Re: Gas planet found orbiting dying red giant star closer than Earth orbits Sun
- From: Bluuuue Rajah <Bluuuuue@Rajah.>
- Date: Mon, 24 Nov 2008 09:35:41 GMT
Yousuf Khan <bbbl67@xxxxxxxxx> wrote in news:492a2822@xxxxxxxxxxxxxxx:
Craig wrote:
On Nov 23, 4:13 pm, Yousuf Khan <bbb...@xxxxxxxxx> wrote:
The red giant phase of a star's aging process is supposed to mean
that it expands out in size and it often swallows up its closest
planets. It's theorized that the Earth might meet this fate when the
Sun goes red giant. But this discovery shows a planet much much more
massive than the Earth (or even Jupiter) orbiting a red giant much
closer than the Earth does. I wonder if this means that the Earth
too might be out at a safe enough distance from the Sun to escape
this fate?
Even if the planet "survives" -- i.e. it is not destroyed or
enveloped by the star -- it will definitely become uninhabitable in
the form that we commonly think of. During the red giant phase, the
total luminosity of the star increases.
That's understood that it will be uninhabitable, but perhaps if it
survives intact after its sun burns out, there is a corpse of a planet
left behind for future archaeological purposes.
The article doesn't say how far away HD 102272 is, or what is its
diameter. If it's close by, an accurate measurement might be made for
it's size, which can be used to calibrate the model that describes the
expansion of main sequence stars into red giants.
That the star did not envelop it's exoplanet suggests that, whatever was
the mass of HD 102272 before it went giant, it did not have enough fuel
to expand as large as the sun will, so it must be of a lighter spectral
class than the sun. The existing model can be used to extrapolate
backwards in time to a pseudo-measurement of HD 102272's mass and
spectral class before it went giant, and therefore, its position on the
Hertzprung-Russell Diagram.
Since the sun is a G2 star, this one must be smaller, meaning that it
must be either G1, G0, K or M. I don't know the threshold for a star to
become a red giant, but it almost certainly doesn't include the M class,
and also maybe not the lower ranges of the K class. Of course, all this
assumes that HD 102272 was a main sequence star before it became a red
giant, but AFAIK, that's a reliable assumption, since becoming a red
giant is a normal evolutionary process for main sequence stars.
If I had a book with the equations for that process, I'd look at them
myself, to see if I could figure out the procedure for making that
calculation. But I only have a first year astrophysics book, which
doesn't go into detail on the process of how a main sequence star
becomes a red giant.
Also, note that the article says that the exoplanet is inside the
equivalent orbit of Venus, not that of Earth, meaning that the star may
have been a *lot* smaller than the sun, when it was on the main
sequence.
.
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