Essay/Term paper: Beta pictoris: planets? life? or what?

Essay, term paper, research paper:  Science Reports

BETA PICTORIS: PLANETS? LIFE? OR WHAT?


JARA

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 only one tenth of
the area just outside this zone (3).
Lagage and Pantin believe that the inner zone may have been swept clean by
the gravitational pull of a planet orbiting around Beta Pictoris (3). A planet
would gravitationally deflect the particles out of the inner zone. This planet,
which is only believed to exist, may also be deflecting comets into the star, as
indicated by the presence of highly variable absorption lines in the spectrum of
Beta Pictoris (3).
The infrared image by Lagage and Pantin also provide information that the
edge-on disk is not symmetrical around the star (3). This suggests a more
intimate relationship between the asymmetry and the properties of the inner disk.
As the orbital timescale for particles is relatively short (less than 100
years), one would expect that the irregularities in the disk would have been
smoothed out by now (3). Unless, there was something stirring it up, such as a
planet (3).
If there is a planet orbiting Beta Pictoris, its orbit is probably
eccentric, as are most of the planetary orbits in our solar system (4). A
planet with even a moderately eccentric orbit would generate the asymmetry that
is been noted in the dust disk surrounding Beat Pictoris (4).
The Hubble Space Telescope, using the high-resolution spectrograph, found
that the disk surrounding beta Pictoris consists of two parts: an outer ring of
small, solid particles, and an inner ring of diffuse gas within a few hundred
miles of the star (5).
Albert Boggess, an astronomer at NASA"s Goddard Space Flight Center,
suspects that the gas comes from the ring of solid particles (5). If he is
correct, then the gas may be a sign that planets are being born there. The gas
could be a result from the collision of solid particles in the outer ring
accreting into planets that are still too small to see because of the brightness
of the star itself (5). During the collisions some of the particles would be
vaporized and drawn toward the star. The planets in our own solar system are
believed to have formed through countless numbers of such collisions (5).
Boggess also believes that Beta Pictoris is very similar to a very early
phase of our own solar system (5).
Additional evidence, from the Hubble, also suggests that Beta Pictoris
might be following in our footsteps. The gaseous inner ring appears to contain
clumps of material spiraling toward the star (5). These clumps may be comets,
diverted from the normal paths by close calls with protoplanets (5). This also
fits with current ideas about the evolution of our own solar system. Gases from
comet impacts may have been the creating factor of the Earth"s atmosphere and
oceans (5).
Wetherill argues that life on Earth is reliant upon the existence of
Jupiter and Saturn, because they cleansed our Solar System of most of its
planetesimals (comets) that, otherwise, would be striking the Earth (6). In
order for a planet to survive long enough for life to begin, it is necessary for
the existence of gas giants (Jupiter and Saturn) to get rid of the hazardous
comets.
No one person can say for sure whether there are planets in the Beta
Pictoris System, or not. However, it is definitely a possibility. There is a
circumstellar disk surrounding Beta Pictoris. It is a highly flattened disk, as
was the disk that once surrounded the Sun. The disk contains the necessary
elements for planet formation. The star is a young one. The inner zone of the
disk is clear. All of these things point to the almost probable formation of
planets. Richard Terrile, from the Jet Propulsion Laboratory, says, "It"s hard
not to form planets from material like this (7)."
To answer whether or not there could be life on one of these planets, is
not easy to say. No one can really even speculate. I, believe that it is
possible, if all the variables come together in just the right way. I am not "
earthnocentric" to assume that the earth is the only planet in the Universe that
can sustain life. Whether or not a planet in the Beta Pictoris system has what
it takes, who knows, we can only wait and watch. BIBLIOGRAPHY

(1) Moons And Planets, third edition; William K.
Hartman; Wadsworth Publishing company;
California; 1993.

(2) A Circumstellar Disk Around Beta Pictoris; Science;
volume 226; pages 1421-1424.

(3) Footprints in The Dust; Charles M. Telesco;
Nature; volume 369; pages 610-611.

(4) Dust Depletion In The Inner Disk Of Beta Pictoris
As A Possible Indicator Of Planets; P. O. Lagage
and E. Pantin; Nature; volume 369; pages 628-
630.

(5) Birth Of A Solar System?; Tim Folger; Discover;
volume 13; page 27.

(6) Inhibition Of Giant-planet formation By Rapid Gas
Depletion Around Young Stars; B. Zucherman,
T. Forveille, and J. H. Kastner; Nature; volume
373; pages 494-496.

(7) A Planet Around Beta Pictoris?; Sky and Telescope;
Volume 88; page 10.

ADDITIONAL BIBLIOGRAPHY

A Closer Look At Beta Pictoris; Astronomy;
volume 21; Page 18.

Birth Announcements; Scientific American;
volume 256; pages 60+.

Faraway Planets; Science Digest; volume 94;
page 47.

Protoplanetary nebula around Beta Pictoris;
Astronomy; volume 13; page 60.