Global Warming of the Moon: Science Fiction

We have recently been bombarded by claims that there has been global warming on the Moon caused by the Apollo missions.  This is a quantitative claim, and can only be judged on the basis of numerical evidence.

Here’s the claim: footprints and rover tracks on the Moon have turned over some of the lunar soil, exposing deeper and darker layers of soil.  That darker soil of course absorbs more sunlight, which causes the Moon to get warmer.  The claim, based on data from the thermal probes left in drill holes at two Apollo landing sites, is that the “temperature of the Moon” rose by about 2 to 3 degrees Celsius.

But in fact it was only the temperature in a handful of areas of roughly 1 square meter that went up at all.  That’s a wildly different story, one that has universally been misrepresented by websites that claim to be good at interpreting science data for the general public.

So, let’s think about the Moon.  It is very dark (it looks “bright” at night because we see it in the night sky in comparison with the feeble light of distant stars and planets).  It has been established with high reliability that the (undisturbed) total moon absorbs 88% of the sunlight that strikes it, an albedo (reflectivity) of 1-0.88, or 0.12; only 12%.  The reflectivity of natural lunar soil is influenced by what has been called the “fairy castle” structure of lunar soil: the fluffy, very poorly compacted state produced by natural processes.  Where astronauts have walked on the lunar surface their weight has compressed the fluffy regolith, which of course turns it from an excellent insulator with very poor thermal conductivity into something with much better thermal contact between particles.  The same old solar radiation, hitting the boot-compressed surface layer, delivers slightly more heat to the thermal probes, raising their temperature by 2 to 3 degrees Celsius.  So several square meters of the lunar surface at the Apollo landing sites get slightly warmer than the rest of the Moon, and that is precisely where the thermal probes are located!

To say that the whole Moon is experiencing “global warming” is patently absurd.  The original scientific paper on the subject does not mention that phrase.  Any media source that delivers this message is clueless.  There is absolutely no evidence for global warming on the Moon.

Publications Relevant to Space Resources By John S. Lewis

A number of patent claims made recently by a competitor are based on work that I published in the open literature many years ago.  The patents were awarded to a company that did not exist at the time of those publications, with which I have never had any contractual relationship, and which has never produced any evidence of understanding or competence in any of these processing areas.  Since all these technologies are in the public domain, they cannot ethically be patented by anyone, even by myself. The proof of my priority is spelled out in considerable detail in the following publications. All claims to patents based on this work are fraudulent. Most of the other claims in that patent cover standard art and practice in the aerospace industry and are equally invalid.  Caveat emptor.

69.  J.S. Lewis and S. Nozette, Extraction and Purification of Iron-Group and Precious Metals from Asteroidal Feedstocks. Adv. Astronaut. Sci. 53, 351 (1983).

71.  J.S. Lewis, and C. Meinel, Asteroid Mining and Space Bunkers. Defense Science 2001+, 2, No. 3, 33-67 (1983).

77.  J.S. Lewis and C.P. Meinel, Carbonyls: Shortcut from Extraterrestrial Ores to Finished Products. In: Lunar Bases and Space Activities in the 21st Century.  NASA Johnson Space Center, 126 (1984).

80.  J.S. Lewis and R.A. Lewis, Space Resources: Breaking the Bonds of Earth. 407 pp.  Columbia University Press (1987).

83.  J.S. Lewis, Summary of the Conference: Extraterrestrial Resources.  In: Space Manufacturing 6, AIAA, Washington, D.C., 18 (l987).

87.  J.S. Lewis, T.D. Jones and W.H. Farrand, Carbonyl Extraction of Lunar and Asteroidal Metals. In: Engineering, Construction and Operations in Space (S.W. Johnson and J.P. Wetzel, eds.), Amer. Soc. Civil Engineers, N.Y., 111 (1988).

89.  J.S. Lewis, Summary of the Conference: Non-terrestrial Resources.  In: Space Manufacturing 7, 5-10 (1989).

93.  J.S. Lewis, Lunar, Martian and Asteroidal Resources: Programmatic Considerations. In: Proceedings of the 1989 Annual Invitational Symposium on Space Mining and Manufacturing, UA/NASA Space Engineering Research Center, 1-10 (1990).

96.  J.S. Lewis, K. Ramohalli and T. Triffet, Extraterrestrial Resource Utilization for Economy in Space Missions. International Astronautical Federation, IAA 90-604 (1990).

98.  J.S. Lewis, Extraterrestrial Sources of ³He for Fusion Power.  Space Power 10 363-372 (1991).

100.  J.S. Lewis, Non-Terrestrial Resources of Economic Importance to Earth.  International Astronautical Federation IAA 91-656, (1991).

102.  J.S. Lewis, Summary of the Conference: Non-terrestrial Resources.  In: Space Manufacturing 8, 19-22 (1991).

103.  J.S. Lewis, Construction Materials for an SPS Constellation in Highly Eccentric Earth Orbit.  Space Power 10, 353-362 (1991).

104.  J.S. Lewis, Asteroid Resources.  In: Space Resources, Vol. 3: Materials, M.F. McKay, D.S. McKay and M.B. Duke, eds. NASA SP-509, 59-78 (1992).

107.  J.S. Lewis, Processing Non-Terrestrial Materials.  SME Trans. 294, 1864-1868 (1993).

110.  J.S. Lewis, M.S. Matthews and M. Guerrieri, eds., Resources of Near-Earth Space, Univ. of Arizona Press, Tucson.  977 pp. (1993).

111.  J.S. Lewis, D.S. McKay and B.C. Clark, Using Resources from Near-Earth Space.  In: Resources of Near-Earth Space (J.S. Lewis, M.S. Matthews and M. Guerrieri, eds.), Univ. of Arizona Press, Tucson.  3-14 (1993).

112.  J.S. Lewis and M.L. Hutson, Asteroidal Resource Opportunities Suggested by Meteorite Data.  In: Resources of Near-Earth Space (J.S. Lewis, M.S. Matthews and M. Guerrieri, eds.), Univ. of Arizona Press, Tucson.  523-542 (1993).

113.  J.S. Lewis, Summary of the Conference: Transportation and Materials.  In: Space Manufacturing 9, AIAA, Washington D. C., 3-7 (1993)

114.  J.S. Lewis, Logistical Implications of Water Extraction from Near-Earth Asteroids.  In: Space Manufacturing 9, AIAA, Washington D. C., 71-78 (1993)

115.  J.S. Lewis, The Platinum Apples of the Asteroids, Nature 372, 499 (1994).

116.  J.S. Lewis, Planetary Resources for Extraterrestrial Technology.  Quart. J. Roy. Astron. Soc. 36, 445-448 (1995).

118.  J.S. Lewis, Summary of the Conference: Closing Remarks.  In: Space Manufacturing 10, AIAA, Washington D. C., 23-24 (1995)

119.  J.S. Lewis, Banquet Address: The Solar System's Greatest Resource.  In: Space Manufacturing 10, AIAA, Washington D. C., 31-36 (1995).

121.  J. S. Kargel, M.D. Kraft, D. J. Roddy, J. H. Wittke and J. S. Lewis, Impactite melt fragments at Meteor Crater, Arizona: EOS Transactions of the American Geophysical Union 76, p. F337 (1995).

122.  J.S. Kargel, P. Coffin, M. Krafft, J.S. Lewis, D.J. Roddy E. M. Shoemaker and J.H. Wittke, Systematic Collection and Analysis of Meteoritic Materials from Meteor Crater, Arizona.  Lunar and Planetary Conference XXVII, 645-646 (1996).

124.  K. Ramohalli and J.S. Lewis, A Survey of Technology Advances in In-Situ Resource Utilization for Economical Space Missions.  Submitted (1996).

125.  J.S. Lewis, Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets, Addison-Wesley, Reading, MA.  274 pp. (1996).

126.  J.S. Lewis, Physical and Chemical Properties of Near-Earth Objects.  In: Planetary Emergencies: The Collision of an Asteroid or Comet with the Earth (R. Coppola, ed.), Springer-Verlag, New York.  In press (1997).   (Publication abandoned by Springer, 2001.)

127.  J.S. Lewis, Resources of the Asteroids, J. Brit. Interplanetary Soc. 50, 51-58 (1997).

131.  J.S. Lewis, Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets. Revised Edition, Addison-Wesley, Reading, MA, 274 pp. (1997).

133.  J.S. Lewis, Summary of the Conference Sessions: Asteroids and Nonterrestrial Materials.  In: Space Manufacturing 11, AIAA, Washington D. C., 19-20 (1997).

135.  K. Ramohalli, T. Triffet, J.S. Lewis, and A. Cutler, Material Processing Requirements for a Lunar-Based Laboratory. In: A Lunar-Based Analytical Laboratory, Cyril Ponnamperuma Memorial Volume, A. Deepak Publishing, Hampton, VA (1997).

139.  J.S. Lewis, Unbegrenzte Zukunft: Reichtümer aus dem Universum. Bettendorf, Munich.  317 pp. (1998).  (Translated from English to German by Karl-Heinz Ebnet.)

141.  J.S. Lewis, Mining the Sky: Resources of Asteroids.  In: Elements of Change 1998, S.J. Hassol and J. Katzenberger, eds., Aspen Global Change Institute, 107-110 (1998).

143.  J.S. Lewis, Tapping the Waters of Space.  Scientific American Presents: The Future of Space Exploration, 100-103 (1999).

148.  J.S. Lewis, Asteroid Resources, Exploitation, and Property and Mineral Rights.  In:  The High Frontier.  20th Anniversary Edition, Space Studies Institute, pp. 137-149 (2000).

155. J.S. Lewis, Space Resources, Occurrence and Uses.  In: Encyclopedia of Space Science and Technology, H. Mark, M. Silvera, M. I. Yarymovych and M. Salkin, eds., 598-631 J. Wiley Interscience (2004).

157.  J.S. Lewis and C.F. Lewis, A Proposed International Legal Regime for the Era of Private Commercial Utilization of Space.  The George Washington International Law Review 37, 745-767 (2005).

159.  J.S. Lewis, Chemical Diversity and Abundances across the Solar System.  In: Chemical Evolution across Space and Time. L. Zaikowski and J. M. Friedrich, eds., American Chemical Society Symposium Series 981, 130-140 (2007).

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160.  J.S. Lewis, Building the Moon Base: Living off the Land.  In: Space Science, Environmental Ethics, and Policy, in press (available as conference video) (2008).

162.  J.S. Lewis, Asteroid Mining 101, DSI Press, 184 pp. (2014).

163.  M. Sonter, S. Covey, J. S Lewis, and A. Rao, Mineral Resource Estimation for Asteroid Mining Projects.  Lunar and Planetary Science 45 (2014).

164. S.D. Covey, J.S. Lewis, P.T. Metzger, D. T. Britt and S. E. Wiggins, Simulating the Surface Morphology of a Carbonaceous Chondrite Asteroid. ASCE Earth-Space 3 (2016). 

165. P.T. Metzger, D.T. Britt, S.D. Covey, and J.S. Lewis, Results of the 2015 Workshop on Asteroid Simulants.  (2016).

                                     *(Books are indicated by boldface type)

Platinum from the Asteroids?

In a previous millennium, I wrote a number of articles and several books on the nature of asteroids, the threat they pose to life on Earth, and their economic attractiveness as future resources for exploitation.  I will post a list of those publications separately on this site so that those interested can verify what I write here, both its content and its priority. 

Science fiction author Robert Heinlein, although saying little about mining and resources, wrote of converting asteroids into habitats as early as 1939, in his story “Misfit”.  The idea of mining asteroids appears to have been introduced in 1951 by E. E. “Doc” Smith, writer of the “Lensman” series of science fiction novels, who presents his protagonist, Kimball Kinnison, as the discoverer of a massive platinum deposit in an asteroid.   Frederik Pohl, starting in 1977, set many stories against a background of mining for metals in the asteroid belt.  Former astronaut Brian O’Leary proposed in 1981 that certain near-Earth asteroids might contain economically attractive amounts of platinum-group metals, although he was unable to suggest a workable method of extracting and retrieving this material.   I first suggested actual industrial processes for making asteroidal metals useful, including the platinum-group metals, in 1983.

The Near Earth Asteroids (NEAs) are of the most immediate interest as resources: they are readily accessible from Earth, and their compositional attractions (and diversity) are well documented by chemical analyses of many thousands of meteorites which have fallen to Earth.  The overwhelming majority of these meteorites derive from the NEAs and therefore represent not only samples of the materials that threaten Earth, but also of the resources available to us when we exercise modern technology to exploit them.

The NEA swarm contains thousands of known asteroids, ranging in size from mere rocks (1-10 meters) to bodies over 10 km in diameter.  Their orbits range from inside Mercury’s orbit to a few that roam out to Jupiter and beyond.  Their compositions span all the varieties of meteorites that fall on Earth, including material similar to organic-rich lake bottom sediments, the C-type (carbonaceous) asteroids and the corresponding C chondrite meteorites.  They are rich in organic carbon compounds, magnetite, and water-bearing clay minerals, with elemental sulfur, hydrated mineral sulfates, sulfides, phosphates, and a great variety of minor and trace minerals.  These carbonaceous chondrites are relatively fragile, poor at surviving both passage through the atmosphere and long-term residence on Earth’s surface: a single rain storm will utterly destroy them.

Most of the meteorites in our museum collections are stronger, with very low content of water and other volatiles and far less oxidized minerals, being dominated by silicates of iron and magnesium (olivine and pyroxene), feldspars made of aluminum, sodium, and potassium oxides, a sulfide of iron (FeS) called troilite, and particles of metallic iron-nickel alloys.

Also common in our meteorite collections are “iron” meteorites, composed of natural stainless steel, an alloy of iron, nickel, and cobalt.  Irons contain traces of dozens of rare and strategic elements such as gallium, germanium, indium, and other non-metals which dissolve in iron alloys, and the platinum-group metals (PGMs) such as platinum, osmium, iridium and rhodium, along with a trace of gold.  The NEA swarm contains about 1.8x10¹⁵ grams of PGMs; in more familiar terms, that’s 1.8 billion tonnes of stuff worth about $70,000 trillion dollars at present Earth-surface prices.  Obviously returning even a tiny proportion of that material to Earth would cause the market price to crash.

Once assembled into planets (or even the very largest asteroids), these raw materials melt and “differentiate” by density into layered planets with metal-rich cores, iron-and-magnesium silicate mantles, and volatile-rich crusts. After many generations of melting and recrystallization, rich veins of minerals evolve.  Humans, having grown up on such a differentiated world, expect valuable minerals to be found as rare veins of ore that wind their way tortuously through vastly larger bodies of “dross” (economically uninteresting) materials that must be removed or tunneled through to access the “right stuff” in the veins.  Such expectations may apply to one or a few of the very largest asteroids; they are probably irrelevant to most or all or the entire Near-Earth Asteroid family.  The study of meteorites makes it clear that the large majority of the rocks that fall on Earth have not gone through such a process of differentiation and mineral-vein formation.  But even some “space mining” companies seem to be unaware of the meteorite evidence; they adopt irrelevant models of mining based on terrestrial experience, not meteorite evidence.

Now let us suppose that we wanted to break into that market by extracting PGMs from nearby asteroids and throwing them into the Earth-surface marketplace.  How could we do this?  Since these elements are present in small concentrations in all asteroidal metal alloys, the obvious method is to extract them from the metal and ship them back to Earth in concentrated form (that is, we don’t have to engage in the laborious and complex process of separating them into their individual component elements; we can just ship the mixture back to Earth and let processing plants at home separate them into useful products).  Fortunately, we know how to do all this because it involves technologies we already have on Earth.

The essential step, separating the high-value PGMs from the less-pricey major elements, requires the use of what chemical engineers call the Mond process, named after the German chemist Ludwig Mond.  Large, strong (think “really massive”) pressure vessels are filled with carbon monoxide at moderate temperatures of 100 to 200 ^oC and high pressures, typically about 100 atmospheres.  Under these conditions, iron and nickel (and under somewhat different conditions, also cobalt) react with the carbon monoxide gas to produce gaseous compounds called carbonyls, including iron pentacarbonyl, Fe(CO)₅, and nickel tetracarbonyl, Ni(CO)₄.  These can be condensed together as water-like liquids and then separated by distillation into the two separate carbonyls with extremely high purity, better than 99.9999% for each carbonyl.  Cobalt, under modestly different conditions, can also be extracted and separated as its carbonyl.  The solid residue from this extraction process contains many other elements besides the PGMs (such as gallium, germanium, indium, etc.) and particles of silicates that were once dispersed as impurities in the metal.  Also present are carbides, phosphides, silicides and sulfides that were originally dissolved in or trapped inside the metal grains.  Physical and chemical purification processes can separate these less-valuable materials from the very dense PGM dust.

Fine, now we have several products separated and ready for shipment back to Earth or for in-space use:  1) ultrapure iron, 2) ultrapure nickel, 3) ultrapure cobalt, 4) and fairly pure PGM dust, not separated into elements.  These are supplemented by 5) mixed nonmetals (gallium, germanium, arsenic, indium, etc., and 6) particulate sulfides and phosphides of iron, nickel, and (depending on which type of meteoritic metal alloy was used) perhaps other metals as well.

Having invested in building the processing plant and shipping it to an asteroid, our investors would surely be interested in the value of the products made available.  Here’s a tentative list:

            1) ultrapure iron, 99.9999% pure, which is stronger and more corrosion-resistant than normal steel; Earth-side market value perhaps $2000/tonne, and extremely useful for construction of habitats and pressure vessels in space. The total NEA swarm’s market value is about $70 quadrillion (Earthside market prices).

            2) ultrapure nickel, Earth-side market value would be about $28,000/tonne for normal purity Ni; no premium is assumed for the high purity or for its presence in space.  Total NEA swarm value for Ni would then be another $70 quadrillion.

            3) high-purity cobalt, Earth-side market value about $35,000/tonne for normal-purity cobalt; no premium is assumed for the high purity or presence in space.  Total NEA swarm value for the cobalt content would then be another $70 quadrillion.

            4) Mixed Platinum Group Metals, Earth-side market value about $40/gram; $40 million/tonne.  The total NEA swarm value is about $70 quadrillion.

            5)  Mixed non-metals (semiconductor materials): available for use in space to build solar power electrical generation stations.  The value of this resource category is “just gravy”, and the logical market for them is in space.

            6) Sulfides, carbides, phosphides, silicides, etc. (rare metals and nonmetals) available for use in space.  More “gravy”.

These proportions are valid regardless of what fraction of the total NEA resource base is consumed.

To a good first approximation, the PGM contribution to the value of asteroidal metal resources is a little less than 25% of the total value.  As on Earth, exploitation of ferrous metal resources will be done for the economic benefit of “local” uses of the iron, nickel, and cobalt, not the PGMs.

Now consider what would happen to the revenue stream from importation of PGMs to Earth: even as little as a few thousand tonnes per year would lead to a crash of market prices.  Rather than commanding current prices on the order of $1000 per ounce, PGMs would drop precipitously in price in response to their growing supply.  Importation of larger quantities of PGMs would be self-limiting even if lower market prices should encourage wider use of these metals.  It would then become obvious that PGM mining is a far less compelling reason for mining asteroids than those that are provided by the ferrous metals or volatiles.

Why do I take the time to challenge the assertion that mining platinum group metals is the reason to exploit Near-Earth Asteroids?  Because the idea is attributed to me, reflects no appreciation of how that mining would be done, and is quite incredible as it is generally presented.  Let’s be clear: there is so vast a supply of platinum-group elements in the NEA swarm that exploiting even a tiny fraction of them would cause the market value to crash, bringing to an end the economic incentive to mine and import them.  PGMs are valuable on Earth today because they are rare; in a world in which vastly larger supplies of PGMs are available, their value plummets.  Mining PGMs from asteroids is not a get-rich-quick scheme; it is a way of lowering PGM prices dramatically.

When any self-described asteroid mining company plays the “platinum card” as a reason to begin asteroid resource exploitation, it is misrepresenting the truth and displaying a willful ignorance of the facts laid out above.  Platinum-group metals from asteroids are a real benefit reserved for the distant future, a fringe benefit of mining ferrous metals.  But the initial economic motivation for NEA exploitation is, as I have been saying for many years, the manufacture of chemical propellants to enable future deep-space missions—and to open the asteroids to economic activity.  

Another Asteroid Flyby of Earth

The interloper this time is 2002AJ₁₂₉, a body with a highly eccentric, comet-like orbit.  Its perihelion is a near-suicidal 0.116397 AU, far inside Mercury’s orbit, and its orbital eccentricity is 0.915097, typical of short-period “periodic” comets.  That means that the orbital period is short enough so that it actually returns to the inner Solar System, where we humans presently reside, on human time scales.  Its orbital period is only 1.61 years, so we have had several opportunities already to see it since its discovery (in 2002, as its name tells us).

On each trip around the Sun it coasts out to aphelion at 2.625502 AU, comfortably far away from any planet.  The orbit is inclined 15. 47941 degrees relative to the plane of the ecliptic.

This asteroid, because of its size and Earth-crossing orbit, qualifies it as a PHA, a Potentially Hazardous Asteroid.  Its albedo has not been measured, so converting the observed brightness into a size is uncertain.  This uncertainty leads cautious astronomers to estimate a diameter of 600 meters to 1.2 kilometers. The aphelion distance suggests a possible origin in the heart of the asteroid belt, in a region in which dark C-type carbonaceous asteroids outnumber the brighter S-type stony asteroids.  An educated guess, that C-type is moderately more probable than S-type, would place the albedo (reflectivity for visible light) down around 0.04, which favors a size well above 1 kilometer.

By the way, it’s not going to hit us in the foreseeable future.  In the long term, however, all bets are off: since AJ₁₂₉ crosses the orbits of Mercury, Venus, Earth and Mars on every trip around the Sun there are lots of opportunities for tweaking its orbit.  Over millions of years the odds are about even that it will end its career by hitting Earth. 

The threat is real, but not imminent enough for me to change my investment strategy. 

It Came from Outer Space

On the night of October 19 2017 the Pan-STARRS telescope, atop Haleakela on the island of Hawaii, operated by Robert Weryk, discovered a fast-moving body sailing by Earth at a distance of only 0.2 AU (20% of Earth’s distance from the Sun).  The path, after a few days of tracking, showed that the body, now designated C/2017 U1, was “dropping” through the plane of the Solar System from far above the plane of the ecliptic at a phenomenally high speed. 

After a week of tracking it was clear that its speed was higher than any resident of the Solar System could have.  The eccentricity of its orbit was clearly about 1.2, which made it a unique body in the history of terrestrial astronomy.  Bodies in orbit around the Sun pursue elliptical orbits with varying degrees of eccentricity: a perfectly circular orbit has an eccentricity of 0.000, and most of the planets have e of about 0.05.  Mercury and Pluto, at the inner and outer edges of the system, have orbits with e = 0.2056 and 0.2566 respectively.  The most eccentric orbits are traditionally those of comets, with e rarely less than 0.9; long-period comets may have e as high as 0.9999.  The latter corresponds to a comet that approaches within 1 AU of the Sun at perihelion and coasts out to an aphelion distance of 10,000 AU.  A body whose orbit extends out to infinite distance would have an eccentricity of 1.0000.  Solar heating at such a distance would be incredibly feeble; at 100,000 AU other nearby stars would provide nearly as much light and heat as the Sun.

For comparison, Pluto is close to 36 AU from the Sun: a body at 10,000 AU would receive almost 1000 times less intense sunlight than Pluto.   At that distance, depending on the reflectivity of the surface, the body would have a surface temperature that is close to -272 ^oC, about 1 degree above absolute zero. 

After a few more days of observation the general nature of the orbit had become clear, and telescopic observations had revealed that there was no trace of an atmosphere, tail of gases, ices, or dust.  Its appearance was not cometary, but asteroidal.  The name was immediately changed to A/2017 U1.  These few days of further observation refined the orbit enough to fix the orbital eccentricity as 1.195+/- 0.001.  Clearly this body is not on a closed orbit around the Sun: it is an unambiguous visitor from interplanetary space; a citizen of the galaxy, not of the Solar System.  But late in October when this had become clear, A/2017 U1 was retreating from us at a speed of a little over 26 km/s.

It would have been fascinating to launch a spacecraft to fly to this body and even fly with it out of the Solar System, but there simply was not enough time to build and launch a spacecraft designed for such a challenging mission into the dark.

Other comets have been observed to depart at speeds close to Solar System escape velocity after being gravitationally “kicked” by Jupiter; in this case, it arrived from far out of the plane of the Solar System (orbital inclination of 122.55+/-0.05 degrees), already traveling well above the Sun’s escape velocity.

The body is roughly 160 meters in diameter; had it encountered Earth in its headlong rush through the Solar System it would have delivered a blow of 10,000 to 20,000 megatons of TNT, comparable to Earth’s global arsenal of nuclear weapons detonated in a single event.

What is it made of?  Evidence for ices and gases is lacking; astronomers find the surface to be very red, reminiscent of Kuiper Belt bodies, and compatible with a low albedo.

What is its shape?  The light curve of the body (the variation in its brightness as it rotates) would be compatible with it being 4 to 10 times as long as it is wide, an uncomfortably large variation that ranges from “unprecedented” to “fantastic” in comparison with native Solar System bodies.  Variations in brightness with rotation can be caused either by variations in albedo (as is the case for the 7-fold albedo variation with phase for Saturn’s satellite Iapetus) or in cross-section area (such as a highly non-spherical body), or by a combination of these factors.  Measuring the temperature of the body as it rotates (not available in this case) would permit separating these effects.

How common are these titanic “shots in the dark”?  We have less than 100 years of data to draw upon.  One event in the last century is a poor basis for making statistical predictions, but it certainly does merit our attention.  Global extinction events on Earth from all causes occur at a rate of one per several tens of millions of years.  How many of these arrive not only unannounced, but unobserved?

Want a Piece of Mars? It’ll cost you a billion dollars—or be free!

Anyone who wants a piece of Mars can imagine sending an automated spacecraft to land on Mars, grab a sample, and blast off for return to Earth.  No problem; just pay a billion dollars or so and you can have it!  Such a deal!  As they tell everyone in the bazaar in Istanbul, “Just for you!”

But asteroid and comet impacts on Mars happen from time to time, blasting fragments of Mars’ crust into orbit around the Sun.  Some of these fragments drift into Earth-crossing orbits; a few enter Earth’s atmosphere and a very lucky few survive entry heating to fall on the ground and be recovered as meteorites.  Most of them will never be recognized as meteorites, especially once their fusion crust weathers off.  A few decades ago we knew of only about two dozen such Martian meteorites, but since then we have reaped the benefits of meteorite searches in two locations where meteorites are so different from the local country rocks that they virtually stand up and say “look at me”!  One of these is the vast sand seas (ergs) of the Sahara Desert; another is the snowy wastes of Antarctica.  Rocks in either place are rare, and the overwhelming majority of them are meteorites.  In turn, the large majority of these Saharan and Antarctic meteorites are fragments of asteroids—but some are pieces of the Moon or Mars, and possibly other bodies as well.

To date some 200 meteorites found on Earth have been traced back to an origin on Mars.  Virtually all are members of three meteorite classes, shergottites, nakhlites, and chassignites, collectively called SNC meteorites.  They do not sample Mars’ surface either widely or democratically; they may indeed represent only three or four places on Mars where recent and unusually violent impacts occurred.  But they are real pieces of Mars, and they are vastly cheaper than a billion dollars!

Neither Fish nor Fowl; Neither Comet nor Asteroid?

The Hubble Space Telescope has presented us with telling images of a peculiar body that seems to share the attributes of an asteroid and a comet.  It has been christened with the double name 300163 2006 VW139/288P, alias P/2006 VW139, acknowledging its asteroid-like and comet-like traits and declining to make a decision between the two categories. 

The first part of the name attests that the body was discovered as an asteroid in October 2006, but the recognition of its strange appearance and its ambiguous identity had to await the Hubble observations a year ago.  The second part of its name identifies it as a body with cometary appearance (a tail) and a “periodic” orbit, meaning that it has a known orbital period.  And what should we call it?  The exceptional clunkiness of the name suggests nicknames such as “2006 VW”, which unfortunately conjures up a misleading (non-duplicitous) image.

A “video” of the body, constructed out of a number of snapshots taken as it rotates, can be found at http://hubblesite.org/videos/news/release/2017-32.  Form your own opinions (and suggest your own nicknames).

So what do we see when we look at that video?  Two bright, roughly equal-sized apparently solid bodies, just a few body diameters apart, trailing a bright “tail” of generally cometary appearance.  The tail appears to be a dust stream rather than a gaseous tail, tempting us to speculate about the chain of events that produced this strange display. 

The “just-so” story has to take into account the duplicity, proximity, and activity of the body.  There are several possible scenarios to consider:

1a and b. Collisional Fission.  An asteroid in the Belt was recently clobbered by a glancing impact sufficiently violent to get it rotating fast enough to fission into two bodies in very close orbit about each other, perhaps even a contact binary.  This happened so recently that the dust sprayed out by the impact has not had time to dissipate.  Sounds improbable, but there are examples galore to whet our imagination.  The Trojan asteroid 624 Hektor was studied in 1980 by a former student of mine, Stu Weidenschilling, and interpreted as a contact binary; a Wikipedia article on “Contact Binary: Asteroid” lists 13 strong candidates for the same distinction.  At least two comets (67P/Churyumov-Gerasimenko and 8P/Tuttle) also appear to have the same structure.  Such structures can arise either by (1a) the glancing collision of two large independently-orbiting bodies or by (1b) rotational fission of a single asteroid that was spun up to the point of splitting apart by a relatively small but sufficiently violent impact event.  Since the encounter velocity of two asteroids in independent orbits around the Sun is typically several kilometers per second, the overwhelming majority of asteroid/asteroid collisions must result in explosive disruption rather than capture into closed orbits.  Low-velocity encounters must be rare; but contact (or near-contact) binaries ARE rare.  The dust-generating activity can then be attributed to the collision event, which must have been fairly recent; otherwise, the dust would have been swept up by the bodies or blown away by solar radiation pressure.  Oh, we also know from independent evidence that 2006 VWs may survive low-velocity collisions. 

2.  It is just a comet whose gas emission is undetectably small, but sufficient to maintain a dust cloud, according to H. H. Hsieh and 41 other coauthors, Discovery of main-belt comet P/2006 VW139 by Pan-STARRS1, Astrophysical Journal Letters, 748 (1). (L15) 1-7 (2012).  They interpret observations by the Pan-STARRS1 survey telescope as showing a striking similarity to the main-belt cometary object 133P/Elst-Pizarro, which has a rather similar orbit.  Both may be outliers of the Themis family of main-belt asteroids.  They argue that the stable maintenance of the dust cloud is indicative of cometary outgassing, most likely of water vapor, but they are also unable to detect any gaseous molecular emissions spectroscopically.

If I had to bet on the strength of present evidence, I’d have to prefer the latter explanation.  The implication of a very high water content in some Belt asteroids is worth remembering—especially if you are a water-based spacefarer.

See also: 

https://www.space.com/38214-spitting-asteroids-hubble-telescope-discovery.html?utm_source=sdc-newsletter&utm_medium=email&utm_campaign=20170922-sdc