The object that hit Jupiter has been generally called a comet in the press, although no one knows what it was made of or its orbit before hitting Jupiter. It was probably between half a kilometer and a kilometer across. One point that bears repeating is that this impact was discovered by an Australian amateur astronomer, Anthony Wesley. The professional astronomers would not have been able to make their studies had this amateur not alerted them. This new impact scar on Jupiter has stimulated considerable press interest in the impact threat, including some suggestions that we need to devote more resources to protecting the Earth. Coincidentally, there is also news that the U.S. Air Force will re-instate its release of information on space observations of bright fireballs, although there are no details indicating just what information will be provided or how quickly the data release will take place.
Following are various news releases and press commentary on these recent events.
NATURE NEWS: FIREBALL DATA WILL BE AVAILABLE AGAIN
Published online 8 July 2009 | Nature 460, 163 (2009) News in Brief
US Air Force will continue to share meteor data
The United States Air Force says that it will resume sharing data on incoming meteors with astronomers. The Air Force collects the data with a network of satellites and sensors designed as a missile early warning system. For more than a decade, it provided them to astronomers on an ad-hoc basis, but the informal relationship came to a halt earlier this year (see Nature 459, 896-897; 2009). Astronomers feared that the Air Force had put a stop to the practice, but "the data will still flow", says Andy Roake, a spokesman for Air Force Space Command in Colorado Springs, Colorado. The Air Force is developing procedures for releasing data that will be faster, more systematic and in compliance with classification procedures. Data sharing could resume within the next few months.
NEW NASA IMAGES INDICATE OBJECT HITS JUPITER
Jet Propulsion Laboratory, Pasadena, Calif. July 20, 2009
Scientists have found evidence that another object has bombarded Jupiter, exactly 15 years after the first impacts by the comet Shoemaker-Levy 9. Following up on a tip by an amateur astronomer that a new dark "scar" had suddenly appeared on Jupiter, this morning between 3 and 9 a.m. PDT (6 a.m. and noon EDT) scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., using NASA's Infrared Telescope Facility at the summit of Mauna Kea, Hawaii, gathered evidence indicating an impact.
New infrared images show the likely impact point was near the south polar region, with a visibly dark "scar" and bright upwelling particles in the upper atmosphere detected in near-infrared wavelengths, and a warming of the upper troposphere with possible extra emission from ammonia gas detected at mid-infrared wavelengths.
"We were extremely lucky to be seeing Jupiter at exactly the right time, the right hour, the right side of Jupiter to witness the event. We couldn't have planned it better," said Glenn Orton, a scientist at JPL.
The new Jupiter images are online at: http://www.jpl.nasa.gov/news/news.cfm?release=2009-112 .
Orton and his team of astronomers kicked into gear early in the morning and haven't stopped tracking the planet. They are downloading data now and are working to get additional observing time on this and other telescopes.
This image was taken at 1.65 microns, a wavelength sensitive to sunlight reflected from high in Jupiter's atmosphere, and it shows both the bright center of the scar (bottom left) and the debris to its northwest (upper left). "It could be the impact of a comet, but we don't know for sure yet," said Orton. "It's been a whirlwind of a day, and this on the anniversary of the Shoemaker-Levy 9 and Apollo anniversaries is amazing." Shoemaker-Levy 9 was a comet that had been seen to break into many pieces before the pieces hit Jupiter in 1994.
Leigh Fletcher, a NASA postdoctoral student at JPL who worked with Orton during these latest observations said, "Given the rarity of these events, it's extremely exciting to be involved in these observations. These are the most exciting observations I've seen in my five years of observing the outer planets!"
The observations were made possible in large measure by the extraordinary efforts of the Infrared Telescope Facility staff, including telescope operator William Golisch, who adroitly moved three instruments in and out of the field during the short time the scar was visible on the planet, providing the wide wavelength coverage.
JUPITER'S BEEN HIT!
By Richard A. Kerr, Science NOW Daily News, 20 July 2009
A large object has slammed into Jupiter, leaving behind a giant black smudge that was first reported yesterday by an amateur astronomer. The find is only the second time in recorded history that scientists have glimpsed an impact scar in the atmosphere of a giant planet. "I never expected I'd get to see something like this," says astronomer Leigh Fletcher, a postdoc at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.
Amateur astronomer Anthony Wesley had been taking routine images of Jupiter through his 37-centimeter telescope (pros would be on a 1000-centimeter instrument) in Murrumbateman, Australia, at about 11:30 p.m. local time, when he noticed something unusual: a dark spot several thousands of kilometers across rotating into view high in Jupiter's south polar region (see picture). Wesley had been about to end his observing run, and he initially considered passing the spot off as a typical dark polar storm. But he decided to keep at it, and in 15 minutes more he believed he was seeing something else entirely.
Wesley suspected an impact and soon contacted Fletcher and JPL astronomer Glenn Orton. As luck would have it, the duo had previously scheduled time on the NASA Infrared Telescope on Hawaii (remotely operated from JPL), so they took a closer look. They found the same distinctive infrared signature as Orton and others saw 15 years ago this week when the 21-plus fragments of disrupted comet Shoemaker-Levy 9 slammed into Jupiter one after the other (Science, 29 July 1994, p. 601). "We've been incredibly fortunate to have a talented amateur report this within hours," says Fletcher. Such amateurs "are doing some of the fundamental work of observing what's happening on Jupiter," adds Orton.
The impact "was a bit of a surprise," says astronomer Heidi Hammel of the Space Science Institute in Boulder, Colorado, who observed the 1994 impacts with the Hubble Space Telescope. "We all thought these were a little more rare." This one--a solitary event so far--looks like one of Shoemaker-Levy 9's medium-size impacts, says Hammel. How large the rocky asteroid or icy comet was is hard to estimate, says astronomer Harold Weaver of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. There was never any consensus on the size of the Shoemaker-Levy 9 objects, but this one might have been several hundred meters across--a kilometer at most--and traveling at tens of thousands of kilometers per hour.
If scientists are to retrieve any new information about jovian impacts, they'll have to be quick about it. Winds are tearing the black splotch apart even as astronomers race to submit their emergency proposals for telescope time--including time on the recently renovated Hubble Space Telescope.
JUPITER GETS A BLACK EYE
The Wall Street Journal, July 24, 2009, By Michio Kaku
We sometimes forget that the universe is a violent place. This week, astronomers in Hawaii recorded an exceedingly rare event. An amazing photograph revealed a comet or asteroid, probably no more than a mile across, plowing into Jupiter's atmosphere. The impact created a fireball roughly the size of the planet earth.
The good news is that Jupiter was just doing its job, cleaning out the solar system of stray comets and asteroids. Jupiter, 318 times more massive than the earth, acts like a cosmic vacuum cleaner, sucking in or deflecting debris left over from the solar system's birth 4.5 billion years ago. If it weren't for Jupiter's colossal gravitational field, we wouldn't be here, since the Earth would be hit with deadly comet and meteor impacts every month or so. Most of the U.S. would just be an empty graveyard of bleak craters.
The bad news is that a comet impact could happen to us. A black eye for Jupiter would be a body blow to the earth. We got a taste of this back in 1908, when something the size of an apartment building plowed into Tunguska, Siberia. This "city-buster" flattened 100 million trees with the force of a hydrogen bomb. But this recent Jupiter comet, much larger and coming in at perhaps 100,000 miles per hour, would have unleashed the power of hundreds of H-bombs. It might have engulfed most of the East Coast in a huge firestorm, triggering a massive tsunami and destabilizing the weather.
According to Hollywood, we can always send our astronauts on a space shuttle to intercept a comet and blow it up with H-bombs. Wrong. Blowing up a comet with nuclear bombs creates chunks of debris, increasing the area of destruction. So we are sitting ducks to a potential impact from deep space.
So what's the lesson from all of this? Maybe Mother Nature has a sense of humor. An impact like the recent one in Jupiter happened 15 years ago, in late July, after the Shoemaker-Levy 9 comet broke up into 20 pieces, each of which plunged into Jupiter, creating a dazzling display of cosmic fireworks. Scientists used to believe that these collisions took place once every few thousand years, not 15 years. So perhaps Mother Nature was just trying to show what little scientists really understand about these cosmic collisions.
But it also happened on the 40th anniversary of the Moon landing. So maybe Mother Nature was reminding us that the universe is, after all, a violent place?that we may one day need a new home. The Earth lies in the middle of a cosmic shooting gallery. The proof comes out every night when we gaze at the Moon. When viewing the film of Neil Armstrong and Buzz Aldrin bobbing among the barren craters of the Moon, we are reminded that each crater was gouged out by a titanic impact.
In addition, there are more than 5,000 so-called near-Earth objects, carefully tracked by telescope, that can cross near the orbit of the earth. One of them, the asteroid Apophis, is about the size of the Rose Bowl. It will graze the Earth in 2029 and again in 2036, passing below some of our satellites.
But there are also many unnamed comets outside the solar system whose orbits are totally unknown and unpredictable. They would give us little warning and catch us totally off-guard, like the comet that just hit Jupiter.
So in the long term, perhaps we should look at the space program as an insurance policy. Not only has the space program given us a bonanza of benefits (such as weather satellites, the Global Positioning System, telecommunications, etc.), it also provides a gateway to the stars. Over the course of the next few centuries, maybe we should use that gateway to plan to be a "two planet species." Life is too precious to place in one basket.
In August, President Barack Obama will receive a major report from the U.S. human space flight plans committee about the future of space travel, which could be a turning point for NASA in the 21st century. He should remember the Jupiter hit as he considers the report.
?Mr. Kaku is the author of "Physics of the Impossible: a Scientific Exploration into the World of Phasers, Force Fields, Teleportation, and Time Travel" (Doubleday, 2008).
JUPITER: OUR COSMIC PROTECTOR?
By Dennis Overbye, New York Times, July 25, 2009
Jupiter took a bullet for us last weekend. An object, probably a comet that nobody saw coming, plowed into the giant planet's colorful cloud tops sometime Sunday, splashing up debris and leaving a black eye the size of the Pacific Ocean. This was the second time in 15 years that this had happened. The whole world was watching when Comet Shoemaker-Levy 9 fell apart and its pieces crashed into Jupiter in 1994, leaving Earth-size marks that persisted up to a year.
That's Jupiter doing its cosmic job, astronomers like to say. Better it than us. Part of what makes the Earth such a nice place to live, the story goes, is that Jupiter's overbearing gravity acts as a gravitational shield deflecting incoming space junk, mainly comets, away from the inner solar system where it could do for us what an asteroid apparently did for the dinosaurs 65 million years ago. Indeed, astronomers look for similar configurations ? a giant outer planet with room for smaller planets in closer to the home stars ? in other planetary systems as an indication of their hospitableness to life.
Anthony Wesley, the Australian amateur astronomer who first noticed the mark on Jupiter and sounded the alarm on Sunday, paid homage to that notion when he told The Sydney Morning Herald, "If anything like that had hit the Earth it would have been curtains for us, so we can feel very happy that Jupiter is doing its vacuum-cleaner job and hoovering up all these large pieces before they come for us."
But is this warm and fuzzy image of the King of Planets as father-protector really true? "I really question this idea," said Brian G. Marsden of the Harvard-Smithsonian Center for Astrophysics, referring to Jupiter as our guardian planet. As the former director of the International Astronomical Union's Central Bureau for Astronomical Telegrams, he has spent his career keeping track of wayward objects, particularly comets, in the solar system. Jupiter is just as much a menace as a savior, he said. The big planet throws a lot of comets out of the solar system, but it also throws them in.
Take, for example, Comet Lexell, named after the Swedish astronomer Anders Lexell. In 1770 it whizzed only a million miles from the Earth, missing us by a cosmic whisker, Dr. Marsden said. That comet had come streaking in from the outer solar system three years earlier and passed close to Jupiter, which diverted it into a new orbit and straight toward Earth. The comet made two passes around the Sun and in 1779 again passed very close to Jupiter, which then threw it back out of the solar system.
"It was as if Jupiter aimed at us and missed," said Dr. Marsden, who complained that the comet would never have come anywhere near the Earth if Jupiter hadn't thrown it at us in the first place.
Hal Levison, an astronomer at the Southwest Research Institute, in Boulder, Colo., who studies the evolution of the solar system, said that whether Jupiter was menace or protector depended on where the comets came from. Lexell, like Shoemaker Levy 9 and probably the truck that just hit Jupiter, most likely came from an icy zone of debris known as the Kuiper Belt, which lies just outside the orbit of Neptune, he explained. Jupiter probably does increase our exposure to those comets, he said.
But Jupiter helps protect us, he said, from an even more dangerous band of comets coming from the so-called Oort Cloud, a vast spherical deep-freeze surrounding the solar system as far as a light-year from the Sun. Every once in a while, in response to gravitational nudges from a passing star or gas cloud, a comet is unleashed from storage and comes crashing inward.
Jupiter's benign influence here comes in two forms. The cloud was initially populated in the early days of the solar system by the gravity of Uranus and Neptune sweeping up debris and flinging it outward, but Jupiter and Saturn are so strong, Dr. Levison said, that, first of all, they threw a lot of the junk out of the solar system altogether, lessening the size of this cosmic arsenal. Second, Jupiter deflects some of the comets that get dislodged and fall back in, Dr. Levison said. "It's a double anti-whammy," he said.
Asteroids pose the greatest danger of all to Earth, however, astronomers say, and here Jupiter's influence is hardly assuring. Mostly asteroids live peacefully in the asteroid belt between Mars and Jupiter, whose gravity, so the standard story goes, keeps them too stirred to coalesce into a planet but can cause them to collide and rebound in the direction of Earth.
That's what happened, Greg Laughlin of the University of California at Santa Cruz, said, to a chunk of iron and nickel about 50 yards across roughly 10 million to 100 million years ago. The result is a hole in the desert almost a mile wide and 500 feet deep in northern Arizona, called Barringer Crater. A gift, perhaps, from our friend and lord, Jupiter. [Note from DM: The accepted age of Meteor [Barringer] Crater is 50,000 years, orders of magnitude less than 10-100 million years.]
COULD EARTH BE HIT, LIKE JUPITER JUST WAS?
Charles Q. Choi, space.com - Jul 28, 2009
The recent bruising Jupiter received from a cosmic impact is a violent reminder that our solar system is a shooting gallery that sometimes blasts Earth. Still, what are the odds of a cosmic impact threatening our planet?
So far 784 near-Earth objects (NEOs) more than a half-mile wide (1 km) have been found. "If an object of about the same size that just hit Jupiter also hit Earth ? it was probably a typical cometary object of a kilometer or so in size (0.6 miles) ? it would have been fairly catastrophic," explained astronomer Donald Yeomans, manager of NASA's Near-Earth Object program office at the Jet Propulsion Laboratory in Pasadena, Calif.
Scientists have ruled out the chances of an Earth impact for all of these 784 large NEOs. Still, lesser objects also pose a risk, and researchers estimate more than 100 large NEOs remain to be found.
Billions of years ago, impacts were far more common. Our Moon retains a record of the pummeling it and Earth took: the Moon's craters remain, while on Earth, most scars of ancient impacts have been folded back into the planet or weathered away.
Today's solar system is far less crowded, and in fact Jupiter, having more mass and gravity, scoops up a lot of the dangerous objects, as does the sun. Currently just one NEO of all the objects scientists are tracking poses any significant chance of hitting the Earth ? 2007 VK184. If this roughly 425-foot-wide (130 meters) asteroid hit our planet, it would strike with an energy of roughly 150 million tons of TNT, or more than 10,000 times that of the atom bomb dropped on Hiroshima.
Roughly 100 telescopic observations made so far suggest that 2007 VK184 has a 1-in-2,940 chance of hitting Earth 40 to 50 years from now. However, if the past is any guide, further observations to refine computations of its orbit very likely will downgrade its probability of hitting Earth to virtually nothing, Yeomans said.
Of remaining concern are the NEOs that we do not see. Researchers suspect about 156 large NEOs 1 kilometer in diameter or larger remain to be found, and when it comes to dangerous NEOs in general, "when we get down to 140 meters (460 feet) or larger diameter objects, we think we've discovered about 15 percent of them, and with 50 meters (164 feet) or larger diameter, we've discovered less than 5 percent of them," Yeomans explained.
On average, an NEO roughly a half-mile wide or larger hits the Earth roughly every 500,000 years, "so we're not expecting one anytime soon," Yeomans explained. "For 500 meters (1,640 feet), we're talking a mean interval of about 100,000 years," he added. "When you get down to 50 meters, the mean interval is about 700 years, and for 30 meters (98 feet), about 140 years or so, but by then you're getting down to a size where you won't expect any ground damage, as they burn up in the atmosphere at about 25 meters (82 feet) in diameter and smaller, probably for an impressive fireball event."
When it comes to truly monstrous NEOs some 10 kilometers (6.2 miles) or larger, of the size thought to have helped kill off the dinosaurs, "that's a 100 million year event, and in fact, I don't think there is anything like that we see right now," Yeomans said. "The largest near-Earth object that can actually cross the Earth's path, Sisyphus, has a diameter of 8 kilometers (5 miles), and the largest that is termed a potential hazard is Toutatis, which has a diameter of approximately 5.4 km (3.35 miles)."
Keeping watch; There are currently four teams worldwide actively looking for both large and small NEOs, Yeomans said. "We're concentrating on the large ones for now, but hopefully with the next generation of search, we'll be more efficient in finding the smaller objects, to find 90 percent of the total population of potential hazards larger than 140 meters," he added.
Keeping an eye on NEOs might not just be healthy for humanity, but also help lead us out into space. "They're easy objectives to get to, and asteroids have significant metal resources that can be mined, while comets have significant water resources for space habitats or travel," Yeomans said. "If you want to build a habitat in space, you're not going to build it all on the ground and launch it up, since that's too expensive ? you want to go up and look for resources instead."
Furthermore, asteroids and comets are among the objects that have changed the least since the birth of the solar system roughly 4.6 billion years ago, and might reveal vital clues behind the mysterious process. "They may well have delivered the water and carbon-based molecules to Earth that allowed life to form, so they're extremely important for study in that direction," Yeomans added.