Herschel telescope detects water and comets

Enough water vapour in a cosmic cloud to fill Earth’s oceans more than 2,000 times over, and a belt of comets around another star. Those are the two latest exciting discoveries revealed from a space telescope.

An artist's impression of Herschel observing deep in space
An artist’s impression of Herschel observing deep in space. Credit: ESA/AOES Medialab

A highlight of 2007 for this Skymania News writer was a trip to Frederickshafen, in southern Germany, to see this instrument, the European Space Agency’s Herschel observatory.

Wearing a white suit and hairnet, I was allowed into the clean room where final checks were being made to prepare the infrared telescope for launch.

It will be a long time, if ever, before anyone is able to get that close to Herschel again because it was delivered to a point 1.5 million km outside the Earth’s orbit where it orbits the Sun in resonance with our planet.

Herschel was lifted into space by an Ariane 5 rocket in May 2009, together with a separate probe called Planck, to begin a mission that would last around three years before the vital coolant that allows it to observe in the infrared runs out.

Since then it has been making exciting discoveries for astronomers, the latest of which was announced by ESA today. Observations of a cloud of gas and dust that is about to collapse to form a new star like the Sun detected a vast amount of water vapour, which could eventually help alien life to develop.

The vapour, which could refill all our own planet’s seas 2,000 times, has been released from icy dust grains by high-energy cosmic rays passing through the dark nebula from deep in the universe. The cloud, which astronomers term a “cold pre-stellar core”, has been dubbed L1544 and lies in the constellation of Taurus. It contains the vital ingredients needed to create new solar systems like our own.

Dr Paola Caselli, of the UK’s University of Leeds, is lead author of a paper reporting Herschel’s discovery in Astrophysical Journal Letters. He said: “To produce that amount of vapour, there must be a lot of water ice in the cloud, more than three million frozen Earth oceans’ worth.

“Before our observations, the understanding was that all the water was frozen onto dust grains because it was too cold to be in the gas phase and so we could not measure it.

“Now we will need to review our understanding of the chemical processes in this dense region and, in particular, the importance of cosmic rays to maintain some amount of water vapour.”

Herschel’s observations also showed that the water molecules detected are flowing towards the heart of the cloud where a new star will probably form, indicating that gravitational collapse has just started.

Close-up of L1544 with the water spectrum seen by Herschel, taken from the centre of the pre-stellar core. Credit: ESA/Herschel/SPIRE/HIFI/Caselli et al

Dr Caselli said: “There is absolutely no sign of stars in this dark cloud today, but by looking at the water molecules, we can see evidence of motion inside the region that can be understood as collapse of the whole cloud towards the centre.

“There is enough material to form a star at least as massive as our Sun, which means it could also be forming a planetary system, possibly one like ours.”

Formation of the new star will remove some of the water vapour in L1544 but the rest will become part of a disc surrounding it, providing a rich reservoir of water to supply potential new planets.

Last week, astronomers revealed a separate discovery by Herschel about a dusty band already known to exist around a young, 12 million-year old star called Beta Pictoris which lies only 63 light-years away from Earth. A giant planet has previously been discovered within the dust by French astronomers.

The Herschel telescope detected pristine material within this belt that matches that observed in comets within our own Solar System. It suggests that dust in the band could evolve to form a region of icy bodies similar to the Kuiper Belt that lies beyond Neptune.

The discovery, reported in Nature, was made by an international team led by astronomers at the University of Leuven in Belgium. They were particularly interested to find mineral olivine, which crystallises out of the protoplanetary disc material close to newborn stars.

The olivine was of a magnesium-rich variety that is known to be found in primitive, icy bodies like comets. Herschel’s observations showed that crystals of the mineral made up around four per cent of the dust in the region where it was found, 15 to 45 astronomical units (AU) from the star. That led them to conclude that it was released by collisions between comets. (An astronomical unit is approximately equal to the distance of the Earth from the Sun).

Lead author of the study Dr Ben de Vries said: “The four per cent value is strikingly similar to that of Solar System comets 17P/Holmes and 73P/Schwassmann-Wachmann 3, which contain two–ten per cent magnesium-rich olivine.

“Since olivine can only crystallise within about 10 AU of the central star, finding it in a cold debris disc means that it must have been transported from the inner region of the system to the outskirts.”

The astronomers believe that this movement was driven by forces of wind and heat from the star Beta Pictoris itself.

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