Planets of the Solar System

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(P-1) The Solar System--Links and Tables

Index 7.Precession 8. The Round Earth   8a. The Horizon   8b. Parallax 8c. Moon dist. (1) 8d. Moon dist. (2) 9a. Earth orbits Sun? 9b. The Planets ----------------- P-1   Planets ----------------- 9c. Copernicus         to Galileo 10. Kepler's Laws

This section opens a collection of 13 additional sections on selected members of the solar system. This is no more than an introductory overview, supplementing "From Stargazers to Starships." Much more can be found in books and on the web, in particular in www.nineplanets by Bill Arnett (the "nine" on its heading is crossed out and overwritten with an "8", but the old URL remains) and in various Wikipedia web pages.   Please note that these sections were added after the rest of "Stargazers" was in place. Some links therefore direct the user to material covered in later sections. Sorry!     The central question in science is not "what are the facts?" but "how do we know?" and these web pages tell of many discoveries. Such information may not have many applications (unlike the laws and math in other sections of "Stargazers"), but instead provides insight into the way science works, into its community and its instruments. Readers whose interest is aroused (may their numbers increase!) can find much more in books, web sites and even journals.     This summary (with several tabulations below) is followed by 13 additional sections: Mercury--hottest, small, closest to the Sun, moon-like, magnetic, with odd axial spin. Venus--thick atmosphere, hot, non-magnetic, very slow spin which may even be locked onto Earth. Earth--abode of life, benefiting from moderate temperatures, oceans of liquid water and nitrogen-rich atmosphere. Large moon, magnetic core and well-developed magnetosphere. Mars--the one most like Earth, but smaller, cold, very thin atmosphere, polar caps, giant volcanoes, non-central magnetism, 2 tiny moons.

Asteroids--Small and numerous orbiting rockpiles. A rare possibility of one hitting Earth. Jupiter--largest, most strongly magnetized, huge radiation belt, polar aurora, colorful active atmosphere Io and other Jupiter moons--4 big moons: outer ones icy, innermost Io volcanic. Many small moons and a thin ring Saturn--Second to Jupiter in mass and magnetism, famous rings, many moons. --------------------- Telescopes--The astronomer's prime tool, indispensable in studying the distant solar system (and the rest of the universe). The first ones to observe the sky, in 1609, revolutionized astronomy. --------------------- Uranus--Gas giant discovered 1781, axis almost in the ecliptic, magnetic axis steeply inclined to it. Neptune--Gas giant resembling Uranus, magnetic axis steeply inclined, its largest satellite in retrograde orbit. Pluto and the Kuiper Belt--Small icy planets, quite numerous. Comets and other small objects--Some come from the distant "Oort cloud," swing around the Sun, then return to deep space. Others are periodic, depleted and young, and may have come from the Kuiper belt, perhaps as "Centaur objects." And there is Sedna, still unclassified. Tables of the Major Planets Note: These lists may limit accuracy. All angles are in reference to the ecliptic, the orbital plane of the Earth (or rather, the perpendicular to that plane). The orbital inclination, for instance, is the angle between the perpendicular to the orbital plane and the perpendicular to the plane of the ecliptic. Orbits of major planets are inclined only slightly to each other. Many entries in these tables compare properties to those of Earth. The measured values for Earth:       Mean distance from the Sun ("Astronomical Unit") 149,598,000 km (usually rounded to 150 million); Orbital period, 365.256 solar days; mean radius, 6371 km; mass 5.9736 1024kg; acceleration due to gravity 9.8 m/sec2, surface magnetic field at the equator about 30,000 nT. Oblateness if the ratio between (requat–rpolar) and requat. Notice also how eccentric the orbit of Mercury is!   Planet     Mean Dist. from Sun, AU   Orbital eccentricity   Orbital period   Orbital inclination   Mean radius, rel. to Earth   Oblateness:     Mercury     0.381     0.2056     87.97 d.     7.005°     0.3829     small     Venus     0.7233     0.0068     0.6152 yr.     3.3947°     0.9499     small     Earth     1     0.0167     1 yr.     0°     1     0.003353     Mars     1.624     0.0934     1.88     1.85°     0.532     0.0059     Jupiter     5.204     0.04877     11.86     1.3°     10.86     0.06487     Saturn     9.582     0.0557     29.66     2.49°     9.0     0.098     Uranus     19.23     0.0444     84.32     0.77°     3.97     0.0229     Neptune     30.1     0.0112     164.79     1.768°     3.86     0.0171   Note on table below: Gravity, escape velocity and absolute surface temperature are for the visible outline. At Mercury, day and night temperatures differ greatly; for the gas giants, parentheses indicate that temperature increases rapidly with depth in the observed atmosphere. Note that the rotation of Venus is very slow, and technically (minus sign) in the opposite sense.   Planet     Mass (Earth=1)   gravity (Earth=1)   Mean density   Escape vel.   Rotat. period   Abs. surface temp.   Mercury     0.055     0.38     5.427    4.25 km/s    58.646 d. 100(night) 700 (day)   Venus     0.815     0.907     5.204     10.46   –243.02d.   735     Earth     1     1     5.515     11.186   1436 min     287     Mars     0.107     0.377     3.934     5.027   1477 min   227     Jupiter     317.8     (2.364)     1.326     59.5     9.925 hr.     (120)     Saturn     95.15     (0.916)     0.687     35.5     10.7 hr.     (88)     Uranus     14.54     (0.886)     1.27     21.3     17.2     (60)     Neptune     17.15     (1.14)     1.638     23.5     16.1     (55)   Note on table below: Magnetic polarity opposed to Earth's is indicated by minus sign. Since all angles are relative to the perpendicular to the ecliptic, the fact that Uranus and Venus have axes tilted above 90° means that technically they spin in opposite direction from Earth. Note however that the axis of Uranus is almost in the ecliptic (inclin. near 90°), while Venus spins very slowly. Where the field is dominated by a dipole near the center, its strength is given, relative to the Earth's; note that the inclination of the Earth's magnetic axis, often quoted at 10-11°, has been rapidly decreasing in recent years. Planet  Rotat.axis inclin   Centr. dipole (Earth=1)   Magn. axis inclin.   Moons   Surface press. (atm.)   Mercury     ~0     ~0.0006     ?     --     --     Venus     177.36°     ~0             93     Earth     23.43 °     1     ~5°    1     1     Mars     25.19 °     off-center         2     .007     Jupiter     3.13°     ~20,000     –9.6°     63     ---     Saturn     26.73°     ~500     ~0°     60+     ---     Uranus     97.77°     ~50     –59°     27     ---     Neptune     28.32°     ~25     –47°     13     ---

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Next Stop (following "The Planets"): #9c   The Discovery of the Solar System, from Copernicus to Galileo


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Author and Curator:   Dr. David P. Stern

    
Mail to Dr.Stern:   stargaze("at" symbol)phy6.org .


Last updated: 18 February 2008