Category: Planetary and Solar System Characteristics (page 1 of 5)

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

A Young Planet Found That May Well Be Making Moons

An image made by the Very Large Telescope in Chile shows a forming planet, the bright spot at right. The overpowering light of the host star is blocked out by a coronagraph inside the telescope. (ESO/A. Müller et al.)

Astronomers have many theories about how planets are formed within the gas, dust, pebbles and gradually rocks of the circumstellar disks that encircle a star after it has been born.  While the general outlines of this remarkable process are pretty well established, many questions large and small remain unanswered.

One is how and when exomoons are formed around these planets, with the assumption that the process that forms planets must also give birth moons.  But the potential moons have been far too small for the current generation of space and ground telescopes to identify.

Now astronomers have detected something almost as significant:  a circumplanetary disk surrounding a young planet that appears to be in the process of making moons.  The moon itself has not been detected, but a forming planet has been found with a ring of dust and gas that surrounds it.  And within that circumplanetary disk, astronomers infer, a moon is possibly being formed.

“Our work presents a clear detection of a disk in which satellites could be forming,” said Dr. Myriam Benisty, an astronomer at the University of Grenoble and the University of Chile.

“The new … observations were obtained at such exquisite resolution that we could clearly identify that the disk is associated with {the exoplanet} and we are able to constrain its size for the first time,” she said in a release.

While the first detection of the planet was made via the European Southern Observatory’s Very Large Telescope in Chile, the more granular observation of the forming planet and its moon-forming disk was made with the Atacama Large Millimeter/submillimeter Array (ALMA), also in Chile.

This ALMA image shows the young PDS 70 planetary system. The system features a star at its center and at least two planets orbiting it, PDS 70b (not visible in the image) and PDS 70c, surrounded by a circumplanetary disk (the dot to the right of the star). Image credit: ALMA / ESO / NAOJ / NRAO / Benisty et al.)

The finding, published in the Astrophysical Journal Letters, came via direct imaging — in effect through extremely high power photography rather through the indirect methods much more common in exoplanet astronomy.… Read more

And Then There Were Three: ESA Follows NASA in Selecting a Mission to Venus

Artist illustration of the EnVision orbiter at Venus (ESA/VR2Planets/DamiaBouic)

It was quite a week for Venus scientists. Just seven days after NASA announced the selection of two Venus missions, DAVINCI+ and VERITAS, the European Space Agency (ESA) revealed that a third Venus mission had been chosen for the agency’s medium-class mission category.

(See last week’s post here on Many Worlds about DAVINCI+ and VERITAS)

The new mission is named EnVision, and will be ESA’s second Venus mission following Venus Express (2005 – 2014), which investigated the Venusian climate. While EnVision is an orbiter like Venus Express and VERITAS, its focus is the planet’s geological circulation system that links the atmosphere, surface and interior.

In case you are starting to get your Venus missions in a tangle, the set can be broadly divided up as follows:

Venus Express (ESA: 2005 – 2014) and Akatsuki (JAXA: 2015 – current) are both Venus orbiters focussed on the planet’s climate, returning information about the rapidly rotating upper atmosphere and acidic cloud deck of Venus.

DAVINCI+ (NASA: est. 2029 launch) is an orbiter and descending probe that will dive through the Venusian atmosphere to return top-to-bottom data on the planet’s stifling gases.

VERITAS (NASA: est. 2028 launch) is an orbiter focussed on Venus’s surface and the deep interior. VERITAS will bring us global maps in three-dimensions at a resolution of 30m. This will knock the socks off our current images from NASA’s Magellan orbiter (1989 – 1994), which had a resolution of around 200m.

EnVision (ESA: early 2030s) is the mission focused on how these environments are linked together. Equipped with an instrument suite that covers the top of the atmosphere through to below the planet surface, EnVision will probe how the different regions influence one another to create the planet’s internal systems.

“EnVision has a holistic approach,” explained Jörn Helbert who is a member of the EnVision team. “The larger and more complex payload studies Venus from the top of the atmosphere all the way to the subsurface, with a focus on understanding how the coupled system on Venus works.”

Artist illustration of the EnVision spacecraft, reflecting the goal of understanding why Venus and Earth are so different (NASA / JAXA / ISAS / DARTS / Damia Bouic / VR2Planets).

The coupled system is at the heart of how habitability can develop on rocky planets. A major player in the Earth’s environment is the ability to cycle carbon between the atmosphere, surface and planet mantle.… Read more

Return to Hell: NASA Selects Two Missions to Venus to Explore the Pathway to Habitability

Artists’ renderings show the VERITAS spacecraft (left) and DAVINCI+ probe (right) as they arrive at Venus (Lockheed Martin).

For NASA scientists, Venus missions must feel like buses. You wait thirty years for one, and then two come along at once.

Last week, NASA selected two Venus missions for the space agency’s Discovery Program; solar system exploration missions that can tuck under a lower cost cap than candidates for NASA’s New Horizons or Flagship categories. The first of these is DAVINCI+, which is an orbiter equipped with a descending probe that will take a big whiff of Venus’s stifling atmosphere. The second is the VERITAS orbiter that plans to peer through the clouds to scrutinise the Venusian surface.

While Europe and Japan have both visited Venus more recently than NASA (in fact, the Japanese orbiter is still there), there is little doubt that our inner neighbor is dramatically under-explored compared to Mars. But why the past neglect, and why go twice now?

The answer to the first question is perhaps the easiest.

Venus is hell.

The planet is wrapped in a thick atmosphere consisting of carbon dioxide and clouds of sulfuric acid that beat down on the Venusian surface with pressures nearly one hundred times higher than on Earth and create temperatures sufficient to melt lead.

These conditions have made it difficult to follow the usual pattern of planetary exploration from fly-bys and orbiters to landers and rovers. The Venusian surface is so inhospitable that a rover like NASA’s Mars Perseverance would become rover goop. Although recent engineering combined with high-temperature electronics means that the surface is no longer impossible, it does greatly add to the challenge (and therefore cost) of a lander mission.

Professor Stephen Kane, University of California, Riverside.

Hell-scape conditions have also resulted in Venus being overlooked for any astrobiological studies compared to (the still rather nasty but at least you can stand a rover on the surface) Mars. This makes the urgency to explore Venus now particularly surprising. The missions are a quest to understand habitability. The bottom line is that the hell world of Venus is essential to understanding how a planet becomes habitable and to discovering other habitable worlds outside our solar system.

“Imagine you live in a small town full of life,” explains Professor Stephen Kane from the DAVINCI+ team. “The nearest town is the same size and seems it was once identical. But now, it’s burned to the ground with no sign of life.… Read more

The Faint Young Sun Paradox and Mars

This NASA image of Mars at sunset taken by the Spirit  rover, evokes the conditions on early Mars when the planet received only 70 percent of the of the solar energy that it does now.  (NASA/JPL/Texas A&M/Cornell)

When our sun was young, it was significantly less luminous and sent out significantly less warming energy than it does now.  Scientists estimate that 4 million years ago, when the sun and our solar system were 500 million years old, the energy that the sun produced and dispersed was about 75 percent of what it is today.

The paradox arises because during this time of the faint young sun Earth had liquid water on its surface and — as has been conclusively proven in recent years — so did Mars, which is 61 million miles further into space.  However difficult it is to explain the faint young sun problem as it relates to early Earth, it is far more difficult to explain for far more frigid Mars.

Yet many have tried.  And because the data is both limited and innately puzzling, the subject has been vigorously debated from a variety of different perspectives.  In 2018, the journal Nature Geoscience published an editorial on the state of that dispute titled “Mars at War.”

There are numerous point of (strenuous) disagreement, with the main ones involving whether early Mars was significantly more wet and warm than previously inferred, or whether it was essentially cold and arid with only brief interludes of warming.  The differences in interpretation also require different models for how the warming occurred.

Was there a greenhouse warming  effect produced by heat-retaining molecules in the atmosphere?  Was long-term volcanic activity the cause? Or perhaps meteor strikes?  Or heat from the interior of the planet?

All of these explanations are plausible and all may have played a role.  But that begs the question that has so energized Mars scientists since Mars orbiters and the Curiosity rover conclusively proved that surface water created early rivers and valley networks, lakes and perhaps an ocean.  To solve the “faint young sun” paradox as it played out on Mars,  a climate driver (or drivers) that produces significant amounts of heat is required.

Could the necessary warming be the result of radioactive elements in the Martian crust and mantle that decay and give off impressive amounts of heat when they do?

A team led by Lujendra Ojha, an assistant professor at Rutgers University, proposes in Science Advances that may well be the answer, or at least part of the answer.… Read more

Cores, Planets and The Mission to Psyche

The asteroid Psyche will be the first metal-rich celestial body to be visited by a spacecraft.  The NASA mission launches in 2022 and is expected to arrive at the asteroid in late 2026.  A central question to be answered is whether Psyche is the exposed  core of a protoplanet that was stripped of its rocky mantle. (NASA)

Deep inside the rocky planets of our solar system, as well as some solar system moons,  is an iron-based core.

Some, such as Earth’s core,  have an inner solid phase and outer molten phase, but the solar system cores studied so far are of significantly varied sizes and contain a pretty wide variety of elements alongside the iron.  Mercury, for instance, is 85 percent core by volume and made up largely of iron, while our moon’s core is thought to be 20 percent of its volume and is mostly iron with some sulfur and nickel.

Iron cores like our own play a central role in creating a magnetic field around the planet, which in turn holds in the atmosphere and may well be essential to make a planet habitable.  They are also key to understanding how planets form after a star is forged and remaining dense gases and dust are kicked out to form a protoplanetary disk, where planets are assembled.

So cores are central to planetary science, and yet they are obviously hard to study.  The Earth’s core starts about 1,800 miles below the surface, and the cores of gas giants such as Jupiter are much further inward, and even their elemental makeups are not fully understood.

All this helps explains why the upcoming NASA mission to the asteroid Psyche is being eagerly anticipated, especially by scientists who focus on planetary formation.

Scheduled to launch in 2022, the spacecraft will travel to the main asteroid belt between Mars and Jupiter and home in on what has been described as an unusual “metal body,”  which is also one of the largest asteroids orbiting the sun.

While some uncertainty remains,  it appears that Psyche is the  exposed nickel-iron core of a long-ago emerging rocky protoplanet, with the rest of the planet stripped away by collisions billions of years ago.

An artist’s impression of solar system formation, and the formation of a protoplanetary disk filled with gases and dust that over time clump together and smash into each other to form larger and larger bodies. (Gemini Observatory/AURA artwork by Lynette Cook )

That makes Psyche a most interesting place to visit.… 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

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

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