REDNESS OF NEPTUNIAN ASTEROIDS
RAS
Asteroids sharing their orbits with the planet Neptune have been observed to exist in a broad spectrum of red colour, implying the existence of two populations of asteroids in the region, according to a new study by an international team of researchers. The team of scientists from the USA, California, France, the Netherlands, Chile and Hawaii observed 18 asteroids sharing the orbit of Neptune, known as Neptunian Trojans. They are between 50 and 100 km in size and are located at a distance of around 4.5 billion kilometres from the Sun. Asteroids orbiting this far away are faint and so are challenging for astronomers to study. Before the new work, only about a dozen Neptunian Trojans had been studied, requiring the use of some of the largest telescopes on Earth. The new data were gathered over the course of two years using the WASP wide field camera on the Palomar Observatory telescope in California, the GMOS cameras on the Gemini North and South telescopes in Hawaii and Chile, and the LRIS camera on the Keck Telescope in Hawaii. Of the 18 observed Neptunian Trojans, several were much redder than most asteroids, and compared with other asteroids in this group looked at in previous studies. Redder asteroids are expected to have formed much further from the Sun; one population of these is known as the Cold Classical trans-Neptunian objects found beyond the orbit of Pluto, at around 6 billion kilometres from the Sun. The newly observed Neptunian Trojans are also unlike asteroids located in the orbit of Jupiter, which are typically more neutral in colour.
The redness of the asteroids implies that they contain a higher proportion of more volatile ices such as ammonia and methanol. These are extremely sensitive to heat, and can rapidly transform into gas if the temperature rises, so are more stable at large distances from the Sun.
The location of the asteroids at the same orbital distance as Neptune also implies that they are stable on timescales comparable to the age of the Solar System. They effectively act as a time-capsule, recording the initial conditions of the Solar System.
The presence of redder asteroids among the Neptunian Trojans suggests the existence of a transition zone between more neutral coloured and redder objects. The redder Neptunian asteroids may have formed beyond this transition boundary before being captured into the orbit of Neptune. The Neptunian Trojans would have been captured into the same orbit as the planet Neptune as the ice giant planet migrated from the inner solar system to where it is now, some 4.5 billion kilometres from the Sun. The team has more than doubled the sample of Neptunian Trojans studied with large telescopes. Because it has a larger sample of Neptunian Trojans with measured colours, it can now start to see major differences between asteroid groups. Observations also show that the Neptunian Trojans are also different in colour compared to asteroid groups even further from the Sun. A possible explanation may be that the processing of the surfaces of asteroids by the Sun’s heat may have different effects for asteroids at varying solar distances.
THE PLANET THAT COULD END ALL LIFE ON EARTH
University of California - Riverside
A terrestrial planet hovering between Mars and Jupiter would be able to push Earth out of the solar system and wipe out life on this planet, according to a UC Riverside experiment. UCR astrophysicist Stephen Kane explained that his experiment was meant to address two notable gaps in planetary science. The first is the gap in our solar system between the size of terrestrial and giant gas planets. The largest terrestrial planet is Earth, and the smallest gas giant is Neptune, which is four times wider and 17 times more massive than Earth. There is nothing in between. In other star systems there are many planets with masses in that gap. We call them super-Earths. The other gap is in location, relative to the Sun, between Mars and Jupiter. Planetary scientists often wish there was something in between those two planets. These gaps could offer important insights into the architecture of our solar system, and into Earth's evolution. To fill them in, Kane ran dynamic computer simulations of a planet between Mars and Jupiter with a range of different masses, and then observed the effects on the orbits of all other planets. The results, published in the Planetary Science Journal, were mostly disastrous for the solar system. This fictional planet gives a nudge to Jupiter that is just enough to destabilize everything else. Despite many astronomers having wished for this extra planet, it's a good thing we don't have it. Jupiter is much larger than all the other planets combined; its mass is 318 times that of Earth, so its gravitational influence is profound. If a super-Earth in our solar system, a passing star, or any other celestial object disturbed Jupiter even slightly, all other planets would be profoundly affected.
Depending on the mass and exact location of a super-Earth, its presence could ultimately eject Mercury and Venus as well as Earth from the solar system. It could also destabilize the orbits of Uranus and Neptune, tossing them into outer space as well. The super-Earth would change the shape of this Earth's orbit, making it far less habitable than it is today, if not ending life entirely. If the planet's mass was smaller and put it directly in between Mars and Jupiter, it was possible for the planet to remain stable for a long period of time. But small moves in any direction and, things would go poorly. The study has implications for the ability of planets in other solar systems to host life. Though Jupiter-like planets, gas giants far from their stars, are only found in about 10% of the time, their presence could decide whether neighbouring Earths or super-Earths have stable orbits. These results gave a renewed respect for the delicate order that holds the planets together around the Sun. Our solar system is more finely tuned than previously appreciated. before. It all works like intricate clock gears. Throw more gears into the mix and it all breaks,
EXPLANATION FOR COMET ‘OUMUAMUA’S WEIRD ORBIT
University of California - Berkeley
In 2017, a mysterious comet dubbed 'Oumuamua fired the imaginations of scientists and the public alike. It was the first known visitor from outside our solar system, it had no bright coma or dust tail, like most comets, and a peculiar shape -- something between a cigar and a pancake -- and its small size more befitted an asteroid than a comet. But the fact that it was accelerating away from the Sun in a way that astronomers could not explain perplexed scientists, leading some to suggest that it was an alien spaceship. Now, a University of California, Berkeley, astrochemist and a Cornell University astronomer argue that the comet's mysterious deviations from a hyperbolic path around the Sun can be explained by a simple physical mechanism likely common among many icy comets: outgassing of hydrogen as the comet warmed up in the sunlight. What made 'Oumuamua different from every other well-studied comet in our solar system was its size: It was so small that its gravitational deflection around the Sun was slightly altered by the tiny push created when hydrogen gas spurted out of the ice. Most comets are essentially dirty snowballs that periodically approach the Sun from the outer reaches of our solar system. When warmed by sunlight, a comet ejects water and other molecules, producing a bright halo or coma around it and often tails of gas and dust. The ejected gases act like the thrusters on a spacecraft to give the comet a tiny kick that alters its trajectory slightly from the elliptical orbits typical of other solar system objects, such as asteroids and planets. When discovered, 'Oumuamua had no coma or tail and was too small and too far from the Sun to capture enough energy to eject much water, which led astronomers to speculate wildly about its composition and what was pushing it outward. Was it a hydrogen iceberg outgassing H2? A large, fluffy snowflake pushed by light pressure from the Sun? A light sail created by an alien civilization? A spaceship under its own power?
A comet traveling through the interstellar medium basically is getting cooked by cosmic radiation, forming hydrogen as a result. Researchers wondered if this was happening, could you actually trap it in the body, so that when it entered the solar system and it was warmed up, it would outgas that hydrogen? Could that quantitatively produce the force that you need to explain the non-gravitational acceleration? Surprisingly, experimental research published in the 1970s, '80s and '90s demonstrated that when ice is hit by high-energy particles akin to cosmic rays, molecular hydrogen (H2) is abundantly produced and trapped within the ice. In fact, cosmic rays can penetrate tens of metres into ice, converting a quarter or more of the water to hydrogen gas. For a comet several kilometres across, the outgassing would be from a really thin shell relative to the bulk of the object, so both compositionally and in terms of any acceleration, you wouldn't necessarily expect that to be a detectable effect. But because 'Oumuamua was so small, scientists think that it actually produced sufficient force to power this acceleration. The comet, which was slightly reddish, is thought to have been roughly 115 by 111 by 19 metres in size. While the relative dimensions were fairly certain, however, astronomers couldn't be sure of the actual size because it was too small and distant for telescopes to resolve. The size had to be estimated from the comet's brightness and how the brightness changed as the comet tumbled. To date, all the comets observed in our solar system -- the short-period comets originating in the Kuiper belt and the long-period comets from the more distant Oort cloud have ranged from around 1 kilometre to hundreds of kilometres across. What's beautiful about the idea is that it's exactly what should happen to interstellar comets. We had all these stupid ideas, like hydrogen icebergs and other crazy things, and it's just the most generic explanation.
MISSING LINK FOR WATER IN THE SOLAR SYSTEM FOUND
ESO
Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have detected gaseous water in the planet-forming disc around the star V883 Orionis. This water carries a chemical signature that explains the journey of water from star-forming gas clouds to planets, and supports the idea that water on Earth is even older than our Sun. This discovery was made by studying the composition of water in V883 Orionis, a planet-forming disc about 1300 light-years away from Earth. When a cloud of gas and dust collapses it forms a star at its centre. Around the star, material from the cloud also forms a disc. Over the course of a few million years, the matter in the disc clumps together to form comets, asteroids, and eventually planets. The team used ALMA, in which the European Southern Observatory (ESO) is a partner, to measure chemical signatures of the water and its path from the star-forming cloud to planets. Water usually consists of one oxygen atom and two hydrogen atoms. The team studied a slightly heavier version of water where one of the hydrogen atoms is replaced with deuterium — a heavy isotope of hydrogen. Because simple and heavy water form under different conditions, their ratio can be used to trace when and where the water was formed. For instance, this ratio in some Solar System comets has been shown to be similar to that in water on Earth, suggesting that comets might have delivered water to Earth. The journey of water from clouds to young stars, and then later from comets to planets has previously been observed, but until now the link between the young stars and comets was missing. V883 Orionis is the missing link in this case. The composition of the water in the disc is very similar to that of comets in our own Solar System. This is confirmation of the idea that the water in planetary systems formed billions of years ago, before the Sun, in interstellar space, and has been inherited by both comets and Earth, relatively unchanged.
But observing the water turned out to be tricky. Most of the water in planet-forming discs is frozen out as ice, so it’s usually hidden from our view. Gaseous water can be detected thanks to the radiation emitted by molecules as they spin and vibrate, but this is more complicated when the water is frozen, where the motion of molecules is more constrained. Gaseous water can be found towards the centre of the discs, close to the star, where it’s warmer. However, these close-in regions are hidden by the dust disc itself, and are also too small to be imaged with our telescopes. Fortunately, the V883 Orionis disc was shown in a recent study to be unusually hot. A dramatic outburst of energy from the star heats the disc, up to a temperature where water is no longer in the form of ice, but gas, enabling us to detect it. The team used ALMA, an array of radio telescopes in northern Chile, to observe the gaseous water in V883 Orionis. Thanks to its sensitivity and ability to discern small details they were able to both detect the water and determine its composition, as well as map its distribution within the disc. From the observations, they found this disc contains at least 1200 times the amount of water in all Earth’s oceans. In the future, they hope to use ESO’s upcoming Extremely Large Telescope and its first-generation instrument METIS. This mid-infrared instrument will be able to resolve the gas-phase of water in these types of discs, strengthening the link of water’s path all the way from star-forming clouds to solar systems.
WEBB FINDS SWIRLING CLOUDS ON REMOTE PLANET
NASA
Researchers using the James Webb Space Telescope have pinpointed silicate cloud features in a distant planet’s atmosphere. The atmosphere is constantly rising, mixing, and moving during its 22-hour day, bringing hotter material up and pushing colder material down. The resulting brightness changes are so dramatic that it is the most variable planetary-mass object known to date. The team also made extraordinarily clear detections of water, methane, and carbon monoxide with Webb’s data, and found evidence of carbon dioxide. This is the largest number of molecules ever identified all at once on a planet outside our solar system.
Catalogued as VHS 1256 b, the planet is about 40 light-years away and orbits not one, but two stars over a 10,000-year period. “VHS 1256 b is about four times farther from its stars than Pluto is from our Sun, which makes it a great target for Webb. That means the planet’s light is not mixed with light from its stars. Higher up in its atmosphere, where the silicate clouds are churning, temperatures reach 830 degrees Celsius.
Instruments aboard the James Webb Space Telescope known as spectrographs, one on its Near Infrared Spectrograph (NIRSpec) and another on its Mid-Infrared Instrument (MIRI), observed planet VHS 1256 b. The resulting spectrum shows signatures of silicate clouds, water, methane, and carbon monoxide. Within those clouds, Webb detected both larger and smaller silicate dust grains, which are shown on a spectrum. VHS 1256 b has low gravity compared to more massive brown dwarfs, which means that its silicate clouds can appear and remain higher in its atmosphere where Webb can detect them. Another reason its skies are so turbulent is the planet’s age. In astronomical terms, it’s quite young. Only 150 million years have passed since it formed – and it will continue to change and cool over billions of years. In many ways, the team considers these findings to be the first “coins” pulled out of a spectrum that researchers view as a treasure chest of data. They’ve only begun identifying its contents. They have identified silicates, but better understanding which grain sizes and shapes match specific types of clouds is going to take a lot of additional work.
EXTENSIVE CATALOGUE OF SUPERNOVAE
University of Hawaii at Manoa
The largest data release of relatively nearby supernovae containing three years of data from the University of Hawaiʻi Institute for Astronomy's (IfA) Pan-STARRS telescope atop Haleakalā on Maui, is publicly available via the Young Supernova Experiment (YSE). The project, which began in 2019, surveyed more than 1,500 square degrees of sky every three days, and discovered thousands of new cosmic explosions and other astrophysical transients, dozens of them just days or hours after exploding. The newly-released data contains information on nearly 2,000 supernovae and other luminous variable objects with observations in multiple colours. It is also the first to extensively use the multi-colour imaging to classify the supernovae and estimate their distances. Astrophysicists use large imaging surveys -- systematic studies of large areas of the sky over time -- and different parts of the electromagnetic spectrum for many scientific goals. Some are used to study distant galaxies and how they evolve over cosmic time, or look at specific regions of the sky that are especially important, such as the Andromeda Galaxy. Pan-STARRS produces a steady stream of transient discoveries, observing large areas of the sky every clear night with two telescopes. With over a decade of observations, Pan-STARRS operates one of the best calibrated systems in astronomy, with a detailed reference image of the static sky visible from Haleakalā. This enables rapid discovery and follow-up of supernovae and other transient events, well suited for programs like YSE to build up the sample required for analysis and this significant data release. YSE is designed to find energetic astrophysical "transient" sources such as supernovae, tidal disruption events and kilonovae (extremely energetic explosions). These transients evolve quickly, rising to their maximum brightness and then fading away after a few days or months.
The survey and the tools used to analyze the data are critical precursors to the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time, a new 8.4-meter telescope being built in Chile. Rubin Observatory will survey the entire sky every three nights, discovering so many variable and exploding objects that it will be impossible to obtain detailed follow-up observations. The ability to classify these objects from the survey data alone will be vital to choosing the most interesting ones for astronomers to target with other telescopes. Much of the time-domain Universe is uncharted. We still do not know the progenitor systems of many of the most common classes of transients, such as type Ia supernovae, while still using these sources to try and understand the expansion history of our Universe. The team has also seen one electromagnetic counterpart to a binary neutron star merger. There are many kinds of transients that are theoretically predicted, but have never been seen at all.
Topic: Early April Astronomy Bulletin (Read 281 times)