500,000 Near Earth Objects?

Are we going to detect 500,000 near-Earth objects in the next fifteen years as technologies improve? The Association of Space Explorers thinks so, and lays out its view of the danger we face from asteroids and other near-Earth objects in a new report. I’m looking through an executive summary of Asteroid Threats: A Call for Global Response right now, not long after the release of the report’s results late last week. The ASE hopes to involve the United Nations in a global information network that would improve our existing capabilities at finding and tracking dangerous objects. It would also set up an oversight group to advise the Security Council about the risks and the best ways to deflect potential impactors.

Why the UN? Because it’s a global problem. The report points out that trying to deflect an incoming asteroid would create questions of authorization, liability and financial action that inevitably involve the international community. Citing its belief that existing technology can divert the ‘vast majority’ of hazardous objects, the ASE report notes that we’ll need an effective decision-making mechanism that can create swift action between nations. Thus its call for an intergovernmental NEO Threat Oversight group within the UN to develop the necessary guidelines that would lead to any deflection attempt.

From the report:

The Association of Space Explorers and its Panel on Asteroid Threat Mitigation are confident that with a program for concerted action in place, the international community can prevent most future impacts. The Association of Space Explorers and its Panel are equally certain that if the international community fails to adopt an effective, internationally recognized program, society will likely suffer the effects of some future cosmic disaster—intensified by the knowledge that loss of life, economic devastation, and long-lasting societal disruption could have been prevented. Scientific knowledge and existing international institutions, if harnessed today, offer society the means to avoid such a catastrophe. We cannot afford to shirk that responsibility.

Let’s assume that the ASE’s speculation about the discovery of hundreds of thousands of new asteroids plays out. If that occurs, we’re going to be finding more and more objects whose orbits need particular study, some of them doubtless raising alarms about the possibility of a strike on Earth. The following questions then become critical:

Who will issue warnings to evacuate the predicted impact point? Based on what information? How will the public react if there are conflicting predictions? What deflection technologies exist and who approves their use? Who accepts liability if an asteroid deflection doesn’t work? Who decides that it’s acceptable to temporarily increase the risk to some people in order to eliminate it for everyone? What is the biggest asteroid we can safely decide to ignore? Who pays to deflect an asteroid? What does such a mission cost? Who should deflect an incoming asteroid? Will two space agencies decide to take conflicting actions?

The scenario is in many ways dismaying, with nations and agencies bickering about how to respond to a potential threat while precious time is lost. This is why the primary thrust of the ASE report is toward the creation of a solid decision-making system that should be in place before the need ever arises. The method should recall the preparation that goes into a manned spaceflight, when system failures are analyzed well in advance so that the crew will know what actions to take in the event of emergency. The last thing a spacecraft crew needs is surprise, as the Apollo 13 flight demonstrated all too well.

The identification of 500,000 near-Earth objects in the next fifteen years could elevate public awareness of the asteroid threat to the point where policy-makers take the needed actions. We can all hope so, and hope that an NEO Threat Oversight group of the kind the report recommends will also include a mission group to analyze options for deflection. We’ll see more in the full report, to be released after it is introduced to the United Nations Committee on the Peaceful Uses of Outer Space (UN-COPUOS) in Vienna early next year.

Musings on the Ages of Man

Centauri Dreams takes an optimistic view of the human future, one in which interstellar flight becomes a reality at some point in this millennium. My impression is that we’d all better be optimists. Think about the Drake Equation. Perhaps its most significant variable is the lifetime of a technological civilization, a figure that has implications for any creatures who have developed the tools to go into space. If the lifetime of such a civilization averages a million years, then the ‘where are they’ question Fermi asked becomes more charged. Shouldn’t we be detecting them?

But if the average lifetime of a technological culture is, say, five hundred years, then we may be confronted with a galaxy filled with wreckage, planets where life persists in evolving and forming intelligent beings who bring about their own destruction. Like I say, I’d rather be an optimist, but none of us knows the real answer. I note that Jan Zalasiewicz (University of Leicester) has offered up a new book that assumes at least long-range limits for our own species. Thus this comment:

“From the perspective of 100 million years in the future-a geologist’s view-the reign of humans on Earth would seem very short: we would almost certainly have died out long before then. What footprint will we leave in the rocks? What would have become of our great cities, our roads and tunnels, our cars, our plastic cups in the far distant future? What fossils would we leave behind?”

On the other hand, Zalasiewicz is a geologist. He’s used to working with time measured in eons, and even a million year run for humans would be dwarfed from that perspective. The book, called The Earth After Us (Oxford University Press, 2008), asks what alien explorers might discover if they arrived on Earth one hundred million years from now. Their scientists would find evidence of vast tectonic movements, ice ages and the movement of oceans, a geological history sprinkled with life and its occasional catastrophic collapse. They might also find, in a single layer of rock, signs of cities and the creatures who built them.

The concept of ‘deep time’ was originally developed to encompass the perspective changes induced by geological study (thus 18th Century mathematician John Playfair’s comment upon studying a particular site, “the mind seemed to grow giddy by looking so far into the abyss of time.” We might also consider it in terms of communication, as Gregory Benford does in his book Deep Time: How Humanity Communicates Across the Millennia (Bard, 2001). Or maybe we should think about deep time in the sense of placing human awareness in the broadest possible context.

Those of you who have read Greg Laughlin and Fred Adams’ The Five Ages of the Universe (Free Press, 1999) will readily identify with the concept. Laughlin and Adams look at the history of the universe in terms of ‘cosmological decades,’ each decade being ten times as long as the one before. When I say that the end of stellar burning 100 trillion years from now is only the early part of the story, you’ll understand how interesting is the possibility of intelligent life surviving the entire cosmic history.

As to Zalasiewicz (whose book I much look forward to reading), another question posed by alien archaeologists sifting through the traces of our cities in layered rock is this: If a technological civilization does indeed have a sharply limited lifetime, then how long is enough to ensure survival elsewhere? In other words, if 10,000 years is the technological average, is this long enough for that culture to have spread to space habitats or the nearest stars? An optimist’s answer to that one comes easy: Yes, we’ll have that chance to move outward before the big collapse, but given the uncertainties, we won’t want to wait too long.

Latest Carnival: Electric Sails and More

The latest Carnival of Space is stuffed with good things, among them Dave Mosher’s manipulations of an asteroid impact calculator run by Cardiff University’s Ed Gomez. Dave works through a worst-case scenario — a 1300-foot wide asteroid striking the East River, turning most of New York City into a crater. Fascinatingly, the impact calculator lets users adjust the parameters on such strikes, so that turning the impactor into a 400-meter piece of ice produces a crater 3.5 miles wide, two miles less than the first scenario. The calculator looks to be a great educational tool.

NextBigFuture continues to study the electric sail concept, developed at the Finnish Meteorological Institute and under active examination. Electric sails ride the solar wind, but unlike magsails, they use a mesh of tethers kept at high positive voltage, held in place by centrifugal acceleration from the spinning spacecraft. Solar wind protons, repelled by the positive voltage of the mesh, create the needed thrust, with accumulating electrons discharged periodically to keep the mesh voltage positive.

Because the voltage on each tether might be controlled independently, the electric field around the craft could be adjusted to deal with variable solar wind activity, at least in theory. NextBigFuture has details from the ESA electric sail workshop at the European Space Research and Technology Centre in May. A perfectly optimized electric sail, Brian believes, could reach speeds comparable to the solar wind maximum of 800 kilometers per second. This seems like quite a stretch, but we need space-based deployment of a prototype to test the basic principles.

Haumea is the latest dwarf planet to be added to the IAU list, studied this week by Astronomy at the CCSSC. Accompanied by twin moons, the oblong Kuiper Belt world formerly known as 2003 EL61 is fifty times the Earth-Sun distance and seems to have an icy crust over a rocky body, possibly the result of an impact that blew away earlier ices. Regrettably, another discovery controversy has dogged the story, with questions about whether this object was found by Mike Brown’s team at Caltech or a Spanish team that made an earlier announcement.

Says Astronomy at the CCSSC:

[T]here’s a bit of an ugly story that goes along with this one. Briefly, Dr. Brown’s team had been watching and observing this object, gathering data before they decided to announce or publish a discovery. Another team (from an observatory in Spain) made the announcement before Dr. Brown’s team did. However, it turns out that the Spanish team may have looked at web logs showing where Dr. Brown’s team was observing, and “discovered” the planet in Dr. Brown’s data rather than in their own observations. The IAU lists Dr. Brown’s team as the discoverers of Haumea’s moons, and adopted their suggested planetary name; however, they have not committed themselves by listing either team as the “discoverers” of Haumea itself.

The competition for first announcement can get downright unhealthy at times, as Haumea’s sordid story shows. This case verged unusually close to actual cheating, but even when it’s just a case of a race to the finish line, it can have repercussions. For example, a scientist may announce results in the media which never pan out in the long run, leading the public to distrust new scientific findings.

All too true. Read the post for more, but also check Mike Brown’s site for a full rundown. The larger and more gratifying issue is the presence of so many large Kuiper Belt objects, and the growing belief that we have many more such discoveries ahead of us. Could Earth-sized worlds be lurking in these dark outer regions? The Solar System proves to be so much more complex than it seemed just a few decades ago, a situation that is presumably true around other stars as well. What an exciting time as we develop the needed tools to identify and study these objects.

Rough Sailing on the Solar Wind

All of nature is a kind of laboratory, which is why good propulsion ideas can flow from astronomical observations that show us how things work. Recent news about the solar wind is a case in point. An analysis of data from the Ulysses spacecraft shows that the solar wind is now lower than at any time previously measured. That has implications for the heliopause, that region where the solar wind encounters true interstellar space, for this region plays a role in shielding the Solar System from the effects of galactic cosmic rays.

“Galactic cosmic rays carry with them radiation from other parts of our galaxy,” says Ed Smith, NASA’s Ulysses project scientist at the Jet Propulsion Laboratory in Pasadena, Calif. “With the solar wind at an all-time low, there is an excellent chance the heliosphere will diminish in size and strength. If that occurs, more galactic cosmic rays will make it into the inner part of our solar system.”

Image: The Ulysses spacecraft. Credit: Jet Propulsion Laboratory.

Cosmic rays can have ramifications on spacecraft engineering, especially when human crews are involved. As to propulsion, we have to be careful when talking about the solar wind. Sailing it is not similar to working with conventional solar sails, which use the momentum imparted by photons to move the spacecraft. The solar wind involves a much different medium, the stream of charged particles that flows at high speed from the Sun, attaining speeds anywhere from 350 to 800 kilometers per second. In this news release, David J. McComas (SwRI), principal investigator of the Solar Wind Observations Over the Poles of the Sun (SWOOPS) experiment on board Ulysses, confirms what Smith said:

“The heliosphere is a big bubble that’s inflated from the inside by the million-mile-per-hour solar wind blowing out in all directions. The size of the bubble is determined by the balance of pressure of the solar wind pushing from the inside out and the pressure of interstellar space pushing from the outside in. If the solar wind is blowing out a quarter less hard, that means the outer boundaries of the heliosphere must be shrinking. The entire heliosphere must be getting smaller.”

This may sound like a more unusual story than it is. Earlier observations of the solar wind have made it clear that it can weaken and regain strength. We’re learning how the strength of the wind varies, with data from both Ulysses and the Advanced Composition Explorer spacecraft showing that the wind has weakened at all solar latitudes. But remember that Ulysses, which circles the Sun in a polar orbit, is only on the third such orbit since its 1990 launch, so we have a long way to go in compiling the kind of data that will give us a true perspective on wind strength.

Currently, the speed of the solar wind is roughly what it was at the previous minimum phase of the solar activity cycle, but its density and pressure are significantly lower. The findings have a bearing on several propulsion concepts. While we have ingenious proposals for solar wind-driven spacecraft, exactly how to make them work is more problematic than ever. A vessel using a self-generated magnetic field (possibly with plasma trapped within) as a sail could theoretically ride the wind at great speed to the outer Solar System, an idea that researchers like Robert Winglee have done much to investigate.

But the very inconstancy of the solar wind points to the question of how well we could control such a spacecraft. In their new book Solar Sails: A Novel Approach to Interplanetary Travel, Gregory Matloff, Les Johnson and Giovanni Vulpetti note that this variability makes sailing such a craft something like tossing a bottle with a note inside it into the surf at high tide, hoping the ocean will carry it to a specific destination. Because we don’t know how to control the result directionally, it’s clear that we have much work to do in sorting out the magsail concept as it relates to the solar wind. It remains promising, but beamed magsail designs seem to offer a far more straightforward deep space solution.

Colliding Worlds: The Ultimate Extinction Event

When Worlds Collide, the 1932 novel of planetary catastrophe, presented the most extreme extinction event imaginable. A pair of wandering planets enters the Solar System, one on collision course with the Earth, the other destined to be captured into orbit around the Sun. The doughty crew of an escaping rocket, on their way to a new life on the captured world, can only watch in horror as the Earth is destroyed.

Now we learn about a ‘when worlds collide’ scenario that seems to have involved two mature, Earth-sized planets in a distant Solar System. The system in question is BD+20 307, originally thought to be a single star with a massive, warm dust disk, but now known to be a close binary orbiting the common center of mass every 3.42 days. Both stars are similar to the Sun in mass, temperature and size. Moreover, the system seems to have an age comparable to our own Sun, and the sheer amount of dust at roughly Venus to Earth distance is quite interesting.

We would expect the dust particles to be pushed outward from the stars by stellar radiation. That they have not been indicates that the event that produced them must have occurred relatively recently, perhaps within the past few hundred thousand years. A planetary collision is inferred from the evidence of a disk with a million times more dust than is found around our own Sun, says Gregory Henry (Tennessee State University):

“The planetary collision in BD+20 307 was not observed directly but rather was inferred from the extraordinary quantity of dust particles that orbit the binary pair at about the same distance as Earth and Venus are from our sun. If this dust does indeed point to the presence of terrestrial planets, then this represents the first known example of planets of any mass in orbit around a close binary star.”

Once again we have a glimpse of how violent a planetary system can be, although destabilized planetary orbits in a mature system do seem to be rare. Henry goes on in this news release to discuss Jacques Laskar’s work in France and that of Gregory Laughlin (UCSC) and student Konstantin Batygin, whose models make it clear that planets even in our own system can go awry, with Mercury in particular prone to odd behavior if we extrapolate far enough into the future. The odds of collision are indeed small, but that also tracks with the rarity of mature, dusty systems like BD+20 307.

As to When Worlds Collide, I loved the 1951 film version of the Philip Wylie and Edwin Balmer novel as a kid, although it can only be said that the movie doesn’t age well, and a recent viewing made every bit of stilted dialog and lame character interplay all too apparent. Still, the story is captivating, and watching the team of determined scientists racing to complete a space ark in time to save at least a portion of humanity has its pleasures. I notice that a re-make is in the works, scheduled for 2010 or thereabouts. This one seems to posit a near-term collision between our system and the Alpha Centauri stars, so the odds on scientific verisimilitude don’t look good.