Category: Planetary Systems (page 2 of 9)

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

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. 
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A New and Revelatory Window Into Evolution on Earth

A Leanchoilia fossil from at the Qingjiang site in China. A very early arthropod  found with sharply defined appendages is an arthropod and  one of the prime examples of early Cambrian life (D Fu et al., Science 363:1338 (2019)

Virtually every definition of the word “life” includes the capability to undergo Darwinian evolution as a necessary characteristic.  This is true of life on Earth and of thinking about what would constitute life beyond Earth.  If it can’t change, the thinking goes, then it cannot be truly alive.

In addition, evolutionary selection and change occurs within the context of broad planetary systems — the chemical makeup of the atmosphere, the climactic conditions, the geochemistry and more.  If an environment is changing, then the lifeforms that can best adapt to the new conditions are the ones that will survive and prosper.

So evolution is very much part of the landscape that Many Worlds explores — the search for life beyond Earth and effort to understand how life emerged on Earth.  Evolution happens in the context of broad conditions on Earth (and perhaps elsewhere), and finding potential life elsewhere involves understanding the conditions on distant planets and determining if they are compatible with life.

This all came to mind as I read about the discovery of a remarkable collection of fossils alongside a river in China, fossils of soft-bodied creatures that lived a half billion years ago in the later phase of what is termed the the Cambrian explosion.  They are of being compared already with the iconic “Burgess Shale” fossil find in Canada of decades ago, and may well shed equally revelatory light on a crucial time in the evolution of life on Earth.

Artist rendering of Qingjiang life showing characteristics of different early Cambrian taxonomical groups.  More than 50 percent had never been identified before. (ZH Yao and DJ Fu)

The new discovery is reported in the journal Science in a paper authored by Dongjing Fu and a team largely from the Northwest University in Xi’an.  The paper reports on a zoo of Cambrian-era creatures, with more than half of them never identified before in the rock record.

The animals are soft-bodied — making it all the more remarkable that they were preserved — and some bear little resemblance to anything that followed.   Like the Burgess Shale fossils, the Qingjiang discovery is of an entire ecosystem that largely disappeared as more fit (and predatory) animals emerged.… 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

Artifacts In Space

Voyager 2 entered interstellar space last month, becoming a space “artifact” of our civilization. (NASA)

 

All of a sudden, we have spacecraft and objects both coming into our solar system and leaving for interstellar space. This is highly unusual, and very intriguing.

The departing spacecraft is Voyager 2, which launched in 1977 and has traveled spaceward some 11 billion miles.  It has now officially left the heliosphere, the protective bubble of particles and magnetic fields created by the sun.  In this it follows Voyager I – which left our solar system in 2012 — and managers of the two craft have reason to think they can travel until they cross the half-century mark.

This is taking place the same time that scientists are puzzling over the nature of a cigar-shaped object that flew into the solar system from interstellar space last year.

Nobody knows what the object – called Oumuamua, Hawaiian for “first messenger,” or “scout” – really is. The more likely possibilities of it being a comet or an solar system asteroid have been found to be inconsistent with some observed properties of the visitor, and this has led some senior scientists to even hypothesize that it just might be an alien probe.

The likelihood may be small, but it was substantial enough for Harvard University Astronomy Department Chairman Avi Loeb to co-author a paper presenting the possibility.  In the Astrophysical Journal Letters, Loeb and postdoc Shmuel Bialy wrote that the object “may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization.”

They also say the object has some characteristics of a “lightsail of artificial origins,” rather like the one that Loeb is working on as chairman of the Breakthrough Starshot advisory committee.  The well-funded private effort is hoping to develop ways to send a fleet of tiny lightsail probes to the star system nearest to us, Alpha Centauri.

 

This artist’s impression of the first detected interstellar visitor: Oumuamua. This object was discovered in October 2017 by the Pan-STARRS 1 telescope in Hawaii. Subsequent observations from ESO’s Very Large Telescope in Chile and other observatories around the world show that it was traveling through space for millions of years before its seemingly chance encounter with our star system.  But some scientists wonder:  might it be instead a probe sent into the cosmos by intelligent creatures?(NASA)

 

Put the two phenomenon together — the coming into our solar system and the going out — and you have a pathway into the world of alien “artifacts,” products of civilizations near and far. … 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

Probing The Insides of Mars to Learn How Rocky Planets Are Formed

An artist illustration of the InSight lander on Mars. InSight, short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport, is designed to look for tectonic activity and meteorite impacts, study how much heat is still flowing through the planet, and track Mars’ wobble as it orbits the sun. While InSight is a Mars mission, it will help answer key questions about the formation of the other rocky planets of the solar system and exoplanets beyond. (NASA/JPL-Caltech)

In the known history of our 4.5-billion-year-old solar system,  the insides of but one planet have been explored and studied.  While there’s a lot left to know about the crust, the mantle and the core of the Earth, there is a large and vibrant field dedicated to that learning.

Sometime next month, an extensive survey of the insides of a second solar system planet will begin.  That planet is Mars and, assuming safe arrival, the work will start after the InSight lander touches down on November 26.

This is not a mission that will produce dazzling images and headlines about the search for life on Mars.  But in terms of the hard science it is designed to perform, InSight has the potential to tell us an enormous amount about the makeup of Mars, how it formed, and possibly why is it but one-third the size of its terrestrial cousins, Earth and Venus.

“We know a lot about the surface of Mars, we know a lot about its atmosphere and even about its ionosphere,” says Bruce Banerdt, the mission’s principal investigator, in a NASA video. “But we don’t know very much about what goes on a mile below the surface, much less 2,000 miles below the surface.”

The goal of InSight is to fill that knowledge gap, helping NASA map out the deep structure of Mars.  And along the way, learn about the inferred formation and interiors of exoplanets, too.

Equitorial Mars and the InSight landing site, with noting of other sites. (NASA)

The lander will touch down at Elysium Planitia, a flat expanse due north of the Curiosity landing site.  The destination was selected because it is about as safe as a Mars landing site could be, and InSight did not need to be a more complex site with a compelling surface to explore.

“While I’m looking forward to those first images from the surface, I am even more eager to see the first data sets revealing what is happening deep below our landing pads.” Barerdt said.… Read more

What Would Happen If Mars And Venus Swapped Places?

Venus, Earth and Mars (ESA).

 

What would happen if you switched the orbits of Mars and Venus? Would our solar system have more habitable worlds?

It was a question raised at the “Comparative Climatology of Terrestrial Planets III”; a meeting held in Houston at the end of August. It brought together scientists from disciplines that included astronomers, climate science, geophysics and biology to build a picture of what affects the environment on rocky worlds in our solar system and far beyond.

The question regarding Venus and Mars was proposed as a gedankenexperiment or “thought experiment”; a favorite of Albert Einstein to conceptually understand a topic. Dropping such a problem before the interdisciplinary group in Houston was meat before lions: the elements of this question were about to be ripped apart.

The Earth’s orbit is sandwiched between that of Venus and Mars, with Venus orbiting closer to the sun and Mars orbiting further out. While both our neighbors are rocky worlds, neither are top picks for holiday destinations.

Mars has a mass of just one-tenth that of Earth, with a thin atmosphere that is being stripped by the solar wind; a stream of high energy particles that flows from the sun. Without a significant blanket of gases to trap heat, temperatures on the Martian surface average at -80°F (-60°C). Notably, Mars orbits within the boundaries of the classical habitable zone (where an Earth-like planet could maintain surface water)  but the tiny planet is not able to regulate its temperature as well as the Earth might in the same location.

 

The classical habitable zone around our sun marks where an Earth-like planet could support liquid water on the surface (Cornell University).

 

Unlike Mars, Venus has nearly the same mass as the Earth. However, the planet is suffocated by a thick atmosphere consisting principally of carbon dioxide. The heat-trapping abilities of these gases soar surface temperatures to above a lead-melting 860°F (460°C).

But what if we could switch the orbits of these planets to put Mars on a warmer path and Venus on a cooler one? Would we find that we were no longer the only habitable world in the solar system?

“Modern Mars at Venus’s orbit would be fairly toasty by Earth standards,” suggests Chris Colose, a climate scientist based at the NASA Goddard Institute for Space Studies and who proposed the topic for discussion.

Dragging the current Mars into Venus’s orbit would increase the amount of sunlight hitting the red planet.… Read more

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