Mars has an insubstantial atmosphere, consisting almost entirely of carbon dioxide.是什么意思？

Mars has an insubstantial atmosphere, consisting almost entirely of carbon dioxide.

火星的大气层极其稀薄，几乎全部由二氧化碳构成。

mars

abbr. master attitude reference system 主要态度参考系统，midair retrieval system 中空恢复系统，military affiliated radio system 军用附属无线电系统，mathematics anxiety rating scale 数学焦虑等级刻度；n. 毁坏，损坏，玷污( mar的名词复数 )；v. 毁坏，损坏，玷污( mar的第三人称单数 )；

例句
The similarities between Mars and Earth were enough to keep alive hopes of some form of Martian life.
火星和地球之间的诸多相似处足以让人们对火星上存在某种生物抱以希望。

has

v. 有( have的第三人称单数 )，（亲属关系中）接受，拿，买到；

例句
...the operation a patient has had.
病人做过的手术

an

art. 一（在元音字母前代替不定代词a），一任一某一，一个；

例句
He started eating an apple...
他开始吃苹果。

insubstantial

adj. 无实体的，无实质的，非实在的；

例句
Mars has an insubstantial atmosphere, consisting almost entirely of carbon dioxide...
火星的大气层极其稀薄,几乎全部由二氧化碳构成。

atmosphere

n. 大气，空气，大气层，风格，基调，气氛；

例句
There's been an atmosphere of anticipation around here for a few days now...
几天来这里一直有一种满怀期待的气氛。

consisting

v. 由…组成( consist的现在分词 )，包括，存在于，表现为（常与 in 连用）；

例句
Mars has an insubstantial atmosphere, consisting almost entirely of carbon dioxide...
火星的大气层极其稀薄,几乎全部由二氧化碳构成。

almost

adv. 几乎，差不多，将近，快要，近乎；

例句
Despite considerable pain she has been getting out and about almost as normal...
尽管还很痛，她已经基本上行动如常。

entirely

adv. 完全地，完整地，全部地，彻底地；

例句
I say 'boys' advisedly because we are talking almost entirely about male behaviour...
我特意说成“男孩们”因为我们几乎一直在讨论男性的行为。

of

prep. 关于，属于…的，由…制成；aux. 助动词 [非标准用语、方言] =have [主用于虚拟语气]；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

carbon

n. [化学]碳，（一张）复写纸，[电]碳精棒[片，粉]，碳精电极，复写的副本；adj. 碳的，碳处理的；

例句
...the abatement of carbon dioxide emissions.
二氧化碳排放的减少

dioxide

n. [化]二氧化物；

例句
...the abatement of carbon dioxide emissions.
二氧化碳排放的减少