October 31, 2003
For the next few days backyard astronomers can see for
themselves the long lost asteroid Hermes.
- NASA Science News
Oct. 23, 2003
Asteroid Hermes, lost for 66 years, is found to be two objects
orbiting each other. More
Oct. 21, 2003
The re-discovery of Hermes started early on October 15th by
Brian Skiff of the Lowell Observatory Near-Earth-Object Search (LONEOS). More
October 16, 2003
Orbit for Hermes Dynamically Linked from 1937 to 2003 More
Flagstaff, AZ--The re-discovery of Hermes started early on October 15th by Brian Skiff of the Lowell Observatory Near-Earth-Object Search (LONEOS). Not seen since 1937, asteroid 1937 UB (Hermes) continues to astonish and excite astronomers worldwide. Further observations revealed late yesterday that Hermes is actually two objects--called a binary--circling around one another while about to pass by Earth again.
"This re-sighting of Hermes is the Holy Grail of near-Earth asteroid discovery," said Edward Bowell, LONEOS Director. "Its orbit has been better calculated and observers have confirmed its re-appearance and also shown its binary nature... well, an asteroid's return just does not become more profound than this."
The binary object was some 19 million miles out at the time of re-discovery last Wednesday, nearly 66 years after it was first seen. Hermes, which poses no threat to Earth, will make its closest approach on November 4th. By then it will be 4 million miles away and bright enough for amateurs to see using backyard telescopes.
The same day Skiff captured the first images of Hermes, Discovery Communications, Inc. and Lowell Observatory announced a partnership to build the new Discovery Channel Telescope near Flagstaff, Arizona. One research objective for this new $30-million, 4.3-meter telescope will be to significantly accelerate the search for near-Earth objects, including those smaller than Hermes.
First images of the kilometer-size asteroid were captured by a CCD camera during early morning observation through the LONEOS 24-inch Schmidt telescope. More than six decades ago, Hermes was discovered by Karl Reinmuth at Heidelberg, Germany on October 25, 1937. Fast forward to a few days ago when Andrea Boattini of Instituto di Astrofisica Spaziale, Rome, Italy, and Timothy Spahr of the Minor Planet Center in Cambridge, Massachusetts analyzed the new positions of Hermes and determined what it was: the long-lost asteroid.
"Since we find new near-Earth asteroids fairly regularly (I found, for instance, two near-Earth asteroids the same night), my only reaction upon finding it was that it was unusually bright," Skiff told BBC News Online on Friday.
Up before dawn, Spahr quickly posted Skiff's discovery on the web, alerting astronomers to follow the asteroid. James Young, at the Jet Propulsion Laboratory's Table Mountain Observatory in California, was the first to respond, just five hours later. Spahr then located observations made on October 5 by the Near-Earth Asteroid Tracking program, LONEOS observations from September 28, and unpublished observations made by the MIT Lincoln Laboratory Near Earth Asteroid Research program, extending the observational arc back to August 26.
At this point, the identification with Hermes was clear from the similarity of the orbits from the 1937 and 2003 sightings, but it was not a simple matter to compute an orbit that linked all the observations together. Steven Chesley and Paul Chodas of the Jet Propulsion Laboratory found that Hermes' trajectory is very chaotic due to frequent close encounters with the Earth and Venus. Following its flyby of the Earth in 1937 at a distance of 460,000 miles (just 1.8 times the Moon's distance), Hermes made an unobserved close approach to the Earth in 1942 of just 1.6 lunar distance. Using JPL's Sentry impact monitoring software, Chesley and Chodas were able to find twelve distinct dynamical pathways that produced an encounter in 1937. Picking out the true orbit was then an easy matter, and led to the further prediction that Hermes will not approach the Earth more closely than 8 lunar distances within the next century.
On October 16, Andrew Rivkin and Richard Binzel of MIT observed a spectrum of Hermes using the NASA Infrared Telescope Facility in Hawaii, and were able to ascertain that the asteroid is of a type known as S class. Because the surfaces of S-class asteroids reflect, on average, 24% of the sunlight falling on them, Rivkin and Binzel were able to deduce that Hermes is 0.9 km (about 1,000 yards) in diameter.
Over the next few days, the world's most powerful radar, the 1,000-foot dish, at Arecibo, Puerto Rico, projected radar beams on to the asteroid and captured the faint returning echoes. Jean-Luc Margot, of the University of California, Los Angeles, and his team saw that the asteroid is strongly bifurcated. Two separate components, of roughly equal size and almost in contact, are revolving about their common center of mass in up to 21 hours. It appears that the components have tidally evolved into a situation where their spin period is equal to their orbital period and therefore present the same face to one another all the time, just like the Earth-Moon system. There are now about 10 radar-observed binary near-Earth asteroids, about 1 in 6 of NEAs larger than 200 m in diameter. "We certainly did not expect to find a binary with roughly equal-sized components," said Margot. "All the binary NEAs that we have imaged so far show a secondary that is only a fraction of the size of the primary."
Amateur and professional astronomers are collaborating to observe the way Hermes changes in brightness as its components rotate. Eventually, they should be able to determine the components' orbital plane, an accurate period of revolution, and, perhaps, the shapes of the individual bodies. See http://www.asu.cas.cz/~asteroid/binneas.htm for a list of binary NEAs.
The only near-Earth object not also identified by number, Hermes shares a name in Greek mythology with the son of Zeus, messenger of the gods, god of science, commerce, eloquence, and arts of life. "The name `Hermes' also means hastener, and representations of him are symbolic of the messenger or the speed and majesty in flight," according to Schmadel's Dictionary of Minor Planet Names.
Lowell Observatory was founded in 1894 by Percival Lowell with a mission to pursue the study of astronomy, especially the study of our Solar System and its evolution; to conduct pure research in astronomical phenomena; and to maintain quality public education and outreach programs to bring results of astronomical research to the general public.
LONEOS is one of five programs funded by NASA to search for asteroids and comets that may approach our planet closely. Their current goal is to discover 90% of near-Earth asteroids larger than 1 km in diameter by 2008. There are thought to be about 1,200 such asteroids.
For more information on the discovery and images of Hermes, visit the LONEOS website.
ARECIBO, P.R. -- An asteroid that has eluded astronomers for decades turns out to be an unusual pair of objects traveling together in space, a planetary scientist using the National Science Foundation's (NSF) Arecibo Observatory radio telescope and his colleagues report.
The asteroid Hermes was re-discovered last week after being lost for 66 years. Now Jean-Luc Margot, a researcher in the Department of Earth and Space Sciences at the University of California, Los Angeles, has determined that the asteroid is in fact two objects orbiting each other. The two objects together would cover an area approximately the size of Disneyland.
Margot and colleagues are analyzing new radar measurements from the Arecibo Observatory, Puerto Rico, the world's largest single-dish radio telescope, operated by the National Astronomy and Ionosphere Center (NAIC) at Cornell University, Ithaca, N.Y., for the NSF. The astronomers are scheduled to obtain additional measurements using the Arecibo telescope this weekend (Oct. 25-26).
Hermes makes frequent close approaches to Earth, Venus, Mars, as well as Vesta, the third largest asteroid in the main asteroid belt between Mars and Jupiter.
While several other asteroids have satellites, the other known binaries with trajectories that cross the orbit of the Earth consist of a large primary asteroid orbited by a much smaller one.
"Hermes is the first asteroid ever discovered in the near-Earth population where the two components are essentially equal in size," Margot said. "It's a very unusual binary, a puzzle. It may have formed when it swung so close to a planet that it was ripped apart by gravitational forces, but we don't know for sure. One of our goals is to learn more about the two components and how they rotate about each other in the hopes that we may be able to deduce how Hermes became a double asteroid.
"Because the components are close to each other, they raise appreciable tides in each other and each has slowed down the other's spin significantly. They are now likely in a doubly synchronous state, where their spin period is equal to their orbital period. This means they constantly present the same face to each other, just like Pluto and its satellite, Charon."
Hermes, was first observed in 1937 as a fast-moving bright object and then went undetected until last week, although it had circled the sun almost exactly 31 times since then, said Brian Marsden, of the Minor Planet Center in Cambridge, Mass.
On Oct. 15, Brian Skiff of the Lowell Observatory Near-Earth-Object Search sighted a mysterious object; Timothy Spahr at the Minor Planet Center in Cambridge identified similarities with the 1937 observations, and Steven Chesley and Paul Chodas at NASA's Jet Propulsion Laboratory (JPL) linked the observations to Hermes.
The same day, Margot and his team proposed to observe the asteroid with the Arecibo Observatory's high-powered radar system -- a proposal that was accepted within hours.
The goals of the proposal were to measure precisely the distance and velocity of this object, to improve the knowledge of its trajectory and help trace back its history, to characterize Hermes' physical properties, and to search for satellites.
Margot and collaborators have been given five sessions at Arecibo and five sessions at the Goldstone radar telescope in California to observe Hermes. Due to the urgent nature of the proposal, Margot observed from his home computer while his associates, Mike Nolan, Victor Negron, Alice Hine, and Don Campbell, associate director of NAIC, were at the Arecibo telescope.
Hermes gets as close as 378 000 miles from Earth -- which, in astronomical terms, is quite close, about 1.6 times the distance between Earth and the moon. Orbits can change appreciably over time due to gravitational influences of the planets, noted Nolan, an Arecibo Observatory scientist.
Hermes travels on an elliptical orbit and reaches deep into the inner solar system, crossing Venus' orbit. The new research has made it possible to extend the time interval over which the trajectory can be computed reliably, said Jon Giorgini, a senior engineer at JPL and member of the team.
"As far as impact risk, there is no cause for worry in our lifetimes," Giorgini said. "Over hundreds of thousands or millions of years, Hermes could impact the Earth, but only if it doesn't hit Venus first."
Margot and colleagues described their observations and data in an International Astronomical Union Circular this week. Margot's research is funded by NASA. His co-authors are Nolan, Negron, Hine, Campbell, and Ellen Howell at NAIC; Lance Benner, Steven Ostro, and Giorgini at JPL; and Marsden at the Minor Planet Center.
Using sophisticated orbit determination tools, the difficult problem of finding a precise orbit for the long-lost and recently rediscovered asteroid Hermes has been solved.
The recovery of Hermes was announced on October 15, 2003 by the Minor Planet Center (MPC) in Cambridge Massachusetts. The object was initially noted by Brian Skiff of the LONEOS asteroid search program at the Lowell Observatory in Arizona, and key follow-up measurements were provided by James Young of JPL's Table Mountain Observatory in California. Tim Spahr of the MPC located prediscovery observations from the last 7 weeks and computed the new object's orbit. Noticing that the orbit was very similar to that of Hermes, last seen during its close approach in 1937, Spahr concluded that the new object was almost certainly Hermes. Definitive proof of the object's identity was still lacking, however, because an orbit linking the known positions in 1937 to those in 2003 could not be found.
Finding the precise orbit of Hermes is difficult because its trajectory is very chaotic. In the 66 years since it was last seen, the asteroid has made numerous close approaches to both the Earth and Venus. Since the orbital changes at each approach depend highly on the circumstances of the encounter, finding an orbit with the precise sequence of encounter conditions that links positions in 2003 to those in 1937 is a challenging problem in orbit determination.
We have now solved this problem by using the JPL Sentry impact monitoring software in a novel way. Starting from the 2003 positions, Sentry found twelve distinct dynamical pathways that produced encounters in 1937, each with a different sequence of intervening close approach circumstances. Comparing these predicted 1937 encounters with the one determined directly from the 1937 observations, we were able to identify the most consistent candidate, and then zero in on the precise orbit that best matches the positions in both 1937 and 2003. We now know that since it was last seen, Hermes has made eight close approaches to the Earth and Venus to within 0.06 AU, including an Earth approach to within about 1.6 lunar distances in 1942. The new orbit solution allows us to predict future close approaches with great accuracy; we can now predict that Hermes will not approach the Earth any closer than about 0.02 AU (8 lunar distances) within the next hundred years.
October 31, 2003: It's dogma now: an asteroid hit Earth 65 million years ago and wiped out the dinosaurs. But in 1980 when scientists Walter and Luis Alvarez first suggested the idea to a gathering at the American Association for Advancement of Sciences, their listeners were skeptical. Asteroids hitting Earth? Wiping out species? It seemed incredible.
At that very moment, unknown to the audience, an asteroid named Hermes halfway between Mars and Jupiter was beginning a long plunge toward our planet. Six months later it would pass 300,000 miles from Earth's orbit, only a little more than the distance to the Moon. Rhetorically speaking, this would have made a great point in favor of the Alvarezes. Curiously, though, no one noticed the flyby.
1980 wasn't the first time Hermes had sailed by unremarked. Hermes is a good-sized asteroid, easy to see, and a frequent visitor to Earth's neighborhood. Yet astronomers had gotten into the habit of missing it. How this came to be is a curious tale, which begins in Germany just before World War II:
On Oct. 28, 1937, astronomer Karl Reinmuth of Heidelberg noticed an odd streak of light in a picture he had just taken of the night sky. About as bright as a 9th magnitude star, it was an asteroid, close to Earth and moving fast--so fast that he named it Hermes, the herald of Olympian gods. On Oct. 30, 1937, Hermes glided past Earth only twice as far away as the Moon, racing across the sky at a rate of 5 degrees per hour. Nowadays only meteors and Earth-orbiting satellites move faster.
Plenty of asteroids were known in 1937, but most were plodding members of the asteroid belt far beyond Mars. Hermes was different. It visited the inner solar system. It crossed Earth's orbit. It proved that asteroids could come perilously close to our planet. And when they came, they came fast.
Reinmuth observed Hermes for five days. Then, to make a long story short, he lost it.
Hermes approaches Earth's orbit twice every 777 days. Usually our planet is far away when the orbit crossing happens, but in 1937, 1942, 1954, 1974 and 1986, Hermes came harrowingly close to Earth itself. We know about most of these encounters only because Lowell Observatory astronomer Brian Skiff re-discovered Hermes... on Oct. 15, 2003. Astronomers around the world have been tracking it carefully ever since. Orbit-specialists Steve Chesley and Paul Chodas of NASA's Jet Propulsion Laboratory (JPL) have used the new observations to trace Hermes' path backwards in time, and so they identified all the unnoticed flybys.
"It's a little unnerving," says Chodas. "Hermes has sailed by Earth so many times and we didn't even know it."
"Hermes' orbit is the most chaotic of all near-Earth asteroids," he adds. This is because the asteroid is so often tugged by Earth's gravity. Hermes has occasional close encounters with Venus, too. In 1954 the asteroid flew by both planets. "That was a real orbit scrambler," Chodas says. Frequent encounters with Earth and Venus make it hard to forecast Hermes' path much more than a century in advance. The good news is that "Hermes won't approach Earth any closer than about 0.02 AU within the next hundred years." We're safe for now.
Using the JPL ephemeris, we can look back and figure out what happened in 1937 when the asteroid was lost. With hindsight, it's understandable:
Reinmuth first spotted Hermes approaching Earth from the direction of the asteroid belt. At first it was easy to see because the asteroid's sunlit side was facing Earth. Speedy Hermes soon crossed Earth's orbit, however, and began turning its night side toward us. Asteroids are nearly as dark as charcoal, and their night sides are very dim. By Nov. 3rd, six days after its discovery, the asteroid had faded from 9th to 21st magnitude, a factor of 60,000. "Hermes was also heading into the sun's glare, which only made matters worse," notes Chodas. Hermes literally vanished.
No one seemed to care, not much. In 1937, World War II was about to begin in Europe, so people had a lot on their minds. Hermes failed to impress.
Says Chodas: "Astronomers of the day were somewhat biased, perhaps. They had convinced themselves that collisions were too rare to consider. Hermes didn't change their opinion because catastrophism was not in vogue."
It's in vogue now--largely because of comet Shoemaker-Levy 9 (SL9), an object discovered by people hunting for Hermes. Found in 1993 by Gene and Carolyn Shoemaker and David Levy, SL9 hit Jupiter on July 14, 1994, with much of the world watching on CNN. Long before the collision, SL9 had been torn apart by Jupiter's powerful tides. The largest fragments, coincidentally about the same size as asteroid Hermes, exploded with such force when they struck that dark clouds formed in Jupiter's atmosphere as large as Earth itself.
A message from Jupiter: Catastrophes happen.
"Gene always felt that Hermes should have done more to excite the world than it did at the time" recalls David Levy. "Indeed, he and his wife Carolyn were always hoping to find it." Shoemaker was a visionary who realized long before most others did that asteroids and comets posed an ongoing threat to Earth. In the late 1970's he and a few colleagues began to hunt for near-Earth objects using an 18-inch telescope at the Palomar Observatory. For a long while it was the only such survey on Earth. They discovered dozens of asteroids and comets, including SL9--but not Hermes. "When Hermes passed by Earth in 1986 (an encounter identified post-facto by Chodas) it should have been an easy target for us," notes Levy. "But the telescope was down for repairs." Shoemaker died in 1997 not knowing how close he came.
Now backyard astronomers around the world can do something Gene Shoemaker never did--see Hermes.
Hermes is fast approaching Earth, and on Nov. 4th it will pass by our planet 18 times farther away than the moon. Already the asteroid is about as bright as a 13th magnitude star--an easy target for 8-inch telescopes equipped with CCD cameras. Where should you point your 'scope? Consult the JPL Ephemeris for details.
In recent days a group of NASA-supported astronomers led by Jean-Luc Margot of UCLA have pinged the asteroid with radar pulses from the giant Arecibo antenna in Puerto Rico. Hermes, it turns out, is a double asteroid--two space rocks orbiting one another, each about 400 meters across. No one knows how Hermes came to be this way. Margot and colleagues hope to learn more when the asteroid passes by on Nov. 4th as they continue their observations using both Arecibo and NASA's Goldstone radar.
Now that Hermes has our attention, it might teach us a few things after all.
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