WHAT'S NEW SINCE PUBLICATION:
Solar System and Extra-Solar Planets
Sojourner Rover on Mars with Yogi the Rock, 1997.
(Courtesy NASA/JPL)
- It appears that water has existed on the surface of Mars very
recently. Announced in a NASA press release on June 22, 2000, and
published in the June 30, 2000 issue of Science,
Michael C. Malin and Kenneth S. Edgett report that the Mars
Global Surveyor satellite has seen strong evidence of ground-water
seepage and surface runoff.
- Planets have been detected around Sun-like stars. The first detection to be
announced was for the star 51 Pegasi, a main-sequence G2-G3 (the Sun is G2), located 40 ly
away and is magnitude 5.5. The planet has an orbital period of 4.3 days and is only about
0.05 AU from the star. It is believed the that mass of the planet is about one-half the
mass of Jupiter. Since the planet is so near its parent star, it is unlikely that the
planet can be structurally anything like Jupiter since its surface temperature should be
near 1000 K. Data for 70 Virginis and 47 Ursa Majoris suggest the presence of planets with
masses of $M\sin i = 6.5$ and 2.3 Jupiter masses, respectively. So much for the
comment in footnote 1 of Chapter 18 (p. 755)! (For more information about the orbital
mechanics of binary systems, see Chapter 7.) [Refs: (1) Alan M. MacRobert and Joshua Roth,
Sky and Telescope, January 1996, p. 38;
(2)
Extrasolar Planet Search homepage.]
- One star (Upsilon
Andromedae) is now known to have three planets in orbit around it. This
discovery indicates that planetary system formation is indeed possible beyond our
own solar system!
- Another star (HD209458) has recently been observed to have a
planet transiting
across its face. The prediction (from the group of Geoff Marcy, Paul
Butler, and Steve Vogt), that an eclipse would lead to a drop in the light
observed from the star was confirmed by a team led by Greg W. Henry when a
1.7% dip in brightness was detected on November 7, 1999. From
the orbital parameters and the transit times, the planet is now known to
have a mass of 0.64 MJupiter and a radius of about 1.6 RJupiter.
This implies a density of only 0.2 g cm-3. This is
consistent with the planet being very near its parent star and consequently
quite blotted.
- Yet another detection of an extrasolar planet has been made; this time by
direct reflection of light from the planet itself. The observation of
a planet around tau Bootis was made by a team of astronomers from the
University of St. Andrews. and reported by Cameron et al., in Nature,
December 16, 1999.
- A second
asteroid is now known to possess a moon (see Figure 21.9, p. 875 for an
image of the first known asteroid-moon system; Ida and Dactyl). Using CFHT,
ground-based observations have revealed a moon orbiting Eugenia with
a period of 4.7 days. The nearly circular orbit has a radius of 1190
km. Eugenia and its moon have diameters of 215 km and 13 km,
respectively. These data imply a surprising result; Eugenia has a
density that is only about 20% that of water! The results are reported
in the October 7, 1999 issue of Nature.
- Uranus is now known to possess 20 moons. This makes Uranus
the current record holder in our solar system. J.J. Kavelaars' team
made the discovery of two new moons using the 3.5 m Canada-France-Hawaii
Telescope on Mauna Kea.
- It now appears that NASA scientists have determined the source of the debris that forms
the ring system of Jupiter. The Galileo
spacecraft has revealed that the ring system is composed of dust, as suggested in the text
on p. 849. Apparently the dust originates from the small moons orbiting near the
planet. When meteors impact the surface of the moons they vaporize some of the
material, and eject dust into orbit about the planet. September 15, 1998.
- The Mars Global Surveyor is
currently in orbit around Mars and continues to return interesting new science.
Among its observations is increased evidence that liquid water once existed on the surface
of the planet.
- The Mars Pathfinder/Sojourner Rover mission
had a very successful mission during 1997, touching down on the red
planet on July 4. Pathfinder and Sojourner returned wonderful pictures and a great
deal of exciting information. The lander was officially named the Sagan Memorial Station,
in honor of the late Carl Sagan.
- The two great comets, Comet Hyakutake C/1996 B2 and Comet Hale-Bopp have
faded from view; Comet Hale-Bopp peaked in brightness in late March - early April of
1977! Information on these great comets can be found in Sky and Telescope's SKY Online Comet Page.
- Evidence presented by NASA indicates that primitive
life may have existed on Mars more than 3.6 billion years ago. The clues are contained
in a 4.5 billion year-old meteorite of Martian origin (Section 21.4, p. 886). This meteorite landed on Earth some 13,000 years ago and was
collected in Antarctica in 1984. The meteorite contains polycyclic aromatic hydrocarbons
(PAHs; Section 12.1, p. 433) and unusual compounds (iron sulfides and magnetite) that are
known products of microscopic organisms on Earth. Electron microscopy also reveals structures (less than 1/100 the width of a human hair) that
can be interpreted as microfossils of bacteria-like life forms. Click here for the text of the August 7, 1996 NASA press
release. Full details of the discovery may be found in the August 16, 1996 issue of Science. [Courtesy David McKay
(Johnson Space Center) et al., and NASA.]
- According to an article in the 18 July 1996 issue of Nature, there is evidence that Earth's inner core
may rotate faster than its outer core by about 1o/yr (Song, Xiaodong and
Richards, Paul G., "Seismological Evidence for Differential Rotation of the Earth's
Inner Core," Nature, 382, 221,
1996).
- These views of Pluto's surface (Section 21.1) were
obtained by the European Space Agency's Faint Object Camera onboard the Hubble Space Telescope. The images, which were
released to the public in March 1996, reveal a surface with more large-scale
contrast than any planet except Earth. [Courtesy of Alan Stern (Southwest Research
Institute), Marc Buie (Lowell Observatory), NASA, and ESA.]
- The Galileo spacecraft and atmospheric probe arrived at Jupiter on December
7, 1995 (see Section 20.1 of Modern Astrophysics).
The probe survived its decent into the planet's atmosphere for 57 minutes, sending
information back to the orbiter, which was then relayed to Earth. Preliminary results
suggest that much less water was detected by the probe than was anticipated, based on
analysis of the Shoemaker-Levy 9 comet collisions of July 1994. The results do seem to be
consistent with the amount of oxygen in the Sun, however. For the most recent results of
this ongoing mission, visit the Galileo
homepage. There you will find spectacular images of the planet and its moons.
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Last modified September 12, 2005.
