by Jim Bell
a team of three celestial mechanics experts: S. J. Peale, P. Cassen, and R. T. Reynolds, “Melting of Io by Tidal Dissipation,” Science 203, no. 4383 (1979): 892–94 (online at http://dx.doi.org/doi:10.1126/science.203.4383.892).
“Voyager images of Io may reveal . . .”: Ibid., page 894.
the Io images taken for navigation purposes: The “discovery photo” where Linda Morabito and colleagues first noticed the volcanic plumes of Io is online at photojournal.jpl.nasa.gov/catalog/PIA00379.
were eruption plumes from active volcanoes on Io: For a full, detailed, first-person account of the events leading up to the historic discovery of Io’s active volcanic plumes, see Linda Morabito, Discovery of Volcanic Activity on Io, archived online at arxiv.org/pdf/1211.2554; for more stories and details about the study and discovery of volcanoes on other worlds since then, see also Rosaly Lopes and Tracy Gregg, eds., Volcanic Worlds: Exploring the Solar System’s Volcanoes (New York: Springer-Praxis Books, 2004).
I can live to see that exploration pay off: For a great update on the status of the search for life in extreme environments like Europa, as well as upcoming plans for Europa exploration, see Michael D. Lemonick’s “Life beyond Earth” in the July 2014 issue of National Geographic magazine.
“By far the simplest explanation . . .”: Lorenz Roth’s December 2013 press release describing the Hubble Space Telescope’s potential discovery of plumes of water vapor coming from Europa can be found online at http://www.nasa.gov/content/goddard/hubble-europa-water-vapor.
“Decadal Survey of Planetary Science”: The recent 2011 National Academy of Sciences Decadal Survey of Planetary Science, Visions and Voyages for Planetary Science in the Decade 2013–2022 can be found online from the National Academies Press at nap.edu/openbook.php?record_id=13117.
Chapter 5. Drama within the Rings
inner and outer parts orbiting at different speeds: For a fascinating and entertaining account of Maxwell’s work on Saturn’s rings, as well as his fundamental contributions to the physics of electricity and magnetism, see Basil Mahon, The Man Who Changed Everything: The Life of James Clerk Maxwell (Hoboken, NJ: Wiley, 2003).
perspectives to come from the Voyagers that would follow: Amateur astronomer and planetary image processor Ted Stryk has compiled a nice collection of Pioneer 11 “greatest hits” images of Saturn online at strykfoto.org/pioneersaturn.htm.
perhaps some other complex hydrocarbons: This and other early pioneering planetary spectroscopic discoveries were made by the Dutch-American astronomer Gerard P. Kuiper, who is widely regarded as one of the founding fathers of modern planetary science. There’s a nice Wikipedia biography of Kuiper online at en.wikipedia.org/wiki/Gerard_Kuiper.
could have led to the formation of life on Earth: Wikipedia’s entry on the Miller-Urey experiments at en.wikipedia.org/wiki/Miller-Urey_experiment is a great starting point for learning more about these famous early efforts at understanding the possible origins of life on Earth and other habitable worlds.
Voyager’s cameras were blind to the surface itself: Uncovering those secrets, including discovering the hoped-for seas of ethane and methane, would have to wait more than twenty-five years, when the Cassini Saturn orbiter, armed with cloud-penetrating radar inspired by Voyager’s discoveries, would finally map the fascinating geology and hydrology of Titan and when the ESA Huygens probe would get near-surface images just before landing. My planetary science colleagues Ralph Lorenz and Christophe Sotin wrote an exciting and accessible article about our current knowledge of enigmatic Titan, “The Moon That Would Be a Planet,” in the March 2010 issue of Scientific American magazine.
at the time the solar system’s most distant known planet: For some more details about whether Voyager could have encountered Pluto, and other Voyager “Frequently Asked Questions,” see the Voyager Project’s official FAQ at voyager.jpl.nasa.gov/faq.html.
“fresh” ice in the process: It’s a debate that even higher-resolution Cassini Saturn orbiter images and other data have yet to resolve. Cassini camera team leader Carolyn Porco, who was also heavily involved in Voyager imaging of Saturn’s rings earlier in her career, has been careful to note that “there’s a bunch of caveats in all of this. Very little in this area is definite. Each part of the rings may have a different age.” (Porco, as quoted in Richard A. Kerr, “Saturn’s Rings Look Ancient Again,” Science 319 (2008): 21.) It seems that, once again, we find that we really do have to go back. . . .
rocky lava flow would on Earth: A great introduction to cryovolcanism can be found in Rosaly Lopes and Michael Carrol’s book Alien Volcanoes (Baltimore: Johns Hopkins University Press, 2008).
the team was confident that everything would go as planned: A day-by-day, diary-like account of the details of the Voyager Saturn encounters was published by Voyager imaging team member David Morrison in Voyages to Saturn, NASA Special Publication 451 (Washington, DC: National Aeronautics and Space Administration, 1998) (online at babel.hathitrust.org/cgi/pt?id=uiug.30112012462427). Pages 185 to 189 of that book contain a full list of the principal investigators and co-investigators on the Voyager science team and the leaders of the Voyager management teams.
“a million times the normal energy level . . .”: Fred Scarf, quoted in Morrison, Voyages to Saturn, page 123.
almost minute-by-minute account of the Saturn flybys: Morrison, Voyages to Saturn, page 123.
“The quantity of such impacts . . .”: Ibid.
in his diary of events for August 28, 1981: Ibid., page 131.
Cassini orbiter on a “suicide mission” to Saturn: Richard C. Hoagland’s original June 30, 2004, article (and his quote) about this can be found online at http://www.enterprisemission.com/_articles/06-30-2004_Cassini/IsNASA SendingtheCassiniMissiontoitsDoom.htm.
“a sense of gloom . . .”: Ibid., page 119.
Chapter 6. Bull’s-Eye at a Tilted World
a planetary path, well beyond the orbit of Saturn: I recount a lot of the interesting history of William Herschel’s and other pioneering discoveries in astronomy in The Space Book: 250 Milestones in the History of Space and Astronomy (New York: Sterling, 2013).
important work cataloguing faint stars: A nice article about Caroline Herschel’s life and achievements, including her support of her famous brother’s astronomical discoveries, appears in J. Donald Fernie’s “The Inimitable Caroline” in the November/December 2007 issue of American Scientist (online at americanscientist.org/issues/pub/the-inimitable-caroline).
new tilt for a newly formed (potentially merged) planet: For a short summary of some of the latest ideas about the strange tilt of Uranus, see John Matson’s October 7, 2011, article “Double Impact: Did 2 Giant Collisions Turn Uranus on Its Side?” in Scientific American (online at scientificamerican.com/article/uranus-axial-tilt-obliquity).
“That all of this worked so well . . .”: Edward C. Stone and Ellis D. Miner, “The Voyager 2 Encounter with the Uranian System,” Science 233 (1986): 39–43.
ten new, smaller moons: Wikipedia’s “Moons of Uranus” page, at en.wikipedia.org/wiki/Moons_of_Uranus, is a great resource for history, facts, and additional research links on the twenty-seven presently known moons of the seventh planet.
seems to be a leading hypothesis for what happened: Space.com editor and space history author Andy Chaikin posted an excellent article titled “Birth of Uranus’ Provocative Moon Still Puzzles Scientists” on October 16, 2001, summarizing the post-Voyager state of confusion regarding the history of Miranda, online at archive.today/6VTxV.
astronomers led by the late Jim Elliot of MIT: For a firsthand account of the discovery of the Uranian rings, see Jim Elliot and Richard Kerr, Rings: Discoveries from Galileo to Voyager (Cambridge, MA: MIT Press, 1987).
a peer-reviewed scientific journal article: My research paper, coauthored with my PhD dissertation advisor, T. B. McCord, is titled “A Search for Spectral Units on the Uranian Satel
lites Using Color Ratio Images” and was published in the Proceedings of Lunar and Planetary Science 21 (1991): 473–89 (online at http://adsabs.harvard.edu/abs/1991LPSC...21. 473B).
more complex and dynamic weather: For a great summary of the Hubble Space Telescope’s history of imaging of Uranus, check out hubblesite.org/newscenter/archive/releases/solar-system/uranus.
Chapter 7. Last of the Ice Giants
nothing less than solar-system glory: In The Planet Neptune: An Historical Survey before Voyager (New York: Wiley, 1996), the late Sir Patrick Moore, British astronomer and science popularizer, provides additional stories and details about the history of the discovery of Neptune.
taxpayers of an entire nation: For an interesting historical perspective on Voyager within the broader context of exploration over the centuries, see Stephen Pyne, Voyager: Seeking Newer Worlds in the Third Great Age of Discovery (New York: Viking, 2010).
were found to be roughly ten times smaller: Ibid., page 140.
changes in the atmosphere of Neptune over time: For a great summary of the Hubble Space Telescope’s history of imaging of Neptune, check out hubblesite.org/newscenter/archive/releases/solar-system/neptune.
entirely new and unanticipated class of planet: For a fun and educational conversation about ice giants, check out Planetary Society Weekly Hangout blogger Emily Lakdawalla’s April 11, 2013, interview with Voyager imaging team member and Planetary Society vice president Heidi Hammel, online at planetary.org/blogs/emily-lakdawalla/2013/hangout-20130409-heidi-hammel.html.
the entire solar system by nearly 70 percent: Just as for all the other planets with moons, Wikipedia is a great resource to learn more about the fourteen moons presently known around Neptune. See en.wikipedia.org/wiki/Moons_of_Neptune.
the low gravity and atmospheric pressure: For all the gory details, see “Triton’s Geyser-like Plumes: Discovery and Basic Characterization,” by Larry Soderblom and eight other Voyager team colleagues, in the October 19, 1990, issue of Science magazine (vol. 250, no. 4979, 410–15).
KBOs, as they are now known, have been discovered: The International Astronomical Union’s Minor Planet Center, operated by Harvard’s Smithsonian Astrophysical Observatory, keeps up-to-date lists and graphical plots of the orbits and positions of all the more than 650,000 presently known asteroids and comets in the solar system, including the Kuiper Belt Objects. The lists are online at minorplanetcenter.net/iau/lists/MPLists.html; to see the KBO list, click on “Transneptunian Objects,” the more generic name for KBOs.
New Horizons spacecraft flies by Pluto in July of 2015: Visit the New Horizons mission website for more details at pluto.jhuapl.edu.
Chapter 8. Five Billion People per Pixel
human beings who have lived before us: The Population Reference Bureau has an excellent online article explaining their estimate for the total number of people who have ever lived on Earth, posted at prb.org/Publications/Articles/2002/HowManyPeopleHaveEverLivedon Earth.aspx.
the White Sands Missile Range in New Mexico: Tony Reichhardt, “The First Photo from Space,” Air & Space magazine, November 2006 (online at airspacemag.com/space/the-first-photo-from-space-13721411/?no-ist).
after the first Earth-orbiting satellites were launched: For more photos and details about these early photos of the Earth from space, see, for example, (a) http://www.nasa.gov/centers/langley/home/Road2Apollo-11_prt.htm; (b) space.com/12707-earth-photo-moon-nasa-lunar-orbiter-1-anniversary.html; (c) moonviews.com/lunar-orbiter-1-i-or-a; and (d) moonviews.com/2013/05/how-life-magazine-revealed-earthrise-in-1966.html.
“Oh my God. Look at that picture . . .”: Transcripts of conversations and events from the Apollo 8 mission can be found in David Woods and Frank O’Brien, “The Apollo 8 Flight Journal,” available online from the NASA History Division at http://www.history.nasa.gov/ap08fj.
“The point of such a picture . . .”: Carl Sagan, “A Pale, Blue Dot,” Parade Magazine, September 9, 1990, page 52.
“a pale blue dot . . .”: Ibid.
“It has been said that astronomy is . . .”: Carl Sagan, Pale Blue Dot: A Vision of the Human Future in Space (New York: Random House, 1994), pages 8–9.
selfies by subsequent planetary exploration missions: The Planetary Society, the world’s largest nonprofit public space-advocacy organization, hosts a delightful online collection of photographs of the Earth from space at planetary.org/explore/space-topics/earth/pics-of-earth-by-planetary-spacecraft.html.
Cassini orbiter was passing through Saturn’s shadow: Ibid.
“After much work, the mosaic . . .”: Details and photos from the Cassini mission’s “The Day the Earth Smiled” photo event can be found online at photojournal.jpl.nasa.gov/catalog/PIA17171 and on Cassini imaging team leader Carolyn Porco’s Facebook page at facebook.com/carolynporco.
inspirational appeal as the Pale Blue Dot: For lots of stories and beautiful examples of some of the most spectacular photos from the Spirit and Opportunity rover missions, see my book Postcards from Mars (New York: Dutton, 2006).
But the next day when the images were beamed back: For some examples of the photos of Earth taken from the surface of Mars, see photojournal.jpl.nasa.gov/catalog/PIA05547 and also pancam.sese.asu.edu/pancam_instrument/projects_3.html.
Chapter 9. The Edge of Interstellar Space
their “planet” status: For lots more background and detail on the controversy over the demotion of Pluto, see Neil deGrasse Tyson, The Pluto Files (New York: W. W. Norton, 2009); Mike Brown, How I Killed Pluto and Why It Had It Coming (New York: Spiegel & Grau, 2012); and the details about the IAU’s decision to demote Pluto to dwarf planet status, online at iau.org/public/themes/pluto.
maybe 50,000 years ago or more: See astronomer and science evangelist Phil Plait’s Bad Astronomy blog entry titled “The Long Climb from the Sun’s Core” at badastronomy.com/bitesize/solar_system/sun.html for information on how long it takes photons to escape the sun’s core.
are also on escape trajectories out of the solar system: For live updates on the speeds and distances of the five spacecraft that humans have launched on escape trajectories from our solar system, see heavens-above.com/SolarEscape.aspx.
“to extend the NASA exploration of the solar system . . .”: The Voyager Project at JPL hosts an official website describing the goals and achievements of the Voyager Interstellar Mission at voyager.jpl.nasa.gov/mission/interstellar.html.
only 0.0000000000000001 watts, or barely a flea’s whisper: Kohlhase, Voyager Neptune, page 136.
“I feel extremely fortunate . . .”: For more about Suzy Dodd, and a list of the nine previous Voyager project managers before her, see voyager.jpl.nasa.gov/news/dodd_proj_manager.html.
“porous, multi-layered structure threaded by . . .”: M. Swisdak, J. F. Drake, and M. Opher, “A Porous, Layered Heliopause,” Astrophysical Journal 774, L8 (2013): 1 (online at iopscience.iop.org/2041-8205/774/1/L8/pdf/apjl_774_1_8.pdf).
“We think we are outside . . .”: Marc Swisdak interviewed in Richard Kerr, “It’s Official—Voyager Has Left the Solar System,” Science 341 (September 2013): 1158–159.
“When we saw that, it took . . .”: Don Gurnett quoted in Ibid., page 1159.
“Now that we have new, key data . . .”: NASA’s official September 12, 2013, press release, and Ed Stone’s comments, in “Voyager Reaches Interstellar Space” (online at science.nasa.gov/science-news/science-at-nasa/2013/12sep_voyager1).
“I don’t think it’s a certainty”: McComas quoted in Science 341 (September 2013): 1159.
“We have not crossed the heliopause.”: George Gloeckler quoted in Ibid.
particles and magnetic fields within the heliosphere: L. A. Fisk and G. Gloeckler, “The Global Configuration of the Heliosheath Inferred from Recent Voyager 1 Observations,” Astrophysical Journal 776 (2013): 79 (online at iopscience.iop.org/0004-637X/776/2/79/pdf/apj_776_2_79.pdf).
; Chapter 10. Other Stars, Other Planets, Other Life
“One-hundred-six elements”: Glenn T. Seaborg won the Nobel Prize in Chemistry in 1951 for his work on the transuranian elements. See the Prize website’s official biography of him for more details on his life and illustrious career at nobelprize.org/nobel_prizes/chemistry/laureates/1951/seaborg-bio.html.
spacecraft’s lifetimes beyond the mid-2020s: The JPL Voyager Project’s official website for tracking power conservation strategies and limitations is at voyager.jpl.nasa.gov/spacecraft/spacecraftlife.html.
only slightly above the plane of the planets: See heavens-above.com/SolarEscape.aspx.
modern-day spacecraft forensics: For more details, see The Planetary Society’s director of projects Bruce Betts’s April 19, 2012, blog post “Pioneer Anomaly Solved!” at planetary.org/blogs/bruce-betts/3459.html.
just under four light-years away: For information about Voyager 1’s predicted encounter with Gliese 445, see en.wikipedia.org/wiki/Gliese_445, and for information about Voyager 2’s predicted encounter with Ross 248, see en.wikipedia.org/wiki/Ross_248.
“redirect the spacecraft as closely as possible . . .”: Carl Sagan, et al., Murmurs of Earth, pages 235–36.
evidence of planets around other nearby stars: The Extrasolar Planets Encyclopedia, online at exoplanet.eu/catalog, contains lists, plots, and links to the now more than 1,800 planets discovered around nearby stars that are (mostly) like our sun, via a variety of ground-based and space-based methods.
Kepler has found more than 1,000 planets: See the updated tally, and lots more details, on the Kepler mission’s website at kepler.nasa.gov.
never wrote up our results: Trivia fans can, however, find the Biostronomy Symposium paper that Bill Borucki and I presented back in 1993, “Characteristics of Transits by Earth-Sized Planets in Binary Star Systems,” in Progress in the Search for Extraterrestrial Life, ed. Seth Shostak (Astronomical Society of the Pacific Conference Series, no. 74, 1995): 165–72 (online at http://adsabs.harvard.edu/full/1995ASPC...74..165B).
