New spacey stories: killer asteroids, stellar DNA, and rogue planets

I meant to post at least once a month, but I think you’ll understand that it’s hard to find the time while juggling new freelance science writing work with a 9-month-old kiddo at home. Anyway, here’s a couple pieces I’ve published over the past month. Enjoy! (See links below for the full articles.) As usual, thanks go to my helpful editors: Heather D’Angelo, Lisa Grossman, Lauren Morello and Jane Lee.


Maybe Dark Matter Didn’t Kill the Dinosaurs after All

Artist’s impression of the Chicxulub impact. Credit: Donald E. Davis, via Wikimedia Commons

A giant asteroid or comet the size of a city smashed into the Yucatán 66 million years ago, likely causing the demise of dinosaurs and many other species. Scientists have wondered: is that a random, unfortunate event, or has life on Earth been subjected to periodic impacts from outer space?

Some researchers proposed that, if the dinosaur extinction — the last of five mass extinctions — had an astronomical origin, rather than being driven by volcano eruptions or global warming, for example, then maybe others did too. And if impacts from huge boulders of rock and ice drove these extinctions, they had to come from somewhere. It’s possible that dark matter could periodically dislodge distant comets from their tenuous orbits beyond Pluto, sending a few of them dangerously in Earth’s direction — thus linking the fates of dark matter and dinosaurs.

But a new study by a team of physicists and geologists from Durham University and Lancaster University in the United Kingdom appears to shoot down that dark matter interpretation. If it were true, extinctions would have happened in cycles. But these scientists pored over the fossil record over the past 500 million years, looking for extinctions occurring periodically, but they didn’t find any significant patterns like that in the data.

“We needn’t search the heavens to find reasons for these extinction events. The vast majority of them are due to Earth processes, not astronomical ones,” says David Harper, lead author of the study.

The dark matter idea, popularized by Lisa Randall’s 2015 book, “Dark Matter and the Dinosaurs,” might sound far-fetched. But before this study, it was more plausible. Our solar system resides in the middle of the Milky Way galaxy, which has a disk-like structure. It turns out that the solar system doesn’t just stay put; gravity pulls it up and down through the disk, like a pendulum. Lurking in the outskirts of the solar system, comets in what’s known as the Oort Cloud slowly orbit the sun, whose gravity barely holds them on their trajectories. A pass through the galaxy does change the gravitational forces on them, but not enough to let comets loose.

Instead, Randall speculates that within the same plane as the Milky Way is a much thinner and denser disk of dark matter that we can’t see. (Most astrophysicists think dark matter particles only clump up in sphere-like conglomerations, but one flavor of dark matter could form disks.) Then as the solar system passes through that disk every 32 million years or so, it’s as if the dark matter’s gravity provides a little extra tug, nudging a few comets out of their orbits.

While some untethered comets get flung away, never to be seen again, others head toward Earth. Over time, these would produce periodic blips in the Earth’s history of both craters and mass extinctions, which wouldn’t occur randomly. It’s a new incarnation of an older idea, where earlier astronomers suggested the possibility of a faraway solar companion dubbed Nemesis, which would provide the extra nudge, but it was never found.

Harper and his colleagues performed something called a time-series analysis, looking for subtle cycles in the data that would corroborate Randall’s hypothesis. After removing a background trend and running statistical tests, they found that the extinctions don’t occur periodically on any time-scale.

The risk of finding a pattern when there’s not one really there is enormous, says Michael Benton, an Earth scientist at the University of Bristol in the UK. “The fossil record is patchy, biased, and incomplete,” he says.

The structure of our Milky Way makes for another complication. The galaxy looks more like a fluffy pinwheel than a compact disk. It has spiral arms jutting and curving out while neighboring stars in the galaxy move to and fro, so as our solar system passes through the galaxy, its periodic motion will vary. Harper argues that this motion would then be too irregular to pull in more wayward Earthbound comets that result in mass extinctions.

Randall agrees that there’s more than one cause to extinctions on Earth. But she argues that if things like volcanic activity, plate tectonics, and climate change can’t explain them all, some may have been triggered by cosmic events. She and her colleagues developed a model of a dark matter disk which she says fits the crater record better than a bunch of random impacts.

As it turns out, another new study, unrelated to Harper’s, looks at the record of crater impacts with a similar kind of analysis. They come to the same conclusion: there’s currently no evidence for asteroids or comets periodically colliding with Earth.

“I actually like the idea of asteroid impacts. But from the data we have, all I can say is that it’s unlikely,” says Matthias Meier, the lead author and a cosmochemist at Swiss Federal Institute of Technology in Zurich.

It would help to have more and better crater data. Meier studied 22 craters, but there are nearly 190 known craters worldwide. Many of them were dated more than 50 years ago with earlier methods and aren’t very precise, but if one limits the sample to only the most accurate crater ages, there may be too few of them. Once scientists discover more craters and estimate more accurate ages of them, they could settle the debate.

“This study may mark the end of the speculation,” Benton says. Then after a pause, “No wait, it won’t. There’ll be plenty more, I’m sure.”

[Read the entire story in, published on 14 March 2017. Update (8 Sep. 2017): is unfortunately now defunct, so I’ve posted the story in full here.]

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Inside Science: Dark Matter Particles, Cosmic Lenses, and Super-Earths

Here’s a few new stories I reported on and wrote for Inside Science News Service over the past couple weeks:


Physicists Look Beyond WIMPs For Dark Matter

Physicists are on the hunt for elusive dark matter, the hypothesized but as yet unidentified stuff that makes up a large majority of the matter in the universe. They had long favored “weakly interacting massive particles,” known as WIMPs, as the most likely dark matter candidate, but after an exhaustive search, some scientists are moving on to more exotic particles.

Most estimates suggest that there’s 5-6 times as much dark matter as there are things that we can see, such as galaxies, stars, and planets. Yet physicists know very little about what the mysterious dark matter particles actually are, as they cannot be directly observed and barely interact with normal matter.

New research leaves dwindling room for WIMPs, motivating a search for other particles that could fit the bill.

“The WIMPs are getting harsh experimental scrutiny, and may get ruled out,” said Kathryn Zurek, a physicist at Lawrence Berkeley National Laboratory in California. [Note: She later clarified that WIMPs may become more “strongly constrained” rather than “ruled out.”]

Physicists have used the Large Hadron Collider's ATLAS experiment to probe for potential dark matter particles. (Credit: CERN)

Physicists have used the Large Hadron Collider’s ATLAS experiment to probe for potential dark matter particles. (Credit: CERN)

Zurek and others presented ongoing work on dark matter alternatives to WIMPs in April at an American Physical Society meeting in Salt Lake City. “We should broaden the searchlight, and the natural place is to go lighter,” Zurek said.

She and her colleagues are looking into less massive particles that interact more weakly with ordinary matter. These include an array of particles with exotic names like “axion,” “sterile neutrino,” and “Higgsino,” a theoretical super-partner of the famous Higgs boson.

Axions are hypothetically abundant particles originally proposed in the 1970s to solve a problem with nuclear physics. In the presence of a powerful magnetic field, these minuscule particles, which are lighter than electrons, are predicted to turn into detectable photons. In spite of years of searching, however, they have yet to be found. But the Axion Dark Matter eXperiment, currently being upgraded, should definitely determine whether the particle exists, said Leslie Rosenberg of the University of Washington in Seattle.

Kevork Abazajian, a cosmologist at the University of California, Irvine, sees a new trend in the field over the past decade. “The new generation of early-career physicists is more open to dark matter other than WIMPs,” he said.

He argued that physicists should consider sterile neutrinos, which interact even more weakly than their neutrino counterparts. As they decay, the particles—which are tinier than electrons—could produce detectable X-ray radiation such as that observed in clusters of galaxies. But scientists struggle to distinguish between X-rays that could be emitted by sterile neutrinos versus traditional astrophysical events. Research along these lines suffered a setback when Japan’s powerful X-ray satellite Hitomi broke into pieces last month. But it may have accumulated limited science data before it was lost…

[For more, check out the entire story in Inside Science, published on 28 April 2016. Thanks to Chris Gorski and Sara Rennekamp for editing assistance.]

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Exciting and Controversial Science: Gravitational Waves and a New Ninth Planet?

We’ve had some fantastic astronomical news this month. Last week, we encountered evidence of a “new ninth planet” lurking in the outer reaches of our solar system—170 years after the discovery of Neptune. And earlier in January, we heard a cacophony of whispers about minute gravitational waves being detected for the first time ever. Either one, if true, would be amazing to both astrophysicists and space lovers and would be the biggest discovery of 2016. We should be excited about them, but we should be careful about getting our hopes up so soon.

A New Planet, Far, Far Away?

A couple fellow science writers and I went hiking at Castle Rock State Park in the middle of the Santa Cruz Mountains yesterday, and along the trail, we encountered a variety of people. On our way down, we happened to overhear a conversation: “What’s your favorite planet?” followed by a reply, “Did you hear about the new planet scientists discovered?” Isn’t that great? I’m glad that the story got so much media attention and made it to the front pages of newspapers. It intrigued people, and they’re talking about it.

By studying the strangely aligned orbits of Kuiper Belt Objects far beyond Pluto’s realm, astronomers may have inferred evidence of a planet up to 10 times bigger than Earth. It would be much, much farther than Pluto, making it hard to spot. And from that distance, our sun would look almost like any other star. But if it exists, a new world (dubbed “Planet X”) joining our solar system’s family, even such an estranged cousin, would be exciting indeed.

Eric Hand (Science magazine) points out that the Subaru Telescope could search for Planet X. (Data) JPL; Batygin and Brown/Caltech; (Diagram) A. Cuadra/Science

Eric Hand (Science magazine) points out that the Subaru Telescope could search for Planet X. (Data) JPL; Batygin and Brown/Caltech; (Diagram) A. Cuadra/Science

Nevertheless, we should be concerned that the results are still very uncertain. The authors of the paper in Astronomical Journal, Konstantin Batygin and Mike Brown (both at Caltech), argue that there’s only a 0.007% chance, about one in 15,000, that the clustering of the distant objects’ orbits could be a coincidence. But it’s possible that the behavior of the orbits could have other possibly more likely explanations, such as other unseen Kuiper Belt Objects with orbits aligned in the opposite way. (Other astronomers, like Scott Sheppard and Greg Laughlin, estimate the chance of a planet really being out there at 60-70%. I wouldn’t bank on those odds.)

For that reason, we should remain skeptical for now. Some reporters and editors were a bit more careful than others. For example, while some headlines used appropriately hedging words like “suggest” and “may,” papers like the Denver Post and Washington Post had “The New No. 9” or “Welcome to Planet Nine.” This is already an exciting story to tell though, and we don’t need to exaggerate to get readers’ attention. If the planet turns out not to exist, people who read overblown headlines like those will be frustrated and confused.

Finally, we should all recall that Mike Brown was the main force behind Pluto’s demotion by the International Astronomical Union ten years ago. Since he calls himself the “Pluto Killer” (and wrote a book, “How I Killed Pluto and Why It Had It Coming”), it would be ironic if he helped discover a new ninth planet, replacing Pluto. But he and the Caltech news office seem to have hyped up his paper’s findings more than they deserved, given all the uncertainties involved.

Gravitational Waves Discovered?

While procrastinating and flipping through Twitter earlier this month, I came across some juicy gossip. I heard what sounded like the tantalizing detection of gravitational waves—an unprecedented achievement. These tiny ripples in space-time, predicted by Albert Einstein and thought to be produced by collisions of black holes or neutron stars, had been too small to measure before. Gravity is the weakest of forces, after all.

But it turns out that Lawrence Krauss, a well-known cosmologist and provocateur at Arizona State University, had caused the hullabaloo with some ill-advised tweets. He once again drew the media’s limelight to himself by spreading rumors that scientists in the Laser Interferometer Gravitational-Wave Observatory (LIGO) collaboration had detected gravitational waves for the first time. In the process, he put those scientists in a tough spot, as I’m sure they faced pressure to make sensitive statements about their ongoing research.

The LIGO Laboratory operates two detector sites, one near Hanford in eastern Washington (pictured here) and another near Livingston, Louisiana. (Credit: Caltech/MIT/LIGO Lab)

The LIGO Laboratory operates two detector sites, one near Hanford in eastern Washington (pictured here) and another near Livingston, Louisiana. (Credit: Caltech/MIT/LIGO Lab)

The LIGO team is still working on their analysis using a pair of detectors in Louisiana and Washington state, and they haven’t yet produced conclusive results. From what I can tell, they may have evidence but the situation is far from clear. There is nothing wrong with waiting a while until you’ve thoroughly investigated all the relevant issues and sources of error before announcing a momentous discovery. The alternative is to prematurely declare it, only to face the embarrassing possibility of retracting it later (which sort of happened to BICEP2 scientists with their supposed discovery of primordial gravitational waves).

Gravitational waves will have to remain elusive for now. And if and when LIGO physicists do have convincing evidence of gravitational waves, they need not share any of the glory or credit with Krauss.

Fortunately, in spite of this excitement, science writers and editors kept their cool and soberly pointed to Krauss’s rumors before digging into the fascinating and painstaking work LIGO scientists are doing. Here’s some excellent coverage by Clara Moskowitz in Scientific American and by Lisa Grossman in New Scientist.

[26 Jan. update: I decided to tone down my criticism of Mike Brown, but not of Lawrence Krauss.]

New Planetary Science: Habitable Planets and Saturn’s Titan Moon

Here are two new stories I’ve written about interesting new research presented at recent conferences this fall, the National Association of Science Writers meeting in October and the American Geophysical Union meeting this week.


Sara Seager’s Search for Distant Habitable Worlds

Like a 21st-century Spock, Dr. Sara Seager seeks out new worlds and civilizations. With continually improving telescopes, she persistently and passionately pursues her grand quest: to search throughout our galaxy for habitable planets, a few of which might even resemble the Earth.

Sara Seager, MIT planetary physics professor. (Credit: MIT)

Sara Seager, MIT planetary physics professor. (Credit: MIT)

Seager, an accomplished professor of planetary science and astrophysics at MIT, gave an engaging presentation at the 2015 Science Writers meeting. She spoke clearly and intensely about her research and the exciting future of planetary exploration.

She and her research group have made important breakthroughs while characterizing newly discovered planets beyond our solar system, known as exoplanets, using the NASA Kepler space telescope. With powerful next-generation observatories, she also looks forward to the next frontier, where her ongoing mission could come to fruition.

…In most exoplanet work, astronomers consider only certain planets as potentially life-friendly. Their orbit, atmosphere, surface and climate all must be just right, falling within narrow ranges of parameters. A successful search requires a daunting understanding of biology, chemistry, and geology, as well as astronomy and physics.

…Seager argues that the traditional concept of habitable zone is too rigid and should be expanded. “Exoplanets are diverse, covering nearly all masses, sizes and orbits possible,” she says. What scientists mean by habitable should be more inclusive, or they risk missing outlier planets that nonetheless could be conducive to life. Accounting for habitability varying depending on the type of star or planet alleviates the situation.

[For more, check out the entire article on the Minority Postdoc site, published on 14 Dec. 2015. Thanks to Matthew Francis for help with editing.]


Scientists Map Titan’s Lakes, Revealing Clues to their Origins

As Saturn’s largest moon, Titan earns its name. It’s also the only known body other than Earth with seas, numerous surface lakes, and even rainy weather. Now scientists have mapped out Titan’s polar lakes for the first time, revealing information about the moon’s climate and surface evolution. They found that the lakes formed differently than had been previously thought—and differently than any lakes on Earth.

A map of Titan’s North Pole, including its lakes, sediments and complex terrain. (Credit: NASA/JPL-Caltech/Space Science Institute.)

A map of Titan’s North Pole, including its lakes, sediments and complex terrain.
(Credit: NASA/JPL-Caltech/Space Science Institute.)

A collaboration of scientists led by Alexander Hayes of Cornell University presented their findings at the 2015 American Geophysical Union Fall Meeting. They used NASA’s Cassini spacecraft to penetrate Titan’s smoggy atmosphere and probe the complex lake systems below.

Titan’s seas and giant lakes, which are larger than the Caspian Sea and Great Lakes, appear unique in the solar system, the study found. They consist of mostly liquid hydrocarbons like methane and ethane, possibly making them a promising location to search for building blocks of carbon-based extraterrestrial life. Because Titan is tilted with respect to its orbit, it also experiences seasons, which drive these lakes toward its North Pole. But Saturn’s eccentric orbit makes the lakes shift from pole to pole, Hayes explained.

By combining Cassini RADAR mapper observations with other data, Hayes and his colleagues compiled detailed information about Titan’s lake systems and topography, allowing scientists to test ideas for how these lakes developed.

“Topography in geology is the key because it drives the evolution of landscapes,” said Samuel Birch, lead author of one of the Titan studies and a Ph.D. student at Cornell.

[For more, check out the entire article on GeoSpace, published on 14 Dec. 2015. Thanks to Lauren Lipuma for editing assistance.]

Finding Earth 2.0

In honor of Carl Sagan’s birthday, I figured I’d write a few thoughts I had about a fascinatingly unique conference I attended in the Bay Area last week. It was called “Finding Earth 2.0,” and it was organized by 100 Year Starship, a group partially funded by NASA and the Defense Advanced Research Projects Agency (DARPA) to plan for interstellar travel within the next century.

A potential spacecraft called Icarus Pathfinder would be powered by electric propulsion engines called VASIMR, taking it out to 1,000 times the distance between the Earth and Sun. (Credit: NBC News)

A potential spacecraft called Icarus Pathfinder would be powered by electric propulsion engines called VASIMR, taking it out to 1,000 times the distance between the Earth and Sun. (Credit: NBC News)

Like you might imagine such an organization, the conference speakers and attendees appeared rather eclectic, including astronomers and planetary physicists and science journalists—whom I’m usually hanging out with—as well as aerospace engineers, science fiction writers, business people, teachers, space enthusiasts, and many others. But everyone displayed an active interest in exploring the distant universe and imagining what our future might be like.

Dr. Mae Jemison, the first woman of color in space, heads the 100 Year Starship, and she gave a plenary talk. She pointed to many motivations people have for finding another Earth, including conundrums and challenges our planet and species face, such as limited resources, overpopulation, and our own behavior—perhaps a reference to climate change or nuclear weapons. I think we have many other compelling reasons for interstellar space exploration, but I’ve written about that here before.

I also saw many interesting perspectives and presentations about hunting for planets beyond the solar system, called exoplanets, including habitable ones or even inhabited ones. Dr. Jill Tarter, SETI (Search for Extraterrestrial Intelligence) Institute co-founder and inspiration for Sagan’s protagonist in Contact (Dr. Arroway), gave a provocative presentation on attempts to detect “technosignatures” from distant planets. (She clarified that possessing technology doesn’t imply an intelligent civilization; however, technologies serve as a proxy for intelligence.) Advanced species on these planets could be giving off radio and optical signals that could reach the Earth, but we’d have to listen really really hard to hear them. But if they had a Dyson sphere or an “alien superstructure,” that would be easier.

Other astronomers and astrobiologists talked about their work on related subjects. Margaret Turnbull, also of the SETI Institute, spoke about the “massive harvest” of planets reaped by NASA’s Kepler probe, which confirmed more than 1,000 planets in our Milky Way neighborhood and which showed that about 1 in 5 stars has a planet in the “habitable zone.” Stephen Kane (San Francisco State University) made a convincing case that we should view the habitable zone boundaries as uncertain, and that many planets in the zone would actually be not very hospitable to life. Natalie Batalha (NASA Ames) argued that we should be open-minded about planets in other systems. In one of a few relationship-like quotes, she said, “In our search for a [Earth-like] soul-mate, we may be a bit myopic.” But she was talking about the fact that we have no planets between Earth and Neptune sizes here, while according to Kepler observations, such planets seem rather common throughout the galaxy. She and others also made the point that we need detailed imaging or spectra of planetary systems to learn more about their habitability.

Niki Parenteau (SETI) talked about her efforts to study exoplanets and spot signs of life, which would likely be microorganisms and would have to cover the world to be detectable. “There’s no one smoking gun for biosignatures,” she said. “We need multiple lines of evidence.” She looks for things like biogenic gases and certain planetary surface features. But for her, water is the #1 requirement…and then Morgan Cable, a nerdy joke-telling astrochemist from Jet Propulsion Laboratory, considered a range of other liquids life might be able to develop in, including ammonia, carbon dioxide, petroleum, and liquid hydrocarbons. She ended with her main argument: “NASA shouldn’t just be looking for places with liquid water.”

Artist's illustration of NASA's NEA Scout CubeSat, which is scheduled to launch aboard the maiden flight of the agency’s Space Launch System rocket in 2018. (Credit: NASA)

Artist’s illustration of NASA’s NEA Scout CubeSat, which is scheduled to launch aboard the maiden flight of the agency’s Space Launch System rocket in 2018. (Credit: NASA)

A bunch of people gave presentations about propulsion systems, trying to push the boundaries of space travel. I thought the most interesting one was by Les Johnson, Deputy Manager for NASA’s Advanced Concepts Office at Marshall Space Flight Center. In back-to-back talks, he described current efforts to design and construct giant solar and electric sails. The sails involve ultra-thin reflective materials that are unfurled in space and use solar energy to propel a spacecraft to the distant reaches of the solar system and beyond. In an important step toward that goal, Johnson and NASA engineers are currently building a solar sail for the Near-Earth Asteroid Scout mission to transport a CubeSat “nanosatellite” to study asteroids past Mars in two years. He and his colleagues are also currently testing electric sails for fast solar wind-powered spacecraft, which—if as powerful as hoped—could even send a probe to another star.

Finally, I saw a few strange talks at the conference, and I wasn’t sure what to make of them. For example, one person spoke about the new field of “astrosociology.” He avoided giving any specifics though, even though he had been discussing “deviant” behavior, and admitted after the talk that he had envisioned studying multi-year trips transporting tens of thousands of colonists beyond the solar system. Maybe for the 200 Year Starship! Unfortunately, the speaker had not considered small missions, such as handfuls of astronauts traveling to Mars or private ventures conducting asteroid mining. I’d imagine that such small groups of people stuck together for long periods could benefit from sociological study.

Book Review: Five Billion Years of Solitude

As long as humans have roamed the Earth, they have looked up to the skies, speculating and pondering about the celestial wonders populating the distant cosmos. From the early astronomers and natural philosophers until today’s (including me), people have observed and studied the billions of twinkling dots, all the while wondering whether there are other worlds out there and whether they might host lifeforms like us.


In his first book, “Five Billion Years of Solitude: The Search for Life Among the Stars,” Lee Billings explores these and related questions. He chronicles the story of space exploration, planet-hunting and the growing field of astrobiology, while meeting fascinating characters and discussing their research, telescopes, discoveries and challenges. He offers clear and compelling explanations, such as of planetary physics and habitability, and he takes important asides into debates on space exploration budgets and the fate of our own planet, including the ongoing climate change crisis.

Billings is a talented science journalist. Like his work for Scientific American and other publications, the book is excellently written and researched. It won the 2014 American Institute of Physics science communication award in the book category, announced at the American Astronomical Society meeting in January.

Over the course of the book, Billings tracks down and speaks with important figures in planetary astronomy. He begins with Frank Drake, who along with nine other scientists in 1961 attempt to quantify the abundance of life-supporting planets in the galaxy in a calculation now known as the Drake Equation. He also meets with other astrophysicists, including University of California, Santa Cruz professor Greg Laughlin, Space Telescope Science Institute director Matt Mountain and MIT professor Sara Seager.

Since the time-scale or life-time of civilizations plays a role in the Drake Equation, his investigations lead to an examination of our own history and the longevity of humanity on Earth. Billings discusses the planet’s changing climate and other looming threats, for which our society appears unprepared. His reporting takes him to southern California too, where he quotes from my former colleague, UC San Diego physicist Tom Murphy, who considered the question of growing global energy consumption.

Other important questions come up as well. How far away are planets beyond our solar system and how long would it take to get there? What kind of atmospheric, geological and climatic conditions must a habitable planet have? How do astronomers detect planets, when they are so small, so faint and so close to their brightly glowing suns? What are our prospects for finding more Earth-like planets?

And what will happen to the Earth and humankind—if we’re still around—over the next few billion years, as our sun brightens, expands and transforms into a red giant star? As Billings starkly puts it in his interview for The Atlantic, “We may have—we may be—the only chance available for life on Earth to somehow escape a final, ultimate planetary and stellar death.”

Artist's conception of NASA's Kepler spacecraft. (Image credit: NASA/Ames/JPL-Caltech)

Artist’s conception of NASA’s Kepler spacecraft. (Image credit: NASA/Ames/JPL-Caltech)

With the Kepler telescope, we have the good fortune to be living at a time when actually Earth-like worlds, not just super-Earths and gas dwarfs, can be identified. Astronomers have already used the telescope to find a few potential Earth cousins, which have the right size and the right “Goldilocks” distance from their stars, and many many more candidates are on the horizon. Under certain conditions, follow-up observations can measure the planets’ atmospheres and climates to further assess their habitability.

It’s an exciting time! With even more advanced planet-finding telescopes coming up, such as the Hubble successors, the James Webb Space Telescope and High-Definition Space Telescope, we can look forward to more detailed images and observations of exoplanets in the near future. Maybe Earth has twins and maybe we are not alone.

I have a few criticisms of Five Billion Years, but they’re very minor ones. I liked the analysis of federal budget debates at multiple points in the book, but Billings could have written a little more about why as a society we should prioritize space exploration and astronomical research. If, say, a member of the House Science Committee (or more likely, their staffer) were to read this, it would be helpful to spell that out. Early in the book, he provides an engaging historical survey of astronomy, but he neglected Eastern contributions, such as from Persians, Arabs and Chinese. A few chapters meandered quite a bit too, but I enjoyed his writing style.

In any case, this is a beautifully written and thoroughly researched book, and I recommend it. Billings puts the search for extraterrestrial life in a broader context and pushes us to think about our place in the vast universe. The story continues.

[P.S. I’m extremely busy these days with the UC Santa Cruz science communication program and writing internships, so I may write posts here less often. But I will link to pieces I’ve written elsewhere, which have the benefit of rigorous editing, so if you like my blog, you’ll like them even more.]

New Discoveries as New Horizons Flies by Pluto!

You may be wondering, what’s the deal with Pluto? First, astronomers demote Pluto’s planetary status in a controversial move, to say the least, and then NASA sends a spacecraft on a mission to observe it in detail? Why is this important, and what could we learn about Pluto that we didn’t know already?

Image from the Long Range Reconnaissance Imager (LORRI) aboard NASA's New Horizons spacecraft, taken on 13 July 2015. Pluto is dominated by the feature informally named the "Heart." (Image Credit: NASA/APL/SwRI)

Image from the Long Range Reconnaissance Imager (LORRI) aboard NASA’s New Horizons spacecraft, taken on 13 July 2015. Pluto is dominated by the feature informally named the “Heart.” (Image Credit: NASA/APL/SwRI)

Of course, we have quite a bit to learn. Moreover, as one of the least studied objects in the outer regions of our solar system, Pluto is ripe for exploration and investigation. Within a few days, NASA’s New Horizons probe already produced detailed and exquisite photos of Pluto, much better than has been done with Hubble or any other telescope. Its mission is far from over, but it’s already an amazing success and has inspired public interest in space exploration once again.

Back in 1930, 85 years ago, a young astronomer by the name of Clyde Tombaugh at Lowell Observatory in Flagstaff, Arizona noticed a distant possibly planet-like object moving across photographic plates. When other astronomers confirmed the discovery, thousands of people suggested names for the planet. In the end, the name that caught on in the community came from an 11-year-old girl in Oxford, Venetia Burney, and the Lowell astronomers approved “Pluto” unanimously. (Contrary to some rumors, she did not name it after the cartoon dog.) Burney (later Phair) lived to witness the launching of New Horizons, but she passed away in 2009. Some of Tombaugh’s ashes are aboard the spacecraft, and his children and grandchildren were present for the events of New Horizons.

NASA's New Horizons spacecraft.  (Artist's impression.)

NASA’s New Horizons spacecraft.
(Artist’s impression.)

NASA’s New Horizons spacecraft launched from Cape Canaveral in January 2006. Its journey took it 3 billion miles (about 5 billion km) from Earth, including a slingshot around Jupiter—covering nearly 1 million miles per day!—to reach Pluto. To paraphrase Douglas Adams, you may think it’s a long way to the chemist’s, but that’s just peanuts compared to the distance New Horizons traveled. Principal investigator Alan Stern of the Southwest Research Institute in Boulder, Colorado leads the mission, which also includes a relatively large fraction of women on the team. In another important point, the mission had a relatively small cost ($700M) considering its huge impact on planetary physics, space exploration, and science outreach.

Once Pluto was demoted (or even dissed) by the astronomical community back in 2006, it’s never been more popular! New Horizons’ flyby only rekindled interest in Pluto in popular culture. I’ve seen many comics, memes and jokes about it, including XKCD, a cartoon showing Neil deGrasse Tyson and Pluto giving each other the finger, a cartoon with a sad Pluto as New Horizons flies by while saying “HEYWHATSUPGOTTAGOBYE!,” and another cartoon with Pluto saying, “So you dumped me years ago, but now you’re driving by my house real slow?”

As I wrote in a previous post, Pluto has many characteristics, including its small size and mass, that give it a questionable planetary status. It is one of many objects hurtling about the edge of our solar system called the Kuiper Belt, named after Dutch-American astronomer Gerard Kuiper. According to the International Astronomical Union (IAU), these are some of the solar system’s non-planets, ranked by size: Ganymede (Jupiter moon), Titan (Saturn moon), Callisto (Jupiter moon), Io (Jupiter moon), Earth’s moon, Europa (Jupiter moon), Triton (Neptune moon), Pluto, and Eris. Much further down the list comes Ceres (in the asteroid belt between Mars and Jupiter), which is actually smaller than Charon, one of Pluto’s moons. Eris, which was previously known as 2003 UB313 (and also as Planet X, and then Xena, as in the Warrior Princess) is slightly more massive than Pluto. In addition to Pluto, Eris, and Ceres, Haumea (a trans-Neptunian object) and Makemake (another Kuiper Belt object) are the other two dwarf planets the IAU recognizes. In any case, Pluto may be small and may be less unique than we thought and may have an abnormally elliptical orbit, but we all love it anyway.

New Horizons made its closest approach on 14 July, Tuesday morning, about 50 years after the first spacecraft landed on Mars, Mariner 4. It will take many months for New Horizons to transmit all of the Pluto flyby data back to Earth, but what has the probe discovered so far? First, New Horizons already obtained the most detailed images of Pluto ever. Second, based on the imagery, astronomers calculated that Pluto is slightly larger than previously thought: it turns out to have a radius 1.9% larger than Eris’s, making it the largest dwarf planet.

New Horizons scientists also found that Pluto is icier than previously thought, with its polar ice cap and with icy mountains nearly as high as the Rockies. The ice consists of a frozen mixture of methane, ethane, carbon monoxide and nitrogen—not the sort of thing you’d want to put in a drink. Pluto’s mountains likely formed less than 100 million years ago, which is a relatively short time in the history of a (dwarf) planet. At least some of Pluto’s surface might still be geologically active today—some scientists think they have spotted potential geysers as well—but planetary physicists are not sure about what could have caused this activity. Furthermore, Pluto exhibits very few impact craters from Kuiper belt objects (KBOs), which would also be consistent with recent geological activity.

Charon also lacks such craters—a surprising observation considering that it appears to have no atmosphere. Charon’s diameter is over half of Pluto’s, which makes it big enough to cause Pluto to wobble as it orbits. Scientists believe that Charon likely formed from a huge collision with a young Pluto, and debris also settled into Pluto’s four other moons: Nix, Hydra, Kerberos, and Styx. Alternatively, Pluto could have gravitationally captured Charon a few hundred million years ago, which could explain the “tidal interactions” between them.

Finally, New Horizons astronomers discovered vast frozen craterless plains in the center of Pluto’s “heart,” which they have informally named the “Tombaugh Regio.” The plains region has a broken surface of irregularly-shaped segments that either may be due to the contraction of surface materials, like when mud dries, or may be the result of convection. The New Horizons team released the following zoom-in images at a press conference today, and we expect more to come.

What’s next for New Horizons? The probe continues to send more valuable data from its seven instruments in our general direction. Project scientists will sift through these data to try to learn more about Pluto and Charon’s surface, geology, and atmosphere, and therefore to infer how these interesting objects formed and evolved. In the meantime, New Horizons continues on its merry way throughout the Kuiper Belt. Assuming NASA approves funding for its extended mission, in a couple years it will use its limited fuel to investigate much smaller and newly discovered KBOs, such as 2014 MT69. In any case, we shall keep in touch with New Horizons as it follows the Voyager spacecrafts into the outskirts of our solar system and boldly ventures beyond.

[For further reading, you can find great coverage about these exciting discoveries in many places. For example, take a look at Nature (Alexandra Witze), Science, Scientific American, National Geographic (Nadia Drake), Wired, NBC (Alan Boyle), as well as New York Times, Los Angeles Times, Guardian, BBC, etc… For the most up-to-date information, I suggest taking a look at NASA’s website and the Planetary Society (Emily Lakdawalla).]

NASA Missions Exploring Dwarf Planets Ceres and Pluto

Now I’m not a planetary astronomer, but like you, I’m excited by any kind of space exploration, and this year the NASA missions, Dawn and New Horizons, will give us the closest and most detailed views of dwarf planets yet.

What is a “dwarf planet,” you ask? Excellent question. Until about ten years ago, astronomers usually referred to small planet-like objects that were not satellites (moons) as “planetoids.” In some ways, they resembled the eight more massive planets in our solar system as well as Pluto, which had a borderline status. Astronomers discovered Charon, Eris (previously called 2003 UB313), and Ceres, and they expected to discover many more, likely rapidly expanding the ranks of our esteemed class of planets. Either they all had to be included, or a clear classification system would have to be determined and Pluto would be reclassified.

Courtesy: IAU

Courtesy: IAU

At the International Astronomical Union (IAU) meeting in Prague in 2006, astronomers opted for the latter in Resolution 5. They demoted poor Pluto, but I think they did the right thing. (I was working in Heidelberg, Germany at the time, and if I’d known how historic this IAU meeting would be, maybe I would’ve tried to attend!) The IAU’s defines a dwarf planet as “a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.” The criterion (c) is the important one here, because it means that the object has not become gravitationally dominant in its orbital zone, which is the case for Pluto and the other planetoids beyond Neptune and for Ceres, the only dwarf planet in the asteroid belt between Mars and Jupiter. These are contentious issues, and the debate even made it into the New Yorker. But let’s be clear: these things are small, and they’re all less massive than Earth’s moon.

We don’t know as much about dwarf planets as we do about the planets in our system, so let’s go exploring! What do these new space missions have in store for us?


In 2007, NASA launched the Dawn spacecraft to study Ceres up close. A couple days ago, two centuries after Sicilian astronomer Father Giuseppe Piazzi discovered Ceres, Dawn became the first spacecraft to orbit a dwarf planet. As the deputy Principal Investigator Carol Raymond put it on Friday, this is an “historic day for planetary exploration.” Jim Green, NASA’s Planetary Science Division Director, says that with Dawn, we are “learning about building blocks of terrestrial planets in our solar system.”

Dawn has obtained excellent detailed images already, as you can see in the (sped up) animation below.



The pair of bright spots in a crater stand out, and astronomers are trying to figure out what they are. They might be an indication of geological activity on it’s changing surface. Ceres has a rocky core and an ice layer, and it’s also possible that these are reflective patches of ice that have been exposed by space rocks falling in and striking the surface. For more information, check out this blog post by Emily Lakdawalla and these articles in the LA Times and Wired.

As Dawn uses its propulsion systems to reshape its orbit and get closer views, astronomers expect to learn more about those spots, look for plumes, and examine the surface for strange craters or other distinguishing features. The spacecraft will later turn on its spectrometers and determine which minerals are present and how abundant they are.


NASA launched New Horizons in 2006, and it had much farther to travel to reach Pluto. In January, NASA announced that New Horizons is making its approach to the erstwhile planet, though it’s still about 200 million kilometers away. Mark your calendars: it will fly by Pluto (as it will be traveling too fast to orbit) on 14th July, and at a distance of only 13,000 km, New Horizons’ instruments will obtain the best images yet of it. For more information, check out this article by Jason Major in Universe Today and Phil Plait in Slate.

Distant image of Pluto by New Horizons. Credit: NASA/Johns Hopkins APL/Southwest Research Institute.

Distant image of Pluto by New Horizons. Credit: NASA/Johns Hopkins APL/Southwest Research Institute.

A couple ago, leaders in planetary astronomy highlighted the importance of Dawn and New Horizons in their Decadal Survey. I think both space missions will turn out to be worthwhile, and let’s stay tuned to see what they discover over the next few months.