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Groovy young rock stars and the Holy Grail

3 January 2019

Earth from space

Will a telescopic Census of thousands of planets help to pinpoint a new Earth?

For Professor Jane Greaves, such a discovery will be the ‘Holy Grail’ – the culmination of a career spent observing planets forming around young stars.

At the heart of the study, interpreting data on raw material ‘remnants’ from comet collisions around stars like the Sun will be the key to success.

Professor Greaves, who won the 2017 Institute of Physics Fred Hoyle Medal, is marshalling powerful telescopic forces as she searches for the raw materials from which new planets form around young stars, as reported in a recent Nature news feature.

The focus is the Taurus Molecular Cloud, where a ball of gas collapsed and ignited 100,000 years ago, leaving behind material that cooled and coalesced to form dust ‘grains.’

Behind the quest lies an enigma. Five years ago, astrophysicist Subhanjoy Mohanty of Imperial College London and Professor Greaves, now of Cardiff University’s School of Physics and Astronomy, published an initial survey of protoplanetary disks in the cloud.

When they calculated how much gas and dust seemed to be present, they found intermediate-sized stars had disks filled with ‘grains’ that packed much less mass than expected.

How can that happen? Professor Greaves, School of Physics and Astronomy, believes the devil is in the data.

My view is that we have been missing the larger rocks when we count up, which radio data will now allow us to detect.

Professor Jane Greaves Astronomy Group
Cardiff Hub for Astrophysics Research and Technology

While others contend that more mass from the surrounding ‘cloud’ continues to stream onto the system to boost what the planets can collect, Professor Greaves is using the SCUBA-2 camera on the UK-built James Clerk Maxwell Telescope to pursue her theory.

She is also leading the Planet-Earth Building-Blocks Legacy eMERLIN Survey (PEBBLeS) project, observing with UK's network of linked radio telescopes centred at Jodrell Bank, eMERLIN.

The technology uses radio wavelengths to allow astronomers to detect larger rocks that previous studies will have missed.

Uniquely, eMERLIN is able to distinguish rocks on orbits like that of the Earth from those that will build more distant planets, like Jupiter or Saturn.

Professor Greaves aims to compare eMERLIN’s information on planet system 'architectures' at the point of formation to the situation after planets have migrated – the focus of the Atmospheric Remote-sensing Exoplanet Large survey (ARIEL), selected by the European Space Agency for its next medium-class science mission due for launch in 2028.

Cardiff University is supplying vital software for ARIEL. During its four-year mission, it will observe 1,000 planets ranging from Jupiter- and Neptune-size down to super-Earth size in the visible and the infrared with its meter-class telescope - the first large-scale survey of the chemistry of exoplanet atmospheres. It seeks to address fundamental questions on how planetary systems form and evolve.

It will provide very definite data on the composition of a whole planet, i.e. its core and its atmosphere together, but it's unlikely to solve the mass problem unless something very strange is going on, where gas is solidifying into a kind of iceball world.

Professor Jane Greaves Astronomy Group
Cardiff Hub for Astrophysics Research and Technology

Ultimately, her work will align with the Square Kilometre Array project, backed by the UK. It aims to build the world's largest radio telescope in Australia and South Africa with a total collecting area of approximately one square kilometre.

By eventually mapping available data sources, Professor Greaves anticipates the possibility of finding centimetre-scale material swirling around what could be future rocky planets.

“Seeing a spot in a disk that indicated an Earth forming at an Earth-like distance from its star — that’s the new holy grail, at least for me,” Greaves told Nature.

“It's very hard to detect the faint radio emission, so earlier technology could neither see the larger rocks nor pick up faint signals further from the star.

“I hope we'll ultimately see rocks growing together that will form another planet like the Earth!

“We don't really know when and how our own planet formed - if we could see another one forming, it would help to examine what exactly gets collected, some of which is later needed for life, like an atmosphere and the oceans.”

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