Vesta’s Deep Grooves Could Be “Stretch Marks” From Impact

Dawn image of Vesta showing its nearly circumferential equatorial grooves (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Even though NASA’s Dawn spacecraft has departed Vesta the trove of data it’s gathered about this fascinating little world continues to fuel new discoveries. Most recently, some researchers are suggesting that Vesta’s curious grooves — long, deep troughs that wrap around its equator, noticed immediately after Dawn came within close proximity — are actually features called graben, the results of surface expansion along fault lines.

In Vesta’s case, the faults likely may have come from whatever major collision created the enormous central peak that rises almost three times the height of Mt. Everest from its south pole… and the expansion could be the result of differentiation of its interior — a separation of core, mantle and crust that’s much more planet-like than anything asteroidish.

On smaller asteroids and moons, stress fractures tend to have a “V” shape, cutting inwards to a sharp point. But the troughs on Vesta are more rounded, with a “U” shape that results from surface material slumping downwards as the surface pulls apart. Found on larger worlds like Earth, the Moon, Mars, Mercury — and now possibly Vesta as well — graben are shaped by motions below the crust and not just the splitting of the surface.

The biggest of Vesta’s troughs, Divalia Fossa, is 465 kilometers (289 miles) long, 22 km (13.6 mi) wide and 5 km (3 mi) deep… longer and three times deeper than the Grand Canyon.

Animation of Vesta rotating made from Dawn images and assembled by The Planetary Society’s Emily Lakdawalla

If the researchers are correct and these are indeed graben, rather than just fractures or grooves carved into the surface by another process, Vesta probably had a lot more going on inside it than does your typical asteroid.

“By saying it’s differentiated, we’re basically saying Vesta was a little planet trying to happen,” said Debra Buczkowski of the Johns Hopkins University Applied Physics Laboratory (JHUAPL), lead author of a new paper titled “Large-scale troughs on Vesta: A signature of planetary tectonics” scheduled to be published by the AGU on Sept. 29.

Read more: Is Vesta a Planet Among Asteroids?

Unlike its big sister Ceres, the largest world among the asteroids and Dawn’s next destination, Vesta isn’t officially classified as a dwarf planet because its shape isn’t spherical enough — a flagrant violation of IAU Planetary Code Regulation No. 2. Rather it’s more flattened, like a walnut. This of course is also likely the result of the impact Vesta sustained at its south pole (which also may be responsible for its rapid 5.35-hour rotation rate, helping to bulge out the equatorial region and possibly even provide an alternate source for the trough “stretch marks”) and so begs the question, was Vesta once a dwarf planet? And if so, does severe reconstruction by an impact event “reclassify” it as something else? What, then? Ex-dwarf planet? A planet-formerly-known-as-dwarf?An undwarf?

I’m sure the IAU is already anticipating the contretemps.

“We have been calling Vesta the smallest terrestrial planet. The latest imagery provides much justification for our expectations. They show that a variety of processes were once at work on the surface of Vesta and provide extensive evidence for Vesta’s planetary aspirations.”

– Chris Russell, Dawn mission principal investigator at UCLA

Read more on the American Geophysical Union’s press release here, and follow the latest from NASA’s Dawn mission here.

7 Replies to “Vesta’s Deep Grooves Could Be “Stretch Marks” From Impact”

  1. Likely anything above 100 km or so could differentiate. Vesta and Mars is more alike than Mars and Earth, both have lost their outgassed volatiles over time while both have minerals formed by interaction with water and other volatiles.

    As for Vesta’s classification, I am pretty certain IAU doesn’t worry about it. An astronomical body can often be classified into numerous sets, analogous to what happens with biological populations (with more than 26 ways to define species, say).

    For example, Ceres is a former planet historically. And today’s planets weren’t planets before they formed and the protoplanetary disk cleared.

  2. I’m ex-NASA. This writing isn’t quite bad enough to ask Major be removed, but it isn’t that far away, either. I saw two typos. There are several phrases that are imprecise handwaving.

  3. Great article with interesting data, but I really wish we could all get past the whole, “is/was it once a planet, what is it now” semantics silliness. These are all constructs of language and really completely arbitrary/meaningless… “A rose by any other name…” What we call anything MAKES NO DIFFERENCE… 😉

    1. While I can sympathize, and to an extent, agree with your comment, may I beg to disagree that “What we call anything MAKES NO DIFFERENCE…” True if something is called an Asteroid, and it actually fits the Comet profile–it is a Comet still (presuming those objects are now well categorized). However, if you, for example, label an Asteroid by another name, say a “photo-planet”, that characterization does project meaning: it creates its own enclosing field-of-view–an image-frame backdrop: the whole concept wrapped up in the term, or name. It does NOT change the reality, of course. But it DOES change the CONCEPT of that reality–how it is seen and understood. The name will change the meaning–in the mind,–and HOW it is understood, in the broader landscape frame.

      What you call something is relevant to how something is UNDERSTOOD–in context.

      If, for example, one says Asteroids may actually be remnant, ground-down debris, that can sketch-out a whole different CONCEPT. It’s said, Asteroids are leftover “building blocks” from the early Solar System. “[B]uilding blocks” has a nebular concept inextricably compressed into its MEANING: the Nebulae planet-formation theory. With the description, name, label, EVERYTHING related to it will be seen in that light angle of dusty glow.

      A name, or label, can carry its own train of heavy baggage.

      The primary lens of a telescope, if it is not properly formed and correctly polished–and carefully calibrated (I think is the term)–will distort the image of an object’s reality, as centered in the instrument’s finder-scope field-of-view. If it is a planet, you might “see” a star through the lens of aberration–though it remains a planet still.

      A misnomer can deviate from the true-focus of a thing.

Comments are closed.