On June 16, 2018, a brilliant stellar explosion unlike any seen before went off in the skies, quickly capturing the attention of astronomers around the globe. First spotted by theÂ ATLASÂ survey in Hawaii, the event was dubbed AT2018cow through a randomized naming system, and soon earned the nickname "Cow." Just three days after exploding, Cow had become 10 times brighter than a typical supernovaâ€”a powerful explosion that heralds the death of a massive star.
"We still don't know what this is, although it is one of the most intensely studied cosmic events in history," says Anna Ho (MS '17), a graduate student at Caltech and lead author of a new study about the event. Cow was likely a supernova, she says, although some scientists have proposed that it instead may have been caused by a black hole ripping apart a type of star called a white dwarf.Â
In the hours, days, and weeks after the event, telescopes on the ground and in space set their sights on Cow, witnessing a dramatic increase in brightness across the electromagnetic spectrum, from high-energy X-rays to low-energy radio waves. Ho and her colleagues observed millimeter-wave light, which is slightly higher in energy than radio waves.Â
"We've never seen a supernova this bright in millimeter waves," she says. "We were shocked."Â
Ho presented these results on January 10 at the 233rd meeting of the American Astronomical Society in Seattle. She and her team began observing Cow five days after it exploded using the Submillimeter Array in Hawaii, and soon after using the National Science Foundation-funded Atacama Large Millimeter Array (ALMA) in Chile. They observed the event, which has since declined in brightness in millimeter waves, on and off for a total of 80 days.
Ho says that the millimeter-wave data reveal that a shock wave is traveling outward from the explosion at one-tenth the speed of light. "The millimeter-wave data tell us about the early evolution of these fast-paced events, and about their impact on the environment," says Ho. By combining the millimeter-wave data with publicly available X-ray data, the team was also able to conclude that Cow is likely "engine-driven," and that a central object formed from a supernovaâ€”such as a black hole or dense dead star called a magnetarâ€”was behind the flurry of activity.
In the future, Ho says that astronomers should be able to observe more real-time cosmic events like this in millimeter wavelengths, thanks to state-of-the-art surveys like ATLAS and Caltech's Zwicky Transient Facility (ZTF) at Palomar Observatory, which catch these events more quickly than before. "You have to act fast to catch the millimeter waves, but when you do, you are given a new window into what is happening in these brilliant explosions."
Caltech research scientist Brian Grefenstette is co-author of another recent study on Cow, led by Raffaella Margutti of theÂ Center for Interdisciplinary Exploration and Research in Astrophysics and Northwestern University. The team used, among other telescopes, NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, to observe high-energy X-rays emitted in the explosion. NuSTAR captured an unusual "bump" in the high-energy X-ray spectrum, which also suggests an engine-driven explosion generated by a black hole or magnetar formed in a supernova.Â
"Thanks to the agility of the operations team, NuSTAR got on target about a week after Cow was discovered," says Grefenstette, who is a NuSTAR instrument scientist. "Astronomers think that this may be the first live view of a newborn compact object, such as a black hole, glowing brightly in X-rays. Because it is embedded in the ejecta of the supernova explosion, the engine would normally be hidden from view. The high-energy X-ray observations with NuSTAR are essential to piecing together the puzzle of what happened in this dramatic event."
The millimeter-wave study led by Ho, titled, "AT2018cow: a luminous millimeter transient," is accepted for publication inÂ The Astrophysical Journal. Ho is funded by the Global Relay of Observatories Watching Transients Happen (GROWTH) program. Other Caltech authors include Professor of Theoretical Astrophysics Sterl Phinney; Visiting Associate in Physics Vikram Ravi; the George Ellery Hale Professor of Astronomy and Planetary Science Shri Kulkarni; graduate student Nikita Kamraj, and Assistant Professor of Astronomy Mansi Kasliwal.Â
The study led by Margutti with co-author Grefenstette, titled, "An embedded X-ray Source Shines Through the Aspherical AT2018cow: Revealing the Inner Workings of the Most Luminous Fast-Evolving Optical Transients," is accepted for publication inÂ The Astrophysical Journal.Â
NuSTAR is led by Caltech'sÂ Fiona Harrison, the Benjamin M. Rosen Professor of Physics,Â and managed by the Jet Propulsion Laboratory for NASA's Science Mission Directorate in Washington. Caltech manages JPL for NASA.
In a new Caltech-led study, researchers from campus and the Jet Propulsion Laboratory (JPL) have analyzed pulses of radio waves coming from a magnetarâ€”a rotating, dense, dead star with a strong magnetic fieldâ€”that is located near the supermassive black hole at the heart of the Milky Way galaxy. The new research provides clues that magnetars like this one, lyingÂ in close proximity to a black hole, could perhaps be linked to the source ofÂ "fast radio bursts," or FRBs. FRBs are high-energy blasts that originate beyond our galaxy but whose exact nature is unknown.
"Our observations show that a radio magnetar can emit pulses with many of the same characteristics as those seen in some FRBs," says Caltech graduate student Aaron Pearlman, who presented the results today at the 233rd meeting of the American Astronomical Society in Seattle. "Other astronomers have also proposed that magnetars near black holes could be behind FRBs, but more research is needed to confirm these suspicions."
The research team was led by Walid Majid, a visiting associate at Caltech and principal research scientist at JPL, which is managed by Caltech for NASA, and Tom Prince, the Ira S. Bowen Professor of Physics at Caltech. The team looked at the magnetar named PSR J1745-2900, located in the Milky Way's galactic center, using the largest of NASA's Deep Space Network radio dishes in Australia. PSR J1745-2900 was initially spotted by NASA's Swift X-ray telescope, and later determined to be a magnetar by NASA's Nuclear Spectroscopic Telescope Array (NuSTAR), in 2013.Â
"PSR J1745-2900 is an amazing object. It's a fascinating magnetar, but it also has been used as a probe of the conditions near the Milky Way's supermassive black hole," says Fiona Harrison, the Benjamin M. Rosen Professor of Physics at Caltech and the principal investigator of NuSTAR. "It's interesting that there could be a connection between PSR J1745-2900 and the enigmatic FRBs."
Magnetars are a rare subtype of a group of objects called pulsars; pulsars, in turn, belong to a class of rotating dead stars known as neutron stars. Magnetars are thought to be young pulsars that spin more slowly than ordinary pulsars and have much stronger magnetic fields, which suggests that perhaps all pulsars go through a magnetar-like phase in their lifetime.
The magnetar PSR J1745-2900 is the closest-known pulsar to the supermassive black hole at the center of the galaxy, separated by a distance of only 0.3 light-years, and it is the only pulsar known to be gravitationally bound to the black hole and the environment around it.Â
In addition to discovering similarities between the galactic-center magnetar and FRBs, the researchers also gleaned new details about the magnetar's radio pulses. Using one of the Deep Space Network's largest radio antennas, the scientists were able to analyze individual pulses emitted by the star every time it rotated, a feat that is very rare in radio studies of pulsars. They found that some pulses were stretched, or broadened, by a larger amount than predicted when compared to previous measurements of the magnetar's average pulse behavior. Moreover, this behavior varied from pulse to pulse.
"We are seeing these changes in the individual components of each pulse on a very fast time scale. This behavior is very unusual for a magnetar," says Pearlman. The radio components, he notes, are separated by only 30 milliseconds on average.
One theory to explain the signal variability involves clumps of plasma moving at high speeds near the magnetar. Other scientists have proposed that such clumps might exist but, in the new study, the researchers propose that the movement of these clumps may be a possible cause of the observed signal variability. Another theory proposes that the variability is intrinsic to the magnetar itself.Â
"Understanding this signal variability will help in future studies of both magnetars and pulsars at the center of our galaxy," says Pearlman.
In the future, Pearlman and his colleagues hope to use the Deep Space Network radio dish to solve another outstanding pulsar mystery: Why are there so few pulsars near the galactic center? Their goal is to find a non-magnetar pulsar near the galactic-center black hole.
"Finding a stable pulsar in a close, gravitationally bound orbit with the supermassive black hole at the galactic center could prove to be the Holy Grail for testing theories of gravity," says Pearlman. "If we find one, we can do all sorts of new, unprecedented tests of Albert Einstein's general theory of relativity."Â
The new study, titled, "Pulse Morphology of the Galactic Center Magnetar PSR J1745-2900,"Â appeared in the October 20, 2018, issue ofÂ The Astrophysical JournalÂ and was funded by a Research and Technology Development grant through a contract with NASA; JPL and Caltech's President's and Director's Fund; the Department of Defense; and the National Science Foundation. Other authors include Jonathon Kocz of Caltech and Shinji Horiuchi of the CSIRO (Commonwealth Scientific and Industrial Research Organization) Astronomy & Space Science, Canberra Deep Space Communication Complex.
In November, NASA announced that the upcoming Mars 2020 rover mission will be sent to Jezero Crater, a 28-mile-wide feature on the western edge of Isidis Planitia, a giant impact basin just north of the Martian equator.Â
The decision to go to Jezero Crater was the subject of much debate among Mars 2020 scientists. In the end, it came down to a choice between two highly favored landing sites, Jezero and a nearby site called Northeast Syrtis, each of which presented different research opportunities. To determine which to target, the Mars 2020 team relied on assistance from the Bruce Murray Laboratory for Planetary Visualization at Caltech, where researchers compiled disparate data sets about Mars to create multilayered, easy-to-read maps of the landing sites and a 3-D visualization tool.Â
"The Murray Lab was incredibly helpful as we determined where to go in 2020," says Ken Farley, the W. M. Keck Foundation Professor of Geochemistry and project scientist for Mars 2020 at JPL, which Caltech manages for NASA. "The lab has the ability to assemble and manipulate the data in a way that makes it accessible to anyone regardless of their background."
Known as the Murray Lab for short, the facility was established on the second floor of the Charles Arms Laboratory of the Geological Sciences in 2016 to develop next-generation image-processing capabilities for planetary scientists. The facility is named for the late planetary science pioneerÂ Bruce Murray, a faculty member at Caltech for nearly 50 years and director of JPL from 1976 to 1982. On the surface, the lab appears to be just a room with an enormous TV, a long couch, and a lot of computer servers humming away in the background. In reality, it is both a state-of-the-art image-processing facility and meeting space for examining and discussing those images.
For the Mars 2020 mission, a team led by Murray Lab manager Jay Dickson, research scientist in image processing, processed hundreds of gigabytes of data from NASAâ€”images, topographical maps, thermal data, and so onâ€”into files that can be opened using Google Earth. Scientists could do flyovers and generate perspective views based on the data in a free, easy-to-use interface.Â
For previous Mars missions, specialist scientists would pore over data sets and satellite images of ground features and then debate possible landing sites armed with PowerPoint presentations.Â
"It's not that easy to just look at images of Mars in a useful way," says Dickson, who was brought on to the Mars 2020 working group during the summer of 2017. A challenge was that most of the available information about the potential landing sites was gleaned from satellite measurements, and yet many of the scientists tasked with helping to decide which landing site to choose were geologists more used to working directly with samples or in a landscape, not studying it from above.
To overcome that, the Murray Lab team first stitched together images captured by the Context Camera (CTX) on JPL's Mars Reconnaissance Orbiter (MRO) and then folded in information from disparate data setsâ€”mineralogy data, for example, and temperature maps that reveal whether a patch of ground is rock or soil.Â
The final product, which allows users to navigate a region and seamlessly call up relevant data, represents a democratization of information processing, because it allows a more diverse group of researchers to make informed decisions about the landing site regardless of their skill set, says Bethany Ehlmann, a professor of planetary science, JPL research scientist, and member of the Mars 2020 team. "The Murray Lab allowed more people on the Mars 2020 team to get involved in evaluating landing sites."
The Murray Lab's involvement did not end with the creation of these multilayered maps. They also developed a 3-D visualization tool that could be viewed at the Murray Lab. As the home to an 84-inch, 4K resolution 3-D display, the Murray Lab became a regular meeting spot where Mars 2020 scientists could "fly" around the landscapes of the two main potential landing sites (as well as a third, "Midway," located midway between the two) and debate their merits.Â
The Mars 2020 team finally arrived at what Farley calls an "excellent compromise" solution. The rover, which will collect and ultimately cache samples for possible retrieval by a future mission, will land at Jezero andâ€”if the mission lasts long enoughâ€”eventually head toward Midway.
"We know how to land at both locations, so the cache would be safe at either place. And the value of multiple cached samples would be enhanced beyond what you'd get at any one landing site," Farley says.Â
Sample retrieval aside, the Murray Lab has changed the way that landing sites will be evaluated, which could bring more potential partners into the lab for future projects, Dickson says. "This has been a great vehicle for introducing people to the lab," he says.Â
All high-resolution data produced by The Murray Lab are available for streaming using Google Earth through the Murray Lab's website (murray-lab.caltech.edu/Mars2020/). The Murray Lab has received support from Foster and Coco Stanback and the Twenty-Seven Foundation.
Researchers have discovered a young star in the midst of a rare growth spurtâ€”a dramatic phase of stellar evolution when matter swirling around a star falls onto the star, bulking up its mass. The star belongs to a class of fitful stars known as FU Ori's, named after the original member of the group, FU Orionis (the capital letters represent a naming scheme for variable stars, and Orionis refers to its location in the Orion constellation). Typically, these stars, which are less than a few million years old, are hidden behind thick clouds of dust and hard to observe. This new object is only the 25th member of this class found to date and one of only about a dozen caught in the act of an outburst.
"These FU Ori events are extremely important in our current understanding of the process of star formation but have remained almost mythical because they have been so difficult to observe," saysÂ Lynne Hillenbrand, professor of astronomy at Caltech and lead author of a new report on the findings appearing inÂ The Astrophysical Journal. "This is actually the first time we've ever seen one of these events as it happens in both optical and infrared light, and these data have let us map the movement of material through the disk and onto the star."
The newfound star, called Gaia 17bpi, was first spotted by the European Space Agency'sÂ GaiaÂ satellite, which scans the sky continuously, making precise measurements of stars in visible light. When Gaia spots a change in a star's brightness, an alert goes out to the astronomy community. A graduate student at the University of Exeter and co-author of the new study, Sam Morrell, was the first to notice that the star had brightened. Other members of the team then followed up and discovered that the star's brightening had been serendipitously captured in infrared light by NASA's asteroid-huntingÂ NEOWISEÂ satellite at the same time that Gaia saw it, as well as one-and-a-half-years earlier.
"While NEOWISE's primary mission is detecting nearby solar system objects, it also images all of the background stars and galaxies as itÂ sweeps around the sky every six months," says co-author Roc Cutri, lead scientist for the NEOWISE Data Center at IPAC, an astronomy and data center at Caltech. "NEOWISE has been surveying in this way for five years now, so it is very effective forÂ detecting changes in the brightness of objects."
NASA's infrared-sensing Spitzer Space Telescope also happened to have witnessed the beginning of the star's brightening phase twice back in 2014, giving the researchers a bonanza of infrared data.Â
The new findings shine light on some of the longstanding mysteries surrounding the evolution of young stars. One unanswered question is: How does a star acquire all of its mass? Stars form from collapsing balls of gas and dust. With time, a disk of material forms around the star, and the star continues to siphon material from this disk. But, according to previous observations, stars do not pull material onto themselves fast enough to reach their final masses. Â
Theorists believe that FU Ori eventsâ€”in which mass is dumped from the disk onto the star over a total period of about 100 yearsâ€”may help solve the riddle. The scientists think that all stars undergo around 10 to 20 or so of these FU Ori events in their lifetimes but, because this stellar phase is often hidden behind dust, the data are limited. "Somebody sketched this scenario on the back of anÂ envelope in the 1980s, and, after all this time, we still haven't done much better at determining the event rates," says Hillenbrand.
The new study shows, with the most detail yet, how material moves from the midrange of a disk, in a region located around 1 astronomical unit from the star, to the star itself. (An astronomical unit is the distance between Earth and the sun.) NEOWISE and Spitzer were the first to pick up signs of the buildup of material in the middle of the disk. As the material started to accumulate in the disk, it warmed up, giving off infrared light. Then, as this material fell onto the star, it heated up even more, giving off visible light, which is what Gaia detected.Â
"The material in the middle of the disk builds up in density and becomes unstable," says Hillenbrand. "Then it drains onto the star, manifesting as an outburst."Â
The researchers used the W. M. Keck Observatory and Caltech's Palomar Observatory to help confirm the FU Ori nature of the newfound star. Says Hillenbrand, "You can think of Gaia as discovering the initial crime scene, while Keck and Palomar pointed us to the smoking gun."
The study is titled, "Gaia 17bpi: An FU Ori Type Outburst."Â Other authors include: Carlos Contreras PeĂ±a and Tim Naylor of the University of Exeter; Michael Kuhn and Luisa Rebull of Caltech; Simon Hodgkin of Cambridge University; Dirk Froebrich of the University of Kent; and Amy Mainzer of JPL.Â
Facing the certainty of a changing climate coupled with the uncertainty that remains in predictions of how it will change, scientists and engineers from across the country are teaming up to build a new type of climate model that is designed to provide more precise and actionable predictions.Â
Leveraging recent advances in the computational and data sciences, the comprehensive effort capitalizes on vast amounts of data that are now available and on increasingly powerful computing capabilities both for processing data and for simulating the earth system.Â
The new model will be built by a consortium of researchers led by Caltech, in partnership with MIT; the Naval Postgraduate School (NPS); and JPL, which Caltech manages for NASA. The consortium, dubbed the Climate Modeling Alliance (CliMA), plans to fuse Earth observations and high-resolution simulations into a model that represents important small-scale features, such as clouds and turbulence, more reliably than existing climate models. The goal is a climate model that projects future changes in critical variables such as cloud cover, rainfall, and sea ice extent more accurately â€“ with uncertainties at least two times smaller than existing models.
"Projections with current climate modelsâ€”for example, of how features such as rainfall extremes will changeâ€”still have large uncertainties, and the uncertainties are poorly quantified," says Tapio Schneider, Caltech's Theodore Y. Wu Professor of Environmental Science and Engineering, senior research scientist at JPL, and principal investigator of CliMA. "For cities planning their stormwater management infrastructure to withstand the next 100 years' worth of floods, this is a serious issue;Â concrete answers about the likely range of climate outcomes are key for planning."
The consortium will operate in a fast-paced, start-up-like atmosphere, and hopes to have the new model up and running within the next five yearsâ€”an aggressive timeline for building a climate model essentially from scratch.Â
"A fresh start gives us an opportunity to design the model from the outset to run effectively on modern and rapidly evolving computing hardware, and for the atmospheric and ocean models to be close cousins of each other, sharing the same numerical algorithms," says Frank Giraldo, professor of applied mathematics at NPS.
Current climate modeling relies on dividing up the globe into a grid and then computing what is going on in each sector of the grid, as well as how the sectors interact with each other. The accuracy of any given model depends in part on the resolution at which the model can view the earthâ€”that is, the size of the grid's sectors. Limitations in available computer processing power mean that those sectors generally cannot be any smaller than tens of kilometers per side. But for climate modeling, the devil is in the detailsâ€”details that get missed in a too-large grid.Â
For example, low-lying clouds have a significant impact on climate by reflecting sunlight, but the turbulent plumes that sustain them are so small that they fall through the cracks of existing models. Similarly, changes in Arctic sea ice have been linked to wide-ranging effects on everything from polar climate to drought in California, but it is difficult to predict how that ice will change in the future because it is sensitive to the density of cloud cover above the ice and the temperature of ocean currents below, both of which cannot be resolved by current models.
To capture the large-scale impact of these small-scale features, the team will develop high-resolution simulations that model the features in detail in selected regions of the globe. Those simulations will be nested within the larger climate model. The effect will be a model capable of "zooming in" on selected regions,Â providing detailed local climate information about those areasand informing the modeling of small-scale processes everywhere else.
"The ocean soaks up much of the heat and carbon accumulating in the climate system. However, just how much it takes up depends on turbulent eddies in the upper ocean, which are too small to be resolved in climate models," says Raffaele Ferrari, Cecil and Ida Green Professor of Oceanography at MIT. "Fusing nested high-resolution simulations with newly available measurements from, for example, a fleet of thousands of autonomous floats could enable a leap in the accuracy of ocean predictions."
While existing models are often tested by checking predictions against observations, the new model will take ground-truthing a step further by using data-assimilation and machine-learning tools to "teach" the model to improve itself in real time, harnessing both Earth observations and the nested high-resolution simulations.Â
"The success ofÂ computational weather forecasting demonstrates the power of using data to improve the accuracy of computer models; we aim to bring the same successes to climate prediction," says Andrew Stuart, Caltech's Bren Professor of Computing and Mathematical Sciences.
Each of the partner institutions brings a different strength and research expertise to the project. At Caltech, Schneider and Stuart will focus on creating the data-assimilation and machine-learning algorithms, as well as models for clouds, turbulence, and other atmospheric features. At MIT, Ferrari and John Marshall, also a Cecil and Ida Green Professor of Oceanography, will lead a team that will model the ocean, including its large-scale circulation and turbulent mixing. At NPS, Giraldo will lead the development of the computational core of the new atmosphere model in collaboration with Jeremy Kozdon and Lucas Wilcox. At JPL, a group of scientists will collaborate with the team at Caltech's campus to develop process models for the atmosphere, biosphere, and cryosphere.
Funding for this project is provided by the generosity of Eric and Wendy Schmidt (by recommendation of theÂ Schmidt FuturesÂ program); Mission Control Earth, an initiative of Mountain Philanthropies;Â Paul G. Allen Philanthropies;Â the Heising-Simons Foundation; Blaine and Lynda Fetter; Deborah Castleman;Â Caltech trustee Charles Trimble;Â the Chair's Council of the Division of Geological and Planetary Sciences;Â and the National Science Foundation. More information can be found atÂ https://clima.caltech.edu.
For the second time in history, a human-made object has reached the space between the stars. NASA's VoyagerÂ 2 probe now has exited the heliosphereâ€”the protective bubble of particles and magnetic fields created by the sun.
Members of NASA's Voyager team discussed the findings at a news conference today at the meeting of the American Geophysical Union (AGU) in Washington.
Comparing data from different instruments aboard the trailblazing spacecraft, mission scientists determined the probe crossed the outer edge of the heliosphere on November 5. This boundary, called the heliopause, is where the tenuous, hot solar wind meets the cold, dense interstellar medium. Its twin, VoyagerÂ 1, crossed this boundary in 2012, but Voyager 2 carries a working instrument that will provide first-of-its-kind observations of the nature of this gateway into interstellar space.
"There is still a lot to learn about the region of interstellar space immediately beyond the heliopause," said Ed Stone, Voyager project scientist and the David Morrisroe Professor of Physics at Caltech.
VoyagerÂ 2 now is slightly more than 11 billion miles (18 billion kilometers) from Earth. Mission operators still can communicate with VoyagerÂ 2 as it enters this new phase of its journey, but informationâ€”moving at the speed of lightâ€”takes about 16.5 hours to travel from the spacecraft to Earth. By comparison, light traveling from the sun takes about eight minutes to reach Earth.
Read the full story at JPL News.
David Reitze, the executive director of the Laser Interferometer Gravitational-wave Observatory (LIGO) and a research professor of physics at Caltech, has been named a fellow of the American Association for the Advancement of Science (AAAS).
The AAAS has named 416 new members this year for their "scientifically or socially distinguished efforts to advance science or its applications," according to the AAAS. New fellows will be presented with an official certificate and a gold and blue rosette pin (representing science and engineering, respectively) on February 16 at the 2019 AAAS Annual Meeting in Washington, D.C.
According to the AAAS nomination, Reitze is being honored for "outstanding leadership of [LIGO] into the era of the discovery of the first gravitational waves."
As the executive director of LIGO since 2011, Reitze led the team that madeÂ the first direct detection of gravitational wavesâ€”ripples in space and time. The gravitational waves were generated 1.3 billion years ago by the collision of two black holes. Since then, under his continued leadership, LIGO has, together with European-based Virgo detector, identified gravitational waves from other powerful cosmic events, includingÂ the merger of two neutron stars.Â
The AAAS has also named two new fellows from the Jet Propulsion Laboratory, which is managed by Caltech for NASA. Michael Janssen is being honored for his "distinguished scientific contributions to the study of planets, comets, sun and cosmic microwave background radiation using ground and space-based radio techniques," andÂ William Langer for his "exceptional contributions to understanding the physics and chemistry of the Galaxy's interstellar medium, effected through insightful theoretical modeling, novel observations, and thorough interpretation."
Mars has just received its newest robotic resident. NASA's Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) lander successfully touched down on the Red Planet after an almost seven-month, 300-million-mile (458-million-kilometer) journey from Earth.
InSight's two-year mission will be to study the deep interior of Mars to learn how all celestial bodies with rocky surfaces, including Earth and the moon, formed.
InSight launched from Vandenberg Air Force Base in California May 5. The lander touched down Monday, Nov. 26, near Mars' equator on the western side of a flat, smooth expanse of lava called Elysium Planitia, with a signal affirming a completed landing sequence at 11:52:59 a.m. PST (2:52:59 p.m. EST).
"Today, we successfully landed on Mars for the eighth time in human history," said NASA Administrator Jim Bridenstine. "InSight will study the interior of Mars and will teach us valuable science as we prepare to send astronauts to the Moon and later to Mars. This accomplishment represents the ingenuity of America and our international partners, and it serves as a testament to the dedication and perseverance of our team. The best of NASA is yet to come, and it is coming soon."
The landing signal was relayed to the Jet Propulsion Laboratory, which Caltech manages for NASA, via NASA's two small experimental Mars Cube One (MarCO) CubeSats, which launched on the same rocket as InSight and followed the lander to Mars.
"Every Mars landing is daunting, but now with InSight safely on the surface we get to do a unique kind of science on Mars," said JPL director Michael Watkins.
On November 26, NASA's InSight lander will complete its six-and-a-half month journey to Mars, touching down at Elysium Planitia, a broad plain near the Martian equator that is home to the second largest volcanic region on the planet.
There, NASA scientists hope to "give the Red Planet its first thorough checkup since it formed 4.5 billion years ago," according to the InSight mission website. Previous missions have examined features on the surface, but many signatures of the planet's formationâ€”which can provide clues about how all the terrestrial planets formedâ€”can only be found by sensing and studying its "vital signs" far below the surface.
To check on those vital signs, InSight will come equipped with two main instrument packages: a seismometer for studying how seismic waves (for example, from marsquakes and meteorite impacts) travel through the planet and a "mole" that will burrow into the ground, dragging a tether with temperature sensors behind it to measure how temperatures change with depth on the planet. These instruments will tell scientists about Mars's interior structure (similar to the way an ultrasound lets doctors "see" inside a human body) and also about the heat flow from the planet's interior.
Engineers hope that the mole will reach a depth of between three and five metersâ€”far enough down that it will be isolated from the temperature fluctuations of day and night and Mars's annual cycle on the surface above. Meters may not sound like much, but to dig that far using only equipment that can be launched on a spacecraft and controlled from 55 million miles away is a technical challenge that has never been attempted before.
Using a sliding weight inside its narrow body, the mole, which is 15.75 inches (400 millimeters) long and weighs just 1.9 pounds (860 grams), hammers itself into the ground, 1 mm at a time, while dragging a tether that is studded with 14 temperature sensors along its length. A traditional drill attempting to perform the same task would need to be as long as the hole it was attempting to drillâ€”and would need a massive supporting structure. Were it to hammer continuously, the mole would take between a few hours to a few days to reach its final depth, depending on the characteristics of the soil. However, the mole will stop every 50 centimeters to measure the soil thermal conductivity, a process which requires periods of cooling and heating lasting several days. With the additional time needed to assess progress and send new commands, the mole could take six weeks or more to reach its final depth. Â Â
When designing the probe, engineers at JPL, which Caltech manages for NASA, wanted to be certain that the mole would be capable of reaching the necessary depth, and so they called on Caltech's JosĂ© Andrade, George W. Housner Professor of Civil and Mechanical Engineering in the Division of Engineering and Applied Science and an expert on the physics of granular materials.
"About five years ago, when the mole kept getting stuck during testing, the InSight team pulled together what's called a 'tiger team'â€”a bunch of specialists from different areas who are brought in to help resolve an issue," Andrade says. "I was called to serve on this tiger team as an expert in soil mechanics."
Because soil is a granular materialâ€”a conglomeration of solid particles that are each larger than a micrometerâ€”it exhibits somewhat unusual properties. For example, soil composed of round particles will flow easily as the particles slide past one another, like sand in an hourglass. But soil composed of the same sizes of particles but with more jagged and angular shapes will lock together like puzzle pieces and cannot flow without significant outside force.
Granular materials can be described as singular objects that will deform based on their critical state plasticityâ€”an idealized model for how groups of grains will force their way past one another as stress is applied to them. That plasticity is governed by air pressure and the force of gravity. As such, it is difficult to simulate in a laboratory the critical state plasticity of a granular material on Mars, which has one-third the gravity and 0.6 percent of the air pressure of Earth at sea level.
"We kept trying to extrapolate how critical state plasticity would translate to Mars," Andrade says. "Without knowing that, we could not effectively model how much resistance InSight's mole would face when attempting to drill through Mars's soil, and whether it could reach the desired depth. So, this sparked a clear need for more understanding."Â
To help investigate the mole's penetration in a granular material, Andrade and the InSight team hired postdoctoral researcher Ivan Vlahinic, who had recently completed a PhD at Northwestern University. Vlahinic set up tests in which early mock-ups of the mole were monitored and mathematically analyzed as they worked their way through a glass column filled with sand.
Andrade, Vlahinic, and their colleagues found that Mars's lower overburden pressure, compared to Earth, will actually make itÂ harderÂ for the mole to penetrate Mars's soil. Overburden pressure is the pressure on a layer of rock or sand exerted by the material stacked above it. At any given depth, the overburden pressure on Mars is one-third of Earth's, corresponding with the Red Planet's lower gravity. For the same packing fractionâ€”the amount of space filled by materialâ€”the low pressure allows granular materials to exist in a looser state that actually increases the number of individual contacts that each grain has with its neighbors, and this increases the overall resistance of the material to penetration.
Vlahinic's research was eventually taken over by Jason Marshall, who earned a PhD from Carnegie Mellon University in 2014 and worked as a postdoctoral researcher at Caltech from 2015 to 2018.
"We not only studied penetration, but also how heat moves through the soil," Marshall says. "One of the things that InSight seeks to understand is how the temperature of the planet changes with depth. What we found is that as we're deforming the sand, the particles are obviously being rearranged, and that's going to affect the thermal conductivity measurements." As granular materials deform, the amount of space between the individual grains changes, adjusting the amount of space through which heat will either radiate or conduct via the planet's thin atmosphere. It also increases the number of grain-to-grain contacts as the soil is packed more tightly.Â Â
With this knowledge, Andrade was able to develop new computer models that helped the JPL team predict the mole's effectiveness in Martian soil. Unless the mole encounters an obstacle, he is confident that it will be successful.
"The tests show that this thing can go much deeper than two meters. A dealbreaker could be a large formation of rock that blocks the path of the mole, but the InSight landing site selection team have chosen a location on Mars that is as rock-free as possible," he says. In addition, armed with Marshall's information on the effect of particle rearrangement on thermal conductivity, InSight should be in a good position to not only reach its desired depth, but also send back accurate information on the temperature at that depth, Andrade says.
For now, Andrade and his former postdocs can only watchâ€”and wait. "We've done everything we could here on Earth. Now it's up to InSight," he says.
A data-processing artifact may be responsible for evidence cited in a 2015 report that cold salty waters are responsible for forming seasonally dark streaks on the surface of Mars, according to a new study from Caltech.
The study, published online on November 9 by the journalÂ Geophysical Research Letters, shows that a filtering step in the processing of data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) can, in rare circumstances, lead to signatures that mimic the appearance of certain minerals, including perchlorateâ€”a salt whose presence would imply the existence of cold, salty waters at the surface of Mars.Â
MRO has been orbiting Mars since 2006, and during that time, CRISM has been capturing images of visible and infrared light reflected from the planet's surface. Different minerals absorb light at different wavelengths and so the fingerprints of the reflected light provide clues about what minerals might be present at a given location.Â
In 2015, scientists analyzing CRISM images found absorption patterns in a few pixels of the images that appeared to indicate concentrations of perchlorate. The pixels where CRISM detected perchlorate were associated with seasonally changing dark streaks on the slopes of Martian craters (formally named "recurring slope linae," or RSLs), sparking the idea that the dark streaks were, in fact, caused by salty flowing liquid water. The existence of perchlorate brines on Mars has been the subject of speculation and debate ever since.
While analyzing CRISM images of the potential landing sites for the Mars 2020 rover, the Caltech-led research team noted the same strong perchlorate-like signatures in a few of the pixels. That team, led by Bethany Ehlmann, professor of planetary science at Caltech and research scientist at JPL, includes Caltech graduate student Ellen Leask and Murat Dundar, an associate professor at Indiana University-Purdue University Indianapolis.
"Potential residues of salty perchlorate waters at Mars 2020 landing sites would have been big news. We were about to report it, but I wanted to take a second look at the data," says Ellen Leask, lead author of the study.
The second look led to a vigorous analysis, conducted over a year with the CRISM team at the Johns Hopkins University Applied Physics Laboratory, that revealed that when CRISM data are processed, certain "noisy" pixels that occur at the boundary between the light and dark part of an image can be misinterpreted. These pixels have errant spikes in their absorption patterns that, coupled with the signature of carbon dioxide in Mars' atmosphere, are processed in such a way that the end result mimics the absorption pattern from certain hydrated minerals. Those minerals include alunite, kieserite, serpentine, and especially perchlorate, all of which are characteristic of wet environments. The team found the error occurs in less than 0.05 percent of the pixels in all of the CRISM images and only affects very small spots in the images (covering less than 12 pixels).
Armed with this new information, Leask took a fresh look at the published literature of mineral detections on Mars from CRISM. Although the majority of the previous orbital detections of alunite, kieserite, and serpentine could be re-confirmed, none of the perchlorate detections reported in published literature remained convincing, says Ehlmann.
"Ellen's careful sleuthing revealed this issue," Ehlmann says. "It's a case study in the importance of critical skepticism of even one's own data."
The study is titled "Challenges in the Search for Perchlorate and Other Hydrated Minerals with 2.1-ÎĽm Absorptions on Mars." Scott Murchie and Frank Seelos of the Johns Hopkins University Applied Physics Laboratory are also coauthors. This research was funded by the Natural Sciences and Engineering Research Council of Canada, NASA, the Rose Hills Foundation, and the National Science Foundation.