Geoscience: Cosmic diamonds formed during gigantic planetary collisions

International research team solves theory of how diamonds formed inside protoplanets

It is estimated that over 10 million asteroids are circling the Earth in the asteroid belt.

They are relics from the early days of our solar system, when our planets formed out of a large cloud of gas and dust rotating around the sun.

When asteroids are cast out of orbit, they sometimes plummet towards Earth as meteoroids.

If they are big enough, they do not burn up completely when entering the atmosphere and can be found as meteorites.

The geoscientific study of such meteorites makes it possible to draw conclusions not only about the evolution and development of planets in the solar system but also their extinction.

A special type of meteorites are ureilites.

These are fragments of a larger celestial body - probably a minor planet - which was smashed to pieces through violent collisions with other minor planets or large asteroids.

Ureilites often contain large quantities of carbon, among others in the form of graphite or nanodiamonds.

The diamonds on the scale of over 0.1 and more millimetres now discovered cannot have formed when the meteoroids hit the Earth.

Impact events with such vast energies would make the meteoroids evaporate completely.

That is why it was so far assumed that these larger diamonds - similar to those in the Earth’s interior - must have been formed by continuous pressure in the interior of planetary precursors the size of Mars or Mercury.

Together with scientists from Italy, the USA, Russia, Saudi Arabia, Switzerland and the Sudan, researchers from Goethe University have now found the largest diamonds ever discovered in ureilites from Morocco and the Sudan and analysed them in detail.

Apart from the diamonds of up to several 100 micrometres in size, numerous nests of diamonds on just nanometre scale as well as nanographite were found in the ureilites.

Closer analyses showed that what are known as londsdalite layers exist in the nanodiamonds, a modification of diamonds that only occurs through sudden, very high pressure.

Moreover, other minerals (silicates) in the ureilite rocks under examination displayed typical signs of shock pressure.

In the end, it was the presence of these larger diamonds together with nanodiamonds and nanographite that led to the breakthrough.

Professor Frank Brenker from the Department of Geosciences at Goethe University explains:

“Our extensive new studies show that these unusual extraterrestrial diamonds formed through the immense shock pressure that occurred when a large asteroid or even minor planet smashed into the surface of the ureilite parent body.

It’s by all means possible that it was precisely this enormous impact that ultimately led to the complete destruction of the minor planet.

This means - contrary to prior assumptions - that the larger ureilite diamonds are not a sign that protoplanets the size of Mars or Mercury existed in the early period of our solar system, but nonetheless of the immense, destructive forces that prevailed at that time.”

This is a pair of custom moves that operate like a variation of “Soak” or “Trick-or-Treat”.

“Sublimation” (Ice/Status): All Ice-typings become Flying-types.

“Deposition” (Ice/Status): All Flying-typings become Ice-types.

No, There Isn’t A Black Hole At The Center Of The Earth

“Even under the most optimistic, realistic scenario, there can be no black holes that survive for more than a fraction-of-a-second inside the Earth. If we only have three spatial dimensions, the particles that exist — whether in terrestrial particle accelerators or from the natural cosmic accelerators found in space — can never create a black hole here on Earth. But if there’s a fourth spatial dimension, they can theoretically be created, although the LHC has been unsuccessful in creating and detecting them thus far.

Even in that exotic scenario, however, the laws of physics very definitively prohibit them from remaining stable, as they will decay away. Even if you contrive a scenario to maximize their growth rate, it’s extraordinarily unsustainable, as the growth rate will drop below the decay rate in short order, causing them to evaporate completely. We know enough science to robustly conclude that there isn’t a black hole at the center of the Earth, and any scientist or layperson can follow these same steps to figure out that same conclusion for themselves.”

There’s a paper that’s been identified from last year that’s nothing more than a word-salad of scientific terms, likely put together by an artificial intelligence to expose the sham peer review practices of predatory journals. But it began with the notion that there’s a black hole at the center of the Earth causing it all. Is that physically possible? 

Even in the most exotic imaginable (but still realistic) scenarios, it isn’t. Here’s the science behind why, and how you can convince yourself in the process!

SECOND ALIGNMENT PLANE OF SOLAR SYSTEM DISCOVERED

A study of comet motions indicates that the solar system has a second alignment plane. Analytical investigation of the orbits of long-period comets shows that the aphelia of the comets, the point where they are farthest from the Sun, tend to fall close to either the well-known ecliptic plane where the planets reside or a newly discovered “empty ecliptic.” This has important implications for models of how comets originally formed in the solar system.

In the solar system, the planets and most other bodies move in roughly the same orbital plane, known as the ecliptic, but there are exceptions such as comets. Comets, especially long-period comets taking tens of thousands of years to complete each orbit, are not confined to the area near the ecliptic; they are seen coming and going in various directions.

Models of solar system formation suggest that even long-period comets originally formed near the ecliptic and were later scattered into the orbits observed today through gravitational interactions, most notably with the gas giant planets. But even with planetary scattering, the comet’s aphelion, the point where it is farthest from the Sun, should remain near the ecliptic. Other, external forces are needed to explain the observed distribution. The solar system does not exist in isolation; the gravitational field of the Milky Way Galaxy in which the solar system resides also exerts a small but non-negligible influence. Arika Higuchi, an assistant professor at the University of Occupational and Environmental Health in Japan and previously a member of the NAOJ RISE Project, studied the effects of the galactic gravity on long-period comets through analytical investigation of the equations governing orbital motion. She showed that when the galactic gravity is taken into account, the aphelia of long-period comets tend to collect around two planes. First the well-known ecliptic, but also a second “empty ecliptic.” The ecliptic is inclined with respect to the disk of the Milky Way by about 60 degrees. The empty ecliptic is also inclined by 60 degrees, but in the opposite direction. Higuchi calls this the “empty ecliptic” based on mathematical nomenclature and because initially it contains no objects, only later being populated with scattered comets.

Higuchi confirmed her predictions by cross-checking with numerical computations carried out in part on the PC Cluster at the Center for Computational Astrophysics of NAOJ. Comparing the analytical and computational results to the data for long-period comets listed in NASA’s JPL Small Body Database showed that the distribution has two peaks, near the ecliptic and empty ecliptic as predicted. This is a strong indication that the formation models are correct and long-period comets formed on the ecliptic. However, Higuchi cautions, “The sharp peaks are not exactly at the ecliptic or empty ecliptic planes, but near them. An investigation of the distribution of observed small bodies has to include many factors. Detailed examination of the distribution of long-period comets will be our future work. The all-sky survey project known as the Legacy Survey of Space and Time (LSST) will provide valuable information for this study.”

IMAGE….Artist’s impression of the distribution of long-period comets. The converging lines represent the paths of the comets. The ecliptic plane is shown in yellow and the empty ecliptic is shown in blue. The background grid represents the plane of the Galactic disk. (Credit: NAOJ)

ExoMars moves on

Last Sunday night a long, heavy truck hit the road escorted from Italy with a precious cargo. While most of the citizens in Turin prepared to enjoy their dinner, several modules of the ExoMars spacecraft left the Thales Alenia Space facilities. Next stop: Cannes, France.

The journey took less than a day. Besides stringent controls in dedicated clean rooms and tents – amongst the cleanest places on Earth – to avoid any biological contamination from Earth to Mars, Russian and European teams took a number of precautionary measures to minimise the risk of spreading the Coronavirus.

Workers remained fully shrouded within ‘bunny suits’ to control any kind of contamination during the packing of the ExoMars elements before shipment. In this image, two engineers work on ESA’s Rosalind Franklin rover with its solar panels and drill folded.

The white capsule with golden legs in the background corresponds to the carrier module integrated with the Russian surface platform, dubbed Kazachok. These two elements will reunite with the rover in Cannes at the end of October.

The microbiological samples taken after rigorous cleanliness procedures showed that the contamination levels were within the requirements for a safe landing on Mars.

Engineers will be busy with a series of tests in the next months. The whole spacecraft will undergo thermal, vacuum and acoustic tests during the next months in France. Coming up is the deployment of the solar panels that will power up the Rosalind Franklin rover on Mars.

Teleworking is nothing new to the ExoMars spacecraft and teams. There will be some remote operations in France before the year ends. Rosalind Franklin will be commanded from the Rover Operations Control Centre (ROCC) at the ALTEC premises in Turin, Italy, to rehearse cruise and deployment manoeuvres once on the surface of Mars.

ExoMars leaves behind an intense period of testing in Italy since April, from health checks to assembly, maintenance operations and leak tests. Fasteners have been added to the solar panels of the rover to increase robustness during the unfolding and surface operations on the Red Planet.

Rosalind Franklin is fitted with a drill – a first in Mars exploration – to extract samples down to a maximum of two metres, where ancient biomarkers may still be preserved from the harsh radiation on the surface, and hosts a sophisticated laboratory to analyse the samples on Mars.

Both drill and laboratory have been extensively tested using soil similar to that expected on Mars and under conditions representative of the martian environment.

The ExoMars programme is a joint endeavour between ESA and the Russian State Space Corporation, Roscosmos.

Thales Alenia Space

TITAN’S LAKES CAN STRATIFY LIKE THOSE ON EARTH

Lakes on Saturn’s moon Titan, composed of methane, ethane, and nitrogen rather than water, experience density driven stratification, forming layers similar to lakes on Earth. However, whereas lakes on Earth stratify in response to temperature, Titan’s lakes stratify solely due to the strange chemical interactions between its surface liquids and atmosphere, says a paper by Planetary Science Institute Research Scientist Jordan Steckloff.

Stratification occurs when different parts of a lake have different densities, with the less dense layer floating atop the denser layer. On Earth, lakes in temperate climates often stratify into layers in the summer as the Sun heats the surface of the lake, causing this water to expand and become less dense, forming a layer of warm water that literally floats upon the cooler water below. This density-driven stratification can occur on Titan as well; however it happens due to the amount of atmospheric nitrogen that Titan’s surface liquids can dissolve, rather than the liquids warming up and expanding.

“Lakes on Titan, more than mere puddles of liquefied natural gas, are dynamic places that experience complex physical processes. They can stratify, overturn, and possibly erupt,” said Steckloff, lead author of “Stratification Dynamics of Titan’s Lakes via Methane Evaporation” that appears in the Planetary Science Journal.

Because liquid methane is less dense than liquid ethane, it has been long assumed that Titan’s methane would generally float atop its liquid ethane. However, when methane’s affinity for atmospheric nitrogen is accounted for, methane can dissolve sufficient nitrogen at low temperatures to become denser than ethane.

Steckloff and his research team realized that this behavior would inherently drive lake stratification at temperatures only a few degrees cooler than have been typically observed on Titan. “We focused on small, shallow lakes that fill following Titan’s rain events, and found that, if the temperature is low, the evaporation of methane from the surface can drive out dissolved nitrogen, which is heavy, resulting in an ethane-enriched (methane-nitrogen poor) layer floating on top of a methane-rich layer,” Steckloff said.

In spite of its frigid surface temperatures of around 90 Kelvin (-298 degrees Fahrenheit), Titan’s ability to host rain, rivers, and lake naturally draws comparisons with our home planet. “Earth is the most Titan-like planet known. Like Titan, Earth has dynamic lakes. Similar processes are active on both, showing that the complicated behaviors of surface liquids can be controlled by a few simple rules and processes,” Steckloff said.

IMAGE….Saturn’s moon Titan hosts numerous small lakes, dried lakebeds, and disappearing lakes. Credit: NASA/JPL-Caltech/ASI/USGS (Modified from original)

AAS NOVA

Life Finds a Way (Even on M Dwarfs?)

By Astrobites

There are lots of stars out there in the universe, and a large chunk of those are M dwarfs.

These are the smallest and reddest stars, coming last in the sequence of spectral types (O, B, A, F, G, K, and last but not least: M).

Bonus: since they’re so small and dim, it’s actually easier to find smaller, terrestrial planets around them! Given that M dwarfs are so plentiful and we have a good shot at peering into their habitable zones, it makes sense that we’d want to think about what life on a planet around an M dwarf would be like.

But there’s a catch. M dwarfs are also known to be very active stars, flaring and giving off a lot of ultraviolet light and X-rays that are bad news for biological life.

This stellar activity is so strong that it drives atmospheric escape, stripping these rocky planets of their atmospheres, which are critical for habitability.

Extreme ultraviolet light (known as EUV or XUV) is particularly good at stripping away an atmosphere, and young M dwarfs give off more of this since they spend a longer time in their pre-main sequence evolution phase.

So, the beginning of these stars’ lives are extreme, ruining chances for a planet to be habitable.

What about older M dwarfs?

Planets around M dwarfs could have a do-over on their atmosphere, gaining a “secondary atmosphere” created by gases released through impacts or volcanos.

Do M dwarfs mellow with age, quieting down all that radiation and making it possible for their planets’ secondary atmospheres to stick around long enough for life to arise?

Today’s paper seeks to answer these questions by observing a nearby old M dwarf for its UV and X-ray activity, and then computing what would happen to the atmosphere of an Earth-like planet in its habitable zone.

The Search for the Atmosphere Killers

The authors used the Hubble Space Telescope (for UV observations) and the Chandra X-ray Observatory to observe Barnard’s Star, a nearby old M star.

Barnard’s Star is only about six light-years away, making it one of our closest neighbors in space.

It’s only 16% the size of the Sun, but about twice as old.

It’s also known to host a cold (around –300°F!) super-Earth about three times the size of our planet, discovered using the radial velocity method.

The average UV luminosity of Barnard’s star is among the lowest ever measured for an M dwarf, but it still emits more XUV than the Sun, as shown in the lower image.

They also measured a weak (but non-zero) X-ray flux, also among the lowest observed on an M dwarf.

Barnard’s Star still flared just about as frequently as younger M dwarfs, but the flares on the older star were lower intensity (still more intense than a star like our Sun, though!).

Another atmosphere-harming event is the CME, or “coronal mass ejection”, which releases high energy particles from the star; the authors found that these events have similar energies to solar flares, but are much more frequent.

There is a caveat on this, though: M dwarfs have been theorized to have stronger magnetic fields, which may keep CMEs from traveling far from the star and impacting planets, so there’s a bit of uncertainty on the effect of CMEs on an atmosphere discussed here.

The Verdict on the Atmosphere

Now that we know a bit more about the environment around an old M dwarf, what would happen to a planet’s atmosphere?

The authors estimated the atmospheric escape from a hypothetical Earth-like planet in the habitable zone of Barnard’s Star that encounters this observed high-energy radiation.

First, to make sure their models made sense, they tested them on the Sun/Earth system to see if they could reproduce what we observe in our own solar system.

Then, they moved on to look at the thermal and ion escape from our hypothetical planet.

Thermal escape happens when particles are hot enough, and therefore moving fast enough, to exceed the escape velocity of the planet.

Around Barnard’s Star, our hypothetical planet would lose its atmosphere in about 11 million years.

Or, you can think about it as losing 87 times the Earth’s atmosphere in a billion years (for context, Earth is over 4 billion years old!).

They also looked at ion escape, which is actually the main way Earth loses atmosphere.

This is a bit more complicated, since it requires a plasma interaction model.

Their simulations showed that in a normal, quiescent (not flaring) state, Barnard’s Star only slightly increases atmospheric escape compared to Earth.

However, when a flare happens, there is much more atmosphere loss, as seen in the bottom image.

One thing to note is that the hypothetical planet here is unmagnetized; magnetism could make a difference, as it does on Earth, shielding from some of these high energy particles.

The big takeaway here, though, is that atmospheric loss around old M dwarfs will be dominated by the flare periods.

Can Life Find a Way?

Flares might actually have a positive effect on life in a different way.

Other work has shown that near-UV (NUV) photons might drive the formation of precursor molecules to RNA; Barnard’s Star has a little less NUV radiation than is needed for this in its quiet state, but flaring could be enough to support these prebiotic pathways.

Also, now that we know flares might be an issue for keeping an atmosphere, we might want to extend our search for habitable planets out farther from the star; there’s a possibility of an “extended habitable zone” farther out from the star where the radiation is less extreme!

Although they’re less active, this paper has shown that even old M dwarfs can lose a lot of atmosphere, particularly due to flares.

We still need to learn more about the flare cycles, since that seems to be a key parameter in atmospheric retention and M dwarf habitability!

TOP IMAGE….In this artist’s illustration, violent outbursts from an M-dwarf star strip the atmosphere from an orbiting planet. [NASA, ESA and D. Player (STScI)]

CENTRE IMAGE….Artist’s rendering of a flaring dwarf star. [NASA’s Goddard SFC/S. Wiessinger]

LOWER IMAGE….Sun (black) vs. Barnard’s star (red). Barnard’s star shows more extreme ultraviolet! [France et al. 2020]

BOTTOM IMAGE….These simulations for show ion escape for three scenarios: base (unmagnetized Earth around the Sun), quiet (unmagnetized Earth-like planet in Barnard star habitable zone in quiescent conditions), and flare (same planet around Barnard star but during flare). The color bar corresponds to the amount of oxygen ions lost. [France et al. 2020]

Title: The High-Energy Radiation Environment Around a 10 Gyr M Dwarf: Habitable at Last?
Authors: Kevin France, Girish Duvvuri, Hilary Egan, et al.
First Author’s Institution: University of Colorado Boulder
Status: Accepted to AJ

Editor’s note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

About the author, Briley Lewis:
Briley Lewis is a second-year graduate student and NSF Fellow at the University of California, Los Angeles studying Astronomy & Astrophysics. Her research interests are primarily in planetary systems – both exoplanets and objects in our own solar system, how they form, and how we can create instruments to learn more about them. She has previously pursued her research at the American Museum of Natural History in NYC, and also at Space Telescope Science Institute in Baltimore, MD. Outside of research, she is passionate about teaching and public outreach, and spends her free time bringing together her love of science with her loves of crafting and writing.