Category: Exoplanets (page 1 of 8)

Exoplanets With Complex Life May Be Very Rare, Even in Their “Habitable Zones”

The term “habitable zone” can be a misleading one, since it describes a limited number of conditions on a planet to make it hospitable to life. (NASA)

 

For years now, finding planets in the habitable zones of their host stars has been a global astrophysical quest and something of a holy grail.  That distance from a star where temperatures could allow H20 to remain liquid some of the time has been deemed the “Goldilocks” zone where life could potentially emerge and survive.

The term is valuable for sure, but many in the field worry that it can be as misleading or confusing as it is helpful.

Because while the habitable zone is a function of the physics and architecture of a solar system, so much more is needed to make a planet actually potentially habitable.  Does it have an atmosphere?  Does it have a magnetic field. Does it orbit on an elliptical path that takes it too far (and too close) to the sun?  Was it sterilized during the birth of the host star and orbiting planets?  What kind of star does it orbit, and how old and luminous is that star?

And then there’s the sometimes confused understanding that many habitable zones may well support complex, even technologically-advanced life.  They are, after all, habitable.

But as a new paper in the Astrophysical Journal makes clear, the likelihood of a habitable zone planet being able to support complex life — anything beyond a microbe — is significantly limited by the amount of toxic chemicals such as carbon monoxide and excesses of carbon dioxide.

Eddie Schwieterman, a NASA postdoc at the University of California, Riverside and lead author of the article, told me that the odds for complex life on most exoplanets in their habitable zones weren’t great.

“A rough estimate is between 10-20% of habitable zone planets are truly suitable for analogs to humans and animals.” he said. “Of course, being located in this part of the habitable zone isn’t enough by itself – you still need the build-up of oxygen via the evolution of oxygenic photosynthesis and certain planetary biogeochemical cycles.”

 

A rendering of the exoplanet Kepler 442 b, compared in size to  Earth.  Kepler 442 b was detected using the Kepler Space Telescope and is 0ne of a handful of planets found so far deemed to be most likely to be habitable. But it’s 1200 light-years away, so learning its secrets will be challenging.

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A Grand Global Competition to Name 100 ExoWorlds

Within the framework of its 100th anniversary commemorations, the International Astronomical Union (IAU) is organising the IAU100 NameExoWorlds global competition that allows any country in the world to give a popular name to a selected exoplanet and its host star. Exoplanet rendering by IAU.

Four years ago, the International Astronomical Union organized a competition to give popular names to 14 stars and 31 exoplanets that orbit them.  The event encouraged 570,000 people to vote and the iconic planet 51 Pegasi b became “Dimidium, ” 55 Cancri b became “Galileo,” and (among others) Formalhaut b became “Dagon.”

It remains unclear how often those popular names are used in either scientific papers or writing about the papers.  But the idea of giving mythical names, names that describe something unique about the planet (or star)  or that nod to famous astronomer or iconic writers has caught on and the IAU has a new naming contest up and running.

This one is the IAU NameExoWorlds global campaign, and almost 100 nations have signed up to organize public national campaigns that will  give new names to a selected exoplanet and its host star.

“This exciting event invites everyone worldwide to think about their collective place in the universe, while stimulating creativity and global citizenship,” shared Debra Elmegreen, IAU President Elect. “The NameExoWorlds initiative reminds us that we are all together under one sky.”

From a large sample of well-studied, confirmed exoplanets and their host stars, the IAU NameExoWorlds Steering Committee assigned a star-planet system to each country, taking into account associations with the country and the visibility of the host star from most of the country.

The national campaigns will be carried out from June to November 2019 and, after final validation by that NameExoWorlds Steering Committee, the global results will be announced in December 2019. The winning names will be used freely in parallel with the existing technical scientific names.

The bulge of the Milky Way, as imaged by the Hubble Space Telescope. Our galaxy is inferred to have hundreds of billions of stars, and even more planets. (NASA, ESA, and T. Brown (STScI);

 

The naming contest flows from the well-established fact that exoplanets are everywhere — at least one around most stars, scientists have concluded.  Some 4,500 exoplanets have been identified so far, but this is but the beginning.  Astronomers are confident there are hundreds of billions of exoplanets — ranging from small and rocky like Earth to massive gas giants much larger than Jupiter — in our galaxy reaches into the many billions.… Read more

A Magical Solar Eclipse From 1900, Recovered and Instructive

 

Sometimes relics from the past help put the present into better focus.

Recovered footage of a 1900 total eclipse of the sun — believed to be the first captured — has been scanned, restored and then reassembled and retimed frame by frame to create a memorable and kind of spooky look at early astronomy. The film was found at the Royal Astronomical Society in London, reconstructed by the British Film Institute and made public this week.

As explained in a release from the two societies, the film was taken by one Nevil Maskelyne, a British magician, card sharp, levitator and more turned pioneering filmmaker and astronomer.

The eclipse was captured during an expedition to North Carolina with the British Astronomical Association.  As the release explained, at the time magic, the paranormal and science often fit comfortably together, and the emerging film industry was a tool for all and an instigator of invention.

“It was not an easy feat to film,” the release reports. “Maskelyne had to make a special telescopic adapter for his camera to capture the event. ”

The North Carolina expedition was Maskelyne’s second attempt to film a solar eclipse, but the only one to have survived — though it was also considered lost for decades.  He also had traveled to India in 1898 to photograph the phenomenon and apparently succeeded, though his film can was said to be stolen on the way home.

 

Light curve of star as an exoplanet transits between it and an observing telescope.

 

Compelling on its own, the footage also conveniently provides an exaggerated and instructive example of the primary technique now used to discover distant exoplanets: the “transit” method invented a century after Maskelyne filmed his eclipse.

But unlike what occurs a full solar eclipse,  when the moon blots out the sun as viewed from Earth,  the transit method measures the light from a host star to determine whether it dips ever so slightly — a sign that a planet is blocking some of the star’s light.

There are, of course, no total eclipses from transiting exoplanets because the planets are so much smaller than the suns.  But you get the idea.

You perhaps also get the idea that there has long been a certain showmanship in the display of astronomical wonders.  Space agencies certainly understand that and — with some turning of the nobs to make astronomical phenomenon appear in ways our eyes can take them in most dramatically  — have created some of the most majestic and magical images of our times.… Read more

NExSS 2.0

Finding new worlds can be an individual effort, a team effort, an institutional effort. The same can be said for characterizing exoplanets and understanding how they are affected by their suns and other planets in their solar systems. When it comes to the search for possible life on exoplanets, the questions and challenges are too great for anything but a community. NASA’s NExSS initiative has been an effort to help organize, cross-fertilize and promote that community. This artist’s concept Kepler-47, the first two-star systems with multiple planets orbiting the two suns, suggests just how difficult the road ahead will be. ( NASA/JPL-Caltech/T. Pyle)

 

The Nexus for Exoplanet System Science, or “NExSS,”  began four years ago as a NASA initiative to bring together a wide range of scientists involved generally in the search for life on planets outside our solar system.

With teams from seventeen academic and NASA centers, NExSS was founded on the conviction that this search needed scientists from a range of disciplines working in collaboration to address the basic questions of the fast-growing field.

Among the key goals:  to investigate just how different, or how similar, different exoplanets are from each other; to determine what components are present on particular exoplanets and especially in their atmospheres (if they have one);  to learn how the stars and neighboring exoplanets interact to support (or not support) the potential of life;  to better understand how the initial formation of planets affects habitability, and what role climate plays as well.

Then there’s the  question that all the others feed in to:  what might scientists look for in terms of signatures of life on distant planets?

Not questions that can be answered alone by the often “stove-piped” science disciplines — where a scientist knows his or her astrophysics or geology or geochemistry very well, but is uncomfortable and unschooled in how other disciplines might be essential to understanding the big questions of exoplanets.

 

The original NExSS team was selected from groups that had won NASA grants and might want to collaborate with other scientists with overlapping interests and goals  but often from different disciplines. (NASA)

The original idea for this kind of interdisciplinary group came out of NASA’s Astrobiology Program, and especially from NASA astrobiology director Mary Voytek and colleague Shawn Domogal-Goldman of the Goddard Space Flight Center, as well as Doug Hudgins of NASA Astrophysics.  It was something of a gamble, since scientists who joined would essentially volunteer their time and work and would be asked to collaborate with other scientists in often new ways.… Read more

Great Nations Need Great Observatories

This new image from NASA’s Hubble Space Telescope, shows the tentacled Southern Crab Nebula. The nebula, officially known as Hen 2-104, appears to have two nested hourglass-shaped structures that were sculpted by a whirling pair of stars in a binary system. The duo consists of an aging red giant star and a burned-out star, a white dwarf. The red giant is shedding its outer layers and some of this ejected material is attracted by the gravity of the companion white dwarf. The result is that both stars are embedded in a flat disk of gas stretching between them. This belt of material constricts the outflow of gas so that it only speeds away above and below the disk. The result is an hourglass-shaped nebula. The bubbles of gas and dust appear brightest at the edges, giving the illusion of crab leg structures. These “legs” are likely to be the places where the outflow slams into surrounding interstellar gas and dust, or possibly material which was earlier lost by the red giant star.  (NASA and ESA)

The Hubble Space Telescope, arguably the jewel in the crown of NASA’s science missions, was launched 29 years ago.  It has been providing scientists and the public with a steady stream of previously unimagined insights about the cosmos — plus those jaw-dropping, very high-resolution images like the one above — pretty much ever since.

It has also provided the best example to date of what humans can do in space with its five repair and upgrade missions.  It did indeed launch to great skepticism, especially after a near fatal flaw was found in its key mirror.  It was also considered over budget at launch, way behind schedule and questionable scientifically and had to be fixed in orbit 353 miles into space.

The Hubble Space Telescope after its second repair and upgrade mission in 1998. (NASA)

But almost three decades into its mission now — and with decades more service likely — it clearly shows what an exceedingly ambitious project can deliver and the level of excellence that NASA, its European Space Agency partner and space scientists and engineers can achieve.  Talk about soft power.

This is important to remember as the agency’s 40-year-old Great Observatories program –that the Hubble Telescope is a part of –is under considerable threat.

The mission that was supposed to fly in the 2010s, the James Webb Space Telescope, is also way over budget, way behind schedule, and now described as a financial threat to other NASA missions. … Read more

Our Ever-Growing Menagerie of Exoplanets

While we have never seen an exoplanet with anything near this kind of detail, scientists and artists now do know enough to represent them with characteristics that are plausible, given what is known about them..  (NASA)

With so many exoplanets already detected, with the pace of discovery continuing to be so fast, and with efforts to find more distant worlds so constant and global,  it’s easy to become somewhat blase´ about new discoveries.  After so many “firsts,” and so many different kinds of planets found in very different ways, it certainly seems that some of the thrill may be gone.

Surely the detection of a clearly “Earth-like planet” would cause new excitement — one that is not only orbiting in the habitable zone of its host star but also has signs of a potentially nurturing atmosphere in a generally supportive cosmic neighborhood.

But while many an exoplanet has been described as somewhat “Earth-like” and potentially habitable, further observation has consistently reduced the possibility of the planets actually hosting some form of biology.  The technology and knowledge base needed to find distant life is surely advancing, but it may well still have a long way to go.

In just the last few days, however, a slew of discoveries have been reported that highlight the allure and science of our new Exoplanet Era.  They may not be blockbusters by themselves, but they are together part of an immense scientific exploration under way, one that is re-shaping our understanding of the cosmos and preparing us for bigger discoveries and insights to come.

 

Already 3,940 exoplanets have been identified (as of April 17) with an additional 3,504 candidates waiting to be confirmed or discarded.  this is but the start since it is widely held now that virtually every star out there has a planet, or planets, orbiting it.   That’s billions of billions of planets.  This image is a collection of NASA exoplanet renderings.

What I have in mind are these discoveries:

  • The first Earth-sized planet detected by NASA’s year-old orbiting telescope TESS (Transiting Exoplanet Survey Satellite.)  TESS is designed to find planets orbiting massive stars in our near neighborhood, and it has already made 10 confirmed discoveries.  But finding a small exoplanet — 85 percent the size of Earth — is a promising result for a mission designed to not only locate as many as 20,000 new exoplanets, but to find 500 to 1,000 the rough size of Earth or SuperEarth. 
Read more

The Gale Winds of Venus Suggest How Locked Exoplanets Could Escape a Fate of Extreme Heat and Brutal Cold

Two images of the nightside of Venus captured by the IR2 camera on the Akatsuki orbiter in September 2016 (JAXA).

 

More than two decades before the first exoplanet was discovered, an experiment was performed using a moving flame and liquid mercury that could hold the key to habitability on tidally locked worlds.

The paper was published in a 1969 edition of the international journal, Science, by researchers Schubert and Whitehead. The pair reported that when a Bunsen flame was rotated beneath a cylindrical container of mercury, the liquid began to flow around the container in the opposite direction at speeds up to four times greater than the rotation of the flame. The scientists speculated that such a phenomenon might explain the rapid winds on Venus.

On the Earth, the warm equator and cool poles set up a pressure difference that creates our global winds. These winds are deflected westward by the rotation of the planet (the so-called Coriolis force) promoting a zonal (east-west) air flow around the globe. But what would happen if our planet’s rotation slowed? Would our winds just cycle north and south between the equator and poles?

The Moon is tidally locked to the Earth, so only one hemisphere is visible from our planet (Smurrayinchester / wikipedia commons).

Such a slow-rotating scenario may be the lot of almost all rocky exoplanets discovered to date. Planets such as the TRAPPIST-1 system and Proxima Centauri-b all orbit much closer to their star than Mercury, making their faint presence easier to detect but likely resulting in tidal lock. Like the moon orbiting the Earth, planets in tidal lock have one side permanently facing the star, creating a day that is equal to the planet’s year.

The dim stars orbited by these planets can mean they receive a similar level of radiation as the Earth, placing them within the so-called “habitable zone.” However, tidal lock comes with the risk of horrific atmospheric collapse. On the planet side perpetually facing away from the star, temperatures can drop low enough to freeze an Earth-like atmosphere. The air from the dayside would then rush around the planet to fill the void, freezing in turn and causing the planet to lose its atmosphere even within the habitable zone.

The only way this could be prevented is if winds circulating around the planet could redistribute the heat sufficiently to prevent freeze-out. But without a strong Coriolis force from the planet’s rotation, can such winds exist?… Read more

Weird Planets

 

 

Artist rendering of an “eyeball world,” where one side of a tidally locked planet is always hot on the sun-facing side and the back side is frozen cold.  Definitely a tough environment, but  might some of the the planets be habitable at the edges?  Or might winds carry sufficient heat from the front to the back?  (NASA/JPL-Caltech)

The very first planet detected outside our solar system powerfully made clear that our prior understanding of what planets and solar systems could be like was sorely mistaken.

51 Pegasi was a Jupiter-like massive gas planet, but it was burning hot rather than freezing cold because it orbited close to its host star — circling in 4.23 days.  Given the understandings of the time, its existence was essentially impossible. 

Yet there it was, introducing us to what would become a large and growing menagerie of weird planets.

Hot Jupiters, water worlds, Tatooine planets orbiting binary stars, diamond worlds (later downgraded to carbon worlds), seven-planet solar systems with planets that all orbit closer than Mercury orbits our sun.  And this is really only a brief peak at what’s out there — almost 4,000 exoplanets confirmed but billions upon billions more to find and hopefully characterize.

I thought it might be useful — and fun — to take a look at some of the unusual planets found to learn what they tell us about planet formation, solar systems and the cosmos.

 


Artist’s conception of a hot Jupiter, CoRoT-2a. The first planet discovered beyond our solar system was a hot Jupiter similar to this, and this surprised astronomers and led to the view that many hot Jupiters may exist. That hypothesis has been revised as the Kepler Space Telescope found very few distant hot Jupiters and now astronomers estimate that only about 1 percent of planets are hot Jupiters. (NASA/Ames/JPL-Caltech)

 

Let’s start with the seven Trappist-1 planets.  The first three were detected two decades ago, circling a”ultra-cool” red dwarf star a close-by 40 light years away.  Observations via the Hubble Space Telescope led astronomers conclude that two of the planets did not have hydrogen-helium envelopes around them, which means the probability increased that the planets are rocky (rather than gaseous) and could potentially hold water on their surfaces.

Then in 2016 a Belgian team, using  the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, found three more planets, and the solar system got named Trappist-1. Read more

Does Proxima Centauri Create an Environment Too Horrifying for Life?

Artist’s impression of the exoplanet Proxima Centauri b. (ESO/M. Kornmesser)

 

In 2016, the La Silla Observatory in Chile spotted evidence of possibly the most eagerly anticipated exoplanet in the Galaxy. It was a world orbiting the nearest star to the sun, Proxima Centauri, making this our closest possible exoplanet neighbour. Moreover, the planet might even be rocky and temperate.

Proxima Centauri b had been discovered by discerning a periodic wobble in the motion of the star. This revealed a planet with a minimum mass 30% larger than the Earth and an orbital period of 11.2 days. Around our sun, this would be a baking hot world.

But Proxima Centauri is a dim red dwarf star and bathes its closely orbiting planet in a level of radiation similar to that received by the Earth. If the true mass of the planet was close to the measured minimum mass, this meant Proxima Centauri b would likely be a rocky world orbiting within the habitable zone.

 

Comparison of the orbit of Proxima Centauri  b with the same region of the solar system. Proxima Centauri is smaller and cooler than the sun and the planet orbits much closer to its star than Mercury. As a result it lies well within the habitable zone. (ESO/M. Kornmesser/G. Coleman.)

Sitting 4.2 light years from our sun, a journey to Proxima Centauri b is still prohibitively long.

But as our nearest neighbor, the exoplanet is a prime target for the upcoming generation of telescopes that will attempt to directly image small worlds. Its existence was also inspiration for privately funded projects to develop faster space travel for interstellar distances.

Yet observations taken around the same time as the La Silla Observatory discovery were painting a very different picture of Proxima Centauri. It was a star with issues.

This set of observations were taken with Evryscope; an array of small telescopes that was watching stars in the southern hemisphere. What Evryscope spotted was a flare from Proxima Centauri that was so bright that the dim red dwarf star became briefly visible to the naked eye.

Flares are the sudden brightening in the atmosphere of a star that release a strong burst of energy. They are often accompanied by a large expulsion of plasma from the star known as a “coronal mass ejection”. Flares from the sun are typically between 1027 – 1032 erg of energy, released in a few tens of minutes.… Read more

Barnard’s Star, The "Great White Whale" of Planet Hunting, Has Surrendered Its Secret

Barnard’s Star is the closest single star to our sun, and the most fast moving. It has long been attractive to planet hunters because it is so close and so bright, especially in the infared section of the spectrum. But until now, the exoplanets of this “great white whale” have avoided detection.

 

Astronomers have found that Barnard’s star — a very close, fast-moving, and long studied red dwarf — has a super-Earth sized planet orbiting just beyond its habitable zone.

The discovery relied on data collected over many years using the tried-and-true radial velocity method, which searches for wobbles in the movement of the host star.

But this detection was something big for radial velocity astronomers because Barnard-b was among the smallest planet ever found using the technique, and it was the furthest out from its host star as well — orbiting its star every 233 days.

For more than a century, astronomers have studied Barnard’s star as the most likely place to find an extrasolar planet.

Ultimately, said Ignasi Rablis of Spain’s Institute of Space Studies of Catalonia, lead author of the paper in journal Nature, the discovery was the result of 771 observations, an extremely high number.

And now, he said, “after a very careful analysis, we are over 99 percent confident the planet is there.”

The planet is at least 3.2 times the size of Earth and orbits near the snowline of the system, where water cannot be expected to ever be liquid.  That means is it a frozen world (an estimated -150 degrees Celsius) and highly unlikely to support life.

But Rablis and others on the large team say it also an extremely good candidate for future direct imaging and next-generation observing.

 

An artist’s rendering of the Barnard’s star planet at sunset. (Martin Kornmesser/ESO)

 

Thousands of exoplanets have been identified by now, and hundreds using the radial velocity method.  But this one is different.

“Barnard’s star is the ‘great white whale’ of planet hunting,” said Paul Butler, senior scientist at the Carnegie Institution, a radial velocity pioneer, and one of the numerous authors of the paper.

Because the star is so close (but 6 light-years away) and as a result so tempting, it has been the subject of exoplanet searches for 100 years, Butler said.  But until the radial velocity breakthroughs of the mid 1990s, the techniques used could not find a planet.… Read more

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