We’ve found an exo-planet with an extraordinarily eccentric orbit



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An artist’s impression of the exoplanet in close orbit to a star.
ESA, NASA, G. Tinetti (University College London, UK & ESA) and M. Kornmesser (ESA/Hubble)

Jonti Horner, University of Southern Queensland; Jake Clark, University of Southern Queensland; Rob Wittenmyer, University of Southern Queensland, and Stephen Kane, University of California, Riverside

The discovery of a planet with a highly elliptical orbit around an ancient star could help us understand more about how planetary systems form and evolve over time.

The new planet, HD76920b, is four times the mass of Jupiter, and can be found some 587 light years away in the southern constellation Volans, the Flying Fish. At its closest it skims the surface of its host star, HD76920. At its furthest, it orbits almost twice as far from its star as Earth does from the Sun.

Superimposing HD76920b’s orbit on the Solar system shows how peculiar it is. Its orbit is more like that of the asteroid Phaethon than any of the Solar system’s planets.
Jake Clark

Details of the planet and its discovery are published today. So how does this fit into the planet formation narrative, and are planets like it common in the cosmos?


Read more: A fleeting visit: an asteroid from another planetary system just shot past Earth


The Solar system

Before the first exoplanet discovery, our understanding of how planetary systems formed came from the only example we had at the time: our Solar system.

Close to the Sun orbit four rocky planets – Mercury, Venus, Earth and Mars. Further out are four giants – Jupiter, Saturn, Uranus and Neptune.

Scattered in their midst we have debris – comets, asteroids and the dwarf planets.

The eight planets move in almost circular orbits, close to the same plane. The bulk of the debris also lies close to that plane, although on orbits that are somewhat more eccentric and inclined.

How did this system form? The idea was that it coalesced from a disk of material surrounding the embyronic Sun. The colder outer reaches were rich in ices, while the hotter inner regions contained just dust and gas.

The Solar system formed from a protoplanetary disk, surrounding the young Sun.
NASA/JPL-Caltech

Over millions of years, the tiny particles of dust and ice collided with one another, slowly building ever larger objects. In the icy depths of space, the giant planets grew rapidly. In the hot, rocky interior, growth was slower.

Eventually, the Sun blew away the gas and dust leaving a (relatively) orderly system – roughly co-planar planets, moving on near-circular orbits.

The exoplanet era

The first exoplanets, discovered in the 1990s, shattered this simple model of planet formation. We quickly learned that they are far more diverse than we could have possibly imagined.

Some systems feature giant planets, larger than Jupiter, orbiting incredibly close to their star. Others host eccentric, solitary worlds, with no companions to call their own.

Artist’s impression of the Hot Jupiter HD209458b – a planet so close to its star that its atmosphere is evaporating to space.
European Space Agency, A.Vidal-Madjar (Institut d’Astrophysique de Paris, CNRS, France) and NASA

This wealth of data reveals one thing – planet formation and evolution is more complicated and diverse than we ever imagined.

Core accretion vs dynamical instability

As a result of these discoveries, astronomers developed two competing models for planet formation.

The first is core accretion, where planets form gradually, through collisions between grains of dust and ice. The theory has grown out of our old models of Solar system formation.

The competing theory is dynamical instability. Once again, the story begins with a disk of material around a youthful star. But that disk is more massive, and becomes unstable under its own self-gravity, causing clumps to grow. These clumps rapidly form planets, in thousands of years.

Massive protoplanetary disks can become unstable, rapidly giving birth to giant planets.

Both models can explain some, but not all, of the newly discovered planets. Depending on the initial conditions around the star, it seems that both processes can occur.

Each theory offers potential to explain eccentric worlds in somewhat different ways.

How do you get an eccentric planet?

In the dynamical instability model you can easily get several clumps forming and interacting, slinging one another around until their orbits are both tilted and eccentric.

Under the core accretion model things are a bit harder, as this method naturally creates co-planar, ordered planetary systems. But over time those systems can become unstable.

One possible outcome is for one planet to eject the others through a series of chaotic encounters. That would naturally leave it as a solitary body, following a highly elongated orbit.

Chaotic planetary systems can eject planets entirely, leading to lonely rouge planets.
NASA/JPL-Caltech

But there is another option. Many stars in our galaxy are binary – they have stellar companions. The interactions between a planet and its host star’s sibling could readily stir it up and eventually eject it, or place it on an extreme orbit.

An eccentric planet

This brings us to our newly discovered world, HD76920b. A handful of similarly eccentric worlds have been found before, but HD76920b is unique. It orbits an ancient star, more than two billion years older than the Sun.

The orbit HD76920b is following is not tenable in the long-term. As it swings close to its host star, it will experience dramatic tides.

A gaseous planet, HD76920b will change shape as it swings past its star, stretched by its enormous gravity. Those tides will be far greater than any we experience on Earth.

That tidal interaction will act over time to circularise the planet’s orbit. The point of closest approach to the star will remain unchanged, but the most distant point will gradually be dragged closer in, driving the orbit towards circularity.

All of this suggests that HD76920b cannot have occupied its current orbit since its birth. If that were the case, the orbit would have circularised aeons ago.

Extremely eccentric planets have been discovered before, but this is the first around such an ancient star.
Goddard Space Flight Center/NASA

Perhaps what we’re seeing is evidence of a planetary system gone rogue. A system that once contained several planets on circular (or near circular) orbits.


Read more: Exoplanet discovery by an amateur astronomer shows the power of citizen science


Over time, those planets nudged one another around, eventually hitting a chaotic architecture as their star evolved. The result – chaos – with most planets scattered and flung to the depths of space leaving just one – HD76920b.

The truth is, we just don’t know – yet. As is always the case in astronomy, more observations are needed to truly understand the life story of this peculiar planet.

The ConversationOne thing we do know is the story is coming to a fiery end. In the next few million years, the star will swell, devouring its final planet. Then, HD76920b will be no more.

Jonti Horner, Vice Chancellor’s Senior Research Fellow, University of Southern Queensland; Jake Clark, PhD Student, University of Southern Queensland; Rob Wittenmyer, Associate Professor (Astrophysics), University of Southern Queensland, and Stephen Kane, Associate Professor, University of California, Riverside

This article was originally published on The Conversation. Read the original article.

Found: ‘lost’ forests covering an area two-thirds the size of Australia


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A coolabah forest in Western Australia – one of the world’s previously unrecognised dryland forests.
TERN Ausplots, Author provided

Andrew Lowe, University of Adelaide and Ben Sparrow, University of Adelaide

A new global analysis of the distribution of forests and woodlands has “found” 467 million hectares of previously unreported forest – an area equivalent to 60% of the size of Australia. The Conversation

The discovery increases the known amount of global forest cover by around 9%, and will significantly boost estimates of how much carbon is stored in plants worldwide.

The new forests were found by surveying “drylands” – so called because they receive much less water in precipitation than they lose through evaporation and plant transpiration. As we and our colleagues report today in the journal Science, these drylands contain 45% more forest than has been found in previous surveys.

We found new dryland forest on all inhabited continents, but mainly in sub-Saharan Africa, around the Mediterranean, central India, coastal Australia, western South America, northeastern Brazil, northern Colombia and Venezuela, and northern parts of the boreal forests in Canada and Russia. In Africa, our study has doubled the amount of known dryland forest.

The world’s drylands: forested areas shown in green; non-forested areas in yellow.
Bastin et al., Science (2017)

With current satellite imagery and mapping techniques, it might seem amazing that these forests have stayed hidden in plain sight for so long. But this type of forest was previously difficult to measure globally, because of the relatively low density of trees.

What’s more, previous surveys were based on older, low-resolution satellite images that did not include ground validation. In contrast, our study used higher-resolution satellite imagery available through Google Earth Engine – including images of more than 210,000 dryland sites – and used a simple visual interpretation of tree number and density. A sample of these sites were compared with field information to assess accuracy.

Unique opportunity

Given that drylands – which make up about 40% of Earth’s land surface – have more capacity to support trees and forest than we previously realised, we have a unique chance to combat climate change by conserving these previously unappreciated forests.

Drylands contain some of the most threatened, yet disregarded, ecosystems, many of which face pressure from climate change and human activity. Climate change will cause many of these regions to become hotter and even drier, while human expansion could degrade these landscapes yet further. Climate models suggest that dryland biomes could expand by 11-23% by the end of the this century, meaning they could cover more than half of Earth’s land surface.

Considering the potential of dryland forests to stave off desertification and to fight climate change by storing carbon, it will be crucial to keep monitoring the health of these forests, now that we know they are there.

Ground-based observations were a crucial part of the survey.
TERN AusPlots, Author provided

Climate policy boost

The discovery will dramatically improve the accuracy of models used to calculate how much carbon is stored in Earth’s landscapes. This in turn will help calculate the carbon budgets by which countries can measure their progress towards the targets set out in the Kyoto Protocol and its successor, the Paris Agreement.

Our study increases the estimates of total global forest carbon stocks by anywhere between 15 gigatonnes and 158 gigatonnes of carbon – an increase of between 2% and 20%.

This study provides more accurate baseline information on the current status of carbon sinks, on which future carbon and climate modelling can be based. This will reduce errors for modelling of dryland regions worldwide. Our discovery also highlights the importance of conservation and forest growth in these areas.


The authors acknowledge the input of Jean-François Bastin and Mark Grant in the writing of this article. The research was carried out by researchers from 14 organisations around the world, as part of the UN Food and Agriculture Organization’s Global Forest Survey.

Andrew Lowe, Professor of Plant Conservation Biology, University of Adelaide and Ben Sparrow, Associate professor and Director – TERN AusPlots and Eco-informatics, University of Adelaide

This article was originally published on The Conversation. Read the original article.

Parasites: Pugnose Eels and Sharks


The link below is to an article that reports on a parasitic eels found in the heart of a shark.

For more visit:
http://deepseanews.com/2013/10/ill-see-your-horrifying-crab-barnacle-and-raise-you-a-heart-eel/

Brazil: New Ant Species Discovered


The link below is to an article reporting on the discovery of a new ant species found high in the trees of Brazil in bromeliads.

For more visit:
http://www.guardian.co.uk/science/2013/jul/21/new-to-nature-anochetus-hohenbergiae

Australia: Queensland – Night Parrot Found Again


The link below is to an article reporting on the rediscovery of the Night Parrot in western Queensland, Australia.

For more visit:
http://www.australiangeographic.com.au/journal/night-parrot-seen-alive-again-after-30-years.htm

Antarctica: Princess Elisabeth Station – Emperor Penguins


The link below is to an article reporting on the discovery of one of the largest Emperor Penguin colonies found in Antarctica near Princess Elisabeth Station.

For more visit:
http://news.nationalgeographic.com/news/2013/13/130118-emperor-penguin-antarctic-climate-change-animals-science/

Australia: Kimberley Region – New Marine Species Discovered


The link below is to an article that reports on the new marine species found in the Kimberley region of Australia.

For more visit:

New species found in ‘last frontier’ – The West Australian.