonic5188 于 2012-12-22 11:54 编辑
天仓五的岩屑盘尘埃的密度是太阳系的10倍，而且距离都在10AU以内，分布杂乱
可见木星这类巨行星对清除小行星和彗星的贡献是很大的，
天仓五没有类似的气态巨星，这些超级地球引力又大，
受到小行星撞击的概率比地球高多了，再加上高重力，超级火山，
即便温度、大气适宜，存在复杂生命的概率依然渺茫。
圣诞节天文台都放假了...都没有人来确认天仓五系统的真实性了...
在以往这个速度是很快的。
有效温度的计算公式
http://zh.wikipedia.org/wiki/%E6%9C%89%E6%95%88%E6%BA%AB%E5%BA%A6
页:
[1]