Posted on by Matt Williams

Stable Lava Tube Could Provide a Potential Human Habitat on the Moon

The Marius Hills Skylight, as observed by the Japanese SELENE/Kaguya research team. Image by: NASA/Goddard/Arizona State University

On October 5th, 2017, Vice President Mike Pence announced the Trump administration’s plan to return astronauts to the Moon. Looking to the long-term, NASA and several other space agencies are also intent on establishing a permanent lunar base there. This base will not only provide opportunities for lunar science, but will facilitate missions to Mars and beyond.

The only question is, where should such a base be built? For many years, NASA, the ESA and other agencies have been exploring the possibility of stable lava tubes as a potential site. According to new study by a team of international scientists, the presence of such a tube has now been confirmed in the Marius Hills region. This location is likely to be the site of future lunar missions, and could even be the site of a future lunar habitat.

In 2009, data provided by the Terrain Camera aboard JAXA’s SELENE spacecraft indicated the presence of three huge pits on the Moon. These pits (aka. “skylights”) were of particular interest since they were seen as possible openings to subsurface lava channels. Since then, the Marius Hills region (where they were found) has been a focal point for astronomers and planetary scientists hoping to confirm the existence of lava tubes.

Artist’s impression of a surface exploration crew investigating a typical, small lava tunnel, to determine if it could serve as a natural shelter for the habitation modules of a Lunar Base. Credit: NASA’s Johnson Space Center

The recent study, titled “Detection of intact lava tubes at Marius Hills on the Moon by SELENE (Kaguya) Lunar Radar Sounder“, recently appeared in the journal Geophysical Research Letters. The team consisted of members from JAXA’s Institute of Space and Astronautical Science (ISAS), Purdue University, the University of Alabama, AstroLabs, the National Astronomical Observatory of Japan (NOAJ) and multiple Japanese Universities.

Together, they examined data from the SELENE mission’s Lunar Radar Sounder (LRS) from locations that were close to the Marius Hills Hole (MHH) to determine if the region hosted stable lava tubes. Such tubes are a remnant from the Moon’s past, when it was still volcanically active. These underground channels are believed to be an ideal location for a lunar colony, and for several reasons.

For starters, their thick roofs would provide natural shielding from solar radiation, cosmic rays, meteoric impacts, and the Moon’s extremes in temperature. These tubes, once enclosed, could also be pressurized to create a breathable environment. As such, finding an entrance to a stable lava tube would the first step towards selecting a possible site for such a colony.

As Junichi Haruyama, a senior researcher at JAXA and one of the co-authors on the study, explained in a University of Purdue press release:

“It’s important to know where and how big lunar lava tubes are if we’re ever going to construct a lunar base. But knowing these things is also important for basic science. We might get new types of rock samples, heat flow data and lunar quake observation data.”

The city of Philadelphia is shown inside a theoretical lunar lava tube. A Purdue University team of researchers explored whether lava tubes more than 1 kilometer wide could remain structurally stable on the moon. Credit: Purdue University/courtesy of David Blair

Granted, the LRS was not specifically designed to detect lava tubes, but to characterize the origins of the Moon and its geologic evolution. For this reason, it did not fly close enough to the Moon to obtain extremely accurate information on the subsurface. Nevertheless, as SELENE passed near the Marius Hills Hole, the instrument picked up a distinctive echo pattern.

This pattern was characterized by a decrease in echo power followed by a large second echo peak. These two echoes correspond to radar reflections from the Moon’s surface, as well as the floor and ceiling of the open lava tube. When they analyzed this pattern, the research team interpreted it is evidence of a tube. They found similar echo patterns at several locations around the hole, which could indicate that there is more than one lava tube in the region.

To confirm their findings, the team also consulted data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission. Consisting of two spacecraft, this collaborative effort collected high-quality data on the Moon’s gravitational field between 2011 and 2012. By using GRAIL data that identified mass deficits under the surface, which are evidence of caverns, the team was able to narrow down their search.

Jay Melosh, a GRAIL co-investigator and Distinguished Professor of Earth, Atmospheric and Planetary Sciences at Purdue University, was also a co-author on the paper. As he explained:

“They knew about the skylight in the Marius Hills, but they didn’t have any idea how far that underground cavity might have gone. Our group at Purdue used the gravity data over that area to infer that the opening was part of a larger system. By using this complimentary technique of radar, they were able to figure out how deep and high the cavities are.”

Arched passages in the main tube show the classic lava tube shape. The floor was the crust on a former lava lake that fell inward as it drained from beneath. Credit: Dave Bunnell/Under Earth Images/Wikipedia Commons

On Earth, stable lava tubes have been found that can extend for dozens of kilometers. To date, the longest and deepest to be discovered is the Kazumura Cave in Hawaii, which is over a kilometer (3,614 feet) deep and 65.5 km (40.7 mi) long. On the Moon, however, lava tubes are much larger, due to the fact that the Moon has only a fraction of the Earth’s gravity (0.1654 g to be exact).

For a lava tube to be detecting using gravity data, it would need to be several kilometers in length and at least one kilometer in height and width. Since the tube in Marius Hills was detectable, it is likely big enough to house a major city. In fact, during a presentation at the 47th Lunar and Planetary Conference, researchers from Purdue University showed GRAIL data that indicated how the tube beneath the MHH could be large enough to house Philadelphia.

This most recent study was also the subject of a presentation at the 48th Lunar and Planetary Conference. Similar evidence of possible stable lava tubes in the Sea of Tranquility was also obtained by the Lunar Reconnaissance Orbiter (LRO) back in 2010. However, this latest combination of radar and gravity data has provided the clearest picture yet of what a stable lava tube looks like.

Similar evidence of lava tubes has also been discovered on Mars, and possible even Mercury. On Mars in particular,  chains of pit craters, broad lava fans, skylights and partially collapsed lava tubes all indicate the presence of stable tubes. Based on this latest study, future mission to the Red Planet (which could include the creation of a habitat) might also entail the investigation of these features.

In fact, lava tubes could become the means through which a human presence is established throughout the Solar System someday!

Further Reading: Purdue University, Geophysical Research Letters

Posted on by Matt Williams

Metal-Eating Bacteria Could Have Left their “Fingerprints” on Mars, Proving it Once Hosted Life

Future missions could determine the presence of past life on Mars by looking for signs of extreme metal-metabolizing bacteria. Credit: NASA.

Today, there are multiple lines of evidence that indicate that during the Noachian period (ca. 4.1 to 3.7 billion years ago), microorganisms could have existed on the surface of Mars. These include evidence of past water flows, rivers and lakebeds, as well as atmospheric models that indicate that Mars once had a denser atmosphere. All of this adds up to Mars having once been a warmer and wetter place than it is today.

However, to date, no evidence has been found that life ever existed on Mars. As a result, scientists have been trying to determine how and where they should look for signs of past life. According to a new study by a team of European researchers, extreme lifeforms that are capable of metabolizing metals could have existed on Mars in the past. The “fingerprints” of their existence could be found by looking at samples of Mars’ red sands.

For the sake of their study, which recently appeared in the scientific journal Frontiers of Microbiology, the team created a “Mars Farm” to see how a form of extreme bacteria might fare in an ancient Martian environment. This environment was characterized by a comparatively thin atmosphere composed of mainly of carbon dioxide, as well as simulated samples of Martian regolith.

Metallosphaera sedula grown on synthetic Martian Regolith. The microbes are specifically stained by Fluorescence-In-Situ-Hybridization (FISH). Credit: Tetyana Milojevic

They then introduced a strain of bacteria known as Metallosphaera sedula, which thrives in hot, acidic environments. In fact, the bacteria’s optimal conditions are those where temperatures reach 347.1 K (74 °C; 165 °F)  and pH levels are 2.0 (between lemon juice and vinegar). Such bacteria are classified as chemolithotrophs, which means that they are able to metabolize inogranic metals – like iron, sulfur and even uranium.

These stains of bacteria were then added to the samples of regolith that were designed to mimic conditions in different locations and historical periods on Mars. First, there was sample MRS07/22, which consisted of a highly-porous type of rock that is rich in silicates and iron compounds. This sample simulated the kinds of sediments found on the surface of Mars.

Then there was P-MRS, a sample that was rich in hydrated minerals, and the sulfate-rich S-MRS sample, which mimic Martian regolith that was created under acidic conditions. Lastly, there was the sample of JSC 1A, which was largely composed of the volcanic rock known as palagonite. With these samples, the team was able to see exactly how the presence of extreme bacteria would leave biosignatures that could be found today.

As Tetyana Milojevic – an Elise Richter Fellow with the Extremophiles Group at the University of Vienna and a co-author on the paper – explained in a University of Vienna press release:

“We were able to show that due to its metal oxidizing metabolic activity, when given an access to these Martian regolith simulants, M. sedula actively colonizes them, releases soluble metal ions into the leachate solution and alters their mineral surface leaving behind specific signatures of life, a ‘fingerprint’, so to say.”

Microspheroids containing mostly aluminium and chlorine overgrow the mineral surface of synthetic Mars regolith. These microspheroids can only be observed after cultivation of Metallosphaera sedula Credit: Tetyana Milojevic

The team then examined the samples of regolith to see if they had undergone any bioprocessing, which was possible thanks to the assistance of Veronika Somoza – a chemist from the University of Vienna’s Department of Physiological Chemistry and a co-author on the study. Using an electron microscope, combined with analytical spectroscopy technique, the team sought to determine if metals with the samples had been consumed.

In the end, the sets of microbiological and mineralogical data they obtained showed signs of free soluble metals, which indicated that the bacteria had effectively colonized the regolith samples and metabolized some of the metallic minerals within. As Milojevic indicated:

“The obtained results expand our knowledge of biogeochemical processes of possible life beyond Earth, and provide specific indications for detection of biosignatures on extraterrestrial material – a step further to prove potential extra-terrestrial life.”

In effect, this means that extreme bacteria could have existed on Mars billions of years ago. And thanks to the state of Mars today – with its thin atmosphere and lack of precipitation – the biosignatures they left behind (i.e. traces of free soluble metals) could be preserved within Martian regolith. These biosignatures could therefore be detected by upcoming sample-return missions, such as the Mars 2020 rover.

Biotransformed synthetic Martian Regolith after Metallosphaera sedula cultivation. Credit: Tetyana Milojevic

In addition to pointing the way towards possible indications of past life on Mars, this study is also significant as far as the hunt for life on other planets and star systems is concerned. In the future, when we are able to study extra-solar planets directly, scientists will likely be looking for signs of biominerals. Among other things, these “fingerprints” would be a powerful indicator of the existence of extra-terrestrial life (past or present).

Studies of extreme lifeforms and the role they play in the geological history of Mars and other planets is also helpful in advancing our understanding of how life emerged in the early Solar System. On Earth too, extreme bacteria played an important role in turning the primordial Earth into a habitable environment, and play an important role in geological processes today.

Last, but not least, studies of this nature could also pave the way for biomining, a technique where strains of bacteria extract metals from ores. Such a process could be used for the sake of space exploration and resource exploitation, where colonies of bacteria are sent out to mine asteroids, meteors and other celestial bodies.

Further Reading: University of Vienna, Frontiers in Microbiology

Posted on by Matt Williams

Flowing Water on Mars Likely Cold and Frosty, Says New Study

In the past, glaciers may have existed on the surface of Mars, providing meltwater during the summer to create the features we see today. Credit: NASA/Caltech/JPL/UTA/UA/MSSS/ESA/DLR Eric M. De Jong, Ali Safaeinili, Jason Craig, Mike Stetson, Koji Kuramura, John W. Holt

Thanks to decades of exploration using robotic orbiter missions, landers and rovers, scientists are certain that billions of years ago, liquid water flowed on the surface of Mars. Beyond that, many questions have remained, which include whether or not the waterflow was intermittent or regular. In other words, was Mars truly a “warm and wet” environment billions of years ago, or was it more along the lines of “cold and icy”?

These questions have persisted due to the nature of Mars’ surface and atmosphere, which offer conflicitng answers. According to a new study from Brown University, it appears that both could be the case. Basically, early Mars could have had significant amounts of surface ice which experienced periodic melting, producing enough liquid water to carve out the ancient valleys and lakebeds seen on the planet today.

The study, titled “Late Noachian Icy Highlands Climate Model: Exploring the Possibility of Transient Melting and Fluvial/Lacustrine Activity Through Peak Annual and Seasonal Temperatures“, recently appeared in Icarus. Ashley Palumbo – a Ph.D. student with Brown’s Department of Earth, Environmental and Planetary Science – led the study and was joined by her supervising professor (Jim Head) and Professor Robin Wordsworth of Harvard University’s School of Engineering and Applied Sciences.

Extensive valley networks spidering through the southern highlands of Mars suggest that the planet was once warmer and wetter. Credit: NASA/JPL-Caltech/Arizona State University

For the sake of their study, Palumbo and her colleagues sought to find the bridge between Mars’ geology (which suggests the planet was once warm and wet) and its atmospheric models, which suggest it was cold and icy. As they demonstrated, it’s plausible that during the past, Mars was generally frozen over with glaciers. During peak daily temperatures in the summer, these glaciers would melt at the edges to produce flowing water.

After many years, they concluded, these small deposits of meltwater would have been enough to carve the features observed on the surface today. Most notably, they could have carved the kinds of valley networks that have been observed on Mars southern highlands. As Palumbo explained in a Brown University press release, their study was inspired by similar climate dynamics that take place here on Earth:

“We see this in the Antarctic Dry Valleys, where seasonal temperature variation is sufficient to form and sustain lakes even though mean annual temperature is well below freezing. We wanted to see if something similar might be possible for ancient Mars.”

To determine the link between the atmospheric models and geological evidence, Palumbo and her team began with a state-of-the-art climate model for Mars. This model assumed that 4 billion years ago, the atmosphere was primarily composed of carbon dioxide (as it is today) and that the Sun’s output was much weaker than it is now. From this model, they determined that Mars was generally cold and icy during its earlier days.

Nanedi Valles, a roughly 800-kilometre valley extending southwest-northeast and lying in the region of Xanthe Terra, southwest of Chryse Planitia. Credit: ESA/DLR/FU Berlin (G. Neukum)

However, they also included a number of variables which may have also been present on Mars 4 billion years ago. These include the presence of a thicker atmosphere, which would have allowed for a more significant greenhouse effect. Since scientists cannot agree how dense Mars’ atmosphere was between 4.2 and 3.7 billion years ago, Palumbo and her team ran the models to take into account various plausible levels of atmospheric density.

They also considered variations in Mars’ orbit that could have existed 4 billion years ago, which has also been subject to some guesswork. Here too, they tested a wide range of plausible scenarios, which included differences in axial tilt and different degrees of eccentricity. This would have affected how much sunlight is received by one hemisphere over another and led to more significant seasonal variations in temperature.

In the end, the model produced scenarios in which ice covered regions near the location of the valley networks in the southern highlands. While the planet’s mean annual temperature in these scenarios was well below freezing, it also produced peak summertime temperatures in the region that rose above freezing. The only thing that remained was to demonstrate that the volume of water produced would be enough to carve those valleys.

Luckily, back in 2015, Professor Jim Head and Eliot Rosenberg (an undergraduate with Brown at the time) created a study which estimated the minimum amount of water required to produce the largest of these valleys. Using these estimates, along with other studies that provided estimates of necessary runoff rates and the duration of valley network formation, Palumbo and her colleagues found a model-derived scenario that worked.

Was Mars warm and watery (i.e. a blue planet?) or an ice ball that occasionally experienced melting? Credit: Kevin Gill

Basically, they found that if Mars had an eccentricity of 0.17 (compared to it’s current eccentricity of 0.0934) an axial tilt of 25° (compared to 25.19° today), and an atmospheric pressure of 600 mbar (100 times what it is today) then it would have taken about 33,000 to 1,083,000 years to produce enough meltwater to form the valley networks. But assuming for a circular orbit, an axial tile of 25°, and an atmosphere of 1000 mbar, it would have taken about 21,000 to 550,000 years.

The degrees of eccentricity and axial tilt required in these scenarios are well within the range of possible orbits for Mars 4 billion years ago. And as Head indicated, this study could reconcile the atmospheric and geological evidence that has been at odds in the past:

“This work adds a plausible hypothesis to explain the way in which liquid water could have formed on early Mars, in a manner similar to the seasonal melting that produces the streams and lakes we observe during our field work in the Antarctic McMurdo Dry Valleys. We are currently exploring additional candidate warming mechanisms, including volcanism and impact cratering, that might also contribute to melting of a cold and icy early Mars.”

It is also significant in that it demonstrates that Mars climate was subject to variations that also happen regularly here on Earth. This provides yet another indication of how our two plane’s are similar in some ways, and how research of one can help advance our understanding of the other. Last, but not least, it offers some synthesis to a subject that has produced a fair share of disagreement.

The subject of how Mars could have experienced warm, flowing water on its surface – and at a time when the Sun’s output was much weaker than it is today – has remained the subject of much debate. In recent years, researchers have advanced various suggestions as to how the planet could have been warmed, ranging from cirrus clouds to periodic bursts of methane gas from beneath the surface.

While this latest study has not quite settled the debate between the “warm and watery” and the “cold and icy” camps, it does offer compelling evidence that the two may not be mutually exclusive. The study was also the subject of a presentation made at the 48th Lunar and Planetary Science Conference, which took place from March 20th to 24th in The Woodland, Texas.

Further Reading: Brown University, Icarus

Posted on by Matt Williams

Scientists Find Evidence of Extreme Methane Storms On Titan

Titan's atmosphere makes Saturn's largest moon look like a fuzzy orange ball in this natural-color view from the Cassini spacecraft. Cassini captured this image in 2012. Image Credit: NASA/JPL-Caltech/Space Science Institute
According to a study from UCLA, Titan experiences severe methane rainstorms, leading to a the alluvial fans found found in both hemispheres. Credit: NASA/JPL-Caltech/Space Science Institute

Saturn’s largest moon, Titan, is a mysterious place; and the more we learn about it, the more surprises it seems to have in store. Aside from being the only body beyond Earth that has a dense, nitrogen-rich atmosphere, it also has methane lakes on its surface and methane clouds in its atmosphere. This hydrological-cycle, where methane is converted from a liquid to a gas and back again, is very similar to the water cycle here on Earth.

Thanks to the NASA/ESA Cassini-Huygens mission, which concluded on September 15th when the craft crashed into Saturn’s atmosphere, we have learned a great deal about this moon in recent years. The latest find, which was made by a team of UCLA planetary scientists and geologists, has to do with Titan’s methane rain storms. Despite being a rare occurrence, these rainstorms can apparently become rather extreme.

The study which details their findings, titled “Regional Patterns of Extreme Precipitation on Titan Consistent with Observed Alluvial Fan Distribution“, recently appeared in the scientific journal Nature Geoscience. Led by Saun P. Faulk, a graduate student at UCLA’s Department of Earth, Planetary, and Space Sciences, the team conducted simulations of Titan’s rainfall to determine how extreme weather events have shaped the moon’s surface.

Image of Titan’s atmosphere, snapped by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute

What they found was that the extreme methane rainstorms may imprint the moon’s icy surface in much the same way that extreme rainstorms shape Earth’s rocky surface. On Earth, intense rainstorms play an important role in geological evolution. When rainfall is heavy enough, storms can trigger large flows of water that transport sediment into low lands, where it forms cone-shaped features known as alluvial fans.

During it’s mission, the Cassini orbiter found evidence of similar features on Titan using its radar instrument, which suggested that Titan’s surface could be affected by intense rainfall. While these fans are a new discovery, scientists have been studying the surface of Titan ever since Cassini first reached the Saturn system in 2006. In that time, they have noted several interesting features.

These included the vast sand dunes that dominate Titan’s lower latitudes and the methane lakes and seas that dominate it’s higher latitudes – particularly around the  northern polar region. The seas – Kraken Mare, Ligeia Mare, and Punga Mare – measure hundreds of km across and up to several hundred meters deep, and are fed by branching, river-like channels. There are also many smaller, shallower lakes that have rounded edges and steep walls, and are generally found in flat areas.

In this case, the UCLA scientists found that the alluvial fans are predominantly located between 50 and 80 degrees latitude. This puts them close to the center of the northern and southern hemispheres, though slightly closer to the poles than the equator. To test how Titan’s own rainstorms could cause these features, the UCLA team relied on computer simulations of Titan’s hydrological cycle.

False-color mosaic of Titan’s northern lakes, made from infrared data collected by NASA’s Cassini spacecraft. Credit: NASA

What they found was that while rain mostly accumulates near the poles – where Titan’s major lakes and seas are located – the most intense rainstorms occur near 60 degrees latitude. This corresponds to the region where alluvial fans are most heavily concentrated, and indicates that when Titan does experience rainfall, it is quite extreme – like a seasonal monsoon-like downpour.

As Jonathan Mitchell – a UCLA associate professor of planetary science and a senior author of the study – indicated, this is not dissimilar to some extreme weather events that were recently experienced here on Earth. “The most intense methane storms in our climate model dump at least a foot of rain a day, which comes close to what we saw in Houston from Hurricane Harvey this summer,” he said.

The team also found that on Titan, methane rainstorms are rather rare, occurring less than once per Titan year – which works out to 29 and a half Earth years. But according to Mitchell, who is also the principal investigator of UCLA’s Titan climate modeling research group, this is more often than they were expecting. “I would have thought these would be once-a-millennium events, if even that,” he said. “So this is quite a surprise.”

In the past, climate models of Titan have suggested that liquid methane generally concentrates closer to the poles. But no previous study has investigated how precipitation might cause sediment transport and erosion, or shown how this would account for various features observed on the surface. As a result, this study also suggests that regional variations in surface features could be caused by regional variations in precipitation.

On top of that, this study is an indication that Earth and Titan have even more in common than previously thought. On Earth, contrasts in temperature are what lead to intense seasonal weather events. In North America, tornadoes occur during the early to late Spring, while blizzards occur during the winter. Meanwhile, temperature variations in the Atlantic ocean are what lead to hurricanes forming between the summer and fall.

Similarly, it appears that on Titan, serious variations in temperature and moisture are what triggers extreme weather. When cooler, wetter air from the higher latitudes interacts with warmer, drier air from the lower latitudes, intense rainstorms result. These findings are also significant when it comes to other bodies in our Solar System that  have alluvial fans on them – such as Mars.

In the end, understanding the relationship between precipitation and planetary surfaces could lead to new insights about the impact climate change has on Earth and the other planets. Such knowledge would also go a long way towards helping us mitigate the effects it is having here on Earth, where the changes are only unnatural, but also sudden and very hazardous.

And who knows? Someday, it could even help us to alter the environments on other planets and bodies, thus making them more suitable for long-term human settlement (aka. terraforming)!

Further Reading: UCLA, Nature

Posted on by Matt Williams

NASA Undeterred by the Threat of Space Radiation

Artist's impression of the Mars Base Camp in orbit around Mars. When missions to Mars begin, one of the greatest risks will be that posed by space radiation. Credit: Lockheed Martin

When it comes to planning missions to Mars and other distant locations in the Solar System, the threat posed by radiation has become something of an elephant in the room. Whether it is NASA’s proposed “Journey to Mars“, SpaceX’s plans to conduct regular flights to Mars, or any other plan to send crewed missions beyond Low Earth Orbit (LEO), long-term exposure to space radiation and the health risks this poses is an undeniable problem.

But as the old saying goes, “for every problem, there is a solution”; not to mention, “necessity is the mother of invention”. And as representatives from NASA’s Human Research Program recently indicated, the challenge posed by space radiation will not deter the agency from its exploration goals. Between radiation shielding and efforts aimed at mitigation, NASA plans to proceed with mission to Mars and beyond.

Since the beginning of the Space Age, scientists have understood how beyond Earth’s magnetic field, space is permeated by radiation. This includes Galactic Cosmic Rays (GCRs), Solar Particle Events (SPEs) and the Van Allen Radiation Belts, which contains trapped space radiation. Much has also been learned through the ISS, which continues to provide opportunities to study the effects of exposure to space radiation and microgravity.

The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. Credit: ESA/ATG medialab

For instance, though it orbits within Earth’s magnetic field, astronauts receive over ten times the amount of radiation than people experience on average here on Earth. NASA is able to protect crews from SPEs by advising them to seek shelter in more heavily shielded areas of the station – such as the Russian-built Zvezda service module or the US-built Destiny laboratory.

However, GCRs are more of a challenge. These energetic particles, which are primarily composed of high-energy protons and atomic nuclei, can come from anywhere within our galaxy and are capable of penetrating even metal. To make matters worse, when these particles cut through material, they generate a cascade reaction of particles, sending neutrons, protons and other particles in all directions.

This “secondary radiation” can sometimes be a greater risk than the GCRs themselves. And recent studies have indicated that the threat they pose to living tissue can also have a cascading effect, where damage to one cell can then spread to others. As Dr. Lisa Simonsen, a Space Radiation Element Scientist with NASA’s HRP, explained:

“One of the most challenging parts for the human journey to Mars is the risk of radiation exposure and the inflight and long-term health consequences of the exposure. This ionizing radiation travels through living tissues, depositing energy that causes structural damage to DNA and alters many cellular processes.”

To address this risk, NASA is currently evaluating various materials and concepts to shield crews from GCRs. These materials will become an integral part of future deep-space missions. Experiments involving these materials and their incorporation into transport vehicles, habitats and space suits are currently taking place at the NASA Space Radiation Laboratory (NSRL).

At the same time, NASA is also investigating pharmaceutical countermeasures, which could prove to be more effective than radiation shielding. For instance, potassium iodide, diethylenetriamine pentaacietic acid (DTPA) and the dye known as “Prussian blue” have been used for decades to treat radiation sickness. During long-term missions, astronauts will likely need to take daily doses of radiation meds to mitigate exposure to radiation.

Space radiation detection and mitigation technologies are also being developed through NASA’s Advanced Exploration Systems Division. These include the Hybrid Electronic Radiation Assessor for the Orion spacecraft, and a series of personal and operational dosimeters for the ISS. There are also existing instruments which are expected to play an important role when crewed mission to Mars begin.

Who can forget the Radiation Assessment Detector (RAD), which was one of the first instruments sent to Mars for the specific purpose of informing future human exploration efforts. This instrument is responsible for identifying and measuring radiation on the Martian surface, be it radiation from space or secondary radiation produced by cosmic rays interacting with the Martian atmosphere and surface.

Artist depiction of a rover on the surface of Mars. Researchers are developing shielding concepts for transport vehicles, habitats and space suits to protect future astronauts on a journey to Mars. Credits: NASA

Because of these and other preparations, many at NASA are naturally hopeful that the risks of space radiation can and will be addressed. As Pat Troutman, the NASA Human Exploration Strategic Analysis Lead, stated in a recent NASA press statement:

“Some people think that radiation will keep NASA from sending people to Mars, but that’s not the current situation. When we add the various mitigation techniques up, we are optimistic it will lead to a successful Mars mission with a healthy crew that will live a very long and productive life after they return to Earth.

Scientists are also engaged in ongoing studies of space weather in order to develop better forecasting tools and countermeasures. Last, but not least, multiple organizations are looking to develop smaller, faster spacecraft in order to reduce travel times (and hence, exposure to radiation). Taken together, all of these strategies are necessary for long-duration spaceflights to Mars and other locations throughout the Solar System.

Granted, there is still considerable research that needs to be done before we can say with any certainty that crewed missions to Mars and beyond will be safe, or at least not pose any unmanageable risks. But the fact that NASA is busy addressing these needs from multiple angles demonstrates how committed they are to seeing such a mission happen in the coming decades.

Artist’s impression of the the Interplanetary Spacecraft approaching Mars. Credit: SpaceX

“Mars is the best option we have right now for expanding long-term, human presence,” said Troutman. “We’ve already found valuable resources for sustaining humans, such as water ice just below the surface and past geological and climate evidence that Mars at one time had conditions suitable for life. What we learn about Mars will tell us more about Earth’s past and future and may help answer whether life exists beyond our planet.”

Beyond NASA, Roscosmos, the Chinese National Space Agency (CSNA) have also expressed interest in conducting crewed mission to the Red Planet, possibly between the 2040s or as late as the 2060s. While the European Space Agency (ESA) has no active plans for sending astronauts to Mars, they see the establishment of an International Lunar Village as a major step towards that goal.

Beyond the public sector, companies like SpaceX and non-profits like MarsOne are also investigating possible strategies for protecting and mitigating against space radiation. Elon Musk has been quite vocal (especially of late) about his plans to conduct regular trips to Mars in the near future using the Interplanetary Transport System (ITS) – also known as the BFR – not to mention establishing a colony on the planet.

And Baas Landsdorp has indicated that the organization he founded to establish a human presence on Mars will find ways to address the threat posed by radiation, regardless of what a certain report from MIT says! Regardless of the challenges, there is simply no shortage of people who want to see humanity go to Mars, and possibly even stay there!

And be sure to check out this video about the Human Research Program, courtesy of NASA:

Further Reading: NASA

Posted on by Matt Williams

Astronomers Find the Missing Normal Matter in the Universe, Still Looking for Dark Matter, Though

The structure of the universe at the largest scale. Credit: NASA, ESA, and E. Hallman (University of Colorado, Boulder)

For decades, the predominant cosmological model used by scientists has been based on the theory that in addition to baryonic matter – aka. “normal” or “luminous” matter, which we can see – the Universe also contains a substantial amount of invisible mass. This “Dark Matter” accounts for roughly 26.8% of the mass of the Universe, whereas normal matter accounts for just 4.9%.

While the search for Dark Matter is ongoing and direct evidence is yet to be found, scientists have also been aware that roughly 90% of the Universe’s normal matter still remained undetected. According to two new studies that were recently published, much of this normal matter – which consists of filaments of hot, diffuse gas that links galaxies together – may have finally been found.

The first study, titled “A Search for Warm/Hot Gas Filaments Between Pairs of SDSS Luminous Red Galaxies“, appeared in the Monthly Notices of the Royal Astronomic Society. The study was led by Hideki Tanimura, a then-PhD candidate at the University of British Columbia, and included researchers from the Canadian Institute for Advanced Research (CIFAR), the Liverpool John Moores University and the University of KwaZulu-Natal.

All-sky data obtained by the ESA’s Planck mission, showing the different wavelenghts. Credit: ESA

The second study, which recently appeared online, was titled “Missing Baryons in the Cosmic Web Revealed by the Sunyaev-Zel’dovich Effect“. This team consisted of researchers from the University of Edinburgh and was led Anna de Graaff, a undergraduate student from the Institute for Astronomy at Edinburgh’s Royal Observatory. Working independently of each other, these two team tackled a problem of the Universe’s missing matter.

Based on cosmological simulations, the predominant theory has been that the previously-undetected normal matter of the Universe consists of strands of baryonic matter – i.e. protons, neutrons and electrons – that is floating between galaxies. These regions are what is known as the “Cosmic Web”, where low density gas exists at a temperatures of 105 to 107 K (-168 t0 -166 °C; -270 to 266 °F).

For the sake of their studies, both teams consulted data from the Planck Collaboration, a venture maintained by the European Space Agency that includes all those who contributed to the Planck mission (ESA). This was presented in 2015, where it was used to create a thermal map of the Universe by measuring the influence of the Sunyaev-Zeldovich (SZ) effect.

This effect refers to a spectral distortion in the Cosmic Microwave Background, where photons are scattered by ionized gas in galaxies and larger structures. During its mission to study the cosmos, the Planck satellite measured the spectral distortion of CMB photons with great sensitivity, and the resulting thermal map has since been used to chart the large-scale structure of the Universe.

IR map of the whole Galaxy showing the plane and bulge of the Galaxy full of stars and dust. Credit: SDSS

However, the filaments between galaxies appeared too faint for scientists to examine at the time. To remedy this, the two teams consulted data from the North and South CMASS galaxy catalogues, which were produced from the 12th data release of the Sloan Digital Sky Survey (SDSS). From this data set, they then selected pairs of galaxies and focused on the space between them.

They then stacked the thermal data obtained by Planck for these areas on top of each other in order to strengthen the signals caused by SZ effect between galaxies. As Dr. Hideki told Universe Today via email:

“The SDSS galaxy survey gives a shape of the large-scale structure of the Universe. The Planck observation provides an all-sky map of gas pressure with a better sensitivity. We combine these data to probe the low-dense gas in the cosmic web.”

While Tanimura and his team stacked data from 260,000 galaxy pairs, de Graaff and her team stacked data from over a million. In the end, the two teams came up with strong evidence of gas filaments, though their measurements differed somewhat. Whereas Tanimura’s team found that the density of these filaments was around three times the average density in the surrounding void, de Graaf and her team found that they were six times the average density.

“We detect the low-dense gas in the cosmic web statistically by a stacking method,” said Hideki. “The other team uses almost the same method. Our results are very similar. The main difference is that we are probing a nearby Universe, on the other hand, they are probing a relatively farther Universe.”

This illustration shows the evolution of the Universe, from the Big Bang on the left, to modern times on the right. Image: NASA

This particular aspect of particularly interesting, in that it hints that over time, baryonic matter in the Cosmic Web has become less dense. Between these two results, the studies accounted for between 15 and 30% of the total baryonic content of the Universe. While that would mean that a significant amount of the Universe’s baryonic matter still remains to be found, it is nevertheless an impressive find.

As Hideki explained, their results not only support the current cosmological model of the Universe (the Lambda CDM model) but also goes beyond it:

“The detail in our universe is still a mystery. Our results shed light on it and reveals a more precise picture of the Universe. When people went out to the ocean and started making a map of our world, it was not used for most of the people then, but we use the world map now to travel abroad. In the same way, a map of the entire universe may not be valuable now because we do not have a technology to go far out to the space. However, it could be valuable 500 years later. We are in the first stage of making a map of the entire Universe.”

It also opens up opportunities for future studies of the Comsic Web, which will no doubt benefit from the deployment of next-generation instruments like James Webb Telescope, the Atacama Cosmology Telescope and the Q/U Imaging ExperimenT (QUIET). With any luck, they will be able to spot the remaining missing matter. Then, perhaps we can finally zero in on all the invisible mass!

Further Reading: MNRAS, arXiv,

Posted on by Matt Williams

Debris Disks Around Stars Could Point the Way to Giant Exoplanets

This artist's rendering shows a large exoplanet causing small bodies to collide in a disk of dust. Credit: NASA/JPL-Caltech

According to current estimates, there could be as many as 100 billion planets in the Milky Way Galaxy alone. Unfortunately, finding evidence of these planets is tough, time-consuming work. For the most part, astronomers are forced to rely on indirect methods that measure dips in a star’s brightness (the Transit Method) of Doppler measurements of the star’s own motion (the Radial Velocity Method).

Direct imaging is very difficult because of the cancelling effect stars have, where their brightness makes it difficult to spot planets orbiting them. Luckily a new study led by the Infrared Processing and Analysis Center (IPAC) at Caltech has determined that there may be a shortcut to finding exoplanets using direct imaging. The solution, they claim, is to look for systems with a circumstellar debris disk, for they are sure to have at least one giant planet.

The study, titled “A Direct Imaging Survey of Spitzer Detected Debris Disks: Occurrence of Giant Planets in Dusty Systems“, recently appeared in The Astronomical Journal. Tiffany Meshkat, an assistant research scientist at IPAC/Caltech, was the lead author on the study, which she performed while working at NASA’s Jet Propulsion Laboratory as a postdoctoral researcher.

A circumstellar disk of debris around a mature stellar system could indicate the presence of Earth-like planets. Credit: NASA/JPL
Artist’s impression of circumstellar disk of debris around a distant star. Credit: NASA/JPL

For the sake of this study, Dr. Meshkat and her colleagues examined data on 130 different single-star systems with debris disks, which they then compared to 277 stars that do not appear to host disks. These stars were all observed by NASA’s Spitzer Space Telescope and were all relatively young in age (less than 1 billion years). Of these 130 systems, 100 had previously been studied for the sake of finding exoplanets.

Dr. Meshkat and her team then followed up on the remaining 30 systems using data from the W.M. Keck Observatory in Hawaii and the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile. While they did not detect any new planets in these systems, their examinations helped characterize the abundance of planets in systems that had disks.

What they found was that young stars with debris disks are more likely to also have giant exoplanets with wide orbits than those that do not. These planets were also likely to have five times the mass of Jupiter, thus making them “Super-Jupiters”. As Dr. Meshkat explained in a recent NASA press release, this study will be of assistance when it comes time for exoplanet-hunters to select their targets:

“Our research is important for how future missions will plan which stars to observe. Many planets that have been found through direct imaging have been in systems that had debris disks, and now we know the dust could be indicators of undiscovered worlds.”

This artist’s conception shows how collisions between planetesimals can create additional debris. Credit: NASA/JPL-Caltech

This study, which was the largest examination of stars with dusty debris disks, also provided the best evidence to date that giant planets are responsible for keeping debris disks in check. While the research did not directly resolve why the presence of a giant planet would cause debris disks to form, the authors indicate that their results are consistent with predictions that debris disks are the products of giant planets stirring up and causing dust collisions.

In other words, they believe that the gravity of a giant planet would cause planestimals to collide, thus preventing them from forming additional planets. As study co-author Dimitri Mawet, who is also a JPL senior research scientist, explained:

“It’s possible we don’t find small planets in these systems because, early on, these massive bodies destroyed the building blocks of rocky planets, sending them smashing into each other at high speeds instead of gently combining.”

Within the Solar System, the giant planets create debris belts of sorts. For example, between Mars and Jupiter, you have the Main Asteroid Belt, while beyond Neptune lies the Kuiper Belt. Many of the systems examined in this study also have two belts, though they are significantly younger than the Solar System’s own belts – roughly 1 billion years old compared to 4.5 billion years old.

Artist’s impression of Beta Pictoris b. Credit: ESO L. Calçada/N. Risinger (skysurvey.org)

One of the systems examined in the study was Beta Pictoris, a system that has a debris disk, comets, and one confirmed exoplanet. This planet, designated Beta Pictoris b, which has 7 Jupiter masses and orbits the star at a distance of 9 AUs – i.e. nine times the distance between the Earth and the Sun. This system has been directly imaged by astronomers in the past using ground-based telescopes.

Interestingly enough, astronomers predicted the existence of this exoplanet well before it was confirmed, based on the presence and structure of the system’s debris disk. Another system that was studied was HR8799, a system with a debris disk that has two prominent dust belts. In these sorts of systems, the presence of more giant planets is inferred based on the need for these dust belts to be maintained.

This is believed to be case for our own Solar System, where 4 billion years ago, the giant planets diverted passing comets towards the Sun. This resulted in the Late Heavy Bombardment, where the inner planets were subject to countless impacts that are still visible today. Scientists also believe that it was during this period that the migrations of Jupiter, Saturn, Uranus and Neptune deflected dust and small bodies to form the Kuiper Belt and Asteroid Belt.

Dr. Meshkat and her team also noted that the systems they examined contained much more dust than our Solar System, which could be attributable to their differences in age. In the case of systems that are around 1 billion years old, the increased presence of dust could be the result of small bodies that have not yet formed larger bodies colliding. From this, it can be inferred that our Solar System was once much dustier as well.

Artist’s concept of the multi-planet system around HR 8799, initially discovered with Gemini North adaptive optics images. Credit: Gemini Observatory/Lynette Cook”

However, the authors note is also possible that the systems they observed – which have one giant planet and a debris disk – may contain more planets that simply have not been discovered yet. In the end, they concede that more data is needed before these results can be considered conclusive. But in the meantime, this study could serve as an guide as to where exoplanets might be found.

As Karl Stapelfeldt, the chief scientist of NASA’s Exoplanet Exploration Program Office and a co-author on the study, stated:

“By showing astronomers where future missions such as NASA’s James Webb Space Telescope have their best chance to find giant exoplanets, this research paves the way to future discoveries.”

In addition, this study could help inform our own understanding of how the Solar System evolved over the course of billions of years. For some time, astronomers have been debating whether or not planets like Jupiter migrated to their current positions, and how this affected the Solar System’s evolution. And there continues to be debate about how the Main Belt formed (i.e. empty of full).

Last, but not least, it could inform future surveys, letting astronomers know which star systems are developing along the same lines as our own did, billions of years ago. Wherever star systems have debris disks, they an infer the presence of a particularly massive gas giant. And where they have a disk with two prominent dust belts, they can infer that it too will become a system containing many planets and and two belts.

Further Reading: NASA, The Astrophysical Journal

Posted on by Matt Williams

Ancient Hydrothermal Vents Found on Mars, Could Have Been a Cradle for Life

MOLA topographic data, colorized to show the maximum (1,100?m) and minimum (700?m) level of an ancient sea. Credit: NASA/Joseph R. Michalski (et al.)/Nature Communications

It is now a well-understood fact that Mars once had quite a bit of liquid water on its surface. In fact, according to a recent estimate, a large sea in Mars’ southern hemisphere once held almost 10 times as much water as all of North America’s Great Lakes combined. This sea existed roughly 3.7 billion years ago, and was located in the region known today as the Eridania basin.

However, a new study based on data from NASA’s Mars Reconnaissance Orbiter (MRO) detected vast mineral deposits at the bottom of this basin, which could be seen as evidence of ancient hot springs. Since this type of hydrothermal activity is believed to be responsible for the emergence of life on Earth, these results could indicate that this basin once hosted life as well.

The study, titled “Ancient Hydrothermal Seafloor Deposits in Eridania Basin on Mars“, recently appeared in the scientific journal Nature Communications. The study was led by Joseph Michalski of the Department of Earth Sciences and Laboratory for Space Research at the University of Hong Kong, along with researchers from the Planetary Science Institute, the Natural History Museum in London, and NASA’s Johnson Space Center.

 

The Eridania basin of southern Mars is believed to have held a sea about 3.7 billion years ago, with seafloor deposits likely resulting from underwater hydrothermal activity. Credit: NASA

Together, this international team used data obtained by the MRO’s Compact Reconnaissance Spectrometer for Mars (CRISM). Since the MRO reached Mars in 2006, this instrument has been used extensively to search for evidence of mineral residues that form in the presence of water. In this respect, CRISM was essential for documenting how lakes, ponds and rivers once existed on the surface of Mars.

In this case, it identified massive mineral deposits within Mars’ Eridania basin, which lies in a region that has some of the Red Planet’s most ancient exposed crust. The discovery is expected to be a major focal point for scientists seeking to characterize Mars’ once-warm and wet environment. As Paul Niles of NASA’s Johnson Space Center said in a recent NASA press statement:

“Even if we never find evidence that there’s been life on Mars, this site can tell us about the type of environment where life may have begun on Earth. Volcanic activity combined with standing water provided conditions that were likely similar to conditions that existed on Earth at about the same time — when early life was evolving here.”

Today, Mars is a cold, dry place that experiences no volcanic activity. But roughly 3.7 billion years ago, the situation was vastly different. At that time, Mars boasted both flowing and standing bodies of water, which are evidenced by vast fluvial deposits and sedimentary basins. The Gale Crater is a perfect example of this since it was once a major lake bed, which is why it was selected as the landing sight for the Curiosity rover in 2012.

Illustrates showing the origin of some deposits in the Eridania basin of southern Mars resulting from seafloor hydrothermal activity more than 3 billion years ago. Credit: NASA

Since Mars had both surface water and volcanic activity during this time, it would have also experienced hydrothermal activity. This occurs when volcanic vents open into standing bodies of water, filling them with hydrated minerals and heat. On Earth, which still has an active crust, evidence of past hydrothermal activity cannot be preserved. But on Mars, where the crust is solid and erosion is minimal, the evidence has been preserved.

“This site gives us a compelling story for a deep, long-lived sea and a deep-sea hydrothermal environment,” Niles said. “It is evocative of the deep-sea hydrothermal environments on Earth, similar to environments where life might be found on other worlds — life that doesn’t need a nice atmosphere or temperate surface, but just rocks, heat and water.”

Based on their study, the researchers estimate that the Eridania basin once held about 210,000 cubic km (50,000 cubic mi) of water. Not only is this nine times more water than all of the Great Lakes combined, it is as much as all the other lakes and seas on ancient Mars combined. In addition, the region also experienced lava flows that existed  after the sea is believed to have disappeared.

From the CRISM’s spectrometer data, the team identified deposits of serpentine, talc and carbonate. Combined with the shape and texture of the bedrock layers, they concluded that the sea floor was open to volcanic fissures. Beyond indicating that this region could have once hosted life, this study also adds to the diversity of the wet environments which are once believed to have existed on Mars.

A scale model compares the volume of water contained in lakes and seas on the Earth and Mars to the estimated volume of water contained in an ancient Eridania sea. Credit: JJoseph R. Michalski (et al.)/Nature Communications

Between evidence of ancient lakes, rivers, groundwater, deltas, seas, and volcanic eruptions beneath ice, scientists now have evidence of volcanic activity that occurred beneath a standing body of water (aka. hot springs) on Mars. This also represents a new category for astrobiological research, and a possible destination for future missions to the Martian surface.

The study of hydrothermal activity is also significant as far as finding sources of extra-terrestrial, like on the moons of Europa, Enceladus, Titan, and elsewhere. In the future, robotic missions are expected to travel to these worlds in order to peak beneath their icy surfaces, investigate their plumes, or venture into their seas (in Titan’s case) to look for the telltale traces of basic life forms.

The study also has significance beyond Mars and could aid in the study of how life began here on Earth. At present, the earliest evidence of terrestrial life comes from seafloor deposits that are similar in origin and age to those found in the Eridania basin. But since the geological record of this period on Earth is poorly preserved, it has been impossible to determine exactly what conditions were like at this time.

Given Mars’ similarities with Earth, and the fact that its geological record has been well-preserved over the past 3 billion years, scientists can look to mineral deposits and other evidence to gauge how natural processes here on Earth allowed for life to form and evolve over time. It could also advance our understanding of how all the terrestrial planets of the Solar System evolved over billions of years.

Further Reading: NASA

Posted on by Matt Williams

This Meteorite Came From a Volcano on Mars

A sample of nakhlite, a type of volcanic terrain that came to Earth as a Martian meteorite. Credit: University of Glasgow

Today, it is well understood that Mars is a cold, dry, and geologically dead planet. However, billions of years ago when it was still young, the planet boasted a denser atmosphere and had liquid water on its surface. Millions of years ago, it also experienced a significant amount of volcanic activity, which resulted in the formation of it’s massive features – like Olympus Mons, the largest volcano in the Solar System.

Until recently, scientists have understood that Martian volcanic activity has been driven by sources other than tectonic movement, which the planet has been devoid of for billions of years. However, after conducting a study of Martian rock samples, a team of researchers from the UK and United States concluded that eons ago, Mars was more volcanically active than previously thought.

Their study, titled “Taking the Pulse of Mars via Dating of a Plume-fed Volcano“, recently appeared in the scientific journal Nature Communications. Led by Benjamin Cohen, a researcher with the Scottish Universities Environmental Research Center (SUERC) and the School of Geographical and Earth Sciences at the University of Glasgow, the team conducted an analysis of Mars’ volcanic past using samples of Martian meteorites.

Asteroid impacts on Mars have sent samples of Martian rock to Earth in the form of meteorites. Credit: geol.umd.edu

On Earth, the majority of volcanism occurs as a result of plate tectonics, which are driven by convection in the Earth’s mantle. But on Mars, the majority of volcanic activity is the result of mantle plumes, which are highly-localized upwellings of magma that rise from deep within the mantle. This is due to the fact that Mars’ surface has remained static and cool for the past few billion years.

Because of this, Martian volcanoes (though similar in morophology to shield volcanoes on Earth), grow to much larger sizes than those on Earth. Olympus Mons, for example, is not only the largest shield volcano on Mars, but the largest in the Solar System. Whereas the tallest mountain on Earth – Mt. Everest – is 8,848 m (29,029 ft) in height, Olympus Mons stands some 22 km (13.6 mi or 72,000 ft) tall.

For the sake of their study, Dr. Cohen and his colleagues used radioscopic dating techniques, which are commonly used to determine the age and eruption rate of volcanoes on Earth. However, such techniques have not been previously used for shield volcanoes on Mars. As a result, the team’s study of Martian meteorite samples was the first detailed analysis of growth rates in Martian volcanoes.

The six samples they examined are known as nakhlites, a class of Martian meteorite that formed from basaltic magma roughly 1.3 billion years ago. These came to Earth roughly 11 million years ago after being were blasted from the face of Mars by an impact event. By conducting an analysis of Martian meteorites, the team was able to uncover about 90 million years’ worth of new information about Mars’ volcanic past.

Color Mosaic of Olympus Mons on Mars
Color mosaic of Mars’ greatest mountain, Olympus Mons, viewed from orbit. Credit NASA/JPL

As Dr. Cohen explained in a University of Glasgow press release:

“We know from previous studies that the nakhlite meteorites are volcanic rocks, and the development of age-dating techniques in recent years made the nakhlites perfect candidates to help us learn more about volcanoes on Mars.”

The first step was to demonstrate that the rock samples were indeed Martian in origin, which the team confirmed by measuring their exposure to cosmogenic radiation. From this, they determined that the rocks were expelled from the Martian surface 11 million years ago, most likely as a result of an impact event on the Martian surface. They then applied a high-precision radioscopic technique known as 40Ar/39Ar dating.

This consisted of using a noble gas mass spectromomer to measure the amount of argon built up in the samples, which is the result of the natural radioactive decay of potassium. From this, they were able to obtain 90 million years’ worth of new information about the Martian surface. The results of their analysis indicated that there are significant differences in volcanic history between the Earth and Mars. As Dr. Cohen explained:

“We found that the nakhlites formed from at least four eruptions over the course of 90 million years. This is a very long time for a volcano, and much longer than the duration of terrestrial volcanoes, which are typically only active for a few million years. And this is only scratching the surface of the volcano, as only a very small amount of rock would have been ejected by the impact crater – so the volcano must have been active for much longer.”

A triple crater in Elysium Planitia on Mars. Credit: NASA/JPL/University of Arizona

In addition, the team was also able to narrow down which volcanoes their rock samples came from. Previous studies conducted by NASA revealed several candidates for the possible nakhlite source crater. However, only one of the locations matched their results in terms of the age of the volcanic eruptions and the impact that would have ejected the samples into space.

This particular crater (which is currently unnamed) is located in the volcanic plains known as Elysium Planitia, roughly 900 km (560 mi) away from summit of the Elysium Mons volcano  – which stands 12.6 km (7.8 mi) tall. It is also located about 2000 km (1243 mi) north of where the NASA Curiosity rover currently is. As Cohen explained, NASA has some wonderfully detailed satellite images of this particular crater.

“It is 6.5 km wide, and has preserved ejecta rays of debris,” he said. “And we were able to see multiple horizontal bands on the crater walls – which indicating the rocks form layers, with each layer interpreted as a separate lava flow. This study has been able to provide a clearer picture into the history of the nakhlite meteorites, and in turn the largest volcanoes in the solar system.”

In the future, sample return and crewed missions to Mars are sure to clear up this picture even further. Given that Mars, like Earth, is a terrestrial planet, knowing all we can about its geological history will ultimately improve our understanding of how the rocky planets of the Solar System formed. In short, the more we know about Mars’ volcanic history, the most we will be able to learn about the Solar System’s formation and evolution.

Further Reading: University of Glasgow, Nature Communications

 

Posted on by Matt Williams

Scientist Find Treasure Trove of Giant Black Hole Pairs

In February 2016, LIGO detected gravity waves for the first time. As this artist's illustration depicts, the gravitational waves were created by merging black holes. The third detection just announced was also created when two black holes merged. Credit: LIGO/A. Simonnet.
Artist's impression of merging binary black holes. Credit: LIGO/A. Simonnet.

For decades, astronomers have known that Supermassive Black Holes (SMBHs) reside at the center of most massive galaxies. These black holes, which range from being hundreds of thousands to billions of Solar masses, exert a powerful influence on surrounding matter and are believed to be the cause of Active Galactic Nuclei (AGN). For as long as astronomers have known about them, they have sought to understand how SMBHs form and evolve.

In two recently published studies, two international teams of researchers report on the discovery of five newly-discovered black hole pairs at the centers of distant galaxies. This discovery could help astronomers shed new light on how SMBHs form and grow over time, not to mention how black hole mergers produce the strongest gravitational waves in the Universe.

The first four dual black hole candidates were reported in a study titled “Buried AGNs in Advanced Mergers: Mid-Infrared Color Selection as a Dual AGN Finder“, which was led by Shobita Satyapal, a professor of astrophysics at George Mason University. This study was accepted for publication in The Astrophysical Journal and recently appeared online.

Optical and x-ray data on two of the new black hole pairs discovered. Credit: NASA/CXC/Univ. of Victoria/S.Ellison et al./George Mason Univ./S.Satyapal et al./SDSS

The second study, which reported the fifth dual black hole candidate, was led by Sarah Ellison – an astrophysics professor at the University of Victoria. It was recently published in the Monthly Notices of the Royal Astronomical Society under the title “Discovery of a Dual Active Galactic Nucleus with ~8 kpc Separation“. The discovery of these five black hole pairs was very fortuitous, given that pairs are a very rare find.

As Shobita Satyapal explained in a Chandra press statement:

“Astronomers find single supermassive black holes all over the universe. But even though we’ve predicted they grow rapidly when they are interacting, growing dual supermassive black holes have been difficult to find.“

The black hole pairs were discovered by combining data from a number of different ground-based and space-based instruments. This included optical data from the Sloan Digital Sky Survey (SDSS) and the ground-based Large Binocular Telescope (LBT) in Arizona with near-infrared data from the Wide-Field Infrared Survey Explorer (WISE) and x-ray data from NASA’s Chandra X-ray Observatory.

For the sake of their studies, Satyapal, Ellison, and their respective teams sought to detect dual AGNs, which are believed to be a consequence of galactic mergers. They began by consulting optical data from the SDSS to identify galaxies that appeared to be in the process of merging. Data from the all-sky WISE survey was then used to identify those galaxies that displayed the most powerful AGNs.

Illustration of a pair of black holes. Credit: NASA/CXC/A.Hobart

They then consulted data from the Chandra’s Advanced CCD Imaging Spectrometer (ACIS) and the LBT to identify seven galaxies that appeared to be in an advanced stage of merger. The study led by Ellison also relied on optical data provided by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey to pinpoint one of the new black hole pairs.

From the combined data, they found that five out of the seven merging galaxies hosted possible dual AGNs, which were separated by less than 10 kiloparsecs (over 30,000 light years). This was evidenced by the infrared data provided by WISE, which was consistent with what is predicated of rapidly growing supermassive black holes.

In addition, the Chandra data showed closely-separated pairs of x-ray sources, which is also consistent with black holes that have matter slowly being accreted onto them. This infrared and x-ray data also suggested that the supermassive black holes are buried in large amounts of dust and gas. As Ellison indicated, these findings were the result of painstaking work that consisted of sorting through multiple wavelengths of data:

“Our work shows that combining the infrared selection with X-ray follow-up is a very effective way to find these black hole pairs. X-rays and infrared radiation are able to penetrate the obscuring clouds of gas and dust surrounding these black hole pairs, and Chandra’s sharp vision is needed to separate them”.

Artist’s impression of binary black hole system in the process of merging. Credit: Bohn et al.

Before this study, less than ten pairs of growing black holes had been confirmed based on X-ray studies, and these were mostly by chance. This latest work, which detected five black hole pairs using combined data, was therefore both fortunate and significant. Aside from bolstering the hypothesis that supermassive black holes form from the merger of smaller black holes, these studies also have serious implications for gravitational wave research.

“It is important to understand how common supermassive black hole pairs are, to help in predicting the signals for gravitational wave observatories,” said Satyapa. “With experiments already in place and future ones coming online, this is an exciting time to be researching merging black holes. We are in the early stages of a new era in exploring the universe.”

Since 2016, a total of four instances of gravitational waves have been detected by instruments like the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the VIRGO Observatory. However, these detections were the result of black hole mergers where the black holes were all smaller and less massive  – between eight and 36 Solar masses.

Supermassive Black Holes, on the other hand, are much more massive and will likely produce a much larger gravitational wave signature as they continue to draw closer together. And in a few hundred million years, when these pairs eventually do merge, the resulting energy produced by mass being converted into gravitational waves will be incredible.

Artist’s conception of two merging black holes, similar to those detected by LIGO on January 4th, 2017. Credit: LIGO/Caltech

At present, detectors like LIGO and Virgo are not able to detect the gravitational waves created by Supermassive Black Hole pairs. This work is being done by arrays like the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), which relies on high-precision millisecond pulsars to measure the influence of gravitational waves on space-time.

The proposed Laser Interferometer Space Antenna (LISA), which will be the first dedicated space-based gravitational wave detector, is also expected to help in the search. In the meantime, gravitational wave research has already benefited immensely from collaborative efforts like the one that exists between Advanced LIGO and Advanced Virgo.

In the future, scientists also anticipate that they will be able to study the interiors of supernovae through gravitational wave research. This is likely to reveal a great deal about the mechanisms behind black hole formation. Between all of these ongoing efforts and future developments, we can expect to “hear” a great deal more of the Universe and the most powerful forces at work within it.

Be sure to check out this animation that shows what the eventual merger of two of these black hole pairs will look like, courtesy of the Chandra X-ray Observatory:

Further Reading: Chandra Harvard, arXiv, MNRAS