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On 02 February, 1997 in the sci.astro "USENET" forum Van Flandern put forward a prediction regarding the asteroid 433 Eros. This statement included a challenge to astronomers requesting them to give serious consideration to the underlying hypothesis should the prediction be confirmed by observation.

The Near Earth Asteroid Rendezvous (NEAR) spacecraft is the first launch in the Discovery Program, a NASA initiative for small planetary missions. NEAR is managed for NASA by The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland. NEAR was launched in February, 1996 atop a Delta II rocket on a mission to rendezvous with 433 Eros, an S-type asteroid with estimated dimensions of 35x15x13 kilometers. NEAR will be the first spacecraft to orbit an asteroid.

Two asteroids, 951 Gaspra and 243 Ida, were visited by NASA's Galileo spacecraft in 1991 and 1993, respectively. A unique discovery was made when a tiny moon was imaged in orbit around Ida. Unlike the Galileo encounters which were simple flybys at high velocity lasting mere minutes, NEAR will execute a braking maneuver placing it in orbit around Eros for a prolonged close-up inspection. The mission is expected to culminate with NEAR landing on Eros in 2000.

Although the NEAR-Eros challenge has been repeated on numerous occasions no mainstream supporter has been willing to accept the challenge under any terms, even though the terms were open to discussion. This reflects the unfortunate trend in astronomical theories to avoid setting falsification criteria because, if this were done, many favored theories would likely fall.

The NEAR Challenge

I predict that three or more satellites 1-meter in size or larger constitutes a win for eph (thereby conceding a simple binary asteroid with a single, Dactyl-like orbiting moon to the mainstream).

Asteroidal Satellites and the "Exploded Planet Hypothesis"

In "Dark Matter Missing Planets & New Comets" a new theory called the exploded planet hypothesis (eph) was introduced. One of its consequences was the realization that natural satellites of asteroids and comets are commonplace. The book was published before the discovery of Comet Shoemaker-Levy 9 which consisted of more than 20 individual members and before the Galileo spacecraft returned its images of asteroid Ida's moon Dactyl, the first confirmed "minor satellite".

Mainstream astronomy has attempted to explain minor satellites saying they form following a collision between bodies, such as two asteroids. Accordingly, it is possible for two fragments from the ensuing debris cloud to become coupled gravitationally in a mutual orbit. As for multiple comet nuclei we are expected to believe that the gentle tidal forces exerted by a planet are sufficient to break off relatively large chunks of material. Upon closer inspection these argument are found to be wanting.

In a collision, every fragment either escapes or falls back to the impact site. No sideways angular momentum needed for a stable orbit is produced. The mutual distance between any two escaping fragments increases faster than the radius of either gravitational sphere of influence, so they likewise can never become stably bound.

These fatal dynamical objections must be overcome to form stable moons. One way to do that is to have an explosion originating at the center of a planet instead of at the surface of an asteroid. Then many fragments tend to follow nearly parallel, only-slowly-diverging paths away from the planet. Meanwhile, the gravitational spheres of influence of the slower, larger fragments increase rapidly in radius because most of the planet's mass is soon beyond them. So all nearby debris becomes trapped in orbit around those larger fragments. Natural dynamical and collisional evolution eventually sort out this debris, concentrating much of it toward the equatorial plane and toward the synchronous orbit (i.e., toward maximum stability).

So when a large fragment of the exploded planet, such as Comet SL-9, comes too close to Jupiter, its orbiting debris cloud gets stripped off and spreads out along the main fragment's orbit. You no longer need to invoke tidal forces no stronger than blowing gently on a bit of cigar ash to break apart a comet nucleus probably several kilometers in diameter.

Actually, collisions and explosions are surprisingly different dynamically. Collisions cause fragments of both bodies to depart from near the point of impact. This is on the surface of the larger body even if that body is destroyed by the collision. An eph-type explosion originates at the center of the larger body. This results in three differences relevant to satellite formation:

• An impact causes the mutual separation of all fragments to increase linearly with distance traveled away from the impact. A central explosion of a planet-sized body allows many fragments originating far from the center to travel along nearly parallel trajectories with similar speeds that diverge much more slowly.

• In an impact, small fragments tend to leave first and travel fastest, with large fragments lagging behind. Both mutual separation and the radius of the gravitational sphere of influence of each increase linearly with distance traveled away from the impact site. By contrast, in a planetary explosion, small late-leaving fragments are being continually propelled past large early-leaving fragments, rapidly decreasing the exploded planet's mass interior to the large fragments. This accelerates the speed of increase of their sphere of influence above linear with distance traveled, and allows them to capture nearby debris.

• Impacts are almost exclusively destructive. A planetary explosion propels considerable trailing material into the larger fragments that left first, causing them to accrete some additional mass, and enlarge their spheres of influence faster, on the way out.

Gravitational captures from a collision event are nearly impossible. And two adjacent fragments are outside one another's sphere of influence (which is generally smaller than a fragment's own radius) while still in the parent body. When ejected by an impact, the spheres of influence grow linearly with distance from the center of the parent body. But the actual separation grows linearly with distance from the impact site near the surface of the parent body. Since the latter is always greater than or equal to the former, no two co-moving fragments can ever get inside each other's spheres of influence.

With the NEAR-Eros prediction I do not claim that one success "proves" that eph is a better model. But I do claim that it has demonstrated that it is a model worthy to be discussed comparatively by planetary scientists in the light of all new and existing evidence. Moreover, the eph has much to recommend it, not the least of which are:

• Eph eliminates the need for an "Oort cloud".

• Eph predictively explains all the principal statistical properties of new and old comet orbits.

• Eph easily explains why new and old comet physical behavior is so drastically different.

• Eph is the only model that correctly predicts the split comet relative velocity vs. solar distance power law.

• Eph explains why many properties of meteorites are ordinarily associated only with major planets, such as pre-impact micro-diamonds.

• Eph explains the young cosmic ray exposure ages of meteorites, and why we seldom see two-stage exposure ages.

• Eph provides the needed recent source for Earth-crossing asteroids.

• Eph is a natural explanation for "explosion signatures" in main asteroid belt orbital elements.

• Eph explains the distribution of black, carbonaceous material on the airless bodies of the solar system, most notably for Icarus.

The Tale of Two Asteroids

Many asteroid moons were discovered during stellar occultation events in the late 1970s, and binary asteroids were featured in the review volume "Asteroids" published in 1979. When the phenomenon started to become an embarrassment for the standard model, participation in observing efforts by professionals was sharply curtailed by the early 1980s, and asteroid moons were barely mentioned except in one negative chapter in "Asteroids II" a decade later.>

The International Occultation Timing Association (IOTA) provides the predictions and coordinates observers, both professional and amateur. Their newsletter usually reports early results even before the journals publish the final papers. Not only were professional efforts by U.S. astronomers down, but some amateurs were driven away by the stinging criticisms of professionals who have done no analysis of the reports, yet claim that flying birds and such are more likely to explain multiple occultations than objects in the asteroid's environment.

The most famous case was the first asteroid occultation where photometers were used. Visual observer James McMahon in California observed a 21-second occultation of a bright star by a much fainter asteroid, Herculina. He also reported some equally distinct but shorter secondary occultations, the longest of which lasted 5 seconds.

Lowell Observatory recorded a photoelectric record of the combined lightcurve that likewise showed a 21-second occultation of the star by the asteroid, with a magnitude drop of 4-5. David Dunham called Lowell and asked about secondary occultations. The observers reported seeing none. David then questioned McMahon closely for any possible alternate explanation of his visual sightings, telling him that Lowell saw no secondary events in the photoelectric record. Every possibility anyone could conceive was ruled out, especially when considering that the faint asteroid remained visible when the bright star disappeared.

Dunham calculated that only the secondary event that had produced the 5-second occultation for McMahon was large enough that Lowell almost certainly must have seen it too, if it was real. So he called Lowell back and again asked them to scan their record for secondary events. The observers assured him there were none.

Dunham said, "Look at the record at 91 seconds before the primary event. Is there anything unusual there?" The Lowell observers responded rather sheepishly with words to the effect, "Oh, that. That does look like a 5-second, full-light-drop occultation, but the altitude then was only 2 degrees, so we ignored it!"

A visual observer saw an occultation. A major observatory hundreds of miles away obtained a photoelectric record of the same event at the same time relative to the main occultation. The magnitude drop was nearly five magnitudes. The asteroid remained visible when the star disappeared -- both to the visual observer and to the photometer. No other events were seen in the entire photoelectric record besides the main 21-second occultation and this 5-second secondary event. What more could you ask for by way of confirmation?

To put this bluntly, observers sometimes see what they expect to see. The story of the Herculina satellite is another illustration of that, since a definite occultation event was denied to exist by the professional Lowell observers until their attention was directed to that exact place in their lightcurve. Occultations were previously an unchallenged type of reliable observation, even when done by amateurs. But when occultations of stars by asteroids began finding a phenomenon that did not fit in with current thinking, the observers and the technique were faulted. This is bias, pure and simple.

I spent the first half of my career as a part-time observational astronomer, and have observed and timed hundreds of occultations. I feel strongly that one is not fully competent to reduce data without the experience of collecting it to get a feel for the weaknesses first hand. My Melpomene occultation photoelectric lightcurve was published in Asteroids I.

The Melpomene event is another example in reverse: At USNO we had no occultation, but a very close appulse. We recorded for 40 minutes. During all that time, the only time the star's light dimmed significantly was for a few brief periods close to the time of closest approach. But the dimmings were not as deep as total occultations, and were irregular.

Any other observer was likely to have discarded that data as changes in seeing or some such. It might have been. But I saw the statistical improbability of that happening just when the star and asteroid were unresolvably close, but not at other times. And I understood the dynamics of close satellites and how the small bodies would tend to cluster into ring arcs and could produce a series of partial occultations such as those we saw. So I reported the data instead of tossing it.

I suggest these two anecdotes encapsulate the difference between myself and some mainstream astronomers: I would rather err in the direction of presenting possibly significant data and let history judge its usefulness. Others clearly would not publish data of whatever certainty that did not fit in with existing theory. I would question whether such an approach is doing "serious science", since I am convinced it retards progress.

Actually, there are more than three dozen cases of asteroid moons suggested by earlier observations prior to Galileo's discovery of Ida's Dactyl. Of these, perhaps a dozen are strong cases with no other viable explanation. A second observer gave independent confirmation in two cases. See, e.g., "Minor planets: the discovery of minor satellites", R.P. Binzel and T.C. Van Flandern, Science 203, 903-905 (1979), for the status 18 years ago. More recent discoveries are usually reported in IOTA's "Occultation Newsletter".

It is a shame that the individual discoverers of these asteroid moons, and D.W. Dunham in particular who predicted the events and organized the observer efforts, have received so little credit for their discoveries, made at a time when asteroid moons were still thought to be a theoretical near-impossibility. Dunham reported a satellite of 6 Hebe to the AAS in 1977, and the most common response was to assume that Dunham was not a careful observer or a reliable astronomer. Some reward for his role in discovering and publicizing something important and wonderful!

I'll accept a finding that Eros has no moons visible to a working, orbiting NEAR spacecraft as a good indicator that most of the thirty or so previous observations of secondary occultations near asteroids were spurious, and as evidence that my best professional judgment was extremely faulty. OTOH, if NEAR shows us that the spontaneous 1973 observations by relatively inexperienced observers of secondary bodies close to Eros were real moons of that asteroid, then we are probably safe to conclude that most of the later observations by more experienced observers better prepared for the phenomenon were likewise reliable, that phenomena repeatedly reported even by amateur astronomers should be taken seriously, and that asteroid moons are indeed numerous and commonplace.

Tom Van Flandern (December 1997)