Dawn at Ceres

March 2015

The Dawn spacecraft, having completed its lengthy survey of the asteroid 4 Vesta, and having survived the interplanetary cruise from Vesta to Ceres, is now safely in orbit around the largest asteroid in the Belt, 1 Ceres.  One of the first results from Dawn’s survey of Ceres is the discovery of small, intensely bright spots on its surface.

Vesta and Ceres, though nearly at the same distance from the Sun, are not twins; in fact, they are very different creatures.  Vesta is unique among the large (>100 km diameter) asteroids in the Belt: it is a thoroughly reworked body, having undergone extensive melting and differentiation into layers with different composition and density, with a surface dominated by rocks closely similar to terrestrial basalts.  Ceres, in contrast, is a modestly altered body that is genetically related to the very dark, volatile-rich C-type asteroids that dominate the outer half of the Belt.

Back in 1977 Larry Lebofsky studied the infrared reflection spectrum of Ceres and found an absorption feature near a wavelength of 3 micrometers (µm).  This is a region in which water, in all its many chemical forms, is a strong absorber.  Articles in the press tend to assume that any mention of “water” means liquid water, which equates to a well-watered Eden for life.  But the 3-micron feature is simply due to excitation of the stretching mode of the O-H chemical bond: water vapor, liquid water, solid water-ice polymorphs, clay minerals, micas, and hydrated salts such as gypsum all have broad absorption bands in this same spectral region.  Liquid water, if present today, could not occur stably close to the surface (too cold; hard vacuum), but might persist at modest depths if some solute is present to lower the freezing point and depress the vapor pressure.  A plausible candidate for that role is ammonium chloride, NH₄Cl, which I regard as a far more plausible solute than the often-quoted ammonia.  Many years ago (in Low-Temperature Condensation from the Solar Nebula, Icarus 16, 241 (1972) I pointed out that chemical synthesis of ammonia is strongly favored by high pressures, suppressing ammonia synthesis in the Solar Nebula.  My colleagues Ron Prinn and Bruce Fegley showed that the higher pressure in dense protoplanetary nebulae favored ammonia formation there: ammonia should be an important constituent of ices in planetary satellite systems, but not in asteroids, because they are formed in the low-pressure regime of the Solar Nebula. 

Indeed, the freshly fallen Orgueil CI chondrite, which contains all the minerals mentioned above, as well as veins of soluble salts deposited from solution in water, was reported to give off a strong odor of “smelling salts”, ammonium chloride. 

And what about the bright white spots on Ceres?  Liquid water released from the interior of Ceres would boil well below the surface, producing a jet of rapidly cooling vapor.  Water vapor vented from a warm interior into the frigid vacuum of Ceres’ surface would expand irreversibly to produce a jet of snow, which would fall to the ground near the vent.  This would happen whether the source of the water vapor is a shallow layer containing liquid water or deep, hot rocks containing –OH minerals.  Linking water venting on Ceres to the local origin of life is sufficiently far-fetched to deserve skepticism.

Hayabusa 2: On its Way to an Asteroid

March 2015

 

Japan’s second asteroid sampling mission is under way.  Hayabusa 2 was launched from the Tanegashima Space Center in January on its 6-year trip to the Near Earth Asteroid (NEA) named 1999 JU3.  The mission is a follow-up to the ambitious but trouble-plagued Hayabusa 1 flight of 2003-2010, which aspired to grab a substantial sample of the NEA Itokawa, but suffered several failures, including malfunction of its sampling equipment.  Hayabusa 1 nonetheless returned successfully to Earth bearing traces of asteroid dust on its surface.

Hayabusa 2 carries, in addition to a sample-acquisition system, four small probes, one of which is patterned after the Philae probe that recently landed on Comet 67P/Churyumov-Gerasimenko.  These probes are capable of “hopping” about on the asteroid surface; indeed, the main spacecraft is intended to land and collect samples in three different places.

The present target asteroid, despite its uninteresting name, has particular attraction for people interested in the discovery and use of the native resources of space: it is a very dark rock, similar in its reflectivity and spectrum to the carbonaceous chondrite meteorites.  These meteorites contain up to 20% water by weight, plus about 6% of tarry organic polymers and interesting amounts of many other compounds of the volatile elements hydrogen, carbon, oxygen, sulfur, nitrogen, chlorine, and so on.  The dominant minerals are water-bearing clays, magnetite, and a variety of metal sulfides loosely cemented by the organic gunk that coats the mineral grains.  The CI chondrite meteorites also contain veins of various water-soluble and water-bearing minerals, mostly sulfates and carbonates, that run through the otherwise very black groundmass.  Moderate heating releases water vapor; strong heating drives off a rich variety of gases and causes the organic matter to react with the oxygen-rich mineral magnetite to “burn” the organic matter and release copious amounts of carbon oxides and water.  All told, strong heating of CI material drives off ~40% of the total mass of the meteorite as gases of H, C, O, N, S, and Cl compounds. 

1999 JU3 is about 920 meters (0.6 miles) in diameter, with a total mass of about 1 billion tonnes, which upon heating would release some 400 million tonnes of volatiles.  By way of comparison, a fully-fueled Saturn V rocket or Space Shuttle contains about 2000 tonnes of rocket propellant: 1999 JU3 contains enough hydrogen, carbon, and oxygen to fuel 200,000 such flights.

Deep Space Industries (deepspaceindustries.com) is presently studying processes for turning the volatiles extracted from carbonaceous asteroids into fuels and oxidizer for future space missions, and into air and water for life-support and agricultural uses by future spacefarers.  The byproducts from extraction of volatiles, including metals, are also of great economic interest. Plans to manufacture these products await the successful return of samples to Earth.

Return of Hayabusa 2 from the asteroid will commence in late 2019, with entry into Earth’s atmosphere and recovery of the return capsule scheduled for December 2020 in the interior of Australia.

Hayabusa 2 is a difficult and challenging mission.  The Japanese Space Agency JAXA is to be congratulated for learning valuable lessons from their earlier asteroid mission and designing an ambitious and well-conceived successor.  I wish them the very best of luck.

The Franklin Law

February 2015

 

 I was awakened abruptly by pounding at my door. “Mr. Croft! Mr. Croft! Come quickly!”

 I struck a lucifer and touched it to the wick of my bedside lamp. By its light I could see that my alarm clock read a few minutes after 1 AM. I had been late falling asleep because of the evening’s ferocious thunderstorm. Two hours of sleep would not leave me at my best.

 The pounding resumed. “Mr. Croft! Fires are burning in Brooklyn!”

 I hurried to the door in my nightshirt to let him in before the people in my neighboring apartments would become annoyed.  It was Jack Harris from the Tribune.  He was flushed and trembling. He must have run here from the office, fully ten blocks--not a safe thing to do in New York at this time of night, when heavy, poorly-lit delivery wagons fill the streets. “There have been many lightning strikes in Manhattan and Brooklyn. There are at least a dozen fires visible from the Tribune tower, from the Bronx to Coney Island. The fire brigades are out, but of course the streets are congested and they’ll be slow to respond.”

 “What do I need to do?  And who’s on the night news desk? Curtis?”

 “Yeah, Curtis—he wants you to check out the situation in Brooklyn. He wants you to write a front-page story about it.”

 I sent Harris back to the Trib with word that I was on my way to Brooklyn. I dressed quickly, choosing a rainproof overcoat against the cool, blustery October weather and the threat of continuing rain.

At the curb I looked about for a carriage, but at this hour there were none to be seen. The streets were nearly filled with heavy horse carts and ox carts laden with coal, perishable foods and ice, coming in from farms in Jersey by ferry, and down the roads along the Hudson from the train terminus. I decided that the only way I could get about was on foot, and I could walk as fast as these carts were moving. I headed for the Brooklyn Bridge, crossing the streets with care, skirting the business district at the tip of Manhattan with its towering skyscrapers of ten to fifteen stories. Except for the Tribune tower, they were all dark and unoccupied, the stokers for their steam elevators having retired for the night. The streets were left to the carts and animals.

The evening’s rain had made a foul soup of the horse and ox ordure that coated the streets. The wind was at my back. The smell was overwhelming, without even a hint of smoke from the fires ahead. I could not see any fires because my view was blocked by the tenement blocks and warehouses that lined the East River, but an eerie orange glow flickered on the low clouds overhead.

As I approached the bridge I found all of Manhattan at a standstill. Traffic came only from the Brooklyn side, the entire Brooklyn bridge blocked by a river of citizens and carts surging into Manhattan. Wails, sobs, even screams pierced the background rumble of carts, but the general tide of humanity flowed on in silence, grim-faced and bowed under loads of household goods. Flames rose from the opposite side of the East River, no more than a block or two from the water's edge. How could I cross the bridge to Brooklyn as I had been assigned to do?

The first responsibility of a reporter is to interview those who know what was happening. I stepped in front of a man with a heavy load of clothes and household items. “What is going on over there? Do you know how widespread the fire is?”

 He grimaced and shook his head. "Gone, all gone" he seemed to say.

I could see converging fires cut off access to the bridge on the other side of the river, staunching the stream of foot traffic coming across the bridge. I ventured to walk against the flow on the narrow northern sidewalk, leaving the wagon lanes to the refugees. I tried to interview a dozen of them, but they had no heart or mind to share more than a sentence or two about the horrors they had seen. Bundles were abandoned, children lifted up, as the crowd pressed on to safety. 

As I finally neared Brooklyn the flames seemed to grow higher, towering hundreds of feet into the overcast sky, dwarfing the 5- and 6-story wooden tenements. The clouds reflected the glow of the fire, turning the heavens a sullen red. And as the flames pulsed and roared, the wind picked up ever more strength.  Soon I could feel the intense heat of the blaze on my face and found myself being impelled toward the flames by the ever-strengthening wind. 

The last stragglers of the exodus were passing me now. It was a heart-wrenching sight, for many were burned or were carrying victims of the flames in their arms or on their backs. So strong were the winds by this time that some could make no headway against them. Many simply collapsed in the roadway, barely able to crawl into the wind. One last refugee staggered along at the end of the line, terribly burned, the back of his coat smoldering, and collapsed in front of me.  I went to him and found him still alive, but too weak to arise. I beat out the embers in his coat, but there was nothing else I could do for him. I left him there and continued cautiously, the wind propelling me toward the fire.

A gust knocked me off my feet, and I fell on my face on the pavement.  The wind was enough weaker at road level that I could crawl on toward the fire. I was well past the east pier of the bridge, still far above the level of the river. I could see far up the Brooklyn shore, a vista of the most utter devastation. The separate fires I had seen only minutes earlier seemed to have merged into a roaring single wall of flames, whipped by its own winds into a hellish frenzy. I suddenly had the thought that there was nothing left living in front of me; that I, if I wanted to live, should go no farther. I crossed the bridge to the south sidewalk on hands and knees, and there also I saw utter destruction. All approaches to the bridge had been blocked by intense fires and the glowing rubble of collapsed tenements. All that remained standing were masonry chimneys and the occasional iron fire escape, heated red-hot and stretching into the flaming sky. There was indeed nowhere for me to go except back.
 
The enormity of the tragedy struck me so profoundly that I lost all strength. Exhausted, devastated, in despair, I collapsed in the roadway to collect my wits. I must have lain there for an hour before I could muster the strength to continue.

 Rather than return directly to my apartment, I made my way to the Tribune to write my story. The paper was published hours late because of the shortage of press workers, many of whom lived in Brooklyn and normally arrived by streetcar. But Brooklyn was gone, and so were the streetcars.
 I went home to a fitful sleep, haunted by the most gruesome dreams. When I finally awoke, I was obsessed with the idea of writing an op-ed piece on the tragedy. I sat down at my desk and wrote it out in a single sitting. Here it is:

The Franklin Law: Seed of Tragedy, by Arthur Croft

 

Every schoolchild knows the story of Benjamin Franklin, back in 1751, flying a kite in a thunderstorm, and of the tragic lightning strike that killed him. This promising young man, editor of the Pennsylvania Gazette, author of Poor Richard’s Almanack, organizer of the Philadelphia Fire and Police Departments, inventor of the Franklin stove, had just begun the study of lightning in the atmosphere and in the laboratory. Notes found among his personal effects laid out a scheme to protect buildings from lightning by means of metal wires or rods.  

But because of the manifest hazard of studying lightning and other “electrickal” phenomena, and reinforced by the deaths of Franklin, the Russian physicist Georg Richmann, and other imitators of Franklin’s experiment, Parliament passed, in 1753, the well-known “Franklin Law” forbidding further experiments with lightning in all its manifestations. The law was an effective deterrent that doubtless saved lives throughout the Empire. The law was strictly enforced and few dared challenge it. Historians tell of the prosecution of Joseph Priestly in 1767 upon his attempts to publish a book entitled “History and Present State of Electricity”. The first few hundred copies of this book, printed in Leeds, were confiscated and burned by the authorities by order of the Court, and Priestly narrowly averted prison by abjuring the contents of his book, destroying his notes and personal copy of the manuscript, and paying a heavy fine. In Catholic countries, the 1757 encyclical Against Meddling with the Powers of God by Pope Benedict XIV specifically defined the study of lightning as impious, and effectively extended the ban on electrickal research throughout the rest of the Christian world.

Yet now, in the wake of yesterday’s tragic fires, in which the death toll may well exceed one million souls, the value of protection against lightning has become manifest. Had it not been for this well-meaning Law, might not Franklin, or others following in his footsteps, have perfected the means to protect structures against lightning?

It is not the purpose of this writing to incite disobedience to the law and expose this journal to prosecution; however, it may be time to rethink the ban on electrickal research, which has in recent years been conducted with care and safety in Japan and the Netherlands. The benefit of saving one or two lives can scarcely outweigh the cost of the loss of a million.

 

This Law, and this tragedy, are not a legacy that Franklin would have wanted to bear his name.
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Published on the op-ed page of the New York Tribune
New York City, Crown Colony of New York, October 11, 2015
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