Lights in the sky from Elon Musk’s new satellite network have stargazers worried



The panel of 60 Starlink satellites just before they were released to go into orbit around Earth.
Official SpaceX Photos

Michael J. I. Brown, Monash University

UFOs over Cairns. Lights over Leiden. Glints above Seattle. What’s going on?

Starlink satellites travel silently across the skies of Leiden.

The launch of 60 Starlink satellites by Elon Musk’s SpaceX has grabbed the attention of people around the globe. The satellites are part of a fleet that is intended to provide fast internet across the world.

Improved internet services sound great, and Musk is reported to be planning for up to 12,000 satellites in low Earth orbit. But this fleet of satellites could forever change our view of the heavens.

Will we lose the night sky to city lights and satellites?
Jeff Sullivan, CC BY-NC-ND

Starlink’s ambitious mission

Starlink is an ambitious plan to use satellites in low Earth orbit (about 500km up) to provide global internet services.




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This is different from the approach previously used for most communication satellites, in which larger individual satellites were placed in high geosynchronous orbits – that stay in an apparently fixed position above the Equator (about 36,000km up).

Communications with satellites in geosynchronous orbits often require satellite dishes, which you can see on the sides of residential apartment buildings. Communication with satellites in low Earth orbit, which are much closer, won’t require such bulky equipment.

But the catch with satellites in low Earth orbit, which move quickly around the world, is they can only look down on a small fraction of the globe, so to get global coverage you need many satellites. The Iridium satellite network used this approach in the 1990s, using dozens of satellites to provide global phone and data services.

Starlink is far more ambitious, with 1,600 satellites in the first phase, increasing to 12,000 satellites during the mid-2020s. For comparison, there are roughly 18,000 objects in Earth orbit that are tracked, including about 2,000 functioning satellites.

Lights in the sky

It’s not unusual to see satellites travelling across the twilight sky. Indeed, there’s a certain thrill to seeing the International Space Station pass overhead, and to know there are people living on board that distant light. But Starlink is something else.

The first 60 satellites, launched by SpaceX last week, were seen travelling in procession across the night sky. Some people knew what they were seeing, but the silent procession of light also generated UFO reports. If you’re lucky, you may see them pass across your skies tonight.

If the full constellation of satellites is launched, hundreds of Starlink satellites will be above the horizon at any given time. If they are visible to the unaided eye, as suggested by initial reports, they could outnumber the brightest natural stars visible to the unaided eye.

Astronomers’ fears were not put to rest by Musk’s tweets:

Satellites are very definitely visible at night, particularly in the hours before dawn and after sunset, as they are high enough to be illuminated by the Sun. The Space Station’s artificial lighting is effectively irrelevant to its visibility.

In areas near the poles, including Canada and northern Europe, satellites in low Earth orbit can be illuminated throughout the night during the summer months.

Hundreds of satellites being visible to the unaided eye would be a disaster. They would completely ruin our view of the night sky. They would also contaminate astronomical images, leaving long trails across otherwise unblemished images.

The US$466 million Large Synoptic Survey Telescope, based in Chile, is an 8-metre aperture telescope with a 3,200-megapixel camera. It’s designed to rapidly survey the sky during the 2020s.

With the full constellation of Starlink satellites, many images taken with this telescope will contain a Starlink satellite. Longer exposures could contain dozens of satellite streaks.

Dark skies or darkened hopes?

Is there any cause for optimism? Yes and no.

Musk has produced some amazing feats of technology, such as the SpaceX Falcon and Tesla cars, but he’s also disappointed some on other projects, such as the Hyperloop tunnel transport plan.




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While Starlink certainly blew up on Twitter, for now at least, Musk is 11,940 satellites short of his 12,000.

Also, initial reports may have overestimated the brightness of the Starlink satellites, with the multiple satellites closely clustered together being confused with one satellite.

While some reports have indicate binoculars are needed to see the individual satellites, they also report that Starlink satellites flare, momentarily becoming brighter than any natural star.

If the individual satellites usually are too faint to be seen with the unaided eye, that would at least preserve the natural wonder of the sky. But professional astronomers like myself may need to prepare for streaky skies ahead. I can’t say I’m looking forward to that.The Conversation

Michael J. I. Brown, Associate professor in astronomy, Monash University

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

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Rising seas threaten Australia’s major airports – and it may be happening faster than we think



Sydney’s airport is one of the most vulnerable in Australia to sea level rise.
Shutterstock

Thomas Mortlock, Macquarie University; Andrew Gissing, Macquarie University; Ian Goodwin, Macquarie University, and Mingzhu Wang

Most major airports in Australia are located on reclaimed swamps, sitting only a few metres above the present day sea level. And the risk of sea level rise from climate change poses a greater threat to our airports than we’re prepared for.

In fact, some of the top climate scientists now believe global sea-level rise of over two metres by 2100 is likely under our current trajectory of high carbon emissions.




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This makes Cairns (less than 3m above sea level), Sydney and Brisbane (under 4m), and Townsville and Hobart (both around under 5m) airports among the most vulnerable.

Antarctica’s ice sheets could be melting faster than we think.
Tanya Patrick/CSIRO science image, CC BY

In the US, the National Oceanic and Atmospheric Administration (NOAA) has recommended that global mean sea level rise of up to 2.7 metres this century should be considered in planning for coastal infrastructure.

This is two to three times greater than the upper limit of recommended sea level rise projections applied in Australia.

But generally, the amount of sea level rise we can expect over the coming century is deeply uncertain. This is because ice sheet retreat rates from global warming are unpredictable.




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Given the significant disruption cost and deep uncertainty associated with the timing of sea level rise, we must adopt a risk-based approach which considers extreme sea level rise scenarios as part of coastal infrastructure planning.

Are we prepared?

As polar ocean waters warm, they can cause glaciers to melt from beneath, leading to more icebergs breaking off into the ocean and then a rapid rise in global sea level. This has happened multiple times in the Earth’s past and, on some occasions, in a matter of decades.

The Intergovernmental Panel on Climate Change (IPCC) puts sea level rise projections for Australia somewhere between 50 to 90 centimetres by 2090, relative to the average sea level measured between 1986 to 2005. But the emerging science indicates this may now be an underestimate.

Some studies suggest if substantive glacial basins of the West Antarctic Ice Sheet were to collapse, it could contribute at least a further two metres to global sea levels.

Most Australian airports have conducted risk assessments for the IPCC projections.

In fact, there is no state-level policy that considers extreme sea level rise for the most critical infrastructure, even though it is possible sea levels could exceed those recommended by the IPCC within the coming century.




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And for airports, the planning implications are stark when you compare the current projection of less than a metre of sea level rise and the potential of at least a two metre rise later this century.

Taking the most low-lying major airports in Australia as an example, our modelling suggests a collapse of the West Antarctic Ice Sheet would see their near complete inundation – without any adaptation in place.

For more elevated locations, coastal infrastructure may still be inoperable more frequently when the combined effect of storm surges, waves, elevated groundwater or river flooding are considered.

A $200 billion problem

Our airports and other forms of infrastructure near the coastline are critical to the Australian economy. The aviation industry has an estimated annual revenue of over A$43 billion, adding around A$16 billion to the economy in 2017.

While there are many uncertainties around the future cost of sea-level rise, a study by the Climate Council suggests over a metre sea level rise would put more than A$200 billion worth of Australian infrastructure at risk.

It is difficult to assign a probability and time-frame to ice sheet collapse, but scientific estimates are reducing that time frame to a century rather than a millennium.




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Uncertainty generally comes with a cost, so proactive planning would make economic sense.

Adapting our most critical coastal assets while sea levels rapidly rise is not an option – mitigation infrastructure could take decades to construct and may be prohibitively expensive.

Given the deep uncertainties associated with the timing of ice-sheet collapse, we suggest airport and other critical coastal infrastructure is subjected to risk analysis for a two to three metre sea level rise.The Conversation

Thomas Mortlock, Senior Risk Scientist, Risk Frontiers, Adjunct Fellow, Macquarie University; Andrew Gissing, General Manager, Risk Frontiers, Adjunct Fellow, Macquarie University; Ian Goodwin, Associate Professor, Macquarie University, and Mingzhu Wang, Senior Geospatial Scientist, Risk Frontiers, Adjunct Fellow, Macquarie University

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

After decades away, dengue returns to central Queensland



Australia’s dengue cases are usually limited to far north Queensland.
Shutterstock

Cameron Webb, University of Sydney

The Queensland city of Rockhampton was free of dengue for decades. Now, a case of one of the most serious mosquito-borne diseases has authorities scratching their heads.

Over the past decade, dengue infections have tended to be isolated events in which international travellers have returned home with the disease. But the recent case seems to have been locally acquired, raising concerns that there could be more infected mosquitoes in the central Queensland town, or that other people may have been exposed to the bites of an infected mosquito.

What is dengue fever?

The illness known as dengue fever typically includes symptoms such as rash, fever, headache, joint pain, vomiting, diarrhoea, and abdominal pain. Symptoms can last for around a week or so. Four types of dengue virus cause the illness and they are spread by mosquito bites.

Once infected, people become immune to that specific dengue virus. However, they can still get sick from the other dengue viruses. Being infected by multiple dengue viruses can increase the risk of more severe symptoms, and even death.

Hundreds of millions of people are infected each year. It is estimated that 40% of the world’s population is at risk given the regions where the virus, and the mosquitoes that spread it, are active. This includes parts of Australia.




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The last significant outbreak in Australia occurred in far north Queensland in 2009, when more than 900 people were infected by local mosquitoes.

Only a handful of locally acquired cases have been reported around Cairns and Townsville in the past decade. All these cases have two things in common: the arrival of infected travellers and the presence of the “right” mosquitoes.

The dengue virus isn’t spread from person to person. A mosquito needs to bite an infected person, become infected, and then it may transmit the virus to a second person as they bite. If more people are infected, more mosquitoes can pick up the virus as they bite and, subsequently, the outbreak can spread further.

Why are mosquitoes important?

Australia has hundreds of different types of mosquitoes. Dozens can spread local pathogens, such as Ross River virus, but just one is capable of spreading exotic viruses such as dengue and Zika: Aedes aegypti.

Aedes aegypti breeds in water-holding containers around the home. It is one of the most invasive mosquitoes globally and is easily moved about by people through international travel. While these days the mosquito stows away in planes, historically it was just as readily moved about in water-filled barrels on sailing ships.

Aedes aegypti is the mosquito primarily responsible for the spread of dengue viruses.
By James Gathany – PHIL, CDC, Public Domain

The spread of Aedes aegypti through Australia is the driving force in determining the nation’s future outbreak risk.

The mosquito was once widespread in coastal Australia but since the 1950s, it become limited to central and far north Queensland. We don’t really know why – there are many possible reasons for the retreat, but the important thing now is they don’t return to temperate regions of the country.

Authorities must be vigilant to monitor their spread and, where they’re currently found, building capacity to respond should cases of dengue be identified.




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What happened in Rockhampton?

Last week, for the first time in decades, a locally acquired case of dengue was detected in Rockhampton, in central Queensland. The disease was found in someone who hasn’t travelled outside the region, which suggests they’ve been bitten locally by an infected mosquito.

This has prompted a full outbreak response to protect the community from any additional infected mosquitoes.

While the risk of dengue around central Queensland is considered lower than around Cairns or Townsville, authorities are well prepared to respond, with a variety of techniques including house-to-house mosquito surveillance and mosquito control to minimise the spread.

These approaches have been successful around Cairns and Townsville for many years and have helped avoid substantial outbreaks.

The coordinated response of local authorities, combined with the onset of cooler weather that will slow down mosquitoes, greatly reduces any risk of more cases occurring.

What can we do about dengue in the future?

Outbreaks of dengue remain a risk in areas with Aedes aegypti mosquitoes. There are also other mosquitoes, such as Aedes albopictus (the Asian tiger mosquito), that aren’t currently found on mainland Australia but may further increase risks should they arrive. Authorities need to be prepared to respond to the introductions of these mosquitoes.




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While a changing climate may play a role in increasing the risk, increasing international travel, which represents pathways of introduction of “dengue mosquitoes” into new regions of Australia, may be of greater concern.

There is more that can be done, both locally and internationally. Researchers are working to develop a vaccine that protects against all four strains of dengue virus.

Others are tackling the mosquitoes themselves. Australian scientists have played a crucial role in using the Wolbachia bacteria, which spreads among Aedes aegypti and blocks transmission of dengue, to control the disease.

The objective is to raise the prevalence of the Wolbachia infections among local mosquitoes to a level that greatly reduces the likelihood of local dengue transmission.

Field studies have been successful in far north Queensland and may explain why so few local cases of dengue have been reported in recent years.

While future strategies may rely on emerging technologies and vaccines, simple measures such as minimising water-filled containers around our homes will reduce the number of mosquitoes and their potential to transmit disease.The Conversation

Cameron Webb, Clinical Lecturer and Principal Hospital Scientist, University of Sydney

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