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Registration date : 15.11.07
 | Subyek: Asteroid Apophys  Tue Dec 04, 2007 3:06 pm | |
| pada saat ini ada sebuah asteroid yang hendak menghantam Bumi...
diperkirakan asteroid tersebut akan menghantam bumi pada tahun 2029, ada juga yang bilang 2036, memang masih jadi bahan perdebatan... namun yang pasti asteroid tersebut ada dan dalam beberapa tahun lagi akan menghantam bumi......
berikut ulasannya :
- Spoiler:
Asteroid Apophis: Dealing with Earth's Future Troublemaker
By Leonard David
Senior Space Writer
posted: 3 November 2005
9:58 a.m. ET
BOULDER, Colorado - The potential for a newly discovered asteroid smacking into the Earth in 2036 cannot be discounted. NASA has sketched out a response strategy in the outside possibility that the space rock becomes a true threat.
NASA's action plan was the result of prodding by a group of astronauts, scientists and other technical specialists uneasy about the current lack of action to protect the Earth from the impact of near Earth objects (NEOs).
The object was found last year through the efforts of NASA's Spaceguard Survey. In 1998 NASA formally initiated the Spaceguard Survey by adopting the objective of finding 90 percent of the near Earth asteroids larger than 3,280 feet (one kilometer) diameter within the next decade - before the end of 2008.
Asteroid 99942 Apophis - first labeled as 2004 MN4 -- is estimated to be roughly 1,000 feet (320 meters) in diameter. Were it to strike Earth, it would not set off global havoc but would generate significant local or regional damage, experts say.
Worrisome to asteroid watchers is the exceptionally close flyby of Earth by Apophis on April 13, 2029. So close in fact, the space rock will be naked-eye visible as it darts by. And what can't be ruled out at this time is that Apophis may pass through a gravitational "keyhole" - a spot that alters the asteroid's trajectory as it zips by our planet and might put it on the bee-line lane for banging into Earth seven years later.
Issue of critical importance
Concern over asteroid Apophis and the ability to precisely chart its trajectory -- and take steps if needed to deflect the object -- were fervently voiced by the B612 Foundation, chaired by Russell Schweickart, a former Apollo astronaut.
The group requested that NASA carry out an analysis that included the possibility of placing an active radio transponder on the object. Doing so at a fairly early date would yield the requisite orbital accuracy of the asteroid as it sped through space.
In a June 6 letter to NASA Administrator, Michael Griffin, Schweickart on behalf of the B612 Foundation called for support in "resolving an issue of critical importance" - namely whether a scientific mission should be launched to asteroid Apophis in the near term.
Such a probe, if dispatched, Schweickart stated, would provide knowledge of the asteroid's orbit in time to initiate a deflection mission in the unlikely event one should be required. The position of the B612 Foundation was that the mission should be staged, pointing out that NASA's NEO program personnel apparently did not concur with that view. A spacecraft mission to Apophis would augment tracking of the object from the ground, the letter to Griffin explained, and also carry out a number of scientific duties too.
NASA response
NASA provided a formal response to the B612 Foundation's June communique via an October 12 letter from Mary Cleave, Associate Administrator for Science Mission Directorate.
That NASA reply came with an appended detailed analysis by Steven Chesley of NASA'S NEO Program Office at the Jet Propulsion Laboratory (JPL) in Pasadena, California. The study by Chesley dug into Apophis' orbit, under varying conditions, and contained other items pertaining to the space agency's findings about the Apophis matter.
"The key conclusion to be taken from this analysis," Cleave explained in the letter, "is that aggressive (i.e., more expensive) action can reasonably be delayed until after the 2013 observing opportunity. For Apophis, the 16 years available after 2013 are sufficient to recognize and respond to any hazard that still exists after that time."
Cleave noted in the letter that while Apophis "is an object whose motion we will continue to monitor closely in the coming years, we conclude a space mission to this object based solely on any perceived collision hazard is not warranted at this time."
Not ruled out by Cleave, however, is the prospect of Discovery-class, low-cost missions sent to Apophis, "based on purely scientific arguments," she said.
"Indeed, the asteroid's orbit is particularly attractive for spacecraft rendezvous, and the extraordinary close encounter in April 2029 provides a unique opportunity to investigate a number of scientific NEO issues," Cleave explained in the letter.
Pinpointing the object's whereabouts
While Schweickart said that the NASA response to the B612 Foundation's concern is a step forward, there are other issues still to be resolved.
One matter involves radar tracking of Apophis.
On one hand, radar plays a crucial role in being able to rationally determine the future likelihood of a NEO impact and potentially in planning for a deflection mission when required.
Yet the availability of NEO radar tracking, and the budgets to support this work in the future is highly uncertain, even precarious, Schweickart and the B612 Foundation emphasize. Radar hits of Apophis at each opportunity through 2021 are important to keep watch of the object's whereabouts.
"Tracking these asteroids once you know they exist and pinning down their orbits is really not science," Schweickart told SPACE.com. "This is public safety. It's disaster preparedness."
Begging time and bumming bucks
When Apophis swings by Earth, Schweickart said the asteroid will likely change its orbit. Also, its spin characteristics may be altered. Due to Earth's gravity tugging on the object, "asteroid quakes" could reshape Apophis, he said.
Moreover, still far from resolution is a "who's in charge" proclamation about troublemaking NEOs, Schweickart said.
"It would be great if we had NASA doing this as a regular process. Unfortunately, the mindset that's essentially required by their budget is to think about discovery, not to think about the potential need for deflection," Schweickart added. "Until your mindset is oriented that way, you're going to miss things."
Until an agency is identified that is responsible for all of this, Schweickart cautioned, everybody is "begging time and bumming bucks" from some other program. "This whole thing is sort of in a precarious position until somebody gets around to assigning agency responsibility," he said.
Japan's Hayabusa mission
Regarding the skill required to deposit a transponder on Apophis, Schweickart saluted Japan's Hayabusa asteroid sample-return mission, now in progress.
That craft is scheduled to make two landings on its target asteroid - Itokawa -- later this month. The mission is geared to haul back samples of the object to Earth.
Scientists at Japan's Institute of Space and Astronautical Science (ISAS) are working day-by-day issues in readying the probe for contact with the asteroid, including release of a mini-robot onto Itokawa that will move about and survey its rocky surroundings. ISAS is a research arm of the Japan Aerospace Exploration Agency (JAXA).
"It's an impressive mission," Schweickart said, sure to yield operational experience and lessons learned on how best to execute duties on asteroid Apophis.
Global preparedness
The ruin stemming from asteroid Apophis colliding with Earth would potentially be very great.
Indeed, the consequences, Schweickart suggested, would dwarf those seen as a result of the Indian Ocean tsunami in December 2004, hurricanes Katrina and Rita in September of this year, and the Pakistan earthquake last month.
In regards to global preparedness in handling these unusually devastating events of late, "it's basically out of sight...out of mind," Schweickart said. "That's the real challenge for society. The things that you don't know about are one thing. But the things that you do know about, and don't do something about...those are the ones that are really tough."
Refine the impact probability
Fully concurring with NASA's response is Alan Harris, a senior research scientist and asteroid expert for the Space Science Institute headquartered here.
Harris noted, as has been underscored by the B612 Foundation, that if Apophis is indeed on an impact trajectory, then ground-based radar observations will not be able to refine the impact probability to greater than 20 percent. "That is, we would still not know better than one-chance-in-five whether the impact would really occur or not," he told SPACE.com.
"We really would need a transponder to improve tracking enough to firmly establish that an impact would occur," Harris said.
What has been overlooked, or at best under-emphasized, Harris added, is a point raised in the NASA response. Ground-only tracking has a 99.8 percent chance of eliminating any chance at all of an impact. Thus, there is only one-chance-in-500 that ground-based tracking will fail to resolve the issue in favor of no impact. "For this reason I think the NASA conclusion is entirely sensible," he said.
Wait and see strategy
Harris said that there are Apophis observing opportunities every 6-8 years, with each one having about a 90 percent chance of eliminating any possible impact. At each of these "shoulder" times, he said, one can re-evaluate the "wait and see" strategy if the impact possibility does not go away.
"Certainly it seems appropriate to play the 'wait and see' game until after the 2013 observing opportunity," Harris stated. None of this diminishes the opening that Apophis presents for purely scientific investigations, which could incidentally contribute to the NEO hazard issue, he said.
Harris said that he would not recommend a "deep impact" type of scientific mission, "lest we have the misfortune to deflect it into a keyhole, but other than that, Apophis is a very attractive mission target."
A coming of age
Asteroid Apophis, and the discussions it has sparked are welcomed, observed David Morrison, a space scientist and asteroid specialist at NASA's Ames Research Center, situated in Silicon Valley, California.
"I am pleased that this dialog is taking place," Morrison said. "This is the first time that serious possibilities for dealing with a real but low-probability future impact have been discussed in a technically professional way, rather than receiving the 'Hollywood treatment'".
Morrison said that he considers it remarkable that the Spaceguard Survey has reached the
level of maturity where such an asteroid could not only be found, but its orbit understood well enough to deal with "keyholes" and other subtleties. "Apophis represents for me a symbol of the coming of age of Spaceguard and of asteroid impact studies in general," he said.
The possibility of Apophis hitting Earth on April 13, 2036 is real, Morrison said, even if the probabilities now seem to be very small. "These probabilities represent uncertainties in our knowledge of the orbit, not a failure of the science."
But whether the asteroid will strike Earth or not, Morrison concluded, the challenge is to resolve which case is correct. "With more observations over a longer time span, we will be able to tie this down."
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