A group of specialists in biology, chemistry and archaeology have found the earliest evidence of mercury poisoning in 5,000-year-old bones of humans buried in Portugal and Spain. It’s the largest study ever done on the presence of mercury in human bones, looking at a sample of 370 individuals from 50 tombs in 23 archaeological sites.
Mercury is a naturally occurring element found in water, land, and air. When humans are exposed to it, it can cause serious health problems. Nowadays, mercury is mainly used in the chemical industry and production of electrics but in the past, it was also used to extract gold, copper, and silver from ore rocks and as the main ingredient to produce vermilion, a brilliant red or scarlet pigment.
The World Health Organization considers mercury as one of the main chemicals of major public health concern. Exposure to it can have toxic effects on the nervous, immune and digestive systems. This can happen by eating certain fish of shellfish, but the levels are often low and nowadays, mercury poisoning isn’t a widespread problem. But things were different in the past.
Looking back on mercury
A team of scientists from the University of North Carolina and the University of Sevilla analyzed a set of bones dating from the Neolithic, Copper Age, Bronze Age, and Antiquity — and found that the poisoning was because of exposure to cinnabar, a mercury sulfide mineral that forms in thermal and volcanic areas around the world. The term cinnabar was used interchangeably with vermilion for centuries, as the mineral was ground into a powder and used to produce the pigment.
Historically, it was been used to produce paint pigments and consumed as a “wonder drug”, the researchers said in a statement. One of the biggest mines of cinnabar is in fact located in Almaden, Spain – one of the archaeological sites used to look for the human bones.
“The use of cinnabar as a pigment, paint or medical substance began by the Upper Paleolithic and intensified gradually in the Neolithic and Copper Age,’ researchers wrote in the study. ‘There is evidence for mining of the extensive ore deposits at Almadén, in central Spain, by 5300 BC. Its primary use was in rituals.”
The exploitation began in the Neolithic, 7,000 years ago, and the study showed that the highest levels of mercury exposure happened at the early start of the Copper Age, between 2900 and 2600 BC. Back then, the exploitation of cinnabar deposits in central Spain increased considerably. The mineral was a product of big social value and as a result, many must have accidentally inhaled or consumed it.
In fact, the bones of the individuals had levels of up to 400 parts per million (ppm) – which is so high that the researches don’t rule out that cinnabar was deliberately consumed for a ritual purpose. The WHO considers that the normal level of mercury shouldn’t be higher than one or two ppm, revealing a high level of intoxication. As far as we know, this is the oldest evidence of someone suffering from mercury poisoning.
As climate change keeps making our planet hotter and our glaciers melty, scientists report on an unforeseen issue: glacial meltwater from the Greenland Ice Sheet contains high levels of mercury, a toxic heavy metal. According to the report, these levels are comparable to those in rivers where factories dump their waste, creating a major threat to the seafood industry and people who enjoy its products.
It’s never a dull day with environmental woes. A study that began as an effort to analyze the quality of meltwater from the Greenland ice sheet, and how nutrients therein might support coastal wildlife, ended up uncovering very high levels of mercury in the runoff. The finding raises new questions about how global warming will impact wildlife in the region, one of the foremost exporters of seafood worldwide.
“There are surprisingly high levels of mercury in the glacier meltwaters we sampled in southwest Greenland,” said Jon Hawkings, a postdoctoral researcher at Florida State University and the German Research Centre for Geosciences. “And that’s leading us to look now at a whole host of other questions such as how that mercury could potentially get into the food chain.”
Together with glaciologist Jemma Wadham, a professor at the University of Bristol’s Cabot Institute for the Environment, Hawkings initially set out to sample water from three different rivers and two fjords next to the Greenland Ice Sheet. Their aim was to understand how nutrients from glacial meltwater can help to support coastal ecosystems.
Although they also measured for mercury, they didn’t expect to find any meaningful concentrations. Which made the levels of this metal they found in the water all the more surprising.
The baseline for mercury content in rivers is considered to be about 1 to 10 ng / L-1. That’s roughly equivalent to a sand grain of mercury in an Olympic pool of water — so, very low. However, the duo found that mercury levels in the water they sampled were in excess of 150 ng / L-1. Mercury levels in the sediment (called “glacial flour” when it’s produced by glaciers) were over 2000 ng / L-1, which is simply immense.
So far, it remains unclear whether mercury levels drop farther away from this ice sheet, as meltwater gets progressively more diluted. It’s also not yet clear whether the metal is making its way into the marine food web, which would likely make it concentrate further (as animals eat plants and each other).
Although the findings are local, the issue could have global ramifications, as they echo findings in other arctic environments. Greenland is an important producer of seafood, with the export of cold-water shrimp, halibut, and cod being its primary industry. If mercury here does end up in the local food web, it could unknowingly be exported to and consumed by people all over the world.
“We didn’t expect there would be anywhere near that amount of mercury in the glacial water there,” said Associate Professor of Earth, Ocean, and Atmospheric Science Rob Spencer, co-author of the paper. “Naturally, we have hypotheses as to what is leading to these high mercury concentrations, but these findings have raised a whole host of questions that we don’t have the answers to yet.”
“For decades, scientists perceived glaciers as frozen blocks of water that had limited relevance to the Earth’s geochemical and biological processes. But we’ve shown over the past several years that line of thinking isn’t true. This study continues to highlight that these ice sheets are rich with elements of relevance to life.”
Roughly 10% of our planet’s dry land is covered in ice, and the results here raise the worrying possibility that they may be seeping mercury into the waters around them. The issue is compounded by the fact that global warming is making these glaciers melt faster, while we still have an imperfect understanding of how the melting process influences the local geochemistry around them.
So far, the team explains that this mercury is most likely coming from a natural source, not from something like fossil fuel use or industrial activity. While this is very relevant for policy-makers, the fact remains that natural mercury is just as toxic as man-made mercury. If it is sourced from natural processes, however, managing its levels in the wild will be much more difficult to do .
“All the efforts to manage mercury thus far have come from the idea that the increasing concentrations we have been seeing across the Earth system come primarily from direct anthropogenic activity, like industry,” Hawkings said. “But mercury coming from climatically sensitive environments like glaciers could be a source that is much more difficult to manage.”
The paper “Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet” has been published in the journal Nature Geoscience.
When it comes to the surface temperature of planets, distance to the Sun is the main factor, but it’s not the only one. Turns out, the atmosphere (and in some cases geological processes) can have a major impact.
This is why the hottest planet in the solar system isn’t Mercury (the closest to the Sun), but Venus — and the reason has to do with something we’re very familiar with: carbon dioxide.
A familiar culprit: greenhouse gas
Venus, named after the Roman goddess of Love (Aphrodite for the Greeks), is not exactly an inviting place. Its scorching surface can reach 880°F (471°C), and if that doesn’t scare you, Venus is riddled with active volcanoes and hot, toxic sulfur fumes.
It’s no surprise that Venus is hot since it’s much closer to the Sun than the Earth. Venus lies 108.93 million km away from the Sun, 30% closer than the Earth. But why is Venus hotter than Mercury, which lies only 59.187 million km from the Sun?
The answer lies in the Venusian atmosphere.
The atmospheric pressure on Venus is 92 times stronger than that of Earth — it would feel like being 900 m (3,000 ft) underwater. This thick atmosphere wraps the planet like a blanket, and to make matters even hotter, the atmosphere is 96% carbon dioxide — which, as you’re probably aware, is an important greenhouse gas and a driver of rising temperatures. In other words, Venus has a runaway greenhouse gas problem that traps heat in the atmosphere.
Meanwhile, Mercury has a very thin atmosphere. Much of the heat that Mercury receives from the sun is quickly lost back into space, whereas heat on Venus doesn’t escape.
It’s a never-ending cycle of heat being trapped inside by carbon dioxide and releasing more carbon dioxide. This is what happens when an atmosphere absorbs too much carbon dioxide: the heat has nowhere to go and it triggers a self-enforcing feedback loop.
This becomes even more obvious when we look at the difference between the maximum temperature and the average temperature.
The day is longer than the year
Both Mercury and Venus rotate very slowly; on Venus, a day lasts 243 Earth days, while a year lasts 225 Earth days — the Venusian day is longer than the year.
Because they rotate so slowly, you’d expect the planets to have massive temperature differences between the sunny side and the dark side — and that’s exactly what we see on Mercury. There’s a huge, over 1000 °F difference between day and night. But for Venus, that’s not really the case.
Because Venus has such a thick and greenhouse-potent atmosphere, the temperature is relatively constant on the entire planet. While the hottest temperature on Mercury is close to that of Venus, if we we were to take an average, it wouldn’t even be close.
Planet / Satellite
Minimum surface Temperature
Maximum Surface Temperature
-275 °F (- 170°C)
840 °F (449°C)
870 °F (465°C)
870 °F (465°C)
– 129 °F (- 89°C)
136 °F (58°C)
– 280 °F (- 173°C)
260 °F (127°C)
– 195 °F (- 125°C)
70 °F (20°C)
If Venus didn’t have the atmosphere it does, its night temperature would also be much lower, like Mercury’s — and the average temperature would also be lower than Mercury’s.
Another consequence of this atmosphere is that there’s no ice on Venus, which is hardly surprising given the average temperature. While on Mercury, ice can find shelter in the polar, always-shaded impact craters where temperatures are below freezing. NASA’s MESSENGER mission detected evidence of water ice at both of Mercury’s poles, probably delivered by comet impacts.
Meanwhile, the surface of Venus is extremely dry.
It’s not always clear if the planet was always like this. During its early evolution, Venus likely had liquid water on its surface, but it was ultimately evaporated by ultraviolet rays from the Sun. If, through some magical experiment, you were to create some water on Venus, it would boil away almost immediately. Yet despite all these differences, Venus was once considered Earth’s twin.
The reason for this is mostly regarding the planet’s size and mass. Venus and Earth, two neighboring planets, are very similar in some regards: Earth has a mean radius of 6,371 km, while Venus has a radius of about 6,052 km. Meanwhile, the mass of the Earth is 5,972,370,000 quadrillion kg, compared to 4,867,500,000 quadrillion kg for Venus. So essentially, Venus is 0.9499 the size of Earth and 0.815 the mass. It also has an atmosphere… and that’s pretty much where the similarities end.
Around 60% of Venus is covered by flat, smooth plains, marred by thousands of active volcanoes, ranging from 0.5 to 150 miles (0.8 to 240 km) wide. Venus features long, winding canals that run for more than 3,000 miles (5,000 km) — longer than any other planet.
The temperature is ungodly, as we’ve already mentioned, the atmosphere is thick and heavy, permanently covered in clouds. Most man-made materials would melt rapidly on Venus, and a human mission to Venus is nothing more than a pipe dream at this point.
Venus also rotates in the opposite direction than the Earth, and as we mentioned previously, it rotates very slowly.
If Venus is Earth’s twin, it can only qualify as its evil twin.
How we study Venus
Up until the 1960s, there was rich speculation that Venus may harbor life forms — but all that dwindled quickly when spacecraft actually started studying Venus.
Studying Venus is no easy feat. In fact, Venus is so inhospitable that many scientists were skeptical that a mission would even be possible. The Soviets sent a few missions to Venus, but the first ones all failed.
Mariner 2 was the first spacecraft to visit Venus in 1962. Eventually, in 1981, the Venera 13 mission finally managed to make it through the hot layers of the atmosphere and land on the surface. It managed to survive for 127 minutes, during which it sent color photos and measurements to Earth.
Then, transmission stopped and Venera 13 melted.
In 1990, the US spacecraft Magellan used radars to map the Venusian surface — an extremely important step, since Venus is always shrouded by sulfur layers that make it impossible for visible light to pass. Magellan mapped 98% of the surface with a resolution of approximately 100 meters and are still the most detailed maps we have of Venus. In more recent times, interest in Venus has decreased and recent missions have only been flybys, taking snapshots of Venus en route to other destinations. The Japanese mission Akatsuki, plagued by problems, is currently studying Venus’ atmosphere.
Understanding the atmosphere and atmospheric processes on Venus could help us better understand some of the atmospheric phenomena we see here on Earth.
Venus’ runaway greenhouse effect could show us how the Earth might look in the future if we don’t take climate change seriously. It’s an important lesson on what can happen when a planet has a high carbon dioxide level in the atmosphere. According to recent studies, Venus may have had a liquid ocean and a habitable surface for up to 2 billion years of its early history — an important cautionary tale.
Lastly, although Venus is hellish and inhospitable, some researchers still believe that extremophiles (organisms adapted to extreme conditions) could still survive on Venus. In 2019, researchers proposed that an unexplained absorption phenomenon could be explained by colonies of microbes in the atmosphere on Venus. While far from being a promising place to look for life, it’s still intriguing enough to study.
Venus studies have been great lessons, enabling researchers to better understand other rocky planets, as well as the Earth.
It’s a hot, hellish place — the hottest planet in the solar system. But we can still learn from it.
If you’d ask most people what; the closest planet to Earth, you’d probably come across one answer: Venus. That answer, while apparently logical, is not really true. Mercury is the planet closest to us.
Even more surprising is the fact that Mercury is the closest neighbor, on average, to each of the other seven planets in the solar system. How can this be?
Image credits: Image: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington (Wikimedia Commons).
Mercury’s in retrograde
What’s the planet closest to the Earth? Even without any prior knowledge, a decent guess would be Venus or Mars — these are our planetary neighbors, after all. A simple Google search reveals that Venus’ orbit is closer to that of Earth’s so, naturally, Venus must be the answer, right?
Wrong. Mercury is the planet closest to Earth — at least on average.
As it turns out, Venus being the closest planet to Earth is simply a misconception — one that has propagated greatly through the years.
“By some phenomenon of carelessness, ambiguity, or groupthink, science popularisers have disseminated information based on a flawed assumption about the average distance between planets,” write engineers Tom Stockman, Gabriel Monroe, and Samuel Cordner in a commentary published in Physics Today.
Instead, they recommend a different method of measuring which planet is closest, which they demonstrated using the motions of the planets within the last 10,000 years.
“By using a more accurate method for estimating the average distance between two orbiting bodies, we find that this distance is proportional to the relative radius of the inner orbit.”
Using this method, Mercury is closer to Earth on average. A GIF created by Reddit user u/CharcoalCharts does a great job at depicting this (the Earth is in Blue). The Earth is usually closest to Mercury, although, at some points of the year, it’s closest to Venus or Mars.
It feels intuitive that the average distance between every point on two concentric ellipses is closer than ellipses which are farther apart, but this is not necessarily the case. While Venus can get very close to the Earth (at only 0.28 Astronomical Units, with 1 AU being the distance from the Earth to the Sun), the two planets can also be quite far apart, at 1.72 AU. In total, Venus is 1.14 AU from Earth, but Mercury is a much closer 1.04 AU.
There are also two other shocking conclusions from this: first of all, on average, the Sun is closest to the Earth than any other planet (because it’s at 1 AU by definition). Secondly, it’s not just the Earth — Mercury is the closest neighbor of all planets in the solar system. In other words, Uranus is, on average, closer to Mercury than its presumed neighbor, Neptune. The same stands for even the dwarf planet Pluto (we still love you, Pluto!).
A simulation of an Earth year’s worth of orbits by the terrestrial planets begins to reveal that Mercury (gray in orbital animation) has the smallest average distance from Earth (blue) and is most frequently Earth’s nearest neighbor. Image credits: Tom Stockman/Gabriel Monroe/Samuel Cordner.
The whirly-dirly corollary
Researchers also found that the distance between two orbiting bodies is at a minimum when the inner orbit is at a minimum — something which they call the “whirly-dirly corollary” — after an episode of the cartoon Rick and Morty.
The method might also be useful in estimating distances between other orbiting bodies such as satellites or extrasolar planets or stars. In the Physics Today commentary, the researchers explain:
“As best we can tell, no one has come up with a concept like PCM to compare orbits. With the right assumptions, PCM could possibly be used to get a quick estimate of the average distance between any set of orbiting bodies. Perhaps it can be useful for quickly estimating satellite communication relays, for which signal strength falls off with the square of distance. In any case, at least we know now that Venus is not our closest neighbor—and that Mercury is everybody’s.”
Well, I wasn’t expecting climate change to do that, to be honest.
Image credits Tavo Romann / Wikimedia.
Thawing permafrost in the Canadian Arctic is releasing record amounts of mercury into local waterways, according to ecologists from the University of Alberta. The effects are not properly understood right now, but mercury is known to be toxic compound (in high quantities) to both humans and other organisms.
“Concentrations of mercury were elevated for at least 2.8 kilometres downstream of thaw slumps,” says Kyra St. Pierre, who co-led the study. “This suggests that some mercury from thaw slumps may be transported for many kilometres through downstream ecosystems, and into larger waterways.”
Mercury (Hg) is a metal that occurs in a liquid form at room temperature. It’s toxic to most organisms in large quantities and tends to accumulate in food webs (i.e. it’s not processed in the body and gets passed on from prey to predator).
We don’t get much trouble from mercury since it’s simply not that abundant in most natural settings. However, it is in permafrosts — permafrost sediments are estimated to store more mercury than Earth’s oceans, atmosphere, and soil combined, the team report. As climate change thaws these permafrosts, the mercury stored therein becomes mobile and leaches into the surrounding environment.
The issue is exacerbated by increasing precipitation in the Canadian Arctic (also due to climate change), the team adds.
“Climate change is inducing widespread permafrost thaw,” explained St. Pierre. “In regions where this results in thaw slumping, this may release a substantial amount of mercury into freshwater ecosystems across the Arctic.”
For now, the exact implications of this mercury contamination remains unknown. The team says that organisms in the area might absorb the metal from the environment (through food and drinking water), however, they don’t yet have sufficient data to tell. It may well be that local plants and wildlife are absorbing mercury but at too low levels for it to be a threat to the food web. Of course, the opposite may also be true.
The results, the team says, highlight the need for further research on mercury cycling in regions experiencing active permafrost thaw. They also say more research is needed on if (and how) this mercury might enter food webs in surrounding ecosystems.
The paper ” Unprecedented Increases in Total and Methyl Mercury Concentrations Downstream of Retrogressive Thaw Slumps in the Western Canadian Arctic” has been published in the journal Environmental Science & Technology.
Researchers found surprisingly large quantities of mercury in the permafrost of the northern hemisphere. As temperatures rise and ice continues to melt, the mercury can be released, with significant consequences for both wildlife and mankind.
Maps of mercury concentrations (micrograms of mercury per square meter) in Northern hemisphere permafrost zones for four soil layers: 0-30 centimeters, 0-100 centimeters, 0-300 centimeters, and permafrost. The permafrost map represents the mercury bound to frozen organic matter below the Active Layer Depth (ALD) and above 300 cm depth. Credit: Schuster et al./GRL/AGU.
The tentacles of climate change are long and far-reaching. As temperatures rise, it brings along a number of unforeseen changes. Rising temperatures are threatening the oceans, causing more hurricanes, and even causing a coffee crisis. Now, we can add mercury to that long list of problems.
A new study reports that permafrost soils contain more mercury than the rest of the planet’s soils, atmosphere, and oceans combined.
In the new study, geologists assessed the concentrations in permafrost cores from Alaska. They found that permafrost soils contain two times more mercury than soils elsewhere in the world — an unexpected discovery with important consequences.
“This discovery is a game-changer,” said Paul Schuster, a hydrologist at the U.S. Geological Survey in Boulder, Colorado and lead author of the new study. “We’ve quantified a pool of mercury that had not been done previously, and the results have profound implications for better understanding the global mercury cycle.”
This wouldn’t normally be a very high concern, but the problem is that temperatures are now rising.
Permafrost in Alaska is thawing, and a new study finds northern permafrost soils are the largest reservoir of mercury on the planet, storing nearly twice as much mercury as all other soils, the ocean, and the atmosphere combined. Credit: John A. Kelley, USDA Natural Resources Conservation, CC BY 2.0.
Mercury tends to bind with organic material in the soil and gets stuck with that soil. As it gets buried by sediment, it becomes frozen into permafrost, where it can remain for thousands of years. But if temperatures rise, all that can change. When temperatures rise and the permafrost melts, mercury isn’t fixed in place anymore. Instead of being frozen in the permafrost, it can also be transported by waters or microorganisms, or it can slowly seep on its own.
“There would be no environmental problem if everything remained frozen, but we know the Earth is getting warmer,” Schuster said. “Although measurement of the rate of permafrost thaw was not part of this study, the thawing permafrost provides a potential for mercury to be released—that’s just physics.”
Locally, the effects could be dramatic. From microorganisms, things can slowly move up the food chain, and like most toxins, they tend to gather higher up the food chain — and potentially end up on our plates.
The release of mercury could also have far-reaching global consequences. If released into the atmosphere, it could travel quickly at the mercy of air currents, possibly ending up as far as thousands of kilometers away.
But we don’t really know how much and how far the mercury can travel. Scientists are also unsure how much of the stored mercury would affect ecosystems if the permafrost were to thaw.
Schuster hopes to analyze that those issues in further studies, understanding how the mercury can affect humans and natural environments.
“24 percent of all the soil above the equator is permafrost, and it has this huge pool of locked-up mercury,” he said. “What happens if the permafrost thaws? How far will the mercury travel up the food chain? These are big-picture questions that we need to answer.”
Journal Reference: Paul F. Schuster et al. Permafrost Stores a Globally Significant Amount of Mercury. DOI: 10.1002/2017GL075571.
The Sun is losing its gravitational lock on the solar system, new research has found.
Image credits NASA/SDO.
The planets in our solar system are expanding their orbits, according to a team of NASA and MIT scientists. This drift is caused by the Sun slowly losing mass as it ages, which weakens its gravitational pull. The researchers studied Mercury’s orbit to indirectly measure the amount of mass our star lost.
The study began with the team refining Mercury’s ephemeris — its course around the Sun, charted over time. Scientists have been studying this planet and recording its position for centuries now, paying particular attention to its perihelion, the point in its orbit when it comes nearest the Sun.
Because we’ve had such a long observation period of the planet, we know that Mercury tends to shift its perihelion over time — a movement called precession. Part of the cause lies in other planets in the solar system, whose gravitational pulls gently tug at the scorched ball of rock. However, they don’t account for all of the observed precession. Most of what’s left, Einstein tells us, can be explained by the Sun’s mass warping space-time around it — this effect actually helped confirm the theory of general relativity.
But a small part of that precession motion comes down to tiny changes in the Sun’s internal structure and processes. Among them is the Sun’s oblateness (how much it bulges at the equator due to its spin). It was this last category of influences on Mercury’s precession that the team studied.
The researchers drew on radio data which tracked the position of NASA’s MESSENGER spacecraft (Mercury Surface, Space Environment, Geochemistry, and Ranging) while the mission was active. The vessel made three flybys over Mercury in 2008 and 2009 and subsequently orbited the planet from March 2011 through April 2015. By analyzing all the subtle changes in the planet’s motions throughout that time, the team could infer how the Sun’s physical parameters influence Mercury’s orbit.
The position of Mercury over time was determined from radio tracking data obtained while NASA’s MESSENGER mission was active. Image credits NASA / Goddard Space Flight Center.
They were able to separate some of these parameters from the star’s relativistic effects, something which previous research that looked at Mercury’ ephemeris never managed to do. At the same time, they developed a new analytical method that simultaneously estimated and integrated the orbits of Mercury and the MESSENGER craft. The end result is a solution which takes into account both relativistic effects and processes inside the Sun.
“Mercury is the perfect test object for these experiments because it is so sensitive to the gravitational effect and activity of the Sun,” said lead author Antonio Genova.
The researchers obtained an improved estimate of oblateness that is consistent with other types of studies. However, their estimate of the rate at which the Sun loses mass represents one of the first times this value was based on observation rather than calculated through secondary data. Previously, scientists predicted a one-tenth of a percentage loss of the Sun’s mass over 10 billion years — corresponding to any planet widening its orbit by 1.5 cm (0.5 in) per year per AU (one AU, or astronomical unit, is the distance between the Earth and the Sun).
The team’s observations by-and-large reinforce that estimate — their result is just slightly lower, but being based on observation it is much less uncertain. The team’s results also allowed them to more accurately pin the value of G, the gravitational constant, improving its stability by a factor of 10 compared to previous, estimated values.
“We’re addressing long-standing and very important questions both in fundamental physics and solar science by using a planetary-science approach,” said Erwan Mazarico, paper co-author.
“By coming at these problems from a different perspective, we can gain more confidence in the numbers, and we can learn more about the interplay between the Sun and the planets.”
The paper “Solar system expansion and strong equivalence principle as seen by the NASA MESSENGER mission” has been published in the journal Nature Communications.
The nearest planet to the sun is the last place one would expect to find water — or anything — frozen. The universe, however, is always full of surprises. Mercury is well known as the most scorched planet in our solar system. At only 36 million miles from the sun and with extremely long daytimes, the surface of Mercury can reach an astounding 800°F. Hardly the environment for ice.
Image credits: MESSENGER / NASA
What a shock it was then, in 1991, when astronomers at the Arecibo Observatory in Puerto Rico discovered circular patches of “extremely reflective” material radiating from Mercury’s surface. The data from the observation suggested the presence not just of water, but of ice on Mercury, an idea previously thought impossible. Since the data just from radar information alone was inconclusive, the matter was greeted with some skepticism for years.
NASA’s more recent Messenger spacecraft has now gathered the best photos and data ever of the possible crater ice, bringing scientists closer to a conclusion; Mercury, despite its scorch, appears to harbor pockets of perpetual water ice.
History of Mercury
The strongest theories of Mercury’s formation state that Mercury originally formed as a much larger planet, but lost approximately half of its mass to the violent fluctuations of the primitive sun, and/or possibly to a collision with a planetesimal (a small planet). The sun theory proposes that Mercury’s original crust may have been vaporized by 8000° F plus surface temperatures imposed by the early sun’s hot and volatile emissions. Mercury may have been originally composed of material with a different chemical composition, but those with a lower vaporization point would have been eliminated.
This could reasonably explain why today Mercury is the only planet in our solar system to contain such a disproportionate amount of metal and silicate, and little else. The composition is roughly two-thirds metal and one-third silicate. Its planetary rotation is extremely slow; about 60 earth days are required to equal one day on Mercury. This causes some portions of the planet to endure prolonged sun exposure and extreme heat while plunging other areas into long, frozen darkness.
Mercury is covered in the multitude of craters that characterize the rocky planets and satellites of our solar system. There is no geologic surface activity, and it lacks a geologically active core, as evidenced by the long-undisturbed craters. Due to its small size and geological constitution, Mercury also lacks any notable atmospheric layer.
How is water ice possible in such a place?
NASA’s MESSENGER found new evidence for water ice at Mercury’s poles
Because of Mercury’s narrow axis, slow rotation, and lack of heat-trapping atmosphere, it is possible to house pockets of frozen water on Mercury’s surface. Mercury, in fact, exhibits the broadest temperature variation of any of the planets in our solar system. The planetary poles are permanently shadowed as are some of its craters. In contrast to the sun-drenched oven on the regular surface, these dark areas often drop to -290°F, more than cold enough to keep water frozen forever. Modern interpretations of Mercury’s undisturbed, ancient craters indicate that there has not been any geological or volcanic activity in a very long time. Without an atmosphere to trap and disperse heat nor any geothermal heat from Mercury’s center, the craters are in permafrost.
The extraterrestrial origins of water ice on Mercury
Where did all the water come from in the first place? Water is actually fairly plentiful in the galaxy. Hydrogen is found everywhere as the chemical basis of most inorganic matter. Oxygen is produced as a byproduct of star activity. When they meet under cooler temperatures, H2O, or water, is the usual result. As a matter of fact, most of the universe’s oxygen is tied up in water and carbon dioxide, so the availability of extraterrestrial water is in no short supply.
The question, of course, is how it was delivered to Mercury. The most popular theory is that ice-filled comets and asteroids pummeled Mercury and the rest of the solar system at a turbulent time early in the solar system’s history, releasing countless tons of water onto each of the planets. Much of the interest is centered around a class of meteorites known as carbonaceous chondrites, which are known to contain substantial amounts of ice in addition to a fascinating mixture of prebiotic organic ingredients, such as amino acids, a discovery that will surely lead to more astonishing revelations as we learn more.
How was water ice discovered on Mercury?
In 1991, Puerto Rico’s Arecibo radio telescope transmitted a circularly polarized, coded radar wave toward Mercury. The wave was reflected off Mercury and back toward Earth, where Arecibo received its images. What they found was that although Mercury’s silicate component is already very reflective, there were also circular areas of an even brighter reflectivity near the poles. At the time, the areas were suspected to be water ice, but there was no other data on which to investigate.
Doubt has now been almost completely eradicated with the data received from the recently completed MESSENGER spacecraft project. An acronym for “Mercury surface, space environment, geochemistry, and ranging”, MESSENGER began orbiting Mercury in 2011 and continued to send the most comprehensive data ever collected until it ran out of fuel and crashed into Mercury’s surface in 2015. The new data left little question as to whether or not there is water ice on Mercury.
MESSENGER used laser pulses, fired at the planet’s surface, to create highly detailed maps. Like before, reflective anomalies at the poles suggest the presence of water, but this time were correlated with up-to-date temperature models that confirmed the reflective areas as frozen water. Columbia University’s principal investigator, Sean Solomon, is quoted as saying: “For more than twenty years the jury has been deliberating on whether the planet closest to the sun hosts abundant water ice in its permanently shadowed polar regions. MESSENGER has now supplied a unanimous affirmative verdict.”
With one question answered, more are raised
With the question of the existence of water ice on Mercury resolved, it leads to more questions about its origins, those carbonaceous chondritic meteorites. Along with the discovery of extraterrestrial water not only on Mercury, but also on Mars and our moon, has come the more astonishing revelation of extraterrestrial organic compounds, such as amino acids. This has the potential to change everything known about the origins of life on Earth, and the possibility of similar organic evolutions elsewhere. Is life extraterrestrial in origin? Did the building blocks of nucleic replication ride in on a meteorite from a distant, dark unknown? The answer to such questions may never be found, but it will certainly compel the fundamental truth-seeking that is the engine of all of our discoveries.
Lauren Ray John is an astronomy enthusiast and writer. She took on stargazing as a child and she never abandoned it. She is always up to date with the latest discoveries in astronomy and the latest gadgets for both amateur and professional stargazers. She has a personal project called TelescopeReviewer.com where she reviews the latest models and shares her knowledge with her audience.
Where humans congregate, pollution is bound to happen. Often, it’s coastlines and freshwater sources that receive the lion’s share of man-made sludge, toxic chemicals, and garbage. As a result, wildlife suffers, with many individuals getting killed as a result of ingesting microplastics or toxic chemicals. But while many species are threatened by pollution, some have learned to thrive despite it.
Killifish or minnows are abundant in the waterways and marshes along the Atlantic coast. There are some 1270 different species of killifish and they’re often used by biologists as a proxy to gauge ecosystem health because they’re hyper sensitive to pollution.
Usually, killifish stay away from contaminated waters, but not around New Bedford Harbor in Massachusetts, Newark Bay in New Jersey, the Bridgeport area of Connecticut, and the Elizabeth River in Virginia. From these four locations, researchers at the University of California, Davis, collected 400 individuals which looked pretty healthy despite they were swimming in waters with up to 8,000 times the lethal dose of toxic pollution. Some of these sites have been heavily contaminated with dioxins, PCBs or mercury since the 1950s.
When the researchers compared the genomes of the toxic chemical-immune killifish to those sequenced from killifish swimming in unpolluted waters, they found they were dealing with a mutant population.
The killifish which swam in mercury-ridden waters all had mutations that switched off molecular pathways that cause cell damage when interacting with toxic chemicals. These mutations were also found in some fish collected from unpolluted waters, but the mutants were far less common in these populations.
The study published in Science suggest that the killifish is a success story, managing to adapt very quickly to stressful conditions. That’s not to say that its model can be easily replicated by other species.
“Some people will see this as a positive and think, ‘Hey, species can evolve in response to what we’re doing to the environment!'” said lead author Andrew Whitehead, associate professor in the UC Davis Department of Environmental Toxicology. “Unfortunately, most species we care about preserving probably can’t adapt to these rapid changes because they don’t have the high levels of genetic variation that allow them to evolve quickly.”
First of all, the mutations that allow the killifish to tolerate polluted waters was already present in its populations. It’s just that those mutant killifish reproduced far more successfully, in time dominating the local populations in contaminated sites because of their evolutionary edge. And even so, there’s a price to pay: loss of genetic diversity. In contaminated areas, only the mutants thrive but in time if they face some other immediate change in the environment, the killifish might not be this successful anymore.
“If we know the kinds of genes that can confer sensitivity in another vertebrate animal like us, perhaps we can understand how different humans, with their own mutations in these important genes, might react to these chemicals,” Whitehead said.
Mercury becomes the second confirmed tectonically active planet in the Solar System, as new evidence from the MESSENGER spacecraft finds developing fault lines on the scorching planet.
For a long time, Earth was believed to be the only planet in our Solar System which could boast tectonic activity. This geologic liveliness has been linked to our planet’s unique ability to sustain life — but now, NASA found evidence of similar activity on Mercury. The MESSENGER spacecraft swooped in close to the tiny planet on its last 18 months orbiting it and found evidence of shifting pieces of crust and developing fault lines.
The photographs suggest that Mercury is still contracting, joining Earth as a tectonically active planet in the Solar System.
Image credits Watters et al., 2016, Nature Geoscience.
“The young age of the small scarps means that Mercury joins Earth as a tectonically active planet, with new faults likely forming today as Mercury’s interior continues to cool and the planet contracts,” said lead researcher Tom Watters, Smithsonian senior scientist at the National Air and Space Museum in Washington, DC.
Mercury isn’t the first body in the system or the only other planet apart from Earth to show these signs — we’re also suspecting similar activity on Europa, Jupiter’s watery moon, and UCLA professor of Earth and space sciences An Yin is building a strong case for tectonic activity on Mars. It hasn’t yet been confirmed, but scientists suspect that Jupiter’s tidal lock on the planet is what keeps its subsurface warm enough to stay liquid, in essence powering its tectonics. Yin’s paper is still awaiting peer-review.
However, with an 88-day orbit around the Sun, no atmosphere, and temperatures skyrocketing from -173 degrees Celsius (–280 degrees Fahrenheit) at night to a scorching 427 degrees Celsius (800 degrees Fahrenheit) during the day, Mercury sadly remains decidedly uninhabitable.
Researchers hope that by better understanding this activity on this tiny world, we’ll more easily spot similar processes on worlds outside of the Solar System. They’ll keep studying the planet’s magnetic field and surface activity to gain insight into the inner workings of the planet.
“This is why we explore,” said Jim Green, NASA’s planetary science director. “For years, scientists believed that Mercury’s tectonic activity was in the distant past. It’s exciting to consider that this small planet – not much larger than Earth’s moon – is active even today.”
The findings, titled “Recent tectonic activity on Mercury revealed by small thrust fault scarps” have been published in Nature Geoscience.
NASA just released the first ever topographic model of Mercury, the planet closest to the Sun.
This is the first time a digital elevation model (DEM) has been released of Mercury. A DEM is a 3D representation of a terrain’s surface, usually for a planet, moon or an asteroid. The model was created thanks to NASA’s MESSENGER mission, which orbited Mercury from 2011 to 2015 and sent over 10 terabytes of Mercury science data, including nearly 300,000 images, millions of spectra, and numerous map products.
“The wealth of these data, greatly enhanced by the extension of MESSENGER’s primary one-year mission to more than four years, has already enabled and will continue to enable exciting scientific discoveries about Mercury for decades to come,” said Susan Ensor, a software engineer at The Johns Hopkins University Applied Physics Laboratory (APL), in Laurel, Maryland. For the last nine years, Ensor has managed the MESSENGER Science Operations Center, which oversees the collection of data.
The model revealed a trove of interesting facts about Mercury, including rather unexpected topographic features. The highest elevation of Mercury is 2.78 miles (4.48 kilometers) above the average elevation of the planet while the lowest elevation is 3.34 miles (5.38 kilometers) below Mercury’s average, in the intriguing Rachmaninoff basin. Rachmaninoff is a peak-ring impact crater on Mercury believed to be the most recent volcanic feature.
The scale of Mercury’s volcanism is difficult to fathom.
“MESSENGER had previously discovered that past volcanic activity buried this portion of the planet beneath extensive lavas, more than a mile deep in some areas and covering a vast area equivalent to approximately 60 percent of the continental United States,” said APL’s Nancy Chabot, the Instrument Scientist for the Mercury Dual Imaging System (MDIS).
A view of Mercury’s northern volcanic plains is shown in enhanced color to emphasize different types of rocks on Mercury’s surface. In the bottom right portion of the image, the 181-mile- (291-kilometer)-diameter Mendelssohn impact basin, named after the German composer, appears to have been once nearly filled with lava. Toward the bottom left portion of the image, large wrinkle ridges, formed during lava cooling, are visible. Also in this region, the circular rims of impact craters buried by the lava can be identified. Near the top of the image, the bright orange region shows the location of a volcanic vent. Credits: NASA/JHUAPL/Carnegie Institution of Washington
This was actually the most difficult part of Mercury to map. Because the area is near the planet’s North Pole, the Sun is always close to the horizon, which means that the area is always covered in shadows, obscuring many of the geological features and colors. In order to bypass this problem, Mercury’s imaging system used five different narrow-band color filters to minimize the effect of the shadows and reveal Mercury’s true colors, as seen above.
This is quickly becoming one of my favorite maps, and I’m not the only one.
“This has become one of my favorite maps of Mercury,” Chabot added. “Now that it is available, I’m looking forward to it being used to investigate this epic volcanic event that shaped Mercury’s surface.”
Although MESSENGER’s orbital operations have already ended for a year, astronomers and geologists are still analyzing the information it sent, outputting valuable information like this. Even more data is archived for future studies and reference, helping us better understand our planetary neighbors.
“During its four years of orbital observations, MESSENGER revealed the global characteristics of one of our closest planetary neighbors for the first time,” offered MESSENGER Principal Investigator Sean Solomon, Director of Columbia University’s Lamont-Doherty Earth Observatory. “MESSENGER’s scientists and engineers hope that data from the mission will continue to be utilized by the planetary science community for years to come, not only to study the nature of the innermost planet, but to address broader questions about the formation and evolution of the inner solar system more generally.”
When the MESSENGER spacecraft found carbon rich material on Mercury, researchers were surprised and couldn’t quite explain the source. Now, they believe that the material may be the remnants of a primordial graphite crust, which would also explain why Mercury looks darker than expected.
Spectrum scan of Mercury’s surface by MESSENGER
MESSENGER (a backronym of MErcury Surface, Space ENvironment, GEochemistry, and Ranging, and a reference to the Roman mythological messenger, Mercury) orbited the solar system’s most inner planet from 2011 to 2015, becoming the first spacecraft to do so.
Mercury is much darker than the moon. However, iron (thought to be the main darkening agent for atmosphere-less planets) is much more abundant on the moon – so then why is Mercury darker? The proposed theory is that instead, the darkening agent is carbon.
Comparison of relative reflectance of the Moon and Mercury. The lunar mosaic was assembled from images taken with the 643 nm filter of the Lunar Reconnaissance Orbiter Camera Wide-Angle Camera. The Mercury mosaic was assembled from images taken with the 630 nm filter of the Mercury Dual Imaging System wide-angle camera. Image credits: Peplowski et al, 2016.
This was confirmed by MESSENGER towards the end of its mission. The association of this carbon-rich material with large craters is also consistent with an indigenous origin from deep within the crust and later exposure by impact. In this case, researchers propose a dark, graphite crust on Mercury formed in its primordial days.
Patrick Peplowski, a research scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md, believes this primordial crust was later obscured by volcanism and other intense geological processes; however, some patches of graphite were melted and incorporated into other material, causing a general darkening of the surface.
Previously, some astronomers proposed that the carbon was brought by meteorites crashing into Mercury, but this doesn’t seem to be the case. Mercury is the smallest planet in the Solar System and the one closest to the Sun.
The element mercury (Hg) is extremely toxic to most organisms, including humans. It’s deadly effects are thought to be due to it’s ability to block the function of certain key metabolic enzymes. Being so toxic, it has long been thought that mercury had no biological functions in the living world at all. At least that was presumption until a research team published the first evidence that a unique group of organisms can not only stand being around the stuff, but actually benefit by the presence of Mercury. In a paper published this month in Nature Geoscience, D. S. Gregoire and A. J. Poulain show that photosynthetic microorganisms called purple non-sulfur bacteria can use mercury as an electron acceptor during photosynthesis. These bacteria rely on a primitive form of photosynthesis that differs from the type common to plants. In the case of photosynthesis in plants, water is used as an electron donor, with carbon dioxide the electron acceptor. The result of this process is the production of sugars, the release of oxygen, and the removal of carbon dioxide from the air. Purple non-sulfur bacteria, on the other hand, usually prefer to live in watery environments where light is available to them, but the oxygen levels are low.
Image via Wikipedia.
They use hydrogen as the electron donor, and an organic molecule such as glycerol or fatty acids, as the electron acceptor. This also results in the production of sugars, but does not release oxygen or remove carbon dioxide from the atmosphere. This process also generates too many electrons for for their organic electron donor to handle, leading to the potential for damage to other molecules in the cell.
The researcher showed that purple non-sulfur bacteria grow better when mercury is in their environment. The reason seems to be that the bacteria use the mercury to accept those extra electrons, reducing mercury from a high oxidation state to a low one. The oxidation state refers to the number of electrons that an atom can gain or lose. In the case of mercury, when it goes to its low oxidation state after gaining the extra electrons, it becomes a vapor and evaporates away into the atmosphere. In mercury’s high oxidation state it can form the soluble compound methyl-mercury, which can be toxic to other organisms.
It’s quite possible that the impact of mercury reduction by photosynthesis may extend far beyond the health of these unusual little microbes. Jeffry K. Schaefer, in the Department of Environmental Sciences at Rutgers University speculates that, “By limiting methyl-mercury formation and accumulation in aquatic food webs from microorganisms to fish, this process may even contribute to less toxic mercury ultimately ending up on our dinner plates.”
A physiological role for HgII during phototrophic growth. Nature Geoscience. February 2016, Volume 9 No 2 pp121 – 125 D. S. Grégoire & A. J. Poulain doi:10.1038/ngeo2629
The MESSENGER spacecraft spent four years orbiting Mercury, gathering valuable information and sending it back to Earth. But even in its final moments, as it crashed towards the surface of the planet, the spacecraft still did its job – it reported that Mercury has a magnetic field, likely millions of years old.
MASCS/MDIS color mosaics of Mercury. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington.
Mercury is the smallest planet in our solar system, and it’s also the closest to the Sun. It has no atmosphere, and as a result, experiences dramatic temperature shifts, from −173 °C (−280 °F) at night, as it’s facing away from the Sun, to 427 °C (800 °F) during the day. The MESSENGER shuttle was sent to study the planet; launched in 2004, it orbited Mercury from 2011 to 2015, before performing a planned crash onto the surface.
Scientists have suspected for quite a while that Mercury has a significant magnetic field, and MESSENGER confirmed it. Besides Earth, Mercury is the only rocky planet in the inner solar system to have such a large magnetic field. While today it is nowhere near as strong as that of our own planet, it is believed that at one point in the past, Mercury’s magnetic field was 100 times stronger than that of the Earth. We still don’t know for sure why this field exists, but it’s likely that it is due to a liquid core. Another observation which seems to confirm this theory is the fact that the planet’s crust seems to be thicker towards the equator and thinner at the pole. The core accounts for more than 85% of the radius of the planet.
Unfortunately, Mercury’s magnetic field was to small to properly analyze, and MESSENGER had little time to conduct measurements as it was crashing, Mercury’s proximity to the Sun only accounts for about a third of the magnetic influence the planet exerts, so astronomers are still not entirely clear what to make of things, but it seems clear that even after four years of close studies, Mercury still has its secrets.
The Mercury level in tuna has been a subject of debate for decades now. Paul Drevnick, Assistant Research Scientist at University of Michigan and his team analyzed data from over the past 50 years and found that mercury levels in Pacific yellowfin tuna, often marketed as ahi tuna, is increasing at 3.8% per year. If 3.8% per year doesn’t seem like much, that translates into a doubling at every 20 years. So in 50 years, mercury levels have increased 6 times.
Mercury levels in fish. Image via Lean it up.
Mercury is a neurotoxin – it can cause significant damage to nerve tissue. Mercury exists in a number of different compounds, though methylmercury (MeHg+), dimethylmercury and diethylmercury are the only significantly neurotoxic forms. Diethylmercury and dimethylmercury are considered some of the most potent neurotoxins ever discovered. Mercury levels in tuna are now approaching levels deemed unsafe for human consumption by the EPA.
The initial surprise was that high mercury levels were reached consistently throughout the globe, even in pristine areas in Scandinavia or North America. This happens because most of the mercury comes from coal plants; as the coal plants burn coal, mercury can easily travel throughout the globe (even several times) before settling down as dust or rain. As it settles down on water, it is then absorbed by fish. As Drevnik explains, many people have the wrong idea that the world’s ocean is simply too large to be polluted.
“Two manuscripts published in Science in the early 1970s supported this argument. The first stated that mercury pollution could only result in a negligible increase in mercury levels in open ocean water,” he writes.
It took years before people understood how airborne mercury from burning coal at power plants could accumulate in fish. Jim Richmond/Flickr, CC BY-SA
But new research contradicts that idea. Namely, dillution is not a solution to pollution. Mercury is not something easily eliminated from the body, so if it gets absorbed by a plant or an animal, it pretty much travels throughout the food chain, so that top predators contain much more mercury. The study found that methylmercury levels in predatory fish are about a million times greater than in the water in which they swim. Furthermore, mercury levels continue to rise, at an average of 3.8% a year.
“The statistical comparison indicated mercury levels were higher in 2008 than in either 1971 or 1998. As a result, we concluded that mercury levels are increasing in yellowfin tuna near Hawaii. The rate of increase between 1998 and 2008 of 3.8% per year is equivalent to a modeled increase in mercury in ocean waters in the same location.”
The only question mark is now where the mercury is coming from – and the scientific evidence seems to indicate we are doing it. Coal plants are the main source of pollution, closely followed by cement kilns. Other sources are trash burning and gold mining. We need to find better ways to deal with our mercury pollution, and that’s exactly the aim of the new United Nations Environment Programme’s Minamata Convention on Mercury.
In the mean time, we also have to keep avoid eating too much tuna.
If you’ve always wanted to choose the name of stuff from outer space but never got the chance… now’s your time to shine! NASA is offering you the chance to name one of the craters of Mercury in honour of the MESSENGER mission, which is nearing its final days.
NASA, together with Johns Hopkins University and the Carnegie Institution for Science, has kicked off a competition which will allow the general public to decide the name of craters on Mercury. Craters on the closest planet to the sun are typically named after artists, and current examples include Beethoven, Caravaggio and Lennon. You will submit the name of whatever artist you want from anywhere in the world, and then the people will vote. It’s a long shot, but your favorite artist just might be chosen!
“This brave little craft, not much bigger than a Volkswagen Beetle, has travelled more than 8 billion miles since 2004—getting to the planet and then in orbit,” Julie Edmonds, head of the mission’s Education and Public Outreach, said.
The MESSENGER mission was supposed to shut down in 2011, but it has surpassed expectations by more than three years – as so many NASA missions have done. MESSENGER (an acronym of MErcury Surface, Space ENvironment, GEochemistry, and Ranging, and a reference to Mercury being the messenger of the gods) is a robotic NASA spacecraft orbiting the planet Mercury, the first spacecraft ever to do so. The mission has mapped a lot of geological features… all of which are awaiting to be named – by you!
“As scientists study the incredible data returned by MESSENGER, it becomes important to give names to surface features that are of special scientific interest. Having names for landforms such as mountains, craters, and cliffs makes it easier for scientists and others to communicate,” she added.
Scientists have finished analyzing water samples taken from 12 oceanographic cruises from the past 8 years. Among other startling discoveries, they report that the mercury content in the upper oceans has tripled since the Industrial Revolution began.
Interestingly enough, this is the first time we have an accurate, systematic global distribution of mercury in oceans. While mercury is a naturally occurring element both in waters and in the atmosphere, the high concentrations researchers report can only be attributed to burning coal. The mercury pollution was strongest in the deeper parts Northern Atlantic because surface waters sink to intermediate depths and beyond. Meanwhile, deep waters in the Northern Pacific remained relatively unpolluted, while the shallow waters have very high concentrations, because the surface waters do not mix with deep waters there.
In order to isolate the human contribution and see if this is not somehow a natural phenomenon, researchers used a calibration measurement (a proxy): carbon dioxide. By correlating CO2 with mercury, they could then estimate the total mercury due to human activities. The estimate was 60,000 to 80,000 tons, which is a huge quantity.
Not all of the mercury comes as a result of burning fossil fuels (especially coal) though. Some mining activities are also linked with mercury pollution. Gold and silver mining historically used mercury to help improve recovery of the precious ore. Mercury mining is now banned in some countries, but still continues in others. It’s still not clear what the direct effects of this mercury pollution will be, but it almost certainly affects the entire food chain, from plankton, to fish, and ultimately, to us.
The Earth contains a lot of iron, but it is not alone in the solar system in that aspect. Venus, Mars, the Moon and asteroids such as Vesta all have iron in their structure, but Mercury is the champion in that aspect: about 70 percent of its mass is iron! Now, researchers believe they have found why Mercury is so rich in this metal – the planet is the result of a cosmic ‘hit and run’.
The main proposed reason for the lunar iron is that the Moon was formed as a result of a giant impact with proto-Earth – but that can’t account for the much vaster Mercurian iron. Such a scenario requires that proto-Mercury was blasted apart with far greater specific energy than required for lunar formation, but in such a way that it retained substantial volatile elements and did not reaccrete its ejected mantle – in other words, something struck Mercury so hard that the planet lots half its mantle in a collision with proto-Earth or proto-Venus, leaving behind the iron-rich body we see today. The mantle which was torn from Mercury also didn’t re-accrete on to the planet.
Erik Asphaug from Arizona State University and Andreas Reufer of the University of Bern developed a statistical scenario for how planets merge and grow; apparently, Mars and Mercury lucked out, but in different ways.
“How did they luck out? Mars, by missing out on most of the action – not colliding into any larger body since its formation – and Mercury, by hitting the larger planets in a glancing blow each time, failing to accrete,” explains Asphaug.
Their model showed that this was unlikely, but not extremely unlikely.
“It’s like landing heads two or three times in a row – lucky, but not crazy lucky. In fact, about one in 10 lucky.”
The rather surprising result the model projected was that hit and run collisions are might not have been that uncommon in our solar system.
“The surprising result we have shown is that hit-and-run relics not only can exist in rare cases, but that survivors of repeated hit-and-run incidents can dominate the surviving population. That is, the average unaccreted body will have been subject to more than one hit-and-run collision,’ explains Asphaug. We propose one or two of these hit-and-run collisions can explain Mercury’s massive metallic core and very thin rocky mantle.”
Can you put a cost on pollution? Policy makers, not matter how some may deny it, are more astute than they were a few decades ago about subjects like climate change or global warming. Few can deny the adverse effects of immediate particle pollution on health, but whenever environmental regulations were put forth on the table, cost was a significant deterrent. Last week, a court passed one of the most important rules in the U.S.’s environmental history: the Environmental Protection Agency‘s Clean Air Mercury Rule (CAMR).
The law will regulate electrical utilities to keep down their mercury emissions up to a certain level and will supposedly prevent up to 11,000 premature deaths, 4,700 heart attacks and 130,000 asthma attacks a year. The court was divided in passing the rule, however, because of cost. The EPA estimates it will cost $9.6 billion a year, with most of the burden falling on electric utilities. An enormous score that left many of the judges ponder whether there is any justifiable claim to take this action, after all what good is to save lives when you ruin the economy.
Put a cost on pollution, put a cost on lives
Unbent by this rhetoric, the majority of the court ruled, however, that the EPA had indeed considered cost and that ignoring this law will actually have more dramatic economic consequences. The economic benefits have been estimated to be worth from $37 billion to $90 billion, outweighing the costs by a factor of between 3 to 1 and 9 to 1. What’s important to note is that these benefits were identified not to be strictly related to mercury. The substance is indeed very dangerous potentially affecting memory, language, attention and cognition, but to quantify it’s adverse effects is really difficult. Some industry groups have said the EPA was overstating the benefits.
What you can count fairly easily is its cousin – particle emissions. Efforts to reduce mercury emission will come with co-benefits, namely particulate matter reduction. Particle matter pollution causes severe health complications and in our case accounted for about one-third to one-half of the total monetized benefits of all significant federal regulations from 2003 through 2012.
This most likely helped a lot in passing the EPA’s rule, since particle pollution is a very well documented case. For instance, one study looked at two similar populations in China, each living on opposite ends of the Huai River. The people north of the river received free, government-provided coal to heat their homes. The other was made up of people who lived south of the river and did not get free coal. Those heating their homes with the free coal were found to have life expectancies 5.5 years shorter than those who did not, due to the coal-generated particulate matter they inhaled.
Most companies operating power plants will have until March 2015 to meet the standards, but a state could grant an additional year and the EPA could extend the deadline until 2017 if the unit was critical for reliability. Laura Sheehan, senior vice president of communications for the American Coalition for Clean Coal Electricity, said that due in part to regulations like the one in April 16th’s ruling, almost 300 coal-fueled generating units in 33 states have announced they will shut down, costing the electricity sector roughly $200 billion in compliance costs and destroying at least 544,000 jobs.
Nevertheless, decisions such as this passing EPA’s mercury standard should be celebrated. We, the staff of ZME Science, most definitely salute it!
The fist planet from the sun is the unlikeliest place you’d expect to find water ice, but new tantalizing evidence beamed back by the Messenger spacecraft orbiting Mercury suggests just so.
North Pole Mercury Water Ice Shown in red are areas of Mercury’s north polar region that are in shadow in all images acquired by MESSENGER to date. Image coverage, and mapping of shadows, is incomplete near the pole. The polar deposits imaged by Earth-based radar are in yellow (from Image 2.1), and the background image is the mosaic of MESSENGER images from Image 2.2. This comparison indicates that all of the polar deposits imaged by Earth-based radar are located in areas of persistent shadow as documented by MESSENGER images. (c) NASA
On the surface of Mercury, temperatures can reach boiling 752º Fahrenheit (400ºC), clearly water in any state can not exist. At its poles, however, things take a different turn. Since the planet’s axis tilt barely hits one degree, its poles are permanently shadowed from the sun’s rays – apparently, here temperatures range in the other extreme.
On a related note, it’s worth mentioning the contrary to intuitive thinking, Mercury isn’t the hottest planet in the solar system, despite being the first in line – the honor goes to Venus. Beauty triumphs again.
Ice on the first planet from the sun
Water ice has been hypothesized for decades to exist in Mercury’s poles. In 1991, Earth-based observations found that ice may be present after radar signals bounced back in a characteristic pattern. In 1999, the initial measurements were strengthened after astronomers used the more powerful Arecibo Observatory microwave beam in Puerto Rico. Later on, radar pictures beamed back to New Mexico’s Very Large Array showed white areas that researchers suspected was water ice.
Now, the spacecraft has supplied three independent pieces of evidence from its high-precision instruments. The Neutron Spectrometer instrument on-board the spacecraft made first measurements of excess hydrogen at Mercury’s north pole, the Mercury Laser Altimeter (MLA) offered the first readings of reflectance of Mercury’s polar deposits at near-infrared wavelengths, while the same MLA compiled the first detailed models of the surface and near-surface temperatures of Mercury’s north polar regions that utilize the actual topography of Mercury’s surface.
“These reflectance anomalies are concentrated on poleward-facing slopes and are spatially collocated with areas of high radar backscatter postulated to be the result of near-surface water ice,” writes Gregory Neumann of the NASA Goddard Space Flight Center.
“Correlation of observed reflectance with modeled temperatures indicates that the optically bright regions are consistent with surface water ice.”
A monumental find
Moroever temperature gradients surprisingly suggested that dark, volatile materials are mixing in with ice. This is something consistent with climates in which organic matter survives. Neumann suggests that impacts of comets or volatile-rich asteroids could have provided both the dark and bright deposits, a finding corroborated in a third paper led by David Paige of the University of California, Los Angeles.
“This was very exciting. You are looking for bright stuff, and you see dark stuff – gee, it’s something new,” Neumann said.
Sean Solomon of the Columbia University’s Lamont-Doherty Earth Observatory, principal investigator of the MESSENGER mission stated:
“For more than 20 years the jury has been deliberating on whether the planet closest to the Sun hosts abundant water ice in its permanently shadowed polar regions. MESSENGER has now supplied a unanimous affirmative verdict.”
“But the new observations have also raised new questions,” adds Solomon. “Do the dark materials in the polar deposits consist mostly of organic compounds? What kind of chemical reactions has that material experienced? Are there any regions on or within Mercury that might have both liquid water and organic compounds? Only with the continued exploration of Mercury can we hope to make progress on these new questions.”
In the one hour video conference below, Dwayne Brown from NASA’s office of communications, explains Messenger’s historic findings in broad detail.
The readings have only been made for Mercury’s north pole, but scientists are rather confident that water ice is present on its south pole as well. Messenger will spiral closer to the planet in 2014 and 2015, and more comprehensive measurements will then be available.