Two giant leaps for mankind

It’s been an exciting couple of weeks in the field of astronomy, with scientists both discovering new worlds and finding out more about old ones.

A picture-perfect planet

All eyes were on Pluto this week as the NASA spacecraft New Horizons — the fastest spacecraft ever launched from Earth — flew just 12,500 km above the surface of the dwarf planet. It was a major milestone in a 5.3 billion km mission that took nine and a half years.

Although it did not have the fuel to orbit or land on Pluto, the spacecraft spent five hours taking detailed measurements and images of the dwarf planet and its five moons. CSIRO’s Canberra Deep Space Communication Complex (CDSCC), whose role in the mission was to track the spacecraft over the past nine years, was the first place on Earth to receive these images.

Radio signals from New Horizons took around four and a half hours to reach the CDSCC, which is one of only three tracking stations in the world with both the technology and expertise to provide two-way radio contact with the spacecraft at such a vast distance from Earth. CDSCC Director Dr Ed Kruzins explained that the complex uses two key things to capture the images from the New Horizons spacecraft.

“One is our giant, ultrasensitive antenna dishes that receive the weak signals from the spacecraft,” he said. “Think of them like giant ears, listening for radio signals … that can be 20 billion times weaker than the power of a watch battery by the time they reach Earth. When transmitting, the dishes are also like giant mouths, shouting out instructions to the spacecraft at the far reaches of the solar system.

“The other factor in capturing these images is our brilliant team of engineers, technicians and spacecraft communication experts. They are really what makes all this possible. The technology does not operate without their ability to understand, control, maintain and repair the massive dishes and their minute, delicate and sensitive receiver, transmitter and computer processing systems.”

Pluto image sent to Earth on 14 July 2015.

Dr Kruzins said that after New Horizons collects the data, the onboard computer converts the imagery into binary and then transmits the binary via radio signal to Earth. The sheer distance and amount of data collected means it will take 12-18 months before all the images and observations made by the spacecraft are fully transmitted back to Earth; however, the data returned so far has already:

• greatly improved our knowledge of the precise location of Pluto;
• refined knowledge about the size and position of the four orbiting moons;
• revealed the existence of methane ice on Pluto;
• started to uncover intriguing details of the surfaces of Pluto and Charon;
• shown that Pluto has a reddish appearance in areas and large mysterious dark spots up to 500 km across;
• shown that Pluto’s largest moon, Charon, is greyish in colour, meaning it is very different from Pluto’s composition.

The head of CSIRO Astronomy and Space Science, Dr Lewis Ball, noted that reaching this part of the solar system has been “a space science priority for years, because it holds building blocks of our solar system that have been stored in a deep freeze for billions of years”.

“These icy bodies are thought to be relics of the materials that originally built up to become the larger planets,” Dr Ball explained. “A world like Pluto can teach us more about planetary formation.

“Pluto also is a world that has an atmosphere that is escaping into space. This will be the first time that scientists can study this process as it happens. It will lead to important clues to the Earth’s original hydrogen-helium rich atmosphere and how that disappeared and changed.

“Pluto is known to be rich in organic, carbon-bearing molecules as well as water ice, the raw materials from which life develops. No-one is expecting to actually find life there, but understanding the significance of these materials so far from the Sun will help us fill in the gaps in our knowledge of life on Earth and the possibilities for life elsewhere.”

The mission isn’t technically over yet, with New Horizons expected to continue operating for at least another decade. In that time it will make its way past Pluto to the Kuiper Belt, described by Dr Kruzins as “a theoretical belt of external planets, asteroids and other debris which is thought to circle the solar system”. The science team hopes they can tweak the spacecraft’s flight path to allow for flybys of objects in the Kuiper Belt region, confirming and collecting information along the way.

A long time ago, in a galaxy far, far away…

The success of the New Horizons mission followed the discovery last week of a galaxy located five billion light-years away from Earth, detected with CSIRO’s Australian SKA Pathfinder telescope (ASKAP) in remote Western Australia.

In a paper available on arXiv, CSIRO’s Dr James Allison and his team explain how they noticed a change in radio waves coming from within the bright centre of the galaxy PKS B1740-517, located near the Ara constellation. They had picked up on a five-billion-year-old radio emission which had been stamped with the ‘imprint’ of cold hydrogen gas it had travelled through on its way to Earth.

An optical image of the radio galaxy PKS B1740-517, made with the Gemini South telescope. The galaxy is indicated by the green tick marks, which show the location of the slit used to obtain a spectrum of this object. This galaxy has a black hole at its centre: jets flowing away from that create the strong radio source detected with ASKAP. Image credit: M Whiting (CSIRO) from Gemini South data.

The hydrogen gas had absorbed some of the emission, creating a tiny dip in the radio signal. Dr Allison noted that this tiny dip would have been “hidden by background radio noise” at other observatories, making the search for the signal “like hunting for a small fish in a bed of seaweed”.

But the ASKAP is based at the Murchison Radio-astronomy Observatory (MRO) — a unique radio-quiet environment — where the dip “stood out clearly”, according to Dr Allison. “Here, we look through clear water to find the fish,” he said.

In addition to the lack of radio interference, the ASKAP astronomers were able to utilise a chunk of radio spectrum to search through that’s 300 MHz wide. “That’s more than most telescopes have, and it gives us a better chance of finding something new,” Dr Allison said.

CSIRO's Australian SKA Pathfinder telescope. Image credit: CSIRO.

Cold hydrogen gas is the raw material for forming stars and is plentiful in most galaxies. Astronomers can spot a galaxy from its hydrogen gas even when its starlight is faint or hidden by dust. According to Dr Allison, the discovery of the radio signal means “we’re going to bag a big haul of galaxies”.

Professor Elaine Sadler, Professor of Astrophysics at the University of Sydney and director of the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), was a member of the research team for this project. She leads a large ASKAP survey, now in the planning stage, that’s aimed at detecting several hundred galaxies.

“ASKAP looks at a relatively unexplored part of the radio spectrum, 700 to 1800 MHz,” she said. “This means we’ll be able to detect hydrogen gas deeper in space and, thanks to ASKAP’s wide field of view, also over a much larger volume than we could before. We’ll be hunting for galaxies that are five to eight billion years old — a timespan that represents a fifth of the universe’s history.”

The team will use the absorption technique to determine how much hydrogen gas these distant galaxies contain. This will help astronomers understand why star formation, which is fuelled by hydrogen gas, has dropped off in the universe since its peak 10 billion years ago.

Top image caption: Artist’s concept of the New Horizons spacecraft as it approaches Pluto and its largest moon, Charon.