BETA PICTORIS: PLANETS? LIFE? OR WHAT?
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BETA PICTORIS: PLANETS? LIFE? OR WHAT?
ASTRONOMY 102 SEC 013
The ultimate question is; Is there a possibility that life might exist on a
planet in the Beta Pictoris system? First, one must ask, Are there planets in
the Beta Pictoris system?. However, that question would be impossible to answer
if one did not answer the most basic questions first; Where do planets come
from? and do the key elements and situations, needed to form planets, exist in
the Beta Pictoris system?.
To understand where planets come from, one has to first look at where the
planets in our solar system came from. Does or did our star, the sun, have a
circumstellar disk around it? the answer is believed to be yes.
Scientists believe that a newly formed star is immediately surrounded by a
relatively dense cloud of gas and dust. In 1965, A. Poveda stated, “That new
stars are likely to be obscured by this envelope of gas and dust (1).” In 1967,
Davidson and Harwit agreed with Poveda and then termed this occurrence, the “
cocoon nebula” (1). Other authors have referred to this occurrence as, a “
placental nebula” (1), noting that it sustains the growth of planetary bodies.
For a long time, even before there was the term cocoon nebula, planetary
scientists knew that a cocoon nebula had surrounded the sun, long ago, in order
for our solar system to form and take on their currents motions (1).
In 1755, a German, named Immanuel Kant, reasoned that “gravity would
make circumsolar cloud contract and that rotation would flatten it (1)." Thus,
the cloud would assume the general shape of a rotating disk, explaining the fact
that the planets, in our solar system, revolve in a disk-shaped distribution.
This idea, about the disk-shaped nebula that was formed around the early
sun, came to be known as the nebula hypothesis (1). Then, in 1796, a French
mathematician named Laplace, proposed that the rotating disk continued to cool
and contract, forming planetary bodies (1). Also, when investigating the
evolution of stars, it was proposed “that a star forms as a central condensation
in an extended nebula... The outer part remains behind as the cocoon nebula (1)”
. During the same study it was also indicated that under various conditions
such as: rotation, turbulence, etc. the nucleus of the forming star may divide
into two or more bodies orbiting each other (1). This may be the explanation as
to why more than half of all star systems are binary or multiple, rather than
singles stars, like ours, the sun.
This same fragmentation may also form bodies too small to become stars.
However, they could form into large planets, about the same size as Jupiter (1).
In 1966, Low and Smith calculated that the dust must be orbiting the star
at a distance of many tens of astronomical units, in order for planets to from
(1). Others have reasoned that the cocoon nebula must contain silicate and/or
ice particles (planet-forming materials), in order for the presence of planetary
bodies (1). Still others have concluded that planets form during the early life
of a star (1).
After determining that planets are formed in a circumstellar disk
surrounding a star, we must ask ourselves, Does Beta Pictoris have a
cirumstellar disk around it?
Beta Pictoris was found to have a circumstellar disk in 1983. It was first
detected by the Infrared Astronomy Satellite. The disk is seen to extend to
more than 400 astronomical units from the star (2). The orbits of most of the
particles are inclined 5 degrees or less to the plane of the system (2). These
minimal orbital inclinations are typical of the major planets in our own solar
system. There is evidence that the circumstellar material around Beta Pictoris
takes the form of a highly flattened disk, rather than a spherical shell implies
an almost certain association with planet formation (2). The disk material
itself is believed to be a potential source for planet accretion (2). This
retention of nearly coplanar orbits in the Beta Pictoris disk is a qualitative
argument in support of its being a relatively young system (2). Some
astronomers believe that we are witnessing planet formation in the process.
Lagage and Pantin found that the inner region of the disk surrounding Beta
Pictoris is clear of dust, a prime indicator that there is evidence of one or
more planetary bodies (3).
The depletion zone extends to about 15 AU from the star, about the same
size as our solar system; and has an average particle density
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Planetary systems, Planetary science, Exoplanetology, Beta Pictoris moving group, Solar System, Beta Pictoris, Pictor, Nebular hypothesis, Accretion, Circumstellar disc, Comet, Planet
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