Pluto’s dark side reveals clues to its atmosphere and frost cycles

Pluto’s dark side has come into dim view, thanks to the light of the dwarf planet’s moon.

When NASA’s New Horizons spacecraft flew past Pluto in 2015, almost all the images of the dwarf planet’s unexpectedly complex surface were of the side illuminated by the sun (SN: 7/15/15). Darkness shrouded the dwarf planet’s other hemisphere. Some of it, like the area near the south pole, hadn’t seen the sun for decades.

Now, mission scientists have finally released a grainy view of the dwarf planet’s dark side. The researchers describe the process to take the photo and what it tells them about how Pluto’s nitrogen cycle affects its atmosphere October 20 in the Planetary Science Journal.

Before New Horizons passed by Pluto, the team suspected the dwarf planet’s largest moon, Charon, might reflect enough light to illuminate the distant world’s surface. So the researchers had the spacecraft turn back toward the sun to take a parting peek at Pluto.
At first, the images just showed a ring of sunlight filtering through Pluto’s hazy atmosphere (SN: 7/24/15). “It’s very hard to see anything in that glare,” says planetary scientist John Spencer of the Southwest Research Institute in Boulder, Colo. “It’s like trying to read a street sign when you’re driving toward the setting sun and you have a dirty windshield.”

Spencer and colleagues took a few steps to make it possible to pull details of Pluto’s dark side out of the glare. First, the team had the spacecraft take 360 short snapshots of the backlit dwarf planet. Each was about 0.4 seconds long, to avoid overexposing the images. The team also took snapshots of the sun without Pluto in the frame so that the sun could be subtracted out after the fact.

Tod Lauer of the National Optical Astronomy Observatory in Tucson, Ariz., tried to process the images when he got the data in 2016. At the time, the rest of the data from New Horizons was still fresh and took up most of his attention, so he didn’t have the time to tackle such a tricky project.

But “it was something that just sat there and ate away at me,” Lauer says. He tried again in 2019. Because the spacecraft was moving as it took the images, each image was a little bit smeared or blurred. Lauer wrote a computer code to remove that blur from each individual frame. Then he added the reflected Charon light in each of those hundreds of images together to produce a single image.
“When Tod did that painstaking analysis, we finally saw something emerging in the dark there … giving us a little bit of a glimpse of what the dark pole of Pluto looks like,” Spencer says.

That the team got anything at all is impressive, says planetary scientist Carly Howett, also of the Southwest Research Institute and who is on the New Horizons team but was not involved in this work. “This dataset is really, really hard to work with,” she says. “Kudos to this team. I wouldn’t have wanted to do this.”

The image, Howett says, can help scientists understand how Pluto’s frigid nitrogen atmosphere varies with its decades-long seasons. Pluto’s atmosphere is controlled by how much nitrogen is in a gas phase in the air and how much is frozen on the surface. The more nitrogen ice that evaporates, the thicker the atmosphere becomes. If too much nitrogen freezes to the ground, the atmosphere could collapse altogether.
When New Horizons was there, Pluto’s south pole looked darker than the north pole. That suggests there was not a lot of fresh nitrogen frost freezing out of the atmosphere there, even though it was nearing winter. “The previous summer ended decades ago, but Pluto cools off pretty slowly,” Spencer says. “Maybe it’s still so warm [that] the frost can’t condense there, and that keeps the atmosphere from collapsing.”

There was a bright spot in the middle of the image, which could be a fresh ice deposit. That’s also not surprising, Howett says. The ices may still be moving from the north pole to the south pole as Pluto moves deeper into its wintertime.

“We’ve thought this for a long time. It makes sense,” she says. “But it’s nice to see it happening.”

Neutron star collisions probably make more gold than other cosmic smashups

The cosmic origins of elements heavier than iron are mysterious. One elemental birthplace came to light in 2017 when two neutron-rich dead stars collided and spewed out gold, platinum and other hefty elements (SN: 10/16/17). A few years later, a smashup of another neutron star and a black hole left scientists wondering which type of cosmic clash was the more prolific element foundry (SN: 6/29/21).

Now, they have an answer. Collisions of two neutron stars probably take the cake, scientists report October 25 in Astrophysical Journal Letters.

To create heavy elements after either type of collision, neutron star material must be flung into space, where a series of nuclear reactions called the r-process can transform the material (SN: 4/22/16).

How much material escapes into space, if any, depends on various factors. For example, in collisions of a neutron star and black hole, the black hole has to be relatively small, or “there’s no hope at all,” says astrophysicist Hsin-Yu Chen of MIT. “It’s going to swallow the neutron star right away,” without ejecting anything.

Questions remain about both types of collisions, spotted via the ripples in spacetime that they kick up. So Chen and colleagues considered a range of possibilities for the properties of neutron stars and black holes, such as the distributions of their masses and how fast they spin. The team then calculated the mass ejected by each type of collision under those varied conditions. In most scenarios, the neutron star–black hole mergers made a smaller quantity of heavy elements than the neutron star duos — in one case only about a hundredth the amount.

Still, the ultimate element factory ranking remains up in the air. The scientists compared just these two types of collisions, not other possible sources of heavy elements such as exploding stars (SN: 7/7/21).

Here’s what the next 10 years of space science could look like

The Astronomy and Astrophysics Decadal Survey is basically a sneak preview of the next 10 years of U.S. space science. Every decade, experts assembled by the National Academies of Sciences, Engineering and Medicine collect input from astronomers nationwide to recommend a prioritized list of projects to policy makers and federal agencies. Past to-do lists have been topped by specific big-ticket items, such as the James Webb Space Telescope and the Nancy Grace Roman Space Telescope (SN: 10/6/21; SN: 8/13/10). But this year, astronomers are shaking things up.

The latest decadal survey, which charts the course for U.S. astronomy and astrophysics from 2022 to 2032, recommends that NASA create a new program to develop several major space telescopes at a time. Investing early in multiple mission concepts could curb the risk of individual missions becoming too unwieldy and expensive, according to the report released November 4.

“These are super important recommendations,” says Scott Gaudi, an astronomer at the Ohio State University who wasn’t on the National Academies committee that compiled the report. “They really focus the direction of astronomy in the United States — and sort of by extension the rest of the world, because we have lots of international partnerships.”

The proposed multi-mission program would reshape how major space missions are planned. In the past, “you would pick a priority, you’d build it, you’d launch it, and then you would think about what the next priority was,” says Jonathan Fortney, an astrophysicist at the University of California, Santa Cruz and a member of the survey committee.
But space telescopes are getting more ambitious, complex and expensive, Fortney says. The one-at-a-time model doesn’t work so well when a single mission can take decades from blueprint to blastoff.

Having several big projects in the works offers a bit of insurance. If researchers work on one mission for a few years and realize that the technology isn’t there to make it fly on time, NASA could switch gears and send another telescope to space first, Fortney says. Developing multiple missions in parallel could also shrink the long wait time between launches.

“I’m so excited by that. It’s like the best possible outcome,” Gaudi says. This setup could boost confidence that big space missions can stay on budget and on schedule, he adds, after the large cost overruns and delays that have mired the long-awaited James Webb Space Telescope. “It is a really new way of approaching things, and one that’s really needed to advance astronomy into the next few decades.”

The first mission in the new program, according to the survey report, should be a space telescope that views the universe in infrared, optical and ultraviolet wavelengths, filling a gap left by other instruments. The Hubble Space Telescope mainly looks at optical and ultraviolet light, while the James Webb telescope will primarily see the universe in infrared.
With a light-collecting area more than twice as wide as Hubble’s, this newfangled observatory could glimpse planets in other star systems that are a tenth of a billionth as bright as their stars, and could tease out the specific wavelengths of light, or spectra, given off by exoplanets. The telescope could also observe stars, galaxies and other celestial objects. With an estimated price tag of $11 billion, the telescope would be slated to launch in the early 2040s.

Five years after starting work on that first flagship mission, NASA should begin developing both a far-infrared mission and an X-ray mission, each costing an estimated $3 billion to $5 billion, the survey recommends.

A far-infrared window into the universe could help astronomers study how water behaves in forming planetary systems, Fortney says. A successor to NASA’s 22-year-old Chandra X-ray Observatory could reveal new details of galaxy evolution, supermassive black hole behavior and other energetic phenomena (SN: 7/25/19).

On the ground, astronomers’ highest priorities, according to the decadal survey, are continuing to build two major optical observatories, the Giant Magellan Telescope in Chile and the Thirty Meter Telescope in Hawaii — though the latter project has faced controversy (SN: 8/5/20).

The survey also notes that it is time to replace the Very Large Array in New Mexico and the Very Long Baseline Array of telescope dishes scattered across the United States. The proposed successor to these world-class radio observatories is the Next-Generation Very Large Array, which would be 10 times as sensitive.

Fortney is optimistic that NASA and other federal agencies will make the decadal survey’s top-ranked priorities a reality. “The record has been quite good, in terms of the most prominent recommendations being born out,” he says. “I have really high confidence that these things really will happen.”

An easier, greener way to build molecules wins the chemistry Nobel Prize

Making molecules is hard work. Atoms must be stitched together into specific arrangements through a series of chemical reactions that are often slow, convoluted and wasteful. The 2021 Nobel Prize in chemistry recognizes two scientists who developed a tool at the turn of the century that revolutionized how chemists construct new molecules, making the process faster and more environmentally friendly.

Chemists Benjamin List of the Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr, Germany and David MacMillan of Princeton University were awarded the prize for independently developing organic catalysts that speed up chemical reactions necessary for constructing specific molecules, a process called asymmetric organocatalysis. The two will share the prize of 10 million Swedish kroner (more than $1.1 million), the Royal Swedish Academy of Sciences announced October 6 in a news conference in Stockholm.

“This is a fitting recognition of very important work,” says H.N. Cheng, president of the American Chemical Society.

“We can think of chemists as magicians having magic wands in the lab,” Cheng says. “We wave the wand and a reaction goes on.” These Nobel laureates gave chemists “a new wand,” that’s drastically more efficient and less wasteful, he says.

Making new drugs or designing novel materials often requires building new molecules from simpler chemical building blocks. But these chemical building blocks can’t just be thrown together. Instead, they must be carefully combined in precise arrangements through a series of chemical reactions. Many chemical reactions produce two versions of a molecule that are mirror images of one another, and often those two versions can have very different effects. For example, thalidomide, a drug prescribed in the 1950s and ‘60s for morning sickness, caused birth defects in more than 10,000 babies because of one mirror image of this molecule (SN: 12/24/94). Consequently, building these asymmetric molecules and controlling which version of a molecule gets produced is extremely important, especially for drug development.
Chemical reactions can be coaxed along by catalysts — molecular workhorses that accelerate chemical reactions without being transformed by them. Historically, chemists have known about two kinds of catalysts: enzymes and metal complexes. Enzymes are big, clunky proteins that have been honed by evolution to perform very specific chemical actions in the body, but they can be difficult to use on a large scale in the lab. Metals, such as platinum or cobalt, can kick-start some reactions too, but many only work in airless, waterless environments that are difficult to achieve in manufacturing contexts (SN: 2/21/17). Additionally, many metal catalysts are also toxic to the environment and expensive to procure.

For much of the history of chemistry, these were the only tools available to chemists who wanted to make new molecules. “But in the year 2000, everything changed,” Pernilla Wittung-Stafshede, a chemist at Chalmers University of Technology in Gothenburg, Sweden and a member of the Nobel Committee for Chemistry, said during the news conference.

Benjamin List, then at Scripps Research Institute in La Jolla, Calif., was studying the aldol reaction, which links two molecules together through carbon bonds. In organisms, such reactions are crucial for converting food into energy, and depend on a large and complex enzyme called aldolase A. Only a small part of the enzyme actually catalyzes the reaction, however, and List discovered that a single amino acid — proline — could do the work of this big clunky protein while also producing one version of the final product much more often than the other.
“When I did this experiment, I didn’t know what would happen and I thought maybe it’s a stupid idea,” List said during the news conference. “When I saw it work, I did feel it could be something big.”

Unbeknown to List, MacMillan was also looking for alternative organic catalysts around the same time. MacMillan, then at the University of California, Berkeley, focused on another chemical reaction, the Diels-Alder reaction, which forms rings of carbon atoms (SN: 11/18/50). It’s an important reaction, used today to make products as different as rubber and pharmaceuticals, but was very slow and relied on finicky metal catalysts that wouldn’t work when wet. MacMillan designed small organic molecules that mimicked the catalytic action of metals in a simpler way, while also favoring the production of one of two possible mirror images of the final product. He coined this new kind of catalysis “asymmetric organocatalysis.”

List’s and MacMillan’s discoveries set off an explosion of research into finding more organocatalysts over the next two decades, work that’s aided drug discovery among other uses.

About 35 percent of the world’s gross domestic product depends on catalysis, Peter Somfai, a chemist at Lund University in Sweden and a member of the Nobel Committee for Chemistry, said during the news conference. “We now have a new powerful tool available for making organic molecules,” one that can be drastically more efficient and greener than previous methods.

Somfai highlighted this leap forward in efficiency using the neurotoxin strychnine. The molecule itself isn’t useful for chemists, but its complicated structure makes it a good benchmark for comparing different synthesis methodologies. Previously, chemists relied on an extremely wasteful process of 29 different reactions where just 0.0009 percent of the initial material became strychnine. Using organocatalysis, strychnine can now be synthesized in just 12 steps, and the whole process is 7,000 times more efficient, Somfai said. And because this extra efficiency is gained without using toxic metals, organocatalysis is a more environmentally friendly way of synthesizing chemicals.

If building new molecules is like playing chess, organocatalysis has “completely changed the game,” Somfai said. “It’s like adding a new chess piece that can move in different ways.”

This eco-friendly glitter gets its color from plants, not plastic

All that glitters is not green. Glitter and shimmery pigments are often made using toxic compounds or pollutive microplastics (SN: 4/15/19). That makes the sparkly stuff, notoriously difficult to clean up in the house, a scourge on the environment too.

A new, nontoxic, biodegradable alternative could change that. In the material, cellulose — the main building block of plant cell walls — creates nanoscale patterns that give rise to vibrant structural colors (SN: 9/28/21). Such a material could be used to make eco-friendly glitter and shiny pigments for paints, cosmetics or packaging, researchers report November 11 in Nature Materials.

The inspiration to harness cellulose came from the African plant Pollia condensata, which produces bright, iridescent blue fruits called marble berries. Tiny patterns of cellulose fibers in the berries’ cell walls reflect specific wavelengths of light to create the signature hue. “I thought, if the plants can make it, we should be able to make it,” says chemist Silvia Vignolini of the University of Cambridge.

Vignolini and colleagues whipped up a watery mixture containing cellulose fibers and poured it onto plastic. As the liquid dried into a film, the rodlike fibers settled into helical structures resembling spiral staircases. Tweaking factors such as the steepness of those staircases changed which wavelengths of light the cellulose arrangements reflected, and therefore the color of the film.

That allowed the researchers, like fairy-tale characters spinning straw into gold, to transform their clear, plant-based slurry into meter-long shimmery ribbons in a rainbow of colors. These swaths could then be peeled off their plastic platform and ground up to make glitter.
“You can use any type of cellulose,” Vignolini says. Her team used cellulose from wood pulp, but could have used fruit peels or cotton fibers left over from textile production.

The researchers need to test the environmental impacts of their newfangled glitter. But Vignolini is optimistic that materials using such natural ingredients have a bright future.

50 years ago, corporate greenwashing was well under way

Environmental advertising: A question of integrity— Science News, November 27, 1971

A new report published by the Council on Economic Priorities clearly outlines facts showing that much corporate advertising on environmental themes is irrelevant or even deceptive.… A large percentage of the environmental advertising comes from companies that are the worst polluters.

Update
Concerns about “greenwashing,” a term coined in the 1980s to describe the practice of organizations marketing their products as environmentally friendly when they are not, have persisted into the current climate crisis. As more consumers have become environmentally conscious, corporations’ greenwashing tactics have evolved. For instance, some energy companies in the United States have claimed that natural gas is a “clean” energy source because the power plants emit less carbon dioxide than coal plants. But natural gas plants can emit large amounts of methane, a potent greenhouse gas. In 2022, the U.S. Federal Trade Commission plans to review its “Green Guides,” rules for companies that make environmental claims.