ANTARCTICA AS A PLACE TO SEARCH FOR METEORITES? YOU MUST BE KIDDING!

The concept followed no evolutionary path. It was suddenly there, as bright as the comic-strip light bulb that signifies a new idea: meteorites are concentrated on the ice in Antarctica! The occasion was the thirty-sixth annual meeting of the Meteoritical Society, which took place during the last week of August 1973 in Davos, Switzerland. I was listening to a paper by Makoto and Masako Shima, a Japanese husband and wife team who are both chemists. He was describing their analyses of some stony meteorites. These specimens were interesting to me because they had been recovered in Antarctica. The pre-meeting abstract of the paper mentioned four meteorites that had been found within a 5 × 10 km area, lying on the ice at the Yamato Mountains (see Figure 1.1). I was quite aware of how rare meteorites really are, and as far as I knew, when meteorites are found near each other, as these had been, they are invariably fragments of a single fall. This was my assumption in the present case, and I had attended this presentation because of a long-standing, general interest in Antarctica, rather than a specific interest in the meteorites to be described. Actually, the abstract made it clear that these specimens were of distinctly different types, but I had been skimming and had not read that far. The key word, so far as I was concerned, had been Antarctica.

INTRODUCTION

Asteroidal meteorites form the bulk of the collection. The fact that we can find lunar and martian samples in Antarctica has been a very nice dividend for the ANSMET project and has helped significantly in ensuring a continuation of its funding over many years. But these samples are isolated faces in an enormous crowd – memorable and important, true, but very few in number. Almost all antarctic meteorites (and also meteorites fallen in the rest of the world) are believed to be asteroidal meteorites. By this we mean that they are fragments of larger bodies whose abode is (or was) the asteroid belt. The asteroid belt is a region between the orbits of Mars and Jupiter within which we have telescopic evidence of the existence of thousands of bodies in orbit about the sun. All the bodies we have detected telescopically, of course, are larger than the bodies we have collected on the earth as meteorites. If there are thousands of asteroids large enough to see from Earth with a telescope, there must be millions or billions of meteoroid-size particles there, too small to be seen, but each following its individual path in orbit about the sun. What we have in our meteorite collections is a tiny sample of all the meteorites whose orbits have, for one reason or another, become earth-crossing. These earth-crossers, in turn, are only a small fraction of the numbers of meteoroids that must remain in the asteroid belt.

METEORITES AND BLUE ICE

The well known rock cycle describes the ways in which natural processes degrade and disperse geological materials, sorting their components and converting them into the raw materials of new, and often very different, rocks. At the earth's surface, meteorites are further from chemical equilibrium than most terrestrial rocks and therefore are more susceptible to destruction by weathering and dispersal of their components. They are also very rare among the overwhelming background of terrestrial materials. This is not true of the meteorites we find in Antarctica – they resist weathering for long periods of time and are often found in high concentrations on exposed patches of bluish ice at, or above, about 2000 m elevation. If a patch of blue ice contains a concentration of meteorites we call it a meteorite stranding surface. To a meteoriticist, the levels of concentration are almost unbelievable: as of December, 1999, Japanese, US and European field teams had searched only about 3500 km2 of blue ice and recovered around 17 800 meteorite specimens.

Until recently, much emphasis had been put on the “treasure trove” aspect of the meteorite finds and their demonstrated value as scientific specimens, while very little attention had been given to the “treasure chests,” i.e., the sites where they are found. These sites and the meteorites found on them are linked to the history of the ice sheet and to climate change.

FIELD LOGISTICS

If field work is to be carried out within 100 nautical miles (=185 km) of McMurdo Station the preferred mode of travel is by helicopter, but we had begun prospecting for meteorites at sites that were out of helicopter range. For a while, it was sufficient to be put in at Allan Hills by helicopter and travel from there by snowmobile, towing everything on sledges. Our snowmobiles were geared-down machines made by Bombardier Corp. of Canada and were designed for heavy pulling. We found we could tow three fully loaded nansen sledges about as easily as one, so our cargo transport capacity gave us self-sufficiency for long oversnow traverses and long stays at remote sites (Figure 4.1). In this way, we were able to work effectively at the Reckling Peak, Elephant Moraine and Allan Hills Far Western icefields (see Frontispiece). But existing satellite photos gave us the ability to identify ice patches in all parts of the continent, and there were more-distant places that we aspired to visit. Camps at these sites are often referred to as deep-field camps.

Longer lifts are carried out by LC-130s, which actually can reach any part of the antarctic continent. For extreme distances, there is a trade-off between cargo weight and distance flown, but that limitation has not yet affected our field operations. The LC-130s (Figure 4.2) have been fitted with aluminum skis. These are very large, commensurate with the size of the airplane, and have been coated with Teflon®.

INTRODUCTION

Around 4.57 billion years ago, our part of the Galaxy was approaching a cusp in time and space that, once passed, would see the beginning of an irreversible process of star and planet formation. Our solar system would result. Just before it happened, our cloud of gas and dust had a past but no future – it wasn't quite dense enough on its own to begin gravitational contractions that would result in the birth of a star and associated planets. With no external stimulus it probably would just remain a cloud – formless, highly diffuse and without apparent purpose. But in a very intimate sense it was our cloud – we were all there, represented unknowingly by the atoms of which we are today composed.

A cusp is a point defined by the tangential convergence of two curves. The time line of our cloud was converging with the time line of a nearby giant star that had become unstable and was set to collapse inward with unimaginable intensity. This would initiate a supernova and splash part of itself out into space in an ejaculation of cosmic violence. Part of this giant splash was directed toward us (to be). The first signal of the nearby supernova was a flash of electromagnetic radiation, of which the part we call visible light is a tiny segment, washing into and through our cloud; perhaps for the first time illuminating its murky interior for no one to see.

In our model of things, the universe is mainly nothing: an infinite empty space, populated here and there with density nodes of all sizes, from the immeasurably minute, relative to us, to the unimaginably gigantic, relative to us. We seem to be driven to study the universe, and, since the study of nothingness so far has been without profit (except, possibly, to philosophers), we study the density nodes. One aspect of this is the study of meteorites. To study meteorites we must collect examples. To collect examples we have gone to Antarctica.

We have made a good beginning. As of this date (Spring, 2002), there are around 30 000 antarctic meteorite specimens in the combined collections of the US, Japan and Europe. A large fraction of them have not yet been characterized; this is why the Catalogue of Meteorites (5th edition) lists only 17 808. If my guess is correct that the antarctic collection averages 10 specimens per fall, 30 000 specimens represents 3000 falls. This compares to around 1000 observed falls in museum collections from the rest of the world. If meteorite finds (3700) are added in, the world's museums have 4700.

Counting the team that has recently returned from the field (austral summer, 2001–02), 25 field expeditions have been moun-ted by the ANSMET project alone. Since 1977, laboratory space and personnel at the Johnson Space Center have been dedicated to initial processing of the recovered materials and distribution to interested scientists around the world.

EARLY DISAPPOINTMENTS

We had lost a lot of time getting started. I was already 49 years old before I had ever been to Antarctica. Two years that I could ill afford had been wasted in fruitless attempts to convince skeptical reviewers that meteorites occur in concentrations on antarctic ice. This is not a condemnation of the system: I can always be convicted of writing unconvincing proposals.

The system we have in the United States (US) for deciding whether or not to grant funds for new research is probably the best that can be designed. Major granting agencies like the National Institutes of Health (NIH), the National Aeronautics and Space Administration (NASA) and, specific to this case, the National Science Foundation (NSF) invite research ideas from the general community of scientists. These ideas are written in the form of research proposals, which are then sent to three or more reviewers in the same field as that of the proposer. In a majority of cases, the reviewers actually know the proposer and, in order to preserve friendships if possible, they are protected by a cloak of anonymity. This is a wise provision, but very frustrating to the proposer who receives bad reviews and wants to seek out these less insightful colleagues and give them a good shake!

In the case of my proposal to search for meteorites in Antarctica, the reviewers apparently could not accept as significant the early evidence of the Japanese experience that to me seemed so clear.

I am lucky to have induced my colleague, Bob Fudali, to review early drafts of each chapter of this book. One of Bob's major talents is a fine critical faculty. Another is a mindset that allows him to speak without fear or favor. I recently received the following note from him (tucked into a Christmas card).

A characteristic typical of most of us is to be overly impressed with the value of our own research, and I do not claim immunity from this failing. If I give an impression of excessive pride in the following chapters, even after Bob's stern admonition, then I apologize, but let me also point out to the reader that he/she has been warned …

The total of all meteorite specimens recovered from Antarctica by US, Japanese and European teams now numbers somewhere in the neighborhood of 30 000. Among these are a few lunar samples that fell as meteorites after being blasted off the moon as a result of collisions with asteroids.

THE CONTINENT

Antarctica occupies about 9% of the earth's total land surface. For this to be true, of course, you must accept snow and ice as “land surface,” because this is what mainly constitutes that part of the continent that lies above sea level. Think of the antarctic continent as a vast convex lens of ice with a thin veneer of snow. In contrast to the region around the north pole, which is just floating ice at the surface of the ocean, the antarctic ice lens rests on solid rock. In most places the ice is so thick, and weighs so much, that it has depressed the underlying rock to about sea level. If the ice melted completely, the surface of the continent would rebound over a long period of time until its average elevation would be higher than any other continent. As it is, the ice surface itself gives Antarctica a higher average elevation than any other continent.

It is only in a very few places, where mountains defy the ice cover, that we can directly sample the underlying rocks. Most of these places are near the coast, where the ice sheet thins. At the center of the continent the elevation is about 4000 m. At the south geographic pole, which is not at the center of the continent, the elevation is 3000 m.

The contributions of the Hubble Space Telescope to our understanding of starburst galaxies are reviewed. Over the past decade, HST's imagers and spectrographs have returned highquality data from the far-ultraviolet to the near-infrared at unprecedented spatial resolution. A representative set of HST key observations is used to address several relevant issues: Where are starbursts found? What is their stellar content? How do they evolve with time? How do the stars and the interstellar medium interact? The review concludes with a list of science highlights and a forecast for the second decade.

Overview

Almost exactly 10 years ago ST ScI hosted its annual symposium entitled Massive Stars in Starbursts (Leitherer et al. 1991). Those were the weeks immediately prior to HST's launch, and the conference organizers felt it appropriate to have a meeting on the subject of starbursts because HST had the potential for significant contributions. Starbursts are compact (10°—103 pc), young (∼ 106—108 yr) sites of star formation, often with high dust obscuration. These properties make starbursts ideal targets for HST, given its superior spatial resolution, ultraviolet (UV) sensitivity, and (later-on) infrared (IR) capabilities.

As we all know, the high hopes were not immediately fulfilled, and it was not until after the First Servicing Mission that HST lived up to the expectations.

One of the important topics of current astrophysical research is the role that supermassive black holes play in shaping the morphology of their host galaxies. There is increasing evidence for the presence of massive black holes at the centers of all galaxies and many efforts are directed at understanding the processes that lead to their formation, the duty cycle for the active phase and the question of the fueling mechanism. Related issues are the epoch of formation of the supermassive black holes, their time evolution and growth and the role they play in the early ionization of the Universe. Considerable observational and theoretical work has been carried out in this field over the last few years and I will review some of the recent key areas of progress.

Introduction

It is now widely accepted that quasars (QSOs) and Active Galactic Nuclei (AGN) are powered by accretion onto massive black holes. This has led to extensive theoretical and observational studies to elucidate the properties of the black holes, the characteristics of the accretion mechanisms and the mechanisms responsible for the production and transportation of the energy from the central regions to the extended radio lobes.

However, over the last few years there has been an increasing realization that Massive Dark Objects (MDOs) may actually reside at the centers of all galaxies (Ho 1998, Magorrian et al. 1998, Richstone et al. 1998, Gebhardt et al. 2000a, Gebhardt et al. 2000b, Merrit & Ferrarese 2001, van der Marel 1999).

Supernova 1987A has been a prime target for the Hubble Space Telescope since its launch, and it will remain so throughout the lifetime of HST. Here I review the observations of SN1987A, paying particular attention to the rapidly developing impact of the blast wave with the circumstellar matter as observed by HST and the Chandra Observatory.

Introduction

If there was ever a match made in heaven, it is the combination of SN1987A and the Hubble Space Telescope. Although the HST was not available to witness the first three years after outburst, it has been the primary instrument to observe SN1987A since then.

SN1987A in the Large Magellanic Cloud is the brightest supernova to be observed since SN1604 (Kepler), the first to be observed in every band of the electromagnetic spectrum, and the first to be detected through its initial burst of neutrinos. Although the bolometric luminosity of SN1987A today is ≈ 10-6 of its value at maximum light (Lmax ≈ 2.5 × 108 L⊙), it will remain bright enough to be observed for many decades in the radio, infrared, optical, UV, and X-ray bands.

SN1987A is classified as a Type II supernova (SNeII) by virtue of the strong hydrogen lines in its spectrum. It was atypical of SNeII in that its light curve did not reach maximum until three months after outburst and its maximum luminosity was about 1/10 the mean maximum luminosity of SNeII.

The Space Telescope Science Institute Symposium on “A Decade of HST Science” took place during 11–14 April 2000.

There is no doubt that the Hubble Space Telescope (HST) in its first decade of operation has had a profound impact on astronomical research. But HST did much more than that. It literally brought a glimpse of the wonders of the universe into millions of homes worldwide, thereby inspiring an unprecedented public curiosity and interest in science.

HST has seen farther and sharper than any optical/UV/IR telescope before it. Unlike astronomical experiments that were dedicated to a single, very specific goal, HST's achievements are generally not of the type of singular discoveries. More often, HST has taken what were existing hints and suspicions from ground-based observations and has turned them into certainty.

In other cases, the level of detail that HST has provided forced theorists to re-think previous broad-brush models, and to construct new ones that would be consistent with the superior emerging data. In a few instances, the availability of HST's razor-sharp vision at critical events provided unique insights into individual phenomena.

These proceedings represent a part of the invited talks that were presented at the symposium, in order of presentation. We thank the contributing authors for preparing their papers.

It is rare in astronomy to have a purely physics-based technique for studying the distant universe. Rooted in General Relativity, the image distortion and time delay of light from distant objects caused by foreground gravitational lenses offers such a window on the universe. Using only combinations of measured redshifts, angles, and arrival times of source intensity fluctuations, lensing observations can probe the mass distribution of the lens, the rate of expansion of the universe (the Hubble constant), the acceleration of expansion (dark energy), and the total amount of matter in the universe. The HST has made and will continue to make unique contributions to this new window on the universe.

Introduction

The universe is not as it seems: distant galaxies and quasars are in the wrong places. Their apparent positions on the sky have moved relative to where they would normally appear, and the culprit is mass-energy. Specifically, a massive object (a star, a galaxy, a cluster of galaxies) will warp space-time around it, causing light rays to bend as they pass by. If a mass concentration lies between us and a distant source, that source will appear in an altered location. The effect is called gravitational lensing, and it also systematically distorts the images of resolved sources like galaxies.