Since astronomers first measured the size of an extrasolar planet 17 years ago, they have struggled to answer the question: how did the largest planets get to be so large? Thanks to the recent discovery of twin planets by a University of Hawaii Institute for Astronomy team led by graduate student Samuel Grunblatt, we are getting closer to an answer.
Gas giant planets are primarily made out of hydrogen and helium, and are at least four times the diameter of Earth. Gas giant planets that orbit scorchingly close to their host stars are known as “hot Jupiters.” These planets have masses similar to Jupiter and Saturn, but tend to be much larger – some are puffed up to sizes even larger than the smallest stars.
The unusually large sizes of these planets are likely related to heat flowing in and out of their atmospheres, and several theories have been developed to explain this process. “However, since we don’t have millions of years to see how a particular planetary system evolves, planet inflation theories have been difficult to prove or disprove,” says Grunblatt.
To solve this issue, Grunblatt searched through data collected by NASA’s K2 mission to hunt for hot Jupiters orbiting red giant stars. These stars, which are in the late stages of their lives, become themselves significantly larger over their companion planet’s lifetime. Following a theory put forth by Eric Lopez of NASA’s Goddard Space Flight Center, hot Jupiters orbiting red giant stars should be highly inflated if direct energy input from the host star is the dominant process inflating planets.
The search has now revealed two planets, each orbiting their host star with a period of approximately 9 days. Using stellar oscillations to precisely calculate the radii of both the stars and planets, the team found that the planets are 30 per cent larger than Jupiter. Observations using the W. M. Keck Observatory on Mauna Kea also showed that, despite their large sizes, the planets were only half as massive as Jupiter. Remarkably, the two planets are near twins in terms of their orbital periods, radii, and masses.
Using models to track the evolution of the planets and their stars over time, the team calculated the planets’ efficiency at absorbing heat from the star and transferring it to their deep interiors, causing the whole planet to expand in size and decrease in density. Their findings show that these planets likely needed the increased radiation from the red giant star to inflate, but the amount of radiation absorbed was also lower than expected.
It is risky to attempt to reach strong conclusions with only two examples. But these results begin to rule out some explanations of planet inflation, and are consistent with a scenario where planets are directly inflated by the heat from their host stars. The mounting scientific evidence seems to suggest that stellar radiation alone can directly alter the size and density of a planet.
Our own Sun will eventually become a red giant star, so it’s important to quantify the effect its evolution will have on the rest of the Solar System. “Studying how stellar evolution affects planets is a new frontier, both in other planetary systems as well as our own,” says Grunblatt. “With a better idea of how planets respond to these changes, we can start to determine how the Sun’s evolution will affect the atmosphere, oceans, and life here on Earth.”
The search for gas giant planets around red giant stars continues since additional systems could conclusively distinguish between planet inflation scenarios. Grunblatt and his team have been awarded time with the NASA Spitzer Space Telescope to measure the sizes of these twin planets more accurately. In addition, the search for planets around red giants with the NASA K2 mission will continue for at least another year, and NASA’s Transiting Exoplanet Survey Satellite (TESS), launching in 2018, will observe hundreds of thousands of red giants across the entire sky.
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Cassini’s final farewell to Saturn
Members of the imaging team behind the spacecraft have created this magnificent mosaic image of Saturn, taken just days before the mission’s end Before the Cassini spacecraft went down in the blaze of glory in Saturn’s atmosphere, it took a series of pictures that unite into a fitting farewell mosaic image of the ringed planet. After spending 13 years at the gaseous giant, NASA’s hugely successful spacecraft used it’s wide-angle camera to mark its conclusion.
On 13 September 2017, 42 images were taken using Cassini’s wide-angle camera, which combined red, green and blue images covering Saturn’s full framework. When scientists pieced together all the images, it produced a spectacular natural colour mosaic masterpiece, included in the image is Saturn’s illustrious rings along with its moons Prometheus, Pandora, Janus, Epimetheus, Mimas and Enceladus.
There were many discoveries that came from Cassini’s exploration of Saturn and its equally elusive moons. “Cassini’s scientific bounty has been truly spectacular — a vast array of new results leading to new insights and surprises, from the tiniest of ring particles to the opening of new landscapes on Titan and Enceladus, to the deep interior of Saturn itself,” says Robert West, Cassini’s deputy imaging team leader at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.
“It was all too easy to get used to receiving new images from the Saturn system on a daily basis, seeing new sights, watching things change,” says Elizabeth Turtle, an imaging team associate at the Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland. “It was hard to say goodbye, but how lucky we were to be able to see it all through Cassini’s eyes!”
For other scientists in the Cassini team, this goodbye was reminiscent of another goodbye from decades ago.
“For 37 years, Voyager 1’s last view of Saturn has been, for me, one of the most evocative images ever taken in the exploration of the solar system,” says Carolyn Porco, former Voyager imaging team member and Cassini’s imaging team leader at the Space Science Institute in Boulder, Colorado. “In a similar vein, this ‘Farewell to Saturn’ will forevermore serve as a reminder of the dramatic conclusion to that wondrous time humankind spent in intimate study of our Sun’s most iconic planetary system.”
The Cassini spacecraft was launched in 1997 along with the European Space Agency’s Huygens probe, which went on to probe the surface the Saturn’s moon Titan. The surface of Titan showed to have oceans of hydrocarbons, such as ethane and methane, which was a tantalising discovery for astronomers and astrobiologists. Cassini’s analysis of another moon, Enceladus, presented unusual geyser-like streams of icy material, later confirming the existence of a subsurface ocean; presenting another place to look for in the search for microbial life.
New evidence argues against water on Mars’ surface
As dark streaky features extend down the Red Planet’s slopes, scientists now believe it is due to the movement of sand grains and not subsurface water
The search for signs of water on the Red Planet continues, but recent research has been dealt a blow with its analysis of Mars’ downhill, dark, surface streaks. By using NASA’s Mars Reconnaissance Orbiter (MRO) and its High Resolution Imaging Science Experiment (HiRISE) camera, scientists have presented strong evidence that these dark features are not due to subsurface flowing water, but instead granular flows.
MRO has continued to observe the ever-confusing seasonal dark streaks since their discovery in 2011, when scientists claimed they could be a source of enough water to support microbial life. The recent evidence from MRO has shown that the dark features exist only on slopes steep enough for dry grains to descend the way they do on faces of active dunes.
They seasonal behaviour of these dark features consists of extending gradually downhill in warm seasons, then they disappear in the winter and repeat this pattern the next year. Seeping water has shown this sort of geological behaviour on Earth, but how this occurs on the Martian surface is very unclear. The scientists who conducted the research have suggested that there could be very small amounts of water involved. This is supported by the detection of hydrated salts – water molecules in a crystal form – that were observed at some flow sites.
These features have been given the term “recurring slope lineae”, or RSL for short. There has been a abundance of detections, having been identified in more than 50 rocky-slope areas, ranging in location from the equator to halfway to the poles.
Colin Dundas, of the U.S. Geological Survey’s Astrogeology Science Centre in Flagstaff, Arizona, United States, along with his team surveyed 151 RSL features at 10 different sites. From this, they gathered 3-D models of slope steepness using pairs of images for stereo information. Dundas says, “We’ve thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand. This new understanding of RSL supports other evidence that shows that Mars today is very dry.”
Out of all the RSL surveyed, almost all of them have a steepness of at least 27 degrees. The flow ends on a slope that matches the “angle of repose” seen in the slumping dry sands of dunes on Mars and Earth. Alfred McEwen, HiRISE Principal Investigator, says, “The RSL don’t flow onto shallower slopes, and the lengths of these are so closely correlated with the dynamic angle of repose, it can’t be a coincidence.”
These seasonal ever-changing streaks were originally thought to evidence for the presence of liquid water, enough that would be adequate for microbial life. Unfortunately for a lot of hopeful astronomers, the granular-flow explanation for RSLs corresponds with our earlier understanding of the surface of Mars, which is a cold, dry planet with an extremely thin atmosphere. Liquid water on the surface of the Red Planet seems to be limited to traces of dissolved moisture from the atmosphere and thin films, making Mars’ surface virtually inhospitable.
It’s important to note that this is not a complete explanation of the occurrence of RSLs. There are several aspects that cannot be explained yet, such as their gradual growth, their seasonal reappearance, their rapid fading when inactive and the presence of hydrated salts. Scientists conducting this research have drawn some possible connections between these traits are how RSL form, though. One example is that water from the minute atmosphere can be plucked out and hydrate the salts, forming drops of salty water. The seasonal changes in the hydration of salt-containing grains could be a trigger mechanism that starts the granular downfall. The changes in hydration could always be what causes the darkening and fading effect within the features. If this were in fact the case, this wouldn’t explain why RSLs only appear on some slopes and not others.
“RSL probably form by some mechanism that is unique to the environment of Mars,” McEwen says. “So they represent an opportunity to learn about how Mars behaves, which is important for future surface exploration.”
“Full understanding of RSL is likely to depend upon on-site investigation of these features,” says Rich Zurek, MRO Project Scientist. “While the new report suggests that RSL are not wet enough to favour microbial life, it is likely that on-site investigation of these sites will still require special procedures to guard against introducing microbes from Earth, at least until they are definitively characterized. In particular, a full explanation of how these enigmatic features darken and fade still eludes us. Remote sensing at different times of day could provide important clues.”
‘Cigar-shaped’ asteroid is first interstellar visitor to our Solar System
This thing is an oddball,” says Karen Meech of the University of Hawaii’s Institute for Astronomy who leads an international team studying this interstellar interloper
In October, astronomers were surprised by a visitor that came racing into our Solar System from interstellar space. Now, researchers using the Gemini Observatory have determined that the first known object to graze our system from beyond is similar to, but definitely not, your average asteroid or comet. “This thing is an oddball,” says Karen Meech of the University of Hawaii’s Institute for Astronomy who leads an international team studying this interstellar interloper.
Originally denoted A2017 U1, the body now goes by the Hawaiian name ‘Oumuamua, in part because of its discovery by Meech’s team using the Pan-STARRS1 survey telescope on Haleakala in Hawaii. When discovered in mid-October ‘Oumuamua was only about 85 times the Earth-Moon distance away and its discovery was announced in early November.
Since its discovery ‘Oumuamua has faded from view. The object’s rapidly increasing distance from the Earth and Sun now makes it too faint to be studied by even the largest telescopes.
“Needless to say, we dropped everything so we could quickly point the Gemini telescopes at this object immediately after its discovery,” says Gemini Director Laura Ferrarese who coordinated the Gemini South observations for Meech’s group.
What we found was a rapidly rotating object, at least the size of a football field, that changed in brightness quite dramatically,” according to Meech. “This change in brightness hints that ‘Oumuamua could be more than 10 times longer than it is wide – something which has never been seen in our own Solar System,” according to Meech.
‘Oumuamua shares similarities with small objects in the outer Solar System, especially the distant worlds of the Kuiper Belt – a region of rocky, frigid worlds far beyond Neptune. “While study of ‘Oumuamua’s colours shows that this body shares characteristics with both Kuiper Belt objects and organic-rich comets and Trojan asteroids,” says Meech, “its orbital path says it comes from far beyond.”
‘Oumuamua was visible from Chile and Hawaii so both Gemini North and South telescopes were on high alert and ready to track the visitor from outer space. “We observed from both sites for three nights, before it sped away and faded from view,” says Ferrarese. Two additional teams obtained data from Gemini North and their results are currently pending publication.
According to our current understanding of planetary system formation, our Solar System ejected comets and asteroids due to interactions with the larger outer planets. It is presumed that other planetary systems do the same and that these visitors might be more common than previously thought. “We estimate that there is always one of these objects of similar size as ‘Oumuamua between the Earth and the Sun at any given time, so up to about 10 per year,” says Robert Jedicke also on Meech’s team.
“These observations allow us to reach into another planetary system to learn about one of its rocky bodies, and compare this object with the asteroids we know throughout our own solar system,” says Faith Vilas, the solar and planetary research program director at the National Science Foundation who helped support this research.
Surveys like Pan-STARRS and the future Large Synoptic Survey Telescope (LSST, currently under construction near the Gemini South telescope in Chile) will undoubtedly increase the detections of these interstellar wanderers. “The discoveries of rare surprises like ‘Oumuamua from outside our Solar System will be greatly accelerated by the power and grasp of the LSST,” says Richard Green of the US National Science Foundation (NSF). “LSST is going to produce a torrent of data and revolutionise this sort of time domain astronomy when it begins operations early in the next decade,” adds Green.
‘Oumuamua loosely means “a messenger that reaches out from the distant past,” fitting the nature of the object’s interstellar origin. In Hawaiian ‘ou means “to reach out for,” while mua means “first” and is repeated for emphasis.
Astronomers discover Earth-sized planet just 11 light years away
The newly-discovered exoplanet shows promising signs for habitability
A new and exciting exoplanet has been discovered just 11 light years from our Solar System. Discovered using the European Southern Observatory (ESO)’s High Accuracy Radial Velocity Planet Searcher (HARPS) instrument, Ross 128b – as it’s known – is a temperate Earth-sized world orbiting a red dwarf star. The new world is the second closest ‘Earth-like’ planet discovered after Proxima b, and also the nearest orbiting an inactive star. As the star has very little activity, Ross 128 could potentially sustain life, making it a prime target for ESO’s Extremely Large Telescope.
The team using the HARPS instrument at the La Silla Observatory in Chile found Ross 128b orbiting its host star every 9.9 days. The surface temperature of the planet is thought to be mild, possibly close to Earth’s surface temperature.
This discovery is based on more than a decade of HARPS intensive monitoring together with state-of-the-art data reduction and analysis techniques. Only HARPS has demonstrated such a precision and it remains the best planet hunter of its kind, 15 years after it began operations,” explains Nicola Astudillo-Defru, of the University of Geneva, Switzerland.
Red dwarf stars are often the subject of study in the search for exoplanet; this is because they are the coolest, faintest and most common stars in the universe. By using the HARPS instrument, astronomers believe that detecting cool exoplanets like Earth is easier around red dwarfs, rather than Sun-like stars
The issue with habitability on Proxima b, the closest exoplanet just four light years away, is that Proxima Centauri is subject to flares from its red-dwarf host star. This would shower its accompanying planet is harmful radiation such as ultraviolet radiation, killing life as we know it. Ross 128 is much less active, meaning the exoplanet stands a greater chance of sustaining possible lifeforms.
Even though Ross 128b is 11 light years away from us, it is travelling at relatively rapid speeds in universal terms. In 79,000 years, it will surpass Proxima b as the closest exoplanet. The data collected by HARPS has also shown that the new exoplanet orbits Ross 128 at a distance that is 20-times closer than Earth to the Sun. Even taking this close proximity into account, the planet only receives 1.38 times more irradiation than Earth. From this, astronomers estimate that the average temperature lies between minus 60 to 20 degrees Celsius (minus 76 to 68 degrees Fahrenheit), making it almost ideal for habitability. Astronomers still have yet to discover if the planets lies within the star’s habitable zone, which is the region around a star where water can exist as a liquid.
With the number of temperate exoplanets ever-increasing, the next step in determining their true habitability is to understand their atmosphere. ESO’s Extremely Large Telescope will have the capabilities to study an exoplanet’s atmosphere, composition and chemistry. For example, if there were a detection of oxygen molecules in an exoplanet’s atmosphere, it would be a monumental discovery for astronomers.
New facilities at ESO will first play a critical role in building the census of Earth-mass planets amenable to characterisation. In particular, NIRPS, the infrared arm of HARPS, will boost our efficiency in observing red dwarfs, which emit most of their radiation in the infrared. And then, the ELT will provide the opportunity to observe and characterise a large fraction of these planets,” concludes Xavier Bonfils of the Institute of Planetology and Astrophysics of Grenoble, France.
Targets pinpointed for NASA’s James Webb Space Telescope
After much consideration, the next-generation instrument will observe 13 targets in its first five months of scientific observations
The James Webb Space Telescope’s (JWST) targets for initial observation have recently been chosen and include studying Jupiter, planets beyond our Solar System and distant galaxies. After the Space Telescope Science Institute’s call for early results, the JWST will now spend it’s first five months working on 13 science programs, following a six-month commissioning period. The initiative will also include searching for organic molecules around infant stars, studying supermassive black holes and searching the early universe.
“I’m thrilled to see the list of astronomers’ most fascinating targets for the Webb telescope, and extremely eager to see the results. We fully expect to be surprised by what we find,” says Dr. John C. Mather, Senior Project Scientist for the Webb telescope and Senior Astrophysicist at NASA’s Goddard Space Flight Centre, Greenbelt, Maryland.
The results from this observing period will be compiled in the Director’s Discretionary Early Release Science (DD-ERS). This will provide astronomers worldwide with immediate access to the tantalising JWST data in order to swiftly analyse the data and plan future observations.
“We were impressed by the high quality of the proposals received,” says Dr. Ken Sembach, Director of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. “These observing programs not only will generate great science, but also will be a unique resource for demonstrating the investigative capabilities of this extraordinary observatory to the worldwide scientific community.”
The first 13 science programs were carefully chosen to exercise all four of the space telescope’s science instruments, which will give astronomers the chance to explore JWST’s full light-capturing potential. However, because the telescope has a minimum life expectancy of five years, the scientific community will have to be abrupt in understanding its more advanced capabilities.
“We want the research community to be as scientifically productive as possible, as early as possible, which is why I am so pleased to be able to dedicate nearly 500 hours of director’s discretionary time to these ERS observations,” says Sembach.
An aspect of the innovative space telescope that astronomers can’t wait to utilise is the ability to deeply analyse other worlds orbiting stars outside of our Solar System, known as exoplanets. Starlight from an extrasolar star carries important information about its environment, but when it’s orbiting planet eclipses it, this light is now engrained with information about that planet’s atmosphere. JWST will look to measure this particular information to understand the chemical composition of the planets atmosphere using its infrared spectrographs. Initially, the JWST will be used to study Jupiter-sized exoplanets, such as WASP-39b and WASP-43b, because there are easy targets to test out this technique. From this, observing strategies will become clearer, and the telescope will observe targets that are more Earth-like, in order to search for potential habitability.
Looking further into the universe, the JWST will also examine distant galaxies whose light has been stretched into infrared wavelengths due to the expansion of the universe. NASA’s Hubble Space Telescope has seen many of these galaxies, and galaxy clusters, in it’s time. On the contrary, the JWST has the ability to see these targets in a light undetectable by Hubble. The DD-ERS will look to examine distant galaxies already examined by Hubble in an attempt to provide new and groundbreaking discoveries.
Since August 2017, more than 100 proposals for the DD-ERS were submitted. From this, a series of subject experts and Dr. Sembach had to sift thought the proposals. Thus narrowing down the list to 13 candidates that require 460 hours of telescope time.
Astronomers discover star that won’t die
Supernovae traditionally occur once at the end of a star’s life, but this particular star has exhibited multiple supernovae over the last three years
An international team of astronomers have discovered a bizarre star that refuses to stop shining, despite the fact it’s exploded several times over the course of 50 years.
When a star reaches the end of its life, it will expel its outer layers in an explosive fashion, and this is known as a supernova. A supernova most commonly marks the death of a star, but astronomers at Las Cumbres Observatory (LCO) have discovered an anomaly that challenges this theory about the death of stars.
“This supernova breaks everything we thought we knew about how they work,” says Iair Arcavi, a NASA Einstein postdoctoral fellow in UC Santa Barbara’s Department of Physics and at LCO. “It’s the biggest puzzle I’ve encountered in almost a decade of studying stellar explosions.”
Discovered in September 2014, the supernova iPTF14hls was found using the Caltech-led Palomar Transient Factory, and at first glance it appeared to be an ordinary supernova. A normal supernova shows a rise to peak brightness, followed by a gradual fading, over 100 days. In this case, the team of astronomers noticed the star increased in brightness and then dimmed again at least five times in just over three years. This is a phenomenon never seen before.
When scientists delved deeper into the archives, they were incredibly surprised to find evidence for an explosion in the same location in 1954. This indicates that the star exploded over 50 years ago, and then exploded again in 2014. From this study, the astronomers calculated the exploding anomaly was originally at least 50-times the mass of our Sun, and was most probably much larger in size.
“Supernova iPTF14hls may be the most massive stellar explosion ever seen,” explains Lars Bildsten, director of UC Santa Barbara’s Kavli Institute for Theoretical Physics. “For me, the most remarkable aspect of this supernova was its long duration, something we have never seen before. It certainly puzzled all of us as it just continued shining.”
One possible explanation is that iPTF14hls is the first example of a pulsational pair-instability supernova, a theory that was strengthened by the realisation of its 1954 explosion. This theory states that the cores of massive stars burn so hot that energy is converted into matter and antimatter. This could cause an explosion of the star’s outer layers while leaving the core intact. This process would be repeated over decades until there is a final explosion, and the star eventually collapses into a black hole.
“These explosions were only expected to be seen in the early universe and should be extinct today,” says Andy Howell, leader of the supernova group at LCO. “This is like finding a dinosaur still alive today. If you found one, you would question whether it truly was a dinosaur.”
The pulsational pair-instability theory doesn’t fully explain everything in the data collected, however. A major unexplained aspect is that the energy released by the supernova is more than what the theory predicts. This indicates that iPTF14hls could be a completely new kind of supernova.
Astronomers continue to observe iPTF14hls, which still remains bright three years after its discovery. The LCO network is, and will continue to be, ideal for such observations, as it is a global network of telescopes that can provide constant observations. This has allowed astronomers to observe the supernova every few days for the last few years, and they will remain vigilant.
“We could not have kept tabs on iPTF14hls for this long and collected data that challenges all existing supernova theories if it weren’t for the global telescope network,” says Arcavi. “I can’t wait to see what we’ll find by continuing to look at the sky in the new ways that such a setup allows.”
FREE PREVIEW: All About Space issue 71
World-leading astronomers reveal the likelihood that ET has finally phoned home in the latest issue of All About Space – out now!
The latest issue of All About Space is now available from My Favourite Magazines as well as all good supermarkets and newsagents. Read on for a taster of what’s in store for you in issue 71.
Have we made alien contact?
World-leading astronomers reveal the likelihood that ET has finally phoned home.
What’s up with the Sun?
With our nearest star recently displaying even more erratic behaviour, solar physicists have turned their attention to its tempestuous surface – and, for the first time, could have found answers to its greatest puzzle.
The dark planet
One of the hottest exoplanets ever found is also now one of the blackest. All About Space uncovers the reason why.
60 year anniversary: Rise of the space age
Shadowed by the fear of war, the initial launch of Sputnik revealed humanity at its most bold.
We’ve found new gravitational waves!
The detection of colliding neutron stars has sent shock waves through the astronomical community, signalling that we’ve found ripples in space-time from a phenomena beyond black hole mergers.
New images of red giant star could reveal the Sun’s future
W Hydrae had the same starting mass as our nearest star, but it’s billions of years more evolved
Astronomers have used the Atacama Large Millimetre/Submillimetre Array (ALMA) telescope to make the clearest image yet of an aging star that originally had the same mass of the Sun. W Hydrae, a red giant star, is a much more evolved version of the our nearest star, and any direct observations of it could tell us more about our Sun’s future.
W Hydrae lies roughly 320 light years in the constellation of Hydra (the Water Snake), and it’s described as an Asymptotic Giant Branch (AGB) star. This refers to a stage in a star’s life where it has surpassed it’s main sequence stage – in which the Sun currently resides – and the star itself cools, swells and continuously loses mass from its stellar winds.
“For us it’s important to study not just what red giants look like, but how they change and how they seed the galaxy with the elements that are the ingredients of life,” says Wouter Vlemmings of Chalmers University of Technology. “Using the antennas of ALMA in their highest-resolution configuration we can now make the most detailed observations ever of these cool and exciting stars.”
At this stage in a star’s life, the red giant will begin to produce more complex elements in its core, such as carbon and nitrogen. Astronomers estimate that this is what will occur to our Sun in roughly eight billion years. As W Hydrae originally had the same starting mass as our Sun, this is why astronomers want to learn as much as they can about how the star acts in its elderly phase.
The images provided by ALMA have resolved a perplexing component to W Hydrae. Scientists have observed the presence of a compact and bright spot; this spot provides evidence of a surprisingly hot layer of gas above the star’s chromosphere (the outer atmosphere).
“Our measurements of the bright spot suggest there are powerful shock waves in the star’s atmosphere that reach higher temperatures than are predicted by current theoretical models for AGB stars,” says Theo Khouri, also of Chalmers University of Technology.
Another possible explanation is that the star underwent a giant flare whilst the observations were made. In the name of thoroughness, scientists are now undergoing new observations using ALMA and other instruments. This will provide a much clearer picture of the stellar situation, including W Hydrae’s very perplexing atmosphere.
“It’s humbling to look at our image of W Hydrae and see its size compared to the orbit of the Earth,” explains Elvire De Beck, also of Chalmers University of Technology. “We are born from material created in stars like this, so for us it’s exciting to have the challenge of understanding something which so tells us both
about our origins and our future.”
Enceladus’ ‘loose’ core heats up subsurface ocean
This study explains a number of key characteristics of the icy moon that was observed by the Cassini spacecraf
Even though the Cassini spacecraft is no longer active, its data is still aiding astronomers in their studies of our Solar System. In this instance, Cassini’s observations have led astronomers to confirm that it’s possible for the hydrothermal activity within the moon to be powered by heat created from friction inside a highly porous – rock with tiny interstices where liquid and air can pass – core.
From the moment the Cassini spacecraft observed geyser-like jets of water vapour and icy particles – including simple organic material – emerging from warm fractures in the moon’s southern region, astronomers have been trying to explain this complex geological process. Further analysis of the moon revealed a subsurface ocean beneath its icy crust, from which the jets originate. It is because of this, among other pieces of evidence; astronomers strongly suggest that there is hot water chemically interacting with rock, also known as hydrothermal activity, occurring on the seafloor.
Other pieces of evidence include the detection of tiny rock grains from one of Cassini’s dives into the jets. The grains could have only been produced through hydrothermal chemistry taking place at temperatures of at least 90 degrees Celsius (194 degrees Fahrenheit). In this case, there must be another form of internal heating other than radioactive decay, as scientists claim that radioactive decay could not be the sole source in raising the internal temperature that high.
“Where Enceladus gets the sustained power to remain active has always been a bit of a mystery, but we’ve now considered in greater detail how the structure and composition of the moon’s rocky core could play a key role in generating the necessary energy,” says Gaël Choblet of the University of Nantes, France.
In this study, Choblet and her team indicated that a loose, rocky core with 20 to 30 per cent empty space would satisfy the criteria needed to produce such heat. Their simulations showed that during Enceladus’ orbit around the ringed planet, the core would flex and rub together to produce heat. Whilst the core is producing heat, the looseness of the core would allow water to permeate the core, chemically interacting with the rocks in the process. The models also showed that the activity would be at its maximum at the poles, particularly at the south pole where it would thin the crust to only one to five kilometres (0.5 to three miles) thick. To put that into reference, the average thickness of the icy crust is thought to be about 20 to 25 kilometres (12 to 16 miles), meaning this would allow the water to evacuate through the fractures in the icy surface.
These results provide much importance in understanding Enceladus because it explains multiple observed characteristics of the moon. The list includes the global ocean, internal heating, thinner ice at the south pole and the hydrothermal activity. Unfortunately, it doesn’t explain why the north and south poles are so different. Opposed to the south poles’ geologically fresh surface, the northern landscape is a lot more cratered and ancient. The astronomers who worked on this study to mention the fact that because the ice shell is slightly thinner in the south, which would lead to lead to runaway heating there over time.
Previous explanations for the flexing of Enceladus’ crust could be due to the large gravitational pull of Saturn. Models have disproved this theory, as it showed that it would not produce enough sustained power and the ocean would have frozen within 30 million years. Past studies have modelled how the gravitational pull of Saturn heating the core of the moon could generate the heat, but they were simpler assumptions or modelled in only two dimensions. This new model had much more complexity and was simulated in three dimensions to ensure more accurate results.
“This powerful research makes use of newer details – namely that the ocean is global and has hydrothermal activity – that we just didn’t have until the past couple of years,” says Linda Spilker, NASA’s Cassini Project Scientist at the Jet Propulsion Laboratory in Pasadena, California. “It’s an insight that the mission needed time to build, one discovery upon another.”
NASA needs you! Help nickname New Horizons’ next flyby target
The team behind the Pluto mission is looking for your ideas on what to informally name its next flyby destination, a billion miles past the dwarf planet
NASA’s New Horizons mission to Pluto and the Kuiper Belt is looking for your ideas on what to informally name its next flyby destination, a billion miles (1.6 billion kilometres) past Pluto.
On New Year’s Day 2019, the New Horizons spacecraft will fly past a small, frozen world in the Kuiper Belt, at the outer edge of our Solar System. The target Kuiper Belt object (KBO) currently goes by the official designation “(486958) 2014 MU69.” NASA and the New Horizons team are asking the public for help in giving “MU69” a nickname to use for this exploration target.
“New Horizons made history two years ago with the first close-up look at Pluto, and is now on course for the farthest planetary encounter in the history of spaceflight,” says Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington. “We’re pleased to bring the public along on this exciting mission of discovery.”
After the flyby, NASA and the New Horizons project plan to choose a formal name to submit to the International Astronomical Union, based in part on whether MU69 is found to be a single body, a binary pair, or perhaps a system of multiple objects. The chosen nickname will be used in the interim.
“New Horizons has always been about pure exploration, shedding light on new worlds like we’ve never seen before,” says Alan Stern, New Horizons principal investigator from Southwest Research Institute in Boulder, Colorado. “Our close encounter with MU69 adds another chapter to this mission’s remarkable story. We’re excited for the public to help us pick a nickname for our target that captures the excitement of the flyby and awe and inspiration of exploring this new and record-distant body in space.”
The naming campaign is hosted by the SETI Institute of Mountain View, California, and led by Mark Showalter, an institute fellow and member of the New Horizons science team. The website includes names currently under consideration; site visitors can vote for their favorites or nominate names they think should be added to the ballot. “The campaign is open to everyone,” Showalter says. “We are hoping that somebody out there proposes the perfect, inspiring name for MU69.”
The campaign will close at 3 pm EST/12 noon PST on 1 December. NASA and the New Horizons team will review the top vote-getters and announce their selection in early January.
Telescopic observations of MU69, which is more than 6.5 billion kilometres (4 billion miles) from Earth, hint at the Kuiper Belt object being either a binary orbiting pair or a contact (stuck together) pair of nearly like-sized bodies – meaning the team might actually need two or more temporary tags for its target.
“Many Kuiper Belt Objects have had informal names at first, before a formal name was proposed. After the flyby, once we know a lot more about this intriguing world, we and NASA will work with the International Astronomical Union to assign a formal name to MU69,” Showalter says. “Until then, we’re excited to bring people into the mission and share in what will be an amazing flyby on New Year’s Eve and New Year’s Day, 2019!”
First international test to track dangerous ‘Earth-destroying’ asteroids completed
The exercise was led by NASA scientists in a bid to test the International Asteroid Warning Network
An international team of astronomers led by NASA scientists successfully completed the first global exercise that tested the global response to a real asteroid. The planning for the “TC4 Observation Campaign” began in April of this year, as it observed the asteroid 2012 TC4 and tracked its trajectory towards Earth. The aim of this test was to recover, track and characterise a real asteroid as a potential impactor. Also, it was to test the International Asteroid Warning Network for hazardous asteroid observations, modelling, prediction and communication.
Asteroid 2012 TC4, the target of the exercise, is a small asteroid that was originally estimated to be between 10 and 30 metres (30 and 100 feet) in size and was known to make a very close approach to Earth in mid-October. On 12 October 2017, TC4 safely passed by Earth at a distance of roughly 43,780 kilometres (27,200 miles). In the months prior to this, astronomers from the United States, Canada, Colombia, Germany, Israel, Italy, Japan, the Netherlands, Russia and South Africa all tracked TC4 with ground-based and space-based telescope in order to understand it’s orbit, shape, rotation and composition.
“This campaign was an excellent test of a real threat case. I learned that in many cases we are already well-prepared; communication and the openness of the community was fantastic,” says Detlef Koschny, of the near-Earth object (NEO) segment in the European Space Agency (ESA)’s Space Situational Awareness program. “I personally was not prepared enough for the high response from the public and media — I was positively surprised by that! It shows that what we are doing is relevant.”
“The 2012 TC4 campaign was a superb opportunity for researchers to demonstrate willingness and readiness to participate in serious international cooperation in addressing the potential hazard to Earth posed by NEOs,” says Boris Shustov, of the Institute of Astronomy at the Russian Academy of Sciences. “I am pleased to see how scientists from different countries effectively and enthusiastically worked together toward a common goal, and that the Russian-Ukrainian observatory in Terskol was able to contribute to the effort.”
From these observations, scientists at NASA’s Centre for Near-Earth Object Studies (CNEOS) at the Jet Propulsion Laboratory in Pasadena, California were able to calculate the asteroid’s orbit and determine if it was an impact risk. “The high-quality observations from optical and radar telescopes have enabled us to rule out any future impacts between the Earth and 2012 TC4,” says Davide Farnocchia from CNEOS. “These observations also help us understand subtle effects such as solar radiation pressure that can gently nudge the orbit of small asteroids.”
These efforts led to astronomers determining the rotation of TC4, which was expected to be rotating fast due to its small size. The astronomers were surprised to find out that not only did it spin once every 12 minutes, but it was also tumbling. “The rotational campaign was a true international effort. We had astronomers from several countries working together as one team to study TC4’s tumbling behaviour,” says Eileen Ryan of the Magdalena Ridge Observatory. Her team tracked TC4 for about two months using the 2.4-metre (7.9-foot) telescope in Socorro, New Mexico.
NASA’s Goldstone Deep Space Network antenna in California, and the National Radio Astronomy Observatory’s 100-metre (330-feet) Green Bank Telescope in West Virginia, collected the data necessary to confirm the shape and composition of the asteroid. TC4 was confirmed to be very elongated, as it was about 15 metres (50 foot) long and 8 metres (35 foot) wide.
Determining the asteroid composition proved to be a much trickier task because of the adverse weather conditions. Normally, NASA’s assets that study asteroid compositions – such as NASA’s Infrared Telescope Facility (IRTF) at the Mauna Kea Observatory, Hawai’i – were only able to narrow down TC4 to two possible compositions; either dark, carbon-rich or bright igneous material.
“Radar has the ability to identify asteroids with surfaces made of highly reflective rocky or metallic materials,” says Lance Benner of the JPL. “We were able to show that radar scattering properties are consistent with a bright rocky surface, similar to a particular class of meteorites that reflect as much as 50 per cent of the light falling on them.”
NASA also used this exercise as an opportunity to evaluate the communication between the many worldwide observers and the internal U.S. government communications. These internal U.S. communications ran through the executive branch and across government agencies, as it would during an actual predicted impact emergency.
Astronomers discover belt of dust surrounding nearest star
Cold dust has been found to surround our neighbouring star, Proxima Centauri – a feature that resembles our Solar System’s Kuiper Belt
The Atacama Large Millimetre/submillimetre Array (ALMA) Observatory in Chile has exposed a belt of cold dust surrounding the closest star to our Solar System, Proxima Centauri. The new observations reveal a glow, emitted by the dust, that encompasses a region around the red dwarf equivalent to one to four times the distance of Earth from the Sun.
Proxima Centauri lies just four light years from Earth, making it the closest star to our planet. In 2016, it was discovered that there was an Earth-sized planet orbiting the red dwarf star, dubbed Proxima b. However, there is more to the star system then Proxima b, as ALMA has now shown cold cosmic duct surrounding the star. The dust ranges in sizes from less than a millimetre across up to several kilometres in diameter.
Guillem Anglada, of Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain, explains the importance of this discovery. “The dust around Proxima is important because, following the discovery of the terrestrial planet Proxima b, it’s the first indication of the presence of an elaborate planetary system, and not just a single planet, around the star closest to our Sun.”
The dust lies from Proxima Centauri at a distance of a few hundred kilometres and has a total mass of roughly one hundredth of the Earth’s mass. Estimations have also shown that the temperature is roughly -230 degrees Celsius (-382 degrees Fahrenheit), which is similar to the temperature of our Solar System’s Kuiper Belt.
There are signs of another belt of even colder dust about ten times further out. If proven, there will be many questions raised about its environment. “This result suggests that Proxima Centauri may have a multiple-planet system with a rich history of interactions that resulted in the formation of a dust belt,” says Anglada. “Further study may also provide information that might point to the locations of as yet unidentified additional planets.”
These results also have large ramifications for future space exploration projects to the Proxima Centauri system, such as the Starshot project, which aims to send microprobes attached to laser-driven sails for direct exploration. A dusty environment is important to take into account when planning the mission.
“These first results show that ALMA can detect dust structures orbiting around Proxima. Further observations will give us a more detailed picture of Proxima’s planetary system,” says Pedro Amado, also from the Instituto de Astrofísica de Andalucía. “In combination with the study of protoplanetary discs around young stars, many of the details of the processes that led to the formation of the Earth and the Solar System about 4600 million years ago will be unveiled. What we are seeing now is just the appetiser compared to what is coming!”
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