Question: Has Hale-Bopp ever changed course, as far as you can tell?
Stuart Goldman: No. Hale-Bopp is in a well-defined orbit. As comets get closer to the Sun, jets of gas are expelled. These jets act as little rockets, slightly changing the course of a comet. This is why repeat appearances sometimes are "early" or "late." As a comet is better observed, it becomes easier to accurately predict where it will be in the future. But Hale-Bopp has not "changed course".
Q: Is there any danger of Earth coming too close to Hale-Bopp?
Stuart Goldman: Not this time around. When [the comet] is closest to the Sun, the Earth will be 100 million miles away.
Q: How about the next time around? Do you know when that will be?
Stuart Goldman: The comet has an orbit of 3,500 years or so.
Q: I've heard that the comet is already flaring and it's not supposed to do so that far out (2AU beyond Jupiter). Is this true? And what exactly is "flaring"?
Stuart Goldman: Comets are made mostly of frozen gases. As they get nearer to the Sun, they evaporate. Sometimes there is an "outburst," as if the surface has cracked open and spewed out fresh material. This happens a lot with comets. In fact, it was observed in Comet Halley many years after it came close to the Sun. These outbursts are probably the only reason the comet was seen this far out.
Q: On Art Bell's radio show it was said the comet was at one time called 070795-B and that you'd get wild reactions if queried by that name.
Stuart Goldman: I don't even know what "070795-B" means. It is not a proper designation for an astronomical object.
Q: If an anomalous object was sighted over the USA for more than, say, an hour, would it be reported and investigated by astronomical "societies"?
Stuart Goldman: It depends on how reasonable the observation sounds. A lot of unusual objects are just fireballs -- bright meteors. If enough people see it and have good reports, astronomers can pinpoint the location of where a meteorite fell. A lot of people see "anomolous" objects that turn to be Venus (I know a guy who had to call the TV station to tell them that the videotape the station helicoptered in 400 miles, taken by a State Trooper, only showed Venus). If you have a good report, more than likely someone can identify what you saw, even if it mystified you.
Q: How big is Hale-Bopp's core? When does it reach perihelion? Is it of natural origin?
Stuart Goldman: The nucleus of the comet could be as large as 100 km in diameter. Comet Halley's nucleus is about 15 km wide. Halley is the ONLY nucleus ever seen, and that was because it was imaged by a spacecraft that flew by it. It is impossible to see the nucleus of a comet through the cloud of ejected gas and dust. Because HB is bright, it is assumed that the nucleus is large. It reaches perihelion (closest to the Sun) on March 31, 1997. Good viewing will be from January to May 1997. There is a preliminary observing guide for the comet in the November issue of Sky & Telescope magazine (now on newsstands). And there is nothing about Hale-Bopp that suggests an unnatural origin.
Q: What if anything is really unusual about Hale Bopp? And will it be visible to the human eye, unaided?
Stuart Goldman: If it follows predictions, it will quite a sight in the night sky -- possibly as bright as Jupiter with a significant tale. That article I mentioned before has a good summary of what astronomers think might happen. But even so, we have more than a year to follow the comet to see how things develop. In the 1800s there were several really big and bright comets with tales spanning the heavens. There hasn't been one like those since then. Astronomers have been hoping for one. This might be one. If the comet was better placed for viewing (that is, if the Earth was closer to it), such a spectacular view would be likely. However, because of the orientation of the tail when closest the Sun, we will be looking down the tail, so it will be foreshortened. It probably won't look as long as it could.
Q: Is it true that comets are mostly ice? How do they form? What might account for the unusual size of this one? Or is it not that unusual?
Stuart Goldman: All comets could have originally been this big. As they go around the sun, they gradually "melt" away. They probably formed in the early solar system from leftover gas in the solar nebula. Over time, interactions with the large outer planets threw them out of the inner solar system into the Oort cloud, giving them orbits of many, many thousands of years. When they come back in, an encounter with something like Jupiter (remember Shoemaker-Levy 9?) will change the orbit, making it shorter, like Halley.
Q: Have you seen any Hubble images yet? And what about rumors of an H-B spiral organization?
Stuart Goldman: Hubble made observations about two weeks ago. The observations have not been released yet. And images of the comet show that one of the jets had a spiral structure that gradually dissipated.
Q: How close to Earth will Hale-Bopp pass and what effect would an impact of a comet that size have on our planet?
Stuart Goldman: The comet will be 123 million km from the Earth. A piece of rock and ice 10 miles across would disrupt the Earth's environment [so much] that it would likely wipe out much of the life on it (like the dinosaurs). Comet H-B might be 100 miles across. Use your imagination.
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