May 10, 2018May 10, 2018 by Matt Williams

The Giant Planets in the Solar System Stunted the Growth of Mars

A new study led by researchers from OU indicates that the outer planets could be why Mars is significantly smaller than Earth. Credit: NASA

For centuries, astronomers and scientists have sought to understand how our Solar System came to be. Since that time, two theories have become commonly-accepted that explain how it formed and evolved over time. These are the Nebular Hypothesis and the Nice Model, respectively. Whereas the former contends that the Sun and planets formed from a large cloud of dust and gas, the latter maintains the giant planets have migrated since their formation.

This is what has led to the Solar System as we know it today. However, an enduring mystery about these theories is how Mars came to be the way it is. Why, for example, is it significantly smaller than Earth and inhospitable to life as we know it when all indications show that it should be comparable in size? According to a new study by an international team of scientists, the migration of the giant planets could have been what made the difference.

For over a decade, astronomers have been operating under the assumption that shortly after the formation of the Solar System, the gas and ice giants of the outer Solar System (Jupiter, Saturn, Uranus and Neptune) began to migrate outward. This is the substance of the Nice Model, which asserts that this migration had a profound effect on the evolution of the Solar System and the formation of the terrestrial planets.

This model – named for the location of the Observatoire de la Côte d’Azur (in Nice, France), where it was initially developed – began as an evolutionary model that helped explain the observed distributions of small objects like comets and asteroids. As Matt Clement, a graduate student in the HL Dodge Department of Physics and Astronomy at the University of Oklahoma and the lead author on the paper, explained to Universe Today via email:

“In the model, the giant planets (Jupiter, Saturn, Uranus and Neptune) originally formed much closer to the Sun. In order to reach their current orbital locations, the entire solar system undergoes a period of orbital instability. During this unstable period, the size and the shape of the giant planet’s orbits change rapidly.”

For the sake of their study, which was recently published in the scientific journal Icarus under the title “Mars Growth Stunted by an Early Giant Planet Instability“, the team expanded on the Nice Model. Through a series of dynamical simulations, they attempted to show how, during the early Solar System, the growth of Mars was halted thanks to the orbital instabilities of the giant planets.

The purpose of their study was also to address a flaw in the Nice Model, which is how the terrestrial planets could have survived a serious shake up of the Solar System. In the original version of the Nice Model, the instability of the giant planets occurred a few hundred million years after the planets formed, which coincided with the Late Heavy Bombardment – when the inner Solar System was bombarded by a disproportionately large number of asteroids.

This period is evidenced by spike in the Moon’s cratering record, which was inferred from an abundance of samples from the Apollo missions with similar geological dates. As Clement explained:

“A problem with this is that it is difficult for the terrestrial planets (Mercury, Venus, Earth and Mars) to survive the violent instability without being ejected out of the solar system or colliding with one another. Now that we have better, high resolution images of lunar craters and more accurate methods for dating the Apollo samples, the evidence for a spike in lunar cratering rates is diminishing. Our study investigated whether moving the instability earlier, while the inner terrestrial planets were still forming, could help them survive the instability, and also explain why Mars is so small relative to the Earth.”

Clement was joined by Nathan A. Kaib, a OU astrophysics professor, as well as Sean N. Raymond of the University of Bordeaux and Kevin J. Walsh from the Southwest Research Institute. Together, they used the computing resources of the OU Supercomputing Center for Education and Research (OSCER) and the Blue Waters supercomputing project to perform 800 dynamical simulations of the Nice model to determine how it would impact Mars.

These simulations incorporated recent geological evidence from Mars and Earth that indicate that Mars’ formation period was about 1/10th that of Earth’s. This has led to the theory that Mars was left behind as a “stranded planetary embryo” during the formation of the Sun’s inner planets. As Prof. Kaib explained to Universe Today via email, this study was therefore intended to test how Mars emerged from planetary formation as a planetary embryo:

“We simulated the “giant impact phase” of terrestrial planet formation (the final stage of the formation process). At the beginning of this phase, the inner Solar System (0.5-4 AU) consists of a disk of about 100 moon-to-mars-sized planetary embryos embedded in a sea of much smaller, more numerous rocky planetesimals. Over the course of 100-200 million years the bodies making up this system collide and merge into a handful (typically 2-5) rocky planetary mass bodies. Normally, these types of simple initial conditions build planets on Mars-like orbits that are about 10x more massive than Mars. However, when the terrestrial planet formation process is interrupted by the Nice model instability, many of the planet building blocks near the Mars region are lost or tossed into the Sun. This limits the growth of Mars-like planets and produces a closer match to our actual inner solar system.”

*Size comparison between Earth and Mars. Credit: NASA*

What they found was that this revised timeline explained the disparity between Mars and Earth. In short, Mars and Earth vary considerably in size, mass and density because the giant planets became unstable very early in the Solar System’s history. In the end, this is what allowed Earth to become the only life-bearing terrestrial planet in the Solar System, and for Mars to become the cold, desiccated and thinly-atmosphered place that it is today.

As Prof. Kaib explained, this is not the only model for explaining the disparity between Earth and Mars, but the evidence all fits:

“Without this instability, Mars likely would have had a mass closer to Earth’s and would be a very different, perhaps more Earth-like, planet compared to what it is today,” he said. “I should also say that this is not the only mechanism capable of explaining the low mass of Mars. However, we already know that the Nice model does an excellent job of reproducing many features of the outer Solar System, and if it occurs at the right time in the Solar System’s history it also ends up explaining our inner Solar System.”

This study could also have drastic implications when it comes to the study of extra-solar systems. At present, our models for how planets form and evolve are based on what we have been able to learn from our own Solar System. Hence, by learning more about how gas giants and terrestrial planets grew and assumed their current orbits, scientists will be able to create more comprehensive models of how life-bearing planets could merge around other stars.

It certainly would help narrow the search for “Earth-like” planets and (dare we dream?) planets that support life.

Further Reading: University of Oklahoma, Icarus

April 19, 2018 by Evan Gough

This Meteorite is One of the Few Remnants from a Lost Planet that was Destroyed Long Ago

This photos shows a very thing slice of the meteorite in the study. The meteorite, called the Almahata Sitta ureilite, crashed in Sudan's Nubian Desert 2008. Photo: (Hillary Sanctuary/EPFL via AP)

What if our Solar System had another generation of planets that formed before, or alongside, the planets we have today? A new study published in Nature Communications on April 17th 2018 presents evidence that says that’s what happened. The first-generation planets, or planet, would have been destroyed during collisions in the earlier days of the Solar System and much of the debris swept up in the formation of new bodies.

This is not a new theory, but a new study brings new evidence to support it.

The evidence is in the form of a meteorite that crashed into Sudan’s Nubian Desert in 2008. The meteorite is known as 2008 TC3, or the Almahata Sitta meteorite. Inside the meteorite are tiny crystals called nanodiamonds that, according to this study, could only have formed in the high-pressure conditions within the growth of a planet. This contrasts previous thinking around these meteorites which suggests they formed as a result of powerful shockwaves created in collisions between parent bodies.

“We demonstrate that these large diamonds cannot be the result of a shock but rather of growth that has taken place within a planet.” – study co-author Philippe Gillet

Models of planetary formation show that terrestrial planets are formed by the accretion of smaller bodies into larger and larger bodies. Follow the process long enough, and you end up with planets like Earth. The smaller bodies that join together are typically between the size of the Moon and Mars. But evidence of these smaller bodies is hard to find.

One type of unique and rare meteorite, called a ureilite, could provide the evidence to back up the models, and that’s what fell to Earth in the Nubian Desert in 2008. Ureilites are thought to be the remnants of a lost planet that was formed in the first 10 million years of the Solar System, and then was destroyed in a collision.

Ureilites are different than other stony meteorites. They have a higher component of carbon than other meteorites, mostly in the form of the aforementioned nanodiamonds. Researchers from Switzerland, France and Germany examined the diamonds inside 2008 TC3 and determined that they probably formed in a small proto-planet about 4.55 billion years ago.

Philippe Gillet, one of the study’s co-authors, had this to say in an interview with Associated Press: “We demonstrate that these large diamonds cannot be the result of a shock but rather of growth that has taken place within a planet.”

According to the research presented in this paper, these nanodiamonds were formed under pressures of 200,000 bar (2.9 million psi). This means the mystery parent-planet would have to have been as big as Mercury, or even Mars.

The key to the study is the size of the nanodiamonds. The team’s results show the presence of diamond crystals as large as 100 micrometers. Though the nanodiamonds have since been segmented by a process called graphitization, the team is confident that these larger crystals are there. And they could only have been formed by static high-pressure growth in the interior of a planet. A collision shock wave couldn’t have done it.

This is what’s called a High-Angle Annular Dark-Field (HAADF) Scanning Transmission Electron Microscopy (STEM) image. The image on the left shows diamond segments with similar crystal orientations. The image on the right is a magnification of the green square area. The orange lines highlight the inclusion trails, which match between the diamond segments. But those same trails are absent from the intersecting graphite. Image: Farhang Nabiei, Philippe Gillet, et. al.

But the parent body of the ureilite meteorite in the study would have to have been subject to collisions, otherwise where is it? In the case of this meteorite, a collision and resulting shock wave still played a role.

The study goes on to say that a collision took place some time after the parent body’s formation. And this collision would have produced the shock wave that caused the graphitization of the nanodiamonds.

The key evidence is in what are called High-Angle Annular Dark-Field (HAADF) Scanning Transmission Electron Microscopy (STEM) images, as seen above. The image is two images in one, with the one on the right being a magnification of a part of the image on the left. On the left, dotted yellow lines indicate areas of diamond crystals separate from areas of graphite. On the right is a magnification of the green square.

The inclusion trails are what’s important here. On the right, the inclusion trails are highlighted with the orange lines. They clearly indicate inclusion lines that match between adjacent diamond segments. But the inclusion lines aren’t present in the intervening graphite. In the study, the researchers say this is “undeniable morphological evidence that the inclusions existed in diamond before these were broken into smaller pieces by graphitization.”

To summarize, this supports the idea that a small planet between the size of Mercury and Mars was formed in the first 10 million years of the Solar System. Inside that body, large nanodiamonds were formed by high-pressure growth. Eventually, that parent body was involved in a collision, which produced a shock wave. The shock wave then caused the graphitization of the nanodiamonds.

It’s an intriguing piece of evidence, and fits with what we know about the formation and evolution of our Solar System.

Sources:

April 13, 2018 by Evan Gough

Look at This Fascinating Variety of Planet-Forming Disks Around Other Stars

This is just one of the spectacular images of dusky discs from the SPHERE instrument on ESO's Very Large Telescope. It shows the disc around the young star IM Lupi in finer detail than ever before. The collection of images shows the fascinating variety of shapes and sizes of discs. Image: ESO/H. Avenhaus et al./DARTT-S collaboration

The European Southern Observatory (ESO) has released a stunning collection of images of the circumstellar discs that surround young stars. The images were captured with the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument on the ESO’s Very Large Telescope (VLT) in Chile. We’ve been looking at images of circumstellar disks for quite some time, but this collection reveals the fascinating variety of shapes an sizes that these disks can take.

New images from the SPHERE instrument on ESO’s Very Large Telescope are revealing the dusty discs surrounding nearby young stars in greater detail than previously achieved. They show a bizarre variety of shapes, sizes and structures, including the likely effects of planets still in the process of forming. Image: ESO/H. Avenhaus et al./E. Sissa et al./DARTT-S and SHINE collaborations

We have a widely-accepted model of star formation supported by ample evidence, including images like these ones from the ESO. The model starts with a cloud of gas and dust called a giant molecular cloud. Within that cloud, a pocket of gas and dust begins to coalesce. Eventually, as gravity causes material to fall inward, the pocket becomes more massive, and exerts even more gravitational pull. More gas and dust continues to be drawn in.

The material that falls in also gives some angular momentum to the pocket, which causes rotation. Once enough material is accumulated, fusion ignites and a star is born. At that point, there is a proto-star inside the cloud, with unused gas and dust remaining in a rotating ring around the proto-star. That left over rotating ring is called a circumstellar disc, out of which planets eventually form.

There are other images of circumstellar discs, but they’ve been challenging to capture. To image any amount of detail in the disks requires blocking out the light of the star at the center of the disk. That’s where SPHERE comes in.

A detailed view of the SPHERE instrument and its main subsystems. SPHERE is installed on the ESO’s VLT and saw first light in 2014. Image: ESO

SPHERE was added to the ESO’s Very Large Telescope in 2014. It’s primary job is to directly image exoplanets, but it also has the ability to capture images of circumstellar discs. To do that, it separates two types of light: polarized, and non-polarized.

Light coming directly from a star—in these images, a young star still surrounded by a circumstellar disc—is non-polarized. But once that starlight is scattered by the material in the disk itself, the light becomes polarized. SPHERE, as its name suggests, is able to separate the two types of light and isolate just the light from the disk. That is how the instrument captures such fascinating images of the disks.

An edge-on view of the disc surrounding the star GSC 07396-00759. The disc extends from the lower-left to the upper-right and the central grey region shows where the star was masked out. Credit:
ESO/E. Sissa et al.

Ever since it became clear that exoplanets are not rare, and that most stars—maybe all stars—have planets orbiting them, understanding solar system formation has become a hot topic. The problem has been that we can’t really see it happening in real time. We can look at our own Solar System, and other fully formed ones, and make guesses about how they formed. But planet formation is hidden inside those circumstellar disss. Seeing into those disks is crucial to understanding the link between the properties of the disk itself and the planets that form in the system.

The discs imaged in this collection are mostly from a study called the DARTTS-S (Discs ARound T Tauri Stars with SPHERE) survey. T Tauri stars are young stars less than 10 million years old. At that age, planets are still in the process of forming. The stars range from 230 to 550 light-years away from Earth. In astronomical terms, that’s pretty close. But the blinding bright light of the stars still makes it very difficult to capture the faint light of the discs.

One of the images is not a T Tauri star and is not from the DARTTS-S study. The disc around the star GSC 07396-00759, in the image above, is actually from the SHINE (SpHere INfrared survey for Exoplanets) survey, though the images itself was captured with SPHERE. GSC 07396-00759 is a red star that’s part of a multiple star system that was part of the DARTTS-S study. The puzzling thing is that red star is the same age as the T TAURI star in the same system, but the ring around the red star is much more evolved. Why the two discs around two stars the same age are so different from each other in terms of time-scale and evolution is a puzzle, and is one of the reasons why astronomers want to study these discs much more closely.

We can study our own Solar System, and look at the positions and characteristics of the planets and the asteroid belt and Kuiper Belt. From that we can try to guess how it all formed, but our only chance to understand how it all came together is to look at other younger solar systems as they form.

The SPHERE instrument, and other future instruments like the James Webb Space Telescope, will allow us to look into the circumstellar discs around other stars, and to tease out the details of planetary formation. These new images from SPHERE are a tantalizing taste of the detail and variety we can expect to see.

March 22, 2018 by Evan Gough

70,000 Years Ago a Nearby Star Messed With the Orbits Of Comets and Asteroids in our Solar System

70,000 years ago, Scholz's star, a red dwarf, came as close as 1 light-year to our Solar System. It could have perturbed the Oort Cloud. At that time, Neanderthals were still around. Image: Credit: José A. Peñas/SINC — 70,000 years ago, Scholz's star, a red dwarf, came as close as 1 light year to our Solar System. At that time, neanderthals were still around. Image: Credit: José A. Peñas/SINC

70,000 years ago, our keen-eyed ancestors may have noticed something in the sky: a red dwarf star that came as close as 1 light year to our Sun. They would’ve missed the red dwarf’s small, dim companion—a brown dwarf—and in any case they would’ve quickly returned to their hunting and gathering. But that star’s visit to our Solar System had an impact astronomers can still see today.

The star in question is called Scholz’s star, after astronomer Ralf-Dieter Scholz, the man who discovered it in 2013. A new study published in the Monthly Notices of the Royal Astronomical Society by astronomers at the Complutense University of Madrid, and at the University of Cambridge, shows the impact Scholz’s star had. Though the star is now almost 20 light years away, its close approach to our Sun changed the orbits of some comets and asteroids in our Solar System.

When it came to our Solar System 70,000 years ago, Scholz’s star entered the Oort Cloud. The Oort Cloud is a reservoir of mostly-icy objects that spans the range from about 0.8 to 3.2 light years from the Sun. Its visit to the Oort Cloud was first explained in a paper in 2015. This new paper follows up on that work, and shows what impact the visit had.

“Using numerical simulations, we have calculated the radiants or positions in the sky from which all these hyperbolic objects seem to come.” – Carlos de la Fuente Marcos, Complutense University of Madrid.

In this new paper, the astronomers studied almost 340 objects in our Solar System with hyperbolic orbits, which are V-shaped rather than elliptical. Their conclusion is that a significant number of these objects had their trajectories shaped by the visit from Scholz’s star. “Using numerical simulations, we have calculated the radiants or positions in the sky from which all these hyperbolic objects seem to come,” explains Carlos de la Fuente Marcos, a co-author of the study now published in Monthly Notices of the Royal Astronomical Society. They found that there’s a cluster of these objects in the direction of the Gemini Constellation.

A comparison of the Solar System and its Oort Cloud. 70,000 years ago, Scholz’s Star and companion passed along the outer boundaries of our Solar System (Credit: NASA, Michael Osadciw/University of Rochester)

“In principle,” he adds, “one would expect those positions to be evenly distributed in the sky, particularly if these objects come from the Oort cloud. However, what we find is very different—a statistically significant accumulation of radiants. The pronounced over-density appears projected in the direction of the constellation of Gemini, which fits the close encounter with Scholz’s star.”

There are four ways that objects like those in the study can gain hyperbolic orbits. They might be interstellar, like the asteroid Oumuamua, meaning they gained those orbits from some cause outside our Solar System. Or, they could be natives of our Solar System, originally bound to an elliptical orbit, but cast into a hyperbolic orbit by a close encounter with one of the planets, or the Sun. For objects originally from the Oort Cloud, they could start on a hyperbolic orbit because of interactions with the galactic disc. Finally, again for objects from the Oort Cloud, they could be cast into a hyperbolic orbit by interactions with a passing star. In this study, the passing star is Scholz’s star.

In this image the blue is a hyperbolic orbit while the green is a parabolic orbit. Image: By ScottAlanHill [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

The timing of Scholz’s star’s visit to the Oort Cloud and our Solar System strongly coincides with the data in this study. It’s very unlikely to be coincidental. “It could be a coincidence, but it is unlikely that both location and time are compatible,” says De la Fuente Marcos. In fact, De la Fuente Marcos points out that their simulations suggest that Scholz’s star approached even closer than the 0.6 light-years pointed out in the 2015 study.

The one potentially weak area of this study is pointed out by the authors themselves. As they say in their summary, “…due to their unique nature, the orbital solutions of hyperbolic minor bodies are based on relatively brief arcs of observation and this fact has an impact on their reliability. Out of 339 objects in the sample, 232 have reported uncertainties and 212 have eccentricity with statistical significance.” Translated, it means that some of the computed orbits of individual objects may have errors. But the team expects the overall conclusions of their study to be correct.

The study of minor objects with hyperbolic orbits has heated up since the interstellar asteroid Oumuamua made its visit. This new study successfully connects one population of hyperbolic objects with a pre-historic visit to our Solar System by another star. The team behind the study expects that follow up studies will confirm their results.

March 10, 2018 by Matt Williams

Jupiter’s Atmospheric Bands Go Surprisingly Deep

Jupiter's colorful stripes are cloud belts that extend thousand of kilometers deep. NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill

For centuries, astronomers have been observing Jupiter swirling surface and been awed and mystified by its appearance. The mystery only deepened when, in 1995, the Galileo spacecraft reached Jupiter and began studying its atmosphere in depth. Since that time, astronomers have puzzled over its colored bands and wondered if they are just surface phenomenon, or something that goes deeper.

Thanks to the Juno spacecraft, which has been orbiting Jupiter since July of 2016, scientists are now much closer to answering that question. This past week, three new studies were published based on Juno data that presented new findings on Jupiter’s magnetic field, its interior rotation, and how deep its belts extend. All of these findings are revising what scientists think of Jupiter’s atmosphere and its inner layers.

The studies were titled “Measurement of Jupiter’s asymmetric gravity field“, “Jupiter’s atmospheric jet streams extend thousands of kilometres deep” and “A suppression of differential rotation in Jupiter’s deep interior“, all of which were published in Nature on March 7th, 2018. The studies were led by Prof. Luciano Iess of Sapienza University of Rome, the second by Prof. Yohai Kaspi and Dr. Eli Galanti of the Weizmann Institute of Science, and the third by Prof. Tristan Guillot of the Observatoire de la Cote d’Azur.

*Jupiter’s South Pole, taken during a Juno flyby on Dec 16th, 2017. Credit: NASA/JPL-Caltech/SwRI/MSSS/David Marriott*

The research effort was led by Professo Kaspi and Dr. Galanti, who in addition to being the lead authors on the second study were co-authors on the other two. The pair have been preparing for this analysis even before Juno launched in 2011, during which time they built mathematical tools to analyze the gravitational field data and get a better grasp of Jupiter’s atmosphere and its dynamics.

All three studies were based on data gathered by Juno as it passed from one of Jupiter’s pole to the other every 53-days – a maneuver known as a “perijove”. With each pass, the probe used its advanced suite of instruments to peer beneath the surface layers of the atmosphere. In addition, radio waves emitted by the probe were measured to determine how they were shifted by the planet’s gravitational field with each orbit.

As astronomers have understood for some time, Jupiter’s jets flow in bands from east to west and west to east. In the process, they disrupt the even distribution of mass on the planet. By measuring changes in the planet’s gravity field (and thus this mass imbalance), Dr. Kaspi and Dr. Galanti’s analytical tools were able to calculate how deep the storms extend beneath the surface and what it’s interior dynamics are like.

Above all, the team expected to find anomalies because of the way the planet deviates from being a perfect sphere – which is due to how its rapid rotation squishes it slightly. However, they also looked for additional anomalies that could be explained due to the presence of powerful winds in the atmosphere.

This image from Juno’s JunoCam captured the south pole in visible light only. It’s a puzzle why the north and south poles are so similar, yet have a different number of cyclones. Image: NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles

In the first study, Dr. Iess and his colleagues used precise Doppler tracking of the Juno spacecraft to conduct measurements of Jupiter’s gravity harmonics – both even and odd. What they determined was Jupiter’s magnetic field has a north-south asymmetry, which is indicative of interior flows in the atmosphere.

Analysis of this asymmetry was followed-up on in the second study, where Dr. Kaspi, Dr. Galanti and their colleagues used the variations in the planet’s gravity field to calculate the depth of Jupiter’s east-west jet streams. By measuring how these jets cause an imbalance in Jupiter’s gravity field, and even disrupt the mass of the planet, they concluded that they extend to a depth of 3000 km (1864 mi).

From all this, Prof. Guillot and his colleagues conducted the third study, where they used the previous findings about the planet’s gravitational field and jet streams and compared the results to predictions of interior models. From this, they determined that the interior of the planet rotates almost like a rigid body and that differential rotation decreases farther down.

In addition, they found that the zones of atmospheric flow extended to between 2,000 km (1243 mi) and 3,500 km (2175 mi) deep, which was consistent with the constraints obtained from the odd gravitational harmonics. This depth also corresponds to the point where electric conductivity would become large enough that magnetic drag would suppress differential rotation.

Based on their findings, the team also calculated that Jupiter’s atmosphere constitutes 1% of its total mass. For comparison, Earth’s atmosphere is less than a millionth of its total mass. Still, as Dr. Kaspi explained in Weizzmann Institute press release, this was rather surprising:

“That is much more than anyone thought and more than what has been known from other planets in the Solar System. That is basically a mass equal to three Earths moving at speeds of tens of meters per second.”

All told, these studies have shed new light on the Jupiter’s atmospheric dynamics and interior structure. At present, the subject of what resides at Jupiter’s core remains unresolved. But the researchers hope to analyze further measurements made by Juno to see whether Jupiter has a solid core and (if so) to determine its mass. This in turn will help astronomers learn a great deal about the Solar System’s history and formation.

In addition, Kaspi and Galanti are looking to use some of the same methods they developed to characterize Jupiter’s jet streams to tackle its most iconic feature – Jupiter’s Great Red Spot. In addition to determining how deep this storm extends, they also hope to learn why this storm has persisted for so many centuries, and why it has been noticeably shrinking in recent years.

The Juno mission is expected to wrap up in July of 2018. Barring any extensions, the probe will conduct a controlled deorbit into Jupiter’s atmosphere after conducting perijove 14. However, even after the mission is over, scientists will be analyzing the data it has collected for years to come. What this reveals about the Solar System’s largest planet will also go a long way towards informing out understanding of the Solar System.

Further Reading: Weizmann Institute of Science, Nature, Nature (2), Nature (3),

March 9, 2018 by Evan Gough

Gaze in Wonder at Jupiter’s Mysterious Geometric Polar Storms

This wondrous image of Jupiter's south pole shows the arrangement of cyclones that is unique in our Solar System: five circumpolar cyclones perfectly arranged around a single polar cyclone. Image: NASA/SWRI/JPL/ASI/INAF/IAPS

When the Juno spacecraft arrived at Jupiter in July 2016, it quickly got to work. Among the multitude of stunning images of the planet were our first ever images of Jupiter’s poles. And what we saw there was a huge surprise: geometric arrangements of cyclones in persistent patterns.

Jupiter’s polar regions have always been a mystery to Earth-bound observers. The planet isn’t tilted much, which means the poles are always tantalizingly out of view. Other spacecraft visiting Jupiter have focused on the equatorial regions, but Juno’s circumpolar orbit is giving us good, close-up views of Jupiter’s poles.

“They are extraordinarily stable arrangements of such chaotic elements. We’d never seen anything like it.” – Morgan O’Neill, University of Chicago

Juno has a whole suite of instruments designed to unlock some of the mysteries surrounding Jupiter, including an infrared imager and a visible light camera. The polar regions are a particular focus for the mission, and astronomers were looking forward to their first views of Jupiter’s hidden poles. They were not disappointed when they got them.

Each of Jupiter’s poles is a geometric array of large cyclones arranged in persistent, polygonal patterns. At the north pole, eight storms are arranged around a single polar cyclone. In the south, one storm is encircled by five others.

Jupiter’s north pole is an arrangement of 8 cyclones around one central cyclone. Image: NASA/SWRI/JPL/ASI/INAF/IAPS

This was a stunning discovery, and quickly led to questions around the why and the how of these storm arrangements. Jupiter’s atmosphere is dominated by storm activity, including the well-known horizontal storm bands in the equatorial regions, and the famous Great Red Spot. But these almost artful arrangements of polar storms were something else.

The persistent arrangement of the storms is a puzzle. Our current understanding tells us that the storms should drift around and merge, but these storms do neither. They just turn in place.

A new paper published in Nature is looking deeper into these peculiar arrangements of storms. The paper is by scientists from an international group of institutions including the University of Chicago. It’s one of four papers dedicated to new observations from the Juno spacecraft.

One of the paper’s co-authors is Morgan O’Neill, a University of Chicago postdoctoral scholar. Remarking on the storms, she had this to say: “They are extraordinarily stable arrangements of such chaotic elements. We’d never seen anything like it.”

The strange geometrical arrangement of Jupiter’s polar storms reminded O’Neill of something from the library of strange physical phenomena only observed under laboratory conditions. Back in the ’90s, scientists had used electrons to simulate a frictionless, turbulent 2-D fluid as it cools. In those conditions, they observed similar behaviour. Rather than merging like expected, small vortices clumped together and formed equally spaced arrays around a center. They called these arrays “vortex crystals.”

This could help explain what’s happening at Jupiter’s poles, but it’s too soon to be certain. “The next step is: Can you create a model that builds a virtual planet and predicts these flows?” O’Neill said. That’ll be the next step in understanding the phenomenon.

Maybe it’s not surprising that these delicate-looking storms at the poles are so persistent. After all, the Great Red Spot on Jupiter has been visible for over 200 years. Maybe Jupiter is just huge and stable.

But the polar cyclones still require an explanation. And whatever that explanation is, understanding what’s happening on Jupiter will help us understand other planets better.

February 21, 2018 by Evan Gough

How Badly Will Humanity Freak Out if We Discover Alien Life?

The Search for Extraterrestrial Intelligence (SETI) listens for radio signals from other civilizations. In this image, radio-telescopes in SETI's Allen Telescope Array (ATA) are hard at work with the Milky Way in the background. Image: SETI

The discovery of alien life is one of those things that everyone thinks about at some point. Hollywood has made their version of first contact very clear: huge alien vessels appear over Earth’s cities, panic ensues, and Will Smith saves the day with a Windows 3.1 virus. It’s lots of fun—and who knows?—it may end up being accurate. (Not the Windows 3.1 part.) But sci-fi books and movies aside, what do we really know about our attitude to the discovery of alien life?

We have an organization (SETI) dedicated to detecting the presence of alien civilizations, and we have a prominent scientist (Stephen Hawking) warning against advertising our own presence. Those represent the extremes—actively seeking out alien life vs. hiding from it—but what is the collective attitude towards the discovery of alien life? Scientists at Arizona State University (ASU) have studied that issue and detailed their results in a new study published in the journal Frontiers of Psychology.

The team of scientists tried to gauge people’s reactions to the discovery of alien life in three separate parts of their study. In the first case, they examined media reports of past announcements about the discovery of alien life, for example the announcement in 1996 that evidence of microbial life had been found in a Martian metorite.

Secondly, they asked a sample of over 500 people what their own reactions, and the reactions of the rest of humanity, would be to the hypothetical announcement of alien life.

Thirdly, the 500 people were split into two groups. Half were asked to read and respond to a real newspaper story announcing the discovery of fossilized Martian microbial life. The other half were asked to read and respond to a newspaper article announcing the creation of synthetic life by Craig Venter.

Martian meteorite ALH84001 was found in Antarctica in 1984 by a group of meteorite hunters from the US. Scientists who studied it suggested that it contained evidence of ancient Martian microbial life. Image: By Jstuby at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=47556214

In all three cases the life was microbial in nature. Microbial life is the simplest life form, so it should be what we expect to find. This is certainly true in our own Solar System, since the existence of any other intelligent life has been ruled out here, while microbial life has not.

Also, in all three cases, the language of the respondents and the language in the media reports was analyzed for positive and negative words. A specialized piece of software called Linguistic Inquiry and Word Count (LIWC) was used. It’s text-analysis software that scans written language and identifies instances of words that reflect positive affect, negative affect, reward, or risk. (You can try LIWC here for fun, if you like.)

Electron microscope images of the Martian meteorite ALH84001 showed chain-like structures that resembled living structures. Image: NASA

Analyzing Media Reports

The media reports used in the study were all from what the team considers reputable journalism outlets like The New York Times and Science Magazine. The reports were about things like unidentified signals from space that could have been alien in nature, fossilized microbial remains in meteorites, and the discovery of exoplanets in the habitable zones of other solar systems. There were 15 articles in total.

The authors of the study wanted to find out how people would react to the discovery of alien life, and to the discovery of potentially habitable exoplanets which might harbor life. In this artist’s illustration, exoplanets orbit a young, red dwarf star. Credit: NASA/JPL-Caltec

Overall, the study showed that language in media reports about alien life was more positive than negative, and emphasized reward rather than risk. So people generally find the potential of alien life to be a positive thing and something to be looked forward to. However, this part of the study showed something else: People were more positively disposed towards news of alien life that was microbial than they were towards alien life that could be present on exoplanets, where, presumably, it might be more than merely microbial. So, microbes we can handle, but something more advanced and a little doubt starts to creep in.

Reactions to Hypothetical Announcements of Alien Life

This part of the study aimed to assess people’s beliefs regarding how both they as individuals—and humanity as a whole—might react to the discovery of alien microbial life. The same LIWC software was used to analyze the written responses of the 500 people in the sample group.

The results were similar to the first part of the study, at least for the individuals themselves. Positive affect was more predominant than negative aspect, and words reflecting reward were more predominant than words reflecting risk. This probably isn’t surprising, but the study did show something more interesting.

When participants were asked about how the rest of humanity would respond to the announcement of alien life, the response was different. While positive language still outweighed negative language, and reward still outweighed risk, the differences weren’t as pronounced as they were for individuals. So people seem to think that others won’t be looking forward to the discovery of alien life as much as they themselves do.

Actual Reactions to the Discovery of Extraterrestrial Life

This is hard to measure since we haven’t actually discovered any yet. But there have been times when we thought we might have.

In this part of the study, the group of 500 respondents was split into two groups of 250. The first was asked to read an actual 1996 New York Times article announcing the discovery of fossilized microbes in the Martian meteorite. The second group was asked to read a New York Times article from 2010 announcing the creation of life by Craig Venter. The goal was to find out if the positive bias towards the discovery of microbial life was specific to microbial life, or to scientific advancements overall.

Saturn’s moon Enceladus could harbor microbial life in the warm salty water thought to exist under its frozen surface. Respondents in the study seemed to like that possibility. Credits: NASA/JPL-Caltech/Space Science Institute

This part of the study found the same emphasis on positive affect over negative affect, and reward over risk. This held true in both cases: the Martian microbial life article, and the artificially created life article. The type of article played a minor role in people’s responses. Results were slightly more positive towards the Martian life story than the artificial life story.

Overall, this study shows that people seem positively disposed towards the discovery of alien life. This is reflected in media coverage, people’s personal responses, and people’s expectations of how others would react.

This is really just the tip of the iceberg, though. As the authors say in their study, this is the first empirical attempt to understand any of this. And the study was only 500 people, all Americans.

How different the results might be in other countries and cultures is still an open question. Would populations whose attitudes are more strongly shaped by religion respond differently? Would the populations of countries that have been invaded and dominated by other countries be more nervous about alien life or habitable exoplanets? There’s only conjecture at this point.

Maybe we’re novelty-seekers and we thrive on new discoveries. Or maybe we’re truth-seekers, and that’s reflected in the study. Maybe some of the positivity reflects our fear of being alone. If Earth is the only life-supporting world, that’s a very lonely proposition. Not only that, but it’s an awesome responsibility: we better not screw it up!

Still, the results are encouraging for humanity. We seem, at least according to this first study, open to the discovery of alien life.

But that might change when the first alien ship casts its shadow over Los Angeles.

February 16, 2018February 16, 2018 by Matt Williams

Interstellar Asteroid ‘Oumuamua Had a Violent Past

Artist’s impression of the first interstellar asteroid/comet, "Oumuamua". This unique object was discovered on 19 October 2017 by the Pan-STARRS 1 telescope in Hawaii. Credit: ESO/M. Kornmesser

On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) telescope in Hawaii announced the first-ever detection of an interstellar asteroid – I/2017 U1 (aka. ‘Oumuamua). Originally mistaken for a comet, follow-up observations conducted by the European Southern Observatory (ESO) and others confirmed that ‘Oumuamua was actually a rocky body that had originated outside of our Solar System.

Since that time, multiple investigations have been conducted to determine ‘Oumuamua’s structure, composition, and just how common such visitors are. At the same time, a considerable amount of attention has been dedicated to determining the asteroid’s origins. According to a new study by a team of international researchers, this asteroid had a chaotic past that causes it to tumble around chaotically.

The study, titled “The tumbling rotational state of 1I/‘Oumuamua“, recently appeared in the scientific journal Nature Astronomy. The study was led by Wesley C. Fraser, a research fellow at the University of Queens Belfast’s Astrophysics Research Center, and included members from the Academy of Sciences of the Czech Republic, the The Open University and the University of Belgrade.

As they indicate, the discovery of ‘Oumuamua has provided scientists with the first opportunity to study a planetesimal born in another planetary system. In much the same way that research into Near-Earth Asteroids, Main Belt Asteroids, or Jupiter’s Trojans can teach astronomers about the history and evolution of our Solar System, the study of a ‘Oumuamua would provide hints as to what was going on when and where it formed.

For the sake of their study, Dr. Fraser and his international team of colleagues have been measuring ‘Oumuamua brightness since it was first discovered. What they found was that ‘Oumuamua wasn’t spinning periodically (like most small asteroids and planetesimals in our Solar System), but chaotically. What this means is that the asteroid has likely been tumbling through space for billions of years, an indication of a violent past.

While it is unclear why this is, Dr. Fraser and his colleagues suspect that it might be due to an impact. In other words, when ‘Oumuamua was thrown from its own system and into interstellar space, it is possible it collided violently with another rock. As Dr. Fraser explained in a Queen’s University Belfast press release:

“Our modelling of this body suggests the tumbling will last for many billions of years to hundreds of billions of years before internal stresses cause it to rotate normally again. While we don’t know the cause of the tumbling, we predict that it was most likely sent tumbling by an impact with another planetesimal in its system, before it was ejected into interstellar space.”

These latest findings mirror what other studies have been able to determine about ‘Oumuamua based on its object changes in its brightness. For example, brightness measurements conducted by the Institute for Astronomy in Hawaii – and using data from the ESO’s Very Large Telescope (VLT) – confirmed that the asteroid was indeed interstellar in origin, and that its shape is highly elongated (i.e. very long and thin).

However, measurements of its color have produced little up until now other than confusion. This was due to the fact that the color appeared to vary between measurements. When the long face of the object is facing telescopes on Earth, it appears largely red, while the rest of the body has appeared neutral in color (like dirty snow). Based on their analysis, Dr. Fraser and his team resolved this mystery by indicating that the surface is “spotty”.

In essence, most of the surface reflects neutrally, but one of its long faces has a large red region – indicating the presence of tholins on its long surface. A common feature of bodies in the outer Solar System, tholins are organic compounds (i.e. methane and ethane) that have turned a deep shade of reddish-brown thanks to their exposure to ultra-violet radiation.

What this indicates, according to Dr. Fraser, is broad compositional variations on ‘Oumuamua, which is unusual for such a small body:

“We now know that beyond its unusual elongated shape, this space cucumber had origins around another star, has had a violent past, and tumbles chaotically because of it. Our results are really helping to paint a more complete picture of this strange interstellar interloper. It is quite unusual compared to most asteroids and comets we see in our own solar system,” comments Dr Fraser.

*Oumuamua as it appeared using the William Herschel Telescope on the night of October 29. Queen’s University Belfast/William Herschel Telescope*

To break it down succinctly, ‘Oumuamua may have originated closer to its parent star (hence its rocky composition) and was booted out by strong resonances. In the course of leaving its system, it collided with another asteroid, which sent it tumbling towards interstellar space. It’s current chaotic spin and its unusual color are both testaments to this turbulent past, and indicate that its home system and the Solar System have a few things in common.

Since its arrival in our system, ‘Oumuamua has set off a flurry of scientific research. All over the world, astronomers are hoping to get a glimpse of it before it leaves our Solar System, and there are even those who hope to mount a robotic mission to rendezvous with it before its beyond our reach (Project Lyra). In any event, we can expect that this interstellar visitor will be the basis of scientific revelations for years to come!

This study is the third to be published by their team, which has been monitoring ‘Oumuamua since it was first observed in October. All studies were conducted with support provided by the Science and Technology Facilities Council.

Further Reading: Queen’s University Belfast

January 26, 2018 by Evan Gough

NASA’s Insight Lander Spreads Its Solar Wings. It’ll Fly To Mars In May, 2018

The Insight lander responds to commands to spread its solar arrays during a January 23, 2018 test at the Lockheed Martin clean room in Littleton, Colorado. Image: Lockheed Martin Space

May 2018 is the launch window for NASA’s next mission to Mars, the InSight Lander. InSight is the next member of what could be called a fleet of human vehicles destined for Mars. But rather than working on the question of Martian habitability or suitability for life, InSight will try to understand the deeper structure of Mars.

InSight stands for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport. InSight will be the first robotic explorer to visit Mars and study the red planet’s deep interior. The work InSight does should answer questions about the formation of Mars, and those answers may apply to the history of the other rocky planets in the Solar System. The lander, (InSight is not a rover) will also measure meteorite impacts and tectonic activity happening on Mars currently.

This video helps explain why Mars is a good candidate to answer questions about how all our rocky planets formed, not just Mars itself.

InSight was conceived as part of NASA’s Discovery Program, which are missions focused on important questions all related to the “content, origin, and evolution of the solar system and the potential for life elsewhere”, according to NASA. Understanding how our Solar System and its planets formed is a key part of the Discovery Program, and is the question InSight was built to answer.

This artist's illustration of InSight on a photo background of Mars shows the lander fully deployed. The solar arrays are open, and in the foreground two of its instruments are shown. On the left is the SEIS instrument, and on the right is the HP3 probe. Image: NASA/Lockheed Martin — This artist’s illustration of InSight on a photo background of Mars shows the lander fully deployed. The solar arrays are open, and in the foreground two of its instruments are shown. On the left is the SEIS instrument, and on the right is the HP3 probe. Image: NASA/Lockheed Martin

To do its work, InSight will deploy three instruments: SEIS, HP³, and RISE.

SEIS

This is InSight’s seismic instrument, designed to take the Martian pulse. It stands for Seismic Experiment for Internal Structure.

SEIS sits patiently under its dome, which protects it from Martian wind and thermal effects, and waits for something to happen. What’s it waiting for? For seismic waves caused by Marsquakes, meteorite impacts, or by the churning of magma deep in the Martian interior. These waves will help scientists understand the nature of the material that first formed Mars and the other rocky planets.

HP³

HP³ is InSight’s heat probe. It stands for Heat Flow and Physical Properties Probe. Upon deployment on the Martian surface, HP³ will burrow 5 meters (16 ft.) into Mars. No other instrument has ever pierced Mars this deeply. Once there, it will measure the heat flowing deeply within Mars.

In this image, the Heat Flow and Physical Properties Probe is shown inserted into Mars. Image: NASA

Scientists hope that the heat measured by HP³ will help them understand whether or not Mars formed from the same material that Earth and the Moon formed from. It should also help them understand how Mars evolved after it was formed.

RISE

RISE stands for Rotation and Interior Structure Experiment. RISE will measure the Martian wobble as it orbits the Sun, by precisely tracking InSight’s position on the surface. This will tell scientists a lot about the deep inner core of Mars. The idea is to determine the depth at which the Martian core is solid. It will also tell us which elements are present in the core. Basically, RISE will tell us how Mars responds to the Sun’s gravity as it orbits the Sun. RISE consists of two antennae on top of InSight.

InSight will land at Elysium Planitia which is a flat and smooth plain just north of the Martian equator. This is considered a perfect location or InSight to study the Martian interior. The landing sight is not far from where Curiosity landed at Gale Crater in 2012.

InSight will land at Elysium Planitia, just north of the Martian equator. Image: NASA/JPL-CalTech

InSight will be launched to Mars from Vandenberg Air Force Base in California by an Atlas V-401 rocket. The trip to Mars will take about 6 months. Once on the Martian surface, InSight’s mission will have a duration of about 728 Earth days, or just over 1 Martian year.

InSight won’t be launching alone. The Atlas that launches the lander will also launch another NASA technology experiment. MarCO, or Mars Cube One, is two suitcase-size CubeSats that will travel to Mars behind InSight. Once in orbit around Mars, their job is to relay InSight data as the lander enters the Martian atmosphere and lands. This will be the first time that miniaturized CubeSat technology will be tested at another planet.

One of the MarCO Cubesats that will be launched with InSight. This will be the first time that CubeSat technology will be tested at another planet. Image: NASA/JPL-CalTech

If the MarCO experiment is successful, it could be a new way of relaying mission data to Earth. MarCO will relay news of a successful landing, or of any problems, much sooner. However, the success of the InSight lander is not dependent on a successful MarCO experiment.

January 25, 2018 by Evan Gough

Where’s the Line Between Massive Planet and Brown Dwarf Star?

This artist's conception illustrates the brown dwarf named 2MASSJ22282889-431026, observed by NASA's Hubble and Spitzer space telescopes. Brown dwarfs are more massive and hotter than planets but lack the mass required to become stars. Image credit: NASA

When is a Brown Dwarf star not a star at all, but only a mere Gas Giant? And when is a Gas Giant not a planet, but a celestial object more akin to a Brown Dwarf? These questions have bugged astronomers for years, and they go to the heart of a new definition for the large celestial bodies that populate solar systems.

An astronomer at Johns Hopkins University thinks he has a better way of classifying these objects, and it’s not based only on mass, but on the company the objects keep, and how the objects formed. In a paper published in the Astrophysical Journal, Kevin Schlaufman made his case for a new system of classification that could helps us all get past some of the arguments about which object is a gas giant planet or a brown dwarf. Mass is the easy-to-understand part of this new definition, but it’s not the only factor. How the object formed is also key.

In general, the less massive a star, the cooler it is. Though stars smaller than our Sun can still sustain heat-producing fusion reactions, protostars that are too small cannot. These “failed” stars are commonly known as brown dwarfs, and a new definition puts their range from between 10-75 times the mass of Jupiter. This artist’s concept compares the size of a brown dwarf to that of Earth, Jupiter, a low-mass star, and the Sun. (Credit: NASA/JPL-Caltech/UCB).

Schlaufman is an assistant professor in the Johns Hopkins Department of Physics and Astronomy. He has set a limit for what we should call a planet, and that limit is between 4 and 10 times the mass of our Solar System’s biggest planet, Jupiter. Above that, you’ve got yourself a Brown Dwarf star. (Brown Dwarfs are also called sub-stellar objects, or failed stars, because they never grew massive enough to become stars.)

“An upper boundary on the masses of planets is one of the most prominent details that was missing.” – Kevin Schlaufman, Johns Hopkins University, Dept. of Physics and Astronomy.

Improvements in observing other solar systems have led to this new definition. Where previously we only had our own Solar System as reference, we now can observe other solar systems with increasing effectiveness. Schlaufman observed 146 solar systems, and that allowed him to fill in some of the blanks in our understanding of brown dwarf and planet formation.

An image of Jupiter showing its storm systems. According to a new definition, Jupiter would be considered a brown dwarf if it had grown to over 10 times its mass when it was formed. Image: Gemini

“While we think we know how planets form in a big picture sense, there’s still a lot of detail we need to fill in,” Schlaufman said. “An upper boundary on the masses of planets is one of the most prominent details that was missing.”

Let’s back up a bit and look at how Brown Dwarfs and Gas Giants are related.

Solar systems are formed from clouds of gas and dust. In the early days of a solar system, one or more stars are formed out of this cloud by gravitational collapse. They ignite with fusion and become the stars we see everywhere in the Universe. The leftover gas and dust forms into planets, or brown dwarfs. This is a simplified version of solar system formation, but it serves our purposes.

In our own Solar System, only a single star formed: the Sun. The gas giants Jupiter and Saturn gobbled up most of the rest of the material. Jupiter gobbled up the lion’s share, making it the largest planet. But what if conditions had been different and Jupiter had kept growing? According to Schlaufman, if it had kept growing to over 10 times the size it is now, it would have become a brown dwarf. But that’s not where the new definition ends.

Metallicity and Chemical Makeup

Mass is only part of it. What’s really behind his new classification is the way in which the object formed. This involves the concept of metallicity in stars.

Stars have a metallicity content. In astrophysics, this means the fraction of a star’s mass that is not hydrogen or helium. So any element from lithium on down is considered a metal. These metals are what rocky planets form from. The early Universe had only hydrogen and helium, and almost insignificant amounts of the next two elements, lithium and beryllium. So the first stars had no metallicity, or almost none.

This is an image of M80, an ancient globular cluster of stars. Since these stars formed in the early universe, their metallicity content is very low. This means that gas giants like Jupiter would be rare or non-existent here, while brown dwarfs are likely plentiful. Image: By NASA, The Hubble Heritage Team, STScI, AURA - Great Images in NASA Description, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6449278 — This is an image of M80, an ancient globular cluster of stars. Since these stars formed in the early universe, their metallicity content is very low. This means that gas giants like Jupiter would be rare or non-existent here, while brown dwarfs are likely plentiful. Image: By NASA, The Hubble Heritage Team, STScI, AURA – Great Images in NASA Description, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6449278

But now, 13.5 billion years after the Big Bang, younger stars like our Sun have more metal in them. That’s because generations of stars have lived and died, and created the metals taken up in subsequent star formation. Our own Sun was formed about 5 billion years ago, and it has the metallicity we expect from a star with its birthdate. It’s still overwhelmingly made of hydrogen and helium, but about 2% of its mass is made of other elements, mostly oxygen, carbon, neon, and iron.

This is where Schlaufman’s study comes in. According to him, we can distinguish between gas giants like Jupiter, and brown dwarfs, by the nature of the star they orbit. The types of planets that form around stars mirror the metallicity of the star itself. Gas giants like Jupiter are usually found orbiting stars with metallicity equal to or greater than our Sun. But brown dwarfs aren’t picky; they form around almost any star. Why?

Brown Dwarfs and Planets Form Differently

Planets like Jupiter are formed by accretion. A rocky core forms, then gas collects around it. Once the process is done, you have a gas giant. For this to happen, you need metals. If metals are present for these rocky cores to form, their presence will be reflected in the metallicity of the host star.

But brown dwarfs aren’t formed by accretion like planets are. They’re formed the same way stars are; by gravitational collapse. They don’t form from an initial rocky core, so metallicity isn’t a factor.

This brings us back to Kevin Schlaufman’s study. He wanted to find out the mass at which point an object doesn’t care about the metallicity of the star they orbit. He concluded that objects above 10 times the mass of Jupiter don’t care if the star has rocky elements, because they don’t form from rocky cores. Hence, they’re not planets akin to Jupiter; they’re brown dwarfs that formed by gravitational collapse.

What Does It Matter What We Call Them?

Let’s look at the Pluto controversy to understand why names are important.

The struggle to accurately classify all the objects we see out there in space is ongoing. Who can forget the plight of poor Pluto? In 2006, the International Astronomical Union (IAU) demoted Pluto, and stripped it of its long-standing status as a planet. Why?

Because the new definition of what a planet is relied on these three criteria:

a planet is in orbit around a star.
a planet must have sufficient mass to assume a hydrostatic equilibrium (a nearly round shape.)
a planet has cleared the neighbourhood around its orbit

The more we looked at Pluto with better telescopes, the more we realized that it did not meet the third criteria, so it was demoted to Dwarf Planet. Sorry Pluto.

Pluto was re-classified as a dwarf planet based on our growing understanding of its nature. Will Schlaufman's new study help us more accurately classify gas giants and brown dwarfs? NASA's New Horizons spacecraft captured this high-resolution enhanced color view of Pluto on July 14, 2015. Credit: NASA/JHUAPL/SwRI — Pluto was re-classified as a dwarf planet based on our growing understanding of its nature. Will Schlaufman’s new study help us more accurately classify gas giants and brown dwarfs? NASA’s New Horizons spacecraft captured this high-resolution enhanced color view of Pluto on July 14, 2015. Credit: NASA/JHUAPL/SwRI

Our naming conventions for astronomical objects are important, because they help people understand how everything fits together. But sometimes the debate over names can get tiresome. (The Pluto debate is starting to wear out its welcome, which is why some suggest we just call them all “worlds.”)

Though the Pluto debate is getting tiresome, it’s still important. We need some way of understanding what makes objects different, and names that reflect that difference. And the names have to reflect something fundamental about the objects in question. Should Pluto really be considered the same type of object as Jupiter? Are both really planets in the same sense? The IAU says no.

The same principle holds true with brown dwarfs and gas giants. Giving them names based solely on their mass doesn’t really tell us much. Schlaufman aims to change that.

His new definition makes sense because it relies on how and where these objects form, not simply their size. But not everyone will agree, of course.

Let the debate begin.