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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