"Comet P/Shoemaker-Levy's Collision with Jupiter: Covering HST's Planned Observations from Your Planetarium"
Abstract: Comet Shoemaker-Levy 9 (1993e) was discovered in March 1993. Early ground-based observations indicated the comet had fragmented into several pieces. The comet is in a highly inclined, elliptical orbit around Jupiter. P/Shoemaker-Levy 9 was tidally ripped apart during perijove in July 1992. The Hubble Space Telescope has provided the most detailed look to date and resolved 20 separate nuclei. The nuclei are expected to slam into Jupiter over a five-day period beginning on 16 July 1994. The total energy of the collisions will be equivalent to 100 million megatons of TNT (more than 10,000 times the total destructive power of the world's nuclear arsenal at the height of the Cold War). An armada of spacecraft will observe the event: Voyager 2, Galileo, IUE, Ulysses, and the Hubble Space Telescope. HST will be the astronomical instrument of choice to observe P/SL9, and the after effects of the energy imparted into the Jovian atmosphere. NASA Select television may provide planetarium patrons with a ringside seat of the unfolding drama at Jupiter.
Planetaria and science centers worldwide have a unique opportunity to be involved in the understanding and exploration of our solar system when you participate in the P/Shoemaker-Levy collision with Jupiter. Public interest in your program will have been greatly stimulated before and during the series of collisions by daily television broadcasts, newspapers, and magazines. In certain areas of the nation, local cable companies will be carrying the NASA Select signal to further stimulate interest in the event.
We at the Space Telescope Science Institute and National Aeronautics and Space Administration anticipate that the public interest will be extremely high and that you may expect large attendances at your location.
Never before in modern times has a collision between two solar system bodies been observed. The instrument of choice to observe this unique event will be the Hubble Space Telescope.
Responsibility for conducting and coordinating the science operations of the Hubble Space Telescope rests with the Space Telescope Science Institute (STScI) on the Johns Hopkins University Homewood Campus in Baltimore, Maryland. STScI is operated for NASA by the Association of University for Research in Astronomy, Incorporated (AURA).
HST's current complement of science instruments include two cameras, two spectrographs, and fine guidance sensors (primarily used for astrometric observations). Because of HST's location above the Earth's atmosphere, these science instruments can produce high resolution images of astronomical objects. Ground-based telescopes can seldom provide resolution better than 1.0 arc-seconds, except momentarily under the very best observing conditions. HST's resolution is about 10 times better, or 0.1 arc-seconds.
It is generally expected that nearly every observatory in the world will be observing events associated with Comet Shoemaker-Levy's impacts on Jupiter. Most observatories are setting aside time and resources but delaying detailed planning until the last possible minute in order to optimize their observations based on the latest theoretical predictions and the latest observations of the cometary properties. Having the advantage of being above the Earth's turbulent atmosphere, HST is the astronomical spacecraft of choice to observe the unfolding drama of Comet P/Shoemaker-Levy 9 collision with Jupiter. Other spacecraft to observe the event include the International Ultraviolet Explorer (IUE), Extreme Ultraviolet Explorer, Galileo, Voyager 2, Ulysses, and possibly others.
From 16 July through 22 July 1994, pieces of an object designated as Comet P/Shoemaker-Levy 9 will collide with Jupiter, and may have observable effects on Jupiter's atmosphere, rings, satellites, and magnetosphere. Since this is the first collision of two solar system bodies ever to be observed, there is large uncertainty about the effects of the impact. Shoemaker-Levy 9 consists of nearly 20 discernible bodies with diameters estimated at 2 to 4 kilometers (km), depending on method of estimation and assumptions about the nature of the bodies, a dust coma surrounding these bodies, and an unknown number of smaller bodies. All the large bodies and much of the dust will be involved in the energetic, high-velocity impact with Jupiter.
The Hubble Space Telescope has the capability of obtaining the highest resolution images of all observations and will continue to image the morphology and evolution of the comet until days before first fragments of the comet impact with Jupiter. HST's impressive array of science instruments will study Jupiter, P/Shoemaker-Levy 9, and the Jovian environs before, during, and after the collision events. The objective of these observations is to better constrain astrometry, impact times, fragment sizes, study the near-fragment region and perform deep spectroscopy on the comet. During the collision events it is hoped that the HST will be able to image the fireball at the limb, and after collisions the atmosphere, rings, satellites, and magnetosphere will be monitored for changes caused by the collision. The HST will devote approximately 18 hours of time with the Wide Field/Planetary Camera (WF/PC -- pronounced "wif-pik"). The disk of Jupiter will be about 150 pixels across in the images, a resolution of about 1000 km/pixel.
The HST program that has been approved consists of 112 orbits of observations of both the comet and Jupiter. The observations will be made by six different teams.
Principal Science Target Science Objectives Investigator Instrument ======================================================================= _______________________________________________________________________ Hal Weaver WFPC+FOS SL9 morphology, breakup, (STScI) OH emission _______________________________________________________________________ Heidi Hammel WFPC Jupiter seismic/gravity waves (MIT) clouds and wind fields _______________________________________________________________________ Keith Noll FOS+HRS Jupiter composition changes (STScI) at impact sites _______________________________________________________________________ Melissa McGrath FOS+HRS magnetosphere dust contamination (STScI) of magnetosphere _______________________________________________________________________ John Clarke WFPC+FOC Jupiter UV imaging of clouds (U Mich) and aurorae _______________________________________________________________________ Bob West WFPC Jupiter stratospheric haze (JPL) _______________________________________________________________________
The International Astronomical Union's Central Bureau for Astronomical Telegrams immediately issued a circular, announcing the discovery of the new comet. The comet's brightness was reported as about 14th magnitude, more than a thousand times too faint to be seen with the naked eye. Bureau director Brian G. Marsden noted that the comet was some 4 degrees from Jupiter and that its motion suggested that it could be near Jupiter's distance from the Sun.
Before the end of March it was realized that the comet had made a very close approach to Jupiter in mid-1992 and at the beginning of April, after sufficient observations had been made to determine the orbit more reliably, Brian Marsden found that the comet is in orbit around Jupiter.
By late May it became apparent that the comet was likely to impact Jupiter in 1994. Since then, the comet has been the subject of intensive study. Searches of archival photographs have identified pre-discovery images of the comet from earlier in March 1993 but searches for even earlier images have been unsuccessful.
Distance Year/Month/Date 1993e 0.08963 AU from Jupiter on 1971 4 26.0 1993e 0.06864 AU from Jupiter on 1975 4 26.8 1993e 0.07000 AU from Jupiter on 1977 5 7.0 1993e 0.11896 AU from Jupiter on 1980 2 1.8 1993e 0.12453 AU from Jupiter on 1982 5 26.0 1993e 0.11937 AU from Jupiter on 1984 10 4.5 1993e 0.07031 AU from Jupiter on 1987 7 12.4 1993e 0.06090 AU from Jupiter on 1989 8 2.5 1993e 0.00072 AU from Jupiter on 1992 7 8.0 1993e Impacts Jupiter on 1994 7 16.8Because the orbit takes the comet nearly 1/3 of an astronomical unit (30 million miles) from Jupiter, the sun causes significant changes in the orbit. Thus, when the comet again comes close to Jupiter in 1994 it will actually impact the planet, moving almost due northward at 60 km/sec aimed at a point only halfway from the center of Jupiter to the visible clouds.
All fragments will hit Jupiter in the southern hemisphere, at latitudes near 45 degrees south, between 16 and 22 July 1994, approaching the atmosphere at an angle roughly 45 degrees from the vertical. The times of the impacts are now known to within roughly 20 minutes, but continuing observations leading up to the impacts will refine the precision of the predictions. The impacts will occur on the back side of Jupiter as seen from Earth; that is, out of direct view from the Earth (this also means that the comet will strike on Jupiter's nightside). This area will be close to the limb of Jupiter and will be carried by Jupiter's rotation to the front, illuminated side less than half an hour after the impact. The grains ahead of and behind the comet will impact Jupiter over a period of four months, centered on the time of the impacts of the major fragments. The grains in the tail of the comet will pass behind Jupiter and remain in orbit around the planet.
No outgassing has been detected from the comet but calculations of the expected amount of outgassing suggest that more sensitive observations are needed because most ices vaporize so slowly at Jupiter's distance from the sun. The spatial distribution of dust suggests that the material ahead of and behind the major fragments in the orbit are likely large particles from the size of sand up to boulders. The particles in the tail are very small, not much larger than the wavelength of light. The brightnesses of the major fragments were observed to change by factors up to 1.7 between March and July 1993, although some became brighter while others became fainter. This suggests intermittent release of gas and grains from the nuclei.
Studies of the dynamics of the breakup suggest that the structural strength of the parent body was very low and that the parent body had a diameter of order 5 km. This is somewhat smaller than one would expect from putting all the observed fragments back together but the uncertainties in both estimates are large enough that there is no inconsistency.
The longest of the chains, is 620 km long and comprises 25 craters. The first interpretation hinted that these were secondary impact chains, formed by material ejected from large basins -- very much akin to the Earth's Moon. The Callisto chains are much straighter and more uniform than most secondary chains. For 15 years the crater chains remained unexplained. In light of P/SL9's nature, it is logical to conclude that the crater chains on Callisto (and Ganymede) were formed when tidally disrupted comets impacted the Jovian satellites.
To date, thirteen crater chains have been identified on Callisto. Upon recent re-examination of Voyager's data, three more similar chains have now been identified on Ganymede. The next opportunity to identify and re-examine these features will be when the Galileo spacecraft enters Jovian orbit in December, 1995.
The visible "surface" of Jupiter is a deck of clouds of ammonia crystals, the tops of which occur at a level where the pressure is about half that at Earth's surface. The bulk of the atmosphere is made up of 89% molecular hydrogen (H2) and 11% helium (He). There are small amounts of gaseous ammonia (NH3), methane (CH4), water (H2O), ethane (C2H6), acetylene (C2H2), carbon monoxide (CO), hydrogen cyanide (HCN), and even more exotic compounds such as phosphine (PH3) and germane (GeH4). At levels below the deck of ammonia clouds there are believed to be ammonium hydro-sulfide (NH4SH) clouds and water crystal (H2O) clouds, followed by clouds of liquid water. The visible clouds of Jupiter are very colorful. The cause of these colors is not yet known. "Contamination" by various polymers of sulfur (S3, S4, S5, and S8), which are yellow, red, and brown, has been suggested as a possible cause of the riot of color, but in fact sulfur has not yet been detected spectroscopically, and there are many other candidates as the source of the coloring.
The meteorology of Jupiter is very complex and not well understood. Even in small telescopes, a series of parallel light bands called zones and darker bands called belts is quite obvious. The polar regions of the planet are dark. Also present are light and dark ovals, the most famous of these being "the Great Red Spot." The Great Red Spot is larger than Earth, and although its color has brightened and faded, the spot has persisted for at least 162.5 years, the earliest definite drawing of it being Schwabe's of 5 September 1831. (There is less positive evidence that Hooke observed it as early as 1664.) It is thought that the brighter zones are cloud- covered regions of upward moving atmosphere, while the belts are the regions of descending gases, the circulation driven by interior heat. The spots are thought to be large-scale vortices, much larger and far more permanent than any terrestrial weather system.
The interior of Jupiter is totally unlike that of Earth. Earth has a solid crust "floating" on a denser mantle that is fluid on top and solid beneath, underlain by a fluid outer core that extends out to about half of Earth's radius and a solid inner core of about 1,220-km radius. The core is probably 75% iron, with the remainder nickel, perhaps silicon, and many different metals in small amounts. Jupiter on the other hand may well be fluid throughout, although it could have a "small" solid core (upwards of 15 Earth masses) of heavier elements such as iron and silicon extending out to perhaps 15% of its radius. The bulk of Jupiter is fluid hydrogen in two forms or phases, liquid molecular hydrogen on top and liquid metallic hydrogen below; the latter phase exists where the pressure is high enough, say 3-4 million atmospheres. There could be a small layer of liquid helium below the hydrogen, separated out gravitationally, and there is clearly some helium mixed in with the hydrogen. The hydrogen is convecting heat (transporting heat by mass motion) from the interior, and that heat is easily detected by infrared measurements, since Jupiter radiates twice as much heat as it receives from the Sun. The heat is generated largely by gravitational contraction and perhaps by gravitational separation of helium and other heavier elements from hydrogen, in other words, by the conversion of gravitational potential energy to thermal energy. The moving metallic hydrogen in the interior is believed to be the source of Jupiter's strong magnetic field.
Jupiter's magnetic field is much stronger than that of Earth. It is tipped about 11 degrees to Jupiter's rotational axis, similar to Earth's, but it is also offset from the center of Jupiter by about 10,000 km. The magnetosphere of charged particles which it affects extends from 3.5 million to 7 million km in the direction toward the Sun, depending upon solar wind conditions, and at least 10 times that far in the anti-Sun direction. The plasma trapped in this rotating, wobbling magnetosphere emits radio frequency radiation measurable from Earth at wavelengths from 1 m or less to as much as 30 km. The shorter waves are more or less continuously emitted, while at longer wavelengths the radiation is quite sporadic. Scientists will carefully monitor the Jovian magnetosphere to note the effect of the intrusion of large amounts of cometary dust into the Jovian magnetosphere.
The two Voyager spacecraft discovered that Jupiter has faint dust rings extending out to about 53,000 km above the atmosphere. The brightest ring is the outermost, having only about 800-km width. Next inside comes a fainter ring about 5,000 km wide, while very tenuous dust extends down to the atmosphere. Again, the effects of the intrusion of the dust from Shoemaker-Levy 9 will be interesting to see, though not easy to study from the ground.
The times of collision of these fragments with Jupiter can only be currently estimated within about 20 minutes. As measurements of the orbit are made over the next few months the accuracy of these estimates should improve, so by 1 June the impact time will be known with an accuracy of about 16 minutes and by 1 July about 10 minutes. Eighteen hours before the first impact the uncertainty will be approximately 3 minutes. The relative positions of the fragments to each other are known much more accurately than the absolute position, so once the first fragment impacts Jupiter, the collision times of the remaining fragments will be better constrained. The first fragment, A, will collide with Jupiter on 16 July at 19:13 Universal Time (UT). Jupiter will be approximately 5.7 AU (860 million km) from Earth, so the time for light to travel to the Earth will be about 48 minutes, and the collision will be observed on Earth at 20:01 UT (16:01 PM EDT)on 16 July.
For Earth-based observations, Jupiter will rise at about noon and set around midnight, so there will be a limited window to observe the collisions. The head of the dust train around the fragments will reach Jupiter 1 to 2 months before the particles arrive.
The predicted outcomes of the impacts with Jupiter span a large range. This is due in part to the uncertainty in the size of the impacting bodies but even for a fixed size there is a wide range of predictions, largely because planetary scientists have never observed a collision of this magnitude. It is not known what the effects of the impacts of the large fragments will be on Jupiter, the large mass (~10^12 to 10^14 kg) and high velocity (60 km/sec) guarantee highly energetic collisions. Various models of this collision have been hypothesized, and there is general agreement that a fragment will travel through the atmosphere to some depth and explode, creating a fireball which will rise back above the cloud tops. The explosion will also produce pressure waves in the atmosphere and "surface waves" at the cloud tops. The rising material may consist of an equal amount of vaporized comet and Jovian atmosphere, but details about this, the depth of the explosion, the total amount of material ejected above the cloud tops, and almost all other effects of the impact are highly model dependent. Each impact (and the subsequent fall-back of ejected material over a period of ~3 hours after the collision will probably affect an area of the atmosphere from one to a few thousand km around the impact site. It will be difficult to see the objects within about 8 Jovian radii (~570,000 km).
If the cometary nuclei have the sizes estimated from the observations with the Hubble Space Telescope and if they have the density of ice, each fragment will have a kinetic energy equivalent to roughly 10 million megatons of TNT (10^29 to 10^30 ergs). The total energy of the collisions [of all fragments] may be as great as 100 million megatons of TNT; roughly 10,000 times the total destructive power of the world's nuclear arsen at the height of the Cold War. The impacts will be as energetic as the collision of a large asteroid or comet with the Earth 65 million years ago. This latter cosmic catastrophe most probably led to the extinction of the dinosaurs and hundreds of other species at the geologic Cretaceous-Tertiary (K-T) boundary layer.
The predictions of the effects differ in how they model the physical processes and there are significant uncertainties about which processes will dominate the interaction. If ablation (melting and vaporization) and fragmentation dominate, the energy can be dissipated high in the atmosphere with very little material penetrating far beneath the visible clouds. If the shock wave in front of the fragment also confines the sides and causes the fragment to behave like a fluid, then nuclei could penetrate far below the visible clouds. Even in this case, there are disagreements about the depth to which the material will penetrate, with the largest estimates being several hundred kilometers below the cloudtops.
The short-term effects at the atmospheric site of impact may be profound. Thermal plumes may rise to 700 km. Whether permanent disturbances, such as a new Great Red Spot or White Ovals form, is also a subject of great debate. The HST will monitor the atmosphere for changes in cloud morphology as each impact site rotates into view within a couple hours of the impact.
In any case, there will be an optical flash lasting a few seconds as each nucleus passes through the stratosphere. The brightness of this flash will depend critically on the fraction of the energy which is released at these altitudes. If a large fragment penetrates below the cloudtops and releases much of its energy at large depths, then the initial optical flash will be faint but a buoyant hot plume will rise in the atmosphere like the fireball after a nuclear explosion, producing a second, longer flash lasting a minute or more and radiating most strongly in the infrared. Although the impacts will occur on the far side of Jupiter, estimates show that the flashes may be bright enough to be observed from Earth in reflection off the inner satellites of Jupiter, particularly Io, if a satellite happens to be on the far side of Jupiter but still visible as seen from Earth. The flashes will also be directly visible from the Galileo spacecraft.
The shock waves produced by the impact onto Jupiter are predicted to penetrate into the interior of Jupiter, where they will be bent, much as the seismic waves from earthquakes are bent in passing through the interior of Earth. These may lead to a prompt (within an hour or so) enhancement of the thermal emission over a very large circle centered on the impact. Waves reflected from the density-discontinuities in the interior of Jupiter might also be visible on the front side within an hour or two of the impact. Finally, the shock waves may initiate natural oscillations of Jupiter, similar to the ringing of a bell, although the predictions disagree on whether these oscillations will be strong enough to observe with the instrumentation currently available. Observation of any of these phenomena can provide a unique probe of the interior structure of Jupiter, for which we now have only theoretical models with almost no observational data.
The plume of material that would be brought up from Jupiter's troposphere (below the clouds) will bring up much material from the comet as well as material from the atmosphere itself. Much of the material will be dissociated and even ionized but the composition of this material can give us clues to the chemical composition of the atmosphere below the clouds. It is also widely thought that as the material recombines, some species, notably water, will condense and form clouds in the stratosphere. The spreading of these clouds in latitude and longitude can tell us about the circulation in the stratosphere and the altitude at which the clouds form can tell us about the composition of the material brought up from below. The grains of the comet which impact Jupiter over a period of several months may form a thin haze which will also circulate through the atmosphere. Enough clouds might form high in the stratosphere to obscure the clouds at lower altitudes that are normally seen from Earth.
Interactions of cometary material with Jupiter's magnetic field have been predicted to lead to observable effects on Jupiter's radio emission, injection of material into Jupiter's auroral zone, and disruption of the ring of grains that now encircles Jupiter.
Somewhat less certainly the material may cause observable changes in the torus of plasma that circles Jupiter in association with the orbit of Io or may release gas in the outer magnetosphere of Jupiter. It has also been predicted that the cometary material may, after ten years, form a new ring about Jupiter although there are some doubts whether this will happen.
When originally planned in 1979, the Large Space Telescope program called for return to Earth, refurbishment, and relaunch every 5 years, with on-orbit servicing every 2.5 years. Hardware lifetime and reliability requirements were based on that 2.5-year interval between servicing missions. In 1985, contamination and structural loading concerns associated with return to Earth aboard the shuttle eliminated the concept of ground return from the program. NASA decided that on-orbit servicing might be adequate to maintain HST for its 15-year design life. A three year cycle of on-orbit servicing was adopted. The first HST servicing mission in December 1993 was an enormous success. Future servicing missions are tentatively planned for March 1997, mid-1999, and mid-2002. Contingency flights could still be added to the shuttle manifest to perform specific tasks that cannot wait for the next regularly scheduled servicing mission (and/or required tasks that were not completed on a given servicing mission).
The four years since the launch of HST in 1990 have been momentous, with the discovery of spherical aberration and the search for a practical solution. The STS-61 (Endeavour) mission of December 1993 fully obviated the effects of spherical aberration and fully restored the functionality of HST.
WF/PC2 is actually four cameras. The relay mirrors in WF/PC2 are spherically aberrated to correct for the spherically aberrated primary mirror of the observatory. (HST's primary mirror is 2 microns too flat at the edge, so the corrective optics within WF/PC2 are too high by that same amount.)
The "heart" of WF/PC2 consists of an L-shaped trio of wide-field sensors and a smaller, high resolution ("planetary") camera tucked in the square's remaining corner.
WF/PC2 has been used to image P/SL9 and will be used extensively to "map" Jupiter's features before, during, and after the collision events.
There are two complete detector system of the FOC. Each uses an image intensifier tube to produce an image on a phosphor screen that is 100,000 times brighter than the light received. This phosphor image is then scanned by a sensitive electron-bombarded silicon (EBS) television camera. This system is so sensitive that objects brighter than 21st magnitude must be dimmed by the camera's filter systems to avoid saturating the detectors. Even with a broadband filter, the brightest object which can be accurately measured is 20th magnitude.
The FOC offers three different focal ratios: f/48, f/96, and f/288 on a standard television picture format. The f/48 image measures 22 X 22 arc-seconds and yields resolution (pixel size) of 0.043 arc-seconds. The f/96 mode provides an image of 11 X 11 arc- seconds on each side and a resolution of 0.022 arc-seconds. The f/288 field of view is 3.6 X 3.6 arc-seconds square, with resolution down to 0.0072 arc-seconds.
The FOS uses two 512-element Digicon sensors (light intensifiers) to light. The "blue" tube is sensitive from 1150 to 5500 A (UV to yellow). The "red" tube is sensitive from 1800 to 8000 A (longer UV through red). Light can enter the FOS through any of 11 different apertures from 0.1 to about 1.0 arc-seconds in diameter. There are also two occulting devices to block out light from the center of an object while allowing the light from just outside the center to pass on through. This could allow analysis of the shells of gas around red giant stars of the faint galaxies around a quasar.
The FOS has two modes of operation: low resolution and high resolution. At low resolution, it can reach 26th magnitude in one hour with a resolving power of 250. At high resolution, the FOS can reach only 22nd magnitude in an hour (before S/N becomes a problem), but the resolving power is increased to 1300.
The HRS also has three resolution modes: low, medium, and high. "Low resolution" for the HRS is 2000 A higher than the best resolution available on the FOS. Examining a feature at 1200 A, the HRS can resolve detail of 0.6 A and can examine objects down to 19th magnitude. At medium resolution of 20,000; that same spectral feature at 1200 A can be seen in detail down to 0.06 A, but the object must be brighter than 16th magnitude to be studied. High resolution for the HRS is 100,000; allowing a spectral line at 1200 A to be resolved down to 0.012 A. However, "high resolution" can be applied only to objects of 14th magnitude or brighter. The HRS can also discriminate between variation in light from ojbects as rapid as 100 milliseconds apart.
When STScI completes its master observing plan, the schedule is forwarded to Goddard's Space Telescope Operations Control Center (STOCC), where the science and housekeeping plans are merged into a detailed operations schedule. Each event is translated into a series of commands to be sent to the onboard computers. Computer loads are uplinked several times a day to keep the telescope operating efficiently.
When possible two scientific instruments are used simultaneously to observe adjacent target regions of the sky. For example, while a spectrograph is focused on a chosen star or nebula, the WF/PC can image a sky region offset slightly from the main viewing target. During observations the Fine Guidance Sensors (FGS) track their respective guide stars to keep the telescope pointed steadily at the right target.
In an astronomer desires to be present during the observation, there is a console at STScI and another at the STOCC, where monitors display images or other data as the observations occurs. Some limited real-time commanding for target acquisition or filter changing is performed at these stations, if the observation program has been set up to allow for it, but spontaneous control is not possible.
Engineering and scientific data from HST, as well as uplinked operational commands, are transmitted through the Tracking Data Relay Satellite (TDRS) system and its companion ground station at White Sands, New Mexico. Up to 24 hours of commands can be stored in the onboard computers. Data can be broadcast from HST to the ground stations immediately or stored on tape and downlinked later.
The observer on the ground can examine the "raw" images and other data within a few minutes for a quick-look analysis. Within 24 hours, GSFC formats the data for delivery to the STScI. STScI is responsible for data processing (calibration, editing, distribution, and maintenance of the data for the scientific community).
Competition is keen for HST observing time. Only one of every ten proposals is accepted. This unique space-based observatory is operated as an international research center; as a resource for astronomers world-wide.
The Hubble Space Telescope is the unique instrument of choice for the upcoming collision of Comet Shoemaker-Levy 9 into Jupiter. The data gleaned from this momentous event will be invaluable for decades to come.
Ulysses will be 2.5 AU (375 million km) south of Jupiter at the time of impact and will also have a direct line of sight to the impact point. From this position the Ulysses unified radio and plasma wave (URAP) experiment will monitor radio emissions between 1 and 940 KHz, sweeping through the spectrum approximately every 2 minutes. URAP will be able to detect radio emissions down to 10^14 ergs. There are no imaging experiments on Ulysses.
The IUE campaign will be devoted to in-depth studies of the Jovian aurorae, the Jovian Lyman-alpha bulge, the chemical composition and structure of the upper atmosphere, and the Io torus. The IUE observations will provide a comprehensive study of the physics of the cometary impact into the Jovian atmosphere, which can provide new insights into Jupiter's atmospheric structure, composition, and chemistry, constrain global diffusion processes and timescales in the upper atmosphere, characterize the response of the Lyman-alpha bulge to the impacting fragments and associated dust, study the atmospheric modification of the aurora by the impact material deposited by the comet and by the material ejected into the magnetosphere from the deep atmosphere, and investigate the mass loading processes in the magnetosphere.
The airplane typically flies at 41,000 feet (12.5 km), above the Earth's tropopause. The temperature is very cold there, about -50 degrees Celsius, so water vapor is largely frozen out. There is about 10 precipitable microns of water in the atmospheric column above the KAO (about the same amount as in the atmosphere of Mars). This allows the KAO to observe most of the infrared wavelengths that are obscured by atmospheric absorption at ground-based sites. Flights are normally 7.5 hours long, but the aircraft has flown observing missions as long as 10 hours. The comet impact flights are all around 9.5 hours to maximize the observing time on Jupiter after each impact. Because these observations will be made in the infrared and the infrared sky is about as dark in the daytime as it is at night, we will be able to observe in the afternoon and into the evening.
The main advantage that the airborne observatory brings to bear is its ability to observe water with minimal contamination by terrestrial water vapor. The observing projects focus on observing tropospheric water (within Jupiter's cloud deck) brought up by the comet impact, or possibly on water in the comet if it breaks up above Jupiter's tropopause. The KAO team will also look for other compounds that would be unobservable from the ground due to terrestrial atmospheric absorption.
The KAO will be deployed to Australia to maximize the number of times the immediate aftermath of an impact can be observed. The available integration time on each flight will be typically 4-5 hours, from impact time to substantially after the central meridian crossing of the impact point. The KAO will leave NASA Ames on 12 July, return on 6 August. The last part of the deployment will be devoted to observations of southern hemisphere objects as part of the regular airborne astronomy program.
The most important scientific objectives of the cometary investigations are: (1) determine whether or not there are large, solid nuclei at the condensation points in the comet and estimate their sizes, (2) examine carefully the near-nucleus morphology of the brightest objects to search for further fragmentation and outgassing activity, (3) monitor the temporal variability of the largest nuclei, and (4) take deep spectroscopic exposures to search for atoms and molecules in the vicinity of the comet.
Since the energy deposited into the Jovian atmosphere is proportional to the cube of the size of the impacting object, accurate nuclear sizes must be determined before accurate predictions of impact phenomena can be made. HST's high spatial resolution provides higher contrast between each nucleus and its surrounding coma than can be achieved with any other optical telescope. Even in the HST case the observed intensity is primarily due to light scattered from the coma, but the improved contrast in the HST images allows for a more accurate determination of the nuclear magnitudes, from which sizes can be estimated.
The July 1993 HST images of P/Shoemaker-Levy 9 reveal a complex morphology around each nucleus. At least several nuclei that seem to be single objects at ground-based resolution emerge as multiple objects at HST's resolution. Were these neighbors produced during the breakup of the P/SL9's parent body, or has there been continuing fragmentation in the ensuing period? One of the most intriguing results from the currently available HST data is the possibility that the nuclei are continuing to fragment. By careful examination of the HST images near the brighter nuclei, and particularly by searching for temporal variability in the image morphology, we can detect fragmentation and "conventional" cometary activity. Any evidence for fragmentation will provide important information on the strength of the nuclei. Cometary nuclei are known to be extremely fragile and often breakup for no apparent reason (i.e., many nuclei split without being near any massive perturber). Thus, we might expect to see continuing fragmentation of nuclei in this comet well outside the Roche limit of Jupiter. At large distances from Jupiter, the splitting of nuclei could be induced by nuclear rotation, cometary activity (e.g., amorphous-to-crystalline ice transitions, which has been proposed as the source of coma activity in P/Schwassmann-Wachmann 1), or a combination of both.
Our spectroscopic program consists of two relatively deep exposures near the brightest nucleus in order to search for atomic and molecular emissions. Using the G270H grating of the Faint Object Spectrograph (FOS) these observations cover the wavelength range from 2223 to 3278 Angstroms. The new observations should be at least three times more sensitive than previous HST observations. Besides covering the strong hydroxyl (OH) bands, our spectrum will serendipi- tously cover a strong emission band of carbon monoxide (CO) and resonance transitions of several metals (i.e., Mg+, Mg++, and Si+).
Even though the comet's mass is dwarfed by the mass of Jupiter, the impact can cause local disturbances to the composition of the atmosphere that could be detectable with HST. The two spectrometers on HST, the Faint Object Spectrograph (FOS) and the Goddard High Resolution Spectrograph (HRS), will be used to search for the spectral fingerprints of unusual molecules near the site of one of the large impacts.
Jupiter's stratosphere will be subject to two sources of foreign material, the comet itself, and gas from deep below Jupiter's cloudtops. There are large uncertainties in the predictions of how deep the comet fragments will penetrate into Jupiter's atmosphere before they are disrupted. But, if they do penetrate below Jupiter's clouds as predicted by some, a large volume of heated gas could rise into Jupiter's stratosphere. As on the Earth, Jupiter's stratosphere is lacking in the gases that condense out at lower altitudes. The sudden introduction of gas containing some of these condensible molecules can be likened to what happens on Earth when a volcano such as Pinatubo injects large amounts of gas and dust into the stratosphere. Once in this stable portion of the atmosphere on either planet, the unusual material can linger for years.
The spectroscopic investigation will consist of 12 orbits spread over three complementary programs. Several of the observations will be done within the first few days after the impact of fragment G on 18 July at 07:35 UTC. The team also wants to study how the atmosphere evolves so some observations will continue into late August.
The FOS will obtain broad-coverage spectra from ~1750 - 3300 A. Quite a few atmospheric molecules have absorptions in this interval, particularly below 2000 A. One molecule that we will look for with special interest is hydrogen sulfide (H2S), a possible ingredient for the still-unidentified coloring agent in Jupiter's clouds.
The spectroscopy team will focus in on two spectral intervals with the HRS. In one experiment, the team will search for silicon oxide (SiO) which should be produced from the rocky material in the cometary nucleus. The usefulness of this molecule is the fact that it can come only from the comet since any silicon in Jupiter's atmosphere resides far below the deepest possible penetration of the fragments. Measuring this will help sort out the relative contributions of the comet and Jupiter's deep atmosphere to the disturbed region of the stratosphere. Finally, the spectroscopy team will use the HRS to search for carbon monoxide (CO) and other possible emissions near 1500 A. CO is an indicator of the amount of oxygen introduced into the normally oxygen-free stratosphere. Any results obtained with the HRS will be combined with ground-based observations of CO at infrared wavelengths sensitive to deeper layers to reconstruct the variation of CO with altitude.
Researchers at the Massachusetts Institute of Technology have conducted computer simulations of the collisions' effect on Jupiter's weather. These simulations show waves travelling outward from the impact sites and propagating around the planet in the days following each impact. The predicted "inertia-gravity" waves are on Jupiter's "surface" (atmosphere) may emanate from the impact sites and would be analagous to the ripples from dropping a pebble in a pond.
Some theorists believe that the waves will be "seismic" in nature, with the atmosphere of Jupiter ringing like a bell. Such phenomenon may occur within the first hours after an impact. These seismic waves would travel much faster than the inertia-gravity waves, and quite likely more difficult to detect.
Using HST, Hammel's team hopes to detect and observe the inertia-gravity waves which may take hours to days. The temperature deviation in such a typical wave may be as much as 0.1 to 1 deg Celsius; quite possibly visible from Earth in the best telescopic views.
The speed at which these waves travel depends on their depth in the atmosphere and on stability parameters that are only poorly known. While Hammel's team will observe the impact and its aftermath with the Hubble Space Telescope, a team of scientists will utilize the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The IRTF and HST groups hope to measure wave speeds and thus determine the Jovian atmospheric parameters more accurately. Better-known parameters will, in turn, improve understanding of planetary weather systems.
Another exciting possibility is that new cloud features may form at the impact locations. These clouds might then be trapped by surrounding high-speed jets and spun up into vortices that might last for days or weeks.
Finally, cometary material will impact Jupiter's upper atmosphere. This material (ices and dust) could significantly alter the reflectivity of the atmosphere, and could linger for weeks or months. The goal of Hammel's HST observing plan is to observe all of these phenomena, while simultaneously and compre- hensively mapping of Jupiter's atmosphere.
The primary "products" will be multicolor WF/PC "maps" (images) of Jupiter. These new WF/PC2 maps will be compared against the latest Jupiter images with older, WF/PC1 images, as well as Voyager spacecraft images of Jupiter. At the very least, an exquisite time-lapse series of the best images of Jupiter ever acquired by ground-based astronomy and spacecraft will be obtained.
The impact on Jupiter of fragments of P/Shoemaker-Levy 9 will provide an unprecedented opportunity to study the dynamics, chemistry, and aerosol microphysics of Jupiter's stratosphere. Understanding the dynamics of the stratospheres of most planets is difficult because there are usually no markers to track winds (the clouds we normally see on Jupiter are deeper, in the troposphere). For the first time, we expect to see localized stratospheric tracer particles in Jupiter's atmosphere from directly deposited cometary grains and from condensable gases exhumed from the deeper atmosphere.
Dust and small pieces of the comet will be deposited directly into the stratosphere on a global scale, while the largest fragments will enter near latitude 40 degrees South. Some calculations predict the large impactors will penetrate into the troposphere, below the visible clouds and create a fireball which will rebound to the top of the atmosphere. The fireball carries with it Jovian air from below the cloudtops. This deeper gas contains a good deal more of condensible volatiles like water (H20), ammonia (NH3), and hydrogen sulfide (H2S) than is usual in the cold upper atmosphere. This material is ejected over a region a few thousand kilometers in radius. From that localized region, the Jovian stratospheric winds will distribute this material globally.
An analogous situation occurs in Earth's atmosphere when large volcanic eruptions like El Chichon and Pinatubo inject observable particles into the stratosphere. From observations of the number and size of small particles as a function of altitude, latitude, and time, we are able to study meridional (north-south, and vertical) circulation, planetary-scale waves and other dynamical processes by their effects on the spreading of the haze particles.
In the search for the P/SL9 particles in Jupiter's stratosphere, West's team will use a powerful combination of UV and near-IR methane-band filters available with the WF/PC2 to observe the newly created stratospheric haze on Jupiter. The signature of aerosols is strongest at these wavelengths. Further, the UV observations are important in understanding any changes in stratospheric solar heating which may occur as a result of the additional aerosol burden, and which would perturb the stratospheric circulation.
Far-UV wavelengths of light (below 2000 Angstroms) are strongly absorbed by atmospheric gases, and it is necessary to place an instrument above the Earth's atmosphere to take images of celestial objects at these wavelengths. The planets also appear very different in the far-UV. For example, far-UV images of the Earth from space show sunlight reflected from the upper atmosphere (altitudes above 100 km) and also bright emissions from the polar aurora and from diffuse airglow, which is emission from the upper atmosphere produced by a combination of fluorescence of far-UV sunlight and charged particle collisions with atmospheric gases. The emissions provide information about the interaction of the upper atmosphere with charged particles in the planet's magnetic field, and the reflected far-UV sunlight gives information about the altitude and spatial distribution of molecules in the upper atmosphere that absorb far-UV sunlight. Far-UV images in general give information about the highest regions of a planet's atmosphere which interact with the space environment. The far-UV emissions observed from Jupiter are similar to those from the Earth, although Jupiter's aurora (or northern and southern lights) are more than 1000 times more energetic than the Earth's. Far-UV images of Jupiter will be taken while the comet trail and dust clouds are in Jupiter's magnetic field, both before and after the impacts of the comet fragments.
However, the following orbits graze SAA contour 5 (this was not known at the time of the January SOT meeting):
orbit 87 202:06:02 -- 3 min Hammel WFPC 102 203:06:09 -- 2 min Hammel WFPC 117 203:06:17 -- 1 min Hammel WFPC
Delta_t_tot (chg. from EVENT DATE Time (UTC) Jan. SOT mtg.) =================================================================== A=21 16 Jul 19:50 +14 minutes B=20 17 Jul 02:46 +08 minutes C=19 " 06:50 +21 minutes D=18 " 11:11 -20 minutes E=17 " 15:17 +39 minutes F=16 18 Jul 00:16 +02 minutes G=15 " 07:36 +38 minutes H=14 " 19:35 +37 minutes K=12 19 Jul 10:26 +36 minutes L=11 " 22:24 +26 minutes N=9 20 Jul 10:09 +19 minutes P2=8b " 14:58 +05 minutes Q2=7b " 19:40 +57 minutes Q1=7a " 20:07 +1 hr 24 min R=6 21 Jul 05:59 -42 minutes S=5 " 15:39 +1 hr 01 min T=4 " 18:28 +28 minutes U=3 " 22:52 +1 hr 45 min V=2 22 Jul 04:06 -25 minutes W=1 " 08:21 +1 hr 09 min ===================================================================
*****************P/SL9 Timeline Revision History******************* 23 Feb 94: Extended version from Y. Wang. ___________________________________________________________________ 01 Mar 94: Revised by R. Landis to account for new impact times. ___________________________________________________________________ 03 Mar 94: Revised by R. Landis per A. Storrs via R. Prangee. Changing orbit 12 observation to orbit 20. 94.234 ob- servations changed to day 94.220. Deleted fragments J and M from timeline as these do not appear in most recent HST images. ___________________________________________________________________ 14 Mar 94: Renumbered timeline orbits per Y. Wang. (Numbered se- quence has been corrected.) Tabs replaced with spaces in order to better enable H. Hammel's program to utilize this timeline. ___________________________________________________________________ 07 Apr 94: Updated A. Storrs/R. Landis. ___________________________________________________________________ 29 Apr 94: Updated A. Storrs/R. Landis. Revised by R. Landis to account for new impact times based on JPL data from D. Yeomans/P. Chodas. ___________________________________________________________________ 02 Jun 94: Revised by R. Landis to account for new impact times based on JPL data from P. Chodas. ___________________________________________________________________ 07 Jun 94: Included Weaver's last P/SL 9 observations. Updated HST orbit times based upon SPSS' most recent HST ephemeris. R. Landis/A. Storrs. ___________________________________________________________________ 15 Jun 94: Added Shemansky's FOS two-orbit sequence for o/a the 94.213 SMS. Revised by R. Landis to account for new impact times based on JPL data from P. Chodas. ___________________________________________________________________ 16 Jun 94: Removed the day 195 ("non-specific" time) observations from timeline. These are vestigial as R. Prange and K. Noll have specific time slots/HST orbits for their respective FOC and FOS/HRS observations. Orb# Starting Time: SAA Activity: (start--end) 192:19:12:00 WFPC SL9Q-- Weaver 192:20:48:33 WFPC SL9Q-- Weaver 192 193 194 194:14:38:36 FOC-- Prange 194:16:15:08 194:17:51:40 194:19:28:11 HRS-- Noll 194:21:04:43 FOC-- Prange 194:22:41:15 23:17--end (05) 195:00:17:47 00:51--end (05) 00:56--01:07 (02) 195:01:54:19 02:30--end (05) 02:34--end (02) 195:03:30:50 04:12--end (05) 04:14--end (02) 195:05:07:22 05:54--end (05) 05:56--end (02) 195:06:43:54 07:37--end (05) 195:08:20:23 WFPC SL9G-- Weaver 195:09:56:55 WFPC SL9G-- Weaver 195:11:37:45 FOS SL9G-- Weaver 195:13:09:59 FOS SL9G-- Weaver 195:14:50:40 WFPC SL9S-- Weaver 195:16:23:01 WFPC SL9S-- Weaver 195:17:59:36 FOS-- Noll 195:19:36:08 195:21:12:39 21:47--22:02 (05) 195:22:49:11 * 196:00:25:42 * 196:02:02:14 * 196:03:38:45 04:20--end (05) * 04:23--end (02) * 196:05:15:18 06:03--end (05) 06:05--end (02) * 196:06:51:49 07:46--end (05) * 196:08:28:21 * 196:10:04:52 1 196:11:41:24 WFPC map-- Hammel 2 196:13:17:55 WFPC map-- Hammel 3 196:14:54:27 WFPC map-- Hammel 4 196:16:30:59 WFPC map-- Hammel 5 196:18:07:30 WFPC map-- Hammel 6 196:19:44:01 WFPC map-- Hammel 7 196:21:20:32 21:51--22:11 (05) 8 196:22:57:04 23:27--end (05) 23:32--23:42 (02) 9 197:00:33:36 01:06--end (05) 01:09--01:25 (02) 10 197:02:10:07 02:46--end (05) 02:49--end (02) 11 197:03:46:38 04:27--end (05) 04:31--end (02) 12 197:05:23:09 06:11--end (05) 06:14--end (02) 13 197:06:59:42 07:54--end (05) 14 197:08:36:13 15 197:10:12:44 16 197:11:49:15 17 197:13:25:47 18 197:15:02:18 19 197:16:38:49 20 197:18:15:21 21 197:19:51:06 20:35--20:46 (05) WFPC-- Hammel A impact 197:19:50 22 197:21:28:23 21:56--22:19 (05) 23 197:23:04:54 23:34--end (05) 23:37--23:51 (02) 24 198:00:41:26 01:17--end (05) 01:16--01:34 (02) 25 198:02:17:57 02:55--end (05) B impact 198:02:46 02:57--end (02) 26 198:03:54:28 04:37--end (05) 04:39--end (02) 27 198:05:30:59 06:20--end (05) 06:22--end (02) C impact 198:06:50 28 198:07:07:31 29 198:08:43:14 WFPC-- Clarke 30 198:10:20:32 31 198:11:57:04 D impact 198:11:11 32 198:13:33:35 WFPC-- Hammel 33 198:15:10:06 WFPC-- Hammel E impact 198:15:17 34 198:16:46:38 WFPC-- Hammel 35 198:18:23:09 WFPC-- 1/2 Hammel, 1/2 Clarke 36 198:19:59:39 20:26--20:45 (05) 37 198:21:36:11 22:02--22:28 (05) 22:07--22:15 (02) 38 198:23:12:42 23:41--end (05) 3 WFPC DARKS 23:45--00:04 (02) *** SMS BOUNDARY *** *** BEGIN 94.199 SMS *** *** SMS BOUNDARY *** 39 199:00:34:04 01:21--end (05) F impact 199:00:16 01:24--01:42 (02) 40 199:02:10:24: 03:03--end (05) 03:05--03:24 (02) 41 199:03:48:43 04:35--end (05) 04:48--end (02) 42 199:05:38:47 06:28--end (05) FOC--Prange 43 199:07:15:18 WFPC-- Hammel G impact 199:07:36 44 199:08:51:49 WFPC-- Hammel 45 199:10:28:20 FOS-- Noll 46 199:12:04:51 47 199:13:41:22 WFPC-- Clarke 48 199:15:17:52 WFPC SL9K-- Weaver 49 199:16:54:24 50 199:18:30:55 HRS-- Noll (SiO) H impact 199:19:35 51 199:20:07:27 20:32--20:54 (05) 52 199:21:43:58 22:09--22:36 (05) 22:14--22:25 (02) 53 199:23:20:29 23:48--end (05) 23:52--00:07 (02) 54 200:00:57:00 01:28--end (05) 01:32--01:51 (02) 55 200:02:33:30 03:12--end (05) 03:14--end (02) 56 200:04:10:02 04:55--end (05) 04:57--end (02) 57 200:05:48:33 06:37--end (05) HRS-- Noll (SiO) 06:39--end (02) 58 200:07:23:04 WFPC-- Hammel 59 200:08:59:35 WFPC-- Hammel K impact 200:10:26 60 200:10:36:06 WFPC-- 1/2 Hammel, 1/2 Clarke 61 200:12:12:37 62 200:13:49:08 63 200:15:25:39 HRS-- Noll (G140L) 64 200:17:02:11 65 200:18:38:41 19:09--19:18 (05) 66 200:20:15:13 20:37--21:02 (05) 20:45--21:46 (02) 67 200:21:51:43 22:17--22:45 (05) 22:21--22:34 (02) 68 200:23:28:14 23:55--end (05) 3 WFPC DARKS L impact 200:22:24 23:59--00:16 (02) 69 201:01:04:46 01:37--end (05) 01:40--01:59 (02) 70 201:02:41:16 03:20--end (05) 03:22--end (02) 71 201:04:17:48 05:03--end (05) 05:05--end (02) 72 201:05:54:18 06:46--end (05) 06:48--end (02) 73 201:07:32:24 74 201:09:07:20 WFPC SL9Q-- Weaver N impact 201:10:09 75 201:10:43:52 HRS-- Noll (G140L) 76 201:12:20:22 HRS-- Noll (G140L) 77 201:13:56:54 WFPC-- Prange (4 ex) 78 201:15:33:25 WFPC-- 1/2 Hammel, P2 impact 201:14:58 1/2 Clarke 79 201:17:09:55 WFPC SL9S-- Weaver 80 201:18:46:27 19:07--19:27 (05) Q2 impact 201:19:40 81 201:20:22:58 20:45--21:11 (05) WFPC-- Hammel Q1 impact 201:20:07 20:50--20:59 (02) 82 201:21:59:30 22:23--22:53 (05) 22:27--22:42 (02) 83 201:23:38:00 00:04--end (05) 00:07--00:24 (02) 84 202:01:12:32 01:45--end (05) 01:48--end (02) 85 202:02:49:02 03:27--end (05) 03:31--end (02) 86 202:04:25:34 05:11--end (05) 05:13--end (02) R impact 202:05:47 87 202:06:02:05 06:54--end (05) WFPC-- Hammel 88 202:07:38:35 WFPC-- 1/2 Hammel, 1/2 Clarke 89 202:09:15:07 WFPC-- Hammel 90 202:10:51:37 WFPC-- Hammel 91 202:12:28:09 WFPC-- 1/2 Hammel, 1/2 Clarke 92 202:14:04:40 WFPC-- Hammel 93 202:15:41:11 FOS-- Noll S impact 202:15:39 94 202:17:17:42 HRS-- Noll (G140L) T impact 202:18:28 95 202:18:54:12 19:14--19:37 (05) 96 202:20:30:44 20:52--21:19 (05) 20:56--21:08 (02) 97 202:22:07:15 22:31--23:00 (05) U impact 202:22:52 22:34--22:51 (02) 98 202:23:43:46 00:12--end (05) 3 WFPC DARKS 00:14--00:33 (02) 99 203:01:20:17 01:54--end (05) 01:56--end (02) 100 203:02:56:48 03:37--end (05) 03:39--end (02) V impact 203:03:54 101 203:04:33:19 05:20--end (05) 05:22--end (02) 102 203:06:09:50 07:03--end (05) WFPC-- Hammel 103 203:07:46:22 WFPC-- Hammel W impact 203:08:21 104 203:09:22:52 WFPC-- 1/2 Hammel, 1/2 Clarke 105 203:10:59:23 106 203:12:35:35 HRS-- Noll (SiO, 3x8) 107 203:14:12:25 HRS-- Noll (SiO,2x12) 108 203:15:48:57 109 203:17:25:28 17:49--18:02 (05) 110 203:19:01:59 19:20--19:45 (05) 19:26--19:31 (02) 111 203:20:38:30 20:54--21:27 (05) 21:03--21:17 (02) 112 203:22:15:01 22:37--23:08 (05) 23:42--22:59 (02) 113 203:23:51:32 00:20--end (05) 00:23--00:42 (02) 114 204:01:28:04 02:03--end (05) 02:05--end (02) 115 204:03:04:34 03:46--end (05) 03:48--end (02) 116 204:04:41:05 05:27--end (05) 05:31--end (02) 117 204:06:17:37 07:11--end (05) WFPC map-- Hammel 118 204:07:54:08 WFPC map-- Hammel 119 204:09:30:39 WFPC map-- Hammel 120 204:11:07:09 WFPC map-- Hammel 121 204:12:43:41 WFPC map-- Hammel 122 204:14:20:12 WFPC map-- Hammel 123 204:15:56:43 124 204:17:33:14 17:51--18:11 (05) 125 204:19:09:46 19:27--19:54 (05) 19:32--19:42 (02) 126 204:20:46:17 21:06--21:35 (05) 21:10--21:25 (02) 127 204:22:22:48 22:46--23:15 (05) 22:49--23:07 (02) 128 204:23:59:19 00:27--end (05) 00:31--00:50 (02) 129 205:01:35:50 02:12--end (05) 02:14--end (02) 130 205:03:12:22 03:54--end (05) 03:56--end (02) 131 205:04:48:53 05:37--end (05) 05:39--end (02) 132 205:06:25:23 HRS-- McGrath 133 205:08:01:54 HRS-- McGrath 134 205:09:38:25 HRS-- McGrath 135 205:11:14:57 HRS-- McGrath 136 205:12:51:28 HRS-- McGrath 137 205:14:27:59 HRS-- McGrath 138 205:16:04:30 16:33--16:34 (05) HRS (Side 2)-- 139 205:17:41:01 17:56--18:20 (05) 140 205:19:17:32 19:35--20:02 (05) 19:38--19:51 (02) 141 205:20:54:04 21:13--21:48 (05) 21:17--21:33 (02) 142 205:22:30:36 22:55--23:23 (05) 22:57--23:16 (02) . . . *** SMS BOUNDARY *** *** BEGIN 94.206 SMS *** *** SMS BOUNDARY *** 206 . . . 207:23:40:00 208:00:52:45 00:55--01:18 (05) 00:57--01:14 (02) 208:02:29:22 02:37--02:57 (05) 02:39--02:54 (02) 208:04:05:55 04:20--04:36 (05) 04:22--04:28 (02) 208:05:42:31 06:05--06:09 (05) FOS-- McGrath 208:06:48:55 FOS-- McGrath 208:08:25:26 FOS-- McGrath 208:10:01:57 FOS-- McGrath 208:11:38:29 FOS-- McGrath 208:13:15:00 FOS-- McGrath 208:14:51:32 15:12--15:18 (05) FOS-- McGrath 208:16:28:04 16:38--17:03 (05) 208:18:04:35 18:17--18:44 (05) 18:21--18:34 (02) 208:19:41:07 20:56--20:26 (05) 19:59--20:12 (02) 208:21:17:39 21:37--22:06 (05) 21:40--21:58 (02) 208:22:54:11 23:20--23:46 (05) 23:22--23:41 (02) 209:00:30:42 01:03--01:25 (05) 01:05--01:22 (02) . . . 210:04:22:14 04:37--04:47 (05) 210:05:58:46 210:07:35:18 WFPC-- Clarke 210:08:41:17 WFPC-- Clarke 210:10:17:48 210:11:54:20 210:13:30:52 210:15:07:23 15:15--15:37 (05) 210:16:43:55 16:52--17:19 (05) 16:57--17:08 (02) 210:18:20:27 18:31--19:00 (05) 18:34--18:51 (02) 210:19:56:59 20:12--20:41 (05) 20:15--20:33 (02) 210:21:33:31 21:54--22:21 (05) 21:57--22:16 (02) 210:23:10:03 23:37--00:00 (05) 23:39--23:57 (02) 211:00:46:35 01:20--01:40 (05) 01:22--01:36 (02) 211:02:23:07 03:02--end (05) 03:06--03:10 (02) 211:03:59:39 04:48--04:50 (05) 211:05:36:10 211:07:12:42 WFPC map-- Hammel 211:08:49:14 WFPC map-- Hammel 211:10:25:46 WFPC map-- Hammel 211:12:02:18 WFPC map-- Hammel 211:13:38:50 13:52--14:02 (05) . . . *** SMS BOUNDARY *** *** BEGIN 94.213 SMS *** *** SMS BOUNDARY *** . . 213: FOS-- Shemansky (2 orbits) . . *** SMS BOUNDARY *** *** BEGIN 94.220 SMS *** *** SMS BOUNDARY *** 220:21:41:07 begin--21:54 (05) begin--21:48 (02) 220:23:17:35 23:21--23:29 (05) 221:00:54:04 FOC-- Prange 221:02:06:06 FOC-- Prange 221:03:42:36 221:05:19:08 221:06:55:40 221:08:32:10 221:10:08:42 begin--10:20 (05) FOS-- Noll 221:11:45:13 begin--12:03 (05) begin--11:51 (02) . . . 222:20:18:50 begin--20:29 (05) begin--20:25 (02) 222:21:55:18 begin--22:07 (05) HRS-- Noll 222:23:08:39 HRS-- Noll 223:00:45:10 HRS-- Noll 223:02:21:41 223:03:58:12 223:05:34:44 223:07:11:14 223:08:47:45 begin--08:54 (05) . . . 224:02:29:27 224:04:05:57 224:05:42:28 FOC-- Prange 224:07:18:59 . . . *** SMS BOUNDARY *** *** BEGIN 94.227 SMS *** *** SMS BOUNDARY *** . . . *** SMS BOUNDARY *** *** BEGIN 94.234 SMS *** *** SMS BOUNDARY *** . . . 236:15:32:13 236:17:08:42 236:18:45:10 FOS-- Noll 236:20:08:48 FOS-- Noll 236:21:45:21 WFPC-- Hammel . . . ### NOMINAL END OF JUPITER-COMET CAMPAIGN ###Three digit numbers are day of year (1994): day 197 is July 16. All times are UT (at Earth). Orbit times are from the extrapolation done on Feb 4, 1994. Impact times are from the 1 Feb. JPL posting.
All times subject to change due to uncertainty in extrapolation of HST's orbit and in prediction of impact times.
Note that FGS control cannot be used between 197:06 and 198:13, due to the proximity of the Moon.
Each orbit (visibility period) lasts 52 min. In the SAA duration column, ending time labeled "end" means it lasts until the visibility period of the HST ends.
The numbers of the orbits here are rather arbitrary. Orbit # 1 here corresponds to orbit No. 23031 from HST's numbering convention.
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COSTAR Corrective Optics Space Telescope Axial Replacement ESA European Space Agency EVA Extravehicular Activity FOC Faint Object Camera FOS Faint Object Spectrograph FGS Fine Guidance Sensor GO General Observer (also Guest Observer) GHRS Goddard High Resolution Spectrograph, also referred to as HRS. GTO Guaranteed Time Observer HST Hubble Space Telescope JPL Jet Propulsion Laboratory LEO Low-Earth Orbit MT Moving Targets or Moving Targets Group (at STScI) NASA National Aeronautics and Space Administration NICMOS Near-Infrared Camera and Multi-Object Spectrometer OSS Observation Support Branch (at STScI) P/SL9 Shorthand for Periodic Comet Shoemaker-Levy 9 (SL9-A refers to one of the cometary fragments, in this example fragment "A", of the comet) RSU Rate-sensing unit (gyroscope) SAA South Atlantic Anomaly SADE Solar Array Drive Electronics SMOV Servicing Mission Observatory Verification SPB Science Planning Branch (at STScI) SPSS Science Planning & Scheduling Branch (at STScI) SOT Science Observation Team STIS Space Telescope Imaging Spectrograph STS-61 Space Transportation System; the first servicing mission is the 61st shuttle mission on the manifest since the space shuttle first flew in 1981. STScI Space Telescope Science Institute. WF/PC (pronounced "wif-pik") Wide Field/Planetary Camera
One-way light time, Jupiter to Earth: 48 minutes Radius of Jupiter: 71,350 km (equatorial) 67,310 km (polar) Radius of Earth: 6378 km (equatorial) 6357 km (polar) P/Shoemaker-Levy: 4.5? km (equivalent sphere) P/Halley: 7.65 x 3.60 x 3.61 km Mass of Jupiter: 1.90 x 1030 g (~318 ME) Rotation period: 9 hours 56 minutes Number of known moons: 16 Discovery date P/Shoemaker-Levy: 24 March 1993 Time of first impact (P/SL9-A): 16 July 1994, 20:01 UTC Time of P/SL9-Q's impact: 20 July 1994, 19:27 UTC Time of last impact (P/SL9-W): 22 July 1994, 08:09 UTC HST deployment date: 25 April 1990 HST first servicing mission: 2 - 13 December 1993 Diameter of HST's primary mirror: 2.4 meters Cost of HST: $1.5 Billion (1990 dollars)NASA Select is carried on Spacenet 2, transponder 5, channel 9, 69 degrees West, transponder frequency is 3880 MHz, audio subcarrier is 6.8 MHz, polarization is horizontal.
This paper represents the combined efforts of scientists and science writers and is a selected compilation of several texts, original manuscript, and submitted paragraphs. The genesis of this document is due in large part to the FAQ begun by Texas A&M University, background material provided by the University of Maryland, and variety of Internet resources.
Gratitude and many thanks go to Mike A'Hearn (University of Maryland), Reta Beebe (New Mexico State University), Ed Bowell (Lowell Observatory), Paul Chodas (JPL), John Clarke (University of Michigan), Ted Dunham (NASA-Ames), Heidi Hammel (MIT), Joe Harrington (MIT), Dave Levy, Chris Lewicki (SEDS-University of Arizona), Mordecai MacLow (University of Chicago), Lucy-Ann McFadden (University of Maryland), Melissa McGrath (STScI), Ray Newburn (JPL), Keith Noll (STScI), Renee Prange (University of Orsay, France), Elizabeth Roettger (JPL), Jim Scotti (University of Arizona), Dave Seal (JPL), Carolyn & Gene Shoemaker, Zdenek Sekanina (JPL), Ed Smith (STScI), Lawrence Wasserman (Lowell Observatory), Hal Weaver (STScI), Bob West (JPL), Don Yeomans (JPL) and to all others who may have been omitted.
All comments should be addressed to the author:
Space Telescope Science Institute
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