#24 April 1989
Section 18.104.22.168.024.of the Artemis Data Book
Ceres, Pallas, and Vesta
DIAMETER: 1003 kilometers or 621 miles.
SURFACE AREA: 3,160,000 km2 (1,219,000 mi2)
COMPARISONS: slightly larger than either of:
- all the U.S. east of the plains states (i.e. not incl.
Dakotas thru Texas)
- all the U.S. west of the plains states
- Queensland plus Northern Territory
- All the Moon's nearside seas together except the Ocean of Storms,
CLASS AND COMPOSITION: Carbonaceous chondrite.
Stony (silicates and metal oxides) with admixed ice and hydrates.
ROTATION PERIOD (one sol): 9.08 hrs.
POSSIBLE RATIONALIZATION: A two date cycle of 5 periods would yield
dates of 22 hrs 42 min. A three date cycle of 8 periods would yield
24 hrs 12.8 min.
GRAVITY: 19% Moon's, 8.31% Mars', 3% Earth's.
DISTANCE FROM SUN: 381-447 million km
237-278 million mi.
COMPARISONS: Ceres averages 2.77 times the Earth/Moan distance from
the Sun. To collect the same amount of solar energy as a 1 meter diameter
collector on the Moon (or a 1.512 meter collector on Mars), a collector
on Ceres would have to be 2.77 meters in diameter (7.67 x the area).
Ceres was the first asteroid to be discovered and is by far the largest and may contain as much as one third of the total asteroidal mass. As you can see from the 'illustrated' statistics above, Ceres may be a small body in comparison with Earth and even the Moon, but it is quite a big little world all the same. In diameter Ceres compares to the Moon (1:3.48) as the Moon to Earth (1:3.67). What would it be like to live on Ceres? All the clues lie in the data above.
Ceres gravity, the largest in the Belt at 33 cm/sec2, may yet be too low for human physiology to adjust to without degrading to a level most might consider unacceptable. All the same, it is a sure bet that some humans will ignore the recommendations and make that adjustment for better or for worse.
Those not wishing to put human adaptability to the test, could have any level of gravity they desired, Lunar, Martian, or Terrestrial, if they lived in a rotating habitat. This could be achieved in three basic ways:
Each of these would require shielding. The second option would be easiest to shield, the third possibly cheapest to build. It is likely Ceresians (Cerians?, Cerealians?) would spend part of their day on the low-grav surface, the rest in the higher-grav habitat. What works for Lunar architecture will not work on Ceres. On the Moon (and Mars), internal habitat air pressure can be counterbalanced, at least in part, by the overburden of shielding soil. In Ceres' low gravity, it would take five to six times as much shielding mass as on the Moon to achieve the same stress relief. So habitats on Ceres must be built as if they are spaceships or surface vehicles, probably cylindrical or spherical. Secondly, the soil on Ceres may be in a permafrost condition. It would then be necessary to excavate a larger trough and backfill with dry rock to prevent the heat-radiating habitat from slowly settling deeper into the soil.
What purpose could an outpost on Ceres serve? The asteroid itself probably has enough of everything (clay-like hydrated silicates, some metals, water-ice, carbon rich compounds etc.) to supply its essential needs but is unlikely to have export-grade mineral wealth. Rather, such an outpost would serve as a regional outfitting, resupply, maintenance, and service center (including hospital, educational, judicial, cultural etc.) for mining ventures to more richly endowed asteroid bits within easy delta-V range.
If the stats for the first 100 asteroids to be discovered are typical, 44% have orbital periods within 1O% of Ceres' so that one third of these or almost 15% of all asteroids would be within 60 degrees of Ceres at any given time and remain there for fifteen years or longer before drifting out of range. Some asteroids will 'fly in formation' with Ceres for centuries. Two target groups suggest themselves: the 'out-fronts' ahead of Ceres but in slower larger orbits, and the 'in-backs' behind Ceres but in faster smaller orbits. At any rate access to 15% of the Belt should do us well for quite a while. To compliment Ceres as regional centers, 210 km wide #88 Thisbe (takes 1415 yrs to drift 120 degrees with respect to Ceres) and 163 km wide #39 Laetitia (3540 yrs to drift 120 degrees) might serve.
In time, engineering development for belt needed equipment (prospector ships and tools, mining equipment, mass drivers, smelting equipment) could switch from the Moon to this regional center. Experience gained on this colder, wetter world could prove useful for ventures beyond the Belt.
Here is a short pool of names from which features and installations might be named. PIAZZI discovered Ceres in PALERMO, Sicily on the first day of CENTURY NINETEEN. Ceres was the Roman goddess of grain, and she chose the mortal TRIPTOLEMUS to carry her knowledge (the plow, agriculture) to humankind. The AMBARVAILIA were rites of spring celebrated by Roman farmers in Ceres' honor. Of course, miners will also bring with them more whimsical names e.g. The King Solomon's Mines Hotel (a real rat trap!)
With an average diameter of 608 km or 378 miles, Pallas, the second asteroid to be discovered, is a smaller world than Ceres. It's surface area compares with Mare Imbrium plus Serenitatis; or with Washington, plus Oregon, California, and Nevada; or with New South Wales, plus Victoria, and Tasmania. Still enough land in which to get thoroughly lost. It is classified as 'peculiar chondrite' and from its radar signature appears to be rather smooth.
While its orbit is much more elliptical (bringing it about 66 million km or 41 million miles closer to the Sun than Ceres and taking it the same distance further out), its mean distance from the Sun is almost exactly the same as Ceres'. There are reports that Pallas has a 90 km satellite orbiting some 300 km above the surface. If confirmed*, this could be quite an asset especially if the composition of this unnamed body is complementary. Pallas has a 10 hour hour day-night cycle, a dozen of its days to every five of ours.
But the most significant statistic about Minor Planet #2 is its 35 degree orbital inclination to the ecliptic. We'd like to suggest that Pallas' relatively smooth surface is due to less total exposure to micrometeorite bombardment owing to this high orbital inclination. Seven other asteroids have orbits with a family resemblance but only a few very small ones have orbits more steeply inclined.
Pallas would thus be considerably harder to reach, requiring extra delta V. This could make it a mecca for pilgrim-type settlers wanting a world as off-the-beaten-path as possible, isolated and insulated from the cultural, religious, social, or economic ways of the rest of the Solar System. As influx of fresh blood will be inhibited, they might want to start with as diversified a gene pool as possible. Palladians [an adjective coined by the Romans] might trade knowledge and information gathered in their monastic isolation, via radio for essential imports by drone rocket. This world is very poorly placed to be a regional outfitting, supply, and service center.
Yet precisely because of this high inclination, Pallas offers easily the best observatory platform in the Solar System for studies of the Sun's north and south polar regions, when it is either high above or deep below the ecliptic on opposite legs of its 4.6 year long orbit. And this could be reason enough for establishing an outpost there.
It takes Ceres almost 3000 years to lap Pallas - an extreme example of the disadvantage of orbital proximity. This century they are about 60 degrees apart (about 270 million miles) but as seen from Ceres, Pallas swings alternately nearly 100 million miles above and below its mean position. Travel in between is unlikely.
Name pool: NUMBER TWO in order of discovery, Pallas was found by Wilhelm OLBERS, in BREMEN. The PALLADIUM was a famous statue of Pallas (Minerva).
*[Observations since have ruled out such a large satellite.]
Recent speckle interferometry studies of Vesta, Minor Planet #4 in order of discovery and the brightest as seen from Earth, have revealed a wealth of new information. A crude map of the surface [see page 14 of this issue] was constructed from the data which showed that Vesta is not quite spherical but something like a 'flattened watermelon' 564 x 531 km (350 x 330 mi.) in diameter along its equator by 467 km (290 mi.) along its polar axis about which it turns in a mere 5 hrs 20.5 min. A two date cycle of nine such periods gives dates 24 hrs 2.2 min long.
Unlike either Ceres or Pallas, both dark bodies, Vesta's surface is relatively bright making it the only asteroid that is ever visible to the naked eye on Earth (but only in dark country skies!)
The spectral studies seem to indicate a basaltic, drier stony composition (eucritic), not unlike the Moon (which, however, is much less reflective). The surprising presence of basalt indicates that at some time in its past, Vesta's interior had melted. A radioactive isotope of Aluminum seems to be the only likely source of the heat required in a body so small and would have done its work swiftly making any lava flow seas on Vesta some hundreds of millions of years older than the Moon's. Some think Vesta may be the parent body of most stony meteorites.
A dry basaltic surface has both advantages and disadvantages. Some Lunar type construction methods might be appropriate. But it is possible that an outpost there would need to import some volatiles. Vesta's gravity might be not much less than Ceres' given its probable higher density. Its surface could include Moonlike lava filled basins and cratered highlands. Surface sampling and orbital mapping are top priority. A French probe, piggybacking on a 1994 Soviet Mars mission is under study.**
Vesta is also considerably closer to the Sun than Ceres or Pallas, ranging from 322 - 383 million km (200 - 238 million mi.) making the circuit in a year less time (3.63 yrs). One can imagine that Ceres-Vesta oppositions every seventeen years one month apart may someday be the occasion of much ado in the Belt, commercial, social, and what have you.
Tourist hype might refer to Vesta as the 'Florida' of the Belt. Even so it receives 2.4 times less solar energy per unit surface area as does Mars (and 5.5 times less than Earth/Moon).
If volatiles are not a problem, Vesta may well be a regional outpost, quite possibly before Ceres itself. Except for the drier soil, the construction game plan will be similar.
But Vesta could be most preeminent as a mecca for Physics. While it was once apparently molten, it is too small to have retained any heat. Add to this its probably dehydrated state, and it may be the only body of size in our system in which it is possible to bore a shaft clear to center. Imagine a large room with negative zero gravity (equal canceling pulls in all directions) shielded by 150 some miles of rock in all directions. That should be good for something! At any rate such conditions could be equaled nowhere else in the System. Given such an asset, an outpost or settlement on Vesta might someday include a major university or institute.
Here is some physics homework for someone: a 10 meter wide shaft to the core would involve removing about 75 million metric tons of material. How fast would this much matter have to be ejected in pulverized form out the end of a mass driver easterly along Vesta's equator to slow significantly Vesta's swift rotation? A terraformer's dream perhaps, but if Vesta's rotation could be slowed to once per orbit (sun-locked) a sizable 'sub-solar' region would then receive as much total sunshine as any spot on Mars, or about three times as much as at present. As a bonus, Vesta's 'farside' would then become the coldest spot in the solar system.
A short pool of names for features and installations on Vesta: OLBERS discovered it in 1807 from BREMEN; Vesta was the Roman goddess of the HEARTH (home, warmth). Words for "hearth" in other languages. VESTALIA were ceremonies in her honor by the vestal virgins.
** [The "Vesta" mission never flew.]
HOW WILL PROSPECTORS STAKE AN ASTEROID CLAIM? They will radio all the identifying information to some central claims office, of course; but perhaps they will want to put an actual marker on the particular orbiting berg they've prospected. A convention of some sorts would be needed to standardize procedure. One possibility would be to put a strobe beacon or radio beeper on the body's north (or south) pole. A hitch here is that, as we discovered with Halley's Comet, a small body can have two axes of rotation at once. In such cases the shortest axis or the one with the shortest period could be picked. Is there a better way to say 'keep out!'? Suggestions welcome.
A CAPITAL FOR THE BELT? It is a tossup whether Belt communities would ever choose to federate or even loosely associate and need a "Capital City". If so, there is no logical spot within the Belt, Ceres' and Vesta's bids to the contrary, that will be easily accessible from anywhere. The Moon offers much more frequent and regular Launch windows than any asteroid and will be a major, if not the major, source of supplies. That's if Belters can stand its (to them) crushing gravity; Phobos and Deimos might offer space for such a headquarters, though with much less frequent launch windows. If Belters insisted on an asteroid site for their headquarters, however, oddly shaped 36 x 15 km (22.3 x 9.3 mi.) Eros would be the best of a poor set of choices, offering reasonable launch window frequencies to most of the Belt yet accessible with perhaps politically desirable difficulty from both Earth and Mars. Of the other Earth-approaching asteroids, 35 km Ganymed is easily the largest but it has a very eccentric, highly inclined orbit with an unsuitably long period.
THIS WOULD BE THE THIRD 'OSCAR' FOR EROS. When the asteroid (#433) was discovered in 1898, it became instantly famous as the first known minor planet to come within the orbit of Mars. Later, as its cigar-shape was deduced from its light curve, Eros inspired some to foresee the possibility of hollowing out suitably shaped asteroids and spinning them up to provide artificial gravity on the new inside surfaces and serve as great space colonies or even as star-bound arks, inspiring many (such as this writer) long before the days of Gerard O'Neill.
#22 AMPHITRITE had its rendezvous with destiny canceled when the Galileo mission had to be postponed after Challenger exploded. Two other targets of opportunity have been selected for flyby inspection during the rescheduled mission to Jupiter: Ida and Gaspra.
EGG-ON-OUR-FACE DEPT. In a filler box entitled "Awaiting Future Museums on the Moon!" on page 2 in the last issue of MMM, we listed fourteen objects left in lunar orbit. Unfortunately they have all long since impacted on the Moon. The orbits of these objects did not decay as there is no appreciable atmospheric drag. However, while the initial orbital periods and mean altitude of these objects was conserved, the eccentricity of their orbits increased, due to the gravitational influence of the Earth, to the point where the 'perilune', the lowest point of the orbit, bringing it in horizontal to the surface eventually impacted some boulder or crater rim or scalp sticking up from the surface and at 1.5 km/sec. the end would be quite abrupt.
Contents of this issue of Moon Miners' Manifesto