Dangerous Space Rocks

Remarkable movies of asteroids and a comet, made by Patrick Wiggins, serve to underline the findings of experts who gathered in Dramstadt, Germany to discuss reducing the danger posed by large Near-Earth Objects.

[Comet 103/P Hartley 2, photographed by Patrick Wiggins the night of Oct. 19-20. NASA’s EPOXI probe is scheduled to make a flyby of the comet on Thursday]

Comets and asteroids are chunks of debris left over from the solar system’s formation 4.5 billion years ago. Varying from microscopic bits to monsters the size of mountains, some are disturbed from their orbits to swoop toward the inner sections of our system. Not counting comets, 500,000 asteroids are known; of these, 6,600 are termed NEOs, rocks that come within about 120 million miles from Earth.
A special category is labeled Potentially Hazardous Objects, material that can pass within 4.65 million miles of the planet and are dangerously massive. “PHOs are in orbits that have the potential to make close approaches to the Earth and of a size large enough to cause significant regional damage in the event of an impact,” says a NASA briefing paper issued in January. The agency has identified about 1,100 of these.
So far, none of the objects that have been tracked show a likely collision, although scientists agree that a great many more space rocks await discovery. The orbits of others may be perturbed at any time by swings past planets or nudges from other comets or asteroids.
This year Wiggins, a NASA solar system ambassador to Utah, has been photographing Comet 103/P Hartley 2, which swung back toward the outer solar system on Oct. 28 after approaching the sun, as well as five asteroids that passed close to Earth. He took multiple still views and assembled them into time-lapse movies.
The following views by Wiggins show objects moving through our solar system just during October. In some, he guided on the stars so that the asteroid is seen as passing unmoving stars. With others, he tracked on the asteroid so that the stars are streaks.
For those with slow Internet connections, the images may take a while to load up, winking forward and pausing, then going again. Once all the astro-snapshots are ready to play, the animation moves swiftly.
The animations are located here:
*** Comet Hartley 2, which he imaged Oct. 19-20.

*** Near Earth Object 2010 TD54, taken the morning of Oct. 12 when the asteroid was only about 80,000 miles from our planet

*** Another movie of NEO 2010 TD54, also made on Oct. 12, about the same distance, with the telescope guiding on the asteroid rather than the background stars,

*** NEO TG19, shot through clouds the evening of Oct. 21, with a couple of satellites showing up in the frames.

*** NEO 2003 UV11, with Wiggins guiding on the stars so that the asteroid whizzes past stationary stars, taken Oct. 27 when the asteroid was about 3 million miles away; its closest approach was 1.2 million miles the next day.

*** NEO 2003 UV11 again, the evening of Oct. 29 when the asteroid was “just past closest approach,” as Wiggins wrote. A little less than two-thirds of the way toward the right border of the frame, the asteroid flies past a dim, distant spiral galaxy.

*** The same asteroid,also on Oct. 29, this time following the asteroid instead of the stars.

Of the looping films, the comet animation is the most dramatic because it is the largest object, spraying out dust and ice released by the sun. But the others were much harder to photograph, because they flew past Earth in a zip. Wiggins had to know exactly where and when to expect them, as he set up his telescope.
Wiggins isn’t scared, personally, about an asteroid striking him because the odds are tremendously against it. The chances of one hitting nearby during his lifetime “are quite small,” he said.
“That doesn’t mean we shouldn’t prepare,” he added. Almost certainly some substantial chunk of space debris will head toward Earth eventually. “It would be a good idea if we could be prepared,” Wiggins said, “we in this case meaning human beings, not just the U.S. or Japan or Russia or whatever. It’s one planet and we should all be together in protecting it.”
The farther away a large Earth-bound asteroid is, the easier it will be to deflect. If it’s too close, efforts to nudge it into a less dangerous course will be too late.
A two-day workshop on the danger of NEOs, hosted by the European Space Agency and organized by the Association of Space Explorers and the Secure Word Foundation, concluded with a press conference on Friday. Experts from Europe and America attended the sessions in Dramstadt.
Dr. Detlef Koschny, an astronomer and researcher for ESA who is based in the Netherlands, summarized the meeting’s recommendations for Nightly News: a Mission Planning and Operations Group, composed of space agencies of different nations, should be established; the group should help the agencies understand “the technical issues involved in planetary defense,” and the group should propose research toward deflecting near-earth objects.
Finally, the workshop “recognizes the value of finding hazardous NEOs early in averting the avoidable costs of future deflection missions. This strategy requires upgraded NEO search and tracking capabilities.”
David Leonard of the Secure World Foundation said during the press conference, “I think there’s always an immediate danger. … The main thing now is to identify these objects, to understand them, track them.”
“We are poised in the position to act now,” said Nicolas Bobrinsky of ESA. He noted that every day Earth absorbs more than 100 tons of dust, mostly from tiny fragments entering the atmosphere. “The bigger the object is … the smaller the chance that it hits the Earth.” But in the past billions of years large objects have slammed into Earth “thousands of times.”
These cause blast waves, tsunamis, atmospheric disturbance and other damage, he said.
Kurt Fisher, a member of the Salt Lake Astronomical Society, used the on-line Earth Impacts Program calculator to see what an asteroid the size of Friday’s close pass would do if it happened to hit Salt Lake City. It would blast out a crater around four miles across, with an initial depth of more than a mile but then filling with melted material so it ended up 1,700 feet deep.
The fireball “would be 10 times the sun’s mean brightness,” he said. “At 100 km [62 miles] distant from the impact — let’s say Nephi or Spanish Fork — anyone outside would suffer first degree burns over 100% of their body, and the town, if not shaken down, would burn down.”
Rusty Schweickart, the Apollo 9 astronaut, told the press conference, “It’s just a matter of time before we find one with our address on it.”
The sort of asteroid or comet impact that is most likely to cause severe damage, like the one that hit Tunguska, Russia, in 1908, seems to have an impact frequency of about 200 or 300 years, said Schweickart, the founder of the B612 Foundation. The group is a nonprofit that works toward the development and testing of asteroid defenses in space.
“The question is, Well, why should we care about something that happens every two or three hundred years?” he asked. The answer was another question: what if someone were throwing rocks at your head and only hit the target once in a while?
“While we may only get hit once every two hundred years, we will have to make a decision every ten years, or that sort of frequency, in order to be assured that we not get hit,” he said. And when you’re talking about approaching asteroids, “you’re not going to move the Earth.”
Ideally, a dangerous space rock could be detected 25 years before possible impact, so that spacecraft and other devices have a chance to deflect its orbit, he said.
Because we now know of the potential impacts and can prevent them, Schweickart said, “We have a moral obligation to do so.”

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