Mercury & Venus the Two most Hostile Planets in the Solar System
Δημοσιεύθηκε στις 11 Δεκ 2013
A look at the two most hostile
planets in the solar system -- Mercury and Venus; one gouged with
craters, the other a greenhouse cauldron of toxic gases and acid rain;
both scorched by their close proximity to the sun. Scientists theorize
about what sort of life could evolve on these alien worlds.
Mercury
is the smallest and closest to the Sun of the eight planets in the
Solar System,[a] with an orbital period of about 88 Earth days. Seen
from the Earth, it appears to move around its orbit in about 116 days,
which is much faster than any other planet. This rapid motion may have
led to it being named after the Roman deity Mercury, the fast-flying
messenger to the gods. Because it has almost no atmosphere to retain
heat, Mercury's surface experiences the greatest temperature variation
of all the planets, ranging from 100 K (−173 °C; −280 °F) at night to
700 K (427 °C; 800 °F) during the day at some equatorial regions. The
poles are constantly below 180 K (−93 °C; −136 °F). Mercury's axis has
the smallest tilt of any of the Solar System's planets (about 1⁄30 of a
degree), but it has the largest orbital eccentricity.[a] At aphelion,
Mercury is about 1.5 times as far from the Sun as it is at perihelion.
Mercury's surface is heavily cratered and similar in appearance to the
Moon, indicating that it has been geologically inactive for billions of
years.
Mercury does not experience seasons in the same way as
most other planets, such as the Earth. It is locked so it rotates in a
way that is unique in the Solar System. As seen relative to the fixed
stars, it rotates exactly three times for every two revolutions[b] it
makes around its orbit. As seen from the Sun, in a frame of reference
that rotates with the orbital motion, it appears to rotate only once
every two Mercurian years. An observer on Mercury would therefore see
only one day every two years.
Because Mercury's orbit lies within
Earth's orbit (as does Venus's), it can appear in Earth's sky in the
morning or the evening, but not in the middle of the night. Also, like
Venus and the Moon, it displays a complete range of phases as it moves
around its orbit relative to the Earth. Although Mercury can appear as a
very bright object when viewed from Earth, its proximity to the Sun
makes it more difficult to see than Venus.
Venus is the second
planet from the Sun, orbiting it every 224.7 Earth days. The planet is
named after the Roman goddess of love and beauty. After the Moon, it is
the brightest natural object in the night sky, reaching an apparent
magnitude of −4.6, bright enough to cast shadows. Because Venus is an
inferior planet from Earth, it never appears to venture far from the
Sun: its elongation reaches a maximum of 47.8°. Venus reaches its
maximum brightness shortly before sunrise or shortly after sunset, for
which reason it has been referred to by ancient cultures as the Morning
Star or Evening Star.
Venus is a terrestrial planet and is
sometimes called Earth's "sister planet" because of their similar size,
gravity, and bulk composition (Venus is both the closest planet to Earth
and the planet closest in size to Earth). However, it has also been
shown to be very different from Earth in other respects. It has the
densest atmosphere of the four terrestrial planets, consisting of more
than 96% carbon dioxide. The atmospheric pressure at the planet's
surface is 92 times that of Earth's. With a mean surface temperature of
735 K (462 °C; 863 °F), Venus is by far the hottest planet in the Solar
System. It has no carbon cycle to lock carbon back into rocks and
surface features, nor does it seem to have any organic life to absorb it
in biomass. Venus is shrouded by an opaque layer of highly reflective
clouds of sulfuric acid, preventing its surface from being seen from
space in visible light. Venus may have possessed oceans in the past, but
these would have vaporized as the temperature rose due to a runaway
greenhouse effect. The water has most probably photodissociated, and,
because of the lack of a planetary magnetic field, the free hydrogen has
been swept into interplanetary space by the solar wind. Venus's surface
is a dry desertscape interspersed with slab-like rocks and periodically
refreshed by volcanism.
planets in the solar system -- Mercury and Venus; one gouged with
craters, the other a greenhouse cauldron of toxic gases and acid rain;
both scorched by their close proximity to the sun. Scientists theorize
about what sort of life could evolve on these alien worlds.
Mercury
is the smallest and closest to the Sun of the eight planets in the
Solar System,[a] with an orbital period of about 88 Earth days. Seen
from the Earth, it appears to move around its orbit in about 116 days,
which is much faster than any other planet. This rapid motion may have
led to it being named after the Roman deity Mercury, the fast-flying
messenger to the gods. Because it has almost no atmosphere to retain
heat, Mercury's surface experiences the greatest temperature variation
of all the planets, ranging from 100 K (−173 °C; −280 °F) at night to
700 K (427 °C; 800 °F) during the day at some equatorial regions. The
poles are constantly below 180 K (−93 °C; −136 °F). Mercury's axis has
the smallest tilt of any of the Solar System's planets (about 1⁄30 of a
degree), but it has the largest orbital eccentricity.[a] At aphelion,
Mercury is about 1.5 times as far from the Sun as it is at perihelion.
Mercury's surface is heavily cratered and similar in appearance to the
Moon, indicating that it has been geologically inactive for billions of
years.
Mercury does not experience seasons in the same way as
most other planets, such as the Earth. It is locked so it rotates in a
way that is unique in the Solar System. As seen relative to the fixed
stars, it rotates exactly three times for every two revolutions[b] it
makes around its orbit. As seen from the Sun, in a frame of reference
that rotates with the orbital motion, it appears to rotate only once
every two Mercurian years. An observer on Mercury would therefore see
only one day every two years.
Because Mercury's orbit lies within
Earth's orbit (as does Venus's), it can appear in Earth's sky in the
morning or the evening, but not in the middle of the night. Also, like
Venus and the Moon, it displays a complete range of phases as it moves
around its orbit relative to the Earth. Although Mercury can appear as a
very bright object when viewed from Earth, its proximity to the Sun
makes it more difficult to see than Venus.
Venus is the second
planet from the Sun, orbiting it every 224.7 Earth days. The planet is
named after the Roman goddess of love and beauty. After the Moon, it is
the brightest natural object in the night sky, reaching an apparent
magnitude of −4.6, bright enough to cast shadows. Because Venus is an
inferior planet from Earth, it never appears to venture far from the
Sun: its elongation reaches a maximum of 47.8°. Venus reaches its
maximum brightness shortly before sunrise or shortly after sunset, for
which reason it has been referred to by ancient cultures as the Morning
Star or Evening Star.
Venus is a terrestrial planet and is
sometimes called Earth's "sister planet" because of their similar size,
gravity, and bulk composition (Venus is both the closest planet to Earth
and the planet closest in size to Earth). However, it has also been
shown to be very different from Earth in other respects. It has the
densest atmosphere of the four terrestrial planets, consisting of more
than 96% carbon dioxide. The atmospheric pressure at the planet's
surface is 92 times that of Earth's. With a mean surface temperature of
735 K (462 °C; 863 °F), Venus is by far the hottest planet in the Solar
System. It has no carbon cycle to lock carbon back into rocks and
surface features, nor does it seem to have any organic life to absorb it
in biomass. Venus is shrouded by an opaque layer of highly reflective
clouds of sulfuric acid, preventing its surface from being seen from
space in visible light. Venus may have possessed oceans in the past, but
these would have vaporized as the temperature rose due to a runaway
greenhouse effect. The water has most probably photodissociated, and,
because of the lack of a planetary magnetic field, the free hydrogen has
been swept into interplanetary space by the solar wind. Venus's surface
is a dry desertscape interspersed with slab-like rocks and periodically
refreshed by volcanism.
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