The return of 6344 P-L won’t light up network switchboards over the weekend, but it’s something to ponder, particularly in light of recent Arecibo happenings. 6344 P-L was first found in 1960 on photographic plates made with the 48-inch Schmidt instrument at Palomar Observatory. The discovery team, working at Leiden Observatory in the Netherlands, had found several thousand asteroids, but this one, recognized as a potential danger to Earth, had not been re-identified until now.
Under its new name of 2007 RR9, the object remains curious. It is one of almost 900 asteroids bigger than 150 meters in diameter that close within 0.05 AU of Earth’s orbit, and observations now indicate it may not be an asteroid at all. SETI Institute astronomer Peter Jenniskens, whose re-discovery of the object was recently confirmed, thinks we’re dealing with something else, a dormant comet. Says Jenniskens:
“This is a now-dormant comet nucleus, a fragment of a bigger object that, after breaking up in the not-so-distant past, may have caused the gamma Piscid shower of slow meteors… that is active in mid-October and early November.”
Dormant comets brighten as they move toward the Sun, and this one should brighten in southern hemisphere skies as we move into mid-October. Will 2007 RR9 ever pose a threat to Earth? The question is problematic, since having just re-discovered it, we have much to learn about its orbit.
Learning things about potentially hazardous objects is something that Arecibo’s planetary radar does quite well, so note the following: The National Science Foundation’s astronomy division has announced that the Arecibo radar will be closed later this month. Cornell University’s
National Astronomy and Ionosphere Center manages the facility for
the NSF. From a letter by Wayne Van Citters, director of the division, referring to budgetary pressures:
Cornell has said that it will cease operations of the planetary radar in October 2007 to meet these budget reductions. We have recently learned that, in fact, they are maintaining the capability to operate the planetary radar, although on a less frequent schedule. In conversations with NASA management, it has been made clear that NASA has no intention of resuming support of the planetary radar, which they terminated in FY 2006.
While Cornell and Arecibo staff pursue business and academic partnerships to provide new support, a bill has been introduced into the US House of Representatives to ensure the continued operation of the Arecibo Observatory for both astronomical and radar-imaging purposes. Congressman Dana Rohrabacher, a co-sponsor of the bill, understands what’s at stake:
“Arecibo is a key resource in understanding the characteristics of potentially hazardous asteroids and comets so that they can be dealt with effectively. There is no room for error when it comes to eliminating a threat that could kill millions.”
The House also goes to work on October 11 in a Congressional hearing dealing with a controversial NASA report on Near Earth Objects. How best to detect and, if necessary, deflect them? Surely the Arecibo situation will hover over these proceedings as well. Another question looms for the rest of us: How best to convince the public that a sustainable search for Earth-crossing objects may be crucial for long-term survival?
I think a state-of-the-art collision detection program for NEOs is extremely prudent. Using the past extinction records of Earth as a benchmark, we are nearing or even past due for another ELE, which seem to happen in cycles, and which are more than likely, based on our evidence, caused by asteroid/comet collisions.
Are mirrors the best way to deflect asteroids?
NewScientist.com news service Oct. 9, 2007
*************************
A swarm of spacecraft with mirrors
focused on asteroids is the best way
to deflect them, a new study finds.
To deflect a
20-kilometer asteroid, about the
size of the one that wiped out the
dinosaurs, it would take the
combined work of 5000 mirror
spacecraft focusing sunlight on the…
http://www.kurzweilai.net/email/newsRedirect.html?newsID=7350&m=25748
Potentially Dangerous Space Rock Lost, and Found
http://bcast1.imaginova.com/t?r=2&ctl=20049:4A48D
The oldest lost Potentially Hazardous Asteroid was recently located.
Campbell, Planetary Society urge Congress to save Arecibo
http://www.news.cornell.edu/stories/Nov07/arecibo.congress.html
Nov. 9, 2007
By Lauren Gold
LG34@cornell.edu
As part of a continuing effort to save the Arecibo Observatory from fatal budget cuts, Cornell astronomy professor Donald Campbell testified before Congress, Nov. 8 on the importance of the telescope’s radar system for the identification and tracking of potentially hazardous near-Earth objects (NEOs).
On the same day, the Planetary Society, a space advocacy organization co-founded by the late Cornell astronomer Carl Sagan, issued a statement to Congress in support of the planetary radar system at Arecibo and its research. “If some object out there really is on a collision course with Earth, and we don’t have the means to track it properly,” the statement said, “the price we would pay would be astronomical.”
The observatory’s future has been in jeopardy since November 2006, when an advisory panel to the Division of Astronomical Sciences at the National Science Foundation (NSF) recommended that its operating funds be reduced to $8 million from $10.5 million over three years and then halved to $4 million in 2011. If the observatory failed to raise funds from external sources to make up the difference, it would be forced to close.
In October, U.S. Rep. Luis Fortuño (R-Puerto Rico) and Dana Rohrabacher (R- Calif.) introduced legislation in the U.S. House of Representatives to ensure continued operation of Arecibo.
Campbell was among five scientists to address the Subcommittee on Space and Aeronautics of the House Committee on Science and Technology. He discussed the role of Arecibo’s radar system, which is one of only two high-powered radars in the world used for studying solar system bodies, on characterizing NEOs and their potential threat to Earth.
Arecibo’s radar is over 20 times more sensitive than its counterpart, NASA’s Deep Space Network 70-meter antenna at Goldstone, Calif., Campbell noted. But because it is less maneuverable, both systems are vital and complementary.
“The more we know about NEOs in general and about specific ones that pose a threat to Earth, the easier it will be to design effective mitigation strategies,” said Campbell. “NEOs form a very diverse population encompassing a large range of sizes, shapes, rotation states, densities, internal structure and binary nature.”
Radar provides the best way to survey and categorize such objects, he said. “For an object that we know poses a direct threat to Earth, radar can provide vital input to mitigation planning, including planning for any precursor space mission.”
Campbell also noted Arecibo’s unique role in supporting research in radio astronomy, radar planetary studies (including the study of NEOs) and ionosphere physics, as well as in education and outreach activities.
“If the Arecibo radar system is decommissioned … a tremendous amount of basic science related to NEOs and other solar system bodies would be lost,” he said.
In its concurrent statement, the Planetary Society called the Senior Review recommendation “a misguided attempt to free up funding for new projects that do not yet exist.”
Arecibo is part of the National Astronomy and Ionosphere Center, a national research center operated by Cornell under a cooperative agreement with the NSF.
Tidal Evolution of Rubble Piles
Authors: Peter Goldreich, Re’em Sari
(Submitted on 4 Dec 2007)
Abstract: Many small bodies in the solar system are believed to be rubble piles, a collection of smaller elements separated by voids. We propose a model for the structure of a self-gravitating rubble pile. Static friction prevents its elements from sliding relative to each other. Stresses are concentrated around points of contact between individual elements. The effective dimensionless rigidity, $\tilde\mu_{rubble}$, is related to that of a monolithic body of similar composition and size, $\tilde\mu$ by $\tilde \mu_{rubble} \sim \tilde \mu^{1/2} \epsilon_Y^{-1/2}$, where $\epsilon_Y \sim 10^{-2}$ is the yield strain. This represents a reduction in effective rigidity below the maximum radius, $R_{max}\sim [\mu\epsilon_Y/(G\rho^2)]^{1/2}\sim 10^3\km$, at which a rubble pile can exist. Densities derived for binary near-Earth asteroids imply that they are rubble piles. As a consequence, their tidal evolution proceeds $10^3$ to $10^4$ times faster than it would if they were monoliths. This accounts for both the sizes of their semimajor axes and their small orbital eccentricities. We show that our model for the rigidity of rubble piles is compatible with laboratory experiment in sand.
Comments: 14 pages including 2 figures
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0712.0446v1 [astro-ph]
Submission history
From: Re’em Sari [view email]
[v1] Tue, 4 Dec 2007 08:31:59 GMT (218kb)
http://arxiv.org/abs/0712.0446
High school students discover asteroid
“Three Wisconsin high school students are credited with discovering an
asteroid while working on a project for their astronomy class.”
The full article here:
http://www.newsdaily.com/Science/UPI-1-20080117-01450000-bc-us-asteroid.xml