In paint form, the world's "whitest white" reflects so much light that surfaces become cooler than the surrounding air.
- Scientists at Purdue University announce the whitest white ever developed. It will be available as paint and a nanofilm.
- The new paint can actually cool surfaces on which it's applied, potentially reducing the need for climate-unfriendly air conditioners.
- This is the second whitest white to come from these researchers, and they believe this is about as white as any material could ever be.
A few years ago, researchers announced the development of the blackest black ever, a place where colors go to die. It was called Vantablack®, and it was so absorptive of visible light that only the tiniest amount escaped its surface to reflect back to our eyes. (All of that light energy is dissipated into the surrounding substrate, so Vantablack doesn't become hot.)
In a new paper published in the journal ACS Applied Materials & Interfaces, scientists at Purdue University announced BaSO4 (barium sulfate), the whitest white ever. BaSO4 is practically impervious to the colors of the visible spectrum. Even better, while it's a very cool invention in the colloquial sense, it's also cool in the thermal sense.
The coolest white
The infrared image on the right shows how a square of the super-white paint and the board on which it's painted — shown in a normal image on the left — are cooler than the surrounding materials.Credit: Purdue University/Joseph Peoples
Most outside paints actually warm the surfaces to which they're applied. While there are already some reflective paints on the market, they only reflect 80 to 90 percent of sunlight, not enough for a cooling effect.
By contrast, BaSO4 results in 98.1 percent of sunlight bouncing off. According to senior investigator Xuilin Ruan, "If you were to use this paint to cover a roof area of about 1,000 square feet, we estimate that you could get a cooling power of 10 kilowatts. That's more powerful than the central air conditioners used by most houses."
Ruan and his colleagues tested BaSO4 using thermocouples, high-accuracy devices that measure voltage to determine temperature. They found that at night, BaSO4 surfaces are 19° F. cooler than surrounding air. Under strong sunlight the effect is not quite so extreme, but still dramatic: 8° of cooling.
The researchers even found the paint works in cold weather. Testing it on a 43° F. day, the surface on which BaSO4 was painted was a brisk 25° F. Their tests also indicate that BaSO4 is hardy enough for outdoor conditions.
How the new white was developed
Xuilin Ruan and a square of BaSO4Credit: Purdue University/Jared Pike
Research in the field of radiative paint for cooling goes back to the 1970s, though Ruan's team has been working toward BaSO4 for only six years. Along the way, they analyzed over 100 reflective materials, trying them out in about 50 experimental formulations.
Lead author, postdoc Xiangyu Li explains, "We looked at various commercial products, basically anything that's white. We found that using barium sulfate, you can theoretically make things really, really reflective, which means that they're really, really white."
The whitest white paint before — developed by the same team just last autumn — depended on calcium carbonate, a compound commonly found in seashells, rocks, and blackboard chalk.
The team crammed as many tiny BaSO4 particles into the paint as possible. Says Li: "Although a higher particle concentration is better for making something white, you can't increase the concentration too much. The higher the concentration, the easier it is for the paint to break or peel off."
Another factor that makes the team's BaSO4 formulation so reflective is that the researchers used barium sulfate particles of many different sizes. When it comes to reflecting light, size matters.
Co-author and PhD student Joseph Peoples said, "A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance."
The team's formulation method, they report, is compatible with commercial paint production.
Cool support for the planet
Purdue has applied for patents relating to BaSO4, though there are as yet no plans to make it commercially available.
However, the sooner they release it, the better. Air conditioning currently accounts for 12% of U.S. energy consumption. Also, many air conditioners use hydrofluorocarbons (HFCs). While HFCs constitute just a small percentage of greenhouse gases, they trap thousands of times the amount of heat as carbon dioxide.
Therefore, BaSO4 can play a role in combating global warming by reducing energy consumption and the emission of HFCs.
Celebrate Science Day 2020 by proving the Earth is not flat.
- Flat-Earthers drive rational people nuts.
- A physicist offers three experiments to confirm it is those people who are crazy, not you.
- The experiments, however, do require a belief in mathematics.
Happy World Science Day! It's been a rough year for ol' science, which probably hasn't been under attack by so many people since the (last) Dark Ages. Conspiracy theorists at heart, anti-maskers, anti-vaxxers, and perhaps most unbelievably of all, flat-Earthers have been loudly calling into question the pretty-much unquestionable.
In any event, physicist Steven Wooding — the guy who brought us the contactable alien civilization calculator last spring — has offered up a lovely gift for science on its special day: the Flat vs. Round Earth Calculator. It consists of three experiments that can prove to anyone who believes in math that the Earth really is round. We can probably assume, of course, that there are now people arguing that 2+2=5. For these folks we'll point out simply that if the Earth really were flat, cats would have long ago pushed everything over its edge.
Be sure to scroll down the calculator page for Wooding's entertaining treatise on why the whole flat-Earth idea is so forehead-smackingly stupid.
Experiment 1: Catch a sunset twice
Credit: Johannes Plenio/Unsplash
At the top of the calculator is the "Select an experiment" drop-down menu. Let's start with the "sunset twice" experiment.
Wooding notes that you can prove the Earth is round by standing up quickly right after the Sun goes down and getting ahead of the shadow cast by the horizon so you can see the sun set a second time. If the planet were flat, once it went over the edge from your first viewing position it would be gone.
You may want to find out the time of sunset before testing out the calculator. There are many places online to find this information. Here's one.
To use the calculator, begin by selecting a city in your time zone. Wooding has pre-entered the sunset duration for you, though you can look up the precise value online for your location.
There are three ways to increase your height, selected from the "Ideas" menu: standing up from a lying down position, taking the sky-lift elevator at the Burj Khalifa Hotel in Dubai, or sending up a drone with a camera on it. Most of us will select the first option.
Next, you enter your starting height (the default for lying down is .6562 feet), how long it will take you to stand up, and then the final standing elevation, presumably of your eyes.
What the calculator finds for you is the percentage of the second sunset you'll see. Note that for the sky-lift and drone tests, you see a lot more of that second sunset given the greater height and your accelerated ascent speed.
Experiment 2: Disappearing object
Credit: Michael Olsen/Unsplash
Thanks to the curvature of the Earth, you can make an object on a distant lake shore seem to disappear with a change in viewing height.
You'll need binoculars for this one. And, um, a lake.
The calculator will tell you how much of the object will become unobservable after you fill in the three values.
(You may also need a boat to measure the distance.)
Experiment 3: Stick shadows
Credit: Logan Radinovich/Unsplash
For this one you'll need a cooperative friend who lives at least some distance away, or a teleporter. Also two sticks and a day with enough sunlight to cast shadows in both locations.
This experiment involves measuring shadows cast at two different locations and calculating the angle between them to arrive at the Earth's circumference.
This experiment is a little advanced mathematically, and Wooding offers a help link if you're confused.
The study identified superhabitable planets outside of our solar system.
- The odds are that if Earth had the right conditions for the development of life, other places probably do, too.
- Scientists have identified two dozen planets that match some items on the list of desirable traits.
- All of these planets are too far away to reach with current tech, but may be valuable research targets.
It's called the "overview effect." You know, the renewed appreciation and protectiveness that astronauts orbiting the globe come to feel looking down on our precious Earth. The sense of profound awe and gratitude that we find ourselves in a place so special among the cold, vast emptiness of space. Now a study from Washington State University (WSU) says there are lots of planets out there better than this one.
The 24 candidates in their habitable zone near K dwarf stars
Credit: Schulze-Makuch, et al./Astrobiology
On the other hand, all that desirable real estate is pretty far away — none of these 24 "superhabitable" planets are less than 100 light years from Earth. They were identified in a study led by geologist Dirk Schulze-Makuch of WSU and Technical University in Berlin, Germany. He was joined in the research by astrophysicists René Heller of the Max Planck Institute for Solar System Research in Germany and Edward Guinan of Villanova University.
The open-access study is published in the journal Astrobiology.
Ignoring the possibility that other planets might be even more likely to support life than ours is, after all, like someone insisting they live in the best country in the world without having visited any others. The study puts it this way: "Neglecting this possible class of 'superhabitable' planets, however, could be considered anthropocentric and geocentric biases."
In searching for superhabitable planets among the 4,500 known candidates, the scientists were not so much looking for somewhere for us to escape to as they were spotting planets that were most likely to be populated by intelligent life. Their hope is to offer up interesting targets for future investigation by instruments such as the European Space Agency's PLATO space telescope, as well as NASA's James Webb Space Telescope and LUVOIR space observatory.
Schulze-Makuch tells WSU Insider:
"With the next space telescopes coming up, we will get more information, so it is important to select some targets. We have to focus on certain planets that have the most promising conditions for complex life. However, we have to be careful to not get stuck looking for a second Earth because there could be planets that might be more suitable for life than ours."
Before one can go searching for superhabitable planets, once must figure out what that word means.
Blame it on the sun
Credit: Tungdil Preston/Unsplash
The scientists first had to work out the type of sun a superhabitable planet would be most likely to orbit. Interestingly, they decided against dwarf type G stars — also known as "dG stars" — similar to our own sun. After all, they write, "Since it took about 3.5 billion years on Earth until complex macroscopic life appeared, and about 4 billion years for technologically advanced life (us), life on many planets orbiting dG stars may simply run out of time."
Another issue is that young dG stars spin 10 times as fast as our mature Sun now does, producing "high levels of magnetic dynamo-driven activity and very intense coronal X-ray and chromospheric FUV emissions, which makes the origin and early evolution of life challenging."
The study settles on planets orbiting type K stars. These stars are a bit cooler than ours and less luminous, but they live a long time, longer than the Sun, from 20 to 70 billion years. This would give their planets more time to get life going.
Planets with a greater mass than ours were deemed desirable for a few reasons, so long as they were not so big as to become gas giants and so on. These planets would have robust, thick atmospheres, slightly higher temperatures for nurturing life, and lots of elbow room: "This would have advantages for the distribution of species and settlements of islands and continents."
The researchers also settled on an environmental checklist for superhabitable planets. Based on the conditions that allowed life to form on Earth, a planet would have to have the following life-supporting conditions as explained in the study:
- Temperatures —"Submarine hydrothermal systems, geothermal hot springs, brine pockets in sea ice at about −30°C, deep continental areas"
- pH — "Acid mine drainage, geothermal sulfurous sites (e.g., Yellowstone) Soda lakes, peridotite-hosted hydrothermal systems (e.g., Lost City vent)"
- Water activity — "Deep-sea brines, soda lakes, evaporate ponds, dry soils and rocks, food with high solute content"
- Lower O2 content — "Anoxic marine or lacustrine sediments, intestinal organs, early Earth environments"
- Pressure — "Deep oceanic trenches such as the 11,100 m deep Marianas Trench, Martian surface conditions (based on laboratory experiments)"
- Radiation — "No natural source of radiation on Earth at levels tolerated by D. radiodurans"
- Chemical extremes — "Submarine hydrothermal vent fluids and sulfides; some high-metal containing lakes"
We have some winners. Sort of.
Of the superhabitable candidates the study detected, none totally meet the researchers' criteria, though one has four of them, meaning it may be more likely to have life on it than Earth did, and it might be a place we could consider quite comfy.
Concludes Schulze-Makuch, "It's sometimes difficult to convey this principle of superhabitable planets because we think we have the best planet. We have a great number of complex and diverse lifeforms, and many that can survive in extreme environments. It is good to have adaptable life, but that doesn't mean that we have the best of everything."
The theory could resolve some unanswered questions.
- Most stars begin in binary systems, why not ours?
- Puzzles posed by the Oort cloud and the possibility of Planet 9 may be solved by a new theory of our sun's lost companion.
- The sun and its partner would have become separated long, long ago.
If most stars form in binary pairs, what about our Sun? A new paper presents a model supporting the theory that the Sun may have started out as one member of a temporary binary system. There's a certain elegance to the idea — if it's true, this origin story could resolve some vexing solar-system puzzles, among them the genesis of the Oort Cloud, and the presence of massive captured objects like a Planet Nine.
The paper is published in Astrophysical Journal Letters.
The Oort cloud
Image source: NASA
Scientist believe that surrounding the generally flat solar system is a spherical shell comprised of more than a trillion icy objects more than a mile wide. This is the Oort cloud, and it's likely the source of our solar system's long-term comets — objects that take 200 years or more to orbit the Sun. Inside that shell and surrounding the planets is the Kuiper Belt, a flat disk of scattered objects considered the source of shorter-term comets.
Long-term comets come at us from all directions and astronomers at first suspected their origins to be random. However, it turns out their likely trajectories lead back to a shared aphelion between 2,000 astronomical units (AU) from the Sun to about 100,000 AU, with their different points of origin revealing the shell shape of the Oort cloud along that common aphelion. (An astronomical unit is the distance from the Sun to the Earth.)
No object in the Oort cloud has been directly observed, though Voyager 1 and 2, New Horizons, and Pioneer 10 and 11 are all en route. (The cloud is so far away that all five of the craft will be dead by the time they get there.) To derive a clearer view of the Oort cloud absent actually imagery, scientists utilize computer models based on planetary orbits, solar-system formation simulations, and comet trajectories.
It's generally assumed that the Oort cloud is comprised of debris from the formation of the solar system and neighboring systems, stuff from other systems that we somehow captured. However, says paper co-author Amir Siraj of Harvard, "previous models have had difficulty producing the expected ratio between scattered disk objects and outer Oort cloud objects." As an answer to that, he says, "the binary capture model offers significant improvement and refinement, which is seemingly obvious in retrospect: most sun-like stars are born with binary companions."
"Binary systems are far more efficient at capturing objects than are single stars," co-author Ari Loeb, also of Harvard, explains. "If the Oort cloud formed as [indirectly] observed, it would imply that the sun did in fact have a companion of similar mass that was lost before the sun left its birth cluster."
Working out the source of the objects in the Oort cloud is more than just an interesting astronomical riddle, says Siraj. "Objects in the outer Oort Cloud may have played important roles in Earth's history, such as possibly delivering water to Earth and causing the extinction of the dinosaurs. Understanding their origins is important."
Image source: Caltech/R. Hurt (IPAC)/NASA
The gravitational pull resulting from a binary companion to the Sun may also help explain another intriguing phenomenon: the warping of orbital paths either by something big beyond Pluto — a Planet 9, perhaps — or smaller trans-Neptunian objects closer in, at the outer edges of the Kuiper Belt.
"The puzzle is not only regarding the Oort clouds, but also extreme trans-Neptunian objects, like the potential Planet Nine," Loeb says. "It is unclear where they came from, and our new model predicts that there should be more objects with a similar orbital orientation to [a] Planet Nine."
The authors are looking forward to the upcoming Vera C. Rubin Observatory (VRO) , a Large Synoptic Survey Telescope expected to capture its first light from the cosmos in 2021. It's expected that the VRO will definitively confirm or dismiss the existence of Planet 9. Siraj says, "If the VRO verifies the existence of Planet Nine, and a captured origin, and also finds a population of similarly captured dwarf planets, then the binary model will be favored over the lone stellar history that has been long-assumed."
Missing in action
Lord and Siraj consider it unsurprising that we see no clear sign of the Sun's former companion at this point. Says Loeb, "Passing stars in the birth cluster would have removed the companion from the sun through their gravitational influence. He adds that, "Before the loss of the binary, however, the solar system already would have captured its outer envelope of objects, namely the Oort cloud and the Planet Nine population."
So, where'd it go? Siraj answers, "The sun's long-lost companion could now be anywhere in the Milky Way."
A recent study tested how well the fungi species Cladosporium sphaerospermum blocked cosmic radiation aboard the International Space Station.
- Radiation is one of the biggest threats to astronauts' safety during long-term missions.
- C. sphaerospermum is known to thrive in high-radiation environments through a process called radiosynthesis.
- The results of the study suggest that a thin layer of the fungus could serve as an effective shield against cosmic radiation for astronauts.
When astronauts return to the moon or travel to Mars, how will they shield themselves against high levels of cosmic radiation? A recent experiment aboard the International Space Station suggests a surprising solution: a radiation-eating fungus, which could be used as a self-replicating shield against gamma radiation in space.
The fungus is called Cladosporium sphaerospermum, an extremophile species that thrives in high-radiation areas like the Chernobyl Nuclear Power Plant. For C. sphaerospermum, radiation isn't a threat — it's food. That's because the fungus is able to convert gamma radiation into chemical energy through a process called radiosynthesis. (Think of it like photosynthesis, but swap out sunlight for radiation.)
The radiotrophic fungus performs radiosynthesis by using melanin — the same pigment that gives color to our skin, hair and eyes — to convert X- and gamma rays into chemical energy. Scientists don't fully understand this process yet. But the study notes that it's "believed that large amounts of melanin in the cell walls of these fungi mediate electron-transfer and thus allow for a net energy gain."
Shunk et al.
Additionally, the fungus is self-replicating, meaning astronauts would potentially be able to "grow" new radiation shielding on deep-space missions, instead of having to rely on a costly and complicated interplanetary supply chain.
Still, the researchers weren't sure whether C. sphaerospermum would survive on the space station. Nils J.H. Averesch, a co-author of the study published on the preprint server bioRxiv, told SYFY WIRE:
"While on Earth, most sources of radiation are gamma- and/or X-rays; radiation in space and on Mars (also known as GCR or galactic cosmic radiation) is of a completely different kind and involves highly energetic particles, mostly protons. This radiation is even more destructive than X- and gamma-rays, so not even survival of the fungus on the ISS was a given."
To test the "radio-resistance" of C. sphaerospermum in space, petri dishes containing a .06-inch layer of the fungus were exposed to cosmic radiation aboard the ISS. Dishes containing no fungus were exposed, too. The results showed that the fungus cut radiation levels by about 2 percent.
Extrapolating these results, the researchers estimated that a roughly 8-inch layer of C. sphaerospermum "could largely negate the annual dose-equivalent of the radiation environment on the surface of Mars." That would be a significant benefit to astronauts. After all, an astronaut who is one year into a Mars mission would have been exposed to roughly 66 times more radiation than the average person on Earth.
International Space Station
To be sure, the researchers said more research is needed, and that C. sphaerospermum would likely be used in combination with other radiation-shielding technology aboard spacecraft. But the findings highlight how relatively simple biotechnologies may offer outsized benefits on upcoming space missions.
"Often nature has already developed blindly obvious yet surprisingly effective solutions to engineering and design problems faced as humankind evolves – C. sphaerospermum and melanin could thus prove to be invaluable in providing adequate protection of explorers on future missions to the Moon, Mars and beyond," the researchers wrote.