Streaks on Martian Hillsides May Be Dry Flows

Streaks on Martian Hillsides May Be Dry Flows[1]

This inner slope of a Martian crater has several of the seasonal dark streaks called “recurrent slope lineae,” or RSL, that a November 2017 report interprets as granular flows, rather than darkening due to flowing water. The image is from the HiRISE camera on NASA’s Mars Reconnaissance Orbiter. Credits: NASA/JPL-Caltech/UA/USGS

Scientists now seem to think the dark streaks or “recurrent slope lineae” (RSL) from Mars’ craters to be more likely related to flows of sand instead of flowing water (Clark, 2017, para. 1-2).  The streaks observed on Mars were discovered in 2011 from NASA’s Mars Reconnaissance Orbiter (Clark, 2017, para. 4).  The confusing part was that hydrated salts (perchlorates) were found around the flows which could lower the freezing point of brine, a salt and water mixture, leading to the assumption water could potentially survive in the cold temperatures/low air pressures (Clark, 2017, para. 6).  This is quite the opposite of the theory that Mars holds water and that instead Mars is very dry. The scientists conducted their analysis by looking at the slopes of 10 sites/151 flows using imagery from a high-resolution camera and comparing the results to what they know best, Earth (Clark, 2017, para. 12-13). By looking at the angles of the slopes, scientists deduced the stopping point was too similar to dunes on Earth instead of a more “gentle” ending caused by slopes full of liquid (Clark, 2017, para. 15).  The fact that the slopes are caused by sand instead of water is a very big deal, this could mean that simple microbial organisms may not exist as previously thought (Clark, 2017, para. 17).  The scientists still would like to conduct on-the-ground analysis to further their understanding because the question still remains, how did the flows begin in the first place (Clark, 2017, para. 17-18)?  By collecting imagery of the flows at different times of the day, may lead to a reduction in the knowledge gap behind the flows.

[1] Clark, Stephen, “Scientists Suggest Streaks on Martian Hillsides are Dry Flows,” Astronomy Now (November 26, 2017). Retrieved November 27, 2017, from


Earth Blocks Neutrinos

According to Deborah Byrd, Earth does block neutrinos. [1]

It used to be said that neutrinos were massless and would pass through anything. But in recent years, scientists have realized that these strange particles–some of which were formed in the first second of the early universe, and which travel at the speed of light – are only practically massless. And now it’s been proven experimentally, by scientists working with data at the IceCube detector at Earth’s South Pole, that very energetic neutrinos can, in fact, be blocked. Doug Cowen at Penn State University was a collaborator on the study. He said:

“This achievement is important because it shows, for the first time, that very-high-energy neutrinos can be absorbed by something—in this case, the Earth.”

The results of this recent experiment were published in the online edition of the peer-reviewed journal Nature on November 22, 2017[2].

At the highest energies, neutrinos will be absorbed by Earth and will never make it to IceCube. Image via IceCube Collaboration.

The IceCube detector is an array of 5,160 basketball-sized sensors frozen deep within a cubic kilometer of very clear ice near the South Pole. The detector made the first detections of extremely-high-energy neutrinos in 2013, but a mystery remained about whether any kind of matter could truly stop a neutrino’s journey through space. Cowen said:

“We knew that lower-energy neutrinos pass through just about anything, but although we had expected higher-energy neutrinos to be different, no previous experiments had been able to demonstrate convincingly that higher-energy neutrinos could be stopped by anything.”

A statement from these scientists said:

“The study … is based on one year of data from about 10,800 neutrino-related interactions, stemming from a natural supply of very energetic neutrinos from space that go through a thick and dense absorber: the Earth. The energy of the neutrinos was critical to the study, as higher energy neutrinos are more likely to interact with matter and be absorbed by the Earth.

Scientists found that there were fewer energetic neutrinos making it all the way through the Earth to the IceCube detector than from less obstructed paths, such as those coming in at near-horizontal trajectories.

The probability of neutrinos being absorbed by the Earth was consistent with expectations from the Standard Model of particle physics, which scientists use to explain the fundamental forces and particles in the universe.”

The Standard Model predicts that the probability that a neutrino interacts with matter increases with energy. Thus the recent results from IceCube agrees with the Standard Model, for energies up to 980 TeV. New physics could show up as deviations to this prediction at higher energies. Image via IceCube Collaboration.

[1] See Deborah Byrd, “Now We Know Earth Blocks Neutrinos,” in Earth|Human World (November 27, 2017). Accessed at Deborah Byrd created the EarthSky radio series in 1991 and founded in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.

[2] See  The IceCube Collaboration, “Measurement of the Multi-TeV Neutrino Interaction Cross-Section with Icecube Using Earth Absorption,” Nature (November 22, 2017), accessed at

New Pulsar Result and Dark Matter

New Pulsar Result and Dark Matter[1]

The nature of dark matter remains elusive, but astronomers are now one step closer to the answer.

Gamma rays from the Geminga and PSR B0656+14 pulsars cannot account for the positron excess measured by satellites in Earth orbit. Courtesy Miguel Mostafa (Penn State)

New results from an unconventional observatory in Mexico are bringing scientists one step closer to solving the dark matter mystery. They lend credence to the idea that some strange non-light-emitting particle is responsible for about 85% of the universe’s mass. This new observation casts serious doubt on the more conventional of two favored theories for the enigmatic excess of antimatter particles in space, leaving dark matter particles as the most likely explanation.

The origin of this mystery dates back to 2008, when the European PAMELA satellite first registered an unexpectedly high number of positrons in near-Earth space. Positrons can be thought of as positively charged electrons, or the antimatter counterparts to electrons. More recently, the Alpha Magnetic Spectrometer (AMS) experiment aboard the International Space Station has extended PAMELA’s finding, seeing roughly three to five times more positrons than scientists predicted.

Theorists came up with two logical explanations for the excess positrons. The more prosaic explanation says that rapidly rotating neutron stars (pulsars) are violently throwing off positrons and other subatomic particles, some of which make their way to Earth. But other scientists proposed a more exotic alternative: that very heavy dark matter particles pervading our galaxy mutually annihilate one another whenever they come into close proximity, self-destructing into a cascade of positrons and other elementary particles.

To test the pulsar hypothesis, an international team of scientists observed the sky with the High-Altitude Water Cherenkov (HAWC) Observatory. This is not your ordinary observatory with one or more astronomical telescopes. HAWC instead consists of 300 large water tanks stationed at an altitude of 13,500 feet in the southern Mexican state of Puebla.

HAWC indirectly picks up very-high-energy gamma rays, the highest-energy form of “light” yet detected in the universe. Each of these gamma rays packs the punch of roughly 10 million dental X-rays. When one of these gamma rays slams into an atom in Earth’s upper atmosphere, it smashes it apart into a shower of secondary particles that rain downward at near-light speed. These minuscule packets of energy pass through HAWC’s water tanks, producing simultaneous flashes of blue light known as Cherenkov radiation after Russian physicist Pavel Cherenkov, who co-discovered this bizarre form of light in 1934.

During observations taken from November 2014 to June 2016, HAWC clearly detected very high-energy gamma rays from the region around two relatively nearby pulsars in Gemini. The pulsars, known as Geminga and PSR B0656+14, are roughly 800 and 900 light-years away, respectively. Detecting such high-energy gamma rays from an extended region around these pulsars was itself a first, made possible by HAWC’s wide field of view. The problem, says team member Miguel Mostafá of Penn State University, is that “the observed flux of gamma rays is not enough to account for the positron excess.”

Each pulsar throws off positrons and electrons, which interact with surrounding photons from the early universe (the cosmic microwave background) to produce gamma rays in an extended region. Unfortunately, scientists cannot trace positrons around Earth back to their point of origin. Because positrons are electrically charged particles, they are deflected by magnetic fields permeating space, meaning they don’t come straight toward us. So HAWC measured the radial extent of gamma-ray emission from each pulsar, which is an indirect measurement of how many positrons are being produced and how fast these particles are moving away from their host pulsar.

The location of the pulsars used in the study; both are found in the constellation Gemini (the twins). Courtesy Jordan Goodman (University of Maryland)

“The gamma rays that we measure are a tracer for the electrons and positrons near the source. Using this, we can map out how fast the electrons and positrons are moving away from the source. Knowing the age and the distance of the pulsars, we can figure out if they can get here,” says HAWC principal investigator and U.S. spokesperson Jordan Goodman of the University of Maryland.

Putting this all together in a paper published in the November 17, 2017 issue of Science, the team concludes that the pulsars aren’t producing anywhere near enough positrons to explain the excess observed by PAMELA and AMS. Because the two pulsars are among the closest to Earth, it seems very clear that pulsars in general cannot account for the anomaly.

So if pulsars can’t explain the positron excess, what can? Some theorists have proposed supernova remnants and black hole jets. HAWC has detected these types of objects, but as Goodman explains, “Most are too far away and too young to send particles all the way to Earth.”

This leaves dark matter particle annihilation as the most likely explanation for the positron excess. This theory has been on the books for many years, and it’s not contradicted by any astronomical observations. Physicists have proposed a number of different types of dark matter particles, with a wide range of properties and masses. If annihilating dark matter is indeed responsible for the positron excess, the particles themselves would have whopping masses of about a thousand protons—approximately the mass of four or five uranium atoms.

Experiments at the Large Hadron Collider (LHC) in Switzerland and in underground laboratories around the world have yet to turn up direct evidence for dark matter particles. So although HAWC seems to have ruled out pulsars as the source of the excess positrons, their origin remains a mystery, as does the nature of dark matter.

[1] Robert Naeye, “New Pulsar Result Supports Particle Dark Matter,” Astronomy (November 16, 2017)

Finding Aliens

Finding Aliens[1]

While SETI has been around since 1960, it has yet to turn up any conclusive proof of intelligent life. The Wow! Signal, pictured at left, is one of the more mysterious signals received, but it has never repeated or been conclusively identified. However see SETI WOW!


The seven new Earth-sized planets around TRAPPIST-1, a red dwarf star 39 light-years away, renewed public speculation about extraterrestrials. Sixty years ago, the consensus among astronomers was that life’s earthly genesis was so convoluted and unlikely that we may be alone in the universe. For some physicists like Enrico Fermi, negative results from the Search for Extraterrestrial Intelligence (SETI) reinforced that pessimism. But these days, very few astronomers feel that way. The current groupthink is that the universe probably teems with life.

Early discovery steps in the near future will include spectroscopic space telescopes studying exoplanet atmospheres, offering the ability to study their composition. Earth’s habitable atmosphere exists solely because of photosynthetic plants exchanging carbon dioxide for oxygen. It would therefore be very encouraging if we detected oxygen around another world, as it may point the way toward life.

But what is life? Scientists can’t agree on a definition. Are viruses alive? They have no metabolism, they don’t feed themselves, and many biologists regard them as inanimate. Yet their RNA coding forces host cells to make lots of viral copies.

And does life begin through chemistry? If certain occurrences cause life to arise from non-living components, we want to know if it happens readily. In other words, is life easy? Or does it require extremely unlikely events?

A good argument for life being “easy” is that earthly life began almost as soon as it was possible. After the molten Earth cooled, there came a long period when asteroids and comets pummeled our surface. This violence stopped some 4 billion years ago. And bingo, the earliest fossils date from right then, within 200 million years of when it was first possible. That’s awfully quick.

A good counterargument, which makes the case for life being “hard,” is that life-origination or abiogenesis happened only once (that we know of). Every earthly creature is a descendant of that first ancestral organism. We know this because all life, from elephants to bacteria, share remarkable genetic similarities. They’re all made of amino acids and sugars with the same kinds of spirals or asymmetries. Amino acids can come with left- or right-handed twists, called chirality. But on Earth, life only uses amino acid molecules with left, handed twists, and is limited to a right-handed direction in all its sugars and DNA—the same as a corkscrew.

If life started a second time from scratch, it likely would show differences in such chirality. Now, there are at least 6 million species of bacteria (even if only 100,000 have had their genomes sequenced). But every single microbe, plant and animal we’ve examined is a descendant of that first life creation. The point: Why didn’t life start a second time, a third, or a hundredth? Four billion years have passed, and yet life originated only once. This suggests that abiogenesis is not easy, but hard.

So which is it? Fred Hoyle, who coined the term “Big Bang,” described an accidental birth of life as akin to a tornado sweeping through a junkyard and creating a jumbo jet. Supporting this, Francis Crick, the co-discoverer of DNA’s double helix, described the origin of life as “almost a miracle, so many are the conditions which would have had to have been satisfied to get it going.” (He wasn’t suggesting a spiritual origin, merely that the process is utterly baffling.) If abiogenesis is really so unlikely, then even given the immense size of the cosmos, it’s possible we’re the only example.

Of course, this assumes abiogenesis only happens accidentally. But what if advanced aliens are creating life, or if nature has immense innate intelligence? I just saw an amazing nature documentary called Flying Monsters 3D by David Attenborough, showing the first flying creatures from millions of years ago. The earliest bird wings had the same shape as modern aircraft. That airfoil configuration is necessary for all flight, and requires a wing’s upper surface to be convex. It’s hard to see how evolution could have created it. Unlike giraffes’ necks, where incremental increases offered survival advantages, a step-by-step process wouldn’t work for a wing design. A slightly wrong shape would be useless and confer no benefit. Some 400,000 cells would all have to simultaneously mutate in just the right way to create a properly shaped wing. This defies an evolutionary hypothesis.

Occam’s razor might suggest some baked-in, overarching intelligence. I’m not invoking spirituality, merely that the effect of random collisions and mutations is not always a work-able answer. So perhaps nature is inherently smart. We cannot visually see this intelligence, just as we cannot see electrical fields; and yes, this is a minority viewpoint. But if true, then the sky’s the limit for ETs.

It’s guesswork. We know of life on only a single world, so our sample size is one. And when you try to draw a line on a graph but you have just one data point, well, good luck. We’ll have no shortcuts when we probe the planetary system of TRAPPIST-1.

[1] Bob Berman, “Finding Aliens,” Astronomy (45, 9, September 2017, p. 10). Contact Bob about his strange universe by visiting

Time Travel

Time Travel[1]

At a winter star party, participant points toward Sirius and asks, “How far away is that star?” Someone replies, “8.6 light-years”, and then briefly explains what a light-year is. Since the distance to Sirius in light-years is the same as the travel time for its light, I like to enhance this answer by noting what earthly events were taking place when the light reaching our eyes exited its surface.

Sirius is the closest of seven stars of 1st magnitude or brighter currently visible after dark from mid-northern latitudes. Listed in order of increasing distance, they are Sirius, Procyon, Pollux, Capella, Aldebaran, Betelgeuse, and Rigel. How far away are they? Our answers include each star’s distance in light-years based on parallax measures made by the Hipparcos satellite, followed by a look at what was happening on our home planet when its light departed for a 2015 arrival.

Sirius (8.6 light-years): What was going on in late May 2006 when the light from Sirius began its 50.6-trillion-mile (81.4 trillion kilometers) journey earthward? NASA’s Cassini spacecraft was in the process of discovering lakes of liquid methane or ethane on Titan’s surface, while Pluto was in its last months as an officially recognized planet. From your perspective, a personal or family-related milestone like a graduation, wedding, birth, or death might have overshadowed these events. Depending on your age, you’ll likely recall lifetime experiences for each of the next four stars.

Procyon (11.4 light-years): When Procyon’s light left around mid-summer 2003, astronomers were enjoying close-up views of Mars as the Red Planet made its nearest approach to Earth in centuries. If you’re a member of the high school class of 2015 anticipating a June graduation, consider this. Back then, you were about to enter first grade. Most of your entire elementary/ high school education is written on a beam of light from Procyon!

Pollux (34 light-years): Light from Pollux departed early in 1981 at the same time the Space Shuttle Program opened with the orbital test flight of Columbia. The Reagan era in American politics was beginning, and Saturday evenings brought us the escape shows Love Boat and Fantasy Island.

Capella (42 light-years): Space aficionados remember 1973 (when Capella’s light took flight for Earth) as the year Comet Kohoutek (C/1973 E1) was discovered and Skylab, the first U.S. space station, was launched. Veterans of the Vietnam War will note that 1973 was the year direct U. S. military involvement in this conflict finally ended. All in the Family was the top-rated TV show, and many of today’s middle-agers were disco dancing beneath a rotating mirror ball.

Aldebaran (65 light-years): In 1950, the year Aldebaran’s light began its earthly journey, Dutch astronomer Jan Oort proposed the existence of an orbiting cloud of comets (now called the Oort Cloud) at the outer reaches of the Solar System. If you’ve arrived at retirement age (typically, mid to late 60s), Aldebaran shines in your honor. Its ruddy light left around the time you were born, continued onward as you went to school, began a career, got married, and had children and then grandchildren. It finally arrived just as you retired—literally the journey of a lifetime!

Betelgeuse (640 light-years): When it comes to accurately knowing a star’s distance, we now enter a realm of uncertainty. The parallax of Betelgeuse is so minuscule that even Hipparcos satellite measurements are iffy. The current accepted figure means the photons striking your retinas left during the latter part of the 14th century. Since none of us was around then, we have to rely or historical events. When light left the surface of Betelgeuse, China’s Ming Dynasty had begun, the Aztecs were settling in what is now Mexico City, and the European Renaissance was in its infancy

Rigel (860 light-years): Rigel’s distance is variously reported as between 700 and 900 light-years, with a Hipparcos measurement hinting at 860 light-years. Imagine a star so luminous that it ranks seventh in brightness in our nighttime sky even though the void separating us is so vast that its light has been traveling since the middle of the 12th century! When we look at Rigel our eyes are picking up starlight launched earthward around the time of the early Crusades.

Defining a star’s distance by the events occurring on Earth when its light began its journey adds a dimension not achieved by mere numbers.

[1] Glenn Chapple, “Time Travel,” Astronomy (43,1, January 2015, p. 18). Questions, comments or suggestions? Email Glann Chapple at Clear skies!

Arecibo Radio Telescope Damaged by Hurricane Maria

Arecibo Radio Telescope Damaged by Hurricane Maria[1]

Until it was surpassed recently by a similar instrument in China, the Arecibo radio telescope in Puerto Rico, completed in 1963, was the world’s single largest. Seth Shostak/AP

When Hurricane Maria raked Puerto Rico September 20, 2017 as a Category 4 storm, it cut off electricity and communications island-wide, including at the Arecibo Observatory, one of the world’s largest radio telescopes.

Initial reports, received via ham radio, indicated significant damage to some of the facility’s scientific instruments. But Nicholas White, a senior vice president at the Universities Space Research Association, which helps run the observatory, told NPR that the latest information is that a secondary 40-foot dish, thought destroyed, is still intact: “There was some damage to it, but not a lot,” he says.

“So far, the only damage that’s confirmed is that one of the line feeds on the antenna for one of the radar systems was lost,” White says. That part was suspended high above the telescope’s main 1,000-foot dish, which lost some panels when it shook loose and fell down.

As all this was happening, the observatory’s staff sheltered in place. Reports were that all were OK. The team managed to post a defiant message on Facebook showing two of the staff displaying an outstretched Puerto Rican flag, with the giant dish in the background.

The observatory, which was used as the backdrop for the James Bond film Golden Eye (1995) and the 1997 movie Contact, starring Jodie Foster, was built in 1963 and has a number of firsts to its credit: it found the first planets around other stars, was the first to image an asteroid and discovered more exotic objects, such as the first binary pulsar.

And then there’s the Arecibo Message, a famous signal sent from the radio telescope to M13, a global cluster some 25,000 light years away. For any sentient extraterrestrials there, it describes who we are and where the signal comes from. (Don’t hold your breath though, as it’ll be at least 50,000 years before we get an answer).

One of Arecibo’s primary areas of research is near-Earth objects, or NEOs, those asteroids and asteroid-like chunks of rock that pass uncomfortably close.

Lance Benner, a scientist at the Jet Propulsion Laboratory in Pasadena, CA, who studies NEOs, has traveled to Arecibo dozens of times and tells NPR it’s probably the best place anywhere to do such research.

“Arecibo just has unparalleled sensitivity as a radar facility,” he says. “It is by far the most sensitive planetary radar in the world.”

But the aging facility’s funding from the National Science Foundation has been under review for the past few years, and it’s unclear how the cost of any repairs might affect that discussion.

Jim Ulvestad, acting assistant director for the National Science Foundation’s directorate for Mathematical and Physical Sciences at NSF, told NPR that Arecibo is doing “excellent science.”

However, “if you look at the overall sweep of things that we’re funding, we do have to make choices and we can’t keep funding everything that’s excellent.”

[1] See

Building the Edifice of Science

Building the Edifice of Science[1]

Astronomy is a peculiar name for a science. In words like biology, geology, and cosmology, the second half comes from the Greek –λογια or –logia, which refers to study and divine communication. Hence the study of life, the study of Earth, the study of the cosmos—you know, science!

Astronomy is different. Instead of “study,” astronomy derives its name from the Greek νόμοϛ (nόmos), for “arranging.” While words like biology and geology date back only a few hundred years, the Greeks combined the root words to describe an already ancient endeavor. The oldest of sciences is άστρνομία (astronomia), the arranging of stars.

And so it was going back thousands of years to the Egyptians, Sumerians, Babylonians, and Chinese. Tycho Brahe’s thousand-star catalog at the end of the 16th century built on the work of Hipparchus and Ptolemy. Today, the U.S. Naval Observatory’s NOMAD database contains more than a billion stars and is only one of hundreds of astronomical catalogs.

The next level of sophistication beyond catalogs—the next tier of scientific thought, if you will—involves description and prediction. Ptolemy described planets and the Sun moving in a complex arrangement of circles within circles within circles, but he offered no explanation for why they moved that way. In one sense, Copernicus’ model of planets, which included Earth moving around a motionless Sun, was a major departure from past thought. But in another sense, Copernicus’ work was kind of like Ptolemy’s. It was a description that traded slightly worse predictions of planetary motions for far greater simplicity.

Galileo Galilei’s name is synonymous with the next tier of scientific thought. In addition to turning a telescope on the heavens, the father of modern science got the ball rolling (literally) with his work on inertia, relative motion, gravitation, and the dynamics of projectiles. Galileo’s truly radical proposal was that universal laws govern the motion of all objects at all times, and that those laws can be known by humans and expressed using the language of mathematics. That shift in thinking found its most profound expression in the 1687 publication of Isaac Newton’s Philosophiæ Naturalis Principia Mathematica, Latin for “Mathematical Principles of Natural Philosophy.”

Each new tier of scientific thought created a stir that went beyond science, per se. Ptolemy’s model of the heavens was a Rube Goldberg device, but it put Earth where it obviously belonged, at the center of all things. Copernicus knew he would upset that apple cart and did not relish the controversy and condemnation he correctly imagined his work would bring. So he put off publication of his masterwork until late in life. De revolutionibus orbium coelestium was not published until 1543, the year of his death.

Galileo was among those who really caught the brunt of the reaction to Copernicanism. Granted, he probably should have known better than to put the ideas of the pope into the mouth of a buffoon named Simplicio in his popular Dialogue Concerning the Two Chief World Systems. Regardless, he stood before the Inquisition, was forced to recant his heretical notions, and spent the last years of his life under house arrest.

We don’t need to look to records of a trial to see the profound impact of the next tier of scientific thought. The advent of knowable, mathematical natural laws is the grand idea behind what we think of as the Scientific Revolution. Here is what made modern technological civilization possible. It also led to shifts in political and philosophical thought reflected in a host of documents, notably the Constitution of the United States. Judged by its practical impact, Newton’s Principia is the most important book ever written, bar none.

And so science progresses in tiers of scientific thought from observation, to catalogs, to description and prediction, to natural law. That description is obviously an oversimplification. Those tiers are not so orderly or well defined. Even so, it reasonably captures the flavor of how science has evolved over the years. So here we are today, at the summit of that evolution.

But here’s a question. Did Hipparchus know that his catalog would help shape the way humans systematize observations of nature? Did Ptolemy understand that by making testable predictions, he was laying the foundation for a new definition of knowledge? When Galileo first noticed the swinging of a chandelier, did he appreciate that he was on the verge of changing the world?

I think not. Shifts in thought obvious in hindsight happen slowly and are far harder to appreciate in the moment. A century and a half passed between the publication of Copernicus’ work and Newton’s Principia. What would it be like to live through such a shift, and how would you know if you were?

That question is not rhetorical, because I think that we are in the midst of one now.

[1] Jeff Hester, “Layer Upon Layer,” Astronomy (44, 5, 2016, p.12). Jeff Hester is a keynote speaker, coach, and astrophysicist. Follow his thoughts at