Tag Archives: planetary formation

This image shows an artist’s impression of what the surface of the 2I/Borisov comet might look like.  2I/Borisov was a visitor from another planetary system that passed by our Sun in 2019, allowing astronomers a unique view of an interstellar comet. While telescopes on Earth and in space captured images of this comet, we don’t have any close-up observations of 2I/Borisov. It is therefore up to artists to create their own ideas of what the comet’s surface might look like, based on the scientific information we have about it. (SO/M. Kormesser)

Interstellar visitor 2I/Borisov is the most pristine comet ever observed

As an interstellar visitor–an object from outside the solar system–the rogue comet 2I/Borisov is already a source of great interest for astronomers. But researchers have now also discovered that this interstellar comet is composed of pristine material similar to that which exists when star systems first form.

Not only does this make 2I/Borisov even more exciting than previously believed, it means that studying the material that composes it and its coma –an envelope of gas and dust that surround comets– could unlock secrets of planetary system formation.

This image was taken with the FORS2 instrument on ESO’s Very Large Telescope in late 2019, when comet 2I/Borisov passed near the Sun. Since the comet was travelling at breakneck speed, around 175 000 kilometres per hour, the background stars appeared as streaks of light as the telescope followed the comet’s trajectory. The colours in these streaks give the image some disco flair and are the result of combining observations in different wavelength bands, highlighted by the various colours in this composite image. (ESO/O. Hainaut)
This image was taken with the FORS2 instrument on ESO’s Very Large Telescope in late 2019 when comet 2I/Borisov passed near the Sun. Since the comet was travelling at breakneck speed, around 175 000 kilometres per hour, the background stars appeared as streaks of light as the telescope followed the comet’s trajectory. The colours in these streaks give the image some disco flair and are the result of combining observations in different wavelength bands, highlighted by the various colours in this composite image. (ESO/O. Hainaut)

“2I/Borisov could represent the first truly pristine comet ever observed,” says Stefano Bagnulo of the Armagh Observatory and Planetarium, Northern Ireland, UK. The astronomer tells ZME Science: “We presume this is because it has travelled in the interstellar medium without interacting with any other stars before reaching the Sun.”

Bagnulo is the lead author of one of two papers published in the Nature family of journals detailing new in-depth analysis of 2I/Borisov.

Reflecting on 2I/Borisov

The team was able to make its detailed study of 2I/Borisov–the second interstellar comet found trespassing in our solar system after the cigar-shaped Oumuamua–using the Very Large Telescope (VLT) located in the Acatma Desert, Northern Chile.

In particular, they employed the FOcal Reducer and low dispersion Spectrograph (FORS2) instrument–a device capable of taking mages of relatively large areas of the sky with very high sensitivity–and a technique called polarimetry to unlock the comet’s secrets.

“Sunlight scattered by material, for instance, reflected by a surface, is partially polarised,” explains Bagnulo comparing this to polaroid sunglasses which absorb the polarised component of the light and thus dampen reflected light suppressing glare. “In astronomy, we are interested in that polarised radiation because it carries information about the structure and composition of the reflecting surface or scattering material.”

Bagnulo continues by explaining that because light reflected by a darker object is polarised more than the light reflected by a brighter object, polarimetry may be used to estimate the albedo of an asteroid. This makes it a tool regularly used to study comets and allowed the team to compare 2I/Borisov to comets that begin life in our solar system.

“We found that the polarimetric behaviour of 2I/Borisov is different than that of all other comets of our solar system, except for one, Comet Hale-Bopp,” Bagnulo says. “We suggest that this is because Hale-Bopp is a pristine comet.”

It also implies that 2I/Borisov and Halle-Bopp formed in similar environments, thus giving us a good picture of conditions in other planetary systems.

Whilst, Bagnulo and his team were conducting this research with data collected by the VLT, another team was using a different method to examine the material that comprises this interstellar comet.

The Secrets in the Dust of 2I/Borisov

Bin Yang, is an astronomer at ESO in Chile, who also took advantage of 2I/Borisov’s intrusion into the solar system to study this mysterious comet, but using the Atacama Large Millimeter/submillimeter Array (ALMA).

This image shows an artist’s impression of what the surface of the 2I/Borisov comet might look like.     2I/Borisov was a visitor from another planetary system that passed by our Sun in 2019, allowing astronomers a unique view of an interstellar comet. While telescopes on Earth and in space captured images of this comet, we don’t have any close-up observations of 2I/Borisov. It is therefore up to artists to create their own ideas of what the comet’s surface might look like, based on the scientific information we have about it. (SO/M. Kormesser)
This image shows an artist’s impression of what the surface of the 2I/Borisov comet might look like.  2I/Borisov was a visitor from another planetary system that passed by our Sun in 2019, allowing astronomers a unique view of an interstellar comet. While telescopes on Earth and in space captured images of this comet, we don’t have any close-up observations of 2I/Borisov. It is therefore up to artists to create their own ideas of what the comet’s surface might look like, based on the scientific information we have about it. (SO/M. Kormesser)

“I had the idea of observing the thermal emission from the dust particles in the coma of 2I/Borisov using ALMA. My co-author Aigen Li constructed theoretical models to fit the ALMA observation and set constraints on the dust properties,” Yang, the lead author of the second paper detailing the 2I/Borisov investigation, tells ZME Science. “The composition of 2I/Borisov is similar to solar system comets, consists of dust and various ices. The major ices are water ice, carbon monoxide ice and the minor species include hydrogen cyanide and ammonia.”

Yang goes on to explain that the team was not able to precisely determine the composition of 2I/Borisov’s dust component. The astronomer adds that it could be composed of silicates or carbonaceous materials or a mixture of both.

This image shows an artist’s close-up view of what the surface of the comet might look like.  2I/Borisov was a visitor from another planetary system that passed by our Sun in 2019, allowing astronomers a unique view of an interstellar comet. While telescopes on Earth and in space captured images of this comet, we don’t have any close-up observations of 2I/Borisov. It is therefore up to artists to create their own ideas of what the comet’s surface might look like, based on the scientific information we have about it. (ESO/M. Kormesser)
This image shows an artist’s close-up view of what the surface of the comet might look like.  2I/Borisov was a visitor from another planetary system that passed by our Sun in 2019, allowing astronomers a unique view of an interstellar comet. While telescopes on Earth and in space captured images of this comet, we don’t have any close-up observations of 2I/Borisov. It is therefore up to artists to create their own ideas of what the comet’s surface might look like, based on the scientific information we have about it. (ESO/M. Kormesser)

The team also found that the comet’s coma contains compact pebbles and grains of around 1mm and above.

Additionally, as 2I/Borisov neared the Sun the relative amounts of water and carbon they detected from it changed quite drastically.

“We found that the dust coma of Borisov consists of compact, millimeter-sized and larger pebble-like grains, which formed in the inner region near the central star,” Yang says. “We also found the cometary nucleus consists of components formed at different locations in its home system.”

“Our observations suggest that Borisov’s system exchanged materials between the inner regions and the outer regions that are far from the central star, perhaps due to gravitational stirring by giant planets much like in our own solar system.”

Bin Yang, ESO.

These characteristics indicate that 2I/Borisov formed by collecting materials from different locations in its own planetary system. It also imnplies that the system from which it originated likelty featured the exchange of materials between its inner and outer regions. Something that Yang says is also common in our solar system.

“So, it is possible that chaotic material exchanging processes are common phenomena for young planetary systems,” says Yang. “We want to know if other planetary systems form like our own. But we cannot study these systems to the level of their individual comets.”

“Interstellar objects represent the building blocks of planets around other stars. Comet Borisov provides a rare and valuable link between our own solar system and other planetary systems.”

The Journey of 2I/Borisov

2I/Borisov was first discovered by Gennedy Borisov, an amateur astronomer and telescope maker, in August 2019. It was only the second visitor from outside the solar system to be found within our planetary system. That means that as it passed the Sun it presented a unique opportunity to compare conditions in our small corner of the galaxy to those found in other planetary systems.

“2I/Borisov is quite a small comet and it didn’t get very close to the Earth and the Sun, so the emission from this comet is quite weak. We were happily surprised that we actually detected the thermal emission from this alien comet. Because of this detection, we are able to set constraints on the dust properties of this comet,” says Yang. “Comets in other planetary systems are simply too far away and too small to be seen by our telescopes.

“We are extremely lucky to find a comet that is from a planetary system far far away from us. Even more luckily, we managed to take many pictures and spectra of this alien comet during its short visit.”

Bin Yang, ESO.

As Yang points out, 2I/Borisov is only in our solar system for a short time before it must continue its interstellar journey, so the time available to astronomers to study it is limited. But, with interstellar visitors to the solar system believed to be fairly common, but difficult to spot, improving telescope technology could offer future opportunities to study other objects with similar interstellar origins.

Bagnulo points to both the upcoming Vera C Rubin telescope and ESA’s comet interceptor, set to launch in 2029, as future technology that could help us spot and investigate interstellar comets.

“We expect to detect at least one interstellar object per year,” Yang concludes. “So, we will have more opportunities to study alien materials.”

This artist’s impression shows the view from the planet in the TOI-178 system found orbiting furthest from the star. New research by Adrien Leleu and his colleagues with several telescopes, including ESO’s Very Large Telescope, has revealed that the system boasts six exoplanets and that all but the one closest to the star are locked in a rare rhythm as they move in their orbits.  But while the orbital motion in this system is in harmony, the physical properties of the planets are more disorderly, with significant variations in density from planet to planet. This contrast challenges astronomers’ understanding of how planets form and evolve. This artist’s impression is based on the known physical parameters for the planets and the star seen, and uses a vast database of objects in the Universe. (ESO/L. Calçada/spaceengine.org)

Astronomers discover an exoplanet system with rhythm

Astronomers have discovered a unique system of exoplanets in which all but one of the planets orbit their parent star in a rare rhythm. The finding could force us to revise our ideas of how planets–including those in our own solar system–form.

The team–including astronomers from the University of Bern and the University of Geneva–used a combination of telescopes and the European Southern Observatory’s (ESO) Very Large Telescope (VLT) to observe the star TOI-178, 200 light-years away from us in the constellation Sculptor.

This artist’s impression shows the view from the planet in the TOI-178 system found orbiting furthest from the star. New research by Adrien Leleu and his colleagues with several telescopes, including ESO’s Very Large Telescope, has revealed that the system boasts six exoplanets and that all but the one closest to the star are locked in a rare rhythm as they move in their orbits.  But while the orbital motion in this system is in harmony, the physical properties of the planets are more disorderly, with significant variations in density from planet to planet. This contrast challenges astronomers’ understanding of how planets form and evolve. This artist’s impression is based on the known physical parameters for the planets and the star seen, and uses a vast database of objects in the Universe. (ESO/L. Calçada/spaceengine.org)
This artist’s impression shows the view from the planet in the TOI-178 system found orbiting furthest from the star based on the known physical parameters for the planets and the star as seen and using a vast database of objects in the Universe. (ESO/L. Calçada/spaceengine.org)

Upon first glance, the astronomers believed that the star was orbited by just two exoplanets, both of which had the same orbits. Closer inspection revealed something surprising, however — six planets, five of which are locked in a rhythmic dance with each other.

“Through further observations, we realised that there were not two planets orbiting the star at roughly the same distance from it, but rather multiple planets in a very special configuration,” says lead researcher Adrien Leleu, University of Bern.

This rhythm reveals a star system that has remained undisturbed by cosmic events since its birth. But, even within this system exists a measure of chaos, with the compositions of the constituent planets displaying some disharmonious densities that are just as rare as their harmonious orbits.

The system consists of planets ranging from one to three times the size of Earth, with masses that range from 1.5 to 30 times that of our planet. Some are rocky and larger than Earth–so-called Super-Earths. Others are gaseous like the solar system’s outer bodies, but much smaller–a class of exoplanets called Mini Neptunes.

“This contrast between the rhythmic harmony of the orbital motion and the disorderly densities certainly challenges our understanding of the formation and evolution of planetary systems,” Leleu adds.

The team’s research is published in the journal  Astronomy & Astrophysics.

This animation shows a representation of the orbits and movements of the planets in the TOI-178 system. In this artist’s animation, the rhythmic movement of the planets around the central star is represented through a musical harmony, created by attributing a note (in the pentatonic scale) to each of the planets in the resonance chain. This note plays when a planet completes either one full orbit or one-half orbit; when planets align at these points in their orbits, they ring in resonance. (ESO/L. Calçada)

Exoplanets in Resonance

All the exoplanets around TOI-178, barring the one closest to the star itself, are exhibiting a resonance can be observed in the repeated patterns in their orbits. These repeating orbits mean that the planets align at regular intervals as they loop their parent star.

A similar–albeit less complex– resonance can be found in our own solar system, not with planets, but with three of the moons of Jupiter. Io completes four full orbits for every orbit of Ganymede, whilst also completing two full orbits for every orbit of Europa. This is what is known as a 4:2:1 resonance.

TOI-178’s five outer planets possess a far more complex chain of resonance than these moons, however. The exoplanets exist in an 18:9:6:4:3 resonance. This means the first exoplanet in the chain–the second closest to the star overall–completes 18 orbits as the second in the chain completes nine, the third completes six, and the fourth completes 4, and the fifth (the sixth planet overall) completes three orbits.

This artist’s animation shows the view from the planet in the TOI-178 system found orbiting furthest from the star, with the inner planets visible in the background. This animation is based on the known physical parameters for the planets and the star seen, and uses a vast database of objects in the Universe. (
ESO/L. Calçada/spaceengine.org)

The team were able to take the resonance of the four planets described above and use it to discover the fifth in the chain, which is the sixth and final planet overall.

The team believes that the exoplanet’s rhythmic orbits could teach them more the system than its current state, though. It could even provide them with a window into its past. “The orbits in this system are very well ordered, which tells us that this system has evolved quite gently since its birth,” explains co-author Yann Alibert from the University of Bern.

In fact, the resonance of the system shows that it has remained relatively undisturbed since its formation. Were it to have been significantly disturbed earlier in its life–by a giant impact or the gravitational influence of another system, for example– the fragile configuration of its orbits would have been obliterated.

Disharmony and Disorder Enter the Picture

It’s not all harmony within the TOI-178 exoplanets., however. Whilst their arrangements and neat and well-ordered, the densities and compositions of the individual exoplanets are much more disordered. It’s a disorder that is very different from what we observe in our solar system.

“It appears there is a planet as dense as the Earth right next to a very fluffy planet with half the density of Neptune, followed by a planet with the density of Neptune. It is not what we are used to,” team member Nathan Hara, University of Geneva, says, describing a system comprised of Super Earths and Mini Neptunes.

As is the case with most exoplanets, the planets in the TOI-178 system were difficult to spot. The team used data collected by the European Space Agency’s CHEOPS satellite, launched in December 2019, with instruments at the VLT located in Chile’s Atacama Desert region.

The astronomers used the transit method that measures tiny dips in light to spot the exoplanets (NASA)

In addition to this data, the team used two of the most common techniques used by astronomers to spot exoplanets. Examing the light emitted by a parent star and how it dips indicates when a planet is transitting in front of it. Also, orbits of exoplanets around a parent star can cause it to ‘wobble’–something that can be seen in its light profile.

This combination of methods allowed the team to discover that the exoplanets in TOI-178 are orbiting their parent star far more rapidly and at a much closer distance than Earth orbits the Sun.

The innermost planet, the one not part of the resonant chain, is the fastest and orbits TOI-178 in just a matter of days. The slowest has an orbit that takes ten times this period to complete.

None of the planets seems to be orbiting in what is believed to be TOI-178’s habitable zone–the area in which water can exist as a liquid. But, the team believes that studying the resonance chain could uncover additional planets in this system, some with orbits that bring them within this region.–also colourfully nicknamed the ‘Goldilocks zone’ because it is neither too hot not too cold.

The researchers will continue to investigate this unique and extraordinary system and suggest that it could be a target for intense observation with the ESO’s Extremely Large Telescope (ELT) when it begins operations later this decade.

The ELT should be able to allow researchers to directly image the exoplanets in Goldilocks zones around stars like TOI-178 as well as study their atmospheres in detail.

This could reveal that the TOI-178 holds even more secrets than this study has revealled.

Original Research

A. Leleu, Y. Alibert, N. C. Hara, et al, ‘Six transiting planets and a chain of Laplace resonances in TOI-178,’ Astronomy & Astrophysics, [2021], (doi: 10.1051/0004-6361/202039767).

Focusing on Arrokoth promises to reveal the Kuiper Belt’s secrets

Out beyond the orbit of Neptune and the solar system’s seven other major planets lies a ring of icy bodies known as the Kuiper Belt. The disc that is 20 times as wide and an estimated 200 times as dense as the asteroid belt houses a wide array of objects, including its most famous inhabitant — the dwarf planet Pluto. But, it holds more than objects of ice and rock. The Kuiper Belt may hold the secrets of how the planets of the solar system formed, and the raw materials that created the worlds around us and our own planet. 

“The Kuiper Belt is a repository of the solar system’s most primordial material and the long-sought nursery from which most short-period comets originate,” explains David C. Jewitt, an astronomer based at the University of California, Los Angeles, who is renowned for his study of the solar system and its smaller bodies. “The scientific impact of the Kuiper Belt has been huge, in many ways reshaping our ideas about the formation and evolution of the Solar System.”

Researchers now stand on the verge of unlocking these secrets with the investigation of the Kuiper Belt contact binary Arrokoth (previously known as ‘Ultima Thule’). On January 2019, the object — named for the Native American word for ‘sky’ — became the most distant object ever visited by a man-made spacecraft.

“Most of what we know about the belt was determined using ground-based telescopes. As a result, Kuiper Belt studies have been limited to objects larger than about 100 km because the smaller ones are too faint to easily detect,” says Jewitt. “Now, 5 years after its flyby of the 2000-km-diameter Kuiper Belt object Pluto, NASA’s New Horizons spacecraft has provided the first close-up look at a small, cold classical Kuiper Belt object.”

The data collected by the New Horizons probe has allowed three separate teams of researchers to conduct the most in-depth investigation of a Kuiper Belt object ever undertaken. In the process, they discovered that our current knowledge of how these objects form is very likely incorrect. From all the evidence the three teams collected, it seems as Kuiper Belts form as a result of a far more delicate, low-velocity process than previously believed. As most astrophysicists believe that these objects — planetesimals — acted as the seeds from which the planets grew, this new model changes our idea of how the solar system formed.

How Kuiper Belt Bodies Get in shape

The majority of the clues as to Arrokoth’s low-velocity formation originate from its unusual binary lobed shape. The larger lobe is joined to the smaller lobe by an extremely narrow ‘neck.’ What is especially interesting about this shape — reminiscent of a bowling pin or a snowman — is that the lobes are perfectly aligned. 

Scientists have used all available New Horizons images of Arrokoth, taken from many angles, to determine its 3D shape, as shown in this animation. The shape provides additional insight into Arrokoth’s origins. The flattened shapes of each of Arrokoth’s lobes, as well as the remarkably close alignment of their poles and equators, point to an orderly, gentle merger of two objects formed from the same collapsing cloud of particles. Arrokoth has the physical features of a body that came together slowly, with ‘locally-sourced’ materials from a small part of the solar nebula. An object like Arrokoth wouldn’t have formed, or look the way it does, in a more chaotic accretion environment. (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Roman Tkachenko)

John Spencer, Institute Scientist in the Department of Space Studies, Southwest Research Institute in Boulder, Colorado, led a team of researchers that reconstructed Arrokoth’s 3-dimensional shape from a series of high resolution black and white images. Spencer’s paper concludes that Arrokoth’s lobes are much flatter than was previously believed but despite this, both lobes are denser than expected.

William McKinnon, Professor of Earth and Planetary Sciences at the Califonia Institute of Technology, and his team ran simulations of different formation methods to see which conditions led to the shape recreated and Spencer and his colleagues.

Velocity simulations of the formation of Arrokoth show that the unique shape of the bi-lobed comtact binary could only be acheived by a low-velocity gathering of small particles. (W.B McKinnon, et al)
Velocity simulations of the formation of Arrokoth show that the unique shape of the bi-lobed contact binary could only be achieved by a low-velocity gathering of small particles. (W.B McKinnon, et al)

McKinnon and his team discovered that the shape of Arrokoth could only be achieved as a result of a low-velocity formation–around 3 m/s. This presents a problem to current theories of how planetesimals form.

The suggested method of planetesimal formation suggests high-velocity particles smashing together in a process called hierarchical accretion. The simulations that McKinnon produced suggest that such high-velocity collisions would not have created a larger body, but rather, would have blown it apart. The geometrical alignment of the larger and smaller lobes indicates to the team that they were once co-orbiting bodies which gradually lost angular momentum and spiralled together, resulting in a merger.

“Arrokoth’s delicate structure is difficult to reconcile with alternative models in which Arrokoth Kuiper Belt objects are fragments of larger objects shattered by energetic collisions,” Jewitt says. This supports a method of planetesimal formation called ‘cloud collapse.’

Jewitt, Science, (2020)

“A variety of evidence from Arrokoth points to gravitational collapse as the formation mechanism.  The evidence from the shape is probably most compelling,” William Grundy of Lowell Observatory says. “Gravitational collapse is a rapid but gentle process, that only draws material from a small region. Not the much more time consuming and violent process of hierarchical accretion – merging dust grains to make bigger ones, and so on up through pebbles, cobbles, boulders, incrementally larger and larger,
with more and more violent collisions as the things crashing into each other.”

Grundy, whose team analysed the thermal emissions from Arrokoth’s ‘winter’ side, goes on to explain that the speed at which cloud collapse occurs and the fact that all the material that feeds it is local to it means that all the Kuiper planetesimals should be fairly uniform.

Cold Classicals: Untouched and unpolluted

Arrokoth is part of a Kuiper Belt population referred to as ‘cold classicals,’ this particular family of bodies is important to astrophysicists researching the origins of the solar systems. This is because, at their distance from the Sun within the Kuiper Belt, they have remained virtually untouched by both other objects and by the violent radiation of the Sun.

As many of these objects, Arrokoth in particular, date back 4 billion years to the very origin of the solar system, they hold an uncontaminated record of the materials from which the solar system emerged and of the processes at play in its birth.

Arrokoth's relative smoothness can be seen from comparisons to comets found in other areas of the solar system (J. R. Spencer et al., Science10.1126/science.aay3999 (2020).
Arrokoth’s relative smoothness can be seen from comparisons to comets found in other areas of the solar system (J. R. Spencer et al., Science10.1126/science.aay3999 (2020).

Arrokoth has a relatively smooth surface in comparison with other comets, moons and planets within the solar system. It does show the signs of a few impacts, with one very noticeable 7km wide impact crater located of the smaller lobe. This few craters dotted across Arrokoth’s surface do seem to point to a few small high-velocity impacts. The characteristics of Arrokoth’s cratering allowed the team in infer its age of around 4 billion years. This places its birth right around the time the planets had begun to form in the solar system.

“The smooth, relatively un-cratered surface shows that Arrokoth is relatively pristine, so evidence of its formation hasn’t been destroyed by subsequent collisions,” Spencer explains. “The number of craters nevertheless indicates that the surface is very old, likely dating back to the time of accretion.

“The almost perfect alignment of the two lobes, and the lack of obvious damage where they meet, indicate gentle coalescence of two objects that formed in orbit around each other, something most easily accomplished by local cloud collapse.”

Heatseekers

As mentioned above, Will Grundy and his team were tasked with the analysis of thermal emissions in the radio band emitted by the side of Arrokoth facing away from the Sun.

W. M. Grundy et al., Science
10.1126/science.aay3705 (2020).

“We looked at the thermal emission at radio wavelengths from
Arrokoth’s winter night side.  Arrokoth is very cold, but it does still emit thermal radiation,” Grundy says. “The signal we saw was brighter, corresponding to a warmer temperature than expected for the winter surface temperature.  Our hypothesis is that we are seeing emission from below the surface, at depths where the warmth from last summer still lingers.”

Grundy’s team also looked at the colour imaging of Arrokoth with the aim of determining what it is composed of. “We looked at the variation of colour across the surface, finding it to be quite subtle,” he says. “There are variations in overall brightness, but the colour doesn’t change much from place to place, leading us to suspect that the brightness variations are more about regional differences in surface texture than compositional differences.”

The team determined that Arrokoth’s dark red colouration is likely to be a result of the presence of ‘messy’ molecular jumbles of organic materials that occur when radiation drives the construction of increasingly complex molecules–known as tholins.

“One open question is where Arrokoth’s tholins came from,” Grundy says. “Were they already present in the molecular cloud from which the Solar System formed?  Did they form in the protoplanetary nebula before Arrokoth accreted? Or did they form after Arrokoth accreted, through radiation from the Sun itself?”

The researcher says that all three are possible, but he considers the uniformity of Arrokoth’s colouration to favour the first two possibilities over the third. The team also searched Arrokoth for more recognisable organic molecules, spotting methanol–albeit frozen solid–but, not finding any trace of water. Something which came as a surprise to Grundy. “It was surprising not to see a clear signature of water ice since that’s such a common material in the outer solar system. Typically, comets have
around 1% methanol, relative to their water ice.”

The team believe that this disparity arises from the fact that Arrokoth accreted in a very distinct chemical environment at the extreme edge of the nebula which collapsed to create the solar system.

“If it was cold enough there for carbon monoxide (CO) and methane (CH4) to freeze as ice onto dust grains, that would enable chemical mechanisms that create methanol and potentially destroy water, too. But those mechanisms could only work where these gases are frozen solid,” Grundy says.  “Arrokoth appears to be sampling a region of the nebula where such conditions held. 

“We have not seen comets so rich in methanol, which probably means we have not seen comets that formed in this outermost part of the nebula.  Most of them probably originally formed closer to the Sun (or else at a different time in nebular history when the chemical conditions were somewhat different).”

Looking to future Kuiper Belt investigations

Investigating Kuiper Belt objects is no walk in the park, with difficulties arising from both the disc’s distance from the Sun and from the fact that Kuiper Belt objects tend to be very small. Grundy explains that as sunlight falls off by the square of its distance, object s as far away as the Kuiper Belt require the most powerful telescopes to do much of anything.

“Sending a spacecraft for a close-up look is great to do, but it took New Horizons 13 years to reach Arrokoth,” Grundy says. “It’ll probably be some time yet before another such object gets visited up-close by a spacecraft.”

Investigations of the Kuiper Belt aren't easy, the next flyby might be decades away ( Kuiper Belt Illustration – laurinemoreau.com)
Investigations of the Kuiper Belt aren’t easy, the next flyby might be decades away ( Kuiper Belt Illustration – laurinemoreau.com)

“For flybys, the journey times are very long–we flew for 13 years to get there–navigation is difficult because we don’t know the orbits of objects out there very well, we’d only been tracking Arrokoth for 4 years,” Spencer explains. “The round-trip light time is long, which makes controlling the spacecraft more challenging, and light levels are very low, so taking well-exposed, unblurred, images is difficult.”

Spencer adds that from Earth, objects like Arrokoth are mostly very faint, meaning only a small fraction of them have been discovered and learning about their detailed properties is difficult even with large telescopes. These difficulties mean that one of the things left to discover is just how common bi-lobed contact binaries like Arrokoth are in the Kuiper Belt. “Some evidence from lightcurves suggests up to 25% of cold classical could be contact binaries,” he says. ” We know that many of them are binaries composed of two objects orbiting each other, however.”

Fortunately, telescope technology promises to make leaps and bounds over the coming decades, with the launch of the space-based James Webb Space Telescope (JWST) in 2021 and the completion of the Atacama Desert based Extremely Large Telescope (ELT) in 2026.

“Both will help,” says Grundy.  “Larger telescopes are needed to collect more light and feed it to more sensitive instruments.  JWST and the new generation of extremely large telescopes set to come online over the coming years will enable new investigations of these objects.”

In terms of future spacecraft visits, Grundy believes that researchers and engineers should be thinking small, literally: “If technical advances were to enable highly miniaturized spacecraft to be flown to the Kuiper belt more quickly, that could enable a lot of things.  The big obstacles to doing that with today’sCubeSats are power, longevity, and communications, but the rapid advance of technology makes me hopeful that it will be possible to do a whole lot more with tiny little spacecraft within a few decades. 

“It’s funny how progress calls for ever bigger telescopes and ever smaller
spacecraft.”

 Future advances in telescope technology promised more detailed examinations of Kuiper Belt objects like Arrokoth. (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/National Optical Astronomy Observatory)
Future advances in telescope technology promised more detailed examinations of Kuiper Belt objects like Arrokoth. (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/National Optical Astronomy Observatory)

Of course one of the most lasting changes that result from this landmark triad of studies on Arrokoth published in Science is the move away from hierarchical formation models and the adoption of a gravitational or cloud collapse model to explain the creation of planetesimals. This shift will resolve one of the long-standing issues with the hierarchical model, the fact that they work quite well to grow things from dust size to pebble size, but once pebble size is reached, the particles quickly spiral-in toward the Sun. 

“I think it will shift the focus to the circumstances that trigger the collapse.  It’s a very fast way of making a planetesimal–decades instead of hundreds of millennia–but the circumstances have to be right for instabilities to concentrate solids enough for them to collapse,” Grundy explains. “It will be interesting to map out where and when planetesimals should form, what their size distributions should be, and where the solids that they are formed from should have originated.”


Original research:

W. M. Grundy et al., Science
10.1126/science.aay3705 (2020).

W. B. McKinnon et al.,
Science 10.1126/science.aay6620

J. R. Spencer et al., Science
10.1126/science.aay3999 (2020).

D. C. Jewitt et al., Science
10.1126/science.aba6889 (2020).

Artist’s impression of the interior of a hot, molten rocky planet.

Molten exoplanets may explain the formation of Earth-like worlds

Artist’s impression of the interior of a hot, molten rocky planet.
Artist’s impression of the interior of a hot, rocky, molten exoplanet. (© University of Bern, illustration: Thibaut Roger)

Researchers from the University of Bern have discovered that the Earth would be approximately 5% larger if it were hot and molten rather than rocky and solid. Pinpointing the difference between rocky exoplanets and their hot, molten counterparts is vital for the search for Earth-like exoplanets orbiting stars outside the solar system. 

The fact that rocky exoplanets that are approximately Earth-sized are small in comparison to other planets, makes them notoriously difficult for astronomers to spot and characterise. Identification of a rocky exoplanet around a bright, Sun-like star will likely not be plausible until the launch of the PLATO mission in 2026. Thankfully, spotting Earth-size planets around cooler and smaller stars such as the red dwarfs Trappist-1 or Proxima b is currently possible. 

But, searching for molten exoplanets could help astronomers probe the darkness of space — and identify Earth-sized rocky-exoplanets around stars like our own. 

“A rocky planet that is hot, molten, and possibly harbouring a large, outgassed atmosphere ticks all the boxes,” says Dan Bower, an astrophysicist at the Center for Space and Habitability (CSH) of the University of Bern. “Such a planet could be more easily seen by telescopes due to strong outgoing radiation than its solid counterpart.”

Learning more about these hot, molten worlds could also teach astronomers and astrophysicists more about how planets such as our’s form. This is because rocky planets such as the Earth are built from ‘leftovers of leftovers’ — material not utilised in either the formation of stars or giant planets. 

“Everything that doesn’t make its way into the central star or a giant planet has the potential to end up forming a much smaller terrestrial planet,” says Bower: “We have reason to believe that processes occurring during the baby years of a planet’s life are fundamental in determining its life path.”

This drove Bower and a team of colleagues mostly from within the Planet S network to attempt to discover the observable characteristics of such a planet. The resulting study — published in the journal Astronomy and Astrophysics — shows that a molten Earth would have a radius 5% or so larger than the actual solid counterpart. They believe this disparity in size is a result of the differences in behaviour between solid and molten materials under the extreme conditions generated beneath the planet’s surface. 

As Bower explains: “In essence, a molten silicate occupies more volume than its equivalent solid, and this increases the size of the planet.”

Artist’s impression of the interior of a hot, rocky, molten exoplanet (with labels). (© University of Bern, illustration: Thibaut Roger)

This 5% difference in radii is something that can currently be measured, and future advances such as the space telescope CHEOPS — launching later this year — should make this even easier. 

In fact, the most recent collection of exoplanet data suggests that low-mass molten planets, sustained by intense starlight, may already be present in the exoplanet catalogue. Some of these planets may well then be similar to Earth in regards to the material from which they are formed — with the variation in size no more than the result of the different ratios of solid and molten rock. 

Bower explains: They do not necessarily need to be made of exotic light materials to explain the data.”

Even a completely molten planet would fail to explain the observation of the most extreme low-density planets, however. The research team suggest that these planets form as a result of molten planets releasing — or outgassing  — large atmospheres of gas originally trapped within interior magma. This would result in a decrease in the observed density of the exoplanet. 

Spotting such outgassed atmospheres of this nature should be a piece of cake for the James Webb Telescope if it is around a planet that orbits a cool red dwarf — especially should it be mostly comprised of water or carbon dioxide. 

The research and its future continuation have a broader and important context, points out Bower. Probing the history of our own planet, how it formed and how it evolved. 

“Clearly, we can never observe our own Earth in its history when it was also hot and molten. But interestingly, exoplanetary science is opening the door for observations of early Earth and early Venus analogues that could greatly impact our understanding of Earth and the Solar System planets,” the astrophysicist says. “Thinking about Earth in the context of exoplanets, and vice-versa offers new opportunities for understanding planets both within and beyond the Solar System.”


Original research: Dan J. Bower et al: Linking the evolution of terrestrial interiors and an early outgassed atmosphere to astrophysical observations, Astronomy & Astrophysics. DOI: https://doi.org/10.1051/0004-6361/201935710

Young Jupiter Swept Through the Solar System, Destroying Super Earths

A new shocking theory suggests that Jupiter may have sweeped through our solar system much like a wrecking ball, knocking planets out of the solar system our moving them outwards, to the position we see them in today. If this is true, then it might explain why our solar system is a rarity and why life emerged the way it did.

Planetary migration

This possible scenario has been suggested by Konstantin Batygin, a Caltech planetary scientist, and Gregory Laughlin of UC Santa Cruz. The results of their calculations and computer models paint a new picture of our solar system’s evolution, and if true, this might explain a number of outstanding questions about our solar system and the Earth itself. Of special interest is the reason why there are no planets closer to the Sun (between the Sun and Mercury).

“It’s a totally empty field. A void. Just solar winds,” said Laughlin, whose proposal is reported in Monday’s Proceedings of the National Academy of Sciences.

According to the two, Jupiter was crucial to the evolution of our solar system.

“Our work suggests that Jupiter’s inward-outward migration could have destroyed a first generation of planets and set the stage for the formation of the mass-depleted terrestrial planets that our solar system has today,” says Batygin, an assistant professor of planetary science. “All of this fits beautifully with other recent developments in understanding how the solar system evolved, while filling in some gaps.”

Their models rely on the so-called Grand Tack scenario, which states that in the very early stages of our solar system’s evolution, Jupiter became so massive and had such a big gravitational attraction that it actually moved in closer to the Sun as though carried on a giant conveyor belt.

“Jupiter would have continued on that belt, eventually being dumped onto the sun if not for Saturn,” explains Batygin.

Then Saturn came in, also closing in on the Sun. But when Jupiter and Saturn reached a specific position, close to the star, they got locked in a special kind of relationship called orbital resonance – their orbital periods became related to each other. In such a relationship, the two proto-planets exerted a gravitational influence on each other, ultimately starting to move away from the Sun.

“That resonance allowed the two planets to open up a mutual gap in the disk, and they started playing this game where they traded angular momentum and energy with one another, almost to a beat,” says Batygin.

Eventually, this tug and pull caused much of the gas in Jupiter and Saturn to be pushed out, reversing their migration and sending them further away from the Sun.

Jupiter came in like a wrecking ball

Today, astronomers no longer believe that the solar system was formed exactly the way we see it today – and they also believe our solar system is a rather strange occurrence in our galaxy. Other solar systems — almost 500, at last count — typically have many planets orbiting much closer to their star than Mercury, so why doesn’t ours?

Researchers believe that Jupiter’s travel back to its current orbit was quite violent, smashing nascent planets into smithereens, including newly formed Super Earths. Much of their debris would have then spiraled into the Sun.

“The ingoing avalanche would have destroyed any newly-formed super-Earths by driving them into the sun,” said Professor Laughlin.

The rocky planets existing today (Mercury, Venus, Earth and Mars) formed from the remaining debris. This would also explain why these planets have much thinner atmosphere than expected, and it would also explain their lower mass – low enough to potentially host life and liquid water.

“It’s the same thing we worry about if satellites were to be destroyed in low-Earth orbit,” said Professor Laughlin. “Their fragments would start smashing into other satellites and you’d risk a chain reaction of collisions. Our work indicates that Jupiter would have created just such a collisional cascade in the inner solar system.”

The study published in Proceedings of the National Academy of Sciences helps explain why our solar system doesn’t have any Super-Earths, like many of the observed solar systems.

To get to this conclusion, they did one simulation in which a population of Super-Earths revolved around the Sun during Jupiter’s migration; according to their simulation, it took only 20,000 years to smash this population – an extremely low period at this scale of events.

This also explains why our planet doesn’t have a hydrogen atmosphere and also why lagged so much in planetary formation – taking shape only 100-200 million years after the development of the Sun.

“We formed from this volatile-depleted debris,” says Batygin.

Of course, this is just a study, and there are serious reasons to be skeptical, as the researchers themselves acknowledge.

“Anytime a theory says ‘Well this happened and then this happened,’ you need to be naturally suspicious. I think that is completely, absolutely valid and the right standpoint to take,” Laughlin said.

But so far, their theory seems to check out with existent observations, and would answer some of the most puzzling questions regarding our solar systems. It remains to be seen if further research will confirm or infirm this theory.

Journal Reference: Konstantin Batygina, and Greg Laughlin. Jupiter’s decisive role in the inner Solar System’s early evolution. doi: 10.1073/pnas.1423252112

 

Credit: Nova ScienceNOW

Meteorites altered by Shock Wave explain how our Solar System formed

After studying ancient minerals in a meteorite, MIT scientists have gained valuable insights that help explain how the sun, the planets and our entire solar system formed.Their work suggest that a powerful shock wave that rippled through the clouds of dust and gas surrounding the sun billions of years ago played a crucial role in clumping matter, which later formed into planets, moons and asteroids.

A solar system is born – our home

Credit: Nova ScienceNOW

Credit: Nova ScienceNOW

Though there are numerous planetary formation theories proposed for our solar system, scientists have yet to reach a definite consensus. By observing other solar systems, astronomers believe it usually takes some five million years for a star’s planets to form from the huge accretion disk of matter the surrounds the star, bounded by gravity. For this to happen, there needs to be a very efficient accretion mechanism that can’t be explained by gravity alone. Magnetism and other forces have been proposed by various models, yet there’s been no way to prove these until now. Remember, we need evidence that survived the 4.5 billion years since our solar system formed, and this is no easy task.

The key might lie in olivine-bearing chondrules – large grains of molted droplets. These chondrules were studied by the MIT team, led by graduate student Roger Fu, from chondrite meteorites, which are pieces of asteroids broken off by collisions. The chondrite analyzed by the researchers is called Semarkona, after the place in India where it fell in 1940. It weighed 691 grams, or about a pound and a half.

Magnetic time capsules

infographic.en_

We first need to understand how these chondrules came into existence in order to realize the significance of this study. In its early days, the sun was surrounded by a solar nebula – a a revolving patch of gas and dust. Some of this matter became heated past its melting point and the dustballs turned into droplets of molten rock, only to later cool and crystallize into chondrules. Yet, as the chondrules cooled, iron minerals inside became magnetized and these magnetic fields remain preserved to this very day as they have been for the past 4.5 billion years. And this is precisely what helped the MIT researchers in their breakthrough.

[ALSO READ] Astronomers discover planet that shouldn’t have been there

 

The researchers found that the chondrules had a magnetic field of about 54 microtesla, similar to the magnetic field at Earth’s surface, which ranges from 25 to 65 microtesla.

“The measurements made by Fu and Weiss are astounding and unprecedented,” says Steve Desch of Arizona State Univ.‘s School of Earth and Space Exploration, a co-author of the paper.”Not only have they measured tiny magnetic fields thousands of times weaker than a compass feels, they have mapped the magnetic fields’ variation recorded by the meteorite, millimeter by millimeter.”

An optical photomicrograph of one of the chondrules. The image at right shows the magnetic field around the chondrule. Red denotes a magnetic field coming out of the screen, blue going into the screen. The chondrule behaves as a tiny bar magnet recording the strength of the magnetic field in the solar nebula gas. The orientation of the magnetic field differs among the chondrules in the same meteorite, indicating magnetization took place before the chondrules came together to make the meteorite. Image: Fu, Science

An optical photomicrograph of one of the chondrules. The image at right shows the magnetic field around the chondrule. Red denotes a magnetic field coming out of the screen, blue going into the screen. The chondrule behaves as a tiny bar magnet recording the strength of the magnetic field in the solar nebula gas. The orientation of the magnetic field differs among the chondrules in the same meteorite, indicating magnetization took place before the chondrules came together to make the meteorite. Image: Fu, Science

The new analysis suggests that the minerals became magnetized well before they joined together to form the meteorite. The researchers gather, after modeling the heating event that melted dust into chondrules, that an intense shock wave passing through the solar nebula is what triggered the event and magnetized the minerals. Depending on the strength and size of the shock wave, the background magnetic field could be amplified by up to 30 times.

“Given the measured magnetic field strength of about 54 microtesla, this shows the background field in the nebula was probably in the range of 5 to 50 microtesla,” Desch says.

According to Fu and colleagues, the registered magnetic field must have been strong enough  to affect the motion of a huge amount of gas at a large scale, in a significant way. Most importantly, the findings provide important evidence that supports the idea that our solar system was shaped by both magnetic and gravitational forces.

Desch says, “This is the first really accurate and reliable measurement of the magnetic field in the gas from which our planets formed.”

Science, 2014. DOI: doi:10.1126/science.1258022

o-ALMA-PLANET-FORMATION-900

Most detailed picture EVER of a new planet being born

Some 450 light-years away in the constellation Taurus, a new planet is being born and astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile were there to capture the moment. It’s the most detailed picture documenting a planetary-forming system.

The cutest planetary baby picture

o-ALMA-PLANET-FORMATION-900

Protoplanetary disc surrounding the young star HL Tau. ALMA (ESO/NAOJ/NRAO)

“This is truly one of the most remarkable images ever seen at these wavelengths,” Dr. Crystal Brogan, an astronomer at the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia, said in a written statement. “The level of detail is so exquisite that it’s even more impressive than many optical images.”

When NASA or other agencies release pictures like these, they’re usually simulations or visual renditions of computer models. The most beautiful are actually artist made illustrations. This image, however, is the real deal.

HL Tau's neighborhood, courtesy of Hubble. Image: ALMA (ESO/NAOJ/NRAO), ESA/Hubble and NASA

HL Tau’s neighborhood, courtesy of Hubble. Image: ALMA (ESO/NAOJ/NRAO), ESA/Hubble and NASA

More specifically, it features the star HL Tau surrounded by an envelope of gas and dust called an accretion disk. See those gaps in the image? This is where new planets will be formed, as gas and dust are cleared from their orbit.

“These features are almost certainly the result of young planet-like bodies that are being formed in the disk,” ALMA Deputy Director Dr. Stuartt Corder said in the statement. “This is surprising since HL Tau is no more than a million years old and such young stars are not expected to have large planetary bodies capable of producing the structures we see in this image.”

[ALSO SEE] Astronomers upset the theory of planetary formation

In the past half-decade, we’ve learned about thousands of planets throughout the galaxy, but we still don’t really know what turns young, spinning baby stars into stable solar systems. In fact, there are multiple theories that try to explain how planets form. The most accepted of these says that the enormous discs that surround baby stars collide and accrete into planet-sized objects. The matter inside the rapidly spinning disk around the parent star starts to gather and form clumps, steadily accumulating until these turn into asteroids, comets, planets and moons. As these get bigger, the objects plow through the accretion disk which is why we see gaps in this latest picture reported by ALMA.

See an artist’s animation below to learn more about planet formation.

his artist's impression shows the dust and gas around the double star system GG Tauri-A. Credit: ESO/L.Calçada

A ‘Ying Yang’ binary system that can sustain Planetary Formation

A group from the Laboratory of Astrophysics of Bordeaux, France, and the National Centre for Scientific Research (CNRS) has made a most exciting discovery. The astronomers found that an odd binary system – a solar system comprised of two stars – actually behaves like a double star, with two disks of matter encircling the system in a beautiful dance of gas and dust exchange. The breakthrough came after observations showed that that two disks – a wheel inside a wheel –  transfer matter from the outside to the inside, thus sustaining the smaller disk and aiding in planetary formation. The discovery has profound implications in exoplanet search efforts.

Two solar wheels

his artist's impression shows the dust and gas around the double star system GG Tauri-A.  Credit: ESO/L.Calçada

his artist’s impression shows the dust and gas around the double star system GG Tauri-A. Credit: ESO/L.Calçada

The outer disk surrounds the entire system, called GG Tau-A, while the inner disk circles the two companion stars closely. The latter disk has a mass roughly equivalent to that of Jupiter, yet it’s existence has perplexed scientists for quite a while. The two stars are constantly feeding matter from the disk, so in time it should have disappeared – why are we still seeing it? Using the  Atacama Large Millimeter/submillimeter Array (ALMA) in Chile,  Anne Dutrey and colleagues found gas clumps in the region between the two disks, which serves to explain the anomaly since it means matter is being transferred from the outer ring to the inner one, thus sustaining it.

“Material flowing through the cavity was predicted by computer simulations but never imaged before. Detecting these clumps indicates that material is moving between the disks, allowing one to feed off the other,” said Anne Dutrey from the Laboratory of Astrophysics, Bordeaux in France.

[RELATED] Most powerful stars are actually vampire binary systems

New planetary formation insight

Artist’s concept of exoplanets in a two-stars system. The planets found so far orbiting such systems are gas giants like Jupiter. Credit: NASA/JPL-Caltech/T. Pyle

Artist’s concept of exoplanets in a two-stars system. The planets found so far orbiting such systems are gas giants like Jupiter. Credit: NASA/JPL-Caltech/T. Pyle

This is where things get interesting. Planets are born from the same spinning disk of gas and dust material that went into forming a star, like our sun. This disk is called a solar nebula and even after some of this material was bound by gravity and collapsed to form a star, it still retains an angular momentum while it orbits the new-born star. Particles in the spinning disc begin to clump together as gravity attracted them to each other and over millions of years these clumps continue to collide and join together, in a process which scientists described as accretion. Because this is an extremely enduring and slow process, the solar nebula needs to have enough material to feed the planetary formation, as well as parent star which also sucks in gas and dust from the disk.

“We may be witnessing these types of exoplanetary systems in the midst of formation,” said Jeffrey Bary, an astronomer at Colgate University in Hamilton, N.Y., and co-author of the paper. “In a sense, we are learning why these seemingly strange systems exist.”

Artist's conception of the Kepler-35 system. Credit: Lynette Cook / extrasolar.spaceart.org / Nature

Artist’s conception of the Kepler-35 system. Credit: Lynette Cook / extrasolar.spaceart.org / Nature

If the same process occurs in binary systems such as GG Tau-A, then it would explain why so many planets have been and continue to be discovered in binary systems. Originally, scientists weren’t interested in binary systems when looking for planets outside our solar system, but now investigators are beginning to take an even closer look and investigate the possibility of planets orbiting individual stars of multiple-star systems.

“This means that multiple star systems have a way to form planets, despite their complicated dynamics. Given that we continue to find interesting planetary systems, our observations provide a glimpse of the mechanisms that enable such systems to form,” concludes Bary.

GG Tau-A  is only a few million years old and lies approximately 460 light-years from Earth in the constellation Taurus. The discovery was reported in the journal Nature.

Astronomers discover planet that shouldn’t be there

The discovery of a giant planet orbiting its star at 650 times the average Earth-Sun distance baffled researchers. So far, they haven’t been able to explain how such a strange system came to be.

Artistic representation. Credit: NASA/JPL-Caltech

The international team of astronomers was led by a University of Arizona graduate student. This is the most distant planet ever found orbiting around a single, sun-like star. As a sidenote, it is also the first exoplanet discovered at the University of Arizona.

The planet in case (HD 106906) has a mass 11 times bigger than that of Jupiter and is 650 times further from its star than the Earth is from the Sun. No currently known mechanism can explain how or why this is happening.

“This system is especially fascinating because no model of either planet or star formation fully explains what we see,” said Vanessa Bailey, who led the research. Bailey is a fifth-year graduate student in the UA’s Department of Astronomy.

There are two main mechanisms of planetary formation currently accepted by astronomers. Planets that form close to their stars from small asteroid-like bodies born in the primordial disk of dust and gas that surrounds a forming star. Since this process is fairly slow, giant plants can’t form this way, only stars comparable in size to Earth. The other one suggests that giant planets can form from a fast, direct collapse of disk material. But there’s a problem with this as well: primordial disks rarely contain enough mass in their outer reaches to allow a planet like HD 106906 b to form. So Bailey started thinking about most exotic solutions.

“A binary star system can be formed when two adjacent clumps of gas collapse more or less independently to form stars, and these stars are close enough to each other to exert a mutual gravitation attraction and bind them together in an orbit,” Bailey explained. “It is possible that in the case of the HD 106906 system the star and planet collapsed independently from clumps of gas, but for some reason the planet’s progenitor clump was starved for material and never grew large enough to ignite and become a star.”

But this model also doesn’t explain things, because the mass ratio of the two stars in a binary system is typically no more than 10-to-1.

“In our case, the mass ratio is more than 100-to-1,” she explained. “This extreme mass ratio is not predicted from binary star formation theories — just like planet formation theory predicts that we cannot form planets so far from the host star.”

Understanding complex, unusual systems like this one is very important – these are the kind of studies that push the border of our knowledge further and further.

“Every new directly detected planet pushes our understanding of how and where planets can form,” said co-investigator Tiffany Meshkat, a graduate student at Leiden Observatory in the Netherlands. “This planet discovery is particularly exciting because it is in orbit so far from its parent star. This leads to many intriguing questions about its formation history and composition. Discoveries like HD 106906 b provide us with a deeper understanding of the diversity of other planetary systems.”

Super-dense celestial bodies may be new types of planet

Despite all the magnificent advancements in the field, we are still in the infancy of our research on extraterrestrial planets, so it shouldn’t really surprise anybody if a new type of planet is found.

neptune stripped

Mysterious dense bodies outside the Solar System which have puzzled astronomers for quite a while may in fact be remnants of Neptune-like planets which went too close to their Sun and got compressed.

NASA’s Kepler space mission to find exoplanets, which launched in 2009 found bodies which appeared to be simply too heavy for their size – the planets in case have radiuses similar to Earth’s, but are denser than pure iron. No conventional planet forming theory can explain this.

“There is no way to explain that in the Solar System,” says Olivier Grasset, a geophysicist at the University of Nantes in France.

Grasset and his team put forth an interesting theory which claims that these planets are actually fossil remains of much larger bodies, which were stripped of their outer, frozen crust – leaving us today with the fossil core.

If these planets were formed far from their stars, but in time, migrated closer to their star – possibly as cloe as Mercury is today, then the hot temperatures of the star would evaporate the outer layers of the planet, which are made mostly from volatile elements (hydrogen, helium and water). The only thing that would remain would be the core (consisting of rock and metal, just like Earth’s) – which is very dense, because during its initial stage (before the outer layers were evaporated) it was formed at about 5 million times atmospheric pressure on Earth and temperatures of approximately 6000 Celsius degrees.

Lars Stixrude, a geologist at University College London, calls the idea “fascinating”, but he does mention that we still don’t understand the behaviour of materials under the extreme temperatures and pressures of an ice-giant core is still incomplete. William Borucki, a space scientist at NASA’s Ames Research Center in Moffett Field, California, and leader of the Kepler mission adds that the theory is plausible, but there are plenty of other ways through which the outer layers could be blasted away. The process could be the result of a cataclysmic collision with another planet-sized object, for example. Either way, the Kepler mission is definitely updating how we understand the Universe we live in.

“This is why we do science.”, Borucki says.

Astronomers upset the theory of planetary formation

The discovery of 9 new planets raises some serious questions on the matter of how planets are formed. Two astronomers from the University of California, Santa Barbara reported the discovery, and of them, two are spinning in the opposite direction the planets in our solar system are spinning. This, along with other recent studies of exoplanets (planets outside the solar system) seems to put the final nail in the primary theory regarding planetary formation.

hot-jupiter-4

Artistic illustration of a Hot Jupiter

This was the highlight at the UK National Astronomy Meeting in Glasgow, Scotland that took place this week, and now researchers from this field will have a whole lot of work to do, basically starting from scratch (almost).

“Planet evolution theorists now have to explain how so many planets came to be orbiting like this,” said Tim Lister, a project scientist at LCOGT. Lister leads a major part of the observational campaigns along with Rachel Street of LCOGT, Andrew Cameron of the University of St. Andrews in Scotland, and Didier Queloz, of the Geneva Observatory in Switzerland.

The 9 planets are pretty interesting by themselves too; they are so-called “Hot Jupiters”. As you could guess by the name, they are giant gas planets that orbit quite close to their star (which is of course why they’re hot). Since this type of planet was discovered no more than 15 years ago, their origin has remained a mystery. However, they are quite easy to detect due to the gravitational effect they have on their star.

The general belief is that at their cores, these planets have a mix of rock and ice particles found only in the cold outer reaches of planetary systems. The logical conclusion is that Hot Jupiters have to form quite far away from their star and then migrate closer as millions of years pass. Numerous astronomers believed this happens due to the interactions the planets have with the dust cloud from which they are formed. However, this idea does not explain why they orbit in a direction contrary to that of the disk.

Another theory suggests that it was not interaction with the disk at all, but rather a slower evolution that was affected by gravitational relationships with more distant planetary or stellar companions over hundreds of millions of years. It would probably be imposed an elongated orbit and would suffer have a “tidal” movement, until it was parked in a more circular orbit close to the star.

“In this scenario, smaller planets in orbits similar to Earth’s are unlikely to survive,” said Rachel Street.