There is certainty in the thought that an asteroid or comet loitering in deep space has Earth’s name on it. While a civilization-snuffing impact is a low probability, it is not zero.
But there are other trouble-makers out there too. They are the smaller asteroids, and far more numerous. They too could mess up the day, but in a more localized way.
The technologies and techniques to defend Earth from such malicious cosmic interlopers were tackled at The Planetary Defense Conference: Protecting Earth from Asteroids held here February 23-26, and sponsored by The Aerospace Corporation and the American Institute of Aeronautics and Astronautics (AIAA).
How best to deflect or defeat nature’s own terrorist attack on our own planetary turf conjures up all kinds of thinking — from nudging to nuking objects that have Earth in their cross-hairs.
Hit to the solar plexus
There were disquieting outcomes from the recent four-day conference. For one, the issue of talking about destructive impacts to Earth by Near Earth Objects (NEOs) has primarily fallen to a loose network of self-appointed worrywarts: astronomers and space scientists, odds-making computer experts, along with a handful of military and weapon strategists, a few politicians, and even some astronauts.
This affiliation of experts has repeatedly raised a cautionary flag that more attention should be paid to the NEO hazard. But trying to find a welcome mat at the doorstep of any "take charge" agency in the United States or elsewhere has been tough to do.
And that leads to another upsetting message from the meeting: It may take a celestial body hit to Earth to literally shake up the responsible authorities.
Maybe with the fate of the world at issue is there need to begin developing the anti-NEO technology now?
Small bodies … big worries
There is little doubt that Earth-orbit-crossing asteroids represent a danger our world and its inhabitants. Moreover, the impact of even a rather small object would have a distressing effect on humanity.
"Impacts are the only natural hazard that can, in principle, be eliminated," reported David Morrison, Senior Scientist at the NASA Astrobiology Institute, situated at the Ames Research Center, Moffett Field, California.
Morrison bracketed part of the NEO hazard problem by asking: Should we develop this technology now? Or wait until a specific threat is identified? Furthermore, should the United States, as the world’s only superpower, assume responsibility, or should this be an international effort?
Additionally, how much should be spent to protect our planet? Then, Morrison posed the topic of who can be entrusted with this responsibility.
Big bruisers and below
Through collaboration between NASA and the U.S. Air Force, scientists are now eye deep in pixels, sweeping the heavens with equipment outfitted with super-sensitive detectors. That effort, known as the Spaceguard Survey, has a goal of discovering and tracking 90 percent of the Near Earth Asteroids (NEAs) with diameter greater than 0.6 miles (1-kilometer) by 2008.
The Spaceguard Survey is geared to spot the big bruisers — the objects that could have global consequences.
But then there are the space rocks around 460 feet (140 meters) in size, able to plow through the Earth’s atmosphere and crater into the Earth’s surface or smack into an ocean. Stepping down in size there are incoming objects about 165 feet (50 meters) across — just at the limit where a rocky body could well produce a significant air blast in the Earth’s atmosphere and damage below.
There is growing support for a next generation search system to scope out smaller hazards, perhaps down to as small as nearly 165 feet (50 meters) in diameter.
Warning time
Looking for smaller denizens of deep space means more money and putting on line new ground-based hardware like the powerful Large-aperture Synoptic Survey Telescope, often called the Dark Matter Telescope. This project may be funded by the National Science Foundation, although the initiative has had trouble in the past finding an organizational home.
Another sky monitoring assist can come from Pan-STARRS — the Panoramic Survey Telescope & Rapid Response System — an innovative facility being developed at the University of Hawaii's Institute for Astronomy.
Also under discussion are orbiting instruments capable of scouring space for problem objects, be they asteroids or comets.
Obtaining adequate warning time for long period comets is a challenge. While they are few and far between, most are new and so their appearance cannot be predicted, said Ivan Bekey of Bekey Designs, Inc., Annandale, Virginia.
Bekey proposed a revolutionary lightweight optical space telescope using "disruptive technologies" — many of which exist in the laboratory. He envisions a blend of adaptive piezoelectric bimorph primary membrane; sensor and spacecraft electronics; a sunshade guided by microthrusters — all this and more — flying in formation to create a no truss structure that takes shape in space. The net result is an affordable imaging spacecraft that sports an 82 feet (25 meter) diameter filled aperture and weighs just a little over 570 pounds (260 kilograms).
"I think this is probably achievable with 10 years of technology work," Bekey said. A six year warning time on a comet less than a mile across could be achieved with such an instrument and would also be a boon for detection of small asteroids, he said.
Gravitational tractor beam
Whether located by ground or space-based equipment — or combination of the two — what next in dealing with an object on a collision course with Earth?
William Ailor of the Aerospace Corporation and general chair of the planetary defense meeting noted that there appears to be strong backing for actually doing several missions to learn about asteroids. That is, for instance, what are they made of and how hard are they.
"The idea would be to visit several — maybe 6 to 10 — to see how characteristics vary. There was also support for doing a mission to actually test techniques to move an asteroid," Ailor said.
Getting to know the enemy, be it rubble pile, hard rock, fluffy snowball, or whatever, is of keen interest to not only planetary defense specialists but space scientists too.
Various proposals were aired to deal with a bothersome NEO.
There was no shortage of ideas, from gas blasts, nuclear warhead explosions, ramming microsatellites, to lasers, mass drivers, and using a large mirror to focus sunlight on an asteroid to create artificial gas jets that modify the object’s trajectory. These concepts and others had their advocates, as well as critics.
Arguably, one of the freshest approaches was offered by NASA space shuttle and space station astronaut, Edward Lu. He likened his idea to a "gravitational tractor beam" whereby the actual mass of a rendezvousing spacecraft with a target would attract that object in free space - enough so that the target’s trajectory is altered.
One technology fits all?
There is a growing awareness, however, that a "one NEO defense technology fits all" approach doesn’t fit the bill.
"The objects are so bizarre. You’ve got ex-cometary clumps, shattered rocks, slabs of solid iron…the deflection or dispersal mechanisms would have to be completely different for all of those," said Donald Yeomans, Manager of the Near-Earth Object Program at Jet Propulsion Laboratory (JPL) in Pasadena, California.
"If you do find something with our name on it … you’d have to go out and investigate that particular object to find out what it’s like before you try and deal with it," Yeomans said.
For example, scientists were surprised by close-up images of comet Wild 2 relayed early January from NASA’s Stardust spacecraft.
Those encounter pictures showed craters on the comet, but as to whether they are impact craters or missing chunks of evaporating ice isn’t clear, Yeomans said. Another surprise is that the comet was shown to be nearly spherical.
The Stardust probe also imaged gas jets erupting from all around the comet, seemingly even on the side facing away from the Sun — and also on the wrong side of conventional wisdom, Yeomans added.
Appointment with doom
Better defining the range of possible properties of near-Earth asteroids contributes little to knowing the properties of the "one with our name on it," said Alan Harris, Senior Research Scientist at the Space Science Institute in La Canada, California.
"As a person involved in physical observations of asteroids and studying their nature, it would be nice to be able to declare that such studies are an essential component of search or mitigation plans, but honestly, I can't say so," Harris said. "When, if ever, ‘the one’ is discovered, then determining its physical properties will indeed be absolutely essential to any mitigation plan, or maybe even for certifying that it is on an impact course," he said.
Harris said he is skeptical of starting plans or running a demonstration in advance of any discovery of an impactor. Comparing the urgently motivated Apollo Moon-landing project to today’s seemingly endless stagger of the International Space Station program is a case in point, he added.
"I suspect that only a couple of months' effort with Apollo-like, or more, motivation following the discovery of a real impactor would cover more ground than decades of
staggering along half-heartedly on some ‘just in case’ mitigation project," Harris noted. "Of course, if we missed our collective appointment with doom by only those couple months, we could regret not having prepared. But I think the time saving is almost that slight."
Old think versus new think
Russell Schweickart, former NASA astronaut and now director of the B612 Foundation, a nonprofit group focused on solutions to deal with disorderly NEOs, senses the start of a transition from "old think" to "new think" concerning the hazard.
"Old thinking on the subject follows along the lines that we find these things as they are about to hit us and we need to get a great deal of energy, or force, applied to them - and in a hurry," Schweickart said. "Given those ‘old’ assumptions the default answer is to get a nuclear bomb into or close to the threatening asteroid as soon as possible."
Schweickart said that new thinking reflects the actual nature of the detection process, which generates a growing catalog of NEOs and their known orbits. "Based on this growing body of knowledge we predict ahead for 100 years or so and know whether or not any of them are an actual threat. So far the answer for all 2,700 or so that are known is no," he told SPACE.com.
Push comes to shove
Schweickart said that — assuming there is an effort to continue and improve our detection program — if and when we do find an object that actually threatens the Earth we will know that decades ahead of the projected impact date.
"This foreknowledge allows us to be far more subtle in our approach to deflection, and far more certain of the result," Schweickart stated. "All it takes, a decade or more ahead of an impact, is to increase, or decrease, the velocity of the asteroid by about .022 miles per hour, roughly one centimeter per second. One does not need — or want — a nuclear bomb for that!"
Given a host of technologies, several of them fostered by NASA’s Prometheus nuclear power and propulsion initiative, there is the prospect of simply rendezvousing with and nudging an asteroid in a controlled way to miss the Earth a decade or more hence, Schweickart explained.
"Why live with the frightening specter of nuclear bombs in space when we don't have to? We do not have to resort to ‘blast and hope’ for asteroid deflection. The alternative to ‘push and know’ is now emerging as a better alternative," Schweickart said.
"And, as a bonus, the new technologies and techniques open up the near Earth asteroids for routine visits and utilization for human activity beyond low Earth orbit," he concluded.