Pluto is undergoing global warming, as evidenced by a three-fold increase in the planet's atmospheric pressure during the past 14 years, a team of astronomers from Massachusetts Institute of Technology (MIT), Williams College, the University of Hawaii, Lowell Observatory and Cornell University announced in a press conference today at the annual meeting of the American Astronomical Society's (AAS) Division for Planetary Sciences in Birmingham, AL.

The team, led by James Elliot, professor of planetary astronomy at MIT and director of MIT's Wallace Observatory, made this finding by watching the dimming of a star when Pluto passed in front of it Aug. 20. The team carried out observations using eight telescopes at Mauna Kea Observatory, Haleakala, Lick Observatory, Lowell Observatory and Palomar Observatory. Data were successfully recorded at all sites.

An earlier attempt to observe an occultation of Pluto on July 19 in Chile was not highly successful. Observations were made from only two sites with small telescopes because the giant telescopes and other small telescopes involved lost out to bad weather or from being in the wrong location that day. These two occultations were the first to be successfully observed for Pluto since 1988.

Elliot said the new results have surprised the observers, who as recently as July thought that Pluto's atmosphere may be cooling. "From the July data, we knew that Pluto's atmosphere had changed since 1988, but the August data allowed us to probe much more deeply into Pluto's atmosphere and have given us a more accurate picture of the changes that have occurred," he said.

Jay Pasachoff, an astronomy professor at Williams College, said that Pluto's global warming was "likely not connected with that of the Earth. The major way they could be connected is if the warming was caused by a large increase in sunlight. But the solar constant-the amount of sunlight received each second-is carefully monitored by spacecraft, and we know the sun's output is much too steady to be changing the temperature of Pluto."

Pluto's orbit is much more elliptical than that of the other planets, and its rotational axis is tipped by a large angle relative to its orbit. Both factors could contribute to drastic seasonal changes.

Since 1989, for example, the sun's position in Pluto's sky has changed by more than the corresponding change on the Earth that causes the difference between winter and spring. Pluto's atmospheric temperature varies between around minus 235 and minus 170 degrees Celsius, depending on the altitude above the surface. The main gas in Pluto's atmosphere is nitrogen, and Pluto has nitrogen ice on its surface that can evaporate into the atmosphere when it gets warmer, causing an increase in surface pressure. If the observed increase in the atmosphere also applies to the surface pressure-which is likely the case-this means that the average surface temperature of the nitrogen ice on Pluto has increased slightly less than 2 degrees Celsius over the past 14 years.

Marc Buie, an astronomer at Lowell Observatory, has been measuring the amount of sunlight reflected by Pluto. "The pressure increase can be explained if the average amount of sunlight reflected by the surface has decreased, which means that more heat is absorbed from the sun," he said. "This could be the reason that the pressure has been pumped up."

David Tholen, an astronomer at the University of Hawaii who measured the size of Pluto in the late 1980s using a series of occultations and eclipses involving Pluto's satellite, noted that even though Pluto was closest to the sun in 1989, a warming trend 13 years later shouldn't be unexpected. "It takes time for materials to warm up and cool off, which is why the hottest part of the day on Earth is usually around 2 or 3 p.m. rather than local noon, when sunlight is the most intense," Tholen said. Because Pluto's year is equal to about 250 Earth years, 13 years after Pluto's closest approach to the Sun is like 1:15 p.m. on Earth. "This warming trend on Pluto could easily last for another 13 years," Tholen estimated.

Pluto and Neptune's largest moon, Triton, are presently about the same distance from the sun, and each has a predominantly nitrogen atmosphere (with a surface pressure 100,000 times less than that on Earth), so one might expect similar processes to be occurring on these two bodies.

A 1997 occultation of a star by Triton revealed that its surface had warmed since the Voyager spacecraft first explored it in 1989. On Triton, "Voyager saw dark material rising up as much as 12 km above the surface, indicating some kind of eruptive activity," Elliot said. "There could be more massive activity on Pluto, since the changes observed in Pluto's atmosphere are much more severe. The change observed on Triton was subtle. Pluto's changes are not subtle."

Researchers study faraway objects through occultations-eclipse-like events in which a body (Pluto in this case) passes in front of a star, blocking the star's light from view. By recording the dimming of the starlight over time, astronomers can calculate the density, pressure and temperature of Pluto's atmosphere. Observing two or more occultations at different times provides researchers with information about changes in the planet's atmosphere. The structure and temperature of Pluto's atmosphere was first determined during an occultation in 1988. Pluto's brief pass in front of a different star on July 19 led researchers to believe that a drastic atmospheric change was under way, but it was unclear whether the atmosphere was warming up or cooling down.

The data resulting from this occultation, when Pluto passed in front of a star known as P131.1, led to the current results. "This is the first time that an occultation has allowed us to probe so deeply into Pluto's atmosphere with a large telescope, which gives a high spatial resolution of a few kilometers," Elliot said.

From MIT, in addition to Elliot, researchers involved were physics seniors Katie Carbonari, Erica McEvoy and Alison Klesman; Kelly Clancy, technical assistant in earth, atmospheric and planetary sciences (EAPS); EAPS graduate student Susan Kern, MIT graduate Joyance Meechai (S.B. 2000); David Osip, EAPS research scientist; Michael Person, EAPS graduate student; and aeronatucs and astronautics junior Shen Qu.

NASA is still deciding whether to send a spacecraft to Pluto, the only planet not yet observed at close range. The Pluto-Kuiper Belt mission in the New Horizons Program, if approved, would be launched in 2006 and would reach Pluto 10 years later. This mission will seek to answer questions about the surfaces, atmospheres, interiors and space environments of the solar system's outermost objects, including Pluto and its moon, Charon.

Researchers are looking forward to observing additional Pluto occultations in the years before the Pluto-Kuiper mission flies by Pluto. Of particular interest is the prospect of using SOFIA, a 2.5-meter airborne telescope being built by NASA in collaboration with the German space agency, for Pluto-occultation events when it begins operating in 2004. Edward Dunham, who leads the occultation effort at Lowell Observatory, also is leading a team that is building HIPO, a SOFIA instrument designed specifically to observe occultations. The combination of HIPO and SOFIA will provide very high-quality data on a much more frequent basis than is possible using ground-based telescopes alone.

"This is a very complex process, and we just don't know what is causing these effects" on Pluto's surface, Elliot said. "That's why you need to send a mission."

Scientists at the Max-Planck-Institute for Radio Astronomy (MPIfR) in Bonn were able to determine the diameters of four of the five largest and most distant minor planets in our solar system. The largest of them was discovered last June by planetary scientists of the California Institute of Technology (Caltech), who named their object "Quaoar" after a creation myth of the Californian native Tongva people. The radio observations of the Bonn astronomers and their Californian colleagues show that Quaoar has a diameter of 1250 km, making it the largest object discovered in the solar system since the discovery of Pluto in 1930.

Minor planets are usually discovered as slowly moving unresolved sources in optical sky photographs taken with astronomical telescopes. Drs. Frank Bertoldi and Wilhelm Altenhoff from the MPIfR recently used the IRAM 30-meter telescope in Spain to measure the thermal radiation of four of the optically brightest minor planets. From the measured intensity they could derive their sizes, which range between 700 and 1200 km (see table below). On October 7 their Caltech colleagues presented their discovery of Quaoar at the annual meeting of the Planetary Sciences Division of the American Astronomical Society, which is held in Birmingham, Alabama. There they also present a direct size measurement of Quaoar from optical images obtained with the Hubble Space Telescope. This unique and first such observation confirms the prior radio size measurement.

The four minor planets are members of a ring of some 100,000 objects in the outskirts of the solar system, beyond Pluto at distances over 4 billion km from the sun, over 30 times the distance between earth and sun. The objects in this "Kuiper belt" circle the sun in stable orbits with periods of about 300 years. In the mid of last century, the existence of a ring of small planetesimals was first suggested by the astronomers Kenneth Edgeworth (1880-1972) and Gerard P. Kuiper (1905-1973), but the first discovery of an "Edgeworth-Kuiper belt object" (EKO) was not until 1992. By now, over 550 EKOs are known.

A direct size determination of an EKO had not been possible until recently due to the large distance of these small objects. However, using the IRAM 30-m telescope and MAMBO, a very sensitive heat sensor built at the MPIfR in Bonn, the Bonn scientists were able to measure the very weak thermal radiation emerging from the four large EKOs.

"The velocity with which a distant solar system object moves reveals its distance," explains Dr. Frank Bertoldi. "From that we can compute the objects' surface temperature, which is mostly given by the solar irradiation. The intensity of the heat radiation we receive from the EKO depends on its distance, temperature, and size, so knowing the distance and temperature, we find its size. On the other hand, the optical brightness of the object, which is simply reflected sunlight, does not tell us much about its size, because the very low surface reflectivity may vary significantly from object to object."

"The discovery of two large EKOs by our American colleagues this year is impressive and important," admits Dr. William Altenhoff, who has researched minor planets and comets for decades. "In the coming years I expect the discovery of many more and even larger of such objects. What is interesting to us is to find out the extend of the Kuiper belt, and particularly what the total mass of all the EKOs together might be. This would allow unique insights into the origin of our solar system. The EKOs are the debris from its formation, an archeological site containing pristine remnants of the solar nebula, from which the sun and the planets formed. A determination of the size and reflectivity of some of the EKOs enables us to estimate also the total mass of the many smaller EKOs, which are too small to measure their individual sizes."

The observations at millimeter wavelengths were made using the IRAM 30-meter telescope at Pico Veleta near Granada in Spain (Fig. 2). The sensitive bolometer detector MAMBO (Fig. 3) used here was developed and built at the MPIfR in Bonn by the group of Dr. Ernst Kreysa. The Institute for Radio Astronomy at Millimeter wavelengths (IRAM) is supported jointly by the German Max-Planck-Society, the French Centre National de Recherche Scientifique (CNRS) and the Spanish Instituto Geografico Nacional.

NASA's Hubble Space Telescope has measured the largest object in the solar system ever seen since the discovery of Pluto 72 years ago.

Approximately half the size of Pluto, the icy world 2002 LM60, dubbed "Quaoar" (pronounced kwa-whar) by its discoverers, is the farthest object in the solar system ever to be resolved by a telescope. It was initially detected by a ground-based telescope, as simply a dot of light, until astronomers aimed the powerful Hubble telescope at it.

Quaoar is about 4 billion miles away from Earth, well over a billion miles farther away than Pluto. Unlike Pluto, its orbit around the Sun is very circular, even more so than most of the planetary-class bodies in the solar system.

Although smaller than Pluto, Quaoar is greater in volume than all the asteroids combined (though probably only one-third the mass of the asteroid belt, because it's icy rather than rocky). Quaoar's composition is theorized to be largely ices mixed with rock, not unlike that of a comet, though 100 million times greater in volume.

This finding yields important new insights into the origin and dynamics of the planets, and the mysterious population of bodies dwelling in the solar system's final frontier: the elusive, icy Kuiper belt beyond Neptune.

Michael Brown and Chadwick Trujillo of Caltech are reporting the findings today at the 34th annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Birmingham, Ala.

Earlier this year, Trujillo and Brown used the Palomar Oschin Schmidt telescope to discover Quaoar as an 18.5-magnitude object creeping across the summer constellation Ophiuchus (it's less than 1/10,000th the brightness of the faintest star seen by the human eye). Brown had to do follow-up observations using Hubble's new Advanced Camera for Surveys on July 5 and August 1, 2002, to measure the object's true angular size of 40 milliarcseconds, corresponding to a diameter of about 800 miles (1300 kilometers). Only Hubble has the sharpness needed to actually resolve the disk of the distant world, leading to the first-ever direct measurement of the true size of a Kuiper belt object (KBO).

Like Pluto, Quaoar dwells in the Kuiper belt, an icy debris field of comet-like bodies extending 7 billion miles beyond Neptune's orbit. Over the past decade more than 500 icy worlds have been found in the Kuiper belt. With a few exceptions all have been significantly smaller than Pluto.

Previous record holders are a KBO called Varuna, and an object called 2002 AW197, each approximately 540 miles across (900 kilometers). Unlike Hubble's direct observations, these diameters are deduced from measuring the objects' temperatures and calculating a size based on assumptions about the KBOs' reflectivity, so the uncertainty in true size is much greater.

This latest large KBO is too new to have been officially named by the International Astronomical Union. Trujillo and Brown have proposed naming it after a creation god of the Tongva native American tribe, the original inhabitants of the Los Angeles basin. According to legend, Quaoar, "came down from heaven; and, after reducing chaos to order, laid out the world on the back of seven giants. He then created the lower animals, and then mankind."

Quaoar's "icy dwarf" cousin, Pluto, was discovered in 1930 in the course of a 15-year search for trans-Neptunian planets. It wasn't realized until much later that Pluto actually was the largest of the known Kuiper belt objects. The Kuiper belt wasn't theorized until 1950, after comet orbits provided telltale evidence of a vast nesting ground for comets just beyond Neptune. The first recognized Kuiper belt objects were not discovered until the early 1990s. This new object is by far the "biggest fish" astronomers have snagged in KBO surveys. Brown predicts that within a few years even larger KBOs will be found, and Hubble will be invaluable for follow-up observations to pin down sizes.

After a year-long study, a National Research Council panel has concluded that sending a spacecraft to several bodies in the Kuiper Belt, including Pluto, should be NASA's highest solar-system priority in the coming decade. The NRC study, conducted by 60 top U.S. planetary scientists and released Thursday, also endorses a Europa Geophysical Explorer (EGE) mission to place a craft in orbit around Jupiter's enigmatic icy moon Europa, as well as several other missions. But the survey committee made it clear that the Kuiper-Pluto mission's technical feasibility and lower cost give it "clear advantages over EGE."

The study's recommendations come as a welcome surprise to the team working on the New Horizons mission, which could be launched as early as 2006 and reach Pluto and Charon (its moon) by 2016. "This is great news," says S. Alan Stern, the mission's principal investigator. "I've lost a lot of sleep this past week." Edward J. Weiler, NASA's associate administrator for space science, has stated that the space agency could not commit to a Pluto-Kuiper effort unless the planetary-science community backed it. The Bush administration excluded New Horizons from NASA's fiscal 2002 budget, but Congress later authorized $30 million to begin its development. Nor was it included in the president's fiscal 2003 budget, though Congress may opt to fund the mission anyway.

"Given the scientific value and the unique timing, we would be missing an historic opportunity if we don't move forward with this project and make this mission a reality," comments Sen. Barbara A. Mikulski (Maryland), who chairs the Senate appropriations subcommittee responsible for NASA. "I intend to restore funding again this year, despite NASA's failure to include money for Pluto in the FY03 budget...."

In the race to find all the interplanetary bodies that threaten Earth, astronomers have tallied more than 600 asteroids with estimated diameters of at least 1 kilometer. However, as several participants noted during a "space roundtable" held July 10th in Washington, D.C., governments should be doing more to find these and other near-Earth objects (NEOs). Titled "The Asteroid Threat: Identification and Mitigation Strategies," the roundtable was organized by ProSpace and the Space Frontier Foundation.

Colleen N. Hartman, NASA's director of solar-system exploration, noted that the space agency funds ground-based searches at roughly $4 million annually toward its goal of finding 90 percent of large near-Earth asteroids by 2008. But Brian G. Marsden (Minor Planet Center) expressed concern that the projected total of such objects -- currently near 1,200 -- may be higher than thought. He explains that when the telescopic census nears completion the discovery rate should start to tail off. Yet astronomers continue to find about 100 kilometer-size objects per year, with no sign of letting up....

"We're at the point of needing to move away from an ad hoc response," says aerospace engineer Warren Greczyn. He notes that the American Institute of Aeronautics and Astronautics recommends the formation of a top-level interagency group to advise the government on planetary-defense issues. Rick Tumlinson, president of the Space Frontier Foundation, adds that such oversight might well be integrated into proposals for a U.S. Department of Homeland Defense. Congressman Dana Rohrabacher, who chairs the House Subcommittee on Space and Aeronautics, likes the idea of utilizing military-derived technology to hunt down threatening NEOs. "The potential danger from global warming," he submits, "is nothing compared to the potential danger from near-Earth objects."

Scientists are making progress in cataloguing and tracking large near-earth objects (NEOs), but a serious threat still remains from smaller objects, an expert panel told the Space and Aeronautics Subcommittee today.

These smaller asteroids (200-500 meters wide) could potentially demolish a city with a direct hit or cause a tsunami capable of wiping out entire coastal areas if they land in the ocean. NASA has catalogued nearly 50 percent of asteroids 1 kilometer wide and larger. Astronomers estimate that between 900 and 1300 of the larger asteroids exist while there could be as many as 50,000 in the smaller range.

Subcommittee Chairman Dana Rohrabacher (R-CA) stated, "The threat posed by incoming asteroids and comets is a serious, potentially life-threatening topic. Given the number of near-earth objects in space, it is a matter of time before we are faced with an event unparalleled in human history. I hope that my legislation, H.R. 5303 [http://www.house.gov/science/press/107/107-286.htm], passed by the House on Tuesday will strengthen existing government capabilities for tracking natural space objects by encouraging private citizens to observe asteroids and comets."

Subcommittee Ranking Member Bart Gordon (D-TN) added, "NASA's Mission Statement says that part of its mission is '... to protect our home planet.' I hope NASA will heed the message of today's hearing and work with other agencies of the U.S. government to craft a timely, cost-effective plan to detect and catalog as many as possible of the Near-Earth asteroids and comets that could potentially threaten our population. We cannot afford to be complacent."

Dr. David Morrison, senior scientist at the NASA Ames Research Center, discussed NASA's goals and accomplishments in monitoring NEOs through the "Spaceguard" program. Morrison noted that Spaceguard was halfway to its goal and he expected that by 2008 NASA will have 90 percent of large, kilometer-sized threatening asteroids catalogued. Morrison added, "Our objective should be to find a large impactor far in advance, and thus provide decision-makers with options for dealing with the threat and defending our planet from cosmic catastrophe."

NEOs also pose a serious concern for the military, Brigadier General Simon P. Worden testified. Worden told of an asteroid that entered the atmosphere and exploded above the Mediterranean during last year's India-Pakistan conflict. U.S. satellites detected an energy release and shockwave comparable to the Hiroshima bomb, and Worden explained that had the event taken place at the same latitude two hours earlier and mistaken for a nuclear detonation it could have had devastating consequences. Worden added, "I believe there is considerable synergy between national security requirements related to man-made satellites and global security requirements related to NEO impacts."

Witnesses also debated the merits of continuing the cataloging effort on smaller NEO's once the Spaceguard program is completed. Dr. Brian Marsden, Director of the Minor Planet Center of the Smithsonian Astrophysical Observatory, testified that handling the large amount of data from surveys of smaller NEOs would be a challenging, but feasible, task. Dr. Joseph Burns, a member of the Solar System Exploration Survey Committee of the National Research Council, testified that NASA should partner with the National Science Foundation to build and operate a large ground-based survey telescope because of NSF's expertise in ground based astronomy and NASA's traditional support of ground-based solar system observations that support space missions.

Dr. Ed Weiler, NASA Associate Administrator for Space Science, disagreed saying, "I feel that it is premature to consider an extension of our current national program to include a complete search for smaller-sized NEOs." He also noted that NASA did not feel the agency "should play a role in any follow-on search and cataloging effort unless that effort needs to be specifically space-based in nature."

Rep. Anthony Weiner (D-NY) said, "For too long we've assumed that the worst asteroid risk would come from Hollywood -- in the form of a sequel to flops like Deep Impact or Armageddon. But the threat posed by Near Earth Objects is real, and if we can plow $100 million into a summer flick, we can certainly give NASA the means to make us safer from real life blockbusters."

Amateur asteroid hunters can hope to win one of three $2,000 awards each year if an act passed by the U.S. House of Representatives this week makes its way into law. The Charles "Pete" Conrad Astronomy Awards (named for one of the Apollo 12 astronauts) would be granted in three categories. One would go to the amateur astronomer who discovers the largest near-Earth asteroid in a given year. The second would go to an amateur who uses professionally acquired data for a discovery or refinement of an orbit, and the third is reserved for the amateur "who provides the greatest service to update the minor planet catalogue." The measure passed the House on a voice vote October 1st and has been referred to the Senate Commerce Committee.

William J. Merline (Southwest Research Institute) found a companion to asteroid 121 Hermione on September 28th. The object, discovered with the 10-meter Keck II telescope in Mauna Kea, Hawaii, appears to be about 13 kilometers across and has a projected separation from Hermione of 630 km. With this find, close to two dozen objects are now confirmed or suspected to be binary asteroids. Merline's discovery also appeared on IAU Circular 7980.

The Kuiper Belt region of the solar system, which stretches from just past Neptune to beyond the farthest reaches of Pluto's orbit, was only discovered in 1992, but continues to reveal new knowledge into the formation processes of the planets. Now, in a paper to be published in the October issue of The Astronomical Journal, a Southwest Research Institute (SwRI) scientist reveals a new mystery about Kuiper Belt Objects (KBOs).

The study examined the formation of KBO satellites, which have been observed only since 2001 and continue to be discovered around an unexpectedly large number of the more than 500 known KBOs.

"In just over a year since the first satellite of a KBO was found, scientists have discovered a total of seven KBO satellites. Surprisingly, observations by both ground-based telescopes and the Hubble Space Telescope have indicated that, in many cases, the KBO satellites are as large or nearly as large as the KBOs around which they orbit," says Dr. S. Alan Stern, director of the SwRI Space Studies Department. "That so many binary or quasi-binary KBOs exist came as a real surprise to the research community."

The focus of Stern's work was not observational in nature, but rather it sought to understand how such large KBO-satellite pairs could form. The standard model for large satellite formation is based on collisions between an interloping body and the parent object around which the satellite orbits. This model has successfully explained binary systems around asteroids and the Pluto-Charon system, and also has direct relevance to the formation of the Earth-moon system.

Stern's findings call into question the formation of KBO satellites by standard collisional processes. Collisions of the magnitude required, Stern found, appear to be energetically improbable, given the number and masses of potential impactors in both the ancient (more massive) and modern day (eroded) Kuiper Belts.

This likely implies one of two alternatives: Either KBO satellites were not formed by collisions, as has been commonly assumed, or the surface reflectivities (which help determine size) of KBOs with satellites, or the reflectivity of the satellites themselves, have been significantly underestimated.

"If the surfaces of KBOs with satellites, or the satellites themselves, are more reflective than previously thought," says Stern, "These objects would be smaller and less massive, and would therefore require smaller, less energetic impacts to create the satellite systems we see."

NASA's new Space Infrared Telescope Facility (SIRTF), set for launch early next year, will help resolve these two alternatives, Stern says, by directly measuring the reflectivities and sizes of numerous KBOs, including those with satellites.

In addition to this work, Stern serves as principal investigator of the NASA New Horizons mission to Pluto and the Kuiper Belt. Expected to launch in January 2006, this spacecraft will make the first ever flyby reconnaissance of the Pluto-Charon system and then go on to explore KBOs as it leaves the solar system. New Horizons is the only NASA mission planned to study Kuiper Belt Objects at close range.

The NASA Origins of Solar Systems program provided funding for this research.

This summer, much of the world watched as India and Pakistan faced-off over the disputed Kashmir region, worried that the showdown could escalate into a nuclear war.

Coincidentally, U.S. early warning satellites detected an explosion in the Earth's atmosphere June 6, at the height of the tension, with an energy release estimated to be 12 kilotons.

Fortunately the detonation, equivalent to the blast that destroyed Hiroshima, occurred over the Mediterranean Sea. However, if it had occurred at the same latitude a few hours earlier, the result on human affairs might have been much worse, said Brig. Gen. Simon P. Worden, U.S. Space Command's deputy director for operations at Peterson Air Force Base, Colo.

Had the bright flash, accompanied by a damaging shock wave, occurred over India or Pakistan, the resulting panic could have sparked a nuclear war, Worden recently told members of the congressionally mandated Commission on the Future of the U.S. Aerospace Industry in testimony here.

Although U.S. officials quickly determined that a meteor caused the explosion, neither India nor Pakistan have the sophisticated sensors that can determine the difference between a natural near-Earth object impact and a nuclear detonation, Worden said in written testimony.

This is one of many threats posed by NEOs, especially as more and more nations acquire nuclear weapons, said Worden, who appeared before the commission as a scientist who has studied NEOs and as a space expert familiar with the technologies that can be used to address the NEO threat.

In recent years, the Department of Defense has been working to provide data about asteroid strikes to nations potentially under missile attack and to the scientific community; however, it takes several weeks for the data to be released since much of it is gathered from classified systems.

Worden suggested that a NEO warning center be established that can assess and release this data as soon as possible to all interested parties while ensuring sensitive data is safeguarded.

He recommended to the commission that a natural impact warning clearinghouse could be formed by adding no more than 10 people to current U.S. Space Command early warning centers.

This organization would catalog and provide credible warning information on future NEO impact problems, as well as rapidly provide information on the nature of an impact.

In order for this clearinghouse to provide accurate information, NEOs must first be detected, cataloged and their orbits defined.

Current ground-based systems are already cataloging large kilometer-sized objects but have a difficult time finding smaller NEOs. Most sail by the earth unnoticed until they have passed, he said.

"Just about everyone knows of the 'dinosaur killer' asteroids," Worden said. "These are objects, a few kilometers across, that strike on time scales of tens of millions of years. While the prospect of such strikes grabs people's attention and makes great catastrophe movies, too much focus on these events has been counterproductive. We need to focus our energies on the smaller, more immediate threats."

The smaller strikes, while not exactly commonplace, have occurred on several occasions over the past century, with potentially devastating results, he said.

"An object probably less than 100 meters in diameter struck Tunguska in Siberia in 1908, releasing the energy equivalent to a 10-megaton nuclear blast," Worden said. "In 1996, our satellite sensors detected a burst over Greenland equal to a 100-kiloton yield. Had any of these struck over a populated area, perhaps hundreds of thousands might have perished."

An even worse catastrophe would be an ocean impact near a heavily populated shore by one of these Tunguska-sized objects.

"The resulting tidal wave could inundate shorelines for hundreds of miles and potentially kill millions," Worden explained.

"There are hundreds of thousands of objects this size that come near the Earth," he said. "We know the orbits of just a few. New space-surveillance systems capable of scanning the entire sky every few days are needed. They could enable us to completely catalog and warn of objects (less than 100 meters in diameter)."

According to Worden, this does not mean other groups, in particular the international scientific community, should not continue their independent efforts. But the United States is likely, for the foreseeable future, to have most of the required sensors to do this job. He added that DOD has the discipline and continuity to ensure consistent, long-term focus.

"I believe various aspects related to NEO impacts, including the possibility that an impact would be misidentified as a nuclear attack, are critical national and international security issues," he said. "The focus of NEO mitigation efforts should shift to smaller objects. The near-term threats are much more likely to come from these 'small' objects, and we might be able to divert such objects without (resorting) to nuclear devices."

The National Defense Authorization Act for Fiscal Year 2001 established the Commission on the Future of the U.S. Aerospace Industry. The commission was formed to study the future of the U.S. aerospace industry in the global economy, particularly in relationship to national security, and provide recommendations to the president and Congress.

From Uzbekistan and the Crimea to the UK, across North America, and on to Hawaii, amateur astronomers around the world had fine views of the close flyby of asteroid 2002 NY40 during the evening of August 17-18, 2002.

The experience of David Nance (Huntsville, Alabama) was typical of the many reports received at Sky & Telescope. He wrote: "I found 2002 NY40 easily and followed it for about 30 minutes. It was very bright (I'd estimate it at magnitude 9.5), and it was really spectacular sailing through the eyepiece, changing the patterns I formed with it and the framework of stars. My wife thought it was neat since it was so obviously not a 'fixed' star ... it looked a lot like a slow moving satellite on a really weird trajectory...."

The last two months have been good ones for Plutophiles. In July a U.S. Senate subcommittee fortified NASA's budget with $105 million to continue work on the New Horizons mission, which could be launched toward the distant planet as soon as 2006. And during the past five weeks telescopes have captured the passage of Pluto in front of not one, but two faint stars. Although analysis of the stars' brief disappearances has only begun, it is already clear that observing teams from the United States and Europe have come to very different conclusions about the state of Pluto's atmosphere.

During the first event, on July 20th (Universal Time), Pluto's shadow crossed South America and, unfortunately, barely missed passing over a string of major observatories in the Andes. The only "hits" came from astronomers with portable setups: Marc Buie and Oscar Saa used a 14-inch Celestron and a CCD camera near the small Chilean town of Mamiña, while Francois Colas had a video-equipped 12-inch telescope a little farther north near Arica. According to Bruno Sicardy, who coordinated the European effort, seven other ground teams in Chile, Ecuador, Peru, and Venezuela were either clouded out or experienced technical difficulties. Fortunes improved for the August 21st occultation, as the broad path passed over observatories in Hawaii and the Far West....

July 26, 2002: I slid a dollar bill across the counter, and the cashier handed back a lottery ticket. The odds for winning: 1-in-250,000. A long shot, but you never know.

Walking out of the store, ticket in hand, I glance at a newspaper. "Tony Phillips wins the lottery!" the headline declared. Gosh, I thought, that seems premature ... not to mention weird.

Indeed, it's fiction. For one thing, I never buy lottery tickets. But mainly, no one would write such a headline based on such slender odds.

Yet that's what happened this week, in real life, to an asteroid.

On July 9, 2002, MIT astronomers discovered 2002 NT7, a 2 km-wide space rock in a curious orbit. Unlike most asteroids, which circle the Sun in the plane of the planets, 2002 NT7 follows a path that is tilted 42 degrees. It spends most of its time far above or below the rest of the solar system. Every 2.29 years, however, the asteroid plunges through the inner solar system not far from Earth's orbit.

After a week of follow-up observations, researchers did some calculations. There was a chance, they concluded, that 2002 NT7 might hit our planet on February 1, 2019. The odds of impact: 1-in-250,000.

"Space Rock 'on Collision Course'," a headline declared days later. "Asteroid Could Wipe Out a Continent in 2019," another one warned. Really.

"In fact," says Don Yeomans, the manager of NASA's Near-Earth Object Program at JPL, "the threat is minimal. One-in-250,000 is a very small number."

The odds are not only low, but also uncertain. Yeomans explains: "We've been tracking 2002 NT7 for a very short time--only 17 days so far," Meanwhile, the asteroid takes 2.29 years to orbit the Sun. Predictions based on such a small fraction of an orbit are seldom trustworthy.

It's becoming a familiar routine: Astronomers discover a near-Earth asteroid. With only meager data at hand, they can't rule out a collision in the distant future. Headlines trumpet the danger. Finally, the alarm subsides when more data lead to a better orbit--one that rules out an impact.

"As far as the public is concerned," says Jon Giorgini of JPL's Solar System Dynamics Group, "it just isn't worth getting worked up about an object with a couple weeks of data showing a possible Earth encounter many years from now. Additional measurements will shrink the uncertainty by a large amount--and Earth will (almost certainly) fall out of the risk zone."

Already this is happening for 2002 NT7. The calculated probability of a collision with Earth is shrinking as astronomers add new data each day. "I suspect it will take only a few more weeks (or maybe months) to completely rule out an impact in 2019," says Yeomans.

Giorgini explains further: "When we calculate an asteroid's position (based on measurements made at a telescope), the result isn't a single point in space. Instead, it's a volume of space where the asteroid could be with some probability. We deal with probabilities, not absolute answers, because the measurements contain errors." For example, optical data can be corrupted by twinkling and refraction in Earth's atmosphere. (Radar is better, notes Giorgini, but no radar data have yet been obtained for 2002 NT7.)

"When you project this initial probability region years into the future, it naturally expands. For a newly discovered object with only a few days tracking, the uncertainty region can easily grow to cover a big part of the inner solar system. Because Earth is in the inner solar system, and can potentially cut through this volume of smeared out probability, we end up with finite impact probabilities."

"A finite probability, however, is not really a prediction of impact," he cautions, "but a statement that one is possible." Of course, many things are possible. Like the newspaper headline "Tony Phillips wins the Lottery!" But most of them do not happen.

JPL lists asteroids like 2002 NT7 on their Internet "risk page" not to raise an alarm, says Yeomans, but to alert astronomers when new discoveries merit attention. "It's important that we continue tracking these asteroids to refine their orbits," he says. The more observers, the better.

What's an ordinary person to do?

The next time you see a headline "Killer asteroid threatens Earth!" ask yourself two questions: Have we known about this space rock for more than a week or so? (If not, check again in a month. It probably won't be considered a killer then.) And what are the odds of impact?

If you're more likely to win the lottery, there's probably nothing to worry about.

Editor's note: Big asteroids have hit Earth before and it's only a matter of time before one threatens us again. Will it be years, decades, millions of years? No one knows. The point of this article is not that we are safe from asteroid strikes. We are not safe. Rather, we hope to give readers some of the information they might need to evaluate popular reports of impending collisions.