Where Is Everybody?

Where Is Everybody?[1]

Perhaps my favorite essay in Aliens: The World’s Leading Scientists on the Search for Extraterrestrial Life is by the astrobiologist Lewis Dartnell, who patiently explains why aliens would not come here to have sex with us or eat us for supper.

I can only assume that he gets these questions a lot.

Here are the answers, should you find these possibilities concerning: The likelihood that we’d be genetically compatible with aliens is terribly remote, which means that they’d almost certainly be immune to our sexual charms. For similar reasons, having to do with biochemistry, we’d be lousy refreshments for them—they would almost certainly lack the proper enzymes to digest us.

As a bonus, Dartnell goes on to reassure us why aliens wouldn’t be especially interested in raiding our planet for raw materials, either (asteroids are a far easier source to mine); and if it were water they were after, they’d be far better off going to Europa, one of Jupiter’s largest moons, which contains more water beneath its icy shell than all the oceans on Earth combined.

If you’re interested in non-Earthly life, don’t look to the movies, is his point.

You could argue that that’s the general point of this modest, eccentric collection. Jim Al-Khalili, a quantum physicist and the editor of Aliens, opens with a question asked by Enrico Fermi in 1950: If the universe is so vast, and its age so old, and its stars so plentiful, where is everybody?

I’m no marketing expert, but “Where Is Everybody?” strikes me as a far catchier title for this book than the one it has, and it’s definitely more accurate. There really is nobody—so far—to write about. (Fighting words, I know. My hands hovered, spaceshiplike, for several minutes over the keyboard before committing that sentence to print.) This doesn’t mean that life elsewhere doesn’t exist. But it probably corresponds very little to what most of us have in mind, and not at all to the ooze-covered beasts of Ridley Scott’s electric dreams[2].

One of the most consistent takeaways from this anthology is just how banal extraterrestrial life might be. Often, when entertaining the possibility of aliens, what we’re really entertaining is the possibility of hardy microbes that can withstand extreme conditions, whether they’re thermophiles (heat lovers), psychrophiles (cold lovers) or halophiles (salt lovers). Read enough of Aliens, and you realize that the search for life is just as much about the most mundane aspects of biology as about the trippier questions of cosmology.

But it is also about philosophy. In this search, it helps to know what life is. Yet there’s no consensus about how to answer this question, strangely. (At the risk of being too Clintonian, it depends on what your definition of “is” is.)

Nor do we know how life began. At some point, the Earth made the transition from chemistry to biology, yes, but we cannot “agree on a definition that separates the nonliving chemistry from life,” as the geneticist Johnjoe McFadden puts it. (He then paraphrases the astronomer Fred Hoyle, who famously said that the odds of assembling something like a bacterium out of the primordial ooze were akin to the odds of a tornado’s assembling a jumbo jet out of a junkyard heap as it sweeps through.)

There are scientists who will go so far as to say that life is a spectacular fluke. Not everyone, mind you: Researchers now estimate that there are one billion Earthlike exoplanets in the Milky Way. “To my mathematical brain, the numbers alone make thinking about aliens perfectly rational,” Stephen Hawking has said.

But a powerful essay by the evolutionary biologist Matthew Cobb will make you wonder whether any form of multicellular life is far less likely than one in a billion. He points out that “there are more single-celled organisms alive on Earth than there are Earthlike planets in the observable universe”; that the number of single-celled organisms that have lived on this planet over the course of 3.8 billion years is beyond calculation; that these organisms have interacted “gazillions” of times (I love it when words of the appropriate magnitude desert even the experts). Yet we’ve never had a second instance of eukaryogenesis—that remarkable moment when one unicellular life form lodged inside another, forming something much more complex—in all this time.

Of course, there are researchers who dispute this theory and Cobb’s reasoning. But you get the idea.

The experience of reading almost any anthology is a bit like traveling across the country in a rental car with only an FM radio for company. Sometimes you get Sinatra; other times you get Nickelback.

This collection has its share of Nickelback. One of its most disappointing essays is about aliens in science fiction, which manages, against stupefying odds, to contain just one interesting insight: that authors tend to be more concerned with physics than with biology. (How did those gigantic sandworms evolve on the desert planet in Dune?)

But the best of these essays are far out in more ways than one. The very first, by the cosmologist Martin Rees, notes that our best hope for interstellar travel isn’t as humans, who don’t live very long and require far too much fuel to get very far, but as post-humans, who will have made the Kurzweilian transition from organic to inorganic, from decaying mortals to silicon-based, eminently portable machines. He adds that alien intelligence, if we ever detect it, will also be in this form.

The final essay, by Seth Shostak, a senior astronomer at the SETI institute (short for Search for Extraterrestrial Intelligence), goes even further, saying that if we really want to be attuned to alien life in the cosmos, it’s so likely to be in the form of machine intelligence that we ought to “be alert to apparent violations of physics.”

These forms of life may well be speaking to us even now. It’s just that our radio telescopes, which listen to the skies for signals from alien beings, can’t understand what they’re hearing. “Even if the search succeeded,” Rees writes, “it would still in my view be unlikely that the ‘signal’ would be a decodable message.”

It’s a whole new twist on George Berkeley’s question. The tree would fall in the forest. We’d hear it. But it would sound nothing like a tree.

[1] See Jennifer Senior, “‘Aliens’ Asks: If the Universe Is So Vast, Where Is Everybody?”, New York Times (May 24, 2017). This article is  review of the book: Al-Khalili, Jim(2007). ALIENS :The World’s Leading Scientists on the Search for Extraterrestrial Life. New York: Picador. Follow Jennifer Senior on Twitter: @jenseniorny. A version of this review appears in print on May 25, 2017, on Page C2 of the New York edition with the headline: “I Think It’s Gonna Be a Long, Long Time.” Downloaded May 26, 2017

[2] Scott is a South African born movie director of sci-fi films, including Alien, and The Martian.

A New Exoplanet and Life

A New Exoplanet May Be Most Promising Yet in Search for Life[1]

At left is an artist’s impression of the newly discovered rocky exoplanet. The exoplanet is close enough that astronomers are hopeful that with the next generation of big telescopes, they will be able to probe its atmosphere for signs of water or other evidence of suitability for life.

A prime planet listing has just appeared on the cosmic real estate market, possibly the most promising place yet to search for signs of life beyond the Solar System, the astronomers who discovered it say.

It is a rocky orb about one and a half times the size of Earth, about 40 light years from here. It circles a dwarf star known as LHS 1140 every 25 days, an orbit that puts it in the “Goldilocks” zone where temperatures are conducive to liquid water and perhaps life as we know it.

It is close enough that astronomers are hopeful that with the next generation of big telescopes, they will be able to probe its atmosphere for signs of water or other evidence of suitability for life.

“This planet is really close to us: If we shrank the Milky Way to the size of the United States, LHS 1140 and the Sun would fit inside Central Park,” David Charbonneau, of the Harvard-Smithsonian Center for Astrophysics, said in an email.

His colleague Jason Dittmann, who led the discovery team and is lead author of a paper published on Wednesday (April 18, 2017) in Nature, said in a statement, “This is the most exciting exoplanet I’ve seen in the last decade.”

The planet was discovered by the MEarth-South survey at the Cerro Tololo Inter-American Observatory in Chile, an array of small telescopes that looks for the dips in starlight when planets pass in front of nearby stars.

The depth of the dip told them how big the new planet is. Then they determined that it was about six times as massive as Earth by using a spectrograph called Harps, for High Accuracy Radial velocity Planet Searcher, at the European Southern Observatory, also in Chile, to measure how much the planet perturbed its home star. The resulting density puts the little world into a rapidly growing class called “superEarths.”

The star LHS 1140 is about one-fifth the size of our Sun. In its close orbit, the planet receives about half as much energy as Earth does from its own Sun, enough for a microbe or something more complicated to make a living.

This discovery continues a recent run of promising new planets circling nearby dwarf stars. Last summer there was the discovery of Proxima b, the nearest star to us, only 4.2 light years from here.

In February astronomers discovered a system of seven Earth-size planets circling a dwarf star known as Trappist-1.

According to Dr. Charbonneau, who originated the MEarth system, red dwarf stars outnumber stars like our Sun by about 10 to 1 in the 30-light-year bubble that constitutes our “block” in the cosmos.

About one in four of them have rocky planets in their habitable zones, according to work by Dr. Charbonneau’s former student Courtney Dressing, now at the California Institute of Technology.

Once upon a time, such planets were not looked upon favorably in the extraterrestrial life sweepstakes, because they were almost undoubtedly tidally locked, keeping one side faced to its star and the other facing out in space. That would result in a burning hell on one side and eternal frostbite on the other, neither side suitable for life.

But recently astronomers have determined that if these planets have thick enough atmospheres, winds can distribute the heat around both hemispheres and make them livable.

“Now we love them,” Sara Seager, a planetary expert at the Massachusetts Institute of Technology, said at a recent meeting on the origins of life sponsored by Harvard at the American Academy of Arts and Sciences in Cambridge. “If they have an atmosphere, they can harbor life.”

Astronomers said that the new planet offered the best hope so far to test that proposition. When the planet crosses in front of LHS 1140 the atmosphere acts like a filter, leaving an imprint on the star’s light that could betray the presence of water and other molecules important for life.

This will be a job for powerful new telescopes like the James Webb Space Telescope, due to be launched next year, or giant ground-based telescopes like the Giant Magellan and European Extremely Large telescopes, now being built in Chile, Dr. Charbonneau said.

Whether such planets actually have atmospheres is still controversial, however. When red dwarf stars are young, Dr. Charbonneau pointed out, they are ferociously luminous and might have blown away the planets’ atmospheres or caused a runaway greenhouse, leaving them barren. But the LHS 1140 planet is heavy enough, he said, that it might have been able to retain its atmosphere or regenerate it by volcanic activity later on.

“But the key point is yes, these are really exciting ideas to test,” he continued. “Do temperate, rocky M-dwarfs planets retain their atmospheres, and do they have life? This world enables those studies.”

[1] Dennis Overbye, “Promising Target in the Search for Extraterrestrial Life”, New York Times (April 20, 2017), p. A19. A version of this article appeared online at the New York Times (April 19, 2017).

Water in Outer Solar System

Water in Outer Solar System[1]

The editors of Astronomy deem the discoveries of water in the outer Solar System the 6th most important astronomy story of 2015.

Saturn’s moon Enceladus continues to show why it’s one of the best in the Solar System to search for life. Astronomers have suspected for years that salty water dredged up from a subsurface sea spews into space out of fissures near the moon’s south pole. But an analysis published in September 2014 in the journal Icarus, of seven years of images from NASA’s Cassini spacecraft indicates that Enceladus has a subsurface global ocean instead of merely a regional sea.

Cornell University planetary scientist Peter Thomas and colleagues measured a slight wobble in the moon’s rotation. If Enceladus were solid, its mass would dampen that motion. The researchers believe, instead, that a liquid water ocean lies between the moon’s icy surface layer and the rocky interior. They say the ocean is deeper and the ice shell thinner at the south polar region where Cassini has spied some 1200 geysers of salt water.

Scientists think that to keep any material in liquid state within Enceladus’ interior requires the push-and-pull tidal energy from Saturn. A global ocean is harder to keep warm than a regional sea, and so this discovery could also indicate that the saturnian satellite has more tidal energy than originally thought. “:If that is correct,” says team member Carolyn Porco, “and its ocean has been around a long, long time, then it may mean that any life within it has had a long time to evolve.”

Some of the material spewing from Enceladus’ underground ocean flows out through the geysers, flows toward Saturn because of the planet’s gravitational pull, and then orbits the planet as its E ring. In the March 12, 2015 issue of Nature, Frank Postberg at the universities of Heidelberg and Stuttgart in Germany and colleagues described how they used the Cassini spacecraft to study some of the material from the E ring. They saw silicon-rich molecules (called silicates) just a few nanometers wide. When this type of material is found in space, it almost always originates from rock being dissolved in water. But to learn the precise characteristics of that water-rock interaction, Postberg’s team collaborated with researchers from Japan to mimic the conditions needed at Enceladus to produce the sizes and composition of silicate particles they observed. They found the water needs to be at least 194 °F and have a pH between 8.5 and 10.56. These characteristics imply hot-spring heated water; the only other place where such hydrothermal vents have ever been see is on Earth, and these sites host extreme organisms.

The chemical reaction that produces the silicates also creates molecular hydrogen, and a different instrument on board Cassini looked for this gas during a late 2015 flight through Enceladus’ plumes. If more molecular hydrogen is detected (to be analyzed in the future) than expected, it will confirm hydrothermal activity, says Postberg.

In 2016 astronomers also found the best evidence so far of water at yet another location in the Solar System: Jupiter’s large moon Ganymede. NASA’s Galileo spacecraft, which studies the jovian system in the late 1990s and early 2000s, studied Ganymede’s magnetic field to learn whether the moon holds a global ocean under its surface. But the analysis from only 20 minutes of flyby observations was inconclusive. Fast forward to 2015, when Joachim Saur of the University of Cologne and his colleagues studied data from two 7-hour Hubble Space Telescope observations.

Ganymede has an auroral belt in each hemisphere just like Earth does. Jupiter’s magnetic field also influences these aurorae and causes them to rock during Jupiter’s 10-hour rotation period. Saur’s team knew that if Ganymede did not have an ocean, the aurora belts would change their positions slightly, tilting about 6°. “However, when a salty and thus electrically conductive ocean is present, this ocean counterbalances Jupiter’s magnetic influence and thus reduces the rocking of the auroras to only 2°,” says Saur. “We observed Ganymede with the Hubble Space Telescope for more than 5 hours and saw that the aurora barely moved and rocked by only 2°. This thus confirms the existence of an ocean.” The researchers think the ocean lies about 90 miles below the moon’s rock-ice crust and is about 60 miles thick. This strong evidence of Ganymede’s ocean continues to increase the number of worlds in our Solar System known to host water.

[1] See Astronomy (44, 1, 2016, p.)