What’s happening over the horizon? Although the scene may appear somehow supernatural, nothing more unusual is occurring than a setting Sun and some well placed clouds. Pictured above are anticrepuscular rays. To understand them, start by picturing common crepuscular rays that are seen any time that sunlight pours though scattered clouds. Now although sunlight indeed travels along straight lines, the projections of these lines onto the spherical sky are great circles. Therefore, the crepuscular rays from a setting (or rising) sun will appear to re-converge on the other side of the sky. At the anti-solar point 180 degrees around from the Sun, they are referred to as anticrepuscular rays. Featured here is a particularly striking display of anticrepuscular rays photographed earlier this month in Westminster, Colorado, USA.
Cassini orbited in Saturn’s ring plane — around the planet’s equator — for most of 2015. This enabled a season of flybys of the planet’s icy moons, but did not allow for angled views of the rings and the planet’s poles, like this one. But in early 2016, the spacecraft began to increase its orbital inclination, climbing higher over the poles in preparation for the mission’s final spectacular orbits in 2017.
This view looks toward the sunlit side of the rings from about 16 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera on Feb. 26 2016 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.
The view was obtained at a distance of approximately 1.7 million miles (2.8 million kilometers) from Saturn. Image scale is 103 miles (165 kilometers) per pixel.
The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.
What’s that over Paris? Cirrus. Typically, cirrus clouds appear white or gray when reflecting sunlight, can appear dark at sunset (or sunrise) against a better lit sky. Cirrus are among the highest types of clouds and are usually thin enough to see stars through. Cirrus clouds may form from moisture released above storm clouds and so may herald the arrival of a significant change in weather. Conversely, cirrus clouds have also been seen on Mars, Jupiter, Saturn, Titan, Uranus, and Neptune. The featured image was taken two days ago from a window in District 15, Paris, France, Earth. The brightly lit object on the lower right is, of course, the Eiffel Tower.
These three bright nebulae are often featured in telescopic tours of the constellation Sagittarius and the crowded starfields of the central Milky Way. In fact, 18th century cosmic tourist Charles Messier cataloged two of them; M8, the large nebula left of center, and colorful M20 near the bottom of the frame The third, NGC 6559, is right of M8, separated from the larger nebula by dark dust lanes. All three are stellar nurseries about five thousand light-years or so distant. The expansive M8, over a hundred light-years across, is also known as the Lagoon Nebula. M20’s popular moniker is the Trifid. In the composite image, narrowband data records ionized hydrogen, oxygen, and sulfur atoms radiating at visible wavelengths. The mapping of colors and range of brightness used to compose this cosmic still life were inspired by Van Gogh’s famous Sunflowers. Just right of the Trifid one of Messier’s open star clusters, M21, is also included on the telescopic canvas.
Like a zombie, the Milky Way galaxy may already be dead but it still keeps going. Our galactic neighbor Andromeda almost certainly expired a few billion years ago, but only recently started showing outward signs of its demise.
Galaxies seem to be able to “perish” – that is, stop turning gas into new stars – via two very different pathways, driven by very different processes. Galaxies like the Milky Way and Andromeda do so very, very slowly over billions of years.
How and why galaxies “quench” their star formation and change their morphology, or shape, is one of the big questions in extragalactic astrophysics. We may now be on the brink of being able to piece together how it happens. And part of the thanks goes to citizen scientists who combed through millions of galactic images to classify what’s out there.
Galaxies grow by making new stars
Galaxies are dynamic systems that continually accrete gas and convert some of it into stars.
Like people, galaxies need food. In the case of galaxies, that “food” is a supply of fresh hydrogen gas from the cosmic web, the filaments and halos of dark matter that make up the largest structures in the universe. As this gas cools and falls into dark matter halos, it turns into a disk that then can cool even further and eventually fragment into stars.
As stars age and die, they can return some of that gas back into the galaxy either via winds from stars or by going supernova. As massive stars die in such explosions, they heat the gas around them and prevent it from cooling down quite so fast. They provide what astronomers call “feedback”: star formation in galaxies is thus a self-regulated process. The heat from dying stars means cosmic gas doesn’t cool into new stars as readily, which ultimately puts a brake on how many new stars can form.
Most of these star-forming galaxies are disk- or spiral-shaped, like our Milky Way.
Left: a spiral galaxy ablaze in the blue light of young stars from ongoing star formation; right: an elliptical galaxy bathed in the red light of old stars. Sloan Digital Sky Survey, CC BY-NC
But there’s another kind of galaxy that has a very different shape, or morphology, in astronomer-parlance. These massive elliptical galaxies tend to look spheroidal or football-shaped. They’re not nearly so active – they’ve lost their supply of gas and therefore have ceased forming new stars. Their stars move on far more unordered orbits, giving them their bulkier, rounder shape.
These elliptical galaxies differ in two major ways: they no longer form stars and they have a different shape. Something pretty dramatic must have happened to them to produce such profound changes. What?
Blue=young and red=old?
The basic division of galaxies into star-forming spiral galaxies blazing in the blue light of massive, young and short-lived stars, on the one hand, and quiescent ellipticals bathed in the warm glow of ancient low-mass stars, on the other, goes back to early galaxy surveys of the 20th century.
But, once modern surveys like the Sloan Digital Sky Survey (SDSS) began to record hundreds of thousands of galaxies, objects started emerging that didn’t quite fit into those two broad categories.
A significant number of red, quiescent galaxies aren’t elliptical in shape at all, but retain roughly a disk shape. Somehow, these galaxies stopped forming stars without dramatically changing their structure.
At the same time, blue elliptical galaxies started to surface. Their structure is similar to that of “red and dead” ellipticals, but they shine in the bright blue light of young stars, indicating that star formation is still ongoing in them.
How do these two oddballs – the red spirals and the blue ellipticals – fit into our picture of galaxy evolution?
Galaxy Zoo allows citizen scientists to classify galaxies. Screenshot by Kevin Schawinski, CC BY-ND
Send in the citizen scientists
As a graduate student in Oxford, I was looking for some of these oddball galaxies. I was particularly interested in the blue ellipticals and any clues they contained about the formation of elliptical galaxies in general.
At one point, I spent a whole week going through almost 50,000 galaxies from SDSS by eye, as none of the available algorithms for classifying galaxy shape was as good as I needed it to be. I found quite a few blue ellipticals, but the value of classifying all of the roughly one million galaxies in SDSS with human eyes quickly became apparent. Of course, going through a million galaxies by myself wasn’t possible.
A short time later, a group of collaborators and I launched galaxyzoo.org and invited members of the public – citizen scientists – to participate in astrophysics research. When you logged on to Galaxy Zoo, you’d be shown an image of a galaxy and a set of buttons corresponding to possible classifications, and a tutorial to help you recognize the different classes.
By the time we stopped recording classifications from a quarter-million people, each of the one million galaxies on Galaxy Zoo had been classified over 70 times, giving me reliable, human classifications of galaxy shape, including a measure of uncertainty. Did 65 out of 70 citizen scientists agree that this galaxy is an elliptical? Good! If there’s no agreement at all, that’s information too.
Tapping into the “wisdom of the crowd” effect coupled with the unparalleled human ability for pattern recognition helped sort through a million galaxies and unearthed many of the less common blue ellipticals and red spirals for us to study.
The galaxy color-mass diagram. Blue, star-forming galaxies are at the bottom, in the blue cloud. Red, quiescent galaxies are at the top, in the red sequence. The ‘green valley’ is the transition zone in between. Schawinski+14, CC BY-ND
Unwittingly living in the green valley?
The crossroads of galaxy evolution is a place called the “green valley.” This may sound scenic, but refers to the population between the blue star-forming galaxies (the “blue cloud”) and the red, passively evolving galaxies (the “red sequence”). Galaxies with “green” or intermediate colors should be those galaxies in which star formation is in the process of turning off, but which still have some ongoing star formation – indicating the process only shut down a short while ago, perhaps a few hundred million years.
As a curious aside, the origin of the term “green valley” may actually go back to a talk given at the University of Arizona on galaxy evolution where, when the speaker described the galaxy color-mass diagram, a member of the audience called out: “the green valley, where galaxies go to die!” Green Valley, Arizona, is a retirement community just outside of the university’s hometown, Tucson.
For our project, the really exciting moment came when we looked at the rate at which various galaxies were dying. We found the slowly dying ones are the spirals and the rapidly dying ones are the ellipticals. There must be two fundamentally different evolutionary pathways that lead to quenching in galaxies. When we explored these two scenarios – dying slowly, and dying quickly – it became obvious that these two pathways have to be tied to the gas supply that fuels star formation in the first place.
Imagine a spiral galaxy like our own Milky Way merrily converting gas to stars as new gas keeps flowing in. Then something happens that turns off that supply of fresh outside gas: perhaps the galaxy fell into a massive cluster of galaxies where the hot intra-cluster gas cuts off fresh gas from the outside, or perhaps the dark matter halo of the galaxy grew so much that gas falling into it gets shock heated to such a high temperature that it cannot cool down within the age of the universe. In any case, the spiral galaxy is now left with just the gas it has in its reservoir.
Since these reservoirs can be enormous, and the conversion of gas to stars is a very slow process, our spiral galaxy could go on for quite a while looking “alive” with new stars, while the actual rate of star formation declines over several billion years. The glacial slowness of using up the remaining gas reservoir means that by the time we realize that a galaxy is in terminal decline, the “trigger moment” occurred billions of years ago.
The Andromeda galaxy, our nearest massive spiral galaxy, is in the green valley and likely began its decline eons ago: it is a zombie galaxy, according to our latest research. It’s dead, but keeps on moving, still producing stars, but at a diminished rate compared to what it should if it were still a normal star-forming galaxy. Working out whether the Milky Way is in the green valley – in the process of shutting down – is much more challenging, as we are in the Milky Way and cannot easily measure its integrated properties the way we can for distant galaxies.
Even with the more uncertain data, it looks like the Milky Way is just at the edge, ready to tumble into the green valley. It’s entirely possible that the Milky Way galaxy is a zombie, having died a billion years ago.
Today the Sun reaches its northernmost point in planet Earth’s sky. Called a solstice, the date astronomically marks a change of seasons — from spring to summer in Earth’s Northern Hemisphere and from fall to winter in Earth’s Southern Hemisphere. The featured image was taken during the week of the 2008 summer solstice at Stonehenge in United Kingdom, and captures a picturesque sunrise involving fog, trees, clouds, stones placed about 4,500 years ago, and a 4.5 billion year old large glowing orb. Even given the precession of the Earth’s rotational axis over the millennia, the Sun continues to rise over Stonehenge in an astronomically significant way.
More CubeSats are due to be deployed today contributing to humanitarian and environmental research. The crew is also continuing biomedical science to improve the health of astronauts in space and humans on Earth.
The final set of CubeSats will be released tonight from a small satellite deployer outside Japan’s Kibo laboratory module. This current fleet of 16 CubeSats, also known as Dove satellites, began deploying Monday and will monitor the Earth to help improve disaster relief and agriculture yields.
The crew is exploring new space exercise techniques today to keep muscles, bones and the heart healthy during long-duration missions. The crew is also tracking its medication intake to determine the effectiveness and any side effects of using medicine in space.
BEAM, or the Bigelow Expandable Activity Module, is still undergoing temperature and pressure checks while some relief valves and ventilation valves are being swapped out. Astronaut Jeff Williams will enter BEAM for the first time next week to install sensors measuring the expandable module’s environment.
Bigelow Expandable Activity Module (BEAM) has finally reached its goal. Following a failed first attempt, NASA has successfully inflated a new experimental pump-powered inflatable room at the International Space Station which took around 7 full hours to fully finish.
The inflatable ISS fitted module was slowly brought to life by opening and closing an air valve from internal air tanks to expand the compartment. SpaceX delivered BEAM to the Space Station early last month. The module was attached to NASA’s $100-billion orbiting lab where it will remain for the next two years. Stretched to its full the room offers an extra 4 meters (13 feet) in length and 3.2 meters (10.5 feet) in diameter for scientists to conduct experiments.
NASA’s chief scientist recently announced that “…we’re going to have strong indications of life beyond Earth within a decade, and I think we’re going to have definitive evidence within 20 to 30 years.” Such a discovery would clearly rank as one of the most important in human history and immediately open up a series of complex social and moral questions. One of the most profound concerns is about the moral status of extraterrestrial life forms. Since humanities scholars are only just now beginning to think critically about these kinds of post-contact questions, naïve positions are common.
Take Martian life: we don’t know if there is life on Mars, but if it exists, it’s almost certainly microbial and clinging to a precarious existence in subsurface aquifers. It may or may not represent an independent origin – life could have emerged first on Mars and been exported to Earth. But whatever its exact status, the prospect of life on Mars has tempted some scientists to venture out onto moral limbs. Of particular interest is a position I label “Mariomania.”
Should we quarantine Mars?
Mariomania can be traced back to Carl Sagan, who famously proclaimed
If there is life on Mars, I believe we should do nothing with Mars. Mars then belongs to the Martians, even if the Martians are only microbes.
Chris McKay, one of NASA’s foremost Mars experts, goes even further to argue that we have an obligation to actively assist Martian life, so that it does not only survives, but flourishes:
…Martian life has rights. It has the right to continue its existence even if its extinction would benefit the biota of Earth. Furthermore, its rights confer upon us the obligation to assist it in obtaining global diversity and stability.
To many people, this position seems noble because it calls for human sacrifice in the service of a moral ideal. But in reality, the Mariomaniac position is far too sweeping to be defensible on either practical or moral grounds.
Streaks down Martian mountains are evidence of liquid water running downhill – and hint at the possibility of life on the planet. NASA/JPL/University of Arizona, CC BY
A moral hierarchy: Earthlings before Martians?
Suppose in the future we find that:
There is (only) microbial life on Mars.
We have long studied this life, answering our most pressing scientific questions.
It has become feasible to intervene on Mars in some way (for instance, by terraforming or strip mining) that would significantly harm or even destroy the microbes, but would also be of major benefit to humanity.
Mariomaniacs would no doubt rally in opposition to any such intervention under their “Mars for the Martians” banners. From a purely practical point of view, this probably means that we should not explore Mars at all, since it is not possible to do so without a real risk of contamination.
Beyond practicality, a theoretical argument can be made that opposition to intervention might itself be immoral:
Humans beings have an especially high (if not necessarily unique) moral value and thus we have an unambiguous obligation to serve human interests.
It is unclear if Martian microbes have moral value at all (at least independent of their usefulness to people). Even if they do, it’s certainly much less than that of human beings.
Interventions on Mars could be of enormous benefit to humankind (for instance, creating a “second Earth”).
Therefore: we should of course seek compromise where possible, but to the extent that we are forced to choose whose interests to maximize, we are morally obliged to err on the side of humans.
Obviously, there are a great many subtleties I don’t consider here. For example, many ethicists question whether human beings always have higher moral value than other life forms. Animal rights activists argue that we should accord real moral value to other animals because, like human beings, they possess morally relevant characteristics (for instance, the ability to feel pleasure and pain). But very few thoughtful commentators would conclude that, if we are forced to choose between saving an animal and saving a human, we should flip a coin.
Simplistic claims of moral equality are another example of overgeneralizing a moral principle for rhetorical effect. Whatever one thinks about animal rights, the idea that the moral status of humans should trump that of microbes is about as close to a slam dunk as it gets in moral theory.
On the other hand, we need to be careful since my argument merely establishes that there can be excellent moral reasons for overriding the “interests” of Martian microbes in some circumstances. There will always be those who want to use this kind of reasoning to justify all manner of human-serving but immoral actions. The argument I outline does not establish that anyone should be allowed to do anything they want to Mars for any reason. At the very least, Martian microbes would be of immense value to human beings: for example, as an object of scientific study. Thus, we should enforce a strong precautionary principle in our initial dealings with Mars (as a recent debate over planetary protection policies illustrates).
For every complex question, there’s a simple, incorrect answer
Mariomania seems to be the latest example of the idea, common among undergraduates in their first ethics class, that morality is all about establishing highly general rules that admit no exception. But such naïve versions of moral ideals don’t long survive contact with the real world.
By way of example, take the “Prime Directive” from TV’s “Star Trek”:
…no Star Fleet personnel may interfere with the normal and healthy development of alien life and culture…Star Fleet personnel may not violate this Prime Directive, even to save their lives and/or their ship…This directive takes precedence over any and all other considerations, and carries with it the highest moral obligation.
Hollywood’s version of moral obligation can be a starting point for our real-world ethical discussion.
As every good trekkie knows, Federation crew members talk about the importance of obeying the prime directive almost as often as they violate it. Here, art reflects reality, since it’s simply not possible to make a one-size-fits-all rule that identifies the right course of action in every morally complex situation. As a result, Federation crews are constantly forced to choose between unpalatable options. On the one hand, they can obey the directive even when it leads to clearly immoral consequences, as when the Enterprise refuses to cure a plague devastating a planet. On the other hand, they can generate ad hoc reasons to ignore the rule, as when Captain Kirk decides that destroying a supercomputer running an alien society doesn’t violate the spirit of the directive.
Of course, we shouldn’t take Hollywood as a perfect guide to policy. The Prime Directive is merely a familiar example of the universal tension between highly general moral ideals and real-world applications. We will increasingly see the kinds of problems such tension creates in real life as technology opens up vistas beyond Earth for exploration and exploitation. If we insist on declaring unrealistic moral ideals in our guiding documents, we should not be surprised when decision makers are forced to find ways around them. For example, the U.S. Congress’ recent move to allow asteroid mining can be seen as flying in the face of the “collective good of mankind” ideals expressed in the Outer Space Treaty signed by all space-faring nations.
The solution is to do the hard work of formulating the right principles, at the right level of generality, before circumstances render moral debate irrelevant. This requires grappling with the complex trade-offs and hard choices in an intellectually honest fashion, while refusing the temptation to put forward soothing but impractical moral platitudes. We must therefore foster thoughtful exchanges among people with very different conceptions of the moral good in order to find common ground. It’s time for that conversation to begin in earnest.
A study published yesterday in the Astrophysical Journal by a group of researchers confirms an additional 1,284 exoplanets have been spotted by Kepler, NASA’s planet-hunting spacecraft. That brings the total number of verified exoplanets from Kepler to more than 2,000 — more than doubling the amount spotted by the spacecraft.
“We have more than doubled the number of known exoplanets smaller than the size of Neptune,” Tim Morton, an associate research scholar at Princeton University.
