1987, in. pp 123-136 |

Their very short lifetime compared to total stellar lifetime accounts for their rarity. It is expected that the Sun will form a planetary nebula at the end of its life cycle. Because the gravity of the giant planets could “stir up” the orbits of the planetesimals, the material impacting on the inner protoplanets could have come from almost anywhere within the solar system. [38] (The Earth's atmosphere, by comparison, contains 2.5×1019 particles per cm3.) The process was most efficient for Jupiter and Saturn; hence, their compositions are most nearly “cosmic.” Much less gas was captured by Uranus and Neptune, which is why these two planets have compositions dominated by the icy and rocky building blocks that made up their large cores rather than by hydrogen and helium. A planetary nebula, abbreviated as PN or plural PNe, is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.[2].

Nevertheless, a full theory must also be prepared to deal with the exceptions to these trends, such as the retrograde rotation (not revolution) of Venus. What is its rotation period when it has shrunk to the size of Pluto’s orbit, which Appendix F tells us has a radius of about 40 AU?

If Jupiter’s orbit has a radius of 5.2 AU, then the diameter is 10.4 AU. Evidence also points to the potential discovery of planetary nebulae in globular clusters in the galaxy M31. [65] Several have been shown to exhibit strong magnetic fields,[66] and their interactions with ionized gas could explain some planetary nebulae shapes. This is similar to the process by which raindrops on Earth condense from moist air as it rises over a mountain. A substantial step up in size is required, however, to go from planetesimal to planet. [41], The huge variety of the shapes is partially the projection effect—the same nebula when viewed under different angles will appear different. A similar idea had led to the discovery of helium through analysis of the Sun's spectrum in 1868. Olnon, F. M. 1977, Ph.D. Thesis, Univ. I have already found four that have a visible diameter of between 15 and 30 seconds. The Butterfly Nebula exhibits the classic hourglass shape of many planetary nebulas… Intricate Crab Nebula Poses for Hubble Close-Up NASA/ESA and Jeff Hester (Arizona State University). In the latter case, there are not enough UV photons being emitted by the central star to ionize all the surrounding gas, and an ionization front propagates outward into the circumstellar envelope of neutral atoms. [49] Nevertheless, the reason for the huge variety of physical shapes is not fully understood. Let’s look in more detail at how material condensed at different places in the maturing disk (Figure 2). Young planetary nebulae have the highest densities, sometimes as high as 106 particles per cm3. The material in the center, however, where it was hottest and most crowded, formed a star that maintained high temperatures in its immediate neighborhood by producing its own energy. (credit: modification of work by NASA/JPL/University of Arizona). [48] On the other hand, spherical nebulae are likely produced by the old stars similar to the Sun.

(See Stellar population. (2011). Each of these protoplanets continued to grow by the accretion of planetesimals. Jacoby, George H.; Ciardullo, Robin; De Marco, Orsola; Lee, Myung Gyoon; Herrmann, Kimberly A.; Hwang, Ho Seong; Kaplan, Evan; Davies, James E., (2013). Cite as.

The angular momentum of an object is proportional to the square of its size (diameter) times its period of rotation (D2/P). [27] This state of equilibrium is known as the main sequence, which can last for tens of millions to billions of years, depending on the mass. [23][24], Under the Morgan-Keenan spectral classification scheme, planetary nebulae are classified as Type-P, although this notation is seldom used in practice.[25].

As far as age is concerned, we discussed that radioactive dating demonstrates that some rocks on the surface of Earth have been present for at least 3.8 billion years, and that certain lunar samples are 4.4 billion years old. This illustration shows the steps in the formation of the solar system from the solar nebula.

About one-fifth are roughly spherical, but the majority are not spherically symmetric. Chapter 4. For example, Saturn’s rings reflect sunlight at 2 micrometers, but not at 3 and 5 micrometers, so they appear blue. Each of the other members of the planetary system is, to some degree, lacking in the light elements. Planetary nebulae are classified by different authors into: stellar, disk, ring, irregular, helical, bipolar, quadrupolar,[46] and other types,[47] although the majority of them belong to just three types: spherical, elliptical and bipolar. Last edited on 15 September 2020, at 00:22, "The Sun Will Produce a Beautiful Planetary Nebula When it Dies", "The Galaxy.



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