On September 18, 2017, ESA astronaut Paolo Nespoli shot this image from the International Space Station showing the Moon rising above the Earth’s horizon together with Mercury, Mars, the star Regulus, and Venus. Credit: ESA/NASA
One has a thick poisonous atmosphere, one has hardly any atmosphere at all, and one is just right for life to flourish – but it wasn’t always that way. The atmospheres of our two neighbors Venus and Mars can teach us a lot about the past and future scenarios for our own planet.
Rewind 4.6 billion years from the present day to the planetary construction yard, and we see that all the planets share a common history: they were all born from the same swirling cloud of gas and dust, with the newborn Sun ignited at the center. Slowly but surely, with the help of gravity, dust accumulated into boulders, eventually snowballing into planet-sized entities.
Rocky material could withstand the heat closest to the Sun, while gassy, icy material could only survive further away, giving rise to the innermost terrestrial planets and the outermost gas and ice giants, respectively. The leftovers made asteroids and comets.
The four terrestrial (meaning ‘Earth-like’) planets of our inner Solar System: Mercury, Venus, Earth, and Mars. These images were taken by the Mariner 10, Apollo 17 and Viking missions. Credit: ESA
The atmospheres of the rocky planets were formed as part of the very energetic building process, mostly by outgassing as they cooled down, with some small contributions from volcanic eruptions and minor delivery of water, gases, and other ingredients by comets and asteroids. Over time the atmospheres underwent a strong evolution thanks to an intricate combination of factors that ultimately led to the current status, with Earth being the only known planet to support life, and the only one with liquid water on its surface today.
We know from space missions such as ESA’s Venus Express, which observed Venus from orbit between 2006 and 2014, and Mars Express, investigating the Red Planet since 2003, that liquid water once flowed on our sister planets, too. While the water on Venus has long since boiled away, on Mars it is either buried underground or locked up in ice caps. Intimately linked to the story of water – and ultimately to the big question of whether life could have arisen beyond Earth – is the state of a planet’s atmosphere. And connected to that, the interplay and exchange of material between the atmosphere, oceans and the planet’s rocky interior.
Planetary recycling
Back at our newly formed planets, from a ball of molten rock with a mantle surrounding a dense core, they stated to cool down. Earth, Venus and Mars all experienced outgassing activity in these early days, which formed the first young, hot and dense atmospheres. As these atmospheres also cooled, the first oceans rained down from the skies.
Mars from horizon to horizon. Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO
At some stage, though, the characteristics of the geological activity of the three planets diverged. Earth’s solid lid cracked into plates, in some places diving below another plate in subduction zones, and in other places colliding to create vast mountain ranges or pulling apart to create giant rifts or new crust. Earth’s tectonic plates are still moving today, giving rise to volcanic eruptions or earthquakes at their boundaries.
Venus, which is only slightly smaller than Earth, may still have volcanic activity today, and its surface seems to have been resurfaced with lavas as recently as half a billion years ago. Today it has no discernable plate tectonics system; its volcanoes were likely powered by thermal plumes rising through the mantle – created in a process that can be likened to a ‘lava lamp’ but on a gigantic scale.
Mars, being a lot smaller, cooled off more quickly than Earth and Venus, and when its volcanoes became extinct it lost a key means of replenishing its atmosphere. But it still boasts the largest volcano in the entire Solar System, the 25 kilometer high Olympus Mons, likely too the result of continuous vertical building of the crust from plumes rising from below. Even though there is evidence for tectonic activity within the last 10 million years, and even the occasional marsquake in present times, the planet is not believed to have an Earth-like tectonics system either.
It is not just global plate tectonics alone that make Earth special, but the unique combination with oceans. Today our oceans, which cover about two-thirds of Earth’s surface, absorb and store much of our planet’s heat, transporting it along currents around the globe. As a tectonic plate is dragged down into the mantle, it warms up and releases water and gases trapped in the rocks, which in turn percolate through hydrothermal vents on the ocean floor.
Extremely hardy lifeforms have been found in such environments at the bottom of Earth’s oceans, providing clues as to how early life may have begun, and giving scientists pointers on where to look elsewhere in the Solar System: Jupiter’s moon Europa, or Saturn’s icy moon Enceladus for example, which conceal oceans of liquid water beneath their icy crusts, with evidence from space missions like Cassini suggesting hydrothermal activity may be present.
Moreover, plate tectonics helps to modulate our atmosphere, regulating the amount of carbon dioxide on our planet over long timescales. When atmospheric carbon dioxide combines with water, carbonic acid is formed, which in turn dissolves rocks. Rain brings the carbonic acid and calcium to the oceans – carbon dioxide is also dissolved directly in oceans – where it is cycled back into the ocean floor. For almost half of Earth’s history the atmosphere contained very little oxygen. Oceanic cyanobacteria were the first to use the Sun’s energy to convert carbon dioxide into oxygen, a turning point in providing the atmosphere that much further down the line allowed complex life to flourish. Without the planetary recycling and regulation between the mantle, oceans, and atmosphere, Earth may have ended up more like Venus.
Extreme greenhouse effect
Venus is sometimes referred to as Earth’s evil twin on account of it being almost the same size but plagued with a thick noxious atmosphere and a sweltering 470ºC surface. Its high pressure and temperature is hot enough to melt lead – and destroy the spacecraft that dare to land on it. Thanks to its dense atmosphere, it is even hotter than planet Mercury, which orbits closer to the Sun. Its dramatic deviation from an Earth-like environment is often used as an example of what happens in a runaway greenhouse effect.
Appearances can be deceiving. This thick, cloud-rich atmosphere rains sulphuric acid and below lie not oceans but a baked and barren lava-strewn surface. Welcome to Venus. Credit: ESA/MPS/DLR-PF/IDA
The main source of heat in the Solar System is the Sun’s energy, which warms a planet’s surface up, and then the planet radiates energy back into space. An atmosphere traps some of the outgoing energy, retaining heat – the so-called greenhouse effect. It is a natural phenomenon that helps regulate a planet’s temperature. If it weren’t for greenhouse gases like water vapor, carbon dioxide, methane, and ozone, Earth’s surface temperature would be about 30 degrees cooler than its present +15ºC average.
Over the past centuries, humans have altered this natural balance on Earth, strengthening the greenhouse effect since the dawn of industrial activity by contributing additional carbon dioxide along with nitrogen oxides, sulfates, and other trace gases and dust and smoke particles into the air. The long-term effects on our planet include global warming, acid rain, and the depletion of the ozone layer. The consequences of a warming climate are far-reaching, potentially affecting freshwater resources, global food production and sea level, and triggering an increase in extreme-weather events.
There is no human activity on Venus, but studying its atmosphere provides a natural laboratory to better understand a runaway greenhouse effect. At some point in its history, Venus began trapping too much heat. It was once thought to host oceans like Earth, but the added heat turned water into steam, and in turn, additional water vapor in the atmosphere trapped more and more heat until entire oceans completely evaporated. Venus Express even showed that water vapor is still escaping from Venus’ atmosphere and into space today.
Venus Express also discovered a mysterious layer of high-altitude sulfur dioxide in the planet’s atmosphere. Sulfur dioxide is expected from the emission of volcanoes – over the mission’s duration Venus Express recorded large changes in the sulfur dioxide content of the atmosphere. This leads to sulphuric acid clouds and droplets at altitudes of about 50-70 km – any remaining sulphur dioxide should be destroyed by intense solar radiation. So it was a surprise for Venus Express to discover a layer of the gas at around 100 km. It was determined that evaporating sulphuric acid droplets free gaseous sulphuric acid that is then broken apart by sunlight, releasing the sulfur dioxide gas.
The observation adds to the discussion what might happen if large quantities of sulfur dioxide are injected into Earth’s atmosphere – a proposal made for how to mitigate the effects of the changing climate on Earth. The concept was demonstrated from the 1991 volcanic eruption of Mount Pinatubo in the Philippines, when sulfur dioxide ejected from the eruption created small droplets of concentrated sulphuric acid – like those found in Venus’ clouds – at about 20 km altitude. This generated a haze layer and cooled our planet globally by about 0.5ºC for several years. Because this haze reflects heat it has been proposed that one way to reduce global temperatures would be to inject artificially large quantities of sulfur dioxide into our atmosphere. However, the natural effects of Mt Pinatubo only offered a temporary cooling effect. Studying the enormous layer of sulphuric acid cloud droplets at Venus offers a natural way to study the longer-term effects; an initially protective haze at higher altitude would eventually be converted back into gaseous sulphuric acid, which is transparent and allows all the Sun’s rays through. Not to mention the side-effect of acid rain, which on Earth can cause harmful effects on soils, plant life, and water.
Global freezing
Our other neighbor, Mars, lies at another extreme: although its atmosphere is also predominantly carbon dioxide, today it hardly has any at all, with a total atmospheric volume less than 1% of Earth’s.
Artist impression (not to scale) idealizing how the solar wind shapes the magnetospheres of Venus (top), Earth (middle) and Mars (bottom). Credit: ESA
Mars’ existing atmosphere is so thin that although carbon dioxide condenses into clouds, it cannot retain sufficient energy from the Sun to maintain surface water – it vaporizes instantly at the surface. But with its low pressure and relatively balmy temperatures of -55ºC (ranging from -133ºC at the winter pole to +27ºC during summer), spacecraft don’t melt on its surface, allowing us greater access to uncover its secrets. Furthermore, thanks to the lack of recycling plate tectonics on the planet, four billion-year-old rocks are directly accessible to our landers and rovers exploring its surface. Meanwhile our orbiters, including Mars Express, which has been surveying the planet for more than 15 years, are constantly finding evidence for its once flowing waters, oceans and lakes, giving a tantalizing hope that it might have once supported life.
The Red Planet too would have started out with a thicker atmosphere thanks to the delivery of volatiles from asteroids and comets, and volcanic outgassing from the planet as its rocky interior cooled down. It simply couldn’t hold on to its atmosphere most likely because of its smaller mass and lower gravity. In addition, its initial higher temperature would have given more energy to gas molecules in the atmosphere, allowing them to escape more easily. And, having also lost its global magnetic field early in its history, the remaining atmosphere was subsequently exposed to the solar wind – a continuous flow of charged particles from the Sun – that, just as on Venus, continues to strip away the atmosphere even today.
With a decreased atmosphere, the surface water moved underground, released as vast flash-floods only when impacts heated the ground and released the subsurface water and ice. It is also locked up in the polar ice caps. Mars Express also recently detected a pool of liquid water buried within two kilometers of the surface. Could evidence of life also be underground? This question is at the heart of Europe’s ExoMars rover, scheduled to launch in 2020 and land in 2021 to drill up to two meters below the surface to retrieve and analyze samples in search for biomarkers.
This image from ESA’s Mars Express shows a network of dried-up valleys on Mars, and comprises data gathered on 19 November 2018 during Mars Express orbit 18831. Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO
Mars is thought to be currently coming out of an ice age. Like Earth, Mars is sensitive to changes in factors such as the tilt of its rotational axis as it orbits the Sun; it is thought that the stability of water at the surface has varied over thousands to millions of years as the axial tilt of the planet and its distance from the Sun undergo cyclical changes. The ExoMars Trace Gas Orbiter, currently investigating the Red Planet from orbit, recently detected hydrated material in equatorial regions that could represent former locations of the planet’s poles in the past.
The Trace Gas Orbiter’s primary mission is to conduct a precise inventory of the planet’s atmosphere, in particular the trace gases which make up less than 1% of the planet’s total volume of atmosphere. Of particular interest is methane, which on Earth is produced largely by biological activity, and also by natural and geological processes. Hints of methane have previously been reported by Mars Express, and later by NASA’s Curiosity rover on the surface of the planet, but the Trace Gas Orbiter’s highly sensitive instruments have so far reported a general absence of the gas, deepening the mystery. In order to corroborate the different results, scientists are not only investigating how methane might be created, but also how it might be destroyed close to the surface. Not all lifeforms generate methane, however, and the rover with its underground drill will hopefully be able to tell us more. Certainly, the continued exploration of the Red Planet will help us understand how and why Mars’ habitability potential has changed over time.
Exploring farther
Despite starting with the same ingredients, Earth’s neighbors suffered devastating climate catastrophes and could not hold on to their water for long. Venus became too hot and Mars too cold; only Earth became the ‘Goldilocks’ planet with the just-right conditions. Did we come close to becoming Mars-like in a previous ice age? How close are we to the runaway greenhouse effect that plagues Venus? Understanding the evolution of these planets and the role of their atmospheres is tremendously important for understanding climatic changes on our own planet as ultimately the same laws of physics govern all. The data returned from our orbiting spacecraft provide natural reminders that climate stability is not something to be taken for granted.
In any case, in the very long term – billions of years into the future – a greenhouse Earth is an inevitable outcome at the hands of the aging Sun. Our once life-giving star will eventually swell and brighten, injecting enough heat into Earth’s delicate system to boil our oceans, sending it down the same pathway as its evil twin.
More than 40 trillion gallons of rain drenched the Southeast United States in the last week from Hurricane Helene and a run-of-the-mill rainstorm that sloshed in ahead of it — an unheard of amount of water that has stunned experts.
That’s enough to fill the Dallas Cowboys’ stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina that much water would be 3.5 feet deep (more than 1 meter). It’s enough to fill more than 60 million Olympic-size swimming pools.
“That’s an astronomical amount of precipitation,” said Ed Clark, head of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. “I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky.”
The flood damage from the rain is apocalyptic, meteorologists said. More than 100 people are dead, according to officials.
Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated the amount of rain, using precipitation measurements made in 2.5-mile-by-2.5 mile grids as measured by satellites and ground observations. He came up with 40 trillion gallons through Sunday for the eastern United States, with 20 trillion gallons of that hitting just Georgia, Tennessee, the Carolinas and Florida from Hurricane Helene.
Clark did the calculations independently and said the 40 trillion gallon figure (151 trillion liters) is about right and, if anything, conservative. Maue said maybe 1 to 2 trillion more gallons of rain had fallen, much if it in Virginia, since his calculations.
Clark, who spends much of his work on issues of shrinking western water supplies, said to put the amount of rain in perspective, it’s more than twice the combined amount of water stored by two key Colorado River basin reservoirs: Lake Powell and Lake Mead.
Several meteorologists said this was a combination of two, maybe three storm systems. Before Helene struck, rain had fallen heavily for days because a low pressure system had “cut off” from the jet stream — which moves weather systems along west to east — and stalled over the Southeast. That funneled plenty of warm water from the Gulf of Mexico. And a storm that fell just short of named status parked along North Carolina’s Atlantic coast, dumping as much as 20 inches of rain, said North Carolina state climatologist Kathie Dello.
Then add Helene, one of the largest storms in the last couple decades and one that held plenty of rain because it was young and moved fast before it hit the Appalachians, said University of Albany hurricane expert Kristen Corbosiero.
“It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain,” Maue said. “That collected at high elevation, we’re talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down.”
The fact that these storms hit the mountains made everything worse, and not just because of runoff. The interaction between the mountains and the storm systems wrings more moisture out of the air, Clark, Maue and Corbosiero said.
North Carolina weather officials said their top measurement total was 31.33 inches in the tiny town of Busick. Mount Mitchell also got more than 2 feet of rainfall.
Before 2017’s Hurricane Harvey, “I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,” Clark said. “And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We’re seeing events year in and year out where we are measuring rainfall in feet.”
Storms are getting wetter as the climate change s, said Corbosiero and Dello. A basic law of physics says the air holds nearly 4% more moisture for every degree Fahrenheit warmer (7% for every degree Celsius) and the world has warmed more than 2 degrees (1.2 degrees Celsius) since pre-industrial times.
Corbosiero said meteorologists are vigorously debating how much of Helene is due to worsening climate change and how much is random.
For Dello, the “fingerprints of climate change” were clear.
“We’ve seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction. ”
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It’s a dinosaur that roamed Alberta’s badlands more than 70 million years ago, sporting a big, bumpy, bony head the size of a baby elephant.
On Wednesday, paleontologists near Grande Prairie pulled its 272-kilogram skull from the ground.
They call it “Big Sam.”
The adult Pachyrhinosaurus is the second plant-eating dinosaur to be unearthed from a dense bonebed belonging to a herd that died together on the edge of a valley that now sits 450 kilometres northwest of Edmonton.
It didn’t die alone.
“We have hundreds of juvenile bones in the bonebed, so we know that there are many babies and some adults among all of the big adults,” Emily Bamforth, a paleontologist with the nearby Philip J. Currie Dinosaur Museum, said in an interview on the way to the dig site.
She described the horned Pachyrhinosaurus as “the smaller, older cousin of the triceratops.”
“This species of dinosaur is endemic to the Grand Prairie area, so it’s found here and nowhere else in the world. They are … kind of about the size of an Indian elephant and a rhino,” she added.
The head alone, she said, is about the size of a baby elephant.
The discovery was a long time coming.
The bonebed was first discovered by a high school teacher out for a walk about 50 years ago. It took the teacher a decade to get anyone from southern Alberta to come to take a look.
“At the time, sort of in the ’70s and ’80s, paleontology in northern Alberta was virtually unknown,” said Bamforth.
When paleontogists eventually got to the site, Bamforth said, they learned “it’s actually one of the densest dinosaur bonebeds in North America.”
“It contains about 100 to 300 bones per square metre,” she said.
Paleontologists have been at the site sporadically ever since, combing through bones belonging to turtles, dinosaurs and lizards. Sixteen years ago, they discovered a large skull of an approximately 30-year-old Pachyrhinosaurus, which is now at the museum.
About a year ago, they found the second adult: Big Sam.
Bamforth said both dinosaurs are believed to have been the elders in the herd.
“Their distinguishing feature is that, instead of having a horn on their nose like a triceratops, they had this big, bony bump called a boss. And they have big, bony bumps over their eyes as well,” she said.
“It makes them look a little strange. It’s the one dinosaur that if you find it, it’s the only possible thing it can be.”
The genders of the two adults are unknown.
Bamforth said the extraction was difficult because Big Sam was intertwined in a cluster of about 300 other bones.
The skull was found upside down, “as if the animal was lying on its back,” but was well preserved, she said.
She said the excavation process involved putting plaster on the skull and wooden planks around if for stability. From there, it was lifted out — very carefully — with a crane, and was to be shipped on a trolley to the museum for study.
“I have extracted skulls in the past. This is probably the biggest one I’ve ever done though,” said Bamforth.
“It’s pretty exciting.”
This report by The Canadian Press was first published Sept. 25, 2024.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
