Posted on by Matt Williams

Here’s the Earth and Moon Seen from OSIRIS-REx

The Earth-Moon system, as imaged by NASA's OSIRIS-REx mission. Credit: NASA/OSIRIS-REx team and the University of Arizona

On September 8th, 2016, NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission was launched into space. In the coming months, this space probe will approach and then rendezvous with the asteroid 101955 Bennu – a Near-Earth Object (NEO) – for the sake of studying it. The mission will also acquire samples of the asteroid, which will be returned to Earth by 2023.

The OSIRIS-REx mission is an historic one, since it will be the first US spacecraft to conduct a sample-return mission with an asteroid. In the meantime, as the probe has makes its way further into space, it has been providing some truly breathtaking images of the journey. Consider the recently-released composite image of the Earth-Moon system, which NASA created using images that were taken by the probe on October 2nd, 2017.

The images were all taken by the probe’s MapCam instrument, a medium-range camera designed to capture images of outgassing around Bennu and help map its surface in color. On this occasion, it snapped three beautiful pictures of Earth and the Moon. These images were all taken when the spacecraft was at a distance of approximately 5 million km (3 million mi) from Earth – about 13 times the distance between the Earth and the Moon.

Black and white image of Earth taken by the OSIRIS-REx’s NavCam 1 instrument. Credit: NASA/OSIRIS-REx team and the University of Arizona

As part of the OSIRIS-REx Camera Suite (OCAMS), which is operated by researchers at the University of Arizona, the CapCam has four color filters. To produce the image, three of them (b, v and w) were used as a blue, green and red filters and then stacked on top of each other. The Earth and Moon were each color-corrected, and the Moon was brightened to make it more easily visible.

A second image of planet Earth (shown above), was taken on September 22nd, 2017, by one of the probe’s navigational cameras (NavCam 1). As the name suggests, this instrument is intended to help OSIRIS-REx orient itself while making its journey to Bennu and while it studies the asteroid. This is done by tracking starfields in space (while in transit) and landmarks on Bennu’s surface once it has arrived.

The image was taken when OSIRIS-REx was at a distance of 110,000 km (69,000 mi) from Earth. This was just after the probe had completed an Earth gravity-assist maneuver, where it used Earth’s gravitational force to slingshot around its equator and pick up more speed. The original image (shown below) was rotated so that the North Pole would be pointed up and the entire image was enlarged to provide more detail.

As you can see in the altered image, North America is visible on the upper right portion, while Hurricane Maria and the remnants of Hurricane Jose are visible in the far upper-right. The acquisition of these images was the result of painstaking calculations and planning, which were performed in advance by engineers and navigation specialists on the mission team using software called Systems Tool Kit (STK).

Original image taken by the OSIRIS-REx NavCam 1 of Earth. Credit: NASA/Goddard/University of Arizona/Lockheed Martin

These plans were developed to ensure that the probe would be able to snap pictures with precise timing, which were then uploaded to the spacecraft’s computer weeks ahead of time. Within hours of the probe executing its gravity-assist maneuver, crews on the ground were treated to the first images from the spacecraft’s navigational cameras, which confirmed that the probe was following the right path.

The probe is scheduled to reach Bennu in December of 2018, with approach operations commencing this coming August. Bennu is also expected to make a close pass with Earth several centuries from now, and could even collide with us by then. But for the time being, it represents a major opportunity to study the history and evolution of the Solar System, since it is essentially a remnant left over from its formation.

By studying this asteroid up close, and bringing samples back to Earth for further study, the OSRIS-REx mission could help us understand how life began on Earth and where the Solar System as a whole is headed. But in the meantime, the probe has been able to provide us with some beautiful snapshots of Earth, which serve to remind us all of certain things.

Much like Voyager 1‘s “Pale Blue Dot” photo, seeing Earth from space helps to drive home the fact that life is rare and precious. It also reminds us that we, as a species, are all in this together and completely and utterly dependent  on our planet and its ecosystems. Once in awhile, we need to be reminded of these things. Otherwise, we might do some stupid – like ruin it!

Further Reading: NASA

Posted on by Matt Williams

Just a Billion Years After the Earth Formed, Life had Already Figured out Plenty of Tricks

J. William Schopf and colleagues from UCLA and the University of Wisconsin analyzed the microorganisms with cutting-edge technology called secondary ion mass spectroscopy. Credit: John Vande Wege/UCLA

Life on Earth has had a long and turbulent history. Scientists estimate that roughly 4 billion years ago, just 500 million years after planet Earth formed, the first single-celled lifeforms arose. By the Archean Eon (4 to 2.5 billion years ago), multi-celled lifeforms are believed to have emerged. While the existence of such organisms (Archaea) has been inferred from carbon isotopes found in ancient rocks, fossil evidence has remained elusive.

All of that has changed, thanks to a recent study performed by a team of researchers from UCLA and the University of Wisconsin–Madison. After examining ancient rock samples from Western Australia, the team determined that they contained the fossilized remains of diverse organisms that are 3.465 billion years old. Combined with the recent spate of exoplanet discoveries, this study strengthens the theory that life is plentiful in the Universe.

The study, titled “SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions“, recently appeared in the Proceedings of the National Academy of Sciences. As the research team indicated, their study consisted of a carbon isotope analysis of 11 microbial fossils taken from the ~3,465-million-year-old Western Australian Apex Chert.

Apex chert in Western Australia, where the 3.465 billion year old fossils were found. Credit: John Valley/UW-Madison

These 11 fossils were diverse in nature and the researchers divided them into five species groups based on their apparent biological functions. Whereas two of the fossil samples appear to have performed a primitive form of photosynthesis, another apparently produced methane gas. The remaining two appear to have been methane-consumers, which they used to build and maintain their cell walls (much like how mammals use fat).

As J. William Schopf – a professor of paleobiology in the UCLA College and the lead author on the study – indicated in a UCLA Newsroom press release:

“By 3.465 billion years ago, life was already diverse on Earth; that’s clear — primitive photosynthesizers, methane producers, methane users. These are the first data that show the very diverse organisms at that time in Earth’s history, and our previous research has shown that there were sulfur users 3.4 billion years ago as well.

This study, which is the most detailed ever conducted on microorganisms preserved as ancient fossils, builds on work that Schopf and his associates have been performing for over two decades. Back in 1993, Schopf and another team of researchers conducted a study that first described these types of fossils. This was followed in 2002 by another study which substantiated their biological origin.

In this latest study, Schopf and his team established what kind of organisms they are and how complex they are. To do this, they analyzed the microorganisms using a technique called Secondary Ion Mass Spectroscopy (SIMS), which reveals the ratio of carbon-12 to carbon-13. Whereas carbon-12 is stable and the most common type found in nature, carbon-13 is a less common but similarly stable isotope that is used in organic chemistry research.

A microorganism analyzed by the researchers. Credit: J. William Schopf/UCLA

By separating the carbon from each fossil into its constituent isotopes and determining their ratios, the team was able to conclude how long ago the microorganisms lived, as well as how they lived. This task was performed by the Wisconsin researchers, who were led by professor John Valley. “The differences in carbon isotope ratios correlate with their shapes,” said Valley. “Their C-13-to-C-12 ratios are characteristic of biology and metabolic function.”

According to the current scientific consensus, advanced photosynthesis had not yet evolved and oxygen would not appear on Earth until 500 million years later. By 2 billion year ago, concentrations of oxygen gas began increasing rapidly. This means that these fossils, being around roughly 1 billion years after Earth formed, would have lived at a time when their was little oxygen in the atmosphere.

Given that oxygen would be poisonous to these types of primitive photosynthesizers, they are quite rare today. In truth, they can only be found in places where there is sufficient light but no oxygen, something which is rarely found in combination. What’s more, the rocks themselves were a source of great interest since the average lifespan of rock exposed to the surface of Earth is only about 200 million years.

When Shopf first began his career, the oldest-known rock samples were 500 million years old. This means that the fossil-bearing rocks he and his team examined are as old as rocks on Earth can get. To find fossilized life in such ancient samples demonstrates that diverse organisms and a life cycle had already evolved on Earth by the early Archaen Eon, something which scientists only suspected up until this point.

In the future, SIMS technology could be used to look for signs of fossilized life on Mars. Credit: NASA/JPL)

These findings naturally have implications for the study of how and when life emerged on Earth. Beyond Earth, the study also has implications since it demonstrates that life emerged when Earth was still very young and in a primitive state. It is therefore not unlikely that a similar process has been taking place elsewhere in the Universe. As Schopf explained:

“This tells us life had to have begun substantially earlier and it confirms that it was not difficult for primitive life to form and to evolve into more advanced microorganisms. But, if the conditions are right, it looks like life in the universe should be widespread.”

This study was made possible thanks to funding provided by the NASA Astrobiology Institute. Looking to the future, Schopf indicated that the same technology used to date these fossils will likely be used to study rocks brought back by NASA’s crewed mission to Mars. Scheduled for the 2030s, this mission will entail retrieving samples obtained by the Mars 2020 Rover and bringing them back to Earth for analysis.

Further Reading: UCLA, PNAS

Posted on by Matt Williams

Maybe Mars and Earth Didn’t Form Close to Each Other

A new study by an international team of scientists considers whether Mars and Earth formed farther away from the Sun than previously thought. Credit: NASA/JPL-Caltech/USGS

In recent years, astronomers have been looking to refine our understanding of how the Solar System formed. On the one hand, you have the traditional Nebular Hypothesis which argues that the Sun, the planets, and all other objects in the Solar System formed from nebulous material billions of years ago. However, astronomers traditionally assumed that the planets formed in their current orbits, which has since come to be questioned.

This has come to be challenged by theories like the Grand Tack model. This theory states that Jupiter migrated from its original orbit after it formed, which had a big impact on the inner Solar System. And in a more recent study, an international team of scientists have taken things a step further, proposing that Mars actually formed in what is today the Asteroid Belt and migrated closer to the Sun over time.

The study, titled “The cool and distant formation of Mars“, recently appeared in the journal Earth and Planetary Science Letters. The study was led by Ramon Brasser of the Earth Life Science Institute at the Tokyo Institute of Technology, and included members from the University of Colorado, the Hungarian Academy of Sciences, and the University of Dundee in the UK.

Composite image showing the size difference between Earth and Mars. Credit: NASA/Mars Exploration

For the sake of their study, the team addressed one of the most glaring issues with traditional models of Solar System formation. This is the assumption that Mars, Earth and Venus formed closely together and that Mars migrated outward to its current orbit. In addition, the theory holds that Mars – roughly 53% as large as Earths and only 15% as massive – is essentially a planetary embryo that never became a full, rocky planet.

However, this has contradicted by bulk elemental and isotopic studies performed on Martian meteorites, which have noted key differences in composition between Mars and Earth. As Brasser and his team indicated in their study:

“This suggests that Mars formed outside of the terrestrial feeding zone during primary accretion. It is therefore probable that Mars always remained significantly farther from the Sun than Earth; its growth was stunted early and its mass remained relatively low.”

To test this hypothesis, the team conducted dynamical simulations that were consistent with the Grand Tack model. In these simulations, Jupiter moved a large concentration of mass towards the Sun at it migrated towards the inner Solar System, which had a profound influence on the formation and orbital characteristics of the terrestrial planets (Mercury, Venus, Earth and Mars).

The theory also holds that this migration pulled material away from Mars, thus accounting for the compositional differences and the planet’s smaller size and mass relative to Venus and Earth. What they found was that in a small percentage of their simulations, Mars formed farther from the Sun and that Jupiter’s gravitational pull pushed Mars into its current orbit.

The Grand Tack model (top) compared to the traditional theories about how the Inner Solar System formed. Credit: Sean Raymond/planetplanet.net

From this, the team concluded that either scientists lack the necessary mechanisms to explain Mars’ formation, or that of all the possibilities, this statistically rare scenario is indeed the correct one. As Stephen Mojzsis – a geological sciences professor at the University of Colorado and a co-author on the study – indicated in a recent interview with Astrobiology Magazine, the fact that the scenario is rare does not make it any less plausible:

“Given enough time, we can expect these events. For example, you’ll eventually get double sixes if you roll the dice enough times. The probability is 1/36 or roughly the same as we get for our simulations of Mars’ formation.”

In truth, a 2% probability (which is what they obtained from the simulations) is hardly poor odds when considered in cosmological terms. And when one considers that such a possibility would allow for the key differences between Mars and its terrestrial cousins (i.e. Earth and Venus), this slim probability appears rather possible. However, the idea that Mars migrated inward during the course of its history also carries with it some serious implications.

For starters, the researchers were pressed to explain how Mars could have possessed a thicker, warmer atmosphere that would have allowed for liquid water to exist on the surface. If Mars actually formed in the modern-day Asteroid Belt, it would have been subject to far less solar flux, and surface temperatures would have been significantly lower than if it had formed in its present-day location.

Scientists were able to gauge the rate of water loss on Mars by measuring the ratio of water and HDO from today and 4.3 billion years ago. Credit: Kevin Gill

However, as they go to indicate, if Mars had enough carbon-dioxide in its early atmosphere, then it is possible that impacts during the Late Heavy Bombardment could have allowed for intermittent periods where liquid water could exist on the surface. Or as they explain it:

“Unless, as our model shows, an intrinsically volatile-rich Mars possessed a strong and sustainable greenhouse atmosphere, its average surface temperature was unremittingly below 0 °C. Such a cold surface environment would have been regularly affected by early impact bombardments that both restarted a moribund hydrological cycle, and provided a haven for possible early life in the martian crust.”

Basically, while Mars would have been subject to less in the way of solar energy during its early lifespan, its possible it could have still been warm enough to support liquid water on its surface. And as Mojzsis stated in a paper he co-authored last year, the many bombardments it received (as attested to by its many craters) would have been enough to melt surface ice, thicken the atmosphere, and trigger a periodic hydrological cycle.

Another interesting thing about this study is how it predicts that Venus likely has a bulk composition (including its oxygen isotopes) that is similar to that of the Earth-Moon system. According to their simulations, this is due to the fact that Venus and Earth always shared the same building blocks, whereas Earth and Mars did not. These findings were consistent with recent ground-based infrared observations of Venus and its atmosphere.

Artist’s impression of the joint NASA-Roscosmos Venera-D mission concept, which wold include a Venus orbiter and a lander designed to survive on Venus’ surface for a few hours. Credit: NASA/JPL-Caltech

But of course, no definitive conclusions can be drawn about that until samples of Venus’ crust can be obtained. This could be accomplished if and when the proposed Venera-Dolgozhivuschaya (Venera-D) mission – a joint NASA/Roscomos plan to send a orbiter and lander to Venus – is launched in the coming decade. In the meantime, there are other outstanding issues in the Grand Tack model and Nebular Hypothesis that need to be addressed.

According to Mojzsis, these include how the gas/ice giants of the Solar System could have formed in their current locations. The idea that they formed in their current orbits beyond the Asteroid Belt seems inconsistent with models of the early Solar System, which show that there was not enough of the necessary material that far from the Sun. An alternative is that they formed closer to the Sun and also migrated outward.

As Mojzsis explained, this possibility is bolstered by recent studies of extra-solar planetary systems, where gas giants have been found to orbit very close to their stars (i.e. “Hot Jupiters”) and farther away:

“We understand from direct observations via the Kepler Space Telescope and earlier studies that giant planet migration is a normal feature of planetary systems. Giant planet formation induces migration, and migration is all about gravity, and these worlds affected each other’s orbits early on.”

If there’s one benefit to being able to look farther out into the Universe, its the way it has allowed astronomers to come up with better and more complete theories of how the Solar System came to be. And as our exploration of the Solar System continues to grow, we are sure to learn many things that will help advance our understanding of other star systems as well.

Further Reading: Astrobiology Magazine, Earth and Planetary Science Letters

Posted on by Matt Williams

Earth and Venus are the Same Size, so Why Doesn’t Venus Have a Magnetosphere? Maybe it Didn’t Get Smashed Hard Enough

At a closest average distance of 41 million km (25,476,219 mi), Venus is the closest planet to Earth. Credit: NASA/JPL/Magellan

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.

The Earth's layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com
The Earth’s layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com

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.

Artist’s concept of a collision between proto-Earth and Theia, believed to happened 4.5 billion years ago. Credit: NASA

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?”

Further Reading: Earth Science and Planetary Letters

Posted on by Matt Williams

New Study Says Earth Avoided a “Carbon Overdose” During Formation

A new study from the University of Heidelberg suggests that flash-heating and carbon depletion could have been intrinsic to the emergence and evolution of life on Earth. Credit: NASA

According to the Nebular Hypothesis, the Sun and planets formed 4.6 billion years ago from a giant cloud of dust and gas. This began with the Sun forming in the center, and the remaining material forming a protoplanetary disc, from which the planets formed. Whereas the planets in the outer Solar System were largely made up of gases (i.e. the Gas Giants), those closer to the Sun formed from silicate minerals and metals (i.e. the terrestrial planets).

Despite having a pretty good idea of how this all came about, the question of exactly how the planets of the Solar System formed and evolved over the course of billions of year is still subject to debate. In a new study, two researchers from the University of Heidelberg considered the role played by carbon in both the formation of Earth and the emergence and evolution of life.

Their study, “Spatial Distribution of Carbon Dust in the Early Solar Nebula and the Carbon Content of Planetesimals“, recently appeared in the journal Astronomy and Astrophysics. The study was conducted by Hans-Peter Gail, from the Institute for Theoretical Astrophysics at the University of Heidelberg, and Mario Trieloff – from Heidelberg’s Institute of Earth Sciences and the Klaus-Tschira-Laboratory for Cosmochemistry.

A slice of the Allende meteorite with silicate globules of the size of a millimetre. Credit: Institute of Earth Science

For the sake of their study, the pair considered what role the element carbon – which is essential to life here on Earth – played in planetary formation. Essentially, scientists are of the opinion that during the earliest days of the Solar System – when it was still a giant cloud of dust and gas – carbon-rich materials were distributed to the inner Solar System from the outer Solar System.

Out beyond the “Frost Line” – where volatiles like water, ammonia and methane and are able to condense into ice – bodies containing frozen carbon compounds formed. Much like how water was distributed throughout the Solar System, that these bodies were supposedly kicked out of their orbits and sent towards the Sun, distributing volatile materials to the planetesimals that would eventually grow to become the terrestrial planets.

However, when one compares the kinds of meteors that distributed primordial material to Earth – aka. chondrite meteorites –  one notices a certain discrepancy. Basically, carbon is comparatively rare on Earth compared to these ancient rocks, the reason for which has remained a mystery. As Prof. Trieloff, who was the co-author on the study, explained in a University of Heidelberg press release:

“On Earth, carbon is a relatively rare element. It is enriched close to the Earth´s surface, but as a fraction of the total matter on Earth it is a mere one-half of 1/1000th. In primitive comets, however, the proportion of carbon can be ten percent or more.”

Artist’s conception of a solar system in formation. Credit: NASA/FUSE/Lynette Cook

“A substantial portion of the carbon in asteroids and comets is in long-chain and branched molecules that evaporate only at very high temperatures,” added Dr. Grail, the study’s lead author. “Based on the standard models that simulate carbon reactions in the solar nebula where the sun and planets originated, the Earth and the other terrestrial planets should have up to 100 times more carbon.”

To address this, the two researches constructed a model that assumed that short-duration flash-heating events – where the Sun heated the protoplanetary disc – were responsible for this discrepancy. They also assumed that all matter in the inner Solar System was heated to temperatures of between 1,300 and 1,800 °C (2372 to 3272 °F) before small planetesimals and terrestrial planets eventually formed.

Dr. Grail and Trieloff believe the evidence for this lies in the round grains in meteorites that form from molten droplets – known as chondrules. Unlike chondrite meteorites, which can be composed of up to a few percent carbon, chondrules are largely depleted of this element. This, they claim, was the a result of the same flash-heating events that took place before the chondrules could accrete to form meteorites. As Dr. Gail indicated:

“Only the spikes in temperature derived from the chondrule formation models can explain today’s low amount of carbon on the inner planets. Previous models did not take this process into account, but we apparently have it to thank for the correct amount of carbon that allowed the evolution of the Earth’s biosphere as we know it.”

Artist impression of the Late Heavy Bombardment period. Credit: NASA

In short, the discrepancy between the amount of carbon found in chondritic-rock material and that found on Earth can be explained by intense heating in the primordial Solar System. As Earth formed from chrondritic material, the extreme heat caused it to be depleted of its natural carbon. In addition to shedding light on what has been an ongoing mystery in astronomy, this study also offers new insight into how life in the Solar System began.

Basically, the researchers speculate that the flash-heating events in the inner Solar System may have been necessary for life here on Earth. Had there been too much carbon in the primordial material that coalesced into our planet, the result could have been a “carbon overdose”. This is because when carbon becomes oxidized, it forms carbon dioxide, a major greenhouse gas that can lead to a runaway heating effect.

This is what planetary scientists believe happened to Venus, where the presence of abundant CO2 – combined with its increased exposure to Solar radiation – led to the hellish environment that is there today. But on Earth, CO2 was removed from the atmosphere by the silicate-carbonate cycle, which allowed for Earth to achieve a balanced and life-sustaining environment.

“Whether 100 times more carbon would permit effective removal of the greenhouse gas is questionable at the very least,” said Dr. Trieloff. “The carbon could no longer be stored in carbonates, where most of the Earth’s CO2 is stored today. This much CO2 in the atmosphere would cause such a severe and irreversible greenhouse effect that the oceans would evaporate and disappear.”

Artist’s impression of the “Venus-like” exoplanet in a nearby star system. Credit: cfa.harvard.edu

It is a well-known fact that life here on Earth is carbon-based. However, knowing that conditions during the early Solar System prevented an overdose of carbon that could have turned Earth into a second Venus is certainly interesting. While carbon may be essential to life as we know it, too much can mean the death of it. This study could also come in handy when it comes to the search for life in extra-solar systems.

When examining distant stars, astronomers could ask, “were primordial conditions hot enough in the inner system to prevent a carbon overdose?” The answer to that question could be the difference between finding an Earth 2.0, or another Venus-like world!

Further Reading: University of Heidelberg, Astronomy and Astrophysics

Posted on by Matt Williams

New Study Sheds Light on How Earth and Mars Formed

Snapshot of a computer simulation of two (relatively small) planets colliding with each other. The colors show how the rock of the impacting body (dark grey, in center of impact area) accretes to the target body (rock; light grey), while some of the rock in the impact area is molten (yellow to white) or vaporised (red). Credit: Philip J. Carter

In accordance with the Nebular Hypothesis, the Solar System is believed to have formed through the process of accretion. Essentially, this began when a massive cloud of dust and gas (aka. the Solar Nebula) experienced a gravitational collapse at its center, giving birth to the Sun. The remaining dust and gas then formed into a protoplanetary disc around the Sun, which gradually coalesced to form the planets.

However, much about the process of how planets evolved to become distinct in their compositions has remained a mystery. Luckily, a new study by a team of researchers from the University of Bristol has approached the subject with a fresh perspective. By examining a combination of Earth samples and meteorites, they have shed new light on how planets like Earth and Mars formed and evolved.

The study, titled “Magnesium Isotope Evidence that Accretional Vapour Loss Shapes Planetary Compositions“, recently appeared in the scientific journal Nature. Led by Remco C. Hin, a senior research associate from the School of Earth Sciences at the University of Bristol, the team compared samples of rock from Earth, Mars, and the Asteroid Vesta to compare the levels of magnesium isotopes within them.

Artist’s impression of the early Solar System, where collision between particles in an accretion disc led to the formation of planetesimals and eventually planets. Credit: NASA/JPL-Caltech

Their study attempted answering what has been a lingering question in the scientific community – i.e. did the planets form the way they are today, or did they acquire their distinctive compositions over time? As Dr. Remco Hin explained in a University of Bristol press release:

“We have provided evidence that such a sequence of events occurred in the formation of the Earth and Mars, using high precision measurements of their magnesium isotope compositions. Magnesium isotope ratios change as a result of silicate vapour loss, which preferentially contains the lighter isotopes. In this way, we estimated that more than 40 per cent of the Earth’s mass was lost during its construction. This cowboy building job, as one of my co-authors described it, was also responsible for creating the Earth’s unique composition.”

To break it down, accretion consists of clumps of material colliding with neighboring clumps to form larger objects. This process is very chaotic, and material is often lost as well as accumulated due to the extreme heat generated by these high-speed collisions. This heat is also believed to have created oceans of magma on the planets as they formed, not to mention temporary atmospheres of vaporized rock.

Until planets become about the same size as Mars, their force of gravitational attraction was too weak to hold onto these atmospheres. And as more collisions took place, the composition of these atmosphere and of the planets themselves would have changes substantially. How exactly the terrestrial planets – Mercury, Venus, Earth and Mars – obtained their current, volatile-poor compositions over time is what scientists have hoped to address.

Artist impression of the Late Heavy Bombardment period. Credit: NASA

For example, some believe that the planets current compositions are the result of particular combinations of gas and dust during the earliest periods of planet formation – where terrestrial planets are silicate/metal rich, but volatile poor, because of which elements were most abundant closest to the Sun. Others have suggested that their current composition is a consequence of their violent growth and collisions with other bodies.

To shed light on this, Dr. Hin and his associates analyzed samples of Earth, along with meteorites from Mars and the asteroid Vesta using a new analytical approach. This technique is capable of obtaining more accurate measurements of magnesium isotope rations than any previous method. This method also showed that all differentiated bodies – like Earth, Mars and Vesta – have isotopically heavier magnesium compositions than chondritic meteorites.

From this, they were able to draw three conclusions. For one, they found that Earth, Mars and Vesta have distinct magnesium isotope rations that could not be explained by condensation from the Solar Nebula. Second, they noted that the study of heavy magnesium isotopes revealed that in all cases, the planets lost about 40% percent of their mass during their formation period, following repeated episodes of vaporization.

Last, they determined that the accretion process results in other chemical changes that generate the unique chemical characteristics of Earth. In short, their study showed that Earth, Mars and Vesta all experiences significant losses of material after formation, which means that their peculiar compositions were likely the result of collisions over time. As Dr Hin added:

“Our work changes our views on how planets attain their physical and chemical characteristics. While it was previously known that building planets is a violent process and that the compositions of planets such as Earth are distinct, it was not clear that these features were linked. We now show that vapour loss during the high energy collisions of planetary accretion has a profound effect on a planet’s composition.”

Their study also indicated that this violent formation process could be characteristic of planets in general. These findings are not only significant when it comes to the formation of the Solar System, but of extra-solar planets as well. When it comes time to explore distant star systems, the distinctive compositions of their planets will tell us much about the conditions from which they formed, and how they came to be.

Further Reading: University of Bristol, Nature

Posted on by Ken Kremer

NASA’s OSIRIS-REx Captures Lovely Blue Marble during Gravity Assist Swing-by to Asteroid Bennu

A color composite image of Earth taken on Sept. 22, 2017 by the MapCam camera on NASA’s OSIRIS-REx spacecraft just hours after the spacecraft completed its Earth Gravity Assist at a range of approximately 106,000 miles (170,000 kilometers). Credit: NASA/Goddard/University of Arizona
A color composite image of Earth taken on Sept. 22, 2017 by the MapCam camera on NASA’s OSIRIS-REx spacecraft just hours after the spacecraft completed its Earth Gravity Assist at a range of approximately 106,000 miles (170,000 kilometers). Credit: NASA/Goddard/University of Arizona

KENNEDY SPACE CENTER, FL – NASA’s OSIRIS-REx asteroid mission captured a lovely ‘Blue Marble’ image of our Home Planet during last Fridays (Sept. 22) successful gravity assist swing-by sending the probe hurtling towards asteroid Bennu for a rendezvous next August on a round trip journey to snatch pristine soil samples.

The newly released color composite image of Earth was taken on Sept. 22 by the spacecrafts MapCam camera.

It was taken at a range of approximately 106,000 miles (170,000 kilometers), just a few hours after OSIRIS-REx completed its critical Earth Gravity Assist (EGA) maneuver.

“NASA’s asteroid sample return spacecraft successfully used Earth’s gravity on Friday, Sept. 22 to slingshot itself on a path toward the asteroid Bennu, for a rendezvous next August,” the agency confirmed after receiving the eagerly awaited telemetry.

OSIRIS-Rex, which stands for Origins, Spectral Interpretation, Resource Identification, and Security – Regolith Explorer, is NASA’s first ever asteroid sample return mission.

As it swung by Earth at 12:52 p.m. EDT on Sept. 22, OSIRIS-REx passed only 10,711 miles (17,237 km) above Antarctica, just south of Cape Horn, Chile.

The probe departed Earth by following a flight path that continued north over the Pacific Ocean and has already travelled 600 million miles (1 billion kilometers) since launching on Sept. 8, 2016.

OSIRIS-REx flight path over Earth’s surface during the Sept. 22, 2017 slingshot over Antarctica at 12:52 a.m. EDT targeting the probe to Asteroid Bennu in August 2018. Credits: NASA’s Goddard Space Flight Center/University of Arizona

The preplanned EGA maneuver provided the absolutely essential gravity assisted speed boost required for OSIRIS-Rex to gain enough velocity to complete its journey to the carbon rich asteroid Bennu and back.

The mission was only made possible by the slingshot which provided a velocity change to the spacecraft of 8,451 miles per hour (3.778 kilometers per second).

“The encounter with Earth is fundamental to our rendezvous with Bennu,” said Rich Burns, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in a statement.

“The total velocity change from Earth’s gravity far exceeds the total fuel load of the OSIRIS-REx propulsion system, so we are really leveraging our Earth flyby to make a massive change to the OSIRIS-REx trajectory, specifically changing the tilt of the orbit to match Bennu.”

The spacecraft conducted a post flyby science campaign by collecting images and science observations of Earth and the Moon that began four hours after closest approach in order to test and calibrate its onboard suite of five science instruments and help prepare them for OSIRIS-REx’s arrival at Bennu in late 2018.

NASA’s OSIRIS-REx spacecraft OTES spectrometer captured these infrared spectral curves during Earth Gravity Assist on Sept. 22 2017, hours after the spacecraft’s closest approach. Credit: NASA/Goddard/University of Arizona/Arizona State University

The MapCam camera Blue Marble image is the first one to be released by NASA and the science team.

The image is centered on the Pacific Ocean and shows several familiar landmasses, including Australia in the lower left, and Baja California and the southwestern United States in the upper right.

“The dark vertical streaks at the top of the image are caused by short exposure times (less than three milliseconds),” said the team.

“Short exposure times are required for imaging an object as bright as Earth, but are not anticipated for an object as dark as the asteroid Bennu, which the camera was designed to image.”

The instrument will gather additional data and measurements scanning the Earth and the Moon for three more days over the next two weeks.

“The opportunity to collect science data over the next two weeks provides the OSIRIS-REx mission team with an excellent opportunity to practice for operations at Bennu,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson.

“During the Earth flyby, the science and operations teams are co-located, performing daily activities together as they will during the asteroid encounter.”

A United Launch Alliance Atlas V rocket lifts off from Space Launch Complex 41 at Cape Canaveral Air Force Station carrying NASA’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, or OSIRIS-REx spacecraft on the first U.S. mission to sample an asteroid, retrieve at least two ounces of surface material and return it to Earth for study. Liftoff was at 7:05 p.m. EDT on September 8, 2016. Credit: Ken Kremer/kenkremer.com

The OSIRIS-Rex spacecraft originally departed Earth atop a United Launch Alliance Atlas V rocket under crystal clear skies on September 8, 2016 at 7:05 p.m. EDT from Space Launch Complex 41 at Cape Canaveral Air Force Station, Florida.

Everything with the launch and flyby went exactly according to plan for the daring mission boldly seeking to gather rocks and soil from carbon rich Bennu.

OSIRIS-Rex is equipped with an ingenious robotic arm named TAGSAM designed to collect at least a 60-gram (2.1-ounce) sample and bring it back to Earth in 2023 for study by scientists using the world’s most advanced research instruments.

View of science instrument suite and TAGSAM robotic sample return arm on NASA’s OSIRIS-REx asteroid sampling spacecraft inside the Payloads Hazardous Servicing Facility at NASA’s Kennedy Space Center. Probe is slated for Sep. 8, 2016 launch to asteroid Bennu from Cape Canaveral Air Force Station, FL. Credit: Ken Kremer/kenkremer.com

Watch for Ken’s continuing onsite NASA mission and launch reports direct from the Kennedy Space Center and Cape Canaveral Air Force Station, Florida.

Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.
Ken Kremer

NASA’s OSIRIS-REx spacecraft OVIRS spectrometer captured this visible and infrared spectral curve, which shows the amount of sunlight reflected from the Earth, after the spacecraft’s Earth Gravity Assist on Sept. 22, 2017. Credit: NASA/Goddard/University of Arizona
Posted on by Nancy Atkinson

Can Astronauts See Stars From the Space Station?

Stars and the limb of Earth seen in the background of the International Space Station on July 29, 2017. Credit: NASA/Jack Fischer.

I’ve often been asked the question, “Can the astronauts on the Space Station see the stars?” Astronaut Jack Fischer provides an unequivocal answer of “yes!” with a recent post on Twitter of a timelapse he took from the ISS. Fischer captured the arc of the Milky Way in all its glory, saying it “paints the heavens in a thick coat of awesome-sauce!”

But, you might be saying, “how can this be? I thought the astronauts on the Moon couldn’t see any stars, so how can anyone see stars in space?”

John W. Young on the Moon during Apollo 16 mission. Charles M. Duke Jr. took this picture. The LM Orion is on the left. April 21, 1972. Credit: NASA

It is a common misconception that the Apollo astronauts didn’t see any stars. While stars don’t show up in the pictures from the Apollo missions, that’s because the camera exposures were set to allow for good images of the bright sunlit lunar surface, which included astronauts in bright white space suits and shiny spacecraft. Apollo astronauts reported they could see the brighter stars if they stood in the shadow of the Lunar Module, and also they saw stars while orbiting the far side of the Moon. Al Worden from Apollo 15 has said the sky was “awash with stars” in the view from the far side of the Moon that was not in daylight.

Just like stargazers on Earth need dark skies to see stars, so too when you’re in space.

The cool thing about being in the ISS is that astronauts experience nighttime 16 times a day (in 45 minute intervals) as they orbit the Earth every 90 minutes, and can have extremely dark skies when they are on the “dark” side of Earth. Here’s another recent picture from Fischer where stars can be seen:

For stars to show up in any image, its all about the exposure settings. For example, if you are outside (on Earth) on a dark night and can see thousands of stars, if you just take your camera or phone camera and snap a quick picture, you’ll just get a darkness. Earth-bound astrophotographers need long-exposure shots to capture the Milky Way. Same is true with ISS astronauts: if they take long-exposure shots, they can get stunning images like this one:

This long exposure image of the night sky over Earth was taken on August 9, 2015 by a member of the Expedition 44 crew on board the International Space Station. Credit: NASA.

This image, set to capture the bright solar arrays and the rather bright Earth (even though its in twilight) reveals no stars:

In this timelapse of Earth at night, a few stars show up, but again, the main goal here was to have the camera capture the Earth:

Universe Today’s Bob King has a good, detailed explanation of how astronauts on the ISS can see stars on his Astro Bob blog Astrophysicist . Brian Koberlein explains it on his blog, here.

You can check out all the images that NASA astronauts take from the ISS on the “Astronaut Photography of Earth” site, and almost all the ISS astronauts and cosmonauts have social media accounts where they post pictures. Jack Fischer, currently on board, tweets great images and videos frequently here.

Posted on by Nancy Atkinson

Satellite Images Show a Trillion Ton Iceberg Broke Off Antarctica

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this image of the gigantic new iceberg on July 12, 2017. NASA Earth Observatory image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response.

For several months, scientists have been keeping an eye on a piece of Antarctica’s Larsen C ice shelf, waiting for the inevitable. And now it has happened.

Sometime between July 10 and July 12, 2017 a trillion ton iceberg split off, “changing the outline of the Antarctic Peninsula forever,” said one scientist.

The new iceberg is now called A68, and at 2,240 square miles (5,800 square km) it is one of the biggest ever recorded, about the size of Delaware in the US, or twice the size of Luxembourg.

A fissure on the ice shelf first appeared several years ago, but seemed relatively stable until January 2016, when it began to lengthen. In January 2017 alone, the crack grew by 20 km, reaching a total length of about 175 km.

Witnessed by the Copernicus Sentinel-1 mission on 12 July 2017, a large iceberg has broken off the Larsen-C ice shelf, one of the largest icebergs on record. Credit: Modified Copernicus Sentinel data (2017), processed by ESA.

The calving of the iceberg was confirmed by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite and was reported this morning by Project MIDAS, an Antarctic research project based in the UK.

The MODIS instrument on NASA’s Aqua satellite also confirmed the complete separation of the iceberg.

Larsen C is a floating platform of glacial ice on the east side of the Antarctic Peninsula, is the fourth largest ice shelf ringing Earth’s southernmost continent. With the break-off of this iceberg, the Larsen C shelf area has shrunk by approximately 10 percent.

Some scientists say the Larsen C rift and iceberg calving is not a warning of imminent sea level rise, and linking climate change to this specific event is complicated. Adrian Luckman, Professor of Glaciology and Remote Sensing from Swansea University wrote a detailed explanation of this for The Conversation.

The new iceberg would barely fit inside Wales. Credit: Adrian Luckman / MIDAS

David Vaughan, glaciologist and Director of Science at British Antarctic Survey (BAS), said, “Larsen C itself might be a result of climate change, but, in other ice shelves we see cracks forming, which we don’t believe have any connection to climate change. For instance on the Brunt Ice Shelf where BAS has its Halley Station, there those cracks are a very different kind which we don’t believe have any connection to climate change.”

While Vaughan said they see no obvious signal that climate warming is causing the whole of Antarctica to break up, he added that there is little doubt that climate change is causing ice shelves to disappear in some parts of Antarctica at the moment.

“Around the Antarctic Peninsula, where we saw several decades of warming through the latter half of the 20th century, we have seen these ice shelves collapsing and ice loss increasing,” he said. “There are other parts of the Antarctica that which are losing ice to the oceans but those are affected less by atmospheric warming and more by ocean change.

Scientists said the loss of such a large piece is of interest because ice shelves along the peninsula play an important role in ‘buttressing’ glaciers that feed ice seaward, effectively slowing their flow.

“The interesting thing is what happens next, how the remaining ice shelf responds,” said Kelly Brunt, a glaciologist with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland in College Park. “Will the ice shelf weaken? Or possibly collapse, like its neighbors Larsen A and B? Will the glaciers behind the ice shelf accelerate and have a direct contribution to sea level rise? Or is this just a normal calving event?”

The U.S. National Ice Center will monitor the trajectory of the new iceberg, but they don’t expect it to travel far very fast, and it shouldn’t cause any immediate problems for navigation of ships.

See additional imagery and animations from Goddard Space Flight Center.

Sources and additional reading:
ESA, British Antarctic Survey, NASA.

Posted on by Matt Williams

How Long is a Day on the Moon?

A photo of the full moon, taken from Apollo 11 on its way home to Earth, from about 18,520 km (10,000 nm) away. Credit: NASA
A photo of the full moon, taken from Apollo 11 on its way home to Earth, from about 18,520 km (10,000 nm) away. Credit: NASA

The Moon has been around since the earliest days of the Solar System. To human beings, there has never been a time when we couldn’t look up in the night sky and either see the Moon hanging there, or know that it would be back the very next night (i.e. a New Moon). And thanks to the development of modern astronomy and space exploration, our understanding of the Moon has grown immensely.

For instance, we know that the Moon formed early in Earth’s history, and that it may have played an important role in the development of life here on Earth. We’ve also learned that Moon is tidally-locked with Earth, which means that one side is constantly facing towards it. But how long is a day on the Moon? With one side facing the Earth and the other side facing out, what constitutes a single day on the lunar surface?

To break it down simply, a day on the Moon lasts as long as 29.5 Earth days. In other words, if you were standing on the surface of the Moon, it would take 29.5 days for the Sun to move all the way across the sky and return to its original position again. However, as with all bodies in the Solar System, distinguishing between different types of days (based on different types of periods) is necessary.

Orbit and Rotation:

Since ancient times, lunar calendars have been based on thirteen months of 28 days each, reflecting the lunar cycle. But as astronomers have discovered from centuries of studying the Moon’s behavior, the Moon’s orbital period (i.e. the time it takes for the Moon to complete a single orbit around the Earth) is actually the equivalent of about 27.3 Earth days – or 27 days 7 hours 43 minutes and 11.5 seconds, to be precise.

And while the Moon rotates on its own axis, the speed at which it rotates (aka. it’s sidereal rotation) is very slow. In fact, it takes the Moon the equivalent of 27.3 Earth days to complete a single rotation on its axis, the same amount of time it takes to complete a single orbit around Earth.  What this means is that the Moon is tidally-locked with Earth.

In other words, the Moon always points the same face towards the Earth, which is why human beings are so familiar with the “face” of the Moon, and refer to the side that faces away from us as the “the dark side”. Therefore, if you were standing on the surface of the Moon, you would always see the Earth in exactly the same position, while the stars and the Sun would continue to move around in the sky.

Sidereal vs. Synodic Day:

However, the Moon’s sidereal rotation is not where we get a the value of a single lunar day from. While it takes 27.3 days for it to orbit the Earth, we have to keep in mind that the Earth is also orbiting the Sun. The Earth returns to its same position in orbit every 365 days. So in order for the Sun to catch up to its same position in the sky from the perspective of the Moon, it has to turn a little more.

The extra 2.2 days is the time for the Moon to catch up in its rotation. And while the amount of time the Moon takes to complete one turn on its axis with respect to the stars is 27.3 days (a sidereal day), the amount of time it takes for the Sun to return to the same position in the sky is called a synodic day, and that’s what takes 29.5 days.

Ergo, a single day on the Moon, with respect to the Sun returning to the same position in the sky, is actually about as long as an average month here on Earth. So if people are planning on living there someday, and aren’t living in the permanently shadowed craters that exist in the southern and norther polar regions, that’s something they might have to get used to.

As with all the bodies of the Solar System, it all comes down to a matter of perspective. And if you’re living on the Moon, your perspective on what constitutes a day will be vastly different from that of a person who was born on Earth.

We have written many interesting articles about how long a day is on the planets of the Solar System. Here’s How Long is a Day on the Other Planets of the Solar System?, How Long is a Day on Mercury?, How Long is a Day on Venus?, How Long is a Day on the Earth?, How Long is a Day on Mars?, How Long is a Day on Jupiter?, How Long is a Day on Saturn?, How Long is a Day on Uranus?, How Long is a Day on Neptune?, and How Long is a Day on Pluto?

For more information, check out NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

Astronomy Cast also has a good episode on the subject. Listen here: Episode 17: Where Did the Moon Come From?

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