Herschel and Planck
I've been meaning to post about this for nigh on two weeks. I fail posting in a timely fashion.
On 14th May, ESA launched two satellites: Herschel and Planck. My flatmates and I (all astronomers) sat and watched the web feed of the launch, which was quite fun. They went up on the same rocket (there are not words enough to describe how crap it would have been if the launch went wrong and something blew up!) but they were detached separately and will make their way to their new home (the L2 point) independently.
I think they're really exciting projects so I've tried to explain them a little, and also say a little bit about where they're going to live and why they're going to live there.
Herschel
Herschel is a 3.5m infrared/sub-millimetre telescope. In order to work properly, it must be cooled to close to absolute zero; this is done using liquid helium. This limits Herschel's lifetime to around three to four years, including commissioning; once the liquid helium is all gone, that's it, Herschel is done. And unlike Hubble, we can't send up a shuttle with more liquid helium because L2 is so far away (see below).
The big questions that Herschel aims to answer are how did galaxies form and evolve in the early universe, how do stars form and evolve, and what is the relationship between stars and the interstellar medium (ISM)?
For this, IR and submm wavelengths are very, very useful. There's a lot of dust in the universe and optical light can't get through it, so if we look at optical wavelengths (eg. with Hubble) there's parts of the universe that are hidden by dust and that we can't see. IR and submm radiation CAN penetrate the dust though and reach our telescopes. (This image demonstrates this pretty well - it has a view of the Milky Way in different parts of the EM spectrum. You can see big black clouds of dust in the optical picture, but in the IR pictures, there's no trace of the dust at all.) Also, there are a lot of things in the universe that are too cold to radiate in the visible so we can only see them in IR or submm.
Problem is, that far IR and submm are very tricky to observe from the ground - the atmosphere absorbs most of the radiation before it can reach our telescopes, so we've got to be out in space. And, as I already mentioned, the telescopes must be cool to work at all - the L2 point is an ideal home for such a satellite because Herschel will stay at a fixed point instead of moving closer to and farther away from the Sun and experiencing associated temperature fluctuations when it does so. Living at L2 will also mean that the Earth's own IR radiation will not interfere with Herschel's measurements.
Herschel also hopes to investigate the chemistry of our Galaxy and the molecular chemistry of planetary, cometary and satellite atmospheres in the Solar System.
More information can be found at the ESA Herschel page.
Planck
The aim of the Planck satellite is to understand the creation of our universe and its subsequent behaviour and evolution. Planck will collect radiation from the Cosmic Microwave Background (CMB) using extremely sensitive detectors that will be able to measure very small anisotropies in the CMB. These tiny anisotropies tell us very important things about how our universe formed and evolved. Again, Planck has to be very cold to do be able to do its thing and so it too has a limited lifetime.
The big questions that Planck aims to address concern obtaining more precise values of fundamental cosmological parameters, showing conclusively that the early Universe passed through an inflationary phase and determining what is the nature of the dark matter that dominates the present Universe?
The CMB was first detected by Penzias and Wilson in 1964. They weren't looking for it; in fact, at first they thought that the CMB radiation they were getting was just noise, they checked all the connections, cleaned the antenna, tried everything they could think of to get rid of the problem, but it didn't go away and they realised that they'd found something, something that other cosmologists were desperately trying to detect. (They eventually got a Nobel Prize for it too, not bad, really.)
The very early universe was made up of a hot plasma of photons, electrons and baryons; this mixture was optically thick - this means that photons were interacting with the plasma and being continually scattered and so we can't see back that far. Then the universe recombined - positive ions and negative electrons formed neutral atoms, and matter and radiation decoupled; now the photons were able to travel freely through space and the universe became optically-thin, meaning that we can see through it. The CMB radiation that we detect are photons that have been travelling freely through space since recombination - this is as far back in the universe as we are able to see. (This picture is a pretty good visualisation.)
In 1992, the Cosmic Background Explorer (COBE) detected the first temperature anisotropy. In 2003, the Wilkinson Microwave Anisotropy Probe (WMAP) first year data release, produced much more detailed and far more accurate maps and results. The fifth-year data release, which was more detailed again, came out early in 2008. This image shows the COBE and WMAP CMBs; you can see how much more detailed the WMAP data is, and you can imagine how much more accurately fundamental constants could be measured and how much more information was obtained. Planck will be a step up again.
More information can be found at the ESA Planck page.
L2
The new home of these satellites is the Lagrange 2 (L2) point. L2 is one of five Lagrange points in the Sun-Earth orbital system where an object will experience a force of gravity from the Sun equal to the force of gravity from the Earth. Because the gravitational forces are equal, this allows an object to remain at a fixed position, relative to the objects it is orbiting, so a satellite placed at a Lagrange point will stay at that Lagrange point as the Earth continues to orbit the Sun. L1 lies between the Sun and the Earth. L2 lies behind the Earth, on the other side from the Sun. L3 lies on the opposite side of the Sun from the Earth. L4 and L5 lie along the Earth's orbits - L4 leads and L5 trails. There are groups of asteroids trapped at the Sun-Jupiter L4 and L5 points, these are known as the Trojan asteroids and so L4 and L5 are often referred to as Trojan points.
L2 has its advantages and disadvantages. As I already mentioned above, an object in orbit at a Lagrange point will stay there and so will remain in a fixed position relative to the rest of the system. L2 is also on the side of the Earth farthest from the Sun; this means that observations can be taken at all times, without the sun interfering.
However, L2 is 1.5 million km away from the Earth. It will be months before the satellites get there. This means that we can't go out and fix them if something breaks, and we can't refuel them when they run out of coolant. The Atlantis just came back from servicing Hubble last week; no such mission is possible for any satellite at L2, it's simply too far away for a manned mission to reach right now.
The advantages far outweigh the disadvantages, and L2 is getting busy. WMAP is already out there and Herschel and Planck are on their way. The James Webb Space Telescope (JWST, Hubble's successor) is also going out to L2, as is Gaia (which aims to create a huge, precise 3d chart of our Galaxy with positions and velocities for over one billion stars in our Galaxy and throughout the Local Group - it's going to be awesome).
On 14th May, ESA launched two satellites: Herschel and Planck. My flatmates and I (all astronomers) sat and watched the web feed of the launch, which was quite fun. They went up on the same rocket (there are not words enough to describe how crap it would have been if the launch went wrong and something blew up!) but they were detached separately and will make their way to their new home (the L2 point) independently.
I think they're really exciting projects so I've tried to explain them a little, and also say a little bit about where they're going to live and why they're going to live there.
Herschel
Herschel is a 3.5m infrared/sub-millimetre telescope. In order to work properly, it must be cooled to close to absolute zero; this is done using liquid helium. This limits Herschel's lifetime to around three to four years, including commissioning; once the liquid helium is all gone, that's it, Herschel is done. And unlike Hubble, we can't send up a shuttle with more liquid helium because L2 is so far away (see below).
The big questions that Herschel aims to answer are how did galaxies form and evolve in the early universe, how do stars form and evolve, and what is the relationship between stars and the interstellar medium (ISM)?
For this, IR and submm wavelengths are very, very useful. There's a lot of dust in the universe and optical light can't get through it, so if we look at optical wavelengths (eg. with Hubble) there's parts of the universe that are hidden by dust and that we can't see. IR and submm radiation CAN penetrate the dust though and reach our telescopes. (This image demonstrates this pretty well - it has a view of the Milky Way in different parts of the EM spectrum. You can see big black clouds of dust in the optical picture, but in the IR pictures, there's no trace of the dust at all.) Also, there are a lot of things in the universe that are too cold to radiate in the visible so we can only see them in IR or submm.
Problem is, that far IR and submm are very tricky to observe from the ground - the atmosphere absorbs most of the radiation before it can reach our telescopes, so we've got to be out in space. And, as I already mentioned, the telescopes must be cool to work at all - the L2 point is an ideal home for such a satellite because Herschel will stay at a fixed point instead of moving closer to and farther away from the Sun and experiencing associated temperature fluctuations when it does so. Living at L2 will also mean that the Earth's own IR radiation will not interfere with Herschel's measurements.
Herschel also hopes to investigate the chemistry of our Galaxy and the molecular chemistry of planetary, cometary and satellite atmospheres in the Solar System.
More information can be found at the ESA Herschel page.
Planck
The aim of the Planck satellite is to understand the creation of our universe and its subsequent behaviour and evolution. Planck will collect radiation from the Cosmic Microwave Background (CMB) using extremely sensitive detectors that will be able to measure very small anisotropies in the CMB. These tiny anisotropies tell us very important things about how our universe formed and evolved. Again, Planck has to be very cold to do be able to do its thing and so it too has a limited lifetime.
The big questions that Planck aims to address concern obtaining more precise values of fundamental cosmological parameters, showing conclusively that the early Universe passed through an inflationary phase and determining what is the nature of the dark matter that dominates the present Universe?
The CMB was first detected by Penzias and Wilson in 1964. They weren't looking for it; in fact, at first they thought that the CMB radiation they were getting was just noise, they checked all the connections, cleaned the antenna, tried everything they could think of to get rid of the problem, but it didn't go away and they realised that they'd found something, something that other cosmologists were desperately trying to detect. (They eventually got a Nobel Prize for it too, not bad, really.)
The very early universe was made up of a hot plasma of photons, electrons and baryons; this mixture was optically thick - this means that photons were interacting with the plasma and being continually scattered and so we can't see back that far. Then the universe recombined - positive ions and negative electrons formed neutral atoms, and matter and radiation decoupled; now the photons were able to travel freely through space and the universe became optically-thin, meaning that we can see through it. The CMB radiation that we detect are photons that have been travelling freely through space since recombination - this is as far back in the universe as we are able to see. (This picture is a pretty good visualisation.)
In 1992, the Cosmic Background Explorer (COBE) detected the first temperature anisotropy. In 2003, the Wilkinson Microwave Anisotropy Probe (WMAP) first year data release, produced much more detailed and far more accurate maps and results. The fifth-year data release, which was more detailed again, came out early in 2008. This image shows the COBE and WMAP CMBs; you can see how much more detailed the WMAP data is, and you can imagine how much more accurately fundamental constants could be measured and how much more information was obtained. Planck will be a step up again.
More information can be found at the ESA Planck page.
L2
The new home of these satellites is the Lagrange 2 (L2) point. L2 is one of five Lagrange points in the Sun-Earth orbital system where an object will experience a force of gravity from the Sun equal to the force of gravity from the Earth. Because the gravitational forces are equal, this allows an object to remain at a fixed position, relative to the objects it is orbiting, so a satellite placed at a Lagrange point will stay at that Lagrange point as the Earth continues to orbit the Sun. L1 lies between the Sun and the Earth. L2 lies behind the Earth, on the other side from the Sun. L3 lies on the opposite side of the Sun from the Earth. L4 and L5 lie along the Earth's orbits - L4 leads and L5 trails. There are groups of asteroids trapped at the Sun-Jupiter L4 and L5 points, these are known as the Trojan asteroids and so L4 and L5 are often referred to as Trojan points.
L2 has its advantages and disadvantages. As I already mentioned above, an object in orbit at a Lagrange point will stay there and so will remain in a fixed position relative to the rest of the system. L2 is also on the side of the Earth farthest from the Sun; this means that observations can be taken at all times, without the sun interfering.
However, L2 is 1.5 million km away from the Earth. It will be months before the satellites get there. This means that we can't go out and fix them if something breaks, and we can't refuel them when they run out of coolant. The Atlantis just came back from servicing Hubble last week; no such mission is possible for any satellite at L2, it's simply too far away for a manned mission to reach right now.
The advantages far outweigh the disadvantages, and L2 is getting busy. WMAP is already out there and Herschel and Planck are on their way. The James Webb Space Telescope (JWST, Hubble's successor) is also going out to L2, as is Gaia (which aims to create a huge, precise 3d chart of our Galaxy with positions and velocities for over one billion stars in our Galaxy and throughout the Local Group - it's going to be awesome).