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Telescope digs for ice on Pluto

Last Updated on Thursday, 26 June 2014 10:50
Published on Wednesday, 25 June 2014 01:01

In just over a year, the New Horizons spacecraft will fly past Pluto, giving us our first detailed look at the dwarf planet. Anticipating this encounter, St Andrews undergraduate student Ailsa Whitelaw and her supervisor Dr Jane Greaves have used forgotten data to map the sub-surface of Pluto, peering beneath its icy coating to uncover hidden chemicals that give a hint of the future of this distant world. Dr Greaves will present the new work in her talk on Wednesday 25 June at the National Astronomy Meeting (NAM 2014) in Portsmouth.

plutoThe track of Pluto across the night sky, as seen from 8 to 20 May 1997 when it was moving southwards in the direction of the constellation of Scorpius. North is at the top in this image. The superimposed red points are the moving point that the JCMT measured for the whole system of Pluto and its moons. Credit: Jane Greaves & George Bendo. Click for a larger versionPluto is remote, orbiting at a distance of between 4.4 and 7.3 billion km from the Sun. For that reason even the best images, made using the Hubble Space Telescope, can only pick out features larger than a few hundred km in size on a world itself just 2300 km across. The dwarf planet rotates every 6.4 days, so researchers also observe Pluto using ground-based telescopes, looking at how its brightness varies to deduce whether light or dark features are facing the Earth and hence construct maps of its surface.

Ailsa and Jane adopted a new approach, using data obtained from the James Clerk Maxwell Telescope (JCMT) on Hawaii in the late-1990s. JCMT's 'SCUBA' cameras operate in the sub-millimetre range of the spectrum, between far-infrared and microwave. Pluto was observed at 0.85 mm wavelength, meaning the waves are about 1000 times as long as our eyes can see and in a completely different region of the spectrum to any other data ever obtained from this distant world.

The two scientists assembled a 'light curve', where brightness is plotted against time. As Pluto is rotating, the data points correspond to different longitudes on its surface. The 0.85 mm waves are emitted from beneath the surface of the dwarf planet as seen in visible light, hinting at a different chemical mix in the sub-soil. One possible explanation is that a relatively dry layer of frozen nitrogen and methane lies below a dark surface patch of water ice and frozen polymers. Because Pluto's surface slowly boils away in sunlight (eventually removing the dark patch), this also gives us a sneak preview of its appearance thousands of years in the future.

As well as their forensic analysis of Pluto's past and future, the new results show a hemisphere of the dwarf planet that New Horizons will miss seeing in detail. The spacecraft zooms through the Pluto system on 14 July 2015, but only has a few minutes to study one side of the dwarf planet and its largest moon Charon at close range.

Jane says: "This was a bit like using a telescope as a digger to mine into Pluto, but with less effort! I'm really excited to see what New Horizons will find a year from now. Some researchers think that even deeper down, Pluto has liquid water, kept fluid by remnant heat from a big crash that formed its moons - if so the surface will probably look wrinkled. But the flyby is so quick that we'll need to follow up – maybe with future radar we can dig down even further."

The new ALMA telescope array now operating in Chile works at similar wavelengths and may be able to peer into the other icy dwarf planets discovered in the last decade.

A simulation of the view of Pluto seen from the New Horizon spacecraft over the 4 hours around the closest flyby. The largest moon, Charon, appears in yellow and the Sun's inner planets are marked as seen post-flyby. Lines of longitude and latitude are marked on Pluto and the nightside is to the left of the yellow line at close approach. New Horizons will only have a detailed view of one hemisphere of Pluto. Credit: NASA / New Horizons / Geoviz

 

Media contacts

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Science contact

Dr Jane Greaves
University of St Andrews
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Images, animation and captions

https://www.ras.org.uk/images/stories/NAM/2014/Greaves_Pluto_flyby_movie.gif
Movie: A simulation of the view of Pluto seen from the New Horizon spacecraft over the 4 hours around the closest flyby. The largest moon, Charon, appears in yellow and the Sun's inner planets are marked as seen post-flyby. Lines of longitude and latitude are marked on Pluto and the nightside is to the left of the yellow line at close approach. New Horizons will only have a detailed view of one hemisphere of Pluto. Credit: NASA / New Horizons / Geoviz

https://www.ras.org.uk/images/stories/NAM/2014/Greaves_Pluto_Labelled_Light_Curve.png
Graph: The light curve of Pluto in the new sub-millimetre data, which corresponds to signals from beneath its surface. The small points are from the SPIRE camera on ESA's Herschel telescope, and the large points are from the SCUBA camera on the JCMT. The darker points represent longitudes on the nightside during the New Horizons closest approach. The red curve is infrared data published from NASA's Spitzer spacecraft (corresponding to the surface); the new sub-millimetre (below the surface) results particularly differ from this curve in the nightside longitudes. Credit: Jane Greaves & George Bendo

https://www.ras.org.uk/images/stories/NAM/2014/Greaves_Pluto_Skytrack.png
Image: The track of Pluto across the night sky, as seen from 8 to 20 May 1997 when it was moving southwards in the direction of the constellation of Scorpius. North is at the top in this image. The superimposed red points are the moving point that the JCMT measured for the whole system of Pluto and its moons. Credit: Jane Greaves & George Bendo

 

Further information

These results were a surprising discovery, uncovered from the archive of the STFC-run James Clerk Maxwell Telescope nearly two decades after they were observed on behalf of the University of Hawaii. The data were analysed by University of St Andrews undergraduate student Ailsa Whitelaw and her supervisor Jane Greaves, with supporting data from the UK-built SPIRE camera on ESA's Herschel satellite processed by University of Manchester mission specialist George Bendo.

 

Notes for editors

The RAS National Astronomy Meeting (NAM 2014) will bring together more than 600 astronomers, space scientists and solar physicists for a conference running from 23 to 26 June in Portsmouth. NAM 2014, the largest regular professional astronomy event in the UK, will be held in conjunction with the UK Solar Physics (UKSP), Magnetosphere Ionosphere Solar-Terrestrial physics (MIST) and UK Cosmology (UKCosmo) meetings. The conference is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and the University of Portsmouth. Meeting arrangements and a full and up to date schedule of the scientific programme can be found on the official website and via Twitter.

The University of Portsmouth is a top-ranking university in a student-friendly waterfront city. It's in the top 50 universities in the UK, in The Guardian University Guide League Table 2014 and is ranked in the top 400 universities in the world, in the most recent Times Higher Education World University Rankings 2013. Research at the University of Portsmouth is varied and wide ranging, from pure science – such as the evolution of galaxies and the study of stem cells – to the most technologically applied subjects – such as computer games design. Our researchers collaborate with colleagues worldwide, and with the public, to develop new insights and make a difference to people's lives. Follow the University of Portsmouth on Twitter.

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter.

The Science and Technology Facilities Council (STFC) is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar. It enables UK researchers to access leading international science facilities for example in the area of astronomy, the European Southern Observatory. Follow STFC on Twitter.

The JCMT's SCUBA camera was built at the UK Astronomy Technology Centre in Edinburgh, and operated from 1996 to 2005. Its replacement, SCUBA-2, has been built by a UK-Canada consortium and is currently in operation.