Yesterday (July 19, 2013), the Cassini probe orbiting Saturn passed directly behind the planet so that it eclipsed the Sun. That’s an opportunity for Cassini to see the Saturn system from another perspective; previous passes resulted in my favorite planet photo and another extraordinary image. However, Cassini imaging team leader and science outreach guru Carolyn Porco, along with the organization Astronomers Without Borders, realized this was also an opportunity: the probe would not only be photographing Saturn, but also Earth. Admittedly, from that distance, Earth is but a pale blue dot, a single pixel of a much larger image, but … it’s our planet. For that reason, people all over the world gathered to wave at Saturn, or just generally be together in the spirit of science and celebration.
I was one of those people, gathering with about 15 others in front of the Science Museum of Virginia in the intense late-afternoon heat. The particular gathering was organized by the Richmond Astronomical Society, but a few other science-lovers braved the temperatures for a photo and camaraderie. (I envy those in Europe who could take their photos at night in the cool, when Saturn would be visible in the sky. We had to wave vaguely at the spot where the planet should be, but it wasn’t really important. The main thing was to be together.)
I’d like to go back there someday
While the Day the Earth Smiled photo won’t be significant, scientifically speaking, the Cassini mission as a whole has been a phenomenal success. Yet, no follow-up space probe to Saturn or its moons is currently planned by any nation; Cassini is only the fourth spacecraft ever to visit the ringed world. (Pioneer 11 and the two Voyagers were the others.) Compared to the continuing efforts to explore Mars and the Moon, with several more missions planned, the outer Solar System is feeling more and more neglected.
Partly that’s a practical matter: the farther from the Sun, the longer a mission must be, with all the problems of making sure the probe can last that long. Additionally, placing a spaceship into orbit around a distant world is harder than the same task for a closer planet, which is why Cassini is the first Saturn orbiter, while the other three were flyby trips. The situation is worse for Uranus and Neptune, each of which has only received one flyby visit from Voyager 2, a mission that exploited the unique positioning of all four giant planets.
However, there are many reasons we should return to the outer Solar System. Saturn’s largest moon Titan is as complex and interesting as any planet, with its thick atmosphere, weird weather, methane lakes, and even rivers. Enceladus, while much tinier, ranks with Jupiter’s moon Europa as one of the best candidates for life beyond Earth in the Solar System. That’s beyond the interest in studying these worlds for their own sake, just to learn as much as possible about our system and its history.
Uranus and Neptune may seem like harder sells on the face of it: no Titan or Enceladus there. However, many of the moons of these planets are interesting as well: Miranda’s fractured surface and Triton‘s active volcanic activity (and probable similarity to Pluto) are but two examples. Just last week, astronomer Mark Showalter of the SETI Institute announced he had found an additional moon of Neptune hiding in data collected by the Hubble Space Telescope, bringing Neptune’s satellite count up to 14.
The planets themselves are interesting and not well understood. Yet, they likely resemble many exoplanets — planets in orbit around other stars. With their wild winds and strange magnetic fields, Uranus and Neptune could be the key to comprehending planet formation in our system and others. For that reason, Mark Hofstadter of the Jet Propulsion Laboratory (which built Voyager, among other missions) has proposed an orbiter for Uranus. The current window of opportunity is not large, though, so it’s time to think about it now.
Science is often given a low priority when money is handed out, but the return on investment is high in the form of employment, development of new technology, and not least payoff in terms of satisfying our need to understand the Universe. So, I’m joining my voice to those in the Planetary Society and calling on everyone to help support the funding of planetary science in the United States and across the world. And of course I don’t limit my call to just planetary science, either: it’s one example, but we should fund all science that brings us better knowledge of the cosmos we inhabit.