It was quite a week for Venus scientists. Just seven days after NASA announced the selection of two Venus missions, DAVINCI+ and VERITAS, the European Space Agency (ESA) revealed that a third Venus mission had been chosen for the agency’s medium-class mission category.
(See last week’s post here on Many Worlds about DAVINCI+ and VERITAS)
The new mission is named EnVision, and will be ESA’s second Venus mission following Venus Express (2005 – 2014), which investigated the Venusian climate. While EnVision is an orbiter like Venus Express and VERITAS, its focus is the planet’s geological circulation system that links the atmosphere, surface and interior.
In case you are starting to get your Venus missions in a tangle, the set can be broadly divided up as follows:
Venus Express (ESA: 2005 – 2014) and Akatsuki (JAXA: 2015 – current) are both Venus orbiters focussed on the planet’s climate, returning information about the rapidly rotating upper atmosphere and acidic cloud deck of Venus.
DAVINCI+ (NASA: est. 2029 launch) is an orbiter and descending probe that will dive through the Venusian atmosphere to return top-to-bottom data on the planet’s stifling gases.
VERITAS (NASA: est. 2028 launch) is an orbiter focussed on Venus’s surface and the deep interior. VERITAS will bring us global maps in three-dimensions at a resolution of 30m. This will knock the socks off our current images from NASA’s Magellan orbiter (1989 – 1994), which had a resolution of around 200m.
EnVision (ESA: early 2030s) is the mission focused on how these environments are linked together. Equipped with an instrument suite that covers the top of the atmosphere through to below the planet surface, EnVision will probe how the different regions influence one another to create the planet’s internal systems.
“EnVision has a holistic approach,” explained Jörn Helbert who is a member of the EnVision team. “The larger and more complex payload studies Venus from the top of the atmosphere all the way to the subsurface, with a focus on understanding how the coupled system on Venus works.”
The coupled system is at the heart of how habitability can develop on rocky planets. A major player in the Earth’s environment is the ability to cycle carbon between the atmosphere, surface and planet mantle. Carbon is taken into the planet mantle as the plates that form the Earth’s crust slide beneath one another and is returned to the surface and atmosphere via volcanism. It is this carbon cycle that defines the edges of the classical habitable zone; the range of orbits in which the Earth can maintain temperate surface conditions by shuffling carbon dioxide in and out of the atmosphere.
Venus’s surface is far from temperate. But Venus Express spotted a change in the heat emitted from the surface of Venus that might indicate a volcanic eruption. Such current activity would make Venus the only other terrestrial planet with a geological cycle we can study.
Volcanic activity may mean the Venusian system has the ability to eject gases into the atmosphere, but have no efficient mechanism for removal. The Venusian crust does not seem to form plates, which facilitate such a carbon sink on Earth. This broken cycle may explain the hellish conditions of the Venusian surface, but it can not be the complete story.
Despite the lack of an obvious crustal movement, the surface of Venus appears extremely young, as if the majority of the planet has been recently resurfaced some time within the last 500 million to a billion years. How and when this occurred is not known, with options including a sudden catastrophic overturn, a storm of volcanism that gradually decreased or maybe a crust that is not as mobile as the Earth’s plate tectonics but is not totally static either. This part of Venus’s geological cycles will be investigated by both VERITAS and EnVision.
“VERITAS and EnVision will put limits on the rate of volcanism and hopefully detect a lot of active volcanos,” says Helbert. “This will help us find out where Venus sits on the spectrum between catastrophic and constantly resurfacing.”
While VERITAS will produce global maps of the Venusian surface, EnVision will focus on examining regions of interest at resolutions down to 10m and at multiple wavelengths.
A key region for this will be the so-called tesserae, that are the oldest parts of the Venusian surface and appear heavily deformed. Data from Venus Express has indicated their composition differs from elsewhere on the planet, but the minerals could not be identified. One possibility is that tesserae are felsic rocks that can only be created in the planet mantle in the presence of water. If the tesserae are felsic, they hail from an era in which Venus had more Earth-like conditions, with water present on the surface and material successfully cycled through the planet.
EnVision will be able to examine the composition of the tesserae regions to see if they are felsic, complimenting the global maps from VERITAS that will provide evidence for any crustal movement. It is a study that will pick apart Venus both in the present and in the past.
Combined, these new missions give a view into the evolution of an Earth-sized rocky planet we have never seen before, and a possible glimpse of how habitability can begin and fail.