Tag: exoplanets

Why Habitable Exoplanets Are Bad News for Humanity’s Future

By Andrew Snyder-Beattie, University of Oxford | April 24, 2014 11:21 am

PIA10363 exoplanetThis article was originally published on The Conversation.

Last week, scientists announced the discovery of Kepler-186f, a planet 492 light years away in the Cygnus constellation. Kepler-186f is special because it marks the first planet almost exactly the same size as Earth orbiting in the “habitable zone” – the distance from a star in which we might expect liquid water, and perhaps life.

What did not make the news, however, is that this discovery also slightly increases how much credence we give to the possibility of near-term human extinction. This because of a concept known as the Great Filter.

The Great Filter is an argument that attempts to resolve the Fermi Paradox: why have we not found aliens, despite the existence of hundreds of billions of solar systems in our galactic neighborhood in which life might evolve? As the namesake physicist Enrico Fermi noted, it seems rather extraordinary that not a single extraterrestrial signal or engineering project has been detected (UFO conspiracy theorists notwithstanding).

This apparent absence of thriving extraterrestrial civilizations suggests that at least one of the steps from humble planet to interstellar civilization is exceedingly unlikely. The absence could be caused because either intelligent life is extremely rare or intelligent life has a tendency to go extinct. This bottleneck for the emergence of alien civilizations from any one of the many billions of planets is referred to as the Great Filter.

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CATEGORIZED UNDER: Space & Physics, Top Posts
MORE ABOUT: exoplanets

Venus’s Day in the Sun: How the Transit Will Help Us Search for Other Earths

By Guest Blogger | June 4, 2012 8:30 am

Mark Anderson has an M.S. in astrophysics, is a contributor to Discover, and has written about science and history for many other publications. His new book The Day the World Discovered the Sun: An Extraordinary Story of Scientific Adventure and the Race to Track the Transit of Venus has just been published by Da Capo.

Also see Paul Raeburns’s explanation of what investigating Venus can teach us about our own planet.


The 2004 Venus transit at sunrise

On Tuesday afternoon—for those in North, Central and parts of South America—the planet Venus will pass directly in front of the sun for seven hours. This rare spectacle, called the Venus transit, occurs twice within a decade, then not again for more than a century. But as fleeting as they are, transits of the past provided invaluable information about our place in the solar system—and, astronomers hope, this transit could help us glean more information on planets elsewhere in the galaxy.

In the 1760s, some of the age’s top explorers and scientists collaborated on dozens of expeditions across the planet to observe the Venus transit. These voyages launched the legendary careers of Captain Cook and the surveyors Mason and Dixon. The expeditions also represented the world’s first big science project—forefather to today’s Large Hadron Collider and Human Genome Project, in which an international community of hundreds or thousands collaborates on a single fundamental scientific problem at the frontier of human knowledge.

In the balance hung two of the greatest scientific and technological puzzles of the 18th century: discovering the Sun’s distance from the Earth and finding one’s longitude at sea.  Read More

CATEGORIZED UNDER: Space & Physics
MORE ABOUT: astronomy, exoplanets, Sun, Venus

Good News, Alien Seekers: E.T. Probably Doesn’t Need a Freaky-Big Moon Like Ours

By Seth Shostak | January 24, 2012 1:01 pm

Seth Shostak is Senior Astronomer at the SETI Institute in California, and the host of the weekly radio show and podcast, “Big Picture Science.”

The Moon is a ball of left-over debris from a cosmic collision that took place more than four billion years ago. A Mars-sized asteroid—one of the countless planetesimals that were frantically churning our solar system into existence—hit the infant Earth, bequeathing it a very large, natural satellite.

OK, that’s a bit of modestly engaging astrophysics. But some scientists think there’s a biological angle here. Namely, that elaborate terrestrial life might never have appeared if that asteroid had arrived a few hours earlier, and sailed silently by. Put another way, if every night were moonless, you wouldn’t be around to notice the lack of a moon.

But is that true? Did our cratered companion really make our existence possible?

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CATEGORIZED UNDER: Environment, Top Posts

The Ultimate Measure of a Planet—Habitability Isn’t a Yes/No Question

By Seth Shostak | December 6, 2011 1:57 pm

Seth Shostak is Senior Astronomer at the SETI Institute in California, and the host of the weekly radio show and podcast, “Big Picture Science.”

Back in the early days of “Star Trek,” whenever the Enterprise would chance upon a novel planet, we’d hear a quick analysis from Science Officer Spock. Frequently he would opine, “It’s an M-class planet, Captain.” That was the tip-off that this world was not only suited for life, but undoubtedly housed some intelligent beings eager for a meet-and-greet with the Enterprise crew.

But what is an “M-class planet” (also referred to as “class M”)? Clearly, it referred to a world on which intelligent life could thrive, and made it easy for the crew (and viewers) to see where the episode was headed. A recent paper by Washington State University astrobiologist Dirk Schulze-Makuch and his colleagues has suggested a somewhat similar way to categorize real-world orbs that might be home to cosmic confreres. Rather than giving planets a Spockian alphabetic designation, Schulze-Makuch prefers a less obscure, and more precise, numerical specification: a value between 0 and 1. A world that scores a 1 is identical to Earth in those attributes thought necessary for life. A score of 0 means that it’s a planet only an astronomer could love—likely to be as sterile as an autoclaved mule.

Schulze-Makuch computes this index—which he calls an Earth Similarity Index, or ESI—by considering both the composition of a planet (is it rocky and roughly the size of Earth?) and some crude measures of how salubrious the surface might be (does it have a thick atmosphere, and are temperatures above freezing and below boiling?) He combines parameters that define these characteristics in a series of multiplicative terms that are reminiscent of the well-known Drake equation, used to estimate the number of technologically adept civilizations in the Milky Way.

At present the number of worlds thought to have an ESI of 0.8 or greater—near-cousins of Earth—is only one: Gliese 581g (though that planet’s existence is disputed). But as additional data from NASA’s Kepler mission continue to stream in, we can expect that more such “habitable” planets will turn up. In particular, Kepler scientists reported this week on a newsworthy object called Kepler-22b. This planet is 2.4 times Earth’s diameter and in an orbit around a Sun-like star that places it securely in the habitable zone—where temperatures might be similar to a summer day in San Francisco.

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CATEGORIZED UNDER: Top Posts

Nevermind Where. *When* Are the Intelligent Aliens?

By Seth Shostak | October 25, 2011 5:49 pm

Only a few decades back, there were serious scientists who thought that planets might be miraculous. Not miracles like a burning bush or a docile teenager, but highly improbable objects. These researchers figured that the conditions necessary for making small, cold worlds could be rare—perhaps extremely rare. Most stars were believed to live their luminous lives alone, bereft of planetary accompaniment.

Well, those thoughts have been banished. In the last 15 years, hard-working astronomers have found many hundreds of so-called exoplanets around nearby stars, and NASA’s Kepler telescope is set to uncover thousands more. (If you don’t know this already, you’ve probably reached this site by mistake. But you’ve come this far already, so keep reading.) Kepler’s principal task is to find habitable exoplanets—worlds with solid surfaces at the right distance from their host star to sport temperatures amenable to the presence of watery oceans and protective atmospheres—planets that might be very much like Earth (depending on some other factors that are harder to measure from light-years away, like geology and chemistry).

Kepler has already found about five dozen candidate objects that, while somewhat larger than our own, seem to meet these criteria. As this space-based telescope continues to peer into the heavens, more such planets will emerge from the data. Indeed, it seems a good bet to guess that at least a few percent of all stars are blessed with “habitable” worlds. That would tally to billions of life-friendly sites, just in our galaxy. This has already prompted SETI scientists to swing their antennas in the directions Kepler’s most promising candidate planets, hoping to pick up the ABCs and MTVs of alien worlds. After all, these systems are arguably the best targets that SETI (the Search for Extraterrestrial Intelligence) has ever had. It’s like discovering a prolific fishing hole.

But there’s a fly in the ointment: While eavesdropping on a small bunch of star systems known to have terrestrial-style worlds is better than taking your chances with random targets, it’s not actually that much better. The reason is simple. The oldest confirmed fossils on Earth are about 3.5 billion years old, and there’s indirect, if sketchy, evidence for life going back 4 billion years. That’s roughly 90 percent of the age of the Earth, which is to say that biology bedecked our planet very early. Life seems to have been an easy chemistry experiment. So that’s yet more encouragement, as it hints that many of those habitable worlds will actually be inhabited. There could be life on billions of planets in the Milky Way.

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CATEGORIZED UNDER: Top Posts
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