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Disclaimer: Term papers are for research purposes only.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.
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