Category: Astrobiology (page 1 of 12)

How Radioactive Elements May Make Planets Suitable or Hostile to Life

An artist’s conception of a super Venus planet on the left and a super Earth on the right.  The question of what makes one planet habitable and one uninhabitable is a focus of many astrobiology researchers.  A new hypothesis looks at the presence of radioactive elements as an important factor in making a solar system habitable. (NASA/JPL-Caltech/Ames)

When describing exoplanets that are potentially promising candidates for life, scientists often use the terminology of the “habitable zone.”  This is a description of planets in orbit where temperatures, as predicted by the distance from the host star,  are not too cold for liquid water to exist on a planetary surface and also not to hot for all the water to burn off.

This planetary sweet spot, which not surprisingly Earth inhabits, is also more casually called the “Goldilocks zone” for exoplanets.

While there is certainly value to the habitable zone concept, there has also been scientific pushback to using the potential presence of liquid water as a primary or singular factor in predicting potential habitability.

There are just too many other factors that can play into habitability, some argue, and a focus on a planet’s distance from its host sun (and thus its temperature regime) is too narrow.  After all, several of the objects that just might support life in our own solar system are icy moons quite far from any solar system habitable zone.

With these concerns in the background, an interdisciplinary team of astrophysicists and planetary scientists at the University of California, Santa Cruz has begun to look at a source of heat in addition to suns and tidal forces that might play a role in making a planet habitable.

This source is the heat generated by the decay of long-lived radioactive elements such as uranium, thorium and potassium, which are found in stars and presumably on and in planets throughout the galaxies in greater or lesser amounts.

Using theory and modeling, they have concluded that the abundance of these radioactive elements in a planetary mantle can indeed give important insights into whether life might emerge there.

Supercomputer models of Earth’s magnetic field,  which is kept going thanks in part to the heat and subsequent convection produced by radioactive decay. (NASA)

Uranium is among the most widespread  elements on Earth — 500 times more common than gold It is present on the surface and in the mantle below. (Atomic Heritage Foundation.)

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Strong Doubts Arise About the Reported Phosphine Biosignature in the Atmosphere of Venus

An artist’s depiction of Venus and, in the inset, phosphine molecules.
(© ESO/M. Kornmesser/L. Calçada & NASA/JPL-Caltech,)

What started as a stunning announcement that the chemical phosphine — a known byproduct of life — had been found in the clouds of Venus and could signal the presence of some lifeform has now been strongly critiqued by a number of groups of scientists.   As a result, there is growing doubt that the finding, published in the journal Nature Astronomy in September,  is accurate.

The latest critique, also submitted to Nature Astronomy but available in brief before publication, is led by NASA’s planetary scientist Geronimo Villaneuva and others at the Goddard Space Flight Center. They reanalyzed the data used to reach the conclusion that phosphine was present and concluded that the signal was misinterpreted as phosphine and most likely came instead from sulphur dioxide, which Venus’s atmosphere is known to contain in large amounts.

The title of their paper is “No phosphine in the atmosphere of Venus.”

Another paper led by Ignas Snellen from the Leiden Observatory came to a similar conclusion, but finding fault elsewhere. She and her team analyzed the data used in the initial research to see if cleaning up the noise with a 12-variable mathematic formula, as was used in the paper, could lead to incorrect results.

According to Snellan, using this formula actually gave the original team —  false results and they found “no statistical evidence for phosphine in the atmosphere of Venus.”

While this critical research does not on its own disprove that phosphine exists in Venus’ atmosphere, it clearly raises doubts about original team’s conclusions.

That original team was lead by Jane S. Greaves, a visiting scientist at the University of Cambridge when when she worked on the phosphine finding.  She herself has also has been unable to replicate the level of phosphine found by her team, and was a co-author on a paper that described that.   It is now almost impossible to collect new data because of the coronavirus pandemic.

 

Venus is roughly the size of Earth but much hotter due to its huge concentrations of carbon dioxide in the atmosphere.  (NASA)

This intense scrutiny continues as staff at the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, discovered a separate, unspecified issue in the data that were used to detect the phosphine. “There are some issues with interpretation that we are looking at,” says Dave Clements, an astrophysicist at Imperial College London and co-author of the original study.… Read more

Surprising Insights Into the Asteroid Bennu’s Past, as OSIRIS-REx Prepares For a Sample-Collecting “Tag”

Artist rendering of the OSIRIS-REx spacecraft as it will approach the asteroid Bennu to collect a sample of ancient, pristine solar system material. The  pick-up”tag” is scheduled for Oct. 20. (NASA Goddard Space Flight Center, University of Arizona)

Long before there was an Earth, asteroids large and small were orbiting our young sun.  Among them was one far enough out from the sun to contain water ice, as well as organic compounds with lots of carbon.  In its five billion years or so as an object,  the asteroid was hit and broken apart by other larger asteroids, probably grew some more as smaller asteroids hit it,  and then was smashed to bits again many millions of years ago.  Some of it might have even landed on Earth.

The product of this tumultuous early history is the asteroid now called Bennu, and the destination for NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) mission.  On October 20, the spacecraft will make its dramatic final descent, will touch the ground long enough to collect some samples of the surface, and then will in the months ahead return home with its prized catch.

The sample will consist of grains of a surface that have experienced none of the ever-active geology on Earth,  no modifications caused by life,  and little of the erosion and weathering.  In other words, it will be a sample of the very early solar system from which our planet arose.

“This will be our first chance to look at an ancient, carbon-rich environment – the most pristine example of the chemistry of the very early solar system,” said Daniel Glavin, an astrobiologist at NASA’s Space Flight Center and a co-investigator of the OSIRIS-REx team.  “Anything as ancient on early Earth would have been modified many times over.”

“But at Bennu we’ll see the solar system, and the Earth,  as it was chemically before all those changes took place.  This will be the kind of pristine pre-biotic chemistry that life emerged from.”

This image of Bennu was taken by the OSIRIS-REx spacecraft from a distance of around 50 miles (80 km).
(NASA/Goddard/University of Arizona)

Bennu is an unusual asteroid.  It orbits relatively close to Earth — rather than in the main asteroid belt between Mars and Jupiter — and that’s one of several main reasons why it was selected for a visit.  It is also an asteroid with significant amounts of primeval carbon and organics, which is gold for scientists eager to understand the early solar system, planet formation and the origin of life on Earth.… Read more

Why Not Assemble Space Telescopes In Space?

Artist rendering of an in-space assembled observatory concept with a 20-meter diameter primary mirror. (NASA’s  In Space Assembled Telescope Study, iSAT)

As we grow more ambitious in our desires to see further and more precisely in space, the need for larger and larger telescope mirrors becomes inevitable.  Only with collection of significantly more photons by a super large mirror can the the quality of the “seeing” significantly improve.

The largest mirror in space now is the Hubble Space Telescope at 2.4 meters (7.9 feet) and that will be overtaken by the long-delayed James Webb Space Telescope (JWST) at 6.5 meters (21.3 feet) when it launches (now scheduled for late 2021.)  But already astronomers and space scientists are pressing for larger mirrors to accomplish what the space telescopes of today cannot do.

This is evident in the National Academies of Sciences Decadal Survey underway which features four candidate Flagship-class observatories for the 2030s.    Three proposals call for telescope mirrors that are significantly larger than the Hubble’s, and the most ambitious by far is LUVOIR  which has been proposed at 15.1 meters (or 50 feet) or at 8 meters (about 30 feet), or maybe something in between.  A primary goal of LUVOIR, and the reason for the large size of its mirrors, is that it will be looking for signs of biology on distant exoplanets — an extremely ambitious and challenging goal.

The LUVOIR team would have argued for an even larger telescope mirror except that 15.1 meters is the maximum folded size that would fit into the storage space available on the super heavy lift rockets expected to be ready by the 2030s.

This desire for larger and larger space telescopes has rekindled dormant but long-present interest in having an alternative to sending multi-billion dollar payloads into space via one launch only.  The alternative is “in-space assembly,” and NASA has shown increased interest in pushing the idea and technology forward.

Nick Siegler, Chief Technologist of NASA’s Exoplanet Exploration Program at the Jet Propulsion Lab, and others proposed a study of robotic in-space assembly in 2018.  The idea was accepted by the NASA Director for Astrophysics Paul Hertz and Siegler said the results are promising.

The International Space Station’s robotic Canadarm2 and Dextre carry an instrument assembly after removing it from the trunk of the SpaceX Dragon cargo ship (upper right), which is docked at the Harmony node of the ISS. (NASA

“For space telescopes larger than LUVOIR, in-space assembly will probably be a necessity because it’s unlikely that heavy-lift rockets will be getting any bigger than what’s being built now,” Siegler said. … Read more

Could Life Exist in the Clouds of Venus?

Nightside of Venus captured with the IR2 (infrared) camera on JAXA’s Akatsuki climate orbiter (JAXA).

On September 14 at 3pm GMT, an embargo lifted on a research paper reporting evidence for biological activity on Venus. Speculation about the discovery had been spreading rapidly through social media for several days, proving that scientists are incapable of keeping secrets.

With a surface temperature sufficient to melt lead, Venus is not the usual candidate for extraterrestrial life. However, the reported signature resides not on the surface of the planet, but in its clouds.

Led by Professor Jane Greaves at Cardiff University, the research team report an observation of phosphine; a molecule consisting of one atom of phosphorous and three atoms of hydrogen (PH3). On Earth, the trace amounts of phosphine in the atmosphere all come from either human or microbial activity. But does that make the presence of phosphine irrefutable evidence of life on Venus?

The case for phosphine as a biosignature

Phosphine has been found in the atmospheres of the gas giant planets, Jupiter and Saturn. However, this phosphine forms at the high temperatures and pressures existing deep within the giants’ colossal hydrogen-rich atmospheres. This process is not possible on the terrestrial planets, where the atmospheres are vastly thinner and hydrogen poor.

Instead of hydrogen, Venus’s atmosphere consists predominantly of carbon dioxide with clouds of sulfuric acid. While both ingredients sound abysmal for the prospect of life, the molecules consist of carbon and sulfur bounded to oxygen atoms. The prevalence of oxygen atoms should have resulted in any phosphorous present in the atmosphere to chemically react in a similar fashion to form a phosphate molecule (phosphorous and oxygen), rather than the observed phosphine (phosphorus and hydrogen).

Surface photographs from the former Soviet Union’s Venera 13 spacecraft, which touched down in March 1982. Temperatures on the surface are sufficient to melt lead, while the sulfur in the clouds gives the air its yellow/orange colour (NASA).

Despite considering thousands of possible reactions that might occur within Venus’s atmosphere, Greaves and her team failed to simulate the production of phosphine on Venus through abiotic (non-biological) means. Energetic processes such as lightening, volcanic activity or delivery via meteorites were also ruled out as possible sources, as the quantities they produced should be too low to explain the detection.

Estimates for the lifetime of phosphine also remove the chance that the molecules are leftover from an earlier epoch when the young Venus hosted a more clement environment.… Read more

An “Elegant” New Theory on How Earth Became a Wet Planet

About 71 percent of the Earth’s surface is covered by water, and vast quantities of water are also locked up in minerals on and beneath the surface.  This image of Earth comes from NASA’s Earth Polychromatic Imaging Camera (EPIC) on NOAA’s Deep Space Climate Observatory (DSCOVR), orbits Earth from a distance of about 1 million miles away. (NASA)

One of the enduring puzzles of our planet is why it is so wet.

Since Earth formed relatively close to the sun,  planetary scientists have generally held that any of the water in the building blocks of early-forming Earth was baked out and so was unavailable to make oceans or our atmosphere.

That led to theories explaining the oceans and wet atmosphere of Earth as a later addition, brought to us by meteorites and comets formed beyond the solar system’s so-called “snow line,” where volatile compounds such as water can begin to condense into ice.

This snow line is a general area between Mars and Jupiter, and that means under this theory that our water would have had to come from awfully far away.   Further complicating this view is that the isotopic makeup of that distant water ice is somewhat different from much of the water on Earth.

Now, a new paper in the journal Science from Laurette Piani of  the Université de Lorraine and colleagues, argues that Earth’s water was simply acquired like most other of our materials, through accretion when the planet formed in the inner solar nebula.

To reach that conclusion, the group re-examined 13 meteorites of the parched type formed between Earth and the sun, and they found more than of enough hydrogen present to explain how Earth got so wet (wet for our solar system, that is.)

In fact, they extrapolated from their data that enough water was available in the nebular cloud  that accompanied the formation of our sun and formed those early meteorites — called enstatite chondrites — to create three times as much water as our oceans hold.

 

 

New measurements of enstatite chondrites indicate that water could have been primarily acquired from Earth’s building blocks. Additional water was delivered to Earth’s early oceans and atmosphere by water-rich material from comets and the outer asteroid belt. (Science)

“Our discovery shows that the Earth’s building blocks might have significantly contributed to the Earth’s water and that hydrogen bearing material was present in the inner solar system at the time of the Earth and rocky planet formation, even though the temperatures were too high for water to condense,'” Piani told me.… Read more

How Many Habitable Zone Planets Can Orbit a Host Star?

This representation of the Trappist-1 system shows which planets could potentially have temperature conditions which would allow for the presence of liquid water, seen generally as essential for life.  The inner three planets are likely too hot, and the outer planet is probably too cold, but the middle three planets might be just right. (NASA / JPL-Caltech)

Our solar system has but one planet orbiting in what is commonly known as the habitable zone — at a distance from the host star where water could be liquid at times rather than always ice or gas.  That planet, of course, is Earth.

But from a theoretical, dynamical perspective, does this always have to be the case?  The answer to that question is no because a number of stars are known to have more than one habitable zone planet.

Now a team from the University of California, Riverside has produced a study that concludes as many as seven Earth-sized, habitable zone planets could orbit a single star — if there were no large Jupiter-sized planets in the system and if the star was of a particular type.

The article, published in the Astronomical Journal, concluded that seven habitable zone planets was the maximum for a star, but a sun such as ours could potentially support six planets with sometimes liquid water — a condition considered essential for life.

Study leader Stephen Kane, an astrobiologist who focuses on potentially habitable exoplanets, said he had been studying the nearby solar system Trappist-1, which has three Earth-like planets in its habitable zone and seven planets all together.

“This made me wonder about the maximum number of habitable planets it’s possible for a star to have, and why our star only has one,” Kane said.

With the discovery of an eighth planet, the Kepler-90 system is the first to tie with our solar system in number of planets. Artist’s concept. Credit: NASA/Ames Research Center/Wendy Stenzel

His conclusion:

“Even though (our solar system) only has one planet in the habitable zone, it’s not necessarily the typical situation. A far more typical scenario may be to have many planets in the habitable zone, depending on the presence of a giant planet.”

More later about the destabilizing effects of giant planet, but the Kane (and others) say that looking for solar systems without Jupiter-size planets has become increasingly important because of this effect on other terrestrial planets.

To determine how many habitable zone planets might be possible in a solar system, his team created a model system in which they simulated planets of various sizes orbiting their stars.

Read more

Sample Return in the Time of Coronavirus

 

Sample return from Mars. Artist rendering of a Mars sample return mission. The mission would use robotic systems and a Mars ascent rocket to collect and send samples of Martian rocks, soils and atmosphere to Earth for detailed chemical and physical analysis.  No rocket has ever taken off from Mars and this NASA and European Space Agency (ESA) project is in early planning stages. Still, blue-ribbon science panels have recommended efforts to begin preparing the public for an eventual Mars sample return. ( Wickman Spacecraft & Propulsion)

For space scientists of all stripes, few goals are as crucial as bringing pieces of Mars, of asteroids, of other planets and moons back to Earth for the kind of intensive study only possible here.  Space missions can, and have, told us many truths about the solar system,  but having a piece of Mars or Europa or an asteroid to study in a lab on Earth is considered the gold standard for learning about the actual composition of other bodies, their histories and whether they could — or once did — harbor life.

In keeping with this ambition, the last National Research Council Decadal Survey listed a Mars “sample return” as the top science priority for large Flagship missions.  And the Perseverance rover that NASA is scheduled to send to Mars next month will — among many other tasks — identify compelling rock samples, collect and cache them so a subsequent mission can pick them up and fly them to Earth.

Two asteroid sample return missions are also in progress, the NASA’s OSIRIS-REx mission to Bennu and the Japan Aerospace Exploration Agency (JAXA’s)  Hayabusa2 mission to the Ryugu.  Both spacecraft are at or have already left their intended targets now and are expected to return with rock samples later this decade, with Hayabusa2 scheduled to complete its round trip later this year.

An illustration of the coronavirus. (Centers of Disease Control)

So sample return is in our future.  And in the case of Mars the samples will not with 100 percent certainty be lifeless — a major difference from the samples brought back from the moon during the Apollo missions and the samples coming from asteroids.

This possibility of a spacecraft bringing back something biological — as in the 1969 book “The Andromeda Strain” — has always been viewed as a very low probability but high risk hazard, and much thinking has already gone into how to bring samples back safely.… Read more

Close and Tranquil Solar System Has Astronomers Excited

An artist’s impression of the GJ 887 planetary system of super Earths. (Mark Garlick)

From the perspective of planet hunters and planet characterizers,  a desirable solar system to explore is one that is close to ours, that has a planet (or planets) in the star’s habitable zone,  and has a host star that is relatively quiet.  This is especially important with the very common red dwarf stars,  which are far less luminous than stars such as our sun but tend to send out many more powerful — and potentially planet sterilizing — solar flares.

The prolific members of the mostly European and Chilean Red Dots astronomy team believe they have found such a system about 11 light years away from us.  The system — GJ 887 — has an unusually quiet red dwarf host, has two planets for sure and another likely that orbits at a life-friendly 50-day orbit.  It is the 12th closest planetary system to our sun.

It is that potential third planet, which has shown up in some observations but not others, that would be of great interest.  Because it is so (relatively) close to Earth, it would be a planet where the chemical and thermal make-up of its atmosphere would likely be possible to measure.

The Red Dots team — which was responsible for the first detection of a planet orbiting Proxima Centauri and also Barnard’s star — describes the system in an article in the journal Science.  Team leader Sandra Jeffers of Goettingen University in Germany said in an email that GJ 887  “will be an ideal target because it is such a quiet star — no starspots or energetic outbursts  or flares.”

In an accompanying Perspective article in Science,  Melvyn Davies of Lund University in Sweden wrote that “If further observations confirm the presence of the third planet in the habitable zone, then GJ 887 could become one of the most studied planetary systems in the solar neighborhood.”

An artist’s impression of a flaring red dwarf star and a nearby planet. Red dwarfs are by far the most common stars in the sky, and most have planetary systems.  But scientists are unsure if they can support a habitable planet because many send out more large and powerful flares than other types of stars, especially at the beginnings of their solar lives. (Roberto Molar Candanosa/Carnegie/NASA)

GJ 877 is roughly half as massive as our sun — large for its type of star — and is the brightest red dwarf in the sky.… Read more

Thinking About Life (or Lyfe) Through The Prism of “Star Trek”

This column was written for Many Worlds by Michael L. Wong and Stuart Bartlett.  Wong is a postdoctoral research associate at the University of Washington’s Astronomy and Astrobiology program and is a member of  NASA’s Nexus for Exoplanet System Science (NExSS) initiative as part of the university’s Virtual Planetary Laboratory team.  Bartlett is a postdoctoral scholar in Geochemistry at the California Institute of Technology and has been a fellow at the Earth-Live Science Institute (ELSI) in Tokyo.

 

Spock communicates with a Horta,  a fictional silicon-based life form composed of molten rock and acid.  (Star Trek; CBS Studios)

By Michael L. Wong and Stuart Bartlett

 

The search for extraterrestrial life is in its early phase still  and, the truth is, we don’t yet know if life exists beyond our pale blue dot.  Or, if it does, whether it will be easily recognizable or truly bizarre.

Predicting what might be out there, and how to find it, is a hypothesis-driven area of research at present — one that has given rise to hundreds of possible definitions for the “life” we are looking for.

But after grounding ourselves in scientific principles, it may be that our greatest tool is to let our imaginations fly. Science fiction often helps us embrace our ignorance of what might be out there.

In the Star Trek universe, our galaxy is teeming with life—both astonishingly familiar and incredibly different.

The familiar variety includes Mr. Spock, the U.S.S. Enterprise’s half-human, half-Vulcan science officer. He is the product of an extraordinary cosmic coincidence: the emergence of nearly identical biochemical machinery on two completely separate worlds. Vulcans—despite their pointy ears, upswept eyebrows, and a nearly religious devotion to bowl cuts—are incredibly similar to humans on the cellular, genetic, and metabolic level.

We can share meals, share air, and, yes, share intimacy. Even their green, copper-based blood is not as alien as it might seem; this trait is typical of most mollusks and crustaceans on Earth.

 

The Crystalline entity was a powerful, spaceborne creature characterized by a crystalline structure that resembled a large snowflake. (Star Trek;  CBS Studios)

But Star Trek also depicts life forms that are incredibly dissimilar from you, me, or Mr. Spock.

Take the Horta, for example. This lumpy mass, like a misshapen meatball crossed with a child’s volcano science experiment, is a silicon-based life form composed of molten rock and acid.

Then there’s Q, a non-corporeal being that possesses god-like powers which, it seems, are directed solely upon harassing Captain Jean-Luc Picard.… Read more

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