A new ring system discovered in our Solar System

Scientists have discovered a new ring system around a dwarf planet on the edge of the Solar System. The ring system orbits much further out than is typical for other ring systems, calling into question current theories of how ring systems are formed.

The ring system is around a dwarf planet, named Quaoar, which is approximately half the size of Pluto and orbits the Sun beyond Neptune.

The discovery, published in Nature, was made by an international team of astronomers using HiPERCAM -- an extremely sensitive high-speed camera developed by scientists at the University of Sheffield which is mounted on the world's largest optical telescope, the 10.4 metre diameter Gran Telescopio Canarias (GTC) on La Palma.

The rings are too small and faint to see directly in an image. Instead, the researchers made their discovery by observing an occultation, when the light from a background star was blocked by Quaoar as it orbits the Sun. The event lasted less than a minute, but was unexpectedly preceded and followed by two dips in light, indicative of a ring system around Quaoar.

Ring systems are relatively rare in the Solar System -- as well as the well-known rings around the giant planets Saturn, Jupiter, Uranus and Neptune, only two other minor planets possess rings -- Chariklo and Haumea. All of the previously known ring systems are able to survive because they orbit close to the parent body, so that tidal forces prevent the ring material from accreting and forming moons.

What makes the ring system around Quaoar remarkable is that it lies at a distance of over seven planetary radii -- twice as far out as what was previously thought to be the maximum radius according to the so-called `Roche limit', which is the outer limit of where ring systems were thought to be able to survive. For comparison, the main rings around Saturn lie within three planetary radii. This discovery has therefore forced a rethink on theories of ring formation.

Professor Vik Dhillon, co-author of the study from the University of Sheffield's Department of Physics and Astronomy, said: "It was unexpected to discover this new ring system in our Solar System, and it was doubly unexpected to find the rings so far out from Quaoar, challenging our previous notions of how such rings form. The use of our high-speed camera -- HiPERCAM -- was key to this discovery as the event lasted less than one minute and the rings are too small and faint to see in a direct image.

"Everyone learns about Saturn's magnificent rings when they're a child, so hopefully this new finding will provide further insight into how they came to be."

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Astronomers discover largest molecule yet in a planet-forming disc

Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, researchers at Leiden Observatory in the Netherlands have for the first time detected dimethyl ether in a planet-forming disc. With nine atoms, this is the largest molecule identified in such a disc to date. It is also a precursor of larger organic molecules that can lead to the emergence of life.

"From these results, we can learn more about the origin of life on our planet and therefore get a better idea of the potential for life in other planetary systems. It is very exciting to see how these findings fit into the bigger picture," says Nashanty Brunken, a Master's student at Leiden Observatory, part of Leiden University, and lead author of the study published today in Astronomy & Astrophysics.

Dimethyl ether is an organic molecule commonly seen in star-forming clouds, but had never before been found in a planet-forming disc. The researchers also made a tentative detection of methyl formate, a complex molecule similar to dimethyl ether that is also a building block for even larger organic molecules.

"It is really exciting to finally detect these larger molecules in discs. For a while we thought it might not be possible to observe them," says co-author Alice Booth, also a researcher at Leiden Observatory.

The molecules were found in the planet-forming disc around the young star IRS 48 (also known as Oph-IRS 48) with the help of ALMA, an observatory co-owned by the European Southern Observatory (ESO). IRS 48, located 444 light-years away in the constellation Ophiuchus, has been the subject of numerous studies because its disc contains an asymmetric, cashew-nut-shaped "dust trap." This region, which likely formed as a result of a newly born planet or small companion star located between the star and the dust trap, retains large numbers of millimetre-sized dust grains that can come together and grow into kilometre-sized objects like comets, asteroids and potentially even planets.

Many complex organic molecules, such as dimethyl ether, are thought to arise in star-forming clouds, even before the stars themselves are born. In these cold environments, atoms and simple molecules like carbon monoxide stick to dust grains, forming an ice layer and undergoing chemical reactions, which result in more complex molecules. Researchers recently discovered that the dust trap in the IRS 48 disc is also an ice reservoir, harbouring dust grains covered with this ice rich in complex molecules. It was in this region of the disc that ALMA has now spotted signs of the dimethyl ether molecule: as heating from IRS 48 sublimates the ice into gas, the trapped molecules inherited from the cold clouds are freed and become detectable.

"What makes this even more exciting is that we now know these larger complex molecules are available to feed forming planets in the disc," explains Booth. "This was not known before as in most systems these molecules are hidden in the ice."

The discovery of dimethyl ether suggests that many other complex molecules that are commonly detected in star-forming regions may also be lurking on icy structures in planet-forming discs. These molecules are the precursors of prebiotic molecules such as amino acids and sugars, which are some of the basic building blocks of life.

By studying their formation and evolution, researchers can therefore gain a better understanding of how prebiotic molecules end up on planets, including our own. "We are incredibly pleased that we can now start to follow the entire journey of these complex molecules from the clouds that form stars, to planet-forming discs, and to comets. Hopefully with more observations we can get a step closer to understanding the origin of prebiotic molecules in our own Solar System," says Nienke van der Marel, a Leiden Observatory researcher who also participated in the study.

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NASA's Roman Mission could snap first image of a Jupiter-like world

NASA's Nancy Grace Roman Space Telescope, now under construction, will test new technologies for space-based planet hunting. The mission aims to photograph worlds and dusty disks around nearby stars with detail up to a thousand times better than possible with other observatories.

Roman will use its Coronagraph Instrument -- a system of masks, prisms, detectors, and even self-flexing mirrors built to block out the glare from distant stars and reveal the planets in orbit around them -- to demonstrate that direct imaging technologies can perform even better in space than they have with ground-based telescopes.

"We will be able to image worlds in visible light using the Roman Coronagraph," said Rob Zellem, an astronomer at NASA's Jet Propulsion Laboratory (JPL) in Southern California who is co-leading the observation calibration plan for the instrument. JPL is building Roman's Coronagraph Instrument. "Doing so from space will help us see smaller, older, and colder planets than direct imaging usually reveals, bringing us a giant leap closer to imaging planets like Earth."

A home far away from home

Exoplanets -- planets beyond our solar system -- are so distant and dim relative to their host stars that they're practically invisible, even to powerful telescopes. That's why nearly all of the worlds discovered so far have been found indirectly through effects they have on their host stars. However, recent advancements in technology allow astronomers to actually take images of the reflected light from the planets themselves.

Analyzing the colors of planetary atmospheres helps astronomers discover what the atmospheres are made of. This, in turn, can offer clues about the processes occurring on the imaged worlds that may affect their habitability. Since living things modify their environment in ways we might be able to detect, such as by producing oxygen or methane, scientists hope this research will pave the way for future missions that could reveal signs of life.

If Roman's Coronagraph Instrument successfully completes its technology demonstration phase, its polarimetry mode will allow astronomers to image the disks around stars in polarized light, familiar to many as the reflected glare blocked by polarized sunglasses. Astronomers will use polarized images to study the dust grains that make up the disks around stars, including their sizes, shapes, and possibly mineral properties. Roman may even be able to reveal structures in the disks, such as gaps created by unseen planets. These measurements will complement existing data by probing fainter dust disks orbiting nearer to their host stars than other telescopes can see.

Bridging the gap

Current direct imaging efforts are limited to enormous, bright planets. These worlds are typically super-Jupiters that are less than 100 million years old -- so young that they glow brightly thanks to heat left over from their formation, which makes them detectable in infrared light. They also tend to be very far away from their host stars because it's easier to block the star's light and see planets in more distant orbits. The Roman Coronagraph could complement other telescopes' infrared observations by imaging young super-Jupiters in visible light for the first time, according to a study by a team of scientists.

But astronomers would also like to directly image planets that are similar to our own one day -- rocky, Earth-sized planets orbiting Sun-like stars within their habitable zones, the range of orbital distances where temperatures allow liquid water to exist on a planet's surface. To do so, astronomers need to be able to see smaller, cooler, dimmer planets orbiting much closer to their host stars than current telescopes can. By photographing worlds in visible light, Roman will be able to image mature planets spanning ages up to several billion years -- something that has never been done before.

"To image Earth-like planets, we'll need 10,000 times better performance than today's instruments provide," said Vanessa Bailey, an astronomer at JPL and the instrument technologist for the Roman Coronagraph. "The Coronagraph Instrument will perform several hundred times better than current instruments, so we will be able to see Jupiter-like planets that are more than 100 million times fainter than their host stars."

A team of scientists recently simulated a promising target for Roman to image, called Upsilon Andromedae d. "This gas giant exoplanet is slightly larger than Jupiter, orbits within a Sun-like star's habitable zone, and is relatively close to Earth -- just 44 light-years away," said Prabal Saxena, an assistant research scientist at the University of Maryland, College Park and NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the lead author of a paper describing the results. "What's really exciting is that Roman may be able to help us explore hazes and clouds in Upsilon Andromedae d's atmosphere and may even be able to act as a planetary thermometer by putting constraints on the planet's internal temperature!"

Opening a new frontier

The Coronagraph Instrument will contain several state-of-the-art components that have never flown aboard a space-based observatory before. For example, it will use specially designed coronagraph masks to block the glare from host stars but allow the light from dimmer, orbiting planets to filter through. These masks have innovative, complex shapes that block starlight more effectively than traditional masks.

The Roman Coronagraph will also be equipped with deformable mirrors, which help counteract small imperfections that reduce image quality. These special mirrors will measure and subtract starlight in real time, and technicians on the ground can also send commands to the spacecraft to adjust them. This will help counteract effects like temperature changes, which can slightly alter the shape of the optics.

Using this technology, Roman will observe planets so faint that special detectors will count individual photons of light as they arrive, seconds or even minutes apart. No other observatory has done this kind of imaging in visible light before, providing a vital step toward discovering habitable planets and possibly learning whether we are alone in the universe.

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The strange orbits of 'Tatooine' planetary disks

ALMA radio antennas at night.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have found striking orbital geometries in protoplanetary disks around binary stars. While disks orbiting the most compact binary star systems share very nearly the same plane, disks encircling wide binaries have orbital planes that are severely tilted. These systems can teach us about planet formation in complex environments.

In the last two decades, thousands of planets have been found orbiting stars other than our Sun. Some of these planets orbit two stars, just like Luke Skywalker's home Tatooine. Planets are born in protoplanetary disks -- we now have wonderful observations of these thanks to ALMA -- but most of the disks studied so far orbit single stars. 'Tatooine' exoplanets form in disks around binary stars, so-called circumbinary disks.

Studying the birthplaces of 'Tatooine' planets provides a unique opportunity to learn about how planets form in different environments. Astronomers already know that the orbits of binary stars can warp and tilt the disk around them, resulting in a circumbinary disk misaligned relative to the orbital plane of its host stars. For example, in a 2019 study led by Grant Kennedy of the University of Warwick, UK, ALMA found a striking circumbinary disk in a polar configuration.

"With our study, we wanted to learn more about the typical geometries of circumbinary disks," said astronomer Ian Czekala of the University of California at Berkeley. Czekala and his team used ALMA data to determine the degree of alignment of nineteen protoplanetary disks around binary stars. "The high resolution ALMA data was critical for studying some of the smallest and faintest circumbinary disks yet," said Czekala.

The astronomers compared the ALMA data of the circumbinary disks with the dozen 'Tatooine' planets that have been found with the Kepler space telescope. To their surprise, the team found that the degree to which binary stars and their circumbinary disks are misaligned is strongly dependent on the orbital period of the host stars. The shorter the orbital period of the binary star, the more likely it is to host a disk in line with its orbit. However, binaries with periods longer than a month typically host misaligned disks.

"We see a clear overlap between the small disks, orbiting compact binaries, and the circumbinary planets found with the Kepler mission," Czekala said. Because the primary Kepler mission lasted 4 years, astronomers were only able to discover planets around binary stars that orbit each other in fewer than 40 days. And all of these planets were aligned with their host star orbits. A lingering mystery was whether there might be many misaligned planets that Kepler would have a hard time finding. "With our study, we now know that there likely isn't a large population of misaligned planets that Kepler missed, since circumbinary disks around tight binary stars are also typically aligned with their stellar hosts," added Czekala.

Still, based on this finding, the astronomers conclude that misaligned planets around wide binary stars should be out there and that it would be an exciting population to search for with other exoplanet-finding methods like direct imaging and microlensing. (NASA's Kepler mission used the transit method, which is one of the ways to find a planet.)

Czekala now wants to find out why there is such a strong correlation between disk (mis)alignment and the binary star orbital period. "We want to use existing and coming facilities like ALMA and the next generation Very Large Array to study disk structures at exquisite levels of precision," he said, "and try to understand how warped or tilted disks affect the planet formation environment and how this might influence the population of planets that form within these disks."

"This research is a great example of how new discoveries build on previous observations," said Joe Pesce, National Science Foundation Program Officer for NRAO and ALMA. "Discerning trends in the circumbinary disk population was only made possible by building on the foundation of archival observational programs undertaken by the ALMA community in previous cycles."

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