Kauri pines are late-blooming rainforest giants



File 20190304 110107 1dehn1k.png?ixlib=rb 1.1

Michael Yuen/Flickr, CC BY-NC

Kevin Glencross, Southern Cross University

Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.


When I first came across the kauri pine (Agathis robusta), I certainly wasn’t impressed by their growth. Mixed among other species in a young rainforest plantation, they seemed destined to be left behind by the faster-growing trees (I did think they looked nice, though).

But today I know I judged the kauri unfairly. They can survive for millennia, so they don’t bother doing all their growing in their first couple of decades. But come back 20 years later, and that unassuming tree will be well on its way to being one of the giants of the forest.




Read more:
Lord of the forest: New Zealand’s most sacred tree is under threat from disease, but response is slow




The Conversation

Impressive by any measure

By any yardstick, kauri pines are truly unique and impressive. If time is our measure, then the kauri family, Agathis, has endured over epochs, with fossils found in Australia from the early to mid-Jurassic period. Having withstood the rise and fall of the dinosaurs and the evolution and diversification of our flora, 17 species of living fossil trees in the Agathis family remain.

Agathis is an iconic genus of large, ecologically important, and economically valuable conifers that now range over lowland to upper montane rainforests from New Zealand to Sumatra. So, if we judge a plant’s success in terms of its geographical spread or its ability to adapt to a range of conditions, the Kauri family is once again outstanding.

If we measure a plant by appearances, then the tall, robust and handsome Queensland kauri pine remains an impressive – albeit little-known – plant. Reaching up to 50 metres, it emerges above rainforest margins in tropical and subtropical eastern Australia. Its straight, round trunk can grow to 3m in diameter and a combination of smooth mottled bark, coppery new growth and dark green canopy make this tree a world-class ornamental. In parks and gardens across Australia, Kauri pine cuts a fine figure, growing to enormous sizes, even in southern regions.




Read more:
Mountain ash has a regal presence: the tallest flowering plant in the world


Our Australian kauri pine, once common in the dry rainforests of Queensland, has become a victim of its own success. A heavy reliance on the highly regarded wood during the earliest stages of the colonial timber industry has left only a few old trees standing, mostly in remote areas or forest reserves. In my role as a research scientist, I have tracked down the kauri’s cousins in the Pacific regions, where the giant pines can now only be found on tops of mountains on remote islands. In New Zealand, the giant kauri that once covered large areas are in danger from the soil-based fungus Phytophora.

Germaine Greer, in her 2014 book White Beech, describes visiting a massive kauri tree on the North Island over 50m tall and 13.5m in girth that is in danger of succumbing to the fungus after a life measured in millennia.

A useful tree

According to the Gymnosperm Database, Queensland kauri was first reported by Europeans in 1842 by Andrew Petrie, who found it growing in the Mary River country, and reported that the native peoples made their nets from its inner bark. A fine, even texture set this timber apart from the more common Hoop pine.

In the South Pacific, the cousins of the Australian kauri have a strong cultural significance and features in the Maori creation myth. The wood from the Southern Kauri (Agathis australis) was used for water craft, and the gum used in traditional tattoos (moko).

Enthusiastic attempts by the Queensland Forest Service to grow the kauri in plantations were devastated by large stick insects. As a result, kauris are now only grown at a very small scale in mixed species rainforest timber plantations, which is where I stumbled upon them.




Read more:
Comic explainer: forest giants house thousands of animals (so why do we keep cutting them down?)


In about 2002, during my PhD study of young (8-15 years old) rainforest plantations, I first measured kauri as a small tree amongst the well-regarded cabinet timber species of mahoganies and white beech. At first glance, the appeal for me of this Jurassic fossil was merely aesthetic. They were not very impressive in terms of early growth in the plantations; so I focused my attention on the rapid, early growing species.

However, having ignored the kauri for about 10 years, I was astonished (upon return to my old study sites) at how rapidly the kauris had progressed. Not only is this species one of the best performers in terms of diameter growth, but it also has excellent form. It produces straight stems free of large branches that indicates excellent quality logs, for those growers who value wood quality.

My regard for the kauri is now much more than aesthetic; or even as quirky relics from deep time. These trees are showing themselves to be extremely resilient and competitive, under challenging climatic conditions, across a very wide range of sites. They have the capacity to withstand severe storms as well as longer term stresses, such as drought.

I now know that, given the kauri pine can live for many centuries, it is not advisable to measure their value according to the first decade or so of growth, but rather their productivity and resilience across their whole lifespan.




Read more:
Where the old things are: Australia’s most ancient trees



Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.. Read previous instalments here.

This article was updated on Tuesday March 12 to correct an error. It previously stated a tree encountered by Germaine Greer was 13.5m in diameter; in fact the tree was 13.5m in girth.The Conversation

Kevin Glencross, Research Fellow, Southern Cross University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The Lord Howe screw pine is a self-watering island giant



File 20180824 149475 1045iq3.png?ixlib=rb 1.1
To grow tall enough to reach the canopy, a species of screw pine unique to Lord Howe Island has evolved its own rainwater harvesting system.
Matthew Biddick, CC BY-SA

Matthew Biddick, Victoria University of Wellington

If you’d like more content like this, sign up for the Beating Around the Bush newsletter for a dose of nature news every two weeks.


Pandanus forsteri, a species of screw pine endemic to Lord Howe Island, grows tall like no other tree on Earth. To reach the canopy, these trees have evolved a rainwater harvesting system that enables them to water themselves.

Originally from Micronesia, the palm-like P. forsteri belongs to a group of trees that have populated almost every coastal habitat of the Pacific. In fact, pandans are used by Oceanic cultures for everything from fishing and cooking to medicine and religious ceremonies.

Our research shows that pandans differ in several fundamental ways from more familiar trees, including how they capture water and grow.




Read more:
Welcome to Beating Around the Bush, wherein we yell about plants


Reaching for the canopy

Most trees lay down concentric rings of vascular tissue as they mature, thickening over time. This enables them to grow tall, yet maintain enough structural integrity to avoid toppling over. It is also arguably the most important evolutionary innovation that has enabled trees to colonise most of terrestrial Earth.

Together with palms, bamboo and yucca, pandans belong to a group known as monocots, because their seedlings produce a single embryonic leaf.

Pandans belong to a group of plants whose vascular tissue is still primitive, making it difficult to grow tall.
Ian Hutton, CC BY-SA

Their vascular tissue is not compartmentalised in the same way. It forms bundles that are positioned somewhat haphazardly within the stem. Consequently, monocots are unable to produce true secondary growth and thicken like other trees do – and reaching the canopy becomes a much more ambitious endeavour.

The canopy offers a good life. The sun is shining, seed-dispersing birds are abundant, and the herbivores of the forest floor are a distant concern. In monocots, natural selection has favoured some inventive ways of stretching to the top.

Pay-as-you-go growth

Palms overcome the limitations imposed by their physiology by spending their younger years laying down enough vascular girth to support their future stature. Think of it like putting aside money for your retirement. You may not need it now, but you will likely later depend on it.

Stilt roots support the crown as it matures.
Kevin Burns, CC BY-SA

Once thick enough, palms shift their efforts to vertical growth. The palm’s tactic of delayed vertical growth may be slow, but it functions well enough to thrust Columbian wax palms (Ceroxylon quindiuense) – the world’s tallest monocot – 45 meters into the clouds.

Pandans, on the other hand, are less patient. Unlike palms, they prefer a sort of “pay-as-you-go” method. They produce stilt roots that extend from the trunk to the ground for support as the crown matures. The end result gives the appearance of an ice cream cone perched on a tepee of stilts. It’s an odd strategy, but it works.

However, on Lord Howe Island, something quite remarkable has transpired. Isolated some 600 kilometres off the east coast of Australia, one species of screw pine has evolved into an island giant.

Lord Howe Island, some 600km off the Australian east coast, is home to countless endemic plants and animals.
Ian Hutton, CC BY-SA

Island syndrome

Most screw pines are lucky to reach four or five meters. Pandanus forsteri trees, however, regularly exceed 15 meters. These kinds of size changes are not uncommon on isolated islands. They are part of a repeated evolutionary phenomenon known as the island syndrome.

Species on isolated islands are free from the stressors of continental life, and they subsequently converge on a more optimal, ancestral form. Large continental species evolve into island dwarfs, while smaller species become comparatively gigantic. Support for the island syndrome primarily comes from animals. However, a growing body of evidence suggests island plants follow a similar evolutionary path.




Read more:
Lord of the forest: New Zealand’s most sacred tree is under threat from disease, but response is slow


A network of aqueducts on the root surface guides water to the absorptive tissue at the tip of the growing root.
Matt Biddick, CC BY-SA

While gigantism may be favourable, it doesn’t come without risks – and for P. forsteri, they are serious. Thanks to their new-found stature, P. forsteri trees must produce enormous stilt roots to support themselves. This process that can take years. Exposed to the air, roots can form air bubbles, and an air bubble in a plant is bad in the same way it is bad in your artery. It is potentially lethal.

Nature appears to have solved this problem through the evolution of a rainwater harvesting system that enables P. forsteri to water its own stilt roots before they reach the ground.

Gutter-like leaves collect rainwater and transport it to the trunk, where it descends. The flow of water is then couriered by a network of aqueducts formed by the root surface. Finally, water is stored in a specialised organ of absorptive tissue encasing the growing root tip.

Back to the drawing board

This is dramatically different from how we traditionally think about plants. It is far from our concept of sessile beings that passively absorb everything they need from the soil, thanks to the capillary action of their vascular tissues. Never before has a plant species been shown to possess a system of traits that operate jointly to capture, transport and store water external to itself.

This species has opened our eyes to an entirely new field of scientific inquiry. It forces scientists to rethink the function of organs like leaves and roots outside of the contexts of photosynthesis and the conduction of soil water.

<!– Below is The Conversation's page counter tag. Please DO NOT REMOVE. –>
The Conversation

Do other plants harvest rainwater in this way? Why have we only just discovered this? Has our overly simplistic view of plants hindered our ability to comprehend their true complexity? Only time, and more research, will tell.

Matthew Biddick, PhD Researcher, Victoria University of Wellington

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

How farming giant seaweed can feed fish and fix the climate



File 20170731 19115 wrfvv1
Giant kelp can grow up to 60cm a day, given the right conditions.
Joe Belanger/shutterstock.com

Tim Flannery, University of Melbourne

This is an edited extract from Sunlight and Seaweed: An Argument for How to Feed, Power and Clean Up the World by Tim Flannery, published by Text Publishing.


Bren Smith, an ex-industrial trawler man, operates a farm in Long Island Sound, near New Haven, Connecticut. Fish are not the focus of his new enterprise, but rather kelp and high-value shellfish. The seaweed and mussels grow on floating ropes, from which hang baskets filled with scallops and oysters. The technology allows for the production of about 40 tonnes of kelp and a million bivalves per hectare per year.

The kelp draw in so much carbon dioxide that they help de-acidify the water, providing an ideal environment for shell growth. The CO₂ is taken out of the water in much the same way that a land plant takes CO₂ out of the air. But because CO₂ has an acidifying effect on seawater, as the kelp absorb the CO₂ the water becomes less acid. And the kelp itself has some value as a feedstock in agriculture and various industrial purposes.

After starting his farm in 2011, Smith lost 90% of his crop twice – when the region was hit by hurricanes Irene and Sandy – but he persisted, and
now runs a profitable business.

His team at 3D Ocean Farming believe so strongly in the environmental and economic benefits of their model that, in order to help others establish similar operations, they have established a not-for-profit called Green Wave. Green Wave’s vision is to create clusters of kelp-and-shellfish farms utilising the entire water column, which are strategically located near seafood transporting or consumption hubs.


Read more: Seaweed could hold the key to cutting methane emissions from cow burps


The general concepts embodied by 3D Ocean Farming have long been practised in China, where over 500 square kilometres of seaweed farms exist in the Yellow Sea. The seaweed farms buffer the ocean’s growing acidity and provide ideal conditions for the cultivation of a variety of shellfish. Despite the huge expansion in aquaculture, and the experiences gained in the United States and China of integrating kelp into sustainable marine farms, this farming methodology is still at an early stage of development.

Yet it seems inevitable that a new generation of ocean farming will build on the experiences gained in these enterprises to develop a method of aquaculture with the potential not only to feed humanity, but to play a large role in solving one of our most dire issues – climate change.

Globally, around 12 million tonnes of seaweed is grown and harvested annually, about three-quarters of which comes from China. The current market value of the global crop is between US$5 billion and US$5.6 billion, of which US$5 billion comes from sale for human consumption. Production, however, is expanding very rapidly.

Seaweeds can grow very fast – at rates more than 30 times those of land-based plants. Because they de-acidify seawater, making it easier for anything with a shell to grow, they are also the key to shellfish production. And by drawing CO₂
out of the ocean waters (thereby allowing the oceans to absorb more CO₂ from the atmosphere) they help fight climate change.

The stupendous potential of seaweed farming as a tool to combat climate change was outlined in 2012 by the University of the South Pacific’s Dr Antoine De Ramon N’Yeurt and his team. Their analysis reveals that if 9% of the ocean were to be covered in seaweed farms, the farmed seaweed could produce 12 gigatonnes per year of biodigested methane which could be burned as a substitute for natural gas. The seaweed growth involved would capture 19 gigatonnes of CO₂. A further 34 gigatonnes per year of CO₂ could be taken from the atmosphere if the methane is burned to generate electricity and the CO₂ generated captured and stored. This, they say:

…could produce sufficient biomethane to replace all of today’s needs in fossil-fuel energy, while removing 53 billion tonnes of CO₂ per year from
the atmosphere… This amount of biomass could also increase sustainable fish production to potentially provide 200 kilograms per year, per person, for 10 billion people. Additional benefits are reduction in ocean acidification and increased ocean primary productivity and biodiversity.

Nine per cent of the world’s oceans is not a small area. It is equivalent to about four and a half times the area of Australia. But even at smaller scales,
kelp farming has the potential to substantially lower atmospheric CO₂, and this realisation has had an energising impact on the research and commercial
development of sustainable aquaculture. But kelp farming is not solely about reducing CO₂. In fact, it is being driven, from a commercial perspective, by sustainable production of high-quality protein.

A haven for fish.
Daniel Poloha/shutterstock.com

What might a kelp farming facility of the future look like? Dr Brian von Hertzen of the Climate Foundation has outlined one vision: a frame structure, most likely composed of a carbon polymer, up to a square kilometre in extent and sunk far enough below the surface (about 25 metres) to avoid being a shipping hazard. Planted with kelp, the frame would be interspersed with containers for shellfish and other kinds of fish as well. There would be no netting, but a kind of free-range aquaculture based on providing habitat to keep fish on location. Robotic removal of encrusting organisms would probably also be part of the facility. The marine permaculture would be designed to clip the bottom of the waves during heavy seas. Below it, a pipe reaching down to 200–500 metres would bring cool, nutrient-rich water to the frame, where it would be reticulated over the growing kelp.

Von Herzen’s objective is to create what he calls “permaculture arrays” – marine permaculture at a scale that will have an impact on the climate by growing kelp and bringing cooler ocean water to the surface. His vision also entails providing habitat for fish, generating food, feedstocks for animals, fertiliser and biofuels. He also hopes to help exploited fish populations rebound and to create jobs. “Given the transformative effect that marine permaculture can have on the ocean, there is much reason for hope that permaculture arrays can play a major part in globally balancing carbon,” he says.

The addition of a floating platform supporting solar panels, facilities such as accommodation (if the farms are not fully automated), refrigeration and processing equipment tethered to the floating framework would enhance the efficiency and viability of the permaculture arrays, as well as a dock for ships
carrying produce to market.

Given its phenomenal growth rate, the kelp could be cut on a 90-day rotation basis. It’s possible that the only processing required would be the cutting of the kelp from the buoyancy devices and the disposal of the fronds overboard to sink. Once in the ocean depths, the carbon the kelp contains is essentially out of circulation and cannot return to the atmosphere.

The deep waters of the central Pacific are exceptionally still. A friend who explores mid-ocean ridges in a submersible once told me about filleting a fish for dinner, then discovering the filleted remains the next morning, four kilometres down and directly below his ship. So it’s likely that the seaweed fronds would sink, at least initially, though gases from decomposition may later cause some to rise if they are not consumed quickly. Alternatively, the seaweed
could be converted to biochar to produce energy and the char pelletised and discarded overboard. Char, having a mineralised carbon structure, is likely to last well on the seafloor. Likewise, shells and any encrusting organisms could be sunk as a carbon store.

Once at the bottom of the sea three or more kilometres below, it’s likely that raw kelp, and possibly even to some extent biochar, would be utilised as a food source by bottom-dwelling bacteria and larger organisms such as sea cucumbers. Provided that the decomposing material did not float, this would not matter, because once sunk below about one kilometre from the surface, the carbon in these materials would effectively be removed from the atmosphere for at least 1,000 years. If present in large volumes, however, decomposing matter may reduce oxygen levels in the surrounding seawater.

Large volumes of kelp already reach the ocean floor. Storms in the North Atlantic may deliver enormous volumes of kelp – by some estimates as much as 7 gigatonnes at a time – to the 1.8km-deep ocean floor off the Bahamian Shelf.

Submarine canyons may also convey large volumes at a more regular rate to the deep ocean floor. The Carmel Canyon, off California, for example, exports large volumes of giant kelp to the ocean depths, and 660 major submarine canyons have been documented worldwide, suggesting that canyons play a significant role in marine carbon transport.

These natural instances of large-scale sequestration of kelp in the deep ocean offer splendid opportunities to investigate the fate of kelp, and the carbon it contains, in the ocean. They should prepare us well in anticipating any negative or indeed positive impacts on the ocean deep of offshore kelp farming.

The ConversationOnly entrepreneurs with vision and deep pockets could make such mid-ocean kelp farming a reality. But of course where there are great rewards, there are also considerable risks. One obstacle potential entrepreneurs need not fear, however, is bureaucratic red tape, for much of the mid-oceans remain a global commons. If a global carbon price is ever introduced, the exercise of disposing of the carbon captured by the kelp would transform that part of the business from a small cost to a profit generator. Even without a carbon price, the opportunity to supply huge volumes of high-quality seafood at the same time as making a substantial impact on the climate crisis are considerable incentives for investment in seaweed farming.

Tim Flannery, Professorial fellow, Melbourne Sustainable Society Institute, University of Melbourne

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

Explainer: what can Tesla’s giant South Australian battery achieve?


Ariel Liebman, Monash University and Kaveh Rajab Khalilpour, Monash University

Last Friday, world-famous entrepreneur Elon Musk jetted into Adelaide to kick off Australia’s long-delayed battery revolution.

The Tesla founder joined South Australian Premier Jay Weatherill and the international chief executive of French windfarm developer Neoen, Romain Desrousseaux, to announce what will be the world’s largest battery installation.

The battery tender won by Tesla was a key measure enacted by the South Australian government in response to the statewide blackout in September 2016, together with the construction of a 250 megawatt gas-fired power station.

//platform.twitter.com/widgets.js

The project will incorporate a 100MW peak output battery with 129 megawatt hours of storage alongside Neoen’s Hornsdale windfarm, near Jamestown. When fully charged, we estimate that this will be enough to power 8,000 homes for one full day, or more than 20,000 houses for a few hours at grid failure, but this is not the complete picture.

The battery will support grid stability, rather than simply power homes on its own. It’s the first step towards a future in which renewable energy and storage work together.

How Tesla’s Powerpacks work

Tesla’s Powerpacks are lithium-ion batteries, similar to a laptop or a mobile phone battery.

In a Tesla Powerpack, the base unit is the size of a large thick tray. Around sixteen of these are inserted into a fridge-sized cabinet to make a single Tesla “Powerpack”.

With 210 kilowatt-hour per Tesla Powerpack, the full South Australian installation is estimated to be made up of several hundred units.

To connect the battery to South Australia’s grid, its DC power needs to be converted to AC. This is done using similar inverter technology to that used in rooftop solar panels to connect them to the grid.

A control system will also be needed to dictate the battery’s charging and discharging. This is both for the longevity of battery as well to maximise its economic benefit.

For example, the deeper the regular discharge, the shorter the lifetime of the battery, which has a warranty period of 15 years. To maximise economic benefits, the battery should be charged during low wholesale market price periods and discharged when the price is high, but these times are not easy to predict.

More research is needed into better battery scheduling algorithms that can predict the best charging and discharging times. This work, which we are undertaking at Monash Energy Materials and Systems Institute (MEMSI), is one way to deal with unreliable price forecasts, grid demand and renewable generation uncertainty.

The battery and the windfarm

Tesla’s battery will be built next to the Hornsdale wind farm and will most likely be connected directly to South Australia’s AC transmission grid in parallel to the wind farm.

Its charging and discharging operation will be based on grid stabilisation requirements.

This can happen in several ways. During times with high wind output but low demand, the surplus energy can be stored in the battery instead of overloading the grid or going to waste.

Conversely, at peak demand times with low wind output or a generator failure, stored energy could be dispatched into the grid to meet demand and prevent problems with voltage or frequency. Likewise, when the wind doesn’t blow, the battery could be charged from the grid.

The battery and the grid – will it save us?

In combination with South Australia’s proposed gas station, the battery can help provide stability during extreme events such as a large generator failure or during more common occurrences, such as days with low wind output.

At this scale, it is unlikely to have a large impact on the average consumer power price in South Australia. But it can help reduce the incidence of very high prices during tight supply-demand periods, if managed optimally.

For instance, if a very hot day is forecast during summer, the battery can be fully charged in advance, and then discharged to the grid during that hot afternoon when air conditioning use is high, helping to meet demand and keep wholesale prices stable.

More importantly, Tesla’s battery is likely to be the first of many such storage installations. As more renewables enter the grid, more storage will be needed – otherwise the surplus energy will have to be curtailed to avoid network overloading.

Another storage technology to watch is off-river pumped hydro energy storage (PHES), which we are modelling at the Australia-Indonesia Energy Cluster.

The ConversationThe South Australian Tesla-Neoen announcement is just the beginning. It is the first step of a significant journey towards meeting the Australian Climate Change Authority’s recommendation of zero emissions by at least 2050.

Ariel Liebman, Deputy Director, Monash Energy Materials and Systems Instutute, and Senior Lecturer, Faculty of Information Technology, Monash University and Kaveh Rajab Khalilpour, Senior Research Fellow, Caulfield School of Information Technology, Monash University

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

Somewhere out there could be a giant new planet in our solar system: so where is it?


Tanya Hill, Museum Victoria and Jonti Horner, University of Southern Queensland

There’s plenty of excitement at the announcement overnight that a new planet is potentially waiting to be found at the extremes of our solar system.

The possible ninth planet is thought to be quite substantial with a mass around ten times that of Earth and a radius that’s two-to-four times bigger than Earth’s. This characterises it as a Neptune-like object.

What’s truly remarkable about Planet Nine, as it has been dubbed, is its very long orbit. It is estimated to take between 10,000 to 20,000 years to orbit our sun, on an elliptical orbit that stretches way beyond the Kuiper Belt.

The Kuiper Belt is a ring of icy objects (which includes Pluto) that circles the sun beyond the orbit of Neptune. Neptune orbits about 30 times further from the sun than the Earth and astronomers refer to Neptune’s distance from the sun as being 30 astronomical units (au) (where one au is the Earth-sun distance). Pluto follows an elliptical orbit that brings it as close as 29.7au from the sun, then out to almost 50au at its most distant point.

Planet Nine’s proposed elliptical orbit takes it from 200au at its closest to the sun (or perihelion) and between 500au to 1,200au at its furthest (aphelion). When it comes in close, it should be bright enough for high-spec backyard telescopes to pick it up.

But unfortunately, most of the time the planet will be much more distant and that represents a greater challenge. It will require the world’s largest telescopes, such as the 10m diameter Keck telescopes and Japan’s 8.2m Subaru telescope (both located on Mauna Kea in Hawaii) to have a hope of seeing it.

Ghostly pull of gravity

The planet has yet to be seen. So why is it thought to be out there? And how can we know so much about it? Planet Nine is the best fit to explain the orbits of six distant objects.

The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Also, when viewed in three dimensions, they all tilt nearly identically away from the plane of the solar system. Batygin and Brown show that a planet with ten times the mass of the earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration. The diagram was created using WorldWide Telescope.
Caltech/R. Hurt (IPAC)

What’s odd about these six objects is that they have peculiar but remarkably similar orbits. These objects have been nudged off kilter and yet they are all shepherded together in the same region of space.

The first of these objects to be discovered was Sedna. It was observed in 2003, as it approached perihelion. When its 11,400-year orbit was calculated, the discovery team realised that this object was orbiting in a kind of “no man’s land” (or more correctly “no person’s land”).

It was too distant to belong to the Kuiper Belt and not far enough away to be among the sphere of comets orbiting the sun in the Oort Cloud.

Sedna was also beyond the gravitational pull of Neptune, so something else, perhaps a large planet or possibly even a passing star (one of the sun’s many siblings perhaps), might have nudged it off course. What makes Planet Nine feasible is that it can explain the orbit of Sedna along with the other five objects.

At their closest approach to the sun, these six objects sit within the plane of the solar system. Planet Nine would have an orbit that is anti-aligned to the six objects and provides the gravitational tug needed to keep those planets in check.

And there’s more. What makes good science is when a proposed model explains something above and beyond its original intention. Simulations of Planet Nine predict that there should also be objects in the Kuiper Belt that have orbits perpendicularly inclined to the plane of the solar system.

Turns out, these objects exist. Five such objects have been known about since 2002, although their orbits have been unexplained until now.

A predicted consequence of Planet Nine is that a second set of confined objects should also exist. These objects are forced into positions at right angles to Planet Nine and into orbits that are perpendicular to the plane of the solar system. Five known objects (blue) fit this prediction precisely. This diagram was created using WorldWide Telescope.
Caltech/R. Hurt (IPAC)

Haven’t we seen this before?

If Planet Nine does exist, it’s not the first time that a planet in our solar system has been discovered theoretically before being directly observed. In 1845, deviations in the orbit of Uranus, suggested there might be an eighth planet to the solar system and in 1846, Neptune was observed exactly where it was predicted to be.

There have also been predictions that haven’t stood the test of time. Back in the 1980s, scientists proposed that the sun might be a binary, with a dim undiscovered companion moving along on elongated orbit. Every 23 million years (or so), this star named Nemesis would pass through the solar system causing a deluge of comets to impact Earth and produce mass extinctions.

More recently, around the turn of the millennium, astronomers noticed an asymmetry in the distribution of new comets coming in from the Oort Cloud. In theory, comets should come evenly from all directions, but there was a slight excess distributed around a great circle on the sky. One of the explanations was that there could be a Jupiter-mass planet in the Oort cloud, known as Tyche.

In 2014, NASA’s Wide-Field Infrared Survey Explorer (WISE) examined the entire sky across infrared wavelengths. It was the perfect telescope to detect Nemesis or Tyche, but failed to find any evidence of either.

Will we find Planet Nine?

Scientists are sceptical by nature. It’s exciting to have a model that predicts the existence of Planet Nine but this prediction must also be tested. Astronomers have begun searching through astronomical surveys, such as the WISE survey, the Catalina Sky Survey, and the Pan STARRS surveys in the hope of making a sighting.

So far, nothing has been seen. The conclusion, as described in a blog by astronomer, Mike Brown (who proposed Planet Nine along with colleague Konstantin Batygin) is that Planet Nine, if it exists, is likely in the hardest place to find.

It seems to currently be at its furthest point from the sun, at least 500au away; it’s probably fainter than 22nd magnitude (that’s 1,500 times fainter than Pluto); and very possibly it’s aligned with the plane of the Milky Way Galaxy (meaning that Planet Nine may currently be hidden against the background stars of our Galaxy).

Regardless, the hunt is on and there just may be a great discovery out there, waiting to happen.

The Conversation

Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museum Victoria and Jonti Horner, Vice Chancellor’s Senior Research Fellow, University of Southern Queensland

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