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Category: Astrobiology (page 2 of 20)

A New Model For How Earth Acquired Its Water

April 26, 2023 / / 1 Comment

One of the best known photographs of Earth, this image was taken by the crew of the final Apollo mission as the crew made its way to the Moon.  Named the “Blue Marble,” the image highlights how much of the planet is covered by water — 71 percent of the surface.  How this came to be remains an open scientific question.
(NASA)

Theories abound on how Earth got its water.

Most widely embraced is that asteroids, and maybe comets, crashed into our planet and released the water they held — in the form of ice or hydrated minerals in their crystal structures — and over time water became our oceans.  The inflow was especially intense during what is called “the Late Heavy Bombardment,” some 4 billion years ago.

The isotopic composition of our water is comparable to water in asteroids in the outer asteroid belt, and so it makes sense that they could have delivered the water to Earth,

But there is also the view Earth formed with the components of water inside the planet and the H₂O was formed and came to the surface over time.  Several hydrous minerals in our mantle store the necessary elements to create water and in this theory the pressure from hot magma rising up and cooler magma sinking down crushes this hydrous material and wrings them like a sponge.  Water would then find its way to the surface through volcanoes and underwater vents.

Now a new model has been proposed and it has a novel interest because it originates in the discovery of thousands of exoplanets in the past quarter century.

This new approach, described by Anat Shahar of the Carnegie Institution for Science and colleagues from UCLA in the journal Nature, says that Earth’s water could have come from the interactions between of a very early and primarily hydrogen atmosphere and the scalding ocean of magma that covered the planet.

That the planet could have had a thick hydrogen atmosphere that wasn’t quickly destroyed is a new idea and it comes from the finding that many so-called “super-Earth” exoplanets have, or had, such an atmosphere.  While super-Earths are larger and more massive than Earth, many are rocky, terrestrial planets and so share characteristics with our planet.

“Exoplanet discoveries have given us a much greater appreciation of how common it is for just-formed planets to be surrounded by atmospheres that are rich in molecular hydrogen, H2, during their first several million years of growth,” Shahar said.… Read more

Pam Conrad: The NASA Astrobiologist Who Also Became a Minister

April 13, 2023 / / 2 Comments

Pan Conrad on her last Sunday as rector of St. Albans Episcopal Church in Glen Burnie, Maryland. (Julian Lahdelma)

Science and religion so often seem to be in conflict, with the chasm between them widening all the time.

For many, the grounding of their religion is in faith and belief in powers beyond our understanding.  For people of science, the grounding is in empirical facts and measurements that can be tested to help explain our world.

The conflicts between science and religion have been many,  perhaps most intensely on issues including evolution, how life on Earth began and how our universe came to be.

The era of pioneering scientists being punished or hounded by religious leaders — think of Galileo, astrobiologist-before-his-time Giordano Bruno, Charles Darwin — is largely in the past.  But so too is the era when the most prominent natural scientists were profoundly religious people, such as Sir Isaac Newton, James Maxwell (who correctly theorized the nature of electromagnetism) and one of the 19th century physicist and scientific titan, Lord Kelvin.

The field of astrobiology presents innumerable issues where a scientific and religious focus certainly could clash.  Astrobiology is focused on the search for life beyond Earth which, if detected, could raise significant issues for some religious people.

The astrobiology effort is grounded in our scientific theories of how the universe began and evolved over its 13.6 billion years, so spiritual and religious views that once dominated thinking about these questions play little role.

And then there is the origin-of-life issue, which is also part of astrobiology and is, of course, an arena where scientific and religious views are often in conflict.

With so many divides between a scientific and a religious approach to astrobiological questions, it might seem that there is little room for overlap.

Conrad has worked on the characterization of biosignatures and the habitability of Mars, first at JPL and now at the Earth and Planets Laboratory at the Carnegie Institution of Science. She worked on the science team of the Curiosity rover on Mars and now she works with three instruments on the Perseverance rover at Jezero Crater, Mars. (NASA)

But then I spoke with the Rev. Pamela Conrad, who I knew from some years ago when we often talked about astrobiology and even took a trip to Death Valley together, where she helped me understand some of the science of life surviving in extreme environments and how to find it.… Read more

What the JWST is Learning About Exoplanet Atmospheres

April 5, 2023 / / 1 Comment

We are now well into the era of exoplanet atmospheres, of measurements made possible by the James Webb Space Telescope.  While prior observatories could detect some chemicals in exoplanet atmospheres,  the limits were substantial. This is an artist’s impression of a hot Jupiter with a thick atmosphere transiting its host star. (NASA, ESA, and G. Bacon (STScI)

The James Webb Space Telescope is beginning to reveal previously unknowable facts about the composition of exoplanets — about the presence or absence of atmospheres around the exoplanets and the makeup of any atmospheres that are detected.

The results have been coming in for some months and they are a delight to scientists.  And as with most things about exoplanets, the results are not always what were expected.

For instance, gas giant planets  orbiting our Sun show a clear pattern; the more massive the planet, the lower the percentage of “heavy” elements (anything other than hydrogen and helium) in the planet’s atmosphere.

The James Webb Space Telescope is returning insights into the atmospheres of exoplanets that scientists have long dreamed about obtaining. Some are predicting a new era in exoplanet research. (NASA)

But out in the galaxy, the atmospheric compositions of giant planets do not fit the solar system trend, an international team of astronomers has found.

Researchers discovered that the atmosphere of exoplanet HD149026b, a “hot jupiter” given the name “Smertrios” that orbits a Sun-like star, is super-abundant in the heavier elements carbon and oxygen – far above what scientists would expect for a planet of its mass.

In its “early release” program for exoplanet results, JWST also observed WASP-39 b, a “hot Saturn” (a planet about as massive as Saturn but in an orbit tighter than Mercury) orbiting a star some 700 light-years away.

The atmosphere around the planet provided the first detection in an exoplanet atmosphere of sulfur dioxide (SO2), a molecule produced from chemical reactions triggered by high-energy light from the planet’s parent star.

The Trappist-1 system –seven Earth-sized planets orbiting a red dwarf star only 40 light-years away — is another subject of great interest and JWST has provided some exciting results there too.

While the first Trappist-1 planet studied — the one nearest to the star — apparently has no atmosphere, JWST was able to in effect take the planet’s temperature.  The telescope captured thermal signatures from the planet, which is another first.

When starlight passes through a planet’s atmosphere, certain parts of the light are absorbed by the atmosphere’s elements.

… Read more

What Would Happen If Our Solar System Had a Super-Earth Like Many Others? Chaos.

March 13, 2023 / / 1 Comment

Our solar system’s rocky planets are tiny compared with the larger gas and ice giants. Exoplanet research has found, however, that the most common planets in the galaxy appear to be super-Earths and sub-Neptunes, types of planets not found in our system. Size comparison of the planets. (Alexaldo/iStock/Getty)

Before astronomers began to find planets — many, many planets — orbiting Suns other than ours,  the scientific consensus was that if other solar systems were ever found they would probably look much like ours.  That would mean small, rocky planets closest to the Sun and large gaseous planets further out.

That assumption crash and burned with the discovery of the first discovery of an exoplanet orbiting a star — 51 Peg.  It was a hot, Jupiter-sized planet that circled its Sun in four days.

That planetary rude awakening was followed by many others, including the discovery of many rocky planets much larger than those in our system which came to be called  super-Earths.  And equally common are gaseous planets quite a bit smaller than any near us, given the name sub-Neptunes.

Many papers have been written theorizing why there are no super-Earth or sub-Neptunes in our solar system.  And now astrophysicist Stephen Kane of the University of California, Riverside has taken the debate another direction by asking this question:  What would happen to our solar system planets if a super-Earth or sub-Neptune was present?

The results of his dynamic computer simulations are not pretty: the orbits of many of our planets would change substantially and that would ultimately result in some being kicked out of the solar system forever.  The forces of orbit-transforming gravity set loose by the addition of a super-Earth are strong indeed.

The term super-Earth is a reference only to an exoplanet’s size – larger than Earth and smaller than Neptune – but not suggesting they are necessarily similar to our home planet. The true nature of these planets, such as Gliese 832c, above, remains ambiguous because we have nothing like it in our own solar system. Super-Earths they are common among planets found so far in our galaxy. (Planetary Habitability Laboratory/University of Puerto Rico at Arecibo)

Let’s go back to our actual solar system for some context.

The gap in size between the size of our terrestrial planets and giant gas planets is great. The largest terrestrial planet is Earth, and the smallest gas giant is Neptune, which is four times wider and 17 times more massive than Earth.… Read more

New Martian Surprise From The Curiosity Rover

February 13, 2023 / / 0 Comments

NASA researchers found that waves on the surface of a shallow lake in Gale Crater stirred up sediment billions of years ago. That sediment eventually creating rippled textures left in rock. (NASA/JPLVCaltech/MSSS)

In its more than a decade of exploring Gale Crater on Mars, the rover Curiosity has found innumerable signs of the presence of long-ago water.

There have been fossil streams, alluvial fans, lakes shallow and deep, deltas and countless examples of rocks infiltrated and chemically transformed in the presence of water.  The picture of the crater as a watery environment in the warmer and wetter days of Martian history — 4 billion to 3 billion years ago — is well established.

Nonetheless. it still came as a wonder that the rover came across the entirely unexpected remains of fossilized ripples in a shallow lake bed.  What was even more surprising is that it was found in an area previously determined to have little likelihood of having ever been wet.

“Billions of years ago, waves on the surface of a shallow lake stirred up sediment at the lake bottom, over time creating rippled textures left in rock,” NASA said in a statement last week.

It was the first time such a feature has been discovered in Gale Crater, although the rover has passed through numerous fossil lake beds.

The Marker Band is a continuous dark, thin and hard layer running from left to right (but thinning out on the left) setting off the region of the rippled rock bed.   Both its composition and origins are not well understood. (NASA/JPL-Caltech)

One of the mission’s main goals has been to find out if this area in the southern highlands of Mars might have once been habitable for microbial life.

It was determined within the first two years of the rover’s time in Gale Crater that the crater was indeed once habitable based on the past presence of significant amounts of water and chemicals left behind by that long-departed water. Understanding the crater’s history of water has been a central goal of the mission.

The Curiosity team was thrilled by their new find.

“This is the best evidence of water and waves that we’ve seen in the entire mission,” said Curiosity project scientist Ashwin Vasavada. “We climbed through thousands of feet of lake deposits and never saw evidence like this.”

The rippled fossils are in an area set off by a black, hard-rock line called the “Marker Band.”… Read more

A New Twist On Planet Formation

January 30, 2023 / / 1 Comment

This image of the nearby young star TW Hydrae reveals the classic rings and gaps that signify planets are being formed in this protoplanetary disk. {ESO, Atacama Large Millimeter/submillimeter Array (ALMA)}

Before the first exoplanets were discovered in the 1990s,  our own solar system served as the model for what solar systems looked like.  The physical and chemical dynamics that formed our system were also seen as the default model for what might have occurred in solar systems yet to be found.

As the number of exoplanets identified ballooned via the Kepler Space Telescope and others, and  it became clear that exoplanets were everywhere and orbiting most every star, the model of our own solar system became obviously flawed.  The first exoplanet identified, after all, was a “hot Jupiter” orbiting very close to its star — a planetary placement previously thought to be impossible.

With the growing number of known exoplanets and their most unusual placements, the field of planet formation — focused earlier on understanding on how the planets of our system came into being and what they were made of — expanded to take in the completely re-arranged planetary and solar system menagerie being found.

This was basic science seeking to understand these newfound worlds, but it also became part of the fast-growing field of astrobiology, the search for planets that might be habitable like our own.

In this context, planet formation became associated with the effort to learn more about the dynamics that actually make a planet habitable — the needed composition of a planet, the nature of its Sun, its placement in a solar system and how exactly it was formed.

So the logic of planet formation became the subject of myriad efforts to understand what might happen when a star is born, surrounded by a ring of gas and dust that will in time include larger and larger collections of solids that can evolve into meteors, planetesimals and if all goes a particular way, into planets.

A thin section of primitive meteorite under a microscope. The various colors suggest different minerals that comprise meteorites. The round-shaped mineral aggregates are called chondrules, which are among the oldest known materials in our solar system. (Science)

As part of this very broad effort to understand better how planets form, meteorites have been widely used to learn about what the early solar system was like. Meteorites are from asteroids that formed within the first several million years of planetary accretion.… Read more

The JWST Discovers its First Earth-Sized Exoplanet

January 17, 2023 / / 0 Comments

Artist rendering of LHS 475 b, an Earth-sized exoplanet recently identified using the James Webb Space Telescope. This was the first planet of its size detected by the JWST. {NASA / ESA / CSA / Leah Hustak (STScI)}

In the search for life on distant planets, scientists generally focus on identifying Earth-sized, rocky planets, finding planets in their host star’s habitable zone, and having available the telescope power to read the chemical make-up of the atmospheres.

A relatively small number of Earth-sized exoplanets discovered by telescopes in space and on Earth have meet some of the key characteristics.  But now with the James Webb Space Telescope in operation, with its 21-foot high-precision mirror, scientists have been looking forward to finding small, rocky planets that meet all the key criteria.

And during its first year of operation, the JWST  has already found and studied one small planet that meets at least some or those criteria.  The planet identified, called LHS 475 b, is nearly the same size as Earth, having 99% of our planet’s diameter, scientists said, and is a relatively nearby 41-light-years away.

The research team that detected the small planet is led by Kevin Stevenson and Jacob Lustig-Yaeger, both of the Johns Hopkins University Applied Physics Laboratory.

The team chose to observe this target with Webb after reviewing targets of interest from NASA’s Transiting Exoplanet Survey Satellite (TESS), which hinted at the planet’s existence. Webb’s Near-Infrared Spectrograph (NIRSpec) captured the planet easily and clearly with only two transit observations.

“There is no question that the planet is there,” said Lustig-Yaeger. “Webb’s pristine data validate it.”

“With this telescope, rocky exoplanets are the new frontier.”

The TRAPPIST-1 system contains a total of seven known Earth-sized planets orbiting a weak red dwarf star. Three of the planets — TRAPPIST-1e, f and g — are located in the habitable zone of the star (shown in green in this artist’s impression), where temperatures are potentially moderate enough for liquid water to exist on the surface.  As a comparison to the TRAPPIST-1 system the inner part of the Solar System and its habitable zone is shown. (NASA)

Earth-sized exoplanets have been found earlier.  The Trappist-1 system, only 39 light-years away, is famously known to include seven small, rocky planets, and it was detected by a small, ground-based telescope.

The Kepler Space Telescope also detected a debated but significant number of Earth-sized planets during its nine-year survey of one small section of the distant sky last decade. … Read more

The World of Water Worlds

December 22, 2022 / / 1 Comment

Artist rendering of a water world exoplanet. NASA predicts that quite a few exist in the galaxies but none has been confirmed. Two new candidates have been put forward. (The Cosmic Companion)

Among the most intriguing types of exoplanet expected to be orbiting distant stars is the  “water world,” planets that are liquid to a far, far greater extent than on Earth.

Astronomers have theorized the existence of such planets and several candidates have been put forward, though not confirmed.  But the logic is strong enough for NASA scientists to conclude there are likely many of them in our galaxy.

Now two new potential water worlds have been proposed in a planetary system 218 light years away.

Using both the Hubble Space Telescope and data from the retired Spitzer Space Telescope, a team from Montreal has identified  the planets circling a red dwarf star.  Water, they propose, may well make up a significant portion of the planets.

Though the telescopes can’t directly observe the planets’ surfaces, other paths to identifying a water world are known.  By determining the planets’ densities through measurements of their weight and radii (and then volume), these planets — which would normally be described as “super-Earths because of their size — are lighter than rock worlds but heavier than gas-dominated ones.

… Read more

Many Complex Organic Compounds –Evolved Building Blocks of Life — Are Formed Where Stars Are Being Born

December 14, 2022 / / 0 Comments

The Taurus Molecular Cloud is an active site for star formation.  It is also filled with complex organic molecules, including the kind that are building blocks for life.  The Cloud is 450 light years away, but similar star-forming regions with complex organics are found thoughout the galaxy. (Adapted, ESA/Herschel/NASA/JPL-Caltech)

Recent reports about the detection of carbon-based organic molecules on Mars by the instruments of the Perseverance rover included suggestions that some of the organics may well have fallen from space over the eons, and were then preserved on the Martian surface.

Given the cruciality of organics as building blocks of life –or even as biosignatures of past life — it seems surely important to understand more about how and where the organics might form in interstellar space, and how they might get to Mars, Earth and elsewhere.

After all, “follow the organics” has replaced the NASA rallying cry to “follow the water” in the search for extraterrestrial life in the solar system and cosmos.

And it turns out that seeking out and identifying organics in space is a growing field of its own that has produced many surprising discoveries.  That was made clear during a recent NASA webinar featuring Samantha Scibelli of the University of Arizona, a doctoral student in astronomy and astrophysics who has spent long hours looking for these organics in space and finding them.

She and associate professor of astronomy Yancy Shirley have been studying the presence and nature of complex organics in particular in a rich star-forming region, the Taurus Molecular Cloud.

Using the nearby radio observatory at Kitt Peak outside of Tucson, she has found a range of complex organics in starless or pre-stellar cores with the Cloud.  The campaign is unique in that some 700 hours of observing time were given to them, allowing for perhaps the most thorough observations of its kind.

The results have been surprising and intriguing.

In this mosaic image stretching 340 light-years across, the James Webb’s Near-Infrared Camera (NIRCam) displays the Tarantula Nebula star-forming region in a new light, including tens of thousands of never-before-seen young stars that were previously shrouded in cosmic dust. The most active region appears to sparkle with massive young stars, appearing pale blue. (NASA/STScI)

A first take-away (surprising to those unfamiliar with the field) is that complex organics are often detected in these star-forming regions throughout the galaxy and cosmos — just as they were found in many regions of the Taurus cloud.… Read more

Tantalizing Organic Compounds Found on Mars

November 29, 2022 / / 1 Comment

The NASA/ESA Perseverance rover on xxx. New findings tell of the presence of organic material — the building blocks of life — in several locations at Jezero Crater — for the first time found in igneous rock.  The long-ago environment when the organics were deposited were deemed to have been “habitable.” (NASA/JPL-Caltech/MSSS)

When searching for signs of ancient life on Mars, NASA scientists increasingly focus on organic material — the carbon-based compounds that are the building blocks of life.  Organics were found by the Curiosity rover in Gale Crater, and now new papers report they have also been identified by the instruments of the Perseverance rover in very different kinds of rock in Jezero Crater.

Unlike the Gale Crater organics that were found in sedimentary rocks, these newly found specimens are in igneous rocks — formed when molten rock cools and crystallizes — and are mixed with other compounds known to preserve organics well.

These rock samples are part of the NASA and European Space Agency Mars Sample Return mission, and so they could be brought to Earth in the future for more intensive study. Scientists are excited about what might some day be found.

The new findings about organics and the geology of Jezero Crater are part of a trio of articles in the journal Science published Wednesday.

The lead author of one of the papers, Michael Tice of Texas A&M University, gave this overview of what the Perseverance team is reporting:

“These three papers show that samples collected in the floor of Jezero should be able to tell us a lot about whether living organisms ever inhabited rocks under the surface of the crater over the past several billion years,”  he wrote to me.

The paper he led, Tice said, shows that small amounts of water passed through those rocks at three different times, and that conditions at each of those times could have supported life. “Even more importantly, minerals were formed from the water that are known to be able to preserve organic matter and even fossils on Earth.”

Different kinds of carbon-based organic compounds were viewed within a rock called “Garde” by SHERLOC, one of the instruments on the end of the robotic arm aboard the Perseverance rover. The rover used its drill grind away a patch of rock so that SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) could analyze its interior.

… Read more
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