火星上曾经有生命存在过吗?

当我们问“我们在哪里可以找到外星生命”时,许多科学家会首先转向火星,因为它与地球相似的地方很多。火星的过去或许像地球一样适宜生命的存在。尽管我们现在还没有发现火星上有生命存在的迹象,但科学家们从未放弃对它的寻找,因为他们知道在极端环境中生命的潜力是很强大的,一切都有可能。

火星上生命的可能性是天体生物学的一个重要课题,因为它与地球的相似之处非常多而且又是我们的近邻。不过迄今为止,还没有发现火星上过去或现在有任何生命存在过的直接证据。累积的证据表明,在远古的挪亚时期,火星的地表环境具有液态水,可能适合微生物的生存。不过可居住条件的存在并不一定表明生命的存在。

对生命证据的科学搜索始于十九世纪,他们今天则通过望远镜和探测器的调查来继续进行着是否存在生命的探索。虽然早期的研究主要集中在现象学上,并且与幻想接壤,但现代科学研究强调的是对水、行星表面土壤和岩石中的化学生物标记以及大气中生物标记气体的研究。

艺术家的想像图,展示了火星被地球化后表面和大气的样子,图:Ittiz

我们对火星生命起源的研究特别感兴趣,因为它与早期的地球非常相似。火星气候寒冷,缺乏板块构造论(Plate tectonics)或大陆漂移学说(Continental drift),所以自赫斯伯利亚纪(Hesperian period)末期以来几乎没有什么变化。火星表面至少有三分之二地区的历史都已经超过了35亿年,因此,即使火星重来没有生命存在过,最佳的记录也可能保存了导致非生物发生的原生生物的条件。

在确认了火星过去存在地表液态水之后,好奇号和机遇号探测器便开始寻找过去是否存在生命的证据,这里包括基于自养型、化学营养型(化能)、或化学自养微生物过去的生物圈,以及远古时代的水,包括河流 – 湖泊等可能适合居住的环境(古代河流或湖泊相关的平原)。在火星上寻找行星适居性、埋藏学(与化石有关的)和有机化合物的证据是现在美国国家航空航天局和欧空局的主要目标。

沉积岩石中的有机化合物和火星上硼的发现使得我们对火星生命越来越感兴趣,因为它们是生物体形成(前生命化学)的前身。这些发现和先前在古代火星上明显存在液态水的发现,进一步的支持了盖尔撞击坑(Gale Crater)在早期的火星上具有可居住性这一观点。目前,火星的表面被太阳辐射所侵蚀,当太阳辐射与地表上的高氯酸盐反应时,它对微生物的毒性可能比之前想象的要大。因此,人们一致认为,如果火星上存在生命,那么必须存在于地表之下,这样才可以防止太阳辐射以及化学反应产生的毒性物质。

电子显微镜下的ALH84001火星陨石显现类似细菌的结构,图:NASA

2018年6月,美国宇航局宣布将探测火星上甲烷含量的季节变化。甲烷可以通过微生物或地质手段产生。欧洲外火星痕量气体轨道飞行器在2018年4月开始绘制火星大气甲烷的分布图,2020年外火星探测器将钻探并分析地下样品,而NASA火星2020探测器将储存数十个钻探样品。到21世纪20年代末或30年代,它们可能被运送到地球实验室。

2018年6月,美国宇航局宣布将探测火星上随其季节变化的甲烷含量。甲烷的产生机制可以通过微生物或地质来实现。在2018年4月欧洲的火星微量气体任务卫星(ExoMars Trace Gas Orbiter)开始绘制甲烷在火星大气中的分布图,2020年ExoMars探测器将钻探到火星地下并分析其物质成分,NASA的火星2020探测车任务将储存数十个钻探的火星地下样品。并可能会在2020年后期或2030年将样品送回到地球实验室。

适居性

化学、物理、地质和地理属性塑造了火星上的环境。这些孤立测量的因素可能还不足以满足适合居住的环境条件,但是累积的测量数据可以帮助我们预测到或多或少可能适宜居住的地点。目前用于预测火星表面具有潜在可居住性的两种生态方法分别使用了19种和20种环境因素,其中重点的是水的可用性、温度、营养物质必须的存在、能量来源的存在以及具有防止太阳紫外线辐射和银河宇宙辐射到达火星表面的保护措施。

好奇号在火星表面发现含硫有机物,图:NASA/GSFC

参考资料

1.WJ百科-英文版本(Life on Mars

2.NASA – Exploratour: Life on Mars?

3.天文学名词

 

文章作者:零度星系(天文在线)

审核人员:小抽

最终审核:零度星系(天文在线)

编辑用时:2018年11月28日 -2018年11月28日(花费时长:约3个小时)

审核用时:2个小时

最后更新2018年11月30日星期五

注意:所有信息数据庞大,难免出现错误,还请指出错误所在好加以改之。

结束,感谢您的阅读与关注

全文排版:天文在线(零度星系)

转载请取得授权,并注意保持完整性和注明出处

本文由天文在线原创,欢迎关注,带你一起长知识!!

 

 

Bookmark the permalink.

20 Responses to 火星上曾经有生命存在过吗?

  1. best CBD oil says:

    I like the valuable information you provide in your articles.
    I will bookmark your weblog and check again here regularly.
    I am quite sure I will learn many new stuff right here!

    Good luck for the next!

  2. Have you ever thought about including a little bit more than just your articles?
    I mean, what you say is important and everything.
    But think of if you added some great images or video
    clips to give your posts more, “pop”! Your content is excellent but with
    pics and clips, this blog could undeniably be one of the greatest in its niche.
    Excellent blog!

  3. Howdy! This is kind of off topic but I need some guidance from an established blog.

    Is it tough to set up your own blog? I’m not very techincal
    but I can figure things out pretty quick. I’m thinking about making my own but I’m not sure where to start.
    Do you have any tips or suggestions? Many thanks

  4. best CBD oil says:

    Appreciating the time and effort you put into your website
    and detailed information you present. It’s awesome to come across a blog every once in a while that isn’t the same unwanted rehashed information. Excellent read!
    I’ve saved your site and I’m adding your RSS feeds to my Google account.

  5. CBD pills says:

    Hi friends, nice article and nice arguments commented here,
    I am genuinely enjoying by these.

  6. Pretty nice post. I just stumbled upon your blog and wanted to say
    that I’ve really enjoyed surfing around your blog posts.
    After all I’ll be subscribing to your feed and
    I hope you write again very soon!

  7. Very good write-up. I certainly love this website.
    Thanks!

  8. First off I would like to say fantastic blog! I had a quick question that I’d like to ask if you don’t mind.

    I was interested to know how you center yourself and clear
    your mind before writing. I have had a hard time clearing my mind in getting my ideas
    out there. I do take pleasure in writing but it just seems like the first 10 to 15
    minutes are generally lost simply just trying to figure out how
    to begin. Any ideas or tips? Kudos!

  9. best CBD oil says:

    Why users still use to read news papers when in this technological world the
    whole thing is accessible on web?

  10. CBD gummies says:

    Hello my loved one! I wish to say that this
    article is awesome, nice written and include approximately all important infos.
    I’d like to see more posts like this .

  11. You need to take part in a contest for one of the finest sites on the net.
    I am going to highly recommend this web site!

  12. bookmarked!!, I really like your website!

  13. I don’t even know how I ended up here, but I thought this post was great.

    I do not know who you are but definitely you’re going
    to a famous blogger if you aren’t already 😉 Cheers!

  14. I was able to find good advice from your blog articles.

  15. This is my first time pay a visit at here and i am in fact happy to read all at single place.

  16. best CBD oil says:

    Since the admin of this web site is working, no uncertainty
    very rapidly it will be well-known, due to its quality contents.

  17. best CBD oil says:

    What’s up, I log on to your blogs regularly. Your writing style is witty,
    keep doing what you’re doing!

  18. best CBD oil says:

    Yesterday, while I was at work, my sister stole my iphone and tested to see if it can survive a
    twenty five foot drop, just so she can be a youtube sensation. My apple ipad is now broken and she has 83
    views. I know this is totally off topic but I had to share it with someone!

  19. Heya i’m for the first time here. I came across this board and
    I find It really useful & it helped me out much.
    I’m hoping to provide something again and aid others such as you aided me.

  20. simgiagoc says:

    magnificent publish, very informative. I ponder why the other specialists of this sector don’t realize this.
    You must continue your writing. I’m confident, you have a huge readers’ base already!

发表评论

电子邮件地址不会被公开。 必填项已用*标注