Asteroid of the Half-Month: 89 Julia

Wow, what a summer. Two missions aside, the IAU just had its big meeting.

Our Solar System is a vast place, with almost a million known bodies, and a few million more lurkers, mostly in the smaller (sub-km) size bins. They formed from hundreds of planetesimals, themselves formed from smaller chunks. Some of the planetesimals crashed to bits; some of those re-formed with other fragments. We trace this jigsaw puzzle with chemistry (elemental and isotopic tracers) and dynamics (perturbation and impact studies).

If two puzzle pieces are the S-type (stony) asteroids and C-types (carbonaceous chondrites), then solving the puzzle includes the relationship between the two, and between them and other Solar System pieces. We already saw that there’s no true line between wet asteroids and depleted comets. We saw at 88 Thisbe that the C-complex actually includes a wide range of bodies and materials. Let’s look next to… asteroid 89 Julia, a ‘carbonaceous stony’!

In recent years, we’ve gotten much better at classifying asteroids (not that we’re there yet). We have also collected far more meteorites, clearly pieces of astero-cometary materials. Meteorites are a bewildering variety of classes and subclasses. What chemicals and their mineral forms link which meteorites to which SSSBs (Small Solar System Bodies)?

In the past decade, we have not only found a key link, fitting two (or more!) puzzle pieces, but there’s some chance we hold a linked sample: a lucky bit of 89 Julia itself.

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 III

Of all the challenges found by the new Hayabusa space probe (and there were lots), none involved lugging giant instruments around the Solar System. The entire craft weighed just over 500 kg, and a quarter of that was propellants. Scientifically, the investigations aboard Hayabusa were sufficient, not bleeding-edge. Things like high-resolution telescopes were left on Earth, as they should. Instead, particles of 25143 Itokawa were taken to our giant instruments- a sample return mission. Such were the open questions left by the Galileo mission, NEAR, etc.

Hayabusa did not visit 4660 Nereus as first planned. That would have been nice, but a C-type body was left to Hayabusa 2. Itokawa is, rather, an S-type; a sample would settle the issue of ordinary chondrite meteorites and S-types in a way that Galileo and NEAR only inferred. We see lots of S-type asteroids in our telescopes- they’re the number one type in the inner Solar System. And we have plenty of ordinary chondrites that fall to Earth- again, they’re the most common. Yet S-types don’t look like OCs, but like stony-iron meteorites.

Itokawa flew past Earth in 2001. Telescopes around the globe got observing runs, if for no other reason to lower risks for Hayabusa operations. Jun 2004, as Hayabusa was in flight, Itokawa made its next Earth pass. It came within two million km, under half its 2001 range. This was part of the logic for Itokawa: an easy target, with a favorable, Earth-crossing orbit (“low ΔV”). Even if Hayabusa failed, mustering the astronomy world was an achievement.

Hayabusa did not fail, but got over 1500 particles from a known body. The craft’s (lightweight) instruments also rendered data (and knowledge) of the sampling site. We know how our samples fit into contexts- of Itokawa as one example of asteroid diversity, and the site as one example over Itokawa’s surface. Not some random outlier, from some random body.

Ground telescopes, flight probes, and sample examination combine in complementary ways. Let’s look at not just a space body, but the investigation process: Solar System science.

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: 25143 Itokawa Part I

If you’re reading this- in English, off the internet- odds are good you’re not Buddhist. But you are a driver, or you trust car owners. Drivers are in your community, your circle of friends, workplace, likely your household. And you’re all certainly eaters. We can thank the Japanese (later Taiwanese, Koreans, etc.) for cars and consumer electronics. Yet not large-scale rockets, airliners, and similar aerospace pursuits. Why not? What’s the difference?

We (as in Western, educated, industrialized, rich democracies) hold positive images of ‘Japanese things’. That phrase, for a long stretch of time, conjured thoughts of your Sony stereo, the Honda in the driveway (and not in the shop), maybe the Lexus you wish was in the driveway. In this same period, the Japanese image of ‘Made in America’ was of substandard quality, possibly including the Space Shuttle blowing up. And that Americans are fat. They do buy tickets to Hollywood blockbuster productions, though, and ride Boeing airliners if not Chevy pickups. Tacitly, Japan’s space efforts are substandard. Again, why?

Like most nations, Japan started with sounding rockets- small, suborbital launchers for atmospheric studies, the aurora and ionosphere, etc. Since these are smaller, cheaper vehicles, they’re appropriate and accessible to learn rocketry and space hardware and operations. (This is where Brazil is now.) They also resemble tactical missiles- the short-range weapons most armies, navies, etc. buy, which makes production rates high. Japan’s sounding rockets include the Lambda series. As in Western practice, Greek is built into academia and science.

If one tries larger and larger rocket classes, though, the curve doesn’t just taper off, it breaks…

AotHM: Eros Part 4

For as long as there has been an S-type, 433 Eros was called an S-asteroid. See: Chapman Morrison Zellner 1975, Zellner Gradie 1976, Bowell et al. 1978, Tholen 1984, and Bus Binzel 2002. A probe to Eros- the closest, best-studied, big S-asteroid- was sought, to get many answers. What are S-types like, and made of? (Implying their history, and the conditions of the early Solar System.) Do we have samples, via meteorites? Which?

(This would be a good time to review meteorites, per my last post. There are stony, iron, and stony-iron meteorites. Stonys are further divided into achondrites (fully molten, once) and chondrites (never molten). A few are primitive achondrites (barely molten).)

S-type asteroids dominate the inner Main Belt, and the planet-crossing zone (that is, near-Earth objects). We backtrack the trails of meteors; they, like Eros’ orbit, lead out to the Belt. One would expect to find S-pieces on Earth. Of the meteorites, stonys dominate irons and stony-irons. Stonys (technically, ‘ordinary chondrites’, OCs) are ~80% of all falls. Yet, the most common asteroids do not look like the most common falls. S-asteroids’ minerals look like stony-irons, only ~1% of all meteorites. This would imply stony-iron fragments are missing or shy, but there’s a secret pool of stonys, bombarding Earth somehow.

The Galileo mission to Jupiter seemed to find an answer. Passing 951 Gaspra (in 1991) and 243 Ida (1993) on its way, it observed younger areas to be a bit bluer and more ordinary-chondrite-like, than old areas. S-types get ‘space weathering,’ a thin coat hiding the bulk minerals (which are OCs). A flyby of course gives a less than thorough view, while chronic Space Shuttle delays made Galileo fly with late ’70s/early ’80s technology… and a busted antenna. The NEAR mission (Near-Earth Asteroid Rendezvous) would orbit an S-type in 1999, using many, modern instruments, and to be sure a rigid antenna. What did it find?

Asteroid of the Half-Month: 15 Eunomia

We’ve seen 4 Vesta to be a differentiated body (core-mantle-crust). We’ve seen 16 Psyche to be a fragment, post-differentiation (likely metal core, with minimal rock layers left). In hand, we have HED meteorites as Vesta samples, and iron meteorites as Psyche-like samples (possibly actual samples of Psyche). But these aren’t the only differentiations seen in the small bodies. 15 Eunomia looks like a piece of differentiated body, going from deep mantle on one side, up to crust material on the other. If so, Eunomia may be our first “tree rings” asteroid.

In the course of astronomy, we refine our understanding of any one target. Solar System points of light are tracked (orbit determination) and measured in brightness (photometry), then sorted via their reflectance properties (colorimetry at first, then spectrometry). One pixel turns into a Solar System object; with enough orbit and color data, a target is sorted by our small-body types. Each type seems to be some variation of minerals. Some minerals, with prominent spectral features, can be found via good spectroscopes.

Sorting Eunomia, a rare thing happened. As nonround bodies spin, brightness changes- first broadside, then, end-on. Broadside reflects more. But if we break down overall light into its colors, each color may cycle differently. The sides must be different colors. As Eunomia spins, good enough spectroscopes see two minerals cycling. One side is metal-rich olivine, one, pyroxene. Meanwhile, Eunomia’s region has many asteroids in similar orbits- the Eunomia family, likely fragments of a parent body. Eunomia, at 200-300 km, is the largest fragment by far. Since olivine is mantle rock, and pyroxene is found in basalt (a lava, flowing onto surfaces), that says the parent body was even bigger, molten, and grew a core, crust, etc. Eunomia is then a “layer cake” of differentiation, and thus planet formation.

Asteroid of the Half-Month: 243 Ida I Dactyl

You didn’t think the first asteroid moon we’ve found would get off that easily, did you?

Asteroid satellites had long been suspected before Ida/Dactyl. Scientists had rejected “the exploded planet” origin for all asteroids, but later found “many, exploded parents” for many of the asteroids. Meteorites are pretty much assumed to be asteroid fragments; small asteroids appear in many ways to be fragments of bigger asteroids. Comets were seen to break apart sometimes. Double craters and multi-crater chains have been found on the Earth, Moon, etc. with the same age indicators, suggesting paired impactors, or swarms. A reasonable person would expect some fragments would stay around some parent bodies.

The Galileo mission then spotted Dactyl (formally, 243 Ida I Dactyl), around the second asteroid ever visited by a mission. (All this, despite not being originally designed to observe asteroids.) A moon would tell us Ida’s mass, by showing the pull of gravity between the two. More generally, craters and fragments should be an indication of the impact history and overall dynamics of that region of the solar system. But, like Lutetia, this body offers some answers and begs more questions. Some of this was just blind, dumb luck, not (just) the technology and skill of the Galileo spacecraft and operations team.

Asteroid of the half-month: 243 Ida

Galileo looks bad today. Its camera (SSI- Solid State Imager) was one of the first digital (CCD) probe imagers. At 800×800 pixels (0.64 megapixels), and 8 bits, the builtin camera in your laptop or in your pocket embarrasses it. The SSI optics were the Voyager spares, themselves based on Mariner 10’s glass. Galileo’s infrared instrument was IRAS-era. To make matters worse, the jammed radio dish and limited tape recorder (remember those?) meant even 0.64 megapixel images came in very slowly. Yet, Galileo made important discoveries at 951 Gaspra and 243 Ida- that’s first mover advantage for you.

Ida, a ‘fast rotator,’ did a full pirouette before Galileo; the entire surface, except for some deep shadows, was seen down to 25 meters resolution in places. The stuck antenna meant that ‘jailbars’ (occasional lines of the full frame) were sent down first, to prioritize later downloads. Those jailbars already revealed a larger Ida than ground telescopes indicated; a very jagged shape, and the first asteroid satellite- 243 Ida I Dactyl. If a moon was found without even really trying, then asteroid moons, one would figure, should be common.

The albedo was darker, the mass and density lower, but the classification stayed the same. Ground observers had called Ida an S-type asteroid, and a link to the ordinary chondrite meteorites was then announced. This was no stretch- S is a broad asteroid complex, not a declaration of a single type. It’s the most visible single complex in the sky. Meanwhile the ordinary chondrites are around 80% of all meteorites. Connecting the S asteroids to OC meteorites is hardly bold. Yet, LL chondrites were soon hypothesized too. Twenty years later, P. Heck would postulate that a recent, nearby collision of a chondrite explains the prevalence of such meteorites, not (necessarily) the S asteroids. And we’ll get to the Qs later.

Stone Sweet Stone

Apollo objects- no apollo-program knockoffs

S-type