Ever since NASA’s Magellan orbiter was able to peak beneath Venus’ dense cloud layer and map out the surface, scientists have puzzled over the planet’s geological history. One of the greatest mysteries is the role volcanic activity has played in shaping Venus’ surface. In particular, there are what is known as “tesserae,” tectonically deformed regions on the surface that often stand above the surrounding landscape.
These features comprise about 7% of the planet’s surface and are consistently the oldest features in their immediate surroundings (dating to about 750 million years ago). In a new study, an international team of geologists and Earth scientists showed how a significant portion of these tesserae appear to be made up of layered rock, which is similar to features on Earth that are the result of volcanic activity.
Despite the similarities our world has with Venus, there is still much don’t know about Earth’s “Sister planet” and how it came to be. Thanks to its super-dense and hazy atmosphere, there are still unresolved questions about the planet’s geological history. For example, despite the fact that Venus’ surface is dominated by volcanic features, scientists have remained uncertain whether or not the planet is still volcanically active today.
While the planet is known to have been volcanically active as recent as 2.5 million years ago, no concrete evidence has been found that there are still volcanic eruptions on Venus’ surface. However, new research led by the USRA’s Lunar and Planetary Institute (LPI) has shown that Venus may still have active volcanoes, making it the only other planet in the Solar System (other than Earth) that is still volcanically active today.
The surface of Venus has been a mystery to scientists ever since the Space Age began. Thanks to its dense atmosphere, its surface is inaccessible to direct observations. In terms of exploration, the only missions to penetrate the atmosphere or reach the surface were only able to transmit data back for a matter of hours. And what we have managed to learn over the years has served to deepen its mysteries as well.
For instance, for years, scientists have been aware of the fact that Venus experiences volcanic activity similar to Earth (as evidenced by lighting storms in its atmosphere), but very few volcanoes have been detected on its surface. But thanks to a new study from the School of Earth and Environmental Sciences (SEES) at the University of St. Andrews, we may be ready to put that particular mystery to bed.
The study was conducted by Dr. Sami Mikhail, a lecturer with the SEES, with the assistance of researchers from the University of Strasbourg. In examining Venus’ geological past, Mikhail and his colleagues sought to understand how it is that the most Earth-like planet in our Solar System could be considerably less geologically-active than Earth. According to their findings, the answer lies in the nature of Venus’ crust, which has a much higher plasticity.
This is due to the intense heat on Venus’ surface, which averages at 737 K (462 °C; 864 °F) with very little variation between day and night or over the course of a year. Given that this heat is enough to melt lead, it has the effect of keeping Venus’ silicate crust in a softened and semi-viscous state. This prevents lava magmas from being able to move through cracks in the planets’ crust and form volcanoes (as they do on Earth).
In fact, since the crust is not particularly solid, cracks are unable to form in the crust at all, which causes magma to get stuck in the soft, malleable crust. This is also what prevents Venus from experiencing tectonic activity similar to what Earth experiences, where plates drift across the surface and collide, occasionally forcing magma up through vents. This cycle, it should be noted, is crucial to Earth’s carbon cycle and plays a vital role in Earth’s climate.
Not only do these findings explain one of the larger mysteries about Venus’ geological past, but they also are an important step towards differentiating between Earth and it’s “sister planet”. The implications of this goes far beyond the Solar System. As Dr. Mikhail said in a St. Andrews University press release:
“If we can understand how and why two, almost identical, planets became so very different, then we as geologists, can inform astronomers how humanity could find other habitable Earth-like planets, and avoid uninhabitable Earth-like planets that turn out to be more Venus-like which is a barren, hot, and hellish wasteland.”
In terms of size, composition, structure, chemistry, and its position within the Solar System (i.e. within the Sun’s habitable zone), Venus is the most-Earth like planet discovered to date. And yet, the fact that it is slightly closer to our Sun has resulted in it having a vastly different atmosphere and geological history. And these differences are what make it the hellish, uninhabitable place that is today.
Beyond our Solar System, astronomers have discovered thousands of exoplanets orbiting various types of stars. In some cases, where the planets exist close to their sun and are in possession of an atmosphere, the planets have been designated as being “Venus-like“. This naturally sets them apart from the planets that are of particular interest to exoplanet hunters – i.e. the “Earth-like” ones.
Knowing how and why these two very similar planets can differ so dramatically in terms of their geological and environmental conditions is therefore key to being able to tell the difference between planets that are conducive to life and hostile to life. That can only come in handy when we begin to study multiple-planet systems (such as the seven-planet system of TRAPPIST-1) more closely.
Venus is often referred to as “Earth’s Twin” (or “sister planet”), and for good reason. Despite some rather glaring differences, not the least of which is their vastly different atmospheres, there are enough similarities between Earth and Venus that many scientists consider the two to be closely related. In short, they are believed to have been very similar early in their existence, but then evolved in different directions.
Earth and Venus are both terrestrial planets that are located within the Sun’s Habitable Zone (aka. “Goldilocks Zone”) and have similar sizes and compositions. Beyond that, however, they have little in common. Let’s go over all their characteristics, one by one, so we can in what ways they are different and what ways they are similar.
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!
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.
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.
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.”
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.
Venus is often referred to as our “sister planet,” due to the many geophysical similarities that exist between it Earth. For starters, our two planets are close in mass, with Venus weighing in at 4.868 x 1024 kg compared to Earth’s 5.9736×1024 kg. In terms of size, the planets are almost identical, with Venus measuring 12,100 km in diameter and Earth 12,742 km.
In terms of density and gravity, the two are neck and neck – with Venus boasting 86.6% of the former and 90.7% of the latter. Venus also has a thick atmosphere, much like our own, and it is believed that both planets share a common origin, forming at the same time out of a condensing clouds of dust particles around 4.5 billion years ago.
However, for all the characteristics these two planets have in common, average temperature is not one of them. Whereas the Earth has an average surface temperature of 14 degrees Celsius, the average temperature of Venus is 460 degrees Celsius. That is roughly 410 degrees hotter than the hottest deserts on our planet.
In fact, at a searing 750 K (477 °C), the surface of Venus is the hottest in the solar system. Venus is closer to the Sun by 108 million km, (about 30% closer than the Earth), but it is mainly due to the planet’s thick atmosphere. Unlike Earth’s, which is composed primarily of nitrogen, oxygen and ozone, Venus’ atmosphere is an incredibly dense cloud of carbon dioxide and sulfur dioxide gas.
The combination of these gases in high concentrations causes a catastrophic greenhouse effect that traps incident sunlight and prevents it from radiating into space. This results in an estimated surface temperature boost of 475 K (201.85 °C), leaving the surface a molten, charred mess that nothing (that we know of) can live on. Atmospheric pressure also plays a role, being 91 times that of what it is here on Earth; and clouds of toxic vapor constantly rain sulfuric acid on the surface.
In addition, the surface temperature on Venus does not vary like it does here on Earth. On our planet, temperatures vary wildly due to the time of year and even more so based on the location on our planet. The hottest temperature ever recorded on Earth was 70.7°C in the Lut Desert of Iran in 2005. On the other end of the spectrum, the coldest temperature ever recorded on Earth was in Vostok, Antarctica at -89.2 C.
But on Venus, the surface temperature is 460 degrees Celsius, day or night, at the poles or at the equator. Beyond its thick atmosphere, Venus’ axial tilt (aka. obliquity) plays a role in this temperature consistency. Earth’s axis is tilted 23.4 ° in relation to the Sun, whereas Venus’ is only tilted by 3 °.
The only respite from the heat on Venus is to be found around 50 km into the atmosphere. It is at that point that temperatures and atmospheric pressure are equal to that of Earth’s. It is for this reason that some scientists believe that floating habitats could be constructed here, using Venus’ thick clouds to buoy the habitats high above the surface. Additionally, in 2014, a group of mission planners from NASA Langely came up with a mission to Venus’ atmosphere using airships.
These habitats could play an important role in the terraforming of Venus as well, acting as scientific research stations that could either fire off the excess atmosphere off into space, or introduce bacteria or chemicals that could convert all the CO2 and SO2 into a hospitable, breathable atmosphere.
Beyond the fact that it is a hot and hellish landscape, very little is known about Venus’ surface environment. This is due to the thick atmosphere, which has made visual observation impossible. The sulfuric acid is also problematic since clouds composed of it are highly reflective of visible light, which prevents optical observation. Probes have been sent to the surface in the past, but the volatile and corrosive environment means that anything that lands there can only survive for a few hours.
What little we know about the planet’s surface has come from years worth of radar imaging, the most recent of which was conducted by NASA’s Magellan spacecraft (aka. the Venus Radar Mapper). Using synthetic aperture radar, the robotic space probe spent four years (1990-1994) mapping the surface of Venus and measuring its gravitational field before its orbit decayed and it was “disposed of” in the planet’s atmosphere.
The images provided by this and other missions revealed a surface dominated by volcanoes. There are at least 1,000 volcanoes or volcanic centers larger than 20 km in diameter on Venus’ harsh landscape. Many scientists believe Venus was resurfaced by volcanic activity 300 to 500 million years ago. Lava flows are a testament to this, which appear to have produced channels of hardened magma that extend for hundreds of km in all directions. The mixture of volcanic ash and the sulfuric acid clouds is also known to produce intense lightning and thunder storms.
The temperature of Venus is not the only extreme on the planet. The atmosphere is constantly churned by hurricane force winds reaching 360 kph. Add to that the crushing air pressure and rainstorms of sulfuric acid, and it becomes easy to see why Venus is such a barren, lifeless rock that has been hard to explore.