Artist's impression of the European Space Agency/JAXA BepiColombo mission in operation around Mercury. Credit: Astrium
The BepiColombo mission, a joint effort between JAXA and the ESA, was only the second (and most advanced) mission to visit Mercury, the least explored planet in the Solar System. With two probes and an advanced suite of scientific instruments, the mission addressed several unresolved questions about Mercury, including the origin of its magnetic field, the depressions with bright material around them (“hollows”), and water ice around its poles. As it turns out, BepiColombo revealed some interesting things about Venus during its brief flyby.
Specifically, the two probes studied a previously unexplored region of Venus’ magnetic environment when they made their second pass on August 10th, 2021. In a recent study, an international team of scientists analyzed the data and found traces of carbon and oxygen being stripped from the upper layers of Venus’ atmosphere and accelerated to speeds where they can escape the planet’s gravitational pull. This data could provide new clues about atmospheric loss and how interactions between solar wind and planetary atmospheres influence planetary evolution.
Venus is a difficult place to explore. Only a few missions have ever made it to the surface, in no small part because of how difficult it is to traverse the planet’s atmosphere. That difficulty was confirmed recently by a team led researchers at the University of Lisbon, who found that the upper part of Venus’ atmosphere suffers from hurricane-force winds of up to 360 kilometers per hour.
Artist's impression of Venus with the solar wind flowing around the planet, which has little magnetic protection. Venus Express found that a lot of water has bled into space over the years from the planet, which happens when the sun's ultraviolet radiation breaks oxygen and hydrogen molecules apart and pushes them into space. Credit: ESA - C. Carreau
Named for the ancient goddess of fertility, the planet Venus could not be more hostile to life as we know it. Aside from being the hottest planet in the Solar System, Venus has also an atmosphere that is 92 times denser than Earth’s, and regularly experiences sulfuric acid rain. But as we’ve learned from multiple surveys, Venus was once a much milder climate and even had vast oceans on its surface.
For astronomers and geologists alike, the burning question is, how much of its water did Venus hold onto during this massive transition? According to research presented by Moa Persson of the Swedish Institute of Space Physics (IRF), Venus actually retained most of its water over the past 4 billion years. Contrary to what researchers previously thought, Venus lost only a small amount of its water to a runaway Greenhouse Effect.
A radar image of Maat Mons on Venus, from the Magellan spacecraft. Image Credit: NASA/JPL
Venus’ surface is no stranger to volcanoes. Radar images show more than 1,000 volcanic structures on the planet. But for the most part, they appear to be ancient and inactive.
Now a new study says that Venus is still volcanically active, and has identified 37 volcanic structures that were recently active. If true, there’s more going on inside Venus than thought.
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”.
Artist's impression of the Venus Express spacecraft in orbit around Venus. Credit: ESA
Venus’ atmosphere is as mysterious as it is dense and scorching. For generations, scientists have sought to study it using ground-based telescopes, orbital missions, and the occasional atmospheric probe. And in 2006, the ESA’s Venus Express mission became the first probe to conduct long-term observations of the planet’s atmosphere, which revealed much about its dynamics.
Using this data, a team of international scientists – led by researchers from the Japan Aerospace and Exploration Agency (JAXA) – recently conducted a study that characterized the wind and upper cloud patterns on the night side of Venus. In addition to being the first of its kind, this study also revealed that the atmosphere behaves differently on the night side, which was unexpected.
The study, titled “Stationary Waves and Slowly Moving Features in the Night Upper Clouds of Venus“, recently appeared in the scientific journal Nature Astronomy. Led by Javier Peralta, the International Top Young Fellow of JAXA, the team consulted data obtained by Venus Express’ suite of scientific instruments in order to study the planet’s previously-unseen cloud types, morphologies, and dynamics.
The atmospheric super-rotation at the upper clouds of Venus. While the super-rotation is present in both day and night sides of Venus, it seems more uniform in the day. Credits: JAXA, ESA, J. Peralta and R. Hueso.
Whereas plenty of studies have been conducted of Venus’ atmosphere from soace, this was the first time that a study was not focused on the dayside of the planet. As Dr. Peralta explained in an ESA press statement:
“This is the first time we’ve been able to characterize how the atmosphere circulates on the night side of Venus on a global scale. While the atmospheric circulation on the planet’s dayside has been extensively explored, there was still much to discover about the night side. We found that the cloud patterns there are different to those on the dayside, and influenced by Venus’ topography.“
Since the 1960s, astronomers have been aware that Venus’ atmosphere behaves much differently that those of other terrestrial planets. Whereas Earth and Mars have atmospheres that co-rotate at approximately the same speed as the planet, Venus’ atmosphere can reach speeds of more than 360 km/h (224 mph). So while the planet takes 243 days to rotate once on its axis, the atmosphere takes only 4 days.
This phenomena, known as “super-rotation”, essentially means that the atmosphere moves over 60 times faster than the planet itself. In addition, measurements in the past have shown that the fastest clouds are located at the upper cloud level, 65 to 72 km (40 to 45 mi) above the surface. Despite decades of study, atmospheric models have been unable to reproduce super-rotation, which indicated that some of the mechanics were unknown.
As such, Peralta and his international team – which included researchers from the Universidad del País Vasco in Spain, the University of Tokyo, the Kyoto Sangyo University, the Center for Astronomy and Astrophysics (ZAA) at Berlin Technical University, and the Institute of Astrophysics and Space Planetology in Rome – chose to look at the unexplored side to see what they could find. As he described it:
“We focused on the night side because it had been poorly explored; we can see the upper clouds on the planet’s night side via their thermal emission, but it’s been difficult to observe them properly because the contrast in our infrared images was too low to pick up enough detail.”
This consisted of observing Venus’ night side clouds with the probe’s Visible and Infrared Thermal Imaging Spectrometer (VIRTIS). The instrument gathered hundreds of images simultaneously and different wavelengths, which the team then combined to improve the visibility of the clouds. This allowed the team to see them properly for the first time, and also revealed some unexpected things about Venus’ night side atmosphere.
What they saw was that atmospheric rotation appeared to be more chaotic on the night side than what has been observed in the past on the dayside. The upper clouds also formed different shapes and morphologies – i.e. large, wavy, patchy, irregular and filament-like patterns – and were dominated by stationary waves, where two waves moving in opposite directions cancel each other out and create a static weather pattern.
Examples of new types of cloud morphology discovered on the night side of Venus thanks to Venus Express (ESA) and the infrared telescope IRTF (NASA). Credits: ESA/NASA/J. Peralta and R. Hueso.
The 3D properties of these stationary waves were also obtained by combining VIRTIS data with radio-science data from the Venus Radio Science experiment (VeRa). Naturally, the team was surprised to find these kinds of atmospheric behaviors since they were inconsistent with what has been routinely observed on the dayside. Moreover, they contradict the best models for explaining the dynamics of Venus’ atmosphere.
Known as Global Circulation Models (GCMs), these models predict that on Venus, super-rotation would occur in much the same way on both the dayside and the night side. What’s more, they noticed that stationary waves on the night side appeared to coincide with high-elevation features. As Agustin Sánchez-Lavega, a researcher from the University del País Vasco and a co-author on the paper, explained:
“Stationary waves are probably what we’d call gravity waves–in other words, rising waves generated lower in Venus’ atmosphere that appear not to move with the planet’s rotation. These waves are concentrated over steep, mountainous areas of Venus; this suggests that the planet’s topography is affecting what happens way up above in the clouds.“
This is not the first time that scientists have spotted a possible link between Venus’ topography and its atmospheric motion. Last year, a team of European astronomers produced a study that showed how weather patterns and rising waves on the dayside appeared to be directly connected to topographical features. These findings were based on UV images taken by the Venus Monitoring Camera (VMC) on board the Venus Express.
Schematic illustration of the proposed behaviour of gravity waves in the vicinity of mountainous terrain on Venus. Credit: ESA
Finding something similar happening on the night side was something of a surprise, until they realized they weren’t the only ones to spot them. As Peralta indicated:
“It was an exciting moment when we realized that some of the cloud features in the VIRTIS images didn’t move along with the atmosphere. We had a long debate about whether the results were real–until we realised that another team, led by co-author Dr. Kouyama, had also independently discovered stationary clouds on the night side using NASA’s Infrared Telescope Facility (IRTF) in Hawaii! Our findings were confirmed when JAXA’s Akatsuki spacecraft was inserted into orbit around Venus and immediately spotted the biggest stationary wave ever observed in the Solar System on Venus’ dayside.“
These findings also challenge existing models of stationary waves, which are expected to form from the interaction of surface wind and high-elevation surface features. However, previous measurements conducted by the Soviet-era Venera landers have indicated that surface winds might too weak for this to happen on Venus. In addition, the southern hemisphere, which the team observed for their study, is quite low in elevation.
And as Ricardo Hueso of the University of the Basque Country (and a co-author on the paper) indicated, they did not detect corresponding stationary waves in the lower cloud levels. “We expected to find these waves in the lower levels because we see them in the upper levels, and we thought that they rose up through the cloud from the surface,” he said. “It’s an unexpected result for sure, and we’ll all need to revisit our models of Venus to explore its meaning.”
Artist’s impression of Venus Express performing aerobreaking maneuvers in the planet’s atmosphere in June and July 2014. Credit: ESA–C. Carreau
From this information, it seems that topography and elevation are linked when it comes to Venus’ atmospheric behavior, but not consistently. So the standing waves observed on Venus’ night side may be the result of some other undetected mechanism at work. Alas, it seems that Venus’ atmosphere – in particular, the key aspect of super-rotation – still has some mysteries for us.
The study also demonstrated the effectiveness of combining data from multiple sources to get a more detailed picture of a planet’s dynamics. With further improvements in instrumentation and data-sharing (and perhaps another mission or two to the surface) we can expect to get a clearer picture of what is powering Venus’ atmospheric dynamics before long.
With a little luck, there may yet come a day when we can model the atmosphere of Venus and predict its weather patterns as accurately as we do those of Earth.
The planet Venus, as imaged by the Magellan 10 mission. The planet's inhospitable surface makes exploration extremely difficult. Credit: NASA/JPL
Welcome back to our series on Settling the Solar System! Today, we take a look at Earth’s “sister planet”, the hellish, yet strangely similar planet Venus. Enjoy!
Since humans first began looking up at the skies, they have been aware of Venus. In ancient times, it was known as both the “Morning Star” and the “Evening Star”, due to its bright appearance in the sky at sunrise and sunset. Eventually, astronomers realized that it was in fact a planet, and that like Earth, it too orbited the Sun. And thanks to the Space Age and numerous missions to the planet, we have learned exactly what kind of environment Venus has.
With an atmosphere so dense that it makes regular surface imaging impossible, heat so intense it can melt lead, and sulfuric acid rain, there seems little reason to go there. But as we’ve learned in recent years, Venus was once a very different place, complete with oceans and continents. And with the right technology, colonies could be built above the clouds, where they would be safe.
So what would it take to colonize Venus? As with other proposals for colonizing the Solar System, it all comes down to having the right kinds of methods and technologies, and how much are we willing to spend.
At a closest average distance of 41 million km (25,476,219 mi), Venus is the closest planet to Earth. Credit: NASA/JPL/Magellan
Examples in Fiction:
Since the early 20th century, the idea of colonizing Venus has been explored in science fiction, mainly in the form of terraforming it. The earliest known example is Olaf Stapleton’sLast And First Men(1930), two chapters of which are dedicated to describing how humanity’s descendants terraform Venus after Earth becomes uninhabitable; and in the process, commit genocide against the native aquatic life.
By the 1950s and 60s, terraforming began to appear in many works of science fiction. Poul Anderson also wrote extensively about terraforming in the 1950s. In his 1954 novel, The Big Rain, Venus is altered through planetary engineering techniques over a very long period of time. The book was so influential that the term term “Big Rain” has since come to be synonymous with the terraforming of Venus.
In 1991, author G. David Nordley suggested in his short story (“The Snows of Venus”) that Venus might be spun-up to a day-length of 30 Earth days by exporting its atmosphere of Venus via mass drivers. Author Kim Stanley Robinson became famous for his realistic depiction of terraforming in the Mars Trilogy – which included Red Mars, Green Mars and Blue Mars.
In 2012, he followed this series up with the release of 2312, a science fiction novel that dealt with the colonization of the entire Solar System – which includes Venus. The novel also explored the many ways in which Venus could be terraformed, ranging from global cooling to carbon sequestration, all of which were based on scholarly studies and proposals.
Artist’s conception of a terraformed Venus, showing a surface largely covered in oceans. Credit: Wikipedia Commons/Ittiz
Proposed Methods:
All told, most proposed methods for colonizing Venus emphasize ecological engineering (aka. terraforming) to make the planet habitable. However, there have also been suggestions as to how human beings could live on Venus without altering the environment substantially.
For instance, according to Inner Solar System: Prospective Energy and Material Resources, by Viorel Badescu, and Kris Zacny (eds), Soviet scientists have suggested that humans could colonize Venus’ atmosphere rather than attempting to live on its hostile surface since the 1970s.
More recently, NASA scientist Geoffrey A. Landis wrote a paper titled “Colonization of Venus“, in which he proposed that cities could be built above Venus’ clouds. At an altitude of 50 km above the surface, he claimed, such cities would be safe from the harsh Venusian environment:
“[T]he atmosphere of Venus is the most earthlike environment (other than Earth itself) in the solar system. It is proposed here that in the near term, human exploration of Venus could take place from aerostat vehicles in the atmosphere, and that in the long term, permanent settlements could be made in the form of cities designed to float at about fifty kilometer altitude in the atmosphere of Venus.”
Artist’s concept of a Venus cloud city — a possible future outcome of the High Altitude Venus Operational Concept (HAVOC) plan. Credit: Advanced Concepts Lab/NASA Langley Research Center
At an altitude of 50 km above the surface, the environment has a pressure of approximately 100,000 Pa, which is slightly less than Earth’s at sea level (101,325 Pa). Temperatures in this regions also range from 0 to 50 °C (273 to 323 K; 32 to 122 °F), and protection against cosmic radiation would be provided by the atmosphere above, with a shielding mass equivalent to Earth’s.
The Venusian habitats, according to Landis’ proposal, would initially consists of aerostats filled with breathable air (a 21:79 oxygen-nitrogen mix). This is based on the concept that air would be a lifting gas in the dense carbon dioxide atmosphere, possessing over 60% of the lifting power that helium has on Earth.
These would provide initial living spaces for colonists, and could act as terraformers, gradually converting Venus’ atmosphere into something livable so the colonists could migrate to the surface. One way to do this would be to use these very cities as solar shades, since their presence in the clouds would prevent solar radiation from reaching the surface.
This would work particularly well if the floating cities were made of low-albedo materials. Alternately, reflective balloons and/or reflecting sheets of carbon nanotubes or graphene could be deployed from these. This offers the advance of in-situ resource allocation, since atmospheric reflectors could be built using locally-sourced carbon.
In addition, these colonies could serve as platforms where chemical elements were introduced into the atmosphere in large amounts. This could take the form of calcium and magnesium dust (which would sequester carbon in the form of calcium and magnesium carbonates), or a hydrogen aerosol (producing graphite and water, the latter of which would fall to the surface and cover roughly 80% of the surface in oceans).
NASA has begun exploring the possibility of mounting crewed missions to Venus as part of their High Altitude Venus Operational Concept (HAVOC), which was proposed in 2015. As outlined by Dale Arney and Chris Jones from NASA’s Langley Research Center, this mission concept calls for all crewed portions of the missions to be conducted from lighter than air craft or from orbit.
Potential Benefits:
The benefits of colonizing Venus are many. For starters, Venus it the closest planet to Earth, which means it would take less time and money and send missions there, compared to other planets in the Solar System. For example, the Venus Express probe took just over five months to travel from Earth to Venus, whereas the Mars Express probe took nearly six months to get from Earth to Mars.
In addition, launch windows to Venus occur more often, every 584 days when Earth and Venus experience an inferior conjunction. This is compared to the 780 days it takes for Earth and Mars to achieve opposition (i.e. the point in their orbits when they make their closest approach).
Compared to a mission to Mars, a mission to Venus’ atmosphere would also subject astronauts to less in the way of harmful radiation. This is due in part to Venus’ greater proximity, but also from Venus’ induced magnetosphere – which comes from the interaction of its thick atmosphere with solar wind.
Also, for floating settlements established in Venus’ atmosphere, there would be less risk of explosive decompression, since there would not be a significant pressure difference between the inside and outside of the habitats. As such, punctures would pose a lesser risk, and repairs would be easier to mount.
In addition, humans would not require pressurized suits to venture outside, as they would on Mars or other planets. Though they would still need oxygen tanks and protection against the acid rain when working outside their habitats, work crews would find the environment far more hospitable.
Venus is also close in size and mass to the Earth, resulting in a surface gravity that would be much easier to adapt to (0.904 g). Compared to gravity on the Moon, Mercury or Mars (0.165 and 0.38 g), this would likely mean that the health effects associated with weightlessness or microgravity would be negligible.
In addition, a settlement there would have access to abundant materials with which to grow food and manufacture materials. Since Venus’ atmosphere is made mostly out of carbon dioxide, nitrogen and sulfur dioxide, these could be sequestered to create fertilizers and other chemical compounds.
CO² could also be chemically separated to create oxygen gas, and the resulting carbon could be used to manufacture graphene, carbon nanotubes and other super-materials. In addition to being used for possible solar shields, they could also be exported off-world as part of the local economy.
Challenges:
Naturally, colonizing a planet like Venus also comes with its share of difficulties. For instance, while floating colonies would be removed from the extreme heat and pressure of the surface, there would still be the hazard posed by sulfuric acid rain. So addition to the need for protective shielding in the colony, work crews and airships would also need protection.
Second, water is virtually non-existent on Venus, and the composition of the atmosphere would not allow for synthetic production. As a result, water would have to be transported to Venus until it be produced onsite (i.e. bringing in hydrogen gas to create water form the atmosphere), and extremely strict recycling protocols would need to be instituted.
Solar shades placed in orbit of Venus are a possible means of terraforming the planet. Credit: IEEE Spectrum/John MacNeill
And of course, there is the matter of the cost involved. Even with launch windows occurring more often, and a shorter transit time of about five months, it would still require a very heavy investment to transport all the necessary materials – not to mention the robot workers needed to assemble them – to build even a single floating colony in Venus’ atmosphere.
Still, if we find ourselves in a position to do so, Venus could very become the home of “Cloud Cities”, where carbon dioxide gas is processed and turned into super-materials for export. And these cities could serve as a base for slowly introducing “The Big Rain” to Venus, eventually turning into the kind of world that could truly live up to the name “Earth’s sister planet”.
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At a closest average distance of 41 million km (25,476,219 mi), Venus is the closest planet to Earth. Credit: NASA/JPL/Magellan
A common question when looking at the Solar System and Earth’s place in the grand scheme of it is “which planet is closest to Earth?” Aside from satisfying a person’s general curiosity, this question is also of great importance when it comes to space exploration. And as humanity contemplates mounting manned missions to neighboring planets, it also becomes one of immense practicality.
If, someday, we hope to explore, settle, and colonize other worlds, which would make for the shortest trip? Invariable, the answer is Venus. Often referred to as “Earth’s Twin“, Venus has many similarities to Earth. It is a terrestrial planet, it orbits within the Sun’s habitable zone, and it has an atmosphere that is believed to have once been like Earth’s. Combined with its proximity to us, its little wonder we consider it our twin.
Venus’ Orbit:
Venus orbits the Sun at an average distance (semi-major axis) of 108,208,000 km (0.723 AUs), ranging between 107,477,000 km (0.718 AU) at perihelion and 108,939,000 km (0.728 AU) at aphelion. This makes Venus’ orbit the least eccentric of all the planets in the Solar System. In fact, with an eccentricity of less than 0.01, its orbit is almost circular.
Earth and Venus’ orbit compared. Credit: Sky and Telescope
When Venus lies between Earth and the Sun, it experiences what is known as an inferior conjunction. It is at this point that it makes its closest approach to Earth (and that of any planet) with an average distance of 41 million km (25,476,219 mi). On average, Venus achieves an inferior conjunction with Earth every 584 days.
And because of the decreasing eccentricity of Earth’s orbit, the minimum distances will become greater over the next tens of thousands of years. So not only is it Earth’s closest neighbor (when it makes its closest approach), but it will continue to get cozier with us as time goes on!
Venus vs. Mars:
As Earth’s other neighbor, Mars also has a “close” relationship with Earth. Orbiting our Sun at an average distance of 227,939,200 km (1.52 AU), Mars’ highly eccentric orbit (0.0934) takes it from a distance of 206,700,000 km (1.38 AU) at perihelion to 249,200,000 km (1.666 AU) at aphelion. This makes its orbit one of the more eccentric in our Solar System, second only to Mercury
For Earth and Mars to be at their closest, both planets needs to be on the same side of the Sun, Mars needs to be at its closest distance from the Sun (perihelion), and Earth needs to be at its farthest (aphelion). This is known as opposition, a time when Mars appears as one of the brightest objects in the sky (as a red star), rivaling that of Venus or Jupiter.
The eccentricity in Mars’ orbit means that it is . Credit: NASA
But even at this point, the distance between Mars and Earth ranges considerably. The closest approach to take place occurred back in 2003, when Earth and Mars were only 56 million km (3,4796,787 mi) apart. And this was the closest they’d been in 50,000 years. The next closest approach will take place on July 27th, 2018, when Earth and Mars will be at a distance of 57.6 million km (35.8 mi) from each other.
It has also been estimated that the closest theoretical approach would take place at a distance of 54.6 million km (33.9 million mi). However, no such approach has been documented in all of recorded history. One would be forced to wonder then why so much of humanity’s exploration efforts (past, present and future) are aimed at Mars. But when one considers just how horrible Venus’ environment is in comparison, the answer becomes clear.
Exploration Efforts:
The study and exploration of Venus has been difficult over the years, owing to the combination of its dense atmosphere and harsh surface environment. Its surface has been imaged only in recent history, thanks to the development of radar imaging. However, many robotic spacecraft and even a few landers have made the journey and discovered much about Earth’s closest neighbor.
The first attempts were made by the Soviets in the 1960s through the Venera Program. Whereas the first mission (Venera-1) failed due to loss of contact, the second (Venera-3) became the first man-made object to enter the atmosphere and strike the surface of another planet (on March 1st, 1966). This was followed by the Venera-4 spacecraft, which launched on June 12th, 1967, and reached the planet roughly four months later (on October 18th).
The first color pictures taken of the surface of Venus by the Venera-13 space probe. Credit: NASA
NASA conducted similar missions under the Mariner program. The Mariner 2 mission, which launched on December 14th, 1962, became the first successful interplanetary mission and passed within 34,833 km (21,644 mi) of Venus’ surface. Between the late 60s and mid 70s, NASA conducted several more flybys using Mariner probes – such as the Mariner 5 mission on Oct. 19th, 1967 and the Mariner 10mission on Feb. 5th, 1974.
The Soviets launched six more Venera probes between the late 60s and 1975, and four additional missions between the late 70s and early 80s. Venera-5, Venera-6, and Venera-7 all entered Venus’ atmosphere and returned critical data to Earth. Venera 11 and Venera 12 detected Venusian electrical storms; and Venera 13 andVenera 14 landed on the planet and took the first color photographs of the surface. The program came to a close in October 1983, when Venera 15 and Venera 16 were placed in orbit to conduct mapping of the Venusian terrain with synthetic aperture radar.
By the late seventies, NASA commenced the Pioneer Venus Project, which consisted of two separate missions. The first was the Pioneer Venus Orbiter, which inserted into an elliptical orbit around Venus (Dec. 4th, 1978) to study its atmosphere and map the surface. The second, the Pioneer Venus Multiprobe, released four probes which entered the atmosphere on Dec. 9th, 1978, returning data on its composition, winds and heat fluxes.
Artist’s impression of NASA’s Pioneer Venus Orbiter in orbit around Venus. Credit: NASA
In 1985, the Soviets participated in a collaborative venture with several European states to launch the Vega Program. This two-spacecraft initiative was intended to take advantage of the appearance of Halley’s Comet in the inner Solar System, and combine a mission to it with a flyby of Venus. While en route to Halley on June 11th and 15th, the two Vega spacecraft dropped Venera-style probes into Venus’ atmosphere to map its weather.
NASA’s Magellan spacecraft was launched on May 4th, 1989, with a mission to map the surface of Venus with radar. In the course of its four and a half year mission, Magellan provided the most high-resolution images to date of the planet, was able to map 98% of the surface and 95% of its gravity field. In 1994, at the end of its mission, Magellan was sent to its destruction into the atmosphere of Venus to quantify its density.
Venus was observed by the Galileo and Cassini spacecraft during flybys on their respective missions to the outer planets, but Magellan was the last dedicated mission to Venus for over a decade. It was not until October of 2006 and June of 2007 that the MESSENGER probe would conduct a flyby of Venus (and collect data) in order to slow its trajectory for an eventual orbital insertion of Mercury.
The Venus Express, a probe designed and built by the European Space Agency, successfully assumed polar orbit around Venus on April 11th, 2006. This probe conducted a detailed study of the Venusian atmosphere and clouds, and discovered an ozone layer and a swirling double-vortex at the south pole before concluding its mission in December of 2014. Since December 7th, 2015, Japan’s Akatsuki has been in a highly elliptical Venusian orbit.
Because of its hostile surface and atmospheric conditions, Venus has proven to be a tough nut to crack, despite its proximity to Earth. In spite of that, NASA, Roscosmos, and India’s ISRO all have plans for sending additional missions to Venus in the coming years to learn more about our twin planet. And as the century progresses, and if certain people get their way, we may even attempt to send human colonists there!
NASA's latest round of Discovery Program missions. Credit: NASA
It’s no secret that there has been a resurgence in interest in space exploration in recent years. Much of the credit for this goes to NASA’s ongoing exploration efforts on Mars, which in the past few years have revealed things like organic molecules on the surface, evidence of flowing water, and that the planet once had a denser atmosphere – all of which indicate that the planet may have once been hospitable to life.
But when it comes to the future, NASA is looking beyond Mars to consider missions that will send missions to Venus, near-Earth objects, and a variety of asteroids. With an eye to Venus, they are busy investigating the possibility of sending the Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) spacecraft to the planet by the 2020s.
Led by Lori Glaze of the Goddard Spaceflight Center, the DAVINCI descent craft would essentially pick up where the American and Soviet space programs left off with the Pioneer and Venera Programs in the 1970s and 80s. The last time either country sent a probe into Venus’ atmosphere was in 1985, when the Soviet probes Vega 1 and 2 both orbited the planet and released a balloon-supported aerobot into the upper atmosphere.
Model of the Vega 1 probe and landing apparatus at the Udvar-Hazy Center, Dulles International Airport, Chantilly, Virginia. Credit: historicspacecraft.com
These probes both remained operational for 46 hours and discovered just how turbulent and powerful Venus’ atmosphere was. In contrast, the DAVINCI probe’s mission will be to study both the atmosphere and surface of Venus, and hopefully shed some light on some of the planet’s newfound mysteries. According to the NASA release:
“DAVINCI would study the chemical composition of Venus’ atmosphere during a 63-minute descent. It would answer scientific questions that have been considered high priorities for many years, such as whether there are volcanoes active today on the surface of Venus and how the surface interacts with the atmosphere of the planet.”
These studies will attempt to build upon the data obtained by the Venus Express spacecraft, which in 2008/2009 noted the presence of several infrared hot spots in the Ganis Chasma region near the the shield volcano of Maat Mons (shown below). Believed to be due to volcanic eruptions, this activity was thought to be responsible for significant changes that were noted in the sulfur dioxide (SO²) content in the atmosphere at the time.
What’s more, the Pioneer Venus spacecraft – which studied the planet’s atmosphere from 1978 until its orbit decayed in 1992 – noted a tenfold decreased in the density of SO² at the cloud tops, which was interpreted as a decline following an episode of volcanogenic upwelling from the lower atmosphere.
3-D perspective of the Venusian volcano, Maat Mons, generated from radar data from NASA’s Magellan mission. Credit: NASA/JPL
Commonly associated with volcanic activity here on Earth, SO² is a million times more abundant in Venus’ atmosphere, where it helps to power the runaway greenhouse effect that makes the planet so inhospitable. However, any SO² released into Venus’ atmosphere is also short-lived, being broken down by sunlight within a matter of days.
Hence, any significant changes in SO² levels in the upper atmosphere must have been a recent addition, and some scientists believe that the spike observed in 2008/2009 was due to a large volcano (or several) erupting. Determining whether or not this is the case, and whether or not volcanic activity plays an active role in the composition of Venus’s thick atmosphere, will be central to DAVINCI’s mission.
Along with four other mission concepts, DAVINCI was selected as a semifinalist for the NASA Discovery Program‘s latest calls for proposed missions. Every few years, the Discovery Program – a low-cost planetary missions program that is managed by the JPL’s Planetary Science Division – puts out a call for missions with an established budget of around $500 million (not counting the cost of launch or operation).
The latest call for submissions took place in February 2014, as part of the Discovery Mission 13. At the time, a total of 27 teams threw their hats into the ring to become part of the next round of space exploration missions. Last Wednesday, September 30th, 2015, five semifinalists were announced, one (or possibly two) of which will be chosen as the winner(s) by September 2016.
Artist rendition of NASA’s Mars InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) Lander, which was selected as part of the Discovery Programs 2010 call for submissions and will be launched by 2016. Credit: JPL/NASA
These finalists will receive $3 million in federal grants for detailed concept studies, and the mission (or missions) that are ultimately chosen will be launched by December 31st, 2021. The Discovery Program began back in 1992, and launched its first mission- the Mars Pathfinder – in 1996. Other Discovery missions include the NEAR Shoemaker probe that first orbited an asteroid, and the Stardust-NExT project, which returned samples of comet and interstellar dust to Earth.
NASA’s MESSENGER spacecraft, the planet-hunting Kepler telescope, and the Dawn spacecraft were also developed and launched under the Discovery program. The winning proposal of the Discovery Program’s 12th mission, which was issued back in 2010, was the InSight Mars lander. Set to launch in March of 2016, the lander will touch down on the red planet, deploy instruments to the planet’s interior, and measure its seismic activity.
NASA hopes to infuse the next mission with new technologies, offering up government-furnished equipment with incentives to sweeten the deal for each proposal. These include a supply of deep space optical communications system that are intended to test new high-speed data links with Earth. Science teams that choose to incorporate the laser telecom unit will be entitled to an extra $30 million above their $450 million cost cap.
If science teams wish to send entry probes into the atmospheres of Venus or Saturn, they will need a new type of heat shield. Hence, NASA’s solicitation includes a provision to furnish a newly-developed 3D-woven heat shield with a $10 million incentive. A deep space atomic clock is also available with a $5 million bonus, and NASA has offered to provide xenon ion thrusters and radioisotope heater units without incentives.
As with previous Discovery missions, NASA has stipulated that the mission must use solar power, limiting mission possibilities beyond Jupiter and Saturn. Other technologies may include the NEXT ion thruster and/or re-entry technology.
False color radar topographical map of Venus provided by Magellan. Credit: Magellan Team/JPL/NASA
Venus was once considered a twin to Earth, as it’s roughly the same size and is relatively close to our planet. But once astronomers looked at it seriously in the past half-century or so, a lot of contrasts emerged. The biggest one — Venus is actually a hothouse planet with a runaway greenhouse effect, making it inhospitable to life as we know it. Here are some more interesting facts about Venus.
1. Venus’ atmosphere killed spacecraft dead very quickly: You sure don’t want to hang around on Venus’ surface. The pressure there is so great that spacecraft need shielding to survive. The atmosphere is made up of carbon dioxide with bits of sulfuric acid, NASA says, which is deadly to humans. And if that’s not bad enough, the temperature at the surface is higher than 470 degrees Celsius (880 degrees Fahrenheit). The Soviet Venera probes that ventured to the surface decades ago didn’t last more than two hours.
2. But conditions are more temperate higher in the atmosphere: While you still couldn’t breathe the atmosphere high above Venus’ surface, at about 50 kilometers (31 miles) you’ll at least find the same pressure and atmosphere density as that of Earth. A very preliminary NASA study suggests that at some point, we could deploy airships for humans to explore Venus. And the backers suggest it may be more efficient to go to Venus than to Mars, with one large reason being that Venus is closer to Earth.
Artist’s conception of the High Altitude Venus Operational Concept (HAVOC) mission, a far-out concept being developed by NASA, approaching the planet. Credit: NASA Langley Research Center/YouTube (screenshot)
3. Venus is so bright it is sometimes mistaken for a UFO: The planet is completely socked in by cloud, which makes it extremely reflective to observers looking at the sky on Earth. Its brightness is between -3.8 and -4.8 magnitude, which makes it brighter than the stars in the sky. In fact, it’s so bright that you can see it go through phases in a telescope — and it can cast shadows! So that remarkable appearance can confuse people not familiar with Venus in the sky, leading to reports of airplanes or UFOs.
4. And those clouds mean you can’t see the surface: If you were to look at Venus with your eyes, you wouldn’t be able to see its surface. That’s because the clouds are so thick that they obscure what is below. NASA got around that problem when it sent the Magellan probe to Venus for exploration in the 1990s. The probe orbited the planet and got a complete surface picture using radar.
Artist’s impression of the surface of Venus Credit: ESA/AOES
5. Venus has volcanoes and a fresh face: Venus has fresh lava flows on its surface, which implies that volcanoes erupted anywhere from the past few hundred years to the past three million years. What this means is there are few impact craters on the surface, likely because the lava flowed over them and filled them in. While scientists believe the volcanoes are responsible, the larger question is how frequently this occurs.
6. Venus has a bizarre rotation: Venus not only rotates backwards compared to the other planets, but it rotates very slowly. In fact, a day on Venus (243 days) lasts longer than it takes the planet to orbit around the Sun (225 days). Even more strangely, the rotation appears to be slowing down; Venus is turning 6.5 minutes more slowly in 2014 than in the early 1990s. One theory for the change could be the planet’s weather; its thick atmosphere may grind against the surface and slow down the rotation.
Artist’s conception of Venus Express doing an aerobraking maneuver in the atmosphere in 2014. Credit: ESA–C. Carreau
7. Venus has no moons or rings: The two planets closest to the Sun have no rings or moons, which puts Venus in the company of only one other world: Mercury. Every other planet in the Solar System has one or the other, or in many cases both! Why this is is a mystery to scientists, but they are doing as much comparison of different planets as possible to understand what’s going on.
8. Venus appears to be a spot where spacecraft go to extremes: We briefly mentioned the Venera probes that landed on the surface, but that’s not the only unusual spacecraft activity at Venus. In 2014, the European Space Agency put an orbiter — that’s right, a spacecraft not designed to survive the atmosphere — into the upper parts of Venus’ dense atmosphere. Venus Express did indeed survive the encounter (before it ran out of gas), with the goal of providing more information about how the atmosphere looks at high altitudes. This could help with landings in the future.
As you can see, Venus is an interesting, mysterious, and extremely hostile world. With such a corrosive atmosphere, such incredible heat, a volcanically-scarred surface, and thick clouds of toxic gas, one would have to be crazy to want to live there. And yet, there are some who believe Venus could be terraformed for human use, or at the very least explored using airships, in the coming generations.
But that’s the thing about interesting places. Initially, they draw their fair share of research and attention. But eventually, the dreamers and adventurers come.
