by Paul Gilster | Jan 17, 2009 | Asteroid and Comet Deflection |
By Larry Klaes
It was while I was working on our recent story on Near Earth Objects that Larry Klaes’ obituary for Steve Ostro arrived, a serendipitous event given Ostro’s landmark work in identifying planetoids and especially those that come perilously close to us. Ostro’s death last December came at a time of increasing public understanding of the threat posed by these objects. Yet the JPL radar astronomer, who used Arecibo’s facilities to such good effect, worked with tools that are now in danger of losing their funding, a commentary on how flexible our priorities can be even on issues of planetary survival. Ostro’s voice in Arecibo’s defense will be deeply missed.
Steven J. Ostro, a major player in radar astronomy who was both an alumnus and teacher at Cornell University, passed away on December 15 from pneumonia brought on by a long bout with cancer. He was 62 years old.
Ostro received his Master’s Degree in engineering physics from Cornell in 1974. Ostro then went to the Massachusetts Institute of Technology (MIT), where he graduated in 1978 with a Ph.D. in planetary science. While at MIT, Ostro used the Cornell-run Arecibo Observatory’s giant radio telescope on the island of Puerto Rico to bounce radar beams off the rings of the planet Saturn and the four large Galilean moons of Jupiter to study their properties.
Arecibo would become an important astronomical tool for Ostro in his ground-based exploration of the Solar System as his science career advanced. In 2003, Ostro was a member of the team led by Cornell astronomer Donald Campbell that utilized Arecibo’s powerful radar capabilities to study the surface of Titan, the largest moon of Saturn. Perpetually shrouded in thick orange clouds of nitrogen and methane, the distant moon’s surface is most effectively examined by radar. The 2003 radar exploration of Titan provided some of the first scientific evidence for hydrocarbon lakes there.
After completing his postdoc at MIT, Ostro returned to Cornell at the personal invitation of Cornell astronomer and science popularizer Carl Sagan to become an assistant professor of astronomy at the university. In 1984, Ostro moved to Pasadena, California to head the Jet Propulsion Laboratory (JPL) Asteroid Radar group. He also became a member of the Cassini-Huygens radar team studying the varied moons of Saturn in conjunction with the robot probe that has been orbiting the ringed planet since 2004.
At JPL, Ostro focused much of his scientific career on the study of planetoids using the radar facilities at Arecibo. The data returned from the radar beams bounced off those celestial chunks of rock changed humanity’s previous understanding of the vast numbers of relatively small objects that exist throughout our star system. Many of these objects exist due to the gravitational influence of Jupiter, whose great mass kept them from forming into large planets during the early days of the Solar System’s formation.
Through May of 2008, Ostro and his colleagues discovered 340 planetoids. Of this collection, the scientists confirmed that some of these minor bodies contained minerals such as nickel-iron and platinum in large amounts. They also provided the first radar images of planetoids, including objects known as contact binaries where two planetoids are in physical contact with each other. In early February of 2008, Ostro helped to find the first triple planetoid system that passes near our planet.
Image: These are radar images of asteroid 4179 Toutatis made during the object’s close approach to Earth on December 8, 1992. The work was carried out at the Goldstone Deep Space Communications Complex by a team led by Steven Ostro of JPL. The images reveal two irregularly shaped, cratered objects about 4 and 2.5 kilometers (2.5 and 1.6 miles) in average diameter which are probably in contact with each other. The four frames shown here (from left to right) were obtained on Dec. 8, 9, 10 and 13 when Toutatis was an average of about 4 million kilometers (2.5 million miles) from Earth. The large crater shown in the Dec. 9 image (upper right) is about 700 meters (2,300 feet) in diameter. Credit: Steve Ostro/JPL.
Ostro’s radar studies of planetoids, especially the ones known as Near Earth Objects, or NEOs, have done much to assist science both in understanding the nature and composition of these bodies and in gaining a wider appreciation of the potential threat they pose to our world. It is now recognized that some of these NEOs could one day impact Earth and wipe out most of the life on this planet, as likely happened with the dinosaurs 65 million years ago and in several other epochs.
To cite just two examples, Ostro and his team observed a half-mile wide planetoid named 1950 DA which they discovered has the highest known potential of any such celestial body to strike Earth, although not until the year 2880. If 1950 DA is not deflected or destroyed in the intervening centuries, its possible impact on our globe could cause major damage to the biosphere and disrupt human civilization.
The other potentially deadly planetoid is named 99942 Apophis, the Greek designation of the ancient snakelike Egyptian deity Apep, who constantly tried to destroy the creator god Ra. Ostro’s radar studies determined that initial concerns over Apophis striking Earth in 2029 and especially 2036 were overblown, but the planetoid, which is roughly the width of the Arecibo radio telescope, has warranted further study due to continued uncertainties in its orbit about the Sun. Former Apollo 9 astronaut Rusty Schweickart, who is now chairman of the B612 Foundation, a private organization dedicated to protecting Earth from space impacts, has suggested that a transponder be planted on Apophis to allow better tracking of that alien rock in the future.
In 1994, Ostro collaborated with Carl Sagan just two years before the latter’s untimely death on the potential consequences of celestial object impacts in a paper titled “Cosmic Collisions and the Longevity of Non-Spacefaring Galactic Civilizations.” In this paper, Sagan argued that species which do not eventually start colonizing other worlds run the risk of extinction due to a major impact event on their home planet. Ostro noted that while preventing a deadly strike by a planetoid or comet is an important task, the technology required to deflect a space object away from Earth could also be used by certain groups to deflect the same object towards our planet. Nevertheless, the authors voiced support for the continued radar studies of planetoids with Arecibo for both scientific and protection purposes. The paper may be read online.
Appropriately enough, a planetoid was named after Steve Ostro in honor of his important work with what astronomers used to call the “vermin of the Solar System.” Designated 3169 Ostro, this small and faint object orbiting the Sun between the celestial paths of Mars and Jupiter was found by Edward Bowell of Flagstaff, Arizona in June of 1981. Bowell also discovered another Main Belt planetoid which later bore the name 2709 Sagan, after the man who invited Ostro to join the Cornell faculty.
by Paul Gilster | Jan 16, 2009 | Culture and Society, Exotic Physics |
Seth Shostak and I independently hit upon the same topic yesterday, Seth in his regular venue on Space.com and I with a Centauri Dreams post that asked how advances in observational technology might replace actual interstellar travel. Seth’s take is somewhat different from mine, arguing as he does that while we’ll spread through the Solar System, we’ll likely explore the galaxy from home. I, on the other hand, argue that at least a small number of humans will find the means to make the long journey, but perhaps not in ways we often imagine.
Changing How We See Things
I return to the topic to get some of Seth’s observations into play here. For the point of both articles was that we’re making remarkable advances in how we see things, advances that are far more striking than what we’ve managed in propulsion. Thus it took seven decades to go from the V-1 moving at one mile per second to New Horizons, which moves toward Pluto/Charon at ten miles per second. A factor of ten increase in speed in seven decades, this occurred in a time when, as Shostak notes, our camera technology improved by a factor of ten thousand. Then this:
Now you might argue that human exploration is qualitatively different than sending mechanical proxies. We humans want to experience the frontier, not just watch it come up on our computer screen. We want to smell it, feel it, and look around.
OK, but what if we could send back all those sensations with a fidelity as good as being there? That’s becoming more and more practical. The bandwidth of a single human eye, recently measured at the University of Pennsylvania medical school, is roughly 2 megabytes per second. The bandwidth of your ears is much smaller – no more than a few hundred kilobytes per second. Your fingertips and other parts of your anatomy require even less of a data pipe.
In other words, we could send back everything a human could sense with a telemetry channel of, say, 10 megabytes per second. This is roughly the data rate you’ll soon be getting off a blue-ray disk. It’s not trivial to send data at this rate from star to star, but it’s a lot easier than sending ourselves.
Sending even the tiniest probe to a nearby star is a mammoth undertaking, one whose demands we’re nowhere near being able to meet. But it’s also clear that a robotic probe carrying the kind of remote sensing technologies Seth is talking about is a more attainable goal, for the near term, at least, than a crewed mission requiring life support over a period measured in decades if not longer. Throw nanotechnology into the mix and we could be talking about pushing tiny probes with assemblers that can create the needed facilities from asteroid debris upon arrival. Space-based lasers could supply the propulsion.
My hunch is that both outcomes are likely, with human missions obviously emerging later as propulsion technologies give us new options for getting there quicker. I’m also a believer in the Freeman Dyson notion that deep space exploration is not likely to happen as a result of massive government programs, but rather in the fashion of oceanic discovery in the 17th and 18th centuries. Yes, government-sponsored voyages opened up new territories (and let’s not forget Cook in the Pacific, working off Royal Society funding) but doughty bands of colonists driven by their own agendas played a huge role and, in doing so, re-defined the relationship between liberty and frontiers.
A Slow Scenario to Centauri
Here’s a slow scenario, just one of many: A culture capable of building space habitats and terraforming planets moves ever further into the Edgeworth/Kuiper Belt, harvesting resources and gaining expertise. Over a period of thousands of years, it moves deeply into the Oort Cloud and eventually to its outer edges, where the boundaries between the stellar debris of our own Sun and that of the Centauri stars may become indistinct. We find ourselves moving across the interstellar gulf in a series of small steps, an evolutionarily transformed spacefaring race.
It’s just a scenario. Faster is obviously better, but one way or another, a human presence in interstellar space seems as inevitable to me as tomorrow’s sunrise. And think of the reality shows it will provide the stay-at-homes! They’ll be watching people doing what Captain Cook said he would do, going not only “… farther than any man has been before me, but as far as I think it is possible for a man to go.”
by Paul Gilster | Jan 15, 2009 | Culture and Society, Exoplanetary Science |
From the standpoint of pure research, one of the arguments for not going to nearby stars is that by the time we develop the needed technologies, we’ll have no need to make the journey. After all, we’ll soon be able to learn vast amounts about nearby worlds from space-based telescopes, not to mention planned Earth-side instruments like the European Extremely Large Telescope, a 42-meter powerhouse 100 more sensitive than the best of today’s optical telescopes. Putting observatories on the far side of the Moon is another way we’ll see deeper than ever before.
Extend space research out fifty years, a hundred, and you have to reckon with capabilities we can only dream about today. Webster Cash (University of Colorado) has been championing one Sun-shade design (there are others) that in its fullest deployment could give us views of an exoplanet as if we were no more than a hundred kilometers away. Or consider the fusion of new propulsion technologies with space-based observatories that can tap the Sun’s gravitational focus. This would open up the galaxy for the detailed exploration of countless planetary systems, with the potential for exoplanet finds as far away as Andromeda.
An Earth-based Perspective
All this is given relevance (and perspective) by the upcoming launch of Kepler, which will look for transiting planets down to terrestrial size. And as I was pondering these issues, there came the news of not one but two ground-based detections of exoplanet atmospheres. Six hundred images of the hot Jupiter OGLE-TR-56b, from the ESO’s Very Large Telescope and Carnegie’s Magellan-Baade instrument in Chile, produced the first result. This one is quite a catch, the planet being some 5,000 light years away in the direction of galactic center. Listen to Mercedes López-Morales (Carnegie Institution) on last summer’s work:
“Others have tried to detect planetary atmospheres from Earth, but to no avail… The successful recipe is a planet that emits a lot of heat and has little to no wind in its atmosphere. Plus it has to be a clear, calm night on Earth to measure accurately the differences in thermal emissions when the planet is eclipsed as it goes behind the star. Only about one of every 3,000 photons from the star comes from the planet. This eclipse allows us to separate the emissions of the planet from those of the star. The magic moments came on July 2nd…”
In the same issue of Astronomy & Astrophysics comes news of the measurement of thermal emissions in the near-infrared from TrES-3b, another hot Jupiter studied from the ground. This work is out of the University of Leiden in the Netherlands, again relying on accurate information about the planetary transit that allows the strength of the planet’s light to be measured. The instruments involved were the William Herschel Telescope (WHT) on La Palma (Canary Islands, Spain) and the United Kingdom Infrared Telescope (UKIRT) on Mauna Kea in Hawaii.
Given this early work on exoplanetary atmospheres from Earth, where will we be in fifty years? And if, let’s say in a century, we find ourselves with the capability of studying distant planetary systems in exquisite detail, will we still have the motivation to build ships to make the journey to them? From a planetary security perspective, we can theoretically safeguard our species by expanding out in our own system with space-based habitats and possibly terraforming as options. The question then remains: What is it that drives the push to interstellar flight?
Philosophy and Realism
Many answers suggest themselves, and I’m not inclined to wax philosophical here. I think a realistic answer is that as we expand into the Solar System and build the infrastructure to support human populations in space, we will inevitably develop the tools that make further explorations possible, including propulsion technologies to get us to the Oort Cloud and beyond. Human history tells me that there is always a portion of the population that is willing to get on a cramped ship and go to the other side of nowhere for reasons that vary from the pure exploratory impulse to the need to escape political or religious persecution.
And my guess is that at some point interstellar flight will begin in much the same way. Protecting the species by spreading into the cosmos is a laudable goal, but it couples neatly with this exploratory imperative that has shown up in the behavior of our ancestors and shows no signs of abating now. Indeed, a universal exploratory urge is part of the puzzle noted by Fermi’s paradox — ‘Where are they’ indeed, for we would expect anyone with the capability of making an interstellar journey to set about the task. That’s because we know deep down that that is exactly what we would do — will do — assuming we survive our technological coming of age and can develop the engines to make it happen.
by Paul Gilster | Jan 14, 2009 | Interstellar Medium, Sail Concepts |
Riding the solar wind with some kind of magnetic sail is one path into the outer Solar System, but before we can develop an operational technology around the idea, we have to learn much more about how the solar wind works. This stream of charged particles flows outward from the Sun at great speed — up to well over 400 kilometers per second — creating the ‘bubble’ in the interstellar medium known as the heliosphere, within which our Solar System exists. Understanding how that wind interacts with the true interstellar space that lies beyond will give us a better idea of its properties and those of the boundary region at system’s edge.
Image: The Solar System in context, placed within the heliosphere created by the solar wind. Credit: Southwest Research Institute.
IBEX (Interstellar Boundary Explorer) is a space mission that may tell us more as it examines the edge of the heliosphere. Tuned up after two months of commissioning, the spacecraft is now gathering data, mapping the interactions between the solar wind and the interstellar medium by measuring energetic neutral atoms from the Solar System’s edge. Thus we complement and extend the early heliosphere data provided by the Voyagers and investigate how charged solar wind particles behave in this critical area, through which any mission into the interstellar void will have to pass. The data thus far are useful, but only a beginning:
“We are seeing fabulous initial results from IBEX, but just as artisans use looms to build up colorful textiles by weaving one thread at a time, the IBEX sensors also need time — six months — to build up a complete map of the sky,” says Dr. David McComas, IBEX principal investigator and senior executive director of the Space Science and Engineering Division at Southwest Research Institute. “So far, the intricate pattern of this fascinating interaction is only just beginning to disclose itself to us.”
This is useful information not only in terms of understanding how our local neighborhood interacts with the galaxy around it, but also in analyzing how this distant region helps to shield the Earth from a great deal of cosmic ray radiation. Also useful would be an accurate picture of the shape of the heliosphere, and how it may be affected by magnetic fields in the interstellar medium. Given the target of its study, it’s interesting to reflect that IBEX is relatively close — in Earth orbit — although a very high one reaching five-sixths of the way to the Moon. Much of that orbit is outside Earth’s magnetosphere, critical for accurate observations.
by Paul Gilster | Jan 13, 2009 | Asteroid and Comet Deflection |
The Spaceguard program, originally mandated by Congress in the 1990s, is in the business of detecting, tracking and cataloging near-Earth objects (NEOs). Spaceguard’s goal has always been as ambitious as it is crucial: To locate ninety percent or more of the objects that approach the Earth and are more than one kilometer in diameter. So how is Spaceguard doing? According to Stephen M. Larson (University of Arizona), who manages the Catalina Sky Survey, “We’re about 85 percent there.”
But even when we reach 100 percent, the story is far from over. An object just a third of a kilometer in diameter would explode with an energy more than twenty times that of the largest thermonuclear bomb. NASA received another mandate in 2005 to identify near-Earth asteroids and comets down to 140 meters in diameter, still large enough to destroy a city. And even though impacts like these seem to occur only once every several thousand years, no one can say when the next potential strike could happen.
I’m looking at a University of Arizona news release that notes the Catalina Sky Survey’s score in 2008: 565 NEO discoveries, following 460 in 2007. A $3.16 million NASA grant has now been awarded to continue the search through 2012 using the CSS facilities, which include a new 1-meter telescope to be housed next to the existing 1.5-meter instrument on Mount Lemmon, north of Tucson. Used to follow up NEO discoveries, the telescope boosts CSS’ survey time on other instruments by 20 to 25 percent.
But CSS also includes a southern hemisphere presence in New South Wales using Australian National University’s 0.5-meter telescope, a reminder of the need for global search facilities. It was CSS that identified 2008 TC3, a six-foot object that disintegrated over Sudan last fall. Says Larson:
“There’s a bit of a misperception that what we do is find objects that are incoming, like the Sudan object. That’s not the case.
“We’re hoping to find objects that many orbits down the road might be hazardous, so that we have enough time to do something about them. We can calculate orbits quite accurately. We hope that we would have a few decades to study and characterize these things, and come up with the best plans to nudge them into another orbit so that it misses the Earth.”
The numbers here are stark. NASA’s Near Earth Object Program reports that we’ve found 5,955 NEOs, some 763 of which are at least one kilometer in diameter. 1008 NEOs larger than 140 meters across come within 4.5 million miles of Earth’s orbit, dangerous to us because perturbing influences could change their trajectories in the future. Centauri Dreams believes that the discovery of an object on a collision course with Earth would galvanize the space program as researchers looked for the best ways to deflect its path. The problem is time.
Would we find the object soon enough to be able to develop the needed technologies? Ponder this: 2008 TC3 was discovered when it was well outside the orbit of the Moon. Moving at 12 kilometers per second, it struck some nineteen hours later.
The more accurate our sky surveys, the more likely we are to find objects while we still have a chance to deflect them. The best insurance program for our planet involves not only observing programs to detect and characterize the potential trouble-makers, but a robust effort to study deflection strategies. Part of this must include a mission to a near-Earth asteroid, not only to learn more about the object itself, but to tune up the procedures for getting a payload on site quickly if the need arises.
