Chapter 15: The Formation of the Solar System
Images Archive


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Protoplanetary Disks!

As discussed in the text, solar system formation theory has been undergoing someexciting recent experimental tests, with discoveries by the Hubble Telescope of large numbers ofProtoplanetary Disks inthe Orion Nebula and elsewhere.

Dust Disk around Beta Pictoris
This picture shows in detail for the first timethe inner region of a 200-billion-mile diameter dust disk around thestar Beta Pictoris. This region has long been hidden fromground-based telescopes because of the glare from the central star.
Source: NASA Space Telescope Science Institute,Hubble Space Telescope Public Pictures,Image ID: PR 96-02;(copyright notice)

The disk is slightly warped. If the warp were there when the starformed, it would long since have flattened out, unless it is producedand maintained by the gravitational pull of a planet. The suspectedplanet would dwell inside a five-billion-mile diameter clear zoneinside the inner edge of the disk.

The top portion is a visible-light image of the disk, which appears spindle-likebecause it is tilted nearly edge-on to our view. The disk is made upof microscopic dust grains of ices and silicate particles, and shinesby reflected light from the star. The bright star,which lies at the center of the disk, is blocked out in this image.

At the bottom of the image,false color processing has been used to accentuate detailsin the disk structure. The pink-white inner edge ofthe disk is slightly tilted from the plane of the outer disk(red-yellow-green) as identified by a dotted line. A simple explanationis that a large planet is pulling on the disk. It is not possible tosee the planet directly because it is close to the star, and perhaps abillion-times fainter.

Extrasolar Planets!

Since the announcement of the probable discovery in 1995 of a Jupiter-mass planet in orbit around the star 51 Pegasi, researchers have continued to study other nearbystars with great interest and to amass further candidates. The original claimwas based on 18 months of precise Doppler measurements done at the Observatoirede Haute-Provence (France). 51 Peg is a solar-like star 40 light years away. The most straightforward interpretation of these observations, according to theresearchers, was that 51 Pegasi is orbited by an unseen companion having a massof about 0.5 Jupiter masses, and orbiting the star at a distance of 1/20 theEarth–Sun distance.

Many questions remain unanswered, such as how a Jupiter-like planet could be stable so close to its host star, and the composition of the planet.It would not have the atmosphere and composition of our Jupiter,since its surface temperature would be about 1000°C.

Discovery of 51 Pegasi b
Confirmation of the above report and further extrasolar planet news has comeswiftly from the team of Geoff Marcyand Paul Butler at San Francisco State University. Using a similarhigh-precision velocity measurement technique, they were ableto confirm the Swiss discovery,making this the first verified planet ever found orbiting a solar-type star.Their initial velocity plot for 51 Pegasi is shown in this image.

Discovery of 47 Ursa Majoris b
In early 1996, shortly after the above news was relesed,Marcy and Butler announced the discovery of two moreplanets outside of our solar system, one each orbiting the stars 47 Ursa Majorisand 70 Virginis. This graph shows the velocity curve of 47 UMa over amultiyear period from 1988 to 1996. This planet orbits its parent at adistance of approximately 2.2 astronomical units and has a mass of about 3.5times that of Jupiter.

Discovery of 70 Virginis b
This graph shows the velocity versus orbital phase of 70 Virginis b. (Comparethis, for example, to the previous graph, which simply showed measurements ofvelocity versus time.) This planet orbits its parent star at a distance ofapproximately 0.6 astronomical units and has a mass about 8 times that ofJupiter.

Masses of These Planets
The distribution of masses of the known large planets (including our ownJupiter) follows approximately the predicted theoretical distribution, as shownin this graph. Unlike 51 Pegasi b,the other two planets are at larger distances from their parent stars, and havetemperatures that are reported to be in a range that could support liquid water(if water exists on them). Although the number of measurements is limited, this plot givesencouraging news to both theorists and experimenters that the technique is capable of makingmore such extrasolar planet discoveries in the future.

Credit for the above images:M. Mayor, D. Queloz (Geneva Obs.);G. Marcy, P. Butler (SF State Univ., UC Berkeley);R. Noyes, S. Horner (Harvard, Penn St.);G. Burki, M. Burnet, M. Kuenzli (Geneva Obs., Lausanne University)
Source: San Francisco State University, Planetary Searches,Image ID: (Various)

Enough other candidate solar systems have since been found to prompt intensespeculation on what these systems might be like as possible habitats forlife, or at least indicators of such habitable solar systems beyond our own.

Exploration of Neighboring Planetary Systems

Finally, as part of a broad theme for the scientificinvestigation of the origins of stars and planets, NASA has launched a newprogram for the Exploration ofNeighboring Planetary Systems (ExNPS) having as its eventual goal the detection and imaging of much smaller planets around nearby stars.

Kuiper Belt object observed!
Where do comets come from? In 1951, Gerard Kuiper proposed that a population of small bodies inhabits the furthest reaches of our solar system, and that some of these bodies occasionally stray closer to the Sun, thus becoming comets. An important confirmation of this conjecture was revealed when Dave Jewitt (University of Hawaii) and Jane Luu (University of California at Berkeley) discovered the small object in this photo -- its orbit is consistent with membership in the Kuiper Belt. If confirmed, this would be the first known member, and may help us to understand the source of comets, and the conditions in the early stages of our solar system.
Source: University of Hawaii, Institute for Astronomy, 1992 QB1. Image ID: qb1.gif

Planet Exploration Timescale
The ExNPS project aims to design and build a set of4 infrared telescopes linked together as an interferometerand operating from the darkest part of our solar system beyond the orbit ofJupiter. The interferometer componentscould be launched as early as 2005 to search for Earthlike planets aroundnearby stars and to identify carbon dioxide (CO2), ozone (O3) and water vapor (H2O) in the atmospheres of the brightest such planets. This ambitious plan issummarized in the following timeline graph.
Source: NASA Jet Propulsion Laboratory,The Exploration of Neighboring Planetary Systems,Image file: Timeline

ExNPS Interferometer Spacecraft Design
This schematic overview image shows the arrangement of the essential componentsof the interferometer spacecraft for the ExNPS program. Cryogenic opticalcomponents, along with beam control elements, focal plane instruments, anda propulsion system would be mounted on an active, vibration-damped frame.
Source: NASA Jet Propulsion Laboratory,The Exploration of Neighboring Planetary Systems,Image file: CoreTech


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