Asteroid Sticks Together While Theories Disintegrate

[Guest article]  In an story entitled “Rubbly Itokawa revealed as ‘impossible’ asteroid,” New Scientist Space reported on findings gathered from the recent visit of Japanese spacecraft Hayabusa to the asteroid Itokawa (see 11/28/2005 bullet).  There seems to be no end of problems for scientists trying to fit the solar system into billions of years.  Now they must deal with evidence that shows that asteroid Itokawa must be very young.  The article’s frankness about the severity of the problem is astonishing:

What they found was completely unexpected.  “Five years ago, we thought that we would see a big chunk of monolithic rock, [we thought] that something so small doesn’t have the ability to hold onto any pieces,” says Erik Asphaug, a planetary scientist at the University of California in Santa Cruz, US, who is not involved with the mission.  “Everything we suspected about it turned out to be wrong.”

Astronomers assumed that small asteroids would have to be very solid, like a single giant boulder, or else their weak gravity would have caused them to be quickly disintegrated by collisions with other rocks in space.  It turns out that Itokawa is about as solid as a sponge.  And to make it worse, collisions with small rocks, not big enough to break the asteroid apart, should, after billions of years, have caused it to pack into a more solid mass.  That compaction apparently never occurred:

Measurements of the asteroid’s gravity field also suggest it coalesced from the debris of a previous collision.  Hayabusa scientists used the data – combined with measurements of the space rock’s size – to estimate its density.  It appears to be 40% porous, or filled with empty space.  “That is astonishing,” says Asphaug, adding that a handful of sand has a porosity of 20%.  “It’s very hard to get porosities greater than that.  You’ve got to start balancing things delicately, like you were building a house of cards,” he says.  “The only way to do it is to gently pack the stuff together.”  But that raises another mystery, he says, since repeated impacts with other space rocks over millions of years should have made Itokawa denser.  “Every time you have an impact, you’re going to tamp it down,” he says.

The article mentions no proposed solution to the mystery.

Some day it may begin to dawn on scientists that they are starting with wrong assumptions about time.  A loose collection of dust and rock just a few thousand years old would probably look just like what they found.  That explanation, however, is ruled out from the start because it conflicts with their preconceived ideas of the time required for evolution.  Is this objective science?
—DK