From: Ames Research Center
Posted: Thursday, December 28, 2006
As 2006 draws to a close, NEOs are back in the news. Much of this news is bad, as the U.S. National Science Foundation moves to implement the recommendations of its Senior Review committee to close down the unique Arecibo radar facility. This is happening in spite of evidence that the Senior Review did not even consider the unique radar capability of Arecibo and was unaware of the critical role Arecibo plays in studies of NEOs, including determination of the hazard of Earth impacts. Several of the articles and comments below expand on this situation.
Best wishes to all for 2007! May Pan-STARRS prove as capable as hoped for NEA surveys, the Arecibo radar be rescued from extinction, and no NEA be found on a collision course with our planet.
ARECIBO PLANETARY RADAR: CONSEQUENCES OF THE NSF ASTRONOMY SENIOR REVIEW RECOMMENDATIONS
Robert L. Brown, NAIC (Arecibo) Director, November 15, 2006
The Arecibo planetary radar is a unique facility whose achievements are well known to planetary scientists and the public. There is only one other active planetary radar in the world, the NASA Goldstone Deep Space Tracking Station, which provides a complementary capability to Arecibo. The Goldstone antenna is fully steerable, but it is only 4 percent as sensitive as the Arecibo planetary radar; hence it can only observe objects that are much larger than those that are routine targets for Arecibo.
The NSF Astronomy Senior Review report includes only a single, brief, reference to the Arecibo planetary radar. Perhaps because of the composition of the Senior Review (SR) panel, its description of the Arecibo planetary radar remarkably neglects to mention adequately the unique current capabilities of Arecibo for radar studies of the Solar System. The report itself mentions only the discoveries of several decades ago, ignoring the long list of recent achievements given, for example, in the NAIC report to the SR. We find this particularly unfortunate considering the recent publicity surrounding the discoveries at Arecibo about the lack of water-ice on the Moon reported in the Oct. 19th issue of Nature and the extraordinary dynamics of the Near Earth Asteroid (NEA) 1999 KW4, which is the cover article in the November 24, 2006 edition of Science. In addition there are recent studies of Mercury, Mars, Jupiter and its satellites, Saturn's rings and satellites and both main-belt and near-Earth asteroids. NSF astronomy is receiving wide praise for its support of the unique Arecibo planetary radar as a consequence of publications such as these.
Regrettably, the failure of the SR to appreciate the critical role of the Arecibo planetary radar may lead to its demise. The SR report (6.2.1, p. 62) states "The SR was advised that a minimum feasible operating cost for Arecibo is $8M, even when it is largely working in survey mode." The $8M budgetary number does not include any support for the planetary radar program: the $8M operating budget applies, as the report notes, when the Observatory is doing astronomical surveys. The operating cost of the Arecibo planetary radar is $1M per year, a figure NAIC supplied to the SR. Therefore, the SR recommendation that the funding for NAIC be decreased to $8M, together with the SR recommendation that the NAIC astronomy program focus on survey programs, is a recommendation to terminate the Arecibo planetary radar program. The community should have been told this explicitly in the SR report if indeed that was the intended conclusion of the SR panel. Cornell/NAIC has expressed its concern about the lack of clarity, and candor, in the SR report regarding the Arecibo planetary radar program.
Cornell/NAIC fully supports the goals of the Senior Review and shares in the view that science is a forward-looking enterprise; the construction of new research facilities is essential to future progress. One of the telescopes NSF Astronomy is seeking to build from funds reprogrammed from NAIC and the other national centers is the ~$200M Large Synoptic Survey Telescope (LSST), a telescope with two main scientific objectives: (1) to compile a complete sample of distant galaxies as a probe of dark energy, and (2) to compile a complete sample of NEOs with special emphasis on Earth-crossing objects. It is NAIC's position that the Arecibo planetary radar is a necessary adjunct to the LSST NEO mission requirement owing to its unrivaled capability to characterize the physical properties of NEOs and to determine their orbital parameters with sufficient precision that the few Earth-threatening objects can be reliably identified from among the enormous sample of NEOs LSST will discover and catalog.
It is the position of Cornell/NAIC that the Senior Review failed to understand the role of the Arecibo Planetary Radar and, in particular, it failed to appreciate that the two primary SR recommendations for NAIC had the effect of terminating this critical program. This error can be rectified by revising the SR recommendation for NAIC from "the SR recommends a decrease in AST support for Arecibo to $8M ...", to "the SR recommends a decrease in AST support for Arecibo to $9M ...." The additional $1M per year in NAIC operations funding preserves the operation of the Arecibo planetary radar without violating the apparent SR objective of diminishing NAIC funding overall. The $1M per year in incremental operations funding is one-half of one-percent of the current AST annual budget. NAIC believes this change should be a key element in the AST implementation plan for the Senior Review recommendations. We have communicated precisely this suggestion to Wayne van Citters, the AST division director.
NAIC will continue operating the Arecibo Planetary Radar until the end of FY2007. Operation beyond this date depends on the availability of funds.
ARECIBO AND PLANETARY DEFENSE
Bill Ailor (organizer of both the 2004 and 2007 AIAA planetary defense workshops) wrote:
Ground-based radar is uniquely able to reduce uncertainty in trajectories and physical properties of NEOs. Radar can prevent the loss of a newly discovered object, can add decades or centuries to the interval over which close Earth approaches can accurately be predicted, can significantly refine collision probability estimates that are based on optical astrometry alone, can reveal whether an object is single or binary, and can produce detailed information about the sizes, shapes, spin states, and surface characteristics of potentially hazardous asteroids. If a small body is on course for a collision with Earth in this century, delay-Doppler radar reconnaissance could almost immediately allow one to recognize this by distinguishing between an impact trajectory and a near miss, and would dramatically reduce the difficulty and cost of any effort to prevent the collision.
I would argue that if there really is a small body headed for collision with Earth in this century, and radar is not used to investigate the object's orbit and physical properties, then mitigation efforts will be much more likely to fail, or at best will be enormously more expensive than if radar had been used. This issue has urgency because the world's most powerful radar system, at Arecibo, is facing termination. Implementation of the recommendations of the NSF's Senior Review Committee would terminate the Arecibo radar program next year and begin to decommission (and dismantle) the telescope a few years later.
RADAR LOVE: ASTEROID DETECTION AND SCIENCE JPL press notice. December 19, 2006
They are the celestial equivalent of sonograms. But their hazy outlines and ghostly features do not document the in-vivo development of a future taxpayer. Instead, they chronicle the exo-planetary comings-and-goings of some of Earth's least known, most nomadic, and at times most impactful neighbors. They are radar echoes that are bounced off of asteroids. Scientists from NASA's Jet Propulsion Laboratory and around the world rely on their ethereal images to tell some out-of-this-world tales of near-Earth objects.
"The standard ground-based tools for asteroid science require a night's sky, and what you come away with in the end is an image of a dot," said JPL radar astronomer Dr. Steve Ostro. "With radar astronomy, the sky at high noon is just as inviting as that at midnight, and without launching a full-blown space mission we can actually get valuable information about the physical makeup of these objects."
In some respects, radar astronomy utilizes the same technology as your microwave oven. But do not bother to haul your glorified croissant warmer outside -- it will just confuse the neighbors. Radar astronomy employs the world's most massive dish-shaped antennas, which beam directed microwave signals at their targets, which can be as close as our moon and as far away as the moons of Saturn. These pulses bounce off the target, and the resulting "echo" is collected and precisely collated. The results can be astounding. "The closer the target, the better the echo," said Ostro. "From them we can generate detailed three-dimensional models of the object, define its rotation precisely and get a good idea of its internal density distribution. You can even make out surface features. A good echo can give us a spatial resolution finer than 10 meters."
Radar astronomy has detected echoes from over 190 near-Earth asteroids to date and has found that, like snowflakes, no two are the same. The returning echoes have revealed both stony and metallic objects, some flying through the cold, dark reaches of space alone, while others have their own satellites. The data indicate that some asteroids have a very smooth surface, while others have very coarse terrain. And finally, their shapes are virtually anything that can be imagined.
One thing that does not have to be imagined is radar astronomy's ability to nail down the location of an object in time and space. This invaluable capability came in handy in the winter of 2004 when JPL's Near-Earth Object office was looking for a potentially hazardous asteroid called Apophis. Discovered by astronomers using optical telescopes, Apophis quickly drew the interest of the near-Earth object monitoring community when its initial orbital plots indicated there was a possibility the 1,300-foot-wide chunk of space rock could impact Earth in 2029. The Near-Earth Object office knew what was needed was more detailed information about Apophis' location, which they could then use to plot out a more accurate orbit.
Under the watchful eye of Ostro and three other radar astronomers, microwaves from the Arecibo Observatory in Puerto Rico reached out and touched asteroid Apophis on Jan. 27, 29, and 30, 2005. The Arecibo data significantly improved the asteroid's orbital estimate, ruling out a potential Earth collision in 2029.
The 1,000-foot diameter Arecibo telescope is one of only two places in the world where radar astronomy is effectively performed. The other is at the 70-meter Goldstone antenna in California's Mojave Desert. The two instruments are complementary. The Arecibo radar is not fully steerable (while Goldstone is), but it is 30 times more sensitive. Together they make a formidable asteroid reconnaissance team.
The future of radar astronomy may be just as amazing as some of the images and shape models of nearby space objects that its practitioners have already obtained. There is new technology in the pipeline that will allow imaging of surface features with up to four times more detail than what exists today. And then there are proposals on the table for a potential space mission to a near-Earth asteroid. Candidate asteroids for said mission will need to be pre-approved via detail scientific analysis. The kind of scientific analysis you can only get with radar astronomy.
Comments from Clark Chapman, Southwest Research Institute, Boulder, Nov 29, 2006:
Closure of Arecibo means permanent shutdown of the chief radar facility in the world. None of the big future radio astronomy projects involve radar. This is not just a hardship, it is virtually ending an entire, highly productive field of science. (Just look at the front cover of the current, 24 Nov. issue of "Science".)
The most appalling thing about the Senior Review treatment of planetary radar is that it doesn't even discuss it. Apart from a single bland statement about past radar accomplishments, the word "radar" does not even appear in the 92-pg. Senior Review document. I wrote to Dr. Vern Pankonin at NSF and asked him to supply me with any documents in which the Senior Review evaluated, in any way, the merits and issues with radar. He replied that there are no such documents. To propose closing down a unique facility without even hinting at why is irresponsible and disrespectful. One suspects that the panel members may even have been unaware of the radar capabilities of Arecibo; otherwise, why wouldn't they have been mentioned in the rather lengthy evaluation of Arecibo in the report?
Many persons have noted the role of Arecibo in improving the orbit of Apophis (see JPL story above). Alan Harris (Space Science Institute) notes:
Apophis isn't the only fish in the ocean -- there may be "sharks" out there we haven't even discovered. And when we do, we'll want Arecibo available to let us know we even have a problem. I wouldn't be surprised that without Arecibo, the impact probability for Apophis might be less than it is now, but because of ignorance: we would have no idea where in the solar system it would be by 2036 or whatever, so the impact probability would be low, but low because of our ignorance, not because it really is going to miss us. That's the point to be driven home.
NEO News (now in its twelfth year of distribution) is an informal compilation of news and opinion dealing with Near Earth Objects (NEOs) and their impacts. These opinions are the responsibility of the individual authors and do not represent the positions of NASA, the International Astronomical Union, or any other organization. To subscribe (or unsubscribe) contact firstname.lastname@example.org. For additional information, please see the website http://impact.arc.nasa.gov. If anyone wishes to copy or redistribute original material from these notes, fully or in part, please include this disclaimer.
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