It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Saturday, December 23, 2023
Pancake stack of films on a balloon most accurate gamma-ray telescope
A SINGLE PANCAKE MAY CAPTURE WHERE YOU POKE A STRAW INTO IT, BUT IT TAKES A WHOLE STACK TO RECORD THE STRAW'S DIRECTION. SIMILARLY, KOBE UNIVERSITY RESEARCHERS COULD ACCURATELY IMAGE A GAMMA-RAY-EMITTING PULSAR (THE SKY’S LIGHTHOUSES) WITH A STACK OF RADIOACTIVITY-SENSITIVE FILMS ON A BALLOON. TO BE ABLE TO TELL THE ORIENTATION OF THE DANGLING GONDOLA RELATIVE TO THE STARS, THEY ADDED A STAR CAMERA AND A DEVICE TO TIMESTAMP THE GAMMA-RAYS’ IMPACTS.
A pancake stack of radioactivity-sensitive films carried through the sky by a balloon was able to take the world's most accurate picture of a neutron star's gamma ray beam. To achieve this, Kobe University researchers combined the oldest method of capturing radioactive radiation with the newest data capturing techniques and a clever time-recording device.
The stars shine their light on us in the full range of the spectrum of light, from infra-red to gamma rays. For each of these bands, different sensing equipment is needed. The most challenging one is gamma rays, famous for being a high-energy product of nuclear fission, because their very short wavelength means that they don't interact with matter in the same way as other forms of light and thus can't be deflected with lenses or detected by standard sensors. Thus, there is a gap in our ability to detect the light coming from fascinating stellar objects such as supernovae and their remnants.
To resolve this issue, Kobe University astrophysicist AOKI Shigeki and his team turned to the very first material that was used to detect radioactivity, photographic films. "Our group has been focusing on the excellent capability of emulsion film to trace gamma rays with high precision and proposed that it could become an excellent gamma-ray telescope by introducing several modern data capture and analysis features," explains Aoki. Based on the high sensitivity of these films and a novel, automated, high-speed process of extracting data from them, the physicists' idea was to stack up a few of them to accurately capture the trajectory of the particles that the gamma ray produces on impact, just like a single pancake may capture where you poke a straw into it, but it takes a whole stack to record the straw's direction.
To reduce atmospheric interference, they then mounted the stack of films onto a scientific observation balloon to lift it to a height between 35 and 40 kilometers. However, since a balloon is swaying and twisting in the wind, the direction of the "telescope" is not stable, so they added a set of cameras to record the gondola's orientation relative to the stars at any time. But this created another issue, because as anybody who has ever taken a photograph with long exposure knows, photographic film does not record the passage of time and so it is not directly possible to know at what time any given gamma ray impact occurred. To overcome this problem, they made the bottom three layers of film move back and forth at regular but different speeds, just like the hands of a clock. From the relative dislocation of the traces in those lower plates they could then calculate the precise time of the impact and thus correlate it with the cameras' footage.
They have now published the first image resulting from this setup in the journal The Astrophysical Journal. It is the most accurate image ever produced of the Vela pulsar, a fast-spinning neutron star that projects a beam of gamma rays into the sky like a lighthouse at night. "We captured a total of several trillion tracks with an accuracy of 1/10,000 millimeters. By adding time information and combining it with attitude monitoring information, we were able to determine ‘when’ and ‘where’ the events originated with such precision that the resulting resolution was more than 40 times higher than that of conventional gamma-ray telescopes," Aoki summarizes his group's achievements.
While these results are impressive already, the new technique opens the possibility of capturing more details in this frequency band of light than ever before. The Kobe University researcher explains, "By means of scientific balloon-borne experiments, we can attempt to contribute to many areas of astrophysics, and in particular to open up gamma-ray telescopy to 'multi-messenger astronomy' where simultaneous measurements of the same event captured through different techniques are required. Based on the success of the 2018 balloon experiment these data were generated with, we will expand the observation area and time in upcoming balloon flights and are looking forward to scientific breakthroughs in the field of gamma-ray astronomy."
This work was supported by JSPS KAKENHI grants 17H06132, 18H01228 and 18K13562. It was conducted in collaboration with researchers from Okayama University of Science, Aichi University of Education, Nagoya University and Gifu University.
Kobe University is a national university with roots dating back to the Kobe Commercial School founded in 1902. It is now one of Japan's leading comprehensive research universities with nearly 16,000 students and nearly 1,700 faculty in 10 faculties and schools and 15 graduate schools. Combining the social and natural sciences to cultivate leaders with an interdisciplinary perspective, Kobe University creates knowledge and fosters innovation to address society’s challenges.
The balloon carrying the gondola with the telescope takes off from Alice Springs, Australia.
A section of the emulsion film after development. The traces of the particles produced by gamma ray impacts can be seen as tiny greyish dots throughout the plane.
The image of the Vela pulsar. The image has a resolution more than 40 times better than what could be achieved previously: The circle at the bottom left indicates the pulsar’s image spread for comparison with the image spread of the previously best gamma ray image (of a different stellar object), indicated by the dashed circle.
THIS NASA HUBBLE SPACE TELESCOPE IMAGE FEATURES A BRIGHT SPIRAL GALAXY KNOWN AS MCG-01-24-014, WHICH IS LOCATED ABOUT 275 MILLION LIGHT-YEARS FROM EARTH.
This whirling image features a bright spiral galaxy known as MCG-01-24-014, which is located about 275 million light-years from Earth. In addition to being a well-defined spiral galaxy, MCG-01-24-014 has an extremely energetic core known as an active galactic nucleus (AGN) and is categorized as a Type-2 Seyfert galaxy. Seyfert galaxies, along with quasars, host one of the most common subclasses of AGN. While the precise categorization of AGNs is nuanced, Seyfert galaxies tend to be relatively nearby and their central AGN does not outshine its host, while quasars are very distant AGNs with incredible luminosities that outshine their host galaxies.
There are further subclasses of both Seyfert galaxies and quasars. In the case of Seyfert galaxies, the predominant subcategories are Type-1 and Type-2. Astronomers distinguish them by their spectra, the pattern that results when light is split into its constituent wavelengths. The spectral lines that Type-2 Seyfert galaxies emit are associated with specific ‘forbidden’ emission lines. To understand why emitted light from a galaxy could be forbidden, it helps to understand why spectra exist in the first place. Spectra look the way they do because certain atoms and molecules absorb and emit light at very specific wavelengths. The reason for this is quantum physics: electrons (the tiny particles that orbit the nuclei of atoms and molecules) can only exist at very specific energies, and therefore electrons can only lose or gain very specific amounts of energy. These very specific amounts of energy correspond to the wavelengths of light that are absorbed or emitted.
Forbidden emission lines should not exist according to certain rules of quantum physics. But quantum physics is complex, and some of the rules used to predict it were formulated under laboratory conditions here on Earth. Under those rules, this emission is ‘forbidden’ – so improbable that it’s disregarded. But in space, in the midst of an incredibly energetic galactic core, those assumptions don’t hold anymore, and the ‘forbidden’ light gets a chance to shine out toward us.
This photo of Saturn was taken by NASA's Hubble Space Telescope on October 22, 2023, when the ringed planet was approximately 850 million miles from Earth. Hubble's ultra-sharp vision reveals a phenomenon called ring spokes.
Saturn's spokes are transient features that rotate along with the rings. Their ghostly appearance only persists for two or three rotations around Saturn. During active periods, freshly-formed spokes continuously add to the pattern.
In 1981, NASA's Voyager 2 first photographed the ring spokes. NASA's Cassini orbiter also saw the spokes during its 13-year-long mission that ended in 2017.
Hubble continues observing Saturn annually as the spokes come and go. This cycle has been captured by Hubble's Outer Planets Atmospheres Legacy (OPAL) program that began nearly a decade ago to annually monitor weather changes on all four gas-giant outer planets.
Hubble's crisp images show that the frequency of spoke apparitions is seasonally driven, first appearing in OPAL data in 2021 but only on the morning (left) side of the rings. Long-term monitoring show that both the number and contrast of the spokes vary with Saturn's seasons. Saturn is tilted on its axis like Earth and has seasons lasting approximately seven years.
"We are heading towards Saturn equinox, when we'd expect maximum spoke activity, with higher frequency and darker spokes appearing over the next few years," said the OPAL program lead scientist, Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland.
This year, these ephemeral structures appear on both sides of the planet simultaneously as they spin around the giant world. Although they look small compared with Saturn, their length and width can stretch longer than Earth's diameter!
"The leading theory is that spokes are tied to Saturn's powerful magnetic field, with some sort of solar interaction with the magnetic field that gives you the spokes," said Simon. When it's near the equinox on Saturn, the planet and its rings are less tilted away from the Sun. In this configuration, the solar wind may more strongly batter Saturn's immense magnetic field, enhancing spoke formation.
Planetary scientists think that electrostatic forces generated from this interaction levitate dust or ice above the ring to form the spokes, though after several decades no theory perfectly predicts the spokes. Continued Hubble observations may eventually help solve the mystery.
This Hubble Space Telescope time-lapse series of Saturn images (taken on October 22, 2023) resolves a phenomenon called ring spokes appearing on both sides of the planet simultaneously as they spin around the giant world. The video zooms into one set of spokes on the morning (left) side of the rings. The spokes are transient features that rotate along the ring plane. The spokes may be a product of electrostatic forces generated by the interaction of the planet's magnetic field with the solar wind. This interaction levitates dust or ice above the ring to form the spokes. Credit: NASA, Amy Simon (NASA-GSFC); Animation: Joseph DePasquale (STScI)
The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble and Webb science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.
IMAGE OF JUPITER TAKEN BY NASA'S JUNO SPACECRAFT IN FEBRUARY 2022. THE DARK SPOT IS THE SHADOW OF THE MOON GANYMEDE. THE COLORFUL PATTERNS ARE FORMED BY CLOUDS AT DIFFERENT ALTITUDES AND MADE UP MAINLY OF AMMONIA ICE, AMMONIUM HYDROSULFIDE AND WATER.
CREDIT: NASA/JPL-CALTECH/SWRI/MSSS. IMAGE PROCESSING BY THOMAS THOMOPOULOS CC BY
For the first time, an instrument to find planets light years away was used on an object in the Solar System, in a study on Jupiter's winds.
We find ourselves at a time when it has become almost commonplace to discover planets orbiting another star, with more than 5,000 already registered. The first distant worlds to incorporate this list were mainly giant planets, similar to but also very different in many ways from Jupiter and Saturn.
Astrophysicists have already begun to obtain data on the atmospheres of exoplanets, but fundamental questions about the atmosphere of the largest planet in the Solar System are yet to be answered. To understand what happens in Jupiter’s clouds and air layers, it is necessary to study it over time, in continuous observations. Now, for the first time, an instrument developed to find and analyze worlds light years away, exoplanets, has been pointed at a target in the Solar System, 43 light minutes away from Earth: the planet Jupiter.
The method that the team developed is called Doppler velocimetry and is based on the reflection of visible light from the Sun by clouds in the target planet’s atmosphere. This reflected light is bent in wavelength in proportion to the speed at which the clouds are moving relative to the telescope on Earth. This gives the instantaneous wind speed at the observed point.
The method now used with ESPRESSO was developed by the Planetary Systems research group of IA, with other spectrographs, to study the atmosphere of Venus. The researchers have been measuring the winds of this neighboring planet and have been contributing to the modelling of its general atmosphere for several years. Now, the exploratory application of this method with a “top of the range” instrument such as ESPRESSO has resulted in a success that opens new horizons to the knowledge of our cosmic neighborhood. This work affirms the feasibility of systematically monitoring the most distant atmospheres on gaseous planets.
For five hours, in July 2019, the team pointed the VLT telescope at the equatorial zone of Jupiter, where light clouds are located at a higher altitude, and at the north and south equatorial belts of this planet, which correspond to descending air and which it forms bands of dark, warmer clouds in a deeper layer of the atmosphere.
“Jupiter’s atmosphere, at the level of the clouds visible from Earth, contains ammonia, ammonium hydrosulfide and water, which form the distinct red and white bands”, says Pedro Machado, from IA and Ciências ULisboa, “The upper clouds, located in the pressure zone of 0.6 to 0.9 bars, are made of ammonia ice. Water clouds form the densest, lowest layer, and have the strongest influence on the dynamics of the atmosphere”, adds the researcher.
With ESPRESSO, the team was able to measure winds on Jupiter from 60 to 428 km/h with an uncertainty of less than 36 km/h. These observations, applied with a high-resolution instrument to a gaseous planet, have their challenges: “One of the difficulties centered on ‘navigation’ over Jupiter’s disk, that is, knowing exactly which point on the planet’s disk we were pointing to, due to the enormous resolution of the VLT telescope”, explains Pedro Machado.
“In the research itself, the difficulty was related to the fact that we were determining winds with an accuracy of a few meters per second when Jupiter’s rotation is on the order of ten kilometers per second at the equator and, to complicate matters, because it is a gaseous planet, and not a rigid body, it rotates at different speeds depending on the latitude of the point we observe”, adds the researcher.
To verify the effectiveness of Doppler velocimetry from telescopes on Earth in measuring winds on Jupiter, the team also gathered measurements obtained in the past in order to compare the results. Most of the existing data was collected by instruments in space and used a different method, which consists of obtaining average values of wind speed by following cloud patterns in images captured at nearby times.
The consistency between this history and the values measured in the study now published confirms the feasibility of implementing Doppler velocimetry in a program for monitoring Jupiter’s winds from Earth.
The monitoring will allow the research team to collect data on how winds change over time and will be essential for developing a reliable model for the global circulation of Jupiter’s atmosphere. This computational model should reproduce the differences in winds depending on latitude, as well as Jupiter’s storms, to help understand the causes of the atmospheric phenomena we observe on this planet. Conversely, the model will help prepare future observations with information about the pressure and altitude of the clouds in telescope’s sights.
The team intends to extend observations with ESPRESSO to a greater coverage of planet Jupiter’s disk, as well as temporally, collecting wind data throughout the planet’s entire rotation period, which is almost 10 hours. Restricting observations to certain ranges of wavelengths will also make it possible to measure winds at different altitudes, thus obtaining information on the vertical transport of air layers.
Once the technique has been mastered for the largest planet in the Solar System, the team hopes to apply it to the atmospheres of other gaseous planets, with Saturn as the next target. The success of these observations with ESPRESSO proves to be important at a time when its successor, ANDES, is being designed for the future Extremely Large Telescope (ELT), also from ESO and currently under construction in Chile, but also the future JUICE mission, from the European Space Agency, dedicated to Jupiter and which will provide additional data.
ESPRESSO spectrograph control console, during the observation of Jupiter with one of the VLT telescopes, at the Paranal Observatory, in Chile.
CREDIT
Pedro Machado.
Room at the Paranal Observatory, in Chile, where VLT images and data from the ESPRESSO spectrograph are received. The unprecedented observation of an object in the Solar System – Jupiter – with this spectrograph, designed to observe planets at least one hundred thousand times further away, attracted the interest of other astrophysicists and technicians present.
CREDIT
Ruben Gonçalves
Researcher Pedro Machado, from IA and Ciências ULisboa, next to the four telescopes of the VLT (ESO), at the Paranal Observatory, Chile.
CREDIT
Pedro Machado
Image of Jupiter obtained by NASA's Juno probe in May 2019, where storm zones are visible in the planet's northern hemisphere.
CREDIT
Enhanced image by Kevin M. Gill (CC-BY) based on images provided courtesy of NASA/JPL-Caltech/SwRI/MSSS.
THESE IMAGES OF ASTEROID APOPHIS WERE RECORDED IN MARCH 2021 BY RADIO ANTENNAS AT THE DEEP SPACE NETWORK’S GOLDSTONE COMPLEX IN CALIFORNIA AND THE GREEN BANK TELESCOPE IN WEST VIRGINIA. THE ASTEROID WAS 10.6 MILLION MILES (17 MILLION KILOMETERS) AWAY, AND EACH PIXEL HAS A RESOLUTION OF 127 FEET (38.75 METERS).
The former OSIRIS-REx spacecraft sets off on a journey to study asteroid Apophis and take advantage of the asteroid’s 2029 flyby of Earth, the likes of which hasn’t happened since the dawn of recorded history.
At the end of a long-haul road trip, it might be time to kick up your feet and rest awhile – especially if it was a seven-year, 4 billion-mile journey to bring Earth a sample of asteroid Bennu. But OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification and Security – Regolith Explorer), the NASA mission that accomplished this feat in September, is already well on its way (with a new name) to explore a new destination.
When OSIRIS-REx left Bennu in May 2021 with a sample aboard, its instruments were in great condition, and it still had a quarter of its fuel left. So instead of shutting down the spacecraft after it delivered the sample, the team proposed to dispatch it on a bonus mission to asteroid Apophis, with an expected arrival in April 2029. NASA agreed, and OSIRIS-APEX (Origins, Spectral Interpretation, Resource Identification, and Security – Apophis Explorer) was born.
A Rare Opportunity at Apophis
After considering several destinations (including Venus and various comets), NASA chose to send the spacecraft to Apophis, an “S-type” asteroid made of silicate materials and nickel-iron – a fair bit different than the carbon-rich, “C-type” Bennu.
The intrigue of Apophis is its exceptionally close approach of our planet on April 13, 2029. Although Apophis will not hit Earth during this encounter or in the foreseeable future, the pass in 2029 will bring the asteroid within 20,000 miles (32,000 kilometers) of the surface – closer than some satellites, and close enough that it could be visible to the naked eye in the Eastern Hemisphere.
Scientists estimate that asteroids of Apophis’ size, about 367 yards across (about 340 meters), come this close to Earth only once every 7,500 years.
“OSIRIS-APEX will study Apophis immediately after such a pass, allowing us to see how its surface changes by interacting with Earth’s gravity,” said Amy Simon, the mission’s project scientist based at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Apophis’ close encounter with Earth will change the asteroid’s orbit and the length of its 30.6-hour day. The encounter also may cause quakes and landslides on the asteroid’s surface that could churn up material and uncover what lies beneath.
“The close approach is a great natural experiment,” said Dani Mendoza DellaGiustina, principal investigator for OSIRIS-APEX at the University of Arizona in Tucson. “We know that tidal forces and the accumulation of rubble pile material are foundational processes that could play a role in planet formation. They could inform how we got from debris in the early solar system to full-blown planets.”
Apophis represents more than just the opportunity to learn more about how solar systems and planets form: As it happens, most of the known potentially hazardous asteroids (those whose orbits come within 4.6 million miles of Earth) are also S-types. What the team learns about Apophis can inform planetary defense research, a top priority for NASA.
OSIRIS-APEX: Travel Itinerary
By April 2, 2029 – around two weeks before Apophis’ close encounter with Earth – OSIRIS-APEX’s cameras will begin taking images of the asteroid as the spacecraft catches up to it. Apophis will also be closely observed by Earth-based telescopes during this time. But in the hours after the close encounter, Apophis will appear too near the Sun in the sky to be observed by ground-based optical telescopes. This means any changes triggered by the close encounter will be best detected by the spacecraft.
OSIRIS-APEX will arrive at the asteroid on April 13, 2029, and operate in its proximity for about the next 18 months. In addition to studying changes to Apophis caused by its Earth encounter, the spacecraft will conduct many of the same investigations OSIRIS-REx did at Bennu, including using its instrument suite of imagers, spectrometers, and a laser altimeter to closely map the surface and analyze its chemical makeup.
As an encore, OSIRIS-APEX will reprise one of OSIRIS-REx’s most impressive acts (minus sample collection), dipping within 16 feet of the asteroid’s surface and firing its thrusters downward. This maneuver will stir up surface rocks and dust to give scientists a peek at the material that lies below.
Although the rendezvous with Apophis is more than five years away, the next milestone on its journey is the first of six close Sun passes. Those near approaches, along with three gravity assists from Earth, will put OSIRIS-APEX on course to reach Apophis in April 2029.
What OSIRIS-APEX will discover about Apophis remains to be seen, but if the mission’s previous incarnation is any indication, surprising science lies ahead. “We learned a lot at Bennu, but now we’re armed with even more questions for our next target,” Simon said.
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NASA’s Goddard Space Flight Center provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-APEX. Dani Mendoza DellaGiustina of the University of Arizona, Tucson, is the principal investigator. The university leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Littleton, Colorado, built the spacecraft and provides flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-APEX spacecraft. International partnerships on this mission include the spacecraft’s laser altimeter instrument from CSA (the Canadian Space Agency) and science collaboration with JAXA’s (the Japan Aerospace Exploration Agency) Hayabusa2 mission. OSIRIS-APEX (previously named OSIRIS-REx) is the third mission in NASA’s New Frontiers Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.
Live Christmas trees affect indoor air chemistry, NIST researchers find
NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY (NIST)
IMAGE:
NIST RESEARCHERS PLACED A COMMON TYPE OF CHRISTMAS TREE IN A SEALED CHAMBER FOR 17 DAYS TO MONITOR AND MEASURE THE CHEMICALS IT EMITS. THESE CHEMICALS CALLED VOLATILE ORGANIC COMPOUNDS (VOCS) GIVE THAT PINE SMELL AND CAN REACT WITH OZONE TO FORM BYPRODUCTS. THEY FOUND LOW AMOUNTS OF THESE CHEMICALS, WHICH MAY BE A POTENTIAL CONCERN FOR PEOPLE WHO ARE SENSITIVE TO THEM.
Every holiday season, Americans buy nearly 30 million live Christmas trees. Many families enjoy not only having a live tree inside their homes but also smelling the fresh fragrance it creates. That smell comes from chemicals called volatile organic compounds (VOCs). However, little is known about how much is emitted and whether they have any health impacts.
“Our nose is a good chemical sensor,” said Dustin Poppendieck, an environmental engineer at the National Institute of Standards and Technology (NIST). “We know that these trees are emitting something, and the question then becomes: How big of a source is it? We wanted to explore which chemicals are emitted and how much, and to put that into the context of other sources of chemicals in a house,” he said.
To answer these questions, Poppendieck and his NIST colleagues took a common type of Christmas tree — a Douglas fir— and sealed it inside a chamber. They then measured the amount and type of VOCs it emitted over 17 days. They also investigated whether the VOCs reacted with other components of indoor air to create new compounds.
The fresh smell that is commonly associated with Christmas trees comes from a group of VOCs called monoterpenes, which are also found in air fresheners, candles and some personal care products. In the outdoors, conifers, the group of plants that includes most Christmas trees, release monoterpenes, and they can affect outdoor air quality. But little is known about how much monoterpene is released when a tree is cut down and placed indoors.
Studies also show monoterpenes can react with ozone. Ozone in the upper atmosphere serves as a protective barrier against the Sun. At ground level, ozone is created through chemical reactions with light and can cause symptoms such as coughing and throat irritation. Ozone also reacts readily with other chemicals in the air to form new compounds. So, the researchers were interested in seeing the effects of ozone in the presence of an indoor tree.
They placed it inside an environmentally controlled chamber, where they could measure the chemicals emitted from the tree in real time. Using a technique that can detect airborne organic compounds, known as proton-transfer reaction mass spectrometry (PTR-MS), they measured the VOCs emitted over a 17-day period.
In their experiment, the researchers simulated a home environment. They decorated the tree in a typical holiday lighting setup and shone bright lights on it to mimic the day-night cycle. They turned off the lights every 12 hours and watered the tree every day. They brought in outside air at a rate typical for households, and constantly measured chemicals in the indoor air.
Monoterpenes were the most abundant VOC emitted from the tree. They peaked during the first day before diminishing significantly by the third day. Their concentration was initially at the same level of a plug-in air freshener or newly constructed house before it quickly dropped by nearly 10 times its original amount, said Poppendieck. The researchers detected 52 distinct types of monoterpenes.
Researchers then injected ozone into the chamber to see how it affected indoor air chemistry. They found that ozone reacted with the monoterpenes, forming byproducts such as formaldehyde, another type of VOC, as well as other reactive chemicals. The monoterpene concentration diminished even more with the introduction of ozone, while formaldehyde levels rose, which showed an impact on indoor air chemistry. However, the amount of formaldehyde created was relatively small at around 1 part per billion. Typical U.S. houses have formaldehyde concentrations ranging from 20 to 30 parts per billion.
For people who are sensitive to VOCs, Christmas trees could be one possible cause for watery eyes and noses, especially when initially brought indoors. In that case, Poppendieck suggests, opening a window near the tree will reduce exposure. In addition, newly cut trees can be left outdoors or in a garage for three days before bringing them into the home as the emission strength naturally decays over time.
“But for most people,” Poppendieck said, “this shouldn’t be a major concern. I’m still going to have a Christmas tree in my house.”
Don’t forget to water your Christmas tree every day. The greatest risk is a dried-out tree, which can become a fire hazard for your home. NIST has safety tips available on our website.
Researchers report December 22 in the journal Current Biology that the more time reindeer spend ruminating, the less time they spend in non-rapid eye movement (non-REM) sleep. EEG recordings revealed that reindeer’s brainwaves during rumination resemble the brain waves present during non-REM sleep, and these brainwave patterns suggest that the reindeer are more “rested” after ruminating. The researchers speculate that this multitasking might help reindeer get enough sleep during the summer months, when food is abundant and reindeer feed almost 24/7 in preparation for the long and food-sparse arctic winter.
“The more reindeer ruminate, the less additional non-REM sleep they need,” says first author and neuroscientist Melanie Furrer of the University of Zurich. “We think it's very important that they are able to save time and cover their sleep and digestive needs at the same time, especially during the summer months.”
Light-dark cycles are absent in the Arctic during winter and summer, and previous studies showed that Arctic-dwelling reindeer don’t display circadian behavioral rhythms during these seasons, though they tend to be more active during the daytime during the spring and autumn equinox, when light-dark cycles are present. However, it was unknown whether these seasonal differences also impacted how much—and how well—reindeer sleep.
To investigate the influence of seasonal light-dark cycles on reindeer sleep patterns, the researchers performed non-invasive electroencephalography (EEG) on Eurasian tundra reindeer (Rangifer tarandus tarandus) in Tromsø, Norway (69°N), during the autumn equinox, summer solstice, and winter solstice. The reindeer, who were all adult females, were part of a captive herd at UiT The Arctic University of Norway in Tromsø, and the experiments were conducted in indoor stables with controlled lighting, unlimited food, and constant temperature.
They found that reindeer slept approximately the same amount during winter, summer, and autumn, despite the fact that they were much more active during the summer. This is in contrast to other species who change the amount they sleep in response to environmental conditions. On average, the reindeer spent 5.4 hours in non-REM sleep, 0.9 hours in REM sleep, and 2.9 hours ruminating during a given 24-hour period, regardless of season.
“The fact that reindeer sleep the same amount during winter and summer implies that they must have other strategies to cope with limited sleep time during the arctic summer,” says Furrer.
One possible strategy is the opportunity for rest during rumination—the re-chewing of partially digested food, which is an important component of digestion for reindeer and other ruminants. Domestic sheep, goats, cattle, and Lesser mouse-deer have all been previously observed to produce sleep-like brain waves during rumination, but it was unclear whether rumination could serve a similar restorative function to sleep.
The researchers found that the reindeer’s EEG readings during rumination resembled brainwave patterns that are indicative of non-REM sleep including increased slow-wave activity and sleep spindles. Sleeping and ruminating reindeer also displayed similar behavior, tending to quietly sit or stand during both activities, and were less reactive to disturbances such as a neighboring reindeer sitting down or getting up—reindeer directly responded to these disturbances (by looking toward the neighboring reindeer) 45% of the time if they were awake, but only 25% of the time if they were ruminating, and 5% of the time if they were in non-REM sleep.
Next, the researchers tested whether rumination could reduce the reindeer’s drive to sleep by depriving the reindeer of sleep for 2 hours and measuring their brain waves during sleep before and after this deprivation. Following sleep deprivation, the reindeer’s EEG readings showed increased slow-wave activity, which is indicative of a build-up of “sleep pressure”—the unconscious biological drive for more and deeper sleep—suggesting that reindeer experience deeper sleep following sleep deprivation.
However, when the reindeer ruminated, this slow-wave activity was decreased during subsequent sleep, and the more they ruminated, the more the slow-wave activity decreased. “This suggests that rumination reduces sleep pressure, which could benefit the reindeer because it means they don’t have to compromise on sleep recovery when they spend more time ruminating,” says Furrer.
This is especially important during the summer, because the more they eat, the more time the reindeer need to spend ruminating. “Rumination increases nutrient absorption, so it’s crucial for reindeer to spend enough time ruminating during the summer in order to gain weight in anticipation of winter,” says Furrer.
Since reindeer appear to sleep while ruminating only some of the time, follow-up studies should compare the impact of rumination while sleeping with rumination while awake and would also ideally measure reindeer behavior and sleep in more natural outdoor conditions, the researchers say. However, such measurements would require surgically implanted EEG sensors rather than the non-invasive surface electrodes used in this study.
“Another thing we could add is to look at young reindeer,” says Furrer. “We know sleep need is much higher in young children and babies compared to adults, so it would be interesting to look at sleep in younger reindeer.”
Screenshot of reindeer surveillance
CREDIT
Current Biology/Furrer et al.
This research was supported by the Swiss National Science Foundation and UiT The Arctic University of Norway.
Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit http://www.cell.com/current-biology. To receive Cell Press media alerts, contact press@cell.com.
