SETI [ASTRO] Comet Hale-Bopp Fails Emission Tests But Reveals Comet Origin


Larry Klaes (lklaes@bbn.com)
Thu, 17 Jun 1999 13:33:26 -0400


>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender to owner-astro using -f >Date: Thu, 17 Jun 1999 16:47:23 GMT >From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> >To: astro@lists.mindspring.com >Subject: [ASTRO] Comet Hale-Bopp Fails Emission Tests But Reveals Comet Origin >Sender: owner-astro@brickbat12.mindspring.com >Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> > >Bill Steigerwald >Goddard Space Flight Center June 16, 1999 >Greenbelt, MD >William.A.Steigerwald.1@gsfc.nasa.gov >(Phone: 301-286-5017) > >RELEASE NO: 99-76 > >HALE-BOPP FAILS EMISSION TESTS BUT REVEALS COMET ORIGIN > >Thrill seekers may want to hitch a ride on the giant comet Hale-Bopp, but >they would fail vehicle emission tests miserably. When it was the same >distance from the Sun as Earth, Hale Bopp produced carbon monoxide (CO) >emissions equal to that given off by 5.5 billion cars every day. > >Just like the results of an emission test help a mechanic diagnose an engine >problem, the results of NASA measurements help pin down where Hale-Bopp >and many other comets formed. When compared to the quantity of water in >the comet, the amount of CO indicates that comet Hale-Bopp was formed in >the region between Jupiter and Neptune, according to recent observations. > >"Comets are interesting because they are frozen relics from the formation of >our solar system, and by studying them, we can learn more about how we got >here," said Dr. Michael DiSanti of Catholic University and NASA's Goddard >Space Flight Center (Greenbelt, Md.). "Our observations of Hale-Bopp >indicate that comets now in the distant Oort cloud were originally part of >the solar system's ancient proto-planetary disk. It was thought that comets >could have formed in the cold, dense cloud of gas and dust that existed >before the proto-planetary disk formed. However, if this were so, we would >have seen even more carbon monoxide emission from Hale-Bopp. The amount >of carbon monoxide ice compared to water (12 percent) indicates that these >comets formed somewhere between the orbits of Jupiter and Neptune. We >hope to learn more about what was going on when the giant planets formed >by investigating the chemistry of this comet." > >CO is a molecule made from a carbon and an oxygen atom. It is normally a >gas on Earth, and is monitored in vehicle emissions because it is toxic. > >The new results were announced by a team of astronomers from Goddard, >Catholic University of America, Rowan University, Iona College, and Notre >Dame University. The researchers used an infrared spectrometer on a three- >meter telescope -- the NASA Infrared Telescope Facility (IRTF), Mauna Kea >Observatory, Hawaii -- to make the observations. "Our observational approach >combined with the unusually large size of Hale-Bopp permitted the first >definitive measurements of the amounts of carbon monoxide and water >present as ices in comets," said Dr. Michael Mumma of Goddard. The research >will be published in the June 17 issue of Nature. > >Comets, nicknamed "dirty snowballs," are lumps of ice and dust a few miles >to a few tens of miles in diameter. Conditions were warmer in the >proto-planetary disk than in the gas and dust cloud that preceded it, due to >radiation from the nascent Sun. Since water ice freezes at higher >temperature than carbon monoxide ice, comets forming in the relatively >warm disk would have more water and less carbon monoxide, the researchers >believe. After the comets formed, gravitational pulls from gas giant planets >in the outer solar system cast them into cold storage about a trillion miles >from the Sun, in a roughly spherical region called the Oort cloud. Over the >ages, gravity from passing stars perturbs some of these comets, sending >them back toward the solar system as celestial visitors from our distant >past. > >As a comet approaches the Sun, solar heat and radiation liberate gas and >dust from the comet's frigid surface, forming a cloud of material (the coma) >that is later pulled into the familiar comet tail by pressure from solar >wind and radiation. Gas molecules in the coma absorb light from the Sun and >emit it again as specific colors. The colors are unique for each chemical in >the gas, and serve as an optical "fingerprint" to identify various substances, >including CO. Special instruments called spectrometers separate the emitted >light, much like a prism separates white light into a rainbow of distinct >colors, permitting the identification of these fingerprints. > >As the comet nears the Sun, solar heat and light break down different >chemicals in its coma. This creates a distributed source of additional >carbon monoxide, making it difficult to determine the original amount >present as ice in the comet nucleus. The NASA spectrograph can detect the >amount of carbon monoxide near the comet nucleus as well as farther out in >its coma. "Because Hale-Bopp was so bright, we were able to observe it while >still very distant from the Sun before the distributed source was activated. >We were thus able to measure carbon monoxide emission solely from the >nucleus, and determine the true carbon monoxide to water ratio. Later, >as the comet approached the Sun, both sources were active and our >measurements then revealed the characteristic spatial signature of the >distributed source of CO," said Dr. Neil Dello Russo of Catholic University >and Goddard. > >"There is another group of comets that may be more like the cold, dense >cloud that preceded the solar system disk. Kuiper belt objects lie beyond >the orbit of Pluto, and probably formed from remnants at the fringes of the >proto-planetary disk. They are believed to be the source of comets with >short orbital periods and low inclinations to the ecliptic plane. This >region is remote from the Sun, and that part of the disk would have been >less influenced by radiation from the young Sun, so ices in Kuiper belt >objects are probably more like those in the original cloud from which the >solar system formed," said Mumma. "Future measurements may reveal this >difference." > >----------------------------------------------------------------------- > >University of Notre Dame >Notre Dame, Indiana > >From: Cynthia Day > >Released: June 16, 1999 > >ND Astronomer Helps Pinpoint Birth/History of Hale-Bopp > >The most precise measurement to date of the carbon monoxide to water ratio >in a comet is reported by a team of astrophysicists in the June 17 issue of >Nature. The article suggests that the comet Hale-Bopp was likely formed in >the region between Jupiter and Neptune some 4 billion years ago. > >The researchers, from the University of Notre Dame, NASA's Goddard Space >Flight Center, and Rowan College in New Jersey, made their observations of >the giant comet Hale-Bopp in 1997-1998 using an infrared spectrometer on >NASA's three meter telescope at the Infrared Telescope Facility at the Mauna >Kea Observatory in Hawaii. They determined that the carbon monoxide/water >ratio was 12 percent. > >It's fundamentally important to know the amount and source of carbon >monoxide, says Terrence W. Rettig, associate professor of physics at Notre >Dame, who participated in the observations. "These data provide our most >comprehensive clues about where and how Hale-Bopp was formed and give >us a better understanding of its history." > >According to Rettig, Hale-Bopp has spent most of its life in a deep freeze at >great distances from the sun. It returned to the inner solar system recently >in a sling-shot-like orbit, providing astronomers an opportunity for detailed >examination. The comet will not return for another 10,000 years. > >"Astronomers have been studying the visible attributes of comets for hundreds >of years but until recently, infrared observations were not possible," says >Rettig, "In the past several years, infrared detectors have become much more >efficient, making these observations now possible." This new observational >technique, the unusually large size of Hale-Bopp and the closeness by which >it passed earth during it's recent orbit around the sun all combined to provide >the most precise measurements to date of carbon monoxide and water in a >comet. > >"Comets are interesting because they are frozen relics from the formation of >our solar system, and by studying them, we can learn more about how we >got here," says coauthor Michael Mumma, a scientist at Goddard. Comets, >essentially dirty snowballs, range in size from a few miles to dozens of miles >across. The ice in comets is predominantly carbon monoxide and water, and >knowing the exact composition of the icy structure helps scientists pinpoint >its origin. > >For more information, contact Rettig at (219) 631-7732 or by email at >trettig@nd.edu; coauthor Mike DiSanti (Goddard) at (301) 286-7036 or by >email at disanti@kuiper.gsfc.nasa.gov; Michael Mumma (Goddard) by email >at mmumma@lepvax.gsfc.nasa.gov; or Neil Dello-Russo (Goddard) at >(301)286-1528. > >



This archive was generated by hypermail 2.0b3 on Sun Jul 11 1999 - 00:43:13 PDT