Astronomers Look “Inside” an Asteroid for the First Time

From directly inferring the inside of an asteroid for the first time, astronomers have discovered these space rocks can have strange variations in density. The observations of Itokawa — which you may remember from the Japanese Hayabusa mission that landed on the asteroid in 2005 — not only teach us more about how asteroids came to be, but could help protect Earth against stray space rocks in the future, the researchers said.

“This is the first time we have ever been able to to determine what it is like inside an asteroid,” stated Stephen Lowry, a University of Kent scientist who led the research. “We can see that Itokawa has a highly varied structure; this finding is a significant step forward in our understanding of rocky bodies in the solar system.”

It’s not clear why Itokawa has such different densities at opposite sides of its peanut shape; perhaps it was two asteroids that rubbed up against each other and merged. At just shy of six American football fields long, the space rock has density varying from 1.75 to 2.85 grams per cubic centimetre. This precise measurement came courtesy of the European Southern Observatory’s New Technology Telescope in Chile.

The telescope calculated the speed and speed changes of Itokawa’s spin and combined that information with data on how sunlight can affect the spin rate. Asteroids are generally tiny and irregularly shaped sorts of bodies, which means the effect of heat on the body is not evenly distributed. That small difference makes the asteroid’s spin rate change.

This heat effect (more properly called the Yarkovsky-O’Keefe-Radzievskii-Paddack effect) is slowly making Itokawa’s spin rate go faster, at a rate of 0.045 seconds every Earth year. This change, previously unexpected by scientists, is only possible if the peanut bulges have different densities, the scientists said.

“Finding that asteroids don’t have homogeneous interiors has far-reaching implications, particularly for models of binary asteroid formation,” added Lowry.  “It could also help with work on reducing the danger of asteroid collisions with Earth, or with plans for future trips to these rocky bodies.”

More details on the research will be available in the journal Astronomy and Astrophysics.

Source: European Southern Observatory

5 Replies to “Astronomers Look “Inside” an Asteroid for the First Time”

  1. should be fun when the spin rate exceeds the gravitational binding between the two halves. Somehow I think the outcome will be more spectacular than 2 co-orbiting bodies. More of a freefloating redistribution of regolith between the two until they either recombine /again/ (due to regolith mass, like you see now) or finaly can be considered two separate bodies.

  2. Boffins,

    Based on the densities, with water ice at 1000kg/m^3, isn’t this “cobble pile” surprisingly dense? And I do mean, surprisingly.

    1. Not particularly. The more dense side is roughly the density of granite while the less dense side is roughly the density of dry loose sand. Compared to a nickel-iron meteorite at a density of ~8,500 kg/m^3 it’s not all that high.

  3. You give us the density of the asteroid in g/cm³, but when it came to the length, you resort to that lamest of comparisons to an American football field. Trust me, many of us learned the metric system at a early age, and would more readily understand a simple measurement like 549 metres.

    1. I dunno, they have to make it “accessible”, or something. After all they insist on referring to Aeolis Mons as “Mt Sharp”. Makes me wince every time.

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