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 peri-Jove 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.
Introduction
The author and Steve Fentress (Strasenburgh Planetarium) had
remarkable success covering the Voyager 2/Neptune encounter during August 1989
using existing NASA video and still images. No special effects were needed --
nor used -- to bring Voyager 2's odyssey to the Upstate New York community.
During the first week of December 1993, several major planetaria achieved
similar success in their coverage of the first servicing mission to the Hubble
Space Telescope. Another opportunity for planetaria to cover fast- breaking
astronomical and space science news awaits this summer as P/Shoemaker-Levy 9
collides with Jupiter. What follows is background material on the HST, the
comet, Jupiter, and the planned observations of the upcoming collisions.
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. The Hubble Space Telescope: Planned
Observations of Periodic Comet Shoemaker-Levy 9 (1993e) and Jupiter.
The Hubble Space Telescope is a NASA project with international
cooperation from the European Space Agency (ESA). HST is a 2.4-meter
reflecting telescope which was deployed in low-Earth orbit (600 kilometers) by
the crew of the space shuttle Discovery (STS-31) on 25 April 1990.
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.
HST Jupiter/Shoemaker-Levy Campaign Programs
o UV Observations of the Impact of Comet SL9 with Jupiter
o A Search for SiO in Jupiter's Atmosphere
o Abdundances of Stratospheric Gas Species from Jovian Impact Events
o SL9's Impact on the Jovian Magnetosphere
o Observations of Io's and Europa's Regions of Jovian Magnetosphere
for Cometary Products
o Dynamical Parameters of Jupiter's Troposphere and Stratosphere
o HST Observations of the SL9 Impacts on Jupiter's Atmosphere
o Comparison of Meterological Models with HST Images
o FUV Imaging of Jupiter's Upper Atmosphere
o Auroral Signature of the Interaction of SL9 with the Jovian
Magnetosphere
o HST Imaging Investigation of SL9
o Cometary Particles as Tracers of Jupiter's Stratospheric Circulation
A bit more than 1/3 of the observations will be of the comet with the remainder
focused on Jupiter and environs. The comet observations have already begun,
the first being made in late January. The next will be in late March, with
three more observations spaced in time up to mid-July, just before impact. The
Jupiter observations begin the week before impact. The impact week has many
observations, and followup observations continue sporadically until late
August. Details of the observing program are being finalized.
Some Background on Comet Shoemaker-Levy 9 and Jupiter
A comet, already split into many pieces, will strike the planet Jupiter in the
third week of July of 1994. It is an event of tremendous scientific interest
but, unfortunately, one which is likely to be unobservable by the general
public. Nevertheless, it is a unique phenomenon and secondary effects of the
impacts will be sought after by both amateur and professional astronomers.
Significance
The impact of Comet Shoemaker-Levy 9 onto Jupiter represents
the first time in human history that people have discovered a body in the sky
and been able to predict its impact on a planet more than seconds in advance.
The impact will deliver more energy to Jupiter than the largest nuclear
warheads ever built, and up to a significant percentage of the energy delivered
by the impact which is generally thought to have caused the extinction of the
dinosaurs on Earth, roughly 65 million years ago.
History
Periodic Comet Shoemaker-Levy 9 (1993e) is the ninth short-
period comet discovered by husband and wife scientific team of Carolyn and Gene
Shoemaker and amatuer astronomer David Levy. The comet was photographically
discovered on 24 March 1993 with the 0.46-meter Schmidt telescope at Mt.
Palomar. On the original image it appeared 'squashed'. Subsequent confirmation
photographs at a larger scale taken by Jim Scotti with the Spacewatch telescope
on Kitt Peak showed that the comet was split into many separate fragments.
Scotti reported at least five condensations in a very long, narrow train
approximately 47 arc-seconds in length and and about 11 arc- seconds in width,
with dust trails extending from either end of the nuclear train. Its discovery
was a serendipitous product of their continuing search for near-Earth objects.
Near-Earth objects are bodies whose orbits come nearer to the Sun than that of
Earth and hence have some potential for collisions with Earth.
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.
Cometary Orbit
According to the most recent computations, the comet passed less than
1/3 of a Jovian radius (120,000 km) above the clouds of Jupiter late on 7 July
1992 (UT). The individual fragments separated from each other 1-1/2 hours
after closest approach to Jupiter and they are all in orbit around Jupiter with
an orbital period of about two years. Calculations of the orbit prior to 7
July 1992 are very uncertain but it seems very likely that the comet was
previously in orbit around Jupiter for two decades or more. Ed Bowell and
Lawrence Wasserman of the Lowell Observatory have integrated the best currently
available orbit for P/Shoemaker-Levy 9 in a heliocentric reference frame, and
noted that the calculations put the "comet" in a "Jupitergrazing" orbit before
about 1966. Wasserman and Bowell's possible Jupiter close approaches are in
2-, 3-, and 4-year intervals.
Possible Close Approaches of 1993e with Jupiter 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 16.8
Because 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.
The Nature of the Comet
The exact number of large fragments is not certain since the best
images show hints that some of the larger fragments may be multiple. At least
21 major fragments were originally identified. No observations are capable of
resolving the individual fragments to show the solid nuclei. Images with the
Hubble Space Telescope suggest that there are discrete, solid nuclei in each of
the largest fragments which, although not spatially resolved, produce a single,
bright pixel that stands out above the surrounding coma of grains. Reasonable
assumptions about the spatial distribution of the grains and about the
reflectivity of the nuclei imply sizes of 2 to 4 km (diameter) for each of the
11 brightest nuclei. Because of the uncertainties in these assumptions, the
actual sizes are very uncertain and there is a small but not negligible
possibility that the peak in the brightness at each fragment is due not to a
nucleus but to a dense cloud of grains.
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.
Crater Chains
Although none of the fragments will hit any of Jupiter's large
satellites, Voyager data indicate that tidally split comets have hit the
Galilean satellites in the past. Until the discovery of Comet P/Shoemaker-Levy
9, the strikingly linear crater chains on Callisto and Ganymede had remained
unexplained. It is quite likely that these crater chains were formed by comets
similar to P/SL9.
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 Planet Jupiter
Jupiter is the largest of the nine known planets, almost 11 times the
diameter of Earth and more than 300 times its mass. In fact, the mass of
Jupiter is almost 2.5 times that of all the other planets combined. Being
composed largely of the light elements hydrogen (H) and helium (He), its mean
density is only 1.3 times that of water. The mean density of Earth is 5.2
times that of water. The pull of gravity on Jupiter at the top of the clouds
at the equator is 2.4 times greater than Earth's surface. The bulk of Jupiter
rotates once in 9 hours and 56 minutes, although the period determined by
watching cloud features differs by up to five minutes due to intrinsic cloud
motions.
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 Impact into Jupiter
All 20-plus major impacts will occur at approximately the same position
on Jupiter relative to the center of the planet, but because the planet is
rotating the impacts will occur at different points in the atmosphere. The
impacts will take place at approximately 45 degrees south latitude and 6.5
degrees of longitude from the limb, just out of view from Earth (approximately
15 degrees from the dawn terminator). Jupiter has a rotation period of 9.84
hours, or a rotation rate of about 0.01 degrees/sec, so the impacts will occur
on the farside of the planet but the point of impact in the atmosphere will
rotate across the limb within about 11 minutes after the impact, and cross the
dawn termninator within about 25 minutes from the impact. From this point on
the effects on the atmosphere should be observable from Earth, but the viewing
of the atmosphere where the impact occurred will improve as the site rotates
towards the center of the disk and we can see it face on. The comet particles
will be moving almost exactly from (Jovian) south to north at the time of the
impact, so they will strike the planet at an angle of 45 degrees to the
surface. (The surface is defined for convenience as the Jovian cloud tops.) The
impact velocity will be Jovian escape velocity, 60 km/sec.
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 June 1 the impact time will be known with an accuracy of about 16 minutes
and by July 1 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 thedensity- 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.
Overview of the Hubble Space Telescope
The Hubble Space Telescope is a coooperative program of the European
Space Agency (ESA) and the National Aeronautics and Space Administration (NASA)
to operate a long-lived space-based observatory for the benefit of the
international astronomical community. HST is an observatory first dreamt of in
the 1940s, designed and built in the 1970s and 80s, and operational only in the
1990s. Since its preliminary inception, HST was designed to be a different
type of mission for NASA -- a permanent space-based observatory. To accomplish
this goal and protect the spacecraft against instrument and equipment failures,
NASA had always planned on regular servicing missions. Hubble has special
grapple fixtures, 76 handholds, and stabilized in all three axes.
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.
The Science Instruments
Wide Field/Planetary Camera 2
The original Wide Field/Planetary Camera (WF/PC1) was changed out and
displaced by WF/PC2 on the STS-61 shuttle mission in December 1993. WF/PC2 was
a spare instrument developed in 1985 by the Jet Propulsion Laboratory in
Pasadena, California.
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.
Corrective Optics Space Telescope Axial Replacement
COSTAR is not a science instrument; it is a corrective optics package
that displaced the High Speed Photometer during the first servicing mission to
HST. COSTAR is designed to optically correct the effects of the primary
mirror's aberration on the three remaining scientific instruments: Faint Object
Camera (FOC), Faint Object Spectrograph (FOS), and the Goddard High Resolution
Spectrograph (GHRS).
Faint Object Camera
The Faint Object Camera is built by the European Space Agency. It is
the only instrument to utilize the full spatial resolving power of HST.
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
broad-band 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.
Faint Object Spectrograph
A spectrograph spreads out the light gathered by a telescope so that it can be
analyzed to determine such properties of celestial objects as chemical
composition and abundances, temperature, radial velocity, rotational velocity,
and magnetic fields. The Faint Object Spectrograph (FOS) exmaines fainter
objects than the HRS, and can study these objects across a much wider spectral
range from the UV (1150 A) through the visible red and the near-IR (8000 A).
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.
Goddard High Resolution Spectrograph
The High Resolution Spectrograph also separates incoming light into its
spectral components so that the composition, temperature, motion, and other
chemical and physical properties of the objects can be analyzed. The HRS
contrasts with the FOS in that it concentrates entirely on UV spectroscopy and
trades the extremely faint objects for the ability to analyze very fine
spectral detail. Like the FOS, the HRS uses two 521-channel Digicon electronic
light detectors, but the detectors of the HRS are deliberately blind to visible
light. One tube is sensitive from 1050 to 1700 A; while the other is sensitive
from 1150 to 3200 A.
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.
Mission Operations and Observations
Although HST operates around the clock, not all of its time is spent
observing. Each orbit lasts about 95 minutes, with time allocated for
housekeeping functions and for observations. "Housekeeping" functions includes
turning the telescope to acquire a new target, or avoid the Sun or Moon,
switching communications antennas and data transmission modes, receiving
command loads and downlinking data, calibrating and similar activities.
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.
Other Spacecraft
Galileo
Galileo is enroute to Jupiter and will be about 1.5 AU (230 million km)
from Jupiter at the time of the impact. At this range, Jupiter will be ~60
pixels across in the solid state imaging camera, a resolution of ~2400
km/pixel. Galileo will have a direct view of the impact sites, with an
elevation of approximately 23 degrees above the horizon as seen from the impact
point. The unavailability of the main antenna, forcing use of the low-gain
antenna for data transmission, severely limits the imaging options available to
Galileo. The low-gain antenna will be able to transmit to Earth at 10 bits/sec,
so real-time transmission of imaging will not be possible. The Galileo tape
recorder can store ~125 full-frame equivalents. On- board data compression and
mosaicking may allow up to 64 images per frame to be stored, but playback of
the recorded images must be completed by January, 1995 when Galileo reaches
Jupiter. This will only allow transmission of ~5 full-frame equivalents, or
approximately 320 images. There will be the capability for limited on-board
editing and the images can be chosen after the impacts have occured, so the
impact timing will be well known, but the imaging times must be scheduled weeks
before the impacts. Each image requires 2.33 seconds, so a full frame of 64
images will cover ~2.5 minutes, and consist of ~2400 kilobits. A new mosaic
can be started in ~6 seconds. The camera has a number of filters from violet
through near-IR and requires 5 to 10 seconds to change filters. In addition to
imaging data, Galileo has a high time resolution photopolarimeter radiometer,
near-infrared mapping spectrometer, radio reciever, and ultraviolet
spectrometer which can be used to study the collisions. The limited storage
capacity and low transmission rate of Galileo make the timing of all the impact
observations critical.
Ulysses
The Ulysses spacecraft is in a high inclination orbit relative to the
ecliptic plane, which will carry it under the south pole of the Sun in
September 1994. Its payload includes sensitive radio receivers that may be
able to observe both the immediate consequences of the collisions of Comet
Shoemaker-Levy 9 fragments with Jupiter and the long-term effects on the Jovian
magnetosphere.
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 1014 ergs. There are no imaging experiments on Ulysses.
Voyager 2
Voyager 2 is on it's way out of the solar system, 44 AU from Jupiter at
the time of the impact. The planetary radio astronomy (PRA) experiment will be
monitoring radio emissions in the 1 KHz to 390 KHz range with a detection limit
of 1019 to 1020 ergs. PRA will sweep through this spectrum every 96 seconds.
The Voyager 2 imaging system will not be used.
International Ultraviolet Explorer
The International Ultraviolet Explorer (IUE) satellite will be devoting
55 eight-hour shifts (approximately 2-1/2 weeks total) of ultraviolet (UV)
spectroscopic observations to the Comet Shoemaker-Levy 9 impact events, with 30
shifts allotted to the American effort (Principal Investigators: Walt Harris,
University of Michigan; Tim Livengood, Goddard Space Flight Center; Melissa
McGrath, Space Telescope Science Institute) and 25 shifts allotted to the
European effort (PIs: Rene Prange, Institute d'Astrophysique Spatiale; Michel
Festou, Observatoire Midi-Pyrenees). The observing campaign will begin with
baseline observations in mid-June, and continue through mid-August. During the
week of the actual impacts, IUE will be observing the Jovian system
continuously.
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.
Ground-Based
Many large telescopes will be available on Earth with which to observe
the phenomena associated with the Shoemaker-Levy 9 impacts on Jupiter in
visible, infrared, and radio wavelengths. Small portable telescopes can fill
in gaps in existing observatory locations for some purposes. Imaging,
photometry, spectroscopy, and radiometry will certainly be carried out using a
multitude of detectors. Many of these attempts will fail, but some should
succeed. Apart from the obvious difficulty that the impacts will occur on the
back side of Jupiter as seen from Earth, the biggest problem is that Jupiter in
July can only be observed usefully for about two hours per night from any given
site. Earlier the sky is still too bright and later the planet is too close to
the horizon. Therefore, to keep Jupiter under continuous surveillance would
require a dozen observatories equally spaced in longitude clear around the
globe. A dozen observatories is feasible, but equal spacing is not. There
will be gaps in the coverage, notably in the Pacific Ocean, where Mauna Kea,
Hawaii, is the only astronomical bastion.
The Kuiper Airborne Observatory (KAO)
The KAO is a modified C-141 aircraft with a 36-inch (0.9 meter)
telescope mounted in it. The telescope looks out the left side of the airplane
through an open hole in the fuselage. No window is used because a window would
increase the infrared background level. The telescope is stabilized by: 1) a
vibration isolation system (shock absorbers); 2) a spherical air bearing; 3) a
gyroscope controlled pointing system; and 4) an optical tracking system. The
telescope can point to a couple of arc-seconds even in moderate turbulence.
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.
HST Science Observation Teams
Spectroscopy
The Jupiter spectroscopy team headed by Keith Noll (STScI) will search
for molecular remnants of the comet and fireball in Jupiter's upper atmosphere.
The team consists of seven investigators: Noll (STScI), Melissa McGrath
(STScI), L. Trafton (University of Texas), Hal Weaver (STScI), J. Caldwell
(York University), Roger Yelle (University of Arizona), and S. Atreya
(University of Michigan).
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.
Atmospheric Dynamics
The HST Jupiter atmospheric dynamics team, led by Heidi Hammel
(Massachusetts Institute of Technology), will be carefully monitoring Jupiter
to observe how its atmosphere reacts to incoming cometary nuclei. The
atmospheric dynamics team consists of four investigators: Hammel (MIT), Reta
Beebe (New Mexico State University), Andrew Ingersoll (California Institute of
Technology), and Glenn Orton (JPL/Caltech).
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! 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, researchers Joseph Harrington and Timothy Dowling, also of MIT, will
utilize the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. Both 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 comprehensively 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.
ATTACHMENT A
Current [as of 16 May 1994] HST Observing and Collision Event Timeline for
P/Shoemaker-Levy and Jupiter 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.
__________________________________________
_________________________
Orb# Starting Time: SAA Activity:
(start--end)
195 FOC-
- Prange
195
FOC-- Prange
195
FOS-- Noll
195 HRS--
Noll (SiO)
* 195:23:40:00
* 196:00:23:57
* 196:02:00:21
* 196:03:45:42 4:27--end (05)
* 4:30--end (02)
* 196:05:22:13 6:10--end (05)
6:13--end (02)
* 196:06:58:46 1 min (02)
* 196:08:35:17
* 196:10:11:49
1 196:11:48:21 WFPC
map-- Hammel
2 196:13:24:53 WFPC
map-- Hammel
3 196:15:01:24 WFPC map-- Hammel
4 196:16:37:57 WFPC map--
Hammel
5 196:18:14:28 WFPC map--
Hammel
6 196:19:51:00 WFPC map--
Hammel
7 196:21:27:32 21:57--22:17 (05)
8 196:23:04:04 23:33--end (05)
9 197:00:40:36 01:13--end (05)
01:17--01:30
(02)
10 197:02:17:07 02:53--end (05)
02:57--end (02)
11 197:03:53:40 04:36--end (05)
04:39--end (02)
12 197:05:30:11 06:18--end (05)
06:22--end (02)
13 197:07:06:43
14 197:08:43:15
15 197:10:19:46
16 197:11:56:18
17 197:13:32:50
18 197:15:09:21
19 197:16:45:53
20 197:18:22:25 A impact
197:20:01
21 197:19:58:56 20:35--20:44 (05) WFPC-- Hammel
22 197:21:35:28 22:02--22:27 (05)
23 197:23:12:00 23:41--end (05)
23:46--23:57 (02)
24 198:00:48:32 01:21--end (05)
01:24--01:38 (02)
25 198:02:25:03 03:02--end (05) B impact
198:03:11 03:05--end (02)
26 198:04:01:35 04:45--end (05)
04:47--end (02)
27 198:05:38:07 06:27--end (05)
06:30--end (02) C impact
198:07:03
28 198:07:14:39
29 198:08:51:10 WFPC-- Clarke
30 198:10:27:42 D impact
198:11:58
31 198:12:04:14
32 198:13:40:45 WFPC-- Hammel E impact
198:14:56
33 198:15:17:17 WFPC-- Hammel
34 198:16:53:48 WFPC--
Hammel
35 198:18:30:20 WFPC--
1/2 Hammel,
1/2 Clarke 36 198:20:06:52 20:34--20:53 (05)
37 198:21:43:23 22:09--22:36 (05)
22:17--22:22 (02)
38 198:23:19:55 22:48--end (05) 3 WFPC DARKS
23:53--00:05 (02)
39 199:00:56:26
40 199:02:32:58 03:10--end (05) F impact
199:02:37 03:13--end (02)
41 199:04:09:29 04:53--end (05)
04:57--end (02)
42 199:05:46:01 06:36--end (05) FOC--Prangee
43 199:07:22:33 WFPC-- Hammel G impact
199:07:35
44 199:08:59:04 WFPC-- Hammel
45 199:10:35:35 FOS-- Noll
46 199:12:12:07
47 199:13:48:39 WFPC-- Clarke
48 199:15:25:10
49 199:17:01:42
50 199:18:38:12 HRS-- Noll (SiO) H impact
199:19:23
51 199:20:14:44 20:39--21:02 (05)
52 199:21:51:16 22:17--22:44 (05)
22:22--22:31 (02)
53 199:23:27:47 23:46--end (05)
00:00--00:14
(02)
54 200:01:04:19 01:37--end (05)
01:40--01:57
(02)
55 200:02:40:51
56 200:04:17:22 05:02--end (05)
05:05--end (02)
57 200:05:53:53 06:45--end (05) HRS--
Noll (SiO)
06:47--end (02)
58 200:07:30:24 WFPC-
- Hammel
59 200:09:06:56 WFPC-
- Hammel
60 200:10:43:26 WFPC-- 1/2 Hammel,
K impact
200:10:40 1/2 Clarke
61 200:12:19:59
62 200:13:56:31
63 200:15:33:02 HRS-- Noll (G140L)
64 200:17:09:34
65 200:18:48:04 19:15--19:27 (05)
66 200:20:22:38 20:45--21:11 (05)
67 200:21:59:08 22:24--22:53 (05) L
impact
200:21:55 22:29--22:39 (02)
68 200:23:35:39 00:03--end (05) 3 WFPC DARKS
00:07--00:23 (02)
69 201:01:12:12 1:45 --end (05)
1:48 --2:05 (02)
70 201:02:48:42 3:28 --end (05)
3:31 --end (02)
71 201:04:25:14 5:11 --end (05)
72 201:06:01:45 6:53 --end (05)
73 201:07:38:17
74 201:09:14:47 N
impact
201:10:25
75 201:10:51:19 HRS-- Noll (G140L)
76 201:12:27:51 HRS-- Noll
(G140L)
77 201:14:04:22 WFPC-- Prange
(4 ex)
78 201:15:40:54 WFPC-- 1/2 Hammel, P2
impact
201:15:29 1/2 Clarke
79 201:17:17:26
80 201:18:53:58 19:17--19:37 (05) Q2
impact
201:19:27
81 201:20:30:29 20:42--21:19 (05) WFPC-- Hammel Q1
impact 201:19:54 20:58--21:05 (02)
82 201:22:07:00 22:31--23:02 (05)
22:36--23:44 (02)
83 201:23:43:31 00:12--end (05)
00:15--00:32 (02)
84 202:01:20:03 1:53--end (05)
1:57--2:14 (02)
85 202:02:56:35 3:37--end (05)
3:39--end (02)
86 202:04:33:06 5:19--end (05)
5:22--end (02) R
impact
202:05:41
87 202:06:09:38 WFPC-- Hammel
88 202:07:46:09 WFPC-- 1/2 Hammel,
1/2 Clarke 89 202:09:22:41 WFPC-- Hammel
90 202:10:59:12 WFPC--
Hammel
91 202:12:35:43 WFPC--
1/2 Hammel,
1/2 Clarke
92 202:14:12:15 WFPC-- Hammel
S impact
202:15:24
93 202:15:48:46 FOS-- Noll
94 202:17:25:18 HRS-- Noll (G140L) T
impact
202:18:30
95 202:19:01:50 19:22--19:45 (05)
96 202:20:38:20 20:59--21:28 (05)
21:05--21:14 (02) U
impact
202:21:43
97 202:22:14:52 22:38--23:09 (05)
22:43--22:57
98 202:23:51:23 0:20 --end (05) 3 WFPC DARKS
0:23 --0:39 (02)
99 203:01:27:55 2:02 --end (05)
2:05 --end (02)
100 203:03:04:27 3:16 --end (05)
3:18 --end (02)
101 203:04:40:57 5:28 --end (05) V
impact
203:04:48 5:31 --end (02)
102 203:06:17:29 WFPC-- Hammel
103 203:07:54:01 WFPC-- Hammel
W impact
203:08:19
104 203:09:30:32 WFPC-- 1/2 Hammel,
1/2
Clarke 105 203:11:07:04
106 203:12:43:35 HRS-- Noll
(SiO, 3x8)
107 203:14:20:07 HRS-- Noll
(SiO,2x12)
108 203:15:56:38
109 203:17:33:10 17:55--18:10 (05)
110 203:19:09:41 19:28--19:54 (05)
1 min (02)
111 203:20:46:12 21:07--21:36 (05)
21:12--21:23 (02)
112 203:22:22:44 22:46--23:17 (05)
22:50--23:06 (02)
113 203:23:59:16 0:28 --end (05)
0:32 --0:48 (02)
114 204:01:35:47 2:12 --end (05)
2:14 --end (02)
115 204:03:12:19 3:54 --end (05)
3:57 --end (02)
116 204:04:48:50 5:37 --end (05)
5:39 --end (02)
117 204:06:25:21 WFPC
map-- Hammel
118 204:08:01:53 WFPC
map-- Hammel
119 204:09:38:25 WFPC
map-- Hammel
120 204:11:14:57 WFPC map--
Hammel
121 204:12:51:27 WFPC map--
Hammel
122 204:14:27:59 WFPC map--
Hammel
123 204:16:04:31
124 204:17:41:02 17:58--18:20 (05)
125 204:19:17:34 19:35--20:02 (05)
19:42--19:48 (02)
126 204:20:54:08 21:14--21:44 (05)
21:18--21:32 (02)
127 204:22:30:58 22:50--23:24 (05)
22:58--23:14 (02)
128 205:00:07:09 0:37 --end (05)
0:40 --end (02)
129 205:01:43:41 2:20 --end (05)
2:23 --end (02)
130 205:03:20:13 4:03 --end (05)
4:05 --end (02)
131 205:04:56:44 5:45 --end (05)
5:49 --end (02)
132 205:06:53:16
HRS-- McGrath
133 205:08:09:47
HRS-- McGrath
134 205:09:46:19
HRS-- McGrath
135 205:11:22:51
HRS-- McGrath
136 205:12:59:22
HRS-- McGrath
137 205:14:35:54
HRS-- McGrath
138 205:16:12:26 16:38--16:44 (05)
139 205:17:48:57 18:04--18:28 (05)
140 205:19:25:29 19:42--20:11
(05) 19:48--
19:57 (02)
141 205:21:02:00 21:22--21:52
(05) 21:25--
21:40 (02)
142 205:22:38:32 23:03--23:32
(05) 23:07--
23:23 (02)
143 206:00:15:04 0:46 --end (05)
0:48 --end (02)
144 206:01:51:36 2:28 --end (05)
2:32 --end (02)
145 206:03:28:07 4:12 --end (05)
4:14 --end (02)
146 206:05:04:39 5:54 --end (05)
147 206:06:41:11 FOS--
McGrath
148 206:08:17:42 FOS--
McGrath
149 206:09:54:15 FOS--
McGrath
150 206:11:30:46 FOS--
McGrath
151 206:13:07:17 FOS-- McGrath
(Shemansky)
152 206:14:43:49 FOS-- McGrath
(Shemansky)
206:16:20:21 16:35--16:54 (05)
206:17:56:53 18:11--18:37 (05)
18:18--18:23 (02)
206:19:33:24 19:50--20:19 (05)
19:54--20:07 (02)
206:21:09:57 21:29--21:59 (05)
21:33--21:49 (02)
206:22:46:28 23:12--23:39 (05)
23:14--23:32 (02)
206:00:23:00 0:54 --end (05)
0:57 --1:14 (02)
207:01:59:32 2:37 --end (05)
2:40 --end (02)
207:03:36:04 4:20 --end (05)
4:23 --end (02)
207:05:12:36 6:03 --end (05)
207:06:49:07
207:08:25:40
207:10:02:11
207:11:38:43
207:13:15:15
207:14:51:46
207:16:28:19 16:41--17:03 (05)
207:18:04:50 18:18--18:45 (05)
18:24--18:32 (02)
207:19:41:23 19:57--20:27 (05)
20:01--20:15 (02)
207:21:17:55 21:38--22:07 (05)
21:42--21:57 (02)
210 WFPC-- Clarke
211 (for 4 orbits) WFPC map--
Hammel
222 FOC-- Prangee (2
orbits)
222 FOS-- Noll
222 HRS-- Noll
(G140L)
234
234
234 (for 5 orbits) WFPC map--
Hammel
242 +/- 7d FOS-- Noll
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.
ATTACHMENT B
HST, Jupiter, and Comet Bibliography
Popular Books
Kerr, Richard and Elliot, James, Rings: Discoveries from Galileo to
Voyager, The MIT Press, Cambridge, Massachusetts, 1984.
Littman, Mark, Planets Beyond: Discovering the Outer Solar System,
Wiley Science Editions, New York, New York, 1988.
Peek, Bertrand M., The Planet Jupiter: The Observer's Handbook,
Faber & Faber Limited, London, England, 1958 [revised, 1981].
Smith, Robert W., The Space Telescope: A Study of NASA, Science,
Technology and Politics, Cambridge University Press, Cambridge,
England, 1989 [revised, 1993].
Shea, J.F. et al., Report of the Task Force on the Hubble Space
Telescope Servicing Mission (1993).
Magazine Articles
Articles on HST and Comet P/Shoemaker-Levy have appeared in
popular magazines such as Astronomy, Sky & Telescope, Mercury,
Discover, Science News, New Frontier, and The Planetary Report.
Asker, James R., "Spacecraft Armada to Watch Comet Collide with
Jupiter," Aviation Week & Space Technology, 24 January 1994.
Chaisson, E.J. and Villard, R., "Hubble Space Telescope: The Mission,"
Sky & Telescope, April, 1990.
Fienberg, Richard T., "HST: Astronomy's Discovery Machine," Sky &
Telescope, April, 1990.
Fienberg, Richard T. "Hubble's Road to Recovery," Sky & Telescope,
November 1993.
Hawley, Steven A., "Delivering HST to Orbit," Sky & Telescope, April
1990.
Hoffman, Jeffrey A., "How We'll Fix the Hubble Space Telescope," Sky
& Telescope November 1993.
Landis, Rob, "Jupiter's Ethereal Rings," Griffith Observer, May 1991.
O'Dell, C.R., "The Large Space Telescope Program," Sky & Telescope,
December 1972.
Peterson, Ivars, "Jupiter's Model Spot," Science News, 19 February
1994.
Smith, Douglas L., "When a Body Hits a Body Comin' Through the Sky,"
Caltech Alumni Magazine Engineering & Science, Fall 1993.
Tucker, W., "The Space Telescope Science Institute," Sky &
Telescope, April 1985.
Villard, Ray, "From Idea to Observation: The Space Telescope at
Work," Astronomy, June, 1989.
Villard, Ray, "The World's Biggest Star Catalogue," Sky & Telescope,
December 1989.
Scientific Articles
HST science results are published in professional journals such as
Geophysical Research Letters, Icarus, Astronomical Journal,
Astrophysical Journal, Nature, Science, Scientific American, and
Space Science Reviews, as well as in the proceedings of
professional organizations. Some specific articles of interest
include:
Chevalier, Roger A. and Sarazin, Craig L., "Explosions of Infalling
Comets in Jupiter's Atmosphere," submitted to Astrophysical
Journal, 20 July 1994.
Kerr, Richard A., "Jupiter Hits May be Palpable Afterall," Science,
262:505, 22 October 1993.
Melosh, H.J. and Schenk, P., "Split Comets and the Origin of Crater
Chains on Ganymede and Callisto," Nature, 365:731-733, 21 October
1993.
Scotti, J.V. and Melosh, H.J., "Estimate of the Size of Comet
Shoemaker-Levy 9 from a Tidal Breakup Model, " Nature, 365:733-
735, 21 October 1993.
Weaver, H.A. et al., "Hubble Space Telescope Observations of Comet
P/Shoemaker-Levy 9 (1993e)," Science, 263:787-790, 11 February
1994.
ATTACHMENT C
Abbreviations/Acronym List
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
ATTACHMENT D
A variety of line art supplied by JPL, Lowell Observatory, the
University of Maryland-College Park, and the STScI. Most is self-
explanatory.
Facts at a Glance
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 1994
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: 24 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 TELEVISION 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.
Acknowledgements
This document would not be possible if not for the support of the Science
Observation Team and the Science Planning Branch/Moving Targets Group at the
Space Telescope Science Institute. The selection of material and any errors are
the sole responsibility of the author.
This paper represents the combined efforts of scientists and science writers
and is a selected compilation of several texts, original manuscript, and sub-
mitted paragraphs. 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), 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),
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), Don Yeomans (JPL) and to
all others who may have been omitted.
All comments should be addressed to the author:
Rob Landis
Space Telescope Science Institute
Science Planning Branch/Moving Targets Group
3700 San Martin Drive,
Baltimore, MD 21218
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