Space & Astronomy Updates vol.103

December 11th 2024

Check out latest research updates in the field

TL;DR

Uranus’s swaying moons and hidden oceans
Magnetic tornado is stirring up the haze at Jupiter’s poles
Most energetic cosmic-ray electrons and positrons ever observed
Novel supernova observations grant astronomers a peek into the cosmic past
Researchers deal a blow to theory that Venus once had liquid water on its surface

Space industry in numbers

The global smart space market size is projected to grow from USD 9.4 billion in 2020 to USD 15.3 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 10.2% during the forecast period. The increasing venture capital funding and growing investments in smart space technology to drive market growth.

Analysts at Morgan Stanley and Goldman Sachs have predicted that economic activity in space will become a multi-trillion-dollar market in the coming decades. Morgan Stanley’s Space Team estimates that the roughly USD 350 billion global space industry could surge to over USD 1 trillion by 2040.

Source: Satellite Industry Association, Morgan Stanley Research, Thomson Reuters. *2040 estimates.

Latest Research

Looking for Subsurface Oceans Within the Moons of Uranus Using Librations and Gravity

by D. J. Hemingway, F. Nimmo in Geophysical Research Letters

When NASA’s Voyager 2 flew by Uranus in 1986, it captured grainy photographs of large ice-covered moons. Now nearly 40 years later, NASA plans to send another spacecraft to Uranus, this time equipped to see if those icy moons are hiding liquid water oceans.

The mission is still in an early planning stage. But researchers at the University of Texas Institute for Geophysics (UTIG) are preparing for it by building a new computer model that could be used to detect oceans beneath the ice using just the spacecraft’s cameras.

The research is important because scientists don’t know which ocean detection method will work best at Uranus. Scientists want to know if there’s liquid water there because it’s a key ingredient for life.

The new computer model works by analyzing small oscillations — or wobbles — in the way a moon spins as it orbits its parent planet. From there it can calculate how much water, ice and rock there is inside. Less wobble means a moon is mostly solid, while a large wobble means the icy surface is floating on a liquid water ocean. When combined with gravity data, the model computes the ocean’s depth as well as the thickness of the overlying ice.

Amplitude of forced physical librations (at the equator) for several possible ocean worlds as a function of ice shell thickness.

Uranus, along with Neptune, is in a class of planets called ice giants. Astronomers have detected more ice giant-sized bodies outside of our solar system than any other kind of exoplanet. If Uranus’s moons are found to have interior oceans, that could mean there are vast numbers of potentially life-harboring worlds throughout the galaxy, said UTIG planetary scientist Doug Hemingway, who developed the model.

“Discovering liquid water oceans inside the moons of Uranus would transform our thinking about the range of possibilities for where life could exist,” he said.

The UTIG research will help mission scientists and engineers improve their chances of detecting oceans. UTIG is a research unit of the Jackson School of Geosciences at The University of Texas at Austin.

All large moons in the solar system, including Uranus’s, are tidally locked. This means that gravity has matched their spin so that the same side always faces their parent planet while they orbit. This doesn’t mean their spin is completely fixed, however, and all tidally locked moons oscillate back and forth as they orbit. Determining the extent of the wobbles will be key to knowing if Uranus’s moons contain oceans, and if so, how large they might be.

Moons with a liquid water ocean sloshing about on the inside will wobble more than those that are solid all the way through. However, even the largest oceans will generate only a slight wobble: A moon’s rotation might deviate only a few hundred feet as it travels through its orbit. That’s still enough for passing spacecraft to detect. In fact, the technique was previously used to confirm that Saturn’s moon Enceladus has an interior global ocean.

To find out if the same technique would work at Uranus, Hemingway made theoretical calculations for five of its moons and came up with a range of plausible scenarios. For example, if Uranus’s moon Ariel wobbles 300 feet, then it’s likely to have an ocean 100 miles deep surrounded by a 20-mile-thick ice shell. Detecting smaller oceans will mean a spacecraft will have to get closer or pack extra powerful cameras. But the model gives mission designers a slide rule to know what will work, said UTIG Research Associate Professor Krista Soderlund.

“It could be the difference between discovering an ocean or finding we don’t have that capability when we arrive,” said Soderlund, who was not involved in the current research.

Soderlund has worked with NASA on Uranus mission concepts. She is also part of the science team for NASA’s Europa Clipper mission, which recently launched and carries an ice penetrating radar imager developed by UTIG.

The next step, Hemingway said, is to extend the model to include measurements by other instruments to see how they improve the picture of the moons’ interiors.

UV-dark polar ovals on Jupiter as tracers of magnetosphere–atmosphere connections

by Troy K. Tsubota, Michael H. Wong, Tom Stallard, Xi Zhang, Amy A. Simon in Nature Astronomy

While Jupiter’s Great Red Spot has been a constant feature of the planet for centuries, University of California, Berkeley, astronomers have discovered equally large spots at the planet’s north and south poles that appear and disappear seemingly at random.

The Earth-size ovals, which are visible only at ultraviolet wavelengths, are embedded in layers of stratospheric haze that cap the planet’s poles. The dark ovals, when seen, are almost always located just below the bright auroral zones at each pole, which are akin to Earth’s northern and southern lights. The spots absorb more UV than the surrounding area, making them appear dark on images from NASA’s Hubble Space Telescope. In yearly images of the planet taken by Hubble between 2015 and 2022, a dark UV oval appears 75% of the time at the south pole, while dark ovals appear in only one of eight images taken of the north pole.

The dark UV ovals hint at unusual processes taking place in Jupiter’s strong magnetic field that propagate down to the poles and deep into the atmosphere, far deeper than the magnetic processes that produce the auroras on Earth.

False-color ultraviolet image of the entire planet, showing the hood or cap of hydrocarbon haze that covers the south pole. The edge of the north polar hood is visible at the top. Troy Tsubota and Michael Wong, UC Berkeley

Dark UV ovals were first detected by Hubble in the late 1990s at the north and south poles and subsequently at the north pole by the Cassini spacecraft that flew by Jupiter in 2000, but they drew little attention. When UC Berkeley undergraduate Troy Tsubota conducted a systematic study of recent images obtained by Hubble, however, he found they were a common feature at the south pole — he counted eight southern UV-dark ovals (SUDO) between 1994 and 2022. In all 25 of Hubble’s global maps that show Jupiter’s north pole, Tsubota and senior author Michael Wong, an associate research astronomer based at UC Berkeley’s Space Sciences Laboratory, found only two northern UV-dark ovals (NUDO).

Most of the Hubble images had been captured as part of the Outer Planet Atmospheres Legacy (OPAL) project directed by Amy Simon, a planetary scientist at the NASA Goddard Space Flight Center and a co-author of the paper. Using Hubble, OPAL astronomers make yearly observations of Jupiter, Saturn, Uranus and Neptune to understand their atmospheric dynamics and evolution over time.

HST/WFC3 F275W north pole maps.

“In the first two months, we realized these OPAL images were like a gold mine, in some sense, and I very quickly was able to construct this analysis pipeline and send all the images through to see what we get,” said Tsubota, who is in his senior year at UC Berkeley as a triple major in physics, mathematics and computer science. “That’s when we realized we could actually do some good science and real data analysis and start talking with collaborators about why these show up.”

Wong and Tsubota consulted two experts on planetary atmospheres — Tom Stallard at Northumbria University in Newcastle-upon-Tyne in the UK and Xi Zhang at UC Santa Cruz — to determine what could cause these areas of dense haze. Stallard theorized that the dark oval is likely stirred from above by a vortex created when the planet’s magnetic field lines experience friction in two very distant locations: in the ionosphere, where Stallard and other astronomers previously detected spinning motion using ground-based telescopes, and in the sheet of hot, ionized plasma around the planet shed by the volcanic moon Io.

The vortex spins fastest in the ionosphere, progressively weakening as it reaches each deeper layer. Like a tornado touching down on dusty ground, the deepest extent of the vortex stirs up the hazy atmosphere to create the dense spots Wong and Tsubota observed. It’s not clear if the mixing dredges up more haze from below or generates additional haze.

Based on the observations, the team suspects that the ovals form over the course of about a month and dissipate in a couple of weeks.

“The haze in the dark ovals is 50 times thicker than the typical concentration,” said Zhang, “which suggests it likely forms due to swirling vortex dynamics rather than chemical reactions triggered by high-energy particles from the upper atmosphere. Our observations showed that the timing and location of these energetic particles do not correlate with the appearance of the dark ovals.”

The findings are what the OPAL project was designed to discover: how atmospheric dynamics in the solar system’s giant planets differ from what we know on Earth.

“Studying connections between different atmospheric layers is very important for all planets, whether it’s an exoplanet, Jupiter or Earth,” Wong said. “We see evidence for a process connecting everything in the entire Jupiter system, from the interior dynamo to the satellites and their plasma torii to the ionosphere to the stratospheric hazes. Finding these examples helps us to understand the planet as a whole.”

High-Statistics Measurement of the Cosmic-Ray Electron Spectrum with H.E.S.S.

by F. Aharonian, F. Ait Benkhali, et al in Physical Review Letters

The Universe teems with extreme environments, ranging from the very coldest temperatures to the highest energy sources possible. As a consequence, extreme objects such as supernova remnants, pulsars and active galactic nuclei are capable of emitting charged particles and gamma rays with incredibly high energies, so high that they exceed the energy produced by the nuclear fusion in stars by several orders of magnitude.

The gamma rays detected on Earth tell us a great deal about these sources, since they travel through space undisturbed. However, in the case of charged particles, also known as cosmic rays, things are more complicated because they are constantly buffeted by the magnetic fields present everywhere in the Universe, and impact the Earth isotropically, in other words from all directions. What’s more, these charged particles lose some of their energy along the way, when they interact with light and magnetic fields. These energy losses are especially significant for the most energetic electrons and positrons, known as cosmic-ray electrons (CRe), whose energy exceeds one teraelectronvolt (TeV) (i.e. 1000 billion times greater than that of visible light)1. It is therefore impossible to determine the point of origin of such charged particles in space, although their detection on Earth is a clear indicator that there are powerful cosmic-ray particle accelerators in its vicinity.

Artist’s impression of a pulsar with its powerful magnetic field rotating around it. The clouds of charged particles moving along the field lines emit gamma rays that are focused by the magnetic fields, rather like the beams of light from a lighthouse. In these magnetic fields, pairs of positrons and electrons are created and accelerated, making pulsars potential sources of high-energy cosmic electrons and positrons. ©NASA/Goddard Space Flight Center Conceptual Image Lab

However, detecting electrons and positrons with energies of several teraelectronvolts is particularly challenging. Space-based instruments, with detection areas of around one square metre, are unable to capture sufficient numbers of such particles, which become increasingly rare the higher their energy. Ground-based instruments on the other hand, which indirectly detect the arrival of cosmic rays via the showers of particles they produce in the Earth’s atmosphere, are faced with the challenge of differentiating the showers triggered by cosmic-ray electrons (or positrons) from the much more frequent showers produced by the impact of the heavier cosmic-ray protons and nuclei. The H.E.S.S. Observatory2 located in Namibia uses five large telescopes to capture and record the faint Cherenkov radiation produced by the heavily charged particles and photons that enter the Earth’s atmosphere, producing a shower of particles in their wake. Although the Observatory’s main purpose is to detect and select gamma rays in order to investigate their sources, the data can also be used to search for cosmic-ray electrons.

In the most extensive analysis ever carried out, H.E.S.S. collaboration scientists have now obtained new information about the origin of these particles. The astrophysicists did this by combing through the huge data set collected over the course of a decade by the four 12-metre telescopes, applying new, more powerful selection algorithms capable of extracting the CRe from the background noise with unprecedented efficiency. This resulted in an unrivalled set of statistical data for the analysis of cosmic-ray electrons. More specifically, the H.E.S.S. researchers were able to obtain for the first time data about CRe in the highest energy ranges, all the way up to 40 TeV. This enabled them to identify a surprisingly sharp break in the energy distribution of the cosmic-ray electrons.

“This is an important result, as we can conclude that the measured CRe most likely originate from very few sources in the vicinity of our own solar system, up to a maximum of a few 1000 light years away, a very small distance compared to the size of our Galaxy,” explains Kathrin Egberts, from the University of Potsdam, one of the corresponding authors of the study.
“We were able to put severe constrains on the origin of these cosmic electrons with our detailed analysis for the first time,” adds Prof. Hofmann from the Max-Planck-Institut für Kernphysik, co-author of the study. “The very low fluxes at larger TeV limit the possibilities of space-based missions to compete with this measurement. Thereby, our measurement does not only provide data in a crucial and previously unexplored energy range, impacting our understanding of the local neighbourhood, but it is also likely to remain a benchmark for the coming years,” Mathieu de Naurois, CNRS Researcher from the Laboratoire Leprince-Ringuet, adds.

The Extremely Metal-poor SN 2023ufx: A Local Analog to High-redshift Type II Supernovae

by Michael A. Tucker, Jason Hinkle, Charlotte R. Angus,et al in The Astrophysical Journal

An international team of researchers has made new observations of an unusual supernova, finding the most metal-poor stellar explosion ever observed.

This rare supernova, called 2023ufx, originated from the core collapse of a red supergiant star, exploded on the outskirts of a nearby dwarf galaxy. Results of the study showed that observations of both this supernova and the galaxy it was discovered in are of low metallicity, meaning they lack an abundance of elements heavier than hydrogen or helium.

Since the metals produced within supernovae inform their properties, including how stars evolve and die, learning more about their formation can tell astronomers much about the state of the universe when it began, especially since there were essentially no metals around during the time of its birth, said Michael Tucker, lead author of the study and a fellow at the Center for Cosmology and AstroParticle Physics at The Ohio State University.

Preexplosion imaging of the host galaxy from Pan-STARRS. Yellow reticles are 1'’ (0.3 kpc) in length and mark the location of SN 2023ufx.

“If you’re someone who wants to predict how the Milky Way came to be, you want to have a good idea of how the first exploding stars seeded the next generation,” said Tucker. “Understanding that gives scientists a great example of how those first objects affected their surroundings.”

Dwarf galaxies in particular are useful local analogs to conditions scientists might expect to see in the early universe. Because of them, astronomers know that while the first galaxies were metal-poor, all the big, bright galaxies near the Milky Way had plenty of time for stars to explode and increase the amount of metal content, said Tucker.

The amount of metals a supernova has also influences aspects like the number of nuclear reactions it may have or how long its explosion remains bright. It’s also one of the reasons that many low-mass stars also occasionally run the risk of collapsing into black holes. While the event observed by Tucker’s team is only the second supernova to be found with low metallicity, what’s most unusual about it is its location relative to the Milky Way, said Tucker.

Typically, any metal-poor supernova that astronomers would expect to find would likely be too faint to see from our galaxy because of how far away they are. Now, due to the advent of more powerful instruments like NASA’s James Webb Space Telescope, detecting distant metal-poor galaxies has been made exponentially easier.

“There are not that many metal-poor locations in the nearby universe and before JWST, it was difficult to find them,” said Tucker.

But the sighting of 2023ufx turned out to be a happy accident for researchers. New-found observations of this particular supernova revealed that many of its properties and behaviors are distinctly different from other supernovae in nearby galaxies.

For example, this supernova had a period of brightness that stayed steady for about 20 days before declining, whereas the brightness of its metal-rich counterparts usually lasted for about 100 days. The study also showed that a large amount of fast-moving material was ejected during the explosion, suggesting that it must have been spinning very quickly when it exploded.

This result implies that rapidly spinning metal-poor stars must have been relatively common during the early days of the universe, said Tucker. His team’s theory is that the supernova likely had weak stellar winds — streams of particles emitted from the atmosphere of the star — which led it to cultivate and release so much energy.

Overall, their observations lay the groundwork for astronomers to better investigate how metal-poor stars survive in different cosmic environments, and may even help some theorists more accurately model how supernovae behaved in the early universe.

“If you’re someone who wants to predict how galaxies form and evolve, the first thing you want is a good idea of how the first exploding stars influenced their local area,” said Tucker.

Future research may aim to determine if the supernova was larger at one point, whether just by being a super-massive star or if its materials were stripped away by a still undiscovered binary companion. Until then, researchers will have to wait for more data to become available.

“We’re so early in the JWST era that we’re still finding so many things we don’t understand about galaxies,” said Tucker. “The long-term hope is that this study acts as a benchmark for similar discoveries.”

A dry Venusian interior constrained by atmospheric chemistry

by Tereza Constantinou, Oliver Shorttle, Paul B. Rimmer in Nature Astronomy

A team of astronomers has found that Venus has never been habitable, despite decades of speculation that our closest planetary neighbour was once much more like Earth than it is today.

The researchers, from the University of Cambridge, studied the chemical composition of the Venusian atmosphere and inferred that its interior is too dry today for there ever to have been enough water for oceans to exist at its surface. Instead, the planet has likely been a scorching, inhospitable world for its entire history.

The results have implications for understanding Earth’s uniqueness, and for the search for life on planets outside our Solar System. While many exoplanets are Venus-like, the study suggests that astronomers should narrow their focus to exoplanets which are more like Earth.

From a distance, Venus and Earth look like siblings: it is almost identical in size and is a rocky planet like Earth. But up close, Venus is more like an evil twin: it is covered with thick clouds of sulfuric acid, and its surface has a mean temperature close to 500°C.

The dichotomous climate pathways proposed for Venus.

Despite these extreme conditions, for decades, astronomers have been investigating whether Venus once had liquid oceans capable of supporting life, or whether some mysterious form of ‘aerial’ life exists in its thick clouds now.

“We won’t know for sure whether Venus can or did support life until we send probes at the end of this decade,” said first author Tereza Constantinou, a PhD student at Cambridge’s Institute of Astronomy. “But given it likely never had oceans, it is hard to imagine Venus ever having supported Earth-like life, which requires liquid water.”

When searching for life elsewhere in our galaxy, astronomers focus on planets orbiting their host stars in the habitable zone, where temperatures are such that liquid water can exist on the planet’s surface. Venus provides a powerful limit on where this habitable zone lies around a star.

“Even though it’s the closest planet to us, Venus is important for exoplanet science, because it gives us a unique opportunity to explore a planet that evolved very differently to ours, right at the edge of the habitable zone,” said Constantinou.

There are two primary theories on how conditions on Venus may have evolved since its formation 4.6 billion years ago. The first is that conditions on the surface of Venus were once temperate enough to support liquid water, but a runaway greenhouse effect caused by widespread volcanic activity caused the planet to get hotter and hotter. The second theory is that Venus was born hot, and liquid water has never been able to condense at the surface.

“Both of those theories are based on climate models, but we wanted to take a different approach based on observations of Venus’ current atmospheric chemistry,” said Constantinou. “To keep the Venusian atmosphere stable, then any chemicals being removed from the atmosphere should also be getting restored to it, since the planet’s interior and exterior are in constant chemical communication with one another.”

The researchers calculated the present destruction rate of water, carbon dioxide and carbonyl sulphide molecules in Venus’ atmosphere, which must be restored by volcanic gases to keep the atmosphere stable.

Volcanism, through its supply of gases to the atmosphere, provides a window into the interior of rocky planets like Venus. As magma rises from the mantle to the surface, it releases gases from the deeper portions of the planet.

On Earth, volcanic eruptions are mostly steam, due to our planet’s water-rich interior. But, based on the composition of the volcanic gases necessary to sustain the Venusian atmosphere, the researchers found that volcanic gases on Venus are at most six percent water. These dry eruptions suggest that Venus’s interior, the source of the magma that releases volcanic gases, is also dehydrated.

At the end of this decade, NASA’s DAVINCI mission will be able to test and confirm whether Venus has always been a dry, inhospitable planet, with a series of flybys and a probe sent to the surface. The results could help astronomers narrow their focus when searching for planets that can support life in orbit around other stars in the galaxy.

“If Venus was habitable in the past, it would mean other planets we have already found might also be habitable,” said Constantinou. “Instruments like the James Webb Space Telescope are best at studying the atmospheres of planets close to their host star, like Venus. But if Venus was never habitable, then it makes Venus-like planets elsewhere less likely candidates for habitable conditions or life.
“We would have loved to find that Venus was once a planet much closer to our own, so it’s kind of sad in a way to find out that it wasn’t, but ultimately it’s more useful to focus the search on planets that are mostly likely to be able to support life — at least life as we know it.”