Super-Earth and mini-Neptune in synchronized dance
Among exoplanets in our galaxy, super-Earths and mini-Neptunes are two of the most common types. Even though neither exists in our own solar system, astronomers have discovered many in other solar systems. Now, researchers at the University of Liège in Belgium say they have found a pair of these worlds in another solar system 150 light-years away. What makes this system extra interesting, however, is that these two planets are in a synchronous dance around their red dwarf star. The astronomers made the discovery using NASA’s Transiting Exoplanet Survey Satellite (TESS) and ground-based telescopes.
The researchers first published their peer-reviewed findings in Astronomy and Astrophysics on April 12, 2023. The University of Liège announced the discovery on May 25, 2023.
A collaborative discovery
Researchers in Europe and the U.S. collaborated to make the discovery, using data from both TESS and ground-based telescopes. Astrophysicist Francisco J. Pozuelos, the lead author, explained:
TESS is conducting an all-sky survey using the transit method, that is, monitoring the stellar brightness of thousands of stars in the search for a slight dimming, which could be caused by a planet passing between the star and the observer. However, despite its power to detect new worlds, the TESS mission needs support from ground-based telescopes to confirm the planetary nature of the detected signals.
TESS is designed specifically to search for exoplanets, planets orbiting other stars. This includes planets like super-Earths and mini-Neptunes, as well as Earth-sized rocky worlds.
A super-Earth and mini-Neptune
The two planets – TOI-2096 b and TOI-2096 c – are both larger than Earth. TOI-2096 b isn’t much bigger though, with a radius only 1.2 times that of Earth. This makes it a super-Earth, a rocky world larger than our own planet, but smaller than Neptune.
TOI-2096 c, on the other hand, is 1.9 times Earth’s radius. The researchers say that this likely makes it a mini-Neptune. It may have a small rocky and icy core, but it would be enveloped in a deep, thick atmosphere rich in either hydrogen or water. That means it would be similar to the ice giants in our solar system, Uranus and Neptune, but smaller. But these exoplanets also offer a unique look at both super-Earths and mini-Neptunes and how they may have formed. Co-author Mathilde Timmermans said:
These planets are of crucial importance given their sizes. The formation of super-Earths and mini-Neptunes remains a mystery today. Several formation models try to explain it, but none fits the observations perfectly. TOI-2096 is the only system found to date with a super-Earth and a mini-Neptune precisely at the sizes where the models contradict each other. In other words, TOI-2096 may be the system we’ve been looking for to understand how these planetary systems have formed.
Two worlds in a synchronized dance
A super-Earth and mini-Neptune in the same system is interesting on its own. But there’s more. The orbits of the two planets are synchronized with each other.
In the same time that the outer planet completes one orbit, the inner planet completes two. You could say that the planets are in a kind of cosmic dance with each other. Timmermans explained:
Making an exhaustive analysis of the data, we found that the two planets were in resonant orbits: for each orbit of the outer planet, the inner planet orbits the star twice.
Their periods are, therefore, very close to being a multiple of each other, with about 3.12 days for planet b and about 6.38 days for planet c. This is a very particular configuration, and it causes a strong gravitational interaction between the planets. This interaction delays or accelerates the passage of the planets in front of their star and could lead to the measurement of the planetary masses using larger telescopes in the near future.
Super-Earth and mini-Neptune observations with Webb
Luckily, these two planets are well-suited for observations with NASA’s Webb Space Telescope. Pozuelos said:
Furthermore, these planets are among the best in their category to study their possible atmospheres. Thanks to the relative sizes of the planets with respect to the host star, as well as the brightness of the star, we find that this system is one of the best candidates for a detailed study of their atmosphere with the JWST space telescope. We hope to be able to do this quickly by coordinating with other universities and research centers. These studies will help confirm the presence of an atmosphere, extensive or not, around planets b and c, thus giving us clues as to their formation mechanism.
Bottom line: Astronomers say they’ve discovered a super-Earth and mini-Neptune exoplanet system where the orbits of the two worlds are synchronized in a cosmic dance.
Searching for habitable exoplanets in the soot zone
We think of habitable exoplanets as residing in a star’s habitable zone. That makes sense, right? It’s the region around a star where liquid water might exist, perhaps on a rocky planet similar to Earth. But there might be another important zone – related to habitability – that astronomers have mostly overlooked: the soot zone. Researchers at the University of Michigan said on May 25, 2023, that astronomers could expand the search for habitable exoplanets by taking the soot zone into account.
This zone in a protoplanetary disk – or planet-forming – is the space between the star and the soot line.
The researchers published their peer-reviewed findings in The Astrophysical Journal Letters on May 25, 2023.
Expanding the search for habitable exoplanets
The habitable zone is typically the first place that astronomers look for potentially habitable planets. That is based on what we know about our own solar system, and how the Earth has been able to hold onto its oceans and other water. Earth resides within the sun’s habitable zone while Mars and Venus are near the outskirts.
But astronomer Ted Bergin, who led the study, and his colleagues want to also consider the soot zone. The soot zone is the space between the star and the soot line. The soot line, specifically, is the outer boundary near a star where solid carbon molecules are destroyed and sublimate into gas. They become volatile carbon compounds instead of remaining as solid ones. Volatiles are chemical elements and compounds that can vaporize easily.
Planets in this zone may be rich in volatile carbon compounds, and those compounds could be quite different than anything on our own planet. What would such planets be like? Could they be habitable?
Bergin said:
It adds a new dimension in our search for habitability. It may be a negative dimension or it may be a positive dimension. It’s exciting because it leads to all kinds of endless possibilities.
Water-poor and carbon-poor Earth
But these planets may also be water-poor. That sounds bad for habitability, but Earth is water-poor as well. Surprisingly, our planet contains only 0.1% water by mass.
Because of such little water content, scientists have long thought that Earth formed inside the frost line, or water-ice line, which is farther out from the sun. Bodies beyond that line tend to have a greater amount of water, percentage-wise, like the icy moons with subsurface oceans.
We also think of Earth as carbon-rich, but, as with water, it’s carbon-poor. Scientists say that while our planet was forming, it received only about one carbon atom per 100 that were available in the protoplanetary disk. The soot line may be responsible for this. If the building blocks of the young Earth formed inside the soot line, closer to the sun, then the volatile carbon compounds would have been turned into gas. That would limit the amount of solid carbon available for the forming planet.
Planets between the soot line and frost line
The study also focuses on exoplanets born between the soot line and frost line. There aren’t any in our own solar system, but astronomers have discovered many in other solar systems. They are typically super-Earth and mini-Neptune worlds. Both are larger in mass than Earth, but smaller in mass than Neptune. They are also the most common type of exoplanets found so far. Bergin said:
These are either big rocks or small gas giants; that’s the most common type of planetary system. So maybe, within all those other solar systems out in the Milky Way galaxy, there exists a population of bodies that we haven’t recognized before that have much more carbon in their interiors. What are the consequences of that? What this means for habitability should be explored.
Hazy methane atmospheres
The researchers modeled what these planets would be like, and found that they would likely have very hazy atmospheres. In the study, these planets, in the soot zone, are silicate-rich, with between 0.1% and 1% carbon by mass. They also have variable amounts of water. The models suggested that these worlds would outgass volatile carbon compounds and develop methane-rich atmospheres. The methane atmosphere would produce hazes, due to interaction with photons from the planets’ host stars. This is similar to how the hydrocarbon haze in Titan’s atmosphere is produced. Bergin explained:
Planets that are born within this region, which exists in every planet-forming disk system, will release more volatile carbon from their mantles. This could readily lead to the natural production of hazes. Such hazes have been observed in the atmospheres of exoplanets and have the potential to change the calculus for what we consider habitable worlds.
So, are those exoplanets habitable?
This could mean that a planet like this is potentially habitable, since the haze is evidence for a possibly carbon-rich mantle on the planet. And life – as we know it on Earth – is based on carbon. But with potentially more carbon and methane-rich atmospheres, these worlds would be quite unlike Earth in many ways.
Bergin added:
If this is true, then there could be a common class of haze planets with abundant volatile carbon, and what that means for habitability needs to be explored. But then there’s the other aspect: What if you have an Earth-sized world, where you have more carbon than Earth has? What does that mean for habitability, for life? We don’t know, and that’s exciting.
NASA’s James Webb Space Telescope (JWST) will be able to look at some of these worlds, as the paper notes:
Such hazes, and the methane that drives their formation, are detectable via JWST transit spectroscopy, as demonstrated here, especially around stars lower in mass (and therefore size) than the sun.
That, too, will be exciting.
Bottom line: Astronomers say that habitable exoplanets could form in the soot zone around young stars. They could be rich in volatile carbon compounds, different from Earth.
Source: Exoplanet Volatile Carbon Content as a Natural Pathway for Haze Formation
Ancient ocean on Mars? Chinese rover finds marine sediments
We know that Mars had rivers and lakes in the distant past. But what about oceans? There is indeed tentative evidence for an ancient ocean in the northern hemisphere. However, scientists have been debating that evidence for decades. But now, researchers in China and the U.S. say they have found new clues in marine sedimentary rocks in Utopia Planitia that may prove the existence of that ocean. China’s Zhurong rover discovered the sedimentary formations. The researchers announced the tantalizing findings in Science China Press on May 21, 2023.
Professor Long Xiao from the School of Earth Sciences at China University of Geosciences led the research team. The team published its accepted peer-reviewed paper in National Science Review on May 18, 2023. The paper, still undergoing final editing, is available as a PDF.
New evidence for ancient ocean on Mars
China’s Zhurong rover has been exploring its landing site on the southern edge of Utopia Planitia in the northern hemisphere of Mars. This is within the northern lowlands that some scientists say was likely once an ocean floor. The rover’s newest findings now bolster that possibility. The rover has been studying the rocks in the area with its multispectral camera (MSCam), and the science team says that Zhurong has found marine sedimentary rocks. While most other data supporting the ocean hypothesis has come from orbiting spacecraft, this new data is in situ (on site).
It is the Vasitas Borealis Formation (VBF) that the mission scientists interpret to be marine sedimentary rocks. As the paper explains:
Decades of research using remotely-sensed data have extracted evidence for the presence of an ocean in the northern lowlands of Mars in the Hesperian, but these claims have remained controversial due to the lack of in situ analysis of the associated geologic unit, the Vastitas Borealis Formation (VBF). The Tianwen-1/Zhurong rover was targeted to land within the VBF near its southern margin and has traversed almost 1.2 miles (2 km) southward toward the interpreted shoreline. We report here on the first in situ analysis of the VBF that reveals sedimentary structures and features in surface rocks that suggest that the VBF was deposited in a marine environment, providing direct support for the existence of an ancient (Hesperian) ocean on Mars.
Multispectral images provide clues
Zhurong has been gradually moving south toward what is thought to be an ancient coastline. The rover has taken 106 panoramic images so far during its travels. Mission scientists have been studying the multispectral images for clues about the rocks’ composition and origin. They found bedding structures that are different from the usual volcanic rock deposits on Mars.
In addition, they were different from rock formations created by blowing sand.
A shallow sea environment
Indeed, the images revealed bidirectional flow, a sign of possible low-energy tidal currents. They are similar to formations created in shallow marine environments on Earth. The mission team named this region the Zhurong Member. The rocks feature small-scale cross-bedding, lens-shaped flaser bedding and small channel structures.
The paper says:
Bidirectional current orientations are characteristically formed by regular opposite directions of tidal currents in terrestrial shallow marine environments, and uncommonly in fluvial environments. Although aeolian deposits on Mars also contain some small-scale cross-laminations, the lack of larger structures indicative of aeolian environments supports the interpretation that these are of shallow marine origin.
The images also showed that the layers in the cross-bedding overlap and tilt in two opposite directions. The thickness of the strata, as well as the size of sand grains, also differs. This is evidence for a bidirectional water flow pattern. On Earth, this is common in littoral-shallow sea environments.
Ancient shorelines of an ocean on Mars and a wild river
Last year, researchers at Penn State and Caltech said they discovered definitive traces of an old shoreline in Mars’ northern hemisphere.
And just last week, scientists announced that the Perseverance rover has found evidence for a rollicking river. It was the deepest and fastest-flowing river yet observed – now all dried up of course – by any rover or lander.
The new findings from the Zhurong rover would seem to support this, adding another crucial piece to the puzzle. That ocean would have been vast, covering most of the northern hemisphere of Mars. The next question, of course, is whether it supported any kind of life. It will be interesting to see what else Zhurong finds in its travels, as well as any future missions to this now-dry ocean wonderland.
Bottom line: Scientists in China say that the Zhurong rover has found new evidence for an ancient ocean on Mars, sedimentary rocks formed in a shallow marine environment. The ocean would have covered hundreds of thousands of square kilometers. They estimate the ancient Martian shoreline to be 3.5 billion years old.
Source: Evidence for marine sedimentary rocks in Utopia Planitia: zhurong rover observations
Via Science China Press/ Eurekalert!
News from Enceladus via Webb: A huge water plume!
Saturn’s moon Enceladus is famous for its huge, active plumes of water vapor. They erupt like geysers at this little moon’s south pole. NASA’s Cassini spacecraft discovered them in 2005. And scientists quickly surmised that the plumes originate from a global ocean below the surface of Saturn’s moon. That subsurface ocean might be inhabited by living things. So the plumes might contain evidence of life. In May 2023, we began to hear that the James Webb Space Telescope (JWST) has now taken a new close look at Enceladus. Webb has observed a new, much larger plume.
The water vapor plumes on Enceladus can be huge, generally speaking. They tower above the moon’s icy surface. Consider that Enceladus itself is only about 314 miles (505 km) wide. The plumes spotted by Cassini were known to be at least as tall as the moon’s diameter. But this new plume – observed by Webb – is the biggest one ever seen, many times the diameter of Enceladus itself. As Sara Faggi, a planetary astronomer at NASA’s Goddard Space Flight Center, said:
It’s immense.
Biggest water plume on Enceladus ever seen
We haven’t seen a statement from scientists about the new plume. And we haven’t seen the Webb image. It apparently hasn’t been released yet.
But Alexandra Witze wrote about the new plume in Nature on May 18, 2023.
And Faggi mentioned the plume and the Webb observations at a conference at the Space Telescope Science Institute in Baltimore, Maryland, on May 17.
While few details were presented at the conference, Faggi said that a new paper will be coming out soon.
Many times Enceladus’ diameter
The water vapor erupts through large cracks in Enceladus’ icy surface. Scientists call these cracks tiger stripes.
The venting was known for sending the water vapor and other particles it contains a long way from Enceladus, out into space. But this newest eruption sent spray from the moon’s interior even farther out, up to many times Enceladus’ diameter of 314 miles (505 km).
Webb was able to observe this plume on November 22, 2022, and scientists have been studying the data sent back ever since.
Cassini analyzed particles in the plume that were relatively close to Enceladus itself. But Webb has the advantage of being able to look at plume particles that travel much farther away from the little moon. The ability to study both will help scientists better understand the plumes and the rich variety of ingredients they contain.
New analysis of Enceladus’ plumes
The analysis of the plume material, to be presented in the forthcoming paper, should be quite interesting. Cassini previously found that the plumes contain water vapor, ice particles, salts, silica, carbon dioxide, ammonia, methane and organic molecules.
Webb observed the plume for only 4.5 minutes, but that was ample time to obtain the data needed. The analysis will provide more details about how much water vapor the plume contained and the temperature. This plume, however, since it is so spread out away from Enceladus, is likely much more diffuse than the plumes Cassini saw (and actually flew through!). That may make it more difficult to determine what kinds of organic molecules were in the plume. Cassini did find a variety of both simple and complex organic molecules during its mission, however. As Witze wrote:
But the plume is likely to be of low density, more like a diffuse, cold cloud than a damp spray. That’s not great news for anyone looking to grab samples from the plume and hoping to find life, because the signs of life might be too sparse to detect. Ice grains seen by Cassini much closer to Enceladus are more likely to have high concentrations of organic particles, says Shannon MacKenzie, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.
With that in mind, Webb did find an abundance of intriguing chemicals in the plume. Witze wrote:
JWST also analyzed the spectrum of sunlight reflecting off Enceladus and found evidence of many chemicals, including water and possibly other compounds that could hint at geological or biological activity in the moon’s ocean.
What are they? We’ll have to wait to find out, but as Faggi noted:
We have many more surprises.
Life on Enceladus?
The plumes are of special interest to science because they might contain clues about possible life in Enceladus’ subsurface ocean. The ingredients found so far are tantalizing, although not proof yet that the ocean harbors living organisms.
Cassini did also find evidence suggesting that there are hydrothermal vents on the ocean floor. If so, they could possibly be a source of heat and nutrients, just as they are in oceans on Earth.
Future missions
As of now, there are no confirmed missions going back to Enceladus. But there are ideas on the drawing boards, such as a combination of orbiter and lander called Orbilander. Read the concept study here. A return mission will be essential to find out whether life ever has existed on Enceladus, or still does.
Bottom line: NASA’s Webb Space Telescope has observed the largest water plume on Enceladus ever seen. Details about the analysis results will be published in a new paper.
Weird comet in asteroid belt targeted by Webb
Comets are rare in the asteroid belt between the planets Mars and Jupiter. But some comets do reside there, including Comet Read (238P/Read). Asteroids tend to be rocky or metallic. Unlike them, Comet Read – an icy body – sometimes looks fuzzy, displaying, like other comets, a coma and a tail. On May 15, 2023, NASA said the Webb space telescope has taken a close look at Comet Read. Webb confirmed water vapor, a first for a comet in the asteroid belt. More unexpected was what Webb didn’t find. It found no sign of carbon dioxide, a gas expected and observed in most comets.
A team of scientists in the U.S. published the peer-reviewed results on May 15, 2023, in Nature.
Weird comet 238P/Read
Comets are typically rich in water vapor and water ice, as well as gas and dust. Scientists think they may even have brought much of Earth’s original water to our planet billions of years ago. But when it comes to the rarer comets in the main asteroid belt, proof of water vapor or ice has been hard to come by … until now.
For the first time, water vapor has been definitively detected on a comet – Comet Read – in the main asteroid belt. Lead author Michael Kelley of the University of Maryland said:
In the past, we’ve seen objects in the main belt with all the characteristics of comets, but only with this precise spectral data from Webb can we say yes, it’s definitely water ice that is creating that effect. With Webb’s observations of Comet Read, we can now demonstrate that water ice from the early solar system can be preserved in the asteroid belt.
Missing carbon dioxide
There was, however, another result that surprised scientists. Webb found no carbon dioxide (CO2) on the comet. The paper stated:
Here, we present JWST [James Webb Space Telescope] observations which clearly show that main-belt comet 238P/Read has a coma of water vapor, but lacks a significant CO2 gas coma.
Carbon dioxide tends to compose about 10% of the volatile material in comets. So why is it missing in Comet Read?
The researchers pose two possible scenarios to explain the missing carbon dioxide. The first possibility is that the comet did have it a long time ago but ended up losing it because of the warmer temperatures in the asteroid belt. (Comets generally reside and originate in the Kuiper Belt and Oort Cloud, out past Neptune). As Kelley explained:
Being in the asteroid belt for a long time could do it; carbon dioxide vaporizes more easily than water ice, and could percolate out over billions of years.
The other theory is that Comet Read originated in a warmer region of the solar system where there was no carbon dioxide to begin with.
Additional observations and maybe even a mission?
The results are interesting, but do they represent asteroid-belt comets in general, or is Comet Read simply unusual? To find out, astronomers will now use Webb to look at other comets in that part of the solar system as well. This will be part of Webb’s Guaranteed Time Observations. Co-author Heidi Hammel is with the Association of Universities for Research in Astronomy (AURA). She said:
These objects in the asteroid belt are small and faint, and with Webb we can finally see what is going on with them and draw some conclusions. Do other main-belt comets also lack carbon dioxide? Either way it will be exciting to find out.
There is even the possibility of sending a robotic spacecraft mission out to one of these comets. Co-author Stefanie Milam, Webb deputy project scientist for planetary science, surmised:
Now that Webb has confirmed there is water preserved as close as the asteroid belt, it would be fascinating to follow up on this discovery with a sample-collection mission and learn what else the main belt comets can tell us.
The findings show how comets aren’t all alike as much as we might tend to think. The differences, and similarities, between comets in various parts of the solar system can provide valuable clues as to how they – and the solar system overall – first formed. And maybe even how life first originated on Earth, and perhaps elsewhere in our sun’s family of worlds.
Bottom line: The Webb telescope has observed Comet Read, a weird comet in the main asteroid belt. Among the findings … water vapor, yes. But carbon dioxide, no.
Source: Spectroscopic identification of water emission from a main-belt comet
Distant volcano-covered world is the size of Earth
A potentially volcano-covered world
Volcanoes are common in our solar system. They are on some planets and on some of their moons. On May 17, 2023, a team of astronomers from around the world said it had discovered an Earth-sized exoplanet in a distant solar system. They said it might be covered in active, erupting volcanoes. The planet has been labeled as LP 791-18 d. It might be as volcanically active as Jupiter’s moon Io, which is the most volcanically active world in our solar system. But this new volcano-covered planet is located far beyond our solar system, some 90 light-years away. It might also have an atmosphere and water on its cooler night side.
The research team, led by graduate student Merrin Peterson at the Trottier Institute for Research on Exoplanets (iREx) at the University of Montreal, published its tantalizing peer-reviewed findings in Nature on May 17, 2023.
Co-author Björn Benneke at iREx said:
The discovery of this exoplanet is an extraordinary find. The similarity in the properties of LP 791-18 d and Earth as well as the prospect of detectable geological activity and volcanism on it make it a key object to better understand how terrestrial worlds form and evolve.
Meet exoplanet LP 791-18 d
LP 791-18 d orbits a red dwarf star, in the direction of our constellation Crater. The astronomers estimate it to be only slightly larger and more massive than Earth. Its density is also similar to Earth’s. The astronomers also calculated the equilibrium temperature of the planet to be 300-400 Kelvin (27-127 C or 80-260 F). The planet resides in the inner edge of the star’s habitable zone.
The researchers discovered the planet using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) and the retired Spitzer Space Telescope, as well as multiple ground-based observatories.
Unlike Earth, however, it is tidally locked, meaning that it always keeps the same side facing its star. If there was no atmosphere, then one side of the planet would be perpetually hotter than the other. But there is a good probability that the planet does have an atmosphere, given all the volcanic activity. If so, the night side may be cool enough for water to condense on the surface. Benneke explained further:
LP 791-18 d is tidally locked, which means the same side constantly faces its star. The day side would probably be too hot for liquid water to exist on the surface. But the amount of volcanic activity we suspect occurs all over the planet could sustain an atmosphere, which may allow water to condense on the night side.
The researchers say the planet’s atmosphere, if present, is likely similar to that of Earth, Venus or Titan.
Neighboring bigger planet plays a role
So, how did LP 791-18 d become so volcanically active? The researchers say that you can thank another planet in the system for that. LP 791-18 c, discovered in 2019, is farther out from the star. It’s 2.5 times the size of Earth and more than seven times its mass. This makes it either a super-Earth or a mini-Neptune. As the planet orbits, it periodically comes very close to LP 791-18 d. At their closest, the two planets are only 0.9 million miles (1.5 million km) apart, 33 times closer than Mars and Earth ever get to each other. Since it is larger and more massive than planet d, planet c exerts a strong gravitational pull on planet d.
According to the new data, it’s enough to cause internal friction and heat in planet d. This could create on-going volcanic activity. This is also similar to Io, where the gravitational pull of Jupiter helps creates heat and sustain persistent volcanic eruptions. As Caroline Piaulet at iREx explained:
The significant friction generated by tidal heating in the planet is responsible for heating its interior to a considerable extent, ultimately enabling the existence of a subsurface magma ocean. In our solar system, we know that Jupiter’s moon Io is affected by Jupiter and its other moons in a similar way, and that world is the most volcanic we know.
Life on a volcano-covered world?
If LP 791-18 d is volcanically active and has an atmosphere, could it harbor life? While we have no way of knowing right now, it does seem possible. As co-author Jessie Christiansen at the NASA Exoplanet Science Institute at the California Institute of Technology (Caltech) said:
A big question in astrobiology, the field that broadly studies the origins of life on Earth and beyond, is if tectonic or volcanic activity is necessary for life. In addition to potentially providing an atmosphere, these processes could churn up materials that would otherwise sink down and get trapped in the crust, including those we think are important for life, like carbon.
Benneke added:
This system provides astronomers with a precious laboratory for testing various hypotheses related to the formation and evolution of terrestrial planets. The newly found planet d, an Earth-size world likely covered in volcanoes in a multiplanetary system, provides unprecedented opportunities to advance not only astronomy but many other fields of science, notably geology, planetary sciences, atmospheric sciences, and possibly astrobiology.
There is also a third known planet in this system. LP 791-18 b, also found in 2019, orbits closer to the star and is approximately 20% larger than Earth. LP 791-18 c is already a target for the Webb Space Telescope, and the astronomers think that LP 791-18 d will be an exceptional target as well. So do we!
Bottom line: Astronomers say they have discovered an Earth-sized exoplanet 90 light-years away that may be a volcano-covered world, possibly as active as Jupiter’s moon Io.
Source: A temperate Earth-sized planet with tidal heating transiting an M6 star
Via Trottier Institute for Research on Exoplanets/ University of Montreal
Evidence for ancient river on Mars in new rover images
Mars used to be warmer and wetter, with a thicker atmosphere. It had lakes, streams and maybe even an ocean at one time, billions of years ago. Orbiting spacecraft show scores of ancient riverbeds, and some of the Mars rovers have found direct evidence for streams and groundwater that long since dried up. On May 11, 2023, NASA shared two new mosaic images from the Perseverance rover, showing what appear to be the remaining traces of a deep, fast-flowing river in Jezero Crater on Mars.
The river is thought to have been part of a network of waterways that emptied into the ancient crater lake a few billion years ago. Scientists already knew there were streams that fed the lake, leaving behind deltas that we can still clearly see today. But scientists had debated how deep or fast-moving these ancient martian waterways might have been.
Rollicking ancient river on Mars
Mission scientists say the images appear to show signs of what was once a rollicking river. Long, curving layers of sedimentary bedrock strongly suggest that the river flowed right through where the rover is now. Currently, Perseverance is on top of this pile of rock, which is 820 feet (250 meters) tall.
But was that river shallow and slow-moving, or deeper and faster-moving? The new images provide clues pointing to the latter: course grains of sand cemented together and larger cobbles. Libby Ives, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory, said:
Those indicate a high-energy river that’s truckin’ and carrying a lot of debris. The more powerful the flow of water, the more easily it’s able to move larger pieces of material. It’s been a delight to look at rocks on another planet and see processes that are so familiar.
Scientists stitched together hundreds of separate original images from Perseverance’s Mastcam-Z cameras to create the two mosaic images. They clearly show the sweeping curves of the bedrock layers.
Ground-level evidence at Shrinkle Haven
As with many other ancient river systems, scientists first noticed this one from orbit. That river, the deltas and the lake in the crater are why Perseverance landed here in the first place. But ground-level truth is always essential, whenever possible. The first signs of a powerful river are in a location called Shrinkle Haven. The curving layers look like old riverbanks that shifted a bit in position over time. Or they could be sandbars that formed in the river itself. The scientists are debating whether this river was more like the mighty Mississippi River or the Platte River, in Nebraska.
The scientists say they were likely larger when they first formed. Since then, winds have whittled them down to their present size. There are similar features on Earth, but they are harder to see. Michael Lamb of Caltech is a river specialist and collaborator on the Perseverance science team. He said:
The wind has acted like a scalpel that has cut the tops off these deposits. We do see deposits like this on Earth, but they’re never as well exposed as they are here on Mars. Earth is covered in vegetation that hides these layers.
Pinestand
There is additional evidence for the rollicking river about a quarter mile (402 meters) away. At this location, named Pinestand, there is an isolated hill with similar sedimentary layers. These, however, curve skyward, up to 66 feet (20 meters). Mission scientists don’t know for sure yet if a river created this formation, but they say it is likely. Ives said:
These layers are anomalously tall for rivers on Earth. But at the same time, the most common way to create these kinds of landforms would be a river.
The mission team will continue to study the images to gain a better understanding of just how these sedimentary layers formed. They will also use the rover’s ground-penetrating radar called called Radar Imager for Mars’ Subsurface Experiment (RIMFAX). Seeing features created by smaller streams or groundwater is one thing, but this is the first time that a rover has seen in-situ evidence for a larger, more powerful river. This could have implications not only for understanding the local geology but the possibility of ancient microbial life. It is Perseverance’s primary mission to search for such evidence. As Katie Stack Morgan, Perseverance’s deputy project scientist at the Jet Propulsion Laboratory, noted:
What’s exciting here is we’ve entered a new phase of Jezero’s history. And it’s the first time we’re seeing environments like this on Mars. We’re thinking about rivers on a different scale than we have before.
Bottom line: NASA’s Perseverance rover has spotted new signs of an ancient river on Mars, indicating it was deeper and more fast-flowing than any seen before. Curving layers of rocks provide the clues.
Saturn’s rings much younger than Saturn itself
How old are Saturn’s rings? Are they as old as the planet itself or younger? Scientists have debated those questions for many decades. Now, a new study from an international group of researchers, announced on May 12, 2023, shows that the rings are young, much younger than Saturn itself. This idea fits with previous studies also suggesting a young age for the rings.
Physicist Sascha Kempf at the University of Colorado Boulder led the new study. The researchers published their new peer-reviewed findings in Science Advances on May 12, 2023.
Saturn’s rings are only 400 million years old
Saturn itself is about as old as the rest of the solar system, at 4.5 billion years. But the new results from Kempf and colleagues, show the planet’s rings as far younger, only about 400 million years at most. (The paper notes a possible range from 100 million to 400 million years). As Kempf noted:
In a way, we’ve gotten closure on a question that started with James Clerk Maxwell.
Is it an answer to the decades-old question regarding the age of the rings? Time will tell, as other scientists weigh in on the study.
Dust provides clues
How did these researchers make a determination for the age of Saturn’s rings? They looked at something that is common everywhere in the solar system: dust (referred to as micrometeoroids in the paper). Even the icy particles that make up the rings – ranging from microscopic to large boulders – have a coating of dust on them. Kempf and his team had the idea of figuring out how old Saturn’s rings are by seeing how long it takes for dust to build up on them. Kempf said:
Think about the rings like the carpet in your house. If you have a clean carpet laid out, you just have to wait. Dust will settle on your carpet. The same is true for the rings.
Cassini analyzes ring particles
It wasn’t going to be an easy task, but it was possible. NASA’s Cassini spacecraft used an instrument called the Cosmic Dust Analyzer (CDA) to study dust particles around Saturn. From 2004 to 2017, it collected 163 dust grains. That’s not a lot, but it was enough – these scientists said – to calculate how long dust has been accumulating on the rings.
The answer, it turned out, was a few hundred million years, but no more than 400 million years. That sounds like a long time, and it is. But Saturn itself is thought to be 4.5 billion years old.
If these scientists are correct, the rate of dust accumulation is slow, much less than a gram of dust added to each square foot of the rings every year. But over millions of years (as over the days or weeks in your house), the dust adds up. Other than the dust, the ring particles are almost pure water ice – 98% by volume – and “squeaky clean.” Kempf said:
It’s almost impossible to end up with something so clean.
How did Saturn’s rings form?
The results contribute to the mystery of how old Saturn’s rings are. But we still don’t know how Saturn’s rings first formed. Kempf commented:
We know approximately how old the rings are. But it doesn’t solve any of our other problems. We still don’t know how these rings formed in the first place.
In another study last year, scientists reported new evidence that Saturn’s rings formed after a former large moon, Chrysalis, broke apart after getting too close to Saturn. According to that study, a small part of the debris later became the rings. And, in that scenario, the rings formed about 160 million years ago, a number that agrees well with Kempf’s study.
The vanishing rings
What’s more, earlier research had suggested that the ring particles are very slowly falling back onto Saturn itself, as ring rain. In other words, according to the study, Saturn’s rings are gradually disappearing. They might completely vanish in another 100 million years or so. As Kempf noted:
If the rings are short-lived and dynamical, why are we seeing them now. It’s too much luck.
And indeed it might be luck for us. Consider that the oldest hominins are thought to have appeared as early as 7 million B.C.E. The earliest species of the Homo genus appeared around 2 million to 1.5 million B.C.E. If humans had evolved on Earth a billion years earlier, we might have peered through our telescopes to see a ringless Saturn. If the rings are truly much younger than Saturn, then we’re lucky to see them at all, from our human vantage point in space and time.
Bottom line: How old are Saturn’s rings? A new study suggests they’re only about 400 million years old at most, much younger than Saturn itself. Dust provided new clues.
Via University of Colorado Boulder
Moonâs inner core is solid just like Earthâs, scientists say
Humans and robotic landers, rovers and orbiters have all explored the moon in great detail over the past several decades. But there are still many mysteries about Earth’s companion that need to be solved. One of those puzzles concerns the moon’s inner core. Is it solid or liquid? How large is it? On May 3, 2023, a team of scientists in France finally announced the answers to those questions. They said that the moon has a solid inner core, like Earth, and it is about 300 miles (500 km) in diameter.
The researchers published their peer-reviewed conclusions in Nature on May 3, 2023.
Moon’s inner core is solid, like Earth’s
Researchers from several institutions in France – CNRS, Université Côte d’Azur, the Côte d’Azur Observatory, Sorbonne Université and the Paris Observatory-PSL – conducted the new study. The research combined geophysical and geodesic constraints and thermodynamical simulations from various techniques to model and compare different possible internal structures of the moon. This included characteristics such as deformations formed due to gravitational interactions with the Earth, the moon’s distance from Earth and the moon’s density.
The results resolve long-standing questions about the moon’s core. Scientists already knew that the moon has a liquid outer core, but what about its inner core? As it turns out, it is solid, just like Earth’s core. It is about 300 miles (500 km) in diameter, making up approximately 15% of the moon’s overall size. The density of the inner core is approximately 7,822 kilograms per cubic meter. The researchers also re-confirmed the outer core is fluid, and 450 miles (724 km) in diameter.
Because the inner core is relatively small, it was more difficult for scientists to definitively detect it and analyze it.
In 2011, NASA scientists used seismic data from the moon, recorded by Apollo 11 astronauts, to estimate the size of the inner core. They estimated the inner core to be 298 miles (480 km) in diameter, so pretty close to the new findings.
Movement of material in moon’s mantle
The new details about the moon’s core aren’t the only thing that the study has revealed. The analysis also found evidence of movement within the moon’s mantle, between the core and outer crust. Scientists call this movement of material the lunar mantle overturn. Denser material is pulled closer to the core over time, while lighter material is forced upward. Scientists had previously hypothesized that this kind of movement was possible, and now the new study shows that is indeed the case.
The process involves material in the mantle rising up to the surface. This results in volcanic rock deposits in the upper crust. It would also help explain the presence of iron-rich material on the moon’s surface.
Other material, however, would have been too dense to rise upward. This material, instead, sank lower down, to the boundary between the mantle and core.
Moon’s magnetic field
The findings even have implications for the moon’s magnetic field, or rather lack of it. The moon used to have a magnetic field estimated to be 100 times stronger than the one Earth has today. But now, it has almost completely disappeared. The paper said:
Our results question the evolution of the moon magnetic field thanks to its demonstration of the existence of the inner core and support a global mantle overturn scenario that brings substantial insights on the timeline of the lunar bombardment in the first billion years of the solar system.
Interestingly, in 2019, scientists also reported the discovery of an unknown mass of material beneath the moon’s largest crater, the South Pole-Aitken Basin. Scientists don’t yet know exactly what it is, but one likely possibility is the iron-nickel core of an asteroid that lodged into the upper mantle of the moon created the enormous crater during the impact.
Bottom line: Researchers in France say that the moon’s inner core is solid, with a density close to that of iron, solving a long-standing debate about the heart of the moon.
Source: The lunar solid inner core and the mantle overturn
Oceans for 4 Uranus
Oceans for 4 Uranus’ moons?
Jupiter’s moon Europa and Saturn’s moon Enceladus both are thought to have a liquid water ocean beneath an outer icy crust. Neptune’s largest moon, Triton, might also have a subsurface ocean. But what about Uranus? Are any of its moons ocean worlds? On May 4, 2023, several researchers across the U.S. announced that at least four of Uranus’ moons do have oceans of their own.
The researchers first published their peer-reviewed paper on December 14, 2022, in JGR Planets. They later re-published it with a correction on February 6, 2023.
Re-analyzing data from Voyager 2
The research team re-analyzed data from the old NASA Voyager 2 mission, which flew past Uranus on January 24, 1986. They applied new computer modeling to the data and found that four of Uranus’ largest moons – Ariel, Umbriel, Titania and Oberon – likely have an ocean layer deep inside them. The oceans, between the cores and outer crusts of the moons, are estimated to be up to dozens of miles deep. The paper says:
The major moons of Uranus – Miranda, Ariel, Umbriel, Titania and Oberon – are interesting targets for a future space mission because they might host liquid at present. Studying these bodies would help address the extent of habitable environments in the outer solar system. We model their thermal, physical and chemical evolution. Because their heat budget is limited, with little or no tidal heating at present, we find that most of the moons can preserve only a few tens of kilometers of liquid until present.
The computer models used additional findings from NASA’s Galileo, Cassini, Dawn and New Horizons missions. This includes the chemistry and geology of Saturn’s moon Enceladus, and Pluto and its moons Charon and Ceres. All of these icy bodies are about the same size as the four Uranian moons, and are known or suspected to have subsurface oceans. Lead author Julie Castillo-Rogez of NASA’s Jet Propulsion Laboratory stated:
When it comes to small bodies – dwarf planets and moons – planetary scientists previously have found evidence of oceans in several unlikely places, including the dwarf planets Ceres and Pluto, and Saturn’s moon Mimas. So there are mechanisms at play that we don’t fully understand. This paper investigates what those could be and how they are relevant to the many bodies in the solar system that could be rich in water but have limited internal heat.
Heat and antifreeze keep oceans liquid on Uranus’ largest moons
How could these cold, icy and rocky bodies have liquid water inside them? Especially being so far from the sun? The answer is the same as for the other ocean moons and dwarf planets: internal heat. The new modeling showed that the moons’ surfaces are insulated enough to maintain some internal heat inside the moons. There may also be another heat source within the mantles of the moons. That heat source could release hot liquid. Overall, this should be enough heat to keep the oceans warm, in particular on Titania and Oberon.
Scientists have also previously seen possible evidence of icy volcanoes on Ariel, where liquid water and other material flowed onto the surface before freezing. The paper explains:
Ariel is particularly interesting as a future mission target because of the potential detection of NH3-bearing species on its surface (Cartwright et al., 2021) that could be evidence of recent cryovolcanic activity, considering these species should degrade on a geologically short timescale. Geologic features, visible in Voyager 2 Imaging Science Subsystem images of Ariel, show some evidence for cryovolcanism in the form of double ridges and lobate features that may represent emplaced cryolava (Beddingfield & Cartwright, 2021).
The results also suggest that heat alone isn’t keeping the moons’ oceans liquid. Chlorides, ammonia and salts also likely play a role, acting as a natural antifreeze.
Miranda used to be an ocean moon too
A fifth moon, Miranda, also displays surface features consistent with a subsurface ocean, but in the past. The modeling suggests that Miranda, the fifth-largest moon, is too small to have retained enough heat for an ocean in the present day. Therefore, its ocean is probably frozen solid now. As the paper states:
Despite its intriguing geology and candidate ocean world categorization by Hendrix et al. (2019), this study could not find scenarios that would preserve a deep ocean in that moon until present.
A new future mission to Uranus will be needed to determine more about the conditions in these alien oceans, and whether any of them might be habitable. Spectrometers on the spacecraft could study compounds such as ammonia and chlorides by analyzing the subsurface oceans with a wavelength that can detect them. The spectrometers could also look for electrical currents in the oceans.
Such a mission is still a long way off, but it would be exciting, wouldn’t it? Voyager 2 is still the last mission to ever visit Uranus, in 1986. A Uranus Orbiter and Probe mission has been proposed, although as of now it is still on the drawing board, and likely wouldn’t launch until the mid-late 2030s. It would study both Uranus and its moons in-depth.
Uranus has 27 known moons. The largest is Titania, at 980 miles (1,580 km) in diameter. All of them are named for characters in the works of Shakespeare and Alexander Pope.
Bottom line: A new study suggests oceans for four of Uranus’ moons. If true, they’d join a growing number of ocean worlds in the outer part of our solar system.
Recent Comments