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[sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9)
Section - E.06 What happens to the planets when the Sun dies?

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Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9)
Previous Document: E.05 When will the Sun die? How?
Next Document: E.07 Could the Sun explode?
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A couple of possibilities exist.  Prior to forming a planetary nebula,
a low-mass star (i.e., one with a mass similar to that of the Sun)
forms a red giant.  Planets close to the star are engulfed in the
expanding star, spiral inside it, and are destroyed.  In our own solar
system, Mercury and Venus are doomed.

As the star expands to form a red giant, it also starts losing mass.
All stars lose mass.  For instance, the Sun is losing mass.  However,
at the rate at which the Sun is currently losing mass, it would take
over 1 trillion years (i.e., 100 times longer than the age of the
Universe) for the Sun to disappear.

When a star enters the red giant phase, the rate at which it loses
mass can accelerate.  The mass of a star determines how far a planet
orbits from it.  Thus, as the Sun loses mass, the orbits of the other
planets will expand.  The orbit of Mars will almost certainly expand
faster than the Sun does, thus Mars will probably not suffer the same
fate as Mercury and Venus.  It is currently an open question as to
whether the Earth will survive or be engulfed.

The orbits of planets farther out (Jupiter, Saturn, Uranus, Neptune,
and Pluto) will also expand.  However, they will not expand by much
(less than double in size), so they will remain in orbit about the Sun
forever, even after it has collapsed to form a white dwarf.

(Any planets around a high-mass star would be less lucky.  A high-mass
star loses a large fraction of its mass quickly in a massive explosion
known as a supernova.  So much mass is lost that the planets are no
longer bound to the star, and they go flying off into space.)

As for the material in the planetary nebula, it will have little
impact on the planets themselves.  The outer layers of a red giant are
extremely tenuous; by terrestrial standards they are a fairly decent
vacuum!

User Contributions:

1
Keith Phemister
Sep 13, 2024 @ 11:23 pm
Copied from above: If the Universe were infinitely old, infinite in extent, and filled
with stars, then every direction you looked would eventually end on
the surface of a star, and the whole sky would be as bright as the
surface of the Sun.
Why would anyone assume this? Certainly, we have directions where we look that are dark because something that does not emit light (is not a star) is between us and the light. A close example is in our own solar system. When we look at the Sun (a star) during a solar eclipse the Moon blocks the light. When we look at the inner planets of our solar system (Mercury and Venus) as they pass between us and the Sun, do we not get the same effect, i.e. in the direction of the planet we see no light from the Sun? Those planets simply look like dark spots on the Sun.
Olbers' paradox seems to assume that only stars exist in the universe, but what about the planets? Aren't there more planets than stars, thus more obstructions to light than sources of light?
What may be more interesting is why can we see certain stars seemingly continuously. Are there no planets or other obstructions between them and us? Or is the twinkle in stars just caused by the movement of obstructions across the path of light between the stars and us? I was always told the twinkle defines a star while the steady light reflected by our planets defines a planet. Is that because the planets of our solar system don't have the obstructions between Earth and them to cause a twinkle effect?
9-14-2024 KP

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Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9)
Previous Document: E.05 When will the Sun die? How?
Next Document: E.07 Could the Sun explode?

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