Amateur astronomers play a critical role in retiring the risk of impact from near-Earth objects. When the Shoemaker NEO Grant program began in 1997, the focus was on finding previously undiscovered objects one kilometer in diameter and larger. Thanks to professional NEO survey programs like LINEAR (the Lincoln Near-Earth Asteroid Research program run by MIT’s Lincoln Laboratories) and the Catalina Sky Survey (run from the University of Arizona’s Lunar and Planetary Laboratory), the goal of discovering the vast majority of large NEOs is within reach, and the focus of the Shoemaker NEO Grant Program has shifted to astrometric follow-up and physical studies. Astrometric follow-up observations extend the time and space over which an object's position is mapped, enabling its orbit to be determined with higher certainty, while physical studies help scientists understand the composition, construction, origin, and orbital evolution of these bodies. Physical studies also will be critical for evaluating methods for any future necessary asteroid mitigation (for example, moving an asteroid’s orbit to avoid Earth).
Tracking Faint Objects
The magnitude of an object in the sky is a measure of its relative brightness and is a logarithmic scale. Objects that differ in magnitude by 5 differ in brightness by a factor of 100. The greater the brightness, the lower the magnitude; most stars have positive magnitudes, while the naked-eye planets, Moon, and Sun have negative magnitudes. The Sun has an apparent magnitude of -26; the brightest star in the sky, Sirius, has an apparent magnitude of -1.46. So the objects being detected at magnitudes of about 23.5 by Robert Holmes at the Astronomical Research Institute are fainter than Sirius by roughly the same factor that Sirius is fainter than the Sun.
Several of the 2007 Shoemaker NEO Grant winners used their funds to purchase CCD cameras capable of capturing large swaths of the sky or imaging very faint objects, or both. Robert Holmes, of the Astronomical Research Institute in Illinois, reports that with the new CCD camera purchased with NEO grant funds, 84,600 images of near-Earth objects were taken in the year from June 1, 2007 to May 31, 2008. From these, the Astronomical Research Institute reported a staggering 5,835 targeted measures of comets and near-Earth asteroids to the Minor Planet Center. The faintest object Holmes captured on camera was 2001 SD170, observed at an unfiltered magnitude of about 23.5.
In Tahiti, Jean-Claude Pelle also used his NEO Grant award to purchase a CCD camera permitting him to capture a view of the sky 39 arcminutes square. This relatively broad field of view has facilitated Pelle's efforts to follow up on just-discovered NEOs whose orbits were only observed over a very short arc (often less than one hour) and so suffer from large uncertainties in their position. By aggressively following these recently-discovered objects, Pelle and his collaborators at Southern Stars Observatories have multiplied the length of the known arcs of some bodies by factors as large as 20. The wide field of view also brings a collateral benefit: many other objects are also often present in a single image. As a by-product of near-Earth object follow-up, Southern Stars Observatories workers have discovered 150 discoveries of main-belt asteroids.
The benefit of the NEO Grant to Giovanni Sostero and his coworkers at the Associazione Friulana di Astronomia e Meteorologia in Remanzacco, Udine, Italy has been to improve their computing power with two new PCs, speeding up their reaction times in following up new, fast-moving objects. His group now conducts astrometric and photometric follow-up from two sites in Italy, a permanent observatory at Remanzacco and a site for their portable telescopes in Comeglians, with a third position under construction at Mount Matajur, 1,320 meters above sea level. They and also observe remotely, from New Mexico and Australia. In a period of fifteen months, Sostero's group has confirmed 27 NEOs to be comets, has performed confirmation observations on the discoveries of nearly 50 NEOs (some of them very faint, at magnitudes near 21), and has recovered seven periodic comets.
Brian Warner, at the Palmer Divide Observatory in Colorado, has put his Shoemaker NEO Grant to slightly different use. His grant allowed him to purchase a second telescope, which he employs to do photometry (studies of how the brightness of asteroids vary with the observing angle and the asteroid's rotation), which, in turn, helps to provide information on the size and shape of larger asteroids. Although these studies don't directly address the problem of whether a given asteroid will or won't hit Earth, they provide important data to the broader research into the range of sizes and shapes of the asteroid population, and into studies on YORP, the various ways that asteroid orbits change as sunlight is absorbed, reflected, and re-radiated by spinning, odd-shaped, inhomogeneously colored asteroids. As a by-product of his studies, Warner has discovered that at least a dozen asteroids are binaries. Don Pray of the Carbuncle Hill observatory has been performing similar photometric studies, helping to confirm that at least four asteroids are binaries.
Grants Create Cooperation
Although the Gene Shoemaker NEO Grant program now focuses more on follow-up than discovery, Grant awardees continue to discover new NEOs. But in order for a NEO discovery to be credited or to figure out if the NEO is a danger to Earth, there needs to be follow-up tracking of the new object on subsequent nights, allowing an orbit to be calculated. On July 11, 2007, Quanzhi Ye of the Lulin Observatory in Taiwan discovered a NEO, 2007 NL1. He could not perform follow-up observations because of an approaching typhoon, and in fact it appeared to be a cloudy day across much of Earth. But he noticed that the southern Pacific Ocean was relatively cloud-free, and asked fellow 2007 Grant awardee Jean-Claude Pelle in Tahiti to perform follow-up observations. Pelle was able to obtain them, confirming the discovery and starting the process of defining the NEO's orbit.
Giovanni Sostero's group has leveraged the $4,400 of their Shoemaker NEO Grant to win even larger support for their efforts to discover, track, and study NEOs. Sostero reports that other institutions and foundations in Italy provided further funding to refurbish their observatories after learning of the grant award; and that more collaborators joined his team after learning of the team's work from television and newspaper reports about the NEO threat and the award of the Shoemaker NEO Grant. "The benefits of the Gene Shoemaker NEO Grant has exceeded our expectations," Sostero said.
Bringing the Public Along for the Ride
Though not required to do so, many of the Shoemaker NEO Grant winners have independently embarked on programs to educate their communities about the night sky and the hazard of potential asteroid impact. Some also involve classrooms around the world in the work to discover and track potentially hazardous objects.
For example, the Astronomical Research Institute in Illinois is participating in the worldwide "Killer Asteroid Project," which raises awareness about the threat of near-Earth objects to teachers and students around the world. Holmes says, "Each night up to one gigabyte of data is imaged using The Planetary Society SBIG STL-1001E CCD camera, uploaded to the Internet, and made available to high schools, colleges, and universities for use in their classrooms within 5 hours of acquisition. In May 2008, the Astronomical Research Institute presented more than 450 awards to schools, teachers, and students in nine countries including China, Germany, Italy, Japan, Morocco, Poland, Portugal, Russia, and the United States."
For Eric Allen of Quebec, the publicity generated by his grant award gave him the argument he needed to convince his superiors to permit him to open the observatory to the public for the first time since 2003. Now the observatory is open to the public six nights a week, and Allen educates the visitors about the night sky and NEOs. He was also interviewed for a Discovery Canada documentary on the 100th anniversary of the Tunguska impact event. His effort to automate his dome (the focus of his grant award) has been delayed because of the work involved in performing public outreach, but he expects fully automated observing runs to begin in late August.