Category: Planetary Systems (page 2 of 11)

Theorized Northern Ocean of Mars; now long gone.  (NASA)

Change is the one constant in our world– moving in ways tiny and enormous,  constructive and destructive.

We’re living now in a time when a rampaging pandemic circles the globe and when the climate is changing in so many worrisome and potentially devastating ways.

With these ominous  changes as a backdrop, it is perhaps useful to spend a moment with change as it happens in a natural world without humans.  And just how complete that change can be:

For years now, planetary scientists have debated whether Mars once had a large ocean across its northern hemisphere.

There certainly isn’t one now — the north of Mars is parched, frigid and largely featureless.  The hemisphere was largely covered over in a later epoch by a deep bed of lava, hiding signs of its past.

The northern lowlands of Mars, as photographed by the Viking 2 lander. The spacecraft landed in the Utopia Planitia section of northern Mars in 1976. (NASA/JPL)

Because our sun sent out significantly less warmth at the time of early Mars (4.2-3.5  billion years ago,) climate modelers have long struggled to come up with an explanation for how the planet — on average, 137 million miles further out than Earth — could have been anything but profoundly colder than today. And if that world was so unrelentingly frigid, how could there be a surface ocean of liquid water?

But discoveries in the 21st century have strongly supported the long-ago presence of water on a Mars in the form of river valleys, lakes and a water cycle to feed them.  The work done by the Curiosity rover and Mars-orbiting satellites has made this abundantly clear.

An ocean in the northern lowlands is one proposal made to explain how the water cycle was fed.

And now, In a new paper in Journal of Geophysical Research: Planets,  scientists from Japan and the United States have presented modelling and analysis describing how and why Mars had to have a large ocean early in its history to produce the geological landscape that is being found.

Lead author Ramses Ramirez, a planetary scientist with the Earth-Life Science Institute in Tokyo, said it was not possible to determine how long the ocean persisted, but their team concluded that it had to be present  in that early period around 4 billion to 3.5 billion years ago.  That is roughly when what are now known to be river valleys were cut in the planet’s southern highlands.… Read more

Exploring Our Sun Will Help Us Understand Habitability

The surface of the sun, with each “kernel” or “cell” roughly the size of Texas. The movie is made up of images produced by the Daniel Inouye SolarTelescope in Hawaii.  Novel and even revolutionary data and images are also expected from the Parker Solar Probe (which will travel into the sun’s atmosphere, or corona) and the just launched Solar Orbiter, which will study (among many other things) the sun’s polar regions. (NSO/NSF/AURA)

 

Scientists have been  studying our sun for centuries, and at this point know an awful lot about it — the millions of degrees Fahrenheit heat that it radiates out from the corona, the tangled and essential magnetic fields that it creates, the million-miles-per-hour solar wind and the charged high-energy solar particles that can be so damaging to anything alive.

But we have now entered a time when solar science is taking a major leap forward with the deployment of three pioneering instruments that will explore the sun and its surroundings as never before.  One is a space telescopes that will get closer to the sun (by far) than any probe before, another is a probe that will make the first observations of the sun’s poles, and the third is a ground-based solar telescope that can resolve the sun in radically new ways — as seen in the image above, released last month.

Together, NASA’s Parker Solar Probe, the joint European Space Agency-NASA Solar Orbiter mission and the National Science Foundation’s Inouye Solar Telescope on Hawai’i will provide pathways to understand some of the mysteries of the sun.  They include resolving practical issues involving the dynamics  of “space weather” that can harm astronauts and telecommunications systems, and larger theoretical unknowns related to all the material that stars scatter into space and onto planets.

Some of those unresolved questions include determining how and why heat and energy flow from the sun’s inner core to the outer corona and make it so much hotter, determining the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind, the make-up and effects of solar flares and coronal mass ejections, and how and why the sun is able to create and control the heliosphere — the vast bubble of charged particles blown by the solar wind into interstellar space.

 

An illustration of Kepler2-33b, , one of the youngest exoplanets detected to date using NASA Kepler Space Telescope.

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Exactly How Like Our Earth is an Earth-like Planet?

Explainer video for Earth-Like. (Vimeo edition with subtitles here)

Are we alone? The question hangs over each discovery of an Earth-sized planet as we speculate on its habitability. But how different and varied could these worlds really be? Perhaps the best way to get a flavor of this potential diversity is to build a few planets.

This is the idea behind Earth-Like: a website and twitter bot that lets you build your own Earth-like world. Earth-Like begins with a planet that resembles our Earth today, with oceans flowing over the surface and an atmosphere that maintains the global average temperature at a comfortable 15°C (59°F) on our orbit within the habitable zone. By making changes to the fraction of exposed land, the volcanic rate and position within the habitable zone, you can change the conditions on our planet into wildly different environments from desert to snowball.

Earth-Like can create a visualisation of what your planet might look like. This one is 91% covered with land, sitting in the middle of the habitable zone with 5 x the volcanic rate of Earth today! Its average temperature is about 9°C (48°F).

The concept for Earth-Like began during a workshop on planet diversity held at the Earth-Life Sciences Institute (ELSI) in Tokyo. The discussions highlighted that the potential for variation between rocky worlds is vast. A planet rich in carbon could have a mantle of diamond. A stagnant surface rather than mobile continental plates could throttle volcanism. The gravity on a large rocky planet might flatten the topology to allow shallow seas to cover all the land.

At the moment, observations can only tell us the physical size (either radius or mass) and the orbit of the majority of extrasolar planets. As we do not know what the surface of these worlds is like, we dub new discoveries Earth-like or potentially habitable if their size and the amount of radiation they receive from the star is similar to Earth. But this fails to convey how incredibly alien these worlds could be.

Earth-Like was spearheaded by undergraduate student, Kana Ishimaru, at the University of Tokyo (now a graduate student at the University of Arizona), working with myself, Julien Foriel (now a researcher at Harvard University) and Nicholas Guttenberg at ELSI. We wanted to build a model that would give a feel of the diversity of potentially habitable worlds and which could be run easily on a web browser.… Read more

Tales From the Deep Earth

Cross section of the varying layers of the Earth .  (Yuri Arcurs via Getty images)

When especially interesting new planets are discovered in the cosmos, scientists around the world begin the process of identifying their characteristics — their orbit, their mass and density,  their composition, their thermal properties and much more.  It’s all part of a drive that seems to be innate in humans to learn about the workings of the world (or worlds) around us.

This began millennia ago when our distant ancestors started to learn about the make-up and processes of Earth.   We now know enormous amounts about our planet, but I was recently introduced to a domain where our knowledge has some substantial holes.  The area of the Earth least well understood is, not surprisingly, what lies deep below us, in the mantle — the inner 2,900 kilometers (2000 miles) of the planet between the outer crust and the iron core.

The on-going exploration of this vast region — made up substances including some which cannot remain intact on the Earth’s surface — struck me as in some ways comparable to the study of exoplanets.   It’s also a realm where scientific observation is limited, but what knowledge is gained then leads through induction, deduction, modeling and exacting lab work to a gradual expansion back of our knowledge.

And in the case of some high-temperature, high-pressure minerals, this has led to a most unusual technique for identifying and naming key components of our inner planet.  Unable to reach or preserve some of the most important components of the mantle,  geochemists and other deep Earth scientists go to incoming meteorites to learn about what’s beneath (deeply beneath, that is) our feet.

With this in mind, here is a look at the discovery and recent naming of the mineral hiroseite, an unusual but quite widespread component of the very deep Earth.

 

ELSI director Kei Hirose has been honored for his pioneering work in identifying and describing components of the Earth’s lower mantle. In recognition of his work, a newly identified lower mantle mineral has been given the name of hiroseite. (Nerissa Escanlar)

 

It was two decades ago when Kei Hirose – a Japanese geochemist expert in high-pressure, deep-Earth phenomena, then at the Tokyo Institute of Technology – began researching a long-standing problem in understanding the working of the lower depths of our planet’s enormous mantle: the last 300 kilomiles above the boundary with the scalding iron core.

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Tatooine Worlds

Science fiction has become science.  No habitable planets orbiting two suns like the fictional Tatooine have been detected so far, but more than a dozen “circumbinary planets” have been identified and many more are predicted.  Exoplanets orbiting a host star that orbits its own companion star are even more common. (Lucasfilm)

When the the first Star Wars movie came out in 1977, it featured the now-iconic two-sun, “circumbinary” planet Tatooine.  At that time astronomers didn’t really know if such solar systems existed, with more than one sun and at least one planet.

Indeed, the first extra-solar planet wasn’t detected until the early 1990s.  And the first actual circumbinary planet was detected in 2005, and it was a Jupiter-size planet orbiting a system composed of a sun-like star and a brown dwarf.  Tatooine was definitely not a Jupiter-size planet.

But since then, the presence and distribution of circumbinaries has grown to a dozen and some the planets discovered orbiting the two stars have been smaller.  The most recent discovery was announced this week and was made using the Transiting Exoplanet Survey Satellite (TESS) space telescope

The new planet, called TOI (TESS Object of Interest)-1338 b, is about 6.9 times larger than Earth. It orbits its pair of host stars every 95 days, while the stars themselves orbit each other in 15 days.

As is common with binary stars, one is more massive and much brighter than the other (5976 K and 3657 K, respectively, with our sun at  5780 K),  and as the planet orbits around it blocks some of the light from the brighter star.

This transit allows astronomers to measure the size of the planet.  The transit — as scientific luck, or skill, would have it — was first found in the TESS data by a high school student working at NASA with over the summer,  Wolf Cukier

“I was looking through the data for everything the volunteers had flagged as an eclipsing binary, a system where two stars circle around each other and from our view eclipse each other every orbit,” Cukier said. “About three days into my internship, I saw a signal from a system called TOI 1338.”

“At first I thought it was a stellar eclipse, but the timing was wrong. It turned out to be a planet.”

With all of the data available from observations past and current, planet hunting clearly isn’t the scientific Wild West that it used to be — although the results remain often eye-popping and surprising.… Read more

How Long Were the Wet Periods on Early Mars, and Was That Water Chemically Suitable For Life?

 

An artist rendering, based on scientific findings, of Gale Crater in Mars during one of its ancient, wet periods. (NASA)

There is no doubt that early Mars had long period of warmer and much wetter climates before its atmosphere thinned too much to retain that liquid H20 on the surface.

As we know from the Curiosity mission to Gale Crater and other orbital findings, regions of that warmer and wetter Mars had flowing water and lakes periodically over hundreds of millions of years.  That’s one of the great findings of planetary science of our times.

But before approaching the question of whether that water could have supported life, a lot more needs to be known than that water was present.  We need answers to questions like how acidic or basic that water likely was?  Was it very salty? Did it have mineral and elemental contents that could provide energy to support any potential life?

And most especially, how long did those wet periods last, and the dry periods as well?

In a recent paper for Nature Communications, some more precise answers are put forward based on data collected at Gale Crater and interpreted based on geochemical modeling and Earth-based environmental science.

The water, say geochemist Yasuhito Sekine of the Earth-Life Science Institute (ELSI) in Tokyo and colleagues from the U.S. and Japan, had many important characteristics supportive of life.  It was only mildly salty, it had a near-neutral pH, it contained essential minerals and elements in state of disequilibrium — meaning that they could give and receive the electrons needed to provide life-supporting energy.   The  area was hardly lush — more like the semi-arid regions of Central Asia and Utah’s Great Salt Lake — but it contained water that was plausibly life supporting.

Based on an analysis of the patterns and quantities of salt remains, they estimate the water was present numerous times for between 10,000 to one million years each period.

Were those warm eras long enough for life to emerge, and the dry period short enough for it to survive?

“We don’t have a clear answer,” Sekine said. “But it is now more clear that the key question is which is more important:  the chemistry of the water or the duration of its presence?”

And the way to address the question, he said, is through a mix of planetary science and environmental science.

“This is a first step in the application of environmental chemistry to Mars,” Sekine said.… Read more

Icy Moons and Their Plumes

The existence of water or water vapor plumes on Europa has been studied for years, with a consensus view that they do indeed exist.  Now NASA scientists have their best evidence so far that the moon does sporadically send water vapor into its atmosphere.  (NASA/ESA/K. Retherford/SWRI)

Just about everything that scientists see as essential for extraterrestrial life — carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur and sources of energy — is now known to be pretty common in our solar system and beyond.  It’s basically there for the taking  by untold potential forms of life.

But what is not at all common is liquid water.  Without liquid water Earth might well be uninhabited and today’s Mars, which was long ago significantly wetter, warmer and demonstrably habitable,  is widely believed to be uninhabited because of the apparent absence of surface water (and all that deadly radiation, too.)

This is a major reason why the discovery of regular plumes of water vapor coming out of the southern pole of Saturn’s moon Enceladus has been hailed as such a promising scientific development.  The moon is pretty small, but most scientists are convinced it does have an under-ice global ocean that feeds the plume and just might support biology that could be collected during a flyby.

But the moon of greatest scientific interest is Europa, one of the largest that orbits Jupiter.  It is now confidently described as having a sub-surface ocean below its crust of ice and — going back to science fiction writer extraordinaire Arthur C. Clarke — has often been rated the most likely body in our solar system to harbor extraterrestrial life.

That is why it is so important that years of studying Europa for watery plumes has now paid off.   While earlier observations strongly suggested that sporadic plumes of water vapor were in the atmosphere, only last month was the finding nailed, as reported in the journal Nature Astronomy.

“While scientists have not yet detected liquid water directly, we’ve found the next best thing: water in vapor form,” said Lucas Paganini, a NASA planetary scientist who led the water detection investigation.

 

As this cutaway shows, vents in Europa’s icy crust could allow plumes of water vapor to escape from a sub-surface ocean. If observed up close, the chemical components of the plumes would be identified and could help explain the nature and history of the ocean below. ( NASA) 

The amount of water vapor found in the European atmosphere wasn’t great — about an Olympic-sized pool worth of H2O.  … Read more

Mapping Titan, the Most Earth-Like Body in Our Solar System

In an image created by NASA’s Cassini spacecraft, sunlight reflects off lakes of liquid methane around Titan’s north pole.  Cassini radar and visible-light images allowed researchers to put together the first global geological map of Saturn’s largest moon.  (NASA/JPL-Caltech/University of Arizona/University of Idaho)

Saturn’s moon Titan has lakes and rivers of liquid hydrocarbons, temperatures that hover around -300 degrees Fahrenheit, and a thick haze that surrounds it and has cloaked it in mystery.   An unusual place for sure, but perhaps what’s most unusual is that Titan more closely resembles Earth of all the planets and moons in our solar system.

This is because like only Earth it has that flowing liquid on its surface, it has a climate featuring wind and rain that form dunes, rivers, lakes, deltas and seas (probably of filled with liquid methane and ethane), it has a thick atmosphere and it has weather patterns that change with the seasons.  The moon’s methane cycle is quite similar to our water cycle.

And now astronomers have used data from NASA’s Cassini-Huygens mission to map the entire surface of Titan for the first time.  Their work has found a global terrain of mountains, plains, valleys, craters and lakes .  Again, this makes Titan unlike anywhere else in the solar system other than Earth.

“Titan has an atmosphere like Earth. It has wind, it has rain, it has mountains,” said Rosaly Lopes, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena.  She and her colleagues wove together images and radar measurements taken by the spacecraft to produce the first global map of the moon.

“Titan has an active methane-based hydrologic cycle that has shaped a complex geologic landscape, making its surface one of most geologically diverse in the solar system,” she said.  “It’s a really very interesting world, and one of the best places in the solar system to look for life,”

Cassini orbited Saturn from 2004 to 2017 and collected vast amounts of information about the ringed gas giant and its moons. The mission included more than 100 fly-bys of Titan,  which allowed researchers to study the moon’s surface through its thick atmosphere and survey its terrain in unprecedented detail.

The first global geologic map of Titan is based on radar and visible-light images from NASA’s Cassini mission.

Their work, which now adds the surface of Titan to the kind of geological mapping done of the surfaces of Mars, Mercury and our moon, was published in Nature Astronomy.Read more

A Southern Sky Extravaganza From TESS

Candidate exoplanets as seen by TESS in a southern sky mosaic from 13 observing sectors. (NASA/MIT/TESS)

NASA’s Transiting Exoplanet Survey Satellite (TESS) has finished its one year full-sky observation of  Southern sky and has found hundreds of candidate exoplanets and 29 confirmed planets.  It is now maneuvering  its array of wide-field telescopes and cameras to focus on the northern sky to do the same kind of exploration.

At this turning point, NASA and the Massachusetts Institute of Technology — which played a major role in designing and now operating the mission — have put together mosaic images from the first year’s observations, and they are quite something.

Constructed from 208 TESS images taken during the mission’s first year of science operations, these images are a unique  space-based look at the entire Southern sky — including the Milky Way seen edgewise, the Large and Small Magellenic galaxies, and other large stars already known to have exoplanet.

“Analysis of TESS data focuses on individual stars and planets one at a time, but I wanted to step back and highlight everything at once, really emphasizing the spectacular view TESS gives us of the entire sky,” said Ethan Kruse, a NASA Postdoctoral Program Fellow who assembled the mosaic at NASA’s Goddard Space Flight Center.

Overlaying the figures of selected constellations helps clarify the scale of the TESS southern mosaic. TESS has discovered 29 exoplanets, or worlds beyond our solar system, and more than 1,000 candidate planets astronomers are now investigating. NASA/MIT/TESS

The mission is designed to vastly increase the number of known exoplanets, which are now theorized to orbit all — or most — stars in the sky.

TESS searches for  the nearest and brightest main sequence stars hosting transiting exoplanets, which are the most favorable targets for detailed investigations.

This animation shows how a dip in the observed brightness of a star may indicate the presence of a planet passing in front of it, an occurrence known as a transit. This is how TESS identified planet.
(NASA’s Goddard Space Flight Center)

While previous sky surveys with ground-based telescopes have mainly detected giant exoplanets, TESS will find many small planets around the nearest stars in the sky.  The mission will also provide prime targets for further characterization by the James Webb Space Telescope, as well as other large ground-based and space-based telescopes of the future.

The TESS observatory uses an array of wide-field cameras to perform a survey of 85% of the sky.… Read more

A Telling Nobel Exoplanet Faux Pas

This is the Doppler velocity curve displayed by the Nobel Committee to illustrate what Mayor and Queloz had accomplished in 1995. But actually, the graph shows the curve from the Lick Observatory in California that an American team had produced to confirm the initial finding. Such was the interweaving of the work of the Swiss and the American teams searching for the first exoplanet orbiting a sun-like star. (Image courtesy of Geoff Marcy and Paul Butler, San Francisco State University)

Given the complex history of the discovery and announcement in 1995 of the first exoplanet that orbits a sun-like star, it is perhaps no surprise that errors might sneak into the retelling.  Two main groups were racing to be first, and for a variety of reasons the discovery ended up being confirmed before it was formally announced.

A confusing situation prone to mistakes if all involved aren’t entirely conversant with the details.  But an error — tantamount to scientific plagiarism — by the Nobel Committee?   That is a surprise.

The faux pas occurred at the announcement on October 8 that Michel Mayor of the University of Geneva and Didier Queloz of the the University of Cambridge had won the Nobel for physics to honor their work in detecting that first exoplanet orbiting a sun-like star.

As Nobel Committee member Ulf Danielsson described the achievement, a powerpoint display of important moments and scientific findings in their quest was displayed on a screen behind him.

When the ultimate image was on deck to be shown  — an image that presented the Doppler velocity curve that was described as the key to the discovery — the speaker appeared to hesitate after looking down to see what was coming next.

If he did hesitate, it was perhaps because to those in the know, the curve did not come from Mayor and Queloz.

Rather, it was the work of a team led by Geoffrey Marcy and Paul Butler — the San Francisco State University group that confirmed the existence of the hot Jupiter exoplanet 51 Pegasi b several days after the discovery was made public (to some considerable controversy) at a stellar systems conference in Florence.  So at a most significant juncture of the Nobel introduction of the great work of Mayor and Queloz, hard-won data by a different team was presented as part of the duo’s achievement.

This is both awkward and embarrassing, but it also indirectly points to one of the realities that the Nobel Committee is forced, by the will of Alfred Nobel, to ignore:  That science is seldom the work now of but two or three people.… Read more

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