Observations suggest Venus may have had water oceans in its distant past. A land-ocean pattern like that above was used in a climate model to show how storm clouds could have shielded ancient Venus from strong sunlight and made the planet habitable. Credits: NASA
Thanks to evidence provided by missions like NASA’s Magellan spacecraft, scientists have theorized that Venus likely experienced a catastrophic resurfacing event about 500 million years ago (give or take 200 Mya). This is believed to be the reason why Venus is such a hellish place today, with an atmosphere that is 92 times as dense as Earth’s, predominantly composed of carbon dioxide (CO2), and temperatures hot enough to melt lead.
The question of what Venus was like before this event took place – particularly, whether or not it had oceans – has been the subject of debate ever since. While many believe that Venus’s surface was covered in large bodies of water, a recent study has contradicted this claim. Using a state-of-the-art climate model, a team of French researchers has developed an alternative scenario of how Venus evolved to become what it is today.
Venus is often referred to as “Earth’s sister planet“, owing to the number of similarities between them. Like Earth, Venus is a terrestrial (aka. rocky) planet and it resides with our Sun’s Circumstellar Habitable Zone (CHZ). And for some time, scientists have theorized that billions of years ago, Venus had oceans on its surface and was habitable – aka. not the hot and hellish place it is today.
However, after examining radar data on the Ovda Fluctus lava flow, a team scientists at the Lunar and Planetary Institute concluded that the highlands on Venus are likely to be composed of basaltic lava rock instead of granite. This effectively punches a hole in the main argument for Venus having oceans in the past, which is that the Ovda Regio highlands plateau formed in the presence of water.
Artist's conception of a terraformed Venus, showing a surface largely covered in oceans. Credit: Wikipedia Commons/Ittiz
In 1978, NASA’s Pioneer Venus (aka. Pioneer 12) mission reached Venus (“Earth’s Sister”) and found indications that Venus may have once had oceans on its surface. Since then, several missions have been sent to Venus and gathered data on its surface and atmosphere. From this, a picture has emerged of how Venus made the transition from being an “Earth-like” planet to the hot and hellish place it is today.
It all started about 700 million years ago when a massive resurfacing event triggered a runaway Greenhouse Effect that caused Venus’s atmosphere to become incredibly dense and hot. This means that for 2 to 3 billion years after Venus formed, the planet could have maintained a habitable environment. According to a recent study, that would have been long enough for life to have emerged on “Earth’s Sister”.
Observations suggest Venus may have had water oceans in its distant past. A land-ocean pattern like that above was used in a climate model to show how storm clouds could have shielded ancient Venus from strong sunlight and made the planet habitable. Credits: NASA
There’s no sense in sugar-coating it – Venus is a hellish place! It is the hottest planet in the Solar System, with atmospheric temperatures that are hot enough to melt lead. The air is also a toxic plume, composed predominantly of carbon dioxide and sulfuric acid rain clouds. And yet, scientists theorize that Venus was once a much different place, with a cooler atmosphere and liquid oceans on its surface.
Unfortunately, this all changed billions of years ago as Venus experienced a runaway greenhouse effect, changing the landscape into the hellish world we know today. According to a NASA-supported study by an international team of scientists, it may have actually been the presence of this ocean that caused Venus to experience this transition in the first place.
Artist's concept of the VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) spacecraft, a proposed mission for NASA's Discovery Program that would launch by the end of 2021. Credit: NASA/JPL-Caltech
In February of 2014, NASA’s Discovery Program asked for proposals for the their 13th mission. Last week, five semifinalist were selected from the original 27 submissions for further investigation and refinement. Of the possible missions that could be going up, two involve sending a robotic spacecraft to a planet that NASA has not been to in decades: Venus!
The first is the DAVINCI spacecraft, which would study the chemical composition of Venus’ atmosphere. Meanwhile, the proposed VERITAS mission – or The Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy spacecraft – would investigate the planet’s surface to determine just how much it has in common with Earth, and whether or not it was ever habitable.
In many respects, this mission would pick up where Magellan left off in the early 1990s. Having reached Venus in 1990, the Magellan spacecraft (otherwise known as the Venus Radar Mapper) mapped nearly the entire surface with an S-band Synthetic Aperture Radar (SAR) and microwave radiometer. From the data obtained, NASA scientists were able to make radar altimeter measurements of the planet’s topography.
Deployment of the Magellan spacecraft with the Inertial Upper Stage (IUS) booster during the STS 30 Atlantis flight. Credit: NASA
These measurements revolutionized our understanding of Venus’ geology and the geophysical processes that have shaped the planet’s surface. In addition to revealing a young surface with few impact craters, Magellan also showed evidence of volcanic activity and signs of plate tectonics.
However, the lack of finer resolution imagery and topography of the surface hampered efforts to answer definitively what role these forces have played in the formation and evolution of the surface. As a result, scientists have remained unclear as to what extent certain forces have shaped (and continue to shape) the surface of Venus.
With a suite of modern instruments, the VERITAS spacecraft would produce global, high-resolution topography and imaging of Venus’ surface and produce the first maps of deformation and global surface composition. These include an X-band radar configured as a single pass radar interferometer (known as VISAR) which would be coupled with a multispectral NIR emissivity mapping capability.
Three-dimensional simulation of Gula Mons captured by the Magellan Synthetic Aperture Radar (SAR) combined with radar altimetry. Credit: NASA/JPL
Using these, the VERITAS probe will be able to see through Venus’ thick clouds, map the surface at higher resolution than Magellan, and attempt to accomplish three major scientific goals: get a better understanding of Venus’ geologic evolution; determine what geologic processes are currently operating on Venus (including whether or not active volcanoes still exist); and find evidence for past or present water.
Suzanne Smrekar of NASA’s Jet Propulsion Laboratory (JPL) is the mission’s principal investigator, while the JPL would be responsible for managing the project. As she explained to Universe Today via email:
“VERITAS’ objectives are to reveal Venus’ geologic history, determine how active it is, and search for the fingerprints of past and present water. The overarching question is ‘How Earthlike is Venus?’ As more and more exoplanets are discovered, this information is essential to predicting whether Earth-sized planets are more likely to resemble Earth or Venus.”
Venus, as imaged by the Magellan spacecraft using Synthetic Aperture Radar (SAR). Credit: NASA/JPL
In many ways, VERITAS and DAVINCI represent a vindication for Venus scientists in the United States, who have not sent a probe to the planet since the Magellan orbiter mission ended in 1994. Since that time, efforts have been largely focused on Mars, where orbiters and landers have been looking for evidence of past and present water, and trying to piece together what Mars’ atmosphere used to look like.
But with Discovery Mission 13 and its five semi-finalists, the focus has now shifted onto Venus, near-Earth objects, and a variety of asteroids. As John Grunsfeld, astronaut and associate administrator for NASA’s Science Mission Directorate in Washington, explained:
“The selected investigations have the potential to reveal much about the formation of our solar system and its dynamic processes. Dynamic and exciting missions like these hold promise to unravel the mysteries of our solar system and inspire future generations of explorers. It’s an incredible time for science, and NASA is leading the way.”
Each investigation team will receive $3 million to conduct concept design studies and analyses. After a detailed review and evaluation of the concept studies, NASA will make the final selections by September 2016 for continued development. This final mission (or missions) that are selected will launcd by 2020 at the earliest.
