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.

We discovered 20 new fish in northern Australia – now we need to protect them


Matthew Le Feuvre, University of Melbourne; James Shelley, University of Melbourne; Stephen Swearer, University of Melbourne, and Tim Dempster, University of Melbourne

We recently discovered 20 new species of fish in the Kimberley region of north-west Australia (one of them has been named after writer Tim Winton).

But that’s only the start of the story. At a time when the federal government is redoubling efforts to develop northern Australia, our discovery is a timely reminder of how little we know about our country.

A 2014 CSIRO report found 1.4 million hectares of land in northern Australia could be irrigated. Underlying this expansion would be approximately 90 large dams and numerous smaller water-regulating structures such as weirs.

While this could boost the northern Australian economy, impacts on aquatic ecosystems from altered flow regimes, habitat modification and reduced water quality are likely to be significant.

The long-nosed sooty grunter is found in a single river in the Kimberley.
Matthew Le Feuvre & James Shelley, Author provided

Threatened waterways

Fish are the most researched group of species living in Australia’s freshwater ecosystems. As such, we can use them as indicators of how much we know about these environments.

To date, research effort has been focused on south-east Australia. What stands out is a lack of research across much of the country, particularly in the north.

Despite this, northern Australia’s freshwater fish fauna is very diverse and includes many fish found across tiny areas. Unfortunately the lack of research means that for many of northern Australia’s fishes, all we know is that they exist.

Under the federal Environment Protection and Biodiversity Conservation (EPBC) Act, 16% of Australia’s freshwater fish are listed as threatened. But most of the species analysed are from the rivers of south-east Australia, which are most affected by people.

In a recent study we identified another 55 potentially vulnerable species that meet the criteria for conservation listing.

When we mapped the already listed and potentially vulnerable fish species, we found hotspots for fish conservation in the Kimberley, the Wet Tropics and Arnhem Land.

Map a) shows the number of currently listed threatened fish. Map b) shows the number of species that we identified as potentially vulnerable. Map c) shows river condition (1=best quality; 8=worst). Map shows d) freshwater fish research effort across Australia (red=most effort).
Matthew Le Feuvre, Tim Dempster, James Shelley and Steve Swearer, Author provided

While often overlooked, Australia’s freshwater fish are almost as unique as our kangaroos and koalas: 74% of these fish are found nowhere else in the world.

If enigmatic northern Australian species, such as the saratoga (Scleropages leichardti), the long-nosed sooty grunter (Hephaestus epirrhinos) or the Prince Regent gudgeon (Hypseleotris regalis) are lost, we contribute to an ongoing global freshwater fish extinction crisis. Australia’s freshwater fish deserve adequate protection.

Exploring the north

The Kimberley in northern Western Australia is rugged, remote, pristine and holds a number of species found nowhere else. We decided to investigate the region’s freshwater fishes.

Before our project began, we knew that the region was home to 50 species of freshwater fish, or almost a quarter of Australia’s freshwater fish species. Eighteen of these are found only in the Kimberley region.

Over the past three years, we spent nine months surveying over 70 sites on 17 of the Kimberley’s rivers. We found that many of the endemic species are potentially particularly vulnerable if their environment were to change. For example, the long-nosed sooty grunter is large, found in a single river, rare and exclusively carnivorous, making it vulnerable to extinction.

Excitingly, we also uncovered 20 new species of freshwater fish. This increases the known freshwater fish species in Australia by roughly 10% and, with 70 species in total, it makes the Kimberley the most diverse region for freshwater fish.

Many of the new species are large, clearly distinct fish, which could be identified as new species when we observed them from the riverbank. We found most of these new species in rivers we could only access by helicopter.

Put simply, due to the difficultly and expense of sampling the remote Kimberley wilderness, we just haven’t looked hard enough in the region’s rivers. Entire river systems in the Kimberley remain unsampled and we should not be surprised to uncover more species unknown to science.

What else is out there?

Our findings raise questions about the environmental sustainability of developing northern Australia. If we can find 20 new species of freshwater fish in nine months of fieldwork in the Kimberley, how many more species are present across the rest of northern Australia?

Fish are big and easy to find compared to most of the smaller aquatic life. They represent the conspicuous tip of the iceberg of what lives in our rivers. What happens if we investigate more cryptic or poorly known taxa such as amphibians or invertebrates?

The Prince Regent gudgeon.
Matthew Le Feuvre & James Shelley, Author provided

How can we manage and protect species we don’t know exist? Before we develop the north, we need to know what’s out there.

The majority of northern rivers remain in relatively good condition, so there is ample opportunity to ensure that species are not lost as a result of development. Fortunately, most major developments are a decade or more away, so there is time to gather this information.

Learning from the south

Many rivers in southern Australia have been degraded by habitat modification, altered flow patterns, invasive species, barriers to fish movement, reduced water quality and overexploitation.

Many fish species are threatened. Of 46 species found in the Murray-Darling Basin, 19 are listed as threatened at the state or national level.

What have we learned?

River flow, infrastructure and land use all need to be actively managed to maintain healthy rivers and allow key ecological processes, such as migrations and the inundation of floodplains, to continue. We need to be vigilant to prevent alien species invading.

A major source of conflict in the Murray-Darling Basin Plan was the allocation of water to the environment. Considering the environment as a stakeholder at the beginning of this process could have avoided future conflicts.

These practices will need to be adapted to the highly seasonal rainfall of northern Australia, which will be challenging. Intact rivers with particularly high numbers of species found nowhere else may be good candidates for freshwater protected areas, which are rare in Australia.

We need to ensure that our unique freshwater fishes are properly conserved. With research and good planning, we can ensure we do not repeat the sins of the past in northern Australia.

The Conversation

Matthew Le Feuvre, PhD candidate, School of BioSciences, University of Melbourne; James Shelley, PhD candidate, School of Biosciences, University of Melbourne; Stephen Swearer, Professor of Marine biology, University of Melbourne, and Tim Dempster, Associate professor in Marine Biology, University of Melbourne

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

Concrete jungle? We’ll have to do more than plant trees to bring wildlife back to our cities


Peter Fisher, RMIT University

The federal environment and acting cities minister, Greg Hunt, on Tuesday pledged to increase the number of trees in Australian cities. In a bid to fight higher urban temperatures, the plan will set targets for tree cover.

This is part of a green revolution spreading through the world’s cities. From New York to Singapore, urban areas are undertaking bold “greenspace” initiatives – removing concrete and allowing trees and vegetation back in.

Some of the benefits include replacing the ugly infrastructural trappings of vehicles and motorways as well as cooling cities, absorbing air pollution and minimising runoff. These greenings further have mental health benefits, by bringing residents and visitors alike back into contact with the land.

But what about wildlife? Trees alone aren’t enough to bring back nature. In the rush to create greenspace, we have to make sure we build it in a way to help wildlife thrive. That will take careful thought and planning.

Nature paved over

Many of the world’s cities don’t have anything special to offer in terms of nature – either because they never had all that much in the first place, or they’ve long since been lost to urban development.

Melbourne is a case of the latter. James Boyce (in his book 1835) records:

By the time Anthony Trollope visited, then a city of 206,000 “souls” in the early 1870s, the city had already largely turned its back on the Yarra [River], drained the swamps, filled in the lakes and flattened the hills, so that Trollope knew “of no great town in the neighbourhood of which there is less to see in the way of landscape beauty”.

That sounds like many a world city.

Reconstruction of Williams Creek, Melbourne, which now lies under the city’s asphalt.
RMIT

London, New York, Hamburg, Madrid, Detroit, Chicago, Seoul and Singapore are among cities that have undertaken bold greenspace initiatives. These cities have recognised the distinct benefits that flow from connecting people back to the natural world.

Detroit and Singapore have strong biodiversity themes and that’s needed too given the global decline in wildlife. Such initiatives help us to view cities from a non-human-centric perspective.

i-Tree world

Back in Australia “green infrastructure” has similarly taken hold with councils, property owners and private companies signing up to a national 202020 vision to create 20% more greenspace by 2020. The main underpinning of that “greenspace” is the “urban forest”.

While urban forest has a broad definition, cities usually take it to mean tree cover. This has been revolutionised and driven by satellite mapping (known as i-Tree) from the US Department of Agriculture.

This mapping has recently been used to shed light on the performance of Australia’s municipalities. Ranking them according to their percentage of tree cover, parts of Melbourne and Sydney scored badly, with many suburbs having less than 20% tree cover overall. Brisbane scored well, with most areas having more than 50% tree cover.

As cities attempt to increase canopies, it’s worth noting that these trees will have to deal with increasing extreme weather as the world warms.

Rewilding the city

However, trees on their own won’t bring wildlife back into our cities. In fact, canopies tend to create spaces for dominant native birds such as the Noisy Miner and Red Wattlebird, which by their behaviour exclude smaller birds.

Birdlife Australia suggests that a dense understory of shrubs up to two metres high is required for small ground birds like thornbills, robins, scrubwrens and fairy-wrens to roost in and make brief forays into grassed areas. Thickets also provide protection from eagles and hawks and other predators.

The late Victorian naturalist Alan Reid suggested:

a mixture of fine-leaf and broad-leaf plants with a high percentage of native species, especially at intermediate and ground levels, will provide the greatest opportunities for attracting and holding wildlife.

Private gardens have inadvertently edged towards this prescription, along the way forming “nuclei” for wildlife. To create these on public land, areas will need to be set aside in parklands and other community spaces where small birds and small animals can congregate, breed and flourish.

This may require fencing to counter fox and cat predation, and possibly incorporate bird hides, interpretative apps and surveillance to ensure personal security. We need to give attention to the subtle connections between species.

Wildlife corridors are another construct – in effect they’re flyways for larger birds. Some of these already take advantage of the routes provided by revegetated creek and river banks.

Reid suggests that “corridors as narrow as 5 metres will allow passage of lorikeets and wattlebirds even when gaps exceed 30 metres”.

But if the gaps in 20-metre-wide corridors grow to more than 30 metres they will block many upper-level feeders including butterflies, pygmy possums and marsupial mice.

As the take-up of greening in places like New York, Hamburg and Seoul shows, it’s becoming mainstream in city halls around the world. And we now know that it helps settle the brains of those otherwise enmeshed in asphalt, glass and concrete.

There are some encouraging signs that developers “get it”: witness Singapore building an entire forest in a high-rise apartment atrium. A connection-to-nature element also forms part of the revamped Green Building Council of Australia’s Innovation Challenge Program. Let’s hope it won’t be long before that awareness spills over into popular planning thought.

As the world continues to change under human pressure, we need to make sure our cities can be homes for wildlife too.

The Conversation

Peter Fisher, Adjunct Professor, Global, Urban and Social Studies, RMIT University

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