Capturing the shadow of Saturn’s moon Titan from right here on Earth

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NASA’s Cassini spacecraft captures Saturn’s largest moon, Titan, passes in front of the planet and its rings.
NASA/JPL-Caltech/Space Science Institute

David Coward, University of Western Australia

Titan is Saturn’s largest moon, and it is more like a planet than a moon in many respects.

It has a thick atmosphere as well as wind, rivers, lakes made of hydrocarbons such as methane, and a liquid water ocean. Understanding its atmosphere may help us in the search for life on other planets.

Hence the excitement this July when a rare opportunity was available to further study Titan, from right here on Earth. On July 18 at 11:05pm (WAST, Western Australian time) Titan passed in front of a faint star, as seen by observers across most of Australia.




Read more:
The secrets of Titan: Cassini searched for the building blocks of life on Saturn’s largest moon


This event, known as an occultation, lasted only a few minutes and about 2% of the star’s light was blocked by Titan’s atmosphere.

The effect was so small it required large telescopes and a special camera to record it. But the data gathered should have profound implications for our understanding of an atmosphere on another world.

Saturn’s moon Titan compared (by diameter) to the Earth and its Moon.
Wikimedia/The Conversation

Examining Titan’s atmosphere

Scientists have developed a very clever technique to examine Titan’s atmosphere using stellar occultations. As Titan enters and exits an occultation, the star’s light would illuminate the atmosphere from behind, but be blocked by the moon itself.

Scientists then record subtle changes in brightness of the star over a few minutes, which represents a profile of the atmosphere’s density with height.

This method was used to study Titan’s atmosphere before, during a stellar occultation in 2003.

Artist’s concept of Cassini’s June 4, 2010, flyby of Saturn’s moon Titan.
NASA/JPL

But in 2005, when Cassini’s Huygens lander arrived at Titan and descended to its surface, the atmospheric profile measured from its instruments did not match that derived from the 2003 occultation. This fuelled the question of how variable is the state of Titan’s atmosphere.

Composite of Titans surface taken by Huygens at different heights.
ESA/NASA/JPL/University of Arizona

Since the Cassini mission ended in 2017, NASA’s Karsten Schindler said there was keen interest in any new atmospheric observations from occultations:

Occultations remain the only means to study Titan’s upper atmosphere and its evolution for the foreseeable future.

Countdown to the July occultation

So how were the latest observations made, and how was the data gathered?

From the air, the plan was for the July 18 occultation to be recorded by a camera mounted on a telescope of the Stratospheric Observatory of Infrared Astronomy (SOFIA) on board a Boeing 747 aircraft.

SOFIA takes off from Christchurch International Airport in 2017.
SOFIA/ Waynne Williams

That’s right: a telescope mounted inside a modified passenger plane imaging an object more than 1 billion kilometres away! SOFIA would fly above the clouds between Australia and New Zealand.

From the ground, several facilities across Australia were to attempt to record the occultation.

The University of Western Australia’s Zadko Telescope, located about 80km north of Perth (see map, below), was identified by NASA as a ground facility sensitive enough to contribute to the project.

The most obvious deal breaker was the weather. July is one of the wettest months at the Zadko telescope site. But, as we found out, there were other unforseen challenges.

Three days to occultation

NASA’s Karsten Schindler arrived at the UWA research site, at Gingin, on Monday July 16, armed with a case filled with delicate cameras, cables and electronics.

The camera was the key to record the event. The current Zadko telescope camera cannot record fast enough to capture the rapid changes in brightness of the occulted star.

The Zadko Telescope was fitted out with a fast shooting (a frame every few seconds), NASA camera, more like a movie camera than a standard astronomical camera. After hours of installation, the new imaging system needed to be tested.

Ground occultation team: John Kennwell, Arie Verveer, Karsten Schindler with the Zadko Telescope in the background.

Unfortunately, the observatory roof would not open because of a faulty sensor. No Monday test, but hey, we still had Tuesday to test the system? Onsite engineers scrambled to fix the sensor ready for Tuesday.

Two days to occultation

On Tuesday, I received the following text message from the site.

11:07pm: Rain sensor working but clouded out … cheers Arie. So no chance testing the camera and weather forecast for Wednesday was bleak.

The day of occultation

Despite the cloud and nearly constant rain showers, team occulation (Karsten, Arie and John) were on site ready to start pointing the telescope and activate the imaging.

“Up to 10pm it was still raining,” Karsten told me the next morning. “Then a miracle happened.”

Less than an hour before the event, and he said the weather changed.

“The clouds seemed to vaporise away, leaving a totally cloudless sky with 100% visibility. I have never seen anything like it.”

The team swung into action, pointing the telescope at the target star, focusing the camera. At the designated occulation time 11:05pm, Karsten hit the image acquisition button, enabling the camera to take hundreds of images over a few minutes.




Read more:
What Cassini’s mission revealed about Saturn’s known and newly discovered moons


Eager to see if the data contained the signature of an occulation, the team performed a preliminary analysis within minutes. Yes, there was a clear occulation signature, a big dip in the brightness of the star at exactly the predicted time of the occulation.

Next morning I was informed that SOFIA had also captured the event.

The data recorded from the Australian ground stations and by SOFIA will be analysed over the coming weeks and published in peer reviewed journals.

The ConversationBut one thing the journals won’t highlight is the excitement of the observation, and the enormous effort by a few individuals who helped acquire this data that should hopefully give us a better understanding of the atmosphere of Titan.

David Coward, Associate professor, University of Western Australia

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

Male dolphins use their individual ‘names’ to build a complex social network

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Three allied male dolphins in Shark Bay, Western Australia.
Simon J Allen, Author provided

By Stephanie King, University of Western Australia

In life it often pays to keep a close eye on competitors and rivals. Historian Doris Kearns Goodwin’s book, Team of Rivals, tells how US president Abraham Lincoln persuaded each of his political rivals to join his cabinet, thereby turning them into his allies.

But the formation of alliances with potential competitors is not unique to humans. In a study published in Current Biology, my colleagues and I describe how such behaviour is also found among bottlenose dolphins.

We found that individual male dolphins retain their unique signature whistle, allowing them to recognise many different friends and rivals in their social network, something not currently known from any other non-human animal.




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Tackling the kraken: unique dolphin strategy delivers dangerous octopus for dinner


The Shark Bay network

In Shark Bay, Western Australia, pairs and trios of unrelated male dolphins work together in alliances to herd single females for mating opportunities. On a second level, teams of alliances work together to steal females from opposing alliances and to defend against such theft attempts.

A trio of allied male bottlenose dolphins (Tursiops aduncus) from Shark Bay, Western Australia.
Simon J Allen

The males are therefore cooperating with individuals with whom they are in direct reproductive competition, since paternity success cannot be shared. But the bonds between these teams of rivals are as strong as those between mothers and calves, and these friendships and alliances can last entire lifetimes.

So how do these males keep track of all these different relationships, and how do they maintain such strong social bonds? The answer may lie closer to home than you think.

Vocal labels for dolphins

Previous research has shown that bottlenose dolphins develop an individual vocal label known as their signature whistle, which they use to broadcast their identity.

A bottlenose dolphin signature whistle.
Stephanie L King

Bottlenose dolphin signature whistle.
Stephanie L King, Author provided629 KB (download)

These dolphins aren’t born with their own signature whistle. Rather, each dolphin develops a signature whistle within the first few months of life that is structurally unique from those of its companions.

It has been shown that these signature whistles are somewhat comparable to human names. Dolphins use them to introduce themselves or even copy others as a means of addressing specific individuals.

For decades it was thought that male dolphins would converge onto a shared signature whistle when they formed alliances with one another.

It was proposed that such an alliance signature would allow males to advertise alliance membership to competing males or to sexually receptive females. A type of vocal badge or group label.

Intriguingly, we found that male dolphins in Shark Bay retain individual vocal labels distinct from their allies.

Signature whistles of two different male dolphins from Shark Bay, Western Australia.
Stephanie L King

Male dolphin signature whistles.
Stephanie L King, Author provided485 KB (download)

Individually ‘named’ dolphins

This is an unexpected finding as it is well known that animals that form strong social bonds will vocally accommodate one another, making their calls more similar. By doing so, animals are not only advertising the strength of their relationships but also their group membership.

Such vocal convergence is found in many animals including parrots, songbirds, bats, elephants and primates.

Yet, it appears that in the complex network of dolphin alliances in Shark Bay, retaining individual “names” is more important than sharing calls. It allows male dolphins to recognise many different friends and rivals in their social network.

Even within these dolphin alliances males can show preferences and avoidances for with whom they cooperate.

Bottlenose dolphins have been shown to remember the signature whistles of other individuals even after 20 years of separation. This long-term social memory combined with the use of individual vocal labels, allows dolphins to keep track of many different relationships, as well as the history of those relationships.

Our research suggests that vocal labels play a central role in the recognition of cooperative partners and competitors in biological markets.

Male bonding, dolphin style

If allied male dolphins do not converge onto similar calls, then how do they reinforce their strong bonds?

Well, males in Shark Bay invest a lot of time in gentle contact behaviours, such as petting.

Drone footage shows a trio of adult male dolphins that spend time petting each other, using pectoral fins and tail flukes to rub against each other.

This may be similar to grooming behaviour in primates, which has been linked to oxytocin release. Oxytocin is a hormone that is known to facilitate social bonding between both humans and non-human animals, as well as promoting both trust and cooperation.

Dolphin alliances in Shark Bay are also characterised by high levels of synchronous behaviour. Males in alliances can perform the same behaviours at exactly the same time, surfacing in precise synchrony or performing coordinated displays.

It appears that synchrony, rather than shared calls, is what represents alliance unity.




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Tourism puts dolphins at risk in Southeast Asia – here’s what to look for on your next holiday


In human societies, synchronous behaviour, such as choreographed dancing, military marching or parades, is believed to have evolved to signal the quality of relationships.

The ConversationIt appears, then, that the multi-level dolphin alliances in Shark Bay share some traits with humans societies, where individual vocal labels help with the recognition of cooperative partners, and synchrony is a signal indicating the strength of those partnerships.

A trio of male dolphins from Shark Bay, Western Australia, synchronously push a female put of the water.
Stephanie L King

Stephanie King, Branco Weiss Research Fellow, University of Western Australia

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

Half of Earth’s satellites restrict use of climate data

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Dust storms in the Gulf of Alaska, captured by NASA’s Aqua satellite.
NASA

By Mariel Borowitz, Georgia Institute of Technology

Scientists and policymakers need satellite data to understand and address climate change. Yet data from more than half of unclassified Earth-observing satellites is restricted in some way, rather than shared openly.

When governments restrict who can access data, or limit how people can use or redistribute it, that slows the progress of science. Now, as U.S. climate funding is under threat, it’s more important than ever to ensure that researchers and others make the most of the collected data.

Why do some nations choose to restrict satellite data, while others make it openly available? My book, “Open Space,” uses a series of historical case studies, as well as a broad survey of national practices, to show how economic concerns and agency priorities shape the way nations treat their data.

The price of data

Satellites can collect comprehensive data over the oceans, arctic areas and other sparsely populated zones that are difficult for humans to monitor. They can collect data consistently over both space and time, which allows for a high level of accuracy in climate change research.

For example, scientists use data from the U.S.-German GRACE satellite mission to measure the mass of the land ice in both the Arctic and Antarctic. By collecting data on a regular basis over 15 years, GRACE demonstrated that land ice sheets in both Antarctica and Greenland have been losing mass since 2002. Both lost ice mass more rapidly since 2009.

Satellites collect valuable data, but they’re also expensive, typically ranging from US$100 million to nearly $1 billion per mission. They’re usually designed to operate for three to five years, but quite often continue well beyond their design life.

Many nations attempt to sell or commercialize data to recoup some of the costs. Even the U.S. National Oceanic and Atmospheric Administration and the European Space Agency – agencies that now make nearly all of their satellite data openly available – attempted data sales at an earlier stage in their programs. The U.S. Landsat program, originally developed by NASA in the early 1970s, was turned over to a private firm in the 1980s before later returning to government control. Under these systems, prices often ranged from hundreds to thousands of dollars per image.

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In other cases, agency priorities prevent any data access at all. As of 2016, more than 35 nations have been involved in the development or operation of an Earth observation satellite. In many cases, nations with small or emerging space programs, such as Egypt and Indonesia, have chosen to build relatively simple satellites to give their engineers hands-on experience.

Since these programs aim to build capacity and demonstrate new technology, rather than distribute or use data, data systems don’t receive significant funding. Agencies can’t afford to develop data portals and other systems that would facilitate broad data access. They also often mistakenly believe that demand for the data from these experimental satellites is low.

If scientists want to encourage nations to make more of their satellite data openly available, both of these issues need to be addressed.

Landsat 8, an American Earth observation satellite.
NASA, CC BY

Promoting access

Since providing data to one user doesn’t reduce the amount available for everyone else, distributing data widely will maximize the benefits to society. The more that open data is used, the more we all benefit from new research and products.

In my research, I’ve found that making data freely available is the best way to make sure the greatest number of people access and use it. In 2001, the U.S. Geological Survey sold 25,000 Landsat images, a record at the time. Then Landsat data was made openly available in 2008. In the year following, the agency distributed more than 1 million Landsat images.

For nations that believe demand for their data is low, or that lack resources to invest in data distribution systems, economic arguments alone are unlikely to spur action. Researchers and other user groups need to raise awareness of the potential uses of this data and make clear to governments their desire to access and use it.

Intergovernmental organizations like the Group on Earth Observations can help with these efforts by connecting research and user communities with relevant government decision-makers. International organizations can also encourage sharing by providing nations with global recognition of their data-sharing efforts. Technical and logistical assistance – helping to set up data portals or hosting foreign data in existing portals – can further reduce the resource investment required by smaller programs.

Promise for future

Satellite technology is improving rapidly. I believe that agencies must find ways to take advantage of these developments while continuing to make data as widely available as possible.

Satellites are collecting more data than ever before. Landsat 8 collected more data in its first two years of operation than Landsat 4 and 5 collected over their combined 32-year lifespan. The Landsat archive currently grows by a terabyte a day.

This avalanche of data opens promising new possibilities for big data and machine learning analyses – but that would require new data access systems. Agencies are embracing cloud technology as a way to address this challenge, but many still struggle with the costs. Should agencies pay commercial cloud providers to store their data, or develop their own systems? Who pays for the cloud resources needed to carry out the analysis: agencies or users?

The ConversationSatellite data can contribute significantly to a wide range of areas – climate change, weather, natural disasters, agricultural development and more – but only if users can access the data.

Mariel Borowitz, Assistant Professor of International Affairs, Georgia Institute of Technology

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