Religion and Science: From Galileo to Aliens

One of the most famous examples of the clash between religion and science is the trial of Galileo Galilei. Galileo supported Copernicus’ view that the Earth orbited the sun, a “heliocentric” theory which the church declared contrary to Scripture. Galileo was warned to abandon his support for this theory and instead embrace the traditional “geocentric” notion that the Earth was an unmovable point around which the universe revolved.
Instead, in 1632 Galileo published “Dialogue Concerning the Two Chief World Systems.” The book was structured as a conversation between Salviati, a heliocentric philosopher, Simplicio, a geocentric philosopher, and Sagredo, a neutral layman. Pope Urban VIII had actually given Galileo permission to write the book as long as he didn’t promote one viewpoint over the other. However, Salviati forcefully argued Galileo’s beliefs, while Simplicio was often ridiculed as a fool.
An often-repeated view about the furor which followed the publication of Galileo’s book is that the pope was insulted by having his words expressed by Simplicio. Not only was the character made to look ridiculous, but the name itself likely was a double entendre for “simple-minded” (simplice in Italian). However, Vatican astronomer Brother Guy Consolmagno disputes this analysis.

“First, ‘Simplicio’ was a well-established name in philosophical discourses, not something invented by Galileo, to represent a person who was able to see through the fog generated by the more clever and learned philosophers who invent elaborate theories and lose sight of simple obvious truths, like the innocent child who can recognize that the emperor has no clothes,” said Consolmagno. “In this context, its use could be seen as a compliment. Second, this kind of punning is quite common in English but my impression is that it is not really done all that much, or in the same way, in Italian; I do not know if anyone at that time and place would have interpreted it the way we English speakers do. And finally, the book was originally approved by the Pope’s censors before being published; if he were going to be insulted by the name, he’d have noticed it long before it was ever printed.”
Still, the political fallout eventually led the church to withdraw its permission to publish the book. Galileo faced a specially convened panel of ten judges, who found him guilty of suspicion of heresy. By abjuring – saying that he never believed in the heliocentric point of view expressed in the book – Galileo’s sentence was reduced to house arrest.
“He served (his sentence) first as the honored guest of the bishop of Siena before returning to his own villa, where he lived for another decade, had a regular string of visitors, and wrote another book,” said Consolmagno. “I don’t want to whitewash the mistakes the church made in the Galileo affair, but…it certainly was not a simple knee-jerk reaction against science.”
Consolmagno said that to truly understand what happened, we need to take into account the philosophical thinking of the time and the events that were taking place both within the Church and in the larger society. This context can be glimpsed in the original documents from the trial, which have been translated into English in various publications, such as Maurice Finocchiaro’s “The Galileo Affair” (University of California Press, 1989).
“They got Galileo on a technicality, and he was guilty of that technicality; but why they decided to go after him, in that way, at that time, is an open question,” said Consolmagno. “We can see today that he should never have been brought to trial in the first place.”
By 1992, Pope John Paul II issued a declaration acknowledging errors in Galileo’s trial. No such apologetic statement has been made for Giordano Bruno, whom the Church burned at the stake in 1600.
Bruno not only supported the heliocentric view, he also claimed there are multiple worlds beyond Earth, each orbiting their own sun. Consolmagno and his colleague, Vatican astronomer Father Paul Pavel Gabor, say Bruno’s death sentence was not due to him advancing these notions.
“The old joke is that if he was burned for anything back then, it was for plagiarism,” said Consolmagno. “Nicholas of Cusa published those same ideas 200 years earlier, and he was a Cardinal.”
Nicholas of Cusa’s book, “On Learned Ignorance,” in which he discussed the possibility of multiple worlds, was published in 1440. He also wrote that aliens could exist on the moon and the sun.
“He was made a cardinal in 1448, so it’s quite obvious that it didn’t damage his career,” noted Gabor.
Consolmagno said the most probable reason for the church’s enmity was that Bruno denied the divinity of Christ, as well as some other fundamental doctrines of Christianity.
A bronze statue of Giordano Bruno stands in the Campo de’ Fiori in Rome, where he was executed in 1600

“I think the real problem with Bruno was he was accused of being an English spy,” added Gabor. He said that Bruno was imprisoned in various places throughout Europe before landing in jail in Venice, which then led to his death in Rome. Gabor said that the file on last 7 years of his trial is gone, because Napoleon looted the Vatican for paper.
“Everybody who keeps writing about it as if they knew what happened is actually just fantasizing,” said Gabor.
Both Consolmagno and Gabor stress that the idea of aliens and multiple worlds is not a new idea for the church, and doesn’t challenge or threaten the central beliefs of their religion. The Vatican even sponsored an astrobiology workshop in 2009. According to Consolmagno, the church did so in order to create a forum for top scientists in the field to have a conversation.
“It was not the way it was reported on CNN, where the Catholic church was worried about aliens,” he said.
They say there was no religious discussion during this workshop; instead the focus was purely on the science of astrobiology. The philosophical crossover between religion and science was only discussed informally, during coffee breaks and other social gatherings.
Philosophers have been grappling with the implications of alien life for hundreds of years, if not longer. But until aliens are found, said Consolmagno, these issues will remain in the realm of science fiction instead of religion or science.
“I think that’s a very important role that science fiction has to play, because at this point we’re just playing with ideas,” said Consolmagno. “We’re just exploring the space where the ideas could be. We don’t know – we don’t have the answers. That’s why it’s so much fun!”

Water geysers erupt on Europa! Could Jupiter’s icy moon host life?

Jupiter’s icy moon Europa squirts water like a squishy bath toy when it’s squeezed by the gas giant’s gravity, scientists say. Using NASA’s Hubble Space Telescope, they caught two 124-mile-tall geysers of water vapor spewing out over seven hours from near its south pole.

Water on Jupiter's moon Europa

The discovery, described in the journal Science and at the American Geophysical Union meeting in San Francisco, shows that Europa is still geophysically active – and that this world in our own solar system could hold an environment friendly to life.

“It’s exciting,” said Lorenz Roth, a planetary scientist at the Southwest Research Institute in San Antonio and one of the study’s lead authors. “The results are actually more convincing than I would have thought before.”

Europa isn’t the only squirty moon in our planetary system: Saturn’s moon Enceladus has also been caught shooting water out of its south pole in so-called tiger stripes. These pretty plumes are caused by tidal forces. Just as our moon’s gravity squeezes and stretches the Earth a bit, causing the oceans to rise and fall, Saturn’s massive gravitational pull squeezes and stretches its tiny moon, causing cracks on its icy surface to open and allowing water to shoot out.

Scientists have long wondered whether something similar was happening on Jupiter’s moon Europa. After all, its surface is about 65 million years old, which is extremely young by our solar system’s standards, little more than 1.5% of the solar system’s age. This should mean that some geophysical processes must be constantly renewing the surface.

But over several decades, researchers repeatedly failed to catch the moon in action, said Robert Pappalardo, a Jet Propulsion Laboratory planetary scientist who was not involved in the study.

When the Voyager spacecraft, launched in 1977, flew by Europa, it caught a tiny blip on the moon’s edge that people thought might be a plume, but it could not be confirmed. Then the 1989 Galileo spacecraft saw a potential plume of its own. But this turned out to be digital residue, traces of a previous image, Pappalardo said.

Even Hubble probably wasn’t able to properly see such plumes until space shuttle astronauts on the very last servicing mission for the iconic space telescope in 2009 fixed one of its cameras. Even now, looking for water vapor in the ultraviolet wavelengths of light tests the limits of Hubble’s abilities, scientists said.

To catch Europa in the act, the researchers also knew they had to time their observations right. Saturn’s icy moon, Enceladus, shoots water near the farthest point in its orbit from Saturn, when the tidal forces cause cracks at the moon’s south pole to open. Around Jupiter, Europa was probably doing the same thing.

Sure enough, when the scientists looked at Europa when it was close to Jupiter in its orbit, they saw nothing. But in December 2012, when the ice moon was at its farthest point from the gas giant, they caught a pair of plumes bearing clear signs of oxygen and hydrogen – the components of water vapor – shooting from near the southern pole.

Scientists can’t say exactly where the plumes are coming from. It could be that they’re going directly from solid ice to gas, as Europa’s ice sheets rub against each other. But it could also be that the these plumes of vapor may be coming from the ocean of liquid water thought to lie under the moon’s frozen surface.

If the moon is still geophysically active, that could make it a prime environment for life.

Another study out of this week’s American Geophysical Union meeting found signs of clays on Europa’s surface. Clays are often associated with organic matter, which is why NASA’s Mars rover Curiosity is headed to Mt. Sharp, whose clay-rich layers could hold signs of life-friendly environments.

Those clays were probably brought to Europa by comets or asteroids, and if such material was able to make it into Europa’s subsurface ocean, it could provide the nutrient-rich soup that could allow life to emerge.

“We’re trying to understand, could this be a habitable environment today? Could there be life there today?” Pappalardo said. “At Europa, it seems the processes that could permit habitability may be going on now.”

Perhaps future studies can analyze all the contents of that watery plume and see if there are any signs of organic matter, Pappalardo said. Perhaps a future mission to Europa could fly through the plume and directly sample its contents.

For now, it’s important to replicate the results, he added.

“I will sleep better knowing that there are follow-up observations that confirm it,” Pappalardo said.

Five of NASA’s Most ambitions undertaking.

Over the last few decades, NASA helped develop several revolutionary technologies, which have greatly benefited society as a whole. Said technologies have also revealed the universe to be an exceptionally strange place; From the discovery of giant space blobs, that could encompass our galaxy hundreds of times over – to hidden portals in the Earth’s magnetic field – we are obviously inching our way toward the dominance of space – or at the very least, the dominance of our own backyard. We obviously have quite a long way to go, which requires a bit of thinking-outside-of-the-box. Thankfully, the folks from NASA are working on several far flung conceptions. In fact, they even developed an entire branch, called theInstitute for Advanced Concepts (NIAC), solely to delve into this sort of research. Unfortunately, it was disbanded in 2007. (A similar program was recently reinstated) Still, many of the ground breaking concepts can still be found online, others are still in development – giving us an opportunity to blow your mind.

5. Solar Probe Plus Will Meet the Sun

NASA seems to have some kind of fetish for intentionally destroying sophisticated technology. They’ve bombed the moon several times now (once in 2009 and again in 2012, when “Ebb” and “Flow” finished their primary missions) and they sent the Galileo spacecraft spiraling into the Jovian atmosphere in 2003 (the same fate awaits the beloved Hubble Space Telescope when it ceased to be useful). Most of those missions were not developed for the sole purpose of being disintegrated, but NASA outdid themselves with the Solar Probe Plus.


The spacecraft, which is in development, will make close-up observations of Venus – before face-diving into the sun’s corona. The temperatures in this region can exceed 2,550 degrees Fahrenheit (1,400 degrees Celsius), which is about five times hotter than the temperature in Low-Earth orbit. Needless to say, it’s freaking hot.  The searing heat is further compounded by the stark increase in luminosity, as it’s estimated that from the corona, the sun appears more than 500 times brighter than it does on Earth.  (We can’t forget about the high energy particles that reside near the sun’s atmosphere) Obviously, this is ambitious for several reasons. Not least of all because the sun’s environment makes Venus look like the Bahamas in comparison.

If this one sounds vaguely familiar, it should. This concept is very similar to the main plot of a film entitled “Sunshine.” In the movie, which is set in the near future, a team of Earth-based scientists are sent on a mission to rejuvenate a dying sun, by bombing it – creating a “star within a star;” with a payload equivalent in mass to the island of Manhattan. Like Icarus 2 – from the movie – the Solar Probe Plus will have a huge sun-shield to temporarily protect it from the elements, until it, quite literally, is incinerated by our local star. (It’s expected to make it about 4 million miles from the sun beforehand)

and to think.. this has absolutely nothing on:

4. A Giant Sun- Shield – to Combat Global Warming

Discussing the merits of global warming has now eclipsed the discussions held about the moon landing conspiracy. (It happened. Get over it) Everyone seems to have an opinion on the subject (and as Neil deGrasse Tyson said, “Science is true. Whether or not you believe in it.”) With that said, regardless of the mechanism driving it – be it man-made, or something less nefarious – the temperatures are rising, which means something must be done to staunch the damage before the United States is relegated to the ocean floor.

Credit: Dan Roam (Source)

In this particular solution (many different concepts have came to light before), a scientist from the University of Arizona proposed that we develop trillions of free flying mirror units. After the individual units are deployed into space (using a large cannon that operates using electromagnetic propulsion, with the barrel alone coming in at about 0.06 miles across), they would collectively act as a lens, forming a huge shade that would extend some 100,000 square miles across. When sun rays come in contact with the units, they would be defected slightly (instead of hitting Earth) – thus lowering the soaring temperatures.

All it would cost is some 200 trillion dollars (or about 100 billion dollars per year) Kickstarter, anyone? (On a more serious note, the units could be manufactured in a way that would be conductive to collecting solar energy. Maybe eventually; the project would pay for itself)

3. Spray-on Space Suits

Evolution of the spacesuit (Credit: Cam Brensiger)
Evolution of the spacesuit (Credit: Cam Brensiger)

The number one cause of death in space is space itself.. It’s an extremely hostile environment. Exposure to the vacuum alone can kill you in a hundred different – all equally terrifying – ways. If any of them fail to turn you into a space kabob, the physical side effects ofmicrogravity will eventually. To get around that, space agencies have invested billions of dollars toward developing a functional space suit that can shield cosmonauts from the brunt of the dangers, whilst allowing them to effectively work and preform their necessary experiments. However, most of our modern spacesuits are completely ineffective at accomplishing most of those goals – a problem that will only become worse whenever we venture beyond low-Earth-orbit, into deep space.

Credit: Douglas Sonders (Source) :
Credit: Douglas Sonders (Source)

One of the most interesting concepts that came from NIAC revolved around spray-on polymer fabric spacesuits, which encompass most of the things researchers want to see in a next-generation space suit. The team of researchers discussed the possibility of covering an astronauts body with this organic, biodegradable technology, working similarly to a spray-on tan. Underneath the layer of flexible material, the person would alsobe equipped with temperature-controlled underwear, biosensors, electronic equipment and even artificial muscle fibers, which could improve strength, stamina and mobility (All of which can prevent the effects of muscle degradation in space) Such a technology could have practical applications here on Earth too – particularly for firefighters.

2. Inflatable Space Habitats

Like with our current spacesuits – another problematic aspect of space colonization is developing technologies that can give astronauts the needed space for living quarters, while still having proper room to carry out their experiments. Not to mention, we would also need a rocket that could carry all of this into space.


A rather ingenious solution to both of these problems is developing expandable modules – created using a strong and rigid, but highly effective material – which can be deployed into space using traditional rockets. Once they arrive to their destination, they can be inflated using pressurized air, providing us with a safe, roomy enclosure. (Ironically, the atypical structures are more durable than conventional metal ones. They could even better shield astronauts from micrometeorite impacts and harmful radiation) Incredibly, we may see inflatable structures in space sooner than one might think. Earlier this year, NASA andBigelow Aerospace (a private company that has done a tremendous amount of research on the topic) reached an agreement that would actually put an inflatable module on-board the ISS. Assuming all goes well, the technology could evolve into a functional prototype for a lunar space station.

Perhaps by creating a series of these habitats, scattering them about the solar system, it could even provide a cost effective way to explore our own neighborhood.

1. Laser Propulsion Systems

Modern space-shuttles – like the one used to carry men to the moon – accelerate using three different types of chemical propulsion systems (each of which require specific fuel). Unfortunately, the conventional methods are somewhat dangerous and they don’t offer too many advantages as far as interstellar travel is concerned. Because of this, a lot of exciting work is being done in developing more effective propulsion systems. (My personal favorite is ion thruster propulsion)

How it works (source)

Another concept NASA is currently exploring completely throws the need for multiple propulsion systems out, capitalizing instead on photonic laser thrusters! Such a system would operate using a photon beam amplification system and a photonic laser. As trapped photons – which have no mass, mind you; only momentum – bounce between mirrors on a series of spacecrafts, they produce substantial thrust (through photonic energy) that can accelerate a spacecraft to exceptional, energy-efficient, speeds. (Given enough time for acceleration, a vehicle using this type of system could propel to speeds approaching that of the speed of light. Never at – or above – that speed though, as it would take an infinite amount of energy to accelerate an object with mass to light-speed)

On a more relatable note – according to Dr. Young Bae (of the Bae Institute) – using photonic laser thrusters, we could make the trip from Earth to Mars in merely one week! (Compared to the typical 6 month journey)

Space fuel crisis: NASA confronts the plutonium pinch.

The cold war plutonium reserves that fuel NASA’s deep space probes are running low. How will we power our way to the outer solar system in future?

MORE than 18 billion kilometres from home, Voyager 1 is crossing the very edge of the solar system. If its instruments are correct, the craft is finally about to enter the unknown – the freezing vastness of interstellar space. It is the culmination of a journey that has lasted 35 years.

Voyager has a nuclear tiger in its tank <i>(Image: NASA)</i>

NASA’s most distant probe owes its long life to a warm heart of plutonium-238. A by-product of nuclear weapons production, the material creates heat as it decays and this is converted into electricity to power Voyager’s instruments. Engineers expect the craft will continue to beam back measurements for another decade or so, before disappearing into the void.

Since the 1960s, this plutonium isotope has played a crucial role in long-haul space missions, mainly in craft travelling too far from the sun to make solar panels practical. The Galileo mission to Jupiter, for instance, and the Pioneer and Voyager probes all relied on it, as does the Cassini orbiter, which has revealed the ethane lakes and icy geysers on Saturn’s moons, among other wonders.

Yet despite many successes, this kind of mission may soon be a thing of the past. The production of plutonium-238 halted decades ago and the space agency’s store is running perilously low. Without fresh supplies, our exploration of the outer solar system could soon come to a grinding halt.

The problem is that plutonium-238 is neither simple nor cheap to make, and restarting production lines will take several years and cost about $100 million. Though NASA and the US Department of Energy (DoE) are keen, Congress has so far refused to hand over the necessary funds.

But there could be a better way to make it. At a NASA meeting in March, physicists from the Center for Space Nuclear Research (CSNR) in Idaho Falls proposed a radical approach that they claim should please all parties. It will be quicker, cleaner and cheaper and could offer a production line run in a commercial fashion that not only meets NASA’s needs, but also turns a tidy profit into the bargain.

So what to do? Putting the production of this material on a commercial footing, as CSNR suggests, might prove easier on the public purse, but critics are concerned this could compromise safety. Plutonium is one of the most poisonous substances known – the isotope is a powerful emitter of alpha particles and deadly if inhaled. They argue that the time and money needed to restart production would be better spent developing safer alternatives. So is this the perfect opportunity to say farewell to this cold war technology and devise new, cleaner sources of space power that could benefit us earthlings too?

Plutonium-238 has played a key role in almost all of NASA’s long-duration space missions for good reason: it produces heat through the emission of alpha particles, and with a half-life of about 87 years, the material decays slowly. Sealed into a device called a radioisotope thermoelectric generator, the decaying plutonium heats a thermocouple to create electricity. Each gram of plutonium-238 generates approximately half a watt of power. On average, NASA has used a couple of kilograms of the isotope each year to power its various craft.

It does not occur naturally. Like its weapons-grade cousin, plutonium-239, it was originally created in the reactors that made material for nuclear bombs, but US production halted when those facilities were shut down in 1988. To fill the gap, the US purchased plutonium-238 from Russia until 2009, when a contract dispute ended the supply. With Russia now also running short, it is doubtful that any new deal will be struck.

So the US government must decide whether or not to resume production. According to a 2009 report by the US National Research Council, NASA has access to about 5 kilograms of the stuff, which could last it until the end of the decade (see diagram). Officials at the DoE say that if they get the go-ahead now, 2 kilograms could be made annually by 2018 – just in time to restock NASA’s cupboards. But funding is proving hard to come by. NASA has agreed to share the burden and released about $14 million for studies to work out the costs of restarting the production line – which would most likely be at Oak Ridge National Laboratory in Tennessee. However, costs could eventually spiral to $150 million, suggest some at the research council, and Congress seems loath to provide any funding directly to the DoE.

Clearly, making plutonium-238 is an expensive business. The conventional way to produce it involves placing a batch of neptunium-237 inside a powerful nuclear reactor and irradiating it with neutrons for up to a year (see diagram). The sample must then be put through a series of purification steps to separate plutonium-238 from the other fission products that also form.

At the NASA Innovative Advanced Concepts (NIAC) symposium in March, however, Steven Howe of CSNR proposed what could be a simpler and cheaper way to make it. The trick is to use a mechanical feed line, a coiled pipe surrounding the reactor core. Small capsules containing just a few grams of neptunium-237 are pushed continuously along this pipe, each one spending just days in the reactor. As they pop out the other end, the plutonium-238 is extracted and the remaining neptunium-237 is sent through the line again. About 0.01 per cent of the neptunium is converted on each pass, so this cycle would need to be repeated thousands of times to create the kilos of material required by NASA.

This technique brings some significant advantages, including shorter irradiation times causing far fewer fission products to be generated. This simplifies the subsequent chemical separation steps and reduces the amount of radioactive waste. In addition, it can work in small reactors that are far cheaper to run than the powerful national lab facilities that are required for the batch processing of old. Howe even envisions operating along commercial lines, so NASA and the DoE would just purchase the final product, rather than footing the bill for the entire production process.

The CSNR team working on this concept is already funded by a $100,000 NIAC grant and has submitted a proposal to build a prototype feed line and to demonstrate that they can mechanically push the capsules through it, as well as perform the subsequent separation steps. Howe believes they can have their process up and running in just three years, at a cost of about $50 million – half the proposed cost of restarting conventional production – and could create about 1.5 kilograms of plutonium-238 each year.

Though the team still has to determine the optimum irradiation time, operating the process continuously instead of converting several kilograms in batches twice a year should help keep costs and the facility size down. And if they charge $6 million per kilogram – less than the latest Russian asking price – this process would be cost-effective for private industry, Howe says. “Like commercial space travel, we’re doing commercialised plutonium production,” he says.

Whether or not Howe’s technique saves money, or even makes it, breathing fresh life into plutonium production is not popular with everyone. Plutonium-238 is highly toxic, and an accident during or after launch could release it into the atmosphere. In 1964, for example, a US navy navigation satellite re-entered the atmosphere and broke up, dispersing 1 kilogram of plutonium-238 around the planet, roughly double the amount released into the atmosphere by weapons testing. Though the plutonium’s containers have been redesigned to survive re-entry intact, the Cassini probe’s near-Earth fly-by in 2006 triggered widespread public protests. Restarting plutonium production is “a very frightening possibility”, says Bruce Gagnon of the Global Network Against Weapons and Nuclear Power in Space based in Brunswick, Maine. “It obviously indicates that the nuclear industry views space as a new market,” he says. “It’s like playing Russian roulette.” Gagnon is also worried by the prospects of a commercialised production line. “When you introduce the profit incentive, you start cutting corners,” he says.

Then there are concerns over proliferation and political capital. While plutonium-238 cannot be used to make a nuclear weapon, it is a different story with neptunium-237. This is weapons-grade material: bombarded by fast neutrons, it is capable of sustaining a chain reaction without unstable heat decay. Edwin Lyman at the Union of Concerned Scientists based in Cambridge, Massachusetts, believes that given these safety and security issues, non-nuclear power generation systems should be a priority for space applications. “Alternatives need to be explored fully,” he says. “If the US proceeds with the restart, it will be more difficult for us to dissuade other countries from doing the same, should they decide they need to produce their own plutonium-238 supply.”

Can sunlight help fill the gap? The intensity of light drops with distance from the sun, following an inverse square law, so sending solar-powered spacecraft to the outer planets looks like a non-starter. In Pluto’s orbit, for example, it would take a solar array of 2000 square metres to generate the same amount of power as a 1-square-metre array in Earth’s orbit. Nevertheless, in August 2011, NASA launched Juno, the first mission to Jupiter using solar energy instead of plutonium. Juno relies on three 10-metre-long solar panels to gather the power it needs to operate. And according to a 2007 NASA report, solar-powered missions beyond Jupiter are not out of the question.

What’s needed, says James Fincannon of NASA’s Glenn Research Center, are new solar cells that can cope with the extreme conditions in the outer solar system. Great strides are being made in developing lightweight, high-efficiency solar cells, he says. If the cost and mass of these arrays can be reduced further, and if a spacecraft’s power needs can be reduced to less than 300 watts – about half that of the Galileo probe – Fincannon suggests that a craft powered by a 250-square-metre solar array could operate as far away as Uranus. Gagnon agrees. “For years we’ve said that solar would work even in deep space,” he says.

There are even plutonium-free ways to power craft exploring the darker reaches of the solar system where Fincannon’s arrays would not work. At the NIAC symposium where Howe discussed his plutonium production process, Michael Paul of Pennsylvania State University’s Applied Research Laboratory described a novel engine that could power craft on the surface of cloud-wrapped worlds where little sunlight penetrates.

Take Venus. Paul proposes combining lithium fuel with carbon dioxide from the greenhouse-planet’s atmosphere, and burning it to provide heat for a Stirling engine – a heat pump that uses a temperature difference to drive a piston linked to a generator (see “Cloud power”). The system would not need nuclear launch approval, could operate at very high power levels and could be modified to work on Titan, Mars or even in the permanent dark of the moon’s south pole, he says. With further development Paul believes the technology could be ready to launch by 2020. “I see this power system as a way to enable a whole new set of opportunities that are closed off because we just don’t have enough plutonium,” he says.

Paul admits that his lithium-powered landers would last just a fraction of the decades-long lifetime achievable using plutonium. “Fifty years of work has shown that there are applications where there are no alternatives – period,” says Ralph McNutt of the Johns Hopkins University Applied Physics Laboratory. But, he adds, “to the extent that there are alternatives to radioactive power sources, we should take them”. Fincannon agrees: “It is always a good time to come up with alternative power sources,” he says.

Besides, spending money developing lightweight solar cells or more efficient Stirling engines could offer benefits on, as well as off, Earth. Engineers are already exploring ways to turn metal powder into fuel for vehicle engines, and Paul suggests his technology could help expand underwater exploration missions, too. The same can no longer be said for plutonium-238. Once used to power cardiac pacemakers, security and health concerns mean that the material is no longer welcome.

So which way will NASA jump? Howe remains determined to fight in plutonium’s corner and recently presented his case to the agency. As far as space is concerned, this power struggle isn’t over yet.

When this article was first posted, it contained an incorrect reference to Isaac Newton

Cloud power

Solar power is not an option for landers heading through thick clouds like those surrounding Venus. That’s where the generator conceived by Michael Paul and his team at Pennsylvania State University comes in. Paul’s team suggest powering a Venus lander by burning lithium with carbon dioxide sucked in from the planet’s atmosphere – eliminating the need to carry along an oxidiser with the fuel.

The heat from combustion would drive a small turbine or Stirling engine, which would power the lander’s electronics. But on boiling-hot Venus, the biggest challenge is keeping the lander’s electronics cool. Paul predicts that four-fifths of the engine’s power output will go towards pumping heat away from the craft’s electronics. Previous missions to Venus have lasted no more than 2 hours beyond touchdown before their batteries petered out. Paul calculates that 200 kilograms of lithium will be enough to keep sensors running for a week.

He believes that adding the planet’s carbon dioxide to lithium is the only way to pack enough punch to power a Venus lander. To provide electrical power and cooling for a week-long mission would otherwise require 850 kilograms of batteries, for instance, or 50 plutonium-powered generators. Even NASA’s colossal Cassini probe – “the flagship of all flagship missions” – doesn’t have that many, says Paul.