Astrobiology Archives

November 18, 2014December 23, 2015 by Vanessa Janek

The Origins of Life Could Indeed Be “Interstellar”

This image shows a star-forming region in interstellar space. A new study used AI and radiotelescope data to find 140,000 regions in the Milky Way that will eventually form stars like this region. Image credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

Some of science’s most pressing questions involve the origins of life on Earth. How did the first lifeforms emerge from the seemingly hostile conditions that plagued our planet for much of its history? What enabled the leap from simple, unicellular organisms to more complex organisms consisting of many cells working together to metabolize, respire, and reproduce? In such an unfamiliar environment, how does one even separate “life” from non-life in the first place?

Now, scientists at the University of Hawaii at Manoa believe that they may have an answer to at least one of those questions. According to the team, a vital cellular building block called glycerol may have first originated via chemical reactions deep in interstellar space.

Glycerol is an organic molecule that is present in the cell membranes of all living things. In animal cells this membrane takes the form of a phospholipid bilayer, a dual-layer membrane that sandwiches water-repelling fatty acids between outer and inner sheets of water-soluble molecules. This type of membrane allows the cell’s inner aqueous environment to remain separate and protected from its external, similarly watery world. Glycerol is a vital component of each phospholipid because it forms the backbone between the molecule’s two characteristic parts: a polar, water-soluble head, and a non-polar, fatty tail.

Many scientists believe that cell membranes such as these were a necessary prerequisite to the evolution of multicellular life on Earth; however, their complex structure requires a very specific environment – namely, one low in calcium and magnesium salts with a fairly neutral pH and stable temperature. These carefully balanced conditions would have been hard to come by on the prehistoric Earth.

Icy bodies born in interstellar space offer an alternative scenario. Scientists have already discovered organic molecules such as amino acids and lipid precursors in the Murchison meteorite that landed in Australia in 1969. Although the idea remains controversial, it is possible that glycerol could have been brought to Earth in a similar manner.

The Murchison Meteorite. Image credit: James St. John — The Murchison Meteorite.
Image credit: James St. John

Meteors typically form from tiny crumbs of material in cold molecular clouds, regions of gaseous hydrogen and interstellar dust that serve as the birthplace of stars and planetary systems. As they move through the cloud, these grains accumulate layers of frozen water, methanol, carbon dioxide, and carbon monoxide. Over time, high-energy ultraviolet radiation and cosmic rays bombard the icy fragments and cause chemical reactions that enrich their frozen cores with organic compounds. Later, as stars form and ambient material falls into orbit around them, the ices and the organic molecules they contain are incorporated into larger rocky bodies such as meteors. The meteors can then crash into planets like ours, potentially seeding them with building blocks of life.

In order to test whether or not glycerol could be created by the high-energy radiation that typically bombards interstellar ice grains, the team at the University of Hawaii designed their own meteorites: small bits of icy methanol cooled to 5 degrees Kelvin. After blasting their model ices with energetic electrons meant to mimic the effects of cosmic rays, the scientists found that some molecules of methanol within the ices did, in fact, transform into glycerol.

While this experiment appears to be a success, scientists realize that their laboratory models do not exactly replicate conditions in interstellar space. For instance, methanol traditionally makes up only about 30% of the ice in space rocks. Future work will investigate the effects of high-energy radiation on model ices made primarily of water. High-energy electrons fired in a lab are also not a perfect substitute for true cosmic rays and do not represent effects on ice that may result from ultraviolet radiation in interstellar space.

More research is necessary before scientists can draw any global conclusions; however, this study and its predecessors do provide compelling evidence that life as we know it truly could have come from above.

November 8, 2014December 23, 2015 by Tim Reyes

Review: In “Interstellar,” Christopher Nolan Shows He Has The Right Stuff

Mathew McConnaughey wades through an ocean on another planet. This is not a fishing expedition. He is out to save his children and all humanity. Image courtesy Paramount.

Science fiction aficionados, take heed. The highly-anticipated movie Interstellar is sharp and gripping. Nolan and cast show in the end that they have the right stuff. Nearly a three hour saga, it holds your attention and keeps you guessing. Only a couple of scenes seemed to drift and lose focus. Interstellar borrows style and substance from some of the finest in the genre and also adds new twists while paying attention to real science. If a science-fiction movie shies away from imagining the unknown, taking its best shot of what we do not know, then it fails a key aspect of making sci-fi. Interstellar delivers in this respect very well.

Jessica Chastain, the grown daughter of astronaut McConnaughey starts to torch the cornfields. Interstellar viewers are likely to show no sympathy to the ever present corn fields. — Jessica Chastain, the grown daughter of astronaut McConnaughey takes a torch to the cornfields. *Interstellar* viewers are likely to show no sympathy to the ever present corn fields. Image courtesy Paramount.

The movie begins quite unassuming in an oddly green but dusty farmland. It does not rely on showing off futuristic views of Earth and humanity to dazzle us. However, when you see a farming family with a dinner table full of nothing but variations of their cash crop which is known mostly as feedstock for swine and cattle, you know humanity is in some hard times. McConaughey! Save us now! I do not want to live in such a future!

One is left wondering about what got us to the conditions facing humanity from the onset of the movie. One can easily imagine a couple of hot topic issues that splits the American public in two. But Nolan doesn’t try to add a political or religious bent to Interstellar. NASA is in the movie but apparently after decades of further neglect, it is literally a shadow of even its present self.

Somehow, recent science fiction movies — Gravity being one exception — would make us believe that the majority of American astronauts are from the Midwest. Driving a John Deere when you are 12, being raised under big sky or in proximity to the home of the Wright Brothers would make you hell-bent to get out of Dodge and not just see the world but leave the planet. Matthew McConaughey adds to that persona.

Dr. Kip Thorne made it clear that black is not the primary hue of Black Holes. His guidance offered to Nolan raised science fiction to a new level. Image courtesy Paramount.

We are seemingly in the golden age of astronomy. At present, a science fiction movie with special effects can hardly match the imagery that European and American astronomy is delivering day after day. There is one of our planets that gets a very modest delivery in Interstellar. An undergraduate graphic artist could take hold of NASA imagery and outshine those scenes quite easily. However, it appears that Nolan did not see it necessary to out-do every scene of past sci-fi or every astronomy picture of the day (APOD) to make a great movie.

Nolan drew upon American astro-physicist Dr. Kip Thorne, an expert on Einstein’s General Relativity, to deliver a world-class presentation of possibly the most extraordinary objects in our Universe – black holes. It is fair to place Thorne alongside the likes of Sagan, Feynman, Clarke and Bradbury to advise and deliver wonders of the cosmos in compelling cinematic form. In Instellar, using a black hole in place of a star to hold a planetary system is fascinating and also a bit unbelievable. Whether life could persist in such a system is a open question. There is one scene that will distress most everyone in and around NASA that involves the Apollo Moon landings and one has to wonder if Thorne was pulling a good one on old NASA friends.

Great science fiction combines a vision of the future with a human story. McConaughey and family are pretty unassuming. John Lithgow, who plays grandpa, the retired farmer, doesn’t add much and some craggy old character actor would have been just fine. Michael Cane as the lead professor works well and Cane’s mastery is used to thicken and twist the plot. His role is not unlike the one in Children of Men. He creates bends in the plot that the rest of the cast must conform to.

There was one piece of advice I read in previews of Interstellar. See it in Imax format. So I ventured over to the Imax screening at the Technology Museum in Silicon Valley. I think this advice was half correct. The Earthly scenes gained little or nothing from Imax but once they were in outer space, Imax was the right stuff. Portraying a black hole and other celestial wonders is not easy for anyone including the greatest physicists of our era and Thorne and Nolan were right to use Imax format.

According to industry insiders, Nolan is one of a small group of directors with the clout to demand film recording rather than digital. Director Nolan used film and effects to give Interstellar a very earthy organic feel. That worked and scenes transitioned pretty well to the sublime of outer space. Interstellar now shares the theaters with another interesting movie with science fiction leanings. The Stephen Hawking biography, “The Theory of Everything” is getting very good reviews. They hold different ties to science and I suspect sci-fi lovers will be attracted to seeing both. With Interstellar, out just one full day and I ran into moviegoers that had already seen it more than once.

Where does Interstellar stand compared to Stanley Kubricks works? It doesn’t make that grade of science fiction that stands up as a century-class movie. However, Thorne’s and Nolan’s accounting of black holes and worm holes and the use of gravity is excellent. Instellar makes a 21st Century use of gravity in contrast to Gravity that was stuck in the 20th Century warning us to be careful where you park your space vehicle. In the end, Matthew McConaughey serves humanity well. Anne Hathaway plays a role not unlike Jody Foster in Contact – an intellectual but sympathetic female scientist.

Jessica Chastain playing the grown up daughter of McConaughey brings real angst and an edge to the movie; even Mackenzie Foy playing her part as a child. Call it the view ports for each character – they are short and narrow and Chastain uses hers very well. Matt Damon shows up in a modest but key role and does not disappoint. Nolan’s directing and filmography is impressive, not splashy but one is gripped by scenes. Filming in the small confines of spaceships and spacesuits is challenging and Nolan pulls it off very well. Don’t miss Interstellar in the theaters. It matches and exceeds the quality of several recent science fiction movies. Stepping back onto the street after the movie, the world seemed surprisingly comforting and I was glad to be back from the uncertain future Nolan created.

October 27, 2014October 17, 2016 by Fraser Cain

What Strange Places Are Habitable?

Everywhere we look on Earth, we find life. Even in the strangest corners of planet. What other places in the Universe might be habitable?

There’s life here on Earth, but what other places could there be life? This could be life that we might recognize, and maybe even life as we don’t understand it.

People always accuse me of being closed minded towards the search for life. Why do I always want there to be an energy source and liquid water? Why am I so hydrocentric? Scientists understand how life works here on Earth. Wherever we find liquid water, we find life: under glaciers, in your armpits, hydrothermal vents, in acidic water, up your nose, etc.

Water acts as a solvent, a place where atoms can be moved around and built into new structures by life forms. It makes sense to search for liquid water as it always seems to have life here. So where could we go searching for liquid water in the rest of the Universe?

Under the surface of Europa, there are deep oceans. They’re warmed by the gravitational interactions of Jupiter tidally flexing the surface of the moon. There could be life huddled around volcanic vents within its ocean. There’s a similar situation in Saturn’s Moon Enceladus, which is spewing out water ice into space; there might be vast reserves of liquid water underneath its surface. You could imagine a habitable moon orbiting a gas giant in another star system, or maybe you can just let George Lucas imagine it for you and fill it with Ewoks.

The white dwarf G29-38 (Image Credit: NASA)

Let’s look further afield. What about dying white dwarf stars? Even though their main sequence days are over, they’re still giving off a lot of energy, and will slowly cool down over the coming billions of years. Brown dwarfs could get in on this action as well. Even though they never had enough mass to ignite solar fusion, they’re still generating heat. This could provide a safe warm place for planets to harbor life.

It gets a little trickier in either of these systems. White and brown dwarfs would have very narrow habitable zones, maybe 1/100th the size of the one in our Solar System. And it might shift too quickly for life to get started or survive for very long. This is our view, what we know life to be with water as a solvent. But astrobiologists have found other liquids that might work well as solvents too.

Artist concept of Methane-Ethane lakes on Titan (Credit: Copyright 2008 Karl Kofoed). Click for larger version.

What about life forms that live in oceans of liquid methane on Titan, or creatures that use silicon or boron instead of carbon. It might just not be science fiction after all. It’s a vast Universe out there, stranger than we can imagine. Astronomers are looking for life wherever makes sense – wherever there’s liquid water. And if they don’t find any there, they’ll start looking places that don’t make sense.

What do you think? When we first find life, what will be its core building block? Silicon? Boron? or something even more exotic?

And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!

October 16, 2014December 23, 2015 by Paul Patton

Moons of Confusion: Why Finding Extraterrestrial Life may be Harder than we Thought

NASA's James Webb Space Telescope, scheduled for launch in Dec. 2021, will be capable of measuring the spectrum of the atmospheres of Earthlike exoplanets orbiting small stars. Credit: NASA, Northrop Grumman

Astronomers and planetary scientists thought they knew how to find evidence of life on planets beyond our Solar System. But, a new study indicates that the moons of extrasolar planets may produce “false positives” adding an inconvenient element of uncertainty to the search.

More than 1,800 exoplanets have been confirmed to exist so far, with the count rising rapidly. About 20 of these are deemed potentially habitable. This is because they are only somewhat more massive than Earth, and orbit their parent stars at distances that might allow liquid water to exist.

Astronomers soon hope to be able to determine the composition of the atmospheres of such promising alien worlds. They can do this by analyzing the spectrum of light absorbed by them. For Earth-like worlds circling small stars, this challenging feat can be accomplished using NASA’s James Webb Space Telescope, scheduled for launch in 2018.

They thought they knew how to look for the signature of life. There are certain gases which shouldn’t exist together in an atmosphere that is in chemical equilibrium. Earth’s atmosphere contains lots of oxygen and trace amounts of methane. Oxygen shouldn’t exist in a stable atmosphere. As anyone with rust spots on their car knows, it has a strong tendency to combine chemically with many other substances. Methane shouldn’t exist in the presence of oxygen. When mixed, the two gases quickly react to form carbon dioxide and water. Without some process to replace it, methane would be gone from our air in a decade.

On Earth, both oxygen and methane remain present together because the supply is constantly replenished by living things. Bacteria and plants harvest the energy of sunlight in the process of photosynthesis. As part of this process water molecules are broken into hydrogen and oxygen, releasing free oxygen as a waste product. About half of the methane in Earth’s atmosphere comes from bacteria. The rest is from human activities, including the growing of rice, the burning of biomass, and the flatulence produced by the vast herds of cows and other ruminants maintained by our species.

By itself, finding methane in a planet’s atmosphere isn’t surprising. Many purely chemical processes can make it, and it is abundant in the atmospheres of the gas giant planets Jupiter, Saturn, Uranus, and Neptune, and on Saturn’s large moon Titan. Although oxygen alone is sometimes touted as a possible biomarker; its presence, by itself, isn’t rock solid evidence of life either. There are purely chemical processes that might make it on an alien planet, and we don’t yet know how to rule them out. Finding these two gases together, though, seems as close as one could get to “smoking gun” evidence for the activities of life.

A monkey wrench was thrown into this whole argument by an international team of investigators led by Dr. Hanno Rein of the Department of Environmental and Physical Sciences at the University of Toronto in Canada. Their results were published in the May, 2014 edition of the Proceedings of the National Academy of Sciences USA.

Suppose, they posited, that oxygen is present in the atmosphere of a planet, and methane is present separately in the atmosphere of a moon orbiting the planet. The team used a mathematical model to predict the light spectrum that might be measured by a space telescope near Earth for plausible planet-moon pairs. They found that the resulting spectra closely mimicked that of a single object whose atmosphere contained both gasses.

Unless the planet orbits one of the very nearest stars, they showed it wasn’t possible to distinguish a planet-moon pair from a single object using technology that will be available anytime soon. The team termed their results “inconvenient, but unavoidable…It will be possible to obtain suggestive clues indicative of possible inhabitation, but ruling out alternative explanations of these clues will probably be impossible for the foreseeable future.”

References and further reading:

The Habitable Exoplanets Catalog, Planetary Habitability Laboratory, University of Puerto Rico at Arecibo

Kaltenegger L., Selsis F., Fridlund M. et al. (2010) Deciphering spectral fingerprints of habitable exoplanets. Astrobiology, 10(1) p. 89-102.

Major J. (2013) Earthlike exoplanets are all around us. Universe Today

Rein H., Fujii Y., and Spiegel D. S. (2014) Some inconvenient truths about biosignatures involving two chemical species on Earth-like exoplanets. Proceedings of the National Academy of Sciences, 111(19) p. 6871-6875.

Sagan C., Thompson W. R., Carlson R., Gurnett, D., Hord, C. (1993) A search for life on Earth from the Galileo spacecraft. Nature, 365 p. 715-721.

June 20, 2014December 23, 2015 by Shannon Hall

A New Mantra: Follow the Methane — May Advance Search for Extraterrestrial Life

Extrasolar planet HD189733b rises from behind its star. Is there methane on this planet? Image Credit: ESA

The search for life is largely limited to the search for water. We look for exoplanets at the correct distances from their stars for water to flow freely on their surfaces, and even scan radiofrequencies in the “water hole” between the 1,420 MHz emission line of neutral hydrogen and the 1,666 MHz hydroxyl line.

When it comes to extraterrestrial life, our mantra has always been to “follow the water.” But now, it seems, astronomers are turning their eyes away from water and toward methane — the simplest organic molecule, also widely accepted to be a sign of potential life.

Astronomers at the University College London (UCL) and the University of New South Wales have created a powerful new methane-based tool to detect extraterrestrial life, more accurately than ever before.

In recent years, more consideration has been given to the possibility that life could develop in other mediums besides water. One of the most interesting possibilities is liquid methane, inspired by the icy moon Titan, where water is as solid as rock and liquid methane runs through the river valleys and into the polar lakes. Titan even has a methane cycle.

Astronomers can detect methane on distant exoplanets by looking at their so-called transmission spectrum. When a planet transits, the star’s light passes through a thin layer of the planet’s atmosphere, which absorbs certain wavelengths of the light. Once the starlight reaches Earth it will be imprinted with the chemical fingerprints of the atmosphere’s composition.

But there’s always been one problem. Astronomers have to match transmission spectra to spectra collected in the laboratory or determined on a supercomputer. And “current models of methane are incomplete, leading to a severe underestimation of methane levels on planets,” said co-author Jonathan Tennyson from UCL in a press release.

So Sergei Yurchenko, Tennyson and colleagues set out to develop a new spectrum for methane. They used supercomputers to calculate about 10 billion lines — 2,000 times bigger than any previous study. And they probed much higher temperatures. The new model may be used to detect the molecule at temperatures above that of Earth, up to 1,500 K.

“We are thrilled to have used this technology to significantly advance beyond previous models available for researchers studying potential life on astronomical objects, and we are eager to see what our new spectrum helps them discover,” said Yurchenko.

The tool has already successfully reproduced the way in which methane absorbs light in brown dwarfs, and helped correct our previous measurements of exoplanets. For example, Yurchenko and colleagues found that the hot Jupiter, HD 189733b, a well-studied exoplanet 63 light-years from Earth, might have 20 times more methane than previously thought.

The paper has been published in the Proceedings of the National Academy of Sciences and may be viewed here.

May 6, 2014December 23, 2015 by Shannon Hall

Are we Ready for Contact?

A common criticism of science is its quick decision to experiment, without thinking about whether or not it should. While many argue that philosophical implications do not belong within the realm of science, others argue that scientists should absolutely consider the broader implications of their results.

Now, neuro-psychologist Gabriel G. de la Torre from the University of Cádiz is questioning whether or not astronomers, who have previously only looked for signs of extraterrestrial life, should actively send messages from Earth.

The idea that we might not be alone in the universe has been around since at least the fifth century B.C., when the Greek philosopher Democritus posited innumerable worlds, none of which were devoid of life.

With the founding of NASA and other space agencies in the 20th century, human beings began to explore the solar system and actively search for alien life. The most ambitious search began in 1960, when astronomer Frank Drake pointed a radio telescope at two stars similar to our Sun and listened for a signature of intelligence.

Drake’s work inspired the Search for ExtraTerrestrial Intelligence (SETI) project, an initiative that began in the 70s with funding from NASA, but has now evolved toward the collaboration of millions of Internet users for the processing of data from the Arecibo Observatory.

But then there is “Active SETI — also known as METI (Messaging to Extra-Terrestrial Intelligence) — which is the attempt to send messages to potential ETs via radio signals. Some astrophysicists, such as Stephen Hawking, have already warned against the risk this implies for humanity. It would favor the arrival of beings with more advanced technology and unknown intentions.

So “can such a decision be taken on behalf of the whole planet?” asked De la Torre. “What would happen if it was successful and ‘someone’ received our signal? Are we prepared for this type of contact?”

To answer these questions, De la Torre surveyed 116 American, Italian and Spanish university students. The questionnaire assessed their knowledge of astronomy, their religious beliefs, and their beliefs on the likelihood of contact with extraterrestrial intelligent life.

The results indicate that as a species, humanity is still not ready to actively contact a supposed extraterrestrial civilization. The students lacked awareness on many astronomical aspects, despite the enormous progress of science and technology. It also revealed that they lack preparation and would instead rely on political and religious figures.

De la Torre encourages SETI researchers to look for alternative strategies until society can better prepare itself. “This pilot study demonstrates that the knowledge of the general public of a certain education level about the cosmos and our place within it is still poor,” said De la Torre. “Therefore, a cosmic awareness must be further promoted – where our mind is increasingly conscious of the global reality that surrounds us – using the best tool available to us: education.”

The paper has been published in the journal Acta Astronautica.

May 5, 2014December 23, 2015 by Shannon Hall

NASA Seeks Ideas for Mission to Europa

Jupiter's icy moon: Europa. Image Credit: NASA

Europa — a moon of Jupiter first discovered by Galileo — never ceases to surprise and amaze astronomers and amateurs alike.

Last December astronomers announced water plumes erupting 100 miles high from the moon’s icy south pole. It was the best evidence yet that Europa, heated internally by the powerful tidal forces generated by Jupiter’s gravity, has a deep subsurface ocean. It caused the search for life in the outer solar system to take quite a turn.

Now, NASA has issued a Request for Information (RFI) to science and engineering communities for ideas for a mission to the enigmatic moon. Any ideas need to address fundamental questions about the subsurface ocean and the search for life beyond Earth.

“This is an opportunity to hear from those creative teams that have ideas on how we can achieve the most science at minimum cost,” said John Grunsfeld, associate administrator for the NASA Science Mission Directorate, in a press release.

The RFI’s focus is for concepts for a mission that costs less than $1 billion.

“Europa is one of the most interesting sites in our solar system in the search for life beyond Earth,” said Grunsfield. “The drive to explore Europa has stimulated not only scientific interest but also the ingenuity of engineers and scientists with innovative concepts.”

The Decadal Survey deemed a mission to Europa as an extremely high priority for scientific pursuits by NASA. It lists five key science objectives that are necessary to improve our understanding of this potentially habitable moon. Primarily, the mission will need to:

— Characterize the extent of the ocean and its relation to the deeper interior

— Characterize the ice shell and any subsurface water, including their heterogeneity, and the nature of surface-ice-ocean exchange

— Determine global surface, compositions and chemistry, especially as related to habitability

— Understand the formation of surface features, including sites of recent or current activity, identify and characterize candidate sites for future detailed exploration

— Understand Europa’s space environment and interaction with the magnetosphere.

Although Europa has been visited by spacecraft and imaged distantly by Hubble, more detailed research is necessary to understand the complexities of this moon and its potential for life. NASA’s Galileo spacecraft, launched in 1989 was the only mission to visit Europa, passing close by the moon fewer than a dozen times.

What are your ideas for a mission to the icy moon? Comment below.

April 3, 2014December 23, 2015 by Nancy Atkinson

Cassini Spacecraft Confirms Subsurface Ocean on Enceladus

Jets of icy particles bursting from Saturn's moon Enceladus are shown in this Cassini image taken on November 2005. Credit: NASA/ESA/ASI.

Ever since the Cassini spacecraft first spied water vapor and ice spewing from fractures in Enceladus’ frozen surface in 2005, scientists have hypothesized that a large reservoir of water lies beneath that icy surface, possibly fueling the plumes. Now, gravity measurements gathered by Cassini have confirmed that this enticing moon of Saturn does in fact harbor a large subsurface ocean near its south pole.

“For the first time, we have used a geophysical method to determine the internal structure of Enceladus, and the data suggest that indeed there is a large, possibly regional ocean about 50 kilometers below the surface of the south pole,” says David Stevenson from Caltech, a coauthor on a paper on the finding, published in the current issue of the journal Science. “This then provides one possible story to explain why water is gushing out of these fractures we see at the south pole.”

Artist’s impression of the possible interior of Enceladus based on Cassini’s gravity investigation. The data suggest an ice outer shell and a low-density, rocky core with a regional water ocean sandwiched between at high southern latitudes. Cassini images were used to depict the surface geology in this artwork. The mission discovered plumes of ice and water vapour jetting from fractures – nicknamed ‘tiger stripes’ – at the moon’s south pole in 2005. Credit: NASA/JPL-Caltech.

On three separate flybys in 2010 and 2012, the spacecraft passed within 100 km of Enceladus, twice over the southern hemisphere and once over the northern hemisphere.

During the flybys, the gravitational tug altered a spacecraft’s flight path ever so slightly, changing its velocity by just 0.2–0.3 millimeters per second.

As small as these deviations were, they were detectable in the spacecraft’s radio signals as they were beamed back to Earth, providing a measurement of how the gravity of Enceladus varied along the spacecraft’s orbit. These measurements could then be used to infer the distribution of mass inside the moon.

For example, a higher-than-average gravity ‘anomaly’ might suggest the presence of a mountain, while a lower-than-average reading implies a mass deficit.

On Enceladus, the scientists measured a negative mass anomaly at the surface of the south pole, accompanied by a positive one some 30-40 km below.

“By analyzing the spacecraft’s motion in this way, and taking into account the topography of the moon we see with Cassini’s cameras, we are given a window into the internal structure of Enceladus,” said lead author Luciano Iess.

“This is really the only way to learn about internal structure from remote sensing,” Stevenson added.

The only way to get more precise measurements would be to put seismometers on Enceladus’s surface. And that’s not going to happen anytime soon.

Stevenson said the key feature in the gravity data was the negative mass anomaly at Enceladus’s south pole. This happens when there is less mass in a particular location than would be expected in the case of a uniform spherical body. Since there is a known depression in the surface of Enceladus’s south pole, the scientists expected to find a negative mass anomaly. However, the anomaly was quite a bit smaller than would be predicted by the depression alone.

“The perturbations in the spacecraft’s motion can be most simply explained by the moon having an asymmetric internal structure, such that an ice shell overlies liquid water at a depth of around 30–40 km in the southern hemisphere,” Iess said.

While the gravity data cannot rule out a global ocean, a regional sea extending from the south pole to 50 degrees S latitude is most consistent with the moon’s topography and high local temperatures observed around the fractures – called ‘tiger stripes’ at Enceladus south pole.

Many have said Enceladus is one of the best places in the Solar System to look for life. Noted scientist Carolyn Porco and Chris McKay have a recent paper out titled, “Follow the Plume: The Habitability of Enceladus,” where they say that since analysis of the plume by the Cassini mission indicates that the “steady plume derives from a subsurface liquid water reservoir that contains organic carbon, biologically available nitrogen, redox energy sources, and inorganic salts” that samples from the plume jetting out into space are accessible with a low-cost flyby mission. “No other world has such well-studied indications of habitable conditions.”

These latest findings by Cassini make a mission to Enceladus even more enticing.

Paper in Science (paywall) “The Gravity Field and Interior Structure of Enceladus.”

Sources: ESA, Caltech

March 6, 2014December 23, 2015 by Shannon Hall

New Technique Could Measure Exoplanet Atmospheric Pressure, an Indicator of Habitability

Artistic representations of the only known planets around other stars (exoplanets) with any possibility to support life as we know it. The authors of this study wanted to know how people react to the discovery of alien life and potentially habitable planets. Credit: Planetary Habitability Laboratory, University of Puerto Rico, Arecibo.

Measuring the atmospheric pressure of a distant exoplanet may seem like a daunting task but astronomers at the University of Washington have now developed a new technique to do just that.

When exoplanet discoveries first started rolling in, astronomers laid emphasis in finding planets within the habitable zone — the band around a star where water neither freezes nor boils. But characterizing the environment and habitability of an exoplanet doesn’t depend on the planet’s surface temperature alone.

Atmospheric pressure is just as important in gauging whether or not the surface of an exoplanet may likely hold liquid water. Anyone familiar with camping at high-altitude should have a good understanding of how pressure affects water’s boiling point.

The method developed by Amit Misra, a PhD candidate, involves isolating “dimers” — bonded pairs of molecules that tend to form at high pressures and densities in a planet’s atmosphere — not to be confused with “monomers,” which are simply free-floating molecules. While there are many types of dimers, the research team focused exclusively on oxygen molecules, which are temporarily bound to each other through hydrogen bonding.

We may indirectly detect dimers in an exoplanet’s atmosphere when the exoplanet transits in front of its host star. As the star’s light passes through a thin layer of the planet’s atmosphere the dimers absorb certain wavelengths of it. Once the starlight reaches Earth it’s imprinted with the chemical fingerprints of the dimers.

Dimers absorb light in a distinctive pattern, which typically has four peaks due to the rotational motion of the molecules. But the amount of absorption may change depending on the atmospheric pressure and density. This difference is much more pronounced in dimers than in monomers, allowing astronomers to gain additional information about the atmospheric pressure based on the ratio of these two signatures.

While water dimers were detected in the Earth’s atmosphere as early as last year, powerful telescopes soon to come online may enable astronomers to use this method in observing distant exoplanets. The team analyzed the likelihood of using the James Webb Space Telescope to make such a detection and found it challenging but possible.

Detecting dimers in an exoplanet’s atmosphere would not only help us evaluate the atmospheric pressure, and therefore the state of water on the surface, but other biosignature markers as well. Oxygen is directly tied to photosynthesis, and will most likely not be abundant in an exoplanet’s atmosphere unless it is regularly produced by algae or other plants.

“So if we find a good target planet, and you could detect these dimer molecules — which might be possible within the next 10 to 15 years — that would not only tell you something about pressure, but actually tell you that there’s life on that planet,” said Misra in a press release.

The paper has been published in the February issue of Astrobiology and is available for download here.

February 5, 2014December 23, 2015 by Shannon Hall

High Potential for Life Circling Alpha Centauri B, our Nearest Neighbor

While exoplanets make the news on an almost daily basis, one of the biggest announcements occurred in 2012 when astronomers claimed the discovery of an Earth-like planet circling our nearest neighbor, Alpha Centauri B, a mere 4.3 light-years away. That’s almost close enough to touch.

Of course such a discovery has led to a heated debate over the last three years. While most astronomers remain skeptical of this planet’s presence and astronomers continue to study this system, computer simulations from 2008 actually showed the possibility of 11 Earth-like planets in the habitable zone of Alpha Centauri B.

Now, recent research suggests that five of these computer-simulated planets have a high potential for photosynthetic life.

The 2008 study calculated the likely number of planets around Alpha Centauri B by assuming an initial protoplanetary disk populated with 400 – 900 rocks, or protoplanets, roughly the size of the Moon. They then tracked the disk over the course of 200 million years through n-body simulations — models of how objects gravitationally interact with one another over time — in order to determine the total number of planets that would form from the disk.

While the number and type of exoplanets depended heavily on the initial conditions given to the protoplanetary disk, the eight computer simulations predicted the formation of 21 planets, 11 of which resided within the habitable zone of the star.

A second team of astronomers, led by Dr. Antolin Gonzalez of the Universidad Central de Las Villas in Cuba, took these computer simulations one step further by assessing the likelihood these planets are habitable or even contain photosynthetic life.

The team used multiple measures that asses the potential for life. The Earth Similarity index “is a multi-parameter first assessment of Earth-likeness for extrasolar planets,” Dr. Gonzalez told Universe Today. It predicts (on a scale from zero to one with zero meaning no similarity and one being identical to Earth) how Earth-like a planet is based on its surface temperature, escape velocity, mean radius and bulk density.

Planets with an Earth Similar index from 0.8 – 1 are considered capable of hosting life similar to Earth’s. As an example Mars has an Earth Similar index in the range of 0.6 – 0.8. It is thus too low to support life today.

However, the Earth Similarity index alone is not an objective measure of habitability, Gonzalez said. It assumes the Earth is the only planet capable of supporting life. The team also relied on the P model for biological productivity, which takes into account the planet’s surface temperature and the amount of carbon dioxide present.

At this point in time “there is no way to predict, at least approximately, the partial pressure of carbon dioxide with the known data, or the variations from a planet to another,” Gonzalez said. Instead “we assumed a constant partial pressure of carbon dioxide for all planets simplifying the model to a function of temperature.”

Gonzalez’s team found that of the 11 computer-simulated planets in the habitable zone, five planets are prone for photosynthetic life. Their Earth Similarity index values are 0.92, 0.93, 0.87, 0.91 and 0.86. If we take into account their corresponding P model values we find that two of them have better conditions than Earth for life.

According to this highly theoretical paper: if there are planets circling our nearest neighbor, they’re likely to be teeming with life. It’s important to note that while these indexes may prove to be very valuable years down the road (when we have a handful of Earth-like planets to study), we are currently only looking for life as we know it.

The paper has been published in the Cuban journal: Revista Cubana de Fisica and is available for download here. For more information on Alpha Centauri Bb please read a paper available here published in the Astrophysical Journal.