Men on a mission talk about working with space observatories

Researchers from the Department of Physics talk about their work with Herschel and Planck satellites

Monday 8 November 2010
By Lucy Goodchild

Last week, astronomers revealed that they have discovered a new way of finding cosmic zoom lenses, which allow scientists to peer at galaxies in the distant Universe, using the European Space Agency’s Herschel Space Observatory.

Image taken by Planck of a region in the constellation Perseus. Credit: ESA/LFI & HFI Consortia

Herschel and its sister observatory, Planck, are providing new insights into the way stars and galaxies form, and telling us how the Universe came into being after the Big Bang.

Several researchers at Imperial College London work on the two observatory missions, being responsible for data analysis and interpretation, and ensuring the instruments are calibrated correctly. Imperial is the only place in the UK where scientists are involved in functional work and scientific analysis on both Planck and Herschel.

Both observatories are collecting data to enable scientists to map out the cosmic background radiation and take images of the early Universe. The two satellites were launched together in May 2009, separating shortly afterwards, and now orbit a point called L2 at the far side of the Earth to the sun.

The common feature that both missions will be exploring is tiny rocks known as ‘dust’, which drive planet and star formation and absorbed half of all the energy created since the Big Bang. These particles are much smaller than household dust, at a similar size to particles in fumes and smoke, with each particle measuring under one micrometre.

Here, Professor Andrew Jaffe and Dr Dave Clements, from the Department of Physics, tell us about working on the missions.

Launching the satellites

Artist’s impression of Planck cruising to the L2 region. Credit: ESA – D. Ducros

According to Professor Jaffe, "You can go old and grey waiting for stuff to happen in this field." The idea for Herschel and Planck was first seeded in 1990 and the satellites were launched together 19 years later. "People with this career see three or four missions," said Dr Clements.

Having worked on the missions themselves since 2000, both scientists were excited by the launch. "I watched it live on TV. When it launched, there was 30 minutes before the two were separate and fairly safe. It was a long 30 minutes," recalled Dr Clements.

Professor Jaffe, who was at the live launch, added "I recommend going to a launch if you get the chance – it's a gamut of emotions: scary, moving, scary again, overwhelming. The satellite becomes its own little creature floating in space – it made me anxious."

Planck

Planck is a telescope that observes the sky with a frequency of light from 30GHz up to 850 GHz (millimetres to centimetres in wavelength). It is looking at light from 400,000 years after the Big Bang.

The young universe was hot and light. The heat made protons and electrons bounce around and ionised the gas in the universe, making it opaque to light. Looking at the early universe is like looking at the surface of a cloud – light bounces around inside and some gets out.

Dr Clements explains: "The universe was nearly uniform early on after the Big Bang. With Planck you can take images of the small variations in density and project these back and forward to get a better understanding of the history of the Universe. Without these fluctuations, there would be no stars, no planets, no us. If we look really far away, we eventually see light from the Big Bang."

On Planck, light reflects off of two accurately placed mirrors and onto a focal plane, producing pictures of the sky at certain wavelengths. The mission is meant to do two complete scans of the sky – each takes around six months. The limiting factor is the amount of liquid helium the mission can carry. Liquid helium is there to cool the instrument, so when it runs out the mission ends. The researchers hope it will be able to get two more scans from Planck than they had expected (four in total), as the helium has lasted longer than required.

Professor Jaffe says Planck has been a success so far: "Planck is coming out with fantastic data every day – it’s a full time job!"

Herschel

Herschel is an observatory with three instruments, one of which is the Spectral and Photometric Imaging Receiver, or SPIRE. The instrument is made up of two halves: a spectrometer and a photometer, which measure different properties of light. SPIRE scans regions of the sky, using the largest mirror ever launched into space for scientific purposes.

Infrared image of the Rosette molecular cloud, as seen by Herschel. Credit: ESA/PACS & SPIRE Consortium/HOBYS Key Programme Consortia

Herschel can see smaller-scale features than Planck. It is more like the sort of telescope people use on the ground. Any astronomers can apply to use it and scientists who worked on the mission get guaranteed time. Researchers can point it wherever they want, to look at different objects in space.

Herschel will look at the formation of dust, something that is not well understood at the moment. According to Dr Clements, researchers still have a lot to learn about it: "We don’t know the shape of the grains – they could be cigars, discs, spheres or 'woofly' – amorphous – shapes. We know they can be small and large, with some sitting on the boundary of being small grains or large molecules."

Working on the missions

On Planck, the functional work is figuring out what part of the universe the instrument is revealing.

Professor Jaffe explains how the instrument can shift: "At the launch, Planck was attached to explosives and it bounces around a lot in space – even if it has been calibrated, the instrument may have moved. Also, it is heated by the sun and the Earth, so liquids on it, like helium, shift around, making it wobble. Planck is not tied down to anything, so we need to measure its position so we know what we're looking at."

There is an extra camera, the 'star tracker', which points to the front, and little telescopes that see optical wavelengths. The researchers use these to calculate the position of the satellite to 1/3600 of a degree.

On Herschel, scientists need to manage an Instrument Control Centre (the SPIRE ICC). The Imperial researchers are also writing software that can simplify the vast amounts of data produced by Herschel, and they are involved in testing and calibrating the instrument to make sure it is working correctly.

Herschel has already produced lots of useful data, according to Dr Clements: "There are already hundreds of papers out, based on this data; I've been an author on over 40 of them. Herschel was producing images within a month of the first set of data, which is astounding!"

Professor Jaffe says working on Planck has been an inte resting experience: "Working with teams of 400 peo ple isn't something any of us expected to do when we got into science. That presents its own challenges!" Herschel presents similar challenges, with 150-200 scientists from countries as widespread as Canada and China working on SPIRE. "It's exhausting!" said Dr Clements.

"It's a lot more fun since we launched," said Professor Jaffe. "We were relative latecomers to the projects; we've worked on Herschel and Planck for about a decade. During the early stages the work can be tedious – there are a lot of meetings. It's more fun when you have data to interpret."

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