Various groupings of Jovian moons with the newly discovered ones shown in bold. The ‘oddball,’ called Valetudo after the Roman god Jupiter’s great-granddaughter, has a prograde orbit that crosses the retrograde orbits.By Roberto Molar-Candanosa, courtesy of Carnegie Institution for Science.
Twelve new moons orbiting Jupiter have been found—11 “normal” outer moons, and one that they’re calling an “oddball.” This brings Jupiter’s total number of known moons to a whopping 79—the most of any planet in our Solar System.
A team led by Carnegie’s Scott S. Sheppard first spotted the moons in the spring of 2017 while they were looking for very distant Solar System objects as part of the hunt for a possible massive planet far beyond Pluto.
In 2014, this same team found the object with the most-distant known orbit in our Solar System and was the first to realize that an unknown massive planet at the fringes of our Solar System, far beyond Pluto, could explain the similarity of the orbits of several small extremely distant objects. This putative planet is now sometimes popularly called Planet X or Planet Nine. University of Hawaii’s Dave Tholen and Northern Arizona University’s Chad Trujillo are also part of the planet search team.
“Jupiter just happened to be in the sky near the search fields where we were looking for extremely distant Solar System objects, so we were serendipitously able to look for new moons around Jupiter while at the same time looking for planets at the fringes of our Solar System,” said Sheppard.
“It takes several observations to confirm an object actually orbits around Jupiter,” Williams said. “So, the whole process took a year.”
May 2018 recovery images of Valetudo from Carnegie’s Magellan telescope’s at our Las Campanas Observatory in Chile. The moon can be seen moving relative to the steady state background of distant stars. Jupiter is not in the field but off to the upper left. Credit: Carnegie Institution for Science
Nine of the new moons are part of a distant outer swarm of moons that orbit it in the retrograde, or opposite direction of Jupiter’s spin rotation. These distant retrograde moons are grouped into at least three distinct orbital groupings and are thought to be the remnants of three once-larger parent bodies that broke apart during collisions with asteroids, comets, or other moons. The newly discovered retrograde moons take about two years to orbit Jupiter.
Two of the new discoveries are part of a closer, inner group of moons that orbit in the prograde, or same direction as the planet’s rotation. These inner prograde moons all have similar orbital distances and angles of inclinations around Jupiter and so are thought to also be fragments of a larger moon that was broken apart. These two newly discovered moons take a little less than a year to travel around Jupiter.
“Our other discovery is a real oddball and has an orbit like no other known Jovian moon,” Sheppard explained. “It’s also likely Jupiter’s smallest known moon, being less than one kilometer in diameter”.
This new “oddball” moon is more distant and more inclined than the prograde group of moons and takes about one and a half years to orbit Jupiter. So, unlike the closer-in prograde group of moons, this new oddball prograde moon has an orbit that crosses the outer retrograde moons.
As a result, head-on collisions are much more likely to occur between the “oddball” prograde and the retrograde moons, which are moving in opposite directions.
“This is an unstable situation,” said Sheppard. “Head-on collisions would quickly break apart and grind the objects down to dust.”
SheppardJupiterMoonsMovie - YouTube
12 new moons of Jupiter were discovered, including one so-called ‘oddball.’ See what makes its orbit so strange. By Roberto Molar-Candanosa, courtesy of Carnegie Institution for Science.
It’s possible the various orbital moon groupings we see today were formed in the distant past through this exact mechanism.
The team think this small “oddball” prograde moon could be the last-remaining remnant of a once-larger prograde-orbiting moon that formed some of the retrograde moon groupings during past head-on collisions. The name Valetudo has been proposed for it, after the Roman god Jupiter’s great-granddaughter, the goddess of health and hygiene.
Elucidating the complex influences that shaped a moon’s orbital history can teach scientists about our Solar System’s early years.
For example, the discovery that the smallest moons in Jupiter’s various orbital groups are still abundant suggests the collisions that created them occurred after the era of planet formation, when the Sun was still surrounded by a rotating disk of gas and dust from which the planets were born.
Because of their sizes—one to three kilometers—these moons are more influenced by surrounding gas and dust. If these raw materials had still been present when Jupiter’s first generation of moons collided to form its current clustered groupings of moons, the drag exerted by any remaining gas and dust on the smaller moons would have been sufficient to cause them to spiral inwards toward Jupiter. Their existence shows that they were likely formed after this gas and dust dissipated.
The initial discovery of most of the new moons were made on the Blanco 4-meter telescope at Cerro Tololo Inter-American in Chile and operated by the National Optical Astronomical Observatory of the United States. The telescope recently was upgraded with the Dark Energy Camera, making it a powerful tool for surveying the night sky for faint objects. Several telescopes were used to confirm the finds, including the 6.5-meter Magellan telescope at Carnegie’s Las Campanas Observatory in Chile; the 4-meter Discovery Channel Telescope at Lowell Observatory Arizona (thanks to Audrey Thirouin, Nick Moskovitz and Maxime Devogele); the 8-meter Subaru Telescope and the Univserity of Hawaii 2.2 meter telescope (thanks to Dave Tholen and Dora Fohring at the University of Hawaii); and 8-meter Gemini Telescope in Hawaii (thanks to Director’s Discretionary Time to recover Valetudo). Bob Jacobson and Marina Brozovic at NASA’s Jet Propulsion Laboratory confirmed the calculated orbit of the unusual oddball moon in 2017 in order to double check its location prediction during the 2018 recovery observations in order to make sure the new interesting moon was not lost.
When it comes to extrasolar planets, appearances can be deceiving. Astronomers have imaged a new planet, and it appears nearly identical to one of the best studied gas-giant planets. But this doppelgänger differs in one very important way: its origin.
“We have found a gas-giant planet that is a virtual twin of a previously known planet, but it looks like the two objects formed in different ways,” said Trent Dupuy, astronomer at the Gemini Observatory and leader of the study.
Image of the 2MASS 0249 system taken with Canada-France-Hawaii Telescope’s infrared camera WIRCam. 2MASS 0249 c is located 2000 astronomical units from its host brown dwarfs, which are unresolved in this image. The area of sky covered by this image is approximately one thousandth the area of the full moon. Credits: T. Dupuy, M. Liu
Emerging from stellar nurseries of gas and dust, stars are born like kittens in a litter, in bunches and inevitably wandering away from their birthplace. These litters comprise stars that vary greatly, ranging from tiny runts incapable of generating their own energy (called brown dwarfs) to massive stars that end their lives with supernova explosions. In the midst of this turmoil, planets form around these new stars. And once the stellar nursery exhausts its gas, the stars (with their planets) leave their birthplace and freely wander the Galaxy. Because of this exodus, astronomers believe there should be planets born at the same time from the same stellar nursery, but are orbiting stars that have moved far away from each other over the eons, like long-lost siblings.
“To date, exoplanets found by direct imaging have basically been individuals, each distinct from the other in their appearance and age. Finding two exoplanets with almost identical appearances and yet having formed so differently opens a new window for understanding these objects,” said Michael Liu, astronomer at the University of Hawai`i Institute for Astronomy, and a collaborator on this work.
Dupuy, Liu, and their collaborators have identified the first case of such a planetary doppelgänger. One object has long been known: the 13-Jupiter-mass planet beta Pictoris b, one of the first planets discovered by direct imaging, back in 2009. The new object, dubbed 2MASS 0249 c, has the same mass, brightness, and spectrum as beta Pictoris b.
After discovering this object with the Canada-France-Hawaii Telescope (CFHT), Dupuy and collaborators then determined that 2MASS 0249 c and beta Pictoris b were born in the same stellar nursery. On the surface, this makes the two objects not just look-alikes but genuine siblings.
However, the planets have vastly different living situations, namely the types of stars they orbit. The host for beta Pictoris b is a star 10 times brighter than the Sun, while 2MASS 0249 c orbits a pair of brown dwarfs that are 2000 times fainter than the Sun. Furthermore, beta Pictoris b is relatively close to its host, about 9 astronomical units (AU, the distance from the Earth to the Sun), while 2MASS 0249 c is 2000 AU from its binary host.
The infrared spectra of 2MASS 0249 c (top) and beta Pictoris b (bottom) are similar, as expected for two objects of comparable mass that formed in the same stellar nursery. Unlike 2MASS 0249 c, beta Pictoris b orbits much closer to its massive host star and is embedded in a bright circumstellar disk. Credit: T. Dupuy, ESO/A.-M. Lagrange et al.
These drastically different arrangements suggest that the planets’ upbringings were not at all alike. The traditional picture of gas-giant formation, where planets start as small rocky cores around their host star and grow by accumulating gas from the star’s disk, likely created beta Pictoris b. In contrast, the host of 2MASS 0249 c did not have enough of a disk to make a gas giant, so the planet likely formed by directly accumulating gas from the original stellar nursery. “2MASS 0249 c and beta Pictoris b show us that nature has more than one way to make very similar looking exoplanets,” says Kaitlin Kratter, astronomer at the University of Arizona and a collaborator on this work. “beta Pictoris b probably formed like we think most gas giants do, starting from tiny dust grains. In contrast, 2MASS 0249 c looks like an underweight brown dwarf that formed from the collapse of a gas cloud. They’re both considered exoplanets, but 2MASS 0249 c illustrates that such a simple classification can obscure a complicated reality.”
The team first identified 2MASS 0249 c using images from CFHT, and their repeated observations revealed this object is orbiting at a large distance from its host. The system belongs to the beta Pictoris moving group, a widely dispersed set of stars named for its famous planet-hosting star. The team’s observations at W. M. Keck Observatory determined that the host is actually a closely separated pair of brown dwarfs. So, altogether, the 2MASS 0249 system comprises two brown dwarfs and one gas-giant planet. Follow-up spectroscopy of 2MASS 0249 c with the NASA Infrared Telescope Facility and the Astrophysical Research Consortium 3.5-meter Telescope at Apache Point Observatory demonstrated that it shares a remarkable resemblance to beta Pictoris b.
The 2MASS 0249 system is an appealing target for future studies. Most directly imaged planets are very close to their host stars, inhibiting detailed studies of the planets due to the bright light from the stars. In contrast, the very wide separation of 2MASS 0249 c from its host binary will make measurements of properties like its surface weather and composition much easier, leading to a better understanding of the characteristics and origins of gas-giant planets.
This work has been posted to the ArXiv is accepted for publication in the Astronomical Journal.
This annotated image highlights the location of the new heat source close to the south pole of Io. The scale to the right of image depicts of the range of temperatures displayed in the infrared image. Higher recorded temperatures are characterized in brighter colors – lower temperatures in darker colors. Image credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM
Data collected by NASA’s Juno spacecraft using its Jovian InfraRed Auroral Mapper (JIRAM) instrument point to a new heat source close to the south pole of Io that could indicate a previously undiscovered volcano on the small moon of Jupiter. The infrared data were collected on Dec. 16, 2017, when Juno was about 290,000 miles (470,000 kilometers) away from the moon.
“The new Io hotspot JIRAM picked up is about 200 miles (300 kilometers) from the nearest previously mapped hotspot,” said Alessandro Mura, a Juno co-investigator from the National Institute for Astrophysics in Rome. “We are not ruling out movement or modification of a previously discovered hot spot, but it is difficult to imagine one could travel such a distance and still be considered the same feature.”
The Juno team will continue to evaluate data collected on the Dec. 16 flyby, as well as JIRAM data that will be collected during future (and even closer) flybys of Io. Past NASA missions of exploration that have visited the Jovian system (Voyagers 1 and 2, Galileo, Cassini and New Horizons), along with ground-based observations, have located over 150 active volcanoes on Io so far. Scientists estimate that about another 250 or so are waiting to be discovered.
Juno has logged nearly 146 million miles (235 million kilometers) since entering Jupiter’s orbit on July 4, 2016. Juno’s 13th science pass will be on July 16.
Juno launched on Aug. 5, 2011, from Cape Canaveral, Florida. During its mission of exploration, Juno soars low over the planet’s cloud tops — as close as about 2,100 miles (3,400 kilometers). During these flybys, Juno is probing beneath the obscuring cloud cover of Jupiter and studying its auroras to learn more about the planet’s origins, structure, atmosphere and magnetosphere.
The Gravity Assist Podcast is hosted by NASA’s Chief Scientist, Jim Green, who each week talks to some of the greatest planetary scientists on the planet, giving a guided tour through the Solar System and beyond in the process. This week,he’s joined by Steve Squyres of Cornell University, who tells the story of the twin Mars rovers, Spirit and Opportunity, which both launched in 2003 and landed on Mars in January 2014.
You can listen to the full podcast here, or read the abridged transcript below.
Jim Green:Steve, originally Spirit and Opportunity’s nominal mission was to last for 90 Martian days. Spirit lasted six years; Opportunity is still going today. What happened?
Steve Squyres: A lot happened.You’ve got to realize that 90 days was when the warranty expired. None of us expected the wheels to fall off when the Sun came up on the 91st day.But why did they last so long? There are really three reasons. One is that we built good hardware. The second thing was that we got lucky with the weather. One of the things that we thought was going to kill these vehicles was a buildup of dust on the solar arrays. Mars has this very fine-graineddust, cigarette smoke–sized particles in the Martian atmosphere. It settles out onto the solar arrays and what had been seen on previous missions was that the dust just builds up continuously.
An artist’s impression of one of the Mars Exploration Rovers. Image credit: NASA/JPL/Cornell University.
What we have experienced with both of our rovers are cleaning events – gusts of wind that clean the dust off the solar arrays. In fact, we just had a gigantic one for Opportunity very recently. These have cleaned the solar arrays over and over again, and each time it happens, it gives us a new lease on life.
The third thing is that we discovered a very simple trick. We have no way to articulate the solar arrays. We can’t tilt them up and down. We don’t have motors that do that.
But Mars has seasons, just like Earth. During the winter on Mars – we’re in the Southern Hemisphere – the Sun goes low in the northern sky. What we wish we could do is tilt the solar arrays to the north and get more sunlight. What we do instead is we simply drive the vehicle onto north-facing slopes, tilting the entire vehicle towards the Sun, boosting our power. By operating only on north-facing slopes in the wintertime, we’ve been able to survive multiple winters on Mars.
Jim Green:Another thing that’s really spectacular about these two rovers is some of the things that they’ve found. What are some of the surprises?
Steve Squyres: It’s a long list at this point. I’ll give you a couple of favorites.
Very quickly with Opportunity, right after we landed, we found these little weird spherical things. We called them blueberries because they were embedded in the rock like blueberries in a muffin. They’re what geologists call concretions. They’re made of hematite, which is an iron oxide. The way concretions form on Earth is you have rock that is saturated with liquid water, and there’s some mineral in it that’s super-saturated and wants to precipitate out, and it does, and it finds the little nucleation point, and then it grows by adding layer upon layer and building a little hard spherical nodule, like the way an oyster builds a pearl. The blueberries were clear evidence that the ground here had been soaked with liquid water in the past.
The little hematite ‘blueberries’ discovered by Opportunity in a rock that subsequently became known as ‘Berry Bowl’. Image credit: NASA/JPL/Cornell.
Another thing was the silica that Spirit found. We were driving through this little valley with the Spirit rover, late in Spirit’s mission when the right front wheel] had failed.It wouldn’t turn, and so to drive, we had to drag that dead wheel through the soil, and we kind of dug a trench. One day, after one of these drives, we were in this little valley which we later came to call Silica Valley, and we dredged up some soil that turned out to be as bright as white snow, and this caught our attention. We went over and we measured its composition. It was not snow at all. This stuff was more than 90% pure silica, SIO2.
Jim Green:So, what did that tell you about that ancient environment?
Steve Squyres: What it told us was that there was some kind of hydrothermal activity there, either caustic steam coming out of the ground and leeching some elements away and leaving behind enriched silica deposits, which happens around some volcanic fumaroles on Earth. Or, it was a place where there were hot springs bubbling out of the ground and precipitating out silica.
The thing about both fumaroles and hot springs is that when you go to those on Earth, they are teaming with microbial life. Now, I don’t know if there was microbial life, but this was a habitable place, and that silica discovery showed us that.
Jim Green:Spirit was doing so well, and then it ran into a problem. What happened?
Steve Squyres: I always felt there were two honorable ways for the mission to end. One would be if Mars just reached out and killed us, like a major dust storm or some other event that killed a rover.The other would be if we wore it out, just flat out wore the thing out. And it was a combination of those two that killed Spirit.
When we lost the right front wheel it made it very difficult to drive, but we could still move, we were driving around, and we were doing kind of okay. We weren’t a speedy vehicle, by any means, but we could move. Then what happened was we lost another wheel. We lost the right rear wheel. Once we had lost two wheels, the vehicle could no longer drive. It became a stationary vehicle, and because we were on flat ground, we could no longer do that trick of tilting towards the Sun. We couldn’t get through the winter by driving onto a steep slope because we couldn’t move anymore. We knew that it was inevitable that the final winter it experienced was going to kill the vehicle, and it did.
Jim Green:How did you feel about that?
Steve Squyres: It was funny. I felt okay about it, for two reasons. One was that, as I say, it was an honorable death. The vehicle lasted far longer than we expected, and the reasons that we lost it were fine.The other reason it was that we had a kind of Irish wake. We [the mission team] got together and drank a few beers and told a few stories.Then, the next day, we went back to work operating Opportunity. That softened the blow quite a bit.
Jim Green:One of the things that Opportunity has done was rolling up to Victoria Crater, which just absolutely blew me away.
A view seen by Opportunity in 2007 as it was looking over the rim of Victoria Crater at one of the rocky promontories jutting out from the crater walls. Image credit: NASA/JPL/Cornell.
Steve Squyres: Yeah, we’ve had several of those. When we first got to Endurance Crater, that was the first big crater that we peered down into. And boy, the day that we pulled up to the rim of that thing, none of us had ever seen anything like that in our lives. We just stopped and stared. It was like coming up to the edge of the Grand Canyon, if you’ve never seen it, you know?
The same thing happened to us at Victoria Crater. Endeavor Crater was a little bit different. Endeavor is the big one that we’re at right now and we had a 16-kilometer drive to it that took us three years to get there.
The thing that’s different about Endeavor is that it’s got this big, tall rim. So we were driving across these flat featureless plains, and we could see the crater rim on the horizon, kilometers away, and it was like being on a ship at sea, and you could see land, and we’re trying to get to land, and we finally got there. As soon as we pulled up onto that rim, it was like a new landing site, with a whole bunch of new science questions.
The minute we pulled up onto the rim of Endeavor crater, we started seeing all these white stripes on the ground. It literally looked like somebody had gone out there with a can of white paint and a brush about half an inch or an inch wide and had just painted stripes on the ground.Theyturned out to be veins of calcium sulfate, or gypsum, which is a mineral. It’s a salt that precipitates from liquid water. This was a place where water had gushed through fractures in the ground.
Another thing that we discovered was clay deposits. One of the things about clays is that in contrast to some of these other minerals, which typically require fairly acidic conditions to form, you can only form clays when you have neutral or maybe even a little bit alkaline PH.So the clays pointed to water with a chemistry that would have been more suitable for habitability.
Opportunity approaching the western rim of Endeavor Crater. Image credit: NASA/JPL–Caltech/Cornell/ASU.
Right now, as we speak, Opportunity is driving down a little gulley that looks like it was carved by a flowing fluid, water, debris flow, something like that. These things have been seen from orbit on Mars for decades, but we’re the first to actually get into one and explore one. We call it Perseverance Valley because it took so long for us to get there.
Jim Green:How does the team come up with these names?
Steve Squyres: The naming is both necessary and fun. We discovered very quickly that it’s necessary. I remember some of our early rover tests, you know, we’d start off as rock 1, rock 2, rock 3, and that gets old real fast.So once we got to Mars, we started assigning random names to things. You know, it looked like this or it looked like that. But then, I remember when we finally figured out naming. It was our first Thanksgiving on Mars. We wanted to give the whole team four days off, but we also wanted to keep the rovers busy. So, the Spirit rover spent four solid days taking a gorgeous 360-degree panorama. We called it the Thanksgiving Pan.
We come back from Thanksgiving, and people start naming rocks, and they start naming them cranberry and drumstick and mashed potatoes and that sort of stuff. Which was funny, but then we drove on, and the mission continued. And eight months down the road, two years down the road, and somebody shows you a rock called cranberry sauce. And you go cranberry sauce, Thanksgiving. Oh, yeah, I remember where that was.That was the key. We discovered that if you have a set of names that have a theme that connects them, and it’s somehow connected in space or in time to a particular place and a particular time in which it’s happening, then it provides a really valuable little tool to help you remember where a particular rock was.
Jim Green:What do you think Opportunity has yet to learn about Mars?
Steve Squyres: I don’t know. That’s the fun part. We really, really want to nail down the formation process for Perseverance Valley. We’re going down it from top to bottom, and currently we’re only a third of the way down. We think that the most important clues of how it formed are going to be towards the bottom where the deposits of the erosion are located, so we’re really excited about that.
Another thing that’s really important to us is that we think we may have already once found, and we hope to find more of them, rocks that are older than the Endeavor crater event itself, because those would be the oldest rocks ever seen by any Mars rover. They will give us a deeper glimpse into the past than anything else.
Jim Green:Were these rocks uncovered in the impact?
Steve Squyres: What happens is the impact jumbles and jostles rocks around, and some things will be kind of shoved upwards relative to others. And you may lift some of them to up to the point where you’d be able to see them.
With Spirit dragging its damaged right front wheel through the Martian dirt, it unearthed bright patches that turned out to be almost pure silica. Image credit: NASA/JPL–Caltech.
Jim Green:The next big rover that NASA is building is Mars 2020. What do you think it’s going to find?
Steve Squyres: What intrigues me about Mars 2020 is that its primary job is to collect and cache a suite of samples to come back to Earth. I’m a huge fan of sample-return. The thing about sample-return missions is that, instead of using instruments that have been miniaturized and toughened so that you can fly them into space and launch them and land them, you can use state of the art laboratory equipment.
Samples are a gift that keeps on giving. I mean, the best science ever done with the Apollo samples that were collected in the late 1960s and early 1970s is being done today by scientists who were not born when those samples came back, using instrumentation no one had ever dreamed of at the time.
So, Mars 2020 is the initiation of this Mars sample-return process. It’s going to take a while before we can get those samples and bring them back to Earth, but what to me is the exciting thing about 2020 is what we’re going to find in those samples when we do get them.
Jim Green:You know, Steve, all my guests have to answer this question because it’s really so important for us to remember how we got into this field. What was the event, or perhaps several events, that gave you that gravity assist that propelled you forward to become the scientist you are today.
Steve Squyres: For me, there were two, very clearly. The first one was my third year as an undergraduate student at Cornell University. I was a geology major and I was still looking for the thing that I wanted to do. I signed up for a course in 1977 that was being taught by a professor named Joe Veverka, on the results of the Viking mission to Mars, which was flying at the time. It was a graduate level course. I was the only undergraduate in the course. Since it was a graduate course, we were expected to do some piece of original research.
So, a few weeks into the semester, I thought, all right, I’m going to go to the Mars room, where they keep all the prints and all the photographs of the Viking pictures, and flip through them for 15 or 20 minutes and see if I can come up with an idea for a term paper.It was just this big kind of warehouse with cardboard boxes full of these pictures that nobody had really seen at that point.I walked out of that room four hours later knowing exactly what I wanted to do with the rest of my life. I didn’t understand what I was seeing in the pictures, but that was the beauty of it. Nobody did. Scientifically, it was a blank canvas. That lure of the unknown was just irresistible to me.
The second event for me was incredibly fortunate. I was asked by Carl Sagan to participate in the Voyager mission to Jupiter and Saturn. I was this little junior baby grad student on the science team for the Voyager fly-bys of Jupiter and Saturn.And the Voyager I fly-by of Jupiter was absolutely the formative event of my career. After that, I was utterly convinced that what I wanted to do was flight projects. In the space of 48 hours, the whole Jupiter system went from being these little points of light that you could observe through a telescope to whole worlds that we could map.So those two events crystallized for me what I wanted out of my career.
This is an artist’s impression of the Jupiter-size extrasolar planet, HD 189733b, being eclipsed by its parent star. Credits: ESA, NASA, M. Kornmesser (ESA/Hubble), and STScI
In April 2018, NASA launched the Transiting Exoplanet Survey Satellite (TESS). Its main goal is to locate Earth-sized planets and larger “super-Earths” orbiting nearby stars for further study. One of the most powerful tools that will examine the atmospheres of some planets that TESS discovers will be NASA’s James Webb Space Telescope. Since observing small exoplanets with thin atmospheres like Earth will be challenging for Webb, astronomers will target easier, gas giant exoplanets first.
Some of Webb’s first observations of gas giant exoplanets will be conducted through the Director’s Discretionary Early Release Science program. The transiting exoplanet project team at Webb’s science operations center is planning to conduct three different types of observations that will provide both new scientific knowledge and a better understanding of the performance of Webb’s science instruments.
“We have two main goals. The first is to get transiting exoplanet datasets from Webb to the astronomical community as soon as possible. The second is to do some great science so that astronomers and the public can see how powerful this observatory is,” said Jacob Bean of the University of Chicago, a co-principal investigator on the transiting exoplanet project.
“Our team’s goal is to provide critical knowledge and insights to the astronomical community that will help to catalyze exoplanet research and make the best use of Webb in the limited time we have available,” added Natalie Batalha of NASA Ames Research Center, the project’s principal investigator.
Transit – An atmospheric spectrum
When a planet crosses in front of, or transits, its host star, the star’s light is filtered through the planet’s atmosphere. Molecules within the atmosphere absorb certain wavelengths, or colors, of light. By splitting the star’s light into a rainbow spectrum, astronomers can detect those sections of missing light and determine what molecules are in the planet’s atmosphere.
For these observations, the project team selected WASP-79b, a Jupiter-sized planet located about 780 light-years from Earth. The team expects to detect and measure the abundances of water, carbon monoxide, and carbon dioxide in WASP-79b. Webb also might detect new molecules not yet seen in exoplanet atmospheres.
Phase curve – A weather map
Planets that orbit very close to their stars tend to become tidally locked. One side of the planet permanently faces the star while the other side faces away, just as one side of the Moon always faces the Earth. When the planet is in front of the star, we see its cooler backside. But as it orbits the star, more and more of the hot day-side comes into view. By observing an entire orbit, astronomers can observe those variations (called a phase curve) and use the data to map the planet’s temperature, clouds, and chemistry as a function of longitude.
How Do We Learn About a Planet's Atmosphere? - YouTube
This animation describes how Webb will use transmission spectroscopy to study the atmospheres of distant exoplanets.Credits: NASA, ESA, CSA, and L. Hustak (STScI)
The team will observe a phase curve of the “hot Jupiter” known as WASP-43b, which orbits its star in less than 20 hours. By looking at different wavelengths of light, they can sample the atmosphere to different depths and obtain a more complete picture of its structure. “We have already seen dramatic and unexpected variations for this planet with Hubble and Spitzer. With Webb we will reveal these variations in significantly greater detail to understand the physical processes that are responsible,” said Bean.
Eclipse – A planet’s glow
The greatest challenge when observing an exoplanet is that the star’s light is much brighter, swamping the faint light of the planet. To get around this problem, one method is to observe a transiting planet when it disappears behind the star, not when it crosses in front of the star. By comparing the two measurements, one taken when both star and planet are visible, and the other when only the star is in view, astronomers can calculate how much light is coming from the planet alone.
This technique works best for very hot planets that glow brightly in infrared light. The team plans to study WASP-18b, a planet that is baked to a temperature of almost 4,800 degrees Fahrenheit (2,900 K). Among other questions, they hope to determine whether the planet’s stratosphere exists due to the presence of titanium oxide, vanadium oxide, or some other molecule.
Ultimately, astronomers want to use Webb to study potentially habitable planets. In particular, Webb will target planets orbiting red dwarf stars since those stars are smaller and dimmer, making it easier to tease out the signal from an orbiting planet. Red dwarfs are also the most common stars in our galaxy.
“TESS should locate more than a dozen planets orbiting in the habitable zones of red dwarfs, a few of which might actually be habitable. We want to learn whether those planets have atmospheres and Webb will be the one to tell us,” said Kevin Stevenson of the Space Telescope Science Institute, a co-principal investigator on the project. “The results will go a long way towards answering the question of whether conditions favorable to life are common in our galaxy.”
This artist’s impression shows the temperate planet Ross 128 b, with its red dwarf parent star in the background. It is provided courtesy of ESO/M. Kornmesser.
Last autumn, the world was excited by the discovery of an exoplanet called Ross 128 b, which is just 11 light years away from Earth. New work from a team led by Diogo Souto of Brazil’s Observatório Nacional and including Carnegie’s Johanna Teske has for the first time determined detailed chemical abundances of the planet’s host star, Ross 128.
Understanding which elements are present in a star in what abundances can help researchers estimate the makeup of the exoplanets that orbit them, which can help predict how similar the planets are to the Earth.
“Until recently, it was difficult to obtain detailed chemical abundances for this kind of star,” said lead author Souto, who developed a technique to make these measurements last year.
Like the exoplanet’s host star Ross 128, about 70 percent of all stars in the Milky Way are red dwarfs, which are much cooler and smaller than our Sun. Based on the results from large planet-search surveys, astronomers estimate that many of these red dwarf stars host at least one exoplanet. Several planetary systems around red dwarfs have been newsmakers in recent years, including Proxima b, a planet which orbits the nearest star to our own Sun, Proxima Centauri, and the seven planets of TRAPPIST-1, which itself is not much larger in size than our Solar System’s Jupiter.
Using the Sloan Digital Sky Survey’s APOGEE spectroscopic instrument, the team measured the star’s near-infrared light to derive abundances of carbon, oxygen, magnesium, aluminum, potassium, calcium, titanium, and iron.
“The ability of APOGEE to measure near-infrared light, where Ross 128 is brightest, was key for this study,” Teske said. “It allowed us to address some fundamental questions about Ross 128 b’s `Earth-like-ness’,” Teske said.
When stars are young, they are surrounded by a disk of rotating gas and dust from which rocky planets accrete. The star’s chemistry can influence the contents of the disk, as well as the resulting planet’s mineralogy and interior structure. For example, the amount of magnesium, iron, and silicon in a planet will control the mass ratio of its internal core and mantle layers.
The team determined that Ross 128 has iron levels similar to our Sun. Although they were not able to measure its abundance of silicon, the ratio of iron to magnesium in the star indicates that the core of its planet, Ross 128 b, should be larger than Earth’s.
Because they knew Ross 128 b’s minimum mass, and stellar abundances, the team was also able to estimate a range for the planet’s radius, which is not possible to measure directly due to the way the planet’s orbit is oriented around the star.
Knowing a planet’s mass and radius is important to understanding what it’s made of, because these two measurements can be used to calculate its bulk density. What’s more, when quantifying planets in this way, astronomers have realized that planets with radii greater than about 1.7 times Earth’s are likely surrounded by a gassy envelope, like Neptune, and those with smaller radii are likely to be more-rocky, as is our own home planet.
The estimated radius of Ross 128 b indicates that it should be rocky.
Lastly, by measuring the temperature of Ross 128 and estimating the radius of the planet the team was able to determine how much of the host star’s light should be reflecting off the surface of Ross 128 b, revealing that our second-closest rocky neighbor likely has a temperate climate.
“It’s exciting what we can learn about another planet by determining what the light from its host star tells us about the system’s chemistry,” Souto said. “Although Ross 128 b is not Earth’s twin, and there is still much we don’t know about its potential geologic activity, we were able to strengthen the argument that it’s a temperate planet that could potentially have liquid water on its surface.”
Perspective view of Pluto’s highest mountains, Tenzing Montes, along the western margins of Sputnik Planitia, which rise 3-6 kilometers above the smooth nitrogen-ice plains in the foreground. The mounded area behind the mountains at upper left is the Wright Mons edifice interpreted to a volcanic feature composed of ices. Area shown is approximately 500 kilometers across. Image credit: Lunar and Planetary Institute/Paul Schenk
Until 2015, it was not known whether icy Pluto or its largest moon, Charon, had mountains, valleys or even impact craters. After the spectacular success of New Horizons in July 2015, scientists were amazed at the towering peaks and deep valleys that were revealed in the returned data. Now, thanks to the efforts of the New Horizons team, the first official validated global map and topographic maps of these two bodies have been published and are available to all. The maps and the process of creating them are described in two new research articles published in the journal Icarus.
To create the maps, New Horizons researchers, led by Senior Staff Scientist, Paul Schenk, at the Lunar and Planetary Institute, registered all the images from the Long Range Reconnaissance Imager (LORRI) and Multispectral Visible Imaging Camera (MVIC) systems together and assembled the mosaics. This was a labor-intensive effort requiring detailed alignment of surface features in overlapping images. Digital analysis of stereo images obtained by both cameras were used to create topographic maps for each region; these were then assembled into integrated topographic maps for each body. These new maps of Pluto and Charon were produced painstakingly over a two-year period as data were slowly transmitted to Earth from the New Horizons spacecraft. The quality of geographically and topographically accurate maps improved with each new batch of images that were returned to Earth.
The validated global cartographic and topographic maps show the best resolution for each area illuminated by the Sun, and their elevations. These maps reveal a rich variety of landforms on both Pluto and Charon. The topographic maps confirm that the highest known mountains on Pluto are the Tenzing Montes range, which formed along the southwestern margins of the frozen nitrogen ice sheet of Sputnik Planitia. These steep-sided icy peaks have slopes of 40° or more and rise several kilometers above the floor of Sputnik Planitia. The highest peak rises approximately 6 kilometers (3.7 miles) above the base of the range, comparable to base-to-crest heights of Denali in Alaska, and Kilimanjaro in Kenya. Pluto’s mountains must be composed of stiff water ice in order to maintain their heights, as the more volatile ices observed on Pluto, including methane and nitrogen ice, would be too weak and the mountains would collapse.
The topographic maps also reveal large-scale features that are not obvious in the global mosaic map. The ice sheet within the 1000-kilometer (625-mile) wide Sputnik Planitia is on average 2.5 kilometers (1.5 miles) deep while the outer edges of the ice sheet lie an even deeper 3.5 km (or 2.2. miles) below Pluto’s mean elevation, or ‘sea level’ surface. While most of the ice sheet is relatively flat, these outer edges of Sputnik Planitia are the lowest known areas on Pluto, all features that are evident only in the stereo images and elevation maps. The topographic maps also reveal the existence of a global-scale deeply eroded ridge-and-trough system more than 3000 kilometers (or 2,000 miles) long, trending from north-to-south near the western edge of Sputnik Planitia. This feature is the longest known on Pluto and indicates that extensive fracturing occurred in the distant past. Why such fracturing occurred only along this linear band is not well understood.
Perspective view of mountain ridges and volcanic plains on Pluto’s large moon Charon. The ridges reach heights of 4 to 5 kilometers above the local surface and are formed when the icy outer crust of Charon fractured into large blocks. The smoother plains to the right are resurfaced by icy flows, possibly composed of ammonia-hydrate lavas that were extruded onto the surface when the older block sank into the interior. Area shown is approximately 250 kilometers across. Image credit: Lunar and Planetary Institute/Paul Schenk
On Charon the topographic maps also reveal deep depressions near the north pole that are ~14 kilometers (8.7 miles) deep, deeper than the Marianas Trench on Earth. The equatorial troughs that form the boundary between the northern and southern plains on Charon also feature high relief of ~8 kilometers. The mapping of fractured northern terrains and tilted crustal blocks along this boundary could be due to cryovolcanic resurfacing, perhaps triggered by the foundering of large crustal blocks into the deep interior of Charon. The rugged relief also indicates that Charon retains much of its original topography caused by its history of fracturing and surface disruption.
The global image and topography maps of Pluto and Charon have been archived into the Planetary Data System and will be available for use by the scientific community and the public.
Laguna Negra in the Chilean Andes is a glacial lake that contains the remains of ancient life and is exposed to ultraviolet light. Image: Wamba Wambez/Wikimedia Commons.
Detecting biomarkers in glacial lakes on Earth could pave the way for astrobiologists to detect evidence for life on other worlds, and also unravel the properties of the environments in which that life lived.
High in the Andes Mountains in Chile, unrelenting ultraviolet (UV) radiation blasts the nutrient-poor waters of Laguna Negra and Lo Encañado, two lakes fed by rapidly melting glaciers. In this hostile and remote environment, researchers are trialling life-detection technology to see if we can use it on other planets.
Understanding these lake systems will help scientists to interpret biomarkers in ancient lakes both on Earth or other planets. Although the organisms themselves are long dead, the traces and history of their deaths are encoded in the biomolecules that litter the lakes’ sediments.
The implications of these biomolecules extend far beyond the boundaries of these lakes: they could help scientists to recreate the evolutionary history of extraterrestrial life. The scientists’ findings were described in a recent article in Astrobiology.
“Once a microbe dies, different physiochemical factors – such as humidity, temperature, oxygen, or the presence of metals – affect the degradation or chemical alteration of its structures and molecular components,” says lead author Victor Parro, based at the Centro de Astrobiología, in Madrid, Spain.
Certain biomarkers are characteristic of certain groups of microbes and even particular metabolisms, he says. “From this information it is possible to infer what the environment where they developed was like.”
In the Andes, this can tell us about the paleoclimate of the mountains and their rapidly thawing glaciers. But it could possibly unravel the geochemical and atmospheric histories of other worlds, such as Mars and Saturn’s moon Titan.
“These high-altitude lakes in the Andes mountains are interesting for astrobiology because they are exposed to high levels of ultraviolet radiation,” says Lewis Dartnell, an astrobiologist at the University of Westminster, in London, who was not involved in the research. “Understanding how microbial life in the lake copes with these UV levels is important for the search for life beyond Earth – on Mars, for example, where there are believed to have once been crater lakes but also very high UV levels. “
The researchers used a Life Detector Chip (LDChip) to hunt for these fragments of life. An LDChip is a biosensor that can detect the presence of life (recent or ancient) from protein fragments and other biomolecules.
“An LDChip doesn’t need entire living microbes, it just needs biological material, whether it is alive or dead, recent or ancient, free or as part of large polymers or even organo-mineral particles [which are mineral by-products of life],” Parro says. The chip needs between four and ten amino acids to identify the protein or family of proteins that the amino acids came from.
Gale Crater on Mars, which NASA’s Curiosity rover is exploring, used to contain a lake that was exposed to the ultraviolet radiation incident on the surface of the red planet, and which may contain evidence for past life. Image: NASA/JPL–Caltech.
Testing for life in situ
The LDChip is the core of the Spanish Signs Of LIfe Detector (SOLID), an instrument that can liquidize up to two grams of solid rock, soil or ice, which can then be screened for biopolymers.
Importantly, especially when viewed through the lens of astrobiology, it can test for life in situ.
Researchers can treat these extreme environments as proxies for the remote and harsh conditions on other planets, allowing them to test their theories and technologies on Earth. Astrobiologists often view Laguna Negra as a stand-in for the lakes of Titan.
Understanding water, glaciers and ice is a fundamental part of astrobiology. “Ice and glaciers were and are common in other planetary bodies, such as Mars, and they must have played a critical role in the hydrogeology of those planets, the formation and behavior of ancient lakes, as well as in the development and evolution of potential Martian microbiology,” says Parro.
In their study, Parro’s team investigated the shallow sediments of the lakes. They reported the presence of sulphate-reducing bacteria, methanogenic (methane producing) archaea, and exopolymeric substances (polymers, such as biofilms, secreted by organisms) from Gammaproteobacteria.
Proof of life
Don Cowan, a professor of microbial ecology at the University of Pretoria, in South Africa, says that their presence is unsurprising and “just what one would expect in a glacial lake sediment”.
Asked if they were significant biomarkers, he says that “All are important, in a general sense, in that identification of any of these biomarkers (which are examples of many possible biomarkers) in an ‘astrobiological’ sample, such as from Mars, would be definitive evidence of life.”
A library of biomarkers is the next step in Parro’s research. “We need further studies and understanding of what biomarkers we can expect to find in different planetary environments,” he says. This involves identifying the most universal ones, discovering how they are preserved and how they respond to radiation and other environmental conditions, and then using that information to hone their tests for the presence of life.
The end game is to see the SOLID instrument with its LDChip on extraplanetary missions to test for biomarkers or assist astronauts in biohazard detection. Until then, the researchers plan to deploy it in as many terrestrial environments as they can, from extreme environments to the veterinary sector, Parro says.
NASA’s Cassini spacecraft’s Grand Finale orbits found a powerful interaction of plasma waves moving from Saturn to its rings and its moon Enceladus. Credits: NASA/JPL-Caltech
New research from NASA’s Cassini spacecraft’s up-close Grand Finale orbits shows a surprisingly powerful and dynamic interaction of plasma waves moving from Saturn to its rings and its moon Enceladus. The observations show for the first time that the waves travel on magnetic field lines connecting Saturn directly to Enceladus. The field lines are like an electrical circuit between the two bodies, with energy flowing back and forth.
Researchers converted the recording of plasma waves into a “whooshing” audio file that we can hear — in the same way a radio translates electromagnetic waves into music. In other words, Cassini detected electromagnetic waves in the audio frequency range — and on the ground, we can amplify and play those signals through a speaker. The recording time was compressed from 16 minutes to 28.5 seconds.
Much like air or water, plasma (the fourth state of matter) generates waves to carry energy. The Radio Plasma Wave Science (RPWS) instrument on board NASA’s Cassini spacecraft recorded intense plasma waves during one of its closest encounters to Saturn.
“Enceladus is this little generator going around Saturn, and we know it is a continuous source of energy,” said Ali Sulaiman, planetary scientist at the University of Iowa, Iowa City, and a member of the RPWS team. “Now we find that Saturn responds by launching signals in the form of plasma waves, through the circuit of magnetic field lines connecting it to Enceladus hundreds of thousands of miles away.”
Sulaiman is lead author of a pair of papers describing the findings, published recently in Geophysical Research Letters.
The interaction of Saturn and Enceladus is different from the relationship of Earth and its Moon. Enceladus is immersed in Saturn’s magnetic field and is geologically active, emitting plumes of water vapor that become ionized and fill the environment around Saturn. Our own Moon does not interact in the same way with Earth. Similar interactions take place between Saturn and its rings, as they are also very dynamic.
The recording was captured Sept. 2, 2017, two weeks before Cassini was deliberately plunged into the atmosphere of Saturn. The recording was converted by the RPWS team at the University of Iowa, led by physicist and RPWS Principal Investigator Bill Kurth.
The GRL research is available on the American Geophysical Union’s website:
The Jeerinah Formation in Western Australia, where a UW-led team found a sudden shift in nitrogen isotopes. “Nitrogen isotopes tell a story about oxygenation of the surface ocean, and this oxygenation spans hundreds of kilometers across a marine basin and lasts for somewhere less than 50 million years,” said lead author Matt Koehler.Roger Buick
Earth’s oxygen levels rose and fell more than once hundreds of millions of years before the planetwide success of the Great Oxidation Event about 2.4 billion years ago, new research from the University of Washington shows.
The evidence comes from a new study that indicates a second and much earlier “whiff” of oxygen in Earth’s distant past — in the atmosphere and on the surface of a large stretch of ocean — showing that the oxygenation of the Earth was a complex process of repeated trying and failing over a vast stretch of time.
The finding also may have implications in the search for life beyond Earth. Coming years will bring powerful new ground- and space-based telescopes able to analyze the atmospheres of distant planets. This work could help keep astronomers from unduly ruling out “false negatives,” or inhabited planets that may not at first appear to be so due to undetectable oxygen levels.
“The production and destruction of oxygen in the ocean and atmosphere over time was a war with no evidence of a clear winner, until the Great Oxidation Event,” said Matt Koehler, a UW doctoral student in Earth and space sciences and lead author of a new paper published the week of July 9 in the Proceedings of the National Academy of Sciences.
“These transient oxygenation events were battles in the war, when the balance tipped more in favor of oxygenation.”
In 2007, co-author Roger Buick, UW professor of Earth and space sciences, was part of an international team of scientists that found evidence of an episode — a “whiff” — of oxygen some 50 million to 100 million years before the Great Oxidation Event. This they learned by drilling deep into sedimentary rock of the Mount McRae Shale in Western Australia and analyzing the samples for the trace metals molybdenum and rhenium, accumulation of which is dependent on oxygen in the environment.
Now, a team led by Koehler has confirmed a second such appearance of oxygen in Earth’s past, this time roughly 150 million years earlier — or about 2.66 billion years ago — and lasting for less than 50 million years. For this work they used two different proxies for oxygen — nitrogen isotopes and the element selenium — substances that, each in its way, also tell of the presence of oxygen.
“What we have in this paper is another detection, at high resolution, of a transient whiff of oxygen,” said Koehler. “Nitrogen isotopes tell a story about oxygenation of the surface ocean, and this oxygenation spans hundreds of kilometers across a marine basin and lasts for somewhere less than 50 million years.”
The team analyzed drill samples taken by Buick in 2012 at another site in the northwestern part of Western Australia called the Jeerinah Formation.
The researchers drilled two cores about 300 kilometers apart but through the same sedimentary rocks — one core samples sediments deposited in shallower waters, and the other samples sediments from deeper waters. Analyzing successive layers in the rocks years shows, Buick said, a “stepwise” change in nitrogen isotopes “and then back again to zero. This can only be interpreted as meaning that there is oxygen in the environment. It’s really cool — and it’s sudden.”
The nitrogen isotopes reveal the activity of certain marine microorganisms that use oxygen to form nitrate, and other microorganisms that use this nitrate for energy. The data collected from nitrogen isotopes sample the surface of the ocean, while selenium suggests oxygen in the air of ancient Earth. Koehler said the deep ocean was likely anoxic, or without oxygen, at the time.
The team found plentiful selenium in the shallow hole only, meaning that it came from the nearby land, not making it to deeper water. Selenium is held in sulfur minerals on land; higher atmospheric oxygen would cause more selenium to be leached from the land through oxidative weathering — “the rusting of rocks,” Buick said — and transported to sea.
“That selenium then accumulates in ocean sediments,” Koehler said. “So when we measure a spike in selenium abundances in ocean sediments, it could mean there was a temporary increase in atmospheric oxygen.”
The finding, Buick and Koehler said, also has relevance for detecting life on exoplanets, or those beyond the solar system.
“One of the strongest atmospheric biosignatures is thought to be oxygen, but this study confirms that during a planet’s transition to becoming permanently oxygenated, its surface environments may be oxic for intervals of only a few million years and then slip back into anoxia,” Buick said.
“So, if you fail to detect oxygen in a planet’s atmosphere, that doesn’t mean that the planet is uninhabited or even that it lacks photosynthetic life. Merely that it hasn’t built up enough sources of oxygen to overwhelm the ‘sinks’ for any longer than a short interval.
“In other words, lack of oxygen can easily be a ‘false negative’ for life.”
Koehler added: “You could be looking at a planet and not see any oxygen — but it could be teeming with microbial life.”
Koehler’s other co-authors are UW Earth and space sciences doctoral student Michael Kipp, former Earth and space sciences postdoctoral researcher Eva Stüeken — now a faculty member at the University of St. Andrews in Scotland — and Jonathan Zaloumis of Arizona State University.
The research was funded by grants from NASA, the UW-based Virtual Planetary Laboratory and the National Science Foundation; drilling was funded by the Agouron Institute.