Jupiter: giant planetary overlord of our solar system. From Earth, Jupiter’s gargantuan presence is hardly evident on a daily basis; to us it is a far-away dot in the night sky (albeit the third-brightest after the Moon and Venus).
But, Jupiter is special and significant. With a mass equal to 2.5 times that of all the other planets combined, it is by far the largest planet in the solar system. Light from Jupiter can be bright enough to cast shadows on Earth, which is impressive given that its average distance from us hovers between ~ 460 million and 510 million miles. And, while it is the great giant of our planets, Jupiter is made up primarily of the lightest of gases: hydrogen (primarily) and helium. While it may have a rocky core, it has no solid surface to speak of, rendering it most difficult to imagine as either a haven for extraterrestrial life, or a destination for futuristic human space travelers.Due to its large mass and consequently strong gravitational pull, Jupiter acts as a “cosmic vacuum cleaner,” protecting Earth from being pelted with many more asteroids and comets than have reached the surface throughout its history. The impact rate on Jupiter has been estimated to be between two- and eight- thousand times greater than Earth, and without Jupiter it is hypothesized that life on Earth may not have made it this far. In fact, scientists think that habitability on any Earth-like planet — in exoplanetary systems in the Galaxy — may in part depend on a nearby Jupiter-like giant that attracts a large percentage of space debris.
As recently as the 1990s, Jupiter has shown it can do the job. In 1992, astronomers witnessed the break up of comet Shoemaker-Levy 9, torn apart by Jupiter’s gravitational forces, leading to it being described as a “string of pearls”:In 1994, the comet’s 21 discernible fragments, with diameters up to 2 km (~ 1.2 miles), collided with Jupiter at speeds exceeding 130,000 miles per hour. If even one of those fragments had reached a populated region of Earth, the result would likely have been more than just a cosmic light show.
In addition to their physical grandeur, Jupiter and its four most prominent moons — Io, Europa, Io, Ganymede, and Callisto (see the image montage, above) — figure prominently in the evolution of our understanding of the solar system. Now aptly referred to as the “Galilean Satellites”, these four moons were discovered by Galileo Galilei in 1610, marking one of the most significant contributions to science. Galileo used a homemade telescope to make these observations which helped him prove that, without doubt, the Sun, not the Earth (as thought at the time), was the center of the solar system.
Galileo Galilei is often referred to as “the father of modern observational astronomy” for his work on the Jupiter system, the phases of Venus, and sunspots, and he laid the foundation for today’s modern space probes and telescopes. In the more than 400 years since, we’ve certainly come a long way technologically. Data and images from the Voyager and Galileo missions to Jupiter and the outer planets have revealed incredible details of these foreign worlds. The year 2012 marked the 35th Anniversary of Voyager, now in interstellar space, making it the farthest spacecraft ever launched from Earth.
While our record of state-of-the-art space exploration is, rightfully, marked by missions backed by multinational consortia of space agencies and years of development, it should also be remembered developments in technology now give us hand-held devices that can help put astronomy at your fingertips.
I was recently involved in a public observing night, led by my colleague Professor Daniel Caton, at Appalachian State University’s Dark Sky Observatory in the mountains of Boone. It was a wonderfully clear night, during which we got a wonderful glimpse of the Geminid meteor shower. At one point, Jupiter and its four sparkling moons were put into view through the Observatory’s excellent 32-inch telescope. After the crowd dispersed I took a few minutes to fiddle with aligning my iPhone just so, and captured the image below:
I’ll stay tuned for a device one can whip out to capture 200x magnification of the celestial object of their choice — an “iTelescope”, if you will. For now, I like knowing that it’s not that hard to take a pretty decent image of a far-away system through the eyepiece of a moderately sized telescope, just with an iPhone. And now I have Jupiter in my pocket.