11.12.2021

A false-color image of the sulfurous Venusian cloud cover was produced using two ultraviolet channels from Akatsuki, the Japanese PLANET-C, and Venus Climate Orbiter, which highlights the convective turbulence of the planet's tropical regions, in contrast with the clear, smoother polar regions.

With multiple rovers landed and a mission set to return samples to Earth, Mars has dominated the search for life in the solar system for decades. But Venus has some fresh attention coming its way.

In a new report published Friday, a team led by MIT researchers lays out the scientific plan and rationale for a suite of scrappy, privately-funded missions set to hunt for signs of life among the ultra-acidic atmosphere of the second planet from the sun.

"We hope this is the start of a new paradigm where you go cheaply, more often, and in a more focused way," says Sara Seager, Class of 1941 Professor of Planetary Sciences in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS) and principal investigator for the planned Venus Life Finder Missions. "This is a newer, nimbler, faster way to do space science. It's very MIT."

The first of the missions is set to launch in 2023, managed and funded by California-based Rocket Lab. The company's Electron rocket will send a 50-pound probe on board its Photon spacecraft for the five-month, 38-million-mile journey to Venus, all for a three-minute skim through the Venusian clouds.

Using a laser instrument specially designed for the mission, the probe will aim to detect signs that complex chemistry is occurring within the droplets it encounters on its brief descent into the haze. Fluorescence or impurities detected in the droplets could indicate something more interesting than sulfuric acid might be wafting around up there, and add ammunition to the idea that parts of Venus' atmosphere might be habitable.

"People have been talking about missions to Venus for a long time," says Seager. "But we've come up with a new suite of focused, miniaturized instruments to get the particular job done."

Seager, who also holds joint appointments in the departments of Physics and of Aeronautics and Astronautics, says that compared to Mars, Venus is the "neglected sibling" of astrobiology. The last probes to enter Venus' atmosphere were launched in the 1980s, and were limited by instrumentation available at the time. And while NASA and the European Space Agency have missions to Venus planned for later in the decade, neither will search for signs of life.

"There are these lingering mysteries on Venus that we can't really solve unless we go back there directly," says Seager. "Lingering chemical anomalies that leave room for the possibility of life."

These anomalies include significant levels of oxygen; unexplained ratios of sulfur dioxide, oxygen, and water; and the presence of cloud particles with unknown composition. More controversially, Seager was part of a team that reported last year a detection of phosphine gas in Venus' atmosphere, which on Earth is produced only by biological and industrial processes.

Other astrophysicists have since challenged the phosphine detection, but Seager says the finding has overall brought positive momentum to the Venus missions. "The whole phosphine controversy made people more interested in Venus. It allowed people to take Venus more seriously," she says.

Phosphine or not, the planned missions will focus on Venus' atmosphere because it is the environment most likely to be habitable on the planet. While a runaway greenhouse effect left Venus' surface a waterless hellscape hot enough to melt lead, clouds high in the atmosphere retain temperatures suitable for life as we know it.

"If there's life on Venus, it's some kind of microbial-type life, and it almost certainly resides inside cloud particles," says Seager.

However, the clouds of Venus, though relatively temperate, pose other challenges to habitability. For one, they are primarily composed of concentrated sulfuric acid billions of time more acidic than any habitat on Earth. The atmosphere outside of the clouds is also extremely dry, 50 to 100 times drier than the Atacama Desert in Chile.

To assess the potential habitability of these acidic, parched clouds, the report team reviewed the literature and conducted a number of experiments. "We set out to do some new science to inform the mission," says Seager.

The international team behind the report included researchers from Georgia Tech, Purdue University, Caltech, and Planetary Science Institute, and was funded by Breakthrough Initiatives. In addition to Seager, who led the team, MIT EAPS Research Affiliate Janusz Petkowski served as deputy principal investigator.

Drawing from experimental results, the report speculates that life could persist within sulfuric acid droplets in various ways. It could reside within vesicles of acid-resistant lipids, or it could neutralize sulfuric acid by producing ammonia, which can reduce the pH of sulfuric acid to a level tolerated by acid-loving microbes on Earth. Or, in theory, Venus cloud-life could rely on a biochemistry capable of tolerating sulfuric acid, distinct from anything on Earth.

Regarding dryness, the report points out that while the atmosphere on average might be too arid for life, there may exist habitable regions with relatively high humidity.

Based on their research, the team also selected the scientific payload for the mission - which was restricted to just 1 kilogram. Seager says they settled on an instrument called an autofluorescing nephelometer because it could get the job done and was small, cheap, and could be built quickly enough for the compressed mission timeline.

The instrument is currently being built by a New Mexico-based company called Cloud Measurement Solutions, and a Colorado-based company called Droplet Measurement Technologies. The instrument is partially funded by MIT alumni.

Once the probe is in Venus' atmosphere, the instrument will shine a laser out of a window onto cloud particles, causing any complex molecules within them to light up, or fluoresce. Many organic molecules, such as the amino acid tryptophan, have fluorescent properties.

"If we see fluorescence, we know something interesting is in the cloud particles," says Seager. "We can't guarantee what organic molecule it is, or even be certain it's an organic molecule. But it's going to tell you there's something incredibly interesting going on."

The instrument will also measure the pattern of light reflected back from the droplets to determine their shape. Pure sulfuric acid droplets would be spherical. Anything else would suggest there's more going on than meets the autofluorescing nephelometer.

But whatever the 2023 mission finds, the next mission in the suite is already being planned for 2026. That probe would involve a larger payload, with a balloon that could spend more time in Venus' clouds and conduct more extensive experiments. Results from that mission might then set the stage for the culmination of the Venus Life Finder Missions concept: return a sample of Venus' atmosphere to Earth.

"We think it's disruptive," says Seager. "And that's the MIT style. We operate right on that line between mainstream and crazy."

Quelle: SD

+++

WVU engineers creating software for aerobots to explore Venus

Engineers at West Virginia University are propelling exploration forward by creating control software for a group of aerial robots (aerobots) that will survey the atmosphere of Venus, the second planet from the sun.

According to researchers, Venus went through a climate change process that transformed it from an Earth-like environment to an inhospitable world. Studying Venus can help model the evolution of climate on Earth and serve as a reference for what can happen in the future.

Guilherme Pereira and Yu Gu, associate professors in the Department of Mechanical and Aerospace Engineering, tasked with developing the software for the aerobots, which are balloon-based robotic vehicles, hope to play a pivotal role in these discoveries. Their study is supported by a $100,000 NASA Established Program to Stimulate Competitive Research.

"The main goal of the project is to propose a software solution that will allow hybrid aerobots to explore the atmosphere of Venus," Pereira said. "Although hybrid vehicles were proposed before this project, we are not aware if any software has been created."

One aerobot concept is the Venus Atmosphere Maneuverable Platform, which is a hybrid airship that uses both buoyancy and aerodynamic lift to control its altitude. The benefit of a hybrid aerobot is its ability to, during the day, behave like a plane, collecting and using energy from the sun to drive its motors, and, during the night, float like a balloon to save energy.

The buoyancy of the vehicle would prevent it from going below 50 km - or 31 miles, below the surface of Venus where the temperature is very high and would damage the vehicle, according to Pereira.

"One of the ideas of our project is to extend the battery life of the vehicle by planning energy-efficient paths, thus allowing it to fly during the night as well," Pereira said.

The aerobot lifespan at cruise altitude is several months to a year.

Pereira and Gu said their software will have three main goals. The first is to create a motion planer for the vehicles, so they can be commanded to go from their current position to a goal position specified by NASA's science team using minimum energy and leveraging the winds in the planet. The motion planner is a software that will run in the aerobot's computer.

"The motion planner will be created by understanding the dynamics of the aerobot, the properties of its solar panels and batteries and the properties of Venus atmosphere," Pereira said. "With the dynamics of the vehicle, the planner will only consider movements that are feasible given certain inputs to the aircraft, such as thrust coming from the propellers or deflections of the control surfaces."

Pereira said that understanding the solar panels and batteries is important to account for how much charge the vehicle has to power its systems and what its recharging rate is according to the solar intensity.

"The understanding of the atmosphere provides the robots quantities like wind direction and magnitude, pressure, temperature and solar intensity," Pereira said.

With these models, the motion planner will calculate the best route for the aerobot.

"We are trying to come up with an optimal energy strategy," Pereira said. "This is important since the vehicle will be orbiting the atmosphere of Venus in around four days. It will be exposed to long periods without light on the dark side of the planet and it needs to have enough energy to survive these periods."

According to Pereira, the motion planner will have access to the position of the aerobot in Venus atmosphere and to a desired goal location. It will also have access to information about the atmosphere in between these two positions.

"Starting from the initial position, the planner will simulate different movements the aerobot could make and associate costs for each of them depending on the quantities mentioned before," Pereira said.

For example, if the wind is blowing in the same direction as the movement of the aerobot, that would be less costly than moving against the wind direction.

"After that, the motion planner will keep propagating the movements of the aerobot with smaller cost, creating a tree of possibilities until we reach our destination," Pereira said.

The second goal of this project is to localize the aerobot vehicles in the atmosphere using information from other vehicles and maps of the planet. There is currently no GPS in Venus, so localization is difficult.

This localization approach will allow several robots to be less lost as a group when they are exploring Venus.

Gu and Pereira plan on using different types of maps for localization.

"We are evaluating the possibility of using maps created before the mission, most likely a Venus topographic map to help the robots to localize themselves," Gu said.

The third goal for this project is to coordinate the vehicles so that they have improved localization and a better estimation of atmosphere conditions.

The spatial distribution of the aerobots in the atmosphere may allow each aerobot to have a better knowledge of the 3D wind field if each vehicle shares the wind flow in its neighborhood, according to Pereira.

Pereira and Gu's research will be based on wind models of Venus created by NASA. The researchers also propose that the aerobots carry wind sensors that can be used to estimate the local wind.

"The importance of the wind flow is related to the fact that it can be exploited to take the aerobot to desired locations," Pereira said. "Just as with sprinters in the Olympics when they get better marks if they are experiencing tail-wind. If the wind is directed towards the goal of the aircraft, the aerobot movement will be aided by the wind and, by consequence, the path will be more energetically efficient."

To test this, Pereira and Gu plan to develop a Venus atmosphere simulator, where they will evaluate the aerobots' functionality.

"Several exploratory missions to Venus collected data of wind, temperature, pressure and air density," Pereira said. "This information was then used to create a simulator where, given the latitude, longitude and altitude of the vehicle, we compute all the forces acting on the vehicle."

Joining Pereira and Gu on the project are Bernardo Martinez Rocamora Jr. and Chizhao Yang, doctoral students in aerospace and mechanical engineering, and Anna Puigvert i Juan, master's student in mechanical engineering.

Quelle: SD