Saturn is officially losing its rings – and they’re disappearing much faster than scientists had anticipated


  • Saturn is losing its rings.
  • New data from NASA’s former Cassini spacecraft has revealed that the rings will be gone 200 million years sooner than previously estimated.
  • We explain what’s going on with Saturn’s rings and why they’re disappearing at a faster rate than previously thought.

If you were to pick Saturn out of a lineup you’d probably recognize it by its iconic rings. They’re the biggest, brightest rings in our solar system. Extending over 280,000 km from the planet; wide enough to fit 6 Earths in a row. But Saturn won’t always look this way. Because its rings are disappearing.

That’s right, Saturn is losing its rings! And fast. Much faster, even, than scientists had first thought. Right now, it’s raining 10,000 kilograms of ring rain on Saturn per second. Fast enough to fill an Olympic-sized pool in half an hour.

This rain is actually the disintegrated remains of Saturn’s rings. Saturn’s rings are mostly made up of chunks of ice and rock. Which are under constant bombardment: Some by UV radiation from the Sun and others by tiny meteoroids.

When these collisions take place, the icy particles vaporize, forming charged water molecules that interact with Saturn’s magnetic field; ultimately, falling toward Saturn, where they burn up in the atmosphere.

Now, we’ve known about ring rain since the 1980s when NASA’s Voyager mission first noticed mysterious, dark bands that turned out to be ring rain caught in Saturn’s magnetic fields. Back then, researchers estimated the rings would totally drain in 300 million years. But observations by NASA’s former Cassini spacecraft give a darker prognosis. Before its death dive into Saturn in 2017, Cassini managed to get a better look at the amount of ring-dust raining on Saturn’s equator.

And discovered that it was raining heavier than previously thought. With these clearer observations, scientists calculated the rings had only 100 million years left to live. Now, it’s tough to imagine a ringless Saturn.

But for much of its existence, the planet was as naked as Earth. While Saturn first formed around 4.5 BILLION years ago, studies suggest the rings are only 100- 200 million years old, tops. That’s younger than some dinosaurs.

So when you think about it, we’re pretty lucky we happened to be around to see those magnificent rings. Really lucky, in fact. Because efforts to study those rings have led us to other discoveries.

For example, as Cassini explored Saturn’s moon Enceladus, it uncovered a trail of ice and gas leading back to Saturn’s E ring. Enceladus is the whitest, most reflective moon in our solar system.

And by studying the ring more closely, scientists now know why. Turns out, the moon is constantly gushing out gas and dust.

Some of it ends up in space and in the E ring while the rest snows back onto the moon’s surface, creating a blinding white frost.

So, who knows what other discoveries might be hiding within the rings? At the very least, it’s clear we’d better keep looking while we still can.

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Why NASA is going to vaporize one of its best spacecraft.


 cassini

Artist illustration of Cassini preparing to dip its toes into Saturn’s atmosphere. The spacecraft will meet a violent end as it plummets through the atmosphere on September 15, 2017.

All good things must come to an end. On April 23, Cassini will begin its final quest into oblivion.

Flying at over 76,000 miles per hour, the spacecraft will zip through an uncharted gap between Saturn and its rings, where no spacecraft has flown before. In September, after 22 laps through this region, the spacecraft will dive into the gas giant’s atmosphere, where it will “break apart, melt, vaporize, and become a part of the very planet it left Earth 20 years ago to explore,” Cassini project manager Earl Maize said in a press conference on Tuesday.

It’ll be a sad ending for a mission that brought us amazing views of Saturn and its rings and moons. Cassini revealed the geysers of Enceladus, which hint at a subsurface ocean, and showed scientists just how how Earthlike—yet alien—Titan is. Why does the spacecraft have to die?

 Some space probes are allowed to keep orbiting their targets in perpetuity after their mission ends—like the Dawn spacecraft at the dwarf planet Ceres. But things are a lot more complicated around Saturn.

Whereas Ceres is essentially just a really big rock with no moons, Saturn has 62 satellites, at last count. The gravitational push and pull from those moons—especially the largest, Titan—wreak havoc on Cassini’s trajectory, which it normally corrects by burning fuel.

But the spacecraft’s fuel is running out, and ultimately its fate is sealed by its own discoveries; scientists don’t want to risk the spacecraft crashing into Titan and Enceladus, which may be capable of supporting life.

cassini grand finale trajectories

In April, Cassini will begin the first of 22 dives through the relatively narrow, 1200-mile gap between Saturn and its rings.

 “[Without fuel], the orbit would become less and less predictable,” Cassini project scientist Linda Spilker told Popular Science. “Cassini’s orbit would slowly change enough to eventually risk crashing into one of the moons.”

Although Cassini launched 20 years ago, experiments on the Space Station have suggested microbes can survive for years in the extreme temperatures, radiation, and airless vacuum of space. If NASA were to accidentally put water bears on Enceladus, the tiny Earthlings could potentially wipe out any native lifeforms that the moon may harbor, and/or complicate the search for those alien organisms later. This is why Cassini must die now, while NASA can still control its last swan dive.

But scientists are hoping to get some new information from the mission’s dramatic ending. They hope to learn more about the composition of Saturn’s atmosphere and rings, and figure out how big the planet’s core is, and how fast it’s rotating. Cassini will also get the closest view ever of the auroras and strange hexagonal storm at the north pole.

 Cassini will continue to beam back data until the very end, when atmospheric drag severs the spacecraft’s connection with Earth. That’s expected to happen about three minutes into Cassini’s dive on September 15.

“Once the signal is lost,” said Spilker at Tuesday’s press conference, “that heartbeat of Cassini is gone.”

Source:popsci.com

Thousands of Worlds Could Lurk Beyond Pluto – This New Animation Shows Them AlI


Welcome to our cosmic neighbourhood.

 You may be familiar with our Solar System’s eight planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. There’s also their famous dwarf-planet companion, Pluto.

But this icy world may just be an appetiser to what lurks beyond in a region called the Kuiper Belt.

 

As this stunning animation suggests, dwarf planets may outnumber regular planets 100- or even 1,000-fold.

However, if a small group of astronomers gets its way, most of these worlds may become fully fledged planets and drop the “dwarf” label.

Where the animation comes from

We first saw the animation in a Reddit post by user Nobilitie. It’s actually a recording of a physics-based simulator game called Universe Sandbox2, according to Dan Dixon, the creator and director of the software.

Each ring represents an object’s orbit, and the mess of rings beyond the inner eight rings all belong to dwarf planets.

In response to the Reddit post, Dixon said the orbits are based on a constantly updated list of candidate worlds maintained by Mike Brown, an astronomer at Caltech.

 “[I]t’s a nice illustration of what is out there!” Brown wrote in an email to Business Insider. “The striking difference between the orderly giant planets and the randomness of the dwarf planets is quite apparent.”

Brown is the person who discovered Eris, a 10th solar system object that’s about 27 percent more massive than Pluto.

artist impression of the dwarf planet Eris

Artist impression of Eris, ESO/L. Calçada and Nick Risinger

His find eventually ‘killed‘ Pluto as a bonafide planet in 2006. That’s when thousands of astronomers voted on new celestial terminology, categorising the world as a “dwarf planet” alongside Eris.

Some astronomers disagreed with the decision, with one going so far as to call it “bullsh-t”. The public also didn’t take it well: Brown has since received a torrent of hate mail from schoolchildren.

Definitions aside, the list kept by Brown sorts objects detected in deep space based on the likelihood of their existence. Larger, inner objects tend to be more certain while farther-out objects are less certain.

Pluto, Eris, Ceres, Makemake, Haumea, and five others meet Brown’s “near certainty” criteria – in other words, they’re definitely dwarf planets and not comets or some other astronomical object. Thirty are “highly likely” to be dwarf planets, 75 are “likely,” and nearly 850 other objects are “probably” or “possibly” dwarf planets.

Brown guessed that about half of the dwarf planet candidates have yet to be detected, bringing their numbers close to 2,000 or more.

Redefining “planet” again?

Pluto's orbit and Kuiper's belt objects

Even Brown’s best estimate may be low, though. In the illustration above, Pluto’s orbit is shown in yellow, and the dots beyond it are Kuiper Belt objects.

“[A]s you can see from the illustration, some of them are on exceedingly elliptical orbits. Those guys are going to spend most of their time at the outer edge of their orbit, so they’re hard to see,” Brown said. “There might be a factor of ~5 more of those objects that we don’t know about!”

Brown doesn’t think nuclear-powered spacecraft like New Horizons, which can last for decades and is now exploring the Kuiper Belt, will discover most of those missing worlds.

“The fact that there are so many of these things out there really shows that the future of their exploration is going to mostly rely on telescopes,” he said.

A twist in all of this is that astronomers are once again wondering what to call floating orbs of rock, metal, and ice in space, according to a poster that seven researchers are presenting this week at the 48th Lunar & Planetary Science Conference.

Instead of categorising worlds as planets, dwarf planets, and moons – terms based on their orbits around the sun and one other – the team wants to simplify the system: As long as an object is big enough to be mostly round and isn’t fusing hot gases (like the Sun), it should be deemed a planet.

If enough astronomers agree with them, the solar system might suddenly contain 110 official planets – and perhaps hundreds or even thousands more if Brown’s list pans out.

Five planets to align in spectacular celestial show


Mercury, Venus, Mars, Jupiter and Saturn will all appear together in the night sky for the first time since 2005

A telescope

Mercury, Venus, Mars, Jupiter and Saturn will all appear together in the night sky this month Photo: AP

Five planets will be visible in the night sky this week in a rare astronomical alignment which has not happened for more than a decade.

Mercury, Venus, Mars, Jupiter and Saturn will all appear together for the first time since 2005.

The alignment will be visible in Britain just before dawn from January 20, but astronomers say the best view is likely to be on the morning of February 5.

“There will be a dance of the planets.It will be well worth getting up for.”
Dr Robert Massey, Royal Astronomical Society

The planets will from a diagonal line from the Moon to the horizon and with clear skies and good eyesight, should be visible with the naked eye.

Dr Robert Massey of the Royal Astronomical Society said spotting Mercury would be a challenge as it will be close to the horizon, but the other planets should be easy to see in before dawn.

“There will be a dance of the planets, and now is the time to get out and have a look,” said Dr Massey. “It will be well worth getting up for.

“People will struggle to see Mercury, it will probably just look like a star but if we get good weather we should be able to see Venus, Saturn, Mars and Jupiter well. But people should have a shot at seeing them altogether.

“Venus will be very obvious in the south east and Saturn will be a little bit higher up to the right. Further over at due south, you’ll see Mars and way beyond in the south east will be Jupiter.

“They won’t be in an exact straight line, because you virtually never get that in astronomy. They will be more scattered.”

Conjunction of Mars, Jupiter and Venus seen in Newcastle upon Tyne

The five planets will be strung out in the night sky together, with Venus appearing the brightest  

Mercury will appear just three degrees above the horizon – the equivalent of three thumb widths with an outstretched arm – so will be the trickiest planet to spot.

The best time to see the alignment is around 6.45am in the morning, just before dawn. It is best to try and see Venus and then look for the rest of the planets.

Four of the five have already been visible in the early morning sky in recent weeks, but Mercury will join them for the first time on Wednesday.

Dr Massey added: “If you have binoculars you will be able to see Jupiter’s moons and the red tinge of Mars. You probably won’t be able to see Saturn’s rings but it will have a funny shape because of the rings which you should be able to pick out.

Jupiter and Venus will appear side by side over the next two nights, according to astronomers.

The planets rarely come together because of their differeing orbits

“If you are using binoculars it’s important not to look towards the sun when it rises.”

The stars Antares and Spica will also be visible in the same patch of sky. Uranus and Neptune are the only two planets that will not be on show.

And if you fail to catch the alignment this month, it will be happen again in August of this year although the late days of summer are likely to make it even more difficult to see in Britain. After that, the five planets will not be seen together again until October 2018.

People hoping to catch a glimpse of the alignment should choose an open spot, away from tall buildings and city lights to avoid light pollution.

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.

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.

Plastic ingredient spied on Titan.


Cassini probe sees plastic ingredient on Titan moon

 

Titan

 

 

The Cassini probe has detected propene, or propylene, on Saturn’s moon Titan.

 

On Earth, this molecule, which comprises three carbon atoms and six hydrogen atoms, is a constituent of many plastics.

 

It is the first definitive detection of the plastic ingredient on any moon or planet, other than our home world, says the US space agency (Nasa).

 

The discovery, made by Cassini‘s infrared spectrometer, is reported in Astrophysical Journal Letters.

 

“This chemical is all around us in everyday life, strung together in long chains to form a plastic called polypropylene,” said Conor Nixon, a Nasa planetary scientist from the agency’s Goddard Space Flight Center. A classic example would be the plastic boxes used to store food in kitchens worldwide.

 

Titan is dominated by hydrocarbons – principally methane, which after nitrogen is the most common component of the atmosphere.

 

Sunlight drives reactions that break apart the methane, allowing the fragments to join up and form even bigger molecules.

 

Other common species seen at the moon as a result are propane, which on Earth is used in portable cooking equipment, and ethane, which is the raw material for another ubiquitous plastic – polyethylene.

 

But the likes of methane, propene, propane and ethane are dwarfed by some truly colossal hydrocarbons that have been detected in Titan’s atmosphere.

 

When the effects of ultraviolet light are combined with the bombardment from particles driven in Saturn’s magnetic field, it becomes possible to cook up some very exotic chemistry.

 

Cassini’s plasma spectrometer has seen evidence for hydrocarbons with an atomic mass thousands of times heavier than a single hydrogen atom.

Shadow Dance: Cassini Captures Dramatic Panorama of Saturn Backlit by the Sun.


cassiniThe giant planet Saturn looks a bit like a delicate Christmas ornament in a new photomosaic released by NASA.

The Cassini orbiter, currently exploring Saturn and its moons, snapped the 60 images that would become the mosaic in October, as the spacecraft swung through the planet’s shadow. At the time Cassini was beneath the plane of the rings. The result is an enhanced-color panorama of the giant world and its rings, backlit by the sun against the blackness of space. The shadow of Saturn itself can be seen as a dark crescent shape cast across the plane of the rings. Just below and to the left of the rings are two white dots: Saturn’s moons Enceladus and Tethys.

“Of all the many glorious images we have received from Saturn, none are more strikingly unusual than those taken from Saturn’s shadow,” Cassini’s imaging team lead Carolyn Porco of the Space Science Institute in Boulder, Colo., said in a prepared statement.

Source: Scientific American