Asteroid of the Half-Month: 2685 Masursky

I went long on the last two, so this one will be shorter. We go to 2685 Masursky, which got a distant flyby from the Cassini mission on its way to Saturn. Cassini passed 1.6 million km (1 million miles) from the asteroid in Jan 2000, and saw it as ‘a dot’. Still, this is an opportunity to demonstrate just how much scientists can learn from ‘just a dot’!

The low number indicates that Masursky had its orbit determined a while ago, before our sky searches really unleashed the asteroid hordes. After brief but indeterminate sightings in the ’70s (and even an old one in the ’50s), Masursky finally got enough of a dataset to become a numbered asteroid in the early ’80s. This was in the film era- remember film?

Masursky’s orbit shows that it’s in the Eunomia family- that is, an asteroid swarm, moving together in space. The numerous family members, and their close orbits, are not felt to be an accident- 15 Eunomia likely split into a family by collisions. Masursky is a bit off, not in the family ‘core’, but not that far. And that was pretty much it for almost twenty years, until Cassini.

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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.

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Asteroid of the Half-Month: 88 Thisbe

Most small bodies fall in two camps: neutral (grey) or “red.” This runs through the Main Belt, even the Kuiper Belt past Neptune, and among comets. Granted, red isn’t like a stop sign, more of a tint in grey. Still, the division’s there. There aren’t green or blue asteroids… except the rare B-types. Large asteroid 88 Thisbe is B, and a crucial puzzle piece.

Most asteroids are C- or S-type, the above greys and reds respectively. Lesser classes like E- and D- fit the division too, for various reasons. In the S-types, iron content, especially when weathered by space exposure, adds a faint redness. C-type is named for measurable carbon contents; this overwhelms iron with an absorbent but neutral color. The C-bodies are thought to be more primitive, formed in cooler temperatures than S-. Carbonaceous meteorites, thought to be C-fragments, have mineral levels like the Sun, and are thought to represent the levels present as our Solar System formed from a cloud- the “presolar nebula.”

When the types were first offered in the late ’70s, C- and S- were obvious, but there were misfit bodies. Various planetary scientists claimed lesser classes, or simply U- (unknown) or X-type. Meanwhile, meteoriticists were subdividing the carbonaceous meteorites. As typing grew firmer in the early- to mid-’80s, it grew clear that C- and S- were groups or supertypes, needing subdividing too. The “C group” or “C complex” covers classical C-bodies, and the lesser B-, F-, and G-types, also thought to be carbonaceous, but varying somehow.

Studying any of the C complex informs us of the other types, by comparison, and counterexample too. This is “comparative planetology”- no part of the Solar System is boring if you want to solve the jigsaw puzzle. Since C bodies inform us of carbonaceous meteorites and the Solar System’s birth, fitting in bodies like 88 Thisbe tells us where we came from, and how we got here. Since carbonaceous bodies are also wet, they’re where we can go.

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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.

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Search Status July 2018

One year later, where are we in the quest to tally the Solar System? As of Jun 30:

-779736 total objects, including 4021 officially designated comets
-18436 Near-Earth Objects (NEOs), regardless of activity or composition
-1914 of those Potentially Hazardous Asteroids (PHAs)

In the past few months, volcanic clouds have had a significant effect on a nexus of astronomy. Activity at Kilauea reduces yields from atop Mauna Kea, and even Haleakala. The past 12 months have been behind the pace of the prior reporting period, and certainly no gain over that period, as the discovery history’s upward curves would imply.

All these are gains, of course- 46,468 more objects than a year ago, 135 more comets, 2,066 more NEOs, and 98 more PHAs. We’re just not as far along as we would be, had we more diversity in observatory sites. LSST in the Southern Hemisphere is still a few years off.

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Comet Of The Quarter: 9P/Tempel 1

Comet hunter David Levy once said ‘comets are like cats have tails do what’ In Comet 9P/Tempel, we had the opportunity to sneak up on the cat, instead of vice versa.

9P/Tempel is often called Tempel 1, versus all of Wilhelm Tempel’s other comet discoveries, or simply Tempel. It was chosen as the target for the Deep Impact mission, part of a next generation of comet probes after the Halley Armada. Tempel 1 was chosen primarily for its favorable orbit, not due to any inherent science like activity (emissions of gas and dust). In fact, there was a period when it was suspected Tempel 1 was dormant or extinct (no activity).

Tempel 1 was never a bright, showy comet. It basically stays past Mars’ orbit, and thus stays fairly cool and inactive. After Wilhelm discovered it during its 1867 pass by Earth, it passed Jupiter in 1870. Jupiter’s gravity tugged its orbit wider; the comet’s 1873 apparition was even further out, and it looked less active still. Another Jupiter flyby was in 1881, and the comet wasn’t spotted again until 1972. Some suspected all volatiles in Tempel 1 had been exhausted. We now know Tempel is a Jupiter Family Comet (JFC): its orbit, and very existence, is bound to that giant planet’s gravity and a 2:1 resonance. Tempel orbits the Sun, alternately under or over two times for every Jupiter orbit, when a tug by Jupiter pulls it closer or farther.

Tempel 1’s orbit is now well-studied; it had not gone dormant, as jetting effects (or their absence) would have varied the comet’s orbit. It is this orbit, and a consistent, mild emission history, that compelled a NASA-funded mission to form a new crater via an artificial crash.

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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.

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