Scientists Gear Up for Big Bang of Comet, Jupiter : Astronomy: An army of sky watchers have their sights trained on the planet. But they won’t get a direct view of the celestial collision because it is expected to occur on the dark side, out of view of Earth.
When the fireworks flare on the far side of Jupiter on Saturday, astronomers around the world will be straining for an indirect glimpse of the collision between a comet and the solar system’s largest planet, like someone outside the stadium trying to follow the Super Bowl by the roar of the crowd.
Scientists and amateur astronomers will be denied a direct look at the collision because the 21 or so fragments of comet Shoemaker-Levy 9 are expected to hit the planet’s night side, which faces away from Earth.
Instead, they will have to seek secondhand evidence of a once-in-a-lifetime celestial event: powerful ripples in the planet’s thick atmosphere, disturbances in Jupiter’s distinctive cloud patterns, bursts of interplanetary static caused by the impacts, and even the momentary glow from the explosive flashes reflected on Jupiter’s many moons.
While it is a daunting challenge, astronomers say they are used to constructing their views of the universe from scant data. They have inferred the existence of planets outside the solar system by timing stellar static, detected a massive black hole by the speed of star systems swirling around it, and heard--in the hum of background radiation--the last faint echo of creation’s Big Bang.
No astronomer has ever had a chance before to watch--even indirectly--when a comet slams into a planet, so professional and amateur observers are marshaling a global network of telescopes, airborne observatories and space probes throughout the solar system to capture hints of the collision.
The first piece of the fragmented comet is expected to hit Jupiter about 1 p.m. PDT Saturday, experts predict, with the second hitting about sundown and the third just before midnight. Other chunks of the comet, traveling at 130,000 m.p.h., are expected to rain on Jupiter for several days, with the last piece hitting early next Friday.
This weekend, the Griffith Observatory and the Los Angeles Astronomical Society are planning gatherings featuring Jupiter for amateur astronomers and the public. The observatory’s main Zeiss telescope will be trained on Jupiter, and smaller telescopes will be set up on the grounds for public use Saturday. The Planetary Society is gathering at the Mt. Wilson Observatory.
For observatories in the Western United States, however, the most favorable viewing opportunities will not come until next week, well into the five-day bombardment.
Comet experts at the Jet Propulsion Laboratory predict that sky watchers in California will have their best viewing chances late Wednesday and Thursday evenings.
Even if the weather cooperates and the night skies are clear, viewing throughout North America will be limited because most of the impacts will occur during daylight or after Jupiter has set.
Although the actual impact will take place on Jupiter’s dark side, the impact zone will rotate into view and be visible from Earth for about five hours after each hit.
Astronomers caution that no matter where on Earth an observer stands, there will be little visible to the naked eye or to most amateur telescopes. The Assn. of Lunar and Planetary Observers says that for the best results, amateurs should use a telescope with high-quality optics and at least a 10-inch aperture.
Some amateur astronomers, frustrated at not being able to see the collision directly, say they will hook up radios and listen to it instead. The U.S.-based Society of Amateur Radio Astronomers does not know what the crash will sound like, but is urging its members to tune in.
Jupiter normally emits radio waves at frequencies between 500 kilohertz and 40 megahertz, which radio astronomers think are caused by electrons breaking free of a magnetic bond between the planet and its moon Io.
On an Earth-based short-wave radio, Jupiter’s transmissions sound like waves crashing onto a beach.
Astronomers emphasized that the collisions should have no adverse effect on Earth.
“There will be no changes on Earth, except among a very excited group of astronomers,” JPL comet expert Donald K. Yeomans said.
They aren’t sure what to expect.
Earlier sightings of comets, such as Kohoutek in 1973 and Halley’s comet’s return in 1986, did not live up to public expectations.
Experts at the University of Arizona’s Seward Observatory predict that the comet--a “rubble pile” whose chunks are composed of hundreds, if not thousands, of small snowballs--will disintegrate high in Jupiter’s atmosphere, going out with a fizzle, not a noticeable bang.
Two reports in the science journal Nature this week suggest that the comet, in a deteriorating orbit around Jupiter and already torn to pieces by the planet’s gravitational field, will disintegrate further before it plunges into Jupiter’s atmosphere. The comet may produce a spectacular meteor shower, but no massive fireball.
Paul Weismann, in JPL’s Earth and Sciences Division, predicts a “cosmic fizzle.”
A University of Chicago astrophysicist, on the other hand, predicts that the fragmented comet will create a spectacular plume of super-heated debris that will shoot hundreds of miles above Jupiter’s multicolored clouds.
His conclusions are based on elaborate computer simulations of the impacts conducted at the Pittsburgh Supercomputer Center.
Willy Benz, an astronomer at the University of Arizona, is optimistic. “Even if this impact is somewhat less spectacular than the media would like to have it, I believe that potentially much can be learned about the structure of comets and the circulation in Jupiter’s atmosphere,” he said.
Slam-Dancing With Jupiter
* What: A collision between the comet Shoemaker-Levy 9 and Jupiter.
* The comet: The remains of a comet that has broken into a string of 21 or so chunks. Some may be more than a mile in diameter.
* The planet: Jupiter is the largest planet in the solar system. More than 88,700 miles in diameter, the planet is composed almost completely of hydrogen and helium.
* First impact: 12:58 p.m. Saturday.
* Last impact: 12:57 a.m. July 22.
* Best West Coast viewing: 10:24 p.m. Wednesday and 9:15 p.m. Thursday.
* Where: Jupiter will be about 400 million miles from Earth when the impacts occur.
* Watching from Earth: Essentially every observatory in the world.
* Watching from space: Voyager 2, Galileo, Ulysses and the Hubble space telescope.
* Watching from Los Angeles: The Griffith Observatory and the Los Angeles Astronomical Society will have telescopes set up for the public until midnight Saturday. A 40-minute lecture on the impacts will be presented at the observatory’s planetarium at 9 p.m. Monday, and Tuesday through Friday at 4:30 p.m.
All times are Pacific Daylight Time.
