The Rosetta Spacecraft Visit of Asteroid Lutetia

Image: Asteroid Lutetia

From a science fiction perspective, asteroids have always been a source of great inspiration. They are the places where strange artifacts are found, the locations of wayward space outposts, and are the villains in big-rock-collides-with-Earth scenarios. From a planetary science perspective, we've learned a great deal about asteroids in the last 15 years, but as is often the case, the research has generated even more new questions to investigate than we had before.

This summer the Rosetta spacecraft had its close flyby of the asteroid Lutetia. Scientists have now had a chance to review the data from that flyby in some detail, and the first reports are being given at the conference I am attending.

More than anything else, the talks are pointing out how very different asteroids are, both from what we were expecting 15 years ago, and from one another. Lutetia is the biggest asteroid humans have gotten close to (so far) and it shows evidence for a very complex history. The surface features include: folds, fractures, troughs, peaks, craters, pit chains, young and old regions, grooves, deep regolith, boulders, landslides, steep slopes, and much more. It might seem like just another potato-shaped asteroid to some, but I continue to find the variations in asteroids to be really intriguing. And given the President's interest in sending humans to an asteroid sometime soon, these variations pose any number of challenges for mission planning.

For example, Lutetia has slopes of loose material steeper than 50 degrees. This is odd, since loose material on any world generally will not form a slope greater than about 30 degrees (called the angle of repose). This very steep slope might be a result of a strangely shaped gravity profile for the asteroid. Or perhaps the material is being weakly held together by electrostatic forces. In this arena, science and science fiction are in the same position, asking how can we get people there safely, and wondering what they will find when they get there. 

I am particularly interested in imagining the differences in trying to 'walk' on such a body, where the gravity is pulling strangely, where the slopes might be either rock or dust, and massive boulders are perched on peaks all around. On smaller asteroids, this effect would be even more pronounced. It might be more like 'floating' around, or as one colleague said, visiting something more akin to a dangerous underwater coral reef while wearing complex scuba gear.

Pax

Image Credit: Rosetta image of asteroid Lutetia, European Space Agency