We recently observed the strongest magnetic field ever recorded in the Universe. The record-breaking field was discovered at the surface of a neutron star called GRO J1008-57 with a magnetic field strength of approximately 1 BILLION Tesla. For comparison, the Earth’s magnetic field clocks in at about 1/20,000 of a Tesla – tens of trillions of times weaker than you’d experience on this neutron star…and that is a good thing for your general health and wellbeing.
Neutron stars are the “dead cores” of once massive stars which have ended their lives as supernova. These stars exhausted their supply of hydrogen fuel in their core and a power balance between the internal energy of the star surging outward, and the star’s own massive gravity crushing inward, is cataclysmically unbalanced – gravity wins. The star collapses in on itself. The outer layers fall onto the core crushing it into the densest object we know of in the Universe – a neutron star. Even atoms are crushed. Negatively charged electrons are forced into the atomic nuclei meeting their positive proton counterparts creating more neutrons. When the core can be crushed no further, the outer remaining material of the star rebounds back into space in a massive explosion – a supernova. The resulting neutron star, made of the crushed stellar core, is so dense that a single sugar-cube-sized sampling would weigh billions of tons – as much as a mountain (though if you’re “worthy” you MIGHT able to lift it since Thor’s Hammer is made of the stuff). Neutron stars are typically about 20km in diameter and can still be a million degrees Kelvin at the surface.
But if they’re “dead,” how can neutron stars be some of the most magnetic and powerful objects in the Universe?
If you’ve ever used a compass, you know that the magnetic needle always points North. Well, almost North. If you just happen to be out camping for the weekend, the difference doesn’t matter. For scientists studying the Earth’s interior, the difference is important. How Earth’s magnetic field changes over time give us clues about how our planet generates a magnetic field in the first place.
The North Pole ain’t what it used to be. Well, the geographic North Pole stays fixed over time (mostly because we define it to stay fixed over time) but the magnetic north pole constantly moves. And over the past decade it’s been moving out of Canada towards Siberia four times faster than it has in the past couple centuries. Armed with data from the ESA’s Swarm satellite, scientists might finally know why: the shifting of our magnetic field north pole is caused by a titanic struggle between two competing massive magnetic plumes.
When NASA’s Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (Insight) lander set down on Mars in November of 2018, it began its two-year primary mission of studying Mars’ seismology and interior environment. And now, just over a year and a half later, the results of the lander’s first twelve months on the Martian surface have been released in a series of studies.
One of these studies, which was recently published in the journal Nature Geosciences, shared some rather interesting finds about magnetic fields on Mars. According to the research team behind it, the magnetic field within the crater where InSight’s landed is ten times stronger than expected. These findings could help scientists resolve key mysteries about Mars’ formation and subsequent evolution.
For decades, scientists have held that the Earth-Moon system formed as a result of a collision between Earth and a Mars-sized object roughly 4.5 billion years ago. Known as the Giant Impact Hypothesis, this theory explains why Earth and the Moon are similar in structure and composition. Interestingly enough, scientists have also determined that during its early history, the Moon had a magnetosphere – much like Earth does today.
However, a new study led by researchers at MIT (with support provided by NASA) indicates that at one time, the Moon’s magnetic field may have actually been stronger than Earth’s. They were also able to place tighter constraints on when this field petered out, claiming it would have happened about 1 billion years ago. These findings have helped resolve the mystery of what mechanism powered the Moon’s magnetic field over time.
For many reasons, Venus is sometimes referred to as “Earth’s Twin” (or “Sister Planet”, depending on who you ask). Like Earth, it is terrestrial (i.e. rocky) in nature, composed of silicate minerals and metals that are differentiated between an iron-nickel core and silicate mantle and crust. But when it comes to their respective atmospheres and magnetic fields, our two planets could not be more different.
For some time, astronomers have struggled to answer why Earth has a magnetic field (which allows it to retain a thick atmosphere) and Venus do not. According to a new study conducted by an international team of scientists, it may have something to do with a massive impact that occurred in the past. Since Venus appears to have never suffered such an impact, its never developed the dynamo needed to generate a magnetic field.
The study, titled “Formation, stratification, and mixing of the cores of Earth and Venus“, recently appeared in the scientific journal Earth and Science Planetary Letters. The study was led by Seth A. Jacobson of Northwestern University, and included members from the Observatory de la Côte d’Azur, the University of Bayreuth, the Tokyo Institute of Technology, and the Carnegie Institution of Washington.
For the sake of their study, Jacobson and his colleagues began considering how terrestrial planets form in the first place. According to the most widely-accepted models of planet formation, terrestrial planets are not formed in a single stage, but from a series of accretion events characterized by collisions with planetesimals and planetary embryos – most of which have cores of their own.
Recent studies on high-pressure mineral physics and on orbital dynamics have also indicated that planetary cores develop a stratified structure as they accrete. The reason for this has to do with how a higher abundance of light elements are incorporated in with liquid metal during the process, which would then sink to form the core of the planet as temperatures and pressure increased.
Such a stratified core would be incapable of convection, which is believed to be what allows for Earth’s magnetic field. What’s more, such models are incompatible with seismological studies that indicate that Earth’s core consists mostly of iron and nickel, while approximately 10% of its weight is made up of light elements – such as silicon, oxygen, sulfur, and others. It’s outer core is similarly homogeneous, and composed of much the same elements.
As Dr. Jacobson explained to Universe Today via email:
“The terrestrial planets grew from a sequence of accretionary (impact) events, so the core also grew in a multi-stage fashion. Multi-stage core formation creates a layered stably stratified density structure in the core because light elements are increasingly incorporated in later core additions. Light elements like O, Si, and S increasingly partition into core forming liquids during core formation when pressures and temperatures are higher, so later core forming events incorporate more of these elements into the core because the Earth is bigger and pressures and temperatures are therefore higher.
“This establishes a stable stratification which prevents a long-lasting geodynamo and a planetary magnetic field. This is our hypothesis for Venus. In the case of Earth, we think the Moon-forming impact was violent enough to mechanically mix the core of the Earth and allow a long-lasting geodynamo to generate today’s planetary magnetic field.”
To add to this state of confusion, paleomagnetic studies have been conducted that indicate that Earth’s magnetic field has existed for at least 4.2 billion years (roughly 340 million years after it formed). As such, the question naturally arises as to what could account for the current state of convection and how it came about. For the sake of their study, Jacobson and his team considering the possibility that a massive impact could account for this. As Jacobson indicated:
“Energetic impacts mechanically mix the core and so can destroy stable stratification. Stable stratification prevents convection which inhibits a geodynamo. Removing the stratification allows the dynamo to operate.”
Basically, the energy of this impact would have shaken up the core, creating a single homogeneous region within which a long-lasting geodynamo could operate. Given the age of Earth’s magnetic field, this is consistent with the Theia impact theory, where a Mars-sized object is believed to have collided with Earth 4.51 billion years ago and led to the formation of the Earth-Moon system.
This impact could have caused Earth’s core to go from being stratified to homogeneous, and over the course of the next 300 million years, pressure and temperature conditions could have caused it to differentiate between a solid inner core and liquid outer core. Thanks to rotation in the outer core, the result was a dynamo effect that protected our atmosphere as it formed.
The seeds of this theory were presented last year at the 47th Lunar and Planetary Science Conference in The Woodlands, Texas. During a presentation titled “Dynamical Mixing of Planetary Cores by Giant Impacts“, Dr. Miki Nakajima of Caltech – one of the co-authors on this latest study – and David J. Stevenson of the Carnegie Institution of Washington. At the time, they indicated that the stratification of Earth’s core may have been reset by the same impact that formed the Moon.
It was Nakajima and Stevenson’s study that showed how the most violent impacts could stir the core of planets late in their accretion. Building on this, Jacobson and the other co-authors applied models of how Earth and Venus accreted from a disk of solids and gas about a proto-Sun. They also applied calculations of how Earth and Venus grew, based on the chemistry of the mantle and core of each planet through each accretion event.
The significance of this study, in terms of how it relates to the evolution of Earth and the emergence of life, cannot be understated. If Earth’s magnetosphere is the result of a late energetic impact, then such impacts could very well be the difference between our planet being habitable or being either too cold and arid (like Mars) or too hot and hellish (like Venus). As Jacobson concluded:
“Planetary magnetic fields shield planets and life on the planet from harmful cosmic radiation. If a late, violent and giant impact is necessary for a planetary magnetic field then such an impact may be necessary for life.”
Looking beyond our Solar System, this paper also has implications in the study of extra-solar planets. Here too, the difference between a planet being habitable or not may come down to high-energy impacts being a part of the system’s early history. In the future, when studying extra-solar planets and looking for signs of habitability, scientists may very well be forced to ask one simple question: “Was it hit hard enough?”
When it comes to the study of planets, moons, and stars, magnetic fields are kind of a big deal. Believed to be the result of convection in a planet, these fields can be the difference between a planet giving rise to life or becoming a lifeless ball of rock. For some time, scientists have known that has a Earth’s magnetic field, which is powered by a dynamo effect created by convection in its liquid, outer core.
Scientists have also long held that the Moon once had a magnetic field, which was also powered by convection in its core. Previously, it was believed that this field disappeared roughly 1 billion years after the Moon formed (ca. 3 to 3.5 billion years ago). But according to a new study from the Massachusetts Institute of Technology (MIT), it now appears that the Moon’s magnetic field continued to exist for another billion years.
The study, titled “A two-billion-year history for the lunar dynamo“, recently appeared in the journal Science Advances. Led by Dr. Sonia Tikoo, an Assistant Professor at Rutger’s University and a former researcher at MIT, the team analyzed ancient lunar rocks collected by NASA’s Apollo 15 mission. What they found was that the rock showed signs of a being in magnetic field when it was formed between 1 and 2.5 billion years ago.
The age of this rock sample means that it is significantly younger than others returned by the Apollo missions. Using a technique they developed, the team examined the sample’s glassy composition with a magnometer to determine its magnetic properties. They then exposed the sample to a lab-generated magnetic field and other conditions that were similar to those that existed on the Moon when the rock would have formed.
This was done by placing the rocks into a specially-designed oxygen-deprived oven, which was built with the help of Clement Suavet and Timothy Grove – two researchers from MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) and co-authors on the study. The team then exposed the rocks to a tenuous, oxygen-free environment and heated them to extreme temperatures.
As Benjamin Weiss – a professor of planetary sciences at EAPS – explained:
“You see how magnetized it gets from getting heated in that known magnetic field, then you compare that field to the natural magnetic field you measured beforehand, and from that you can figure out what the ancient field strength was… In this way, we finally have gotten an accurate measurement of the lunar field.”
From this, they determined the lunar rock became magnetized in a field with a strength of about 5 microtesla. That’s many times weaker than Earth’s magnetic field when measured from the surface (25 – 65 microteslas), and two orders of magnitude weaker than what it was 3 to 4 billion years ago. These findings were quite significant, since they may help to resolve an enduring mystery about the Moon.
Previously, scientists suspected that the Moon’s magnetic field died out 1.5 billion years after the Moon formed (ca. 3 billion years ago). However, they were unsure if this process happened rapidly, or if the Moon’s magnetic field endured, but in a weakened state. The results of this study indicate that the magnetic field did in fact linger for an additional billion years, dissipating about 2.5 billion years ago.
As Weiss indicated, this study raises new questions about the Moon’s geological history:
“The concept of a planetary magnetic field produced by moving liquid metal is an idea that is really only a few decades old. What powers this motion on Earth and other bodies, particularly on the moon, is not well-understood. We can figure this out by knowing the lifetime of the lunar dynamo.”
In other words, this new timeline of the Moon casts some doubt on the theory that a lunar dynamo alone is what powered its magnetic field in the past. Basically, it is now seen as a distinct possibility that the Moon’s magnetic field was powered by two mechanisms. Whereas one allowed for a dynamo in the core that powered its magnetic field for a good billion years after the Moon’s formation, a second one kept it going afterwards.
In the past, scientists have proposed that the Moon’s dynamo was powered by Earth’s gravitational pull, which would have caused tidal flexing in the Moon’s interior (much in the same way that Jupiter and Saturn’s powerful gravity drives geological activity in their moons interiors). In addition, the Moon once orbited much closer to Earth, which may have been enough to power its once-stronger magnetic field.
However, the Moon gradually moved away from Earth, eventually reaching its current orbit about 3 billion years ago. This coincides with the timeline of the Moon’s magnetic field, which began to dissipate at about the same time. This could mean that by about 3 billion years ago, without the gravitational pull of the Earth, the core slowly cooled. One billion years later, the core had solidified to the point that it arrested the Moon;s magnetic field. As Weiss explained:
“As the moon cools, its core acts like a lava lamp – low-density stuff rises because it’s hot or because its composition is different from that of the surrounding fluid. That’s how we think the Earth’s dynamo works, and that’s what we suggest the late lunar dynamo was doing as well… Today the moon’s field is essentially zero. And we now know it turned off somewhere between the formation of this rock and today.”
These findings were made possible thanks in part by the availability of younger lunar rocks. In the future, the researchers are planning on analyzing even younger samples to precisely determine where the Moon’s dynamo died out completely. This will not only serve to validate the findings of this study, but could also lead to a more comprehensive timeline of the Moon’s geological history.
The results of these and other studies that seek to understand how the Moon formed and changed over time will also go a long way towards improving our understanding of how Earth, the Solar System, and extra-solar systems came to be.
Back in of August of 2016, the existence of an Earth-like planet right next door to our Solar System was confirmed. To make matters even more exciting, it was confirmed that this planet orbits within its star’s habitable zone too. Since that time, astronomers and exoplanet-hunters have been busy trying to determine all they can about this rocky planet, known as Proxima b. Foremost on everyone’s mind has been just how likely it is to be habitable.
However, numerous studies have emerged since that time that indicate that Proxima b, given the fact that it orbits an M-type (red dwarf), would have a hard time supporting life. This was certainly the conclusion reached in a new study led by researchers from NASA’s Goddard Space Flight Center. As they showed, a planet like Proxima b would not be able to retain an Earth-like atmosphere for very long.
Red dwarf stars are the most common in the Universe, accounting for an estimated 70% of stars in our galaxy alone. As such, astronomers are naturally interested in knowing just how likely they are at supporting habitable planets. And given the distance between our Solar System and Proxima Centauri – 4.246 light years – Proxima b is considered ideal for studying the habitability of red dwarf star systems.
On top of all that, the fact that Proxima b is believed to be similar in size and composition to Earth makes it an especially appealing target for research. The study was led by Dr. Katherine Garcia-Sage of NASA’s Goddard Space Flight Center and the Catholic University of America in Washington, DC. As she told Universe Today via email:
“So far, not many Earth-sized exoplanets have been found orbiting in the temperate zone of their star. That doesn’t mean they don’t exist – larger planets are found more often, because they are easier to detect – but Proxima b is of interest because it’s not only Earth-sized and at the right distance from its star, but it’s also orbiting the closest star to our Solar System.”
For the sake of determining the likelihood of Proxima b being habitable, the research team sought to address the chief concerns facing rocky planets that orbit red dwarf stars. These include the planet’s distance from their stars, the variability of red dwarfs, and the presence (or absence) of magnetic fields. Distance is of particular importance, since habitable zones (aka. temperate zones) around red dwarfs are much closer and tighter.
“Red dwarfs are cooler than our own Sun, so the temperate zone is closer to the star than Earth is to the Sun,” said Dr. Garcia-Sage. “But these stars may be very magnetically active, and being so close to a magnetically active star means that these planets are in a very different space environment than what the Earth experiences. At those distances from the star, the ultraviolet and x-ray radiation may be quite large. The stellar wind may be stronger. There could be stellar flares and energetic particles from the star that ionize and heat the upper atmosphere.”
In addition, red dwarf stars are known for being unstable and variable in nature when compared to our Sun. As such, planets orbiting in close proximity would have to contend with flare ups and intense solar wind, which could gradually strip away their atmospheres. This raises another important aspect of exoplanet habitability research, which is the presence of magnetic fields.
To put it simply, Earth’s atmosphere is protected by a magnetic field that is driven by a dynamo effect in its outer core. This “magnetosphere” has prevented solar wind from stripping our atmosphere away, thus giving life a chance to emerge and evolve. In contrast, Mars lost its magnetosphere roughly 4.2 billion years ago, which led to its atmosphere being depleted and its surface becoming the cold, desiccated place it is today.
To test Proxima b’s potential habitability and capacity to retain liquid surface water, the team therefore assumed the presence of an Earth-like atmosphere and a magnetic field around the planet. They then accounted for the enhanced radiation coming from Proxima b. This was provided by the Harvard Smithsonian Center for Astrophysics (CfA), where researchers determined the ultraviolet and x-ray spectrum of Proxima Centauri for this project.
From all of this, they constructed models that began to calculate the rate of atmospheric loss, using Earth’s atmosphere as a template. As Dr. Garcia-Sage explained:
“At Earth, the upper atmosphere is ionized and heated by ultraviolet and x-ray radiation from the Sun. Some of these ions and electrons escape from the upper atmosphere at the north and south poles. We have a model that calculates how fast the upper atmosphere is lost through these processes (it’s not very fast at Earth)… We then used that radiation as the input for our model and calculated a range of possible escape rates for Proxima Centauri b, based on varying levels of magnetic activity.”
What they found was not very encouraging. In essence, Proxima b would not be able to retain an Earth-like atmosphere when subjected to Proxima Centauri’s intense radiation, even with the presence of a magnetic field. This means that unless Proxima b has had a very different kind of atmospheric history than Earth, it is most likely a lifeless ball of rock.
However, as Dr. Garcia-Sage put it, there are other factors to consider which their study simply can’t account for:
“We found that atmospheric losses are much stronger than they are at Earth, and the for high levels of magnetic activity that we expect at Proxima b, the escape rate was fast enough that an entire Earth-like atmosphere could be lost to space. That doesn’t take into account other things like volcanic activity or impacts with comets that might be able to replenish the atmosphere, but it does mean that when we’re trying to understand what processes shaped the atmosphere of Proxima b, we have to take into account the magnetic activity of the star. And understanding the atmosphere is an important part of understanding whether liquid water could exist on the surface of the planet and whether life could have evolved.”
So it’s not all bad news, but it doesn’t inspire a lot of confidence either. Unless Proxima b is a volcanically-active planet and subject to a lot of cometary impacts, it is not likely be temperate, water-bearing world. Most likely, its climate will be analogous to Mars – cold, dry, and with water existing mostly in the form of ice. And as for indigenous life emerging there, that’s not too likely either.
These and other recent studies have painted a rather bleak picture about the habitability of red dwarf star systems. Given that these are the most common types of stars in the known Universe, the statistical likelihood of finding a habitable planet beyond our Solar System appears to be dropping. Not exactly good news at all for those hoping that life will be found out there within their lifetimes!
But it is important to remember that what we can say definitely at this point about extra-solar planets is limited. In the coming years and decades, next-generation missions – like the James Webb Space Telescope (JWST) and the Transiting Exoplanet Survey Satellite (TESS) – are sure to paint a more detailed picture. In the meantime, there’s still plenty of stars in the Universe, even if most of them are extremely far away!
If you’ve read enough of our articles, you know I’ve got an uneasy alliance with the Sun. Sure, it provides the energy we need for all life on Earth. But, it’s a great big ongoing thermonuclear reaction, and it’s right there! As soon as we get fusion, Sun, in like, 30 years or so, I tell you, we’ll be the ones laughing.
But to be honest, we still have so many questions about the Sun. For starters, we don’t fully understand the solar wind blasting out of the Sun. This constant wind of charged particles is constantly blowing out into space, but sometimes it’s stronger, and sometimes it’s weaker.
What are the factors that contribute to the solar wind? And as you know, these charged particles are not healthy for the human body, or for our precious electronics. In fact, the Sun occasionally releases enormous blasts that can damage our satellites and electrical grids.
How can we predict the intensity so that we can be better prepared for dangerous solar storms? Especially the Carrington-class events that might take down huge portions of our modern society.
Perhaps the biggest mystery with the Sun is the temperature of its corona. The surface of the Sun is hot, like 5,500 degrees Celsius. But if you rise up into the atmosphere of the Sun, into its corona, the temperature jumps beyond a million degrees.
The list of mysteries is long. And to start understanding what’s going on, we’ll need to get much much closer to the Sun.
Good news, NASA has a new mission in the works to do just that.
The mission is called the Parker Solar Probe. Actually, last week, it was called the Solar Probe Plus, but then NASA renamed it, and that reminded me to do a video on it.
It’s pretty normal for NASA to rename their spacecraft, usually after a dead astronomer/space scientist, like Kepler, Chandra, etc. This time, though, they renamed it for a legendary solar astronomer Eugene Parker, who developed much of our modern thinking on the Sun’s solar wind. Parker just turned 90 and this is the first time NASA has named it after someone living.
Anyway, back to the spacecraft.
The mission is due to launch in early August 2018 on a Delta IV Heavy, so we’re still more than a year away at this point. When it does, it’ll carry the spacecraft on a very unusual trajectory through the inner Solar System.
The problem is that the Sun is actually a very difficult place to reach. In fact, it’s the hardest place to get to in the entire Solar System.
Remember that the Earth is traveling around the Sun at a velocity of 30 km/s. That’s almost three times the velocity it takes to get into orbit. That’s a lot of velocity.
In order to be able to get anywhere near the Sun, the probe needs to shed velocity. And in order to do this, it’s going to use gravitational slingshots with Venus. We’ve talked about gravitational slingshots in the past, and how you can use them to speed up a spacecraft, but you can actually do the reverse.
The Parker Solar Probe will fall down into Venus’ gravity well, and give orbital velocity to Venus. This will put it on a new trajectory which takes it closer to the Sun. It’ll do a total of 7 flybys in 7 years, each of which will tweak its trajectory and shed some of that orbital momentum.
You know, trying to explain orbital maneuvering is tough. I highly recommend that you try out Kerbal Space Program. I’ve learned more about orbital mechanics by playing that game for a few months than I have in almost 2 decades of space journalism. Go ahead, try to get to the Sun, I challenge you.
Anyway, with each Venus flyby, the Parker Solar Probe will get closer and closer to the Sun, well within the orbit of Mercury. Far closer than any spacecraft has ever gotten to the Sun. At its closest point, it’ll only be 5.9 million kilometers from the Sun. Just for comparison, the Earth orbits at an average distance of about 150 million kilometers. That’s close.
And over the course of its entire mission, the spacecraft is expected to make a total of 24 complete orbits of the Sun, analyzing that plasma ball from every angle.
The orbit is also highly elliptical, which means that it’s going really really fast at its closest point. Almost 725,000 km/h.
In order to withstand the intense temperatures of being this close to the Sun, NASA has engineered the Parker Solar Probe to shed heat. It’s equipped with an 11.5 cm-thick shield made of carbon-composite. For that short time it spends really close to the Sun, the spacecraft will keep the shield up, blocking that heat from reaching the rest of its instruments.
And it’s going to get hot. We’re talking about more than 1,300 degrees Celsius, which is about 475 times as much energy as a spacecraft receives here on Earth. In the outer Solar System, the problem is that there just isn’t enough energy to power solar panels. But where Parker is going, there’s just too much energy.
Now we’ve talked about the engineering difficulties of getting a spacecraft this close to the Sun, let’s talk about the science.
The biggest question astronomers are looking to solve is, how does the corona get so hot. The surface is 5,500 Celsius. As you get farther away from the Sun, you’d expect the temperature to go down. And it certainly does once you get as far as the orbit of the Earth.
But the Sun’s corona, or its outer atmosphere, extends millions of kilometers into space. You can see it during a solar eclipse as this faint glow around the Sun. Instead of dropping, the temperature rises to more than a million degrees.
What could be causing this? There are a couple of ideas. Plasma waves pushed off the Sun could bunch up and release their heat into the corona. You could also get the crisscrossing of magnetic field lines that create mini-flares within the corona, heating it up.
The second great mystery is the solar wind, the stream of charged protons and electrons coming from the Sun. Instead of a constant blowing wind, it can go faster or slower. And when the speed changes, the contents of the wind change too.
There’s the slow wind, that goes a mere 1.1 million km/h and seems to emanate from the Sun’s equatorial regions. And then the fast wind, which seems to be coming out of coronal holes, cooler parts in the Sun’s corona, and can be going at 2.7 million km/h.
Why does the solar wind speed change? Why does its consistency change?
The Parker Solar Probe is equipped with four major instruments, each of which will gather data from the Sun and its environment.
The FIELDS experiment will measure the electric and magnetic fields and waves around the Sun. We know that much of the Sun’s behavior is driven by the complex interaction between charged plasma in the Sun. In fact, many physicists agree that magnetohydrodynamics is easily one of the most complicated fields you can get into.
Integrated Science Investigation of the Sun, or ISOIS (which I suspect needs a renaming) will measure the charged particles streaming off the Sun, during regular solar activity and during dangerous solar storms. Can we get any warning before these events occur, giving astronauts more time to protect themselves?
Wide-field Imager for Solar PRobe or WISPR is its telescope and camera. It’s going to be taking close up, high resolution images of the Sun and its corona that will blow our collective minds… I hope. I mean, if it’s just a bunch of interesting data and no pretty pictures, it’s going to be hard to make cool videos showcasing the results of the mission. You hear me NASA, we want pictures and videos. And science, sure.
And then the Solar Wind Electrons Alphas and Protons Investigation, or SWEAP, will measure type, velocity, temperature and density of particles around the Sun, to help us understand the environment around it.
One interesting side note, the spacecraft will be carrying a tiny chip on board with photos of Eugene Parker and a copy of his original 1958 paper explaining the Sun’s solar wind.
I know we’re still more than a year away from liftoff, and several years away before the science data starts pouring in. But you’ll be hearing more and more about this mission shortly, and I’m pretty excited about what it’s going to accomplish. So stay tuned, and once the science comes in, I’m sure you’ll hear plenty more about it.
When the Apollo astronauts returned to Earth, they came bearing 380.96 kilograms (839.87 lb) of Moon rocks. From the study of these samples, scientists learned a great deal about the Moon’s composition, as well as its history of formation and evolution. For example, the fact that some of these rocks were magnetized revealed that roughly 3 billion years ago, the Moon had a magnetic field.
Much like Earth, this field would have been the result of a dynamo effect in the Moon’s core. But until recently, scientists have been unable to explain how the Moon could maintain such a dynamo effect for so long. But thanks to a new study by a team of scientists from the Astromaterials Research and Exploration Science (ARES) Division at NASA’s Johnson Space Center, we might finally have a answer.
To recap, the Earth’s magnetic core is an integral part of what keeps our planet habitable. Believed to be the result of a liquid outer core that rotates in the opposite direction as the planet, this field protects the surface from much of the Sun’s radiation. It also ensures that our atmosphere is not slowly stripped away by solar wind, which is what happened with Mars.
For the sake of their study, which was recently published in the journal Earth and Planetary Science Letters, the ARES team sought to determine how a molten, churning core could generate a magnetic field on the Moon. While scientists have understood how the Moon’s core could have powered such a field in the past, they have been unclear as to how it could have been maintained it for such a long time.
Towards this end, the ARES team considered multiple lines of geochemical and geophysical evidence to put constraints on the core’s composition. As Kevin Righter, the lead of the JSC’s high pressure experimental petrology lab and the lead author of the study, explained in a NASA press release:
“Our work ties together physical and chemical constraints and helps us understand how the moon acquired and maintained its magnetic field – a difficult problem to tackle for any inner solar system body. We created several synthetic core compositions based on the latest geochemical data from the moon, and equilibrated them at the pressures and temperatures of the lunar interior.”
Specifically, the ARES scientists conducted simulations of how the core would have evolved over time, based on varying levels of nickel, sulfur and carbon content. This consisted of preparing powders or iron, nickel, sulfur and carbon and mixing them in the proper proportions – based on recent analyses of Apollo rock samples.
Once these mixtures were prepared, they subjected them to heat and pressure conditions consistent with what exists at the Moon’s core. They also varied these temperatures and pressures based on the possibility that the Moon underwent changes in temperature during its early and later history – i.e. hotter during its early history and cooler later on.
What they found was that a lunar core composed of iron/nickel that had a small amount of sulfur and carbon – specifically 0.5% sulfur and 0.375% carbon by weight – fit the bill. Such a core would have a high melting point and would have likely started crystallizing early in the Moon’s history, thus providing the necessary heat to drive the dynamo and power a lunar magnetic field.
This field would have eventually died out after heat flow led the core to cool, thus arresting the dynamo effect. Not only do these results provide an explanation for all the paleomagnetic and seismic data we currently have on the Moon, it is also consistent with everything we know about the Moon’s geochemical and geophysical makeup.
Prior to this, core models tended to place the Moon’s sulfur content much higher. This would mean that it had a much lower melting point, and would have meant crystallization could not have occurred until much more recently in its history. Other theories have been proposed, ranging from sheer forces to impacts providing the necessary heat to power a dynamo.
However, the ARES team’s study provides a much simpler explanation, and one which happens to fit with all that we know about the Moon. Naturally, additional studies will be needed before there is any certainty on the issue. No doubt, this will first require that human beings establish a permanent outpost on the Moon to conduct research.
But it appears that for the time being, one of the deeper mysteries of the Earth-Moon system might be resolved at last.