This artist’s impression shows several of the planets orbiting the ultra-cool red dwarf star TRAPPIST-1. New observations and analysis have yielded good estimates of the densities of all seven of the Earth-sized planets and suggest that they are rich in volatile materials, probably water. Image Credit: ESO
When we finally find life somewhere out there beyond Earth, it’ll be at the end of a long search. Life probably won’t announce its presence to us, we’ll have to follow a long chain of clues to find it. Like scientists keep telling us, at the start of that chain of clues is water.
The discovery of the TRAPPIST-1 system last year generated a lot of excitement. 7 planets orbiting the star TRAPPIST-1, only 40 light years from Earth. At the time, astronomers thought at least some of them were Earth-like. But now a new study shows that some of the planets could hold more water than Earth. About 250 times more.
The image on the left is what Mars looks like today. On the right is what Mars would look like according to a new study. Image Credit: Wei Luo, Northern Illinois University.
Mars has an extensive network of ancient valleys that were likely carved out by water over geologic time periods. Now a new study suggests that Mars had much more water than previously thought, and the key behind calculating that amount of water is in the valleys themselves.
The issue of exactly how much liquid water Mars had on its surface has been a hotly debated topic. There’s ample evidence that there was liquid water there. Orbiters and rovers have provided most of that evidence. Sedimentary rock, hydrated minerals that only form in the presence of water, and the obvious valleys, lake basins, and deltas all show that Mars was once a world with large quantities liquid water.
This false-color composite image was taken by the Mars rover Opportunity. It shows rocks termed “blueberries” which are geologic concretions that form in the presence of water. It also shows sedimentary rock which forms in the presence of water. Image credit: NASA/JPL/Cornell
But to find out how much water there was in Mars’ past, we have to go beyond what we can see with our orbiters and rovers and construct models. That’s exactly what Northern Illinois University geography professor Wei Luo and his colleagues Xuezhi Cang & Alan D. Howard did. To do this, they relied on what previous studies have found, what we know about erosion and water cycles here on Earth, and on an innovative new algorithm that calculated the volume of Mars’ valleys, and how much water would be required to excavate them.
“Our most conservative estimates of the global volume of the Martian valley networks and the cumulative amount of water needed to carve those valleys are at least 10 times greater than most previous estimates,” Luo said.
Their new estimate of Martian water volume is 4,000 times the volume of the valley cavities on Mars. This means that Mars would have had an active water cycle much like Earth does. Water would have moved from the lakes and oceans through the atmosphere and over the surface via evaporation and precipitation.
“That means water must have recycled through the valley systems on Mars many times, and a large open body of water or ocean is needed to facilitate such active cycling,” Luo said. “I would imagine early Mars as being similar to what we have on Earth–with an ocean, lakes, running rivers and rainfall.”
The Eberswalde delta near Holden Crater on Mars is considered the ‘smoking gun’ for evidence of liquid water on Mars. By NASA/JPL/Malin Space Science Systems
However, as the authors acknowledge, the results of this study are difficult to reconcile with our understanding of the Martian climate. Mars’ paleoclimate was likely never warm enough to support the kind of active hydrologic cycle required for their study to be accurate. “Mars is much farther way from the sun than Earth, and when the sun was younger, it was not as bright as it is today,” Luo said. “So there’s still a lot to work out in trying to reconcile the evidence for more water.”
As the authors write in their paper, “Without an ocean-sized open body of water, it would be hard to imagine the high rate of water cycling suggested by our new estimates.” So where does that leave us?
Some of the largest features on Mars, like the huge Valles Marineris, might have formed as a tectonic crack, which was then further enlarged by erosion. For other valleys, a lot of other causes have been proposed for their formation, including glaciation, and erosion by CO2, lava, and even wind.
This topographic map of the Valles Marineris region on Mars shows clearly visible outflow channels. This is image is from NASA’s Mars Global Surveyor. By NASA / JPL-Caltech / Arizona State University
It’s clear that at some point in the past, Mars had liquid water. How much water exactly is a hotly-debated topic, and this study won’t end that debate. But this study used much higher-resolution techniques, perfected in terrestrial uses, to arrive at its estimates. This study was also conducted globally on Mars, rather than by sampling individual locations. It will affect the debate in some way.
As they say in their paper, “There is no ground truth to assess the real accuracy of our estimation.” There’s really no way for scientists to reach a conclusion yet about the size of Martian oceans in the past, and on how active the hydrological cycle might have been on that planet.
Artist concept of Planet 9. Credit: NASA/JPL-Caltech.
A concentrated three-day search for a mysterious, unseen planet in the far reaches of our own solar system has yielded four possible candidates. The search for the so-called Planet 9 was part of a real-time search with a Zooniverse citizen science project, in coordination with the BBC’s Stargazing Live broadcast from the Australian National University’s Siding Spring Observatory.
A view of data from SAMI, a new multi-object integral field spectrograph at Siding Spring Observatory, which was used to look for the hypothetical Planet 9. Credit: Dilyar Barat via Twitter.
Researcher Brad Tucker from ANU, who led the effort, said about 60,000 people from around the world classified over four million objects during the three days, using data from the SkyMapper telescope at Siding Spring. He and his team said that even if none of the four candidates turn out to be the hypothetical Planet 9, the effort was scientifically valuable, helping to verify their search methods as exceptionally viable.
“We’ve detected minor planets Chiron and Comacina, which demonstrates the approach we’re taking could find Planet 9 if it’s there,” Tucker said. “We’ve managed to rule out a planet about the size of Neptune being in about 90 per cent of the southern sky out to a depth of about 350 times the distance the Earth is from the Sun.
Researchers from Australian National University pose with BBC astronomers Chris Lintott, Brian Cox and Dara O’Brien. Credit: ANU.
Last year, Caltech astronomers Mike Brown and Konstantin Batygin found indirect evidence for the existence of a large planet when they found that the orbits of several different Kuiper Belt Objects were likely being influenced by a massive body, located out beyond the orbit of Pluto, about 200 times further than the distance from the Sun to the Earth. This planet would be Neptune-sized, roughly 10 times more massive than Earth. But the search is difficult because the object is likely 1000 times fainter than Pluto.
The search has been on, with many researchers working on both new observations and sifting through old data. This recent project used archival data from the Skymapper Telescope.
“With the help of tens of thousands of dedicated volunteers sifting through hundreds of thousands of images taken by SkyMapper,” Tucker said, “we have achieved four years of scientific analysis in under three days. One of those volunteers, Toby Roberts, has made 12,000 classifications.”
Mike Brown chimed in on Twitter that he thought this concentrated search was a great idea:
Tucker said he and his team at ANU will work to confirm whether or not the unknown space objects are Planet 9 by using telescopes at Siding Spring and around the world, and he encouraged people to continue to hunt for Planet 9 through Zooniverse project, Backyard Worlds: Planet 9.
A new definition of what is a planet would mean there are at least 110 planets in our Solay System. Image Courtesy of Emily Lakdawalla of the Planetary Society, Data from NASA / JPL, JHUAPL/SwRI, SSI, and UCLA / MPS / DLR / IDA, processed by Gordan Ugarkovic, Ted Stryk, Bjorn Jonsson, Roman Tkachenko, and Emily Lakdawalla. https://creativecommons.org/licenses/by-nc-sa/3.0/
Pluto’s status as a non-planet may be coming to an end. Professor Mike Brown of Caltech ended Pluto’s planetary status in 2006. But now, Kirby Runyon, a doctoral student at Johns Hopkins University, thinks it’s time to cancel that demotion and restore it as our Solar System’s ninth planet.
Pluto’s rebirth as a planet is not just all about Pluto, though. A newer, more accurate definition of what is and what is not a planet is needed. And if Runyon and the other people on the team he leads are successful, our Solar System would have more than 100 planets, including many bodies we currently call moons. (Sorry elementary school students.)
This composite of enhanced color images of Pluto (lower right) and Charon (upper left), was taken by NASA’s New Horizons spacecraft as it passed through the Pluto system on July 14, 2015. Credits: NASA/JHUAPL/SwRI
In 2006, the International Astronomical Union (IAU) changed the definition of what a planet is. Pluto’s demotion stemmed from discoveries in the 1990’s showing that it is actually a Kuiper Belt Object (KBO). It was just the first KBO that we discovered. When Pluto was discovered by Clyde Tombaugh in 1930, and included as the ninth planet in our Solar System, we didn’t know much about the Kuiper Belt.
But in 2005, the dwarf planet Eris was discovered. It was like Pluto, but 27% more massive. This begged the question, Why Pluto and not Eris? The IAU struck a committee to look into how planets should be defined.
In 2006, the IAU had a decision to make. Either expand the definition of what is and what is not a planet to include Eris and other bodies like Ceres, or shrink the definition to omit Pluto. Pluto was demoted, and that’s the way it’s been for a decade. Just enough time to re-write text books.
But a lot has happened since then. The change to the definition of planet was hotly debated, and for some, the change should never have happened. Since the New Horizons mission arrived at Pluto, that debate has been re-opened.
“A planet is a sub-stellar mass body that has never undergone nuclear fusion…” – part of the new planetary definition proposed by Runyon and his team.
The group behind the drive to re-instate Pluto have a broader goal in mind. If the issue of whether Pluto is or is not a planet sounds a little pedantic, it’s not. As Runyon’s group says on their poster to be displayed at the upcoming conference, “Nomenclature is important as it affects how we compare, think, and communicate about objects in nature.”
Runyon’s team proposes a new definition of what is a planet, focused on the geophysics of the object: “A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has enough gravitation to be round due to hydrostatic equilibrium regardless of its orbital parameters.”
The poster highlights some key points around their new planetary definition:
Emphasizes intrinsic as opposed to extrinsic properties.
Can be paraphrased for younger students: “Round objects in space that are smaller than stars.”
The geophysical definition is already in use, taught, and included in planetological glossaries.
There’s no need to memorize all 110 planets. Teach the Solar Systems zones and why different planet types formed at different distances from the Sun.
Their proposal makes a lot of sense, but there will be people opposed to it. 110 planets is quite a change, and the new definition is a real mouthful.
“They want Pluto to be a planet because they want to be flying to a planet.” – Prof. Mike Brown, from a BBC interview, July 2015.
Mike Brown, the scientist behind Pluto’s demotion, saw this all coming when New Horizons reached the Pluto system in the Summer of 2015. In an interview with the BBC, he said “The people you hear most talking about reinstatement are those involved in the (New Horizons) mission. It is emotionally difficult for them.”
Saying that the team behind New Horizons find Pluto’s status emotionally difficult seems pretty in-scientific. In fact, their proposed new definition seems very scientific.
This image from New Horizons shows the true nature of Pluto. What for a long time was just a blurry, round, blob in space, was revealed as a geologically active planet with a seasonal atmosphere. Image: NASA/JPL/New Horizons
There may be an answer to all of this. The term “classical planets” might be of some use. That term could include our 9 familiar planets, the knowledge of which guided much of our understanding and exploration of the Solar System. But it’s a fact of science that as our understanding of something grows more detailed, our language around it has to evolve to accommodate. Look at the term planetary nebula—still in use long after we know they have nothing to do with planets—and how much confusion it causes.
“It is official without IAU approval, partly via usage.” – Runyon and team, on their new definition.
In the end, it may not matter whether the IAU is convinced by Runyon’s proposed new definition. As their poster states, “As a geophysical definition, this does not fall under the domain of the IAU, and is an alternate and parallel definition that can be used by different scientists. It is “official” without IAU approval, partly via usage.”
It may seem pointless to flip-flop back and forth about Pluto’s status as a planet. But there are sound reasons for updating definitions based on our growing knowledge. We’ll have to wait and see if the IAU agrees with that, and whether or not they adopt this new definition, and the >100 planet Solar System.
You can view Runyon and team’s poster here.
You can view Emily Lakdawalla’s image of round objects in our Solar System here.
You can read the IAU’s definition of a planet here.
The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Also, when viewed in three dimensions, they tilt nearly identically away from the plane of the solar system. Batygin and Brown show that a planet with 10 times the mass of the earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration. Credit: Caltech/R. Hurt (IPAC); [Diagram created using WorldWide Telescope.]
Last year, Caltech astronomers Mike Brown and Konstantin Batygin found indirect evidence for the existence of a large planet in the outer reaches of our Solar System — likely located out past Pluto — and since then, the search has been on. The latest research continues to show signs of an unseen planet, the hypothetical Planet 9.
Astronomers using the Gran Telescopio CANARIAS (GTC) in the Canary Islands looked at two distant asteroids called Extreme Trans Neptunian Objects’ (ETNOs), and spectroscopic observations show and their present-day orbits could be the result of a past interaction with a large “superearth”-type object orbiting the Sun at a distance between 300 to 600 AU.
Researchers say the orbits of asteroids 2004 VN112 and 2013 RF98 suggest that the two were once a binary asteroid which separated after an encounter a large body, with a mass of between 10 and 20 Earth masses.
“The similar spectral gradients observed for the pair 2004 VN112 – 2013 RF98 suggests a common physical origin,” said Julia de León, the first author of a new paper, and who is an astrophysicist at the Instituto de Astrofísica de Canarias (IAC). “We are proposing the possibility that they were previously a binary asteroid which became unbound during an encounter with a more massive object.”
Sequence of images taken with the Gran Telescopio CANARIAS (GTC) to identify one of the ETNO´s studied in this article, 2013 RF98, where one can see how it moves during four consecutive nights. Below, right, visible spectra obtained with the GTC of the two objects 2004 VN112 and 2013 RF98. The red lines show the gradients of the spectra. Credit: Julia de León (IAC).
To test their hypothesis, the team performed thousands of simulations to see how the poles of the orbits would separate as time went on. The results of these simulations suggest that a possible Planet 9 could have separated the pair of asteroids around 5 to 10 million years ago.
de León said this could explain, in principle, how these two asteroids, starting as a pair orbiting one another, became gradually separated in their orbits after an encounter with a much more massive object at a particular moment in time.
The tale of Planet 9 started in 2014, when astronomers Chad Trujillo and Scott Shepard were studying the motions of large objects in the Kuiper Belt and realized that a large planet in the outer Solar System must be altering orbits of several ETNOs the in Kuiper Belt.
Brown and Batygin were looking to verify or refute the research of Trujillo and Shepard, and they painstakingly analyzed the movement of various KBOs. They found that six different objects all seem to follow a very similar elliptical orbit that points back to the same region in space.
All the bodies were found to be inclined at a plane of about 30-degrees different from almost everything else in the Solar System. Brown said the odds of these orbits all occurring randomly are about 1 in 100.
But calculations revealed the orbits could be influenced by a massive planet way out beyond the orbit of Pluto, about 200 times further than the distance from the Sun to the Earth. This planet would be Neptune-sized, roughly 10 times more massive than Earth.
It hasn’t been found yet, but the hunt is on by large telescopes around the world, and a new citizen science project allows people around the world to join in the search.
The latest findings of by de León and team could help point the way to where Planet 9 might be lurking.
Artist concept of Planet 9. Credit: NASA/JPL-Caltech.
Citizen science projects are a great way for anyone to be involved in the scientific process. Average, everyday folks have discovered things like supernovae, previously unseen craters on the Moon and Mars and even new planets orbiting a distant star.
Now, you could be part of one of the most exciting quests yet: finding a mysterious, unseen planet in the far reaches of our own solar system. Last year, Caltech astronomers Mike Brown and Konstantin Batygin found indirect evidence for the existence of a large planet, likely located out past Pluto, and since then, the search has been on. But so far, it has come up empty. And so, astronomers decided they would bring in a little help: You.
“Backyard Worlds: Planet 9 has the potential to unlock once-in-a-century discoveries, and it’s exciting to think they could be spotted first by a citizen scientist,” said UC Berkeley postdoctoral researcher Aaron Meisner, who is helping to head up this latest citizen science project.
A previously cataloged brown dwarf named WISE 0855?0714 shows up as a moving orange dot (upper left) in this loop of WISE images spanning five years. By viewing movies like this, anyone can help discover more brown dwarfs or even a 9th planet. Credit: NASA/WISE.
People who sign on to the Backyard World: Planet 9 website will be basically using the same type of technique that was used to find the last planet discovered in our solar system, Pluto. Clyde Tombaugh used a special machine that systematically switched images on glass astronomical plates back and forth, looking for any objects in the night sky that ‘moved’ between the images.
For Backyard Worlds: Planet 9, users will view brief “flipbook” movies made from images captured by NASA’s Wide-field Infrared Survey Explorer (WISE) mission. A faint spot seen moving through background stars might be a new and distant planet in our solar system. Or it could be a nearby brown dwarf star, which would be another exciting discovery.
WISE’s infrared images cover the entire sky about six times over. This has allowed astronomers to search the images for faint, glowing objects that change position over time, which means they are relatively close to Earth. Objects that produce their own faint infrared glow would have to be large, Neptune-size planets or brown dwarfs, which are slightly smaller than stars. WISE images have already turned up hundreds of previously unknown brown dwarfs, including the objects fairly close to us, so astronomers hope that the Backyard Worlds search will turn up a new nearest neighbor to our sun.
NASA wants to bring in all the humans it can for this search, because the human eye is much better than computers at seeing changes between images.
“Automated searches don’t work well in some regions of the sky, like the plane of the Milky Way galaxy, because there are too many stars, which confuses the search algorithm,” said Meisner.
“There are just over four light-years between Neptune, the farthest known planet in our solar system, and Proxima Centauri, the nearest star, and much of this vast territory is unexplored,” said NASA astronomer Marc Kuchner, the lead researcher and an astrophysicist at NASA’s Goddard Space Flight Center. “Because there’s so little sunlight, even large objects in that region barely shine in visible light. But by looking in the infrared, WISE may have imaged objects we otherwise would have missed.”
These two images from the camera on NASA's Mars Global Surveyor show the effect that a global dust storm has on Mars. On the left is a normal view of Mars, on the right is Mars obscured by the haze from a dust storm. Image: NASA/JPL/MSSS
Our ability to forecast the weather here on Earth has saved countless lives from the onslaught of hurricanes and typhoons. We’ve gotten better at predicting space weather, too, and that has allowed us to protect sensitive satellites and terrestrial facilities from bursts of radiation and solar wind. Now, it looks as though we’re getting closer to predicting bad weather on Mars.
NASA’s Jet Propulsion Laboratory is forecasting the arrival of a global dust storm on Mars within weeks. The storm is expected to envelop the red planet, and reduce the amount of solar energy available to NASA’s rovers, Opportunity and Curiosity. The storm will also make it harder for orbiters to do their work.
Dust storms are really the only type of weather that Mars experiences. They’re very common. Usually, they’re only local phenomena, but sometimes they can grow to effect an entire region. In rarer cases, they can envelop the entire globe.
It’s these global storms that concern James Shirley, a planetary scientist at NASA’s Jet Propulsion Laboratory, in Pasadena, California. Shirley published a study showing that there is a pattern to these global storms. If his forecasted storm appears on time, it means that he has correctly determined that pattern.
“Mars will reach the midpoint of its current dust storm season on October 29th of this year. Based on the historical pattern we found, we believe it is very likely that a global dust storm will begin within a few weeks or months of this date,” Shirley said.
Predicting these huge dust storms will be of prime importance when humans gain a foothold on Mars. The dust could wreak havoc on sensitive systems, and can limit the effectiveness of solar power for weeks at a time.
But it’s not just future endeavours that are impacted by Martian dust storms. Spirit and Opportunity had to batten down the hatches when a global dust storm interrupted their exploration of Mars in 2007.
“We had to take special measures to enable their survival for several weeks with little sunlight to keep them powered.
John Callas is JPL’s project manager for Spirit and Opportunity. He describes the precautions that his team took during the 2007 dust storm: “We had to take special measures to enable their survival for several weeks with little sunlight to keep them powered. Each rover powered up only a few minutes each day, enough to warm them up, then shut down to the next day without even communicating with Earth. For many days during the worst of the storm, the rovers were completely on their own.”
This 30-day time-lapse of the Martian atmosphere was capture by Opportunity during the 2007 dust storm. That storm blocked out 99% of the Sun's energy, limiting the effectiveness of the rover's solar panels, and putting the mission in jeopardy. Image: Public Domain, https://commons.wikimedia.org/w/index.php?curid=2475872
We have observed 9 global dust storms on Mars since the first time in 1924, with the most recent one being the 2007 storm that threatened Spirit and Opportunity. Other storms were observed in 1977, 1982, 1994, and 2001. There’ve been many more of them, but we weren’t able to see them without orbiters and current telescope technology. And Earth hasn’t always been in a good position to view them.
These two images show dust build-up on NASA’s Opportunity rover in 2014. In January, a dust storm left a layer of dust on Opportunity’s solar panels (left.) By late March, the wind had blown most of it away. (right) Image: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.
Global dust storms have left their imprint on the early exploration of Mars. In 1971, NASA’s Mariner 9 orbiter reached Mars, and was greeted by a global dust storm that made it impossible to image the planet. Only two weeks later, the Soviet Mars 2 and Mars 3 missions arrived at Mars, and sent their landers to the surface.
Mars 2 crashed into the planet and was destroyed, but Mars 3 made it to the surface and landed softly. That made Mars 3 the first craft to land on Mars. However, it failed after only 14.5 seconds, likely because of the global dust storm. So not only was Mars 3 the first craft to land on Mars, it was also the first craft to be destroyed by a global dust storm.
If we had been able to forecast the global dust storm of 1971, Mars 3 may have been a successful mission. Who knows how that may have changed the history of Martian exploration?
James Shirley’s paper shows a pattern in global dust storms on Mars based on the orbit of Mars, and on the changing momentum of Mars as the gravity of other planets acts on it.
Mars takes about 1.8 years to orbit the Sun, but its momentum change caused by other planets’ gravity is in a 2.2 year cycle. The relationship between these two cycles is always changing.
This graphic indicates a similarity between 2016 (dark blue line) and five past years in which Mars has experienced a global dust storm (orange lines and band), compared to years with no global dust storm (blue-green lines and band). The arrow nearly midway across in the dark blue line indicates the Mars time of year in late September 2016. Image: NASA/JPL-Caltech
What Shirley found is that global dust storms occur while Mars’ momentum is increasing during the first part of the dust storm season. When looking back at our historical record of Martian global dust storms, he found that none of them occurred in years when the momentum was decreasing during the first part of the dust storm season.
Shirley’s paper found that current conditions on Mars are also very similar to other times when global dust storms occurred. Since we are much more capable of watching Mars than at any time in the past, we should be able to quickly confirm if Shirley’s understanding of Martian weather is correct.
This graphic shows the orbit of the planet in the HD 131399 system (red line) and the orbits of the stars (blue lines). The planet orbits the brightest star in the system, HD 131399A. Credit: ESO
This graphic shows the orbit of the planet in the HD 131399 system (red oval) and the orbits of the stars (blue arcs). The planet orbits the brightest star in the triple system, HD 131399A with a period of about 550 years. Credit: ESO
In the famous scene from the Star Wars movie “A New Hope” we recall young Luke Skywalker contemplating his future in the light of a binary sunset on the planet Tatooine. Not so many years later in 2011, astronomers using the Kepler Space Telescope discovered Kepler-16b, the first Tatooine-like planet known to orbit two suns in a binary system. Now astronomers have found a planet in a triple star system where an observer would either experience constant daylight or enjoy triple sunrises and sunsets each day, depending on the seasons, which last longer than human lifetimes.
They used the SPHERE instrument on the European Southern Observatory’s Very Large Telescope to directly image the planet, the first ever found inside a triple-star system. The three stars are named HD 131399A, HD 131399B and HD 131399C in order of decreasing brightness; the planet orbits the brightest and goes by the chunky moniker HD 131399Ab.
This composite image shows the newly discovered exoplanet HD 131399Ab in the triple-star system HD 131399. The image of the planet was obtained with the SPHERE imager. This is the first exoplanet to be discovered by SPHERE and one of very few directly-imaged planets. This picture was created from two separate SPHERE observations: one of the three stars and one to detect the faint planet. The planet appears vastly brighter in this image than in would in reality in comparison to the stars. Credit: ESO/K. Wagner et al.
Located about 320 light-years from Earth in the constellation of Centaurus the Centaur HD 131399Ab is about 16 million years old, making it also one of the youngest exoplanets discovered to date, and one for which we have a direct image. With a temperature of around 1,075° F (580° C) and the mass about four times that of Jupiter, it’s also one of the coldest and least massive directly-imaged exoplanets.
This infrared image of Saturn’s largest moon, Titan, was one of the first produced by the SPHERE instrument soon after it was installed on ESO’s Very Large Telescope in May 2014. This picture shows how effective the adaptive optics system is at revealing fine detail on this tiny disc (just 0.8 arc seconds across). Credit: ESO/J.-L. Beuzit et al./SPHERE Consortium
To pry it loose from the glare of its host suns, a team of astronomers led by the University of Arizona used a state of the art adaptive optics system to give razor-sharp images coupled with SPHERE, an instrument that blocks the light from the central star(s) similar to the way a coronagraph blocks the brilliant solar disk and allows study of the Sun’s corona. Finally, the region around the star is photographed in infrared polarized light to make any putative planets stand out more clearly against the remaining glare.
The planet, HD 131399Ab, is unlike any other known world — its orbit around the brightest of the three stars is by far the widest known within a multi-star system. It was once thought that planets orbiting a multi-star system would be unstable because of the changing gravitational tugs on the planet from the other two stars. Yet this planet remains in orbit instead of getting booted out of the system, leading astronomers to think that planets orbiting multiple stars might be more common that previously thought.
This artist’s impression shows a view of the triple star system HD 131399 from close to the giant planet orbiting in the system. The planet is known appears at the lower-left of the picture. Credit: ESO / L. Calcada
HD 131399Ab orbits HD 131399A, estimated to be 80% more massive than the Sun. Its double-star companions orbit about 300 times the Earth-Sun distance away. For much of the planet’s 550 year orbit, all three stars would appear close together in the sky and set one after the other in unique triple sunsets and sunrises each day. But when the planet reached the other side of its orbit around its host sun, that star and the pair would lie in opposite parts of the sky. As the pair set, the host would rise, bathing HD 131399Ab in near-constant daytime for about one-quarter of its orbit, or roughly 140 Earth-years.
Click to see a wonderful simulation showing how the planet orbits within the trinary system
Planets in multi-star systems are of special interest to astronomers and planetary scientists because they provide an example of how the mechanism of planetary formation functions in these more extreme scenarios. Since multi-star systems are just as common as single stars, so planets may be too.
How would our perspective of the cosmos change I wonder if Earth orbited triple suns instead of a single star? Would the sight deepen our desire for adventure like the fictional Skywalker? Or would we suffer the unlucky accident of being born at the start of a multi-decade long stretch of constant daylight? Wonderful musings for the next clear night under the stars.
This image of Saturn's southern polar vortex reveals previously unseen detail of the giant storm. Image: NASA/JPL/Space Science Institute
Atmospheric features on our Solar System’s gas giants dwarf anything similar on Earth. Earth’s atmosphere spawns hurricanes as larger as 1500 km in diameter. But on Saturn, a feature called the southern polar vortex has an eye that is 8,000 km across, or two thirds the diameter of the entire Earth.
A new high-resolution of Saturn’s southern polar vortex captured by the Cassini probe is ten times more detailed than any previous picture, and reveals details that were previously unseen. The image, which is a composite of two images taken by Cassini in July 2008, was captured when the spacecraft was 392,000 km from Saturn, and 56º below the plane of Saturn’s rings. Despite the distance and position, the image still has a resolution of 2 km per pixel.
Previous images of the vortex revealed clouds of immense proportions ringing the edge of the vortex, but showed the vortex itself to be clear. This is similar to a hurricane on Earth, where the eye itself is clear, but is ringed by wall-clouds of towering heights. This new image shows cloud formations within the vortex itself. The vortex is punctuated with wispy white cloud formations, and a smaller vortex at 10:00 within the larger formation.
The clouds inside the vortex are more than just pretty curiosities, of course. They are deep convective structures welling up from deep within Saturn’s atmosphere, and they form their own distinctive ring. This is all the more interesting because the eye of the vortex itself is generally clear, and is considered by scientists to be an area of downwelling.
The convection on display in Saturn’s southern polar vortex is an important clue to understanding how Saturn transfers energy through its atmosphere. On Earth, hurricanes are caused by warm water, and they move across the surface of the ocean as the warm water does.
Saturn, of course, has no liquid ocean, and the vortex is powered by warm atmospheric gases from deeper in Saturn. As they rise and cool they condense into clouds. The vortex also remains stationary, rather than following a warm mass of water. It’s locked into position over Saturn’s south pole.
Cassini’s narrow angle camera captured this new image, using a combination of two spectral filters. One was sensitive to wavelengths of polarized visible light centered at 617 nanometers, and the other to infrared light centered at 750 nanometers.
These two previously released infrared images of Saturn show the entire south polar region with the hurricane-like vortex in the center. The top image shows the polar region in false color, with red, green, and blue depicting the appearance of the pole in three different near-infrared colors (NASA/JPL/University of Arizona)
Cassini is a joint mission of NASA, the ESA, and the Italian Space Agency. It was launched in 1997, and has had its mission extended to September 2017. Cassini will end its mission in what the team operating Cassini is calling a Grand Finale. This will be a series of deep dives between Saturn and its rings, and will end with the spacecraft plunging into Saturn’s atmosphere.
These dark streaks, called recurring slope lineae (RSL), are on the sloped wall of a crater on Mars. A new study says they may have been formed by boiling water. Credit: NASA/JPL-Caltech/Univ. of Arizona
Finding water on Mars is a primary focus of human efforts to understand the Red Planet. The presence of liquid water on Mars supports the theory that life existed there. Now it looks as though some puzzling features on the surface of Mars could have been caused by boiling water.
Recurring slope lineae (RSL) are dark streaks found on slopes on the surface of Mars. It was thought that these streaks could have been caused by seasonal melting. Other proposed causes were dust avalanches or the venting of carbon dioxide gas. Since the same features are also found on the Moon, they could also be caused by tiny meteorites that cause avalanches. But now a study from researchers at the Open University of England shows that boiling water could have created the patterns.
We don’t have to go looking for thermal vents to find the source of this boiling water. The atmospheric pressure on Mars is so low that any liquid water would boil, without the need for a heat source. At about 1/100th the atmospheric pressure of Earth, Martian water will boil easily.
You don’t have to travel to Mars, or build an atmospheric pressure simulator, to observe the fact that water boils more readily under lower atmospheric pressure. You can see it happen here on Earth. As hikers and mountaineers know from experience, water boils more quickly the higher you go in the mountains. The greater your altitude, the less atmosphere there is pushing down on you, which lowers the boiling point of water. On Mars, that effect is extreme.
The team of researchers, led by M. Masse, performed their experiments in a chamber that can recreate the atmospheric pressure on Mars. Inside the chamber, they built a slope of loose, fine-grained material, and placed a block of ice on it. At first, the team kept the pressure inside the chamber identical to Earth’s atmospheric pressure, and the melting ice had little effect on the slope of loose material.
The ‘Martian Chamber’ used to re-create the atmospheric pressure on Mars. Image: M. Masse
But when they reduced the atmosphere inside the chamber to that of Mars, the water boiled quickly, creating a much more pronounced effect. This vigorous boiling action caused sand grains to fly into the air, creating heaps. As these heaps collapsed, avalanches were triggered. The end result was the same kind of flow patterns observed on Mars.
Numerous other studies have found evidence of liquid water on Mars, and features like the RSL appear to have been caused by water. But though this study seems to add to that growing evidence, it also puts the brakes on the idea that liquid water is present on Mars.
For these RSL to occur on Earth requires a certain amount of water. But because of the ‘boiling water effect’ of the lower pressure atmosphere on Mars, much less water is required to create them. Not only that, but the fact that water boils away so quickly means that any liquid water is short-lived, and would not provide an adequate environment for micro-organisms.
Experimental results from the new study show the effect that the atmospheres of Earth and Mars have on flowing water. Image: M. Masse
Also, the effect that Mars’ lower gravity has on the formation of RSLs is not well understood, and may be another part of the equation. The researchers’ ‘Martian Chamber’ was not built to mimic Mars’ gravity.
These are interesting preliminary results, flawed only by the lack of simulated Martian gravity. For these results to be conclusive, the same process would have to be observed on Mars itself. And that’s not happening anytime soon.
