Soundings: Traveling in space to travel in time
Saturn yesterday was in conjunction with Earth, on the far side of the sun. Glance toward the sun and you’re glancing at Saturn.
The middle “star” in the sword of Orion is not a star at all – even to the naked eye, it’s a fuzzball, a giant cloud of gas and dust, in places collapsing to form new stars and planets.
As it orbits the center of the nebula (“cloud”), gas and dust can’t fall directly downward, but descends in spirals. As more and more dust arrives from outside, it piles up, forming a dense “accretion disk” around the newly-forming star.
Some four-and-a-half billion years ago, our own solar system likely formed thus, the sun in the center, the planets from matter in the accretion disk.
Studying objects the size of planets, stars and galaxies, astronomers rarely perform experiments; rather, they search space for experiments already in progress – exploding stars, colliding galaxies, collapsing clouds of gas and dust forming new star systems.
Nascent star systems, unfortunately, are so far away, they’re hard to resolve – hard to see in detail.
As they flew past Saturn in the early 1980s, Voyager 1 and Voyager 2 revealed Saturn’s rings to be composed of thousands of smaller ringlets, like grooves in a record. The ringlets are themselves made of particles – some the size of a house, most smaller than marbles, many as fine as smoke.
Take a moment to notice gravity, holding you down in your chair. Gravity is nature’s foremost tool for sculpting planets.
A carpenter carries various tools to cut, pound and carve his work. Just as a hammer can be used to either pound or extract a nail, some tools may be used in a number of ways.
Gravity, too, can sculpt in myriad ways: it raises tides; it keeps Earth and moon together as a double planet, orbiting the sun; it brings down mountains; it carves valleys by drawing water downward; it scours rock with dust by driving the winds.
Even though falling in response to gravity is painful, gravity is not very strong. Even with the entire Earth pulling back with gravity, one can easily pick up a nail with a small magnet.
The gravitational attraction of the particles in Saturn’s ringlets is minuscule … but not zero. As they orbit the planet, the particles can feel the pull of their neighbors.
A week and a half ago, the spacecraft Cassini fired its braking rocket to slow its headlong plunge through the rings of Saturn enough to be captured by the planet. Cassini is now one more of the planet’s several dozen moons – a moon with electronic eyes, ears, nose and more, able to transmit its findings to Earth by radio.
As it hurtled through the rings, Cassini saw the ringlets discovered by the Voyagers. And they were undulating, as disturbances in one ringlet were communicated to its neighbors by the infinitesimal pull of gravity. Waves spread through the rings somewhat like ripples in a pond. (Other waves rippled through the rings electromagnetically – more on that later).
The ringlets are not permanent features of Saturn. Ring particles are slowly spiraling down into the planet. In a conversation a few days ago, Carolyn Porco, leader of the Cassini imaging team, emphasized that, in the undulating ringlets of Saturn, we are seeing perhaps the best model of what our planetary system looked like – before there were planets.
The next Sky Watch takes place at the old Nevada City airport on Friday night, July 16, at 9 p.m.
Alan Stahler trained as a biologist and is an amateur astronomer. He teaches enrichment classes for children and adults at Sierra Friends Center. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).
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