Category: Exoplanets (page 1 of 8)

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

The Kepler Space Telescope Mission Is Ending But Its Legacy Will Keep Growing.

An illustration of the Kepler Space Telescope, which is on its very last legs.  As of October 2018, the planet-hunting spacecraft has been in space for nearly a decade. (NASA via AP)

 

The Kepler Space Telescope is dead.  Long live the Kepler.

NASA officials announced on Tuesday that the pioneering exoplanet survey telescope — which had led to the identification of almost 2,700 exoplanets — had finally reached its end, having essentially run out of fuel.  This is after nine years of observing, after a malfunctioning steering system required a complex fix and change of plants, and after the hydrazine fuel levels reached empty.

While the sheer number of exoplanets discovered is impressive the telescope did substantially more:  it proved once and for all that the galaxy is filled with planets orbiting distant stars.  Before Kepler this was speculated, but now it is firmly established thanks to the Kepler run.

It also provided data for thousands of papers exploring the logic and characteristics of exoplanets.  And that’s why the Kepler will indeed live long in the world of space science.

“As NASA’s first planet-hunting mission, Kepler has wildly exceeded all our expectations and paved the way for our exploration and search for life in the solar system and beyond,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate in Washington.

“Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars.”

 

 


The Kepler Space Telescope was focused on hunting for planets in this patch of the Milky Way. After two of its four spinning reaction wheels failed, it could no longer remain steady enough to stare that those distant stars but was reconfigured to look elsewhere and at a different angle for the K2 mission. (Carter Roberts/NASA)

 

Kepler was initially the unlikely brainchild of William Borucki, its founding principal investigator who is now retired from NASA’s Ames Research Center in California’s Silicon Valley.

When he began thinking of designing and proposing a space telescope that could potentially tell us how common distant exoplanets were — and especially smaller terrestrial exoplanets like Earth – the science of extra solar planets was at a very different stage.… Read more

Technosignatures and the Search for Extraterrestrial Intelligence

A rendering of a potential Dyson sphere, named after Freeman A. Dyson. As proposed by the physicist and astronomer decades ago, they would collect solar energy on a solar system wide scale for highly advanced civilizations. (SentientDevelopments.com)

The word “SETI” pretty much brings to mind the search for radio signals come from distant planets, the movie “Contact,” Jill Tarter, Frank Drake and perhaps the SETI Institute, where the effort lives and breathes.

But there was a time when SETI — the Search for Extraterrestrial Intelligence — was a significantly broader concept, that brought in other ways to look for intelligent life beyond Earth.

In the late 1950s and early 1960s — a time of great interest in UFOs, flying saucers and the like — scientists not only came up with the idea of searching for distant intelligent life via unnatural radio signals, but also by looking for signs of unexpectedly elevated heat signatures and for optical anomalies in the night sky.

The history of this search has seen many sharp turns, with radio SETI at one time embraced by NASA, subsequently de-funded because of congressional opposition, and then developed into a privately and philanthropically funded project of rigor and breadth at the SETI Institute.  The other modes of SETI went pretty much underground and SETI became synonymous with radio searches for ET life.

But this history may be about to take another sharp turn as some in Congress and NASA have become increasingly interested in what are now called “technosignatures,” potentially detectable signatures and signals of the presence of distant advanced civilizations.  Technosignatures are a subset of the larger and far more mature search for biosignatures — evidence of microbial or other primitive life that might exist on some of the billions of exoplanets we now know exist.

And as a sign of this renewed interest, a technosignatures conference was scheduled by NASA at the request of Congress (and especially retiring Republican Rep. Lamar Smith of Texas.)  The conference took place in Houston late last month, and it was most interesting in terms of the new and increasingly sophisticated ideas being explored by scientists involved with broad-based SETI.

“There has been no SETI conference this big and this good in a very long time,” said Jason Wright, an astrophysicist and professor at Pennsylvania State University and chair of the conference’s science organizing committee.  “We’re trying to rebuild the larger SETI community, and this was a good start.”

 

At this point, the search for technosignatures is often likened to that looking for a needle in a haystack.

Read more

Water Worlds, Aquaplanets and Habitability

This artist rendering may show a water world — without any land — or an aquaplanet with lots of more shallow water around a rocky planet. (NASA)

 

The more exoplanet scientists learn about the billions and billions of celestial bodies out there, the more the question of unusual planets — those with characteristics quite different from those in our solar system — has come into play.

Hot Jupiters, super-Earths, planets orbiting much smaller red dwarf stars — they are all grist for the exoplanet mill, for scientists trying to understand the planetary world that has exploded with possibilities and puzzles over the past two decades.

Another important category of planets unlike those we know are the loosely called “water worlds” (with very deep oceans) and their “aquaplanet” cousins (with a covering of water and continents) but orbiting stars very much unlike our sun.

Two recent papers address the central question of habitability in terms of these kind of planets — one with oceans and ice hundreds of miles deep, and one particular and compelling planet (Proxima Centauri b, the exoplanet closest to us) hypothesized to have water on its surface as it orbits a red dwarf star.

The question the papers address is whether these watery worlds might be habitable.  The conclusions are based on modelling rather than observations, and they are both compelling and surprising.

In both cases — a planet with liquid H20 and ice many miles down, and another that probably faces its red dwarf sun all or most of the time — the answers from modelers is that yes, the planets could be habitable.   That is very different from saying they are or even might be inhabited.  Rather,  the conclusions are based on computer models that take into account myriad conditions and come out with simulations about what kind of planets they might be.

This finding of potential watery-world habitability is no small matter because predictions of how planets form point to an abundance of water and ice in the planetesimals that grow into planets.

As described by Eric Ford, co-author of one of the papers and a professor of astrophysics at Pennsylvania State University, “Many scientists anticipate that planets with oceans much deeper than Earths could be a common outcome of planet formation. Indeed, one of the puzzling properties of Earth is that it has oceans that are just skin deep” compared to the radius of the planet.… Read more

A National Strategy for Finding and Understanding Exoplanets (and Possibly Extraterrestrial Life)

The National Academies of Science, Engineering and Medicine took an in-depth look at what NASA, the astronomy community and the nation need to grow the burgeoning science of exoplanets — planets outside our solar system that orbit a star. (NAS)

 

An extensive, congressionally-directed study of what NASA needs to effectively learn how exoplanets form and whether some may support life was released today, and it calls for major investments in next-generation space and ground telescopes.  It also calls for the adoption of an increasingly multidisciplinary approach for addressing the innumerable questions that remain unanswered.

While the recommendations were many, the top line calls were for a sophisticated new space-based telescope for the 2030s that could directly image exoplanets, for approval and funding of the long-delayed and debated WFIRST space telescope, and for the National Science Foundation and to help fund two of the very large ground-based telescopes now under development.

The study of exoplanets has seen remarkable discoveries in the past two decades.  But the in-depth study from the private, non-profit National Academies of Sciences, Engineering and Medicine concludes that there is much more that we don’t understand than that we do, that our understandings are “substantially incomplete.”

So the two overarching goals for future exoplanet science are described as these:

 

  • To understand the formation and evolution of planetary systems as products of star formation and characterize the diversity of their architectures, composition, and environments.
  • To learn enough about exoplanets to identify potentially habitable environments and search for scientific evidence of life on worlds orbiting other stars.

 

Given the challenge, significance and complexity of these science goals, it’s no wonder that young researchers are flocking to the many fields included in exoplanet science.  And reflecting that, it is perhaps no surprise that the NAS survey of key scientific questions, goals, techniques, instruments and opportunities runs over 200 pages. (A webcast of a 1:00 pm NAS talk on the report can be accessed here.)

 


Artist’s concept showing a young sun-like star surrounded by a planet-forming disk of gas and dust.
(NASA/JPL-Caltech/T. Pyle)

These ambitious goals and recommendations will now be forwarded to the arm of the National Academies putting together 2020 Astronomy and Astrophysics Decadal Survey — a community-informed blueprint of priorities that NASA usually follows.

This priority-setting is probably most crucial for the two exoplanet direct imaging missions now being studied as possible Great Observatories for the 2030s — the paradigm-changing space telescopes NASA has launched almost every decade since the 1970s.

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15,000 Galaxies in One Image

Astronomers have just assembled one of the most comprehensive portraits yet of the universe’s evolutionary history, based on a broad spectrum of observations by the Hubble Space Telescope and other space and ground-based telescopes.  Each of the approximately 15,000 specks and spirals are galaxies, widely distributed in time and space. (NASA, ESA, P. Oesch of the University of Geneva, and M. Montes of the University of New South Wales)

Here’s an image to fire your imagination: Fifteen thousand galaxies in one picture — sources of light detectable today that were generated as much as 11 billion years ago.

Of those 15,000 galaxies, some 12,000 are inferred to be in the process of forming stars.  That’s hardly surprising because the period around 11 billions years ago has been determined to be the prime star-forming period in the history of the universe.  That means for the oldest galaxies in the image, we’re seeing light that left its galaxy but three billion years after the Big Bang.

This photo mosaic, put together from images taken by the Hubble Space Telescope and other space and ground-based telescopes, does not capture the earliest galaxies detected. That designation belongs to a galaxy found in 2016 that was 420 million years old at the time it sent out the photons just collected. (Photo below.)

Nor is it quite as visually dramatic as the iconic Ultra Deep Field image produced by NASA in 2014. (Photo below as well.)

But this image is one of the most comprehensive yet of the history of the evolution of the universe, presenting galaxy light coming to us over a timeline up to those 11 billion years.  The image was released last week by NASA and supports an earlier paper in The Astrophysical Journal by Pascal Oesch of Geneva University and a large team of others.

And it shows, yet again, the incomprehensible vastness of the forest in which we are a tiny leaf.

Some people apparently find our physical insignificance in the universe to be unsettling.  I find it mind-opening and thrilling — that we now have the capability to not only speculate about our place in this enormity, but to begin to understand it as well.

The Ultra-Deep field composite, which contains approximately 10,000 galaxies.  The images were collected over a nine-year period.  {NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z.

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