After studying computer simulations of planetary collisions, scientists have discovered a possible phase of planetary formation that has, so far, been overlooked by astronomy. And they think this phase is so significant that it deserves its own planetary definition.
After two planetary objects collide, researchers from the University of California Davis and Harvard University in Cambridge, Mass., realized that a bloated, spinning mass of molten rock can form. It looks a bit like a ring doughnut with the hole filled in. What’s more, it is thought that Earth (and other planets in the solar system) probably went through this violent period before becoming the solid spinning globes we know and love today.
They call this partly vaporized rock “synestia” — “syn-” for “together” and “Estia” after the Greek goddess of architecture and structures.
Over a range of masses and collision speeds, planetary scientist Sarah Stewart (Davis) and graduate student Simon Lock (Harvard) simulated planetary collisions and focused on how the angular momentum of colliding bodies might influence the system. Their study has been published in the Journal of Geophysical Research: Planets. Basically, when two bodies — with their own angular momentum — collide and merge, the sum of their momenta must be conserved and this can have a dramatic effect on the size and structure of the merged mass.
“We looked at the statistics of giant impacts, and we found that they can form a completely new structure,” said Stewart.
After colliding, the energetic event causes both planets to melt and partially vaporize, expanding with a connected ring-like structure. And this structure — a synestia — would eventually cool, contract and solidify. It could also form moons; post-collision molten debris in the synestia doughnut ring may emerge in a stable orbit around the planet.
The synestia phase would be a fleeting event in any planet’s life, however. For an Earth-sized mass, the post-collision synestia would likely last only 100 years or so. But the larger the mass, the longer the phase, the researchers theorize.
So, giving this theoretical “planetary object” a classification might be a little generous — a move that would raise recently “demoted” Pluto’s eyebrow — but as telescopes become more advanced, we might one day be lucky enough to spy a synestia in a young star system where dynamic instabilities are causing planets to careen into one another.
The NASA robot continues to rove the unforgiving slopes of Mount Sharp, but dramatic signs of damage are appearing on its aluminum wheels.
In 2013, earlier than expected signs of damage to Curiosity’s wheels were causing concern. Four years on and, unsurprisingly, the damage has gotten worse. The visible signs of damage have now gone beyond superficial scratches, holes and splits — on Curiosity’s middle-left wheel (pictured above), there are two breaks in the raised zigzag tread, known as “grousers.” Although this was to be expected, it’s not great news.
The damage, which mission managers think occurred some time after the last wheel check on Jan. 27, “is the first sign that the left middle wheel is nearing a wheel-wear milestone,” said Curiosity Project Manager Jim Erickson, at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., in a statement.
After the 2013 realization that Curiosity’s aluminum wheels were accumulating wear and tear faster than hoped, tests on Earth were carried out to understand when the wheels would start to fail. To limit the damage, new driving strategies were developed, including using observations from orbiting spacecraft to help rover drivers chart smoother routes.
It was determined that once a wheel suffers three grouser breaks, the wheel would have reached 60 percent of its useful life. Evidently, the middle left wheel is almost there. According to NASA, Curiosity is still on course for fulfilling its science goals regardless of the current levels of wheel damage.
“This is an expected part of the life cycle of the wheels and at this point does not change our current science plans or diminish our chances of studying key transitions in mineralogy higher on Mount Sharp,” added Ashwin Vasavada, Curiosity’s Project Scientist also at JPL.
While this may be the case, it’s a bit of a downer if you were hoping to see Curiosity continue to explore Mars many years beyond its primary mission objectives. Previous rover missions, after all, have set the bar very high — NASA’s Mars Exploration Rover Opportunity continues to explore Meridiani Planum over 13 years since landing in January 2004! But Curiosity is a very different mission; it’s bigger, more complex and exploring a harsher terrain, all presenting very different engineering challenges.
Currently, the six-wheeled rover is studying dunes at the Murray formation and will continue to drive up Mount Sharp to its next science destination — the hematite-containing “Vera Rubin Ridge.” After that, it will explore a “clay-containing geological unit above that ridge, and a sulfate-containing unit above the clay unit,” writes NASA.
Since landing on Mars in August 2012, the rover has accomplished an incredible array of science, adding amazing depth to our understanding of the Red Planet’s habitable potential. To do this, it has driven 9.9 miles (16 kilometers) — and she’s not done yet, not by a long shot.
Mars’ moons were likely formed by a ring of debris blasted into space after the Red Planet was hit by a massive impact and, when the moon Phobos disintegrates in 70 million years, another ring may form.
Mars is currently known as the “Red Planet” of the solar system; its unmistakable ruddy hue is created by dust rich in iron oxide covering its landscape. But in Mars’ ancient past, it might have also been called the “Ringed Planet” of the inner solar system and, in the distant future, it may sport rings once more.
The thing is, we live in a highly dynamic solar system, where the planets may appear static over human (or even civilization) timescales, but over millions to billions of years, massive changes to planetary bodies occur frequently. And should there be a massive impact on a small rocky world — on Mars, say — these changes can be nothing short of monumental.
In new NASA-funded research published in the journal Nature Geoscience, planetary scientists have developed a new model of Mars when it was hit by a massive impact over 4 billion years ago. This catastrophic impact created a vast basin called the Borealis Basin in the planet’s northern hemisphere and the event could be part of the reason why Mars lacks a global magnetic field — it’s hypothesized that a powerful impact (or series of impacts) caused massive disruption to the Martian inner dynamo.
But the impact also blasted a huge amount of rocky debris from Mars’ crust into space, ultimately settling into a ring system, like a miniaturized rocky version of Saturn. Over time, as the debris drifted away from Mars and settled, rocky chunks would have formed under gravity and these “moonlets” would have clumped together to form larger and larger moons. So far, so good; this is how we’d expect moons to form. But there’s a catch.
After forming in Mars orbit, any moon would have slowly lost orbital altitude, creeping toward the planet’s so-called Roche Limit — a region surrounding any planetary body that is a bad place for any moon to hang out. The Roche Limit is the point at which a planet’s tidal forces become too great for the structural integrity of an orbiting body. When approaching this limit, the closest edge of the moon to the planet will experience a greater tidal pull than the far side, overcoming the body’s gravity. At some point, something has to give and the moon will start to break apart.
And this is what’s going to happen to Phobos in about 70 million years. Its orbit is currently degrading and when it reaches this invisible boundary, tidal stresses will pull it apart, trailing pieces of moon around the planet, some debris falling onto the Martian surface as a series of meteorite impacts, while others remain in orbit.
The research, carried out by David Minton and Andrew Hesselbrock of Purdue University, Lafayette in Indiana, theorizes that mysterious deposits of material around Mars’ equator might have come from the breakup of ancient moons that came before Phobos and Deimos.
“You could have had kilometer-thick piles of moon sediment raining down on Mars in the early parts of the planet’s history, and there are enigmatic sedimentary deposits on Mars with no explanation as to how they got there,” said Minton. “And now it’s possible to study that material.”
According to their model, each time a moon broke apart to create a ring, the next moon would be five times smaller than its predecessor.
In short, Mars and its moon may appear to be pretty much unchanged for billions of years, but the researchers think that up to seven moon-ring cycles have occurred over the last 4.3 billion years and Mars is on the verge (on geological timescales) of acquiring rings once more. Fascinating.
The famous exoplanet was the first to be directly imaged by Hubble in 2008 but many mysteries surround its identity — so astronomers are testing the possibility that it might actually be an exotic neutron star.
Located 25 light-years from Earth, the bright star Fomalhaut is quite the celebrity. As part of a triple star system (its distant, yet gravitationally bound siblings are orange dwarf TW Piscis Austrini and M-type red dwarf LP 876-10) Fomalhaut is filled with an impressive field of debris, sharing a likeness with the Lord Of The Rings’ “Eye of Sauron.” And, in 2008, the eerie star system shot to fame as the host of the first ever directly-imaged exoplanet.
At the time, the Hubble Space Telescope spotted a mere speck in Fomalhaut’s “eye,” but in the years that followed the exoplanet was confirmed — it was a massive exoplanet approximately the size of Jupiter orbiting the star at a distance of around 100 AU (astronomical units, where 1 AU is the average distance the Earth orbits the sun). It was designated Fomalhaut b.
This was a big deal. Not only was it the first direct observation of a world orbiting another star, Hubble was the aging space telescope that found it. Although the exoplanet was confirmed in 2013 and the International Astronomical Union (IAU) officially named the exoplanet “Dagon” after a public vote in 2015, controversy surrounding the exoplanet was never far away, however.
Astronomers continue to pick at Fomalhaut’s mysteries and, in new research to be published in the journal Monthly Notices of the Royal Astronomical Society, Fomalhaut b’s identity has been thrown into doubt yet again.
“It has been hypothesized to be a planet, however there are issues with the observed colors of the object that do not fit planetary models,” the researchers write. “An alternative hypothesis is that the object is a neutron star in the near fore- or background of Fomalhaut’s disk.” The research team is lead by Katja Poppenhaeger, of Queen’s University, Belfast, and a preprint of their paper (“A Test of the Neutron Star Hypothesis for Fomalhaut b”) can be found via arXiv.org.
Fomalhaut b was detected in visible and near-infrared wavelengths, but followup studies in other wavelengths revealed some peculiarities. For starters, the object is very bright in blue wavelengths, something that doesn’t quite fit with exoplanetary formation models. To account for this, theorists pointed to a possible planetary accretion disk like a system of rings. This may be the reason for the blue excess; the debris is reflecting more starlight than would be expected to be reflected by the planet alone. However, when other studies revealed the object is orbiting outside the star system’s orbital plane, this explanation wasn’t fully consistent with what astronomers were seeing.
Other explanations were put forward — could it be a small, warm world with lots of planetesimals surrounding it? Or is it just a clump of loosely-bound material and not a planet at all? — but none seem to quite fit the bill.
In this new research, Poppenhaeger’s team pondered the idea that Fomalhaut b might actually be a neutron star either in front or behind the Fomalhaut debris disk and, although their work hasn’t proven whether Fomalhaut b is an exoplanet or not, they’ve managed to put some limits on the neutron star hypothesis.
Neutron stars are the left-overs of massive stars that have run out of fuel and gone supernova. They are exotic objects that are extremely dense and small and, from our perspective, may produce emissions in visible and infrared wavelengths that resemble a planetary body. Cool and old neutron stars will even generate bluer light, which could explain the strange Fomalhaut b spectra.
Neutron stars also produce ultraviolet light and X-rays and, although it is hard to separate the UV light coming from the exoplanet and the UV light coming from the star, X-ray emissions should be resolvable.
So, using observations from NASA’s Chandra X-ray Observatory, the researchers looked at Fomalhaut b in soft X-rays and were able to put some pretty strong constraints on whether or not this object really could be a neutron star. As it turned out, Chandra didn’t detect X-rays (within its capabilities). This doesn’t necessarily mean that it isn’t a neutron star, it constrains what kind of neutron star it could be. Interestingly, it also reveals how far away this object could be.
Assuming it is a neutron star with a typical radius of 10 kilometers, and as no X-ray emissions within Chandra’s wavelength range were detected, this object would be a neutron star with a surface temperature cooler than 90,000 Kelvin — revealing that it is over 10 million years old. For this hypothesis to hold, the neutron star would actually lie behind the Fomalhaut system, around 44 light-years (13.5 parsecs) from Earth.
Further studies are obviously needed and, although the researchers point out that Fomalhaut b is still most likely an exoplanet with an extensive ring system (just with some strange and as-yet unexplained characteristics), it’s interesting to think that it could also be a neutron star that isn’t actually in the Fomalhaut system at all. In fact, it could be the closest neutron star to Earth, providing a wonderful opportunity for astronomical studies of these strange and exotic objects.
Evidence is mounting around the cryovolcanic history of the solar system’s innermost dwarf planet — and its most recent eruptions may have happened within the last four million years.
Since NASA’s Dawn mission arrived at dwarf planet Ceres in 2015, we’ve been treated to some wonderfully detailed images of the small world’s pockmarked terrain. Understanding the underlying processes of what is believed to be an ice-filled celestial body, however, is taking some time to decipher. But with more observations comes more understanding and planetary scientists are getting close to realizing what lies beneath those craters and, possibly, unlocking the secrets behind a very icy and very alien phenomenon we have no experience of in our terrestrial lives.
That phenomenon is cryovolcanoes. And Ceres seems to have them.
The most startling feature on Ceres is Occator Crater. This 57 mile-wide feature is the result of a massive impact tens of millions of years ago. Large craters on small worlds isn’t necessarily a strange thing in our battered solar system, but what is strange about Occator is the very bright feature (and small bright patches surrounding it) in the crater’s center. Even before Dawn arrived in orbit and only fuzzy images of Ceres were available, hopes were high that this bright anomaly in the otherwise gray Cererian landscape could be indicative of ices or some mineral compound that was formed by the presence of water.
Cryovolcanoes — or, simply, ice volcanoes — are hypothetical features that are believed to be common throughout the outer solar system. These ice volcanoes are thought to erupt in a similar fashion to the volcanoes we have on Earth, but instead of molten rock, these volcanoes erupt ice-cold volatiles — like water, methane or ammonia. Dwarf planet Pluto, for example, has features that look like cryovolcanoes, as does Saturn’s moon Titan and Jupiter’s moon Ganymede. These locations are extremely cold and known to contain large quantities of methane and water, so internal heating (caused by radioactive decay or tidal processes) melt the ices and force them to the surface. When they vent through the crust, gases are released and the liquids quickly freeze and sublimate.
Around these vents, cryovolcanoes will grow, and if Ceres really does have its own ice volcanoes, this will be the closest planetary body to the sun (and Earth) known to have them.
Now, in research headed by the Max Planck Institute for Solar System Research (MPS) in Göttingen, Germany, scientists using Dawn data have, for the first time, taken a stab at dating the age of the bright material in the center of Occator Crater and realized that the location has likely been the site of many cryovolcanic eruptions in the recent past.
In the center of Occator, a pit measuring around 7 miles wide can be found, likely formed during the massive impact approximately 30 million years ago. But around the edges of that pit are mountains, some 750 meters high, and in the center is a cracked dome measuring 400 meters high and nearly 2 miles wide. This bright dome is called Cerealia Facula and surrounding it appears to be material that was spewed from a cryovolcanic vent. Analysis has shown that this material contains salts that were formed in the presence of water from Ceres’ interior and then deposited onto the surface. The minerals around Cerealia Facula has been dated to only four million years, meaning that there has been cryovolcanic eruptions long after the Occator impact punctured Ceres’ crust.
“The age and appearance of the material surrounding the bright dome indicate that Cerealia Facula was formed by a recurring, eruptive process, which also hurled material into more outward regions of the central pit,” said Andreas Nathues, lead investigator of Dawn’s Framing Camera. “A single eruptive event is rather unlikely.” As noted in an MPS news release, Jupiter moons Callisto and Ganymede have similar features that are also believed to be related to cryovolcanic eruptions.
“The large impact that tore the giant Occator crater into the surface of the dwarf planet must have originally started everything and triggered the later cryovolcanic activity,” added Nathues.
Previous imagery of haze inside Occator Crater has led to the suspicion that ices remain on the surface today; the haze could be vapor from sublimating water ice exposed on the surface having been forced to the surface from Ceres’ interior. Evidence for this haze has been supported by other studies and appears to vary throughout the day as one would expect — increased sunlight would accelerate sublimation (ice turning from a solid to a vapor without passing through the liquid phase).
If volatiles are still being extruded through this vent today, this would seem to indicate that, in addition to the cryovolcanic eruptions in the last four million years, some form of activity continues to this day. Add this to the recent discovery of organic material on Ceres’ surface, this small world has become a very big asset for planetary science.
For more on Ceres’ icy eruptions, check out one of my last DNews videos: