Relating to the Terrestrial Planets

Mercury, being the smallest of the planets in our solar system (I don't
count Pluto - if it was discovered today, I'm pretty sure it would not be
referred to as a planet) obviously is not as hot as Venus, yet it is
closest to the sun than any of the other planets. Venus is surrounded by
clouds and is sometimes called the "veiled" planet. So why doesn't Mercury
have the hottest surface temperature? I have devoured the internet in
search of an answer, and have gotten some very different ones - what's the
REAL truth?

-Regan.

Regan S. posted:

Mercury, being the smallest of the planets in our solar system (I don't
count Pluto - if it was discovered today, I'm pretty sure it would not be
referred to as a planet) obviously is not as hot as Venus, yet it is
closest to the sun than any of the other planets. Venus is surrounded by
clouds and is sometimes called the "veiled" planet. So why doesn't Mercury
have the hottest surface temperature? I have devoured the internet in
search of an answer, and have gotten some very different ones - what's the
REAL truth?

Mercury is the closest planet to the sun. Its surface temperature can be as
high as 467 degrees C near local noon, but the planet has no significant
atmosphere to trap and hold in heat (at night, the surface temperature plunges
to -183 C). Its mean surface temperture thus is about 167 C (averaged over
its entire surface). However, Venus has a particularly-dense atmosphere which
is made up mostly of Carbon Dioxide. The atmosphere lets in visible light
energy which heats the surface and then is radiated back into the atmosphere
as infrared light (heat "radiation"). However, the Carbon Dioxide traps this
re-radiated infrared radiation, causing heat to build up in the famous
"Greenhouse Effect". This raises the temperature on Venus to where *on
average*, it becomes the hottest planet in the solar system (average surface
temperature about 457 C, hottest surface temperature 482 C).

Now, as to the REAL truth, according to the IAU (the official source on the
subject), Pluto is a planet. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
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"David Knisely" wrote in message
...


Now, as to the REAL truth, according to the IAU (the official source on
the
subject), Pluto is a planet. Clear skies to you.
--

oooh... the IAU... those mean people who won't let me name a star! *pout*
j/k

Actually, his point was not that Pluto is not recognized by the IAU, but if
it was discovered today, it would not be recognized by the IAU as a planet,
and the fact the Quaoar has not been designated as a planet, probably lends
credence to his assertion.

Regan Read Pluto having such a big moon it can said to be a binary
planetary system. Also read that in some of Mercury's craters there
appears to be frost in their shaded areas. Could that frost be ice(H2O)
With so many craters Mercury could have been hit by a few comets.
Bert PS Hubble has taken some great picture of Pluto and its Moon.Its
moon is only 28,000 miles away.

"Regan S." wrote in message .17...
Mercury, being the smallest of the planets in our solar system (I don't
count Pluto - if it was discovered today, I'm pretty sure it would not be
referred to as a planet) obviously is not as hot as Venus, yet it is
closest to the sun than any of the other planets. Venus is surrounded by
clouds and is sometimes called the "veiled" planet. So why doesn't Mercury
have the hottest surface temperature? I have devoured the internet in
search of an answer, and have gotten some very different ones - what's the
REAL truth?

Venus' atmosphere holds in heat. Light filters through the Venusian
clouds and reaches the surface of Venus, where it heats the surface
and the heat reradiates in the infrared (because that's how heat
works). The atmosphere, however, doesn't let infrared through nearly
as well as it lets visible light through. So the sun's energy gets in
more freely and only trickles out. It long ago heated up to its
equilibrium point -- where the trickling-out heat essentially pushes
out really hard because there's so much of it -- and this equilibrium
is several hundred degrees hotter than Mercury's surface, which
follows very straightforward thermodynamic radiation rules.

The Earth does the same thing to a lesser extent, by the way. The
amount of light hitting the Earth and the average reflectivity of the
planet would by itself result in an average surface temperature below
the freezing point of water, were it not for the greenhouse effect of
several of the gasses in our atmosphere -- primarily our water vapor
and carbon dioxide (nitrogen and oxygen are not greenhouse gasses;
they're mostly transparent in the infrared just in visible light).

So our planet is about thirty or forty degrees warmer thanks to the
greenhouse effect. Given that we've doubled the CO2 content in the
last century and our production of CO2 continues to accelerate, this
has some fairly important ramifications.

eyelessgame

"Regan S." wrote in message .17...
Mercury, being the smallest of the planets in our solar system (I don't
count Pluto - if it was discovered today, I'm pretty sure it would not be
referred to as a planet) obviously is not as hot as Venus, yet it is
closest to the sun than any of the other planets. Venus is surrounded by
clouds and is sometimes called the "veiled" planet. So why doesn't Mercury
have the hottest surface temperature? I have devoured the internet in
search of an answer, and have gotten some very different ones - what's the
REAL truth?

Venus' atmosphere holds in heat. Light filters through the Venusian
clouds and reaches the surface of Venus, where it heats the surface
and the heat reradiates in the infrared (because that's how heat
works). The atmosphere, however, doesn't let infrared through nearly
as well as it lets visible light through. So the sun's energy gets in
more freely and only trickles out. It long ago heated up to its
equilibrium point -- where the trickling-out heat essentially pushes
out really hard because there's so much of it -- and this equilibrium
is several hundred degrees hotter than Mercury's surface, which
follows very straightforward thermodynamic radiation rules.

The Earth does the same thing to a lesser extent, by the way. The
amount of light hitting the Earth and the average reflectivity of the
planet would by itself result in an average surface temperature below
the freezing point of water, were it not for the greenhouse effect of
several of the gasses in our atmosphere -- primarily our water vapor
and carbon dioxide (nitrogen and oxygen are not greenhouse gasses;
they're mostly transparent in the infrared just in visible light).

So our planet is about thirty or forty degrees warmer thanks to the
greenhouse effect. Given that we've doubled the CO2 content in the
last century and our production of CO2 continues to accelerate, this
has some fairly important ramifications.

eyelessgame

"G=EMC^2 Glazier" wrote in message...
...

Regan Read Pluto having such a big moon it can said to be a binary
planetary system. . . .

And it indeed *is* called a binary planet system by those
who still consider Pluto to be a planet, Bert. However, i
think it was Jonathan who pointed out that, unlike our
Moon, Pluto's satellite Charon spends about half the
time moving toward the Sun and the other half moving
away from the Sun. So in this respect, Charon behaves
like all the other natural satellites in our Solar System.

As i may have mentioned before g, our Moon always
falls *toward* the Sun, just like a regular planet. So it is
obvious to me that the Earth/Moon system is the only
binary planet system that revolves around the Sun.

happy days and...
starry starry nights!

--
Delight in yourself...
for you are the stuff of stars!

Paine Ellsworth

"Painius" wrote in message
...
"G=EMC^2 Glazier" wrote in message...
...

Regan Read Pluto having such a big moon it can said to be a binary
planetary system. . . .

And it indeed *is* called a binary planet system by those
who still consider Pluto to be a planet, Bert. However, i
think it was Jonathan who pointed out that, unlike our
Moon, Pluto's satellite Charon spends about half the
time moving toward the Sun and the other half moving
away from the Sun. So in this respect, Charon behaves
like all the other natural satellites in our Solar System.

As i may have mentioned before g, our Moon always
falls *toward* the Sun, just like a regular planet. So it is
obvious to me that the Earth/Moon system is the only
binary planet system that revolves around the Sun.

Huh???

Hi Painius Seems Pluto would be more of a gas planet if it was closer
to the sun. seems to be made of ice much like a comet. At its great
distance the sun must appear as a bright star,and adds little heat.The
nice thing about ice is it reflects light well. My email corrected me
Pluto's moon is only 12,000 miles out. I posted 28,000 miles. Bert

Panius wrote:

And it indeed *is* called a binary planet system by those
who still consider Pluto to be a planet, Bert.

I consider Pluto to be a planet, but I do not consider it a "binary planet",
since that term has not been formally defined. It may be called one by a few
individuals, but not by all. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************