Avi Blizovsky
Imaging of Totatis, produced following radar observations in previous passes. Much information is still missing about the bone. Photo: NASA
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There's a little rumor going around the internet that a large and deadly asteroid could hit Earth this fall. Newsgroups cite a 63 percent chance of harm. Astronomers know of no impending danger of this kind.
Rumors still have a grain of truth. On September 29, 2004, an asteroid the size of a small city will make the closest approach to a rock of that size in the last century.
While this asteroid poses no danger, it is at least of interest to astronomers. The asteroid, named Toutatis, behaves strangely and scientists already know it from previous 'appearances' and they pointed the radars at it and created computer simulations of its strange shape and movement. Totatis resembles in its shape a whistle thrown in a jagged track in space. It has a crazy spin that makes days and nights on it impossible. Scientists can't explain its shape or its spin, but they want to learn a lot more in September, when during the approach, even amateurs will be able to observe it.
Totatis' orbit is known with greater precision than any other large asteroid that crosses Earth's orbit. Totatis' four-year path around the Sun varies from just inside Earth's orbit to the main asteroid belt between Mars and Jupiter. The asteroid visits us every four years.
This fall it will pass about a million and a half km from us, or about 4 times the distance of the moon from us. This is considered close in cosmic terms for an object that could cause global commotion. It has not come this close since the year 1353 and will not come close again until the year 2562, according to NASA scientists anyway. No large asteroid has come this close before, although precisely tracking space rocks is a relatively new high-tech skill that still leaves wide margins of error for many objects.
Totatis is about 4.5 kilometers long and about 2 kilometers wide. Many smaller rocks passed much closer, deep within the lunar orbit. Others the size of Totatis probably also passed through this window but not at a time when the Earth's skies are being scanned as rigorously as today. And of course, throughout history, some asteroids and comets did hit the Earth. In fact, an object the size of Mars hit the Earth when it was very young and created the Moon, scientists believe. However, the experts say that the danger of a major collision every year is very low. Any other object the size of Totatis will surely be discovered a decade or even hundreds of years before an expected impact. This kind of prediction will be top of the news and not just a small rumor.
No danger, just a strange asteroid
The asteroid Totatis, whose official number is 4179, was discovered by French astronomers in 1989. Researchers cannot see far enough into the future to rule out the possibility that Totatis will slide into Earth, so it is officially classified as a potentially hazardous asteroid. NASA says that according to the calculations of its scientists, it will not hurt for at least the next six centuries.
In the meantime, previous approaches made it possible to conduct radar studies of one of the strangest objects in space. "Most asteroids and all planets spin around one axis, like a football thrown in a perfect spiral," explains Scott Hudson of Washington State University, "but Totatis spins in a strange way, like a drunk's gait. The result is that there is nothing resembling a normal day and night cycle on the asteroid. Instead of a fixed north pole, the axis of rotation of Totatis moves between two cycles - one between 5.4 days and the other 7.3 days (of the Earth). The stars are seen from every point on the asteroid as crossing the sky lengthwise and horizontally and never repeating the same course," says Hudson.
Further studies are planned
Steven Ostrow of NASA's Jet Propulsion Laboratory, together with Hudson, studied Totatis using radar on previous passes. Ostrow says that there is a large population of near-Earth objects. Hundreds of objects with a diameter of over a kilometer have been discovered in the last six years and there is a whole zoo of shapes. There are other asteroids that do not rotate around a single axis. However, Totatis remains the only body in the solar system that does not have a single axis and whose shape and form of rotation are precisely known." Ostrow said. According to him, this year's radar observations will try to further refine the rotation rate and trajectory. "There is still a lot to learn. For starters, scientists can't tell whether Tutatis' surface is hard or has a layer of dust similar to that of the moon.
"I would like to know if the strange shape of Totatis and its relatively slow rotation are the result of a collision that tore it apart from a larger asteroid or if it is a merger between two objects, and when the phenomenon occurred," Ostrow said.
The answers to all the big questions will probably require a visit by a spacecraft but there are no plans yet to make such a visit. "Thanks to the radar studies, the physical characterization of Totatis is the best we have of all the asteroids that threaten the Earth," Ostro said. "However, an encounter with a spacecraft will allow us to know much more, and I like to see it happen."
On September 29, amateur astronomers on Earth will be able to find Totatis, given its place in the sky. Despite its proximity, it will not be visible to the naked eye. Regular binoculars would be best, if the sky is clear and in a dark place, said Alan Harris, of the Space Science Institute in Boulder, Colorado. However, to know exactly what you are seeing, a small telescope would be more useful, says Harris. This will make it possible to watch the slow motion of Totatis against the background stars. The asteroid will appear as a point of light, like a star. It will be too far away to allow viewing of its details for owners of ordinary telescopes.
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