Tag Archives: #hot

Why Older People Should Chill When it’s Hot Out? (Biology)

Cooling off during extreme heat appears to help preserve cellular defenses

Taking a break from extreme heat, by visiting a cooling center for example, could help our cells protect themselves from damage, according to preliminary findings from a new study. The research, which focused on older people, suggests temporarily cooling down on a hot day helps cells maintain autophagy, a process cells use to rid themselves of dangerous protein buildups caused by stressors like extreme heat.

“By lessening the time spent in a state of elevated internal body temperature, cooling centers may help to preserve autophagy in older adults, which may translate to greater cellular protection and improved health outcomes during an extreme heat event,” said James J. McCormick, PhD, a postdoctoral fellow at the Human and Environmental Physiology Research Unit of the University of Ottawa in Canada, and the study’s first author.

McCormick will present the research at the American Physiological Society annual meeting during the Experimental Biology (EB) 2021 meeting, held virtually April 27-30.

Sustained elevations in internal body temperature can lead to heat stroke, cardiovascular events and kidney failure. Older people are particularly vulnerable since the body’s systems for regulating temperature degrade as we age.

A researcher pipettes blood samples to measure markers of autophagy, a defense mechanism cells use to protect themselves from damage. © James McCormick, University of Ottawa.

During periods of extreme heat, health agencies recommend that people without home air conditioning spend a few hours in a cooled location, such as a cooling center or heat-relief shelter. However, there has been little research into how visiting a cooling center actually affects the physiological processes associated with heat exposure.

“With climate change, the global population is increasingly exposed to protracted periods of extreme heat,” said Robert D. Meade, a doctoral candidate who is part of the research team. “Prolonged exposure to hot temperatures can overwhelm the body’s ability to cool itself, particularly in older adults. Thus, there is a crucial need to develop evidence-based guidance for protecting older adults from extreme heat.”

The researchers analyzed how older people responded to a simulated heat wave with and without a cooling break. A total of 17 volunteers spent nine hours in a room heated to 40° C (104° F). In the middle of the day, seven of the volunteers had a two-hour break in a room that was a comfortable 23° C (73° F).

While the cooling break did not result in lasting reductions in participants’ core body temperature, these participants did show improved markers of autophagic function compared to the group that endured high heat for the full nine hours. The findings suggest that visiting a cooling center could help older people avoid some of the cellular damage that may contribute to serious health impacts of heat exposure, according to researchers.

The researchers plan to conduct further studies to determine whether other cooling strategies, such as using a fan, could also help to preserve autophagic function in older adults.

McCormick will present this research in poster R3744 (abstract). Contact the media team for more information or to obtain a free press pass to access the virtual meeting.

Featured image: A volunteer in the test chamber used for the research. The chamber is heated to simulate a heat wave while devices continually monitor whole-body heat exchange. © James McCormick, University of Ottawa.


Provided by American Physiological Society


About Experimental Biology 2021

Experimental Biology is an annual meeting comprised of thousands of scientists from five host societies and multiple guest societies. With a mission to share the newest scientific concepts and research findings shaping clinical advances, the meeting offers an unparalleled opportunity for exchange among scientists from across the U.S. and the world who represent dozens of scientific areas, from laboratory to translational to clinical research. http://www.experimentalbiology.org 

About the American Physiological Society (APS)

Physiology is a broad area of scientific inquiry that focuses on how molecules, cells, tissues and organs function in health and disease. The American Physiological Society connects a global, multidisciplinary community of more than 10,000 biomedical scientists and educators as part of its mission to advance scientific discovery, understand life and improve health. The Society drives collaboration and spotlights scientific discoveries through its 16 scholarly journals and programming that support researchers and educators in their work. http://www.physiology.org

How Can Some Planets Be Hotter Than Stars? (Planetary Science)

PhD student Quentin Changeat and Dr Billy Edwards (both UCL Physics & Astronomy) explain how we examine the atmospheres of exoplanets (planets outside our solar system) as well as what the benefits of understanding these distant planets could be.

Until the early 2000s, the only known planets were located in our own neighbourhood, the Solar System. They broadly form two categories: the small rocky planets in the inner Solar System and the cold gaseous planets located in the outer part. With the discovery of exoplanets, planets orbiting stars other than the Sun, additional classes of planets were discovered and a new picture started to emerge. Our Solar System is by no means typical.

For example, data from the Kepler mission has shown that large, gaseous exoplanets can orbit very close to their star – rather than far away from it, as is the case in our Solar System, causing them to reach temperatures exceeding 1,000K (727°C). These have been dubbed “hot” or “ultra-hot” Jupiters. And while most other exoplanets are smaller, between the size of Neptune and Earth, we don’t know much about their composition.

Image: L-R: Quentin Changeat, Dr Billy Edwards © UCL

But how can hot, gaseous planets form and exist so close to their star? What kind of extreme physical processes happen here? Answers to those questions have large implications in our understanding of exoplanets and solar system planets. In our recent study, published in The Astrophysical Journal Letters, we have added another piece to the puzzle of planet formation and evolution.

Kelt-9 b

The hottest exoplanet known so far is Kelt-9 b, which was discovered in 2016. Kelt-9 b orbits a star that is twice as hot as our Sun, at a distance ten times closer than Mercury orbits our star. It is a large gaseous exoplanet, with a radius 1.8 times that of Jupiter and temperatures reaching 5,000K. For comparison, this is hotter than 80% of all the stars in the universe and a similar temperature to our Sun.

In essence, hot Jupiters are a window into extreme physical and chemical processes. They offer an incredible opportunity to study physics in environmental conditions that are near impossible to reproduce on Earth. Studying them enhances our understanding of chemical and thermal processes, atmospheric dynamics and cloud formation. Understanding their origins can also help us improve planetary formation and evolution models.

We are still struggling to explain how planets form and how elements, such as water, were delivered to our own Solar System. To find out, we need to learn more about exoplanet compositions by observing their atmospheres.

Observing atmospheres

There are two main methods to study exoplanet atmospheres. In the transit method, we can pick up stellar light that is filtered through the exoplanet’s atmosphere when it passes in front of its star, revealing the fingerprints of any chemical elements that exist there.

The other method to investigate a planet is during an “eclipse”, when it passes behind its host star. Planets also emit and reflect a small fraction of light, so by comparing the small changes in the total light when the planet is hidden and visible, we can extract the light coming from the planet.

Both types of observations are performed at different wavelengths, or colours, and since chemical elements and compounds absorb and emit at very specific wavelengths, a spectrum (light broken down by wavelength) can be produced for the planet to infer the composition of its atmosphere.

The secrets of Kelt-9 b

In our study, we used publicly available data, taken by the Hubble Space Telescope, to obtain the eclipse spectrum of this planet.

We then used open-source software to extract the presence of molecules and found there were plenty of metals (made from molecules). This discovery is interesting as it was previously thought that these molecules would not be present at such extreme temperatures – they would be broken apart into smaller compounds.

Subject to the strong gravitational pull from its host star, Kelt-9 b is “tidally locked”, which means that the same face of the planet permanently faces the star. This results in a strong temperature difference between the planet’s day and night sides. As the eclipse observations probe the hotter day-side, we suggested that the observed molecules could in fact be dragged by dynamic processes from the cooler regions, such as the night-side or from deeper in the interior of the planet. These observations suggest that the atmospheres of these extreme worlds are ruled by complex processes that are poorly understood.

Kelt-9 b is interesting because of its inclined orbit of about 80 degrees. This suggests a violent past, with possible collisions, which in fact is also seen for many other planets of this class. It is most likely that this planet formed away from its parent star and that the collisions happened as it migrated inwards toward the star. This supports the theory that large planets tend to form away from their host star in proto-stellar disks – which give rise to solar systems – capturing gaseous and solid materials as they migrate toward their star.

But we don’t know the details of how this happens. So it is crucial to characterise many of these worlds to confirm various scenarios and better understand their history as a whole.

Future missions

Observatories, such as the Hubble Space Telescope, were not designed to study exoplanet atmospheres. The next generation of space telescopes, such as the James Webb Space Telescope and the Ariel mission, will have much better capabilities and instruments specifically tailored for the rigorous observation of exoplanet atmospheres. They will allow us to answer many of the fundamental questions raised by the extremely hot-Jupiter planet class, but they will not stop there.

This new generation of telescopes will also probe the atmosphere of small worlds, a category that current instruments struggle to reach. In particular, Ariel, which is expected to launch in 2029, will observe about 1,000 exoplanets to tackle some of the most fundamental questions in exoplanet science.

Ariel will also be the first space mission to look in details at the atmosphere of these worlds. It should finally tell us what these exoplanets are made of and how they formed and evolved. This will be a true revolution.

This article was originally published in IOP science on 11 March 2021.

Featured image: Artist impression of KELT-9 b, the orange blob orbiting a blue star. Léa Changeat, Author provided


Reference: Quentin Changeat and Billy Edwards, “The Hubble WFC3 Emission Spectrum of the Extremely Hot Jupiter KELT-9b”, The Astrophysical Journal Letters, Volume 907, Number 1, 2021. https://iopscience.iop.org/article/10.3847/2041-8213/abd84f/meta


Provided by UCL

Human Biology Registers Two Seasons, Not Four (Biology)

A Stanford Medicine study finds that changes in molecular patterns in Californians correspond with two nontraditional “seasons.”

As kids, we learn there are four seasons, but researchers at the Stanford School of Medicine have found evidence to suggest that the human body doesn’t see it this way.

“We’re taught that the four seasons — winter, spring, summer and fall — are broken into roughly equal parts throughout the year, and I thought, ‘Well, who says?’” Michael Snyder, PhD, professor and chair of genetics, said. “It didn’t seem likely that human biology adheres to those rules. So we conducted a study guided by people’s molecular compositions to let the biology tell us how many seasons there are.”

Four years of molecular data from more than 100 participants indicate that the human body does experience predictable patterns of change, but they don’t track with any of Mother Nature’s traditional signals. Overall, Snyder and his team saw more than 1,000 molecules ebb and flow on an annual basis, with two pivotal time periods: late spring-early summer and late fall-early winter. These are key transition periods when change is afoot — both in the air and in the body, said Snyder, who is the Stanford W. Ascherman, MD, FACS, Professor in Genetics.

“You might say, ‘Well, sure, there are really only two seasons in California anyway: cold and hot,” Snyder said. “That’s true, but even so, our data doesn’t exactly map to the weather transitions either. It’s more complicated than that.”

Snyder hopes that observations from this study — of higher levels of inflammatory markers in the late spring, or of increased markers of hypertension in early winter, for example — can provide a better foundation for precision health and even help guide the design of future clinical drug trials.

One caveat, Snyder said, is that the team conducted the research with participants in Northern and Southern California, and it’s likely that the molecular patterns of individuals in other parts of the country would differ, depending on atmospheric and environmental variations.

The study was published online Oct. 1 in Nature Communications. Snyder is the senior author. Postdoctoral scholars Reza Sailani, PhD, and Ahmed Metwally, PhD, share lead authorship.

Spring-ish and winter-ish

The study was conducted in 105 individuals who ranged in age from 25 to 75. About half were insulin resistant, meaning their bodies don’t process glucose normally. About four times a year, the participants provided blood samples, which the scientists analyzed for molecular information about immunity, inflammation, cardiovascular health, metabolism, the microbiome and much more. The scientists also tracked the exercise and dietary habits of all participants.

Over the span of four years, data showed that the late-spring period coincided with a rise in inflammatory biomarkers known to play a role in allergies, as well as a spike in molecules involved in rheumatoid arthritis and osteoarthritis. They also saw that a form of hemoglobin called HbAc1, a protein that signals risk for Type 2 diabetes, peaked during this time, and that the gene PER1, which is known to be highly involved in regulating the sleep-wake cycle, was also at its highest.

In some cases, Snyder said, it’s relatively obvious why levels of molecules increased. Inflammatory markers probably spike due to high pollen counts, for instance. But in other cases, it’s less obvious. Snyder and his team suspect that HbA1c levels are high in the late spring because of the often indulgent eating that accompanies the holidays — HbA1c levels reflect dietary habits from about three months before measurements are taken — as well as a general waning of exercise in the winter months.

As Snyder and his team followed the data into early winter, they saw an increase in immune molecules known to help fight viral infection and spikes of molecules involved in acne development. Signatures of hypertension, or high blood pressure, were also higher in the winter.

The data also showed that there were some unexpected differences in the microbiomes of individuals who were insulin resistant and those of individuals who processed glucose normally. Veillonella, a type of bacteria involved in lactic acid fermentation and the processing of glucose, was shown to be higher in insulin-resistant individuals throughout the year, except during mid-March through late June.

Parsing seasonality

“Many of these findings open up space to investigate so many other things,” Sailani said. “Take allergies, for instance. We can track which pollens are circulating at specific times and pair that with personalized readouts of molecular patterns to see exactly what a person is allergic to.”

The hope is that more information about a person’s molecular ups and downs will allow them to better understand the context of their body’s biological swings and will enable them to use that information to proactively manage their health.

“If, for instance, your HbA1C levels are measured during the spring and they seem abnormally high, you can contextualize that result and know that this molecule tends to run high during spring,” Snyder said. “Or, you could see it as a sort of kick in the pants, so to speak, to exercise more during the winter in an effort to keep some of these measurements down.”

Even more broadly speaking, these findings could also help inform the design of drug trials. For example, if researchers are hoping to test a new drug for hypertension, they would likely benefit from knowing that because hypertension seems to spike in the early winter months, trials that started in winter versus spring would likely have different outcomes.

Other Stanford authors of the paper are former postdoctoral scholars Wenyu Zhou, PhD, Sara Ahadi, PhD, Tejaswini Mishra, PhD, and Lukasz Kidzinski, PhD; instructor of genetics Sophia Miryam Rose, MD, PhD; life science researcher Kevin Contrepois, PhD; graduate student Martin Zhang; and adjunct clinical assistant professor of pediatrics Theodore Chu, MD.

This study was funded by the National Institutes of Health (grants U54DK102556, R01 DK110186-03, R01HG008164, NIH S10OD020141, UL1 TR001085 and P30DK116074).

References: Sailani, M.R., Metwally, A.A., Zhou, W. et al. Deep longitudinal multiomics profiling reveals two biological seasonal patterns in California. Nat Commun 11, 4933 (2020). https://doi.org/10.1038/s41467-020-18758-1 link: https://www.nature.com/articles/s41467-020-18758-1

Provided by Stanford School Of Medicine

The First Ultra-Hot Neptune, LTT 9779b, Is One Of Nature’s Unlikely Planets (Astronomy)

About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet. All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (R⊕), or apparently rocky planets smaller than 2 R⊕. Such lack of planets of intermediate size (the ‘hot Neptune desert’) has been interpreted as the inability of low-mass planets to retain any hydrogen/helium (H/He) envelope in the face of strong stellar irradiation. In a new paper, an international team of astronomers, including a group from the University of Warwick, reported the discovery of tht first Ultra Hot Neptune planet, “LTT 9979b”, orbiting the nearby star LTT 9779.

LTT 9779 is a Sun-like star located at a distance of 260 light-years, a stone’s throw in astronomical terms. It is super metal-rich, having twice the amount of iron in its atmosphere than the Sun. This could be a key indicator that the planet was originally a much larger gas giant, since these bodies preferentially form close to stars with the highest iron abundances.

Data from the Transiting Exoplanet Survey Satellite revealed transits of the bright Sun-like star LTT 9779 every 0.79 days. This ultrashort-period planet has a radius of 4.6 R⊕ and a mass of 29 M⊕, firmly in the hot Neptune desert.

Although the world weighs twice as much as Neptune does, it is also slightly larger and so has a similar density. Therefore, LTT 9779b should have a huge core of around 28 Earth-masses, and an atmosphere that makes up around 9% of the total planetary mass.

The planet’s mean density is similar to that of Neptune. With an equilibrium temperature around 2,000 K, it is unclear how this ‘ultrahot Neptune’ managed to retain such an envelope.

Calculations by Dr. King confirmed that the atmosphere of LTT 9779b should have been stripped of its atmosphere through a process called photoevaporation. According to him, “Intense X-ray and ultraviolet from the young parent star will have heated the upper atmosphere of the planet and should have driven the atmospheric gasses into space.” On the other hand, Dr. King’s calculations showed there was not enough X-ray heating for LTT 9779b to have started out as a much more massive gas giant. “Photoevaporation should have resulted in either a bare rock or a gas giant,” he explained. “Which means there has to be something new and unusual we have to try to explain about this planet’s history.”

While, as per planetary structure models, the planet is a giant core dominated world, but crucially, there should exist two to three Earth-masses of atmospheric gas. But if the star is so old, why does any atmosphere exist at all? Well, if LTT 9779b started life as a gas giant, then a process called Roche Lobe Overflow could have transferred significant amounts of the atmospheric gas onto the star.

Roche Lobe Overflow is a process whereby a planet comes so close to its star that the star’s stronger gravity can capture the outer layers of the planet, causing it to transfer onto the star and so significantly decreasing the mass of the planet. Models predict outcomes similar to that of the LTT 9779 system, but they also require some fine tuning.

Since the planet does seem to have a significant atmosphere, and that it orbits a relatively bright star, future studies of the planetary atmosphere may unlock some of the mysteries related to how such planets form, how they evolve, and the details of what they are made of.

References: Jenkins, J.S., Díaz, M.R., Kurtovic, N.T. et al. An ultrahot Neptune in the Neptune desert. Nat Astron (2020). https://doi.org/10.1038/s41550-020-1142-z link: https://www.nature.com/articles/s41550-020-1142-z

This Newly Developed 3-D Printing Method Of Milk Products Can Maintain Its Temperature-Sensitive Nutrients (Chemistry)

Researchers from the Singapore University of Technology and Design (SUTD) have developed a method perform direct ink writing (DIW) three-dimensional (3D) printing of milk products at room temperature by changing the rheological properties of the printing ink.

A – D: 3D printed milk structures of couch, fortress, wheel, and cloverleaf, respectively. E: 3D printed cone containing liquid chocolate syrup as an internal filling.F: 3D printed cube with four compartments containing liquid blueberry syrup, liquid chocolate syrup, milk cream, maple syrup as internal fillings. Credit: SUTD

3-D printing of food has been achieved by different printing methods, including the widely used selective laser sintering (SLS) and hot-melt extrusion methods. However, these methods are not always compatible with temperature-sensitive nutrients found in certain types of food. For instance, milk is rich in both calcium and protein, but as these nutrients are temperature sensitive, milk is unsuitable for 3-D printing using the aforementioned printing methods which require high temperature. While the cold-extrusion is a viable alternative, it often requires rheology modifiers or additives to stabilize printed structures. Optimizing these additives is a complex and judicious task.

To tackle these limitations, the research team from SUTD’s Soft Fluidics Lab changed the rheological properties of the printing ink and demonstrated DIW 3-D printing of milk (refer to image) by cold-extrusion with a single milk product—powdered milk. The team found that the concentration of milk powder allowed for the simple formulation of 3-D-printable milk inks using water to control the rheology. Extensive characterizations of the formulated milk ink were also conducted to analyze their rheological properties and ensure optimal printability.

Given the versatility of the demonstrated method, they envision that cold extrusion of food inks will be applied in creating nutritious and visually appealing food, with potential applications in formulating foods with various needs for nutrition and materials properties, where food inks could be extruded at room temperature without compromising the nutrients that would be degraded at elevated temperatures.

References: Cheng Pau Lee et al, 3D printing of milk-based product, RSC Advances (2020). DOI: 10.1039/D0RA05035K link: https://pubs.rsc.org/en/content/articlelanding/2020/RA/D0RA05035K#!divAbstract

Rare Hot Neptune Found Orbiting Nearby Dwarf Star(Astronomy)

Astronomers using data from the Transiting Exoplanet Survey Satellite (TESS) reported the detection of a transiting hot Neptune exoplanet orbiting TOI-824 (SCR J1448-5735), a nearby K4V dwarf star located 210 light-years away in the constellation of Circinus. The newly discovered planet has a radius of 2.9 times that of the Earth, a mass of 18.5 Earth masses, and orbital period of 1.39 days.

The planet’s mean density is 4.03 g/cm³, making it more than twice as dense as Neptune.

Researchers detected TOI-824b in data from TESS and then confirmed its existence using the Planet Finder Spectrograph (PFS) and the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph.

TOI-824 b (black diamond) sits on the lower edge of the hot Neptune Desert. Other hot Neptunes discovered within the past year (TOI 132 b, LTT 9779 b, NGTS-4b, and HD 219666 b) are shown as diamonds, while compara￾ble planets with well-studied atmospheres (HAT-P-11b, GJ 3470 b, and GJ 436 b) are shown as squares. TOI-824 b inhabits a notably different region of this parameter space than even the most irradiated of the planets with well stud￾ied atmospheres (HAT-P-11b) and offers an opportunity to investigate how increased irradiation affects a variety of atmospheric characteristics.

TOI-824b’s high equilibrium temperature (980 degrees Celsius, or 1,796 degrees Fahrenheit) makes the planet likely to have a cloud free atmosphere, and thus an excellent candidate for follow up atmospheric studies.

The detectability of its atmosphere from both ground and space is promising and could lead to the detailed characterization of the most irradiated, small planet at the edge of the hot Neptune desert that has retained its atmosphere to date.


References: Jennifer A. Burt et al. 2020. TOI-824 b: A New Planet on the Lower Edge of the Hot Neptune Desert. AJ, in press; arXiv: 2008.11732 link: https://arxiv.org/abs/2008.11732

The Grand Prismatic Spring Is A Rainbow Of Heat-Loving Bacteria (Amazing Places)

The largest hot spring in Yellowstone National Park, the Grand Prismatic Spring, the hot spring radiates extremely hot water and stunning prismatic color from its center.

Don’t adjust your color settings—the Grand Prismatic Spring really is rainbow colored, following the spectrum of white light through a prism (red to blue). The spring was first officially described, and named, by the Hayden Expedition in 1871, which was the first federally-funded exploration of what became Yellowstone.

Grand Prismatic Spring from high viewpoint. Yellowstone National Park, Wyoming, United States of America. (© Don Johnston/All Canada Photos/Corbis)

But what causes the hot spring’s magnificent coloration? It’s all thanks to the heat-loving bacteria that call the spring home.

Hot springs form when heated water emerges through cracks in the Earth’s surface. Unlike geysers, which have obstructions near the surface (hence their eruptions), water from hot springs flows unobstructed, creating a nonstop cycle of hot water rising, cooling and falling. In the Grand Prismatic Spring, this constant cycle creates rings of distinct temperatures around the center: very, very hot water bubbles up from the middle and gradually cools as it spreads out across the spring’s massive surface (370 feet across).

Different color means different life in the spring. (© klaus Lang/All Canada Photos/Corbis)

Water at the center of the spring, which bubbles up 121 feet from underground chambers, can reach temperatures around 189 degrees Fahrenheit, which makes it too hot to sustain most life. Because there’s very little living in the center of the pool, the water looks extremely clear, and has a beautiful, deep-blue color, thanks to the scattering of blue wavelengths. But, as the water spreads out and cools, it creates concentric circles of varying temperatures—like a stacking matryoshka doll, if each doll signified a different temperature. And these distinct temperature rings are key, because each ring creates a very different environment inhabited by different types of bacteria. And it’s the different types of bacteria that give the spring its prismatic colors.

Within these rings live different organisms, including cyanobacteria, a type of bacteria that obtain their energy through photosynthesis. Look at the first band outside of the middle—see that yellow color? That’s thanks to a particular type of cyanobacteria, Synechococcus, that lives in that particular temperature band under extreme stressors. The temperature of that water is just barely cool enough to be habitable, at 165° F, but the bacteria prefer temperatures nearer to 149° F. But an abundance of light also introduces stress to the Synechococcus habitat.

The area around the Grand Prismatic Spring is virtually void of trees, or any kind of shade. That’s not just a problem for tourists, it’s also a challenge for Synechococcus. There’s no escaping the sun, and at the high elevation of Yellowstone, the ultraviolet light from the sun’s rays becomes extremely, extremely harsh.

But even though they’re living in too exposed and too hot water, Synechococcus manage to survive, through a balance of photosynthetic pigments—chemical compounds that reflect only certain wavelengths of visible light, making them appear various colors. The primary pigment for photosynthesis is chlorophyll, which we see as green. But chlorophyll levels can, at times, be surpassed by an accessory pigment known as carotenoids. Carotenoids are red, orange or yellow; the yellow of Synechococcus is exactly the same pigment, beta-Carotene, that in high concentrations makes the orange we see in carrots.

Carotenoids protect Synechococcus cells from extreme sunlight, by capturing harsh wavelengths (like ultraviolet) and passing that energy to chlorophyll pigments, which then convert light energy into chemical energy. So, since the Synechococcus living in the yellow temperature band live under harsh conditions, they produce more carotenoids than they would if they were living in optimal temperature conditions (like in the outer rings), giving the band its yellow color. If you were to skim a small amount of the Synechococcus off of the top of that temperature band, or find Synechococcus living where there is less harsh sunlight, the Synechococcus would look more like the blue-green algae we’re used to seeing in lakes and ponds elsewhere. Since Synechococcus’ color is so dependent on sunlight, it also means that in the winter, when the sun is less harsh, the bacteria produce fewer carotenoids, and therefore look less yellow, and more blue-green.

Depending on the season, the color of the spring can fluctuate. (© David Santiago Garcia/Aurora Photos/Corbis)

Moving outward from the yellow band, the temperature of the hot spring begins to cool, and as the temperature cools, a more diverse set of bacterial life can flourish. Synechococcus still live in the orange band (which is around 149 degrees Fahrenheit), but they’re joined by another type of bacteria, known as chloroflexi bacteria. Some chloroflexi bacteria are also photosynthetic, but produce energy using different types of chlorophyll and different types of carotenoids, which manifest as slightly different colors. The net result of this color diversity is the orange color that you see in pictures—it’s not that every bacterium manifests as orange individually, but that the composite color of all the different bacteria seen together is orange. And that orange color, like the yellow in the ring next to it, comes from carotenoids, which these bacteria produce to help shield themselves from the harsh light of Yellowstone’s summer sun.

The outermost ring is the coolest, at around 131°F, and home to the most diverse community of bacteria. As even more organisms are able to live in the outermost ring, the mix of their various carotenoids produces the darkest color of all—the kind of red brown that you see in the photos.

To view the Grand Prismatic Spring while in Yellowstone, head to the Midway Geyser Basin, about half-way between the Madison and Old Faithful regions of the park. From the parking lot there, take the trail south toward the Firehole River. The path will lead you alongside the hot spring, but for a truly spectacular view of the spring’s colors, get some height.