Tag: Proxima Centauri

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

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

Proxima b Is Surely Not "Earth-like." But It’s A Research Magnet And Just May Be Habitable.

Simulated comparison of a sunset on Earth and Proxima b. The red-dwarf star Proxima Centauri appears almost three times bigger than the Sun in a redder and darker sky. Red-dwarf stars appear bigger in the sky than sun-like stars, even though they are smaller. This is because they are cooler and the planets have to be closer to them to maintain temperate conditions. The original photo of the beach was taken at Playa Puerto Nuevo in Vega Baja, Puerto Rico. Credit: PHL @ UPR Arecibo.

A simulated comparison of a sunset on Earth and Proxima b. The images sets out to show that the red-dwarf star Proxima Centauri appears almost three times bigger than our sun in a redder and darker sky. There is value in illustrating how conditions in different solar systems would change physical conditions on the planets, but there is a real danger that the message conveyed becomes the similarities between planets such as Earth and Proxima b.  At this point, there is no evidence that Proxima b is “Earth-like” at all. The original photo of the beach was taken at Playa Puerto Nuevo in Vega Baja, Puerto Rico. (PHL @ UPR Arecibo))

It is often discussed within the community of exoplanet scientists that a danger lies in the description of intriguing exoplanets as “Earth-like.”

Nothing discovered so far warrants the designation, which is pretty nebulous anyway.  Size and the planet’s distance from a host star are usually what earn it the title “Earth-like,” with its inescapable expectation of inherent habitability. But residing in a habitable zone is just the beginning; factors ranging from the make-up of the planet’s host star to the presence and content of an atmosphere and whether it has a magnetic field can be equally important.

The recent announcement of the detection of a planet orbiting Proxima Centauri, the closest star to our own, set off another round of excitement about an “Earth-like” planet.  It was generally not scientists who used that phrase — or if they did, it was in the context of certain “Earth-like” conditions.  But the term nonetheless became a kind of shorthand for signalling a major discovery that just might some day even yield a finding of extraterrestrial life.

Consider, however, what is actually known about Proxima b:

  • The planet, which has a minimum mass of 1.3 Earths and a maximum of many Earths, orbits a red dwarf star.  These are the most common class of star in the galaxy, and they put out considerably less luminosity than a star like our sun — about one-tenth of one percent of the power.
  • These less powerful red dwarf stars often have planets orbiting much closer to them than what’s found in solar systems like our own.   Proxima b, for instance, circles the star in 11.3 days.
  • A consequence of this proximity is that the planet is most likely tidally locked by the gravitational forces of the star — meaning that the planet does not rotate like Earth does but rather has a daytime and nighttime side like our moon. 
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Earth: A Prematurely Inhabited Planet?

A schematic of the history of the cosmos since the Big Bang identifies the period when planets began to form, but there's indication of when life might have started. Harvard's Avi Loeb wants to put life into this cosmological map, and foresees much more of it in the future, given certain conditions. ( NASA)

A schematic of the history of the cosmos since the Big Bang identifies the period when planets began to form, but there’s no indication of when life might have started. Harvard’s Avi Loeb wants to add life into this cosmological map, and foresees much more of it in the future, given certain conditions. ( NASA)

The study of the formation and logic of the universe (cosmology) and the study of exoplanets and their conduciveness to life do not seem to intersect much.  Scientists in one field focus on the deep physics of the cosmos while the others search for the billions upon billions of planets out there and seek to unlock their secrets.

But astrophysicist and cosmologist Avi Loeb — a prolific writer about the early universe from his position at the Harvard-Smithsonian Center for Astrophysics– sees the two fields of study as inherently connected, and has set out to be a bridge between them.  The result was a recent theoretical paper that sought to place the rise of life on Earth (and perhaps elsewhere) in cosmological terms.

His conclusion:  The Earth may well be a very early example of a living biosphere, having blossomed well before life might be expected on most planets.   And in theoretical and cosmological terms, there are good reasons to predict that life will be increasingly common in the universe as the eons pass.

By eons here, Loeb is thinking in terms that don’t generally get discussed in geological or even astronomical terms.  The universe may be an ancient 13.7 billion years old, but Loeb sees a potentially brighter future for life not billions but trillions of years from now.  Peak life in the universe, he says, may arrive several trillion years hence.

“We used the most conservative approaches to understanding the appearance of life in the universe, and our conclusion is that we are very early in the process and that it is likely to ramp up substantially in the future,” said Loeb, whose paper was published in the Journal of Cosmology and Astroparticle Physics.

“Given the factors we took into account, you could say that life on Earth is on the premature side.”

 

The Earth was formed some 4.5 billions years ago, and life that existed as long ago as 3.5 to 3.8 billion years ago has been discovered. Harvard astrophysicist Avi Loeb argues that life on Earth may well be "premature" in cosmological terms, and that many more planets will have biospheres in the far future. (xxx)

The Earth was formed some 4.5 billion years ago, and signs of life have been discovered that are 3.5 to 3.8 billion years old. Harvard astrophysicist Avi Loeb, with co-authors Rafael Batista and David Sloan of the University of Oxford, argue that life on Earth may well be “premature” in cosmological terms, and that many more planets will have biospheres in the far future. 

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The Pale Red Dot Campaign

Alpha and Beta Centauri are the bright stars; Proxima Centauri is the small, faint one circles in red.

Alpha Centauri A and B are the bright stars; Proxima Centauri, a red dwarf star, is the small, faint one circled in red. (NASA, Julia Figliotti)

Astronomers have been trying for decades to find a planet orbiting Proxima Centauri, the star closest to our sun and so a natural and tempting target.  Claims of an exoplanet discovery have been made before, but so far none have held up.

Now, in a novel and very public way, a group of European astronomers have initiated a focused effort to change all that with their Pale Red Dot Campaign.  Based at the La Silla Observatory in Chile, and supported by  networks of smaller telescopes around the world, they will over the next three months observe Proxima and its environs and then will spend many more months analayzing all that they find.

And in an effort to raise both knowledge and excitement, the team will tell the world what they’re doing and finding over Twitter, Facebook, blogs and other social and traditional media of all kind.

“We have reason to be hopeful about finding a planet, but we really don’t know what will happen,” said Guillem Anglada-Escudé  of Queen Mary University, London, one of the campaign organizers.  “People will have an opportunity to learn how astronomers do their work finding exoplanets, and they’ll be able to follow our progress.  If we succeed, that would be wonderful and important.  And if no planet is detected, that’s very important too.”

The Pale Blue Dot, as photographed by Voyager 1 (NASA)

The Pale Blue Dot, as photographed by Voyager 1 (NASA)

The name of the campaign is, of course, a reference to the iconic “Pale Blue Dot” image of Earth taken by the Voyager 1 spacecraft in 1990, when it was well beyond Pluto.  The image came to symbolize our tiny but precious place in the galaxy and universe.

But rather than potentially finding a pale blue dot, any planet orbiting the red dwarf star Proxima Centauri would reflect the reddish light of the the star, which lies some 4.2 light years away from our solar system.  Proxima — as well as 20 of the 30 stars in our closest  neighborhood — is reddish because it is considerably smaller and less luminous than a star like our sun.

Anglada-Escudé said he is cautiously optimistic about finding a planet because of earlier Proxima observations that he and colleagues made at the same observatory.  That data, he said, suggested the presence of a planet 1.2 to 1.5 times the size of Earth, within the habitable zone of the star.… Read more

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