Scientists have discovered over 4,000 exoplanets outside of our Solar System, according to NASA’s Exoplanet Archive.
Some of these planets orbit multiple stars at the same time. Certain planets are so close to their star that it takes only a handful of days to make one revolution, compared to the Earth which takes 365.25 days. Others slingshot around their star with extremely oblong orbits, unlike the Earth’s circular one. When it comes to how exoplanets behave and where they exist, there are many possibilities.
And yet, when it comes to sizes of planets, specifically their mass and radius, there are some limitations. And for that, we have physics to blame.
I am a planetary astrophysicist and I try to understand what makes a planet able to support life. I look at the chemical connection between stars and their exoplanets and how the interior structure and mineralogy of different sized planets compare to each other.
Rocky versus gaseous planets
In our Solar System, we have two kinds of planets: small, rocky, dense planets that are similar to Earth and large, gaseous planets like Jupiter. From what we astrophysicists have detected so far, most planets fall into these two categories.
In fact, when we look at the data from planet-hunting missions such as the Kepler mission or from the Transiting Exoplanet System Satellite, there is a gap in the planet sizes. Namely, there aren’t many planets that fulfill the definition of a “super-Earth,” with a radius of one and a half to twice Earth’s radius and a mass that is five to 10 times greater.
So the question is, why aren’t there any super-Earths? Why do astronomers only see small rocky planets and enormous gaseous planets?
The differences between the two kinds of planets, and the reason for this super-Earth gap, has everything to do with a planet’s atmosphere – especially when the planet is forming.
When a star is born, a huge ball of gas comes together, starts to spin, collapses in on itself and ignites a fusion reaction within the star’s core. This process isn’t perfect; there is a lot of extra gas and dust left over after the star is formed. The extra material continues to rotate around the star until it eventually forms into a stellar disk: a flat, ring-shaped collection of gas, dust, and rocks.
During all of this motion and commotion, the dust grains slam into each other, forming pebbles which then grow into larger and larger boulders until they form planets. As the planet grows in size, its mass and therefore gravity increases, allowing it to capture not only the accumulated dust and rocks – but also the gas, which forms an atmosphere.
There is lots of gas within the stellar disk – after all, hydrogen and helium are the most common elements in stars and in the universe. However, there is considerably less rocky material because only a limited amount was made during star formation.
The trouble with super-Earths
If a planet remains relatively small, with a radius less than 1.5 times Earth’s radius, then its gravity is not strong enough to hold onto a huge amount of atmosphere, like what’s on Neptune or Jupiter. If, however, it continues to grow larger, then it captures more and more gas which forms an atmosphere that causes it to swell to the size of Neptune (four times Earth’s radius) or Jupiter, 11 times Earth’s radius.
Therefore, a planet either stays small and rocky, or it becomes a large, gaseous planet. The middle ground, where a super-Earth might be formed, is very difficult because, once it has enough mass and gravitational pull, it needs the exact right circumstances to stop the avalanche of gas from piling onto the planet and puffing it up. This is sometimes referred to as “unstable equilibrium” – such that when a body (or a planet) is slightly displaced (a little bit more gas is added) it departs further from the original position (and becomes a giant planet).
Another factor to consider is that once a planet is formed, it doesn’t always stay in the same orbit. Sometimes planets move or migrate towards their host star. As the planet gets closer to the star, its atmosphere heats up causing the atoms and molecules to move very fast and escape the planet’s gravitational pull. So some of the small rocky planets are actually the cores of bigger planets that have been stripped of their atmosphere.
So, while there are no super huge rocky planets or small fluffy planets, there is still a huge amount of diversity in planet sizes, geometries and compositions.
[ You’re smart and curious about the world. So are The Conversation’s authors and editors. You can get our highlights each weekend. ]
Natalie Hinkel receives funding from the NASA Nexus for Exoplanet System Science research coordination network based out of Arizona State University. This funding is used to research exoplanet habitability.
Ancient life may be just one possible explanation for Mars rover's latest discovery – CTV News
In the search for life beyond Earth, NASA’s Curiosity rover has been on a nearly decade-long mission to determine if Mars was ever habitable for living organisms.
A new analysis of sediment samples collected by the rover revealed the presence of carbon — and the possible existence of ancient life on the red planet is just one potential explanation for why it may be there.
Carbon is the foundation for all of life on Earth, and the carbon cycle is the natural process of recycling carbon atoms. On our home planet, carbon atoms go through a cycle as they travel from the atmosphere to the ground and back to the atmosphere. Most of our carbon is in rocks and sediment and the rest is in the global ocean, atmosphere and organisms, according to NOAA, or the National Oceanic and Atmospheric Administration.
That’s why carbon atoms — with their cycle of recycling — are tracers of biological activity on Earth. So they could be used to help researchers determine if life existed on ancient Mars.
When these atoms are measured inside another substance, like Martian sediment, they can shed light on a planet’s carbon cycle, no matter when it occurred.
Learning more about the origin of this newly detected Martian carbon could also reveal the process of carbon cycling on Mars.
A study detailing these findings published Monday in the journal Proceedings of the National Academy of Sciences.
SECRETS IN THE SEDIMENT
Curiosity landed in Gale Crater on Mars in August 2012. The 154.5-kilometre crater, named for Australian astronomer Walter F. Gale, was probably formed by a meteor impact between 3.5 billion and 3.8 billion years ago. The large cavity likely once held a lake, and now it includes a mountain called Mount Sharp. The crater also includes layers of exposed ancient rock.
For a closer look, the rover drilled to collect samples of sediment across the crater between August 2012 and July 2021. Curiosity then heated these 24 powder samples to around 1,562 degrees Fahrenheit (850 degrees Celsius) in order to separate elements. This caused the samples to release methane, which was then analyzed by another instrument in the rover’s arsenal to show the presence of stable carbon isotopes, or carbon atoms.
Some of the samples were depleted in carbon while others were enriched. Carbon has two stable isotopes, measured as either carbon 12 or carbon 13.
“The samples extremely depleted in carbon 13 are a little like samples from Australia taken from sediment that was 2.7 billion years old,” said Christopher H. House, lead study author and professor of geosciences at Pennsylvania State University, in a statement.
“Those samples were caused by biological activity when methane was consumed by ancient microbial mats, but we can’t necessarily say that on Mars because it’s a planet that may have formed out of different materials and processes than Earth.”
In lakes on Earth, microbes like to grow in big colonies that essentially form mats just under the surface of the water.
THREE POSSIBLE CARBON ORIGINS
The varied measurements of these carbon atoms could suggest three very different things about ancient Mars. The origin of the carbon is likely due to cosmic dust, ultraviolet degradation of carbon dioxide, or the ultraviolet degradation of biologically produced methane.
“All three of these scenarios are unconventional, unlike processes common on Earth,” according to the researchers.
The first scenario involves our entire solar system passing through a galactic dust cloud, something that occurs every 100 million years, according to House. The particle-heavy cloud could trigger cooling events on rocky planets.
“It doesn’t deposit a lot of dust,” House said. “It is hard to see any of these deposition events in the Earth record.”
But it’s possible that during an event like this, the cosmic dust cloud would have lowered temperatures on ancient Mars, which may have had liquid water. This could have caused glaciers to form on Mars, leaving a layer of dust on top of the ice. When the ice melted, the layer of sediment including carbon would have remained. While it’s entirely possible, there is little evidence for glaciers in Gale Crater and the study authors said it would require further research.
The second scenario involves the conversion of carbon dioxide on Mars into organic compounds, such as formaldehyde, due to ultraviolet radiation. That hypothesis also requires additional research.
The third way this carbon was produced has possible biological roots.
If this kind of depleted carbon measurement was made on Earth, it would show that microbes were consuming biologically produced methane. While Curiosity has previously detected methane on Mars, researchers can only guess if there were once large plumes of methane being released from beneath the surface of Mars. If this was the case and there were microbes on the Martian surface, they would have consumed this methane.
It’s also possible that the methane interacted with ultraviolet light, leaving a trace of carbon on the Martian surface.
MORE DRILLING ON THE HORIZON
The Curiosity rover will be returning to the site where it collected the majority of the samples in about a month, which will allow for another chance to analyze sediment from this intriguing location.
“This research accomplished a long-standing goal for Mars exploration,” House said. “To measure different carbon isotopes — one of the most important geology tools — from sediment on another habitable world, and it does so by looking at nine years of exploration.”
Mars Was Likely A Cold, Wet World 3 Billion Years Ago – IFLScience
Mars is puzzling. From rover and satellite observations we know that it once had plenty of water on its surface, which usually suggests warm and wet conditions. On the other hand, evidence suggests the planet was always pretty chilly, even in the distant past, but it’s not a cold, dry desert either. These two ideas are often at odds, but new research suggests that they could both be true: ancient Mars was likely a frigid world both cold and wet.
Researchers set out to create a model that can explain the perplexing features witnessed on the Red Planet. If the planet wasn’t warm and wet or cold and dry could there be a third option? Publishing their findings in Proceedings of the National Academy of Sciences, they believe that their cold and wet scenario can explain the existence of a vast liquid ocean in the Northern Hemisphere of Mars, extending to its polar region.
However, the model needed to explain both the presence of a liquid ocean and ice-capped regions, like the presence of glacial valleys and ice sheets in the southern highlands.
Planetary scientists studying Mars have found evidence of ancient tsunamis that rocked the Red Planet. If the ocean was frozen due to a very cold climate, these tsunamis would not have happened. But a milder climate would have meant transferring water from the ocean to the land through precipitation. Cold and wet conditions, however, could have existed.
The team used an advanced general circulation model to work out the necessary parameters for this world. They calculated it was possible for an ocean to be stable even if the mean temperature of Mars was below 0°C (32°F), the freezing point of water, 3 billion years ago. They envisioned ice-covered plateaus in the south with glaciers flowing across the plains and returning to the ocean. Rainfall would have been moderate around the shoreline. In this scenario, the ocean surface could be up to 4.5°C (40°F); not tropical but enough for water to stay liquid.
The key to these conditions is all in the air. The atmosphere of Mars today is about 1 percent in density compared to Earth’s own. But, if in the past it was roughly the same and was made of about 10 percent hydrogen and the rest carbon dioxide, this scenario would actually work. Previous analyses have found strong evidence for a thicker atmosphere before it was ripped from the planet by the steady stream of particles from the Sun.
The model is certainly compelling in explaining the peculiarities of Mars, but of course, much more evidence is needed to understand what the Red Planet was really like billions of years ago.
Explainer-Scientists struggle to monitor Tonga volcano after massive eruption
Scientists are struggling to monitor an active volcano that erupted off the South Pacific island of Tonga at the weekend, after the explosion destroyed its sea-level crater and drowned its mass, obscuring it from satellites.
The eruption of Hunga-Tonga-Hunga-Ha’apai volcano, which sits on the seismically active Pacific Ring of Fire, sent tsunami waves across the Pacific Ocean and was heard some 2,300 kms (1,430 miles) away in New Zealand.
“The concern at the moment is how little information we have and that’s scary,” said Janine Krippner, a New Zealand-based volcanologist with the Smithsonian Global Volcanism Program.
“When the vent is below water, nothing can tell us what will happen next.”
Krippner said on-site instruments were likely destroyed in the eruption and the volcanology community was pooling together the best available data and expertise to review the explosion and predict anticipated future activity.
Saturday’s eruption was so powerful that space satellites captured not only huge clouds of ash but also an atmospheric shockwave that radiated out from the volcano at close to the speed of sound.
Photographs and videos showed grey ash clouds billowing over the South Pacific and metre-high waves surging onto the coast of Tonga.
There are no official reports of injuries or deaths in Tonga https://www.reuters.com/business/environment/impact-assessment-aid-efforts-underway-world-responds-tonga-tsunami-2022-01-16 yet but internet and telephone communications are extremely limited and outlying coastal areas remain cut off.
Experts said the volcano, which last erupted in 2014, had been puffing away for about a month before rising magma, superheated to around 1,000 degrees Celsius, met with 20-degree seawater on Saturday, causing an instantaneous and massive explosion.
The unusual “astounding” speed and force of the eruption indicated a greater force at play than simply magma meeting water, scientists said.
As the superheated magma rose quickly and met the cool seawater, so did a huge volume of volcanic gases, intensifying the explosion, said Raymond Cas, a professor of volcanology at Australia’s Monash University.
Some volcanologists are likening the eruption to the 1991 Pinatubo eruption in the Philippines, the second-largest volcanic eruption of the 20th century, which killed around 800 people.
The Tonga Geological Services agency, which was monitoring the volcano, was unreachable on Monday. Most communications to Tonga have been cut after the main undersea communications cable lost power.
American meteorologist, Chris Vagasky, studied lightning around the volcano and found it increasing to about 30,000 strikes in the days leading up to the eruption. On the day of the eruption, he detected 400,000 lightning events in just three hours, which comes down to 100 lightning events per second.
That compared with 8,000 strikes per hour during the Anak Krakatau eruption in 2018, caused part of the crater to collapse into the Sunda Strait and send a tsunami crashing into western Java, which killed hundreds of people.
Cas said it is difficult to predict follow-up activity and that the volcano’s vents could continue to release gases and other material for weeks or months.
“It wouldn’t be unusual to get a few more eruptions, though maybe not as big as Saturday,” he said. “Once the volcano is de-gassed, it will settle down.”
(Reporting by Kanupriya Kapoor; Editing by Jane Wardell and Michael Perry)
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