Venus may be
a toxic hell-planet, but new evidence suggests it might have more in common
than Earth than we realized.
Scientists
have just found evidence that Venus' crust could have tectonic blocks that rub
together, not dissimilar to broken blocks of pack ice. It's not entirely like
Earth's plate tectonics, but the discovery does suggest that the planet's crust
isn't one globally continuous lithosphere, and that convective motion swirls
below.
This doesn't
just offer insights into Venus - it could help us better understand the
evolution and dynamics of tectonics on early Earth.
"We've identified a previously unrecognized pattern of tectonic deformation on Venus, one that is driven by interior motion just like on Earth," said planetaryscientist Paul Byrne of North Carolina State University.
"Although different from the tectonics we currently see on Earth, it is still evidence of interior motion being expressed at the planet's surface."
Earth really
is a unique little oddball in the Solar System, in many ways. One of those ways
is its system of plate tectonics - shifting scales of crust that grind against
each other and overlap (subduct), moving over a hot, molten interior planetary
layer.
We don't see
this kind of activity on Mercury, or Mars, or the Moon. And nor do we see it on
Venus - which is strange, considering the similar sizes and geological
compositions of Venus and Earth.
The two
planets took quite different evolutionary paths, in spite of their
similarities, and the reasons for that are not very well understood. If we can
work out how and why Earth and Venus turned, respectively, into a lush,
thriving ocean world and a scorching wasteland, we will have a better handle on
similar exoplanets, out there in the wider galaxy.
Byrne and
his team were mapping the surface of Venus, using radar images taken by NASA's
Magellan probe in the 1990s. They noticed that, in the lowlands, some features
seem to suggest large-scale movement - shear stresses and deformations from the
motions and interactions of large blocks of crust.
To figure
out if what they were seeing was what they thought they were seeing, the team
performed modeling. They found that convective flow beneath the crust of Venus
could produce the observed features, if the crust was broken up into large
chunks, rather than plates.
"Plate tectonics on Earth are driven by convection in the mantle. The mantle is hot or cold in different places, it moves, and some of that motion transfers to Earth's surface in the form of plate movement," Byrne explained.
"A variation on that theme seems to be playing out on Venus as well. It's not plate tectonics like on Earth - there aren't huge mountain ranges being created here, or giant subduction systems - but it is evidence of deformation due to interior mantle flow, which hasn't been demonstrated on a global scale before."
Recent
evidence also suggests that Venus may still be volcanically active. A studyreleased last year found that volcanic features on the planet's surface are
relatively recent. We also know that most of the planet has been volcanically
resurfaced in the last billion years or so.
In order to
produce the features Byrne's team observed, the tectonic hijinks must have
taken place after the resurfacing. This suggests that, not only is this
activity relatively recent, it may still be ongoing.
This
suggests an intermediate stage of tectonic activity, on a continuum between the
fixed global shells of Mercury, Mars, and the Moon, and the mobility of Earth's
flimsier tectonic plates. This could help us better understand exoplanets in
the 'Venus zone' of orbit around their host stars, and the interiors of rocky
planets.
It also might
offer some insight into the tectonic processes on early Earth.
"The thickness of a planet's lithosphere depends mainly upon how hot it is, both in the interior and on the surface," Byrne said.
"Heat flow from the young Earth's interior was up to three times greater than it is now, so its lithosphere may have been similar to what we see on Venus today: not thick enough to form plates that subduct, but thick enough to have fragmented into blocks that pushed, pulled, and jostled."
Future
observations by upcoming Venus missions by NASA and the European Space Agency
will tell us more about this fascinating discovery.
The research
has been published in PNAS.