Category: Astrobiology (page 1 of 15)

Why Does Our Solar System Have No Super-Earths, and Other Questions for Comparative Planetology

An artist’s impression of the exoplanet LHS 1140b, which orbits a red dwarf star 40 light-years from Earth. Using the European Southern Observatory’s telescope at La Silla, Chile, and other telescopes around the world, an international team of astronomers discovered this super-Earth orbiting in the habitable zone around the faint star LHS 1140. This world is a little larger and much more massive than the Earth. (ESO)

Before the explosion in discovery of extrasolar planets, the field of comparative planetology was pretty limited  — confined to examining the differences between planets in our solar system and how they may have come to pass.

But over the past quarter century, comparative planetology and the demographics of planets came to mean something quite different.  With so many planets now identified in so many solar systems, the comparisons became not just between one planet and another but also between one solar system and another.

And the big questions for scientists became the likes of:  How and why are the planetary makeups of distant solar systems often so different from our own and from each other; what does the presence  or absence of large planets in a solar system do to the distribution of smaller planets;  how large can a rocky planet can get before it turns to a gas giant planet; and on a more specific subject, why do some solar systems have hot Jupiters close to the host star and others have cold Jupiters much further out like our own

Another especially compelling question involves our own solar system, though as something of an outlier rather than a prototype.

That question involves the absence in our solar system of anything in the category of a “super-Earth” — a rocky or gaseous extrasolar planet with a mass greater than Earth’s but substantially below those of our solar system’s planets next in mass,  Uranus and Neptune.

The term “super-Earth” refers only to the mass and radii of the planet, and so does not imply anything about the surface conditions or habitability. But in the world of comparative planetology “super-Earths” are very important because they are among the most common sized exoplanets found so far and some do seem to have planetary characteristics associated with habitability.

Yet they do not exist in our solar system.  Why is that?

Artist rendition of Earth in comparison to one of the many super-Earth planets. (NASA)

In a recent article in The Astrophysical Journal Letters,  planetary demographer Gijs D.… Read more

NASA Should Build a Grand Observatory Designed to Search For Life Beyond Earth, Top Panel Concludes

The National Academy of Sciences has released it’s “Decadal Survey,” with guidance and recommendations for the fields of astronomy, astrobiology and astrophysics.(NASA)

NASA should begin developing a mission that can tell us whether life in the near galaxy is abundant, rare or essentially absent, The National Academy of Sciences recommended yesterday.

The call for a next Grand Observatory telescope with this ambitious goal represents the first time that the Academy, in its Decadal Survey for Astronomy and Astrophysics, has given top priority to the science of  exoplanets and the search for life far beyond Earth.

The long-awaited NAS survey did not select a single mission concept, although several NASA-commissioned studies were extensively researched and assembled for the Decadal over the past four years.

Rather, they set the science goal of giving an answer – as complete as possible – to the eternally-asked question of whether life exists solely on Earth or can be found on the billions of other planets we now know orbit their own suns.

Decadal steering committee co-chair Robert Kennicutt Jr., a professor at University of Arizona and Texas A & M University, said that a flood of discoveries and astronomical and technological advances in recent decades made clear that the time for such a mission had come.

“We’re laying down a marker here,” Kennicutt said  in a press conference.  “We think that progress in this field has taken us to the point that within the planning horizon of this survey, we can really contemplate imaging  Earth-like planets in their habitable zones around other stars and spectroscopically studying them for atmospheric composition, perhaps including biomarkers. with the ultimate goal of answering one of the most profound questions:  Are we alone in the universe?”

The proposed mission, he said, would as a result have the transformative scientific power of the Hubble Space Telescope and the James Webb Space Telescope, which is scheduled to launch next month.  It would change the way that scientists and citizens see the world.

The telescope envisioned by Decadal Survey would search for small rocky planets in the habitable zone of heir sun — where the temperatures would allow for liquid water to exist rather than just water vapor or ice.  This artist’s concept ia of Kepler-452b, the first near-Earth-size world found in the habitable zone of a distant sun-like star. ( NASA/Ames/JPL-Caltech.)

But the road to an actual mission will be long and definitely uphill.… Read more

A Call To Action on Ensuring That Extraordinary Claims About ET Life Come With Extraordinary Evidence

An artist’s rendering of the sweep of cosmic events important to astrobiology.  They include the formation of molecular clouds of gas and dust where stars are born, the subsequent evolving of a protoplanetary disk surrounding the new star, and then the organizing of a cleaned-up solar systems with planets and moons. (National Radio Astronomy Observatory and Dina Clark/University of California, Santa Cruz)

The global scientific search for signs of life beyond Earth has produced cutting-edge and paradigm-shifting science for several decades now, and it has clearly found eager audiences around the world.  This search is a high-priority goal of NASA and other space agencies, as well as institutions, universities and companies.

While the successes in this broadly defined field of astrobiology are legion, the field has also struggled with a problem that flows precisely from its high-impact subject.

That problem is how to best keep its scientific claims evidence based and how to take into account all the myriad factors that can undermine the strength of a “finding.”  And then comes the question of how to best communicate with the public the nature of the findings and all the caveats involved.

There appears to be a widely-held view that some scientific claims and media reports about potential life beyond Earth have become not only a distraction in the field, but have served to undermine some public confidence in the endeavor.

NASA Chief Scientist Jim Green is the lead author of a Nature paper calling for heightened standards for all extraterrestrial life detection science. With discoveries coming in so fast, he said, some formal new standards are needed to increase scientific and public confidence. (NASA /Carla Cioffi)

And some of the leading figures in the field have written a paper, released today by the journal Nature, that calls for the creation of some as yet undefined guardrails or confidence scales to make exciting scientific findings and news about astrobiology more consistently dependable.

The goal is to find ways to make sure that papers meet the widely-embraced Carl Sagan standard that  “extraordinary claims require extraordinary evidence”.

This is how the authors introduce the paper:

“Ours could realistically be the generation to discover evidence of life beyond Earth. With this privileged potential comes responsibility.”

“The magnitude of the question, “are we alone?”, and the public interest therein, opens the possibility that results may be taken to imply more than the observations support, or than the observers intend.… Read more

Many Planets Form in a Soup of Life-Friendly Organic Compounds

Artist’s depiction of a protoplanetary disk with young planets forming around a star. The right-side panel zooms in to show various organic molecules that are accreting onto a planet. (M.Weiss/Center for Astrophysics | Harvard & Smithsonian)

One of the more persuasive arguments in favor of the potential existence of life beyond Earth is that the well-known chemical building blocks of that life are found throughout the galaxy.  These chemical components aren’t all present in all examined solar systems and planets, but they are common and behave in ways familiar to scientists here.

And when it comes elements and compounds found on distant planets but not found here, there just aren’t many. That doesn’t mean they don’t exist — some unstable compounds in interstellar space, for instance — but rather that the cosmos holds many surprises but none have involved extraterrestrial elements or compounds near planets or stars.

This is in large part the result of how elements are formed in the universe.  Other than hydrogen and helium, all other elements are forged in the thermonuclear explosion of stars that have exhausted their supply of fuel.  These massive explosions (supernovae) then shoot the newly-formed elements out into space where they can and do collect in gas and dust clouds that will form other new stars.  They are spread throughout the disks that form around new stars and over time they become components of new planets in formation.

This galactic evolution includes the bonding together of carbon-based organic compounds — the building blocks of life as we know it.  They are an essential component to any theory of a planet’s habitability and,  while their presence in space and star nurseries has been known for some time,  they have remained a subject of great interest but limited detailed knowledge.

That is why an international team from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass. set out to intensively study five disks forming around young stars to determine more precisely what organic compounds were present and available for objects developing into planets.

And the results are striking:  The abundance of organic material detected was 10 to 100 times more than expected.

“These planet-forming disks are teeming with organic molecules, some of which are implicated in the origins of life here on Earth,” said team leader Karin Öberg. “This is really exciting; the chemicals in each disk will ultimately affect the type of planets that form and determine whether or not the planets can host life.”… Read more

Frigid Europa Holds a Huge and Maybe Habitable Ocean Beneath Its Thick Ice Covering. How is That Possible?

Europa has one of the smoothest surface of any body in the solar system.  A moon as old as Europa that did not have an ice cover — and a likely ocean inside — would be pocked with asteroid craters.  On Europa, these craters appear to be absorbed into the icy surface via geologic and thermal processes.  Giant lakes trapped in Europa’s crust also bust up the icy surface. (NASA)

Jupiter’s moon Europa is almost five times as far away from the sun as Earth is, with surface temperatures that don’t rise above minus 260 degrees Fahrenheit.  It’s slightly smaller than our moon and orbits but 400,000 miles from the solar system’s largest planet, which it takes but 3.5 Earth days to orbit.  As a result it is tidally locked, always showing the same face to Jupiter.

When it comes to potentially habitable objects in our solar system, Europa would not seem to be a terribly likely possibility.

But, of course, it is.  And in three years NASA’s Europa Clipper mission will launch to explore what would appear to be one of the most unlikely yet possible places in our solar system to find potential signs of life.

The reason why is that scientists are almost certain that under Europa ‘s 10-to 15 mile ice covering is a deep, global ocean of salty water.

The size of the ocean has not been well determined yet, with estimates of between 40 and 100 miles of depth.  But a  consensus has been reached that the ocean is likely to be global, and contains two to three times as much liquid water as found on Earth.

This then raises a question with great significance for Europa, other moons in the solar system and quite likely planets and moons well beyond us:  How can there be so much liquid water inside such frigid places?

The spot toward the lower left is one Europa, against the backdrop of Jupiter.  Images from Voyager in 1979 bolster the modern hypothesis that Europa has an underground ocean and is therefore a good place to look for extraterrestrial life. The dark spot on the upper right is a shadow of another of Jupiter’s large moons. Sixteen frames from Voyager 1’s 1979 Jupiter flyby were recently reprocessed and merged to create this image.  (NASA, Voyager 1, JPL, Caltech; Processing & License: Alexis Tranchandon / Solaris)

There are numerous possible answers to that question, and it’s likely that all or most played some role.… Read more

Sample Return from Mars Begins in Earnest

This image taken by NASA’s Perseverance rover on Sept. 7, 2021 shows two holes where the rover’s drill obtained chalk-size samples from a rock nicknamed “Rochette.” They are the first physical manifestations of the NASA’s long-planned Mars Sample Return Mission. (NASA/JPL-Caltech.)

For the first time ever, a sample of pulverized rock from another planet has been drilled, collected and stored for eventual delivery to the highest-tech labs on Earth.

Yes, a storehouse of rocks were collected on the moon by Apollo astronauts and delivered to Houston, and some small samples of two asteroids and one comet were snatched by three spacecraft (two Japanese and one American) and their contents were brought here for study.

But never before has the surface of another planet been the source of precious extraterrestrial material that some day, if all goes well, will be received on Earth for intensive analysis.

The feat was accomplished by the team that operates the Perseverance rover on Mars.  After an unsuccessful effort to drill what turned out to be a very soft rock in August , the rover drill succeeded in digging into a briefcase-sized hard volcanic rock twice this month and pulling out samples to be tubed and stored for later pick-up by a different mission.

That next step isn’t scheduled for another half decade and the samples would not arrived on Earth until well after that.  But a long-dreamed and highly-ambitious effort to bring some of Mars to Earth (called Mars Sample Return) has now formally begun.

“This is a truly historic achievement, the very first rock cores collected on another terrestrial planet — it’s amazing,” Meenakshi Wadhwa, Mars sample return principal scientist at NASA’s Jet Propulsion Laboratory, said during a news conference held Friday

“In our science community, we’ve talked about Mars sample return for decades,” Wadhwa said. “And now it’s actually starting to feel real.”

Perseverance’s first cored-rock sample of Mars is seen inside its titanium container tube in this image taken by the rover’s Sampling and Caching System Camera, known as CacheCam. (NASA/JPL-Caltech)

The press conference was a victory lap of sorts for leaders of a team with many members who have worked eight to ten years for this moment.  Lori Glaze, NASA’s director of the Planetary Science Division, also called it an historic achievement –the culmination of advances pioneered by many other NASA missions to Mars and elsewhere and a milestone for NASA’s Mars program.… Read more

Introducing Hycean Planets

A so-called Hycean planet is one featuring large oceans and a hydrogen atmosphere. A new report from the University of Cambridge suggests this kind of planet, sized between a super-Earth and a mini-Neptunes, could potentially support life. The image features a red dwarf star as the planet’s host star. (Artist rendering by Amanda Smith, University of Cambridge)

Planets beyond our solar system, we now know, come in all shapes, sizes and consistencies.  There are rocky planets, water worlds, gaseous planets, super-Earths, hot Jupiters, tidally locked planets, planets in orbital resonance with each other,  and so much more.

A group of exoplanet researchers at the University of Cambridge have recently proposed a new category of planet, one that has seldom been considered even potentially habitable.  They call them Hycean planets due to the presence of substantial hydrogen in the atmospheres and large oceans (hydrogen and ocean = Hycean) on their surfaces.

And in an article in The Astrophysical Journal, they make the case that under certain conditions, some Hycean planets could, indeed, be habitable.

“Hycean planets open a whole new avenue in our search for life elsewhere,” said Nikku Madhusudhan from Cambridge’s Institute of Astronomy, who led the research.

Many of the prime Hycean candidates identified by the researchers are bigger and hotter than Earth, but the researchers argue that they still have the characteristics to host large oceans that could support microbial life similar to that found in some of Earth’s most extreme watery environments.

Hycean planets, Madhusudhan said in a release, offer a new paradigm for the search for life beyond Earth.

“Essentially, when we’ve been looking for these various molecular signatures, we have been focusing on planets similar to Earth, which is a reasonable place to start,”  he said. “But we think Hycean planets offer a better chance of finding several trace biosignatures.”

Co-author Anjali Piette, also from Cambridge, added: “It’s exciting that habitable conditions could exist on planets so different from Earth.”

An artist rendering of what a possible Hycean planet would look like.  This image is of K2-18b, which has a radius twice that of Earth and is more than eight times as massive as our planet.  The heavy hydrogen atmosphere is present, as is the red dwarf star that it orbits. (Alex Boersma)

There are no planets of this size and type in our solar system, but planets in the Hycean range are quite common in the galaxy.… Read more

Findings Suggest that Red Dwarf Stars May Not Sterilize Many Exoplanets As Feared

An illustration of a red dwarf star with orbiting exoplanet. The question of whether this very common type of star can support habitable planets is a much debated one. (NASA)

Red dwarf suns are the most common in the universe, and many of the exoplanets officially discovered so far orbit this type of “cool” star.  Red dwarfs are much smaller and less powerful than the G type stars such as our own sun, and it is easier to detect exoplanets orbiting them because of their reduced size and energy.

As a result, a number of relatively nearby red dwarf stars — in the Trappist-1 system, Proxima Centauri and Barnard’s star, for instance — are avidly studied for their potential habitability.  The exoplanets of red dwarfs tend to orbit much closer than around other larger stars, but the suns have that lower radiative power and so some are considered habitable candidates.  And if they are indeed habitable, they could be for a very long time because red dwarfs live much longer than most other stars.

But there have been two (at least) problems with the habitable red dwarf exoplanet scenario.  The first is that many of the planets so close to their star are tidally locked, meaning that only one side ever faces the sun.  Some have argued a tidally locked planet can still be habitable, but it would not be easy.

More crucial, however, is that red dwarf stars are known for sending out many, many powerful solar flares, especially during their solar infancy and childhood.  These high radiation and particle flares could and would potentially kill any life emerging on a dwarf exoplanet, and the stellar flares could even sterilize the planets’ atmosphere for all time.  Although direct observations have not shown this deadly scenario to be inevitable or even present, the red dwarf flaring is well documented.  And so potentially the flares have seemed to rule out, or make improbable, life on an estimated 75 percent of the stars in our galaxy.

This is why there is interest in the astrobiology world about a new paper that addresses a particular kind of stellar flare that would hit red dwarf exoplanets.  Such studies of how the behavior of a star effects orbiting planets is one of the less well studied aspects of the exoplanet field, and so the paper is especially welcomed.

And the results suggests that the red dwarf flares would strike orbiting exoplanets from an angle rather than straight on, and therefore would land in a way that would theoretically minimize damage to potential atmospheres and life.… Read more

The Many Ways The James Webb Space Telescope Could Fail

Artist rendering of the James Webb Space Telescope when it has opened and is operating. The telescope is scheduled to launch in November, 2021. (NASA)

When a damaged Apollo 13 and its crew were careening to Earth, mission control director Gene Kranz famously told the assembled NASA team that “failure is not an option.”  Actually, the actor playing Kranz in the “Apollo 13” movie spoke those words, but by all accounts Kranz and his team lived that phrase, with a drive that became a reality.

That kind of hard-driving confidence now seems to be built into NASA’s DNA, and with some tragic exceptions it has served the agency well in its myriad high-precision and high-drama ventures.

So it was somewhat surprising (and a bit refreshing)  to read the recent blog post from Thomas Zurbuchen,  NASA’s Associate  Administrator for the Space Science Directorate, on the subject of the scheduled November launch of the James Webb Space Telescope.

Thomas Zurbuchen, NASA’s Associate Administrator of the Space Science Directorate, with the new eyeglasses he introduced in his blog. (NASA)

“Those who are not worried or even terrified about (the challenges facing the JWST mission) are not understanding what we are trying to do,” he wrote.

“For most missions, launch contributes the majority of mission risk – if the spacecraft is in space, most risk is behind us. There are few types of missions that are very much different with most risk coming after launch.

“We have already performed one such mission in February when we landed on Mars. For the Perseverance rover, only 10-20% of the risk was retired during launch, perhaps 50% during the landing, and we are in the middle of the residual risk burn down as we are getting ready to drill and collect the precious Mars samples with the most complex mechanical system ever sent to another planet.

“The second such mission this year is Webb. Like a transformer in the movies, about 50 deployments need to occur after launch to set up the huge system. With 344 so-called single point failures – individual steps that have to work for the mission to be a success – this deployment after launch will keep us on edge for 3 weeks or so. For comparison, this exceeds single point failures for landing on Mars by a factor of 3, and that landing lasted only 7 minutes.”

Zurbuchen is confident that the Webb team and technology is up to the challenge but still, that is quite a risk profile.… Read more

Earth as a Transiting Exoplanet

A view of Earth and Sun from thousands of miles above our planet. Stars that enter and exit a position where they can see Earth as a transiting planet around our Sun are brightened. (OpenSpace/American Museum of Natural History)

Exoplanet scientists and enthusiasts spend a lot of time trying to find, measure and understand distant planets that can — under specific conditions — be detected as passing in front of their host star.  A majority of the 4000-plus exoplanets discovered so far were indirectly detected this way, by measuring the diminishing of stellar light as the exoplanet passes between the star and us.

In a conceptual turnaround, two researchers have now asked the question of how common it might be for beings on distant exoplanets to be able to similarly detect and measure Earth as it transits in front of our sun.

Astronomers call this special vantage point in space – the point from which Earth transits can be seen – the Earth transit zone.  Because the cosmos is dynamic and ever-changing, they looked for not only stars that are in that zone now, but have also passed through over the past 5,000 years and will in the next 5,000 years.

“From the exoplanets’ point-of-view, we are the aliens,” said Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University.

“We wanted to know which stars have the right vantage point to see Earth, as it blocks the sun’s light.  And because stars move in our dynamic cosmos, this vantage point is gained and lost.”


Transit data are rich with information. By measuring the depth of the dip in brightness and knowing the size of the star, scientists can determine the size or radius of the planet. The orbital period of the planet can be determined by measuring the elapsed time between transits. Once the orbital period is known, Kepler’s Third Law of Planetary Motion can be applied to determine the average distance of the planet from its stars. (NASA/Ames)

How many stars (and their orbiting planets) have this proper vantage point, have had in the past and will in the future?

In Kaltenegger’s paper, published in Nature with Jackie Faherty of the astrophysics department of the American Museum of Natural History, the numbers reported are quite low.

They found that since the earliest human civilization about 5,000 years ago, only 1,715 stars among the 300,000-plus that shine within 300 light years of our sun are in the right geometric alignment for an observation of Earth passing in front of our sun. Read more

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