Human History and Distant Orbits

Human History and Distant Orbits[1]

Human history has always been linked to the influence of distant orbits.

Every astronomer has had the annoying experience of being introduced as an “astrologer”. Students often ask for permission to take one of my “astrology” courses. We then have to explain that astronomy is the study of the universe beyond Earth, while astrology is the belief that this universe controls our lives. There’s no good reason to hold that the position of the planets at your birth decided your personality or life path. But it is true that planetary motions have strongly influenced human history and nature.

For several million years, climate changes in Africa repeatedly shaped our evolution. In large part, these climate swings were forced by a complex series of rhythmic oscillations in Earth’s orbit and spin—oscillations that stem largely from the perturbing gravitational influence of Jupiter, Saturn, and the Moon.

Several evolutionary breakthroughs came about during such periods of extreme, modified climate. Upright posture, which freed up our inventive hands; a rapid increase in brain size; and the use of fire, allowing a meat diet that spurred further increase in brain size—scientists have linked all these to episodes of rapid climate alteration. These great leaps forward transformed us from just another species to one with the abilities that enabled the science and technology through which we’ve uncovered our own natural history.

Later we left Africa and peopled the world, our path set by climate-driven changes in sea level such as the one that opened up the Bering Strait land bridge to North America. Seven thousand years ago a phase of stable sea level coincided with the first large coastal settlements and the rise of complex societies. The origin of many sophisticated technologies and the symbolic language to pass them down also seem to have arisen in response to climate-caused survival threats.

Now in a twist, some of our technology threatens the climate we depend on to survive. Astrology will not save us, but astronomy might. By widening our scope of knowledge and improving our modeling capabilities, planetary exploration is crucial for understanding climate and responding effectively to our current challenges.

Our exploration of the Solar System owes its own path to fortuitous planetary positions. Every 175 years the outer planets arrange themselves perfectly for a “grand tour” mission that can ricochet from one gas giant to the next. One such rare alignment came in the 1970s, when we’d just barely developed the necessary technology to launch the pair of Voyager spacecraft. Another important lineup occurred soon after astronomers discovered Pluto’s moon Charon in 1978 (no doubt causing astrologers to redo their charts).

It’s lucky we found Charon when we did. Just two years later, the plane of its orbit lined up precisely with Earth to create a 5-year-long season of Pluto-Charon eclipses. This won’t happen again for more than a century. More importantly, these events and subsequent studies, along with the puzzling nature of Neptune’s moon Triton, seen in Voyager’s final pass in 1989, helped motivate those who agitated for a dedicated Pluto mission, culminating in last year’s historic flyby.

Maybe a species that has colonized its home world would have emerged on Earth even if the Solar System didn’t work the way it does. Once here, maybe we were bound to explore our neighboring worlds. But route and timing were dictated from above. The planets have indeed always ruled us.

[1] See David Grinspoon, “Thank Our Lucky Planets,” Sky and Telescope (132, 5, November 2016), p. 16. David Grinspoon is an astrobiologist and senior scientist at the Planetary Science Institute. His book, Grinspoon, David Harry (2016). Earth in Human Hands: Shaping Our Planet’s Future. New York, NY: Grand Central Publishing. [LOC: 2016025817] is worth a read. Follow him on Twitter at @ DrFunkySpoon.


Percival Lowell

Percival Lowell—A Life in Astronomy[1]

Percival Lowell was one of the most curious characters in the history of astronomy. He produced a legacy of important work, and established the desert southwest as an astronomical mecca.

In the beginning of the movie It’s a Wonderful Life, angel wannabe Clarence Odbody is called to help downtrodden George Bailey realize his life was not a waste of time, but rather one of importance and meaning. Clarence gets his point across by showing George how much differently the future would have played out if George had never been born. George, for example, isn’t around to save his brother Harry from drowning during a boyhood accident, and thus Harry is not around to save the lives of a transport of soldiers during World War II. The story goes on, and George finally realizes what a significant impact he had on so many lives.

This narrative is an approach that paleontologist Stephen Jay Gould used to illustrate his contingency theory. Essentially, any circumstance is the result of a number of pre-existing factors, and if one of those factors is changed, the future would be altered. This exercise in what might have been can be fruitful in considering how Percival Lowell impacted astronomy as we ponder the 100th anniversary of his death this past November.

Growing up Lowell

Lowell was born into an elite Boston family known for its accomplishments in areas ranging from commerce to academia. The family produced more than its fair share of businessmen, judges, writers, industrialists, ministers, philanthropists, and architects. The family motto, occasionem cognosce, means “know your opportunity,” and family members took this to heart in pursuing excellence. To be a Lowell meant not merely relying on the family wealth to sail through life. Instead, family members were expected to assume leadership roles, whether in their chosen vocation or community activities.

Percival arrived in 1855, the eldest of seven children. As Percival’s brother, Abbott, noted in his biography of Percival, their father instilled in the children the Lowell work ethic: “Somehow he made us feel that every self-respecting man must work at something that is worthwhile, and do it very hard. In our case it need not be remunerative, for he had enough to provide for that; but it must be of real significance.” So was developed the drive and fortitude that would carry Percival through his life, and the passion that would feed his desire to succeed and “plow his own furrow,” as Abbott put it.

Percival studied mathematics at Harvard University and then worked at a desk for eight years, overseeing many of the financial aspects of the family’s mills and other interests. But for a man instilled with a passionate spirit of adventure, discovery, and wanderlust, this arrangement wouldn’t last. He soon bolted overseas, spending the better part of 10 years in Korea and Japan. There he studied the traditions, values, and religious practices of Eastern cultures. In a pattern he would repeat in later years in the field of astronomy, he immersed himself in these studies and then wrote several books articulating his observations and conclusions. His orientology work alone was a contribution of real significance,” as Percival’s father expected of the family, but remains today a footnote in light of Lowell’s far more famous work in astronomy.

Lowell Observatory

Astronomy was one of Percival’s many interests during childhood. Later in life, he recalled, “Donati’s Comet of 1858 was my earliest recollection. I can still feel the small boy inside me, halfway up a winding staircase, gazing with all his soul where the stranger stood.” For Percival’s 15th birthday, his mother bought him a 2 ¼  -inch refracting telescope that he used to observe the polar ice caps of Mars from the roof of the family’s home in Brookline, Massachusetts. For his last visit to the Far East, he carried along a newly purchased 1892-model Clark refracting telescope. All of this was prelude to his decision in 1893 to build his own observatory to study Mars, in particular the canali made famous by Italian astronomer Giovanni Schiaparelli.

On May 28, 1894, Lowell arrived in Flagstaff, Arizona, symbolically kicking off the final stage of his life, one that would bring him mixed doses of admiration (from the public), ridicule (mostly from the scientific community), fame, and notoriety. The 39-year-old self-taught astronomer entered the field with his typical gusto and would never leave it, even when death called on November 12, 1916. The work of the people he hired, the projects he started, and the philosophies he established at his observatory would long outlive him and establish him as an astronomical visionary. Lowell made at least eight different contributions that had far-ranging impact.

First, Lowell committed himself to building his own observatory to study astronomy and supported this decision by paying all the expenses. He chose to establish this facility independent of any university or existing observatory so that he could maintain control over all decisions, including the focus of research, purchase of equipment, and hiring of staff. In his will, he stipulated, “The Lowell Observatory shall at no time be merged or joined with any other institution.” Future observatory leaders maintained this arrangement, and the private, independent nature of the observatory, with no overarching umbrella organization over it, continues to be one of its outstanding features.

Lowell’s commitment to building his observatory in Flagstaff had the unanticipated impact of establishing the town as a center for scientific research. Prior to this, early surveyors through the area made a handful of scientific observations as part of their efforts to establish travel routes. Later, dedicated expeditions led by the likes of John Wesley Powell explored northern Arizona. But scientific study of the area didn’t begin to mature until Lowell built his observatory, the first permanent scientific establishment in an area that now boasts dozens.

Second, toward the end of his life, Lowell established a trust to financially support his observatory in perpetuity. He devised an organizational structure patterned after his family’s educational foundation, the Lowell Institute, in which a sole trustee manages the funds. Again in his will, he stated, “Ten percent of the net income shall be added yearly to the principal, and the balance of the net income shall be used for carrying on the study of astronomy, and especially the study of our Solar System and its evolution.” This nest egg would prove crucial to the survival of the observatory in future years, first as one of its only sources of income, and later to help balance the ledger sheets during times of reduced outside funding. In recent years, observatory leaders leveraged this trust to help complete construction of Lowell’s Discovery Channel Telescope in 2012.

Third, Lowell hired some remarkable astronomers who would give the observatory credibility in scientific circles. The first was Andrew Douglass (1867-1962), who helped Lowell found the observatory. Years after being dismissed due to his criticism of Lowell’s scientific practices, he founded Steward Observatory and established the science of dendrochronology, both at the University of Arizona. The Slipher brothers, Vesta Melvin (V. M.) and Earl Carl (E. C.) spent their entire professional careers at Lowell. Both served as director at some point but are remembered mostly for their scientific contributions. V. M, (1875¬1969) pioneered spectrographic techniques that allowed him to, among other things, measure the radial velocities of several so-called spiral nebulae, critical to unraveling the expanding nature of the universe. E. C. (1883-1964), on the other hand, was a pioneer of planetary photography and laid the groundwork for techniques such as image stacking.

Fourth, Lowell recognized, and located his observatory based on, the need for good atmospheric conditions and dark skies for optimal astronomical observing. In his book Mars and Its Canals, he wrote, “Not only is civilized man actively engaged in defacing such part of the Earth’s surface as he comes in contact with, he is equally busy blotting out his sky. In the latter uncommendable pursuit he has in the last quarter of a century made surprising progress. With a success only too undesirable his habitat has gradually become canopied by a welkin of his own fashioning, which has rendered it largely unfit for the more delicate kinds of astronomic work. Smoke from multiplying factories by rising into the air and forming the nucleus about which cloud collects has joined with electric lighting to help put out the stars.”

Not coincidentally, his chosen home from which to observe, Flagstaff, was in its early days nicknamed the Skylight City because of the brilliance of its stars against the dark background of sky. Thus was born the community’s interest in dark skies, increased by the presence of Lowell and other observatories that were later established in the area. In the 1950s, at the prodding of Lowell astronomers, Flagstaff community leaders enacted the world’s first legislation concerning light pollution, and in 2001 the International Dark-Sky Association recognized Flagstaff as the world’s first International Dark Sky City.

Far-reaching research

The next three contributions by Lowell focus on research programs that he started. First is the study of Mars, in support of his belief of intelligent life inhabiting that planet Lowell was not the first scientist to observe the so-called martian canals—linear features on the planet’s surface—and he was not the first person to suggest they indicated the presence of intelligent life, but he was certainly the most outspoken on this front, writing books and magazine articles and stimulating standing-room-only crowds with compelling speeches. Contrary to many popular accounts, Lowell and others who believed in the superficiality of the canals did not accidently mistranslate Giovanni Schiaparelli’s term, canali (meaning “channels,” a word implying of natural cause) to canals (implying artificiality). Rather, Lowell intentionally used the latter name to support his idea that some form of intelligent life had built them.

Furthermore, Lowell did not speculate much on the exact nature of this supposed life, except that it would likely be much larger than that on Earth due to Mars’ weaker gravitational pull. In his book Mars, Lowell wrote, “The existence of extra-terrestrial life does not involve ‘real life in trousers,’ or any other particular form of it with which we are locally conversant. Under changed conditions, life itself must take on other forms.” With his research and popular accounts, Lowell built a consciousness about life in the universe. While most scientists dismissed his ideas, the general public remained intrigued, thanks largely to subsequent writers—particularly in the burgeoning genre of science fiction—and science popularizers who, often indirectly, built stories based on Lowell’s ideas. Even today, many news stories about life or water on Mars include some mention of Lowell. Last year, [2016] for instance, in reporting about NASA’s discovery of water on Mars, Flagstaff’s newspaper, the Arizona Daily Sun, led with the headline “Was Uncle Percy right after all?”

Another research program Lowell started was V. M. Slipher’s observations of spiral nebulae. Lowell believed these to be protoplanetary systems, and in his theory of planetology (the evolution of planets), the gases in these nebulae would eventually coalesce to form gas planets. Lowell thus directed Slipher to observe their spectra to see if they matched those of the gas giants like Jupiter and Saturn, which would prove the link between the nebulae and planets. The spectra did not match, but the exercise allowed Slipher to detect the incredibly high redshifts of the nebulae (which astronomers now identify as galaxies).

The third research program Lowell started was a search for Planet X, a hypothetical ninth planet. While astronomers later concluded that this planet, as defined by Lowell, doesn’t exist (Lowell was looking for a large planet that was perturbing the orbits of Uranus and Neptune), it did lead to the discovery of Pluto 14 years after Lowell died.

In all three of these research programs, Lowell was fundamentally wrong or made assumptions that were inaccurate. Yet his conviction to carry out the programs led to other results and often to unexpected discoveries. Furthermore, by deciding on what research to pursue, without interference from outside concerns, Lowell set the standard by which the observatory would be operated, a legacy that continues today.

The last of Lowell’s significant contributions was the popularization of science. He captured his sentiments on the subject in Mars and Its Canals: “To set forth science in a popular, that is, in a generally understandable, form is as obligatory as to present it in a more technical manner. If people are to benefit from it, it must be expressed to their comprehension.” Soon after Lowell established his observatory, he invited Flagstaff residents to come and peer through the telescopes, and he became a popular speaker around the country. His engaging style captivated audiences and helped establish him as a promoter of science, a role at which many of his fellow astronomers scoffed. He was in many ways the Carl Sagan or Neil deGrasse Tyson of his time, a scientist who stepped into the spotlight to explain science.

As a result of Lowell’s efforts, the observatory later established education as one of its core mission components and through the years has reached millions of people during traditional on-site visits (97,000 people visited the observatory in 2015), through off-site programs (such as the Navajo-Hopi Astronomy Outreach Program, developed by astronomers Deidre Hunter and Amanda Bosh and now in its 21st year), and via media such as television, radio, and the internet (Disney, Sagan, Bill Nye the Science Guy, Leonard Nimoy, and many others have filmed educational programming at Lowell).

A wonderful life

So what was Lowell’s impact on astronomy, given the benefit of a century of hindsight? If we try to imagine, in the spirit of George Bailey, what astronomy would look like today if Percival Lowell had never entered the field, Lowell’s impact was substantial. Who knows what the science landscape of Flagstaff would look like? There would be no Lowell Observatory and likely no Flagstaff Station of the U.S. Naval Observatory, which was established in the 1950s largely because of the presence of Lowell. Beyond Flagstaff, Douglass likely never would have come to Arizona and thus not established Steward Observatory, which, along with Lowell Observatory, was critical to establishing Arizona as a center for astronomical studies—one that today brings in a quarter of a billion dollars annually to the economy.

Without Lowell, who knows where Douglass and the Sliphers would haveworked, and what they would have studied? Without Lowell’s direction, V. M. Slipher likely would not have mastered use of the spectrograph and detected the recessional velocity of the spiral nebulae. Astronomers would have eventually made these discoveries, but probably not for years. The same goes for Pluto. Without Lowell’s searches that inspired the discovery of Pluto, this small body would not have been discovered until much later, perhaps not until the 1990s, and then possibly would not have been classified as a planet. In fact, the course of planetary research and the search for life in the universe would have played out much differently. In addition, Mars likely would not have been nearly as popular a topic for science fiction writers and, later, moviemakers. The list goes on, but these are a few of the more salient examples.

Lowell craved the acceptance of his ideas by the fraternity of astronomers of his generation, but would never realize it during his lifetime. He was dismissed by many because of his apparent failings in the field, but his vision and conviction resulted in a number of exceptional discoveries and events that would fundamentally impact our understanding of the cosmos. In many cases, the results were unintentional. Yet intentional or not, they came about because of Lowell’s characteristic take-action mentality and willingness to financially back programs in which he believed. Lowell wanted to make a positive impact in his field and had the conviction to follow through with his efforts, even in the face of occasional strong opposition. And with a century of hindsight, we can say that he achieved this goal and left quite an imprint on the field of astronomy.

[1] See Kevin Schindler, “Percival Lowell—A Life in Astronomy,” Astronomy (45, 4, April 2017). Pp. 44-49

Collecting Cosmic Dust

Collecting Cosmic Dust[1]

The image [left] shows cosmic dust particles which can make their way to Earth’s home. This grain, shown through a scanning electron microscope, is about 8 micrometers across—a micrometer is 1/30th the width of a human hair.


You might not know that a small percentage of household dust is extraterrestrial. Some small fraction of 1 percent of the dust consists of interplanetary dust particles, grains of material less than 100 micrometers across that have “floated” down gently through Earth’s atmosphere without burning up.

In 1951, the great astronomer Fred Whipple first proposed this mechanism as a way to deliver cosmic dust to Earth’s surface. Planetary scientists have since found abundant examples of this dust, which originates from asteroids and comets—particularly collisions between small bodies in the inner Solar System and in the Kuiper Belt—and from grains originating in the interstellar medium.

No one knows exactly how much cosmic matter falls to Earth’s surface. Planetary scientists estimate the number lies within the range of dozens of tons per day. The estimate arises from studying the abundances of rare metals believed to be extraterrestrial in origin found in polar ice cores.

So remember the next time you empty that vacuum bin into the trash: You’re undoubtedly tossing out a few very tiny particles from far beyond your home. Astronomy really is an interest you can never quite fully escape.

[1] David J. Eicher, “Collecting Cosmic Dust,” Astronomy (45, 4, April 2017), p. 8

Fate of the Solar System

Fate of the Solar System[1]

On human timescales, it’s easy to think of the Solar System as stable and unchanging. But over the next 6.5 billion years, as the Sun swells into a red giant and goes on to become a white dwarf, the invisible plane in which all the major planets orbit will undergo radical alterations. Mercury will evaporate into the Sun, and Pluto will develop lakes on its surface. There’s a chance life could arise in liquid seas on distant moons, that two or more of the inner planets could collide, or that planets could be flung right out of the Solar System. For Earth in particular, all hell will break loose, with our beloved planet becoming a cinder devoid of all life and possibly destroyed altogether.

Only time separates us from this destiny. Fortunately, there’s lots of it.

In the end, all we know is that the Solar System has been stable for a long time and may remain so for a long time yet, but if and when it becomes unstable, anything could happen. “You might find planets scattering all over the place,” says Robert Smith (University of Sussex, UK). “Which planets would do what is anybody’s guess.”

Konstantin Batygin (Caltech) takes a philosophical stance. “The Solar System, despite its seeming regularity and immutability, is actually an unpredictable beast.” He likens it to a double pendulum, an ostensibly simple dynamical system that can exhibit unpredictable behavior. Change an initial condition even slightly, and the long-term evolution of the double pendulum—or the Solar System—can change incalculably. “We have to stop thinking of the evolution of the Solar System as one thread that will take us somewhere,” he says. “We have to start thinking about it as a statistical ensemble of a billion threads, all of which are pinched together by today. The Solar System could take any one of them, and we can’t predict exactly which.

Below is a time line of the evolution of the Sun. After 6 billion years, the Sun experiences gradual warming.

As time goes on by 10 billion years the Sun will become a red giant. It will begin to collapse toward a white dwarf leaving behind a planetary nebula. After 12.5 billion years after it first ignited, our once-massive star will have a mass about half of today’s and a size not much larger than Earth’s present size. The Sun will remain bright—about 35 times as luminous as today—and its surface temperature will be a ferociously hot 120,000  It will also be extremely compact, and the leftover heat from fusion will take billions of years to leak to the surface. The size and density of white dwarfs mean that as a white dwarf the Sun will have an incredible density: One teaspoon of its matter would weight about a metric ton (2200 lbs. on today’s Earth).

Below a series of figures will show the proposed evolution of the Solar System.

According to solar-evolution models by K.-P. Schröder (U. of Guanajuato, Mexico) and Robert C. Smith (U. of Sussex, UK), our Sun as it expands…

…into a red giant over the next 7.5 billion years, will first engulf Mercury and Venus…

…and finally, Earth. Mars will have drifted out far enough to escape the Sun’s grasp, but it will remain a dead world, the last of the inner planets.

Our Sun is an average start about a third of the way through its lifetime. For most of a star’s existence, its color and brightness depend almost entirely on how much hydrogen it was born with. Stars much more massive than our Sun are hot, bright, and blue-tinted; stars less massive than ours are comparatively cooler, fainter, and red-hued.

As seen above, a scatter plot of color (temperature) versus absolute brightness (luminosity) shows that most stars lie along a broad swath called the main sequence. (Our Sun is about midway along this arc.) Main-sequence stars are busy burning hydrogen in their cores. Red giants and supergiants, for their part, have stopped hydrogen core-burning. Instead, they host vast envelopes of gas that surround nuclear shell-burning layers around an inert, compact core.

Plots like that seen here are called Hertzsprung-Russell diagrams after the two astronomers—one Danish and one American—who independently developed them in the early part of the last century. Mainstays of modern astronomy, H-R diagrams have greatly aided astronomers in teasing out the secrets of stellar evolution.

Despite in many cases truly astronomical longevity, all stars must die, and their initial mass largely determines their fate. Late in their lifetimes, stars that end up with cores of about 1.4 times the mass of our Sun or less will, after burning up the last of their thermonuclear fuel, become white dwarfs. That’s our own star’s destiny, far off in the future. By then it will have shrunk to not much larger than Earth.

Those stars, whose late-life cores weigh between roughly 1.4 and 3 times the Sun’s mass, will, at some sudden moment, cataclysmically explode in a supernova and wind up as neutron stars. The size and density of these objects make white dwarfs seem huge and practically porous in comparison: A teaspoon of a neutron star, which is only 10 to 20 kilometers across, would weigh a billion metric tons.

Finally, those stars with cores over 3 times our star’s mass will, after going supernova, condense into black holes.

[1] See Peter Tyson, “Written in the Star,” Sky and Telescope (October 2017), pp. 22-29

Solar Eclipse Next Visible in San Angelo

Solar Eclipse Next Visible in San Angelo

Surely, you won’t be at ASU in 2024! However, it is just seven years until the next total eclipse will be visible in Texas. No, it won’t come directly over San Angelo, but it will be totality over San Antonio. Austin, and Dallas.

This eclipse will not actually be a total eclipse. The Moon will be at its closest distance to Earth on April 8, 2024 (12:15 pm). Therefore, it will not block out the entire Sun. A ring of the Sun will be visible. Such an eclipse is called an annular eclipse, as shown in the image at left. Because the Moon occludes so much of the Sun at San Angelo, only a crescent of the Sun will be visible at maximum. You can see an animation of what will be seen by going to this link.

What will the path of the eclipse be? It will travel across Mexico, reaching maximum at Mazatlan, into the state of Coahuila, an on to the northeast crossing the cities in Texas listed above. Below is a map of the eclipse path. The blue arrow references San Angelo, where we will have a 97% maximum eclipse, lasing almost 2 hours, 40 minutes from first contact to third contact.









Antares’ Image

Best Ever Image of Another Star’s Surface And Atmosphere[1]

Using ESO’s Very Large Telescope Interferometer astronomers have constructed the most detailed image ever of a star — the red supergiant star Antares. They have also made the first map of the velocities of material in the atmosphere of a star other than the Sun, revealing unexpected turbulence in Antares’s huge extended atmosphere. The results were published in the journal Nature.

To the unaided eye the famous, bright star Antares shines with a strong red tint in the heart of the constellation of Scorpius (The Scorpion). It is a huge and comparatively cool red supergiant star in the late stages of its life, on the way to becoming a supernova.

A team of astronomers, led by Keiichi Ohnaka, of the Universidad Católica del Norte in Chile, has now used ESO’s Very Large Telescope Interferometer (VLTI) at the Paranal Observatory in Chile to map Antares’s surface and to measure the motions of the surface material. This is the best image of the surface and atmosphere of any star other than the Sun.

The VLTI is a unique facility that can combine the light from up to four telescopes, either the 8.2-metre Unit Telescopes, or the smaller Auxiliary Telescopes, to create a virtual telescope equivalent to a single mirror up to 200 metres across. This allows it to resolve fine details far beyond what can be seen with a single telescope alone.

“How stars like Antares lose mass so quickly in the final phase of their evolution has been a problem for over half a century,” said Keiichi Ohnaka, who is also the lead author of the paper. “The VLTI is the only facility that can directly measure the gas motions in the extended atmosphere of Antares — a crucial step towards clarifying this problem. The next challenge is to identify what’s driving the turbulent motions.”

Using the new results the team has created the first two-dimensional velocity map of the atmosphere of a star other than the Sun. They did this using the VLTI with three of the Auxiliary Telescopes and an instrument called AMBER to make separate images of the surface of Antares over a small range of infrared wavelengths. The team then used these data to calculate the difference between the speed of the atmospheric gas at different positions on the star and the average speed over the entire star. This resulted in a map of the relative speed of the atmospheric gas across the entire disc of Antares — the first ever created for a star other than the Sun.

The astronomers found turbulent, low-density gas much further from the star than predicted, and concluded that the movement could not result from convection, that is, from large-scale movement of matter which transfers energy from the core to the outer atmosphere of many stars. They reason that a new, currently unknown, process may be needed to explain these movements in the extended atmospheres of red supergiants like Antares.

“In the future, this observing technique can be applied to different types of stars to study their surfaces and atmospheres in unprecedented detail. This has been limited to just the Sun up to now,” concludes Ohnaka. “Our work brings stellar astrophysics to a new dimension and opens an entirely new window to observe stars.”

[1] See “Best Ever Image of Another Star’s Surface And Atmosphere,”Astronomy Now (28 August 2017)

Voyager Probes

Voyager Probes, Humanity’s Calling Cards[1]

Credit Elwood Smith


In the shadow, one might say, of the Great American Eclipse, a major anniversary in the history of space exploration—and indeed cosmic consciousness—is being celebrated.

It was 40 years ago, on Aug. 20 and Sept. 5, 1977, that a pair of robots named Voyager were dispatched to explore the outer Solar System and the vast darkness beyond.

What resulted was nothing less than a reimagining of what a world might be and what strange cribs of geology and chemistry might give rise to life in some form or other.

It was a real-life Star Trek adventure, but the crew stayed home, communicating with their two spacecraft through a billion-mile bucket brigade of data bits.

New computer programs went one way, and data—including scratchy photos of new landscapes and the whispering moans of interplanetary plasma fields—came back the other way. All of it was being carried out by a robot brain with the memory capacity of an old-fashioned digital watch.

The spacecraft had been designed to make what scientists called the Grand Tour, taking advantage of a once-every-175-year planetary alignment. Voyager 1 and Voyager 2 were to use the gravity of the outer planets to slingshot from Jupiter to Saturn, and to Uranus and Neptune, and then beyond the edge of the Sun’s domain into interstellar space.

In the end, only half the tour—to Jupiter and Saturn—was actually approved. But the Voyager crew packed for a much longer journey. When they lifted off 40 years ago, the two spacecraft carried golden records inscribed with pictures and sounds from Earth, greetings from President Jimmy Carter and instructions on how to play it all.

The Voyagers would observe the universe, and give something back to whoever might one day find them.

The robot emissaries cruised the Solar System through presidential administrations, wars and scandals, and the Challenger disaster, which happened as Voyager 2 was pulling away from Uranus.

At every planetfall, the crew members, a little older and a little grayer each time, reconvened at the Jet Propulsion Laboratory in Pasadena, Calif., for a weeklong marathon of discovery, a circus of science on the fly.

With imagery returned by probes, what had been fuzzy dots in the world’s biggest telescopes bloomed into worlds.

Back on Earth, some theoreticians claimed to be homing in on a putative theory of everything, an Einsteinian dream of an equation simple enough to be inscribed on a T-shirt.

But in space, scientists were finding that such theories were no help against nature’s endless capacity to invent and surprise. Each new world revealed by the Voyagers was a head-scratcher.

Once upon a time, it was presumed that the moons of the outer planets, so far from the Sun and so close to the origins of the Solar System, would be boring ice balls, geologically and in every other way dead.

But then Voyager 2 spotted volcanoes spraying fountains of sulfur from the surface of Jupiter’s innermost moon, Io. On close inspection, Saturn’s rings—the jewels of the Solar System—dissolved into 10,000 grooves, like a vinyl record’s, braided, kinked, and patrolled by tiny moonlets.

Voyager 1 plumbed a fat, smoggy atmosphere of Titan, where nitrogen and methane rains fall on a frozen slush pile of hydrocarbons and oily lakes, and then headed off toward interstellar space.

Voyager 2 cruised on to Uranus, mysteriously tipped on its axis and surrounded by rings that make it look like a bull’s eye.

The probe passed the restful methane blue of Neptune, besmirched by a dark spot, and its moon Triton, an ice rock flowing like soft ice cream with geysering nitrogen.

I’ve never had more fun as a science writer than during those weeklong encounters in Pasadena, when my colleagues and I—a little older and grayer ourselves, humbler but no wiser about the tricks that nature might be up to out there in the realm of dark and ice—gathered to watch the scientists watch their new worlds.

The television screens in the press room showed the latest images as they came in from the Voyager spacecraft. We had the same view as the scientists.

If on some distant world there had been a sign saying “Drink Coke,” or a pyramid, what we liked to call “the press room imaging team” would have had a chance to see it first.

Casting aside years of learned reserve and an addiction to speaking and writing in the passive voice, Voyager scientists had to parade to daily news briefings and venture explanations that they knew they would have to take back a few days later about things they (and we) had seen for the first time only a few hours before.

Part of the joy of “The Farthest: Voyager in Space,” a documentary aired on PBS on August 12, 2017, was reliving those moments of bafflement and intellectual ambition.[2]

It was at the Voyager encounters that I first got to know my colleagues in the newspaper business, and learned by going out to dinner with them that they could drink me under the table before the appetizers arrived.

Other nights were spent in the bluesy, smoky company of science writers and planetary astronomers listening to the space ballads of Jonathan Eberhart, the late correspondent for Science News and a well-known folk singer. A rock band named for a feature of Titan, The Titan Equatorial Band, played at parties and gatherings.

The music stopped the morning after Voyager 2 passed by Uranus, on Jan. 28, 1986, when the Space Shuttle Challenger blew up with seven astronauts aboard, including Christa McAuliffe, the teacher in space.

That morning the televisions in a hushed newsroom at J.P.L. had Uranus on one screen and the Y-shaped cloud of the explosion on the other. By noon, my newspaper friends had packed their bags and headed for Houston or Cape Canaveral.

Voyager 2 went on. By the time it reached Neptune—the gatekeeper of our planetary realm, now that Pluto doesn’t count—the engineers at J.P.L. had enlisted antennas around the Earth to listen in unison, catching the trickle of data bits flowing from almost three billion miles away.

Chuck Berry, whose music was included on the spacecraft records, came to the lab to play for a Voyager farewell party.

There would be one last act. In 1990, as it ascended the void, Voyager 1’s crew commanded it to turn its cameras backward and snap a family portrait of the worlds it was leaving forever behind.

The Earth appears on this picture as the famous “pale blue dot” in a wash of scattered sunlight, a “mote of dust suspended in a sunbeam,” as the astronomer and cosmic sage Carl Sagan later described it.

Voyagers’ cameras are now turned off, but the probes continue to report back on the conditions in deepest space.

In October 2012, magnetic field and cosmic ray measurements indicated that Voyager 1 had reached the edge of the magnetic bubble that the Sun extends like an umbrella over the planets, blocking outside radiation.

Voyager 1 was in interstellar space, the first human artifact to escape the Solar System. It and its twin will go on circling the galaxy, long after it has ceased speaking to us.

In the fullness of galactic time, the Voyagers may be found, but by then the human race may be long extinct. The Voyager record might be the only physical remnant, the last lonely evidence that we, too, once lived in this city of stars, among these islands of ice and rock.

Back then, we were looking forward to an exploration of space that would go on forever. It was magic, and we were all on the spaceship.

[1] Dennis Overbye, “A Reverie for the Voyager Probes, Humanity’s Calling Cards,” New York Times (August 21, 2017). A version of this article appears in print on August 22, 2017, on Page D3 of the New York edition with the headline: “The Voyagers, Humanity’s Calling Cards.”

[2] Correction: August 24, 2017

An article on Tuesday about the accomplishments of the Voyager 1 and Voyager 2 space missions misstated the date on which the PBS documentary “The Farthest” was broadcast. It was shown Wednesday night; it had not already aired at the time the article was published.