By admin in 天文台 on 2019年4月7日

Scientific American 60-second Science, July 4, 2016

作者:Lee 比林s 翻译整理:SophieMen

原来的文章地址:Is Mars Missing a Moon? – Scientific


Transript and Translation

Mars is a planet of outsized splendor. Despite being only half as
big and a tenth as heavy as Earth, it bears the solar system’s tallest
mountain, longest canyon and largest crater. At 22 and 12
kilometers wide, however, its inner moon Phobos and outer moon Deimos
are figurative small potatoes. Scientists suspect both formed much
as Earth’s single large moon did, from a massive debris disk ejected
into orbit by a giant impact eons ago. But if Mars’s moons formed like
Earth’s, why are they so very much smaller?


The answer may be that they did not form alone. New simulations from
Pascal Rosenblatt of the Royal Observatory of Belgium and colleagues
show how the debris disk from a giant impact on Mars could have
generated additional moons a few hundreds of kilometers in size. After
forming in the dense inner regions of the disk, those larger moons would
have stirred the disk’s sparser outer reaches, allowing smaller
companions like Phobos and Deimos to coalesce from the ripples. The
study appears in the journal Nature Geoscience. [Rosenblatt et al.,
Accretion of Phobos and Deimos in an extended debris disc stirred by
transient moons]

et al., Accretion of Phobos and Deimos in an extended debris disc
stirred by transient moons]。

In this scenario, the reason we only see Phobos and Deimos today is that
the bigger moons were destroyed a few million years after their
formation. Their low, fast orbits outpaced Mars’s rotation, creating a
tidal pull that sent them spiraling down to crash into the planet
(Earth’s moon, by contrast, orbited slower than our planet’s rotation,
allowing it to spiral outward and survive). Future investigations could
test the new hypothesis by looking for clusters of Martian craters
produced by the infalling moons, but in the meantime, proof that Mars
can kill its companions is right before our eyes: The orbit of Deimos is
stable, but Phobos is in a death spiral, losing two centimeters of
altitude per year to Mars’s tidal pull. It will plunge into the planet
in 20 [million] to 40 million years, leaving lonely, far-out
Deimos as the last vestige of what may have been a once-mighty system of
Martian moons.



  • splendor, \ˈsplen-dər, noun, 1. great and impressive
    beauty. 2. things that are very beautiful or impressive.

  • canyon, \天文台,ˈkan-yən, noun, a deep valley with steep rock sides
    and often a stream or river flowing through it.

  • crater, \ˈkrā-tər, noun, 1. a large round hole in the ground
    made by the explosion of a bomb or by something falling from the
    sky. 2. the area on top of a volcano that is shaped like a bowl

  • figurative,\ˈfi-g(y)ə-rə-tiv, adjective, 1. used with a
    meaning that is different from the basic meaning and that expresses
    an idea in an interesting way by using language that usually
    describes something else : not literal. 2.showing people and things
    in a way that resembles how they really look : not abstract.

  • debris, \də-ˈbrē, noun, 1.the pieces that are left after
    something has been destroyed. 2.things (such as broken pieces and
    old objects) that are lying where they fell or that have been left
    somewhere because they are not wanted.

  • far-out, \ˈfär-ˌau̇t, adjective, very strange or unusual.


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