An ignorant question

I've been following all the discoveries of the extrasolar planets with
great interest, particularly the recent Neptune-sized discoveries.
However, most of the new discoveries seem to have orbital periods measured
in days, meaning they must be moving extremely fast and very close to the
star. How then can they still be thought to be icy as well as rocky, as
recently reported?

Thanks,
Ian.

On Fri, 03 Sep 2004 10:00:16 +1000
Ian Davis wrote:

How then can they still be thought to be icy as well as rocky, as
recently reported?

I am not sure that they are. There has been some discussion of "Hot" gas giants in close orbits around their primary.

One thing to note is that a solid planet in a very close orbit around its star would be likely to have captured rotation (like the Moon around the Earth) so the dark side would be _very_ cold and able to retain ice.
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Ian Davis wrote in message . ..
I've been following all the discoveries of the extrasolar planets with
great interest, particularly the recent Neptune-sized discoveries.
However, most of the new discoveries seem to have orbital periods measured
in days, meaning they must be moving extremely fast and very close to the
star. How then can they still be thought to be icy as well as rocky, as
recently reported?

By "ice" planetary scientists often mean substances which are "icy"
under prevalent conditions of gas giant planets in our Solar System,
and their moons (don't ask me why). That mostly means water, methane,
ammonia, and carbon dioxide. Obviously, in an orbit measured in days
all these substances are gases, if not decomposing into constituent
elements. I *think* the idea is that they were ices when the planet in
question formed.

It is possible that the rotation of the planet is such that, when
combined with the effect of revolution, one side of the planet faces
away from the star most of the time. I *think* Mercury is like this to
some degree IIRC. This would lead to one side being extremely hot, and
the other extremely cold. I'm not really sure how likely that is
though, can anyone else chip in?

N.


Corbell5571 wrote:
Ian Davis wrote in message . ..

I've been following all the discoveries of the extrasolar planets with
great interest, particularly the recent Neptune-sized discoveries.
However, most of the new discoveries seem to have orbital periods measured
in days, meaning they must be moving extremely fast and very close to the
star. How then can they still be thought to be icy as well as rocky, as
recently reported?


By "ice" planetary scientists often mean substances which are "icy"
under prevalent conditions of gas giant planets in our Solar System,
and their moons (don't ask me why). That mostly means water, methane,
ammonia, and carbon dioxide. Obviously, in an orbit measured in days
all these substances are gases, if not decomposing into constituent
elements. I *think* the idea is that they were ices when the planet in
question formed.

Nalin Ratnayake wrote in message news:w2%5d.114930$yh.7595@fed1read05...
It is possible that the rotation of the planet is such that, when
combined with the effect of revolution, one side of the planet faces
away from the star most of the time.

Not just possible, but all but certain for VERY closely orbiting
planets, i.e "hot Jupiters".

I *think* Mercury is like this to
some degree IIRC.

"To some degree." Mercury rotates on its axis in exactly 2/3 of its
orbit around the Sun. That's a stable configuration - IIRC, it will
never truly "tide-lock".

This would lead to one side being extremely hot, and
the other extremely cold. I'm not really sure how likely that is
though, can anyone else chip in?

If a planet has thick atmosphere - and if these "hot Jupiters" are
like our own Jupiter, they are practically ALL atmosphere, - there
will be enough circulation to mostly even out the dayside and the
nightside. Withe thin atmosphere (such as Earth's) or none at all, it
is a different matter.


Corbell5571 wrote:
By "ice" planetary scientists often mean substances which are "icy"
under prevalent conditions of gas giant planets in our Solar System,
and their moons (don't ask me why). That mostly means water, methane,
ammonia, and carbon dioxide. Obviously, in an orbit measured in days
all these substances are gases, if not decomposing into constituent
elements. I *think* the idea is that they were ices when the planet in
question formed.

Nalin Ratnayake wrote in message news:w2%5d.114930$yh.7595@fed1read05...
It is possible that the rotation of the planet is such that, when
combined with the effect of revolution, one side of the planet faces
away from the star most of the time. I *think* Mercury is like this to
some degree IIRC. This would lead to one side being extremely hot, and
the other extremely cold. I'm not really sure how likely that is
though, can anyone else chip in?

N.


A Better example of lockstep rotation is the moon. The same side of
the moon always faces the earth. So the moon is in lockstep rotation
with the Earth (but not the sun). There is no dark side of the moon,
its just that we always see the same side from the earth. Mercury is
not in lockstep rotation with the sun. Mercury's rotational period is
2/3 of its orbital period. Which results in a day on mercury (sunrise
to sunset) lasting longer than a year on mercury (one complete trip
around the sun). These long days and long nights results in a change
of about 600 degrees from daytime side to nighttime side.

MIKE