50th Landi-versary: Murchison

1969, in retrospect, was the year of the Allende meteor event and its recovery– overall, 2 tons of primitive material from the Solar System’s birth. It’s the single largest carbonaceous chondrite meteorite, which we classify as a CV chondrite. Another groundbreaking event happened 50 years ago: the Murchison meteorite, the largest of the CI or CM (aqueous) meteorites.

Fragments recovered near Murchison, Australia total far less than Allende- about 100 kg. This is still huge: CV carbonaceous chondrites are actually just ~1 percent carbon compounds, and only a bit of that is native carbon (graphite, tiny diamonds, etc.). We call these meteorites ‘carbonaceous’ since the ‘ordinary chondrites’ have even less- a fraction of a percent carbon. At the birth of the Solar System, carbon tended to form gases (carbon oxides and hydrides, i. e., organics) which tend to blow away instead of forming solid objects. Despite the fact that the forming Solar System had appreciable carbon, a lot dispersed to the galaxy. But CI and CM carbonaceous chondrite meteorites have more carbon- ~2 or so percent. The CI/CMs had never been heated, not to magma temperature, and not to serious oven temperatures, either. They now retain more light chemicals- organics, sulfates/sulfides, and water.

This is why 100 kg is big and important. Allende and similar chondrites are overwhelmingly rock and other durable minerals. They hold up, even when plunging through our atmosphere in a fiery display. CI/CM chondrites aren’t rock so much as clay. Water exposure has broken down most of their rock into layers or particles; when heated and stressed by atmospheric entry, the particles/layers often disperse instead of landing. Landing and Earth weather then keep damaging them. CI/CMs are thus rare, sought-after examples of the early Solar System.

And then came Murchison…

Asteroid of the Half-Month: 25143 Itokawa Part IV

I had posted that the Hayabusa project was groundbreaking for Japan. That it was an ordeal in flight, lucky to survive. And that it did valuable work, even in space before any samples of Itokawa were returned. But Hayabusa did return a sample- a gift that keeps on giving.

More words may have been written/”uttered” about Hayabusa/25143 Itokawa than any other asteroid… aside from my posts, three feature films were made about the mission, and played in theaters, homes, etc. Even if you don’t count mass media, the ongoing Hayabusa Symposia- conferences presenting Itokawa research- have no shortage of topics to discuss. The first solicitation (for a chance to do experiments on Itokawa particles) went out to the world’s scientists in 2012; now (2018) we are nearing the 5th Symposium for Itokawa results.

There’s a Hayabusa 2, of course, now at 162173 Ryugu. Less obvious is that NASA’s OSIRIS-REx mission (to 101955 Bennu) is ‘Hayabusa 2.5’ and private space companies are developing ‘Hayabusas: The Next Next Generation.” NASA’s * of *, Jim Green, has billed the coming years as “the Decade of Sample Return”, with sampling missions to Mars and a comet being designed. In the nearer term, Japan’s own MMX (Martian Moons eXplorer) was just approved as a ‘Hayabusa 3.’ It is to bring back material from Mars’ moon Phobos.

Let’s not get ahead of ourselves; Itokawa particles may be tiny, but our results from them go wide. First is that Itokawa material matches one type of meteorite, the LL chondrites. Studying the meteorites alone is like picking up a bottle on a beach, and eventually calling oneself a glass engineer. You have nothing but the broadest inferences about that bottle’s factory and processes.

Asteroid of the Half-Month: 25143 Itokawa Part II

Soichiro Honda (yes, that Honda) once got asked the secret of his success. He reportedly said ‘One word: lucky.’ During the rise of Honda and similar manufacturers, Japan was dismissed as a land of cheap knockoffs. That era is clearly done. Japan has done the world’s first asteroid sample return, Hayabusa, though luck (good and bad) was clearly part of its story.

Japan has long wanted asteroid materials. In Jun 1985, nearly two decades before the launch of Hayabusa, a sample return meeting¹ was gathered. This itself was after NASA and the NSF led an oversubscribed, 1971 international conference² on asteroid exploration. In that and the following years, Peak Oil and the embargos added even more urgency if not funding. Through Hayabusa, we found something even more enabling: water in space.

Quick recap: the Hayabusa mission launched in May 2003, reached asteroid 25143 Itokawa, and gathered a sample. It returned in Jun 2010, dropping a reentry pack.

But back to 1985. That year, a Japanese team was assembled to analyze sample returns. They devised a mission to 1943 Anteros and back. Its trajectory was “surprisingly but accidentally very closely identical to the orbit of Hayabusa.” However, given 1985 technology (like chemical rockets) the mission was far too big and heavy (Kawaguchi et al. 2006). But by 1994, the Clementine probe had tested miniaturization, in flight. Crude forms of electric propulsion were flying, and ion thrusters were about to (gradually) take over communications satellites (such as Japan’s own ETS-6). Before Clementine even disbanded, a new Japanese team had formed, to study electric rockets for Mars and Near-Earth Objects (NEOs). They moved fast (for space), publishing a paper the next year on electric-thrust sample return (Kawaguchi et al. 1995). That mission got approved by Apr 1996, the start of Japan’s next fiscal year.

You may be thinking ‘April 1996 approval to May 2003 launch? What took seven years?’

AotHM: 87 Sylvia

If there’s a touchstone asteroid, this is it: 87 Sylvia invokes everything posted on this site, from asteroid spectral signatures, to asteroid moons, collisional families and other orbital dynamics, organic chemicals in space, asteroidal water ice, and gravity/tide effects. Sylvia also happens to be the eighth largest asteroid by size, at ~380 km long and somewhat less in width.

Going by telescopes alone, Sylvia was a dot. Still, we can study the spectra (color signatures) to classify bodies by surface material. Asteroids usually split into S-type (rocky, plus some metallic character) and C-type (rock, with carbon compounds). Oddballs fell into “X” or “U” (Unknown) classes, before we subdivided those into better categories. There are transitional objects too, not neatly pigeonholed; they may get two letters. Sylvia, at various times, has been called an X, U, or C asteroid, until the P-type emerged as a subtype of X. In the ’70s, one poor scientist simply listed it as “CMEU”- being on the safe side, perhaps. In any case, Sylvia isn’t rock and metal; P-types are primitive, made of stuff little changed in billions of years.

In orbital terms, Sylvia is in the outer Belt. Way out- the Cybele group (named for asteroid 65 Cybele) is a population of objects we take to be the Belt’s edge. (Fuzzy as that may be.) In the Cybeles, Sylvia is in a collisional family, the Sylvias. Asteroid families are assumed to be fragments split from their largest member, or maybe a parent body that was destroyed in the family-forming impact. Other large bodies in the Sylvia family include 107 Camilla; the Sylvias themselves may be related to the other Cybeles somehow.

Sylvia was then found to have a moon- two, in fact, a triple asteroid. With adaptive optics (AO), the shimmer of the atmosphere can be reduced. Large telescopes, aided by AO, can reach stunning resolutions. As AO developed in the late ’90s, we began spotting not only asteroid shapes but asteroid moons. 45 Eugenia had Petit-Prince; then in 2001, we found Romulus orbiting Sylvia. In 2004, Remus was also seen; rechecking Eugenia found Princesse. These moons act as gravity gauges; the moons of Sylvia tell us Sylvia is… a giant comet.

Asteroid of the Half Month: 24 Themis (etc.)

It’s simple: asteroids are rocks, comets are ice, right? So comets shed a coma and tail when they approach the Sun, and warm up, right? No, it’s simplistic thinking: the cosmos does not divide neatly for the convenience of human perception and notions.

The Themis family of asteroids was one of the original asteroid families identified by Kiyotsugu Hirayama in 1918. “It has been identified as a family in all subsequent works” (Florczak et al. 1999) including analyses by multiple sort criteria. We widely assume that families form when a parent body is smashed by collision; its pieces then orbit in scattered but visibly related orbits. In this case, Themis-family objects orbit as a group in the outer Main Belt. A century after Hirayama, we now see that 24 Themis and its kin not only have identical or related spectral types. Many have a similar- icy or otherwise hydrated- composition, too.

The past twenty years have seen the emergence (to humans) of a new Solar System class: main belt comets. The Minor Planet Center gives them dual status: both asteroid and comet. This is apart from 2060 Chiron, orbiting between the gas giant planets, not in the Main Belt. Chiron grew a coma when closest to the Sun, indicating water loss. That wasn’t surprising; gas giants orbit past the “snow line” (inward of Jupiter) where the dim sunlight lets water ice persist. But the entirety of the Main Belt is in the snow line; asteroids were assumed- by definition- to be pretty dry, and incapable of any coma or tail. Let the assumptions end, via Themis “comets.”

Carbonaceous chondrite meteorites test out to 10% water or more, sometimes past 20%. The asteroids of the C-complex, including Themis-family objects, seem to be carbonaceous-like material. Florczak et al. go on: of 36 Themises checked, “Indications of aqueous alteration…is clearly present in the spectra of 15 asteroids… If a more relaxed criterion is adopted, 11 more objects could also present aqueous alteration in their surface.” Main Belt aside, we found comets to be not white like snow, but black, like C-asteroids (plus D-, P-types, etc.).

The past twenty years were no surprise; growing evidence indicated wet asteroids…

Moonies V: Why We Don’t Go Back

Not only is Earth’s Moon less economical (in terms of propellant) and economic (in terms of accessible resources) than near-Earth objects. It’s also less interesting; there is literally less science to be found on the Moon.

Quick recap of differentiation: a large-enough body holds heat. Heat melts rock; molten rock splits into heavy and light parts. The heavy parts (metals) form a core. The light rock forms a mantle, and a lighter crust. The lightest stuff (volatiles) boils off completely. Earth is large, and clearly differentiated.

Before the Apollo program, scientists had ranged widely on the origin of the Moon. After Apollo, there still isn’t a lone model standing. But all options had some impactor hit Earth, and spray out rock which re-formed into a Moon. It’s the various details still being pursued.

Earth’s mantle is distinguishable from its crust; the mantle is rich in olivine, while here at the surface olivine is unstable. Apollo managers, studying the Moon, wanted mantle rocks for comparison. Astronauts found none; later, the South Pole-Aitken Basin was identified as a huge impact site, 2500 km (1560 mi) across. It’s the largest on the entire Moon. Time and again, missions got proposed to return Aitken Basin samples; surely the enormous impact must have excavated through crust, into the lunar mantle. Again, every proposal was rejected. Yet, on Feb. 8, 1969, the Allende meteor had fallen on Mexico. Allende is full of olivines.

Asteroid of the Half-Month: 16 Psyche

16 Psyche is so metal… and it’s still a hydrated asteroid, valuable on multiple levels.

A young planet differentiates when metals drop out of magma, becoming a core. Psyche, at ~186 km across (116 mi), looks like the core of a “planet” that no longer exists. The young Solar System had many planetesimals. Most were destroyed in impacts, hurled into the Sun, or hurled out altogether. A few winners, though, grew from multiple planetesimals to be today’s planets. The best Psyche hypothesis is that a planetesimal, big enough to get a metal core, was small enough to lose in a collision. Yet the small, strong core survived; its rock layers got lost to the ages. If so, it’s our best way to study planet cores- better even than Earth’s own.

We had some prior grasp of planetary metal (small metal asteroids aside). Iron meteors fall to Earth. They’re mostly iron, at least 5% nickel, then iron-soluble elements like cobalt, pulled in by iron. We also see the signs of the elements in the Sun; they leave a spectral imprint in sunlight. Iron meteorites have element abundances like solar abundances, after you shed gases and rocks, as planet formation and differentiation does. The iron had to be in a core, as crystals take time to grow from liquid. More cooling time, larger crystals. Iron alloy crystals are inches, which would take a million years. Cores stay hot for a million years, boulders don’t.

And yet, a possibility exists that Psyche was never a core, but formed other ways. Solar system simulations yield a Psyche in a small percentage of runs. Was our system just lucky, or did something else go on? Is Psyche a coincidental ball of other iron meteoroids? Not the parent body of such meteorites, but really their monster child? NASA wants to find out, like others studying star-system formation… and others studying water resources.

Asteroid of the Half-Month: 10 Hygiea

Every Mars mission is actually an asteroid mission- and I don’t mean Phobos and Deimos as quasi-asteroids (though we’ll get to that eventually).

Gravity’s a funny thing, in slapstick, the cosmos, and our spreadsheets. It permeates space, even around objects, and in places we can’t see. Reading gravity fields can be a sixth sense for those who choose to become literate in it. Miners read higher gravity as one sign of ore deposits; lower gravity is one sign of oil. As we kept learning about our Solar System, the more astute among us learned to use gravity to mine more knowledge; we’ll use that knowledge to literally mine the Solar System.

10 Hygiea was the tenth asteroid to have its orbit determined (back in 1849), hence 10 in its official designation. It’s the fourth largest one, however, since it’s dark, and in an outer range of the Asteroid Belt. Less light reached our telescopes, and six smaller asteroids got seen before Hygiea. But don’t think some sort of boondock dim bulb would be unknown, or unimportant. The more astute of us know how to study even a single pixel. Like Mars, we can use one pixel to read into that body, and other asteroids too. Far more than six other asteroids, and I don’t mean just the Hygiea family (numerous nearby asteroids, likely pieces from it). Being one point of light, in the outer Belt, actually helps in some ways.

Moonies IV: A JU Hope

Previously: Moonies I, II, and III

I’ll say it: Moon mining’s a joke. No one’s due diligence would back lunar material extraction, because what material?

The Moon doesn’t just lack metals compared to asteroids. Asteroids beat it in both metals and volatiles at the same time. By comparison, the Moon looks like reheated leftovers. The 2009 news of lunar ice (at its poles) doesn’t upset any carts because that water is mostly secondhand asteroid water. Asteroid water which is easier to extract and process too. And if, for certain reasons, you want depleted rocks, a suitable choice of depleted asteroids is also there for the taking. This is all independent of the transport issue, which I’ve described in the previous entries.

All planets are differentiated. When forming, they were molten, and things separated by weight. Dense materials sank to form a core, and light ones floated to form a crust; in between, a mantle. The core is basically iron, while crusts are, to the layman, sand. A better question is how much is plain sand (silica), versus exotic stuff like some of the world’s glamorous beaches. In the Moon’s case, all surviving origin scenarios had rock spraying off the Earth, and re-forming in orbit. The new body is big enough to retain the heat of its violent birth for a while, and differentiate again. That is, the lunar crust is double depleted of metals.

Stone Sweet Stone

Apollo objects- no apollo-program knockoffs

Asteroid water