Antipholus and Antipholus:
Frequently Asked Questions
Q: First, in what ways does 2001 QW322 challenge binary-formation and evolution theories?
A: The major challenge posed by the existence of the Antipholus binary is that it exists at all. There are many models of ‘how to make binaries’ but only one of them, by Weidenschiling, has any chance of make them and that mode of formation is highly in-efficient. But Antipholus is VERY loosely bound together and would be pretty easy to disrupt?
Q: And what is so strange about the binary--its width?
A: Yes, its separation, i.e. the semimajor axis of the mutual-orbit. And also the fact that the mutual eccentricity is rather low, hence the two components are always very far away from each other.
Q: Is this the widest binary of any sort we know in the Kuiper belt of just the widest among equal mass objects?
A: This is the widest of all known bianries, in the Kuiper belt and in the asteroid belt. And when expressed in term of the Hill radius, Antipholus is amongst the widest, even compared to irregular satellites of giant planets.
Q: What does the bluish color suggest?
A: We are very surprised by the bluish color. We normally classify Kuiper belt objects based on their orbit, making Antipholus part of the "cold classical main Kuiper belt” (which is quite a mouth full). But cold classicals are typically redder. Perhaps 2001 QW322 is a member of the "hot classical main Kuiper belt”, whose members are bluer, but at the low inclination end of the distribution of those objects. If this is the case, then it is even more difficult to understand how it could survive the "excitation" process. Generally however, the bluish color suggests an icy mantel, which could indicate some ancient collision.
Q: Why might this be an object from early in the solar system?
A: Forming such a binary requires three or more objects to pass close to each other, a 3 body encounter. The current population of the Kuiper Belt is very sparse, making such encounters extremely rare. Early on the density of material in the Kuiper belt was much higher, making the chance for an encounter higher. So we think that likely the system formed early on.
Q: If so, did it start out with such a great gap between the two objects, or did it evolve over time?
A: This is a good question. Till now, people have assumed that it was formed early on in its current state. But some suggestions have been made that it could result from the increase of a more tightly bound binary over time due to interactions with interlopers. Such a scenario needs to be studied and quantify. And we would need a better statistics of the intermediate separation binaries with equal mass in the Kuiper Belt.
Q: How does this object shed light on the nature of the Kuiper belt and its history?
A: When we design models of the Kuiper Belt and its history, we must make sure that the early conditions allowed the formation of the large separation binaries. And also that some of them can survive to the present day. This means that we must eliminate most of the early Belt rather fast, while avoid too many collisions. Using this argument, Petit and Mousis (2004), Icarus, already showed that the existence of 2001 QW322 implies that the depletion of the belt