http://www.space.com/news/asteroid_defense_041227.html

By Leonard David, Senior Space Writer

posted: 27 December 2004, 08:19 am ET

BOULDER, Colo. -- A cautionary yellow-flag has been raised on a Near-Earth Asteroid (NEA) that is calculated to pass near the Earth in April 2029. The flyby distance is uncertain and an Earth impact cannot yet be ruled out.

The object’s brightness suggests that it measures over 1,300 feet (400-meters) in diameter. If indeed the asteroid -- tagged as 2004 MN4 -- does have Earth’s name on it, this errant space rock, given its apparent size, is capable of causing regional devastation.

While the asteroid is likely to be demoted from its current threat level, the case of 2004 MN4 comes at a time when NASA is weighing the prospect of flying a future asteroid mission that could evaluate planetary defense techniques.

Trajectory modification

Last month, a study team sponsored by the Jet Propulsion Laboratory (JPL) culled together a list of Prometheus-class, fission-powered space missions for early next decade. Prometheus is NASA’s nuclear electric propulsion effort.

Within a list of six potential candidate efforts identified for detailed study is a near-Earth object (NEO) asteroid mission.

According to the JPL study obtained by SPACE.com, that mission would visit several NEOs, the first within three years of launch.

Planetary protection: demonstration flight

Since its creation in 2002, the non-profit B612 Foundation has campaigned for the perfection of asteroid deflection skills.

Former NASA astronaut, Russell Schweickart, is Chairman of the B612 Foundation. The goal of the group of scientists, technologists, astronomers, astronauts, and other specialists is to significantly alter the orbit of an asteroid in a controlled manner by 2015.

A candidate for a Prometheus 1 mission, Schweickart told SPACE.com, is a demonstration trek to an asteroid. It would gather critical engineering design information for a planetary protection system. That "D1" flight would dovetail into a D2, dress rehearsal deflection mission, to further refine and ready full-up, Earth-protecting techniques and technologies.

Schweickart notes from the start that, while the probability of a highly destructive asteroid impact on Earth in the immediate future is slight, the consequence of such an occurrence is extreme, and mitigation efforts should begin now.

In regards to the new observations of asteroid 2004 MN4, Schweickart added, the most likely scenario is that this object will disappear from concern in the next few days and/or weeks.

How high is high enough?

But Schweickart does see asteroid 2004 MN4 as a ringing warning bell.

"It is worth realizing that it is only happenstance that the 2004 MN4 impact date is in April 2029. It could just as well have been 2019...or 2009…or any other date," Schweickart said. "Even with the current 2029 date, the calendar suggests that we should be acting now."

But how high is high enough, Schweickart questioned: 1-in-50? 1-in-100? 1-in-20?

"How could we design such a mission unless we knew more about the surface structural characteristics? Our B612 mission seems to have passed most of the NASA ‘sniff’ tests, but we still need to understand the structural characteristics of the surface to design the attachment mechanism for the ‘tugboat’. This is one of the key objectives of our proposed D1 mission," Schweickart stated.

2004 MN4: a wake-up call

"That means that we should be planning, as we have said, a mission to an asteroid -- and in this case probably 2004 MN4 itself - now. It would not necessarily have to be a Prometheus type mission. It could be done using conventional means," Schweickart said.

Whatever the case, there is definite need to begin building the necessary knowledge base -- such as understanding the surface properties of NEOs -- "as soon as possible," Schweickart emphasized. "Asteroid 2004 MN4 is indeed a wake-up call!"

Poke, prod and push

Dan Durda, a space scientist at Southwest Research Institute here, is President of the B612 Foundation. He also highlighted the need to know more about asteroids before hustling out on a deflection mission.

"The reason for a mission to go out, poke, prod and push on an actual near Earth asteroid is precisely because there is still so much we don't yet understand about the structure of these objects," Durda told SPACE.com.

The operational objective and exploration goal of a B612/Prometheus demonstration (D-1) mission, Durda said, "is to learn by doing."

Durda said becoming skilled at how to deploy and operate a power-rich and highly efficient spacecraft system will extend space exploration capabilities. Given that competence, more can be learned regarding the surface properties and internal structure of objects. That data is not only useful for utilizing them for their valuable resources, but also to cancel out an object that is threatening to Earth and our species, he said.

"There's only so much we can learn about near Earth asteroids by studying them from afar," Durda said. "At some point you have to get on the ‘ground’ and get your hands dirty. I hope for that to be literally true someday very soon!"

Key questions

Durda said that computer simulations can only take you so far.

There are several key questions about asteroids in Durda’s mind: How hard can you push on a pile of rubble held together by its own gravity before its internal components begin to shift around?

Furthermore, how much fine debris might cling to an asteroid’s meteoroid-blasted surface? And how might that material mess up the works on your spacecraft if electrostatics makes it stick and creep into every nook and cranny?

"The things that work well and the things that don't work at all on a mission like this will all teach us a great deal about the real world of working on and about the surface of a near Earth asteroid…be it for mining or planetary protection," Durda advised.

Unexpectedly high value

"Every one of these NEA events is different, and often in unexpected ways," noted Clark Chapman, an asteroid expert also at Southwest Research Institute, and a founding member of the B612 group. "Of course, the big thing that is different about this case is the totally unexpectedly high value of 2004 MN4 on the Torino Scale, he explained.

The Torino Scale is used by scientists to categorize the threat of asteroids. The scale uses numbers and colors to indicate risk of collision, all based on complicated analysis of an asteroid's path and calculations of how that path might change as it’s affected by gravity from Earth and other bodies.

The asteroid has been at four on the Torino Scale since last Friday, and the latest observations have actually increased the odds of impact from 1-in-60 to roughly 1-in-40, Clark said. "I hadn't expected to see such a high probability of impact -- recognizing that there are still 39 chances in 40 that it won’t impact -- by such a large object in my lifetime," he said.

Most newsworthy

The other thing that is different about 2004 MN4, Chapman said, is that its discovery was anomalous. Instead of being discovered by any of the major search telescopes, this finding was made using instrumentation that was new and not fully understood. "So it wasn't until a much later, independent discovery was made that the original data could be linked to the more recent data," he said.

Asteroid 2004 MN4 is "the most newsworthy NEA event that has happened since the NEA threat was recognized," Chapman observed.

"I'm not saying that there should be more news coverage than has been given. In all likelihood, in the next few days or weeks, the impact probability will retreat toward zero, and there's no particular reason to alarm people. After all, the potential threat is a quarter-century away. But given the treatment of NEAs in the past, I'm still surprised that a 1-in-40 chance of a country-destroying impact hasn't been noticed by the media," Chapman said.